Torrefaction Effects on the Reactivity and Explosibility of Woody Biomass

Abstract

Biomass is increasingly being used as a fuel for power generation. Torrefaction has helped improve some of the drawbacks associated with the use of raw biomass by making it easier to grind, increasing energy density and reducing transport costs. However, data relevant to the safe handling against the fire and explosion risks associated with the use of biomass is scarce, and in the case of torrefied biomass non-existent (in the open literature). In this work, the effect of torrefaction severity over the explosibility and reactivity of 5 samples of torrefied wood biomass was investigated. All samples were milled using the same procedure to nominally below 63μm.The Leeds modified Hartmann apparatus was used to measure the minimum explosible concentrations (MEC) as well as the rates of pressure rise and flame speeds inside the vessel over a range of concentrations for each of the samples. The results showed a small reduction in reactivity with increasing torrefaction severity and this was attributed to the reduction of volatile content whilst it is thought an increase in the fraction of fines (due to the increase in brittleness) for the more torrefied samples, moderated the effect of volatile content reduction on the reactivity by providing finer particles, easier to burn. The MEC was found to be around 0.2 equivalence ratio (similar to raw biomass), which is less than half that reported for coal.