Effects of oxidative torrefaction on biomass gasification and alkali metal release and transformation characteristics

The effects of oxidative torrefaction on the basic physicochemical, such as composition, torrefaction yield, chemical structure, and microstructure, and gasification properties of corn straw, were studied. The release and transformation of alkali metals during torrefaction and gasification of corn straw were also investigated. The results show that torrefaction can increase the fixed carbon content in corn straw effectively and decrease the values of H/C and O/C. Compared with inert atmosphere torrefaction, oxidative torrefaction has better quality improvement effects, and the best roasting atmosphere is 6% oxygen concentration. Combining H/C, O/C, mass yield and energy yield, it is found that the oxygen concentration of 6% during torrefaction is suitable. The concentration of CO, gas production rate, and gas calorific value of torrefied corn straw increased first and then decreased with the increase of oxygen concentration in the torrefaction atmosphere during gasification. The gasification characteristics were optimal at 6% oxygen concentration, with CO content of 14.73%, gas production rate of 1.09 L/g, and gas calorific value of 4.93 MJ/m³. The alkali metals were enriched in the corn straw during the torrefaction process. The conversion from water-soluble K to ion-exchanged K was also promoted, which helped produce more insoluble K in the gasification process. The oxidative torrefaction promoted the effect more pronounced. The results of the study can provide essential data and technical support for the technological promotion of oxidative torrefaction and gasification of biomass.