A quantitative definition and flow regime diagram for fast fluidization

Takeuchi, Hiromi; Hirama, Toshimasa; Chiba, Tadatoshi; Biswas, J.; Leung, L. S.

doi:10.1016/0032-5910(86)80115-2

Cited by 67 publications

(32 citation statements)

References 2 publications

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“…In gas-solids circulating beds, the termination of fast fluidization regime to the pneumatic transport has been considered to commonly occur when solids become uniformly distributed along the riser with increasing gas velocity at a given solids circulation rate (Takeuchi et al, 1986;Bi et al, 1993). Similarly, the termination of three-phase circulating fluidization to three-phase transport can be defined by the velocity, V,,, at which axial solids segregation disappears from the riser with increasing superficial liquid velocity at given solids circulation rate and superficial gas velocity as shown in Figure 3.…”

Section: Resultsmentioning

confidence: 99%

“…Another boundary is the lower limit of stable operation of three-phase circulating fluidized beds. It has been revealed in gas-solids circulating beds that there exists a maximum solids circulation rate for a given superficial gas velocity beyond which stable operation becomes impossible due to further increase in solids circulation rate being prevented by inappro- priate pressure balance in the whole unit (Takeuchi et al, 1986;Bi and Zhu, 1993). Such a transition in three-phase circulating fluidized bed can be determined by plotting solids circulation rate vs. superficial liquid velocity at constant gas flow rate and secondary liquid flow rate.…”

Section: Resultsmentioning

confidence: 99%

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Flow regimes of the three‐phase circulating fluidized bed

Wang

et al. 1995

AIChE Journal

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Gas-sofids circu fating fluidized beds have been successfully used in cata fytic cracking of heavy oil, coal combustion, and some metallurgical and physical processes (Grace, 1990). Gas-liquid-solids fluidized beds are operated mainly in conventional fluidization regimes without solids circulation or in the transport regime with low solids holdups (less than 5 % ) (Fan, 1989 (Berk et al., 1984). Circulating operation can promote solids mixing and increase product throughput per unit bed cross section, while high shear stress can promote biofilm renewal (Pirozzi et al., 1990 Experimental StudiesThe experimental apparatus is shown in Figure 1. The riser is 140-mm-dia., 3-m-high Plexiglas. Tap water and air were used as liquid and gas phases, respectively. Glass beads of 0.405 mm in mean diameter and density 2,460 kg/m3 were used as the solid phase. In the operation, fluidizing water was introduced from the base of the riser through a liquid distributor, while solids flow rate was regulated by a secondary water flow from a side port near the bottom of the riser. The superficial liquid velocity was calculated based on the total flow rate from both the liquid distributor and the secondary side port. Gas was introduced separately through a gas distributor located well above the bottom liquid distributor. Well-mixed threephase flow was achieved in the test section above the gas distributor. Solids entrained from the top of the riser was separated from the water and returned to a reservoir. The solids circulation rate was determined by measuring the amount of particles collected in a metering tank on the top of the standpipe after the butterfly valve beneath the metering tank was closed, similar to the method used in the gas-solids circulating fluidized bed (Burke11 et al., 1988).Local gas holdup was measured using an electrical conducCorrespondence concerning this article should be addressed to Y. Jin tivity probe. The tip of the probe was a 0.1-mm platinum wire, covered by a 0.2-mm glass tube. The probe was installed with the tip directed downward to minimize the disturbance of local flow patterns. Typical signals from the probe are shown in Figure 2. The output voltage is seen to drop sharply when bubbles pass the probe. The local bubble fraction can thus be determined by:where ti is the exposure time of the probe to bubbles and T is the total record time. The cross-sectional average gas holdup is calculated by:To evaluate the cross-sectional average solids holdup, pressure drops across the test section were also measured. The sectional average solids holdup is evaluated by combining Eqs. 2, 3 and 4:

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Flow regimes of the three‐phase circulating fluidized bed

Wang

et al. 1995

AIChE Journal

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“…The prediction of the solids circulation rate by the equation of Yousfi and Gau (1974) for the choking transition to dense-phase fluidization yields a higher value compared to the present data. Takeuchi et al (1986) noted that the critical gas velocity from fast fluidization to dense-phase fluidization is sensitive to the height of the fluidized bed. Yousfi and Gau (1974) did not consider the effects of bed diameter and height in their equation.…”

Section: Dynamic Behavior Of a Cfb At U G > U Trmentioning

confidence: 99%

ECT studies of the choking phenomenon in a gas–solid circulating fluidized bed

Warsito

Fan

2004

AIChE Journal

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“…Takeuchi et al . [4] also concluded that the FFB should contain both a dense phase and a dilute entrained phase. To characterize the fast fluidization regime, previous researchers have investigated different hydrodynamic aspects of fast beds such as riser axial pressure profile along the riser, loop pressure profile, voidage variation and solid concentration profile.…”

Section: Introductionmentioning

confidence: 99%

A critical analysis of the acceleration length and pressure profile of single‐particle systems in a circulating fluidized bed

Das

Meikap

Saha

2008

Asia-Pacific J Chem Eng

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A study was conducted to explore the hydrodynamic behaviors using both Geldart group A and B materials in a circulating fluidized bed unit consisting of fast column (riser) of 0.1016 m i.d. and 5.62 m height. The materials tested were 120 µm of the fluid catalytic cracking (FCC) catalyst, 166 µm of iron ore, 215 µm of coal and five types of sand particles, ranging in size from 300 to 622 µm. The superficial air velocity ranged between 2.01 and 4.681 m/s and solid fluxes of 12.5-50 kg/m 2 s. Riser static pressure profiles were measured for the FCC catalyst, coal, iron ore and sand particles. Acceleration lengths were determined from the data, and using these and other data from the literature two correlations for the acceleration length were established for Geldart's group A and B particles. 

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A quantitative definition and flow regime diagram for fast fluidization

Cited by 67 publications

References 2 publications

Flow regimes of the three‐phase circulating fluidized bed

Flow regimes of the three‐phase circulating fluidized bed

ECT studies of the choking phenomenon in a gas–solid circulating fluidized bed

A critical analysis of the acceleration length and pressure profile of single‐particle systems in a circulating fluidized bed

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