A New Numerical Approach for a Detailed Multicomponent Gas Separation Membrane Model and AspenPlus Simulation

A new numerical solution approach for a widely accepted model developed earlier by Pan 1] for multicomponent gas separation by high‐flux asymmetric membranes is presented. The advantage of the new technique is that it can easily be incorporated into commercial process simulators such as AspenPlus^TM 2] as a user‐model for an overall membrane process study and for the design and simulation of hybrid processes (i.e., membrane plus chemical absorption or membrane plus physical absorption). The proposed technique does not require initial estimates of the pressure, flow and concentration profiles inside the fiber as does in Pan's original approach, thus allowing faster execution of the model equations. The numerical solution was formulated as an initial value problem (IVP). Either Adams‐Moulton's or Gear's backward differentiation formulas (BDF) method was used for solving the non‐linear differential equations, and a modified Powell hybrid algorithm with a finite‐difference approximation of the Jacobian was used to solve the non‐linear algebraic equations. The model predictions were validated with experimental data reported in the literature for different types of membrane gas separation systems with or without purge streams. The robustness of the new numerical technique was also tested by simulating the stiff type of problems such as air dehydration. This demonstrates the potential of the new solution technique to handle different membrane systems conveniently. As an illustration, a multi‐stage membrane plant with recycle and purge streams has been designed and simulated for CO₂ capture from a 500 MW power plant flue gas as a first step to build hybrid processes and also to make an economic comparison among different existing separation technologies available for CO₂ separation from flue gas.