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 LID 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 cmIs. 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.

Analysis of gamma‐ray imaging data to describe hydrodynamic properties of gas–polyethylene fluidized beds

“…For a fluidized bed at bubbling state, determination of the bed surface is difficult due to bubble eruption a t the bed surface. There are three zones in the fluidized beds tested here as observed by Zarabi and Kantzas (1998): (1) the entrance zone at the bottom of the bed where there are no visible bubbles, the mean density of the bed is high, and the descending particles come to zero velocity; (2) the circulation field in the middle of the bed where there are visible bubbles, distinct emulsion and dense phases, and the mean density of the bed is relatively constant along the axis of the column; (3) the free board where the mean bed density i s very low and the particles are thrown up into it by bubble eruption and return to the bed by free falling.…”

“…Running samples 11 18 and M118 a t the same experimental conditions resulted in different behaviors. The particle morphology is very important in bubble characteristics and consequently the particle movement in the bed, as discussed in Zarabi and Kantzas (1998). The 1118 sample showed higher horizontal velocity but the pattern and shape of the histograms were the same for both samples.…”

“…In other words, the descending particle comes to stop at this elevation until, it is picked up by a bubble. Zarabi and Kantzas (1998) showed that in the first 4 cm of a column there is no visible bubble, the spatial particle distribution is homogenous, and the overall density is slightly higher than in other parts of the bed. Usually, it is observed that both the horizontal and vertical distributions show better homogeneity at higher gas velocities.…”

A Non-Invasive Hydrodynamic Study of Gas-Solid Fluidised Bed of Linear Low Density Polyethylene

“…Outside of these researchers, there are a few interested in the use of x-rays. The majority of the work is being done by Newton (Newton et al, 2001;Smith et al, 1995;Newton et al, 1994) and Kantzas (Zarabi and Kantzas, 1998;Wright et al, 2001;Kantzas et al, 2001;Kantzas, 1994;Holoboff et al, 1995). The main focus of the work conducted by these individuals is the behaviour of the gas phase in the solid beds, phenomena such as bubble growth and splitting, as well as the effect of gas distribution, temperature, and pressure.…”