Waste heat recovery from coal-fired boiler flue gas: Performance optimization of a new open absorption heat pump

Highlights: • Two optimized open absorption heat pump systems are proposed. • The thermodynamic models are established to evaluate the systems performance. • The effect of regeneration pressure on the COP of the systems is analyzed. • Exergy analysis of the optimized systems is operated. After wet desulfurization, coal-fired flue gas contains enormous amounts of water and waste heat that can be recovered for energy savings. Compared with the conventional condensation method, the application of an open absorption heat pump (OAHP) has greater potential for latent heat recovery. However, the performance of an OAHP is greatly affected by the heat consumption during solution regeneration. In response to this problem, this study proposes an OAHP system combined with flash evaporation for coal-fired flue gas. Two optimized systems based on the two-stage regeneration open absorption heat pump (TROAHP) and part regeneration open absorption heat pump (PROAHP) systems are proposed. The thermodynamic models of these three systems are established, and the parameters influencing the coefficient of performance (COP), water and thermal recovery efficiencies are evaluated. Compared with the original OAHP system in heating, the OAHP system combined with flash evaporation achieves an improvement in the COP of 0.5% to 2.2%. For the optimized TROAHP and PROAHP, the maximum COPs increase by 4.2% and 17.3%, respectively. The exergy analysis also indicates better exergy efficiencies of the optimized systems than the original one and shows the greatest exergy destruction parts are the regenerator and the condenser.