Simulation And Optimization Of Membrane Processes For CO₂ Separation

CO₂ separation membranes show a broad application prospect for the purification of energy gas and the capture of CO₂.At present,the research on the CO₂ separation membrane processes is not systematic enough,and there is not an appropriate mathematical model for the calculation of the separation process of the fixed carrier membrane,which shows great potencial in CO₂ separation processes.In this thesis,based on the mathematical model reported in the literature for calculating gas membrane separation processes,the mathematical model to calculate the fixed carrier membrane separation process is established.Based on the improved algorithm,the membrane separation processes,including the post-combustion CO₂ capture,biogas upgrading process,synthesis gas purification process,and natural gas sweetening process are systematically investigated.The results are of great importance for the design of membrane separation process and the development of CO₂ separation membranes.Firstly,using the published industrial data,the mathematical model of multi-component gas membrane separation process based on the cross-flow model is verified.Based on the expression for the CO₂ permeance of the fixed carrier membrane,which is developed by our research group,a mathematical model for calculating the separation process of the fixed carrier membrane is established,considering the change of CO₂permeance in the separation process.Based on this mathematical model,the characteristics of the separation process of the fixed carrier membrane are analyzed.By improving the algorithm,the calculation for the two-stage membrane process with fixed product purity and recovery is realized.With CO₂ purity of 95%and CO₂recovery of 90%,the CO₂ capture process of flue gas from coal-fired power plants is systematically investigated.The result shows that,in the increasing the membrane selectivity of any stage could reduce the energy consumption of the membrane separation process.The combination of a low selectivity membrane in the first stage and a high selectivity membrane in the second stage could effectively reduce the CO₂capture cost.As the operating pressure rises,the energy consumption first decreases and then increases.Moderate feed pressure,varying from 0.55 MPa to 0.65 MPa,is found to provide the minimum energy consumption,with the membrane CO₂/N₂selectivity ranging from 60 to 120.Techno-economic analysis is conducted,finding out that the feed pressure varying from 0.69 MPa to 0.83 MPa provides the minimum CO₂capture cost,with the first stage membrane CO₂/N₂ selectivity ranging from 40 to 70and the second stage membrane CO₂/N₂ selectivity ranging from 70 to 140.The investigation of biogas upgrading process shows similary result,with product CH₄purity and recovery fixed as 98%.When the CO₂/CH₄ selectivity ranges from 30?100,the optimal operating pressure is 0.45 MPa?0.65 MPa,with the minimum energy consumption.The process of syngas purification is calculated.By comparing the hydrogen purity and recovery of the the CO₂ selective membrane and the H₂ selective membrane,it is found that the CO₂ selective membrane is suitable for obtaining high hydrogen purity,while the H₂ selective membrane is suitable for obtaining high hydrogen recovery.The two-stage membrane process with CO₂ selective membrane could achieve high hydrogen purity and recovery,while maintaining low cost,which shows great potential for syngas purification.Finally,this thesis optimizes the operating pressure of natural gas sweetening process and syngas CO₂ removal process.When the product purity and recovery meet the separation requirements,this processs is investigated by employing the membrane performance in the literature.The medium operating pressure of 0.65 MPa?1.5 MPa shows the lowest energy consumption and cost.