An Experimental Study of the Hydrodynamic Characteristics of External Loop Airlift Contactors

Bentifraouine, Chafaa; Xuereb, Catherine; Riba, J. P.

doi:10.1002/(sici)1097-4660(199707)69:3<345::aid-jctb719>3.3.co;2-1

Cited by 9 publications

(18 citation statements)

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“…[1][2][3][4][5][6][7][8][9][10][11] The total pressure drop in the riser corresponds to the hydrostatic head and is related to riser gas holdup. The riser gas holdup measurement was verified by use of the bed expansion method to ensure its accuracy.…”

Section: Methodsmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10] When EALRs are used as biological fermentors, gas holdup and liquid velocity in the riser and downcomer become key hydrodynamic factors that determine if there will be dead zones in the reactor. If the liquid velocity is too slow, dead zones may result and biological growth will cease, reducing the overall reactor productivity.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10] Most of these previous works have focused on airlift reactors with a downcomer-to-riser area ratio greater than 1:9. As the downcomer-to-riser area ratio decreases, there exists a point when some of the EALR hydrodynamics, such as riser gas holdup, may more closely resemble the hydrodynamics observed in bubble column reactors.…”

Section: Introductionmentioning

confidence: 99%

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Hydrodynamic Considerations in an External Loop Airlift Reactor with a Modified Downcomer

Jones

Heindel

2010

Ind. Eng. Chem. Res.

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Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with a downcomer-to-riser area ratio of 1:16. Two downcomer configurations are investigated over a range of superficial gas velocities (0.5 ≤ UG ≤ 20 cm/s) using three aeration plate open area ratios (A = 0.62, 0.99, and 2.22%). These results are compared to a bubble column operated with similar operating conditions. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Results show that riser gas holdup varies slightly with downcomer configuration, while a considerable variation is observed for downcomer gas holdup. The superficial liquid velocity varies considerably for the two downcomer configurations and is a function of superficial gas velocity and flow conditions in the downcomer. Observed variations are independent of aeration plate open area ratio. Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with a downcomer-to-riser area ratio of 1:16. Two downcomer configurations are investigated over a range of superficial gas velocities (0.5 e U G e 20 cm/s) using three aeration plate open area ratios (A ) 0.62, 0.99, and 2.22%). These results are compared to a bubble column operated with similar operating conditions. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Results show that riser gas holdup varies slightly with downcomer configuration, while a considerable variation is observed for downcomer gas holdup. The superficial liquid velocity varies considerably for the two downcomer configurations and is a function of superficial gas velocity and flow conditions in the downcomer. Observed variations are independent of aeration plate open area ratio.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hydrodynamic Considerations in an External Loop Airlift Reactor with a Modified Downcomer

Jones

Heindel

2010

Ind. Eng. Chem. Res.

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“…However, the amount of generalized information available is small. This is due to the fact that, for a given super"cial gas velocity value, any variation of gas or liquid physical properties, downcomer and riser cross-section ratio, top and bottom riser and downcomer connecting sections geometry, phase separation conditions, liquid volume, reactor height or gas distributing plate, generates a modi-"cation in liquid velocity and gas-holdup (Bentifraouine, Xuereb & Riba, 1997). The complexity increases when a third phase (solid) is added to the system.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamics of a three-phase external-loop airlift bioreactor

Freitas

Fialová

Zahradník

et al. 2000

Chemical Engineering Science

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The e!ect of the distributing plate ori"ce diameter, air#ow rate, solids loading and solids density on the hydrodynamic characteristics * gas holdup, circulation time and liquid velocity * of a three-phase external-loop airlift reactor was characterized. It was observed that the gas distributor has a small e!ect on riser gas holdup, circulation time and downcomer liquid velocity. On the contrary, the air#ow rate, solids loading and solids density signi"cantly a!ect the hydrodynamic characteristics of the external-loop airlift reactor. A previously described model was used to estimate simultaneously both the riser gas holdup and the downcomer linear liquid velocity. The model simulated with high-accuracy experimental data obtained with three di!erent distributing plate ori"ce diameters, two solids density and solids loading up to 30% (v/v).

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“…Many studies involving ELALR's have indicated that reactor geometry is a key factor in determining gas holdup and liquid velocity in the downcomer and riser [3,[7][8][9][10][11][12][13][14][15]. When ELALR's are used as biological fermentors, liquid velocity in the riser and downcomer become key hydrodynamic factors as the circulation velocity determines if there will be dead zones in the downcomer.…”

mentioning

confidence: 99%

The Effect of a Modified Downcomer on the Hydrodynamics in an External Loop Airlift Reactor

Jones

Heindel

2006

Volume 1: Symposia, Parts a and B

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Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with an area ratio of 1:16. Two downcomer configurations are investigated consisting of the downcomer open or closed to the atmosphere. Experiments for these two configurations are carried out over a range of superficial gas velocities from UG = 0.5 to 20 cm/s using three aeration plates with open area ratios of 0.62, 0.99 and 2.22%. These results are compared to a bubble column operated with similar operating conditions. Experimental results show that the gas holdup in the riser does not vary significantly with a change in the downcomer configuration or bubble column operation, while a considerable variation is observed in the downcomer gas holdup. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Test results also show that the maximum gas holdup for the three aerator plates is similar, but the gas holdup trends are different. The superficial liquid velocity is found to vary considerably for the two downcomer configurations. However, for both cases the superficial liquid velocity is a function of the superficial gas velocity and/or the flow condition in the downcomer. These observed variations are independent of the aerator plate open area ratio. When the downcomer vent is open to the atmosphere, the superficial liquid velocity is initially observed to increase with increasing superficial gas velocity until the onset of choking occurs in the downcomer. Increasing the superficial gas velocity beyond the onset of choking increases the effect of choking and decreases the superficial liquid velocity. Once maximum choking is reached, the superficial liquid velocity becomes independent of the superficial gas velocity. When the downcomer vent is closed to the atmosphere, the superficial liquid velocity is initially observed to decrease with increasing superficial gas velocity as choking in the downcomer is immediately present. Once maximum choking occurs, the superficial liquid velocity once again becomes independent of the superficial gas velocity. Experimental results show that the gas holdup in the riser does not vary significantly with a change in the downcomer configuration or bubble column operation, while a considerable variation is observed in the downcomer gas holdup. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Test results also show that the maximum gas holdup for the three aerator plates is similar, but the gas holdup trends are different.The superficial liquid velocity is found to vary considerably for the two downcomer configurations. However, for both cases the superficial liquid velocity is a fimction of the superficial gas velocity and/or the flow condition in the downcomer. These observed variations are independent of the aerator plate open area ratio.When the downcomer vent is open to the atmosphere, the superficial liquid velocity is initially observed to ...

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An Experimental Study of the Hydrodynamic Characteristics of External Loop Airlift Contactors

Cited by 9 publications

References 0 publications

Hydrodynamic Considerations in an External Loop Airlift Reactor with a Modified Downcomer

Hydrodynamic Considerations in an External Loop Airlift Reactor with a Modified Downcomer

Hydrodynamics of a three-phase external-loop airlift bioreactor

The Effect of a Modified Downcomer on the Hydrodynamics in an External Loop Airlift Reactor

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