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Invitation for

Editorial Contributions

Chemical Engineering Education publishes editorials in this space that concern subjects

of current relevance to the community of chemical engineers.

The topic is normally controversial

and the author is encouraged to clearly state his or her opinion

on the issue and the rationale for the stated opinion.

The editorial should not exceed one journal page (approximately 400 words) in length

and should be submitted electronically to

[email protected]

Although submissions are not sent out for review,

the editors provide feedback when they feel it is appropriate

and reserve the right to make editorial changes or to refuse to publish material

that the they consider inappropriate.

The deadlines for inclusion in each issue are

Winter Issue

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October 15th

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EDITORIAL AND BUSINESS ADDRESS: Chemical Engineering Education

Department of Chemical Engineering University of Florida • Gainesville, FL 32611

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EDITOR Tim Anderson

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~ PUBLICATIONS BOARD

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Colorado School of Mines

•MEMBERS•

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Winter 2005

Chemical Engineering Education Volume 39 Number 1 Winter 2005

• DEPARTMENT 2 Illinois Institute of Technology

HamidArastoopour. Darsh T. Wasem, Margaret M. Murphy

• EDUCATOR 8 R. Russell Rhinehart of Oklahoma State University

• CLASSROOM 14 Reduction of Disolved Oxygen at a Copper Rotating-Disc Electrode,

Gareth Kear, Carlos Ponce-de-Leon Albarran, Frank C. Walsh

30 Energy Balances on the Human Body: A Hands-On Exploration of Heat, Work, and Power

Stephanie Farrell, Mariano J. Save/ski, Robert Hesketh

38 A Project to Design and Build Compact Heat Exchangers, Richard A. Davis

42 A Method for Determining Self-Similarity: Transient Heat Transfer with Constant Flux,

Charles Monroe, John Newman

76 Environmental Impact Assessment: Teaching the Principles and Practices by Means of a Role-Playing Case Study,

Barry D. Crittenden, Richard England

• CLASS AND HOME PROBLEMS 22 An Open-Ended Mass Balance Problem,

Joaqu[n Ruiz

• RANDOM THOUGHTS 28 Death by Powerpoint, Richard M. Felder, Rebecca Brent

• CURRICULUM 48 Process Security in ChE Education,

Cristina Piluso, Karkut Uygun, Yinlun Huang, Helen H. Lou

62 VCM Process Design: An ABET 2000 Fully Compliant Project, Farid Benyahia

68 ASPEN Plus in the ChE Curriculum: Suitable Course Content and Teaching Methodology,

David A. Rockstraw

• LABORATORY 56 Kinetics of Hydrolysis of Acetic Anhydride by In-Situ FTIR Spectros

copy: An Experiment for the Undergraduate Laboratory, Shaker Haji, Can Erkey

21 Positions Available

CHEMICAL ENGINEERING EDUCATION (ISSN 0009-2479) is p11blished q11arterly by the Chemical E11gi11eeri11g Division, A merican Society for E11gilleerillg Education, and is edited at the Ut1iversity of Florida. Correspondet1ce regardillg editorial matter, circulation, at1d chat1ges of address should be seltt to CEE, Chemical Engineering Department, University of Florida, Gainesville, FL 3261 1-6005. Copyright © 2005 by the Chemical E11gilleeri11g Division, American Society for Engineering Education. The statemellts and opinions expressed i11 this periodical are those of the writers and 1101

11ecessarily those of the Cir£ Division, ASEE, which body assumes 110 responsibility for them. Defective copies replaced if ,rotified within 120 days of pllblicatio11. Write for i11formatio11 on subscription costs a11dfor back copy costs and availability. POSTMASTER: Send address changes to Chemical E11gi11eeri11g Education, Chemical E11gi11een·11g Department., University of Florida, Gainesville, FL 32611-6005. Periodicals Postage Paid at Gainesville, Florida and additional post offices.

.t~1111111ij1111111§.._d_e_:p~a_r_tm_e_n_t _________ )

2

ChE at . ..

Illinois Institute of Technology "A Century of Excellence in

Chemical Engineering Research and Education "

Armour Institute Main Building

Chairman William T. McCleme11t

lIAMrnARAsTooPouR, DARsH T. W ASAN, MARGARET M. MURPHY

Illinois Institute of Technology• Chicago, Illinois

In 2001 , Illinois Institute of Technology (IIT) celebrated a century of excellence in chemical engineering education and research. Among the very oldest programs in the country, IIT's program has closely tracked the origin and evolution of the chemical

engineering discipline itself. This paper hjghlights the unique combination of visionary administrators and talented faculty who piloted a once-fledgling program through more than 100 years of rapid scientific and technological change, while at the same time maintaining its continuous excellence and relevance to the needs of society and industry.

PROGRAM ORIGIN/EARLY HISTORY

The very earliest record of chemical engineering studies at the then Armour Institute surfaced in the year 1894 in the joint Department of Chemjstry and Chemical Engineering. Under the directorship of Dr. James C. Foye, PhD, LL.D, and professor of chemistry, a four-year curriculum leading to the BS degree in chemical engineering was developed and implemented. According to Dr. Foye, the instruction in chemkal engineering was intended "to meet the wants of students who wish to acquire a knowledge of chemistry, as applied to the engineering profession, which will enable them to engage in industries demanding the attainments of both the engineer and the chemist."[ 11 This educational irutiative came only six years after George Davis provided the blueprint for a new profession in a series of twelve lectures on chemical engineering in England and, simultaneously, MIT began "Course X (ten)," the first four-year chemical engineering program in the United States. By 1895, the newly named Armour Institute of Technology had established a stand-alone Department of Chemical Engineering as part of the Technical College to be directed by Professor Foye. f21

A CENTURY OF CHEMICAL ENGINEERING EXCELLENCE

The chemical engineering momentum begun at Armour by Dr. Foye was temporarily halted by his sudden death on July 3, 1897. By the beginning of the fall semester, all references to chemical engineering were dropped and the official name became the Department of Chemistry, headed by Thomas Allen, professor of chemistry. [3J One year later, William T. McClement was appointed director of the department and was promoted, at the same time, to professor of chemical engineering. In September 1901, a degree-granting

© Copyright ChE Division of ASEE 2005

Chemical Engineering Education.

Department of Chemical Engineering was established with Professor McClement serving as director. All work in chemistry was also placed under his supervision as he became responsible for the administration of what were basically two departments in one.

Under Professor McClement's direction, the Armour student chapter of the American Chemical Society was formed and, on June 19, 1901, the department granted its first BS degree in chemical engineering to Charles W. Pierce. Based on preliminary research, it would appear that Mr. Pierce was one of the first-if not the first-African-American chemjcal engineers in the nation. After leaving Armour, Mr. Pierce was named chief engineer at Normal College (now Tuskegee Institute) in Tuskegee, Alabama, later becoming head of the Mecharucal Department at the State Agriculture and Mecharucal College (now North Caro]jnaA&T) in Greensboro, North Carolina. 141 Accoriling to Armour ledgers, Mr. Pierce would have paid $75 .00/yr in tuition fees, with an additional annual lab deposit fee of $5.00!

In addition to the undergraduate curriculum, chemical engineering students could complete one year of resident post-graduate study and investigation or two years of actual engineering work to complete the "degree of chemical engineer." Professor McClement directed the department until 1906. For the next two years, Associate Professor Oscar Rochlitz would direct chemical engineering studies at Armour, which, by May 1907, had conferred a total of 25 BS degrees in chemical engineering.

PROGRAM EVOLUTION

With the department foundation in place, the next rune decades would see brilliant leadership and program evolution that not only kept pace with rapid industrial change, but also prepared its chemical engineers to lead this dynamic revolution. Since the early tenures of Professors McClement and Rochlitz, the department has been served by seven chairmen to date: H. McCormack (1908-1946), J.H. Rushton (1946-1953), R.E. Peck (1953-1967), B.S. Swanson (1967-1971 ), D.T. Wasan (1971-1987), H. Arastoopour (1989-2003), and F. Teymour (2003-present).

Sigruficant development of the educational programs began under the leadership of Professor McCormack. Interestingly, the American Institute of Chemical Engineers (AIChE) was established in 1908, the same year that Professor McCormack became department chair. History shows that Professor McCormack was an exceptionally active member of the society and, in 1924, served as a co-founder of the AIChE Crucago Section- the society 's first local chapter. In honoring his contributions to the society, the Chicago AIChE local chapter offers the "Harry McCormack Outstanding Senior" award to each of the top students in three chemical engineering departments in the Chicago area. During the tenure of Professor Rushton, the department would reach another critical milestone when Miss Lois Bey became the first co-ed to receive a bachelor's degree in chemical engineering from IIT. The department was also moved from Main Building to its present location in Perlstein Hall. 151

In commemoration of Professor Peck's dynarruc teaching style and his famous "tenminute quiz," the Ralph Peck Lecture Series was established in the late 1970s, and was endowed in the 1990s with funding by department alumru.

During the last two decades, the department has undergone extensive reorganization and program revision. In 1985, under Dr. Wasan's leadership, the Gas Engineering education and research activities moved from the Institute of Gas Technology (now Gas Technology Institute) to the Chemical Engineering Department, under the name of the Energy Technology Program. The scope of this program continued to grow and expand to become the IIT Energy+ Power Center. Today, this activity provides the focal point of the Energy and Sustainability Institute, newly established under the leadership of Professors Henry Linden and Hamid Arastoopour.

In 1995, the Pritzker Department of Environmental Engineering merged with the Chemi-

Winter 2005

I

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ChE 1901

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Chairman Harry McCormack (front center) with ChE farnlty.

Chairman Ralph Peck

Lois A. Bey ChE1950

3

4

Undergraduate Program Milestones

1908 Harry McCormack establishes first Unit Operations Laboratory in the nation

1930s Chemical engineering curriculum begins to shift from chemistry to chemical engineering orientation

1936 Program receives ABEi' accreditation Development of cooperative education program with industry

1937 Arrival to campus of Professor Olaf Hougen, unit processes expert

1938 Professor Max Jakob, authority on heat transfer; joins !ff

1940 Merger of Armour Institute of Technology with Lewis Institute of Arts and Sciences to form Illinois Institute of Technology

1940s Specializations developed in chemistry, food technology, instrumentation and control, management and metallurgy

1958 Professor Octave Levenspiel brings chemical reaction engineering to undergraduate curriculum -

1980s Specializations in biomedical and biochemical engineering Gas engineering activities incorporated through energy technology specialization Unit operations expanded to include transport phenomena

1990s Specialized courses developed in particle technology, fluidization, pharmaceutical engineering and statistics

1995 Merger of chemical and environmental engineering programs

2000 Chemical engineering begins to reflect growing trend toward biological engineering

cal Engineering Department, marking the origin of the Department of Chemical and Environmental Engineering (ChEE).

The following sections trace the history161 and evolution of the department's research and education programs and describe the contributions to the profession by its illustrious faculty and dedicated alumni.

UNDERGRADUATE PROGRAM

In 1908, four years after joining the Department of Chemical Engineering, Professor Harry McCormack assumed the chairmanship of the department-a position he would hold until his retirement from IIT in 1946. Under his direction, the department would make great strides in the advancement of its education programs and maintain a top ranking among all fully accredited chemical engineering departments.

The Unit Operations Laboratory, established at Armour in 1908 by Professor McCormack, provided the first real laboratory instruction in chemical engineering. The Unit Operations outlook was immediately accepted by other schools and soon came to be recognized as an essential part of student training. Students worked in teams of two or three to complete 24 independently developed and continuously modified experiments over a span of three semesters. The result was a chemical engineering graduate who could devise a practical way to evaluate the results of industrial processes and determine the best method to develop these processes.

In 1936, the chemical engineering program received accreditation by the Accreditation Board for Engineering and Technology (ABET) under its first accreditation program. At the same time, a cooperative education program was implemented to enhance the Institute 's interaction with industry.

During this time, the development of both undergraduate and graduate education programs received significant impetus from a number of events: the sabbatical visit in 1937 of Professor Olaf A. Hougen, nationally prominent for his work on unit processes in chemical engineering; the arrival in 1938 on the ITT campus of Max Jakob, an internationally recognized authority on heat transfer; and the merger in 1940 of Armour Institute of Technology with the Lewis Institute of Arts and Sciences to form Illinois Institute of Technology.

In addition to core undergraduate courses, IIT faculty began to develop several elective courses. This allowed undergraduate students to specialize in various branches of engineering and science, or in economics, management, and allied fields. The arrival to IIT in 1958 of Octave Levenspiel led to the introduction of chemical reaction engineering in the undergraduate chemical engineering curriculum.

During the 1980s, under the leadership of Professor Wasan, specializations in energy technology, polymer, electrochemical, biochemical and biomedical engineering were added. In 1985, the unit operations course was revised by Hamid Arastoopour to include three courses: fluid dynamics and heat transfer, mass transfer operations, and transport phenomena.

During the 1990s, under the leadership of Professor Arastoopour, several required courses were also introduced in the curriculum, such as process thermodynamics, numerical and data analysis, and process modeling and system theory. In addition, several elective courses and specializations in the areas of particle technology and fluidization, bioengineering, energy, pharmaceutical engineering, and statistics were developed. In 1995, after the merger of the environmental and chemical engineering programs, a series of undergraduate elective courses in environmental engineering was also introduced.

Beginning in 2000, in response to the shift in industrial emphasis on biology applications, the department began to increase its activities in biological engineering by hiring new faculty and expanding elective course offerings in this area.

Chemical Engineering Education

GRADUATE PROGRAM

UT's graduate program in chemical engineering was established in the early 1930s, with the first MS and PhD degree being awarded in 1933 and 1939, respectively. Integration of the chemical engineering faculty of other universities through their visits to UT campus, interaction with distinguished colleagues in other departments such as Professor Max Jakob, and initiation of research activities at the Armour Research Foundation, contributed to the development of a successful graduate program.

At this same time, research activities on the development of processes for making petrochemicals from fossi l and non-fossil fuels were expanding. The graduate curriculum reflected this expansion as courses were developed in applied chemical engineering thermodynamics, catalysis, fuels and combustion, petroleum refining and chemistry of petroleum hydrocarbons. In the 1950s, fundamental courses including chemical engineering process kinetics, non-Newtonian fluid behavior, chemical reaction engineering, and fluidization, were added. Around 1960, several courses were added to the graduate curriculum including application of mathematics to chemical engineering, unit operations, computational techniques, and transport phenomena.

Industrial short courses have been offered in specific areas of chemical engineering since the 1960s when Professor Peck first taught courses in drying theory and technology. Additionally, in the 1970s and 1980s, many advanced courses in conventional and emerging areas of chemical engineering were developed. These included advanced reaction engineering, process optimization, computer-aided design, topics in biomedical and biochemical engineering, separation processes, particle technology, polymer engineering courses, and interfacial and colloidal phenomena. In addition, inclusion of gas engineering research and education and establishment of energy activities resulted in the gradual addition of several new courses, such as flow through porous media, fluidization and fluid particle systems, and energy/environment/economics. During the mid-1970s , through the generosity of chemical engineering alum William Fink! , the interactive instructional television network (UTV) was established that ultimately enable ITT to broadcast its programs and courses to thousands of UT students and employed professionals.

In the 1990s, the merger of the chemical and environmental engineering programs brought more than 30 graduate elective courses in environmental engineering as electives for chemical engineering students. In addition, formation of the Center of Excellence in Polymer Science and Engineering and the Center for Electrochemical Science and Engineering, along with pharmaceutical specializations resulted in the development of several elective courses, such as electrochemical engineering, polymer rheology, drug delivery systems, pharmaceutical engineering, and particle processing and characterization. Process modeling, statistical quality, and process control were also among the elective courses developed and offered. The establishment of the Master of Food Process Engineering with the collaboration of the National Center for Food Safety and Technology at ITT enabled the department to provide a series of food safety and processing courses for graduate students. Additionally, the joint Master of Science in Environmental Management program was developed in cooperation with the UT Stuart Graduate School of Business.

The new millennium brought added program changes and the addition of new courses and faculty in the bioengineering area as the department continued to work to meet the needs of the engineering professional. Fall 2003 saw the introduction of the totally internetbased Master of Gas Engineering program, developed in collaboration with the Gas Technology Institute. A double master of chemical engineering/master of science in computer science program was jointly developed between the ChEE and Computer Science Departments to effectively train the new generation of process engineers.

RESEARCH PROGRAM

In January 1936, Universal Oil Products (UOP), largely through the efforts of Mr. John J.

Winter 2005

Graduate Program Milestones

1930s Graduate education program in

chemical engineering established

1940s Graduate curriculum expanded

to reflect research in petrochemical processing

1950s Curriculum shifted focus from

process design toward engineering fundamentals

1960s Short courses added to curriculum

to ensure continued relevance of program to industrial needs

1970s-1980s Advanced courses added in

emerging areas: advanced reaction engineering, computer-aided design, polymer engineering, biomedical and biochemical

engineering, gas engineering

1990s Merger with environmental

engineering program adds nwre than 30 electives to curriculum.

Graduate specializations expanded through added ChEE

research centers and collaborative programs

2000 New millennium brings expanded programs in bioengineering and delivery modes designed to meet

the changing needs of the engineering professional

5

6

Chairman J. Henry Rushton Renowned researcher in

mixing technology.

~ ·.bi J ~ II ·, · ,f.1

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Chainnan Bernet Swanson and students study refinery model.

Chairman Darsh Wasan (above) and Max McGraw Professor

Henry Linden (below), National Academy of Engineering

members.

Excellence in Teaching Award established in honor of

Chainnan Hamid Arastoopour.

Mitchell, established a research professorship affiliated with the Department of Chemical Engineering. Dr. Vasili Komarewsky was appointed the first UOP Research Professor. His field of research was catalysis in organic chemistry, especially its application to the chemistry of petroleum.

The Armour Research Foundation (ARF, now known as IIT Research Institute), established April 3, 1936, was the first not-for-profit research institute formed in the United States. Research areas that were being conducted in the Department of Chemical Engineering in the late '30s that were compatible with the ARF research activities included catalysis, chemical filtration, chemistry of oils, oil combustion, and heat transfer. In the areas of combustion and heat transfer, significant interaction occurred among researchers between IIT's chemical engineering and mechanical engineering departments and the Institute of Gas Technology (IGT), including Professors Peck and Jakob.

The research interests of the chemical engineering faculty in the 1940s were cataltytic reactors, distillation, drying, liquid-liquid extraction, mixing, process control, and hydrogenolysis of coal, oil shale, and petroleum fractions. During this period, Professor Rushton developed a world-renowned research program in the chemical engineering aspects of mixing.

During the next 50 years, the research interests of the chemical engineering faculty were substantially broadened. In the 1950s, the faculty pursued research in fluid dynamics, fluidized bed systems, heterogeneous catalysis, mass transfer, partial combustion, and thermodynamics, and, in the 1960s, research emphasized dispersed phase systems, interfacial phenomena, and reactor engineering. In the 1970s, the research activities of newly recruited faculty were concentrated in the areas of transport phenomena and electrochemical engineering. Research areas pursued in the 1980s included analysis of energy conversion processes, biochemical engineering, colloidal and interfacial phenomena, combustion, enhanced gas and oil recovery, fluidization and gas/solid flow systems, multi-variable control, process dynamics, and biomedical engineering.

In the 1990s, three research centers that exist today at the university were initiated and led by chemical engineering faculty. They include: the Energy + Power Center, the Center of Excellence in Polymer Science and Engineering, and the Center for Electrochemical Science and Engineering. In addition, in 1995, environmental engineering research became a major part of the department's research activity as a result of the merger of the environmental engineering program with chemical engineering. Since 2000, the department has added two new research centers to its areas of expertise: the Particle Technology and Crystallization Center and the Center for Complex Systems and Dynamics. Additionally, in 2004, the Institute for Energy and Sustainability was established as an offshoot of ChEE faculty activities.

OUTSTANDING FACULTY EDUCATORS AND RESEARCHERS

IIT has been fortunate in its history to have had numerous outstanding educators. Professors Swanson, Peck, Wasan, Arastoopour, and Aderangi were honored as recipients of the IIT Excellence in Teaching Award. Professors Peck, Swanson and Wasan were also recipients of the American Society for Engineering Education 's (ASEE) Western Electric Fund award for excellence in teaching.

In the '60s and '70s, the department was privileged to have the services of another outstanding teacher, Professor William Langdon. In appreciation for his dedication to teaching, the department's award for teaching excellence was named after him until 2001. At that time, the teaching award was renamed for Hamid Arastoopour, recipient of both the IIT and the department's excellence in teaching awards.

Throughout the department's history, the research and teaching contributions of the chemical engineering faculty have been widely recognized by the American Association of Chemical Engineers (AIChE) and numerous other professional societies and scientific organizations (see sidebar on next page).


DYNAMIC AND LOYAL ALUMNI

Many of the department 's alumnj have achieved success and received widespread recognition for their leadersrup roles in the chemical enterprise. A number of alumni have served as the cruef executive officers of major corporations and orgaruzations, some of which include: Martin Marietta (Bernard Gamson), A. Finkl & Sons (William Fink)), Great Lakes Chemical (John Sachs), Energy Research Corporation (Bernard Bak.er), UOP (Maynard "Pete" Venema), Institute of Gas Technology and Gas Research Institute (Henry Linden), ARCO Chemical (Alan Hirsig), Pabst Brewing Company (Harri s Perlstein), and Hyosung Industries (S.R. Cho).

Several ChE alumni have held national office in the American Institute of Cherrucal Engineers (AIChE), including past presidents Dr. James Oldshue and Dr. John Sachs. The late Professor W. Robert Marshall served as past president of AIChE and was a member of the National Academy of Engineering. Joining him in the Academy are ChE alumru Henry Linden, Kenneth Bischoff, David Edwards, and James Oldshue.

Although a majority of our alumni have pursued professional careers in industry, over the years, a significant number have joined the faculties at UT and other institutions. ITT chemical engineering faculty currently include alumru Henry Linden (chemical engineering) and Harrud Arastoopour, Dimitri Gidaspow, and Javad Abbasian (gas engineering/ gas technology). Today, more than 30 IIT department alumni hold academic positions in the United States and abroad, with several of them occupying positions of academic leadership .

IIT alumnj have hjstorically been loyal supporters of the endeavors of their alma mater. The most notable fundraising round to date began on November 2 1, 1996, when longtime trustees Robert A. Pritzker and Robert W. Galvin provided a challenge grant to ITT of $ 125 rrullion. Trus gift, at the time, represented the largest charitable gift ever promised to an institution of higher education in Illinois, launched a five-year $250 rrullion fundrai sing campaign. In 1997, in response to the Pritzker/Galvin Challenge, the ChEE Department launched its own highly successful capital campaign. These funds continue to be used to establish endowed graduate and undergraduate scholarships, endow chaired professorships, and to enhance departmental educational and research fac ilities. At the end of the campaign, the market value of all endowments and pledges, including matcrung funds, stood at more than $ 12 million.

WITH GRATITUDE

On the occasion of the Centennial of its founding , the IIT Department of Cherrucal and Environmental Engineering acknowledges with thanks the visionary adrrunistrators, talented faculty and exemplary alumru for their contributions to the advancement of the chemical engineering profession since its very origin.

REFERENCES l . Annour /ns1i1we Yearbook, 1894-95

2. Macauley, Irene, The Herilage of Illinois lns1i1we of Technology

3. Peebles, James Clinton, "A History of Armour Institute of Technology," a manuscript prepared beginning in 1948

4. Davis, Kevin, "Charles W. Pierce, African-American Pioneer in Chemical Engineering," /IT Magazine, p. 28 (2004)

5. Kinter, R.C., and D. T. Wasan, " Illinois Tech: Chemical Engineering Department," Chem. Eng. Ed. , 5, p.108(1971 )

6. Parulekar, Salish, and Darsh Wasan, "The History of Chemical Engineering at Illinois Institute of Technology (IIT)," chapter in One Hundred Years of Chemical Engineering, N.A. Peppas (ed.), Klu wer Academic Publishers, The Netherlands, p. 363 ( 1989)

*Phorographs have been provided wilh permission of University Archives, Paul V. Galvin Library, Illinois lnstitule of Technology, Chicago. 0

Winler2005

Renowned Facu/Jy Educators and Researchers

[I Hamid Arastoopour AJChE Fluor Daniel Lectureship

Award in Fluidization, Donald Q. Kem Award,

Fluidized Processes Recognition Award,

Ernest W Thiele Award

[IAH Cinar A/ChE Thiele Award

[I Dimitri Gidaspow AJChE Donald Q. Kem Award,

Fluor Daniel Lectureship Award in Fluidization,

NSF Special Creativity Award

[I Octave Levenspiel A/ChE R.H. Wilhelm Award, ASEE Chemical Engineering

Division Lectureship Award

[I Henry Linden Member of the National

Academy of Engineering, Energy Award of the

U.S. Energy Association, ACS Henry Storch Award,

AJChE Thiele Award, Lowry Award of the U.S.

Department of Energy

[I Demetrios Moschandreas Lifetime Achievement Award of

the l11ternatio11al Society for Exposure Analysis

[I Kenneth Noll Rippenon Award of the National

Air and Waste Management Association

[I J. Henry Rushton AJChE William Walker Award

[I J. Robert Selman Research Award of the Energy

Technology Division of The Electrochemical Society

[I Darsh Wasan Member of the National Academy

of Engineering, ASEE Western Electric Teaching

and Lectureship Awards, ACS Colloid or Su,jace

Chemistry and Langmuir Lectureship Awards,

AJChE Thomas Baron and Thiele Awards,

NSF Special Creativity Award

7

J.d_..ij_§..._e_d_u_c_a_to_r _________ )

8

R. Russell Rhinehart of Oklahoma State University

A message written by the federal government at Fort McHenry has more than ordinary meaning for Russ Rhinehart. In the War of 1812, when the British Navy attempted to capture the Fort and to

control the Baltimore harbor, Francis Scott Key was aboard a U.S. flag-oftruce ship as a negotiator for the States. As the 25-hour siege ended, he saw that "in the dawn 's early light, our flag was still there," and, inspired by his countrymen's bravery, he wrote a poem-the Star-Spangled Banner. Consequently, Fort McHenry is a National Historic Shrine. When the government posts a sign that says "Stay off [the] Wall" at such a memorial, Russ feels that people should respect the request. He describes himself as an obedient respecter of authority.

We were implementing Internal Model Control on a heat exchanger. Suddenly Russ asked whether we were ready for a disturbance, ran to the restroom, and rapidly flushed several toilets, which created a cooling water flo wrate disturbance. Fortunately, the controller worked, because the last thing we wanted to include in the manual was a line which said, "Please do not flush toilets during experiment."

Hoshang Subawalla, PhD, (MS ChE 1993) GE Infrastructure

Water and Process Technologies The Woodlands, TX

Russ was raised in Baltimore, Maryland, and whenever he visited his farm cousins in Bucks County, Pennsylvania, or his coastal cousins in Point Pleasant Beach, New Jersey, they labeled him as a "Southerner" because he had a different accent. So although he was raised in an industrial town with Union allegiance and Yankee heritage, he was perceived as a Southerner within the family confines. But language and customs were never barriers to his playing with his Yankee friends, and some of his favorite childhood memories include making forts from bales of hay in the barn loft, saving a breached calf in birth one memorable day, crabbing in the coastal rivers, building castles in the Atlantic sand, and savoring the best submarine sandwiches on earth.

After college, Celanese hired Russ to work in the Carolinas, and without any overt or intentional changes in accent or style, he suddenly became a Yankee! The company promoted him through several engineering levels to supervise engineers, and during his years there he enjoyed teaching gymnastics to children at the YMCA and teaching values to them in Youth Fellowship. The Yankee persona, it seems, did not make him ineffective.



The 2-D photo of this 3-D object mimics an isometric drawing: from the front-left view, its projection is a triangle; from the top view, its projection is a circle; from the front-right view, its projection is

a square. Russ hand-made this peg that fits into square, round, and triangular holes, as a metaphor for human possibility.

Russ is fond of metaphors ; he insists a square peg can fit in a round hole, and he proceeded to prove it. Consider a right circular cylinder with height equal to diameter. Along the cylin

der axis, the "peg" will fit perfectly into a round

hole-and perpendicular to that axis, it fits perfectly

into a square hole. Shapes, how-ever, have three orthogonal axes, and

if the projection on the third is a triangle, the unusual appearing "peg" will fit perfectly into a round, a square, and a triangular "whole." He enjoys woodworking and made a multifunctional peg that sits on the office mantle, with the legend "You can be effective, even if you are not the expected solution." He teaches this view of flexibility to his students.

Dr. Rhinehart has a way of making engineering a philosophical art, and challenges students to look beyond the numbers and equations fo r a deeper meaning. His special ability to relate engineering to life, metaphorically, gives students a fresh and creative outlook on problem solving, one that better prepares them for industry and research.

Cassie S. Mitchell, BS ChE 2004 Graduate Student

Georgia Tech

Russ 's first summer job after high school taught him a valuable life lesson. He was a helper for carpet installers and quickly learned how to sew invisible seams and cut the reverse wall pattern on the back of a folded carpet edge so it unfolds nicely against a wall. Proud of the technical ability he had learned, at summer's end he asked his boss for a letter of recommendation, expecting to be acknowledged for his expertise and productivity. But instead, he got a very disappointing (to him) three-sentence letter describing him with phrases that included "loyal," "dependable," and "good with customers." His Dad saw his disappointment and explained that quite often, those who are in charge think soft skills are more important than technical skills.

After years of managing people in both industry and academe, Russ now concurs with that viewpoint. Technical skill is important, and he stresses that to his students. But he also tells them that working in a manner that makes the enterprise

Winter 2005

successful is of even greater importance. Team effectiveness and understanding the context of the engineering work are really the critical attributes of success.

He made it clear to pursue an all-around development, not just focus on school.

Mahesh Iyer, Ph.D. ChE 1997 Shell Global Solutions (US) Inc.

Russ graduated from Baltimore Polytechnic High Schooldue, in part, (he says) to the kindness of three teachers. When he showed no initiative to progress to the next step, however, his Dad took matters in hand and gave him an alternative: if he paid room and board, he could continue to live at home, or he could go to college and the family would continue to support him. He chose college. State legislation required the University of Maryland to accept all in-State high school graduates, so that was his next destination. When asked to choose a major, however, he was at a loss to pick a subject area, and since he liked math and science, they eventually categorized him as "A&S Undecided." Shortly after that, however, he learned that engineering majors did not have to take a foreign language, so he switched to chemical engineering (because it paid the highest). He made the Dean's list in the first semester, and now claims that he graduated in the upper 99% of his class.

Russ ponders an analogy with nature when meeting new students-he hopes to see larva become butterflies as the year progresses. Unfortunately, he also sees the opposite, where the most promising of matriculates do not survive in a college environment. So his annual welcome letter to new chemical engineering matriculates warns them that the college environment and cognitive expectations level the playing field, and that the "best" from high school should come ready to play harder than they ever expected, because the dark horses have a strong chance of overtaking them.

Just as Russ learned that academic credentials from high school do not predict college performance, he later learned that academic credentials from college do not predict industry performance. The academic and industrial environments are so different that fitness in one has little relevance to fitness in the other. This observation is the root ofRuss's teaching philosophy that past academic credentials should never be used to judge the future-what appears as a root in one environment may provide wonderful fruit in another season. Life, passion, and a willingness to grow should be the traits we look for in others.

Dr. Rhinehart is graceful and humble, and in spite of

9

being the school Head, he was always available to me. He listens hard, provides support and encouragement, and respects and encourages intellectual independence.

Jing Ou, PhD ChE 2001 Senior Control Engineer

Plug Power

He has been the greatest coach that I have met. Vikas Shukla, MS ChE 1996

Senior Control Engineer B. D. Payne Co.

Early in his junior year at college, Russ was actively progressing in gymnastic skills, but was beginning to be afraid of physical injury. The fear made him hold back on the skill. If the "trick" is performed with proper timing, body position, and use of momentum, it is both safe and awesome to watch .. . and to feel. But when protecting yourself from injury, the flip isn' t as high in the air above the bars .. .it's kept lower, which means there is less time and space to reach for the bars properly, which, conversely, increases the chance of hurting yourself. Russ found that the fear was causing him to cut back on the level of difficulty in his routines. By the end of his junior year, however, he wanted to regain a sense of pride and excitement in his routines, so made the conscious decision to concentrate on technique and to ignore fear. The lesson learned: gymnastics is like life, as is every sport. Understanding and working with the laws of nature, and focusing on the details of performance, not failure, can be a successful approach to life. He likes the logo "No Fear," and teaches it, along with the other fundamentals.

He has a talent for using analogies and stories in lectures. One memorable example included showing us a picture of himself doing a handstand on a stack of chairs to illustrate risk management.

Jennie Weber-Fine, BS ChE, 2003

As Editor-in-Chief of ISA Transactions, Russ quickly redefined the aim and scope, recruited a talented pool of associate editors, established a strong editorial advisory board, and set forth to recruit the best experts in the world as article contributors. His success in building the strength of the journal is reflected by an almost 100% growth in subscriptions over his tenure. Russ fulfills his obligations unflaggingly and with verve.

T. S. "Chip " Lee, Director ISA

The Instrumentation, Systems, and Automation Society

Removing fear requires partially eliminating the power relationship that separates a professor from his students. When students feel safe in personally extending their ideas, if imperfection does not automatically mean failure , they can be free to do amazing "tricks."

IO

I say, Good morning D,: Rhinehart. " He responds, "Good morning Ms. Krueger." He always wanted to

Russ participated on an exhibition gymnastics troupe at the U. of MD, 1963-1969, and was

president in 1967. Gymkana shows traveled throughout the region to support High School fundraising.


1946 January, 19, born, Neptune, NJ

1963 Graduated, Baltimore Polytechnic Institute, Baltimore, MD

1968 BS ChE, University of Maryland, College Park, MD

1969 MS Nuclear Engr, University of Maryland, College Park, MD

1969-73 Process Development Engineer, Celanese Fibers Co., Rock Hill, SC

1973-80 Senior Product Development Engineer, Celanese Fibers Co., Charlotte, NC

1980-82 Area Supervisor, Technical Department, Celanese Fibers Co., Rock Hill, SC

1985 PhD ChE, North Carolina State University, Raleigh, NC

1985-89 Assistant Professor, Texas Tech University, Lubbock, TX

1988 President's Award for Teaching Excellence, Texas Tech University

1989-94 Associate Professor, Texas Tech University, Lubbock, TX

1991-94 Director, ISA Automatic Control Systems Division

1992-.. .. Member, Editorial Advisory Board, Control magazine

1994-97 Professor, Texas Tech University, Lubbock, TX

1995 ISA Automatic Control Systems Division, Man-of-the-Year

1996-97 Graduate Administrator, Texas Tech University, Lubbock, TX

1997-... . Bartlett Chair & School Head, Oklahoma State University, Stillwater, OK

1998-.... Editor-in-Chief, ISA Transactions

1999 Established the MS Control Systems Engineering program at OSU

2001 Inducted as Fellow to ISA -the Instrument, Systems, and Automation society

2002 General Chair, American Control Conference

2004 Listed in InTECH's 50 most influential industry innovators in the past 50 years

2004-.... Treasurer, American Automatic Control Council

Winter 2005

the teacher-student level, and encouraged us to call him Russ or coach. Katie Krueger, BS ChE

December, 2004

Russ feels strongly that lifelong learning is fundamentally important for achieving success in life. His first industrial assignment was on a fully-automated pilot plant, but since he had not had any process control courses, he had to learn feedback control and statistical process control through industrial practice, short courses, and product bulletins. Modeling and decision making are important tools for process management, but he had not had a course in statistics or optimization, so he learned them as he went along. Effectively working on teams and managing others is critical in a competitive environment (whether in business or coaching at the "Y"), so he read self-help books on coaching winning teams and took training courses on personal understanding and interpersonal effectiveness. He had to learn the sciences of adhesion, adsorption, and polymers, and the technologies of pneumatic conveying, drying, and milling. He says that while nearly everything that he learned in school was useful , perhaps 90% of what he actually needed had to be learned out of school.

With that thought in mind, Russ strives to prepare students to direct their own education and to be able to self-validate what they think they learned. He teaches a computer programming class where 20% of the credit for each exercise requires the students to demonstrate validation of their program. Russ says that if the professor always structures the course, prescribes assignments and tests , and grades the student, then school is not imparting the critical ability that will enable students to manage their own learning. Engineers should not be trained to submit work and hope that it is right.

He always tries to create a comfortable learning environment for his students. Whenever he explains something to a student he makes them feel as if they already knew what they came to ask about, and the students come out feeling confident about themselves.

Samir Alam, MS ChE, 2004

Russ supervised a group of engineers in the technical support department of a manufacturing plant that hired eight fresh graduates to fill engineering positions. While these new hires had the intelligence and fundamental base to learn the specific science and technology for the job, they retained some student-oriented perspectives that prevented them from being true business participants. So he decided to hold Friday afternoon "industrialization" sessions to help accelerate their path toward team productivity. Session topics included "Doing, bringing to fruition, is valued-not the learning," "People effectiveness is more important than technical or economic proficiency," "Sufficiency is a greater value than excellence," and "Work in a parallel, not sequential manner."

Russ says that if a school's intention is to take the high school students and prepare them to be engineers, then the school needs to teach the aspects that will help them realize their objective, but then adds that the word "teach" is the wrong word-teaching is a professor's activity. A school should provide experiences from which students comprehend and integrate those viewpoints as their own. Engineering is a "way," an approach to working, not simply a collection of technical skills or a memorized set of adages. The "way" must be internalized, not memorized.

In his graduate-level Fluid Dynamics class, he included a personal story from his first job. They had a "sticky fiber" problem. Russ was keen to impress everybody with his technical abilities, went off to his office, developed models and analysis, and came back with a solution a week or two later. Meanwhile, the operator solved the problem by turning the temperature up a notch to dry out the solvent from the polymer fiber. This sto1y, this one nugget that he gave me, has been vital to my success as an engineer and

11

a technology leader. Soundar Ramchandran, PhD ChE, 1994

Group Leader, Solutia.

Russ feels that industrial experience need not be a required qualification of a professor. He sees no difference in the teaching, research, or service effectiveness of professors who have had, or have not had, industrial experience, and strongly feels that success is not predicated on employment history. Acknowledging that the environment and values of industry are substantially different from those in academe, he says the difference is not about technical substance and is not related to the use of profitability indices in making decisions. It is a difference in the work environment that makes the "way" of success in one career inappropriate to fitness in the other. Unless professors understand the difference and include an industrial perspective in their curriculum, a school's program cannot fully prepare graduates for fitness of use.

Roughly 5000 BS chemical engineering students graduate every year in the US, and eventually about I 00 of them end up in academe. Russ feels that it is most important that the undergraduate experience should focus on preparing the 98% for successful futures.

Every year, Dr. Rhinehart invites professionals from industry to evaluate our curriculum. Changes are made accordingly to ensure that we learn the viable tools to be successful in industry and life.

Myszka (Karina) Paprocki, BE ChE 2003 Graduate Student U of JL

Russ enjoyed his years in industry, but it was not a perfect fit. He had always been fascinated by the "why" of things and spent hours at home secretly deriving equations as a way to understand processes. At home in the late '70s, playing with his TRS80 color computer (a 32k RAM, no hard drive, computer connected to the TV), he realized that the games he was programming in BASIC for his children were more advanced than the control algorithms that were being used in industry. That revelation made him decide to explore the possibility of better methods of automating process management.

Since in his spare time he had also always enjoyed coaching gymnasts, leading youth ministry, and developing engineers from fresh graduates, he felt that the job of being a professor might be a good place to pursue both human resource development and discovery in process management automation. He returned to school to get his PhD, choosing North Carolina State University for that endeavor.

12

When Russ came to N. C. State for his doctorate he joined a large research group working on a coal gasification pilot plant. We quickly recognized and admired his maturity, wisdom, common sense, and invariable warmth and cheerfulness, and he may still have been in his first year

when we asked him to take the position of plant supervisor, a position he held until he finished his graduate program. His skill as a leader in the deepest sense of the word was transparently clear. Russ also had a strong interest in teaching then. At his request we put him in charge of a recitation section of the material and energy balance course, and almost immediately he became recognized as one of the strongest teachers in the department. I was pleased but not surprised at his post-graduation successes on the faculty at Texas Tech and as department head at Oklahoma State. Even when I was his doctoral advisor at N. C. State I viewed him as more of a colleague and a friend than an advisee, and he remains one of my very favorite people in our profession.

Richard M. Felder, Emeritus North Carolina State University

"Take your passion, and make it happen" is a line from a popular song of the '70s that has special meaning for Russ. He enjoyed working in industry, but has always been glad that he had the nerve to make his passion a reality and to start a second career, although it was a difficult decision. Several co-workers have expressed envy at his flexibility and determination in breaking out of the situational entrapment of a comfortable life.

D1: Rhinehart 's animated teaching style incorporates humorous anecdotes that integrate the course material.

Jerimiah Cox, BS ChE 2000 Staff Product Support Engineer

National Instruments

His approach has the students grasp the fundamental concepts and the more delicate intricacies. In addition, his enthusiasm engenders students to the material.

Jacob Dearmon, BS ChE, 2000 PhD Candidate, Economics

University of Oklahoma

Russ has retained the industrial values of practicality, which means that he is not exactly the round peg one expects to find in academe. While accepting that theoretical analysis and proofs are important to reveal understanding and limits of a technique, and while he values the insight and direction they provide, he feels their idealized nature makes them insufficient for establishing credibility of a technique in the real world. Credibility requires experimental demonstration, and experimental work reveals the problems that need solutions. So his research program (both synthesis and analysis) has always been, and continues to be, driven by its experimental component and "the possible."

Russ enjoyed growing up in the mid-Atlantic of the '50s and '60s, and in the next two decades he equally enjoyed the contrasting culture, climate, style, and food that the South presented to the "Yankee" among them. He also learned from the contrast and discovered that there are many ways to


achieve an end. For instance, engineers and business leaders of the South were just as creative, productive, and focused on winning as their counterparts in the North, but in a humanly gracious style. He was pleasantly surprised to have unknown perceptions identified and challenged, and to discover that gentleness could be an essential part of the "American way." Accordingly, upon completion of his PhD, he considered that another region might provide additional personal joy and insight, and moved to Lubbock and Texas Tech University. He subsequently enjoyed the many levels of experiences he had there-Tex-Mex food, rodeos, the incredible sun, and Texas-Friendly.

While he was in Lubbock, Russ married Donna, a Texan with three sons (so once again, he was the one with the accent). Planning on staying there forever, they built their ultimate dream house. Russ designed it and Donna decorated it, and while this is not a recommended exercise for spouses, it worked for them. Later, the family moved to Stillwater and placed all their equity into an even grander ultimate house, which they once again designed and decorated. When a new family came to town and told their builder about the sort of house they wanted to build, the contractor responded, "I already built that house, and the owners just might sell it to you." The bottom line is that Russ and Donna have now built four houses in their fifteen years of married life. They have lived in the present home for over a year now, and friends are asking, "When 's the next one?"

I'm sure that other people will also mention Russ ' annual Christmas letter, his creativity always surprises and delights me.

Lisa Bullard, PhD Lecturer and Director of NCSV

Undergraduate Studies

When Oklahoma State University was seeking a new School of Chemical Engineering Head, Russ was looking for an opportunity to contribute on a broader level. The former Heads,

Winter 2005

Russ and Donna and the latest of their "ultimate" homes.

Bob Maddox, Billy Crynes, and Rob Robinson, had created a very strong program legacy, and he felt honored to be chosen to oversee its continued development.

Russ says it is easy to brag about the program at Oklahoma State. Some of the accomplishments he is especially proud of are

• For three of the past ten years, a team of OSU chemical engineering seniors won First Place overall in the A!ChE National Process Design Contest.

• For six years in a row the OSU A!ChE Student Chapter has been honored with an "Outstanding " rating (top 10%) by the A!ChE.

• Last year an OSU senior who placed first in the regional paper competition, placed second overall in the nation.

• This year the OSU juniors won the regional ChemE-Car contest, and will compete nationally, as did three OSU teams in the past four years.

• For the past ten years OSU chemical engineering students have sustained a first-time pass rate of 97% on the FE Exam.

• Last year two undergraduates were recipients of Goldwater scholarships, and last year one of the seniors was selected by USA Today to their AllUSA Academic First Team.

Russ believes that being a professor allows one to make a substantial contribution to the quality of life through developing human resources, through developing the knowledge and tools that can be used throughout a lifetime, and through developing the infrastructure to support those efforts. He thoroughly enjoys helping chemical engineering make that kind of a contribution in society. 0

13

.1;_..511111113._c_l_a_s_s_r_o_o_m _________ )

REDUCTION OF DISOLVED OXYGEN AT A COPPER

ROTATING-DISC ELECTRODE

GARETH KEAR, 1 CARLOS PONCE-DE-LEON ALBARRAN, FRANK C. WALSH

University of Southampton, Highfield, Southampton S017 JBJ, U.K.

I ndustrial electrochemistry, which concerns the controlled interconversion of electrical and chemical energy, has a wide scope. The applications of electrochemistry include

batteries and fuel cells, materials extraction and synthesis, chemical sensors, pollution control, corrosion monitoring and the surface finishing of metals.1 11 The discipline of electrochemical engineering has been defined as "the understanding and development of practical materials and processes which involve charge transfer at electrode surfaces."121 Electrochemical engineering is the branch of engineering that embraces electrochemical processes, the means of processing, the resulting products, and the industrial/commercial/ social use of the products. 1z.31

In contrast to the well-established field of chemical engineering, the specialist discipline of electrochemical engineering is much younger, having evolved over the last forty years or so, as evidenced by the progressive appearance of texts and monographs.14-101 It is important that undergraduate engineers have a working knowledge of electrochemical engineering principles in order to appreciate the scale and scope of electrochemistry and its industrial and technological relevance. Electrochemical engineering has all the challenges of chemical engineering with the added challenge of electrode potential as a controlling influence and current distribution as an essential reaction parameter. A number of educators have realized the importance of the discipline of electrochemical engineering and have described its introduction into chemical engineering process laboratory courses. (1 11

The literature in the field of chemical sciences education contains many papers on electrochemistry experiments; for

1 University of Queensland, Brisbane, Queensland 4072, Australia

example, some 159 articles have been published in the Journal of Chemical Education since 1995, with the emphasis often being on the demonstration of physical aspects of chemistry to the early stages of undergraduate courses and to science courses in schools. Examples include a slide projector corrosion ceUl121 and the determination of Avogadro's number by electroplating.1131 There are still, however, relatively few articles that have been devised for undergraduate engineers in order to demonstrate the principles and practice of electrochemical engineering in a clear, quantitative fashion. Examples of education papers in electrochemical technology include the topics of aluminium-air cells,1141 proton exchange membrane fuel cells, 1151 reduction of ferricyanide ion at a rotating disc electrode,1161 electrodeposition of copper at a ro-

Gareth Kear obtained both his bachelor degree with honors in Applied Chemistry (1998) and his PhD in Applied Electrochemistry (2001) at the University of Portsmouth in the United Kingdom. Gareth is currently a Materials Scientist at the Building Research Association (BRANZ) Limited in Wellington, New Zealand. His work directly concerns the continued development of New Zealand's engineering and construction industries through research, consulting and technology transfer. Carlos Ponce de Leon Albarran has a BSc and an MSc in Chemistry from the Autonomous Metropolitan University, Mexico, and a PhD in Electrochemistry/Electrochemical Engineering from the University of Southampton (1995). His research interests include electrochemical techniques, metal ion removal, characterization of novel electrode materials, electrochemical strategies for pollution control, redox flow cells for energy conversion and electrochemical reactor design. Frank Walsh holds the degrees of BSc in Applied Chemistry from Portsmouth Polytechnic (1975), MSc in Materials Protection following periods of study at UMIST/Loughborough University (1976), and a PhD on electrodeposition in rotating cylinder electrode reactors from Loughborough University (1981 ). He is the author of over 200 papers and three books in the areas of electrochemistry and electrochemical engineering. Currently, he is Professor in Electrochemical Engineering at the University of Southampton and takes a particular interest in the training of students and industrial engineers in the areas of energy conversion and surface engineering.


14 Chemical Engineering Education

We believe that this paper will prove useful to electrochemical engineering and electrochemistry courses involving the study of corrosion processes, materials science, and

environmental electrochemistry. The level of teaching is relevant to second- or final-year undergraduates, master degree students, and to the first

year of postgraduate MPhil/PhD research programs.

tating disc electrode,11 71 and environmental recycling of materials.1181

In the case of metal corrosion, one of the authors has over 25 years experience in dealing with industrial corrosion problems, many of them being attributable to a poor appreciation of the principles of metallic corrosion by practicing engineers. The field of corrosion and protection of metals is well established, as evidenced by many texts.119·211 The subject areas of fluid flow and mass transport, however, are often covered superficially. The reduction of dissolved oxygen is a key cathodic reaction and hence a major contributor to many cases of industrial corrosion, and it is essential to consider the effects of fluid flow and mass transport of dissolved oxygen to the electrode surface in a systematic and quantitative manner. The chemical education literature contains relatively few articles on the electrochemistry of oxygen although topics covered include correlations to describe oxygen transfer from air to water1221 and an oxygen sensor for automotive gas streams .1231

This paper describes a training tool in electrochemical engineering, electrochemical technology, and corrosion. The approach is in line with the desire for students to "learn by doing"1241 and has been used as part of a "consultant-in-the-classroom" approach. 1251 We believe that the paper will prove useful to electrochemical engineering and electrochemistry courses involving the study of corrosion processes, materials science, and environmental electrochemistry. The level of teaching is relevant to second- or final-year undergraduates , master degree students, and to the first year of postgraduate MPhil/PhD research programs. Delegates on short courses in electrochemical engineering and corrosion have found the experiment to be informative and successful in explaining the role of cathodic kinetics in (and mass transport contributions to) corrosion reactions. Students have appreciated that a (typically) 90-minute set of experiments can provide quantitative data on mass transport rates under controlled fluidflow conditions.

The experiment has been used as part of a training program for first-year PhD students in electrochemical engineering and applied electrochemistry at the Universities of Bath, Portsmouth, Queensland, and Southampton. The material has been used as a laboratory exercise leading to BSc degrees in applied chemistry and BSc in environmental sciences (Uni-

Winter 2005

versity of Portsmouth) together with BEng and MEng in chemical engineering and short courses on electrochemical techniques, pure and applied, for industry (University of Bath). The technique has also contributed to the study offlowenhanced materials degradation via MEng and PhD mechanical engineering research projects at the University of Queensland. The early training of PhD students in electrochemical engineering at the University of Southampton has also benefited from studies described in this paper.

The reduction of oxygen at a cathode surfacei261 is important in several areas of technology, including the positive electrode of metal-air batteries ,1 141 fuel cells,1271 batteries,12s1 and gas sensors,1291 a competitive reaction during metal ion removal1301 and a common cathodic process enabling the corrosion of metals .1 19·21 1

In neutral or alkaline electrolytes (as in the present studies in seawater, at approximately pH 8), oxygen reduction can be stated as

(t)

The electrochemistry of oxygen reduction can be studied using linear sweep voltammetry at a disc electrode. In this technique, the electrode potential , E, is controlled (volts, V vs. a reference electrode) by a potentiostat and swept at a constant rate between fixed potentials. The current is continuously monitored during this process and steady-state current vs. potential curves can be recorded on a microcomputer (or an x-y chart recorder) .

DETAILS OF THE EXPERIMENT

The instrumentation and experimental arrangement are shown in Figure I and Figure 2 (next page). All measurements were made at 25 ± 0.2°C in air-saturated, filtered seawater. (The electrolyte used in this study can readily be replaced by the simpler 3.5% NaCl.) An Eco Chemie, Autolab was used with a PGSTAT20 computer-controlled potentiostat system with GPES (General Purpose Electrochemical Software) version 4.5 coupled to the Pine Instruments Company (model AFMSRX) analytical rotator. The rotator mechanism provided better than 1 % accuracy over a 50- to 10,000-rpm speed range. A standard, RDE, three-compartment, electrochemical cell was used with a platinum gauze counter electrode, and a Radiometer Analytical A/S, REF 401, saturated

15

calomel electrode (SCE) was used in conjunction with a Luggin-Haber capillary. The cell was fitted with a thermostatically controlled water jacket.

The counter-electrode and working-electrode sections of the electrochemical cell were separated from each other with a Nafion® 423 ion-exchange membrane. The internal, wetted dimensions of the RDE cell were 5.5-cm diameter and 6.0-cm height. From these values, a mean electrolyte volume of approximately 140 cm3 was used. Electrolytes were aerated for at least five minutes prior to the commencement of measurement with a gas diffuser connected to an air pump. In order to establish the background current, de-aeration was achieved by sparging with standard oxygen-free nitrogen (supplied by British Oxygen Company) for at least 10 minutes prior to measurement. Salinity was measured directly with a ProfiLine LF 197, WTW Measurement Systems, Inc., salinometer and indirectly via conductivity measurements with the Metler-Toledo MPC 227 conductivity/pH meter. Kinematic viscosity was measured directly with a B-type Ostwald U-tube viscometer, and oxygen concentrations were estimated with a Jenway 3420 dissolved oxygen meter. All potentials are quoted relative to the saturated calomel electrode (SCE).

The electrode surfaces were first degreased in ethanol then wet polished, with a 0.3 µm alumina slurry, on micro-polishing cloth, followed by three series of I-minute polishings on double-distilled water soaked polishing cloth.

From a health and safety perspective, the electrolyte has been chosen to provide an inherently safe, low-cost, aqueous, and room-temperature solution. The use of rotating parts requires appropriate care, and demonstrators point this out to the student. A low-power rotator is used and the rotating parts are shielded from the students when in use.

THE OXYGEN REDUCTION REACTION

A simplified relationship for the complete reduction of oxygen involves an overall exchange of four electrons, resulting in the production of hydroxyl ions (or water molecules at low pH). The complete, four-electron reduction of oxygen may occur directly, as in Eq. (1) above, or indirectly, via two steps each involving two electrons

(2)

(3)

Hydroxyl ions or water molecules can be products of a single four-electron step or the result of cumulative twoelectron reduction steps where oxygen is reduced to peroxide, which in tum is reduced to hydroxyl ions. The

16

general scheme describing the reduction mechanism of the reduction of oxygen is shown in Figure 3.126•291

Figure 3 shows the steps involved during the reduction of oxygen. First, oxygen has to be transported to the electrode surfacethis process depends on the convection or mass transport, i.e., fluid velocity or electrode rotation. Once on the electrode surface, the oxygen molecule reacts to produce hydrogen peroxide and hydroxyl ions, a step that is controlled by the electron transfer rate. The kinetics of oxygen reduction are expected to be very specific to the

Visual digital unit

Computer controlled Potentiostat

Motor rotation speed controller

Rotation Motor

Figure 1. Arrangement of instrumentation to obtain current vs. potential (voltammetry) curves at controlled rotation speed of a disc electrode. WE-working electrode ( copper rotating disc electrode: CE-counter electrode (platinum mesh}; RE-reference electrode (saturated calomel electrode).

(a) (b) (c) (g) (h)

(i)

(e)

G)

(d)

Figure 2. Three-electrode electrochemical cell: (a) saturated calomel electrode (SCEJ reference electrode; (b) air gas blanket outlet; (c) Pine Instruments MSRX arbor, ACMDII 906C rotator arm; (d) thermostatic water jacket; (e) copper rotating disc working electrode; (fJ Luggin-Haber capillary; (g) air diffuser; (h) platinum gauze counter electode; (i) perpex cell lid; (j) glass flange containing cation exchange membrane (Nafion 423).


system under study, where the character of the substrate, surface condition, temperature, and electrolyte conditions all have an influence over each step in the reduction mechanism_l26.3 1-331 Once the product is formed, its removal from the electrode surface depends again on mass transport. Delahay performed an early study dealing with the reduction of dissolved oxygen at copper in chloride media in 1950_13 41 Over the whole range of negati ve overpotentials studied in this case, it was determined from polarization curves and oxygen-consumption data that the number of

Bulk solution

0 2 (bulk)

40ff (bulk)

Electrolyte

Mass transport

of reactant 0 2 (surface)

Charge transfer of electrons from surface reactants to products

Mass transport

of reactant

Electrode surface

Figure 3. The stages of oxygen reduction consisting of mass transport to and from the electrode surface and electron transfer reaction .

TABLE 1

electrons consumed was predominantly four. Although hydrogen peroxide was always formed, catalytic decomposition of hydrogen peroxide was found to prevent the build up of the intermediate reduction product.

RESULTS AND DISCUSSION

The experiments described in this paper have a number of learning outcomes, which are summarized in Table 1. The impact of the experiment on parts of a BEng/MEng chemical engineering curriculum can be illustrated by the following examples: (a) mass transport rates and dimensionless group correlations (year 1 or 2), (b) process intensification due to agitation (year 3), (c) fluid flow around rotating systems (year 1), (d) corrosion and materials degradation (years 1 to 3), (e) electrochemical engineering techniques (a year 2 option), and (h) physical transport phenomena (year I).

Application of the rotating disc electrode, RDE, to electrochemical systems is a well-established131-33J 5J method of quantitatively controlling the fluid flow and mass transport conditions. The use of ferricyanide ion reduction or copper deposition have been well rehearsed in the literature but we have preferred in teaching experiments to use the reduction of dissolved oxygen, which (a) is relevant to corrosion and a wide range of other electrochemical technologies, (b) involves no significant phase changes on the electrode surface, (c) provides a simple reactant at a controlled level, (d) facilitates the use of an inexpensive RDE material, and (e) shows regions of potential where the reaction is under charge-, mixed- or mass-transport control.

Learning Outcomes of the Experiments

Instrumentation for electrochemistry

Three-electrode electrochemical cells

Fluid flow and its control

Mechanism of oxygen reduction

Electrochemical voltammetry

Types of rate control

The rotating disc electrode

Winter 2005

LEARNING OUTCOME

Appreciate the typical equipments used to obtain current vs. potential curves at a controlled rotation speed of the disc electrode.

Understand the need for three electrodes.

Appreciate that the rotating di sc electrode provides effecti ve control of fluid flow.

Know the steps involved in transport of oxygen to the electrode surface followed by its reduction.

Understaod the equipment needs for electrochemical voltammetry.

Appreciate the different types of rate control , namely, charge transfer, mass transport, and mixed control.

Understand the relationship between fluid flow and mass transport rates.

EVIDENCED BY. ..

Student's abili ty to describe the properties of the instruments and electrochemical cell (in Figure l ).

Student's ability to define the three electrodes used in the study (i.e., working reference and counter electrodes in Figure 2).

Student's knowledge that the fluid flow is laminar as long as the disc surface is hydrodynamically smooth and the rotation speed is within appropriate limits.

Appreciation of the charge transfer and mass transport steps involved (Figure 3).

Obtaining correct current vs. potential curves (Fig. 4).

The shape of the current vs. potential curves at a fixed rotation speed indicates the potential regions for various types of rate control (Figure 4).

Measurement of limiting current vs. potential for a series of rotation speeds and the application of the Levich equation (Figure 5).

17

Figure 4 shows a family of current vs. potential curves for oxygen reduction at the copper RDE. The potential has been linearly increased, with time, from the opencircuit potential to a value of approximately -1.4 V vs. SCE, at a rate of 0.5 m V s·', while the current is continuously monitored. The linear sweep voltammetry in Figure 4 shows a single wave for oxygen reduction, which indicates an overall 4-electron exchange for this system. The curves can be divided into the following regions:

(a) At low overpotentials, the current rises exponentially with potential and the reaction is under "complete charge transfer control," i.e. , the reaction rate is governed by the speed of electron transfer from the cathode to the oxygen adsorbed at the electrode surface.

(b) At more negative potentials, the current increases with potential; the current is affected both by potential and by the speed of the rotating disc electrode. This is the "mixed control" region.

(c) Further increase of potential reaches a region where the current is approximately constant. This is the limiting current (IL) plateau where the oxygen reduction is under "complete mass-transport control." The rate-determining factor is the speed at which the reactant (dissolved oxygen) can reach the cathode surface. Under complete mass-transport control, the reaction is very flow-dependent. Increasing the relative velocity between the cathode and the electrolyte (i.e., agitation of the solution) will increase the rate of mass transport and, hence, IL will increase. (Students are encouraged to consider alternative methods of agitation, such as impeller stirring, pumped flow and the use of jets or turbulence promoters together with their practicality).

(d) When the potential is made more negative, a secondary cathode reaction, hydrogen evolution takes place in addition to the oxygen reduction

(4)

The entire oxygen-reduction curve can be analyzed (considering charge-, mixed- and mass-transport control) using a Koutecky-Levich approach. 131· 33l Here, we focus complete mass-transport control on the limitingcurrent region. The limiting current depends on several factors, including the bulk concentration of dissolved oxygen, cb, the active area of the electrode A, and the averaged mass transport coefficient km

IL= kmAzFcb (s) where z is the number of electrons transferred per oxygen molecule (=4) and Fis the Faraday constant (96485 C mo)·' ). The mass transport coefficient can be consid-

18

0.1

- - - Mean background

0.0 0

-0.1 <'/ -1 E

u <( <( E

-0.2 E

-2 "E :i-~ -0.3

·u5 C:

:::J Q)

0 -3 -0 ..., C:

-0.4 ~ :::J

-4 0

-0.5 (d)

-5 -0.6

-1 .6 -1.4 -1.2 -1 .0 -0.8 -0.6 -0.4 -0.2

Potential vs. SC E / V

Figure 4. Cathodic polarization curves for oxygen reduction at a copper RDE in aerated seawater at 25°C. Potential sweep rate-0.5 mV s·1

; increasing order of rotation rates-21,42, 84, 126, 188, 251, 366, 503, 681, and 995 rad s·1

• (a) electron transfer control, (b) mixed control, (c) mass transport control, and (d) secondary reaction (hydrogen evolution). The broken lines show the region of mass transport and the vertical lines show the points at which the limiting current was m easured in each current-potential curve. The mean background current was measured in de-aerated electrolytes.

0.30

2.5

0.25 <'/

2.0 E u

<( <( E 0.20 E

c 1.5 :i-~ "iii :5 0.15 C:

Q) u -0 Ol i:: C: 1.0 :;::, ~ .E 0.10 :::J

:.J u Ol C:

0.05 0.5 .E

:.J /

/ /

/ 0.00 0.0

0 5 10 15 20 25 30 35

(Rotation rate, ffi / rad s·1)°-5

Figure 5. Limiting current vs. angular rotation velocity (Levi ch) plot for oxygen reduction at a copper RDE in seawater at 25°C. Limiting current values were taken from the cross of the vertical lines and the current potential curves in the plateaux of Figure 4.


ered as a rate constant that is normalized with respect to dissolved oxygen concentration and cathode area . (Students are encouraged to consider appropriate ways of measuring the disc area and the accuracies involved; e.g., the assumption of a circular area versus direct measurement using an optical microscope.)

In this experiment, the electrode area is kept constant by using the polished, flat surface of a fixed radius, r (0.19 cm) rotating disc (A = '1Tr2 = 0.113 cm2) of pure copper. The bulk concentration of oxygen is held constant by continuous surface aeration of the seawater electrolyte to achieve a saturated concentration (cb = 2.63 x 10-1 mol cm-3) at 25 °C _l351 In other cases of electrode reactions, the bulk concentration of reactant may be varied by volumetric preparation.

For a fixed electrode geometry and constant electrolyte conditions, the mass transport coefficient is dependent on the relative velocity, U, between the electrode and the electrolytel1-101

(6)

The rotating disc electrode (RDE) enables the electrolyte velocity towards the electrode to be carefully controlled under conditions of highly reproducible laminar fluid flow. For a polished RDE, the velocity exponent is very consistent between experimental systems, where x = 0.5. In thi s case, Eqs. (5) and (6) can be combined to give

(7)

Here, the rotation speed, w is in unjts of radians per second. Conversion of rotation rate of the RDE in rpm to angular velocity in rad s-1 can be achieved by

_ ( rev min -I )(2 n rad rev - I) rads 1 = ~--~~---~

60 s min- 1 (8)

The influence of the physical properties of the fluid on mass transport were established by Levich ,'361 who confirmed that, for the smooth RDE, the limiting current, IL will vary to the square root of the rotation rate

(9)

where vis the kinematic viscosity of the electrolyte and Dis the diffusion coefficient of oxygen (sometimes called the diffusivity, in the older literature). Under conditions of complete mass transport control and for constant z, A, v and cb, the Levich equation simplifies to

(IO)

and a Levich plot of the limjting current vs. the square root of rotation rate of the RDE should be linear and through the origin with a gradient, K, where

K = 0.62 zFAD0·666v--O.l 66 cb (11)

Winter 2005

Electrochemical engineering has all the challenges of chemical

engineering with the added challenge of electrode potential as a controlling influence and current distribution

as an essential reaction parameter.

From the slope K, the diffusion coefficient D, can be calculated via a rearrangement of Eq. (11) to give

D0.666 = IKI 0.62 z F Av--0·166 cb

( I 2)

From Eq. (12), the diffusion coefficient of dissolved oxygen is given by

( IKI J3

D = 0.62 z F Av--0· 166 Cb (13)

The experimental program had three objectives

• To characterize the oxygen reduction reaction and to define the electrode potential ranges for kinetic (charge transfer) control, mixed control, masstransport control and the side reaction.

• To show the relationship between flow conditions and mass transport and, hence, the dependence of reaction rate on rotation speed of the disc electrode.

• To determine the diffusion coefficient for dissolved 0

2 under controlled conditions of temperature and

saturated concentration of dissolved Or

As predicted by the Levich equation (Eq. 9), the limiting current of each member of the family of current vs. potential curves showed in Figure 4 depends on the mass transport conditions, i. e., the rate of rotation of the electrode. The limiting current at each rotation rate can be obtained by subtraction of the background current (dotted line), i. e., the current of the electrolyte with no oxygen dissolved. Figure 5 shows the plot of the ]jmiting current vs. the square root of angular velocity of the rotation disc electrode, according to Eqs. (9) and (10). The ]jnear plot passed through the origin according to the theory and demonstrated that the reduction of oxygen at the limiting current is proportional to the square root of the angular velocity. Limiting current densities of approximately -0.32 to -2.38 mA cm-2 were measured for square root angular velocities of 4.6 to 31.6 rad05 s-0-5. The mean diffusion coefficient was calculated as (1.5 ± 0.2) x 10-5 cm2 s-1. The data indicates that, under full mass transport control, the exchange of four electrons controls the rate of oxygen reduction (the reduction of a hydrogen peroxide intermediate was not observed during oxygen reduction in these experiments).

19

SPECIMEN CALCULATION OF D0

USING EQ. (13) 2

[

19,399 x 10-6 A rad0

·5

s0

·5

1 :

3

( 0.62 )( 4 )( 96485 C mo1-1 )( 0.113 cm 3 )( 9.33 x I 0-3 cm 2s- 1 )-0 166 ( 2.625 x I o-7 mo! cm-3 )

( 14)

D02 = ✓( 6.08 X 10--4 )3

= (1.5 ± 0.2) X 10-5 cm 2 s-1 at 25 ± 0.1 °C ( 15)

Using an experimentally derived value of K, the experimentally determined diffusion coefficient for oxygen in filtered seawater compares favorably with literature values obtained at copper of 1.4 x 10-5 cm2 s-1 at 20°C in 0.5 mo! dm-3

NaCl,'341 1.7 X 10-5 cm2 s- 1 at 23°C in 1 mo! dm-3 NaCl,1371 and 1.8 X 10-5 cm2 s-1 at 23°C in 1 mo! dm-3 NaCl.r38•391 The experiments can be extended to rationalize the rate of corrosion of copper in chloride electrolytes under mass-transport controlled conditions, the analysis of the mixed control region of current vs. potential curves using a Koutecky-Levich approach, and the use of a rotating cylinder electrode to study oxygen reduction under turbulent flow conditions. 1401

CONCLUSIONS

Technical achievements

20

1. The experimental current potential curves in Figure 4 showed various zanes: ( a) the charge transfer zane between -0.3 and -0.5 V vs. SCE where the current is independent of the rotation rate, ( b) the mixed zane where the rotation rate partially influences the current values, ( c) the mass transport zane where the current depends completely on the rotation rate and the charge transfer was fast, and (d) the secondary reaction zane where hydrogen evolution occurs together with the desired reaction.

2. Linear sweep voltammetry was used to obtain qualitative data, such as the limiting current for the reduction of oxygen on a copper electrode su,face as a function of rotation speed and the diffusion coefficient of oxygen. A single, 4-electron wave for the reduction of oxygen on a rotating disc copper electrode was observed and under full mass transport control.

3. The rotating disc electrode (RDE) technique allowed the reduction of oxygen to be studied under controlled conditions of laminar fluid flow.

4. The mass transport coefficient, k,,,, was proportional to the square root of the rotation rate of the disc electrode, w112, under the experimental conditions

5. A linear, Levich plot of IL vs. w112 allowed the

diffusion coefficient, D, of oxygen, in air saturated seawater, to be calculated as 1.5 x 10-5 cm2 s·' at 25 °C in good agreement with literature values.

Educational experience

The specific learning outcomes of the experiments together with their relevant subject areas are summarized in Table I. The subject areas concerned include instrumentation and cells for voltarnmetric techniques in electrochernistry, fluid flow and its control, the mechanism of oxygen reduction, types of rate control, and appreciation of mass transport control using a rotating electrode.

ACKNOWLEDGMENTS

Early tutorial studies on oxygen reduction at rotating disc electrodes were carried out in the Applied Electrochernistry Group at the University of Portsmouth, UK. G. Kear and F.C. Walsh are grateful to Dr B. Des Barker (University of Portsmouth) for early tutoring in electrochemical corrosion.

NOMENCLATURE

Meaning [Units/

A active RDE area (A= 0.113 cm2) [cm2]

cb bulk oxygen concenu·ation (cb = 2.63 x 10-7 mol cm-3) [mol cm-3]

d electrode diameter [cm]

D diffusion coefficient of dissolved oxygen [cm2 s-1J F Faraday constant (F = 96 485)[A s moJ-1

]

IL limiting current [A]

current density [A cm-2]

km mass transport coefficient [cm s-1J

K proportionality constant in Levich equation (K = 9.40 x I0-6) [A rad-05s05J

r radius of rotating disc electrode [cm]

U velocity of rotating disc electrode [cm s-1]

z number of electrons transferred (z = 4) [dimensionless]

v kinematic viscosity of electrolyte (v = 9.33 X 10-3cm2s-1 at 25°C and a salinity of 3.5%"~tI371) [cm2 s-1]

w angular velocity of the rotating disc electrode [rad s-1]


REFERENCES I. Pletcher, D. , and F. C. Walsh, Industrial Electrochemistry, 2nd

ed., Chapman and Hall, London, U.K. (1990)

2 . Walsh , F.C. , A First Course in Electrochemical Engineering, The Electrochemical Consu ltancy, Romsey (1993)

3. Walsh , F.C., Bulletin ofElectrochem., 7(5), 2 10 ( 1991 )

4. Mantell , C.L., Electrochemical Engineering, 4th ed. , McGraw Hill , New York , NY (1960)

5. Newman , J .S., Electrochemical Systems , Prentice-Ha ll , Eag lewood Cliffs , NJ ( 1973)

6. Pickett, D.J. , Electrochemical Reactor Design, 2nd ed ., Elsevier, Amsterdam , The Netherlands (1979)

7 . Heitz, E., and G. Kreysa, Principles of Electrochemical Engineering , VCH, Weinheim ( 1986)

8. Rousar, I. , K. Micka, and A. Kimla, Electrochemical Engineering, Vols I and 2 , E lsevier, Amsterdam, The Netherlands ( 1986)

9. Prentice, G., Electrochemical Engineering Principles, PrenticeHall , Eaglewood Cliffs, NJ (1991)

10. Coeu ret, F., ln troduccion a la lngenieria Electroquimica , Editorial Reverte , Barcelona, Spain (1992)

II. Talbot, J ., Chem. Eng. Ed. , 35(1 ), 74 (2004)

12. Tejada, S., E. Guevar and E. Olivares, J. Chem. Ed. , 75(6), 747 (1998)

13 . Seiglie, C.A ., J. Chem. Ed .. , 80(6) , 668 (2003)

14. LeRoux, X., G.A. Ottewill, and F.C. Walsh , Internal. J. Eng. Ed., 18(3), 379 (2002)

15 . Liu , J-C. , H .. Kun z, J.M. Fenton, and S.S. Fenton, Chem. Eng. Ed., 38(1) , 38 (2004)

16. Guinon. J .L. , R. Grima, J. Garcia-Anton, and V. Perez-Herranz, Chem. Eng. Ed., 28(4), 232 (1994)

17. Ponce de Leon, C., and F.C. Walsh , Trans. Inst. Metal Finishing, 81(5), B95 (2003)

18. Ibanez, J.G ., M.Tellez-Giron, D . Alvarez , and E. Garcia-Pintar, J. Chem. Ed., 81 (2), 251 (2004)

I 9. Trethewey, K.R., and J. Chamberlain, Corrosion: For Science and Engineering. Longman Science & Technology ; 2nd ed ., Longman Science & Technology ( 1996)

20. Mattson , E ., Basic Corrosion Technology fo r Scientists and En-g ineers; 2nd ed ., E lli s Horwood Ltd (2001)

21. Kaesche, H ., Corrosion of Metals , Springer Verlag, Berlin (2003)

22. Brown, W.A., Chem. Eng . Ed. , 35(2), 134 (2001 )

23. Schober, T. , and J . Friedri ch, J. Chem. Ed. , 76(12), 1697 (1999)

24. Felder, R.M. , and R. Brent , Chem. Eng. Ed., 37(4), 282 (2003)

25. Ottewill, G.A. , and F.C. Wal sh, J. Chem. Ed. , 74(12) , 1426 (1997)

26. Schi ffrin , D.J., in D. Pletcher (Ed. ), Specialist Periodical Reports: Electrochemistry, The Royal Society of Chemistry, Cambridge, U.K . ( 1983)

27. Larminie, J. , and A. Dicks. Fuel Cell Systems Explained, John Wiley & Sons Ltd., West Sussex, U.K., (2000)

28 . Vincent, C.A ., and B. Scrosatti. Modern Batteries: An Introduction to Electrochemical Power Sources. 2nd ed., ButterworthHeinemann ( 1998)

29. Hsueh, K-L. , D.-T. Chin , and Srinivasan, J. Electroanal. Chem ., 153 79 ( 1983)

30. Reade, G.W. , and F.C. Walsh , in Environmentally Oriented Electrochemistry, C.A.C. Sequeira, (ed .), Elsevier, 3

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JOHNS HOPKINS UNIVERSITY

Faculty Openings: Tenure-Track and Lecturer Department of Chemical and Biomolecular Engineering

The Johns Hopkins University Department of Chemical and Biomolecular Engineering seeks outstanding applicants fo r both tenure-track faculty and lecturer positions at all levels. Candidates who hold a doc

torate in chemical engineering or a related fie ld should apply.

Tenure-track positions: Applicants in all areas of chemical and biomolecular engineering including colloids and surface sciences, bioengineering, nanotechnology, and materials wi ll be considered. Applicants should send (preferred) or e-mail a resume, statement of research plan, and names of at least three references to the Chair at the address listed below.

Lecturer positions: Several non-tenure track Lecturer positions will be avail able for candidates interested in teaching undergraduates. Applicants should send a resume, statement of teaching plan, and three references to the Chair at the address listed below.

Professor Michael J. Betenbaugh, Chair Department of Chemical and Biomolecular Engineering

Johns Hopkins University 3400 N. Charles Street Baltimore MD 21218.

Telephone: (4 10) 516-7170; e-mail: mc1ancy2 @jhu.edu.

Women and minorities are strongly encouraged to apply.

John s Hopkins University is an EEO/AA employer.

31. Pletcher. D., A First Course in Electrode Processes, Romsey, The Electrochemical Consultancy, Romsey ( 1991)

32. Bard, A.J. , and L.R. Faulker, Electrochemical Methods, 2nd ed., John Wiley & Sons, New York, NY (2000)

33. Greef, R., R. Peat , L.M. Peter, D. Pletcher, and M.J. Robinson, Instrumental Methods in Electrochemistry, Elli s Horwood Ltd. , Chichester, England ( 1985)

34. Delahay, P. , J. Electrochem. Soc. , 97, 205 ( 1950)

35. Whitfield , M., and D. Jagner, (Eds), Marine Electrochemistry: A Practical Inrroduction, J. Wiley and Sons, New York, NY ( I 982)

36. Levich , VG. , Physicochemical Hydrodynamics , Prentice-Hall: Englewood Cliffs , NJ (1962)

37. Radford. G .W.J., F.C . Walsh, J.R. Smith , C.D.S. Tuck, and S.A. Campbell , "Electrochemical and Atomic Force Microscopy Studies of a Copper Nicke l A lloy in Sulphide-Contaminated Sodium Chloride Solutions," in: S.A. Campbell , N. Campbell and F.C. Walsh, (Eds) , Developments in Marine Corrosion, The Royal Society of C hemistry, Cambridge, U.K., 41 ( 1998)

38. King, F., C.D. Litke, M.J. Quin and D.M. LeNeveu , Corrosion Sci., 37, 833 (1995)

39. King, F. , M.J. Quin, and C.D. Litke , J. Electroanal. Chem., 385, 45 (1995)

40. Kear, G. , B.D. Barker and F.C. Walsh, Corrosion Sci. , 46, 109 (2004) 0

21

13fi3 class and home problems )

r

The object of this column is to enhance our readers' collections of interesting and novel problems in chemical engineering. Problems of the type that can be used to motivate the student by presenting a particular principle in class, or in a new light, or that can be assigned as a novel home problem, are requested, as well as those that are more traditional in nature and that elucidate difficult concepts. Manuscripts should not exceed fourteen double-spaced pages and should be accompanied by the originals of any figures or photographs. Please submit them to Professor James 0 . Wilkes (e-mail : [email protected]), Chemical Engineering Department, University of Michigan, Ann Arbor, MI 48109-2136.

AN OPEN-ENDED MASS BALANCE PROBLEM

J OAQUfN Rurz University of Zaragoza • £50009 Zaragoza SPAIN

M ass balances, together with energy and momentum balances, are the basis for understanding almost any problem in chemical engineering. When

undergraduate students have a clear understanding of these kinds of problems, they are halfway to success in attaining their chemical engineering degree.

A logical way to teach mass balances is to start with the simplest situation (steady state, few streams, no chemical reaction) and to gradually increase the difficulty of the situations, giving examples and asking the students to solve them. Most of these problems are closed, with just one possible solution, so getting the right answer is often mechanical.

In my first year, I noticed that when I was giving a lecture, many students spent the time simply copying information from the blackboard, instead of thinking about the strategy for solving the problem. I also found that some students had difficulty with unsteady-state situations. As a result, I became interested in making my lessons more practical and closer to reality, as well as more user-friendly. To answer this need for practicality, I devised the following open-ended problem as an additional task that could be useful not only for encouraging students to analyze a real-life situation, but also for discussing different approaches suggested by the students themselves.

BACKGROUND Fresh water is a key factor for progress and a valuable re

source in arid or semi-arid regions, which is the case in most parts of Spain. To address this situation, in July 2001, a hy-

22

drological plan for national water management was approved by the Spanish government. One of the most controversial parts of this plan was to take water from the Ebro river in the north of Spain and redirect it to the Mediterranean regions in the south and east (up to 1050 Hm3 each year). The water would be used to promote development in those areas by creating new agricultural land and developing tourism on the Mediterranean coast (hotels, aquatic parks, golf courses, etc.).

Everyone in the country has an opinion about this plan. Most people in the receiving region are in favor of it because it signals progress and economic development. Ecologists, however, feel that it will contribute to destruction of the coastal areas through unlimited building of hotels and apartments. They also fear that the expectation of vast quantities of water will encourage the cultivation and resulting destruction of virgin land.

People from donor regions in the north do not generally agree with redirecting water to other areas, arguing that they

Joaquin Ruiz received his PhD in 1997 at the University of Zaragoza, where he is currently an Assistant Professor teaching chemical engineering fundamentals. He has worked in environmental protection in regional administration. His research is focused on soil remediation and renewable energy resources.



need the water for their own industrial and agricultural development. In addition to these economic concerns, ecologists point out that talcing away such a vast amount of water from the Ebro river could have a disastrous ecological effect on the mouth of the river. To compound the problem, some farmers agree with the plan because it would involve construction of new reservoirs that would solve their watering needs during the summer dry period-but people living in the mountains, where the reservoirs would be constructed, are not happy with the plan.

fauna) . The newspaper also argued that depending on water from early-spring thawing was not a solution since that source is not reliable.

I showed this information to my students, stressing the need to carefully evaluate numerical data, especially when presented by nontechnical people. Often the media will misunderstand or erroneously report such data, i.e. , the journalist in this case who confused cubic meters and cubic hectome-

ters. I went on to explain that the problem was not how much water currently existed

So, there are many different points of view, often diametrically opposed. The media often fuels the controversy, criticizing or supporting the hydrological plan depend-ing on regional interests.

This paper [presents] an open-ended problem

that can easily be adapted to many

local conditions ...

in the reservoirs , but how much we would need in the future. In February, a 58% capacity did not seem so bad since additional water would likely come from spring rains. Although there could be shortages in some reservoirs, such as Yesa, it was likely that the spring rain and melting snow would provide enough additional water.

PROBLEM STATEMENT

The University of Zaragoza is located in a donor region. In February, 2001 , a local newspaper began publishing articles with dramatic headlines such as "drought menace set to create critical situation for agriculture," "reservoirs at their lowest level for ten years," "serious concern about the situation," etc. Similar news stories have appeared in the past, but they appeared during the summer, not the winter.

The problem is beneficial to students

in many ways: We cannot simply compare one year with another and conclude that there is a problem. The prior year, for example, could have been an exceptionally rainy year. Even in a dry year, alternatives can be designed to reduce water consumption that will help prevent problems.

it can make mass balance classes more

I read the articles and analyzed the numbers given to support this "critical limit situation." Reservoirs that were at 82% capacity last year were only at 58% this year in the same month. The article went on to say that the situation would be even worse ( only 38% capacity) if two of the reservoirs were

realistic, it can facilitate the

assimilation of concepts such as

unsteady state, and it can help students carefully analyze

information provided by daily television,

radio, and

I asked students if they thought this situation was as critical as the media wanted us to believe. I posed this concept as the statement of the problem, but provided no additional information. It would be their job to analyze the problem, to find sources of information, and to make assumptions. While their solutions could, depending on newspaper reports.

taken out of the calculation (curiously, the two largest).

To emphasize this situation, the newspaper pointed out that the Yesa reservoir (470 Hm3 total capacity) contained only 73 Hm3 of water, i.e., 17% of its capacity. This reservoir is in a secondary river of the Ebro and is one of the most controversial parts of the hydrological plan. The proposal is to increase its capacity from 470 Hm3 to 1000 Hm3 in order to guarantee the agricultural water requirements within its area of influence. Some people fear, however, that such a large amount of water will simply guarantee diversion of the water to the south and east regions of Spain. The plan would also mean flooding some villages. One journalist stated that 700 Hm3 of water was required to meet agricultural demands, but there were only 80 Hm3 available, of which a mere 30 Hm3

was available for agricultural use, because 10 Hm3 was required for domestic water supply and 40 Hm3 (10% of the total capacity) was considered "dead water" that could not be used (presumably for ecological reasons , to preserve

Winter2005

the results, be used to support or reject the hydrological plan or the construction of

new reservoirs, this was not the main goal of the exercise.

PROPOSED SOLUTIONS TO THE PROBLEM

The problem statement was challenging to the students, who were a bit confused-they did not know how to start. They had not quite grasped the meaning of the problem. I provided some help by stating that a way to solve the problem could be to

• First, define a "critical situation "-for example, reaching 10% water capacity, which would mean a "dead" reservoir, or 0% water capacity, or would there be enough water to supply the population for a limited period of time or would there be enough water for agricultural, etc.?

• Second, predict if this "critical situation" could be reached in the future.

In the first part, the point selected is a result of personal

23

choice and reasons for or against it can be given. The second part, however, is a quantitative prediction which may or not be valid, depending on how the prediction is made.

There are two approaches to the problem

• Consider a general case of total water reserves

• Consider the evolution of a particular reservoir, such

as Yesa, since the first approach does not consider the water levels of a reservoir that are far below the average of the whole river.

The problem can be solved by an unsteady-state mass balance, i.e.

Accumulation = Final water- Initial water = Inputs - Outputs or

A=V(t)-Vo =l-0 ( I)

Water accumulation in reservoirs is the difference between inputs and outputs. Outputs are defined as water designated for agriculture, industry, and domestic use as well as water that is returned to the river (thus guaranteeing ecological flow). As long as we can quantify initial water reserves, ( v; ), inputs (I*), and outputs (O*), over a future period of time, we can predict the final water reserves at the end of that period, V*(t), by applying Eq. (1) (in which the asterisk refers tofuture values).

INSTRUCTOR'S SOLUTION #1

All Reservoirs in the Ebro

Data pertaining to the current situation, i.e., water accumulated in reservoirs, allows us to control or regulate outputs so we can manage water for different needs . We cannot, however, control global inputs, i. e., water that comes from rain and snow. How we quantify the inputs and outputs of accumulated water will be predicted differently in the future .

The whole system of the reservoirs, the main river, and the secondary rivers are represented in Figure 1.

One of the main sources of data about the Ebro river is the official organization "Confederaci6n Hidrografica del Ebro" (CHE). Historical data can be found at the organization's web site <http://www.chebro.es/>. Information such as average consumption, current relation to the river as a whole, and specifics about each reservoir can be found here.

Part of the site information involves the evolution of water reserves, which is presented by comparing the current year 's evolution with that of the previous year, along with average evolution over the past five years. A prediction of final water at the end of a period of time (t) could be made ( considering the initial situation, with reservoirs at 58% capacity, and knowing inputs and outputs) by simply applying Eq. (1). Although there is no data for individual inputs and outputs, we can assume that inputs (I*) and outputs (0*) in the future will be the average of those of previous years (I and 0). This simpli-

24

fies the problem since alI we need to know is the difference between the two-that is, the difference between the final and the initial accumulated water over several weeks. This can be expressed mathematically by

Mass balance in the future (Eq. 1): v *(t) - v / = 1* - o *

Mass balance in the past during the equivalent period of time

(average last five years) (Eq. 1 ): I-0 = V(t)- Vo

Assumption: I* = I and o• = 0

Combining mass balances with our assumptions, we get

v * (t)= v ; + [V(t)- v0 ] (2)

The average difference can be used to calculate the final water situation every week over a whole year by using Eq. (2), i.e. the evolution of water reserves. Such results can predict if a critical situation, for instance 10% of total capacity, will be reached. The results are shown in Figure 2.

SECONDARY RIVER

SECONDARY RIVER

SECONDARY RIVER

Mediterranean ,__ __ _..., sea

Outputslof consumption

Figure 1. Schematic representation of Ebro 's basin.

6000

5000

4000

Hm3 3000

2000

1000

, ..... ..,., ... ,, Average evolution of

Realevolution2002':> ,~ .. .,."' •••·• . ' ,.. / 5pastyears

.,,. ............. ' .... ,·· ···~ ........... , -1••······,& ·• .. '\" ···~~ .... --....... , ,.

Prediction fOf year 2002 conslderin~ ·• ·• •II.• the averages of last 5 years ·-.• ·• ·

12-25-01 02-13-02 04-4-02 05-24-02 07- 13-02 09-1-02 10-21-02 12-10-02

Figure 2. Predicted and real evolution of water reserves in the year 2002.


The water accumulated in the reservoirs is far from dropping to 650 Hm3

, which would be 10% of the total capacity (6504 Hm3

) . The minimum capacity, during February through October, was approximately 2500 Hm3 (38 % of total capacity.) We can therefore conclude that the situation is not really critical , or at least, not as much as the media want us to believe.

In order to accurately support this prediction, real quantities of water, collected during 2002, are presented in Figure 2, but show a better situation than predicted. This strengthens the argument that the situation, in February 2002, is not critical.

A more conservative approach is shown in Eq. (3) which

illustrates modification by including a coefficient ( cx<l) .

300

250

200

I 150

100

50

12/25/01 02/13/02

v* (t)= v; +cx[V(t)-Vo] (3)

i .... \ ... .. . _ 1,, ·~ ·""-.•• ( • .

,... ,.. \. ,..__________ \

A . • . i Real evolution of2002 •

i

Prediction wi th same inputs and outputs of year 2001

04/4/02 05/24/02 07/13!02

·,

09/ 1/02 10/21/02

Figure 3. Predicted and real evolution of water reserves for Yesa reservoir in the year 2002 without

regulation of outputs.

500

450

400

350

300

Hm3 250

200 --

150 --

100

50 -

// / \ ,,/~) .. ,, : 1 Predic,tion with only 80 %'

11 j l of the inputs of year 2001 \ ~/ /_..,_.., /·-.::\

Prediction with 100% of inputs of 2001

I

f; •·• ·i Real evolution of 2002 ~

l ' ~ :·· ..... ,. .. '\

12/25/01 02/13102 04/4/02 05124/02 07113/02 0911/02 10121/02 12/10/02

Figure 4. Predicted and real evolution of water reserves for Yesa reservoir in the year 2002

with regulation of outputs.

Winter 2005

INSTRUCTOR'S SOLUTION #2

Yesa Reservoir Only

A main criticism of the first approach is the lack of consideration for specific situations of reservoirs where the water levels are far below the 58% average of the whole river. To increase the accuracy of this approach, it is necessary to analyze individual cases such as the Yesa reservoir which was only at 17% capacity (82 Hm3

) .

The same approach can be made ( considering inputs and outputs) to predict the evolution of accumulated water in the future . Data from the previous five years was difficult to obtain, so we substituted it with data from 2001. By applying Eq. (2) to this data we get the result shown in Figure 3, where the real evolution of water reserves has been plotted.

At the beginning of 2001 , the Yesa reservoir was almost full . Considering that it was a rainy year and that no water was accumulated during the following winter and spring ( of 2002), we see that the outputs almost equal the inputs, giving the results shown in Figure 3. This result is unrealistic because it does not take into consideration the regulation of outputs, which is the only option that can be taken when extremely low water reserves (as they were at the beginning of 2002) verge on becoming dead reservoirs.

A different approach to consider involves the regulation of outputs. First, we can assume that 2001 and 2002 inputs will be the same. Second, we can also assume that outputs will remain at 5 Hm3/week, the minimum, until April when agricultural demand for water increases. We arrive at the 5 Hm3

/

week minimum by deducing that outputs rarely drop lower according to historical data. Third, we assume that outputs from the current year and the previous year are the same from April

Assumptions: I* = I O* = 5 Hm3/week until April O* = 0 from April

Taking all these assumptions into account, the results obtained through Eq. (1) are shown in Figure 4, as well as the real evolution of water reserves. The main inconvenience of using input data from 2001 is that it was a rainy year and the inputs could be overestimated. A more reliable prediction could be made by reducing inputs-for example, only 80% of the inputs from 2001 will be achieved in the year 2002. The choice of 80% is arbitrary; any other amount could be chosen. These results can also be seen in Figure 4.

The predicted evolution is quite different depending on the assumed inputs ( 100% or 80% of the year 2001.) In the first case, accumulated water levels do not fall below the initial 17% level (73 Hm3

) ; it always exceeds 100 Hm3 (21 % ) even at the end of the summer dry period, which is well over the critical minimum of 47 Hm3 (10%). In the second case, however, accumulated water descends to the 10% level by the

25

end of August, and reaches zero in September. A minimum decline in water inputs, with respect to the previous year, can therefore lead to a critical situation if outputs are not regulated and restricted.

The fact is, 2002 was not as rainy as 2001. Inputs were down, which led to water restrictions and tighter regulation of water outputs for agriculture. This resulted in a more rational usage of the limited water resources by implementing better efficiency of watering techniques or lowering the demand for growth. No indications have been reported by local media about catastrophic damage to agriculture or significantly lowered production as compared to previous years. We can thus conclude that a largely available resource can be used up inefficiently, even if it is as valuable as fresh water.

STUDENTS' SOLUTIONS

The proposed solutions here represent just one approach to the problem; there are several different approaches that could be made. Apart from merely qualitative solutions or simple compilations of past data without predictions, various solutions were proposed by the students, which are summarized as follows:

Solution 1 Data Source: CHE

Estimations: Current amount of water accumulated in reservoirs is

58.8% of total capacity of

Local Water

4486 Hm3

7630 Hm3

Consumption: domestic drinking water agriculture

313 Hm3/year 6310 Hm3/year

66 Hm3/year 414 Hm3/year 246 Hm3/year

3536 Hm3/year

Critical

livestock industry water transfer to other areas ecological flow

TOTAL CONSUMPTION 10885 Hm3/year

Situation: no water in reservoirs

Assumptions: Flow in the mainstream of the Ebro river is the average of the average flows measured at different points in the mainstream, since all the secondary streams go into this mainstream.

26

average flow 7073 Hm3/year

Conclusion: Variation of accumulated water at the end of the year will be

Input from the river

1000

Output to channels for consumption

I 900 Output to the river

Reservoir 1-----• 100

Figure 5. Schematic representation of a reservoir

Final Amount of Water in Reservoirs:

A = 7073 - 10885 = -3812 Hm3/year

4486 + (-3812) = 674 Hm3/year

Despite a negative accumulation term, at the end of the year there was water in the reservoirs. In conclusion, with 58.8% capacity, there was no critical limit situation.

Instructor's Comments • The assumption that the flow in the mainstream of the Ebro river is the average of the average flows measured at different points in the mainstream involves at least two mistakes. If the average is made upstream and downstream of a reservoir, we are failing to take into account water that is taken out of the river for consumption, as can be seen in Figure 5.

Measured average flow is (1000 + 100) / 2 = 550 Hm3/

year, while in fact it is 1000 Hm3/year. In addition to this effect, not all the water from secondary rivers goes into the main river (Ebro), since part of it could be used for consumption, as can be seen in Figure 6.

The calculated average flow is (200 + 300) / 2 = 250 Hm3/year, while the real available amount of water is 1200 Hm3/year.

Solution 2

Data Source: local newspapers

Estimations: current amount of water accumulated in reservoirs is 3950 Hm3

(60% of total capacity of 6583 Hm3)

Water Accumulated

one year ago: 5394 Hm3

Critical Situation: in reservoirs, less than 1029 Hm3

(for emergency situations 700 Hm3)

(5 % of total capacity that cannot be used because of its low purity 329 Hm3)

Assumptions: Since we are in a dry period, there will be no pre-

200

SECONDARY RIVER 1000

Reservoi 900

100

MAIN RIVER (EBRO)

300

Figure 6. Schematic representation of a secondary river


cipitation at all in the future. The only inputs of water to the Ebro will come from melting of current snow into three secondary rivers: the Aragon, Gallego, and Cinca estimated as a total amount of 202 Hm3

Outputs or consumption in one year are the difference between water one year ago and accumulated water now

5394 - 3950 = 1444 Hm3/year

Conclusion: Since accumulation (A) = Inputs (I) - Outputs (0), then time to reach a critical situation A = final water - initial water

= 1029 - 3950 = - 2921 Hm3

I= water from rain (=0) + water from melted snow = 202 Hm3

O = consumption in one year x time 1444 Hm3/year x time (years)

time is therefore 2921 I 1444 = 2.02 years to reach a critical situation, so the current

situation is not critical.

Instructor's Comments • The assumption of no water precipitation in the future is highly improbable, and the assumption that inputs to the system will come exclusively from snow via three secondary rivers is unrealistic. These assumptions represent, at best, a conservative scenario. The assumption that water consumption in years is the difference between water accumulated now and one year ago is invalid, however. Consumption is not 1444 Hm3/year; actually it is estimated at 7500 Hm3/year plus 3400 Hm3/year ecological flow at the mouth of the Ebro. To know the water consumption figures, inputs and outputs during thi s period need to be known. According to this incorrect assumption, if this year is like the past year, the water accumulated in reservoirs would have been the same and we would not have consumed any water, and if this year had been more rainy that the past year, instead of consuming water, we would have produced water, showing negative consumption. This makes no sense.

Solution 3

Data Source: CHE

Estimations:

Local Water consumption:

Oct. 2000-Oct. 2001

Winter 2005

current amount of water accumulated in reservoirs is

62% of total capacity of

human consumption ecological flow

TOTAL CONSUMPTION

4033 Hm3

6504 Hm3

7405 Hm3/year 3154 Hm3/year

10559 Hm3/year

REAL TOTAL CONSUMPTION 20035 Hm3

human consumption

measured at Ebro's mouth

average precipitations

7405 Hm3

12630 Hm3

Critical

whole basin 658 mm of water/m2

average historical precipitations ( 1940-1995)

with a mimum of

682 mm/m2

526 mm/m2

Situation: no water in reservoirs

Assumptions: since we are in a dry period, there will be no precipitations at all in the future.

Conclusion: since accumulation (A) = Inputs (I) - Outputs (0), then time to reach a critical situation

A = final water - initial water

= 0 - 4033 = - 4033 Hm3

I = water from precipitations 0Hm3

O = consumption in one year x time

10559 Hm3/year x time (years)

time is therefore 0.382 years

i.e. , 4 months and 17 days is the time to reach a critical situation, so the current situation could be critical but this is unlikely to occur because it would require annual precipitations of

10559 / 20035 x 658 = 397 mm water/m2

which is well below the average annual precipitations of 682 mm/m2 during the period 1940-1995, and less than the minimum in this period of 526 mm/m2

•

Instructor's Comments • The implicit assumption is that water demands will be distributed homogeneously throughout the year, but this is not true. Water demand increases in spring and summer, due mainly to agricultural needs. Thus in February we are close to reaching the highest point of water consumption that begins in spring and 4 months and 17 days to consume all the water is very optimistic. In addition to this problem, water reserves are not equal in every reservoir and 62% total capacity could mean that some reservoirs are full and others are almost empty. A "case by case" study should therefore be carried out.

CONCLUSION

This paper has presented an open-ended problem that can easily be adapted to many local conditions, since use of a limited and valuable resource such as fresh water is a problem almost everywhere. The problem is beneficial to students in many ways: it can make mass balance classes more realistic it can facilitate the assimilation of concepts such as unste,ady state, and it can help students carefully analyze information provided by daily television, radio, and newspaper reports. It can also be helpful for finding possible solutions as well as encouraging class discussions on the validity of assumptions made by different solutions proposed by the students themselves. 0

27

Random Thoughts ...

DEATH BY POWERPOINT

R ICHARD M. FELDER, REBECCA BRENT

North Carolina State University • Raleigh, NC 27695

It's a rare professor who hasn't been tempted in recent years to put his or her lecture notes on transparencies or PowerPoint. It takes some effort to create the slides, but

once they ' re done, teaching is easy. The course material is nicely organized, attractively formatted, and easy to present, and revising and updating the notes each year is trivial. You can put handouts of the sljdes on the Web so the students have convenient access to them, and if the students bring copies to class and so don ' t have to take notes, you can cover the material efficiently and effectively and maybe even get to some of that vitally important stuff that' s always omjtted because the semester runs out.

Or so the theory goes.

The reality is somewhat different. At lunch the other day, George Roberts-a faculty colleague and an outstanding teacher- talked about his experience with this teaching model. We asked him to write it down so we could pass it on to you, whkh he kindly did .

"About five years ago, I co-taught the senior reaction engineering course with another faculty member. That professor used transparencies extensively, about 15 per class. He also handed out hard copies of the transparencies before class so that the students could use them to take notes.

"Up to that point, my own approach to teaching had been very different. I used transparencies very rarely ( only for very complicated pictures that might be difficult to capture with freehand drawing on a chalkboard). I also interacted extensively with the class, since I didn 't feel the need to cover a certain number of transparencies. However, in an effort to be consistent, I decided to try out the approach of the other faculty member. Therefore, from Day 1, I used

transparencies (usually about 8 -10 per class), and I handed out hard copies of the transparencies that I planned to use, before class.

"After a few weeks, I noticed something that I had not seen previously ( or since)-attendance at my class sessions was down, to perhaps as low as 50% of the class. ( I don 't take attendance, but a significant portion of the class was not coming.) I also noticed that my interaction with the class was down. I still posed questions to the class and used them to start discussions, and I still introduced short problems to be solved in class. I was reluctant to let discussions run, however, since I wanted to cover the transparencies that I had planned to cover.

"After a few more weeks of this approach, two students approached me after class and said, in effect, 'Dr. Roberts, this class is boring. All we do is go over the transparencies, which you have already

Richard M. Felder is Hoechst Celanese Professor Emeritus of Chemical Engineering at North Carolina State University. He received his BChE from City College of CUNY and his PhD from Princeton. He is coauthor of the text Elementary Principles of Chemical Processes (Wiley, 2000) and codirector of the ASEE National Effective Teaching Institute

Rebecca Brent is an education consultant specializing in faculty development for effective university teaching, classroom and computerbased simulations in teacher education, and K-12 staff development in language arts and classroom management. She co-directs the ASEE National Effective Teaching Institute and has published articles on a variety of topics including writing in undergraduate courses, cooperative learning, public school reform, and effective university teaching.

© Copyrigh t Ch£ Division of ASEE 2004


handed out. It 's really easy to just tune out. ' After my ego recovered, I asked whether they thought they would get more out of the class and be more engaged if I scrapped the transparencies and used the chalkboard instead. Both said 'yes. ' For the rest of the semester, I went back to the chalkboard (no transparencies in or before class), attendance went back up to traditional levels, the class became more interactive, and my teaching evaluations at the end of the semester were consistent with the ones that I had received previously. Ever since that experience, I have never been tempted to structure my teaching around transparencies or PowerPoint. "

The point of this column is not to trash transparencies and PowerPoint. We use PowerPoint all the time-in conference presentations and invited seminars, short courses, and teaching workshops. We rarely use pre-prepared visuals for teaching, however-well, hardly ever-and strongly advise against relying on them as your main method of instruction.

Most classes we've seen that were little more than 50- or 75-minute slide shows seemed ineffective. The instructors flashed rapid and (if it was PowerPoint) colorful sequences of equations and text and tables and charts, sometimes asked if the students had questions (they usually didn't), and sometimes asked questions themselves and got either no response or responses from the same two or three students. We saw few signs of any learning taking place, but did see things similar to what George saw. If the students didn 't have copies of the slides in front of them, some would frantically take notes in a futile effort to keep up with the slides, and the others would just sit passively and not even try. It was worse if they had copies or if they knew that the slides would be posted on the Web, in which case most of the students who even bothered to show up would glance sporadically at the screen, read other things, or doze. We've heard the term "Death by PowerPoint" used to describe classes like that. The numerous students who stay away from them reason (usually correctly) that they have better things to do than watch someone drone through material they could just as easily read for themselves at a more convenient time and at their own pace.

This is not to say that PowerPoint slides, transparencies, video clips, and computer animations and simulations can ' t add value to a course. They can and they do, but they should only be used for things that can't be done better in other ways. Here are some suggested dos and don'ts.

• Do show slides containing text outlines or (better) graphic organizers that preview material to be covered in class and/ or summarize what was covered and put it in a broader con-

text. It 's also fine to show main points on a slide and amplify them at the board, in discussion, and with in-class activities, although it may be just as easy and effective to put the main points on the board too.

• Do show pictures and schematics of things too difficult or complex to conveniently draw on the board (e.g., large flow charts, pictures of process equipment, or three-dimensional surface plots). Don't show simple diagrams that you could just as easily draw on the board and explain as you draw them.

• Do show real or simulated experiments and video clips, but only if they help illustrate or clarify important course concepts and only if they are readily available. It takes a huge amount of expertise and time to produce high-quality videos and animations, but it's becoming increasingly easy to find good materials at Web sites such as SMETE, NEEDS, Merlot, Global Campus, and World Lecture Hall. (You can find them all with Google.)

• Don't show complete sentences and paragraphs, large tables, and equation after equation. There is no way most students can absorb such dense material from brief visual exposures on slides. Instead, present the text and tables in handouts and work out the derivations on the board or-more effectively-put partial derivations on the handouts as well, showing the routine parts and leaving gaps where the difficult or tricky parts go to be filled in by the students working in small groups.[1,21

If there's an overriding message here, it is that doing too much of anything in a class is probably a mistake, whether it's non-stop lectures, non-stop slide shows, non-stop activities, or anything else that falls into a predictable pattern. If a teacher lectures for ten minutes, does a two-minute pair activity, lectures another ten minutes and does another twominute pair activity, and so on for the entire semester, the class is likely to become almost as boring as a straight lecture class. The key is to mix things up: do some board work, conduct some activities of varying lengths and formats at varying intervals, and when appropriate, show transparencies or PowerPoint slides or video clips or whatever else you've got that addresses your learning objectives. If the students never know what's coming next, it will probably be an effective course.

References

I. Felder, R.M. , and R. Brent, "Learning by Doing," Chem. Engr. Ed. , 37(4), 282 (2003). On-line at <http://www.ncsu.edu/felder-public/Columns/Active. pdf>

2. Felder, R.M., and R. Brent, "FAQs. II. Active Learnjng vs. Covering the Syllabus, and Dealing with Large Classes," Chem. Engr. Ed, 33 (4), 276 (1999). On-line at <http://www.ncsu.edu/felder-public/Columns/FA Qs-2.html> 0

All of the Random Thoughts columns are now available on the World Wide Web at http://www.ncsu.edu/effective_teaching and at http://che.ufl.edu/-cee/

Winter 2005 29

JAS=i classroom ) --------------ENERGY BALANCES

ON THE HUMAN BODY A Hands-On Exploration of Heat, Work, and Power

STEPHANIE FARRELL, MARIANO J. SAVELSKI, ROBERT HESKETH

Rowan University • Glassboro, NJ 08028

Rowan's two-semester Freshman Clinic sequence is a multidisciplinary course that introduces all freshmen engineering students to engineering principles in a

hands-on, active learning environment. Engineering measurements and reverse engineering methods are common threads that tie together the different engineering disciplines in the fall and spring semesters, respectively. One of the reverse engineering projects is a semester-long investigation of the interacting systems of the human body. Students discover the function, interaction, and response to changing demands of various systems in the human body: the respiratory, metabolic, cardiovascular, electrical, and musculoskeletal systems. The project introduces a wide range of multidisciplinary engineering principles and reinforces scientific principles learned in chemistry, physics, and biology.

The module described in this paper uses the respiration system to introduce concepts related to energy balances, heat transfer, and chemical reactions. In a hands-on experiment, students measure physiologic variables such as breathing rate and respiratory gas compositions at rest and during exercise on a bicycle ergometer. We have previously described how a similar experiment is used to teach mass balances and related concepts through the determination of the rates of oxygen consumption, carbon dioxide production, and water loss .l '-21 The module is appropriate for an introductory freshman engineering course or for a sophomore-level course on material and energy balances. These concepts can be explored in greater detail in upper level core and elective courses.

The learning objectives of this hands-on experiment are to

• Perform energy balances on the body • Determine the total rate of energy expenditure and

human mechanical efficiency • Determine the composition of food (% fat and %

carbohydrate) oxidized for energy • Use a process simulator to perform mass and energy

balances on the breathing process • Analyze the role of breathing in thermal regulation

Stephanie Farrell is Associate Professor of Chemical Engineering at Rowan University. She received her PhD (1996) from NJIT She has developed innovative classroom and laboratory materials in biomedical, food, and pharmaceutical engineering areas. She is the recipient of the 2000 Dow Outstanding Young Faculty Award, the 2001 Joseph J. Martin Award, the 2002 Ray W. Fahien Award, and the 2004ASEE Outstanding Teaching Medal.

Robert Hesketh is Professor of Chemical Engineering at Rowan University. He received his PhD from the University of Delaware in 1987. He has made significant contributions to the development of inductive teaching methods and innovative experiments in chemical engineering. He is the recipient of the 2002 Quinn Award, 1999 Ray W. FahienAward, 1998 Dow Outstanding New Faculty Award, and the 1999 and 1998 Joseph J. Martin Award.

Mariano Save/ski is Associate Professor of Chemical Engineering at Rowan University. He received his PhD in 1999 from the University of Oklahoma. His research is in the area of process design and optimization, and he has over seven years of industrial experience. His prior academic experience includes two years as Assistant Professor in the Mathematics Department at the University of Buenos Aires.



• Use HYSYS131 process simulator to explore respiratory heat transfer under different conditions.

The engineering concepts introduced through this module are summarized in Table l.

BACKGROUND The air we inspire (inhale) is approximate! y

21 % 0 2 and 79% N2

on a dry basis. After rapid gas exchange in the lungs, the expired (exhaled) gas contains approximately 75 % N2, 16% 0 2, 4% CO2 and 5% Hp.14.51 The

One of the reverse engineering projects is a semester-long investigation of the interacting systems

of the human body. Students discover the function, interaction, and response to changing demands

of various systems in the human body: the respiratory, metabolic, cardiovascular,

electrical, and musculoskeletal

inspired air is at ambient pressure, temperature, and humidity, while the expired air is saturated with water vapor at body temperature and ambient pressure, and respiration accordingly plays a role in temperature regulation. Oxygen consumed during respiration is transported by blood to cells for energy production through the oxidation of carbohydrates and fats from food. The reaction stoichiometry and thermodynamics are well known, and the rate of energy production can be calculated from the rates of 0

2 and CO

2 exchange. 141

This energy is used to maintain the function of the body (basal metabolism, typically about 60-70% of total energy expenditure) and to do external work (exercise, typically about 30-40% of total).

Energy expended internally (e.g., for pumping blood, maintaining organs, etc.) must ultimately be released as heat, and it has been observed that the energy metabolism at rest is related to the surface area (SA) of the body. This ratio of basal metabolic rate (BMR) to the surface area (SA), [(BMR)/ (SA), kcal/h] , is a function of age (Y, in years) and gender: 161

For males:

(BMR) =(54.79 kcal )-( 1.303~]* Y + (SA) m2h m2hyr

(0.0294 kcal ?J* Y2- ( 0.0001228 kcal ]*Y3 -

m2h yr: m2hyr 3

(3.3558 * 10-6 kcal J * Y4 +

m2h yr4

(2.903 * 10-8 :cal J * Y5

m-h yr 5

For females :

(BMR t(55.73 k\al ) - ( 1.757~]* Y + (SA) m-h m2hyr

systems.

(0.0414 ~cal ]* Y2+( 5.216* 10-6 kcal ]* y 3_

m-hyr2 m2hyr 3

(l* LO-s kcal ]* Y4+

m2hyr4

(7.979*10-8 kcal ]* Ys

m2hyr5 (2)

Surface area can be found from the following correlation that relates surface area to body mass and height: 171

(

1.275 J SA= 0.202-m __ * m0.425 * h0.725 ko0.425

0

(3)

TABLE 1 Summary of the Science and Engineering Concepts Introduced in this Module

Engineering Concept Application

Reaction stoichiometry Food oxidation reactions

Heat of reaction Energy production from food oxidation reactions

Energy balance (First Law of Thermodynamics) on an o~n system Calculation of energy stored in one day

Heat transfer-relation to surface area; correlations Determination of energy expenditure

Mechanical efficiency: work, frictional losses, heat Students performing mechanical work (cycling)

Simultaneous material and energy balance-heat capacity, enthalpy, sensible heat, latent heat, Heat transfer during respiration; HYSYS simulation reference state; psychrometric chart

Unit operations (heating, humidification) HYSYS simulation

Winter 2005 31

where SA is in units of (m2), m is mass in kg and h is

height in meters.

The energy needed to maintain the body during rest and during physical activity is derived from the breakdown, synthesis, and utilization of fats, carbohydrates, and protein. Protein is thought to be used primarily in building tissue (anabolic processes), and most of our body's energy needs are met through the intake of carbohydrates and fats . Glucose (a sugar) is a typical carbohydrate, and is oxidized according to the reaction

-673 kcal/mo) ( 4)

Note that the heat of reaction at STP (-673 kcal/mo]) is provided in addition to the reaction stoichiometry. Fats are another class of macronutrient that the body uses to obtain energy. Triolein, a fat, is burned according to the reaction

C 57H 32O 2 +80O 2 • 57CO 2 +52 H 2O -7900kcal/mol (5)

The reactions shown in Eqs. (4) and (5) are for a specific carbohydrate (glucose) and a specific fat (triolein), and the heats of reaction were evaluated at STP. 181 Dietary carbohydrates are a mixture of molecules with the approximate formula [C(Hp)]"; similarly, dietary fats are a mixture of esters of various fatty acids. These two macronutrients are therefore commonly represented as typical mixtures (representing typical dietary intake). In the oxidation of a mixture of carbohydrates, the ratio of CO2 production to 0

2 consumption is 1: 1, and approximately 113

kcal/mo] 02

(STP) is released. The oxidation of a mixture of fats results in a 0.707: l ratio of CO

2 production to 0 2

consumption, and releases about 104.9 kcal/mo] 0 2

(STP). 141 Measure~ent of t~e rates of 0 2 consumption and CO2 production ( V 0 2 and V coz) allows determination of the rates of energy derived from fats and carbohydrates using these heats of reaction and stoichiometric relationships.

The Respiratory Exchange Ratio (RER) is the ratio of 0

2 consumption and CO

2 production and is a convenient

expression for use in metabolic calculations

RER #molesCO 2 produced ~ co2

#molesO 2 consumed V0 2

(6)

Table 2 shows RER values for fats and for carbohydrates, the energy released per LO

2, and the mass of each macro

nutrient oxidized per LO2 consumed. 141 When a mixture of

carbohydrates and fats is oxidized, the RER will lie between 0.707 and 1.0. The RER is a convenient indicator for the proportion of each macronutrient being oxidized and is related to the total energy expenditure. This is illustrated graphically in Figure 1. The equations of the lines provide relationships between EE and RER, and between

32

the composition of the energy source and RER.

Nearly everyone is familiar with the concept of reducing caloric intake and increasing exercise to lose weight. This is simply an application of the First Law of Thermodynamics, which reveals that if the energy equivalent of consumed food exceeds the energy expended, the result is a net storage of energy. This excess energy would be stored primarily as fat.

• • A A •

Q - W s - n air 6H air - n food 6Hr = E st (7)

q is the rate of heat transferred to the body from the surroundings, W s is. the rate of work done by the body on the surroundings, n air6H air is the rate of enthalpy change between the inspired and expired air streams due to a change in temperature, n food 6H r is the rate of enthalpy change due to reaction, and Est is the rate of energy storage in the body. Several simplifying assumptions were made to make the analysis appropriate for freshmen: 1) the effect of composition on the molar enthalpy of the inspired and expired air is neglected, 2) the difference in number of moles of inspired air vs. expired air is neglected, and 3) the enthalpy change of the food due to change in temperature is neglected.

The human body doing exercise can be analyzed as a machine

TABLE2 RER and Energy Expenditure for Carbohydrates and Fats (At Standard Temperature and Pressure, 0°C and 760 mm Hg)

Values taken from Reference 4.

Carboh~drate Fat

RER 1.0 0.707

Energy released per mole of oxygen used (kcal/mo!) 113.0 104.9

En~ released ~r liter of oxygen used (kcal/I..) 5.047 4.686

Grams of macronutrient oxidized per liter oxygen used (g/L) 1.23 1 0.496

114 ~-------------------~ 120

113

112 ',

111

110

109

108

107

106

105

104 /

0.7

....

/

.... .... '

/

/

0.75

' ' ....

/

0.8

.... ....

%carb = 341 .38x • 240.34

/

.'>'.:... / ' .... ....

', %fat= •341 .38x + 340.34

' ---' ' ' ' ....

0.85 0.9 0.95

RER

- - - linear (carbohydrate) - - Linear (fat) - linear (EE )

100

80

60

40

20

1.05

Figure 1. Fuel composition and energy expenditure as a function of RER (0.707 < RER < 1.0).


In a hands-on experiment, students measure physiologic variables such as breathing rate and respiratory gas compositions at rest

and during exercise on a bicy cle ergometer.

doing mechanical work. To do mechanical work such as bicycling or running, the body expends energy. The efficiency, TJ, of this human machine or a human is expressed by

ri= mechanical work done. JOO

energy consumed (8)

Energy not used to perform external work is ultimately released as heat. Since this module focuses on respiration, of interest is the total rate of heat transfer associated with respiration. Under normal conditions, about 14%-20% of the body's total cooling is accomplished through respiration, and this percentage can change with exercise and ambient conditions.r71

During respiration, inspired air is warmed from ambient temperature to body temperature prior to being exhaled. In addition, water evaporates from the moist lung tissue to saturate the air in the lungs prior to expiration. The humid exhaled air removes heat from the body in the form of latent heat of vaporization. The rate of heat transfer ( q , kcal/min) achieved through the process of respiration is

· · ( in out ) A ( • in · out) q = nairCp air T - T + ~H vap nw - nw (9)

where ii is the molar flowrate (mol/min), C is the molar p

heat capacity (kcal/ipol K) of the inhaled humid air, Tis tem-perature (K) and ~H vap is the latent heat of vaporization of water (kcal/mo]). Subscripts represent components air or water, and superscripts represent inlet or outlet air.

EQUIPMENT

The equipment used for all cardiorespiratory measurements was a respiratory gas-exchange system coupled with a cycle ergometer. The MedGraphics (St. Paul, MN) CPX/D cardiorespiratory gas-exchange system includes capability for direct oxygen and carbon dioxide measurement and ventilation (flow rate). The system interfaces with a cycle ergometer (Lode Corvial) for exercise testing. Many universities have such equipment available in a physiology or exercise science laboratory, and several companies offer human physiology teaching kits in the $3,000 range (e.g., Biopac Systems, Santa Barbara, CA; AD Instruments, Colorado Springs, CO; Iworx, Dover, NH).

EXPERIMENT

A detailed experimental procedure was described previously by Farrell , et aL.,121 and a summary is provided here.

Winter 2005

Students work in teams of three, and the team can complete the experiment in approximately 20-30 minutes. One student per team is selected as the test subject for the experiment. Using the MedGraphics CPX/D cardiorespiratory test system coupled with the Corvial Cycle ergometer, measurements are taken for four minutes resting and for four minutes during exercise. During exercise the subject pedals at a rate of 70-80 rpm with a constant braking power set to 30W. (Braking power is product of the tension on the flywheel and the distance covered by the perimeter of the flywheel per unit time).

The following quantities are measured directly and displayed using Med-Graphics Breeze Suite software: Volumetric flowrate of exhaled air and component mole fractions

( y out Yin Yout Yin Yout ) ' 0 2' 0 2' CO2 ' CO2

and braking power. The gas exchange data are reported at BTPS (Body Temperature and Pressure, Saturated) conditions. In addition, the software provides calculated values of

V o2

, V co2

, EE, and RER.

ASSIGNMENTS The first assignment based on this experiment is a labora

tory report that focuses on the food oxidation reactions involved in energy production, determination of energy expenditure at rest and during exercise, and the application of the First Law of Thermodynamics. From their experimental data, students calculate the BMR, RER, EE, and mechanical efficiency. Using RER values, students determine the percentage of energy expenditure derived from carbohydrates and from fats, as well as the number of grams of carbohydrates and grams of fat used as fuel. In addition to the data obtained from the experiment described above, students record everything they eat for an entire day and calculate the energy equivalent of this diet using published nutrition tables. They also keep track of their activities during the day and estimate the total amount of energy expended required for this work. This information is used to determine the total net chemical energy storage using the First Law energy balance.

The second assignment is a calculation-based homework that focuses on a thermal energy balance on the respiration process. This energy balance is simplified (for hand calculations) by using a constant heat capacity independent of composition. Only the energy changes associated with heating and humidifying an air stream are considered. Students cal-

33

cu late the rates of latent heat exchange, sensible heat exchange, and total heat exchange associated with respiration. After performing the hand calculations using tabulated values of CP and i'lH vap , students also use a psychrometric chart to determine the rate of heat exchange during respiration .

A subsequent laboratory period is used for a HYSYS process simulation workshop in which students use HYSYS to simulate the respiration process. Students input their own experimental data, use HYSYS to perform material and energy balances on the respiration process, and compare the results of the simulation to their hand calculations. Several simulations are run to explore the effect of ambient conditions on the relative contributions of sensible and latent heat during respiration. Students explore a range of temperatures and relative humidities that correspond to a range of weather conditions (for instance, a dry winter day, a rainy winter day, a hot desert, and a hot steamy swamp).

As shown in the HYSYS flow diagram in Figure 2, the respiration process can be represented by two unit operations: a heater that heats the inhaled air to body temperature (sensible heat effect), and a humidifier that saturates the inhaled air with water (latent heat effect) . Students enter the ambient conditions of temperature, pressure, and relative humidity into the weather station. Because HYSYS requires a water vapor mole fraction rather than relative humidity to be provided, students use a spreadsheet to calculate the mole fraction of water in the inhaled air using the Antoine equation. The "inhaled humid air" stream represents inspired air at ambient temperature, pressure, and relative humidity. The stream called "exhaled warm saturated air" represents the exhaled air at body temperature and pressure, saturated with water vapor; students supply temperature, pressure, flow rate, and composition of this stream using their experimental data. Temperature and pressure values for the intermediate streams called "warm humid air" and "moisture from lung tissue" are also supplied by students.

RESULTS

Nearly everyone is aware of the body 's physiologic responses to exercise-the body 's increased demand for energy is met with an increased breathing rate and heart rate. By comparing the resting and exercise gas exchange measurements, students quantify this physiologic response. Table 3 shows gas exchange measurements and calculated values for the respiration experiment for a 19-year-old female student (125 lb, 66 in). According to Eqs. (2) and (3), the student has

34

TABLE3 Gas Exchange Measurements and Calculations at Rest and During

Cycling Exercise you1. in ou1 in d oul d · ]I y

0 2, y

02, y CO

2, an y CO

2 are measure expenmenta y

at BTPS conditions.

Vo2 and VcO2 are calculated at STP.

(Ambient Conditions: T=20 °C, P= 759 mm Hg, RH=47%.)

Power yOUI QUI YOUI Vo2 Vco2 EE RER Yo2 CO2 (W) (L/min) (L/min) (L/min) (kcal/min)

0 13.08 0.185 0.023 0.25 0.23 1.38 0.87

30 20.50 0.175 0.031 0.62 0.52 3.07 0.85

TABLE4 Energy Value of Consumed Foods and Activity Performed on a

Given Day for the Female Subject

Food

Carnation Instant Breakfast, IO oz

Meatballs, 3 x 1 oz

Spaghetti, 1 cup

Tomato sauce, 1/4 cup

Kielbasa, 4 oz

Soft pretzel

Cinnamon toast crunch bar

Brownie

Milk, I cup whole

Hawaiian Punch, 12 oz

Pizza, 2 slices plain

Total

Weather Station

Relative Humidity

!

E11ergy Value (kcal)

200

234

159

35

320

95

180

160

150

180

480

2193

Activity

Sleep, 7.5 h

Shower, 0.25 h

Dressing. 0.25 h

Walking, I h

Driving, 0.5 h

Class, 4 h

Homework, 4 h

Talk on phone, I h

Grocery shopping, 0.5 h

Talking with friends standing, 2 hr

Eating, 1.5 h

Watching TV 1.5 h

Total

E11ergy Value

(kcallh)

0

14

14

170

28

178

178

46

72

89

41

9

839

Exhaled Warm Saturate, Air

-------;• ll'X.1---------i

l Inhaled D Air

Inhaled Humid Air

Warm Humid Air

Evaporative Heat Exchange

Humidifier

Figure 2. The HYSYS respiration process flow diagram.


30 ~-----------------

25

? 20 ni " ~ 15 s ;:_ 10

"' :g 5 ..J

0

1§ -5 0 t- -10

--Total , T=O' C

--Total , T=20' C

_,._ Total , T= 30' C

--Total , T=37' C

---Total , T=45' C

-15 +------------------0 20 40 60 80 100 120

Relative Humidity(%)

Figure 3. The effect of ambient temperature and relative humidity on the total heat transfer rate during respiration .

8

7

? 6 ni " 5 ~ s 4 "' Q:

3 "'

--sensible, T=O' C

[3 B B B • -e-Sensible, T=20' C

"' 0 2 ..J

.; 1 ., J: ., 0

-.!,-Sensible, T= 30' C

b. 6 6 6 t, ~Sensible, T=37"C

G e e e 0 -a-sensible, T=45' C

:;; 'iii -1 C: .,

-2 f/)

-3

0 20 40 60 80 100 120


Figure 4. Th e effect of ambient temperature and relative humidity on the sensible heat transfer rate during respiration .

:!: ni

" ~ s "' Q:

"' "' 0 ..J

.; ., J:

i: s "' ..J

25

20

15

10

5

0

-5

-10

-15 +------------.-----,.------t 0 20 40 60 80 100 120


--Latent , T=O' C

--Latent , T=20' C

_,._Latent , T=30'C

--Latent , T=37'C

~ Latent , T=45' C

Figure 5. The effect of ambient temperature and relative humidity on the latent heat transfer rate during respiration.

Wimer 2005

a surface area of about 1.59 m2 and an expected basal metabolic rate of 57.5 kcal/h. The basal metabolic rate is the minimum energy required for maintenance of the body's vital functions and is about 70% of the body 's actual measured energy expenditure at rest (resting energy expenditure, REE). The resting energy expenditure is therefore expected to be 82.2 kcal/h .

Comparison of exercise data to resting data reveals that the breathing rate is substantially faster during exercise, and the oxygen concentration of expired air is slightly lower than its resting value. This translates into higher rates of oxygen consumption and carbon dioxide production during exerc ise. The energy expenditure is calculated using the equation of the line in Figure 1, which provides a relationship between EE and RER. These results are summarized in Table 3. The mechanical efficiency, calculated using Eq. (8), is only 23.4%, because a significant amount of energy is required to overcome internal friction in moving joints and inefficiencies of muscle contraction.r4J (Cycling is, in fact, one of the most efficient exercises!)

The energy equivalent of the food consumed by this student in one day was 2193 kcal , as shown Table 4. From the basal metabolic rate of 57 .5 kcal/h , this student 's minimum resting metabolic requirements are 1380 kcal per day. Since no external mechanical work is done by the body at rest, all of this energy is assumed to be transferred to the surroundings in the form of heat. The energy expended on daily activities (external work) is also shown in Table 4. These values represent the energy required in excess of the basal metabolic rate and are gathered from widely available published and Internet sources (such as <www.caloriesperhour.com> ). This student estimated an energy expenditure of 839 kcal per day for her activities. The result of the First Law energy balance indicates that this student expended 26 kcal more than her intake for the day, which would result in a (very small ) weight loss! It should be noted that the published values of energy expenditure during activity are estimated values based on averages for many test subjects performing. In addition , BMR is determined using correlations based on age, height, mass and gender. These correlations were developed using data of many test subjects, and thus represent physiologic estimates. This provides an ideal opportunity to explore the uncertainties related to the use of estimated values as well as those associated with experimental measurements.

Using the HYSYS process simulator to simulate the sensible heat and latent heat changes during respiration , the role of respiration in thermal regulation of the body is investigated. Figures 3, 4, and 5 show the total, sensible, and latent heat transfer rates (respectively)

35

In using traditional classroom surveys, the students responded that

the module contributed to their enthusiasm for engineering

as evidenced with a score of 4. 75 out of 5.0.

under varying ambient temperature and relative humidity. The data in these figures is obtained using HYSYS, but essentially represents Eq. (9). Graphical representation of the equation is a useful visual tool that helps students grasp the effects of ambient temperature and humidity on the sensible and latent heat exchange rates. Using the resting data above, the overall rate of heat transfer through respiration at rest (and at ambient conditions of the experiment) is about 19 kcal/h, or 23% of the total resting energy expenditure. By performing HYSYS simulations at different combinations of ambient temperature and relative humidity, students can make the following important observations about heat transfer during respiration:

1. The total rate of heat loss via respiration decreases with increasing relative humidity (RH) and with increasing temperature. Heat loss is positive except under the most extreme conditions of high T and RH when the heat loss is negative and heat is transferred to the body via respiration. Heat loss occurs via evaporative cooling in dry conditions, and this effects a net cooling effect even when the ambient temperature is higher than body temperature.

2. The sensible heat transfer contribution becomes more significant when ambient temperatures are

farther from body temperature ( at cold and hot extremes). Sensible heat losses are greater at cool temperatures and show little dependence on relative humidity. When the ambient temperature exceeds body temperature ( 37°C), sensible heat losses are negative.

3. The latent heat loss rate decreases with increasing RH and with increasing temperature. When the ambient air is at 37°C and 100% RH, the total sensible and latent heat losses are exactly zero. In very hot and dry conditions, an overall cooling effect is achieved by a high rate of evaporative cooling (note that at 45 °C and dry conditions the total heat loss and the latent heat loss are both positive, while the sensible heat loss is negative).

ASSESSMENT An assessment plan based on the rubrics developed by

Newell, et al. , 191 was developed to map student work directly to the individual learning outcomes of these freshmen. The learning outcomes specifically address ABET criteria, AIChE, and program-specific goals. This assessment was based on reasonable expectations for freshmen students who have had their first introductory exposure to engineering principles.

Four instruments were chosen for the evaluation: a team laboratory report, an individual in-class quiz, a formal oral presentation, and an interactive poster presentation. These were evaluated for three consecutive years.

Table 5 shows the stated objectives/outcomes that were evaluated on a four-point ordinal scale to describe student performance, using detailed rubrics as discussed previously in the paper by Newell.191 In these rubrics, levels of student performance are assigned values of 1 to 4 on an ordinal scale. A score of 4 represents an expert who has mastered the given

TABLES Desired Educational Objectives for this Project

Obiective/Outcome (to demonstrate ... ! Ma"(l_fl_ed to Goal . . .

1 A working knowledge of chemical engineering principles (energy balances, work, efficiency, psychrometric

~ chart, unit o~rations AIChE Professional ComPQnent

A working knowledge of chemistry (reaction stoichiometry, heat of reaction) AlChE Professional Component

r An ability to function on multidisciplinary and/or diverse teams -ABET-d

An abi lity to approach tasks involving experimental results in a logical and systematic fashion (measurements, recording, analysis, and interpretation) Program

An understanding of contemporary issues relevant to the field (current technical material, find relevant

- current information; and use in curricular assignments ABET- j

An ability to use techniques, skills, and modern engineering tools necessary for engineering practice (spreadsheets, word processors, and process simulators) to assist in problem solving ABET-k

Effective oral and written communication skills ABET-g


objective; a score of 3 represents a skilled problem solver; a score of 2 represents a student who has some skills but lacks competence; a score of I represents a complete novice. The complete rubrics are available on a website at

< http://engineering.rowan.edu/~newell/rubrics>

Students were also surveyed regarding their perceived ability to demonstrate the same skills . The results of the assessment by faculty are shown in Figure 6, and the results of student self-assessment are shown in Figure 7. Both student self-assessment and faculty assessment scores were consistent and highly satisfactory; the percentage of students receiving a rating of 3 or 4 was above 89% for each objective.

We believe that the scores indicate that we were successful in achieving our stated learning objectives. In using traditional classroom surveys, the students responded that the module con-

90

80

,,, 70 Q) ,,,

60 C: 0 a. ,,, 50 ~

~ 40

0 30 ~ 0 20

10

0

~-$:-0., . r;;.<A <l,e, ~

?f -<::-e,

«? (j

tributed to their enthusiasm for engineering-as evidenced with a score of 4.75 out of 5.0.

CONCLUSIONS

This paper describes a module with a hands-on experiment and associated follow-up activities in which principles of energy balances are introduced through application to the process of respiration. Basic physiologic responses are already familiar to students through "common knowledge" and sensory experiences, and most students have a natural curiosity to learn how their own bodies work. This hands-on experiment and the associated assignments focus on quantifying and analyzing the physiologic system. This establishes a framework within which new engineering concepts are introduced. Students learn concepts related to energy balances,

• Expert (4)

• Competent (3)

ls! Inexperienced (2)

• Novice (1)

chemical reaction stoichiometry and heats of reaction, work, power, and mechanical efficiency and are exposed to the use of thermodynamic property tables, psychrometric charts, and process simulation software.

ACKNOWLEDGMENTS

Funding for this project was obtained from the National Science Foundation Course, Curriculum, and Laboratory Improvement Program (NSF DUE #0088437) .

REFERENCES I. Farre ll , S. , R.P. Hesketh , K.Hollar, M.J .

Figure 6. Results of fa culty assessment for this project.

Save ls ki , R.Specht , "Don ' t Waste Your Breath !", Proceedings of the 2002Annual Confe rence of the American Society for Engineering Education, Sess ion I 6 I 3 (2002)

,,, Q) ,,, C: 0 a.

90 T"""----------------------80

70

60

"' 50 ~

]i 40 _g 0 30

?f!. 20

10 0 +i-----,-1--ia.:1.._ i..a_...,...,. _ _ ..1..1

• Expert

• Competent

ls! Inexperienced

• Novice

Figure 7. Results of student assessment of this project.

Winter 2005

2. Farrell , S., R.P. Hesketh, and M.J . Savelski , "A Respiration Experiment to Introduce Chemical Engineering Principles,"Chem. Eng. Ed. , 38(3) (2004)

3. HYSYS, version 2.4.1, Hyprotech Ltd. (2001) 4. McArdle, W.D., F.l. Katch, and V.L. Katch, Ex

ercise Physiology: Energy, Nutrition, and Human Performance, 4th ed. , Lea and Febiger, Philadelphia, PA (1996)

5 . Adams, Gene, Exercise Physiology Laboratory Manual, W.C.B . McGraw Hill, NY (1998)

6. Wasserman, K. , J .E. Hansen, D.Y. Sue, B.J . Whipp, Principles of Exercise Testing and Interpretation, Lea and Febiger, Philadelphia, PA ( 1987)

7 Cameron, J., J. Skofronick, and R. Grant, Physics of the Body, Medical Physics Publishing, Madison, WI (1992)

8 . Cooney, David 0. , Biomedical Engineering Principles, Marcel Dekker (1976)

9. Newell , J.A. , K.D. Dahm, and H.L. Newell, "Rubric Development and Inter-Rater Reliability Issues In Assessing Learning," Chem. Eng. Ed., 36(3) (2002) 0

37

.ta .. 5_§._c_l_a_s_s_r,_o_o_m _ _ ______ __,)

A Project To

DESIGN AND BUILD COMPACT HEAT EXCHANGERS

RICHARD A. DAVIS

University of Minnesota Duluth • Duluth, MN 55812

0 ur department initiated a project for students to design and build a compact shell-and-tube heat exchanger in order to address needs defined by our

educational goals, by industrial advisors, and by our students and alumni. The needs that fit neatly within the scope of this project include putting theory into practice, developing engineering judgment, and gaining hands-on experience. For our purposes, engineering judgment is defined as the aspect of problem solving and design that balances theory with practice, creativity, and common sense.Ill

Recently, members of our department's industrial advisory board provided us with feedback on their experiences with young chemical engineers in the work place. One theme that emerged was that the modem student has a general lack of practical, hands-on, mechanical skills with basic tools and building materials. One company reported on a workshop they started that offers intern and co-op students (as well as new engineers) instruction on topics such as the use of small tools , fittings, piping, filters , valves, automation and instrumentation, pump basics, heat exchanger knowledge, and basic troubleshooting skills . Our experience, along with that of our industrial partners, echoes Finlayson's observation121 that

We see students who have very little hands-on experience in anything and their practical education begins when they get into our laboratory. These people are more susceptible to accepting whatever comes out of the computer. Now, instead of teaching people how to write programs, we are teaching them how to check the results, to use their heads and evaluate the information. We teach them to be skeptical and some specific steps to use in checking their work.

The project for students to design and build a compact shelland-tube heat exchanger was structured to meet several important objectives. First, it was designed to help students become comfortable in industrial environments through exposure to basic hand tools and construction materials; second, it would provide students with an open-ended design prob-

38

!em where they could develop confidence in engineering principles through application; and third, it was meant to develop our students' sense of engineering judgment.

PROJECT DESCRIPTION

The heat-exchanger project was incorporated into a core course on heat transfer, typically taken during the spring semester of the junior year of our program, that covers topics on transport phenomena and unit operations of heat transfer. The assignment was to design and build a compact shell-andtube heat exchanger for water streams such that the temperature of the tube-side fluid changes by a magnitude of at least 20 °C at the operating conditions listed in Table 1. The design objectives were to minimize cost and size. For this project, the cost was assumed to be directly proportional to weight. The size was taken as the largest dimension (e.g., length of exchanger).

A simple double-pipe heat exchanger was constructed as a prototype for the purpose of demonstrating the concept of the project to the students and to provide them with ideas of materials and construction methods. The shell and tube were made from four feet of one-inch schedule 40 PVC pipe and 1/4-inch copper tubing, respectively.

By intentional design, the prototype exchanger did not perform to the required specifications of the project. The students formed teams of two or three students and were told to

Richard A Davis is Professor of Chemical Engineering at the University of Minnesota Duluth, where he teaches transport phenomena, unit operations, separations, biochemical engineering, and computational methods. He received his BS and PhD degrees in chemical engineering from Brigham Young University and the University of California Santa Barbara, respectively. His current research activities include process optimization, modeling, and simulation.



improve the design of the example exchanger to meet or exceed the project performance and design specifications. In order to avoid proposals that simply lengthened the tube, the teams were challenged to consider compact designs that minimized the size and weight of the device. Individual students were required to report their results in a memo report to the instructor. Each team presented its findings to the class.

Materials of Construction • The first objective was to give students hands-on experience with tools and construction materials. The project also served as a learning vehjcle to acquaint students with pipe schedules and fittings (such as

caps, elbows, unions, re

TABLE 1 Heat Exchanger Operating

Specifications

ducers, tees, and connectors). Students were limited to materials available in typical hardware stores or home building centers, including standard schedule 40 or schedule 80 PVC pipe and fittings , 1/4-inch copper tubing, compres-

Feed Temperature Approximate Streams 't' Flow Rate

(Umin)

Cold Water <15 0.50±0.05

Hot Water >55 0.20±0.05

Room Air 20±2

TABLE2 Tools Provided for Building Heat Exchangers

Hand Tools

• 8- and I 0-inch adjustable

wrenches and locking pliers

• l/2- to 9/l 6-in open end and

socket wrenches

• Cutting shears

• Tube cutter and bender

• Miscellaneous files and clamps

• Tap threading tools and drills

• Measuring tape and caliper

Power Tools

• Ski! variable speed 3/8-in drill

• Craftsman 9-in drill press

• Delta 10-in compound miter saw

• Craft sman 9-in band saw

• Craftsman 42-in belt, 6-in disk

sander/grinder

• Dremel rotary tool, attachments

• Ski I variable-speed jig saw

Figure 1. Experimental station to measure hot- and coldstream flow rates and temperatures in student

manufactured heat exchangers.

Winter 2005

sion fittings , and common insulation materials. Compression fittings , PVC cement, and Teflon tape were used to seal the connections. An allocation from the university laboratory fee was used to purchase the materials. The average cost of a heat exchanger was less than $20, and the department maintained ownership of the materials in order to recycle copper tubing and compression fittings when possible.

Tools and Safety • The project also provided students with experience in using a vaiiety of common hand tools and small power tools-a complete list of tools for the project is given in Table 2. While a few students already had significant practice with many of the tools, several indicated that they had little or no experience. Thjs provided an opportunity for instruction in basic safe practice using tools and materials .

Students were given training on the proper and safe use of each hand and power tool, with the safety guidelines supplied by the manufacturer of each power tool being used as the basis for the training. The university 's environmental health and safety officer visited the laboratory to make a presentation and to measure the noise level in the vicinity of the power tools-the conclusion was made that healing protection was necessary around the power saws. Students were issued leather gloves when using sharp hand tools and latex gloves when using PVC pipe cement. Eye protection and closed-toe shoes were required at all times during the construction phase of the project. Students were not permitted to use tools until they had completed the safety training.

Experimental Station • The student-built heat exchangers were tested on the experimental station shown in Figure 1. The hot-water stream was generated in a constant-temperature circulating bath. Consistently cold tap water (straight from the Minnesota shore of Lake Superior!) was used for the coldfluid stream. The flow rates were controlled with small balland-pinch valves in the flow lines. Flow rates were measured with McMillan 112 electronic flow meters. The temperatures of the inlet and outlet streams were measured with type-K thermocouples mounted in 1/4-inch brass tees placed in line with the fluid streams, located near the points of entry and exit. The temperatures and flow rates were monitored to determine steady-state operating conditions, which were typically achieved in less than twenty minutes. By requiring 1/4-inch connections for the feed and effluent tubes, the same experimental setup was used to test all student-built heat exchangers without signjficant rearrangement.

DESIGN AND ANALYSIS

The second objective of this project was to enhance student confidence in engineeiing design principles. They learned the basic principles of heat exchanger design, including mass and energy conservation, overall heat transfer coefficients, and the log-mean temperature difference and effectiveness number of transfer units (E-NTU) methods. They also participated in discussions of nonideal behavior of heat exchang-

39

ers (such as the potential for heat exchange with the surroundings), orientation and fluid mixing, entrance and transition effects, and temperature dependent properties. Armed with these skills, the teams were capable of designing a compact shelland-tube heat exchanger subject to the project constraints.

Each team was required to document its design calculations before it was allowed to begin construction. The teams could not change or modify their basic designs once construction began, to avoid a scenario of empirical design by trial-and-error. The teams were also required to set up and solve their design equations in computer spreadsheet applications, such as Excel, or general-purpose mathematics software such as Mathcad, Polymath, or Matlab. An example of student design calculations for a multipass heat exchanger using Mathcad is available for download at <http:// www.d.urnn.edu/ ~rdavis/htxr>.

Computer software tools allow students to quickly and efficiently perform a sensitivity analysis on their design equations and to investigate potential effects of uncertainty in parameters such as operating conditions, material properties, and heat transfer coefficients. For example, an analysis of the overall heat transfer coefficient revealed that the conduction resistance through the wall of the copper tube was insignificant for this project. It was also determined that heat exchange with the surroundings was negligible. The "design first, build later" feature of the project was important for students to develop their sense of engineering judgment and transformed their skill set from the academic "learning by doing" to the competitive edge of "learning before doing."[3l

A range of creative designs emerged from the various teams. The most common designs, illustrated in Figure 2, were variations on multipass heat exchangers imitating industrial configurations . Students quickly discovered that correlations for heat transfer coefficients specific to their design concepts were not readily available in the literature, so they adapted general-purpose correlations to their geometries and flow conditions . For example, one team decided to coil the tube in the shell and used a heat transfer coefficient correlation for cross flow over a cylinder for the fluid in the shell.

(a)

.--.,.-.,,.-_-_-_-_-_-_-_-_----*::;--:c:/-r ~· -~ __ :)

service for temperatures exceeding 100°F. Other design considerations were tube spacing to allow the fluid to flow over the available surface area for heat transfer and allowances for tube length to include the designed heat transfer area requirement plus accommodating the additional length required by the pipe connections and tube fittings.

RESULTS AND DISCUSSION

A selection of student-built heat exchangers is shown in Figure 3. In two cases, the shells were cut away to reveal the interior tube configurations. The exchangers in Figure 3 are representative of the construction materials used for the project. PVC pipe and end caps were used for the shell, and brass pipe and compression fittings were used for the copper tube connections. The locations of the feed and effluent ports were determined by the student teams to adapt their performance and design calculations.

Teams that came to the laboratory well prepared were able to construct their devices in approximately one hour. Appropriate preparation included team-member assignments for an equal division of labor, a simple schematic with dimensions, and an idea of where to cut, drill , and tap. Thirty more minutes were needed on a following day to test the performance of the device. A few teams arrived at the laboratory ill-prepared to begin construction and found that a considerable amount of additional time was required to implement the fabrication process when they had only a general idea of how the final product might look. In the future, teams will be required to present specific plans and a schematic for manufacturing their device, in addition to the basic design calculations, to avoid unusual laboratory time commitments.

At the end of the course, each student team had successfully designed and built a compact shell-and-tube heat exchanger that met the required performance specifications and

size objectives relative to the

(b)

All of the groups designed their exchangers for operation with the hot stream on the tube side and the cold stream on the shell side, to minimize heat transfer to the surroundings. They also noted from manufacturer's recommendations that PVC pipe is not suitable for hot-water plumbing

(c) (d)

prototype. The most successful exchanger in terms of minimizing size and weight used a single copper tube making four passes through the length of a 2-inch pipe. The success of the designs promoted student confidence in the principles of engineering design. The students also gained an appreciation for the limitations of common assumptions (such as steady-state operation, constant temperature or heat flux, perfect mixing, and constant properties) typically required to solve textbook problems.

40

Figure 2. Schematics of common heat exchanger configurations: (a] single shell-and-tube bundle, countercurrent flow pattern; (b) single shell with coiled tube, cross-flow pattern; (c] single shell, multiple-tube pass; (d] two-shell pass with multiple-tube pass.


Some interesting questions were posed by the teams during the construction phase of the project. For example, where should the fluid inlets and outlets be located on the shell to preserve the heat transfer area determined by the design calculations? Students realized that their choice of feed and effluent port locations might have an effect on the fluid residence time in contact with the working heat transfer area.

Some other questions were posed regarding issues of fluid mixing, stagnation, and entrance effects, as well as insulation requirements and containing leaks. The best start-up procedure to eliminate pockets of air in the exchanger was also considered. One team was particularly less careful than others when assembling its exchanger. This team built a singlepass shell-and-tube heat exchanger and found they could not achieve steady-state operation. The team made the following observations: the circulating bath reservoir was slowly draining, while the outside surface temperature of the shell was increasing. They correctly deduced that the hot water was leaking from the header into the shell side. This experience fostered class discussions about how to improve the design and further developed the students' troubleshooting skills.

Students reported that they enjoyed the project and appreciated the opportunity to apply principles of heat transfer. The teams were proud of their devices, gave them names, and took them home to show friends and family. Much of the learning came from interactions between the different teams. Students were curious about the various designs that emerged from the project and freel y shared ideas for design and manufacturing tips during the construction phase. A friendly atmosphere of competition existed throughout the project and lasted through the oral presentations. All of this combined to generate enthusiasm for the subject matter of the course.

An informal discussion with several students revealed that the project advanced their understanding of film theory, heat transfer coefficients, and heat exchanger performance and design methods. The students were also given a heat-ex-

Figure 3. Examples of student-built heat exchangers and construction materials. At the left are examples with the shell cut away to reveal a multipass and coiled-tube design . At the right are double-pipe and shell-and-tube heat exchangers.

Winier 2005

changer design problem on the final exam in order to assess the effectiveness of the project on student learning. The students involved in the heat exchanger design project outperformed the classes from the previous three semesters on a similar exam question, indicating that this project enhanced their understanding of the material.

A few students claimed extensive experience with common hand tools from summer work experience, living on a farm, or tinkering with engines. We worried that they might find this project trivial and become disinterested, but were pleased to find that they were equally enthusiastic about the project and willingly shared their skill s with the other students. The mixture of students with a range of previous experience enhanced the overall learning experience for all students in the class.

One drawback of this project was the additional time required of the students to be in a laboratory outside of lecture periods. Reducing the lectures or including this project in the unit operations laboratory may minimize the impact on students' time demands. Another disadvantage was limited access to tools. Currently, our department has only one set of power tools, but there are plans to increase the availability of tools to permit multiple teams working simultaneously.

CONCLUSIONS

A simple, inexpensive, hands-on learning project for students to design and build compact shell -and-tube heat exchangers was assigned as part of a course on heat transfer. Students worked in small teams of two or three, using the basic principles of engineering design to propose a heat exchanger that would perform according to predetermined specifications . The teams were required to manufacture their heat exchangers according to their basic design calculations as an integral part of the learning experience to encourage confidence in the engineering principles and to develop their sense of engineering judgment. The students gained mechanical experience with basic tools and common building materials, as well as lessons in safety. They were pleased with the outcome of this exercise and recommended the project to students that followed them.

ACKNOWLEDGMENT This project was sponsored by a UMD Chancellor's Faculty Small

Grant.

REFERENCES I. Peters, M.S. , K.D. Timmerhaus, and R.E. West, Plant Design and

Economics for Chemical Engineers, 5th ed., McGraw Hill, New York, NY, p. 12 (2003)

2. AIChE, The Global Environment for Chemical Engineering, New York, NY, p. A-8 (2001)

3. Mancini , S. , "Chemical Engineering in Process Development and Manufacturing of Pharmaceuticals," ASEE Summer School of Chemical Engineering Faculty, Panel, "Industrial Needs from ChE Graduates," Boulder, CO (2002) 0

41

.(A .. 5-3._c_l_a_s_s_,.,_o_o_m __________ )

A METHOD FOR DETERMINING SELF-SIMILARITY

Transient Heat Transfer with Constant Flux

CHARLES MONROE, JOHN NEWMAN

University of California • Berkeley, CA 94720-1462

When similarity solutions to partial differential equations are introduced in the classroom, the introduction of similarity variables and the approach

to self-similar problems often appears to be something of a "dark art." This paper provides an example to show how proper dimensional analysis can be used to demonstrate the existence of self-similar behavior. The procedure is as follows:

1. State the governing equations and boundary conditions .

2. Rearrange any variables that can be combined in additive or multiplicative groups to simplify the governing equations and boundary conditions. Simplifications that should always be performed if possible include: rearranging the governing equations so one term has no coefficients, translating the independent variables so inner boundary conditions are at zero, setting all but one of the boundary and initial conditions to zero by translation of the dependent variable, and cross-multiplying the boundary conditions so that they equal dimensionless constants (e.g., 0, ±1 , or ±oo).'L11

3. Write the dimensional-variable space of the problem as a system of inequalities. Include dimensional independent variables, dependent variables, and system parameters that remain after performing step two. State all lower and upper bounds of these quantities. This bookkeeping measure concisely

* /11 linear Dirichlet problems, the dependent variable should sometimes be made dimensionless at this point in the procedure. An example is the solution to the Navier-Stokes equation for impulsive motion of a fla t plate i11 a semi-infinite medium (also known as Stokes' fi rst problem, posed in Reference 1 ).

summarizes all variables and their possible values. In addition, it clearly shows variables that can be removed, or bounds that can be relaxed, during asymptotic analysis.

4. Compose a dimensional matrix for the dimensionalvariable space. Determine the rank of this matrix. Subtract the rank from the total number of variable groups. If dimensionless groups arose during rearrangement in step two, add one for each. The result is the number of dimensionless degrees of freedom involved in the problem.

5. If the number of dimensionless degrees of freedom is two, a similarity solution exists. If the degrees of freedom can be reduced to two by taking upper (or lower) bounds of the independent variables to

John Newman joined the Chemical Engineering faculty at the University of California, Berkeley, in 1963, and has been a faculty senior scientist at Lawrence Berkeley National Laboratory since 1978. His research involves modeling of electrochemical systems, including industrial reactors, fuel cells and batteries, and investigation of transport phenomena through simulation and experiment.

Charles Monroe recently completed his graduate study at the University of California, where he investigated dendrite formation in lithium/polymer batteries with Dr. Newman. He earned a BS from Princeton University in 1999, received the 2002 Dow Award for Excellence in Teaching, and was granted a doctoral fellowship for 2003 by the Shell Foundation. Recently, he joined the Department of Chemistry at Imperial College, London, as a Research Associate.



This paper provides an example to show how proper dimensional analysis can be used to demonstrate the existence

of self-similar behavior.

infinity (or negative infinity), a similarity solution describes this asymptotic regime.

We illustrate these steps below with the classic problem of transient constant-flux heat transfer to a stagnant one-dimensional medium between a conductive inner wall and an insulated outer wall.

The earliest experiment under the conditions analyzed here is credited to F. E. Neumann, who performed experiments to measure the thermal conductivity of solids . In 1862 he lectured in Paris, proposing mathematics to describe bars heated electrically at one end. 121 He used the heat equation (with a superfluous generation term) to obtain an expression for thermal conductivity under conditions of constant flux; for cubic bodies of low conductivity, he derived another expression to show that temperature rises with the square root of time. Preston 's Theory of Heat references similar experiments by 0 . J. Lodge (1879), and gives another incorrect mathematical treatment. 13·41 The finite problem was developed accurate! y by Carslaw,151 and several avenues for solution of finite and

Conductive wall q, = - kaT/ch

Insulating wall q, = 0

Figure 1. Experimental geometry for the heat-transfer problem.

* To imagine a more concrete experiment, think of the wall at x = 0 as a metal block, which has high thermal conductivity, and the wall at x = L as a piece of low-density foam, both of which are impenneable to and insoluble in the thennally conductive medium between. Assume the medium is water, which is isotropic, has low viscosity, and is of intermediate conductivity. An electric heater rnpplies constant power to the metal. The system can be oriented with respect to gravity to suppress the effect of f ree convection.

Winter2005

semi-infinite cases were proposed by Carslaw and Jaeger,161

who were the first of these authors to mention a possible solution by integrated error function complement. The similarity solution was introduced as an exercise in the textbook by Bird, Stewart, and Lightfoot.Pl

Figure 1 shows a one-dimensional rectilinear region with spatially uniform initial temperature T

0 and walls at x = 0

and L. At time t = 0, a uniform and constant heat flux q, (which may be positive or negative) is applied in the positive x-direction at the conductive boundary x = O; the boundary at x =Lis well-insulated.· We assume experimental conditions with adiabatic walls parallel to the heat flux, effectively constant and isotropic transport properties, and no homogeneous heat generation.

Three solutions, valid at long times (Eq. 18), intermediate times (Eq. 19), and short times (Eq. 20) are presented here. Dimensional considerations are then used to realize a fourth self-similar solution (Eq. 29), which describes asymptotic behavior in a semi-infinite medium or a medium observed at very short times .

STATEMENT OF GOVERNING EQUATIONS: INITIAL AND BOUNDARY CONDITIONS

We begin by writing the governing equations and boundary conditions. The transient one-dimensional rectilinear heat equation applies in this case

c aT = k a2T

P P at ax 2 (l)

where pis density of the medium, CP is its specific heat capacity at constant pressure, and k is its thermal conductivity. Appropriate initial and boundary conditions are

T(O, x) = T0

-k dTI - q dX (t;?O,O} - x

dTI -0 dx (t,L}

(2)

(3)

(4)

We seek mathematical solutions to Eq. (1) satisfying conditions 2 through 4 that are easily calculated at all experimental time scales.

As a first approach to simplification, we apply the second

43

step of our procedure, which results in this restatement:

a(T-To) k a2(T-To) at pep ax 2

T(O,x)-T0 =0

~ a(T-To)I =-I q ax

X (t<!O,O)

a(T-To)I = o ax

(t ,L)

(5)

(6)

(7)

(8)

The initial condition is now zero, and the governing equation and boundary condition 3 have been rearranged. It is apparent here that T

0 appears only in an additive combination with

T, and that CP and qx occur only in multiplicative combination with k.

STEADY STATE FOURIER-SERIES SOLUTION: LARGE-S LAPLACE-TRANSFORM SOLUTION

We now implement step three of the procedure. The dimensional-variable space of a problem summarizes the domains of remaining dimensional independent variables, the ranges of dimensional dependent variables and system parameters, and all known bounds of these quantities. While not essential, this step is a useful tool to help clarify one's thinking before approaching the differential equation. The dimensional-variable space of the problem stated in Eqs. (5) through (8) is

independent variables

dependent variable

parameters

{o ~ t < 00

O~x~L

{-oo~T(t,x)-T0 < 00 (9)

lo~~< 00

pep

k -00<-<00

qx

Inequalities 9 reflect that physical values of the properties pc\ and k are positive. The flux q, and temperature difference T - T

0 may take positive or negative values, because

heat can be added to or taken from the system, resulting in an increase or decrease of temperature. The distance L between walls has been included as the upper bound of x.

Step four is to apply the "Buckingham pi theorem" (the rigorous development of which may be more appropriately

44

attributed to Bridgman, and the linear algebraic formulation of which owes to Langhaar) to these groups of variables. '8•

9•10

• 11 I

The dimensional matrix is

X T-T0

kip<:\ k/q, L

0 0 -1 0

!] 1 0 2 (10) 0 0 -1

Matrix 10 is created by putting relevant fundamental SI units to the left of the rows and elements of the dimensional-variable space above the columns. The powers to which units are raised in each variable determine the values of the matrix elements.

There are 6 groups of variables, and the rank of the dimensional matrix is 3; therefore, by the pi theorem, the problem can be phrased in a dimensionless-variable space with three degrees of freedom . If a two-dimensional boundaryvalue problem with three dimensionless degrees of freedom is separable and has a closed domain in one independent variable, it can usually be reduced to a Sturm-Liouville system in the closed domain if asymptotic behavior is subtracted from the initial condition. Although our goal here is to illustrate self-similarity, the Fourier-series solution and a Laplace-trans-

0.3

0.2

~ 0.1 ' I

©

0.0

-0.1

---- ln(-c) = - 10 ln('t) = -8

- - ln('t) = -6 - - - ln(-c) = -4 --- --- ln(-c) = -2 ........... ln(-c) = 0

- - = steady-state

-0.2 ....._ _ _ _._ __ __,,._ _ _ __..___ __ ....__ _ _ _.

0.0 0.2 0.4 0.6 0.8 1.0

Figure 2. Plot of the long-time solution given by Eq. 18 and the transient Fourier-series solution given by Eq. 19.


form solution more useful at short times are shown now. The Fourier series results from the standard approach to separable partial differential equations; the next section will reveal that the Laplace-transform solution relates fundamentally to the result by simj)arity transformation .

At this point, the three dimensionless variables can be selected by trial and error, with two dimensionless degrees of freedom allotted to the independent variables and one to the dependent variable. A more physically sound route to a natural set of dimensionless variables is provided by an overall energy balance around the slab,

- tfq ·dS = f pCP (T - T0 )dV (11) S V

Upon simplification of the integrals, multiplication of both sides by k, and some rearrangement, thi s energy balance reduces to the simple form

I

1: = J 0ds (12) 0

In Eq. (12)

kt 1:=---pCPL2

s = !.. L

(13)

which assigns the appropriate number of degrees of freedom to the independent variables and the dependent variable. Substituting these variables into the governing equation and boundary conditions, we find

ae a20 (14) a1: as2

0(O,s)=O (15)

a01 ~ {, ~o,o) = -I (I 6)

a01 as (, ,1)

-0 (17)

Note that® is always positive because the heat flux no longer appears as a parameter.

A first step in the analysis of a transient partial differential equation is to obtain a solution valid at long times .* Usually, long-time solutions are obtained by discarding the terms containing time derivatives, but because thj s problem involves

constant flux of heat, and therefore a constant increase or decrease in system energy, the time derivative of the dimensionless temperature approaches a nonzero value at long times. To obtain long-time behavior when a system accumulates or loses energy, the condition

ael = t (s) a1: ,-.~ should be employed. The solution that satisfies conditions 16 and 17 when t • oo is then

(18)

where the factor of 1/3 is included so that 0 00 satisfies the dimensionless energy balance given in Eq. (12) . The Fourier-series solution valid at all times is

(19)

Equations (18) and (19) are plotted in Figure 2.

The rate of convergence of the Fourier series in Eq. (19) slows as 1: • O. A series that converges much more rapidly is obtained as follows. Take the Laplace transform of the problem with respect to time. A large-s expansion of this result can be obtained by Maclaurin exRansion of the transformed problem with respect to exp(-✓s J. Term-by-term inversion of thjs series by comparison with a table of Laplace transforms11 21 gives an alternative to Eq. (19)

which converges rapidly at small values of,. and is plotted in Figure 3 (next page). The integrated error function complements included in Eq. (20) are defined as the functions which solve the differential equation

d2y dy - 2 +2z--2ny = 0 dz dz

n = -1, 0, 1, 2, ... (21a)

when n is equal to unity.

Ordinary differential Eq. (21a) is satisfied by functions of the form1'31

y = Ai nerfc(z) + Bi nerfc(-z)

where

* Taking the long-time f onn of a transient equation to obtain an ordinary equation exemplifies a basic type of astymptotic analysis: an independent variable (t) can be removed from the variable space by assuming it takes a large value ( t • 00 ). The governing equations and boundary conditions must then be rephrased to reflect insensitivity to this variable (accumulation becomes a f unction ofx only). We applied this type of asymptotic simplification implicitly when reducing the problem to one spatial dimension.

Winter 2005 45

2 00

i0erfc(z) = ✓rr, J exp(-z2 )ctz = erfc(z) z

i "erfc( z) = - ~ i n-Ierfc(z) + _!_ i n- 2erfc(z) n 2n

(21b)

Solutions to Eqs. (14) through (17) given by Eqs. (19) and (20) are identical. Fewer terms of Eq. ( 19) are required for accuracy at long times, and fewer of Eq. (20) are needed at short times.

SELF-SIMILARITY IN AN ASYMPTOTIC REGIME

Previously, we used L to scale position x and time t. Step 5 of the procedure outlined in the first section of this paper yields an asymptotic result for small -r. Physically, the condition that -r << 1 corresponds to systems where the length scale or volumetric heat capacity is large, or the thermal conductivity or time is small; the dimensionless energy balance given by Eq. (12) further shows that when -r is small, the dimensionless energy put into the system is also .

Under any circumstances where -r << 1, L may be considered to approach infinity, the domain of x becomes open, the number of columns in the dimensional matrix reduces by one, and the degrees of freedom reduce to two. Parabolic problems that afford two dimensionless degrees of freedom can be solved by grouping the independent variables together in a single similarity variable . This condition is called complete similarity, or self-similarity of the first kind. 11 41

We choose two dimensionless variables, making sure both independent variables are contained in one of them and the dependent variable is in the other:

(22) ©

We introduced constants 131

and 132

into relations (22); particular values for them can be selected later to simplify solution of the resultant ordinary differential equation and put results in a standard form .

Talcing L -+ oo in Eqs. (5) through (8) and then inserting relations (22) give

d28 I d8 I O= dri 2 + 2~f l'ldri - 2 ~f

8

8( 00) = 0

:~111 =0 = - ~,~ 2

d81 = 0 dri ,1-+ oo

(23)

(24)

(25)

(26)

Boundary condition (26) limits the asymptotic behavior of the solution at large x, and is not as strict as Eq. (8), which restricts the solution at a particular x. Substitution of 'Tl into Eqs. (5) through (8) as L approaches infinity to yield Eqs. (23) to (26) represents a similarity transformation .

0.7 ,--------,-----r----..--- - --,----,

0.6

1'

0.5 ''

0.3

0.1

\ \

\ \

\

\

\ \

\ \

\

\

' '

\

' ' ' ' ' '

....

' '

·········· · ln('t ) = -10 ······ ln('t) = -8 - ·- ·-· ln('t) = -6 - · - ln(-c) = -4 - - ln('t) = -2 -- ln('t) = 0

.... ....

- - -0.0 ...,_-'----=------'--=-=~ - -'---

0.0 0.2 0.4 0.6 0.8 1.0

Here, the similarity variable 'TJ and dependent variable 0 have been chosen because they are relatively simple forms. To put x in the numerator of 'Tl simplifies back-substitution, because second derivatives of 'Tl with respect to position are then zero. There is only one derivative with respect to time in the governing equations and boundary conditions and there are two with respect to x, which suggests choosing a 0 that omits x, if possible. It should be noted that an ordinary differential equation will result for any choice of dimensionless similarity variable, as long as it excludes the dependent variable and contains both independent variables.

Figure 3. Graph of the integrated error-function-complement series solution, Eq. (20).


Note that introduction of the similarity variable has reduced governing Eq. (5) to an equation of second order. In problems that are amenable to similarity transformation, two of the boundary conditions should collapse to a single condition. Either boundary condition (24) or (26) can be di scarded on the basis that it is superfluous-a solution that satisfies governing Eq. (23) and one ofEqs. (24) or (26) must satisfy the other.

If [31

is chosen to be 1/2, then Eq. (23) matches Eq. (21a) with n = 1. Boundary condition (25) takes its simplest form when

{27)

To satisfy Eq. (27), we choose [32

= 2. The dimensionless similarity variables are

17 = ~ ✓ pCP and 2 kt

{28)

A solution to Eqs. (5) through (8) when L - oo is given by

0( 11) = ierfc( 11) {29)

Equation 29 is plotted in Figure 4. Because

0=~ 2-,;. this solution matches the first term of series 20 when reflections from the far wall are neglected. As an exercise, the student can take the limit of series (20) when dimensionless time approaches zero to retrieve the similarity solution.

0.6

0.5

0.4

<D 0.3

0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0

Figure 4. Th e similarity solution yielded by Eq. (29).

Winter 2005

CONCLUSION

A methodology has been proposed that allows stepwise determination of self-similar solutions of the first kind by dimensional and asymptotic analysis. The five-step procedure is given in section 1, and is illustrated by the problem of transient constant-flux heat transfer to a stagnant medium with an insulated far wall in the remaining sections. Our approach illustrates how simplifying governing equations and boundary conditions according to certain rules and writing a dimensional matrix at the outset of a problem can effectively guide its solution.

A procedure to obtain self-similar solutions of the second kind, where the similarity variable can be used but more than two dimensionless degrees of freedom are present, will be addressed in future work. An example of a self-similar problem of the second kind is the transient mass transfer of a solute from a sphere at constant concentration into a stagnant medium in which the solute is homogeneously consumed with first-order kinetics.

ACKNOWLEDGMENTS

This work was supported by the Shell Foundation, and by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U. S. Department of Energy, under contract DEAC03-76SF0098.

REFERENCES

I.

2.

3. 4.

5.

6.

7.

8. 9.

IO. 11.

12.

13.

2.5

14.

Stokes, Sir G.G., Mathematical and Physical Papers, Vol. 1, Cambridge University Press, Cambridge, U.K., 21 (I 880) Dorn, E., et al., Eds. , Franz Neumanns Gesammelte Werke, 2"d Ed., Vol. 2, Kraus reprint, Liechtenstein, 144 (1979) Lodge, O.J. , Phil. Mag. , 251, 198 ( 1879) Preston , T. , Theo,y of Heat, 4th Ed. , Macmillan and Co., London, U.K., 600 (1929) Carslaw, H.S, Introduction to the Mathematical Theory of the Conduction of Heat in Solids, 2"d Ed., Dover Publications, New York, NY, 74 ( 1945) Carslaw, H.S. , and J.C. Jaeger, Conduction of Heat in Solids, 2"d Ed., Oxford University Press, Oxford, U.K. , 52 (1959) Bird, R.B. , W.E. Stewart, and E.N. Lightfoot, Transport Phenomena, I" Ed. , Wiley and Sons, New York, NY, 372 (problem 11.F) ( 1960) Buckingham, E. , Phys. Rev., 4(4), 345 (19 14) Bridgman, P.W., Dimensional Analysis, Yale University Press, 43 (1922) Van Driest, E.R., J. Applied Mechanics, 13( I), A34 (1946) Langhaar, H.L., Dimensional Analysis and Theory of Models, Wiley and Sons, New York, NY, 31 ( 1951 ) Churchill, R.V., Operational Mathematics, 2"' Ed., McGrawHill , New York, NY, 464 (1958) Abramowitz, M. , and I.A. Stegun, Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 4th Printing, National Bureau of Standards Applied Mathematics Series No. 55, Washington, D.C., 299 ( 1965) Barenblatt , G.I., Scaling, Self-Similarity, and Intermediate Asymptotics, Cambridge University Press, Cambridge, U.K., 95 (1996) 0

47

•t9•5111113rc=-:u~r=r=:ic~u~lu~m=--------)

PROCESS SECURITY IN ChE EDUCATION

CRISTINA P ILuso, K oRinJT UYGUN, YINLUN HuANG, HELEN H. Lou*

Wayne State University • Detroit, MI 48202

The tragedy of September 11 , 2001 , and subsequent terrorist attacks have alerted the chemical process industries to the need for plant security assur

ance at all levels: infrastructure-improvement physical security, information-protection cyber security, and design-andoperation-improvement process security. Process security is possibly the most difficult task due to the level of sophistication involved in integrating security with the production process.

Security as a whole is an extremely complex subject due to its unpredictable and improbable nature. Physical security protects against attacks (such as bombings, theft, or sabotage) by armed terrorists, disgruntled employees, political activists , etc.[1J Lemley, et a/. ,111 discuss an approach to enhance the process hazard analysis (PHA) by including a relative risk assessment in order to establish physical security infrastructure and programs. They also discuss physical security countermeasures, including communication with local law enforcement agencies, vehicle barriers that prevent driving through fencing, alarms, access control , security cameras, and double-gate entries.

Cyber security is defined by Baybutt[2J as the protection of manufacturing and process control computer systems, along with their support systems, from adversaries interested in obtaining, corrupting, immobilizing, destroying, or prohibiting access to important information. Baybutt also describes asset-based methods for including cyber security vulnerabilities in the assessment of a security vulnerability analysis (SVA). Examples of cyber resources include computers, servers, operating systems, e-mail, user names and passwords, process control data, and business plans, etc.

Despite these countermeasures being outside the realm of

* Lamar University, Beaumont, TX 77710

typical chemical engineering practice, the significance of physical and cyber security should not be ignored.

Traditional process safety measures alone are no longer sufficient for total plant securityYl Process security is an extended concept and practice of process safety, but while the typical scientific tools for safety assessment are based on probabilistic analysis, security incidents are intentional rather than accidental. In the chemical process security arena, a major concern is the potential for an event that results in a catastrophic outcome, such as an explosion, a toxic release, and/ or loss of life. r4J If such an event is possible, even with a low probability, it must be addressed and solutions must be found.

Process security cannot take probability into accountthe adverse events by terrori sts or saboteurs do not follow likelihood; they are completely unexpected. In this context, attacks are due to harmful manipulations by saboteurs who have sufficient technical knowledge rather than the brute force that traditional security methods address. While no funda-

Cristina Piluso received her BS degree in chemical engineering at Wayne State University in 2003. She is currently an NSF-IGERT fellow and a PhD student working with Professor Yinlun Huang on process security assessment and decision making using advanced computing methods. Korkut Uygun received his BS and MS in chemical engineering from Bogazici University (Turkey) and his PhD from Wayne State University. He is currently a post-doc with Professor Yinlun Huang on the development of dynamic optimization tools for IPD&C and has recently introduced a fast security assessment theory for chemical processes. Yinlun Huang is Professor of Chemical Engineering at Wayne State University. He received his BS from Zhejiang University (China) and his MS and PhD from Kansas State University, all in chemical engineering. His research interests are in process systems science and engineering, information processing and decision making, computational biology, and sustainable engineering. Helen H. Lou is Assistant Professor of Chemical Engineering at Lamar University. She received her BS from Zhejiang University (China), and her MS and PhD (all in chemical engineering) and her MA (in computer science) from Wayne State University. Her research and teaching interests are mainly in the areas of process synthesis, modeling, control, and optimization, information technology, and industrial sustainability.



mental method can hope to prevent the consequences of a bomb being dropped on a facility, developing better-designed processes can reduce the inherent vulnerability of a process. Traditional process safety techniques that rely on steady-state information, likelihood, and preset alarm systems may not be sufficient for addressing process security problems.

With the first work describing process security, Lou, et a/.,131

suggested that process security should be a

and the teaching experience accumulated by the participating universities should be valuable as a model for other chemical engineering programs to integrate process safety into their curriculums .

Today, process safety education has become more important than ever before, especially due to the need of homeland security assurance. The nature of chemical industries, whether

due to the toxicity and hazardousness of in

In the chemical process security

separate subject of interest, under a broader umbrella of safety methodologies, and that the objective in process security studies should be the design of secure processes through use of rigorous and deterministic simulation-oriented methods. Note that while the objective is parallel with inherent safety studies, 151 the suggested method of solution is quite different.

arena, a major concern is the

gredients used, the highly exothermic nature of many reactions involved, or simply because of their importance as an essential component of the infrastructure, presents a possible security target.

The chief responsibility of handling these issues naturally falls on the shoulders of chemical engineers who have the most insight into the process. As such, the concept of process security becomes a critical element in chemical engineering education. Chemical engineers must be made aware of their responsibilities and roles with regard to process safety and security, and must be educated about the existence of process security analysis methods and tools. While this type of education represents a long-term effort, it needs to be addressed immediately. c121

In chemical engineering, the available educational materials on process safety are truly valuable for this purpose. The concepts , scope, and underlying principles and methodologies of process safety, however, should be extended to meet the need for process security.113-141

In this article, we discuss the value and necessity of a process-security concept in undergraduate chemical engineering curriculum, as an addition to or extension of the existing process safety material. We will also introduce a process-security analysis tool, developed for educational use, that enables a seamless and easy integration of the process-security concept to the process safety and process design materials.

potential for an event that results in a catastrophic outcome, such as an explosion, a

toxic release, and/ or loss of life.

PROCESS SAFETY AND SECURITY IN EDUCATION

If such an event is possible, even

with a low probability, it must be addressed and

Since process safety is of primary importance to the chemical process industry and is second nature for chemical engineers,161

solutions must be found.

it should be systematically integrated into chemical engineering education. The Center for Chemical Process Safety (CCPS), under AIChE, has developed much information in the area of safety and has disseminated it to industry and to universities .17·91 For more than a decade, the Safety and Chemical Engineering Education (SACHE) Committee of the CCPS has generated various educational products for undergraduate curricula. 1101 These products have been used, at different levels of details and comprehensiveness, in a number of universities, including Texas A&M University, Wayne State University, and Michigan Technological University. Courses on process-safety fundamentals and risk assessment are very popular at those universities in their chemical engineering programs at both the undergraduate and graduate levels.1111

Wayne State University has also developed several course modules and used them in senior process-design courses, under a grant from NSF's Course, Curriculum, and Laboratory Improvement (CCLI) Program. The process safety materials

Winter2005

PROCESS SECURITY EVALUATION METHODOLOGY

The methodology used in this work is based on a Fast Security Assessment Theory introduced by Uygun, et af.1 15

-

161 A deterministic, model-based, process-security concept is a new subject with few related works.131 Updating the instructional materials will be necessary as progress takes place in this area.

A security threat is defined as an incident that will result in disaster if no effective countermeasure is taken, typically occurring over a span of minutes or seconds.c 151 Under this theory, a process is considered "secure" if the time needed to detect and eliminate the threat ( denoted as Minimum Time to Disaster-MTD) is less than the time it takes for the system to move from a nominal operation to a disaster condition, assuming the worst conditions possible. It is quite apparent that these time limits are dependent on the reaction type and conditions present in the process in question.

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Uygun, et al., 115-161 have developed two fundamental definitions in process security studies

• Definition l.1161 In most chemical systems, a plant model consists of more than one system variable; yet only a few of these need to be used directly to define disaster boundaries, such as pressure. These variables are referred to as critical variables.

• Definition 2.1151 A process is secure if

(1)

where 'T (MTD, the Minimum Time to Disaster) is the minimum time required by the process to move from the nominal operation point to the disaster border; 'T'

(the resolution time) is the minimum time needed for detecting the threat, making decisions, and taking necessary countermeasures to eliminate the threat. While an exact determination of the resolution time is difficult, a large value (e.g., more than 15 minutes)for MTD is generally a mild vulnerability; beyond an hour should be considered secure, as this allows ample time to prevent a disaster.

Accordingly, the process security problem is mathematically given as

s.t.

~

t = min J dt d(t) O

dy - = f(y ,d,p) dt

Yc(t) = Yc,d

Yc(O) = Yc.o

drain ~ d(t) ~ dmax

(2)

(3)

(4)

(5)

(6)

where y is the vector of system variables and d is the vector of disturbances. The reference points for defining the minimum time to disaster ('r) are the nominal operation point, y , c,O

and the disaster border, Yc,d' for the critical variable. Vector p is a constant vector of design parameters. Process security models (Eq. 3) have various requirements different from normal process models . They should be able to describe the system to the limit of disaster. It should also be noted that in a security-threatening situation, both manipulated variables and disturbances can be the causes of security threat; hence they are both included as disturbances. Uygun, et al.,1161

further point out that some state variables are also directly vulnerable to security threats and hence should be treated as disturbances.

-y -ANALYSIS

The process security problem in Eqs. (2-6) can be solved in various ways, including the calculus of variations and con-

50

ventional numerical schemes employed for similar problems, such as model predictive control. The convergence properties of existing dynamic optimization algorithms, however, are generally poor if the models are nonlinear-this limits the reliability of the results. This problem is caused by the complexity introduced by time-dependence, which may cause the optimization algorithm to be trapped in local optima.

Uy gun, et al., 11 51 have devised a novel approach to simplify the solution process. The principal idea in the -y-analysis is to investigate the time derivatives of the system dynamic equations directly. The method involves discretizing the differential equations along the critical variable to create a number of much simpler static-optimization problems. This simplifies the problem significantly and drastically reduces the complexity of the individual optimization problems (as compared to conventional dynamic optimization schemes) so that the results are far more reliable and can be obtained within seconds. The method generates a "confidence interval" where the MTD can fall in, rather than an estimate of the exact value. This allows a fast security assessment for the process either off-line or on-line; hence it is a justifiable engineering solution to the rather difficult problem of predicting how a saboteur's mind works.

In addition to providing a confidence interval for MTD, the -y-analysis method facilitates further process analysis and hence a more thorough process security assessment. This assessment is performed through calculating the importance of each variable on the overall system security and the time to disaster; Uygun, et al. ,1161 define the importance as each variable's "significance." Essentially, this is a sensitivity analysis algorithm using the -y-analysis method, and a calculated significance value is the relative change that would be observed in MTD if the particular variable were under control. A large significance value implies that the variable is critical for a disaster situation to occur. On the other hand, a value of zero significance suggests that the variable in question is not important from a process security point-of-view. Significance analysis is a key function for design/retrofit studies using the -y-analysis method.

INTEGRATION OF PROCESS SECURITY INTO SENIOR DESIGN

The differences in the scope of the problem and implicit assumptions about the nature of the safety and security threats have already been summarized in the preceding sections, but another important difference is the methodology employed. Process safety is typically experience-based and is employed through checklists and other managerial tools that may not be sufficiently adequate for integration into an engineering curriculum except specific safety courses. The vision in process security, however, is to construct first-principles-based deterministic models and use them (for instance with simulations) to gain knowledge about the vulnerabilities of the pro-


cess, and if possible, to eliminate the vulnerabilities through modifying existing processes. As such, process-security problems feature a combination of control, design, and modeling aspects, and thus require the students to be able to combine and apply the skills and information gained in core chemical engineering courses, such as mass and heat transfer, kinetics, unit operations, process control , and design.

The major difficulty in integrating process security into the undergraduate cur-riculum lies in this very

tive in addition to economic and technical feasibility. The first case will be exemplified in the case study section.

THE SOFTWARE

To aid in the instruction of process security, we have developed a MATLAB-based tool for educational use. This tool enables application of the process security assessment theory introduced by U ygun, et al., 116l with a graphical interface and

various reporting tools. The tool enables focusing

multi-subject nature of the problem. It is only in the senior year of an undergraduate curriculum that the students can be expected to have sufficient understanding of the basics and to be able to fully combine them and analyze and synthesize process flowsheets. Note that this is in contrast to process safety that can be integrated earlier. To avoid any problems in this regard, we recommend that pro-

csmoemo I .. /f: 11~ 1 on the conceptual security problem rather than on detailed modeling, if that is the objective of the course. Another important feature is that the software performs an optimization procedure, which is necessary in the specific method emp I oy ed, "behind the scenes," such that a knowledge of optimization is not necessary for sec urity analysis. This renders the software ideal for undergraduate education, where

Process Security Assessment Software Version 1.0

Developed c1W8Yfte Stole University. lcborotory tor Computer-Aided Ptocess Systems Science ond Engineering

Deportment of Olemiccl Engineenng ond Moten!!ls Science

AwiOemo , .. optimization is usually of

cess security be integrated primarily into the senior process design and process safe ty

Figure 1. Process security assessment tool-main window.

fered as an optional course by most chemical engi-neering programs.

courses, so as to maxi-mize the impact per time ratio on the students. Short demonstrations about process security that rely on the software tool introduced in this work, however, can be carried out at any phase of the curriculum since it allows carrying out a basic analysis without much insight into the details of modeling and optimization.

Note that the same diffic ulties make process security an excellent open-ended project for design and safety courses. The analysis and solution require an understanding of dynamic modeling and conceptual design, a basic understanding of optimization, and beyond that, analytical reasoning by the students.

Sample module. The objective of a process security module in a senior design course is to teach students how to analyze process performance under both normal and abnormal conditions and to create retrofit solutions to compensate for the security vulnerabilities by altering the design of existing units, or adding supplementary units. The scope of a retrofit problem can be adjusted to conceptual idea generation for small projects, or completely integrated into a full-scale design project where process security is added as a third objec-

Winter 2005

For educational use, the software is envisioned as a tool that can perform the security analysis for some typical example cases, where the system parameters can be customized so that different problems can be accommodated. These problems can be used as educational modules in related courses. The software can be used for either simple demonstrations of security vulnerabilities in an existing process or for an in-depth process security analysis project where students are asked to analyze a process and to create retrofit solutions to reduce or remove vulnerabilities.

Upon entering the security evaluation program, the user has the option to follow a walk-through demonstration, which is a default example for demonstration purposes (see Figure 1). Another option is to enter a simulation environment where the user can model a specific reaction process. Though future work will involve expanding the capabilities of the security software, the current program is functional only for a nonisothermal CSTR example that will be discussed in the next section .

The software interface is simple and user friendly. If the user runs into some confusion, help boxes are implemented throughout the program, allowing the user to right click on

51

any item for a brief explanation of the button functionality. Ample information on the theory, a stepby-step walkthrough, and other documentation are provided in the information menu (see Figure 2). The case study being analyzed is fully customizable by simply modifying the feed , outlet, and reactor parameters, including properties such as activation energy, overall heat transfer coefficient, and reactor area (see Figure 3).

The software has two main functions : process security assessment and significance analysis. The former is to evaluate a confidence interval on the minimum time to disaster, and the latter enables practical evaluation of the significance for the parameters of the system with regard to their effect on minimum time to disaster. The software is also capable of producing graphical representations of the system temperature profile as it escalates toward the disaster boundary.

Instead of presenting a more detailed explanation of the functions, an example problem is analyzed using the software.

SAMPLE STUDY PROBLEM • Problem Statement

Uygun, et al. ,1 151 present the following differential equations describing a nonisothermal CSTR, based on modification of an example by Luyben 11 71 (see Figure 4)

dV -=F0 -F dt

dVJ = F§N - FPUT dt

(7)

(8)

deA dV ( ) V--+eA - = F0eA0 -Fe A -VkeA 9 dt dt

vdT +TdV =FoTo-FT_AVkeA _ UAH (T-T1) dt dt pep pep

(10)

dT1 dV1 IN OUT UAH ( ) V1 -+T1 -- = F1 T10 -F1 T1 +-- T-T1 dt dt P1e J

(11)

where

k = Ae-E/ RT (12)

The system parameters and variable ranges are listed in Table 1. In this example of a security threat, the current control system is assumed not operational

52

and therefore characterizes manipulated variables as disturbances. The reactor temperature (T) should be considered as a critical variable, since temperature is the main variable of concern when there is a possibility of a runaway reaction. It should be noted that the volumetric holdups in the reactor and the jacket, reactant concentration and jacket temperature are also assumed to be "vulnerable" (i.e., they can be modified instantly in a security threat condition) so are treated as disturbances. In fact, only the reactor temperature is assumed to fully follow the governing differential model.

There are two obvious threat situations that would drive the critical variable, and hence the exothermic reaction in this example, to disaster conditions. First, redirection or shutdown of the cooling water will re-

Fculote MTD Time Rang, Significance Anotysis aose

Figure 2. Process security assessment toolnonisothermal CSTR example.

Hedtlor Properties l~f~fRI Reactor Properties

Yolue

Activation Enera, (E)

Q.,.el HNI T,..,_ Coefficianl (U)

Ar• at the React• IAHI

s .. Constant IHI

HNI Capacily of Liquid in Reactm (Cp)

OenaitJ of Liquid in Reoctor (rho)

Heal CapacilJ of Liquid in Jackel (CJ)

Den.it, of liquid in Jacket (rho J)

HNI of RNCtion (Laabda)

Lowm Bound Rnclor Vollae (V lo)

Noainel Reactor Vollao IV n)

Uppe1 Bound Reacu Vollae fV ubJ

69780

3066.3

23.23

8.314

7.08c+010

3.14

800.95

4.19

!197.95

-69780

0.0198

1.36

1.98

Unil•

kJ/kmol

kJ/h m .. 2K

m· 2

kJ/kmolK

1 /h

kJ/kgK

kg/m" J

kJ/kgK

kg/m• J

kJ/kmol

m· J

m•J

m•J

Load Dela.ts

Help Box

Ait;tt cickonan~emf01help

'""'

Figure 3. Nonisothermal CSTR example-the reactor properties window.


TABLE 1 Variable Ranges and Parameters

Variable Name Minimum Nominal Maximum

suit in a decrease in heat removal from the system, ultimately leading to a runaway reaction. Second, an increase in the reactant concentration could provide similar effects as in the first situation, granted higher concentrations of the reactant are avai lable at the plant.

Reactor Feed Flowrate (F0)(ml/h) 0 1.1 3

Reactor Output Flowrate (F)(ml/h) 0 1.13

Jacket Feed Flowrate (F/")(ml/h) 0 l.41

Jacket Output Flowrate (F,0"')(m3/h) 0 1.41

Reactor Feed Temperature (T0)(K) 222.22 294.44

Temperature in Reactor (T)(K) 222.22 333.33

Temperature in Jacket (T,)(K) 222.22 330.33

Inlet Concentration (CA,)(kmolfml) 0 8.0 1

Concentration (CJ(kmolfml) 0 3.92

Volume of Liquid in Reactor (V)(ml) O.Q2 l.26

Coolant Volume in Jacket (V,)(ml) 0 .002 0. 11

Parameters

Jacket Feed Temperature (T,0

) = 294.44K

E = 69,780 kJ/kmol

U = 3,066.3 kJ/h m2 K

A8 = 23.23 m2

R = 8.3 14 kJ/kmol K

Cl = 7.08 1010 h·1

Cp = 3.14 kJ/kg K

p = 800.95 kg/ml

C, = 4.19 kJ/kg K

p, = 997 .98 kg/ml

X. = -69,780 kJ/kmol

1

.&. Figure 4. Nonisothermal CSTR with a cooling jack et.

Figure 5. Minimum time to disaster (MTD) calculations for the nonisothermal

CSTR problem. • Winter 2005

1.98

1.98

2.83

2.83

555.56

555.56

555.56

16.02

16.02

1.98

0.198

• Tasks

Perform a process security assessment study using the software. Specific questions to answer are

Ql ls the process secure ?

Q2 At what temperature does the temperature runaway begin?

Q3 Which variables have a large impact on the minimum time to disaster (MTD)?

Q4 Suggest multiple retrofit scenarios for the reactor to reduce vulnerability, outline your reasoning, and discuss the effect of your proposed change.

• Solution

The example stated above corresponds to the demo case in the software, and is al so the default value in the simulation environment. As such, modification of parameters is not necessary.

As specified earlier, the software comprises two main functions . The first, "Security Assessment," enables evaluation of a confidence interval for the minimum time to disaster. Again , this interval represents the time it would take during a security threat situation to proceed from the nominal operation to a disaster condition, considering the worst-case scenario. This time range will give the user an understanding of the overall securi ty of their reactor. Choosing this function opens the "Security Assessment" window, which, upon clicking the start button, makes the necessary calculations for evaluation of the confidence interval (Figure 5).

Securny Assessment 1:;::1©.IIB:I

Security Assessment

1 .6 ( Minimum Time lo Disaster ( 67 .•

Lowe, Bound Tillle Liait Upper Bound Tiara Liail:

[This ii the f.ntnl tiae. considering the word case acenerio. (Thia is the aloweal tiae. considming the WCNst cue scenmio. that ii would take for the -,.tea lo go lo diaaaler) thal it would lake Jo, the ayatea lo go to diluter)

Run - j Load Prl!'-'ious Results I aose

Process IS NOT SEaJRE.

53

Answer to QI. The confidence interval of the MTD is between 1.5 seconds and 67.4 seconds. Obviously, this time is too short for any mitigation. The process clearly presents a security vulnerability. The upper bound time limit would have to be more along the line of minutes or even hours, rather than seconds, in order for the security threat to be reasonably eliminated.

It is also possible to graphically depict the system as it moves from the nominal operation to disaster. Two figures are generated: the first representing the transition that yields the lower bound in the confidence interval, and the latter corresponding to the upper bound.

54

Answer to Q2: The transition to disaster is displayed in Figures 6 and 7. The exponential behavior starts around 360 Kfor the upper bound and 450 Kfor the lower bound. The actual response will be somewhere between these two curves. Choosing the lower bound time, it can be stated that runaway reaction begins at 360 K.

Answer to Q3: The second facet of the security evaluation process consists of the generation and analysis of the priority list, which gives the significance and percent significance of each reactor variable ( see Figure 8). For the given nonisothermal CSTR example, it is shown that the two variables with the highest percent significance, and hence the highest effect in sending the process to disaster during a security threat, are the jacket temperature at just over 70% and the volume of liquid in the reactor at about 25%. Significance analysis is quite important in that it illustrates the variables that need to be monitored closely at all times. If a given variable has a low percent significance, it therefore has a low effect on the temperature runaway.

Answer to Q4: The significance values hint at the first clue by pointing out high significance values for jacket temperature and reactor volume: the heat from the jacket is instrumental in kick-starting the runaway reaction, whereas a low volumetric content in the reactor significantly increases the heating rate. Consider changing the coolant and jacket design such that it would start evaporating at 400 K (Figure 9) and yet would not

create a significant pressure buildup in the jacket. This new analysis yields the MTD between 6.4 seconds and 72 seconds. Now consider diluting the reactant feed stock by 50% such that the maximum feed concentration is halved to 8.01 kmol/m3

. A new analysis yields the MTD between 9.2 seconds and 150.4 seconds. Although we have easily doubled the MTD, this is not sufficient to render the system secure. Other modifications are possible but similarly have limited effect. As such, the system displays an inherent vulnerability that cannot be eliminated by a simple retrofit of the reactor.

CONCLUDING REMARKS

Process security addresses the most critical issues in pro-

I 1g u1 c No 1 Ascent to 01s,1s !N I o r Lowe , Bo und I 1mc I mut 1-=. 11 ol IIXI Fie Eck View Insert Tcds Yfndow Help

~Di,.: liiJ • I \ A~/ ~ ~ :)

5!iD ------------------------------------------------------------------------- '

' fill) ,

' ' '

i- // . : .------------------------ 1;;:·~:~::_1

Do--~0~2--o~.4--o~s--~M---'---1~2--1~4--'1.& Time (seconds)

Figure 6. Temperature profile for the lower bound time to disaster.

I 1r.u1 c No 1 A!llc nl lo D1s,v, lc r I 01 Lll'l'CI Do un d lu11c I mnt 1:-1ra11x 1 HeEdtVlewtnsert.ToolsWndowHelp

: .---..,.,..,--, , ... ··:,:::I:.

g 1--- Cri11cal variable I

i --- d1sa~ter bo_undary --- nominal point

,-.

450

400

3iD --------------_______________ _,,

,,

----0:2:::::::::::::::::·-----... ---------------------------------------------

Do'---,,.....J10~-...,.....1llJ~=..,._,_:11~~__.40 ___ 50_.__ __ 60,,__ _ _,70,

Time (seconds)

Figure 7. Temperature profile for the upper bound time to disaster.


cess safety, as it concerns completely unexpected occurrences and the extreme severity of process safety problems. As an integrated part of homeland security, process security must be completely assured. To fully prepare engineers with security knowledge, the authors propose to vertically integrate the undergraduate curricula upon the theme of process security.

This paper has introduced a tool that can be implemented in undergraduate process design and/or process safety courses to aid in the incorporation of simple but illustrative examples of the essential nature of process security in a chemical engineering curriculum. This development is a quantitative tool based on the dynamics of a system, which arise when the process experiences various disturbances that may be set by saboteurs who may have sufficient technical background. The software will be made available for instructors of the relevant chemical engineering courses upon written request to Professor Yinlun Huang.

ACKNOWLEDGMENTS

This work is in part supported by the National Science Foundation under grants CCLI-0127307 , CTS-0211163 , DGE-9987598, and CTS-0407494.

Pno11ly I 1s t I~ l~ [IR

Priority List Calculation

Va,iabte Name Significance Pe1cent Significance

Reactor Feed FkM Rate 0.02 0.04

Output Feed Flow Rate 0.00 0.00

Jacket Feed Flow Rate 0.00 0.00

Jacket Output Flow Rate 0.00 0.00

R-..:tot Feed T eaperature 0.05 0.09

Jacket Feed leapel'ah.-e 0.00 0.00

Jacket T eape,ahae 42.68 73.27

Feed Concentration 0.00 0.00

Reactant Concentration 0.45 0.78

Vokae of Liquid in Reactor 15.05 25.83

Coolant vouae in Jacket 0.00 0.00

CalculatePi-ionl:ylm Load Previous A $de Clo,e

Figure 8. Process security assessment-priority list.

Jacket Output Data 1:;::1 [RI

M-..v- N...,.V_ M-.V-r_,a1 .. 0(1Cl 222.22 330.33 400.00

Flow rate (• "J / hi 0 1.41 2.83

LoadDelds Concel Save

Figure 9. Altered coolant properties.

Winter 2005

REFERENCES I. Lemley, J.R., V.M. Fthenakis, and P.O. Moskowitz,

"Security Risk Analysis for Chemical Process Facilities," Process Safety Progress, 22(3), 153 (2003)

2. Baybutt, P. , "Cyber Security Vulnerability Analysis : An Asset-Based Approach," Process Safety Progress, 22(4), 220 (2003)

3. Lou, H.H., R. Muthusamy, and Y.L. Huang, "Process Security Assessment: Operational Space Classification and Process Security Index," Trans. !Chem£. Part B. Process Safety and En vironmental Protection, 81(6), 418 (2003)

4 . Center for Chemical Process Safety, Guidelines for Analyzing and Managing the Security Vulnerabilities of Fixed Chemical Sites, AlChE, New York, NY (2002)

5. Hendershot, D.C., "Designing for Safety in the Chemical Process Industry: Inherently Safer Design." Accident Precursors Workshop: Linking Risk Assessment With Risk Management , July 17-18, 2003, Washington, DC, Washington, DC: National Academy of Engineering (2003)

6. Crowl, D.A. and J .F. Lou var, Chemical Process Safety: Fundamentals with Applications, 2"" ed., Prentice-Hall, Upper Saddle River, NJ (2002)

7. Center for Chemical Process Safety, Inherently Safer Chemical Processes- A Life Cycle Approach, AlChE, New York, NY ( 1996)

8. Center for Chemical Process Safety, Guidelines for Chemical Process Quantitative Risk Analysis, 2°• Ed., AlChE, New York, NY (2000)

9. Center for Chemical Process Safety, Layer of Protection Analysis, Simplified Process Risk Assessment, AIChE, New York, NY (200 I)

10. Dimitriadis, V.D., J. Hackenberg, N. Shah, and C.C. Pantelides, "A Case Study in Hybrid Process Safety Verification," Computers Chem. Engng ., 20, Suppl. , s503 (1996)

11. Mannan, M.S., A. Akgerman, R.G. Anthony, R. Dabby, P.T. Eubank, and K.R. Hall , "Integrating Process Safety into ChE Education and Research," Chem. Eng. Ed. , 33(3), I 98 ( I 999)

12. Cunningham, S., "What Can the Industrial Chemical Community Contribute to the Nation 's Security," presented at the Workshop on National Security & Homeland Defense: Challenge for the Chemical Science in the 21" Century, National Academies of Sciences and Engineering, Irvine, CA, Jan. 14-16 (2002)

13 . Margiloff, J.B ., "Geopolitics and Chemical Engineering," Chem. Eng. Prog., 97( 12), 7 (200 1)

14. Ragan , P. T. , M.E. Kibum, S.H. Roberts, and N.A.

15.

16.

Kimmerle, "Chemical Plant Safety: Applying the Tools of the Trade to a New Risk," Chem. Eng. Prag., 98(2) , 62 (2002)

Uygun, K., Y.L. Huang, and H.H. Lou, "Process Securi ty Analysis: -y-Analysis and l-maps," A!ChE J. , 49(9), 2445 (2003)

Uygun, K., Y.L. Huang, and H.H. Lou, "Fast Process Security Assessment Theory," A!ChE J., 50(9), 2187 (2004)

17. Luyben, W., Process Modeling, Simulation and Control for Chemical Engineers, 2"" ed., McGraw Hill , New York, NY (1990) 0

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.tA ... 5-4._l_a_b_o_r._a_t_o_r.:.y ________ )

KINETICS OF HYDROLYSIS OF ACETIC ANHYDRIDE

BY IN-SITU FTIR SPECTROSCOPY An Experiment for the Undergraduate Laboratory

SHAKER HA.JI, CAN ERKEY

University of Connecticut • Storrs, CT 06269-3222

The senior-level chemical engineering undergraduate laboratory course at the University of Connecticut consists of two four-hour labs per week, during which

groups of three to four students typically perform five experiments during the course of the semester. Each experiment is studied for either one or two weeks, depending on its complexity and the scale of the equipment. The students are given only the general goals for each experiment and are required to define their own objectives, to develop an experimental plan, to prepare a pre-lab report (including a discussion of safety measures), to perform the experiments and analyze the data, and to prepare group or individual written and/ or oral reports.

One or two of the experiments in this course involve reaction kinetics. Over the years, we have encountered some challenges with reaction kinetics experiments, including inaccurate, tedious, and/or outdated methods for measuring concentrations of reactants or products, and very long or very short reaction times that make it difficult to monitor concentrations with current conventional methods.

We developed a reaction engineering experiment that employs in-situ Fourier Transfer Infrared (FTIR) spectroscopy for monitoring concentrations. The FTIR is a nondestructive technique that is increasingly employed by chemists and chemical engineers to obtain real-time data by in-situ monitoring. Since no sampling is required, this analytical technique allows the reaction kinetics to be observed under experimental conditions without disturbing the reaction mixture. The FTIR provides an effective but expensive analytical capability.

The hydrolysis of acetic anhydride (Acp) to acetic acid (AcOH) was selected as the model reaction.

2

Quite a few studies have been reported in the literature on the kinetics of hydrolysis of acetic anhydride. [J,2A,5l Eldridge and Piretl41 obtained the pseudo-first-order reaction rate constant using a batch reactor. To determine the acetic anhydride concentration, samples from the reactor were withdrawn into tared flasks containing 15-20 times the quantity of saturated anilinewater required to react with the sample. Since the anhydride rapidly acetylates the aniline, producing acetanilide and acetic acid, the samples were then titrated to determine the concentration of acetic acid. In another study, Shatyski and Hanesianrsi determined the kinetics of the above reaction by using temperature-vs-time data obtained under adiabatic conditions in a batch reactor.

Shaker Haji received his BSc in chemical engineering from King Abdul Aziz University in Jeddah (Saudi Arabia) in 1999. He is currently a full-time PhD student in the Department of Chemical Engineering at the University of Connecticut. His research focuses on removal of organosu/fur compounds from diesel for fuelcell applications.

Can Erkey received his BS degree from Bogazici University (Turkey), his MS from University of Bradford (England), and his PhD from Texas A&M University. He is currently an associate professor in the Chemical Engineering Department at the University of Connecticut and teaches chemical reaction engineering and catalysis courses, both at the graduate and undergraduate levels. His main research interests are in catalysis and nanostructured materials.



For this laboratory, the reaction is carried out in a batch reactor at a minimum of three different temperatures. The concentration of acetic anhydride is measured as a function of time using in-situ FTIR spectroscopy. The data are then analyzed to determine the reaction order and the rate constant for this reaction. The resulting rate equation is used to predict the performance of a semi batch reactor, which is then compared to experimental data. This experiment requires three laboratory periods if the students construct the calibration curve themselves-otherwise, the teaching assistant can do the calibrations and it requires only two laboratory periods.

The hydrolysis of acetic anhydride reaction is a suitable reaction for many reasons. The final reaction product is a harmless acetic acid solution with concentrations in water ranging from 8 to 20 vol %. As with most chemicals, however, acetic anhydride and acetic acid should be handled in the hood. Safety glasses are needed when handling concentrated or moderately concentrated acid solutions. Butyl rub-

---- Water -- Acetic Anhydride · · · ··· ·· · Acetic Acid

2000 1800 1600 1400 1200 1000

Wavenumber, cm- 1

Figure 1. IR spectra of pure water, acetic anhydride, and acetic acid.

Funnel

Remspec Detector

FTIR

Computer

Thermometer

500 mL Flask

Figure 2. Schematic diagram of the experiment setup.

Winter 2005

ber or neoprene gloves should be used when handling concentrated solutions of acetic acid. Contact with eyes or skin should be avoided. Furthermore, both the reactant (acetic anhydride) and the product (acetic acid) can be monitored. The IR spectra of the reactants and the product (see Figure 1) indicate that each species has its own distinctive absorption peaks that are not obscured by those of the other two species. In addition, the rate of the reaction is such that a few experiments can be carried out in a four-hour laboratory period.

THE EXPERIMENT SETUP

A schematic diagram of the laboratory apparatus is shown in Figure 2. The reactor used in the experiment is a threenecked, 500-mL jacketed flask equipped with a magnetic stirrer. Water is circulated through the jacket to keep the reaction mixture at a constant temperature. A thermometer is fitted into one of the side necks of the flask and immersed in the reaction mixture. A mid-IR probe consisting of a zinc selenide ATR (attenuated total reflectance) crystal is fitted into the middle neck of the flask and submerged into the reaction mixture. The probe is connected to a Remspec mid-IR fiber-optic system comprising a bundle of 19 optical fibers, which transmits in the mid-IR range, 5000-900 cm- 1

• Seven of these fibers are attached to a signal-launch module attached to the collimated external beam port of a Bruker Vector 22 FTIR spectrometer; twelve fibers are attached to an external liquid-nitrogen-cooled MCT detector fitted with specialized optics to optimize capture of the mid-IR signal from the end of the fiber bundle. The data are processed using computer software to obtain the IR absorption spectra.

For batch operation, the reactant (acetic anhydride) is introduced at initial time through a glass stopper that is fitted into the open neck of the reaction flask . For semibatch operation, a graduated addition funnel is fitted to the neck that can be calibrated to add acetic anhydride to the flask at a desired rate. The reactor is initially filled with a known quantity of water at the beginning of each experiment.

PROCEDURE

Before acquiring IR spectra during the reaction, a background spectrum of the empty reactor with optical fibers attached is acquired. For each experiment, 150 ml of distilled water is placed in the reactor. After heating or cooling the reactor to the desired temperature, a background spectrum is acquired again with the probe immersed in water.

For the batch mode, 10 ml of acetic anhydride is added to the stirred reactor, and the reactor is sealed with a glass stopper. The spectra are acquired using the repeated measurements option enabled by the software controlling the FTIR. The settings are adjusted for the acq uisition of a spectrum every 50 seconds for 35 minutes. Spectral scans are taken at 4 cm·1 resolution and signal averaged over 32 scans. The ab-

57

sorbances of the selected peaks are measured from the individual spectra. It takes around 30 seconds for the 32 scans to be acquired.

Care should be exercised in selecting the operating conditions or the scan number to make sure that the concentration does not change significantly during the acquisition of each spectrum. For example, at the beginning of the reaction at 35°C, the concentration of acetic anhydride changes by 11 % during the acquisition of the second spectrum (50-80 s) .

For the sernibatch reactor operation, an addition funnel is placed in the unoccupied neck. The acetic anhydride addition rate can be set between 2 to 5 ml/min. Once the first drop hits the water, the repeated measurements function is activated so that a spectrum is acquired every 50 seconds for one hour. The level in the addition flask is read at various times to determine the rate of addition as a function of time. The reaction mixture's temperature is recorded manually with each IR spectra acquired or as needed.

THEORY

For a constant-volume batch reactor, the rate of appearance of reactant A (acetic anhydride), r A' is given by

dC A rA=dt

where r A can be expressed as

( 1)

(2)

where k is the reaction rate constant, n and m are the reaction orders with respect to species A (acetic anhydride) and B (water), respectively. Since water is in excess, C8 remains essentially unchanged during the course of the reaction, and

-rA = k'Cl

where k' is a pseudo rate constant

k' = kClr "'kClro

(3)

(4)

The specific reaction rate, k, is a function of reaction temperature and is given by the Arrhenius equation

k = Ae-E/RT (5)

where A is a pre-exponential factor, E is the activation energy for the reaction, and T is the absolute temperature.

The reaction order and rate constant can be determined by the integral method of analysisP 1 In this method, the rate expression is guessed and the differential equation used to model the batch system is integrated. If the assumed order is correct, the appropriate plot (determined from the integration) of concentration-time data should be linear. For a zero order reaction with -rA = k, integration ofEq. (1) yields

(6)

58

For the first-order case where -rA = kCA, integration of Eq. (1) yields

£n CAO = kt C A

(7)

For the case where -rA = kC/, integration ofEq. (1) yields

I I ----=kt C A C AO

(8)

The differential method can also be used to analyze the rate data. l31 In this method, the reaction rate at each concentration is determined by differentiating concentration-versustime data. By combining the mole balance (Eq. 1) with the rate law (Eq. 3), we obtain

- dCA = kCn dt A

(9)

Taking the natural logarithm of both sides of Eq. (9) gives

5 ~---------------~ 0.6

[Ac20J = 2.93 1 •x R2 = 0.9979

[AcOH] =1 3.4 14*X

R2 = 0.9997

" Acetic Acid • Acetic Anhydride

::E 0.5 g

·.c g

0.4 ~ u C: 0

0.3 ~ -0

:§ 0.2 £

§ u

0. 1 '£ u

<(

0 +-- -------~------____,_ 0.0

0 .0 0.1 0.2 0.3

Absorption intensity

Figure 3. Calibration curves of acetic anhydride and acetic acid.

0.1 2

0.10

., 0 .08 u § -f: 0.06 0 "' ..0

<I'. 0.04

0.02

0.00

-- 5min ---- 7.5 min

12.5 min

1800 1600 1400 1200

Wavenumber, cm-1

Figure 4. The hydrolysis of acetic anhydride at different times [the acetic anhydride concentration is decreasing ( 1107 cm·') and that of acetic acid is increasing (1287 cm·')}.


0.6

0.5

0.4

::E d 0.3

0.2

0.1

0.0

0

a

4.0

3.5

3.0 ,,....._

u""'- 2.5 'o u""'- 2.0

'--' 1.5 i::

1.0

0.5

0.0

0

b

60

50 c::,

u""" 40

--- 30

u""" 20 ---10

0

0

5 10 15

Time , min

Y = 0.169 *X R2 =0 .975

•

5 10 15

Time , min

5 10 15

Time , min

20 25

• •

20 25

•

•

20 25

Figure 5. Plots of the appropriate concentration function vs. time (a) zero order, (b) first order, and (c) second order reaction with respect to acetic anhydride (integral m ethod). Data acquired at 25°G.

Winter 2005

en(-d~t J = en(k)+n enC A (10)

The slope of a plot of en(-ctc A / dt ) vs. ( f n C A) is the reaction order.

For the semibatch reactor where species A is being added to the system with a concentration of C Ao' the following relation can be derived from the mole balance relationship:

dC A dV V -- +C A - = r AV + v 0C AO

dt dt ( 1 I)

where v0

is the volumetric flow rate into the system and Vis the volume of the reacting mixture and is a function of time.

LAB SESSIONS AND RESULTS

Laboratory Period 1: Calibration Curve

In this session, the students learn how to operate the FTIR spectrometer and acquire data. Before they construct a calibration curve, IR spectra of the pure reactants ( water and acetic anhydride) and the product (acetic acid) are acquired. The three spectra are compared, and the compounds that would be monitored along with their distinctive bands are selected (see Figure 1). Since water is present in excess , its concentration is not monitored. The concentration of acetic anhydride is monitored via the band at 1107 cm·1 associated with the stretching of C-O-C bond because it's the strongest peak and also does not overlap with the other peaks. The peaks due to carbonyl could also be monitored (1821 or 1750 cm·1

).

The concentration of acetic acid is monitored via its C-OH absorption peak at 1287 cm·1 even though other peaks can also be used, e. g. , the carbonyl peak at 1703 cm·1

, which is the strongest peak in the acetic acid spectrum, or the peak at 1407 cm·1

• The peak at 1287 cm·' does not overlap with the other peaks, however.

The calibration curve for the concentration of acetic acid solution in water vs. its absorption intensity is obtained by acquiring the spectra of solutions with known concentrations (e.g., 0.6 M, 1.0 M, 2.0 M, and 4 .0 M ), as shown in Figure 3. It is not trivial to obtain a similar calibration curve for acetic anhydride, for it readily reacts with water. It is possible, however, to obtain a calibration curve for acetic anhydride using the calibration curve for acetic acid. At room temperature, 12 ml of acetic anhydride is added to 150 ml of water. The spectra are acquired every 2.5 minutes (see Figure 4). In each spectrum, the concentration of acetic acid is determined by measuring the absorbance of the designated peak and using the calibration curve. Given the reaction stoichiometry and the initial concentration, the acetic anhydride concentration can be calculated. Accordingly, a calibration curve for concentration of acetic anhydride vs. absorption intensity of the assigned band is constructed, as shown in Figure 3. Students are expected to determine the ranges in which the calibration curves for both acetic anhydride and acetic acid should be obtained.

59

The calibration curves are obtained at room temperature and are assumed to be valid over the range of temperatures at which the experiments were carried out. It is also assumed that the calibration of acetic acid in water solution is not affected by the presence of a third species (acetic anhydride) in the solution. Furthermore, it is possible to base the calculations only on measurements of the AcOH concentration and then back calculating the Acp concentration without the need to obtain a calibration curve for the latter.

Laboratory Period 2: Isothermal Batch Reactor

Once the calibration curves are obtained, experiments are carried out in a batch reactor to determine the rate expression. Specifically, the hydrolysis of acetic anhydride in the presence of excess water (78.3 : 1 Hp! Acp) mo! ratio, or 15:1 vol ratio) is carried out isothermally at room temperature (25°C). The concentrations of acetic anhydride and acetic acid are measured as a function of time. The concentration of acetic anhydride through the course of the reaction is shown in Figure 5(a). The data collected are analyzed using the integral method. The plot of CA vs. time, as shown in Figure 5(a), and that of (1/C A -1/C Ao) vs . time, as shown in Figure 5(c), are not linear, indicating that the reaction is neither zero nor second order with respect to acetic anhydride. As Figure 5(b) illustrates, the plot of Rn( CAO IC A) as a function of time is linear, which suggests that the rate law is first order with respect to acetic anhydride concentration under given reaction conditions of excess water. The slope represents the rate constant, k. The rate constant is found to be 0.169 ± 0.0047 min·1 at 25°C, which is 7% higher compared to that reported in the literature,l4l which is 0.158 miff1 at the same temperature. The same reaction is repeated at temperatures of 15, 20, and 35°C. The data show the reaction is first order at all temperatures studied and the rate constants are found to be 0.0631, 0.0924, 0.2752 miff1 at 15, 20, and 35°C, respectively.

According to the Arrhenius equation (Eq. 5), a plot of Rn(k) vs. 1 / T should be a straight line and the slope is proportional to the activation energy. Thus, knowing the reaction rate constant at four different temperatures, the students determine the activation energy and the pre-exponential factor. Once these values are known, k at any temperature could be determined using the Arrhenius equation. The pre-exponential factor is found to be 3.19* 108 miff 1 and the activation energy to be 53,408.3 J/mol (see Figure 6) . The average activation energy reported in the literaturel5l is 50,241.6 J/mol, which differs by -5 .9% from the value reported by the students.

The differential method can also be used to analyze the data collected. For instance, the data collected for the reaction at 15°C are analyzed to obtain the reaction order and the reaction rate constant. Only the data for conversion between 15% and 85% are used to increase the accuracy of the analy-

60

--;-C ·a C .....

.!,c -.!,c '-' C -

-1.0

-1.2

-1.4

-1.6

-1.8

-2.0

-2.2

-2.4

-2 .6

-2.8

•

Y = 19.5809 - 6423.9*X R2 = 0.988

•

• -3.0 +------------------<

3.2e-3 3.3e-3 3.3e-3 3.4e-3 3.4e-3 3.5e-3 3.5e-3

1/T, K 1

Figure 6. Determination of the activation energy and the pre-exponential factor using the Arrhenius equation.

::E c.;;""-

a

Q ~ u""-~

I '-"' i::: .....

0.6

0.5 CA=0.6332-0.03416*t+0.00056*t2

R2

= 0.997 0.4

0.3

0.2

0.1

0.0 0 5 10 15 20 25 30

Time, min

-3 .0 ~---------------~

Y = -2.743 + 0.9996*X -3.5 R2 = 0.949

-4.0

-4.5

-5 .0 • •

-5.5 -2.5 -2.0

• •••

••

-1.5 -1.0 -0.5

Figure 7. (a) Acetic anhydride concentration vs. time for the batch reactor at 15°G fitted to a polynomial. (b) Differential method used to determine the reaction rate constant and order.


sis. First, the concentration-time data are fitted to a polynomial, as shown in Figure 7a. The polynomial is differentiated to obtain the rate ofreaction (dC /dt). As Eq. (10) illustrates, a plot of Rn(-dC A / dt) vs. Rn( CA) should give a slope equal to the reaction order and an intercept of Rn(k) . Figure 7b represents a reaction with an order of one and a specific reaction rate of0.0644 min-1, which differs by 2% from the value obtained by the integral method and -20% from that reported in the literature,141 which is 0.0806 min- 1

•

Laboratory Period 3: Isothermal Semibatch Reactor

In this part of the experiment, the students use the rate expression obtained in the previous laboratory period to predict the concentration profile in an isothermal Semibatch reactor. The software "Polymath" is used to solve the differential equation given above (Eq. 11). In this experiment, the run is divided into two periods. In the fust period, the Acp is added to water at a particular rate. Subsequently, the addition of Ac

20 is stopped and the reaction proceeds in batch mode until

all the Ac20 is consumed. The experiments can be varied for

different groups by changing the addition rate, the amount of Ac

20 added, or the reaction temperature. Figure 8 illustrates

the simulated and experimental concentration profiles for a run carried out at 25°C where a total of 29 ml of acetic anhydride was added at an average rate of 3.55 ml/min. There is close agreement between the predicted and the experimental data, with a maximum difference of around 10% in the case of acetic acid at the end of the run and around 20% in the case of the acetic anhydride at the end of the addition. The slight discrepancy may be due to errors in the measurement of concentration of acetic acid, due to errors in the parameters of the rate expression, due to a slight deviation from isothermal operation because of heat of mixing and exothermic nature of the reaction, and/or due to errors in de-

::8 d' 0

·@ I-...... = Q) u = 0 u

3.5 ------------ ----- --, • Experimental [Ac2OJ

3.0 -- Predicted [Ac2OJ --2.5

2.0

1.5

1.0

0.5

0.0

0

--Predicted [AcOHl / ,.,,,.,.. .._.a.A. A A Experimental [AcOHl / .._.._.., A

5

/ ............ / ......

/ ... / .........

1 ...... 1 ...

; ...

10 15

Time, min

20 25 30

Figure 8. Comparison between the predicted and experimental data obtained for an isothermal semibatch reactor at room temperature.

Winter 2005

termination of the volumetric addition rate.

CONCLUSIONS

The use of in-situ FTIR spectroscopy for following the hydrolysis of acetic anhydride reaction has been demonstrated. The analysis of the batch reactor data showed that the hydrolysis of acetic anhydride is a pseudo-first-order reaction. The rate constants were calculated from the batch data using both integral and differential methods of analysis and were used to predict the performance of a semibatch reactor. Predicted acetic anhydride and acetic acid concentrations were in good agreement with the experimental concentrations. The undergraduate students found this laboratory experience a good opportunity to implement many of the concepts they learned in their reaction engineering course.

NOMENCLATURE A Arrhenius pre-exponential factor C concentration

CA acetic anhydride concentration CA

0 initial or entering acetic anhydride concentration

C8

water concentration C

80 initial water concentration

E activation energy k reaction rate constant

k' pseudo reaction rate constant N number of moles

n,m reaction order r reaction rate

R uni versa I gas constant t time

T temperature V volume v

0 volumetric flow rate

ACKNOWLEDGMENTS We would like to thank the following students, whose data

are presented here: Joanna Domka, Sofia Simoulidis, Justin McNeill , Allison Foss, Cliff Weed, and Jessica Zimberlin. We are also grateful for the financial support of the School of Engineering at the University of Connecticut for purchasing this equipment.

REFERENCES I. Wojciechowski , B.W. , S.P. Asprey, N.M. Rice, and A. Dorcas, "Ap

plications of Temperature Scanning in Kinetic Investigations: The Hydrolysis of Acetic Anhydride," Chem. Eng. Sci., 51, 4681 ( 1996)

2. Glasser, D. , and D.F. Williams, "The Study of Liquid-Phase Kinetics Using Temperature as a Measured Variable," Ind. Eng. Chem. Fundam., IO, 516 (1971 )

3. Fogler, H.C. , Elements of Chemical Reaction Engineering, 3rd ed., Prentice Hall , New Jersey (1 999)

4. Eldridge, J .W. , and E.L. Piret, "Continuous-Flow Stirred-Tank Reactor Systems. I. Design Equations for Homogeneous Liquid-Phase Reactions. Experimental Data," Chem. Eng. Prag., 46, 290 ( 1950)

5. Shatynski, J.J. , and D. Hanesian, "Adiabatic Kinetic Studies of the Cytidine/ Acetic Anhydride Reaction by Utilizing Temperature versus

Time Data," Ind. Eng. Chem. Res., 32, 594 ( 1993) 0

61

.ta_...511111113._c_u_rr._i_c_u_l_u_m _________ )

VCM PROCESS DESIGN An ABET 2000 Fully Compliant Project

FARID BENYAHIA

United Arab Emirates University • Al Ain, United Arab Emirates

Process design projects constitute the ideal vehicle for applying and acquiring chemical engineering knowledge in all its forms. Indeed, accreditation bodies such

as ABET (USA) and IChernE (on behalf of the Engineering · Council, UK) view the quality of senior design projects as a sort of health check of the programs that lead to an undergraduate degree. When properly researched by advising faculty members, senior design projects involving petrochemical processes can provide the complete ABET 2000 learning outcomes from a to k. Indeed, when the overall chemical engineering program learning outcomes show deficiencies in certain areas, a design project is often the balancing mechanism for bridging gaps in educational outcomes in the form of "integrating learning umbrellas."

From the author's long experience in supervising a wide range of senior design projects, the vinyl chloride monomer (VCM) process can be considered one of the most diverse, challenging, and complete design missions chemical engineering undergraduate student groups can engage in. Indeed, the VCM process history is well established, its safety and environmental impact attributes are well documented, and the diversity of process equipment associated with VCM plant operations is second to none.

The VCM process is the subject of a case study in process synthesis in the latest edition of the textbook written by Sieder, et al. r11 In fact the VCM process is so "rich" in chemical engineering principles and plant operations that it can be offered to several groups of students in the same year with little or no overlap--or it can be offered to single groups every year, tweaking design objectives to make the successive years of student design work experience complementary and cumulative. This latter approach has been very powerful and generates useful educational data for faculty members interested in surveying collaborative and cooperative learning in major design assignments.

In this paper, the author shares his experience in supervising senior design projects in accredited chemical engineer

ing departments (by the Institution of Chemical Engineers, UK and ABET, UAE) by providing full details on the VCM process, on the typical design tasks expected from groups of students, and on the wider learning outcomes that make such senior design projects fully compliant with ABET 2000. The details of the process described in this paper are based on extracts compiled from nonconfidential actual plant data supplied by the European Vinyl Corporation to assist process design at UK chemical engineering departments.

THE VCM PROCESS DESIGN BRIEF

Staged Learning Outcomes• The design groups comprised teams of 3 to 5 students. In the United Kingdom (Teesside University) the groups had mixed-ability students, according to GPA scores, and in the United Arab Emirates (UAE University), students were allowed to choose partners. The instructor acted as a client at the beginning of the project, but thereafter acted as a consultant where "penalty points" were incurred for excessive requests for help. The rule was clearly explained to students at the outset and did not pose any particular concern. Such a rule is primarily aimed at showing the degree of independence in the work achieved and is somewhat related to the final grade. This approach allows weaker groups to make progress at a "cost," does not give unfair disadvantage to more independent groups, and is considered fair by students themselves.

The design project was presented to the students as a for-

Farid Benyahia is currently an associate professor in chemical engineering at the United Arab Emirates University. He was previously senior lecturer in chemical engineering at Teesside University (UK) and post-doctoral research fellow at Leeds University (UK). He obtained his BSc from the University of Aston in Birmingham (UK) and his MSc and PhD from the University of Newcastle (UK). His process design experience, both industrial and academic spans a period of over 20 years.



mal "invitation for tender" from a "local" client in a suitably phrased letter. A "standard starter pack" consisting of initial references, essential design data or information not easily available in the library was also distributed to the student groups. [2•

141 An extract of the content of this pack is presented in the sections below.

The student groups were either allocated names of fictitious contractor companies or allowed to name themselves as such . They responded to the invitation for tender by submitting a design proposal that included details of the approach to be adopted, milestones, and deliverables.

Students are exposed to a strong element of project management at the outset. The grading philosophy takes into account the following ABET learning outcomes that were staged (denoted by the letters shown in parenthesis):

• Literature study: market, available technologies, safety/ environment, societal impact, process route selection (f, h, j)

• Acquisition or analysis of provided plant design data (b)

• PFD, material and energy balance of selected process after evaluating alternatives (a,c,d,e,k)

• PID and HAZOP study (d,e,f)

• Costing and project economic evaluation (h,k)

• Mechanical design of major items of equipment and application of suitable standards (c,d,e,k)

• Final report, poster, presentation, web site (d,g,k)

DESCRIPTION OF THE PROCESS AGREED TO BETWEEN CLIENT AND CONTRACTOR

The process agreed to (after a thorough literature review and technical evaluation of alternatives) is based on the "balanced" VCM process. It comprises 3 reaction sections, a purification section for the intermediate 1,2-Dichloroethane (EDC), and a purification section for VCM. Process information and data from real plants, compiled in a condensed form,[21 are made available to students along with a list of start-up referencesY· 141 The substance and structure of infor-

TABLE 1 Extent of Side-Product Formation

FeC/1 in EDC Oxygen in feed Temperature B-tri formed

(g/1111 as Fe) (% vlv i11 Cl,) (C) (ppm wlw)

so 0.5 60 2000

2000 0.5 60 1500 so 2.5 60 500

2000 2.5 60 400

so 0.5 84 50000

2000 0.5 84 5000 so 2.5 84 10000

2000 2.5 84 2000

Winter 2005

mation supplied to students were designed to encourage cooperative work and critical thinking. This is presented in the following sections and constitutes a sizeable amount of the undergraduate design experience described in this paper.

DIRECT CHLORINATION SECTION

Process Chemistry • The reaction between gaseous ethylene and gaseous chlorine to form EDC takes place readi ly in a liquid EDC phase at moderate temperature and is strongly exothermic . The further ch lorination of EDC to betatricholoroethane, or B-tri , (substitution reaction) takes place to a limited extent. The substitution reaction is inhibited by the presence of iron (in the form of FeCl

3) and dissolved oxy

gen. The effect of these inhibitors is additive. The degree of substitution is also temperature-dependent. These relationships (shown in Table 1) constitute a subject for discussion among the students.

As can be deduced from Table 1, there are two possible processes: 1) the "sub-cooled process" at 60°C where EDC is maintained below boiling temperature by circulation through an external cooler, and 2) the "boiling process" where the reactor contents are maintained at boiling by allowing vapor to boil off and condense externally, with some of it being returned to maintain the liquid inventory. The subcooled process produces a purer organic product but is iron contaminated, while the boiling process gives more B-tri but can in principle be obtained iron free .

The material fed to the cracking furnace is

B-tri 500 ppm w/w

Fe 1 ppm w/w

Process Details • The reaction of ethylene and chlorine proceeds very rapidly. The rate-limiting factor is believed to be the dissolution of ethylene in EDC. Therefore the reactor, whether sub-cooled or boiling, should be designed to provide adequate residence time for the gas dissolution , to avoid excessive liquid carry-over in the vapor stream leaving the reactor, and for proper sparging of the feed gases into the reactor. Actual production data suggests that a production of 500 kg/h EDC per m3 hold-up of liquid can be achieved. In addition, sparging velocities of around 100 m/sec are appropriate.

To ensure complete reaction of the chlorine, it is normal to work with a slight ethylene excess in the ratio of gases fed to the reactor. The excess ethylene should be of the order 0.5 -1.0 % by volume compared to chlorine. The presence of oxygen in the chlorine feed, together with other flammables that are present, gives rise to a potential flammability hazard in the final vent from the direct chlorination reactor and must be prepared for in some way.

If a sub-cooled reactor is chosen, the EDC product must be

63

[The] VCM process can be considered one of the most diverse, challenging, and complete design mission [for] chemical engineering undergraduate student. [The] process

history is well established, its safety and environmental impact attributes are well documented, and the diversity of process equipment

associated with VCM plant operations is second to none.

washed to remove iron chloride. This is preferably done in two stages-the first stage using water and the second stage using dilute caustic soda. In each case, the volume of aqueous and organic phases continuously in contact should be approximately equal. The wet EDC must then be dried by azeotropic distillation.

If a boiling reactor is chosen, there is no need to wash the bulk of the product (providing precautions are taken against liquid entrainment), and therefore no drying is required. There will sti!J be a need to periodically wash the purge stream, however, when the solids content becomes too high. This is norma!Jy done by pumping out the vessel contents batch-wise to a wash system and replenishing it with a fresh catalyst charge. This should be done when the ratio of EDC made to vessel contents exceeds, say, 200. As stated before, boiling reactor material will have to be processed through a distillation column to remove B-tri.

Vent gases can be released into the atmosphere providing the total emission of chlorinated hydrocarbons is less than I 0 kg/h , but precautions must be taken against a breakthrough of chlorine due to loss of ethylene feed or any other reason. It is normal to provide a large scrubbing tower that has a caustic soda solution permanently recycled through it and is capable of neutralizing the full flowsheet rate of chlorine.

Feedstocks • Ethylene is available at 100 psig (690 kPa) pressure and ambient temperature. It will contain up to 400 ppm by volume of ethane.

Chlorine is available either as cell gas or as revaporized liquid. Both can be made available at 30 psig (207 kPa). Cell gas will contain the following impurities:

Oxygen 2% v/v Nitrogen 0.5% vlv Hydrogen 0.1 % v/v CO

2 0.15% v/v

Revaporized liquid chlorine can be assumed 100% pure.

CRACKING SECTION

Process Chemistry • EDC pyrolysis is an endothermic reaction and is normally carried out as a homogeneous noncatalytic gas-phase reaction at elevated temperature and pressure in a direct-fired furnace. Free-radical chain reactions are involved with chlorine atoms acting as the chain propagators. The product of the main reaction, vinyl chloride (VC), is itself highly reactive towards free radicals. This gives rise to a significant group of by-products that includes acetylene,

64

chloroprene, and dichlorobutenes.

The quantity of by-products formed per ton of VC made increases rapidly as the fractional conversion of EDC per pass ("depth of cracking") increases (see Table 2).

Other factors such as the pressure, the level of impurities (especially iron) in the EDC feed, the residence time of gases in the cracking reactor, and the tube wall material used in that reactor, all have some bearing on the by-product spectrum but it can be assumed that the depth of cracking is the dominating parameter.

One by-product in the EDC feed, beta-trichloroethane, will partially undergo pyrolysis to vinylidene chloride. Empirical data indicates that the ratio of B-tri converted to EDC is roughly 0.4.

As can be deduced from Table 2, a low depth of cracking is desirable to minimize by-product formation . A low crack, however, implies increased steam use in the distillation columns used to separate the cracked gases and to further purify the uncracked EDC before it can be recycled to the cracking furnace. An optimum depth of crack is thus sought.

In addition to volatile by-products, tarry and carbonaceous materials are formed in the cracker. They deposit inside the reactor tubes and eventually cause reduced heat transfer and increased pressure drop to such an extent that the reactor must be shut down for "decoking." Real plant data shows that (not surprising) the fouling is also a strong function of depth of crack-this can be seen in Table 3.

Each decoke causes a shutdown of the reactor for about 72 hours . Fixed costs for the plant are $400/hour.

Process details • Purified EDC is stored as a liquid at ambient temperature in an atmospheric-pressure storage tank. It has to be pumped up to pressure, vaporized, and passed into the cracking furnace. The cracked gases are quenched by a recirculation stream of liquid EDC to terminate the cracking reaction, and then they pass through one or more con-

TABLE2 Impurities Formed ppm w/w of VC Product

45% 50% 55% 60% Crack Crack Crack Crack

Acetylene (C2H

2) 1000 1600 2500 4000

Chloroprene (C,H5Cl) 2000 3000 4500 7500

Dichlorobutenes (C4H

6Cl

2) 3000 4500 7000 12000


densers to partially condense the products.

The mixture is then separated into three constituents-HCI, VC, and EDC. It is conventional to remove the HCl as the overhead product from a first column and then to separate the VC and EDC in a second column. The HCI overhead product can be taken off as a vapor, but there is still the need of a refrigerated condenser to provide reflux for the column. Economics require that the VC column condenser avoid refrigeration.

A key parameter to select is the operating pressure. EDC has to be vaporized at the front end of the process at one pressure and HCl condensed at some lower pressure at the back end, allowing for the pressure drop through the process train. To help determine the appropriate pressure we need to bear in mind that

1. The mjnimum pressure at the top of the HCl column should be 100 psig (690 kPa) to enable HCl to pass to the oxychlorination section without compression.

2. The maximum temperature at which it is advisable to

vaporize EDC is about 220 C because above thjs it tends to thermally degrade

Definition of lights and heavies:

Cl lights:

C2 lights:

C2 heavies:

C4 lights:

C4 heavies:

(CHCl3

+ CC14)

(C2H

5Cl, C

2H

2Cl

2, C

2HC1

3, C

2H

2)

(C2H

3Cl

3, C

2H

2Cl

4, C

2Cl

4)

(C4H

5Cl)

(C4H

6Cl

2)

The final vinyl chloride (VC) product produced should not contain more than 100 ppm by weight total impurities.

HCl and EDC separated from the cracked gas mixture should each not contain more than 200 ppm by weight ofVC.

OXYCHLORINATION SECTION

Process Chemistry • The oxychlorina-tion of ethylene by HCl and oxygen is catalyzed by copper chloride, normally supported on alumina. In addition, a direct oxidation of ethylene to CO

2 occurs. Normally, oxychlorination is the domi

nant mechanism and the oxidation reaction accounts for only a few percent of the ethylene converted. Catalyst activity in-

creases with temperature but an increased

and cause fouling of heat transfer surfaces . TAB LE3

temperature favors oxidation at the expense of oxychlorination. There is thus an optimum temperature, and the acceptable operating temperature range in the reactor is small. This factor, combined with the high exothermicity of the reaction, has led to the use of fluidized-bed catalytic reactors for large-scale operations. For fluidized-bed operations, a mean catalyst particle size of about 100 microns can be assumed. The

3. We must allow a reasonable pressure drop through the cracking furnace, especially when fouled. Minimum values are typically 20 psig ( 138 kPa) clean, 35 psig (241 kPa) fouled and we would allow 1/4" (0.635 cm) coke layer formation inside the cracker tube wall before decoking.

4. ln the refrigeration machjne for the HCl condenser we would consider using an environmentally friendly fluorocarbon refrigerant as the working fluid , making sure that we do not go much below atmospheric pressure in the boiling refrigerant on the service side of the HCl condenser. This is to avoid having to handle very large volumes of gas into the suction of the refrigeration compressor and also to avoid air ingress into the machine.

Other Design Parameters • Maximum radiant heat flux to cracker furnace tubes: 12000 Btu/hr.ft2 ( 37.85 kW/m2) . Maximum inside tube wall temperature for stainless steel grade 321: 570 C. Number of parallel tube passes in furnace: l or 2 (more makes control difficult).

Table 4 shows the equivalence of residence time and cracker exit temperature to give the same VC output at same depth of crack.

Feedstocks and Products • EDC fed to the cracker should have a minimum purity of 99% by weight. Specific impurity maxima are shown in Table 5.

Wimer2005

Depth of Crack and Run Life

Average Depth of Crack(%)

45

50

55

60

Average Rull Life (days)

300

250

180

100

TAB LE4 Residence Time and Cracker

Exit Temperature

Meall Residence Time of Gases ill Radiallt Sectioll

( calculated Oil exit collditiolls) (sec)

Exit Gas (C)

5

9

16

525

500

475

TAB LES Impurity Maxima for

Cracking Section

CJ lights 2000 ppm w/w

C2 lights 4000 ppm w/w

C4 lights JOO ppm w/w

C2 heavies 1000 ppm w/w

C4 heavies 50 ppm w/w

particle size distribution can also be assumed if it is not available in the literature. In the absence of contact-time data for fluidized-bed operations, data for fixed-bed reactors can be used.

Some processes do employ multitubular fixed beds, however. Comments on drawbacks of fixed-bed reactor technology for highly exothermic systems are encouraged.

Experimental data obtained with a certain catalyst formulation is shown in Table 6, next page, (on a once-through, i.e., no-recycle basis). In addition to the main oxychlorination reaction to produce EDC, there are other chlorinated hydrocarbons formed. On analysis, an approximate composition of the dry organic product is found to be

Cl lights (CHCl3

+ CC14)

8000 ppm w/w C2 lights (C

2H

5Cl , C

2H

2Cl

2, C

2HC1

3)

5000 ppm w/w

65

C2 heavies (C2H

3Cl

3, C

2H

2Cl

4, C

2Cl

4)

Balance EDC 12000 ppm w/w

It can be assumed that any acetylene and VC brought in with the HCl is directly oxidized.

Process Details • A major decision to be taken concerns the construction material used for the reactor shell and cooler bundle. Obviously, the gas mixture has to be kept above the dew point or very rapid corrosion will ensue, but industrial data shows that the onset of corrosion occurs at temperatures well above the theoretically calculated dew point. This is due to complex erosion/corrosion mechanisms that are not well understood. There is also an upper temperature threshold above which corrosion increases, but the effect is not so clearcut as the lower limit.

The key parameter to be studied in a metallurgical analysis is the partial pressure of steam in the reactor product gas mixture because this has a prime influence on the dew point. Table 7 shows recorded data.

The reactor must contain means of properly introducing the main feeds, bearing in mind that ethylene and oxygen ( or air) should not be premixed outside the reactor. Facilities to remove most of the catalyst particles entrained in the reactor exit gases are also needed.

Upon leaving the reactor, the gases have to be quenched and condensed, and residual HCl must be neutralized. The organic and aqueous phases are separated, with the former being sent to an azeotropic drying column and the latter to a stripping column to recover dissolved EDC.

If an air fed process is chosen, the vent gasses leaving the main oxy condenser must pass through equipment to recover as much EDC as practical before being vented. If an oxygen process is chosen, most of the gas will be recycled to the reactor to achieve the desired gas partial pressures, and only a small amount is vented to maintain pressure control.

Feedstocks and Products • The compositions of ethylene and HCl were given earlier in this paper. Oxygen purity is not critical and will normally be supplied as 99% by volume at whatever pressure required. The EDC product purity was also given. The aqueous effluent should be steam stripped to give less than 5 ppm EDC by weight in the final effluent discharge. Assume that the vent gas hydrocarbon content does not exceed 10 kg/hour.

Plant Operation Data

• Plant attainment: 94% • Annual production ofVCM: 150 000 000 kg

Cost and Economic Data

66

• Average market price for VCM (over period 2000-03): $700/1000 kg

• Average market prices for Ethylene, Oxygen ,and Chlorine (over 2000-03) are 360, 45, and 150 US Dollars per metric ton, respectively.

• Expected plant life: 25 years • Capital: To be estimated from step-counting methodrsi in

US dollars; prices must be adjusted for inflation using the cost index in the United States. The total investment can be distributed as follows: • Year 1 - Design costs: 9% of capital cost • Year 2 - Construction phase I costs: 45.45% of capital cost • Year 3 - Construction phase 2 costs: 45.45% of capital cost • Year 4 - Working capital: 13 .60% of capital cost

• Fixed operating costs were estimated to be • 3.7% of the capital cost per year, up to year 10 • 4.6% of the capital cost per year after year 10, up to year 17 • 5% of the capital cost per year from year 17 onward

• The variable operating costs were estimated to be • $15 per ton (1 ton= 1000 kg) of product up to year 17

• $18 per ton of product from year 17

TYPICAL DESIGN TASKS

In the structured report, the student is instructed to

• Write a cover letter to your client when you hand in your design report.

TABLE6 Oxychlorination Kinetic Information

Conversions at contact time of 15 sec

% HCI converted % C2H4 to EDC % C2H4 to CO2

% C2H

4 converted

Conversions at operating temperature of 250 C

% HCl converted % total C

2H

4 converted

% total 02

converted

Operating temperatllre (C) 230 240 250 260

95 97 98.5 97.5 93 95 95 93 2 2.5 3.5 5 5 2.5 1.5 2

Contact time (sec) 10 15 20

96 98.5 97.5 95.5 98.5 98.5 90 96 98

TABLE7 Water Partial Pressures and Corresponding Acceptable

Temperature Ranges

Metal pp H,O (bar abs) Acceptable Temp. Range (C)

Mild steel 1 200-260 1.5 None

Stainless steel 316 I 190-300 1.5 210-300 2 None

Iconel 1 160-280 1.5 190-280 2 220-280

Hastelloy I 160-300 1.5 170-300 2 180-300


• Write an introduction section that provides information about VCM, its applications and safety issues, the world market situation , and a balanced societal impact (benefits and potential problems).

• Select a suitable site (in the country of residence of students during their studies) to locate the VCM plant. Justify your site selection and carry out an environmental impact assessment, using accident or accidental spill/release scenarios.

• Produce the complete PFD for the process described above. Use a computer drawing tool.

• Carry out a complete material balance using the spreadsheet presentation method. You may find it convenient to divide the process into smaller sections when reporting the material balance tables with portions of the PFD in the spreadsheet.

• Carry out a complete energy balance, stating clearly any assumptions made. You may also employ HYSYS for part of the energy balance calculations where there is a justification for doing so.

• Produce a complete PID for the oxychlorination section justifying all instruments implemented.

• Carry out a detailed HAZOP analysis on 4 streams in the oxychlorination section using keywords: NO, LESS, MORE on deviation FLOW. You must refer to the PID symbols produced before in the HAZOP table. Adjust your PID in the light of recommendations from your HAZOP study.

• Carry out a detailed mechanical design of the oxychlorination reactor and its ancillary equipment. State and justify any assumptions made, and refer to appropriate design standards.

• Carry out the following economic analysis of the process:

• The net cash flow in each year of the project and plant operation

• The future worth of the project, NFW • The present worth, NPW, at a discount rate of 15% • The discounted cash flow rate of return, DCFRR.

Explore discount rates 25%, 35% and 40% to tabulate values, but use Excel Solver for the final answer. Produce a suitably labeled cash flow diagram too.

• Estimate the pay back time.

ALTERNATIVE DESIGN TASKS

Different annual production rates may be given to different groups or in successive years, according to situations in departments (e.g., do students readily have access to past design reports? Are students monitored and quizzed periodically for original contribution? etc.). Mechanical design of different major items (there are a few in the VCM process and most are challenging) for each group or in successive years (direct chlorination reactor, cracking furnace, distillation columns, etc). Depending on whether simulation tools

Winter2005

are allowed, the level of design complexity can be adjusted accordingly. The process economic evaluation can be made more complicated by assuming variable raw material costs over the plant lifetime. HAZOP and operability studies can also be made more challenging-that would be an ideal exercise for team cooperative work. The same approach can be adopted for process instrumentation and control.

CONCLUSION

The VCM process design project has been offered to a multitude of groups of international students in the UK and UAE for a period spanning ten years and was found to be an excellent vehicle for integrating scientific knowledge, chemical engineering principles, and a whole range of transferable and interpersonal skill s, thus making it a truly ABET 2000 compliant senior-design project. The way design information has been provided to students enables them to engage in critical thinking and to evaluate constrained alternatives. On completion of the demanding design tasks, virtually all students recognized the benefits of working on such projects. The faculty member advising the students also benefited from the experience of supervising such project and became in a stronger position to revise curricula and propose relevant changes where appropriate. Details of the VCM process presented in this paper are based on real plant data that are believed not to be available anywhere else, thus making this article of major benefit to faculty members and students alike.

REFERENCES

1. Sieder W.D. , J.D. Seader, and D.R. Lewin, Product and Process Design Principles, Second Edition, John Wiley & Sons (2004)

2. Benyahia, F, "VCM Design Notes," Department of Chemical Engineering, University ofTeesside, UK (1995)

3. McPherson, R.W, C.M. Starks, and G.J . Fryar, "Vinyl Chloride Monomer ... What You Should Know," Hydrocarbon Processing, p. 75, March ( 1979)

4. Wong, E.W. , C.P. Ambler, W.J . Baker, and J.C. Parks Jr., "Produce High Purity VCM Product," Hydrocarbon Processing, p. 129, August (1992)

5. Schillmoller, C.M., "Alloy Selection for VCM Plants," Hydrocarbon Processing, p. 89, March (1979)

6. Balasubramanian , S.N., D.N. Rihani , and L.K. Doraiswarni, "Film Model for Ethylene Dichloride Formation", Ind. & Eng. Chemistry Fund., 5(2), 184, May ( I 966)

7. Encyclopedia of Chemical Technology, 23, p 865 (1990) 8. Coulson, J.M. , J.F. Richardson, and R.K. Sinnott, Chemical Engi

neering Design, Vol 6, Butterworth-Heinemann (2000) 9. Perry, R.H. and C.H. Chilton, Chemical Engineer 's Handbook, 7••

edition, McGraw-Hill ( 1998) 10. Treybal, R. , Mass Transfer Operations, 3rd edition, McGraw-Hill

(1989) 11. Kem, D.Q., Process Heat Transfer, McGraw-Hill (1965) 12. Kletz, T., HAZOP and HAZAN: Identifying and Assessing Process

Industry Hazards, IChemE publication distributed by Hemisphere Publishing Corporation ( 1992)

13 . Kunii , D. and 0. Levenspiel, Fluidization Engineering, 2nd edi tion (1989)

14. HYSYS 3.2 Process Simulation Package (physical properties, energy balance) 0

67

·,~1!111151111113rc=-:u~r=r=:ic=u::,u=m=------ --)

ASPEN PLUS® IN THE ChE CURRICULUM

Suitable Course Content and Teaching Methodology

D AVID A. RocKSTRAW

New Mexico State University • Las Cruces, New Mexico 88003

A SPEN Plus® software represents the standard in the chemical process industries (CPI) for process simulation. This software serves industries such as refin

ing, oil and gas, chemicals and petrochemicals, polymers, pharmaceuticals and specialty chemicals, power and utilities, consumer goods, food and beverage, and engineering and construction. It is used by forty-six of the world's fifty largest chemical companies, twenty-three of the world's twenty-five largest petroleum refiners, eighteen of the world's twenty largest pharmaceutical companies, and seventeen out of the world's twenty largest engineering and construction firms that serve the CPI. This popularity is also evidenced in the academic community, where ASPEN Plus continues to be the simulator of choice for studying process design and simulation_ [5- 17i As such, providing undergraduates with a strong background in ASPEN Plus is a desirable program trait for many chemical engineering (ChE) departments, and is a recruiting consideration to many employers of ChE graduates.

This paper does not attempt to teach the software, nor does it contain teaching materials for use by instructors. Lecture resources drawn from numerous sources114l are available online on the homepage of the author on the Chemical Engineering Department's web server at New Mexico State University <chemeng.nmsu.edu>. Demonstration files can be obtained from the author as well as from the Knowledge Base of the ASPENTech website <www.aspentech.com>.

INCORPORATING ASPEN PLUS INTO THE CURRICULUM

The topic of chemical process simulation is taught as a computing laboratory integrated with a senior-level design course at New Mexico State University. The ASPEN Plus simulator is taught as a one-credit hour laboratory that is taken concurrently with a three-credit lecture on process design during the first semester of the senior year. Students must demon-

68

strate competency with the simulator in their last semester by providing an independently worked solution to a chemical plant design problem.

It has been found that the fundamental ASPEN Plus education is best taught through a watch-and-do method, using a short discussion of a concept, followed by a live application. Consequently, lectures become a forum for demonstration. The homework assignments associated with each lecture are then slightly modified, requiring the students to follow the same keystrokes as they observed during the lecture. In doing so, students learn to navigate the location of the major features of the software , while interpreting the response of the software.

The design project(s) for the course (and subsequent courses) are designed to compel the students to demonstrate a more advanced level of understanding of these features than the laboratory homework. Whenever possible, it is recommended that previously built examples be used to demonstrate new concepts . Homework should also be designed around this principle.

DEFINING BASIC SKILL SETS IN ASPEN PLUS

Because of the many levels of complexity associated with

David A. Rockstraw is Associate Professor of Chemical Engineering at New Mexico State University. He worked at DuPont, Conoco, Ethyl, and Kraft prior to joining the NMSU faculty, and has been an active ASPEN Plus user since 1990, applying the simulator to numerous commercial syntheses. He was a coauthor of the problem statement for the 1999 American Institute of Chemical Engineers' national design contest and received the 2004 Aspen Tech Educational Innovation Award.



ASPEN Plus, preparing to teach the tool in an undergraduate curriculum can be as intimidating as preparing to learn the software in that same environment. Preparation of a reasonable curriculum that builds upon knowledge learned in previous lessons is critical in the training of students to begin using the software independently. Such a program of study must teach students to

• Specify unit operations in rating and design modes • Manipulate physical property models and estimate

physical property parameters • Access variables to perform sensitivity analyses and

variable optimizations, or to specify design criteria • Insert user-specified code • Work with non-conventional materials, pseudocompo

nents, electrolytes, and solids • Understand the interoperability of ASPEN Plus

Weekly computation laboratories permit fourteen topics for a standard semester-based program ( one of the fifteen three-hour sessions is used

Specifying Unit Operations • Early in the course, topics of discussion center on specification of the most important unit operations: the RADFRAC distillation column and the reactor blocks. While these primary units are discussed, units of lower complexity (such as the simple HEATER heat exchanger block) are included in demonstrated process flow diagrams, and are thus also learned. The student becomes comfortable with graphical user-interface (GUI) during these discussions, and is prepared for the more difficult concepts that follow.

Manipulating Physical Property Information • Having established students as "users" of the software, the next step is to demonstrate the methods by which the software treats physical property models and data. In two sessions, the students are shown how ASPEN Plus obtains physical property data, where the information is located within the GUI, and how to generate parameters for components not present in the database. Students initially make property comparisons

and generate parameters in the stand

for student presentations). Each week gives the opportunity to build up on the concepts of the previous week.

TABLE 1 alone mode, then convert their files to simulations.

HOMEWORK SUBMISSIONS

While the students should be aware of the information that can be included in an ASPEN Plus report fi le, and how to modify such content, it is unnecessary (and a waste of paper) for students to submit a lengthy report for grade evaluation. Most of the simulations in this semester course can be evaluated from a three-page document that includes copies of the flowsheet , the stream table, and the input file . Consequently, it is worthwhile for the instructor to learn to interpret a simulation from the input fi le. In addition, the input summary generates a header that contains time/date/user information that

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

Weekly Topic Summary

Graphical User Interface, Basic Unit Ops

Distillation Models, Rating Mode

Distillation Models, Design Mode

Stoichiometric Reactor Models

Kinetic Reactor Models

Physical Property Methods

Property Constant Estimation System

Accessing Variables: Sensitivity Analysis

Accessing Variables: Design Specs

Accessing Variables: FORTRAN

Electrolytes

Non-Conventional Solids and Substreams

Optimization and PFD Customization

Interoperability

Accessing Variables • Once students have learned the basics of building a flowsheet, specifying unit operations, and manipulating physical properties, they are ready to begin learning to access and manipulate variables within the software. The ability to create managed objects based on accessed variables is a necessary skill for students to derive from the program of study. Without an understanding of how to access variables, one is unable to perform a sensitivity study, converge process design specifications, or insert user-defined code into a simulation. Thus, the fundamentals of accessing variables in ASPEN Plus is the most important con-cept beyond flowsheet construction and requires a minimum of three sessions to complete. Tear stream convergence

is unique for each user and file generated. This information is useful in assuring that each student is submitting a unique document.

is also considered during these sessions.

Nonstandard components • By this point, students are capable of preparing a relatively sophisticated flowsheet of a traditional chemical process in the sense that it contains only conventional database components. Undoubtedly, students have sought to perform simulations of processes that contain aqueous salt systems, non-conventional components, or solids. While performing a simulation with such components is not difficult, specifying such components differs from and is slightly more difficult than simply selecting a species from the database, as is done with standard conventional components. Consequently, it is important that examples and prob-

SUBJECT TOPIC SCHEDULE

The basic schedule of topics discussed in this course (see Table I) can be categorized into five groups:

(]) (2) (3) (4) (5)

Specifying unit operations Manipulating physical properties Accessing variables Specifying nonstandard components Applying advanced features

Winter 2005 69

]ems to this point in the course only include conventional components.

The first feature covered in this section is the inclusion of electrolytes in a simulation. The Electrolyte Wizard GUI makes this the simplest of the concepts in this section to apply, yet greatly expands the students capabilities within ASPEN Plus.

In the second discussion, non-conventional solids and solid substreams are introduced, affording the student the capability of including heterogeneous solids in a simulation. This discussion leads quickly to the ability to specify Solids separation unit operations.

Advanced User Features • Students have now become proficient in applying the simulator, and many have developed the confidence to explore and apply some of the advanced features on their own. The final two sessions supplement the students' simulation capabilities by presenting them with options for fine tuning their programs, and enhancing the presentation of their works. In the first session, the optimization and constraint capabilities are demonstrated. These features are contained with the sensitivity analysis feature in the model analysis tools folder, thus students already know of their existence, and some have likely used these attributes. Customization of the PFD is also considered.

In the final session, students learn of the software interoperability, with emphasis on integrating the numerical results of the simulation with a spreadsheet. The spreadsheet can be designed to perform subsequent equipment sizing and economic calculations.

Advanced Elective Content • The described fundamental education in ASPEN Plus prepares the student for an elective course containing advanced simulator concepts, including : specifying pseudocomponents; working with the MULTIFRAC multiple column model; minimizing utilities with MHeatX, rating exchangers with the HeatX block, writing ActiveX code to run the simulator in the background of a spreadsheet, and ultimately, preparing a USER2 block based on FORTRAN code and seamlessly integrating the block into the software.

Demonstration Lecture Details

[I Week 1: Graphical User Interface, Basic Unit Ops

The introductory session should be informative, entertaining, and, most importantly, not intimidating. The instructor should open the software and build the first flowsheet from a blank page, rather than start with the program opened to a completed flowsheet. It is critical that the first example be simplistic, with the emphasis of the first session more on becoming familiar with navigating the software than with the details of the unit operations. A suggested protocol for this

70

session is

1. Discuss the need for chemical process simulation.

2. Explain the origin of ASPEN Plus (Advanced Simulator for Process Engineering).

3. Discuss good flowsheeting practices (build large flowsheets a few blocks at a time to facilitate troubleshooting; check that units for input data match values entered; ensure inputs are reasonable; check that results are consistent and reasonable).

4. Navigate through the key features of the software, including such items as the menu bar, tool bars , process flowsheet window, model library, the "Next" button, and the reporting functions .

5. Demonstrate common operations, such as switching between the data browser and the process flowsheet window. Perform these common operations by using the toolbar and by using the menu, thereby allowing each user to determine their individual preference, rather than forcing them to use those of the presenter.

6. Establish the variety of unit operations available in the software by scrolling through the items in the module library. Comment on those that will be used regularly, pointing out when each will be covered in the curriculum.

7. Build and solve a simple material and energy balance flowsheet employing only simple unit operations, such as the Heater, Pump, and Flash2 blocks. Use the "Next" button to fill in data upon completing construction of the flowsheet.

8. Specify which property package to use without justification, noting that later sessions will cover physical properties in greater detail.

9. Prepare a report file and manipulate the content of the report file.

10. Demonstrate to the students how to access the input summary for purposes of preparing the submitted documentation of their simulation.

11. Assign a flowsheet identical to the one prepared in class, but request the material and energy balances be performed for a different set of operating conditions associated with the unit operations (i.e., the heat exchanger and flash units operate at different temperatures than used in class).

[I Weeks 2 and 3: Distillation Models

The rigorous distillation model RADFRAC is the workhorse of the separation models in ASPEN Plus. The number of options and capabilities associated with the RADFRAC block are tremendous. Consequently, it should be introduced early in the course to give the student as much time as possible to become comfortable with using it. Each use of the block should be directed toward specific goals to avoid over-


whelming the student, however.

RADFRAC simulations can be per-formed in design or rating modes. In design mode, the simulation determines the value of operating parameters to achieve specified product criteria; while in rating mode, the simulation provides performance data (i.e ., flowrates and compositions of product streams) for a

The design project(s) for the course are designed to compel the students to demonstrate a

more advanced level of understanding of these features than the laboratory homework. Whenever possible, it

is recommended that previously built examples be used to demonstrate new concepts.

column of specified geometry. The modes of operation create a natural break for two lectures.

Begin Week 2 with a one-column, two-component, rating mode, RADFRAC simulation. Use a binary system for which data is plentiful (methanol/water) and avoid systems that form an azeotrope (ethanol/water). In rating mode, Design Specifications and Vary statements are unnecessary since one only seeks to understand the performance of a given column for a specified feedstock. In the absence of these complications, demonstration of Murphree efficiencies and the inclusion of a pressure profile are simplified. Time should be dedicated during this week to considering the wealth of results provided by RADFRAC, as well as to demonstrating the use of the Plot Wizard to visualize results graphically.

Begin the discussion of the design mode in Week 3 by demonstrating use of the DSTWU block (Winn-UnderwoodGilliland method) to estimate the reflux ratio and number of physical stages that are necessary to meet the design specifications of the product stream. Continue working with the same chemical system that was used in demonstrating the rating mode in Week 2. Reinforce to the student that DSTWU results are starting points, based on non-rigorous calculations.

Demonstrate replacing the DSTWU column with a RADFRAC column once the needed design information has been estimated with DSTWU, reconnecting the source and destination streams to the new column. This simulation with RADFRAC will employ the Design Specification and Vary folders to complete the design calculation, which will also be the firs t exposure to Object Managers in ASPEN Plus. Upon completion of the basic material and energy balance calculations, the simulation can be enhanced with little additional effort to perform tray-sizing calculations, another object manager-based block.

Upon completing these two lectures, students will have been introduced to the basic functions of the RADFRAC block. In addition, the concept of an object manager will no longer be foreign, allowing students to confidently explore similar fo lders .

[] Weeks 4 and 5:Stoichiometric and Kinetic Reactor Models

The p1imary reactor models with which the student should

Winter 2005

become familiar can be categorized into three classes: balance-based (RStoich and RYield), equilibrium-based (REquil and RGibbs), and kinetics-based (RBatch, RCSTR, and RPLUG). The first class are the non-rigorous blocks that simply complete a material balance based on specified conversion and yields. The equilibrium-based and kinetics-based blocks use the rigor of equilibrium constants and kinetic rate equations, respectively. As such, this natural distinction should be used to divide the discussion of reactors into two parts.

In Week 4, the reactor blocks are introduced using the balance-based reactors. The object manager into which stoichiometric information is assembled can be demonstrated without the need for a rate equation at this point. In addition, the effect of using this non-rigorous method on the energy balance can be pointed out by performing the simulation by ignoring, specifying, and allowing the simulator to calculate the heat of reaction based on heats of formation, then observing the effect on the duty of the reactor.

In the fifth week, the reactor block capabilities are extended to include the equilibrium-based and kinetics-based blocks, which share kinetic data from the Chemistry and Reactions subfolders. Students are already familiar with the methods for entering stoichiometry for each reaction at this point. Emphasis can thus be afforded to assuring students understand the reaction types ( equilibrium, salt, di ssociation, reaction) and the power laws kinetic model (power law, LangmuirHinshelwood-Hougen-Watson, reactive distillation, and userdefined models based on FORTRAN code) at their disposal.

[] Week 6: Physical Property Methods

The selection of a property model package tends to be an arduous task for students. To this point in the course, property packages have been specified in demos and on homework assignments without justification, but there have undoubtedly been questions from the more inquisitive students concerning how to select appropriate models.

To address this question , two tasks must be accomplished first. A series of terms relevant to ASPEN Plus physical properties must be defined: property method, model, parameter, and set. Secondly, management of Henry's Law components

71

must be discussed. Point out that Henry 's Law can only be used with the Ideal & Activity Coefficient models.

Deliberating justifications for specifying a particular method is usually a necessary aside at this point in the course. It is helpful to summarize this discussion with a graphic decision tree as that provided in Figure 1, providing a quick mechanism for dividing the lengthy list of property methods into two classes. Yet, this interchange does little to further the students' knowledge of the simulator. The educational endeavors associated with Week 6 should include: selecting an appropriate method for a simulation based on the components present; identifying and changing the model used for a physical property calculation when a given method is applied; performing a stand-alone properties analysi s; and preparing an object manager containing a user-defined property set for tabulation.

[1 Week 7: Property Constant Estimation System

While the ASPEN Plus Database of constituent chemicals is quite large, there is often the need to work with a chemical that is not in the database. The Property Constant Estimation System (PCES) is used to estimate parameters required by physical property models. It is used to estimate (i) pure component physical property constants, (ii) temperature-dependent property constants, (iii) binary interaction parameters, and (iv) group parameters for UNIQUAC. Estimations are based on "group contribution methods" and "corresponding state correlations." Experimental data can be incorporated into the estimation to improve accuracy of results.

The capabilities of the PCES are best demonstrated sequentially. The connectivity of a component is first built in the molecular structure folder, and its properties are generated based strictly on atomic connectivity and molecu-lar weight. The results are improved by then adding some laboratory data for this pure component. In-

experimental values

• Apply the PCES Compare function to identify appropriate estimation methods when generating parameters and properties for a component that is similar to a component contained in the ASPEN Plus database.

[1 Week 8: Accessing Variables: Sensitivity Analysis

The ability to access and manipulate the value of a variable in ASPEN Plus represents a knowledge level at which the student becomes capable of preparing simulations of a higher degree of sophistication. The need to modify/record a variable value occurs often in generating a process simulation, particularly when one is attempting to define operating conditions to meet a design specification. The concept of accessing a variable refers to references made to flowsheet quantities. It is important to stress that the values of userentered variables may be manipulated directly; while ASPEN Plus-calculated variables should not be overwritten, but should be varied indirectly.

Emphasis on the introduction to this topic must be on the process of accessing variables, and thus the first application should be the least complicated. Introduction of the Sensitivity Analysis function provides a tool for applying the accessing variables technique, while providing a user-friendly process evaluation tool that the students can begin using immediately with their design projects, allowing students to study the effect of changes in input variables on process outputs and thus perform rudimentary optimizations. It should also be noted that this method allows one to study the effect of time varying variables using a quasi-steady-state approach. The instructor should demonstrate displaying the results

cluding vapor pressure data demonstrates the input of temperature-dependent data into the data subfolder for a pure component. The estimations are then further improved by including one or more

Are polar components present in the system?

of the functional group contribution methods.

72

Recommended exercises include

• Estimate pure component parameters using the general structure method

• Define molecular structure using functional group methods and approximate a structure when ASPEN Plus is unable to completely determine all functional groups from the general structure

• Incorporate experimental data into a parameter estimation simulation

• Compare estimated property results versus

Are operating conditions near the critical region of l-f-ig..-..1

the mixture?

Are light gases or supercritical components r,c,,,..---

in the system? E

Equation of State Model

Activity Coefficient Model

Activity Coefficient Model w/ Henry's Law

Figure 1. Decision tree used in selecting an appropriate physical property method in ASPEN Plus.


graphically based on data in the Results form of the sensitivity block object manager, and should point out that changes to flowsheet inputs made by the sensitivity analysis do not affect the simulation as the base-case is run independently.

Homework developed to assess knowledge of the sensitivity analysis should be based on a simulation from a previous homework assignment. A flowsheet with a recycle stream can lead to some interesting results and can lead into a discussion of manual selection and convergence of a tear stream (i.e., a process in which effective convergence of the recycle loop requires user intervention). Emphasis on this material is thus dedicated to the application and interpretation of the accessing variables and sensitivity analysis tools, and expectations of the workload related to these concepts can be increased.

[I Week 9: Accessing Variables: Design Specifications

The Design Specification tool in the Flowsheeting Options folder provides a type of feedback controller for setting the value of a calculated flowsheet quantity to a particular value. This objective is achieved by manipulating a specified input variable. The specification portion of this tool provides a second exercise with accessing variables.

It is important to note during this section that design spec calculations are iterative; thus, providing a good estimate for a manipulated variable will help convergence in fewer iterations. This can be best learned by demonstrating a problem that does not seem to work the first time the simulation is run, allowing the students to contemplate the apparent difficulties. During the brainstorming to identify the convergence problem, a checklist of things to investigate can be generated:

• See if manipulated variable is at one of the bounds

• Verify that solution exists over range (hide the design spec and perform a sensitivity analysis)

• Confirm the manipulated variable affects the sampled variables

• Attempt to provide an improved initial guess

• Change the convergence block characteristics (step-size, number of iterations, algorithm, etc.)

[I Week JO: Accessing Variables: In-Line FORTRAN

The last session covering accessing variables involves manipulating variables within ASPEN Plus through the use of FORTRAN code executed during a simulation run. ASPEN Plus can translate simple FORTRAN statements, with the simulation engine; but complex code requires a FORTRAN compiler. Many engineering degree programs no longer teach FORTRAN, but this does not preclude teaching this tool as the simple FORTRAN is understood by anyone with a structured language background.

When building the simulation that demonstrates the use of

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inline FORTRAN code, indicate that one must provide access to all flowsheet variables that are to be used within FORTRAN statements, and that all read or written variables must be declared. The execution sequence must also be specified. Further remind students that, as with other accessing variable techniques, only input to the flowsheet should be overwritten by the FORTRAN. When reviewing the simulation output, show that the results of the execution of the FORTRAN block must be viewed by directly examining the values of the variables modified by the FORTRAN block.

[I Week JJ: Electrolytes

As noted earlier, the fust feature covered in the non-standard materials section is electrolytes. The "Electrolyte Wizard" walks the user through the process of including electrolytes in a simulation. While the wizard makes specifying an electrolyte system simple, there is some information and definitions that need to be provided during this demonstration.

Use of the Electrolyte Wizard

• Generates new components (ions & solid salts)

• Revises pure component databank search order so that first databank searched is ASPENPCD

• Generates reactions among components

• Sets the property method to ELECNRTL

• Creates a Henry's Component List

• Retrieves parameters for reaction equilibrium constant values, salt solubility parameters, ELECNRTL interaction parameters, and Henry's constant correlation parameters.

The student must ensure the simulated chemistry represents the actual system, modifying the wizard-based process as needed. Typical modifications may include

• Adding to the list of Henry's components

• Eliminating irrelevant salt precipitation reactions

• Eliminating irrelevant species

• Adding species and/or reactions that are not in the electrolyte expert system database

• Eliminating irrelevant equilibrium reactions.

The difference between the True Component Approach (results reported in terms of ions, salts, and molecular species present after considering solution chemistry) and the Apparent Component Approach (results reported in terms of base components present before considering solution chemistry) must be explained.

The limitations of the two approaches should be pointed out. In particular, in the true component approach, liquid/liquid equilibrium cannot be calculated and a number of models cannot be used (Equilibrium reactors: RGibbs, REquil ; Kinetic reactors: RP!ug, RCSTR, RBatch; Shortcut distillation: Di st!, DSTWU, SCFrac ; Ri gorous distillation:

73

MultiFrac, PetroFrac). For the apparent component approach, the chemistry may not contain any volatile species on the right side of the reactions, the chemistry for liquid/liquid equilibrium may not contain dissociation reactions, and the input specification cannot be in terms of ions or solid salts.

[I Week 12: Conventional-Inert solids, Non-conventional solids & substreams

ASPEN Plus uses the concepts of component types, component attributes, substreams, and stream classes to segregate components that require separate equilibria calculations. Conventional components are likely the only component type used to this point in the course. Conventional components participate in vapor/liquid, salt, and chemical equilibria, have a defined molecular weight, and are located in the MIXED substream. Demonstrations and homework to this point should have used only the CONVEN stream class, the default for simulations containing only a MIXED substream.

Understanding the need for multiple substreams, and thus the other stream classes, requires an understanding of the two other component types: Conventional Inert Solids (Cl Solids) and Nonconventional Solids (NC Solids). At minimum, it should be pointed out that CI Solids are solids that

• Are inert to phase equilibrium and salt precipitation/ solubility

• May undergo chemical equilibria and reaction with conventional components

• Have a molecular weight

• Are located in a substream called CISOLID

while NC Solids are heterogeneous substances that

• Are inert to phase, salt, and chemical equilibria

• Are heterogeneous substances that do not have a molecular weight ( e.g., coal, ash, wood pulp, deposited catalytic materials)

• May react with conventional or CI Solid components

• Are located in the NC substream

Although these materials are common to commercial chemical processes, they are not necessarily trivial to represent in ASPEN Plus.

Component attributes are typically defined to represent the composition of a component in terms of some set of identifiable constituents as illustrated in Table 2 for the major attribute types. Students must be aware that component attributes are assigned by the user, initialized in streams, and can be modified by unit operation models. An example of a fluidized bed reactor with catalyst regeneration unit is useful to show all three of these concepts.

The number and types of substreams, together with their attributes, define a stream class. A stream class can have any number of substreams, but the first substream for each stream class must be of type MIXED. Stream classes include CONVEN, MIXNC, MIXCISLD, MIXNCPSD, MIXCIPSD, MIXCINC, MCINCPSD; where the acronym contains some combination of the substream acronyms MIXED, CISOLID, and NC, and may end with PSD to specify that a particle size distribution has been defined.

Solid properties calculated for conventional components and conventional solids include enthalpy, entropy, free energy, and molar volume using property models in the property method on the Properties/Specification/Global form. Enthalpy and mass density are computed by property models specified in the Properties/Advanced/NC-Props form.

[I Week 13: Optimization Function and Constraints I PFD Customization

The last couple of sessions of the computation laboratory are used to present subject matter beyond that of the casual user. In the first of the final two sessions, the Optimization function is demonstrated as a means to find extrema of an objective function. The objective function is expressed in terms of flowsheet variables and in-line FORTRAN using variable accessing techniques. Constraints may be equalities or inequalities. Equality constraints in an optimization are similar to design specifications.

A simple demonstration simulation using both features should be built by following the following steps, identifying each step of the process as it is performed in the simulator:

• Identify the measured (sampled) variables

• Specify the objective function

• Specify maximization or minimization of the objective

TABLE2 Details of Component Attributes

Attribute D/J.e Elements Descrif!.tion

PROXANAL Moisture, fixed carbon, volatile matter, ash Proximate analysis, weight o/o dry basis

ULTANAL Ash, C, H, N, CI, S, 0 Ultimate analysis , weight o/o dry basis

SULFANAL Pyritic, sulfate, organic Forms of sulfur analysis, weight o/o of original coal, dry basis

GENANAL Up to 20 constituents General constituent analysis, weight or volume o/o


function

• Specify constraints ( optional)

• Specify the manipulated variables

• Specify the bounds for the manipulated variables

Like design specifications, the convergence of an optimization can be sensitive to the initial values of the manipulated variables. It is best if the objective, constraints, and manipulated variables are in the range of 1 to 100 (accomplished by normalizing the function). Furthermore, it should be stressed that the optimization algorithm only finds local minima and maxima in the objective function. With some objective functions , it is possible to obtain different extrema by starting at a different point in the solution space. A visual demonstration to emphasize this effect will have a lasting impact.

Presentation of the Optimization function tends to be completed quickly because the students have already been drilled in the art of accessing variables. Consequently, this discussion can be augmented with a demonstration of the numerous PFD customizations that can be applied to the graphical look of the flow diagram, including annotations and OLE Objects. Use the PFD mode to change flowsheet connectivity by adding or deleting unit operation icons to the flowsheet for graphical purposes only. Since the PFD-style drawing is completely separate from the graphical simulation flowsheet, students can improve the visual aesthetics of their flow diagram for use in reports and presentations. One must return to simulation mode to change the simulation flowsheet.

[] Week 14: Windows Interoperability

ASPEN Plus has been designed to achieve a high degree of Windows interoperability. This includes the ability to copy and paste simulation data into spreadsheets or reports, copy/ paste flowsheet graphics and plots into reports, create active links between ASPEN Plus and other Windows applications, embed OLE, and automate with ActiveX.

Students value the ability to perform Paste Links (live data links that update applications as the process model is changed automatically propagate results of changes). Most students learn to perform a net present worth analysis in a spreadsheet as a means of comparing project cash flows. Link an ASPEN Plus sensitivity analysis to a spreadsheet that performs a complete net present worth analysis by sizing equipment and estimating capital cost based on key simulation parameters, as well as calculating direct costs based on material and energy balance data. A worksheet based on each run of the sensitivity analysis can be used to graphically build a cost vs . operating parameter figure. If the appropriate operating parameter is used in the sensitivity analysis, a minimum in total cost will be observed in the figure . The direct and indirect costs can be shown as separate additive functions, giving rise to the minimum. Such a demonstration thus represents a strong

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reinforcement of basic engineering economy concepts.

SUMMARY ASPEN Plus is the most powerful chemical process simu

lation tool available, but is not a typical Windows-based program that can be learned by trial-and-error. The most efficient manner to learn the software is through a thought-out curriculum in which examples are introduced in an order that builds on previously learned concepts, and all concepts are reinforced with hands-on demonstrations. Students can complete an undergraduate degree and enter the workforce of the chemical industry with more than a working knowledge of the ASPEN Plus. This can be accomplished without requiring an overly demanding academic workload if the instructor assembles an appropriate curriculum.

REFERENCES I. ASPEN Plus software documentation 2. ASPE Tech Process Simulation course materials 3. ASPENTech Physical Properties in ASPEN Plus course materials 4. ASPENTech instructor Toolkit 5. Kim, J.K., and P.C. Wankat, "Quaternary Distillation Systems with

Less than N-1 Columns," In d. & Eng. Chem. Res., 43(14), 3838 (2004) 6. Van Hoof, V, L.Van den Abeele, A. Buekenhoudt, C. Dotremont, and

R. Leysen, "Economic Comparison Between Azeotropic Distillation and Different Hybrid Sys tems Combining Distillation with Pervaporation for the Dehydration of Isopropanol," Sep. and Purification Tech.; 37(1 ), 33 (2004)

7. Bisowarno, B.H., Y.C. Tian, and M.O. Tade, "Interaction of Separation and Reactive Stages on ETBE Reactive Distillation Columns," AIChE J., 50(3), 646 (2004)

8. Kaantee, U, R. Zevenhoven, R. Backman, and M. Hupa, "Cement Manufacturing Using Alternative Fuels and the Advantages of Process Modeling," Fuel Proc. Tech., 85(4), 293 (2004)

9. Dirk-Faitakis, C.B, and K.T. Chuang, "Simulation Studies of Catalytic Distillation for Removal of Water from Ethanol Using a RateBased Kinetic Model," Ind. & Eng. Chem. Res., 43(3), 762 (2004)

10. Jayawardhana, K, and G.P. Van Walsum, "Modeling of Carbonic Acid Pretreatment Process Using ASPEN-Plus (R)," Appl. Biochem. and Biotech. , 113-16, I 087 (2004)

11. Smejkal, Q., and M. Soos, "Comparison of Computer Simulation of Reactive Distillation Using ASPEN Plus and HYSYS Software," Chem. Eng. and Proc., 41(5), 413 (2002)

12. Pacheco, M, J. Sira, and J.Kopasz, "Reaction Kinetics and Reactor Modeling for Fuel Processing of Liquid Hydrocarbons to Produce Hydrogen: lsooctane Reforming," Appl. Cata/. A-General, 250(1 ), 161 (2003)

13. De Simon, G.F. Parodi, M. Fermeglia, and R. Taccani, "Simulation of Process for Electrical Energy Production Based on Molten Carbonate Fuel Cells," J. of Power Sources, 115(2), 210 (2003)

14. Zheng, L.G. and E. Furimsky, "ASPEN Simulation of Cogeneration Plants," Energy Conv. and Management, 44(11 ), 1845 (2003)

15. Lim, C.S, Z.A. Manan, and M.R. Sarmidi, "Simulation Modeling of the Phase Behavior of Palm Oil-Supercritical Carbon Dioxide," J.of the Amer. Oil Chem. Soc., 80( 11 ),1 147 (2003)

16. Kuchonthara, P., S. Bhattacharya, and A. Tsutsumi, "Energy Recuperation in Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) Combined System," J. Power Sources, 117(1-2), 7 (2003)

17. Ri vera, W. , J. Cerezo, R. Rivero, J. Cervantes, and R. Best, "Single Stage and Double Absorption Heat Transformers Used to Recover Energy in a Distillation Column of Butane and Pentane," Inter. J. of Energy Res., 27(14), 1279 (2003) 0

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JASQ classroom ) _____________ __..

ENVIRONMENTAL IMPACT ASSESSMENT

Teaching the Principles and Practices by Means of a Role-Playing Case Study

BARRY D CRITTENDEN AND RICHARD ENGLAND

University of Bath • Bath, UK, BA2 7AY

E nvironmental impact assessment (EIA) is an important technique to help ensure that all the likely environmental effects of a new development are under

stood and taken into account before permission to proceed with a development is given. The governing legislation varies from country to country. In the USA, the 1969 National Environmental Policy Act (NEPA) requires that an EIA must be carried out for federally funded projects likely to have an impact on the environment. This policy set the precedent for European legislation (EC Directive 85/337). In the UK, the most recent regulations are Statutory Instrument 1999 No 293 (The Town and Country Planning [Environmental Impact Assessment][England and Wales] Regulations 1999) available from the HMSO web site at<http://www.hmso.gov.uk/ si/si1999/19990293 .htm>.

Since many developments in chemical engineering undoubtedly have the potential to create significant environmental impacts, EIA should form a key component of the undergraduate chemical engineering curriculum. Suitable texts are Wathem,r 11 Petts and Eduljee,r21 Kreske,r31 Marriou,141

etc. Environmental Impact Statements (EISs) to illustrate teaching are readily available in the public domain and for the USA are listed on the EPA Office of Federal Activity 's web site <http://www.epa.gov/compliance/nepa/current/ index.html> by date of distribution. A keyword search for environmental assessment information can be completed by searching the Federal Registry at <http://www.epa.gov/ fedrgstr/index.html>.

Role playing provides an opportunity for students to understand in a practical way that there can often be opposing views on the impacts arising from a particular development. An ideal way of teaching the importance of understanding all viewpoints is to create an adversarial situation in which

key issues of a proposed development can be researched and debated. Clearly, the most meaningful debates not only center around controversial issues, but also involve participants from a wide variety of backgrounds with a wide range of viewpoints. To facilitate this, a group of chemical engineering students (around 15) in the final year of their MEng program at the University of Bath is joined by a similarly sized group of students from an MS program in Environmental Science, Policy, and Planning.

The MS students bring to the case study a broad range of educational backgrounds that includes biology, chemistry, business management, estate management, environmental science, European studies, geography, geology, health education, mathematics, physics, psychology, zoology, etc. They strengthen the role-playing case study since they bring a much broader range of personal opinions, as well as expertise, than would come from chemical engineering students alone, who

Barry Crittenden is Professor of Chemical Engineering at the University of Bath. He received both his BS and PhD in chemical engineering from the University of Birmingham. His teaching and research interests include all forms of environmental management and nanoporous solids for selective separations.

Richard England is Senior Lecturer in Chemical Engineering. He received his BS, MS, and PhD in chemical engineering from the University College Swansea, University of Wales. His teaching and research interests are in waste management and the application of membranes.



tend (quite naturally) to be in favour of any development being made within their own discipline. If the case study were to be run with only ChE students, it would be necessary to provide additional teaching and time to allow them to take on roles that are outside the normal scope of chemical engineering.

In view of the complexity of environmental regulations, the role-playing case study would be strengthened further if law school students could also be involved. The two instructors at Bath are both experienced in environmental legislation and in giving expert opinions. Indeed, one has an educational qualification in law and is a coauthor of three EISs, including one on the regeneration of GAC. Both instructors teach on a parallel Environmental Legislation module.

AIMS AND OBJECTIVES

The educational aim of the Environmental Impact Assessment module (an elective) at Bath is to develop a deeper understanding of environmental, technical, and social issues associated with the preparation and defense of an environmental impact statement for a chemical (or bioprocess) development. For the student, the learning objective is an ability to critically analyze the content of an environmental impact statement and to prepare the outline of an expert opinion. It is not a learning objective for students to be able to actually prepare an EIA.

Of the 167 hours involved in this double module, the majority (147) are assigned to private study, while 15 are given to the role-playing exercise and 5 are devoted to tutorials and seminar support by two senior members of the academic staff. While at the final-year MEng and MS levels, students at Bath are expected to work in a substantially independent manner; their work on EIA is nevertheless supported beyond the required hours by almost unrestricted access to both the library learning facilities and the two instructors.

THE CASE STUDY

The case study concerns a planning appeal for a proposed

TAB LE 1 Six Environmental Issues

• Emission of carbon monoxide, hydrogen chloride, oxides of nitrogen, particulates, and dioxins

• The possibility of the GAC being contaminated by polychlorinated biphenyls

• The increase in traffic on a minor access road

• Access to and from the site by large articulated trucks (carrying the GAC) at a very busy junction with a main highway through a residential district

• Alternative sites for the regeneration plant, including the "do nothing" option

• Visual impact

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development to regenerate granular activated carbon (GAC), which is used in packed beds to remove triazine pesticides (such as atrazine and simazine) from drinking water. The removal of pesticides is the duty of the regional, private water companies. Once spent, the GAC must be regenerated because it is too expensive and environmentally unsatisfactory to be disposed of in a landfill. Thermal regeneration is the most commercially viable technology for removing organic contaminants from GAC to a level where it can be safely returned for reuse in water-treatment works. For economies of scale, GAC regeneration plants are built in only a few locations strategic to a number of water-treatment works in which the pesticides are removed. Thus, the spent and regenerated GAC must be transported as an aqueous slurry in tankers to and from the regeneration plant. No one can dispute the need to provide wholesome drinking water. On the other hand, both the technology (involving combustion) and the siting of the thermal regeneration plant is often controversial. To many observers, a thermal regeneration plant with its chimney is viewed as nothing other than an incinerator.

The case study involves an appeal by a GAC regeneration company against an adverse planning decision made by a local authority. The principal reason for using an appeal is that the case study becomes adversarial since the local authority must defend its original decision in the appeal. The appeal process thereby demands that both sides of the argument must be debated unless prior agreement can be reached by the two principal sides (the developer and the defendant).

The original planning application was to build two 17 .5 tonne/day thermal regeneration plants in a common building on unused low-quality industrial land owned by the company. The site is in close proximity (about 300 m) to a residential housing area, an old but operational iron foundry, and a relatively modem metal fabrication factory in a heavily populated region of the UK. The land was previously used for effluent treatment and the sewerage connection to a modem treatment facility remains in existence.

In the case study, the local authority refused planning permission for the development because inadequate attention had been paid in the original Environmental Impact Statement to six environmental issues (shown in Table 1). Each of these issues is debated in the appeal, and other aspects surrounding the issues, such as industrial accidents, are naturally drawn into the debate. The environmental and health risks center around the six issues in Table 1. Thus, for example, the uncertain, controversial, and emotional aspects associated with the impact of dioxin releases on human health, animals , and the food processing factory are researched and debated by the students.

The GAC thermal regeneration process is a waste disposal and recycling process that is prescribed by the UK's Environment Agency for Integrated Pollution Control (IPC, to be superseded by Integrated Pollution and Prevention Control

77

(IPPC)) . While the agency 's Guidance Note S2 5.03151 describes matters relating to what must be done in order to obtain an authorization (permit) to operate, the contents of this 21-page document provide substantial information on what would constitute an acceptable design. Students are informed that conformation with provisions in this document does not, by itself, constitute sufficient grounds to win the appeal. This is because an authorization (permit) to operate can only be granted if permission to build the plant has been granted in the planning process.

THE GAC THERMAL-REGENERATION PROCESS

A simplified process-flow diagram is shown in Figure I. Students are provided with a more detailed diagram. GAC granules are typically 0.5-1 mm in size and are probably loaded to no more than 30% by weight with organic matter, of which only a very small fraction is pesticide (about 10 µg/ kg of GAC). Each of the two 17 .5 tonne/day plants is planned to operate continuously between periodic shut-downs for maintenance. Between three and six purpose-built 38-tonne road tankers would arrive at and leave the GAC regeneration plant each working day, excluding weekends. The incoming carbon slurry is pumped to a bulk water-carbon separator located at the top of the regeneration furnace, which is of the multiple-hearth type.

The cylindrical, refractory-lined steel shell of the furnace carries a series of refractory hearths one above the other. A revolving central shaft, with attached rabble arms, sweeps the carbon from the inlet port on the outside of the top hearth to the center, where it drops onto the hearth beneath. It is then rabbled to the outside and falls to the next hearth, and so on. The upper hearths form a heating zone where water and volatiles are driven off. The carbon regeneration and reactivation oc-curs on the lower hearths under a

Road

Tankrr

controlled range of temperature and composition conditions. Steam and some air are added as required so that the combustion conditions are non-oxidizing and the atmosphere contains significant concentrations of carbon monoxide. Red hot regenerated GAC falls from the bottom hearth into a water-quench tank, from which it is pumped as a slurry into road tankers to return to

DtW fl lt-rlng

the water treatment facility.

Road

Tsnkrn

Mnltiplt Hra1·1h Furn a rr

N11tt11•11)

G us

burner contains natural gas burners and an excess of air to create 6% by volume of oxygen at the outlet. The residence time of gases in the afterburner is set to be two seconds, conforming with information in the Environment Agency Guidance Note_l51

The process is designed not only to generate all the steam, which must be injected into the furnace, but also to put sufficient energy into the gases entering the base of the stack in order to ensure that the plume leaving the stack is invisible except for the occasional appearance of water vapor in exceptional meteorological conditions. The gases leaving the afterburner pass through a waste-heat boiler and then through a heat exchanger in which air is heated prior to injection into the stack. This air (which is not in contact with the GAC being regenerated) is taken from the hot central shaft of the multiple hearth furnace.

Gases leaving the energy recovery unit pass into a venturi scrubber (to remove particulates) and then to a trayed scrubber (to remove acid gases) before passing into a 20-m stack via an induced draft fan. The fan provides for a pressure slightly below atmospheric throughout the process and does not allow carbon monoxide to escape from the multiple-hearth furnace. Should the fan cease to operate for any reason, then (after some predetermined time as the pressure increases) the emergency by-pass stack would open, an alarm would be sounded, and the plant would automatically go into shutdown. During this period, of course, the contents of the multiple-hearth furnace would burn, thereby releasing gases into the atmosphere that had not passed through the gas-cleaning parts of the process. This aspect is inevitably one of the more hotly debated aspects in the case study.

The benchmark release levels set by the Environment Agencyr5i are given in Table 2. They are not emission limits.

Emrrguiry V rnt

Na tur al Gas Ah'

A Hr-rburnrr

Str am

\Vatrr

Enrrgy RHOVrry

Unit

Venturi Srrubbtl'

S ta rk

lndurtd Draught

ran

Gases leaving the top of the regeneration furnace pass directly into a separate afterburner that is designed to operate with an outlet temperature of 850°C. The after- Figure 1. Schematic of the granular activated carbon regeneration process.


They are values that are subject to consideration of site-specific environmental issues by the Environment Agency when framing conditions in an authorization (permit) to operate. The Guidance Notes state that the emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) should be reduced as far as possible by progressive techniques. The aim should be to achieve a guide International Toxicity Equivalent (ITEQ) value of 0.1 ng/m3_151 Controversy is introduced into the case study by including some fictitious emission data from a similar plant showing that some of the benchmark levels of carbon monoxide and dioxins are periodically exceeded.

THE ROLES AND THE TIMETABLE

Typical roles for the students, together with the written (and assessable) material each must produce, are shown in Table

TABLE2 Environmental Agency Benchmark Release Levels to Air

Substance Achievable

• Total particulate matter 20 mg/m3

• Hydrogen chloride 30 mg/m3

• Sulphur dioxide (as SO2

) 50 mg/m3

• Oxides of nitrogen (as NO2) 350 mg/m3

• Carbon monoxide (after last injection of air) 50 mg/m3

• Volatile organic compounds 20 mg/m3

• Dioxins and furans (International Toxicity Equivalent - ITEQ

• Smoke

I ng/m3

Free from smoke during normal operation and within five minutes of start- up

TABLE3

3 for both the GAC Carbon Company (the appellant) and the local authority (the defendant). The full range of environmental issues is covered with matching experts on opposing sides, thereby helping to ensure lively debate on all the issues in Table 1. In addition, two students take the roles of lawyers, two students act as journalists (one for a local newspaper, the other for a national newspaper), and the remaining students take third-party roles that include, among others, the chairperson of a local environmental pressure group, a professional chemist residing in the area, an elderly resident, and a lawyer acting on behalf of a local food-processing company.

The ChE and MS classes are divided more-or-less equally between the three groups, so that each side can bring expert opinions on the full range of subjects and facilitate the required debate. Thus, for example, a chemical engineering expert for the appellant would provide an expert opinion on the technology with which emissions will be abated on the proposed GAC plant, while a technology expert for the defendant would try to expose weaknesses in the appellant's proposed technology. Quantitative work is required of many experts. For example, either new calculations or checks on the values in the Environmental Impact Statement (EIS) would be carried out on the emission and di spersion of gases, particulates, and dioxins released through the emergency vent. This is a very difficult area for debate, not only because the frequency with which the vent opens is ill-defined but also because rather uncertain estimates have to be made for the quantity and duration of each emission. Working in this way, in areas of uncertainty, is a thought-provoking exercise for ChE students.

The appellant and defendant teams are provided with separate offices to maintain confidentiality but the press officers

Roles for the Appellant and Local Authority

publish daily releases for the benefit of the opposing side, the journalists, and the third-party group. The journalists try to get interviews to help them prepare their daily articles. Daily press releases and newspaper articles are posted on a notice board for all to read.

Au.fl.ella11t Local Authority_

Lawyer #I (barrister/advocate) Lawyer #2 (barrister/advocate)

GAC company project engineer Engineering consultant

Engineering consultant #1 Engineering consultant #8

Engineering consultant #2 Engineering consu ltant #9






Planning consultant Deputy Chief Planning Officer

Press Officer #I Press Officer #2

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Material to be submitted

Opening and closing statements

Statement on process technology

Statement on PCBs

Statement on dioxins

Statement on particulates

Statement on CO

Statement on HCI

Statement on N0

,

Statement on water quality and pesticides

Statement on land quality, planning, and transport

Series of press releases

The case study runs over a two-week (full-time) period commenci ng on a Monday morning when students select their preferred roles. Students acting as experts then have one full week to research their roles and to become

79

experts. During this period, the two lawyers guide their teams in preparing thorough and expert cases. At a set time during the Monday of the second week, the expert statements are exchanged. Between this exchange and early Wednesday morning, each side needs to determine how to counter the now-declared, opposing arguments and the lawyers need to prepare their opening statements. The two instructors assist the appellant and defendant groups in developing their research and arguments, as well as advising what constitutes good practice in an expert opinion.

The appeal is formally held on the Wednesday and Thursday of the second week in a room that is laid out in the style of a courtroom. Each expert, in turn, is led through his/her expert opinion by his/her lawyer and then is cross-examined by the opposition lawyer. If the expert has experienced a difficult cross-examination, another chance is given for re-examination. The two lawyers finally present their closing statements.

The two instructors sit in judgment over the appeal process (and can ask questions of the experts to clarify points made), but they do not make a final decision on the Thursday as to whether or not the appeal should be upheld ; thi s reflects UK practice whereby further research might be required before the final decision is made by the appropriate Government department.

MATERIALS SUPPLIED TO STUDENT GROUPS

Several documents are provided in order to enable the student groups to prepare their expert opinions and for the lawyers to prepare their arguments. The principal document is an adaptation of the original Environmental Impact Statement (EIS), an 85-page report containing a six-page nontechnical summary, together with descriptions of the proposed development, measures proposed to abate pollution, residual environmental impact, benefits to the local community, and appendices comprising site plans, a survey of flora and fauna, likely conditions to be imposed on discharges to sewer, airemission surveys from a similar plant already in operation, dispersion calculations from the chimney and emergency vent, drawings of the building elevations, and a noise survey. The original EIS has been adapted firstly to avoid using references to actual company and individual names, and secondly to bring it up to date in terms of the new European IPPC legislation. The EIS is supported by a 20-page document containing maps, plans, and photographs of the area before development. The scale of the maps ranges from l :625,000 (showing the location of the site in the context of the UK and its major highways) to 1:5000 (showing the proposed site and its neighborhood in detail).

Other documents supplied include the IPC Guidance Note,151

a practical guide to IPC,161 a guide for incorporating environmental assessments into chemical engineering projects,171 a guide for assessing releases to the environment, 181 and a guide

80

on discharge-stack heights for polluting emissions .C91 Students are also shown examples of written expert opinion and provided with specialist references to aid research in their roles as experts.

ASSESSMENT

Each student submits the written material required for each role (some of which is li sted in Table 3) as well as a 1000 word critique, which identifies the strengths and weaknesses of both sides in the appeal. The overall assessment is divided equally between the two. No attempt is made to assess oral activities. Assessment of the role-playing material is subdivided equally into quality of presentation, content, structure, originality, and conclusion in the context of the role played. The second submission is a critical evaluation of the strengths and weaknesses of both sides to the appeal. This reflective exercise is set to be the same for all students ; its assessment is subdivided equally into quality in setting out aims, degree of impartiality in reflection, quality of arguments, quality of conclusion, and quality of English and presentation.

CONCLUSION

A lively review and feedback session is held at the end of the second Friday. Refreshments are provided and discussion centers around both the quality of the technical arguments and the emotional aspects of cross-examination. Informal and written feedback from the MEng and MS students confirms that not only is the role-playing case study a most enjoyable way of learning the subject, but it also provides a firm basis for the need to understand all sides to the argument on environmental issues.

REFERENCES

I. Wathem, P., Environmental Impact Assessment Theory and Practice, Un win and Hyman, London ( I 989)

2. Petts, J. , and G. Eduljee, Environmental Impact Assessment for Waste Treatment and Disposal Facilities, John Wiley and Sons, Chichester ( 1994)

3. Kreske, D. L. , Environmental Impact Statements: A Practical Guide for Agencies, Citizens and Consultants, John Wiley and Sons, New York (1996)

4. Marriott, B. B. , Practical Guide to Environmental Impact Assessment, McGraw-Hill, New York ( 1997)

5. Environment Agency. Processes Subject to Integrated Pollution Control, Cleaning and Regeneration of Carbon, IPC Guidance Note S2 5.03, HMSO, London (1996)

6. Department of the Environment. Integrated Pollution Control: A Practical Guide, HMSO, London, (1993)

7. Institution of Chemical Engineers. Don't Forget the Environment, A Guide for Incorporating Environmental Assessment into Your Project, Rugby (I 999)

8. Institution of Chemical Engi neers. Emissions and Your licence to Operate: A Guide for Assessing Releases to the En vironment, Rugby ( 1999)

9. Her Majesty 's Inspectorate of Pollution, Guidelines 011 Discharge Stack Heights for Polluting Emissions, Technical Guidance Note (Dispersion) DI , The Stationery Office, London ( 1993) 0


AUTHOR GUIDELINES

This guide is offered to aid authors in preparing manuscripts for Chemical Engineering Education (CEE), a quarterly journal published by the Chemical Engineering Division of the American Society for Engineering Education (ASEE).

CEE publishes papers in the broad field of chemical engineering education. Papers generally describe a course, a laboratory, a ChE curriculum, research program, machine computation, special instructional programs, or give views and opinions on various topics of interest to the profession. (Note: Articles for the special series on outstanding ChE departments and ChE educators are invited articles.)

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TITLE • Use specific and informative titles. They should be as brief as possible, consistent with the need for defining the subject area covered by the paper.

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