Emission performance of type-1 pulverized coal flames operating under oxy-fired conditions

This work addresses the emission performance (CO, NOx, SO2) on pulverized coal flames generated by a staged feed-gas burner operating with pre-dried lignite under oxy-fired conditions. While previous studies provided information on the impacts of recycle ratios and O2 fraction, this works focuses on the impacts of swirl strength and feed gas distribution on the combustion process. The overall O2 fraction upstream of the burner operating under oxy-fired condition was defined with basis on a similar adiabatic flame temperature as air-firing. Images obtained with visualization techniques show evidence of a stratified flame structure resembling a diffusion type-1 flame. Measurements of CO concentration and particle burnout at the furnace exit indicated that carbon in ash is not an obstacle for the use of staged feed-gas burner in oxy-firing. Experimental results do show a great potential for NO abatement through an appropriate burner setting. In particular, a combination of high swirl strength and high secondary/tertiary flow ratio results in significant NO reduction. Evaluation of SO2 levels show that oxy-fuel combustion does not affect the release of sulfur from the pre-dried lignite under the conditions evaluated in this work, indicating that SO2 emissions are exclusively dependent on the sulfur content of the coal.