Performance evaluation of a novel hybrid open absorption heat pump for efficient flue gas heat recovery at high return water temperatures

Conventional heat recovery systems are less efficient under the high temperature return water conditions. This research proposes a novel hybrid system that integrates a vapor compression heat pump with a parallel double stage open absorption heat pump to recover the latent waste heat from flue gas deeply. To assess the flue gas heat recovery potential of proposed hybrid system and to compare its energy performance with that of a conventional single stage open absorption heat pump, especially at high return water temperatures, the simulation models are created using aqueous potassium formate. The parametric analyses indicate that the proposed system can achieve 12.94–23.24 % higher heat recovery efficiency by operating with a thermal COP of 1.81 at return water temperatures of 45–55 °C, compared to the conventional configuration. In comparison to the hybrid single stage configuration, the parallel stage system demonstrates 10.4 % higher thermal COP and 5.2 % higher primary energy efficiency as compared to hybrid single stage system along with a 28.2–31.7 % reduction in external heat source reliance. The critical analysis's findings highlight that the recovery performance of the hybrid system can be enhanced by decreasing the solution temperature. Furthermore, the optimal performance of the hybrid system is significantly contingent upon the refrigerant flow ratio, regeneration solution ratio, and the solution to flue gas ratio. Under ideal conditions, the hybrid parallel double stage system can attain a heat recovery efficiency of approximately 94.2 % by operating at an optimal solution to flue gas ratio between 4.2 and 4.5 range and a solution temperature of 34.71 °C. These analytical outcomes suggest that the proposed hybrid parallel double stage heat pump system offers enhanced energy efficiency and operational flexibility, reinforcing its viability for practical use in industry.