Optimal Synthesis Of Batch Distillation Process

Batch distillation is widely used in fine chemical and pharmaceutical industries, for the purification or recovery of high value-added products. Batch distillation is a dynamic process, and its transient nature provides great flexibilities in both various operation policies and alternative complex configurations. Such unique characteristics also offer broad space and motivations for researchers to further explore the economic potential and process efficiency through the optimal synthesis of batch distillation process. However, the time-variant characteristic of decision variables and complicated economical trade-offs also make a huge challenge for the synthesis problem.In this paper, we aim at developing a systematic framework for the optimal synthesis of batch distillation process. The proposed framework will cover all the feasible process and provide complete solution space for the optimal synthesis problem. Moreover, it also considers both structure configurations in space dimension and operation strategies in time dimension on the total time horizon to judge and weigh the best-matched relationship between design and operation variables, in order to find out the optimal batch distillation process on both space and time dimension. This framework contains two phases:(1) Phase of problem definition and analysis:The variables can be optimized are proposed, mainly includes the configuration, design and operation of batch distillation. The complex trade-offs among these three kinds of interdependent and interacted variables are analyzed. The results will provide needed variable information for the construction of superstructure in the next phase.(2) Phase of state-time-space superstructure based optimization:Based on the variable information provided in the first phase, the state-time-space superstructure of complex batch distillation system which treats trays and vessels as basic separation units is proposed. Then the Mixed Integer Dynamic Optimization (MIDO) problem is formulated accordingly. A comprehensive objective function is set up with the consideration of operating period, space of flow sheet which includes the factors of process equipments, streams and utilities. Finally, the optimal equipment parameters, trays-vessels connection configuration and dynamic control schemes of decision variables are obtained simultaneously, and thus we can achieve the optimal synthesis of batch distillation process.Under this framework, all the streams in the superstructure can be mixed and split arbitrarily, and the fully connected structure is constructed between each equilibrium stage to cover every potential optimal batch distillation process. So the feasible area is significantly expanded because of the features above.At the same time, different connecting forms of streams between trays and vessels generate different configurations and structure designs of batch distillation columns, and different variations of stream properties form different operating strategies. So the whole optimal synthesis of batch distillation process problem can be presented by every stream’s own properties and connecting forms between each other to achieve the simultaneous optimization of design and operation variables.At last, binary system of benzene-toluene and ternary system of benzene-toluene-ethylbenzene separation case studies will be presented to illustrate the validity and effectiveness of the proposed framework.