Comparative analysis and optimization of waste-heat recovery systems with large-temperature-gradient heat transfer

Abstract

Efficient utilization of waste heat is crucial for reducing waste heat emissions and minimizing environmental impact. Organic Rankine cycle (ORC) systems are commonly employed for waste heat recovery. However, conventional ORC systems have limitations in effectively harnessing waste heat resources because of differences in the pinch point temperature and the relatively small temperature difference between the heat source inlet and outlet. To address this issue, we designed two absorption organic Rankine cycle (AORC) systems in this study based on absorption heat exchangers. We analyzed the energy, exergy, and economy of three ORC system models with heat source temperatures within the range from 363.15 K to 413.15 K. The results indicated that the AORC system represented a optimal waste heat recovery system, capable of reducing the outlet temperature to 298.70 K and achieving a high temperature efficiency of 1.037. Thus, an AORC system can facilitate heat exchange with substantial temperature differences, enabling the efficient utilization of heat sources. The AORC system in this study exhibited a high net power of up to 151.8 kW, and an electrical exergy efficiency of 55.45%. Additionally, the AORC consistently outperformed other systems in terms of economy, as evidenced by its electricity production cost, which was the lowest among all three systems with heat source temperatures lower than 398.15 K.