Effect of horizontal staging of secondary air on NOx emissions in a 600 MW tangentially coal-fired utility boiler

Numerical simulations have been carried out to numerically investigate the characteristics of flow, combustion, heat transfer and nitrogen oxides (NO_x) emission with the deflection angles of CFS nozzle flows for a 600 MW tangentially coal-fired utility boiler. The simulated results, such as the carbon content in fly ash, NO and oxygen concentrations in flue gas at the furnace exit, agree well with the experimental data. The results show that the deflection angles of CFS nozzle flows have obvious influences on the effect of horizontal air staging in the burner region. Increasing the deflection angle can enhance the effect of horizontal air staging in the burner region, decreasing both fuel- and thermal-type NO formation and consequently the NO emissions. The results also indicate that increasing the deflection angle has no negative effect on the pulverized-coal burnout. The present study provides helpful information in understanding the low NO_x characteristics of air staging for the studied boiler.