Performance Prediction of Structured Packing Column for Cryogenic Air Separation with Hybrid Model

A detailed investigation of a thermodynamic process in a structured packing distillation column is of great importance in prediction of process efficiency. In order to keep the simplicity of an equilibrium stage model and the accuracy of a non-equilibrium stage model, a hybrid model is developed to predict the structured packing column in cryogenic air separation. A general solution process for the equilibrium stage model is developed to solve the set of equations of the hybrid model, in which a separation efficiency function is introduced to obtain the resulting tri-diagonal matrix and its solution by the Thomas algorithm. As an example, the algorithm is applied to analyze an upper column of a cryogenic air separation plant with the capacity of 17000 m3·h-1. Rigorous simulations are conducted using Aspen RATEFRAC module to validate the approach. The temperature and composition distributions are in a good agreement with the two methods. The effects of inlet/outlet position and flow rate on the temperature and composition distributions in the column are analyzed. The results demonstrate that the hybrid model and the solution algorithms are effective in analyzing the distillation process for a cryogenic structured packing column.

The calculated distributions of compositions N2 and O2 are in good agreement with Aspen and hybrid model. The results from the hybrid model are between the values from equilibrium stage and non-equilibrium stage models of Aspen, which implies that the proposed algorithm is effective in solving the model equations for distillation process in a cryogenic column.Figure optionsDownload as PowerPoint slide