Recent progress in waste heat recovery technology for boiler flue gas: A comprehensive review

With the urgent need to improve energy utilization efficiency and reduce pollutant emissions, developing advanced technologies of flue gas waste heat recovery from coal-fired and gas-fired boilers has become a key issue in industrial green transformation. This paper systematically reviews the current research progress on the boiler flue gas waste heat recovery technologies. The working principles, key characteristics, and application status of sensible heat waste heat recovery, latent heat recovery, and synergistic recovery have been thoroughly analyzed. It is summarized that sensible heat recovery technologies are focused on coupling and optimizing them with existing thermal systems. Low-temperature economizers and bypass flue gas design are adopted to improve overall utilization efficiency. Heat pumps exhibited significant advantages in latent heat recovery technologies due to their capability of upgrading the low-grade thermal energy. Synergistic recovery technologies, utilizing innovative processes such as ceramic membrane condensers, heated and humidified air denitrification, and heat pump-coupled carbon dioxide capture, have been demonstrated to achieve not only waste heat recovery but also reduce water consumption, pollutant emissions, and energy consumption for carbon dioxide capture. Therefore, the multi-objective collaboration in flue gas waste heat recovery presents significant potential for future work. To further enhance the utilization level of boiler flue gas waste heat, future research is recommended to focus on the following issues: constructing a full-temperature-range cascade utilization system for sensible and latent heat, optimizing the design of synergistic recovery processes, and improving the performance of thermal equipment for synergistic recovery.