Evolution of Chlorine-Bearing Gases during Corn Straw Torrefaction at Different Temperatures

Release of chlorine during combustion of raw biomass in boilers is detrimental as it contributes to slagging, fouling, and corrosion. Combustion of torrefied biomass can alleviate such issues, as it contains less chlorine than its raw biomass precursor. This work assessed the effect of the furnace temperature on the chlorine content of generated torrefied biomass and the released gaseous species during the torrefaction process (a mild pyrolysis). The selected biomass was corn straw, which was torrefied at furnace temperatures in the range of 250-400 °C under atmospheric pressure in an inert nitrogen flow. Upon torrrefaction, corn straw lost 32-50% of its original mass to the gas phase, accompanied by more than half of its original mass of chlorine in nearly all cases. The major chlorinated species in the evolving pyrolysis gas ("torgas") were identified as CH₃Cl and HCl. The former was more prevalent at the lower temperatures (<350 °C), whereas the latter dominated at the highest temperature (400 °C). Finally, emissions of other released gases, such as CO, CO₂, C₂H₆, NO_x, HCN, and NH₃, were also monitored and reported herein.