Energetic, exergetic and economic analysis and multi-objective optimization of two novel ammonia-water absorption combined power and cooling cycles driven by low-grade heat sources

Abstract

This study proposed and investigated two novel absorption combined power and cooling cycles using ammonia-water as working fluids driven by low-grade heat sources. The two proposed systems which combined the Kalina cycle and the absorption refrigeration cycle were named the double-pressure series cycle (DSC) and the double-pressure parallel cycle (DPC) according to the different configurations. The thermodynamic and economic models were developed and then the combined system performances were evaluated. The results showed that, under given conditions, the exergy efficiency and the total exergy efficiency of DSC (34.44%, 24.63%) were higher than those of the DPC (30.05%, 23.81%), but the higher cost rate of DSC was achieved, which is 3.6% higher than DPC’s. Moreover, the parameter analysis showed that increasing the heat source temperature and the basic ammonia concentration has a positive effect on the thermodynamic performance of DSC and DPC, while increasing the separation pressure, rectification pressure and the pinch temperature difference led to performance degradation. Furthermore, the multi-objective optimization genetic algorithm (NSGA-Ⅱ) was employed to obtain the Pareto frontier, and the optimal solution was obtained through the comprehensive decision-making method (TOPSIS). The research results can provide references for the establishment and evaluation of innovative combined cycles driven by low-grade waste heat.