Experimental study on NO emission and burnout characteristics during semi-coke preheating combustion

To explore the De-NO_x potential of the semi-coke preheating combustion technique at higher preheating temperatures(>1000 ℃), the effects of preheating temperature(600-1400 ℃), combustion temperature(1200-1400 ℃) and excess air coefficient(α=0.6-1.4) on the NO emission and burnout of semi-coke combustion were studied on a two-stage drop-tube furnace. The results show that higher preheating temperature can reduce both NO emissions and carbon content in fly ash. Besides, under the fuel-rich conditions, the reduction of NO caused by increasing preheating temperature is larger than that under the fuel-lean conditions. When the preheating temperature increases from 800 to 1400 ℃, there is a maximum NO reduction of 74%(α=0.6), which is much higher than that of 20.6%(α=1.4) under fuel-lean conditions. On the contrast, under fuel-rich conditions, the decrease of carbon content in fly ash caused by increasing preheating temperature is smaller than that under fuel-lean conditions. Under fuel-lean conditions, the maximum decrease of fly ash carbon content is 26.8% (α=1.4), which is higher than that of 15.95% (α=0.6) under fuel-rich conditions. About the effect of combustion temperature on the NO emission, it is found that there is a critical excess air coefficient. When the excess air coefficient is higher than the critical value, the NO emissions increase as the combustion temperature increases. However, when the excess air coefficient is lower than the critical value, the trend is opposite.