Experimental investigation into pulverized-coal combustion performance and NO formation using sub-stoichiometric ratios

The influence of using sub-stoichiometric ratios on pulverized-coal combustion and NO formation and reduction in a pulverized-coal combustion test system with a swirl burner was investigated. Local gas components, gas temperature, the char burnout rate, and carbon and nitrogen release rates were measured at different positions in the test facility. A method for determining the fuel-rich zone boundary within the swirl pulverized-coal flame is proposed, and a new parameter, for scaling the degree of released fuel-N conversion to NO is defined. The maximum NO concentration was at the boundary between the primary-air and secondary-air jets along the cross-sections near the burner, at different stoichiometric ratios. The overall NO emission concentration decreased from 661.89 mg/N m³ (at 6% O₂) to 169.99 mg/N m³ (also at 6% O₂) when the stoichiometric ratio decreased from 1.0 to 0.7. The conversion of released fuel-N to NO dominated the overall NO emissions at sub-stoichiometric ratios. Decreasing the stoichiometric ratio did not significantly affect the ignition performance of the burner, but the position of the flame center moved downstream and the slagging tendency increased.