Thermodynamic Analysis and Optimization of the Dynamic Cycle of an R170/CO <sub>2</sub> Mixture for Biomass Flue Gas Waste-Heat Recovery

Abstract

To recover waste heat from biomass flue gas in cold areas, the azeotropic mixture medium CO2 and ethane was used as the working medium of the transcritical dynamic cycle. The analysis models of the first and second laws of thermodynamics are established, and the system performance is studied and analyzed. In addition, this study also included a genetic algorithm (GA) for system performance optimization analysis. When the system performance is in the optimal state, the thermal efficiency of R170/CO2 (0.78/0.22) is 12.73%, the exergy efficiency is 48.92%, the flue gas outlet temperature is 332.31°C, the expansion ratio is 3.58, and the net work output of the system is 4772.66 W. When the thermal efficiency of CO2 is 12.74%, the exergy efficiency is 48.54%, the flue gas outlet temperature is 335.22°C, the expansion ratio is 4.14, and the net output work of the system is 4623.38 W. The above data showed that the exergy efficiency of the former increased by 0.38%, the flue gas outlet temperature decreased by 2.91°C, the expansion ratio of the working fluid decreased by 13.52% compared with CO2, and the net output power of the system increased by 149.28 W.