Two Answers to the Question
How Important Is the Pilot Plant? This is no easy pro and con issue, but opinion differs among chemical engineers from
‘‘Indispensable
”
“A Trend Away” Design
frocess Development In-many instances, there is a tendency to curtail unjustifiably or even omit completely, the pilot plant stage in process development. This frequently results in a pennywise and pound-foolish situation. Baekeland’s classic comment, “Commit your blunders on a small scale and make your profits on a large scale,” still applies. Start-up of a new process is tricky a t best, but it is made worse by unforeseen difficulties. When a new plant produces an off-specification product, yields are low, and costs in time and material are high. Corrosion develops, surface-volume effects are encountered, impurities build up in recycle, and a million other things seem to go wrong. Frequently, despite advances in using models and scale-up techniques, certain factors cannot be detected unless the process is carried out under conditions approaching those of the planned production unit. Corrosion alone can be a major problem and sometimes in process development it develops in peculiar ways. Crystals for subsequent recovery by filtration grow differently in production-type equipment than they do in a round-bottomed flask vigorously stirred with a laboratory mixer. Models and scale-up relationships, useful now, will become even more dependable as additional data are developed. But these are only additional tools for process development and design-they will not replace the pilot plant, which will remain a valuable and necessary step. For design engineers also, who are charged with devising a production unit, good pilot plant data will continue to be a valuable aid.
JAMESA. KENT University of West Virginia
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In 1954, Michel, Beattie, and Goodgame published the results of a survey on scale-up practice. With the exception of plate and frame filters, rotary filters, and hammer mills, design engineers felt that reliable scale-up of all unit operations considered could be achieved from laboratory data without an intermediate pilot plant development phase. How valid &e these findings? Do they indicate a trend away from the use of pilot plants for design information? The answer is tentatively “yes.” This conclusion is supported by several factors : The design engineer not only has a continually growing fund of data and experience to draw on in solving his scaleup problems, but his confidence in applying this information correctly is constantly increasing. New and vastly improved experimental techniques are becoming available : more precise analytical methods, analog and digital computer analysis, statistical control of experiments, use and interpretation of model studies. Thus more exact correlations are possible because basic phenomena are better understood. What obstacles are encountered by those who advocate less use of pilot plants for obtaining design information? Design and development engineers frequently form prejudices resulting from their knowledge, lack of knowledge, or experience. Laboratory investigators may not understand the design problem and fail to collect the type of laboratory data later needed by the design engineer. Also, management may lack the confidence or gambling instinct needed when it comes to risking the capital involved in a large commercial venture that has not been piloted. We are all familiar with instances where difficulties in operating a pilot plant arose from deficiencies in the plant itself rather than from the process-in a commercial plant, these problems may disappear or never exist. Whether or not pilot plants are needed for design information may be irrelevant. The real objective, of course, is to achieve successful commercial operation with optimum cost, confidence, and time. Thus it seems that use of pilot plants for routine design purposes may be abated without compromising the success of the commercial venture. R.B. FILBERT, JR. Battelle Memorial Institute
A. 1. FRYE, Minnesota Mining and Manufacturing Co., Symposium Chairman VOL. 50, NO. 4
APRIL 1958
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