Peculiarities of rapid pyrolysis of biomass covering medium- and high-temperature ranges

Rapid pyrolysis of Hinoki cypress sawdust was conducted over a wide temperature range from 600 to 1400 degrees C in a lab-scale drop-tube furnace (DTF). Attention was paid to the influence of temperature on carbon conversion, gas yield, tar destruction, and coke deposition. A new observation was the decrease in carbon conversion from 900 to 1100 degrees C followed by a positive increase as the temperature was raised. Gravimetric analysis and gas chromatography were used as tools for determining heavy tar and light tar, respectively. It was found that temperature had a significant effect on tar destruction. The achievement of complete tar destruction in the product gas required an extremely high pyrolysis temperature of at least 1200 degrees C. An attractive result of this study was the satisfactory separation of the char and coke produced in pyrolysis, which described an unfamiliar behavior of the char formation and coke deposition. Char yield indicated a sharp drop between 600 and 800 degrees C then followed an almost plateau up to 1100 degrees C. Apparent coke deposition was observed from 900 degrees C accompanied by the secondary decomposition of tars and light hydrocarbon gases. It was concluded that the enhanced carbon conversion at the pyrolysis temperatures above 1100 degrees C was attributed to the enhancement of the gasification reactions between solid products (char and coke) and reactive gases (H2O and CO2).