Torrefaction Temperature Effects on Grindability of Wheat Straw Using TG-FTIR Analysis

Abstract Torrefaction used for pretreatment of biomass can enhance grindability along with significant reduction of energy consumption required for pulverization to aid in large-scale utilization of biomass energy. In this study, torrefaction experiments of wheat straw were conducted at different temperatures using an experimental furnace facility. The influence of torrefaction temperature on the grindability of resulting wheat straw was explored using a Hardgrove grindability index tester and thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR). Increase in torrefaction temperature significantly enhanced the carbon content of wheat straw and decreased oxygen content to result in decreased O/C ratio from 0.66 to 0.39. The calorific value increased by 24% from 15.42 MJ/kg to 19.17 MJ/kg. Increase in torrefaction temperature from 220 °C to 269 °C increased the grindability index from 29 to 115. The grindability of wheat straw can be controlled to values similar to that of coal by tuning the torrefaction temperature. The main gas components released during torrefaction were H2O, CH4, CO2, and CO. Thermogravimetric data showed 29% solid residue from the raw wheat straw. Increase in torrefaction temperature increased the solid residue to 41%. Pyrolysis of wheat straw at different torrefaction temperatures can be grouped into three stages of dehydration, rapid pyrolysis, and carbonization. This study reveals effective large-scale utilization of torrefied wheat straw biomass having high heating value of the solid fuel after torrefaction pretreatment.