Variation in fuel reactivity and ash characteristics of biomass feedstocks for large scale gasification

Reactivity and ash sintering of biomass fuel are important parameters to be considered for large-scale biomass gasification process. The reactivity affects the extent and time required for the completion of fuel conversion, and ash sintering can lead towards the blockage problems in the gasifier. This task was about studying the effect of temperature, pressure and gasifying medium on the variation of fuel reactivity and ash sintering for different types of biomass feedstock relevant to large-scale biomass gasification. The variables in selecting the same and different types of sample material (biomass feedstock) were the location (e.g. various parts of Finland), contact with water (transportation, storage time, debarking etc.). The samples were different barks (spruce, pine, birch and aspen), forest residue and stump chips. The tests were performed in the thermogravimetric apparatus. The conditions were selected mainly to aim at oxygen gasification. The tests were carried out in the temperature and pressure ranges of 800oC - 900oC and 1 bar-10 bar, respectively. The range of particle size was 0.5 - 1.5mm. Gasifying mediums were steam and carbon dioxide. The inhibition effect was characterised by adding H2 to steam, carbon monoxide to CO2 and a gas mixture containing all the gas components. It was observed that there was a significant variation of reactivities and ash sintering among different types of biomass in the presence and the absence of the product gases. Inside one biomass type the variation in the reactivity was small, and no clear differences in the ash sintering was found. The contact with water was observed to have a weakening effect on ash sintering, most probably due to the leaching of low melting alkaline compounds, and no difference in reactivity was found.