Evolutionary synthesis of separation processes

Abstract

sequence of separation units that will isolate desired products from given feed at the minimum cost. Multicomponent products can be specified. An evolutionary Drocedure is Dresented. This method consists of two Dhases. In the first Dhase. a &od initial siructure is created by heuristic methods. In the second phase, the initial structure is successively modified by making evolutionary structural changes. This logic has been programmed on a digital computer and has been tested on several problems. Seader and Westerberg (1977) have addressed the same problem. This work is an extension of the latest work in the field, combining eight heuristic selection rules to provide an initial structure and five evolutionary rules plus a strategy to refine the separation sequence configuration.The product set, the key components, the type of separator, the mass separating agent, if required, are chosen in a systematic way with the help of a heuristic evaluation function. The product set and product recoveries are specified by the user, but the program redefines the product set if it is cheaper to isolate separate species in a product and remix. The system handles distillation and extractive distillation separator types (with any of several mass separating agents) and can readily be extended to other separator types. Recovery and recycle of mass separating agent will be delayed, if the cost of processing will be reduced by using the same agent in several serially connected columns. The final criterion of quality is the total annual cost of the complete sequence, fixed charges plus operating cost. CONCLUSIONS AND SIGNIFICANCEAn evolutionary approach to the synthesis of sharp separations has been proposed. The synthesis problem is decomposed into two phases. In the first phase, an initial feasible structure is created by using heuristic rules. In the second phase, the initial structure obtained in the first phase is successively improved by applying evolutionary rules. The heuristic rules embody knowledge of the general behavior of separation units and separation sequences, and the evolutionary rules question the validity of these heuristic rules for the particular problem under consideration. This approach closely mimics the problem-solving procedures commonly employed by engineers, especially with regard to relatively large systems.The proposed procedure does not suffer from t h e shortcomings of the dynamic programming based synthesis procedures such as the one proposed by Hendry and Hughes (1972). The calculations are performed only on the subproblems selected by the heuristic and evolutionary rules thereby reducing the amount of computer time used. The proposed procedure also does not suffer from the problem of "cycling" (Thompson and King, 1972), since separation types are not selected on the basis of estimated costs. The proposed procedure is practical and has been tested on several problems. For each problem, the procedure creates the best separation sequence in a reasonable amount of computational time.In the course of pro...

Mass/heat‐exchange network representation of distillation networks

“…Heat integration of distillation columns has also been discussed in the context of separation system design as far back as 1974 (Rat-hore et al, 1974a,b). Many articles have analyzed the problem of using such tools as branch and bound (Morari and Faith, 1980), evolutionary design (Nath and Motard, 1981;Umeda et al, 1979a,b), thermodynamic availability (Naka et al, 1982), pinch design (Dundorf and Linnhoff, 1982;Linnhoff et al, 1983) and utility bounding (Andrecovich, 1983;Andrecovich and Westerberg, 1985), among others.…”

“…By doing so, the scope of previous definitions of the problem (Rudd and Watson, 1968; Nath and Motard, 1978; Nishida et al, 1981;Westerberg, 1985) is enlarged, including the possibility of using classical distillation one-feed, two-product columns, but also allowing the usage of massseparating agents, the incorporation of power-supplying utilities such as compressors, the undertaking of the separation task at various pressure levels and the usage of thermodynamic cycles such as heat pumps. Driven by the energy crisis of the 70s, minimization of utility consumption has been the primary goal of process design for many years.…”

Multicomponent products separation process synthesis with separation sharpness.

“…2. It is noticeable that there are two subproducts (4,5) in the same outflowing stream. Secondly, the compositions of these subproducts can be computed from the degrees of separation sharpness based on their separation histories.…”

Separation synthesis of multicomponent feed streams into multicomponent product streams

“…It is apparent that due to many complications involved in problem P2 there has not been developed a synthesis approach that can tackle the problem in an efficient and rigorous manner. Nath (1977) presented a case study of a subproblem of P2, that is the separation of a single multicomponent feed stream into two multicomponent products, which we will consider as problem P3. In this case study two structures are determined directly by the use of several heuristic rules that are case-study dependent, and it is not clear how to extend this method to cases where the number of species in a product is more than three.…”