Unit Operations in Action
Lewis himself offers perhaps the best example of the new profession at work. During the 1920s and 1930s, one of the few clouds shadowing the explosive growth of the American automobile industry was the high cost and difficulty of refining high-grade fuel. A significant fraction of that cost could be traced to one vexing problem: all the refining techniques then in use produced a layer of carbon that gunked up the equipment, forcing operators to interrupt the refining process after frustratingly short periods of operation. The only way to get continuous operation was to build two refineries and put one online when the other was being cleaned. Many people took a crack at this problem; eventually Doc Lewis got involved.
After beating his head against the wall for a bit, Lewis, who was working with another MIT professor, Edwin R. Gilliland, dreamed up an ingenious solution to the problem. By the mid-1930s, refinery engineers had discovered materials, typically clays, that accelerate the chemical reactions that shorten hydrocarbon molecules and improve their octane ratings. Engineers arranged clay grains on a fixed bed and passed hydrocarbon vapor through them. -Unfortunately, the clay particles quickly became covered with carbon. To address this problem, engineers began experimenting with fluidized beds, in which hydrocarbon vapors are forced through the clay grains from below, causing the grains to float. Lewis knew that, in theory, it would be possible to persuade these grains to flow into a separate tank for cleaning. Since the particles were too abrasive to be handled by pumps or conveyors, Lewis borrowed an idea from fluid mechanics – unit operations in action – and used the pressure generated by forcing the hydrocarbon-vapor and grain mixture through a column to drive the particles where they were needed. Today, these columns define much refinery architecture.
The first refinery built around the process, called fluid catalytic cracking (FCC), started operation in 1942. It worked brilliantly and was immediately pressed into use for the war, giving the Allies adequate supplies of fuel, especially the high-octane fuel used in airplanes. After the war, FCC was generalized into a whole new unit operation, the fluidization and transport of solids, and spread to dozens of sectors, from uranium processing and coal gasification to the incineration of solid waste and the manufacture of semiconductors and soy sauce.
Lewis retired from MIT in 1948 and died in 1975. He did so much to change the world, and yet he would not have recognized the landscape he helped create. Today, 56 percent of Course X undergraduate students are female, whereas Lewis operated in a man’s world; women were unusual and put a cramp in his colorful style. Likewise, chemical engineering is increasingly shifting its focus to biotechnology, and administrators at MIT now worry quite a bit about how their students are feeling. Most important, the fraternity of the engineer has been at least partially dissolved by the increasing complexity of industrial processes. Today, more than ever, engineers do anything and work with anybody to solve the problems at hand. The definition of the very term “engineer” is beginning to blur.
But Lewis would have had every reason to look on his legacy with pride. In helping establish a new profession, he gave many young men (and a few young women) the common identity of chemical engineer. He gave them a virtuous calling. He gave them their grip on life. Even more broadly, Lewis was a great problem solver: optimistic, ingenious, indefatigable. It is hard to look at his photos and not want to break the glass, to turn him loose on the problems caused by our own damned blockheadedness.
Sidebar: The Prose That Launched 10,000 Careers
Excerpted from the preface to the first edition of Principles of Chemical Engineering
Just as the arts of tanning and dyeing were practiced long before the scientific principles upon which they depend were known, so also the practice of Chemical Engineering preceded any analysis or exposition of the principles upon which such practice is based. The unit operations of chemical engineering have in some instances been developed to such an extent in individual industries that the operation is looked upon as a special one adapted to these conditions alone, and is, therefore, not frequently used by other industries. All important unit operations have much in common, and if the underlying principles upon which the rational design and operation of basic types of engineering equipment depend are understood, their successful adaptation to manufacturing processes becomes a matter of good management rather than of good fortune.
In this book we have attempted to recall to the reader’s mind those principles of science upon which chemical engineering operations are based, and then to develop methods for applying these principles to the solution of such problems as present themselves in chemical engineering practice. We have selected for treatment basic operations common to all chemical industries, rather than details of specific processes, and so far as is now possible, the treatment is mathematically quantitative as well as qualitatively descriptive. We venture to hope that the book will stimulate engineers to design apparatus adapted for any particular purpose, rather than just to build it and then to rely on large scale experimentation with expensive changes in construction to effect efficient operation.
William H. Walker
Warren K. Lewis
William H. McAdams
Cambridge, Mass., February, 1923