Impacts of Torrefaction on PM10 Emissions from Biomass Combustion

Abstract

Typical biomass torrefaction is a mild pyrolysis process under conditions of ordinary pressure, low temperature (200–300°C) and inert atmosphere. Torrefaction is considered to be a competitive technology for biomass pretreatment, but its impacts on the emissions of particulate matter from biomass combustion are worthy of further study. In this paper, three kinds of biomass, i.e., bagasse, wheat straw and sawdust were selected for torrefaction pretreatment and the impacts of torrefaction on the emission characteristics of PM10 from biomass combustion were investigated. The combustion experiments were carried out on a drop tube furnace. The combustion-generated particulate and bulk ash samples were collected and subjected to analyses by various techniques. The results show that torrefaction tends to result in a reduction of PM1 (particulates with an aerodynamic diameter less than 1 μm) emissions from combustion, but the extent of reduction is dependent on biomass type. The reduction of PM1 from the combustion of torrefied biomass is mainly because that the torrefaction process removes some Cl and S from the biomass, thereby suppressing the release of alkali metals and the emissions of PM1 during the combustion process. As for PM1–10 (particulates with an aerodynamic diameter within 1–10 μm), its emissions from combustion of torrefied biomasses are consistently reduced, compared with their untreated counterparts. This observation is primarily accounted for the enhanced particle coalescence/agglomeration in combustion of torrefied biomasses, which reduces the emissions of PM1–10.