Vapor/liquid mass-transfer columns often must contend with solids. A systematic approach and proper hardware selection are the keys to optimizing operation.
Many distillation, absorption, and stripping columns operate
with solids present in the system. The presence of solids may
be either intentional or unintentional. But, in all cases, the
solids must be handled or tolerated by the vapor/liquid mass-transfer
equipment. Such solids should be dealt with by a combination of
four methods. From most favorable to least favorable, these are:
1. keep the solids out;
2. keep the solids moving;
3. put the solids somewhere harmless; and
4. make it easier to clean the hardware.
The key precept for all these approaches is the realization the solids present in a system just don't disappear. Schantz and Elliot sum-marized this succinctly by stating, "Solids never die - they just move around." In this article, we review the techniques and design issues involved in making a vapor/liquid mass-transfer system operate with solids present. We assume that the solids cannot be kept out, elimi-nating the first choice. The type of mass-transfer service does not matter. The same principles apply equally well to distillation, adsorption, and stripping.
We include equipment design criteria based on the methods outlined above. Detailed recommendations will be included for each of the major equipment choices that can be made for mass-transfer devices. Then we illustrate the approach via an example)a vinyl chloride monomer (VCM) unit having solids as an inherent part of its feed.
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