Numerical simulation research on heat transfer characteristics of platen superheater of 660 MW coal⁃fired boiler

Due to the “dual carbon” target，coal⁃fired thermal power units are developing to higher parameters and deeper peaking，which causes higher requirements for coal⁃fired boilers. Preventing the over⁃temperature of the tube wall caused by the thermal deviation of the heating surface is one of the key issues. Therefore，accurate pre⁃ diction of thermal deviation and wall temperature of the heating surface of coal⁃fired boilers is of great significance for safe and stable unit operation. The heat transfer and wall temperature characteristics of the heating surface of the boiler are affected by the combined action of the flue gas side and the steam side. When predicting the thermal deviation problem through numerical simulation，the simulation process and boundary conditions are often simplified，and it is difficult to accurately analyze the heat transfer and wall temperature distribution characteristics of the heating surface. For the above problems，numerical simulation of the 660 MW front and rear wall⁃hedged coal⁃fired boilers is car⁃ ried out by Fluent，and the coupled heat transfer model inside and outside the tube of the platen superheater is estab⁃ lished. The sequential calculation method according to the flow direction of the steam in the tube is proposed， and the coupled calculation of heat transfer between the flue gas side and the steam side is realized based on UDF. Meanwhile，the influence of different swirl angles of the external secondary air on the heat transfer of the platen superheater is studied，which requires the heat transfer and wall temperature characteristics of the platen superheat⁃ er considering both the flue gas side and the steam side. From the results，it can be concluded that the relative error of the outlet wall temperature at the No.22 tube of the platen superheater is within 4% of the test values. The swirl an⁃ gle of the external secondary air increases from 15° to 60°，the rigidity of the pulverized coal flow is weakened， the combustion is not violent，the ignition of the pulverized coal is delayed，and the flame surface of the furnace is raised. And the temperature distribution of the platen superheater changes from “high at both ends and low in the mid⁃ dle” to “low at both ends and high in the middle”. When the swirl angle is 45° and 60°，the maximum wall tempera⁃ ture of the platen superheater is 945 K and 965 K respectively，which exceeds the maximum allowable temperature of the heating surface material. However，when the swirl angle is 15° and 30°，the maximum wall temperature of the platen superheater is less than the maximum allowable temperature of the heating surface material. The better external swirl angle should be 15°-30°.