A unified approach for the simultaneous synthesis of reaction, energy, and separation systems

Abstract

Previous studies on process integration have generally considered reaction and separation as processes that occur sequentially in a flowsheet. In this paper, a unified formalism is presented for the synthesis of reaction-separation systems, while ensuring optimal energy management. The synthesis model stems from a target-based approach for reactor networks due to an earlier study. It is shown that, by postulating a species-dependent residence time distribution function, one can arrive at a general representation for a reaction-separation network. Optimization of this distribution function leads to a separation profile as a function of time along the length of the reactor. The synthesis model is formulated as a mixed integer optimal control problem, where the integer variables account for the fixed costs of separation. The control profiles include the temperature, the separation profile, and residence time distribution defined for the network. Costs for maintaining a separation profile are handled through a separation index (defined to model the intensity of separation), and a fixed charge for any separation between two components in the reaction mixture. Also, using an energy targeting formulation, the maintenance of the optimal temperature profile is integrated to the energy flows within the flowsheet. Strategies based on simultaneous optimization and modelmore » solution are presented for the optimization problem and demonstrated for two case studies.« less