Effects of combined pretreatment with rod-milled and torrefaction on physicochemical and fuel characteristics of wheat straw

The mechanism of rod-milling combined with torrefaction as well as its effects on physicochemical and fuel properties of wheat straw were investigated. Rod-milling and hammer-milling samples were torrefied under three temperatures (250, 275, and 300 °C) with a duration time of 30 min. The results indicated that combined rod-milling and torrefaction pretreatment (CRT) significantly elevated carbon content, higher heating value, fuel ratio, and reduced oxygen content and atomic H/C and O/C ratios in wheat straw. Moreover, CRT significantly reduced cellulose crystallinity, and increased the specific surface area and pore volume of wheat straw, which lowered the wheat straw's degrading pyrolysis temperature. These peak values appeared under 300 °C. Devolatilization index (D_i) was improved by rod-milling pretreatment under identical torrefaction conditions except 275 °C. Therefore, the combination of rod-milling with torrefaction under 300 °C has the advantage of enhancing fuel properties of lignocellulosic biomass materials.