Numerical Simulation of NO(x) Emission Characteristics of a Cyclone Boiler with Slag-Tap Furnace

[Image: see text] In order to optimize the parameters of boilers and realize the burning of pure, high-alkali coal, the velocity field, temperature field, and component distribution characteristics of a new cyclone boiler with slag-tap furnace were numerically studied using ANSYS software. The influence law of the over-fire air rate on the NO(x) emission of the cyclone boiler with slag-tap furnace was established, and the optimal over-fire air rate was determined. The renormalization-group k–ε double equation model was used to simulate the gas phase flow, the discrete phase model was used to compute the gas–solid two-phase flow, and the high-alkali coal combustion model was revised based on experimental data. The results show that the overall aerodynamic field in the entire boiler with slag-tap furnace is favorable, the flue gas is completely formed, and the cyclone burners in a staggered and reversed arrangement can enhance combustion. The temperature near the wall of the cyclone can reach 1700–2100 K, which satisfies the requirements of a liquid slag discharge. The temperature under various over-fire air rate conditions can allow the high-alkali coal to burn normally and ensure fluidization of its ash. The greater the over-fire air rate, the lower the average temperature in the furnace and the lower the NO(x) concentration at the outlet of the furnace. Considering that it is not easy to fluidize the ash of high-alkali coal when the average temperature in the cyclone boiler with slag-tap furnace is very low, an over-fire air rate of 10% is selected for the optimal air-staged combustion scheme.