Synergistic effect of co-firing woody biomass with coal on NOx reduction and burnout during air-staged combustion

Hybrid technologies combining fuel blending and air-staging processes have been applied to a pulverized coal fired furnace to reduce NOx emissions. In this study, an Australian bituminous coal (Whitehaven), an Indonesian sub-bituminous coal (Adaro), and an Indonesian woody biomass were selected as fuel with blending ratio of 10%, 20%, and 30% of the low-rank fuels, and the air-staging levels were set to 235 mm, 390 mm, 585 mm, and 760 mm. The purpose of this study was to investigate the synergistic effect of woody biomass co-firing on the level of NOx emissions and the degree of carbon burnout under air-staged conditions. For single coals, sub-bituminous coal was more favorable than that for bituminous coal to reduce NOx emissions due to low fuel-N composition. This tendency was more dominant with increasing the air staging levels. In the co-firing of woody biomass with coal, as the biomass is highly volatile but has a low carbon content, it could be successfully applied to low-NOx combustion under air-staged conditions. In addition, the degree of carbon burnout and the flame temperature both increased. As a result of this research, we determined that hybrid NOx reduction technologies have the potential to reduce exhaust gas emissions and enhance combustion performance. A dominant synergistic effect on NOx reduction and carbon burnout was observed when woody biomass co-firing with coal was applied to air-staged combustion.