Influence of surrounding conditions and fuel size on the gasification rate of biomass char in a fluidized bed

• Effects of surrounding conditions on gasification rate of biomass char were examined.
• Experiments were carried out in a 7 cm i.d. fluidised bed reactor.
• Fuel location during pyrolysis and char gasification affected the gasification rate.
• The gasification rate was affected by fuel size and concentration, and char cooling.
• The pyrolysis atmosphere had no significant effect on the gasification rate.

While the operational conditions of a fluidized bed are known to influence the fuel axial mixing, the effect of the resulting axial location of the fuel particles on the char gasification rate remains unexplored. In this work, a laboratory-scale bubbling fluidized bed was used to investigate how the gasification rate of biomass char was influenced by the fuel axial location (during pyrolysis and char gasification), the pyrolysis atmosphere, the fuel size, and the fuel concentration. When pyrolysis at the bed surface was followed by char gasification inside the dense bed the char gasification rate was up to 2-fold lower than the other combinations of the fuel axial location, which held similar rates. Cooling the char after pyrolysis decreased the char gasification rate in all cases studied. The gasification rate increased when the fuel particle size was decreased, and its dependence on the degree of char conversion was also affected. Thus, the operational conditions of a fluidized bed reactor, through modified fuel axial mixing, can influence the char gasification rate. Furthermore, experimental determination of reactivity data in laboratory-scale systems must account for the axial location of the fuel at the desired end-scale, using similar fuel particle sizes.