Performance Analysis of a Compound Absorption Heat Pump System for Waste Heat and Moisture Recovery from Flue Gas

The temperature of the flue gas is about 130 °C before desulfurization and 50 °C after desulfurization. The high-humidity flue gas discharged after desulfurization contains a significant amount of waste heat and vapor that cannot be effectively recovered. In this study, a compound absorption heat pump (COAHP) system was proposed to recover the waste heat and vapor in the flue gas. A mathematical model is developed to analyze the system, optimize the configuration of the COAHP, compare and analyze the thermodynamic performance of the single-stage absorption compound open absorption heat pump (SAOAHP) and the two-stage absorption compound open absorption heat pump (TAOAHP), and primarily investigate the impact of the solution shunt ratio on the thermodynamic performance of the TAOAHP system. The results show that the heat load of the condenser in the TAOAHP increases by 14.5% and the heat output of the TAOAHP increases by 23.4% compared to that of the SAOAHP. In the TAOAHP, as the shunt ratio increases from 30% to 60%, compared to the SAOAHP, the temperature of regeneration reduces from 6.5% to 9.9% in the TAOAHP, and the power consumption of regenerator decreases from 41.9% to 68.6%, the amount of vapor recovery increases to 34.2%. The temperature and the humidity of the flue gas at the outlet of absorber 3 decrease by 6.8 °C and 14.37 g/kg, respectively, the heat load of condensers in the TAOAHP is 61.08 MW, and the total heat output of the TAOAHP is 145.1 MW. This study establishes a framework for enhancing the efficiency of high-moisture flue gas waste heat recovery following wet desulfurization in coal-fired power plants, thereby providing a theoretical foundation for the effective utilization of waste heat in industrial high-moisture flue gas systems. The payback period of the COAHP system is found to be around 5.41 years.