Experimental study on NO emission and ash deposition during oxy-fuel combustion of high-alkali coal under oxygen-staged conditions

Abstract

The oxygen-staged combustion is an effective strategy to reduce NO emission, but its effects on ash deposition in oxy-fuel combustion of Zhundong high-alkali coal still remain unclear. This paper simultaneously focused on the NO emission and ash deposition during the oxygen-staged oxy-fuel combustion of Zhundong coal using a vertical two-stage furnace system. The air- and oxygen-staged combustion were compared and the impacts of oxygen content and stoichiometric ratio in primary zone (SR1) in oxygen-staged combustion were further evaluated. The results show that compared to air-staged combustion, the oxygen-staged case in oxy-fuel combustion leads to smaller conversion ratio of fuel-N to NO (XNO) and smaller mass of ash deposit. Under oxygen-staged conditions, both the XNO and deposit mass have an upward trend as the oxygen content increases (15%–50%). About 20 mg more ash could be collected for every 10% increase in oxygen content. The XNO increases when SR1 gets elevated from 0.5 to 1.2, however, the deposit mass exhibits a downtrend at SR1 ≤ 0.9 and becomes nearly independent of oxygen supply when the SR1 further increases. The SR1 of 0.9 is a reasonable choice, and some measures should be taken to alleviate the ash-related problems if smaller SR1 is needed.