Volatile yields and solid grindability after torrefaction of various biomass types

Raw biomass grinding is a highly energy-intensive step due to the fibrous structure of the material. Torrefaction, which enables the partial destruction of this fibrous structure through mild thermal treatment, appears as an attractive option. In this work, a complete quantification of species released during torrefaction was performed on four various biomass types: softwood, a perennial crop, an agricultural residue, and a short rotation coppice. A specially designed fixed-bed reactor was used to characterize the different products released during torrefaction under controlled conditions. The mass balance was evaluated by quantification of the biomass weight loss and species released. For each sample of torrefied biomass, weight loss, a proximate analysis, and lower heating value were quantified, and detailed mass balances including an analysis of condensable species were performed. The results showed that, under the explored torrefaction conditions, the nature of the feedstock had a significant effect on solid weight loss and compositions, and on the yields of volatile and condensable species. A specific grinding protocol was used to evaluate torrefied biomass grindability. The grindability of torrefied biomass was significantly improved compared to raw biomass, but this tendency was less marked in the case of the agricultural residue than for the other biomasses. (c) 2014 American Institute of Chemical Engineers Environ Prog, 34: 1180-1186, 2015