Production of gaseous VOC/SVOC during softwood torrefaction under various technological conditions

Abstract

Torrefaction is a technology that can contribute to improving the properties of softwood biomass used for energy purposes (combustion, pyrolysis). As a result of the thermal treatment, the chemical composition of major compounds of biomass is changed, creating new compounds that were not contained in the original biomass. The article deals with the occurrence of organic compounds that are considered precursors of secondary organic aerosols (SOA) in gaseous emissions under different conditions of torrefaction (temperature, reaction time). Compounds considered precursors or intermediaries for the formation of secondary organic aerosol (SOA) have been identified based on data published in the literature. The concentration of SOA precursors in gaseous emissions decreases with increasing temperature of torrefaction. The mass balance shows that the gaseous component containing compounds that are considered by SOA precursors forms 6 % at torrefaction operated at 300 °C, 13 % at 250 °C, and up to 16.6 % at 200 °C. A statistically significant inversely proportional relationship between the amount of SOA emitted and the concentration of fixed carbon in the torrefied biomass has been demonstrated. With increasing concentrations of fixed carbon in the torrefied biomass, concentrations of emitted SOA precursors decrease. At 200 and 250 °C, SOA precursors are released at the highest concentrations and arise from the thermal conversion of hemicellulose. The lowest concentrations of SOA precursors released from hemicellulose and lignin were found at 300 °C. The article highlights the problem of SOA formation, which may affect not only human health but also climate change.