Particle ejection and entrainment from fluidised beds

Do, Hebb; Grace, John R.; Clift, Roland

doi:10.1016/0032-5910(72)83013-4

Cited by 68 publications

(30 citation statements)

References 3 publications

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“…In order to calculate the maximum height attained by the projected particles, some theories are proposed in the literature, based in the integration of the momentum equation for isolated or grouped particles (Do et al, 1972;Peters and Prybylowski, 1983;Demmich, 1984;Fung and Hamdullahpur, 1993) and based in the momentum transferred to the particles by the gas bubble (Pemberton and Davidson, 1986). Each of these theories requires the initial velocity of the ejected particles.…”

Section: Introductionmentioning

confidence: 99%

A new model for ejected particle velocity from erupting bubbles in 2-D fluidized beds

Almendros-Ibáñez

Sobrino

Vega

et al. 2006

Chemical Engineering Science

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A new model is proposed for obtaining the velocity profile of the particle ejected from the bubble dome in a freely bubbling 2-D fluidized bed. Its basis is the supposition that the initial velocity of the ejected particles, with a direction perpendicular to the dome contour, depends on bubble velocity and bubble growth velocity. This model differs from those previously appearing in the literature in that it is valid not only for vertical-ascent circular bubbles.Experiments were carried out in a freely bubbling 2-D fluidized bed using a high-speed video camera to measure the velocity profile. Upon comparing these results with the proposed model, it was established that, excepting some isolated cases, the model properly predicts the magnitude and direction of the maximum particle ejection velocity and the velocity profile.Using the work of Shen et al. (2004. Digital image analysis of hydrodynamics two-dimensional bubbling fluidized beds. Chemical Engineering Science 59, 2607-2617), we obtain two general equations for the bubble velocity and the bubble growth velocity in a 2-D fluidized bed. These expressions, together with the proposed model, can be used to calculate the initial velocity of the ejected particles.

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Section: Introductionmentioning

confidence: 99%

A new model for ejected particle velocity from erupting bubbles in 2-D fluidized beds

Almendros-Ibáñez

Sobrino

Vega

et al. 2006

Chemical Engineering Science

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“…Early measurements in fluidized beds were restricted to the freeboard region using point measurements techniques, such as X-ray photography [6], cine films [11], laser Doppler anemometry (LDA) [12] and hot wire anemometry [9]. These yields a time history in a point of the bed, normally far from the bed surface, from which mean and RMS-fluctuation velocities can be calculated.…”

Section: Introductionmentioning

confidence: 99%

Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

et al. 2005

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Some results on particle image velocimetry (PIV) in 2 D freely bubbling fluidized beds are presented. The PIV applications were used in order to determine the initial particle velocity of bubble eruptions. A two dimensional non reacting fluidized bed was constructed to measure the origin of the ejected particles and the initial particle velocity distribution, using coarse sand particles. The bubble ejection mechanism was observed taking into account the origin of particles ejected, the initial particle velocity distributions as well as the effect of other neighbor exploding bubbles. Our results show that the assumption of linear dependence of initial velocity with the angle predicts the velocity faithfully only for purely vertical ascent bubbles. Measurements of ejection velocities show that initial velocities in the combined layer are higher than those of the particles in the nose of the leading bubble. Avoiding coalescence of bubbles at the bed surface can lead to less particle entrainment out of the bed and consequently to shorter fluidized beds.

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“…In addition, this mechanism ejects particles from the wake of the bubble where the mean particle size is higher than in the bubble nose (usually fine particles accumulate at the bed surface [8]). Thus, the ejection velocity and the particle sizes are higher, and consequently the solids ejected by this mechanism will reach higher heights in the freeboard [16,39]. The maximum height reached by the solids ejected by the wake and jet spike mechanisms cannot be observed experimentally due to the 2D geometry of the experimental facility.…”

Section: Discussionmentioning

confidence: 99%

Experimental observations on the different mechanisms for solid ejection in gas-fluidized beds

Almendros-Ibáñez

Sánchez-Delgado

Sobrino

et al. 2009

Chemical Engineering and Processing: Process Intensification

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a b s t r a c tThis work presents an experimental study of the ejection velocity for different mechanisms of solid ejection in fluidized beds. The experiments were carried out in a 2D fluidized bed, where the bubble eruptions were recorded with a frequency of 250 frames per second using a high speed video camera with a resolution of 1.3 Megapixels.The results show that in isolated bubble eruption, the dome velocity is significantly reduced by the effect of a group of raining particles in the form of stalactites within the bubble. Higher velocities are observed when bubble coalescence takes place. If bubbles coalesce before the leading bubble breaks, the momentum of the trailing bubble together with the increase in the throughflow accelerate the dome of the leading bubble. In contrast, when coalescence occurs after the breakage of the leading bubble, the wake of the trailing bubble is projected into the freeboard with a very high velocity (wake spike mechanism). The last observed mechanism, the jet spike mechanism, occurs when a stream of bubbles reaches the bed surface following the path opened by the previous bubbles. A cloud of particles moving upward is observed, although their velocities are not as high as in the wake spike mechanism due to the interchange of momentum during the collisions with other particles.Finally, an explanation for some of the patterns of gas release from erupting bubbles recently observed by Hartung et al.

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Particle ejection and entrainment from fluidised beds

Cited by 68 publications

References 3 publications

A new model for ejected particle velocity from erupting bubbles in 2-D fluidized beds

A new model for ejected particle velocity from erupting bubbles in 2-D fluidized beds

Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

Experimental observations on the different mechanisms for solid ejection in gas-fluidized beds

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