Study on the ammonia-water two-stage evaporation absorption refrigeration system for the cooling process with temperature-distributed heat load

Abstract

The absorption refrigeration system can recover low-grade heat and produce cooling capacity, which can realize low-carbon refrigeration. However, due to the constant-temperature evaporation, the conventional system fails to provide efficient cooling for temperature-distributed heat load with large temperature spans, including process cooling, mixture liquefaction and ice slurry making. In this paper, a modified ammonia-water absorption refrigeration system with two pairs of evaporation and absorption processes at different pressure levels is proposed, in order to enhance the temperature matching with the temperature-distributed heat load and promote the absorption heat recovery. A process model is developed and validated, and comparison and parametric studies are conducted to illustrate the advantages of the new system and optimize operating conditions. Results show that the proposed system is suitable for the cooling process with temperature-distributed heat load with large temperature span, and the exergy destruction during the cooling process with temperature-distributed heat load decreases by nearly 40%. Moreover, the system internal heat recovery is improved by harvesting absorption heat. As a consequence, the COP increases by 31% and reaches 0.75, when providing cooling capacity with temperature below -10 °C. It is hoped that this study raises concerns about the characteristics of temperature-distributed heat load and provides feasible approach for efficient cooling with large temperature span.