Emission Mitigation by Aluminum-Silicate-Based Fuel Additivation of Wood Chips with Kaolin and Kaolinite

This study investigates the transferability of aluminum-silicate-based fuel additivation as a primary, fuel-based mitigation measure for inorganic alkali-based particulate matter (PM) emissions during the complete combustion of wood chips. Therefore, wood chips are additivated with 0.5 wt% of three different types of the aluminum-silicate-based additive kaolin, which differ mainly in their particle size distribution, and with one type of kaolinite. The subsequent combustion trials with non-additivated and additivated wood chips are carried out in a small-scale combustion plant. To evaluate the effect of the additivation of the wood chips, the total particulate matter (TPM) emissions, the potassium (K) emissions, the ultra-fine PM emissions and the carbon monoxide (CO) emissions, as well as the chemical composition of the resulting ashes, are analyzed. In order to compare the primary, fuel-side mitigation measure of fuel additivation with the established secondary mitigation measures, an electrostatic precipitator (ESP) is additionally utilized. The respective result shows that the aluminum-silicate-based fuel additivation of the wood chips with kaolin and the use of the ESP lead to comparable reductions in the TPM emissions, as well as the share of the ultra-fine particle fraction in the PM emissions. The addition of the additive kaolin additionally causes the significant mitigation of the K and CO emissions. Overall, the obtained results suggest that the combined utilization of fuel-side aluminum-silicate-based fuel additivation, together with the secondary mitigation measure of the ESP, might be very promising to further reduce PM emissions from combustion devices that operate with wood chips.