A method for simulation and optimization of multiphase distillation

Simulation and optimization of multiphase distillation are often required i n the design and operation of process plants. In this work, a simultaneous solution method (tau-method) is proposed and studied for simulating/optimiz ing two-and three-phase distillation. This method involves modification of mole fraction summations such that the same set of governing equations is v alid for different phase regions, and hence phase identification and soluti on of the governing equations can be performed simultaneously and effective ly. The optimization problem involved in the tau-method has a linear object ive function and nonlinear constraints, and it can be solved using an itera ted linear programming (ILP) or nonlinear programming (NLP) approach. The t au-method is applied to steady state simulation and optimization of two- an d three-phase distillation. The results obtained for several examples and c onditions are shown to be consistent and comparable to those in the literat ure. The tau-method is successful for simultaneous simulation and optimizat ion of multiphase distillation. For the distillation examples tried by the tau-method with the ILP approach, initialization based on feed is often sat isfactory, major iterations (similar to those in Newton method) for converg ence is 5 to 10, and CPU time on a personal computer is less than 1 minute. On the other hand, the tau-method with the NLP approach generally requires better initialization and/or more computations for convergence. (C) 2000 E lsevier Science Ltd. All rights reserved.