Torrefaction of corn straw in oxygen and carbon dioxide containing gases: Mass/energy yields and evolution of gaseous species

Abstract

Pulverized corn straw biomass was torrefied in carrier gases which contain oxygen and carbon dioxide gases with the following proportions (3–7% O2, 13–17% CO2, 80% N2). Torrefaction took place at 275–375 °C, under atmospheric conditions. Upon such oxidative torrefaction, the mass and energy yields of this biomass decreased with increasing temperature and increasing oxygen concentration. Most of the chlorine and sulfur contents of the biomass were released to the gas phase, 52–90% and 55–98% respectively, with amounts increasing with increasing both torrefaction temperature and oxygen concentration. In the examined parameter ranges, temperature had a pronounced effect on the mass and energy yields and on the evolution of chlorine and other elements to the gas phase. Low temperatures decrease the energy input to the process and enhance the mass and energy yields of the solid product. At the examined temperatures, the mass and energy yields were also affected by the variation in the oxygen content of the input gas.