Design Optimization Of Multi-stage Gas Membrane Separation Process

Gas membrane separation has been widely used in various systems.With the increasing of membrane materials and process variety,it is of great importance to add rigorous membrane unit operation into flowsheeting for optimization problem.In order to solve the difference equations of membrane module on the platform of algebraic equations,a program for solving the differential mathematical model of gas membrane separation is developed for process simulation.Membrane separation process design optimization problem with multiple membrane materials,multi-stage membrane structure and uncertain feed were established.Three strategies were proposed and utilized to provide theoretical guidance for membrane material selection,process feed uncertainty analysis and process integration.The main work of this paper includes the following aspects,(1)Compile a series of gas membrane separation module programs.The programs are used to solve the differential mathematical model of gas membrane separation.A model library for different gas flow patterns and different calculation software has been established.Model accuracy is verified by literature experimental data.(2)Taking the multi-stage membrane separation process of air as an example,the optimization of multiple membrane materials and multi-stage membrane separation are discussed.Optimization objectives are to minimize the dimensionless membrane area,minimize the dimensionless membrane area required for unit nitrogen product and maximize the annual economic benefit,respectively.Various membrane material types,multi-stage membrane separation process structures,operating parameters and equipment parameters are considered as decision variables.Driving force of the processes were analyzed to support the optimizing design with mass transfer mechanism.(3)Taking the multi-stage membrane separation process of landfill gas as an example,the simultaneous optimization of multi-stage membrane separation design and operation based on superstructure is discussed.A superstructure with multiple multi-stage membrane separation processes was designed.The objective is to maximize the annual economic benefit,a design optimization proposition considering uncertain operation was established for the characteristics of feed concentration and flow uncertainty.Three different optimization strategies are gradually compared,the sequential reference-structure-based strategy,the sequential superstructure-based strategy and the simultaneous superstructure-based strategy.The results show that the annual economic benefit of the optimal solution based on the sequential superstructure-based strategy is about 5.3% higher than the annual economic benefit of the optimal solution based on the sequential reference-structure-based strategy,and the number of calculations is greatly reduced.Further,the optimal solution based on the simultaneous superstructure-based strategy has higher annual economic benefits and fewer calculations than the optimal solution based on the sequential superstructure-based strategy.