An improved absorption refrigeration system for recovering two waste heat with different temperatures: Parametric analysis and comparative study

Heat capacity and temperature matching between the heat sources and energy system is of vital importance to improve energy efficiency, especially in occasions with multiple temperature-distributed heat sources. In this paper, an improved ammonia-water absorption refrigeration system with additional intermediate-pressure generator and absorber is proposed, aiming at recovering two kinds of heat sources with different grades. To match the heat capacity of two sources, solution distribution to the high- and intermediate-pressure generator can be adjusted. Moreover, heating areas of the two generators are extended from the reboilers to the stripping sections, in order to improve the heat utilization ratio. Simulation study shows that as the solution split ratio to the intermediate-pressure generator increases, the capacity for recovering low-grade heat sources is improved. The coefficient of performance of the proposed system is 5% higher than that of the modified vapor exchange system within a large range of the intermediate pressure. Under the baseline working condition with evaporation temperature of -15 degrees C and condensation temperature of 31 degrees C, a significant increment in exergy efficiency is achieved by the proposed system, which is 32.6% and 56.5% higher than that of the conventional single-effect and conventional vapor exchange system, respectively.

Automated summary

The key to improving energy efficiency lies in matching heat capacity and temperature between heat sources and energy systems, especially in scenarios with multiple temperature-distributed heat sources. An improved ammonia-water absorption refrigeration system is proposed in this paper, featuring an additional intermediate-pressure generator and absorber to recover two different grade heat sources. Adjusting solution distribution and extending heating areas of generators result in improved heat utilization ratio and capacity for recovering low-grade heat sources, with 5% higher coefficient of performance compared to a modified vapor exchange system within a large range of intermediate pressure. Additionally, the proposed system shows significantly higher exergy efficiency compared to conventional single-effect and vapor exchange systems under baseline working conditions.