Comparative advantages of gas-pressurized torrefaction for corn stalk conversion to achieve solid biofuel production

Torrefaction is a feasible approach to produce biochar. Several new torrefaction methods have been conducted for biochar production. Among them, gas-pressurized torrefaction is considered a new technology to produce solid biofuel with better fuel performance, without carrier gas, and higher deoxygenation. This study conducts a comparative analysis between conventional torrefaction and gas-pressurized torrefaction to identify the potential applications of the latter. The results indicate that increasing reaction pressure can achieve biochar volume reduction and HHV improvement, thus leading to a higher energy density. The conventional torrefied biochar yield is in the range of 54.13-90.11%, and it is 48.59-80.13% for gas-pressurized one. Moreover, a more extensive surface area, higher carbonization degree, and more stable pyrolysis characteristics are obtained compared to conventional torrefaction. The carbonization index values of conventional and gas-pressurized conditions are 1.04-1.42 and 1.06-1.48. The correlation analysis results suggest that biochar grindability is highly correlated to carbonaceous properties, regardless of torrefaction methods. The expense and environmental impact analysis indicates that gas-pressurized torrefaction possesses lower cost and environmental pollution potential for biochar production.