Study On The Heat Integration In Complex Distillation System Synthesis

The purpose of heat integrated distillaion system synthesis, which is an optimization problem, is to find the best distillation sequence and heat integrated structure among a great number of feasible alternatives in terms of economic competence. Mathematically, it can be formulated as an Mixed Integer Nonlinear Programming (MINLP) problem that includes both structural and parametric variables optimization. When complex column configurations are considered, that is often the case for industrial applications, this problem would become extremely complicated due to its large-scale combinatorial feature and non-linearity, and its solution is very difficult. The work presented in this thesis aims at creating a systematic and stable method to tackle this problem.In this paper the pinch analysis method is applied in the heat exchanger's design of heat integrated distillation system synthesis. For simple columns, a MINLP model with the variables of separation sequence and operation pressures is established. For complex columns, a MINLP model with the continuous variables of the recoveries of key components in the prefractionators and reflux ratios and the discrete variables of separation sequence and thermal-coupling scheme is established. The solution to the problems could be achieved with an improved simulated annealing algorithm. This approach is able to avoid the heat exchange network structure as independent variables, then to increase the possibility and efficiency of finding the optima with a randomized search optimizer. In this paper, as one condenser or reboiler is allowed to have heat exchanges with several reboilers or condensers of other columns, the energy recovery can be more sufficiently increased.Examples of different separation problems are solved and the optimized parameters and economic benefits of different optimal schemes are analyzed and compared. The results demonstrate that it can evidently reduce the system's annual total cost by using the heat integrated distillation configuration. The solutions of example problems also demonstrate that the proposed method is efficient for the heat integrated distillation synthesis problem.