Hydrodynamic Study of a Bench Scale Fountain Confined Conical Spouted Bed Reactor for Biomass Torrefaction

Torrefaction of biomass is a mild pyrolysis process conducted at 200 – 300 ºC in an inert atmosphere, which allows attaining high energy density solid feedstock. Accordingly, torrefaction of biomass is commonly carried out in a great variety of reactors, such as rotary drums, and fixed and fuidised beds. Furthermore, spouted beds are a promising alternative, as they allow operating with large particle size materials, such as those of biomass. However, continuous torrefaction of biomass in spouted beds is commonly conducted using beds of inert materials. Thus, the biomass is fed from the top of the reactor and the torrefied biomass is entrained through the top outlet pipe. Nevertheless, this configuration leads to coarse particle accumulation in the bed. Accordingly, new alternatives are required in continuous operation, preferably those involving beds made up of only biomass and high solid circulation. Thus, the presence of a fountain confiner on top of the bed allows increasing the gas-solid contact, with the torrefied biomass being removed through a solid outlet pipe located at the same level as the bed upper surface.

Therefore, this study deals with the performance of a fountain confined conical spouted bed, in which hydrodynamics was evaluated using different biomasses (rice husk, almond shell and olive stone). Moreover, the effect of the draft tube and the fountain confiner was analysed and the configurations leading to stable operation were identified. Furthermore, the minimum spouting velocity and operating pressure drop were measured. The hydrodynamic behaviour of beds made up of almond shells has clear similarities with those of olive stones, which is explained by the common features of these solids. Overall, the results allow delimiting the operating conditions for biomass torrefaction in fountain confined conical spouted beds.