Characterization of fine particulate matter generated in a large woody biomass-firing circulating fluid bed boiler

Abstract

The formation and emission of ash particles in biomass combustion is one of the most intractable challenges in the biomass-firing utility boilers. In present study, field measurements of PM10 at the inlets and outlets of the baghouse equipped on a 50 MW biomass-firing CFB boiler were carried out. The results showed that PM10 generated from the combustion of the biomass fuels in the CFB boiler exhibited a uni-modal size distribution. The sole modal peak (appeared at 5 μm) in the PSD curve was located in the size range >1 μm, while there was no visible peak in the size range <1 μm. The coarse PM mainly exhibited rough and angular surfaces with elements Ca, Si and Al as the principal constituents. The mass concentrations of PM1, PM2.5 and PM10 after the bagshouse were reduced to 0.95, 5.58 and 25.70 mg/Nm3 respectively, corresponding to the capture efficiencies of 97.80%, 98.52% and 98.64%. Moreover, the PM capture efficiency was observed to decrease with decreasing particle size in PM0.2. More Cl migrated into the fine PM when passing through the baghouse. Further comparisons revealed that the mass ratios of PM1 in PM10 in the flyash generated in the CFB boilers were <10%, which was much lower than that in the grate boilers firing biomass (40–80%), which is beneficial to PM removal in the dust removers and reduce the final PM emission during biomass combustion.