Enhancing the performance of autocascade steam generating heat pumps through advanced exergy methods

Abstract

Air-source autocascade steam generating heat pumps have the capability to produce high-temperature steam from low-temperature air, thereby playing a critical role in the global energy transition by aiding the industrial decarbonization. Among the key elements influencing the performance of autocascade steam generating heat pumps is the mixed refrigerant gas–liquid phase separation efficiency. This research proposes an optimization strategy for two-phase refrigerant separation through using the advanced exergy method to address this challenge. An improved autocascade steam generating heat pump model is developed based on this strategy. The study conducts an extensive comparison between the conventional and improved systems of autocascade steam generating heat pump over prolonged operational periods, assessing their performance across energy, exergy, economic, and environmental dimensions. The results indicate that the improved system significantly outperforms the conventional system. Specifically, when the waste heat temperature of 30 °C, the improved system demonstrates an average increase of 20.36 % in the coefficient of performance and a 51.37 % rise in steam mass flow rate under year-round ambient conditions. Furthermore, the improved system achieves an average CO₂ reduction rate of 84.37 % and a comparable enhancement in operational economic efficiency. However, the performance gains of the improved system diminish as the availability of waste heat temperature increases, with performance degradation observed when waste heat temperature reaches a critical threshold. These results underscore the potential of the proposed optimization strategy to guide the design of autocascade cycles and the development of steam generating heat pumps, offering valuable theoretical insights for advancing sustainable industrial heating technologies.