20. Numerical Investigation on Combustion Characteristics and NO_x Emission of Double-Reheat Tower Boiler at Different Loads

In this study, a three-dimensional numerical investigation using a finite volume method is presented to obtain the velocity, temperature, and species distributions in a 660 MW double-reheat tower boiler fed with bituminous coal. The refined oxidation model of HCN and NO-char reaction model were used to substitute the default model by the user-defined functions (UDFs). The effects of different loads and excess air ratios on combustion characteristics and NO_x emission were studied numerically. The results show that temperature distribution is more uneven at the upper part of the furnace and the NO_x emission increases as the load decreases. The temperature distributions in the furnace have little differences under three different excess air ratios. That the oxygen concentration increases significantly as the increase of excess air ratios leads to an increase of NO_x emission at the furnace outlet. The minimum NO_x concentration at the furnace outlet, 308 ppm, appears under 100% THA with excess air ratio of 1.15. The simulation results in this study can provide reference for optimization of combustion characteristics in double-reheat tower boiler and illustrate a method to reduce NO_x emission.