Mixing Behavior of Binary Mixtures of Biomass and Silica Sand in a Fluidized Bed

Mixing and segregation of binary mixtures involving biomass materials in a fluidized bed was experimentally investigated. Three different biomass materials were studied: willow sawdust, pelletized soy and oat hull materials. Each of these three materials was prepared as a binary mixture with silica sand at six compositions ranging from 5% - 30% with an increment of 5%. The experiment was carried out at different superficial gas velocities in the bed ranging from the initial minimum fluidization velocity Umf of each sample mixture up to 4Umf with an increment of 0.5 Umf. The extent of mixing for each of the biomass composition was investigated using a mixing index based on the standard deviations of the sample at different axial positions in the bed. The radial composition was also investigated by means of digital imaging analysis using a high resolution digital camera located at the top of the bed. Ten uniform axial and radial positions were used during the experimental process. The experiment revealed the differences in the extent of particle distribution for pelletized biomass materials vs non-densified materials as a result of differences in particle size, density and importantly, particle shape of the material utilized. The results showed an increase in the extent of mixing as Umf increased for both pellet materials while the mixing index for sawdust decreased beyond a loading of 20%. With an increase in biomass loading, an increase in mixing index was found for the two pellet materials. A similar trend was observed for sawdust at the lower loading level. However, the mixing index started to decrease at higher loading level beyond 20%. The results would further help understand hydrodynamics of binary and multicomponent mixtures involving biomass materials in fluidized beds.