Study Of Cryogenic Air Separation Distillation With Heat-Pump Based On Exergy Analysis

Exergy analysis is effective to evaluate the energy utilization of chemical process and to guide the energy saving. It is used to evaluate the energy efficiencies of cryogenic air separation distillation processes with double-effect column and heat-pump cycles. A shortcut method is proposed to provide approximated optimal design of heat-pump distillation system with multi-stage compression cycles.The study mainly includes the following three aspects:1. Exergy analysis is used to determine the exergy efficiency and bottleneck of the double-effect air separation process. Energy saving improvement of compression stages, compression efficiency and intermediate reboiler are also evaluated. Moreover, a heat-pump process of air separation distillation is constructed, and through the exergy analysis which confirms the idea of energy saving design is that reheat the work fluid before compresses and install multistage compression of heat-pump cycles.2. Due to the complexity of optimization for multistage compression heat-pump distillation process, a shortcut method based on T-s diagram and CEGCC is proposed to provide approximate optimal design of multi-stage heat-pump cycles. In the case of propylene/propane distillation process with vapor compression heat-pump, the accuracy of energy target estimation and design parameters of optimization structure which given by the shortcut method is proved.3. The shortcut method of heat-pump distillation with multi-stage compression is used to estimate the energy target of the process with two-stage compression heat-pump cycles, and gives initial values which are used for rigorous simulation. By rigorous simulation and sensitivity analysis of process energy saving optimization, confirms the minimum compressor work consumption and the optimal design parameters of the improved heat-pump air separation process. Compare them with values given by the shortcut method, the result shows that the method has great accuracy at both aspects. Finally, the method is used to estimate the energy target of three-stage compression heat-pump air separation process.