Simulation study of an open compression absorption heat pump in water and heat recovery of low-temperature and high-humidity flue gas

Realizing the recovery of latent heat and moisture from low-temperature and high-humidity flue gas (LHFG) can effectively improve energy efficiency and reduce carbon emissions. A novel open compression absorption heat pump (OCAHP) is proposed to fulfill the demand for flue gas water and heat recovery. In this paper, Aspen Plus is used to establish a model, and the coefficient of performance (COP), water and heat recovery rate are evaluated to investigate the effects of the gas inlet temperature, compression ratio, liquid-to-gas ratio, and absorber inlet solution temperature parameters on water and heat recovery performance for OCAHP. The parameters are optimized, and exergy analysis is carried out. The simulation results show that wet flue gas with successive adiabatic compression and CaCl2/H2O solution absorption has significant water and heat recovery performance. The results also prove that the water recovery efficiency of the OCAHP system is 82.4% at a compression ratio of 1.4, which is approximately 12.3% higher than that of the conventional open absorption heat pump (OAHP) system, and it is suitable for wet flue gas with a higher saturation temperature. Furthermore, exergy analysis shows that the exergy efficiency of the OCAHP system is higher than that of the conventional OAHP system, while the exergy loss is mainly concentrated in the regenerator heating process and the solution-water heat exchanger.