Energy, exergy and exergoeconomic analysis of an ultra low-grade heat-driven ammonia-water combined absorption power-cooling cycle for district space cooling, sub-zero refrigeration, power and LNG regasification

Abstract

An ultra low-grade waste heat (≤100 °C) driven ammonia-water combined absorption power-cooling (APC) cycle-based multi-generation system with liquefied natural gas (LNG) cold exergy recovery is thermodynamically and exergoeconomically investigated for sustainable district cooling (DC) at two different temperature levels, and electricity generation in coastal hot climate regions serviced by LNG regasification terminals. At 70 °C heat source temperature, the system yields a specific net equivalent power output of 51.4 kWh/tonLNG at a cooling-to-power ratio of 7.3, and effective first-law and effective exergy efficiencies of 39% and 36%, respectively. Per million ton per annum (MTPA) LNG regasification capacity, the system would deliver 9.4 MW of space cooling, 6.5 MW of sub-zero refrigeration, and 2.2 MW of electricity for the district, while saving 8.4 ktons of natural gas and 19.3 kt of CO2-equivalent emissions per year, compared with conventional cooling, power and regasified LNG provision systems. The LNG refrigeration heat exchanger and APC absorber-evaporator are the most important components from exergoeconomic viewpoints. In addition to enhancing overall cooling and power generation capacity, the use of LNG as a cold source/sink reduces the minimum APC driving heat source temperature and rectification requirements, relative to an ambient water-cooled absorber sink. Additional benefits include the avoided use of conventional refrigerants, and reduced impact of LNG regasification on marine ecosystems.