Effect of Pressure Variation at Downcomer Bottom on Axial Bed Density Distribution in a Circulating Gas Fluidized Bed Riser

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The effect of static pressure variation at a downcomer bottom, Pdo, on axial bed density (ABD) distribution in a riser was examined in a circulating gas fluidized bed system consisting of a 0.1 m i.d. and 10.0 m high riser, a 0.2 m i.d. and 8.2 m high downcomer and a screw feeder between them. The ABD distribution and Pdo were determined from simultaneous measurements of static pressure distributions in the riser and the downcomer at a fixed superficial gas velocity of 1.3 m·s–1 as a function of the circulating solid flux, Gs, and the initial height of solid particles in the downcomer, Hsd, employing 0.054 mm FCC particles as a bed material. For most combinations of Gs and Hsd, no essential effect of the variation of Pdo was found on steady-state ABD distributions. The distributions depended appreciably on Pdo only when Gs takes a certain value where a dense region appears in the lower part of the riser. Under such conditions, a fluctuation of the height of the lower dense region was observed in correspondence to a transitional change in the pressure distribution in the downcomer. In addition, the steady-state dense region height was found to increase with the static pressure at the downcomer bottom which was varied through the change of Hsd and by aeration to the downcomer bottom.