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Recovering Low-Grade Heat from Flue Gas in a Coal-Fired Thermal Power Unit

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  • Linbin Huang

    (State Key Laboratory of Low-Carbon Smart Coal-Fired Power Generation and Ultra-Clean Emission, Nanjing 210023, China
    Guoneng Nanjing Electric Power Testing and Research Co., Ltd., Nanjing 210046, China)

  • Guoqing Chen

    (State Key Laboratory of Low-Carbon Smart Coal-Fired Power Generation and Ultra-Clean Emission, Nanjing 210023, China)

  • Xiang Xu

    (State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China)

  • Rui Tan

    (Guoneng Nanjing Electric Power Testing and Research Co., Ltd., Nanjing 210046, China)

  • Xinglong Gao

    (Guoneng Changzhou Secondary Power Generation Co., Ltd., Changzhou 213000, China)

  • Haifeng Zhang

    (Guoneng Changzhou Secondary Power Generation Co., Ltd., Changzhou 213000, China)

  • Jie Yu

    (State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan 430074, China)

Abstract

To achieve the goals of carbon peaking and carbon neutrality, the retrofitting of existing coal-fired power plants is crucial to achieving energy-saving and emission reduction goals. A conventional recovery system of waste heat typically occurs downstream of the air preheater, where the energy quality in flue gas is low, resulting in limited coal-saving benefits. This study proposes a scheme involving a flue gas exchanger bypassing the air preheater and low-temperature economizers, which is used to transfer the waste heat from flue gas to primary and secondary air (System I). Additionally, a heat pump can be introduced to provide supplementary energy for primary and secondary air, as well as the condensate from the steam turbine (System II). The coal consumption rate and exergy efficiency are used to evaluate the two schemes. The results show that both waste heat recovery systems can increase the power output of the coal-fired unit by recovering waste heat. System II can boost power output by approximately 13.98 MW. The power increase in both waste heat recovery systems show a declining trend as the unit load decreases. This increased power is primarily attributed to the medium- and low-pressure cylinders, while the contributions from ultra-high-pressure and high-pressure cylinders are negligible. The increased power output for the medium-pressure cylinder ranges from approximately 3.49 to 3.58 MW, while the low-pressure cylinder has an increased power output of around 10.10 to 10.19 MW. The coal consumption rate is decreased from 250.3 g/(kW·h) to 247.5 g/(kW·h) under a full load condition for both systems, which can be augmented at lower load conditions. System II outperforms System I at 30% load condition, achieving a reduced coal consumption rate of 3.36 g/(kW·h). System I has an exergy efficiency of 40%, while System II shows a higher efficiency of 44%.

Suggested Citation

  • Linbin Huang & Guoqing Chen & Xiang Xu & Rui Tan & Xinglong Gao & Haifeng Zhang & Jie Yu, 2024. "Recovering Low-Grade Heat from Flue Gas in a Coal-Fired Thermal Power Unit," Energies, MDPI, vol. 17(20), pages 1-11, October.
  • Handle: RePEc:gam:jeners:v:17:y:2024:i:20:p:5204-:d:1502126
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    References listed on IDEAS

    as
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