Compartmental modeling and solving of large-scale distillation columns under variable operating conditions

Abstract

Distillation columns are critical unit equipment of cryogenic air separation plants. Variable operating adjustment of distillation columns is to optimally change the products and recycle rates under wide variable operating conditions. The distillation column models are used to calculate the temperature and molar fractions of each stage for the variable operating adjustments. The classical calculation based on the stage-by-stage model is quite time consuming, hence in this paper a new compartmental model based on variable liquid holdups of the large-scale distillation column is established. Criterions for both partitioning the distillation column and selecting sensitivity stages are proposed, and the method of solving the liquid holdup factor is presented. The physical property data is pre-solved and the dimensions of the compartmental model are reduced to speed up the calculation under variable operating conditions. The new compartmental model is compared with the stage-by-stage model and the aboriginal compartmental model to assess the merit of the proposed modeling and solving strategy with regard to prediction accuracy and computational efficiency.