Modeling and analysis of an ammonia–water absorption refrigeration system utilizing waste heat with large temperature span

Waste heat sources such as flue gas generate large temperature span during recovery process. In order to improve the temperature match with such waste heat sources, a novel absorption refrigeration system with continuous-temperature-changing generation process is proposed. Internal heat recovery process is introduced to both the generator and absorber, and a premixer is added to take the place of the solution heat exchanger in traditional system. A numerical model of the system is built, in which the continuous-temperature-changing generation process is simulated based on a stripping column with heat input at each stage. New parameters are defined and optimized to strengthen the internal heat recovery process, and thus to improve system efficiency. Simulation results show that the system can operate under a large waste heat temperature span of 67.5 K, almost twice of the conventional system. With the evaporation temperature, waste heat inlet temperature, and cooling water temperature at −15 °C, 150 °C and 20 °C, respectively, a maximum COP of 0.93 and exergy efficiency of 49.7% is acquired while the waste heat temperature span is 60 K, showing that the system can acquire larger utilization rate of waste heat with higher system efficiency.