The comprehensive solution to decrease cooling wall temperatures of sCO₂ boiler for coal fired power plant

Compared with water-steam cycle, supercritical carbon dioxide (sCO₂) cycle has higher efficiency when applied in coal fired power plant. However, it also introduces challenges in boiler: because of the higher working fluid temperature and the lower convective heat transfer coefficient in boiler tubes, the cooling wall is more prone to overheating and bursting due to higher wall temperatures. Here, based on fundamental consideration of the thermal coupling between 3D radiation heat flux in furnace side and CO₂ fluid in cooling wall tubes, we propose a comprehensive solution to decrease cooling wall temperatures. The solution includes four consecutive techniques: improved coupling in furnace width direction (CWD), flue gas recirculation for heat flux reduction (FGR), improved coupling in furnace height direction (CHD), and enhanced heat transfer in cooling wall tubes (EHT). A comprehensive thermal-hydraulic model is developed for a 1000 MWe power plant. It is found that the new solution can reduce the cooling wall temperatures from 670.5 °C to 635.0 °C, among which CWD, FGR, CHD and EHT contribute to the decrement of cooling wall temperatures by 13.3 °C, 4.4 °C, 6.8 °C and 11.0 °C, respectively, concluding that CWD and EHT are more effective than other techniques.