Thermochemical technologies for industrial waste heat recovery: A comprehensive review

The industrial sector releases a considerable amount of energy as waste heat. Recovering this waste heat potential and reusing that for process heat applications is valuable from both economic and sustainability points of view. In most cases, however, direct reuse of the recovered heat is challenging, and a temperature-lifting step using heat upgrading technologies is inevitable. Thermochemical heat transformers are a group of technologies that have gained remarkable attention for this purpose. Unlike mechanical heat pumps that use electricity as the driving force, thermochemical machines use thermal energy to upgrade the waste heat streams, which is an advantage in many cases. Additionally, some of these offer much higher temperatures than those of heat pumps, giving them a broader applicability. This comprehensive review evaluates the effectiveness and potential use of thermochemical heat transformers, exploring their potential for recovering industrial waste heat in various applications, with a certain focus on temperatures below 200^oC where both waste heat streams and process heating demand are most abundant. The literature survey indicates that these systems have mostly been used for lower temperatures in the past, but with further innovations and technological advances, their coverable temperature in different technological classes has increased significantly, making them highly advantageous for waste heat recovery and upgrading in diverse industries. The deep insight that this article provides into this technological transition, the pros and cons of various classes of these, and their development perspectives, make it a must-read piece of research for scientists, engineers, and professionals working in this area.