Difference between revisions of "Mapping of Regimes"

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(Region A', Miyauchi et al)
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The general flow features of a fluid bed operated under relatively high gas velocity are illustrated in Fig below. The dense bed consists of the emulsion phase and bubble phase; '''The emulsion phase''' exhibits liquid-like properties, in the case of the fluid bed. Intense circulation of dense phase results from the central rapidly ascending bubble-rich phase and the peripheral descending emulsion phase of low bubble content. The boundary of the dense phase and the dilute phase is rather ambiguous; '''a transition region exists''' in which bubbles collapse and particles are blown in from the emulsion phase. '''In the transition region''', inversion of the circulating flow can occur. '''In the dilute phase''', particles are suspended particulately in the stream of ascending gas. The content of suspended particles decreases with height, except in the upper part of the dilute phase where it stays constant.
 
The general flow features of a fluid bed operated under relatively high gas velocity are illustrated in Fig below. The dense bed consists of the emulsion phase and bubble phase; '''The emulsion phase''' exhibits liquid-like properties, in the case of the fluid bed. Intense circulation of dense phase results from the central rapidly ascending bubble-rich phase and the peripheral descending emulsion phase of low bubble content. The boundary of the dense phase and the dilute phase is rather ambiguous; '''a transition region exists''' in which bubbles collapse and particles are blown in from the emulsion phase. '''In the transition region''', inversion of the circulating flow can occur. '''In the dilute phase''', particles are suspended particulately in the stream of ascending gas. The content of suspended particles decreases with height, except in the upper part of the dilute phase where it stays constant.
  
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Revision as of 11:13, 23 November 2020

The Geldart Classification of Particles

Geldart came up with four clearly recognizable kinds of particle behavior. From smallest to largest particle, they are as follows:

Group C: cohesive, or very fine powders. Normal fluidization is extremely difficult for these solids because interparticle forces are greater than those resulting from the action of the gas.

Group A: aeratable, or materials having a small mean particle size and/or low particle density ( < ~ 1.4 g/cm3 ). These solids fluidize easily, with smooth fluidization at low gas velocities and controlled bubbling with small bubbles at higher gas velocities. FCC catalyst is representative of these solids.

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                         Region A': Range of properties for well-behaved FCC catalyst; from Miyauchi et al.

Group B: sandlike, or most particles of size 40 μm < dp < 500 μm and density 1.4 < ps < 4 g/cm3. These solids fluidize well with vigorous bubbling action and bubbles that grow large.

Group D: spoutable, or large and/or dense particles. Deep beds of these solids are difficult to fluidize.

Region A', Miyauchi et al

Considering Squires’ criteria and observed industrial performance, Ikeda modified the criteria as shown in Table I

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The general flow features of a fluid bed operated under relatively high gas velocity are illustrated in Fig below. The dense bed consists of the emulsion phase and bubble phase; The emulsion phase exhibits liquid-like properties, in the case of the fluid bed. Intense circulation of dense phase results from the central rapidly ascending bubble-rich phase and the peripheral descending emulsion phase of low bubble content. The boundary of the dense phase and the dilute phase is rather ambiguous; a transition region exists in which bubbles collapse and particles are blown in from the emulsion phase. In the transition region, inversion of the circulating flow can occur. In the dilute phase, particles are suspended particulately in the stream of ascending gas. The content of suspended particles decreases with height, except in the upper part of the dilute phase where it stays constant.

alt text