Engineering: Residence Time Distributions
L. Levine. Leon Levine & Associates, Albuquerque, NM. Cereal Foods World 53(4):244-245.
Over the years, I have discovered that residence time distributions are often misunderstood. In that light, I’ve decided to devote a few columns, beginning with this one, to the subject. First we should define what a residence time distribution is and where the concept comes from. The idea of residence time distributions comes from classical chemical engineering literature on the design of chemical reactors. The idea is a fusion of the concepts of probability theory and chemical reaction kinetics. It is best explained by example. In a batch process, every “particle” of the material being processed, if we neglect filling and emptying of the batch, stays in the process for exactly the same period of time, the total batch time, or residence time of the process. Now, if one were to convert this process from a batch operation to a continuous operation, one would want to end up with the same degree of reaction. In order to theoretically do this, we would need to design a process for which every particle stays in the continuous process for the same time as in the batch process. Such a process is not, for simple mechanical reasons, really possible to design, but through various mathematical means, we can calculate residence time distributions.