Promoting effect of CO2 on torrefaction of woody biomass

摘要

Pine sawdust (PS) was torrefied in both screw conveyor and fixed-bed reactors under the condition of three atmospheres (N-2, CO2, and air) and two temperatures (280 degrees C and 320 degrees C). A mass balance analysis was conducted to investigate the effects of temperature and atmosphere on product distributions and properties of torrefied PS. Results showed that torrefaction pretreatment under these conditions achieved evident improvements in grindability and energy densification of the solid products. The results of fixed-bed reactor could be more accurate than screw conveyor reactor, which had mass balance error of less than 1%. In addition, the mass balance and FTIR results provided conclusive evidence that both CO2 and air atmospheres promoted the decomposition of raw PS and produced about 2-12 wt% higher liquid products than N-2 atmosphere. Results revealed that CO2 was a non-inert atmosphere at such low temperatures. The promotion effect of CO2 on the decomposition of PS became more pronounced as the torrefaction temperature increased. The severity of torrefaction in air was higher than that in CO2. The findings of this study provided important implications for the potential application of CO2 and the selection of oxidative torrefaction atmospheres in biomass torrefaction.

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