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Considering pressure effects in 1-D modelling of hydrodynamics and oxygen transfer in deep bubble
columns
T. Larsson, Y. Fayolle, Arnaud Cockx, S. Gillot, Céline Duran
To cite this version:
T. Larsson, Y. Fayolle, Arnaud Cockx, S. Gillot, Céline Duran. Considering pressure effects in 1-D modelling of hydrodynamics and oxygen transfer in deep bubble columns. 14th International Con- ference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering GLS-14, May 2019, Guilin, pp.2.
�hal-02609236�
Considering pressure effects in 1-D modelling of hydrodynamics and oxygen transfer in deep bubble columns
Timo Larsson1, Yannick Fayolle1,* , Camilo Duran1, Arnaud Cockx2, Sylvie Gillot3
1 Irstea, UR HBAN, Centre d’Antony, F-92761 Antony, France
2 Université de Toulouse, INSA, UPS, INP, LISBP, 135, Avenue de Rangueil, Toulouse, France
3 Irstea, UR REVERSAAL, Centre de Lyon-Villeurbanne, F-69625 Villeurbanne Cedex, France
*Corresponding author: [email protected]
Keywords: oxygen transfer; hydrodynamics; bubble column; 1D-model Introduction
In literature, the effect of liquid depth on hydrodynamics and mass transfer in bubble columns is generally neglected in modeling approaches due to relatively small experimental setup (approximately 1 meter of water height). The aim of this work is to show that pressure impacts have to be taken into account for deep columns with low gas hold up (< 5%), through a comprehensive review of literature processes and models. The literature review includes pressure effects, bubble size evolution, drag laws and mass transfer models and is illustrated through sensitivity analyses using a 1D-model confronted to an extended experimental database.
Methods
Experimental database = Experimental measurements were performed in a deep cylindrical bubble column of 4.5 m height and 0.29 m diameter filled with tap water. For gas superficial velocities (jG) from 1.1 to 6.1 mm/s, global gas hold-up (εG), bubble size (dB) and mass transfer measurements were performed. The experimental set up is presented in details in Duran et al. (2016).
1D-Model = A 1D-modelling approach is proposed for hydrodynamics and mass transfer modelling in the bubble column [Talvy et al., (2007)], based on the local resolution of mass and momentum conservation and concentration transport equations. All variables are averaged and considered constant in each cross section of the column. The variation of superficial gas velocity and bubble diameter with pressure along the column and its impact on simulation results such as global gas hold up and mass transfer is studied.
Results and Discussion
Figure 1a shows the experimental gas hold-up as a function of the superficial gas velocity (jG) and a comparison with the results obtained using the drag models proposed by Karamanev and Nikolov (1992) and Tomiyama et al., (1998). In Figure 1b, experimental dissolved oxygen concentration over time during reoxygenation tests are confronted to modeled values computed with two different mass transfer coefficients models (Higbie (1935) and Frössling (1938)) usually used respectively for clean bubbles and contaminated ones.
14th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering GLS-14, Guilin, China, May 30 - June 3, 2019
Figure 1. (a) Global gas hold-up versus superficial air velocity (dash-circle line = model with Karamanev drag law / dash-dot line = model
with Tomiyama drag law / crosses = experimental); (b) Oxygen transfer concentration as function of time during oxygenation tests for jG = 1.1 and 6.1 mm/s respectively (–dash-dot curve = Higbie Model /continuous curve = Frössling model / purple = Experimental points* ).
For each gas superficial velocity, the experimental curve lies between the simulated ones. For increasing jG, the Higbie penetration model allows to reproduce better experimental data as in the same time the average bubble size increases from 2.2 to 4.1 mm due to membrane sparger impact.
Moreover, analyses of these curves yield an “apparent global oxygen transfer coefficient (kLa)” different from the kLa resulting from the local modeled values of liquid side mass transfer coefficient (kL) multiplied by the local interfacial area (a). This analysis will be further developed and discussed in the full version of the manuscript.
Conclusion
The main objective of the article is to propose a review of hydrodynamic and mass transfer models in deep bubble column with low gas hold-up. A 1D-Model is developed to illustrate the sensitivity of simulations to processes and models proposed in literature to represent bubble size evolution and pressure effects on mass transfer. The proposed model can mimic experimental data of global gas hold-up and mass transfer coefficient in an experimental bubble column with a clear water/air system. Moreover, this model will be used to investigate the mass transfer evolution along the deep bubble column and extended to other data from the literature.
References
[1] Talvy, S., Cockx, A., Liné, A., 2007. Modeling of oxygen mass transfer in a gas-liquid airlift reactor, AIChE J., 53(2) , 316-326.
[2] Duran C., Fayolle Y., Pechaud Y., Cockx A., Gillot S., 2016. Impact of suspended solids on the activated sludge non-newtonian behaviour and on oxygen transfer in a bubble column, Chemical Engineering Science 141, 154-165.
[3] Frössling, N., 1938. Uber die verdunstung fallenden tropfen . Gerlans Beitage Geophysik 52(1), 170-216.
[4] Higbie, R., 1935. The rate of absorption of a pure gas into a still liquid during short periods of exposure.
Transactions AIChe 31, 365-389.
[5] Karamanev,D., Nikolov N., 1992. Free rising sphere do not obey Newton’s laws for free settling. AIChe Journal 38(11), 1843-1846.
[6] Tomiyama, A., Kataoka, I., Zun, I., Sakaguchi, T., 1998. Drag coefficients of single bubbles under normal and micro gravity conditions. JSME International Journal 41(2).
14th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering GLS-14, Guilin, China, May 30 - June 3, 2019
