Enhancing fuel characteristics and combustion performance of cellulose-rich straws through CO2-assisted torrefaction

Cellulose-rich straws of corn and rice were torrefied under carbon dioxide, and the fuel characteristics and combustion performance of the obtained biochar were investigated. A high severity resulted in surface collapse, greater pore volume, elimination of oxygen, elevated calorific value, and improved hydrophobicity in biochar. Following carbon dioxide torrefaction, the cellulose content in solid biochar experienced a slight decrease when the temperature was raised to 220 degree celsius for longer residence durations. At 300 C, the cellulose content in the biochar was nearly eliminated, while the relative proportion of non-sugar organic matter in corn stover and rice straw increased to 87.40 % and 77.27 %, respectively. The maximum calorific values for biochar from corn and rice straws were 22.38 +/- 0.03 MJ/kg and 18.72 +/- 0.05 MJ/kg. The comprehensive combustion indexes of rice and corn straw samples decreased to 1.06 x 10(- 7) and 1.31 x 10(-7) after torrefaction at 300 degree celsius, respectively. In addition, the initial decomposition temperatures increased by 38degree celsius and 45 degree celsius, while the ultimate combustion temperatures rose by 13 degree celsius and 16 degree celsius for corn and rice straws, respectively. These results imply an extended combustion timeframe for the torrefied samples.