Experimental Study on Coal-Nitrogen Release and NO_x Evolution in Oxygen-Enriched and Deep-Staging Combustion

Abstract

Oxygen-enriched and deep-staging (OE and DS) combustion has drawn increasing attention due to its superior nitrogen oxide reduction efficiency and combustion efficiency. To clarify the NO x generation and burnout characteristics of coal in OE and DS combustion, the effects of temperature, oxygen concentration, and stoichiometric ratio in the fuel-rich zone (SR1) on conversions of coal nitrogen and char in fuel-rich (FR) and fuel-lean (FL) zones were experimentally studied in a drop-tube furnace. The results show that the decrease of SR1 leads to a dramatic decrease of NO x in the FR zone but an increase of NO x in the FL zone. When the SR1 is less than 0.8, the formation of NO x in the FL zone is much higher than that in the FR zone, which is mainly attributed to the oxidation of char-N in the FL zone. A high temperature promotes the formation of NO x in the FR zone and inhibits the NO x formation in the FL zone. The inhibiting effect of temperature in the FR zone (T 1) on NO x formation in the FL zone is stronger than its promoting effect on NO x formation in the FR zone, which indicates that the reduction of NO x by high temperature is mainly attributed to NO x reduction in the FL zone. The NO x formations in the FR and FL zones can all be remarkably reduced with the rise of oxygen concentration, and the inhibiting effect of O2 concentration on NO x generation in the FL zone is more remarkable. In addition, the FR zone is the main place for the heterogeneous conversion of coal, where the conversion rate of CO and CO2 can reach more than 75%.

Thermal Analysis Kinetics Study of Pulverized Coal Combustion under Oxygen-Rich Atmosphere

“…Daood et al 23 found that oxygen-enriched combustion reduced NO emissions and improved carbon burnout. Zhu et al 24 found that high temperature promoted NO x formation in FR (fuelrich) zone, and under staging conditions, the increase of oxygen concentration can reduce NO x generation in the FR (fuel-rich) zone and FL (fuel-lean) zone. On the contrary, Lei et al 25 found that when coal is burned in an oxygen-rich atmosphere, SO 2 emissions are reduced under different pressures.…”