Sustainable energy recovery from thermal processes: a review

Abstract Background With the increasing concerns on the energy shortage and carbon emission issues worldwide, sustainable energy recovery from thermal processes is consistently attracting extensive attention. Nowadays, a significant amount of usable thermal energy is wasted and not recovered worldwide every year. Meanwhile, discharging the wasted thermal energy often causes environmental hazards. Significant social and ecological impacts will be achieved if waste thermal energy can be effectively harnessed and reused. Hence, this study aims to provide a comprehensive review on the sustainable energy recovery from thermal processes, contributing to achieving energy security, environmental sustainability, and a low-carbon future. Main text To better understand the development of waste thermal energy utilization, this paper reviews the sustainable thermal energy sources and current waste energy recovery technologies, considering both waste heat and cold energy. The main waste heat sources are prime movers, renewable heat energy, and various industrial activities. Different waste heat recovery technologies to produce electricity, heating, and cooling are analyzed based on the types and temperatures of the waste heat sources. The typical purposes for waste heat energy utilization are power generation, spacing cooling, domestic heating, dehumidification, and heat storage. In addition, the performance of different waste heat recovery systems in multigeneration systems is introduced. The cold energy from the liquified natural gas (LNG) regasification process is one of the main waste cold sources. The popular LNG cold energy recovery strategies are power generation, combined cooling and power, air separation, cryogenic CO 2 capture, and cold warehouse. Furthermore, the existing challenges on the waste thermal energy utilization technologies are analyzed. Finally, potential prospects are discussed to provide greater insights for future works on waste thermal energy utilization. Conclusions Novel heat utilization materials and advanced heat recovery cycles are the key factors for the development of waste high-temperature energy utilization. Integrated systems with multiply products show significant application potential in waste thermal energy recovery. In addition, thermal energy storage and transportation are essential for the utilization of harnessed waste heat energy. In contrast, the low recovery rate, low utilization efficiency, and inadequate assessment are the main obstacles for the waste cold energy recovery systems.