Pressure Effect on Hydrodynamics of a High Pressure X-ray Transparent Polyethylene Fluidized Bed

Abstract

Hydrodynamics of a polyethylene fluidized bed were studied at different operating pressures (191-2908 kPa) and constant temperature of 30 • C. Minimum fluidization velocity (U mf ) decreased with increasing of operating pressures. Measured U mf agree well with calculated U mf as derived from the standard deviation of pressure fluctuations using Puncochar's Method (1985). As expected, with the increase of superficial velocity, amplitude and standard deviation of pressure fluctuation series also increase, which is indication of more vigorous bubbling behavior inside the bed. Power spectral density of pressure fluctuation series indicates similar frequency distribution of the bubbling behavior at different superficial velocities. The dominant frequency from the power spectral was found to be around 1 Hz. Bubble diameter and bubble velocity were estimated from X-ray fluoroscopy images. Bubble diameter and bubble velocity increase with increasing bed height and superficial gas velocity due to bubble coalescence and more gas flowing upwards. At the same fluidization number, the average bubble size slightly decreases with increasing pressure at all bed heights because there is less gas flowing and the bubbles coalesce less rapidly. The bubble velocity is observed to have a small decrease from 191 kPa up to 2200 kPa, and then a substantial increase due to the fact that at higher pressure, the solid circulation increases at the bed.

Effect of Fluidization Pressure on Electrostatic Charge Generation of Polyethylene Particles

“…Overall, the frequency of bubbles with size range of 0.1–0.15 m was quite low (approximately 10%) and declined with the increase in pressure. The aforementioned results agree well with those reported in the literature. − …”

“…They found that bubble rise velocity increased with the increase in pressure, although the influence of pressure was smaller at elevated pressures. However, Orta et al, who used polyethylene particles, concluded that the operating pressure did not influence bubble rise velocity.…”

Implementation of Faraday cup electrostatic charge measurement technique in high-pressure gas–solid fluidized beds at pilot-scale

“…From the studies reported in literature it is found that with fluidization of Geldart group B particles, increasing operating pressure decreases bubble size [18,19] as well as slightly increasing bubble rise velocity [12]. Higher bubble rise velocities enhance the movement and mixing of particles within the bed, and thus increase particle contacts with other particles and also with the column wall.…”

Numerical Investigation on the Effect of Pressure on Fluidization in a 3D Fluidized Bed

“…28,29 The strength of these fluctuations depends upon the activity of bubbles in the bed and phenomena such as coalescence and splitting of bubbles. 6 Goldschmidt 29 reported that a strong intensity in pressure drop fluctuations indicates more vigorous bubbling of the fluidized bed. Different fluidization regimes are identified with a change in characteristics of the pressure fluctuations (Cai et al 30 ).…”