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

More efficient use of biomass in producing energy, both electrical and thermal, may reduce the imports of fossil fuels such as coal, petroleum, and natural gas. The effect of the biomass blending ratio in the fuel mixture and the excess air ratio on the combustion behavior was studied. The combustion temperature and the energy output from the co-firing process were reduced compared to coal combustion alone due to the fact that biomass has lower heating value compared to coal. However, the high volatile matter content of biomass reduced the combustion time scale so that CO and particle emissions were reduced substantially. The fuel nitrogen and sulfur content in biomass were lower than that of coal and thus suppressed the formation of NO_x and SO₂. The increase of excess air ratio could also help to increase the combustion temperature. The pollutant emission per unit energy output was studied. An operational range between 10 and 30% of biomass/coal ratio was the optimum range in terms of minimum pollutant emissions per unit energy output. This is an abstract of a paper presented at the 100th Annual Conference and Exhibition of the Air and Waste Management Association (Pittsburgh, PA 6/26-29/2007)