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 (O 2 , 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. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.