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Hydrodynamics of spout fluid beds Sutanto, Willy


Experiments were conducted in a spout-fluid bed, a modified version of a standard spouted bed, incorporating auxiliary flow in addition to central flow. The auxiliary flow was supplied in three different ways through the perforated conical distributor base. The vessel used was a cylindrical half column, 0.15 m in diameter and 1.05 m high fitted with an inlet orifice plate with a diameter of either 19.1 mm or 25.4 mm. The three solid materials studied were: polystyrene, millet and high density polyethylene (HDPE). Aspects studied included regime maps, minimum fluid flowrate for spouting with aeration and spout-fluidization, annulus gas velocity profile, total bed pressure drop, annulus solids circulation, fountain shape and height and spout shape and diameter. For different central flow/auxiliary flow combination, four types of flow behaviour were established: packed bed; spouting with aeration; spout-fluidization and jet in a fluidized bed. The minimum total fluid flowrate for spouting with aeration and spout-fluidization was always found to be greater than the minimum spouting velocity. Greater fluid percolation through the annulus in the cylindrical part of the column was achieved by increasing the amount of auxiliary flow for a constant total flow. As much as a 50% increase could be realized for a 1:1 split between central/auxiliary flow compared with the case where there is no auxiliary flow. The circulation rate of solid particles was affected little by small rates of aeration. At higher rates of aeration and for deeper bed heights aeration led to an increase of solids circulation. However, at lower bed heights, the solid circulation rate decreased as a result of aeration. The overall bed pressure drop for spouting with aeration under minimum conditions increases linearly with auxiliary flow. Fountain height was found to decrease as the fraction of auxiliary flow increased. A greater total gas flow is required to reach a given fountain height for spouting with aeration. However, with aeration, the fountain was observed to have a greater solids concentration than that for pure spouting. The empirical correlation due to McNab was found to predict the average spout diameter very well under various central and auxiliary flow combinations if the sum of central and auxiliary flows is used in the correlation.

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