Thermal conditioning of remoistened wheat straw to produce durable pellets

Abstract

Agricultural biomass like wheat straw is known to be lacking natural binders to form durable pellets. Our previous research had shown that steam explosion of wood improved the durability of pellets. However, treated wood required drying prior to pelletization. Thermal conditioning is practiced in the animal feed industry to modify the ingredients of animal feed to produce high quality pellets. We hypothesized that thermal treatment of straw would result in biomass pellets with improved durability when compared to pellets made from untreated biomass. To test this hypothesis, the moisture content (mc) of the straw samples was adjusted to 5%, 10%, and 15% (wet basis). The moistened samples were subjected to dry heat in a sealed reactor set at 80, 100, and 120 °C for 5, 10, and 15 min. The treated straw samples were pelletized by using a single piston cylinder system. The highest durability 91.5% belonged to the treatment of 10% mc straw at 100 °C for 5 min. A response surface method confirmed that the initial mc 10%, treatment temperature 100 °C, and treatment time 5 min, produced the most durable pellets with the lowest unit energy input in forming pellets.