Effect of inner secondary air cone length of a centrally fuel-rich swirl burner on combustion characteristics and NO_x emissions in a 0.5-MW pulverized coal-fired furnace with air-staging

Low NO_x burners and air staging technology are the most economic and effective means of reducing NO_x emissions from coal-fired furnaces. However, it is difficult to significantly reduce NO_x emissions through air-staged combustion in the furnace without reducing the boiler efficiency. The aim of this work was to study the effect of the inner secondary air cone length of a centrally fuel-rich swirl coal combustion burner on combustion and NO_x characteristics using a 0.5-MW laboratory furnace with air-staging. Gas temperature and concentrations of gaseous species (O₂, CO, and NO_x) were measured in the primary combustion and burnout zones for different inner secondary air cone lengths. It was found that the inner secondary air cone length had significant effects on NO_x emissions, unburned carbon content in the fly ash, and ignition performance of the burner. As the inner secondary air cone length increased, the unburned carbon content in the fly ash level increased, NO_x emissions decreased, and pulverized-coal ignition occurred later. The optimized results provide an important reference for engineering design.