Effect of biomass co-firing position on combustion and NOX emission in a 300-MWe coal-fired tangential boiler

Co-firing biomass in an existing coal combustion boiler is a promising way to mitigate carbon emission in the context of global carbon neutrality. This paper investigated the effect of biomass injection location on combustion and NOX formation characteristics in a 300-MWe tangential boiler co-firing with coal. Numerical models have been validated against experimental measurement for both pure coal firing and biomass/coal co-firing cases. Compared to pure coal firing, co-firing case with biomass injected into the highest layer can sustain a comparable temperature distribution profile along the furnace height, and generate a lower NO emission by around 20 ppm. By moving the biomass injection location downward, the temperature difference between co-firing and pure coal firing cases becomes larger, and the final NO emission increases continually from 222 to 240 ppm. When biomass is injected through the lowest layer, N element in biomass volatile is oxidized to NO directly because of the abundant oxygen; thus, NO emission turns to be the highest among all co-firing cases. Contrarily, when biomass is injected through the highest layer, the majority of N in biomass volatile is released as NH3, and it further acts as a reduction agent for NO, thus leading to the lowest NO emission.