Effect of particle size on particulate matter emissions during biosolid char combustion under air and oxyfuel conditions

In an industrial scale furnace, solid fuels can be fired in a wide range of particle sizes. This study aims to investigate the effect of the particle size on particulate matter (PM) emissions during combustion under air and oxyfuel (30% O2/70% CO2) conditions. Biosolid chars prepared from the pyrolysis of three different biosolid particle sizes at 1300 °C were burned in a drop tube furnace. The experimental results indicate that a shift from small to large char particles leads to >55% reduction in PM1-10 emission when combustion occurs in air, likely due to less intense char fragmentation experienced by the large char particles. Such a reduction originates from a decrease in Mg, Ca, P, Si, Al and some trace elements (V, Co, Cu, Zn and Mn) release as PM1-10. In contrast, PM1 emission is not affected by the char particle size. However, under oxyfuel conditions, the PM1-10 emission from the small char particles is ∼65% of that released during combustion in air. In addition, the PM1-10 emission from large char particles only reduced by ∼27% when compared to that from small char particles. This observation is likely to result from the coalescence of ash particles to form PM with particle sizes >10 µm due to the increase surface mobility caused by repeated formation and decomposition of CaCO3 in the ash.