The Flow of Gas in a Fluidized Bed at Low Pressure

Kawamura, Sukeharu; Suezawa, Yoshitada

doi:10.1252/kakoronbunshu1953.25.524

Cited by 17 publications

(7 citation statements)

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“…At the same time, a safer process outside of flammability limits can be achieved through low-pressure operation.Nevertheless, relatively few papers have been published on fluidization under vacuum conditions. In one of the first studies on the hydrodynamics of fluidized beds at reduced pressure, a bed behaviour similar to that found at atmospheric pressure was observed by Kawamura and Suezawa (1961) . Cermain and Claude1 ( 1 976) detected the coexistence of an upper fluidized layer and a zone of fixed bed.…”

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confidence: 56%

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Drying of solids in vacuum fluidized bed

et al. 2002

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significant number of researchers have devoted their interest to fluidized bed drying and a good number of papers have been A published in the area, covering theoretical as well as experimental aspects. In this type of process three different tasks have to be accomplished by gas fluidization: establish proper dynamic fluidization conditions, bring enough heat, and remove all evaporated moisture without saturation. A good contact between particles and fluid provides very high rates of heat and mass transfer in the bed. Also, through a very good level of solids mixing a practically homogeneous bed temperature is achieved to facilitate temperature control. Due to these qualities, fluidization is considered one of the most appealing processes in the chemical industry. A particular type of fluidization, spouted bed, has also been used for drying grain over the last 40 years.However, the use of the fluidized bed in the drying process has been abandoned in some fields, such as in the fine chemicals and the pharmaceutical industries, because of complications with thermal degradation and safety. Thermolabile products can be subject to the partial degradation in drying processes at relatively high temperatures or long residence times. At the same time, in the pharmaceutical industry the process is oftenly involved with evaporation of an organic solvent; as a result, a mixture within the flammability limits but with a high risk of explosion can be formed. Operating a fluidized bed under vacuum conditions offers the possibility of eliminating these problems. The degree of thermal degradation can be reduced by lowering operating temperatures provided under vacuum conditions. At the same time, a safer process outside of flammability limits can be achieved through low-pressure operation.Nevertheless, relatively few papers have been published on fluidization under vacuum conditions. In one of the first studies on the hydrodynamics of fluidized beds at reduced pressure, a bed behaviour similar to that found at atmospheric pressure was observed by Kawamura and Suezawa (1961). Cermain and Claude1 ( 1 976) detected the coexistence of an upper fluidized layer and a zone of fixed bed. The existence of a fluidized upper layer in the bed was also observed by Kusakabe et al. (1989), at the point when the bed pressure drop and the absolute operating pressure basically have the same order of magnitude. In their low pressure experiments, Wraith and Harris (1 992) measured the same type of pressure drop characteristics and observed a fluidization front progressing downwards with increasing gas flow. In a later study, Llop e t al. (1996) proposed an equation to calculate the minimum *Author to whom correspondence may be addressed. E-mail address: bulent@mail. udlap. my A drying process in a fluidized bed under vacuum conditions is experimentally and theoretically studied. A fluidized bed operating in reduced pressure presents a possibility for a better quality of production, with safer process conditions. A mathematical model is developed for...

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confidence: 56%

“…In one of the first studies on the hydrodynamics of fluidized beds at reduced pressure, a bed behaviour similar to that found at atmospheric pressure was observed by Kawamura and Suezawa (1961). Cermain and Claude1 ( 1 976) detected the coexistence of an upper fluidized layer and a zone of fixed bed.…”

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confidence: 61%

Drying of solids in vacuum fluidized bed

et al. 2002

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“…[11] using particles of sand, silica gel, and glass beads, at air pressures from 0.1 to 101 kPa, observed bed behavior similar to that found at atmospheric pressure. Expanding the pressure drop equation to the Knudsen flow regime, they developed a correlation for the minimum fluidization velocity during low-pressure operations.…”

Section: Introductionsupporting

confidence: 60%

“…Kawamura and Suezawa. [11] were also the first researchers to observe that the bed pressure drop just over the distributor is much stronger in a reduced pressure operation than that in an atmospheric pressure operation. This phenomenon generates a steep gas velocity gradient through the bed.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamics of Reduced Pressure Fluidization Employing Particles with Variable Density

et al. 2012

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A series of experiments was carried out to study the hydrodynamics of a fluidized bed operating at reduced pressure and employing particles with variable moisture content; that is, of variable density. In these experiments, four different types of particles were used and fluidization characteristics very similar to the ones encountered in atmospheric pressure operations were observed. A novel method to measure the minimum fluidization velocity of particles with varying density was proposed. The experimental results demonstrated that the minimum fluidization velocity increased with decreased operating pressure, increased operating temperature, and increased particle moisture content. However, the bed voidage under minimum fluidization conditions showed very little sensitivity to variations in operating pressure. Two equations were developed to predict the minimum fluidization velocity and the results were compared with the experimental data as well as with the predictions of equations available in the technical literature.

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“…In one of the early studies on the hydrodynamics of fluidized beds, employing pressures between 0.1 and 101 kPa, Kawamura and Suezawa [1] observed a bed behavior similar to that encountered at atmospheric pressure. Germain and Claudel [2] carried out experiments fluidizing glass balls using nitrogen and hydrogen at pressures between 0.533 and 4.0 kPa and detected an upper fluidized layer over a zone of a fixed bed.…”

Section: Introductionmentioning

confidence: 90%

Influence of Particle Size on Vacuum–Fluidized Bed Drying

et al. 2011

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The effect of particle size on the vacuum-fluidized bed drying process was experimentally studied using pepper seed particles with two distinct diameters. In the constant drying rate period, the small particles demonstrated stronger drying rates resulting from higher mass transfer coefficient values and larger contact area for per unit particle humidity.The experimental results also showed that the falling drying rate period was controlled in the beginning by the particle diameter and later by the effective porosity of the particle. Consequently, in the beginning of the falling drying rate period the small particles presented higher drying rates, whereas toward the end of the period, the large particles, with higher effective porosity, produced stronger drying rates than the small ones.The effects of the vacuum pressure and the superficial gas velocity throughout the process were only observed in the constant drying rate period, whereas the higher operating temperatures enriched the drying rates in both periods.

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The Flow of Gas in a Fluidized Bed at Low Pressure

Cited by 17 publications

References 0 publications

Drying of solids in vacuum fluidized bed

Drying of solids in vacuum fluidized bed

Hydrodynamics of Reduced Pressure Fluidization Employing Particles with Variable Density

Influence of Particle Size on Vacuum–Fluidized Bed Drying

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