Effect of combining water washing and carbonisation on the emissions of PM10 generated by the combustion of typical herbs

Abstract

To overcome the shortcomings of biomass, such as poor fuel characteristics and high alkali metal content, two typical herbs (rice straw and sesame stalk) were processed by pretreatments combining water washing and carbonisation (T-W: water washing after torrefaction; W-T: torrefaction after water washing; and HTC: hydrothermal carbonisation), and the effects on PM10 (particulate matter with an aerodynamic diameter of 10 μm or less) emissions were determined. For both biomasses, PM1 was mainly composed of K, Cl, and S, and all three pretreatments perform well in its reduction (HTC > W-T > T-W). The emission reduction effect on PM1 was determined by the removal extent of the above elements by various pretreatments. Regarding PM1–10, for rice straw, its emission only increased after HTC, and the other two pretreatments did not change substantially. As for sesame stalk, its emissions increased significantly after the three pretreatments. The change in the mineral content of the sample and the degree of fragmentation during combustion together determined the effect of pretreatment on PM1–10 emission. Based on equal energy input, the three pretreatments performed better on PM10 reductions for both typical herbs.