CO2 as a Carhon Neutral Fuel Source via Enhanced Biomass Gasification

The gas evolution, mass decay behavior and energy content of several woods, grasses, and agricultural residues were examined with steam and CO2 gasification using thermogravimetric analysis and gas chromatography. CO2 concentrations were varied between 0 and 100% with steam as a coreactant. Carbon conversion was complete with 25% CO2/75% steam compared to 90% conversion with pure steam in the temperature range of 800-1000 degrees C. The largest effect was from 0-5% CO2 introduction where CO concentration increased by a factor of 10 and H-2 decreased by a factor of 3.3 at 900 degrees C. Increasing CO2 from 5 to 50% resulted in continued CO increases and H-2 decrease by a factor of 3 at 900 degrees C. This yielded a H-2/CO ratio that could be adjusted from 5.5 at a 0% CO2 to 0.25 at a 50% CO2 concentration. Selection of the gasification parameters, such as heating rate, also enabled greater control in the separation of cellulose from lignin via thermal treatment. 100% CO2 concentration enabled near complete separation of cellulose from lignin at 380 degrees C using a 1 degrees C min(-1) heating rate. Similar trends were observed with coal and municipal solid waste (MSW) as feedstock. The likely mechanism is the ability for CO2 to enhance the pore structure, particularly the micropores, of the residual carbon skeleton after drying and devolatilization providing access for CO2 to efficiently gasify the solid.