Reducing NOx emissions of an opposed swirling coal-fired utility boiler by optimizing in-service burner mode

A computational fluid dynamics (CFD) model of a 600 MW opposed swirling coal-fired utility boiler has been established to numerically investigate the characteristics of flow, combustion, heat transfer and nitrogen oxides (NO_x) emission under the different modes of in-service burner layers. The current CFD model has been validated by comparing the simulated results with the experimental data. The results show that the different in-service burner layer modes have different influences on the residence time of the pulverized-coal particles, effect of air staging in the burner region and flue gas temperature at the exit of the lower furnace. Stopping the upper burner layers can increases the residence time of the pulverized-coal particles, resulting in the reduction of the carbon content in the fly ash and the increase of the pulverized- coal burnout. It can also enhance the effect of air staging in the burner region. Consequently, the NO_x emission decreases. The flue gas temperature at the exit of the lower furnace can also decrease, being helpful to reducing the slagging tendency on the surfaces of the platen superheaters.