Torrefaction of woody biomass (Juniper and Mesquite) using inert and non-inert gases

Abstract

Torrefaction has been shown to be a viable pre-treatment process for thermally upgrading biomass and making it better suited for use as a fuel. Results are presented here from the torrefaction of two different woody biomass (Mesquite and Juniper) using thermogravimetric analysis (TGA). Samples were torrefied in two different mediums (Nitrogen and Carbon-dioxide) to investigate the impact of inert and non-inert gases on the thermal degradation of the biomass, specifically mass loss as well as the breakdown of hemicellulose, cellulose, and lignin. A wide range of torrefaction temperatures ranging from 200 to 300°C was investigated at a single residence time. TGA thermograms showed increased amounts of weight loss when the biomass was torrefied in a Carbon-dioxide environment compared to inert environments, while derivative thermogravimetric analysis (DTA) showed a drop in the peak rate of hemicellulose and cellulose weight loss when using Carbon-dioxide as the torrefaction medium. Fuel properties analysis of samples subjected to a mild torrefaction process (240°C) showed increases in ash and fixed carbon content of the biomass, independent of torrefaction medium. Furthermore, comparison of the grindability of raw and torrefied samples showed torrefaction in a Carbon-dioxide environment further improved the grindability of the torrefied biomass. The effect of inert and non-inert torrefaction mediums on the volatile species (CO2, CO, CH4, and C2H6) released from torrefied Mesquite during pyrolysis was further investigated via TGA–FTIR analysis.