Reactivity and ash sintering characterisation of high-alkali agro-biomass fuels for pressurised gasification

Pressurised biomass gasification systems have promising prospects in the IGCC application and in large scale production of liquid fuels based on Fischer-Tropsch synthesis process. Many biomass fuels, especially those originated from agriculture, contain high amounts of alkali metals that can cause bed sintering and fouling problems in gasifiers and downstream gas lines. In planning suitable gasification conditions for these high-alkali feedstocks, it is essential to know the ash sintering behaviour and, as well, the reactivity of the char. The characterisation method based on thermogravimetry consists on simultaneous determination of both parameters. The basis of the conditions selected is the temperature range from 750-850C and pressure mainly 5 bar, but also pressures from 1 to 10 bar. The reactivity results obtained for the different biomasses indicate a great scattering in their gasification behaviour. In what concerns to pressure effect in the gasification process, there is no rule to follow about reaction rate, meanwhile it was proved that the ash sintering is enhanced at higher pressure conditions. Some biomass fuels showed a slow decrease in weight at 1 bar due to volatilisation of potassium chloride, which was not observed at higher pressure.