Liquid Mixing in Internal Loop Airlift Reactors

Lu, Wen-Jang; Hwang, Shyh-Jye; Chang, Chun‐Min

doi:10.1021/ie00033a023

Cited by 33 publications

(32 citation statements)

References 9 publications

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“…The Peclet number values in Table 1 are somewhat low, suggesting that the computed dispersion coefficients, although consistent with those in bubble columns, are still high for an airlift device. Earlier measurements in concentric-tube internal-loop vessels and in external-loop airlift devices have yielded Pe r values of 20-30 in the riser zone, and Pe d > 40 in the downcomer channel [2, 5,20,21]. No previous measurements of Peclet numbers are available for split-cylinder airlift vessels, but these devices are expected to behave the same as the others until it is realized that the small but finite gaps between the splitting baffle and the column walls allow significant interchange of fluid between the riser and the downcomer sections.…”

Section: Resultsmentioning

confidence: 99%

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Rubio

García

Molina

et al. 2001

Chemical Engineering Journal

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Models were developed for prediction and interpretation of the observed steady-state axial dissolved oxygen concentration profiles in tall airlift bioreactors. The observed concentration profiles were non-linear because of a combination of hydrodynamic and mass transport factors. The profiles were influenced mainly by the liquid-phase axial dispersion coefficient, the volumetric overall gas-liquid mass transfer coefficient, the gas velocity, the induced liquid circulation velocity. The model-predicted concentration profiles agreed within ±2% with the measured data in a tall (working aspect ratio ∼ 15) airlift vessel operated under aeration regimens that are typically used during wastewater treatment. Axial inhomogeneities in dissolved oxygen increased with increasing aeration rate. This phenomenon may influence activated sludge processes in airlift and deep-shaft reactors. The maximum attainable concentration of dissolved oxygen at the bottom of a typically aerated airlift reactor, ≥ 3.5 m deep, always remained at <80% of air saturation value even when oxygen was not being consumed. Also, at steady state and without a net transfer of oxygen, the gas-phase mole fraction of oxygen varied by > 10% axially up the reactor.

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Section: Resultsmentioning

confidence: 99%

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Rubio

García

Molina

et al. 2001

Chemical Engineering Journal

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“…The validity of using this simple model as a first approximation is supported by experimental evidence that shows that the mixing time decreases when the separator volume increases (38,129). When the volume of the separator is increased substantially without changing the reactor diameter, the gas separator becomes tall and slender and may depart from total mixing behavior.…”

Section: Liquid Mixingmentioning

confidence: 86%

“…The top section of the airlift bioreactors is usually considered the best-mixed part of these bioreactors (61,86,(128)(129)(130)(131). Merchuk and Yunger (86) presented a model for airlift bioreactors in which the top section was considered to be perfectly mixed, while the riser and the downcomer were considered as two plug-flow sections.…”

Section: Gas Holdupmentioning

confidence: 99%

“…The mathematical model and consequently the analysis of the experimental data become much more complicated in this case. Nevertheless, this approach has been used (81,129,245,246), and the mass transfer experiments render in this case the k L a for each of the regions of the ALR. Figure 25 shows the results reported by Hwang and Lu (246) in an IL-ALR.…”

Section: Mass Transfer Rate Measurementmentioning

confidence: 99%

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Bioreactors: Airlift Reactors

Merchuk

Camacho

2010

Encyclopedia of Industrial Biotechnology

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ALRs are popular in modern bioprocess research and development and, in many cases, they have found industrial uses. The distinctive characteristics of ALRs are conferred by the fluid dynamics of the liquid‐gas or liquid gas‐solid mixtures: holdup, liquid velocity, and mixing in the riser, gas separator, and downcomer. Only a correct understanding of the interconnection of these regions can make possible the scale‐up of a laboratory device, to pilot or industrial size. Several correlations are available in the literature for the prediction of the fluid dynamic characteristics of the reactor and of the mass and heat transfer coefficients, and a selection is presented in this review. Significant progress has been made in the application of modern computational tools to the simulation and design of ALRs. In parallel, innovative and sophisticated methods have been applied to obtain a deeper insight into the mechanisms of fluid motion and the flow patterns in the reactor. However, no single research group has managed to cover all the variables over a wide range. The engineer confronting scale‐up or de novo design of an ALR must analyze the validity of the correlations and computation methods used for the calculations.

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“…, Lu and Hwang (1994) analyzed mixing using the axial dispersion model (ADM) which can be expressed in as: Mixing time although is easy to measure has a drawback.…”

Section: Techniques For Measuring Liquid Circulation and Mixing Timementioning

confidence: 99%

Characteristics of Local Flow Dynamics and Macro-Mixing in Airlift Column Reactors for Reliable Design and Scale-Up

Gumery¹,

Ein‐Mozaffari²,

Dahman³

2009

International Journal of Chemical Reactor Engineering

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There has been tremendous development within mixing operations in industry. Incomplete knowledge of this process caused serious economic losses to process industries. For optimum yields and the economic potential that goes with better understanding of mixing, research in this field continues to grow. The major forms of mixing in industry are either by mechanical or pneumatic agitation. Airlift bioreactors achieve mixing through pneumatic agitation and have gained attention over two decades for their fluid dynamic characteristics and low power consumption. It has been widely applied in bioprocess industries for production of biochemicals, to wastewater treatment in which the performance of this reactor has been overwhelming with respect to its production levels as compared to the conventional mechanical agitation.In this review, mixing through mechanical and pneumatic agitation is compared. An extensive literature is distilled from various investigators on the hydrodynamics and mixing characteristics of airlift bioreactors. This review has emphasis on factors that affect mixing such as the geometrical parameters of the vessel, gas flow rate, properties of the liquid medium, sparger design and measuring techniques employed. In an attempt to understand process related issues, sophisticated advances in the measuring techniques provides more insight into mixing in this reactor. Thus extensive correlations have been proposed by various investigators to predict the hydrodynamic and mixing parameters. Some design modifications proposed by several scholars have also been reviewed.

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Liquid Mixing in Internal Loop Airlift Reactors

Cited by 33 publications

References 9 publications

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Bioreactors: Airlift Reactors

Characteristics of Local Flow Dynamics and Macro-Mixing in Airlift Column Reactors for Reliable Design and Scale-Up

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