Experimental study on combustion, flame and NOX emission of pulverized coal preheated by a preheating burner

Experimental researches on combustion characteristics of pulverized Ningdong bitumite preheated by a preheating burner were carried out in a 0.2 MW coal preheating combustion test rig, and the effects of preheating temperature, secondary air equivalence ratio and the positions of tertiary air nozzles on combustion, flame and NOX emissions of preheated fuels were studied. The results showed that the 0.2 MW coal preheating combustion test rig can operate stably and the combustion efficiency can be higher than 97% while the NOX emissions are lower than 100 mg/Nm3. With the increase of preheating temperature, NOX emissions increase, and the combustion efficiency does not change obviously. With the increase of secondary air equivalence ratio, the combustion efficiency increases, and NOX emissions increase as well. With the increase of the distance between the tertiary air nozzle and the preheated fuel nozzle, NOX emissions decrease, and the combustion efficiency decreases as well. The flame characteristic is not sensitive to preheating temperature, but closely related to the air distribution of down-fired combustor. With reasonable air supply positions, flameless combustion can be realized.