I/EC
SPECIAL
some contaminant which interferes with the reaction? If the latter, how do we clean it up? If the amount of the impurity formed is small a n d / o r the tolerance for it in the reaction is high, it m a y suffice to remove a purge from the stream. If the solvent is cheap enough this purge may be burned. If not, it will be necessary to clean u p the purge stream. Perhaps the tolerance of the process for the impurity formed may be such that the entire recycle stream has to be processed. A common method of dealing with this on the preliminary flow sheet is to show a topping column to remove low-boiling impurities, then to distill the solvent overhead from the high boilers. This latter step gets expensive, as all the solvent is vaporized and condensed, plus some for reflux. Will a n adsorbent such as silica gel or activated carbon replace the column economically, or perhaps remove both low boilers and high boilers, thus replacing both stills? Has the recycle process been operated long enough to demonstrate feasibility? T h e r e have been cases where the cost of treating the recycle streams has upset process economy when unsuspected impurities a p peared and proved difficult to remove. Looking again at the two-still alternative for cleaning u p this solvent, if A a n d B are waste materials, a n economic balance can usually indicate how m u c h solvent we can afford to lose with each. But how much A and how m u c h B can we tolerate in the recycle stream? W e may first expect the answer, " N o n e . " T o which we facetiously reply, "Fine, let's stop and get another process because this will require two columns of infinite height." O r we may say "As little as possible." But how much is this? O n e per cent? One gram in a ton? T h a t sounds like very little, but there are cases where such a concentration could kill a valuable catalyst—or a customer. Equipment can be at least approximately sized and possible problems can be defined long before they would be met in the final plant de- sign. Consider a recent case where a flow sheet called for a conveyor to move a product from a dryer to a bin to feed the next process step. T h e layout of the proposed plant was such 64 A
FEATURE
that a pneumatic conveyor looked attractive, so one pertinent question was, " W h a t are the explosive limits of this powder in air?" Research personnel were not sure it would burn. Touching a m a t c h to a bit of it on an ash tray quickly answered that question; and some of the dreamed-of uses for this material based on its nonflammability disappeared in the same puff of smoke. This one factor completely revised the magnitude of this program by drastically reducing the market potential of the product. Sizing for the Future Another important consideration in the design for a commercial plant is the extent of expansion plans or the probability of eventual expansion. If the market analyses indicate an increase in product sales in the reasonably near future, it m a y be economical to oversize some of the facilities. This is frequently true particularly for service facilities. T h e costs involved in this approach can be compared with the costs of providing additional complete lines. Early in the research effort, estimates must be m a d e of the profits which will come to the company if the research is successful. These earliest estimates should be optimistic, but this optimum should not transgress the bounds of probability. As soon as possible, preliminary flow sheets are d r a w n complete with energy and material balances and equipment is chosen, sized, and estimated as previously discussed. I n choosing and sizing equipment it will be necessary to make assumptions. With reasonably optimistic assumptions, one must be able to show a profit on the process. If such profit is lacking, so is the incentive for further research. Before the research has progressed much further, sufficient data will be at hand to estimate a process for a commercial plant which will % produce the required quality and quantity of product. If the profit on such a sure process is attractive, the time to build a plant is approaching, as early realization of profits is important. At first the conservative plant may not offer sufficient profit. An examination of the differences between the optimistic and conservative estimates should point out the areas re-
INDUSTRIAL AND ENGINEERING CHEMISTRY
quiring further research. As research throws more light on the subject, some of the optimism will disappear from one side, some of the pessimism from the other. At last a point is reached where the difference between the two estimates does not justify further research. Now the decision can be m a d e to build the plant or to drop the project and start on something more promising. We have been using this method of "converging estimates" more or less informally for years without necessarily calling it by that n a m e . Economic evaluations of this nature can be carried out on individual process steps and alternate equipment items as well as for the complete facilities. Besides such work toward designing the finished plant, engineers can assist the research and development people in designing or scaling a pilot plant or semiworks unit. M u c h of this work is similar to directing the work effort toward the full scale plant. Where pilot or semiworks facilities are desirable, the best approach is to visualize the commercial plant first, and to size the pilot unit by scaling down from the plant concepts rather than to scale u p laboratory glassware to a pilot plant. T h e necessity for designing the commercial unit from information developed in the pilot plant clearly indicates this course, which eliminates headaches that otherwise result during scale-up. During the design of a pilot plant, insight is gained into such items as utility requirements and potential maintenance problems which are likely to be encountered in the commercial plant and provision is m a d e for their evaluation. T h e need for specific development work requiring specialists is defined at a n early stage. Organized communication is the key to adequate engineering assistance. T h e thinking of each one of the many different interests represented in any new facilities must be considered. This thinking must be contributed at the proper time for every industrial project. It must have the required breadth to permit effective design work. T o keep the entire program " o n the b e a m " requires early and complete analysis of the project, accurate scheduling, and continual liaison, follow-up, review, and reporting.
his vessels. As a result, perhaps he follows the line of least resistance and carries out his work at "room temperature." H e may not have determined what effect a higher temperature will have on yields or quality. It may turn out that the plant's cooling water is 30° C. or even hotter during the summer, and even a 50° C. process temperature may be difficult to hold on a commercial scale. In order to attain temperatures of 25° to 30° G. in the plant, several hundred thousand dollars worth of refrigeration may be necessary. T h e engineer reviews the process and asks, " C a n we increase this operating temperature? W h a t are the limits of operating temperatures?" T h e r e are Raw Material
-^— Reaction
^^^^^^^2j^st
Separation
Solvent Recovery
Product Engineering assistance can help decide what kind of reactor to use or how to separate the product
several possible answers: "The product cannot tolerate the high temperature." If this is true, the only alternative to abandoning the process is to provide refrigeration. "The operating temperature can be set by economic design." This is often true, but without experimental proof of adverse chemical or quality consequences one takes an unknown risk. "We can get the answer. We don't know yet, but we will find out." "Finding out" may result in considerable delay of the project. How much better to realize the need to find out while carrying out the basic process development work. "We don't know, but it will delay us too much to find out. We know we can operate using refrigeration." Unfortunately, if assessing such factors is delayed and if the project is attractive even with the questionable facilities included, it might seem necessary to proceed on such a safe basis, saddling the business with the
load of added investment. Unhappily, 5 or 10 years later when the plant is expanded, the matter may still be unresolved and the questionable step retained at further penalty. A still less fortunate consequence may be that the resulting high cost and investment may limit the market, and expansion may not be possible.
What Are Researc] A s s i s t a n c e Engine Made Of?
A review of the research and development program by the engineer with plant design experience can assure that the necessary data are developed to permit adequate design of the facilities. T h e degree of precision required of the data can also be indicated to guide the research m a n . T h e second major area for engineering assistance is in visualizing the final plant facilities. Here the engineers must start with the results of market evaluations in the form of forecast production schedules. This, obviously, determines the size of the plant. Following this, utilizing the process data developed by the research m a n , the engineer prepares flow sheets and the material and energy balances required to describe the plant in terms of design criteria. T h e work done in preparing or analyzing flow sheets will usually point up the need for data which have not yet been obtained. Choosing specific equipment to fit these flow sheets will indicate special measures which have to be taken in design out of consideration for safety, cost, or quality. This work will highlight areas where alternative processes or steps may be more economical or warrant further evaluation. T a k e a process wherein a material and a solvent are fed to a reactor, a reaction takes place, the solvent is separated from the product and recycled. A n u m b e r of choices immediately face the designer. For instance ; W h a t type of reactor shall be
Process Experience •
^
Technical Areas^V'orH En^pering EccHbics V
F * ;, used? How do we get the heat out or in? D o the surfaces remain clean? W h a t is the rate of reaction? W h a t pressures and temperatures are necessary? How much variation can be tolerated? How do we separate the product? (Distillation? Filtration? Centrifuging?, etc.) Assume that a centrifuge is selected to remove a solid product from the recycle stream. T h e product will usually be wet with solvent. If the solvent is valuable (and it usually is unless it is water), it must be recovered. How will this be done? If by a dryer, what type will be used? Has the solvent sufficient vapor pressure to permit easy drying, or is its volatility so high that condensation with available water will be impossible or require high pressure? Is the solvent suitable for recycle as it comes from the centrifuge, or will it contain
"A" to Burner
Impure Solvent from Separation and Recovery
Topping Still
Pure Solvent to Process
" B " to Burner One w a y to clean up the solvent VOL. 50, NO. 9
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SEPTEMBER 1958
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S P E C I A L
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Engineering Assistance to Research and Development W . S. GILFOIL and L. E. RASMUSSEN Engineering Department, E. I. d u Pont d e Nemours & Co., Inc., Wilmington, Del.
It can help in minimizing both investment and operating costs H o w Engineers Can Help Turn Research into Commercial Products ^
Assist in programming o f R & D t o obtain all the information needed for p l a n t design as quickly as possible
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A i d in visualizing plant facilities
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Prepare cost estimates
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Assist in designing and scaling pilot plant o r semiwork units
VV HY are engineers so concerned about research? General experience in the chemical industry shows that for every dollar spent on research, $3 will be spent for construction. In recent years, the chemical industry has been spending more than $400,000,000 a year on research and development work. This results in an average annual rate of expansion and construction of production facilities of well over 1 billion dollars. That is a lot of engineering and it is also the answer to the question.
Engineering K n o w - H o w : a Must
It is essential that the engineers providing assistance to research and development organizations have a broad background of industrial process experience. In obtaining this background, these engineers have developed judgment in determining what will make a sound commercial process. They can visualize the various choices that are available—• not only in the over-all process, but in the individual process steps. The research assistance engineers
$400,000,000 62 A
INDUSTRIAL AND ENGINEERING CHEMISTRY
$1,000,000,000
must also have know-how in fundamental technical areas and in engineering economics. They must have an understanding of the chemistry of the process; they must be able to analyze the economic consequences of various decisions which are made in the laboratory. These decisions may involve utility requirements, raw material specifications, or finished product qualities. Finally, these engineers must have an uninhibited and an unbiased attitude. Effective research and development work requires enthusiasm. Those engaged in such activities must exhibit a high personal identi-* fixation with their developments. They may even be pardoned for thinking, "This is good, because I developed it." Engineering Caution: Desirable
In programming research and development studies, the engineer should aid in setting up the proper timetables and routes to be followed. It is important to be first in the market place with an acceptable product. But it is also important not to forget that a costly process, developed in our zeal to get there early, may also be the first one out of the market place. Engineers can assist in outlining the range of test programs to determine desirable operating conditions. The research man does not always realize that because of the conditions in his air-conditioned laboratory, it may, for example, become necessary to provide extensive refrigeration in the commercial plant. A given reaction may occur nicely in the laboratory at room "temperature with ready control of evolved heat. The researcher working on a small scale may experience no difficulty in holding a temperature of 25° or 30° C. Heat is easy to remove on a small scale and the researcher usually has ample cold tap water available. In fact, it may be simpler for him to carry out his research at such a temperature than to hold an elevated temperature in the order of 50° C. in
