Techno-economic study of full-open absorption heat pump applied to flue gas total heat recovery

Full-open absorption heat pump (FOAHP) is a new approach to total heat recovery of gas boiler flue gas. With the flue gas dehumidified deeply, the latent heat can be recovered efficiently. The prototype FOAHP system using LiBr has experimentally achieved the COP of 1.6 and the total heat recovery efficiency of 0.626 in our previous study. In this paper, CaCl₂-FOAHP is simulated to compare with LiBr-FOAHP. Due to the synthetic effects of vapor pressure and specific heat capacity of liquid desiccant, the total heat recovery performances of the two systems result to be similar. The primary energy ratio of natural gas boiler can be improved by 16.3% and 15.3% by applying LiBr-FOAHP and CaCl₂-FOAHP, respectively. An economic analysis is conducted to compare FOAHP with other waste heat recovery systems. Since the main parts including the generator, condenser and absorber all operate on direct-contact heat and mass transfer without any heat transfer walls, FOAHP exhibits remarkable superiority in economics. The initial investment costs per recovering 1 kW heat of LiBr-FOAHP and CaCl₂-FOAHP are 648 CNY (96.4 USD) and 562 CNY (83.6 USD), respectively. In short, FOAHP performs better than most of the conventional waste heat recovery systems in thermodynamics and economics.