Fine Particulate Formation During Switchgrass/Coal Cofiring

Experiments to examine the effects of biomass/coal cofiring on fine particle formation were performed in the Sandia Multi-Fuel Combustor using fuels of pure coal, three combinations of switchgrass and coal, and pure switchgrass. For this work, fine particles with aerodynamic diameter between 10 nm and 1 μm were examined. A constant solid-fuel thermal input of 8 kW was maintained. The combustion products were cooled from 1200 to 420°C during passage through the 4.2 m long reactor to simulate the temperatures experienced in the convection pass of a boiler. Fine particle number densities, mass concentrations, and total integrated number and mass concentrations at the reactor exit were determined using a scanning mobility particle sizer. The fine particle number concentrations for cofiring were much higher than those achieved with dedicated coal combustion. However, the total integrated mass concentration of particles remained essentially constant for all levels of cofiring from 0% coal to 100% coal. The constant mass concentration is significant because pending environmental regulations are likely to be based on particle mass rather than particle size.