BIOMASS TORREFACTION – GRINDABILITY AND DUST EXPLOSIBILITY

Abstract

Torrefaction, a thermo-chemical process, improves properties such as energy density, grindability, hydrophobicity of the biomass. As a result of the altered properties, the biomass behaves more like coal increasing the feasibility of co-firing. The first part of the work examined how torrefaction affects dust explosbility characteristics. Both the minimum ignition temperature (MIT) and the minimum explosible (MEC) concentration for a given particle size distribution were measured. Two extremes cases were tested, both under-torrefied samples (200˚C) and over-torrefied samples (300˚C) as well as a common torrefaction temperature of 250 ˚C. Three different particle size distributions were tested. Torrefaction temperatures showed minimal to no impact on MEC and MIT. The second part of the study examined how torrefaction changed the grindability of biomass. Experiments were performed for torrefaction temperature ranges between 200-300 ˚C using a Hardgrove Grinding Index (HGI) Machine. For co-firing it is necessary to grind coal and torrefied biomass together. Varying volume percentages of coal and biomass were mixed and their overall HGI value was measured. This value was compared with that predicted using individual HGI values of coal and biomass. The predicted values showed reasonable correlation to the actual values.