Optimization of air staging in a 1 MW tangentially fired pulverized coal furnace

This paper deals with an experimental study of air staging in a 1 MW (heat input power) tangentially fired pulverized coal furnace. The influences of several variables associated with air staging on NO_x reduction efficiency and unburned carbon in fly ash were investigated, and these variables included the air stoichiometric ratio of primary combustion zone (SR₁), the locations of over-fire air nozzles along furnace height, and the ratio of coal concentration of the fuel-rich stream to that of the fuel-lean one (RRL) in primary air nozzle. The experimental results indicate that SR₁ and RRL have optimum values for NO_x reduction, and the two optimum values are 0.85 and 3:1, respectively. NO_x reduction efficiency monotonically increases with the increase of OFA nozzle location along furnace height. On the optimized operating conditions of air staging, NO_x reduction efficiency can attain 47%. Although air staging can effectively reduce NO_x emission, the increase of unburned carbon in fly ash should be noticed.