Emission of NOx and N2O from co-combustion of coal and biomasses in CFB combustor

Utilization of biomass in combustion processes is a promising way to reduce net emission of greenhouse gas, e.g. CO2, to atmosphere. However, biomass is not likely to be successfully employed as a single feedstock due to its low energy density compared to coal. The co-combustion of coal and biomass in a circulating fluidized bed combustor (CFBC) can be employed to address this issue by improving the overall calorific value. This work investigated the influences of different biomass types on CFBC emissions. Sub-bituminous coal along with four biomass types such as palm shell, coconut shell, sawdust and rice husk were employed in study. The results indicated that the temperature profile in the riser was matter relevant to the heating value of fuel mixtures. The co-combustion of coal and palm shell gave the highest average combustion temperature, due to comparable heating value of both fuels. On the other hand, the co-combustion of coal and rice husk, which has relatively lower heating value, gave the lowest temperature. The presence of biomass in combustion was found to lead to a reduction of NOx and N2O in flue gas. The fuel-nitrogen content was observed to be a major factor for determining both NOx and N2O emission. Moreover, this work exhibited that the injection of secondary air with different position into the riser influenced the NOx and N2O concentration in the flue gas.

► Effect of biomass types on NO and N2O emissions from co-combustion with coal was investigated in a CFB combustor.
► Nitrogen content in biomass feedstock was found to have more significant effect than nitrogen in air on the NO and N2O formation during co-combustion in the CFB.
► The emission of NO and N2O in the CFB can be controlled by manipulating air injection along the riser.