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Energy efficiency of polyimide membrane modules for air separation in zero-emission power plants: a computational analysis

A fundamental part of oxy-combustion zero-emission power plants is the ambient air separation unit. Amongst the various technologies utilized to perform this process, membrane gas separation might be applied as well. This paper is a continuation of previous research on operation of polyimide membranes in such power units. The presented results of computational analysis are based on experimental research, regarding the energy-related parameters of the nitrogen/oxygen separation from ambient air using commercial capillary polymer membranes. Empirical, continuous functions describe the variability of the essential parameters for membrane separation modules of variable configuration and are used as a fundamental part of the model, used within the presented research. Energy consumption and efficiency of the air separation unit are investigated as the most influencing of these parameters. Analyses are performed for three variants of unit configuration: serial connection of membrane modules, unit with retentate recirculation and unit with permeate recirculation. The results of the research indicate the essential differences in total energy consumption for the subsequent configurations. Both the highest energy demand of the air separation module, equal to 1.61 kJ/m3 O2, and the lowest, equal 0.02 to kJ/m3 O2, were obtained for the retentate recirculation (for the 800 and 1,500 L/h stream flows, respectively). Satisfactory operational parameters of the separation process were indicated for both the permeate recirculation and serial modules connection variants, with an acceptable rise in power demand, corresponding to a maximum value of 205 W and 88 W, respectively.