Abstract: The high sodium content in Zhundong coal leads to serious fouling and slagging on the heating surface of the boiler during combustion.Adding kaolin to the combustion process of Zhundong coal and reducing the alkali metal concentration through its reaction with alkali metal vapors in the flue gas is an effective method to attenuate the problem of fouling and slagging. A 600 MW opposed-fired boiler is focused on, and a mathematical model is established for the processes of sodium release from coal during combustion, the gas-phase reaction of sodium, the reactions of sodium with kaolin, and the condensation of NaCl vapor on heated surfaces. A numerical simulation was conducted on the combustion of Zhundong coal under varying proportions and methods of kaolin addition.The results indicate that within the range of 0% to 3% kaolin addition, both the concentration of NaCl vapor in the flue gas and the condensation rate of NaCl vapor on the heated surfaces significantly decrease with increasing kaolin proportions.However, when the kaolin addition exceeds 3%, the reduction in NaCl concentration and condensation rate begins to stabilize. Furthermore, changing the add method of kaolin addition from the lower burners to all burners results in an additional reduction in both the NaCl concentration and the condensation rate of NaCl vapor on the heated surfaces.