Thermal characterization of coal/straw combustion under air/oxy-fuel conditions in a swirl-stabilized furnace: a CFD modelling

Global warming is mainly due to increase of CO2 from fossil fuel based power generation in developed countries. The level of CO2 increase in the atmosphere is alarming. International effort imposed some strict obligations to control these emissions. To reduce the greenhouse gas emissions, shifting from coal based production to biomass resources is a must. The present study investigates the combustion behaviour of biomass (straw) compared with the coal combustion in air and O2/CO2 mixtures. Reference air-fuel and oxy-fuel (25%, 30% and 35% O2) cases were considered maintaining a constant thermal load of 30 kW in a semi-technical scale once-through swirl-stabilized furnace. The main objective of this study is to illustrate the impact on the combustion characteristics including flame temperature, burnout, and emissions for pure coal to pure biomass (straw) combusted in air and oxy-fuel atmospheres. Good agreement between the results obtained in this numerical work and results reported in literature was observed. This work has shown that significant changes occur to the fundamental combustion characteristics for straw when burned in the O2/CO2 atmosphere compared to air firing case. Comparatively higher flame temperatures were observed for oxy-firing case. The CO levels are predicted to decrease in the downstream section during oxy-fuel combustion compared to air-firing flames due to O2 availability. The burnout is reliably advanced during oxy-fuel combustion to 99.8% than air firing