A review of boiler waste heat recovery technologies in the medium-low temperature range

The technology of waste heat recovery from medium-low temperature flue gas has been widely studied in the past decade. In this paper, the principle and characteristics of the main technologies are extensively reviewed. The condensing boiler, as the primary waste heat recovery system, can achieve higher boiler efficiency by transferring waste heat to feedback water. As the temperature of feedback water is generally not cold enough to serve as the cold source, the waste heat recovery efficiency of condensing boilers is limited. More advanced waste heat recovery systems are proposed. The common principle of them is to enhance the difference between the cold source and the flue gas. Specific systems reviewed are classified according to working principles: (I) to decrease the temperature of the cold source; (II) to decrease the dew point temperature of the cold source; (III) to increase the dew point temperature of the flue gas. System performances are analyzed involving efficiency, entransy dissipation, economic benefits and pollutant emissions. The heat recovery efficiency of several heat pump systems and vapor pump boiler systems can exceed 80 %. The vapor pump boiler system has a relatively short payback period (i.e. 1.4 years). Future perspectives and essential conclusions are presented in the end. (c) 2021 Elsevier Ltd. All rights reserved.