1360_Ch05

chapter 5

Process definition and feasibility tests

The first review of the proposed idea was done inside the R&D group (seeChapter 2, Section 2.2.1). It was shown in that review that the process canmake sense, did correspond to a real need, and, on the face of it, was notscientifically incorrect. As a result of these early consultations, a green lightwas given to the promoters group for the commissioning of the literaturesurvey, for the preparation of this preliminary process working definitionand for their formal presentation for a second review in a larger forum.

5.1 Translation of the idea into a process definition

5.1.1 Scope of the preliminary process definition

An essential

starting point

for any development program is a preliminaryprocess definition, which will allow:

Bringing everybody concerned to an

explicit common reference basis

Illustrating a

concrete venture

in order to develop the interest of thehard-nosed decision-makers in the continuation of the work

Outlining a proper experimental program and starting its detaileddesign

This field of

synthesis and design of chemical processes

has been the subjectof a number of excellent

theoretical textbooks

.

14

These manuals can be usefulmostly for the analysis and understanding of the fundamental principles,and for the definition of

the data which would be needed

for the use of thesophisticated models available. Unfortunately, at the beginning of a newdevelopment program,

most of such data would have to be assumed

.Therefore, this preliminary process definition should be assembled and

presented by an

experienced process engineer

who, in addition to the generalknowledge published, would use:

1360_frame_C05 Page 57 Monday, April 29, 2002 3:36 PM

Copyright 2002 by CRC Press LLC

Personal interaction with the inventors and promoters Past experience in similar cases Some reasonable assumptions (which will always be presented as such) More specific considerations, which are detailed below

The written preliminary process definition document also will include:

Results from a comprehensive literature survey describing what isgenerally known in this particular field

Division of the process into defined sections and interconnectingstreams, as shown on a block diagram

Calculation of the first process material and heat balances (the so-called revision 0)

Definition of at least one feasible implementation scheme Projection of an industrial implementation framework and timetable A detailed list of critical feasibility tests

5.1.2 Comprehensive literature survey

The inventors and the promoters have probably already done the best liter-ature survey they could with the means available to them on the core aspectsof their proposal. Now that the field of interest has been both enlarged andmore focused with the participation of additional experienced professionals,a renewed literature survey can be commissioned, in parallel to the otherwork described below (see also Chapter 3, Section 3.6.1).

This publications search can be subcontracted nowadays to specialistsor to academic libraries where it is done by computer screening of largedatabases, according to agreed key-words. The first result of such screen-ing is generally a very long list of items, including titles, authors, journal,date of issue, language, and possibly a couple of lines of abstract. A firstmanual selection has to be made from the computers output, according tosome criteria to be agreed upon. However, the ordering and collection ofworkable copies of the selected publications (and their translation, if needed)could be sometimes lengthy and expensive.

The senior process team should devote a

continuous

effort to supervisingsuch screening and to the study of these copies/references as they arrive,looking in particular for any factual information, and for any possible numer-ical correlation of the included relevant experimental data. In addition, suchanalysis may give some interesting hints about the reasons for any previousresearch work on this subject and about their potential projection on theindustrial scale up to now.

The continuous recording and distribution of the results and the analysisfrom this survey to the core team and to the relevant consultants had oftenprovoked important

practical responses and proposals

concerning the work athand. In the end, all such findings have to be summarized and included inthe material submitted to the second review.



5.1.3 Block diagram

The overall process will be separated, as far as possible, into

different sections

and represented in a

block diagram

with

numbered interconnecting process streams

.This division is very important for all the following work and, therefore, itneeds to be carefully devised so that each block ( = section of the whole process)would contain, as far as possible,

only one well-defined operation

.In this context, a

section

is a definite part of the process in which the flowrates and compositions of the exiting streams are determined uniquely by:

Flow rates and composition of the entering streams Operating conditions that can be controlled by the operator, such

as temperature, pressure, residence time, velocities, reflux ratio, andthe like

The presence of recycle (reflux) streams between certain sections and theexact location of their return point are very important aspects in manyprocesses. The two typical examples given below have been chosen in ordernot to trespass into any actual process or new technology handled by anoperating company.

First Example

A typical illustration of a block-diagram is given inFigure 5.1 as an example describing a new process, which was not completelydeveloped, for producing diammonium phosphate (DAP) from phosphaterock, HCl solution, phosphoric acid, and ammonia following a patentedsolvent extraction process.

21

However, this proposed process also incorporates a

new process concept

,which is hereby offered to the consideration of the readers, as it may haveapplications in many other fields. Instead of an organic solvent cycle circu-lating inside the plant, there is an

internal cycle of ferric ions

(in various forms)kept inside. In short, the incoming HCl solution (stream 1) encounters aferric hydroxide cake (stream 2, with some solid impurities originating fromthe phosphate ore) and dissolves it, giving a FeCl

3

solution. The solid impu-rities are taken out and the hot FeCl

3

with some HCl excess (stream 3) isused to dissolve phosphate ore (4). FePO

4

is precipitated and separated (6)from the resulting CaCl

2

solution (5). The washed FePO

4

cake is dissolvedin WPA (7) wet phosphoric acid as a mixture of soluble mono- anddiferric phosphate (8). Ammonia (9) is added to that mixture and to a motherliquor DAP recycle (10); more DAP is formed and ferric hydroxide is pre-cipitated. The later is filtered and recycled, the DAP solution (11) is cooledand crystallized, and the DAP crystals are separated and dried (12).

In total, half of the phosphoric acid in the final product originated fromthe reaction of HCl with phosphate rock. The ferric ions are acting as aseparation tool between phosphoric acid and the resulting CaCl

2

and otherimpurities,

including most of the impurities from the WPA,

which precipitatedin the higher pH section. This proposal is also illustrated as an example ofa black box in Chapter 10, Section 10.4.3 and Figure 10.3.



Second Example

This example of a process block diagram (Figure 5.2)is the Gorin-Mizrahi patented process

8

for the recovery of zirconium fromthe natural zircon mineral. (See Chapter 1, Section 1.4. A more detaileddiscussion of the process choices and issues in the high-temperature sectionscan be found in Chapter 6, Section 6.4.4 and in Figure 6.9.)

A commercial grade of zircon heavy sand is finely ground and mixedwith a concentrated solution of CaCl

2

, granulated and dried at 180 to 300

C.The process flow sheet of that section is illustrated in Figure 7.5, Chapter7. In these free-flowing aggregates, the CaCl

2

, with up to 6% water, isdistributed in intimate contact with the solid surfaces. The granules areheated and calcined successively in two rotating kilns in series, at differenttemperatures, in direct contact with combustion gases. In the first kiln, thecalcium chloride melts at 782

C, reacts with the zircon solids and with thewater vapor, and decomposes, giving very active CaO while releasing HClinto the exit gas stream.

This HCl is then absorbed adiabatically to give an HCl aqueoussolution while scrubbing the exit gases. The overall reaction is completedin the second kiln at 1400

C. The reacted clinker is quenched in waterand ground, then partially attacked with the recycled HCl solution. Thecalcium silicate and other impurities are dissolved in the waste solutionand only zirconium oxide remains in the solid phase, which is filtered,

Figure 5.1

Process block diagram for a DAP process.

FePO4 separation

FePO4dissolution

centrifuge

cooling-crystallyzer

solid /liquid

separation

DAPReactor

Phosphateleaching

wastesolids

separationHydroxidedissolution

HCl solutioninsol. waste

phosphate

CaCl2 brine

FePO4 cake

Phosphoric acid

Ammonia

ferrichydroxide

cake

DAP filtrate

1

2

3

4

5

6

7

8

9

10

11

12

DAP crystals

mother-liquor

filtrate slurry



completely washed, and dried. The basic technology of all these opera-tions is more or less conventional, and the novelty of the process residesin the exact conditions in the calcination, which give a

liquidsolid reactingfront

and an

intermediate double salt

of calcium silicate and calcium zir-conate. More details on the high-temperature chemistry are discussed inChapter 6.

5.1.4 Quantitative definitions of the different sections

For

each section

, the quantitative definition should consist of two parts,which have to be detailed in the textual description and presented togetherwith the block diagram, in addition to the available data or the agreedassumptions.

Formal

characterization

of the prevailing mechanisms in the generallyaccepted terminology (and in more detail if there is any doubt)

Quantification

of the aims to be achieved

This

physical-chemical

mechanism can be, for example:

A chemical reaction

1116

A heat/mass transfer operation

17,19

A separation operation (see Chapter 6, References 1 to 9) It also can be a conventional material handling or a storage operation

Figure 5.2

Process block diagram for a zirconium process.

slurry mixing andgranulation

granulesdrying

second kiln

leaching andfiltration

adiabaticabsorption

ground zircon CaCl2 solution

water

fluegases

wash water

HClmakeup

productdrying

waste stream

first kiln

hotgases

hotgases

HCl solution

quenching andgrinding



For example, such mechanisms can be defined as:

Homogeneous (one-phase) mixing and equilibration of certainstreams

Neutralization reaction resulting from mixing and reacting differentphases

Multiple-stages, countercurrent, liquidliquid extraction battery,which involves

in every stage

the mixing of liquid streams in order toachieve mass transfer of specific components and approach to equi-librium, followed by the separation of the resulting liquids

Similar batteries for different process functions, such as extractwash or back extraction in solvent extraction

Concentration of a solution by evaporation and the subsequent cool-ing of the resulting solution and of the evaporated condensate

Filtration and washing of crystals on a wedge-wire screen centrifuge Drying of the solids from a wet filter or centrifuge cake Separation of a solids stream into (different, defined) size frac-

tions, etc.

The

aims to be achieved in each separate section

also should be given

quan-titative indexes

, such as the minimum concentration, the specification in theexiting stream, the acceptable upper energy consumption, the minimumrecovery of a valuable component, an acceptable waste composition fordisposal, and so forth.

5.1.5 Process calculations for the preliminary process definition

The chemical engineering calculations can follow well-established proce-dures, which are listed and detailed in some of the basic reference books.

612

As far as possible, these calculations will be done

in parallel

and will include:The

correlation and analysis

of all the relevant data already available,either from the previous work of the inventors/promoters, of the processengineer, or from previous publications on related subjects, which may havebeen obtained from an extensive literature search (see Section 5.1.2). Thesecorrelation formulas can be

carefully extended

by extrapolation, if needed, aslong as this is clearly recorded as a provisional mean.

The formulation of the

quantitative relations

(known or assumed) that canaffect the process mechanism for each separate section (e.g., the yield ofreaction, the solubility). These relations sometimes can be based on thetheoretical thermodynamics or the physical chemistry knowledge, as givenin basic reference books.

18,19

But it is seldom that in the first stages of adevelopment effort, these sources could be useful or justifiable. Therefore,quite often at this stage, some of these assumptions have to be based on

known analogies with other processes

from the process engineers own back-ground (although he may have to keep some of these references secret, andpersonal trust will be essential).



The

evaluation

of the effect that each of the different operating variablesmay have (for instance) on distribution, solubility, recovery, heat effects, andtheir combinations for each separate section, on the basis of the abovequantitative relations.

The preparation of computer spreadsheets for

each separate section

with the preliminary design material balance and with the heat balance(if the heat effects are important in such sections, which is not alwaysthe case), on a reasonable arbitrary basis, e.g., 1000 units of the main rawmaterial. These balances are prepared by conventional chemical engineer-ing calculations, and this task should give the process engineer a

goodinsight

into the importance of each of the different factors in the

play-of-forces

inside such process (

leverage

). Of course, there are interactionsbetween the different spreadsheets, since each section starts whereanother ends. These spreadsheets can be easily converted at a later stageto any other basis needed.

A list is also prepared of the

critical feasibility tests

that should be doneto define or confirm

some

of the

high-leverage assumptions

taken in thesecalculations before these are presented for the review (see Section 5.3).

5.1.6 Presentation of one feasible implementation formula

This description is, in fact, a

concrete, possibly optimistic

,

illustration

of theimplementation of the concept,

if it could be made to work as intended

. Thestarting point is the

integration

of the above

quantitative assumptions

into one

possible

implementation case, describing an operating plant with the speci-fications of the raw materials and the products, the material and heat bal-ances, the process control, the recoveries, the disposal or treatment of theresulting waste streams, the relevant safety aspects, the choice of materialsof construction for the contact equipment, and so on. Typically, if one of theraw materials have to be transported in large lots, the material handlingfacilities and storage can be significant.

For example, it may be projected that the new process would need largeheat exchangers made from expensive materials (graphite, glass-lined, tan-talum), or that the rapid scaling of such heat exchangers should be expected,considering the composition of the solutions being heated. In such case, onedesign option could be to resort to the technology of organic heat carrier(stable liquid or vapor hydrocarbons) and, if this is considered a practicaldesign possibility, it should be studied, defined, and included in the exper-imental program (see Chapter 6, Section 6.2.1)

5.1.7 Possible industrial implementation framework

A projection of one possible industrial implementation framework (

known

or

assumed

) is presented for the proposed novel process with its specificfeatures, such as the possible site, the scale of production, the equipmentsize and function, the different raw materials available, existing connections



to critical services, any possible synergetic coproduction. Such projectionshould help

specify the technological factors which will have to be solved

.For example, the maximum

supply temperature of the cooling water

thatcould be reliably procured or produced in this site depends on the recordedclimatic conditions. It often has been found in warm countries that suchtemperature can have a

critical

importance for the design of a new processbased on evaporation or distillation

under vacuum

, or involving materialswith

low

boiling points

. If the normal cooling water at this site isnt coldenough, the cost of supplying

artificially chilled

water would have to beincluded or the process scheme radically changed.

5.1.8 Timetable

A reasonable projected timetable for the whole development and implemen-tation project prior to the plants start-up and to the market penetration isalso essential to the decision-making forum, in order to:

Evaluate the availability of the required resources Coordinate the assistance of the many different support groups and

experts Connect with the market projection studies

5.1.9 Important note

Obviously, in the beginning, the above

preliminary

process working defini-tion would have to be based, in a large part, on weighted and explicit

assumptions

and on

previous professional experience

.Its purpose is to focus the teams attention as well as to plan any future

work on the

limited scope of application that is of interest in real life

, and to allowfor a more effective allocation of the available industrial R&D resources.

It is agreed that this process working definition will be progressivelychanged, enlarged, and refined in

future numbered revisions

, as more informationwill be gathered and analyzed, and more promising avenues will be defined.

However, such a

working method

has not always been accepted by all. Inmany cases, it has been resisted and even ridiculed by senior scientists, whowere used to the open-ended academic research approach, claiming, Whatdo we really know for sure? Lets collect some data first and then we willsee what kind of process will result.

Bluntly speaking, their

noncommittal

approach represents the

more seriousdanger

to the development of

any

novel chemical process (like gamblingwithout knowing the odds). The least damage can be that a large part of theexperimental data collected would be

outside the scope that is relevant

forimplementation, resulting in a loss of time, resources, and good will. Moreserious damage could be caused if wasting of time and repeated abortivetrials would erode the corporate managements interest and promising ideaswould be lost.



5.2 Critical and systematic review of the process definition

5.2.1 Review forum

This

second critical review

aimed at reaching operative decisions with regardto the next steps (no or maybe) is generally called in by the decision-makerwho can be, for instance, the managing director of the R&D organization,the corporate vice president for new business, or the director of the fundingcommittee, and comparable in function or in title.

This discussion is conducted in a larger forum with ranking colleaguesof the inventors/promoters (peers) and with outside experts who areinvited, if and as needed. It should cover all the essential elements, such asthe technology and patents, the corporate strategy and markets, the profitpotential, and the capability to handle the proposed development programwith the resources available.

In a larger organization, there can often be a competition for the priorityin allocations between different projects. The raising and discussion of themore difficult subjects in such a review can sometimes be unpleasant, ifit is seen as a personal criticism among working colleagues with complexhuman relations. Therefore, it can be useful to appoint a merciless devilsadvocate to present the pros and cons of the problematic aspects, in advanceand in writing. His contribution would then avoid wasting time in rhetoricand personal maneuvers.

As a result of the first part of this review, a number of specific activitiesshould be approved for immediate execution, and an additional meeting ofthe critical review forum generally would be reconvened by the decision-maker a few months later. This additional meeting will then study andreview the different reports prepared on the

feasibility tests

, the

patent discus-sions

, and the clarification of the

critical economic factors

.

5.2.2 Fundamental process issues

In this review, all the fundamental process issues should be raised andfocused on, and a list prepared all information requested to arrive at thefinal clarification of these issues in the future.

Any apparent reason why this cannot work? Have we forgottenanything?

Could any wishful thinking bias be included in the conceptualreasoning?

Does any quantitative factor have a leverage large enough that mightturn the balance critically away in the wrong direction?

How to deal with any relevant existing patent claim (see below). Is the process flexibility sufficient to accommodate some changes that

could be needed to bypass such typical claims, should they appearin the future?

Is there a sufficient profitability potential (see below)?



As a result of this review, a list of

critical tests for process feasibility

shouldbe defined and agreed upon (see Section 5.3).

5.2.3 Patent situation

Relevant

patent claims granted to another party, which may have been foundin the first survey, will be discussed in this review. In many cases, suchprevious claims may still be avoided quite fairly, on the basis of their exactformal definition, but such constrain can dictate some changes in the devel-opment program.

Unfortunately, patent applications are not made public for 2 to 3 yearsafter their filing and many inventors are using perfectly legal tactics todelay their publication, so one also may have to look for

hints

fromprofessional circuits and to prepare for eventual surprises from thisdirection.

The promoters will also draw up and present to this forum a verydetailed list of

every possible patentable claim

for the new process. After thisreview and the approval to proceed farther, this list will be used for addi-tional discussions with the patent attorneys and the specialists, and after anelimination and selection procedure, for the drafting of a comprehensivepatent application (see Chapter 8).

Note that all the formal procedures of patenting are now quite rigid andvery few procedural decisions are really needed, apart, of course, from the

delicate issue of the names listed as the inventors. In particular, since theestablishment of the PCT (Patent Cooperation Treaty), all international appli-cations can be based on the examination done in one patent office (i.e., inWashington, D.C.).

Therefore, the main deliberations with the patent attorneys on any newpatent and the resulting decisions will be related to the exact formulationand wording of the claims in the application. Even among patent attorneys,there is a certain degree of specialization, since only a professional with areal knowledge of the particular scientific technological field can contributeeffectively to such formulation.

However, in some corporations, any talk about a patent applicationwould immediately involve their top lawyers (who usually are very busy)and, therefore, the patenting procedure could become very slow and veryexpensive without any real additional contribution. This frustrating situationis often a pitfall.

As a curiosity, in the U.S., a corporation is legally bound to pay theinventors cash in return for their assignment of the patent rights, even if theinventors are their own employees or their regular consultants under con-tract. This cash payment is often done in the form of a brand new $1 bill,which is handed over to each inventor with his signature, and which is oftenframed together with the invention certificate.



5.2.4 Profit potential

It also should be shown and agreed in this review that the profit potential ofthe proposed process could be attractive enough to justify the estimated costsof the next stages of a development program.

There can be many different definitions of the profit potential, which areused by different corporations and industrial sectors in various countriesand tax situations. In general, this profit potential should quantify the expectedincrease in ROI (Return On Investment) above what would be the ROI foran available, safe, no-risk investment, over a 10-year period.

The profit potential, as an absolute number for a particular proposal(i.e., in dollars per year) is obviously getting higher as the contemplatedscale of production or the sales turnover are higher, while the costs of theprocess development (the risk?) are much less affected by the size, if at all.Thus, a new process could be brilliant and sophisticated, but if its finalproduct has only a small market potential, the straight prospects of approv-ing funds for its development will be dim. Such a proposal then will begenerally presented as a strategic investment, opening the way to (asthe popular joke says, One can save more money by running behind a taxithan by running behind a bus).

At this early stage, the standard economic calculations can only berudimental and based on reasonable assumptions. The bottom-line resultswill generally not be clear-cut either way, but they will indicate mostlyorders of magnitude (so-called back of an envelope calculation type). Thedebatable issues should focus on the degree of confidence that can beattributed to some high-leverage factors, e.g., sale prices, cost of certain rawmaterials, possibly transportation, taxes and customs duties ofexport/import, commissions, royalties, etc. As a result of this review, afact-finding program will be defined to confirm or correct the requiredquantitative assumptions for such critical economic factors, in addition tothe publicly available information.

According to their specific strategic considerations, most corporationswould be ready to gamble a certain percentage (say between 1 and 20%)of the yearly profit potential on the net costs of a comprehensive develop-ment program. Obviously, such a budget would only be released progres-sively, in installments, as certain objectives are achieved with positive results.

5.3 Design and execution of the feasibility tests5.3.1 Purposes of the feasibility tests

Feasibility tests should convince the decision-makers and demonstrate thatthe results from the new aspects can be achieved more or less as expectedin each stage of the process in order to justify a more extensive experi-mental program.



As for the more or less qualification in this context, it is generallyagreed that the better results cannot be obtained in the first attempts, butshould be achieved more likely in the more favorable conditions that will bedefined later, after an extensive process optimization.

It is also realized that such demonstrations can generally be attemptedonly with severe limiting conditions, such as:

Small, bench-scale, batch tests Standard or improvised laboratory equipment and analytical facilities While starting with synthetic clean mixtures and reactants from

the bottle

The results from each stage can either be shown by the direct analysisof the phases obtained after the test or calculated indirectly on the basis ofthose analyses by accepted chemical engineering methods.

For example, a wet filter cake can contain some impurities, which aredissolved into the layer of liquid that is retained on the solids. This layercan be washed out almost completely on a conventional industrial filter, buta similar washing operation cannot be done conveniently on a small-scalelaboratory batch filter with the same results. In this case, the level of theseimpurities related to the retained filtrate can be calculated on the basis ofthe retained water (or of another soluble component) and then deduced fromthe level found in the unwashed filter cake.

5.3.2 Equilibrium conditions

In the limiting experimental conditions mentioned above, a more convenientfeasibility demonstration can be achieved for those process operations that arebased on equilibrium conditions.

For instance, a particular vaporliquid equilibrium system can be gov-erning some distillation, rectification, or stripping operations in the proposednovel process. A reliable calculation of the results from these operationscan be obtained on the basis of the correlation of the composition of thevapor phase with respect to that of the liquid phase at equilibrium. Thetheoretical background for the calculations is well established and severalcorrelation formulas were published on the subject. A limited number ofexperimental points on the particular system under consideration can beinterpolated quite safely and used for such process calculations. All suchpoints connect the two compositions of the phases at equilibrium inspecific external conditions of temperature, pressure, and the partial pres-sure of inert gases present.

Similarly, a liquidliquid equilibrium system can be relevant to a proposedsolvent extraction process. The composition of the two liquid phases, foundin a specific equilibrium test in certain defined conditions, can be translatedinto a distribution coefficient for each of the components of interest. Thecorrelation of this distribution coefficient with the operating conditions can



be used for calculation of a multiple-stage countercurrent process, in whichthe two exit liquid phases from every stage are assumed to be at equilibrium.

Solidsliquid equilibrium data can regulate certain dissolution and precip-itation processes, which are widely used in the inorganic salts industriesand mineral treatments, and also in the production of organic crystals. Inall of these processes, the determination of the quantitative relations forthe solubility at equilibrium, in several conditions in the projected range,can be sufficient, at least for the preliminary process design and feasibilitydemonstration.

5.3.3 Scale up of reactors

The scale up of batch reactions in mixed vessels is well established in chemicalengineering using the reaction kinetic curves and the definition of the mixingregimes. Continuous mixed reactors can also be designed reasonably wellfrom small-scale batch tests, or upscaled from small continuous mixed reac-tors, using correction factors. Thus, the feasibility demonstration of suchreactions can be based on straightforward batch reaction tests.

Similarly, the mixing and the reaction between gases flowing in a pipereactor are also relatively easy conditions for the process feasibility demon-stration on a quite small scale, and for reliable scale up based on hydrody-namics conditions and residence time.

5.3.4 Physical separation operations

The scale up of solidliquid separation equipment has been well estab-lished.21 Many continuous separation operations (solids from liquid or liquidfrom liquid) can be demonstrated, sized, and upscaled quite well from batchtests made in standardized conditions. In this context, the term standard-ized conditions" involves the definition of a particular set of conditions whichare recommended for a batch test in order to obtain applicable results.

For example, the separation obtained in an industrial decanter or thick-ener from a feed suspension into a more concentrated underflowslurry and a clear liquid overflow can be demonstrated and quantifiedfrom a standardized settling test in a 1-liter glass cylinder starting from awell-homogenous slurry (in a thermostatic bath, if necessary). The settlingcurve of the upper limit of the concentrated slurry obtained from each test(see typical example in Figure 5.3) depends on the initial solid concentration,on the differences in density between the solids and the liquid, on the liquidviscosity, and on the degree of flocculation.

The plotting of an empirical settling curve allows the calculation of themaximum solid concentration in the underflow, the level of entrained fines inthe overflow (if any), and the horizontal area of the settler needed, per ton-hour of solids, by the well-established Kinch method following Coe-Clavenger(see p. 4.121 in Chapter 6, Reference 1). This experimental procedure is usedalso for studying the effects of the addition and dozing of flocculating agents.



Similarly, the separation of a cake of solids (including the washing ofthe cake) from a particular slurry in a filter or in a centrifuge can be dem-onstrated and quantified on a small scale with the same type of results.Note, however, that a continuous filter is, in fact, a batch filter that happensto be moving on a belt during the filtration cycle. The difference obtainedin the rate of filtration derives from the operating variables: the pressuredifferential on the filter or the G-forces in the centrifuge, and the hydraulicresistance of the formed cake. Flocculation, however, does not affect sig-nificantly these operations.

5.3.5 Scale-dependant and dynamic flow operations

In contrast with the operations discussed in the above three sections, a feasi-bility demonstration cannot be readily performed for such operations in whichthe results are scale-dependant, such as, for instance, the crystal size distributionobtained in a continuous crystallization (see Chapter 6, Section 6.4).

The feasibility demonstration also cannot be readily performed if themechanisms are based on dynamic flow conditions concerning mostly separa-tions between phases (see Chapter 6, Section 6.3) In such cases, any feasibilitydemonstration has to be connected to a particular equipment choice, and somespecific form of piloting is necessary to determine the dimensions and results.

Figure 5.3 Slurry settling curve Kinch procedure.

time

final

initial

height

settling curve ofsolids front

point of mostrapid change of

slope

Tx



A shortcut sometimes can be found if a logical analogy can be establishedto another known process, which is in actual operation and accessible to theR&D team or their consultants. Then, if it can be established that the newproposed process and the operating process behave more or less similarlyin simple bench-scale tests, this analogy could justify further piloting.

For example, the feasibility demonstration of many proposed wastestream treatments, based on dynamic flow conditions, is very problematic,but these treatments generally fall in a small number of categories.

5.3.6 Extreme conditions

It is not a simple proposition to improvise on laboratory bench-scale afeasibility demonstration for a process operation which has to be done inextreme conditions of temperature, pressure, electrical fields, etc. If such anextreme operation is an essential element in the new process, small testingequipment could probably be specially designed and operated, but thiswould be expensive, require a long time and expertise, and would divertthe teams attention.

In certain cases, small-scale testing equipment with associated services(and valuable advice) can be rented from one of many suppliers of furnaces,kilns, autoclaves, electrostatic and magnetic separators, plasma torches, etc.These suppliers can also provide experienced engineers to perform thesetests, since they are interested in promoting good will towards their know-how. The main concerns against such services are the unavoidable secrecyleaks and possibly the geographical distances.

If the extreme operation is a self-contained side element in the newprocess, it should be well defined, isolated, and subcontracted to one of thesespecialized suppliers.

5.3.7 Actual raw materials

In certain processes, it can be very important to perform such feasibility testswith the actual raw materials, since a synthetic mixture cannot duplicateexactly the complex phases structure and/or the compositions of these mate-rials in which a large number of impurities can sometimes be involved.

In many actual projects, the use of certain raw materials in later testsdid result in serious nonexpected problems; for example, the precipitation ofsolids causing incrustation on the walls of the equipment and pipes, or atendency to emulsify, or the precipitation of colloid suspensions, or a coloringphenomenon, etc.

In other cases, the reaction kinetics with the actual solid raw materialswas much slower (by orders of magnitude) than the reaction kinetics withthe synthetic mixtures.

If a practical solution to such troubles cannot be provided in time andincluded in the proposed industrial process design, the project will bekilled sooner or later, at least in its initial form. Therefore, it is important



to discover these problems as early as possible by using representative samplesof the actual raw materials in the feasibility demonstration tests.

Unfortunately, such representative samples cannot always be procuredat the start. This difficult situation was typically encountered when the newprocess involved the treatment of mineral concentrates from new depositsthat, as of yet, have not been fully explored, or the down-stream treatmentof some material that was expected from certain future operations.

5.3.8 Analytical difficulties

In some situations, the available analytical laboratory personnel may nothave previous experience with the exact type of analyses required for thesefeasibility tests and they will have to learn, introduce, and calibrate newmethods. This can be a lengthy procedure, and the time needed can possiblybe reduced with outside help. The allocation of priority in this area, or theneed to compromise on a second-best method, had often caused delaysand personal tension.

5.4 Analysis of the results from feasibility testsWhen these results become available, it is advisable that the promoting teamprepares and presents two separate reports, which will be studied and dis-cussed in different contexts and review meetings (sometimes again manyyears later).

1. A report on the results of the feasibility tests, which should bepresented in the normal format for R&D experimental reports witha complete description of all the laboratory procedures and equip-ment, all data collected, and, in particular, any observation aboutunusual features.

2. Another report discussing the significance of the experimental resultsand observations from these tests, as regards the process feasibilitydemonstration and the design issues of the proposed novel process.This report may also include further chemical engineering calcula-tions or economic evaluations.

The discussion in this report should also define exactly a limited rangefor each of the variables to be covered in any future experimental programas basis for the process design.

5.5 Second review of the process definitionThe forum of the second critical review is generally reconvened by thedecision-maker along with participating colleagues (peers) and the called-in experts to study and review the different reports that were distributed inadvance and in writing. The reports include:



Feasibility demonstration tests Patent discussions Clarification of the critical economic factors

This second review can end up in one of the following ways:

A. In most cases, the analysis and discussion of these reports wouldgive the green light for proceeding with the experimental program(see Chapter 6), the preliminary process design (see Chapter 7), and theeconomic analysis (see Chapter 8). If this program is agreed upon, thiswould be the appropriate time to formalize a contract transmittingthe implementation rights from the promoters to the corporation. Thecorporation would then confirm the appointment of a project managerto carry on the responsibility of the future program. This managerhas most probably already been a member of the process evaluationteam up to this point.

B. In other cases, the results and calculations could indicate a need tocorrect or readjust some of the initial process working definitions. Thefile would be given back to the promoters for the repeat of certaintests, additional reports, and back for another similar review.

C. In certain cases, the continuation of the project could not be logicallyjustified in the present framework, and it would be terminated at thispoint, at least until the promoters prayers for some surprising de-velopment are granted.

5.6 Worth another thought

An essential starting point is a preliminary process definition to bringeverybody concerned to an explicit common reference basis, illustratea concrete venture, outline a proper experimental program and startits detailed design while focusing on the limited scope of applicationthat is of interest in real life, and allowing for a more effective allo-cation of the available industrial R&D resources. This process work-ing definition will be based, in a large part at the beginning, onweighted and explicit assumptions and on previous professional ex-perience, but it will be progressively changed, enlarged, and refined.However, such a working method has often been resisted and evenridiculed by senior scientists who were used to the open-ended ac-ademic research approach.

A novel process could be brilliant and sophisticated, but if its finalproduct would have only a small market potential, the straight pros-pects of approving funds for its development will be dim. Such aproposal will then be generally presented as a strategic investment,opening the way to new potential products.



The feasibility tests should convince the decision-makers and dem-onstrate that the results from the novel aspects in each stage of theprocess can be achieved more or less as expected to justify a moreextensive experimental program.

References1. Biegler, L.T., Grossman, I.E., and Westerberg, A.W., Systematic Methods of

Chemical Process Design, Prentice Hall, New York, 1997.2. Douglas, J.M., Conceptual Design of Chemical Processes, McGraw-Hill, New

York, 1988.3. Duncan, T.M. and Reimer, J.A., Chemical Engineering Design and Analysis:

Introduction, Cambridge Press, London, 1999.4. Seider, W.D., Lewin, D.R., and Seader, J.D., Process Design Principles: Synthesis,

Analysis, and Evaluation, John Wiley & Sons, New York, 1999.5. McCabe, W.L., Smith, J.C., and Harriot, P., Unit Operations in Chemical Engi-

neering, 5th ed., McGraw-Hill, New York, 1993.6. Hicks, T.G., Ed., Standard Handbook of Engineering Calculations, Section 6.

Davidson, R.L., Chemical Engineering, McGraw-Hill, New York, 1972.7. Clarke, L. and Davidson, R.L., Manual for Process Engineering Calculations,

McGraw-Hill, New York, 1975.8. Branan, C.R., Rules of Thumb for Chemical Engineers, 2nd ed., Gulf Publishing

Co., 1998.9. Meyers, R.A., Handbook of Petroleum Refining Processes, 2nd ed., McGraw-Hill,

New York, 1996.10. Perry, R.H. et al., Chemical Engineers Handbook, various editions, McGraw-

Hill, New York, 1999.11. Froment, G.F. and Bishoff, K.B., Chemical Reactor Analysis and Design, 2nd ed.,

John Wiley & Sons, New York, 1990.12. Smith, J., Chemical Engineering Kinetics, 3rd ed., McGraw-Hill, New York, 1990.13. Schmidt, L.D., The Engineering of Chemical Reactions, Oxford University Press,

Oxford, 1998.14. Fogler, H.S., Elements of Chemical Reaction Engineering, 3rd ed., Prentice Hall,

New York, 1998.15. Levenspiel, O., Chemical Reaction Engineering, 3rd ed., John Wiley & Sons, New

York, 1998.16. Butt, J.B., Reaction Kinetics and Reactor Design, 2nd ed., Marcel Dekker, New

York, 1999.17. Honig, J.M., Thermodynamics Principles Characterizing Physical and Chemical

Processes, 2nd ed., Academic Press, New York, 1990.18. Klotz, I.M. and Rosenberg, R.M., Chemical Thermodynamics: Basic Theory and

Methods, 6th ed., John Wiley & Sons, New York, 2000.19. Coulson, J.M. and Richardson, J.F., Chemical Engineering Fluid Flow, Heat Trans-

fer, and Mass Transfer, different editions, last 6th eds., Butterworth-Heineman,Oxford, 1999.

20. Rohsenow, W.M. et al., Handbook of Heat Transfer, 3rd ed., McGraw-Hill, NewYork, 1997.

21. Purchas, D.B., Ed., Solid/Liquid Separation Equipment Scale Up, Upland Press,Croydon, U.K., 1977.



22. Mizrahi, J., New process producing phosphoric acid from phosphate rockand hydrochloric acid via ferric phosphate, paper presented at the Int.Solvent Extraction Conference, Barcelona, July 1999. Also Israel Patent120,963, June 1997.



Developing an Industrial Chemical Process, An Integrated ApproachTable of ContentsChapter 05: Process definition and feasibility tests5.1 Translation of the idea into a process definition5.1.1 Scope of the preliminary process definition5.1.2 Comprehensive literature survey5.1.3 Block diagram5.1.4 Quantitative definitions of the different sections5.1.5 Process calculations for the preliminary process definition5.1.6 Presentation of one feasible implementation formula5.1.7 Possible industrial implementation framework5.1.8 Timetable5.1.9 Important note

5.2 Critical and systematic review of the process definition5.2.1 Review forum5.2.2 Fundamental process issues5.2.3 Patent situation5.2.4 Profit potential

5.3 Design and execution of the feasibility tests5.3.1 Purposes of the feasibility tests5.3.2 Equilibrium conditions5.3.3 Scale up of reactors5.3.4 Physical separation operations5.3.5 Scale-dependant and dynamic flow operations5.3.6 Extreme conditions5.3.7 Actual raw materials5.3.8 Analytical difficulties

5.4 Analysis of the results from feasibility tests5.5 Second review of the process definition5.6 Worth another thoughtReferences

Date post:	10-Sep-2015
Category:	Documents
Upload:	vasucristal
View:	213 times
Download:	0 times

1360_Ch05

Documents