Numerical Simulation of NOx Emission Characteristics of a Cyclone Boiler with Slag-Tap Furnace

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-e 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.