Predictions on Bubble and Solids Movement in Laboratory Polyethylene Fluid Beds as Visualized by X-Ray Computer Assisted Tomography (CAT) Scanning

ABSTRACT

Solid and gas distributions are tomographically quantified as a function of position with high resolution in a series of laboratory fluid beds containing air and polyethylene particles. The resolution used is 0.4 mm by 0.4 mm by 3 mm. The laboratory models are Plexiglas columns of 10 cm in diameter and the settling bed L/D ratios vary between one and three. Large particles (up to 1.5 mm in diameter) of high density polyethylene and linear low density polyethylene are used. The superficial gas velocities vary from the minimum fluidization velocity to 50 cm/s. In this paper, the analysis of fluid bed CAT scanner images is extended to show bubble, emulsion and dense phase distribution. The analysis is also used to determine the bubble diameter and to predict the flow direction of solid particles as well as the velocity of descending solids. The voidage frequency distributions of a bed at different gas flow rates are compared to each other and the voidage threshold values corresponding to gas, emulsion and dense phases are determined. These threshold values are used to prepare ternary images that clearly show the parts of the bed cross-section corresponding to bubble, emulsion and dense phases.

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