Response surface analysis of elemental composition and energy properties of corn stover during torrefaction

This research studied the effects of torrefaction temperature (250-250 °C) and time (30-120 minutes) on elemental composition and energy properties changes in corn stover. Torrefied material was analyzed for moisture content, moisture-free carbon (%), hydrogen (%), nitrogen (%), sulfur (%), and higher heating value (MJ/kg). Results at 350 °C and 120 minutes indicated a steep decrease in moisture content to a final value of about 1.48% - a reduction of about 69%. With respect to carbon content, the increase was about 23%, while hydrogen and sulfur content decreased by about 46.82% and 66.6%, respectively. The hydrogen-to-carbon ratio decreased as torrefaction temperature and time increased, with the lowest value of 0.6 observed at 350 °C and 120 minutes. Higher heating value measured at 350 °C and 60 minutes increased by about 22% and the maximum degree of carbonization observed was about 1.21. Further, the regression models developed for chemical composition in terms of torrefaction temperature and time adequately described the process with coefficient of determination values (R ²) in the range of 0.92-0.99 for the elemental composition and energy properties studied. Response surface plots indicated that increasing both torrefaction temperature and time resulted in decreased moisture content, hydrogen content, and the hydrogen to-carbon ratio, and increased carbon content and higher heating value. This effect was more significant at torrefaction temperatures and times >280 °C and >30 minutes.