Novel two-stage waste heat recovery in a natural gas engine to boost single-effect absorption refrigeration system performance: 5-E research

This study presents a new two-stage waste heat recovery concept from a natural gas engine, integrated with a single-effect ammonia-water absorption refrigeration system (ARS). The proposed configuration harnesses heat from both exhaust gases and engine cooling jackets through the conceptual substitution of the conventional coolant with the pressurized working fluid, eliminating the need for an intermediate heat exchanger, radiator, and auxiliary water pump, and enhancing heat recovery without high operating temperatures. A comprehensive 5-E (Energy, Exergy, Environmental, Economic, and Exergoeconomic) analysis is performed in EES under steady-state conditions, evaluating performance over a generator temperature range of 100–115 °C. Results show that the configuration increases cooling capacity by 34.7 %, improves exergy efficiency by 1.1 %, and reduces exergy destruction by 2.1 %. Environmentally, it can avoid up to 2812.87 tCO2/year compared with vapor-compression systems. Economically, it achieves a payback period of 4.77 years and an internal rate of return of 54.89 %, while the specific exergy cost of cooling decreases by 19.7 %. The exergoeconomic analysis identifies the evaporator as the costliest and most sensitive component for improvement. The originality of this study lies in proposing, for the first time, the substitution of the engine coolant by the pressurized ARS working fluid as a conceptual heat-recovery strategy to assess the maximum theoretically recoverable heat, and evaluating it through an integrated 5-E framework. The findings reveal the maximum-attainable 5-E performance, showing that higher generator temperature improves overall efficiency and establishing the performance levels these systems may aspire to in industrial applications.