SYNTHESIS OF NON-SHARP SEPARATION SEQUENCES

This dissertation deals with the generation, and search for the few better ones, of ordinary distillation schemes, for separating a multicomponent feed into desired products. The emphasis is placed on product specifications such that feed components are present, in appreciable amounts, in more than one product, a case termed "non-sharp (sloppy) product set". Such sets lead naturally to distillation units with incomplete separation of the key components, including one-section columns (rectifiers or strippers) and single-stage flash units. Furthermore, stream bypassing around separators, as well as stream splitting into parts that undergo different processing in parallel, are permitted. Restrictions imposed are that product fragmentation can occur only at sharp separators, or via feed bypassing, and that sequences cannot have separators (in series) with identical key components. Also no stream recycling is considered.;A heuristic ordering of separation options, coupled with a depth-first application on a matrix representation of a stream, is proposed for generating schemes containing up to a given number of separators. In a distinct, second step, a best-first technique identifies the few better schemes. Heuristic rules are employed to (sub)optimize the partially developed sequences. For an example problem, of four components and four products, savings in annual cost of 42% were realized using the techniques of this work, over the best among the sequences that completely isolate (and remix) the feed components.