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A hierarchical design procedure for solids processes

Shankar Rajagopal, University of Massachusetts Amherst


Solids processes are an important part of the chemical process industries. Roughly 60% of the petrochemical processes involve solids processing in various stages. In spite of this fact, little attention has been paid systematic design procedures for solids processes. The goal of this research is to provide a systematic procedure for the synthesis/conceptual design of solids processes. We have developed a hierarchiral conceptual design procedure for a limited class of solids processes. This procedure will help in systematic selection of the process units and their feasible interconnections, as well as in the identification of important design variables in the process and their associated trade-offs. All the important process alternatives can also be identified and systematically evaluated by this procedure. The results obtained from this procedure will be mainly helpful in obtaining a quick, preliminary estimate of the best alternative. For more detailed design, conventional simulators can be used or the alternatives can be consolidated into a superstructure and then can be solved more rigorously for the optimum conditions using nonlinear optimization packages like MINLP. In the process of generalizing our hierarchical procedure, we have identified two new extractive crystallization process flowsheet alternatives that can be used to separate a wide range of binary mixture of components with different solid-liquid phase behaviors, and we have formulated the design equations for both of these alternatives. The new flowsheet alternatives with two crystallizers and two filters have also been compared with the traditional alternative, which uses three crystallizers and three filters, and are found to be much more general and economically more attractive. The feasible region of operation of these crystallizers have been identified for a general problem, and all the other constraints on the important design variables have been formulated. In the case of separation of a mixture of solid components, we have identified a new flowsheet alternative to the conventional selective dissolution and crystallization technique. Using this technique, the order of separation of the solid components can be modified. This new alternative can also be used to separate components with very different solubility--temperature behavior. This alternative is essential to selective crystallization of a particular component during the process of separation. Two important fractional crystallization process flowsheet alternatives have been compared on the basis of the final product purity obtained for different values of fractional recovery of the product and new heuristics have been identified. This hierarchical procedure has also been implemented into a computer code so that it can be tested for a variety of solid process case studies.

Subject Area

Chemical engineering

Recommended Citation

Rajagopal, Shankar, "A hierarchical design procedure for solids processes" (1991). Doctoral Dissertations Available from Proquest. AAI9120930.