Effect of biomass blending ratio and excess air ratio on co-firing of coal with rice husk and bamboo

An experimental study of co-combustion of coal and biomass was conducted in a laboratory scale flow reactor to investigate the combustion and pollutant emission performance under different operating parameters. Rice husk and bamboo were used as the biomass fuels in this study. This paper described the influence of the biomass blending ratio in the fuel mixture and the excess air ratio on the combustion behavior. It was noted that the combustion temperature and the energy output from the co-firing process were reduced compared to coal combustion alone owing to the fact that biomass has lower heating value compared to coal. However, the high volatile matter (VM) content of biomass reduced the combustion time scale so that Carbon monoxide (CO) and particle emissions were reduced substantially. In addition, the fuel nitrogen and sulfur content in biomass were lower than that of coal and hence suppressed the formation of Nitrogen oxides (NO_x) and Sulfur dioxide (SO₂). The increase of excess air ratio could also help to increase the combustion temperature. The pollutant emission per unit energy output was investigated in detail in this paper. An operational range between 10% and 30% of biomass to coal ratio was found to be the optimum range in terms of minimum pollutant emissions per unit energy output. Attention should be paid to the high potential for slagging and fouling in the boiler when co-firing coal with biomass.