Numerical simulation of combustion characteristics and NO_x emissions in a 300 MW_e utility boiler with different outer secondary-air vane angles

We experimentally and numerically studied the pulverized-coal combustion process and NO_x emissions for a 300 MW_e wall-fired boiler burning bituminous coal. Measurements of the polar components of the gas velocity made with a particle-dynamics anemometer and calculated values are found to be in good agreement. Good agreement was also found for the CO ₂ concentration, NO_x concentration, and combustible material content in the fly ash between simulation and industrial experiments performed on full-scale boilers. For enhanced ignition-dual register (EI-DR) burners, pulverized coal is spread widely from the burner. Some pulverized-coal particles are thrown to the furnace hopper, and much pulverized coal is swept to the furnace hopper at the bottom of the boiler. As the outer secondary-air vane angle increases, the temperature of the water-cooled tube wall region near the burners and furnace hopper increases. Changes in the NO_x concentration at the furnace outlet are not simply linear with changes in the outer secondary-air vane angle. The NO_x concentration at the furnace outlet was lowest (420.2 ppm at 6% O₂) for an outer secondary-air vane angle of 35° and highest (468.2 ppm at 6% O₂) for an outer secondary-air vane angle of 30°. This represents an increase of 11.4%.