Impact of the Blending of Kaolin on Particulate Matter (PM) Emissions in a Biomass Field-Scale 250 Kw Grate Boiler

The aim of the study was to investigate the impact of adding kaolin on the partitioning of chemical elements in the particulate matter (PM) when virgin and waste woody biomass fuels were fired in a 250 kW grate boiler. A comprehensive analysis of the chemical compositions of the PM has been conducted, including alkali and nonvolatile species, size-fractionated mass concentrations and micromorphology images. The results showed that the PM emission levels were significantly decreased by approximately 70-76 % and 60-66 % after the addition of kaolin to virgin wood (VW) and grade A recycled wood (RW), respectively, which inhibited the partitioning of the alkali species into fine and ultrafine PM. On the other hand, the concentration of the non-volatile elements, SiO2 and Al2O3, significantly increased in the PM emissions after the addition of kaolin due to the adhesion and aggregation of particulates between airborne kaolin and the fine and ultrafine PM. Moreover, the addition of the kaolin at 1.55 wt% showed comparable effects with that at 2.5 wt% on the chemical composition of PM emission. Furthermore, the SEM morphology suggested that KCl salts were diminished after the addition of the kaolin. These findings demonstrate the practicality of adding kaolin to mitigate PM emissions and their impacts in actual biomass combustion scenarios.