Thermodynamic investigation of an efficient combined power and refrigeration cycle designed for providing variable energy output

Abstract

To efficiently recover waste flue gas heat and meet various demands for electricity and cooling, this paper proposes a novel ammonia-water combined power and refrigeration cycle enabling flexible energy output adjustment. The adjustment of energy output is achieved by expanding a portion of ammonia-rich vapor, which is destined for refrigerant production, in a low-pressure turbine. Thermodynamic analysis results demonstrate that the cycle can efficiently reclaim the waste gas heat across a wide range of temperature grades, while offering high flexibility in energy output adjustment. Under the heat source condition of 300 °C/10 kg s⁻¹, the adjustable ranges for the refrigeration capacity and net power are 0–538.2 kW and 348.9–440.4 kW, respectively, while consistently maintaining a sufficient recovery of the heat source (exhaust temperature at around 109 °C). When the cycle achieves the maximum refrigeration capacity and net power, the corresponding effective exergy efficiencies are 0.4119 and 0.3801, respectively. The results also reveal that as the energy output is regulated arbitrarily, the high-pressure turbine sustains a near-constant base power load (361.7–364.7 kW), and only the exergy destruction occur in components associated with refrigeration and low-pressure turbine significantly changes. Furthermore, when compared to two other combined power/cooling cycles in literature and the triple-pressure Kalina cycle, the proposed cycle can achieve 94.15 %, 44.45 % and 10.36 % relatively higher effective exergy efficiency, respectively.