Effects of Ash Composition and Combustion Temperature on Reduced Particulate Matter Emission by Biomass Carbonization

Thermochemical pretreatment, including carbonization, has been suggested as a method to reduce particulate matter (PM) emissions during the combustion of biomass. However, the carbonization efficiency might not be equal for all types of biomass because of composition heterogeneity and differences in combustion conditions. Therefore, an assessment of PM emission reduction by carbonization of various types of biomass at different combustion temperatures is required. In this study, seven different types of biomass (larch, poplar, miscanthus, bamboo grass, rice straw, rice husk, and dairy manure) and their biochars (prepared at 400 degrees C) were combusted at 650, 750, and 850 degrees C. The results showed that PM emission was reduced as much as 95.45% after carbonization as a result of volatile matter removal. The efficiency of PM reduction was greatest at low combustion temperatures for all feedstocks. Although the combustion temperatures did not strongly affect PM emissions from low-ash (<= 6.7%) biomass, higher heating temperatures (>= 750 degrees C) stimulated PM emissions from ash-rich rice straw and dairy manure biochar. The transformation of minerals in rice straw, rice husk, and dairy manure was also investigated at different combustion temperatures (650, 750, and 850 degrees C). Mineral analysis revealed that enhanced PM emission from ash-rich biochar samples was attributable to a greater concentration of Na and K, which likely resulted from melting at higher combustion temperatures. We found that carbonization can substantially reduce PM emissions for low-alkali-containing biomass and that a lower combustion temperature of biochar is preferable to suppress PM emissions for high-alkali-containing biomass. Our findings reveal a possible approach to waste-to-energy production with reduced health risks.