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PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS 4 Credit-Hour Core Course INTRODUCTION
PLANT DESIGN AND ECONOMICS FOR
CHEMICAL ENGINEERS
4 Credit-Hour Core Course
INTRODUCTION
INTRODUCTION
CHEMICAL ENGINEERING PLANT DESIGN
PROCESS DESIGN DEVELOPMENT
FLOWSHEET DEVELOPMENT
COMPUTER-AIDED DESIGN
COST ESTIMATION
PROFITABILITY ANALYSIS OF INVESTMENTS
OPTIMUM DESIGN
OPTIMUM ECONOMIC DESIGN
OPTIMUM OPERATION DESIGN
PRACTICAL CONSIDERATION IN DESIGN
ENGINEERING ETHICS IN DESIGN
Contents
INTRODUCTION
In this modern age of industrial competition, a
successful chemical engineer needs more than a
knowledge and understanding of the fundamental
sciences and the related engineering subjects such as
thermodynamics, reaction kinetics, and computer
technology.
Chemical engineering design of new chemical
plants and the expansion or revision of existing
ones require the use of engineering principles
and theories combined with a practical
realization of the limits imposed by industrial
conditions. Development of a new plant or
process from concept evaluation to profitable
reality is often an enormously complex
problem.
INTRODUCTION
A plant-design project moves to completion through a series of stages such as is
shown in the following:
1. Inception
2. Preliminary evaluation of economics and market
3. Development of data necessary for final design
4. Final economic evaluation
5. Detailed engineering design
6. Procurement
7. Erection
8. Startup and trial runs
9. Production
CHEMICAL ENGINEERING PLANT DESIGN
the general term plant design includes all engineering aspects involved in the
development of either a new, modified, or expanded industrial plant. In this
development, the chemical engineer will be making economic evaluations of new
processes, designing individual pieces of equipment for the proposed new venture,
or developing a plant layout for coordination of the overall operation. Because of
these many design duties, the chemical engineer is many times referred to here as a
design engineer.
On the other hand, a chemical engineer
specializing in the economic aspects of the
design is often referred to as a cost engineer. In
many instances, the term process engineering
is used in connection with economic evaluation
and general economic analyses of industrial
processes, while process design refers to the
actual design of the equipment and facilities
necessary for carrying out the process.
CHEMICAL ENGINEERING PLANT DESIGN
PROCESS DESIGN DEVELOPMENT
The development of a process design, as outlined in Chap. 3,
involves many different steps. The first, of course, must be
the inception of the basic idea. This idea may originate in the
sales department, as a result of a customer request, or to
meet a competing product. It may occur spontaneously to
someone who is acquainted with the aims and needs of a
particular company.
A complete market analysis is made, and samples of
the final product are sent to prospective customers to
determine if the product is satisfactory and if there is
a reasonable sales potential. Capital-cost estimates for
the proposed plant are made. Probable returns on the
required investment are determined, and a complete
cost-and-profit analysis of the process is developed.
PROCESS DESIGN DEVELOPMENT
FLOWSHEET DEVELOPMENT
Basic Steps in flowsheet synthesis
- Gathering Information and Database creation
• Basic thermo-physical properties for all chemicals considered
• Information about reaction and conditions
• Yield
• Product purity
• Raw materials
• Process bounding (restrictions)
• Utilities
• Environmental Impact and toxicity of components
• Cost of equipment, utilities and sub-products. Chemical prices
Once the process concept has been designed which produces process flowsheet,
the equipment design then has to be performed…..
Distillation
FLOWSHEET DEVELOPMENT
COMPUTER-AIDED DESIGN
Various types of computer programs and techniques are used to carry out the
design of individual pieces of equipment or to develop the strategy for a full
plant design. This application of computer usage in design is designated as
computer-aided design
COST ESTIMATION
The final process-design stage is completed, it, becomes possible to make
accurate cost estimations because detailed equipment specifications and definite
plant-facility information are available. Direct price quotations based on detailed
specifications can then be obtained from various manufacturers. However, as
mentioned earlier, no design project should proceed to the final stages before
costs are considered, and cost estimates should be made throughout all the early
stages of the design when complete specifications are not available.
Evaluation of costs in the preliminary design phases
is sometimes called “guesstimation” but the
appropriate designation is predesign cost estimation.
Such estimates should be capable of providing a basis
for company management to decide if further capital
should be invested in the project.
COST ESTIMATION
In finalising the process and equipment design, several stages of economic analysis could be conducted …
First step;
EP 1 = Revenue – Cost of Raw Material
Second Step (after mass balance developed)
EP 2 = Revenue – Cost of Raw Material - Utility
Third Step (after equipments designed)
EP 3 = Revenue – Cost of Raw Material – Utility – Annualised Cost of Equipment
The economics analysis continues with other costs (manpower, insurance etc) ….
with profitability analysis conducted at the end to assess project viability ……
Pay back time,
Return on Investment
Internal Rate of Return
Cost Estimation
PROFITABILITY ANALYSIS OF INVESTMENTS
A major function of the directors of a manufacturing firm is to maximize the long-
term profit to the owners or the stockholders. A decision to invest in fixed facilities
carries with it the burden of continuing interest, insurance, taxes, depreciation,
manufacturing costs, etc., and also reduces the fluidity of the company’s future
actions. Capital-investment decisions, therefore, must be made with great care.
Since all physical assets of an industrial facility decrease in value with age, it is
normal practice to make periodic charges against earnings so as to distribute the
first cost of the facility over its expected service life.
This depreciation expense as detailed in Chap. 9,
unlike most other expenses, entails no current outlay
of cash. Thus, in a given accounting period, a firm has
available, in addition to the net profit, additional
funds corresponding to the depreciation expense. This
cash is capital recovery, a partial regeneration of
the first cost of the physical assets.
PROFITABILITY ANALYSIS OF INVESTMENTS
OPTIMUM DESIGN
In almost every case encountered by a chemical engineer, there are several
alternative methods which can be used for any given process or operation. For
example, formaldehyde can be produced by catalytic dehydrogenation of
methanol, by controlled oxidation of natural gas, or by direct reaction between
CO and H2 under special conditions of catalyst, temperature, and pressure. Each
of these processes contains many possible alternatives involving variables such
as gas-mixture composition, temperature, pressure, and choice of catalyst. It is
the responsibility of the chemical engineer, in this case, to choose the best
process and to incorporate into the design the equipment and methods which
will give the best results.
OPTIMUM ECONOMIC DESIGN
One typical example of an optimum economic design is determining the pipe
diameter to use when pumping a given amount of fluid from one point to another.
Here the same final result (i.e., a set amount of fluid pumped between two given
points) can be accomplished by using an infinite number of different pipe
diameters. However, an economic balance will show that one particular pipe
diameter gives the least total cost.
OPTIMUM OPERATION DESIGN
Many processes require definite conditions of temperature, pressure, contact
time, or other variables if the best results are to be obtained. It is often possible
to make a partial separation of these optimum conditions from direct economic
considerations. In cases of this type, the best design is designated as the
optimum operation design.
An excellent example of an optimum
operation design is the determination of
operating conditions for the catalytic
oxidation of sulfur dioxide to sulfur
trioxide.
PRACTICAL CONSIDERATION IN DESIGN
The chemical engineer must never lose sight of the practical limitations
involved in a design. It may be possible to determine an exact pipe diameter for
an optimum economic design, but this does not mean that this exact size must be
used in the final design. Suppose the optimum diameter were, 3.43 in. (8.71
cm). It would be impractical to have a special pipe fabricated with an inside
diameter of 3.43 in. Instead, the engineer would choose a standard pipe size
which could be purchased at regular market prices. In this case, the
recommended pipe size would probably be a standard 3.5 in.-diameter pipe
having an inside diameter of 3.55 in. (9.02 cm).
System of moral principles
Principles of right and wrong
Principles of conduct governing
behavior of an individual or a group
ENGINEERING ETHICS IN DESIGN
A person’s behavior is always ethical when one:
A. Does what is best for oneself
B. Has good intentions, no matter how things turn
out
C. Does what is best for everyone
D. Does what is legal
Quick Questions
Ethics in an Engineering Course????
We have been studying engineering, such as design, analysis, and performance
measurement.
Where does ethics fit in?
How Ethics Fits into Engineering
Engineers . . .
Build products such as cell phones, home appliances, heart valves,
bridges, & cars. In general they advance society by building new
technology.
Develop processes, such as the process to convert salt water into
fresh water or the process to recycle bottles. These processes
change how we live and what we can accomplish.
Products and processes have consequences for society:
If the bridge has an inadequate support, it will
fail.
If the gas tank is positioned too close to the
bumper, it might explode from a small accident.
If the process for recycling bottles produces too
much pollution, then it is counterproductive.
If the process for refining gas produces too
much toxins, it harms the local community.
Decisions made by engineers
usually have serious
consequences to people --
often to multitudes of people.
Ethics and ethical reasoning
guide decision-making.
Consider the March 11, 2011
8.9 magnitude earthquake
near Sendai, Japan.
The damage to the Fukushima I Nuclear
Power Plant (Fukushima Dai-ichi)
has led people worldwide to rethink the
ethics of nuclear power.
ISSUE #1: HEALTH AND SAFETY
RISKS: Danger to current and future
generations from leakage of radio-
isotopes used in nuclear power.
Plutonium-239 (half-life = 24,110 yrs)
is a particularly toxic radio-isotope.
Normally, 10 half lives are required
before a Pu-239 contaminated area is
considered safe again, in the case of
plutonium, roughly 250,000 years.
So if Pu leaked, -- say, due to an
earthquake -- it would cause a
health risk for roughly 8000
generations!!
Notice the issues that come up in these discussions:
Issues (cont.):
ISSUE #1: HEALTH AND SAFETY
RISKS, FURTHER
CONSIDERATIONS:
a) The possibility of medical science
discovering a cure for cancer
sometime in the current or next
centuries adds uncertainty to the
long-term health risks of leakages of
radio-active isotopes.
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Issues (cont.):
ISSUE #1: HEALTH AND SAFETY
RISKS, FURTHER
CONSIDERATIONS:
b) The use of nuclear power may
increase our knowledge of
radioisotopes used for medical
purposes (possible benefit?).
Finally ….. You will develop the construction details for a process plant ….
Thank you
