Minimum and Complete Fluidization Velocity for Sand-Palm Shell Mixtures, Part I: Fluidization Behavior and Characteristic Velocities

Abstract

Problem statement: Palm shell on its original state cannot be fluidized solely. However, mixing palm shell with a second fluidizable material can facilitate proper fluidization. Approach: The minimum and complete fluidization velocity (U_mf and U_cf) for sand/palm shell binary mixtures had been studied in a partitioned reactor known as Compartmented Fluidized Bed Gasifier (CFBG). The pilot scale reactor ID is 66 cm with 60:40 cross sectional area ratio for combustor and gasifier respectively. The bed materials constitute of sand and palm shell up to 15 weight percent (wt%). The particle size and density ratio for palm shell and sand are about 5÷53 and 0.55 respectively. Results: Despite of the unique reactor feature, the mixture bed pressure drop profiles were closely resemble to those observed in the laboratory scale cylindrical column. It was found that partial fluidization occurred for the smallest sand size with any palm shell size and weight percent in the gasifier. Poor fluidization was also found with the same sand in the combustor but limited to the largest palm shell and higher weight percent. The U_mf and U_cf values increase with the increase of palm shell size and weight percent in both compartments and are in tandem with the increase of effective particle diameter. However, although increase in the sand size also increased the effective particle diameter, the characteristic velocities show both increasing and decreasing trends. These findings proved that the characteristic velocities of the sand-palm shell binary mixtures not only depend on the effective bed properties, but also influenced by the mixing/segregating condition. In addition, bed geometry is an equally important factor for the present system. Conclusion/Recommendation: Despite of the large difference in particle size and density, palm shell in sand can be fluidized well, making it a suitable biomass feedstock for gasification in CFBG pilot plant.