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

Abstract

Torrefaction used for the pretreatment of biomass can enhance grindability along with a 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 (TG-FTIR) spectroscopy. The results indicated that an increase in torrefaction temperature significantly increased the carbon content of wheat straw and decreased the oxygen content to result in a decrease in the 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. An 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 residues from the raw wheat straw. An increase in torrefaction temperature increased solid residue to 41%. The pyrolysis of wheat straw at different torrefaction temperatures can be grouped into three stages such as dehydration, rapid pyrolysis, and carbonization. This study reveals effective large-scale utilization of wheat straw biomass as a high heating value solid fuel using torrefaction pretreatment.