Segregation and Fluidization Behavior of Poly-disperse Mixtures of Biomass and Inert Particles

This paper reports on the results of an experimental study aimed at investigating the fluidization and segregation behavior of poly-disperse binary mixtures consisting of small and dense inert particles mixed with less dense and coarse pieces of biomass fuels. In more details, orange peels (OP), conditioned to a moisture content of about 6% wt. and cut in square pieces (0.5 cm x 0.5 cm), were used as biomass feedstock. Three different materials (i.e., Ticino sand, quartz sand, alumina powder and alumina spheres) were tested as inert bed component in order to determine the prevalence of the effect of either size or density on the fluidization and segregation behavior of the investigated binary systems. Fluidization experiments were performed at room temperature in order to prevent that the formation of endogenous bubbles from devolatilizing fuel particles could come into play, which also impacts mixing and segregation phenomena in real fluidized bed reactors. Tests with different biomass weight fraction in the bed (XB) were performed both to study the effect of the bed composition on the characteristic velocities of the investigated binary systems (i.e., minimum and complete fluidization velocities) and to determine their maximum batch loading, i.e. the critical value of XB beyond which the fluidization quality deteriorate (e.g., channelling, irreversible segregation, slugging).