Evaluation of CO2-reactivity patterns in cokes from coal and woody biomass blends

Cokes produced at 1000 °C from blends made up of a coking coal and lignocelulosic biomass -Eucalyptus and Olive woods and their charcoals- were evaluated under dynamic and isothermal gasification conditions in a CO2 environment. The effects of adding different types of biomass to coal in quantities as low as 2 wt% were compared with the effects caused by the addition of wood constituents -xylan, cellulose and lignin-. Not only were cokes more reactive than the coke produced without the addition of biomass, but they also exhibited a lower threshold temperature during the Boudouard reaction. Comparison of the CO2-reactivity profiles of the cokes showed to be a suitable protocol for detecting differences in low-temperature gasification caused by the residual biomass present in the matrix of high-temperature coke and also for selecting biomass to be blended with coking coals. An additional CO2-gasification cycle of the partially-gasified cokes showed that the inner core of the coke exhibited a lower reactivity and conversion degree than the original parent cokes. Differences in CO2-reactivity between the partially-gasified cokes were found to be negligible. The effects of the oxygen content and the ash chemistry of the biomass, the Gieseler fluidity of its blend with coal, the presence of char particles in the coke matrix and the CO2 surface area of the cokes were shown to contribute to explain the differences found in coke reactivity.