Effects of ash composition and combustion temperature on reduced particulate matter emission by biomass carbonization

Abstract Biomass is a potential substitute for fossil fuels but has some drawbacks, such as low energy density, high moisture content, and particulate matter (PM) emissions during combustion, that need to be addressed. Thermochemical pretreatment, including carbonization, has been suggested to address these issues. However, the efficiency of carbonization is not equal for all types of biomass due to composition heterogeneity. Therefore, this study involved the carbonization of seven types of biomass (larch, poplar, miscanthus, bamboo grass, rice straw, rice husk, and dairy manure) at 400°C to evaluate efficiency in enhancing fuel properties and reducing PM emissions. All raw and carbonized samples were combusted at 650, 750, and 850°C to assess the effect of combustion temperature on PM emission. Results showed that PM emission was greatly reduced up to 95.45% after carbonization via volatile matter removal. The efficiency of PM reduction was greatest at low burning temperatures for all feedstocks. Although combustion temperatures had no major impact on PM emissions from low-ash (≤ 6.6%) biomass, higher heating temperatures (750°C or above) stimulated PM emissions from ash-rich rice straw and dairy manure biochar. The transformation of minerals in rice straw, rice husk, and dairy manure also was investigated at different combustion temperatures (650, 750, and 850°C). Data revealed that enhanced PM emission from ash-rich biochar samples was due to a greater concentration of Na and K, likely through Na and K melting at higher temperatures. Therefore, to limit PM emissions from the chars produced by high-alkali-metal biomass, a lower combustion temperature is preferable.