Thermodynamic analysis of an ammonia-water double absorption-resorption heat transformer system

Absorption heat transformer (AHT) presents an effective solution for enhancing energy efficiency through the utilization of low-grade industrial waste heat. To reduce the high operating pressures of traditional ammonia AHT and elevate waste heat to a higher temperature level, a novel ammonia-water double absorption-resorption heat transformer (DARHT) incorporating a coupled middle absorber-generator is proposed in this paper. A thermodynamic simulation model of the system is established using MATLAB software to analyze the effects of operating pressures and temperatures on the COP, temperature lift, solution circulation ratio and bypass ratio, thereby determining the optimal operating conditions of the system. The simulation results indicate that there exist optimal PH/PL pairs and middle absorber-generator temperatures which lead to the maximum COP of the system. COP decreases with the increase of absorber and resorber temperatures while increases with the increase of generator and desorber temperatures. When PH/PL pair is 1.5/0.36 MPa, the DARHT system can provide a temperature lift exceeding 70 degrees C, while the working pressures are significantly lower compared to conventional AHT, thereby reducing the requirements of robust components and enhancing the operational stability of the system.