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Fluidization and mixing characteristics of biomass particles in a bubbling fluidized bed

İnanlı, Sinan
Fluidized bed is a suitable technology for combustion and gasification of biomass materials. Hydrodynamics occurring in the bed is crucial for the design and operation of the combustion or gasification unit. In the present study, hydrodynamic behavior of binary mixtures of biomass-silica sand in a bubbling fluidized bed was experimentally investigated. Five different biomass materials and silica sand with three different particle sizes were employed to form binary mixtures. Biomass materials were rice husk, sawdust, wheat straw, hazelnut shell and olive cake which are all potential energy sources for Turkey. Effects of mass percentage of biomass and particle size of silica sand on minimum fluidization velocity of the mixtures were determined. Comparisons between results of the present study and predictions of available correlations proposed for minimum fluidization velocity of binary mixtures were carried out. Mixing and segregation characteristics of biomass-silica sand binary mixtures were investigated for mixtures having different mass fraction of biomass and different silica sand particle sizes. Fluidization and bubbling behaviors of mentioned mixtures were observed in a 2-D fluidized bed and images taken during steady-state operation of bed were presented as visual tools to guide fluidization characteristics of the bed. Mass percentage increase of rice husk, wheat straw and sawdust resulted in increase in minimum fluidization velocity of the mixture whereas change in mass fraction of olive cake and hazelnut shell had no effect on minimum fluidization velocity. Minimum fluidization velocity increased with increase of silica sand particle size for all biomass-silica sand mixtures having same mass percentage of biomass. Vertical mixing pattern in the bed at steady state conditions were found almost same for all biomass-silica sand mixtures. Biomass acted as flotsam and accumulated mostly at the top of the bed and silica sand acted as jetsam and accumulated mostly at the bottom of the bed. 2-D bed experiments showed that mixing biomass materials with silica sand provides desired bubbling behavior in the bed.