359 / 2018-07-23 09:25:16

Characterization of torrefied cotton stalk and combustion kinetics of pellets from torrefied biochar

全体主题 > 生物质固体成型燃料

Biomass is a green energy source full of potential, but direct use is inefficient. Torrefaction is an effective pretreatment method to improve biomass performance. In this work, the characteristics of cotton stalk by torrefaction at different temperatures (240~320℃) and residence times (1~8h) were investigated. Also, the manufacture of torrefied pellets and their pelletization energy consumption, mass density, compressive strength and durability were investigated. The results indicated that the part properties of cotton stalk were improved after torrefaction. For example, the HHV increased from 19.05 MJ/kg to 21.00 MJ/kg by torrefaction at 280℃-4h. The O/C and H/C ratios of 0.97 and 0.14 for raw material decreased to 0.31and 0.06 at 320℃-4h because of dehydroxylation and decarboxylation reactions. The pelletization energy consumption of torrefied biochar was higher than biomass raw material, and torrefied pellets showed low mass density, compressive strength and durability compare to raw material pellets. Mass density, compressive strength and durability were all lowest at 320℃-4h. Transitions of activation energy levels between different torrefied biochar pellets were discussed on the basis of Coats-Redfern kinetics. Activation energy levels tended to decrease with increasing temperature, so high temperature was beneficial to improve the combustion performance of biochar pellets. Compared with biomass raw material pellets, torrefied pellets had a higher ignition point, wider combustion range and longer burning time.