An Index for Quantifying the Degree of Torrefaction

Abstract

Torrefaction, a thermochemical pre-treatment process, is used to enhance the properties of biomass to make it more compatible with solid fossil fuels. A quantitative index (TI) is proposed here to define the degree or quality of torrefaction especially for its use in the energy industries. Torrefaction index is defined as the ratio of energy density enhancement factor of the product at the specified condition to that at a reference condition, which is torrefaction at 300 °C for 60 min. The index, calculated for a wide range of data shows a linear dependence on torrefaction temperature. Numerical values of this index were in range of 0.93 to 0.95, 0.95 to 0.97, and 0.97 to 1.0 for light, medium, and severe torrefaction conditions, respectively. Based on a wide range of experimental data of woody biomass, two empirical correlations for mass and energy yields were developed. These correlations permitted prediction of TI without performing torrefaction of the biomass.