Investigating pellet charring and temperature in ultrasonic vibration-assisted pelleting of wheat straw for cellulosic biofuel manufacturing

Biofuels are only alternative solution for liquid transportation fuels among different kinds of renewable energy. To avoid the competition with the food, cellulosic biomass has been proposed as feedstock for manufacturing of cellulosic biofuels. Costs associated with collection, transportation, and storage of cellulosic biomass account for more than 80% cost of the feedstock. By processing cellulosic biomass into high density pellets, handling efficiency of cellulosic feedstocks can be improved, leading to costs reduction in transportation and storage. Ultrasonic vibration-assisted (UV-A) pelleting is a recently developed pelleting method, which can not only produce higher density but also break the lignin shell, to some extent, to increase cellulose accessibility and then increase sugar and biofuel yield. The reported investigations on UV-A pelleting provided little information about the relationship between charring and pelleting temperature under different input variables of pelleting. In this paper, effects of different input variables of pelleting on both charring ratio and pelleting temperature were studied. This paper, for the first time, reported the relationship between charring ratio and pelleting temperature. The obtained results will be helpful in understanding the mechanism of UV-A pelleting and providing guide to control pellet charring for a higher biofuel yield.