This work proposes an optimization model for heat-exchanger network synthesis that includes a heat-exchanger design model. This model takes into account several detailed design variables: number of tubes, number of tube passes, internal and external tube diameters, tube arrangement pattern, number of baffles, head type, and fluid allocation (i.e., to the shell or tubes). The network superstructure with individual heat-exchanger designs is solved using the logic-based outer approximation method (Turkay, M.; Grossmann, I. E. Comput. Chem. Eng. 1996, 20, 959-978). An interesting feature of the model is that it contains disjunctions for topology selection, which in turn has disjunctions for the heat-exchanger design. The proposed model determines the heat-exchanger network that minimizes the total annualized cost accounting for area, pumping, and utility expenses. Examples are presented to illustrate this method.
This paper addresses the optimal design of shell-and-tube heat exchangers via a mathematical programming approach. It is shown that it is possible to develop a design model for shell-andtube heat exchangers that takes into account some important construction variables: number of tubes, number of passes, internal and external tube diameters, tube arrangement pattern, number of baffles, head type, and fluid allocation (i.e., the allocation of the fluid streams to the shell or tubes). The model is based on generalized disjunctive programming and is optimized with a mixed-integer nonlinear programming reformulation to determine the heat-exchanger design that minimizes the total annual cost accounting for area and pumping expenses. Examples are presented to illustrate the model performance.
This paper presents an explanation of why methyl tert-butyl ether (MTBE) production by reactive distillation may yield multiple solutions. Widely different composition profiles and conversions may, as already reported by Krishna and others, result with identical column specifications, depending on the initial estimates provided. A hypothesis yielding a qualitative understanding of this phenomenon has been developed. The inert n-butene plays a key role in the proposed explanation: As the reaction mixture is diluted with n-butene, the activity coefficient of methanol increases substantially and the temperature decreases. This dilution has a profound effect on the equilibrium conversion, enabling MTBE to escape from the reactive zone without decomposition. When methanol is fed below or in the lower part of the reactive zone of the column, the "lifting capacity" of the minimum boiling point MTBE-methanol azeotrope will also be important.
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