Devolatilization and attrition behavior of fuel pellets during fluidized bed gasification

Devolatilization, fragmentation, and attrition phenomena occurring to fuel pellets during fluidized-bed gasification have been studied. Three pelletized fuels, one based on wood and the other two based on a mixture of wood and coal, were characterized in a lab-scale fluidized-bed reactor under gasification, inert, and combustion conditions, for comparison. Similar and relatively long devolatilization times were observed for the three types of pellets. Pellet breakage by primary fragmentation upon devolatilization appeared to be rather limited for all fuels, indicating that fuel pelletization gives sufficient mechanical strength to the particles. On the contrary, secondary fragmentation and attrition by abrasion of char particles during gasification were extensive, suggesting a gasification-assisted attrition enhancement effect. This mechanism, associated with the low reactivity of the generated fines, made the loss of carbon by fine elutriation during char gasification much more significant than that found under combustion conditions. Larger carbon losses were associated with fuel pellets with a lower reactivity.