A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings
-
Li Liangchao
,
Chen Ning
Abstract
The computational fluid dynamics (CFD) combined with a population balance model (PBM) was applied to simulate gas-liquid dispersion in a stirred tank with low and high gas loadings. The model predictions were validated by using the data in the literature. The simulation results show that the flow patterns and gas dispersion characteristics are very different in the stirred tank for low and high gas loadings. A typical two-loop flow pattern forms as that in single-phase stirred tank for low gas loadings, while a triple-loop flow pattern, with two recirculation loops above and one below the impeller is found in the tank for high gas loadings. Shaft power input of impeller agitation plays a major role for gas dispersion with low gas loadings. For high gas loadings, the potential energy due to gas sparging has significant effect on gas dispersion and can not be neglected. Compared to low gas loading, high gas loading causes average gas holdup increased in the stirred tank, while relative local gas holdup in the lower circulation-loop region and near-wall region reduced. The ability of impeller agitation for gas dispersion reduces with high gas loadings, and mean bubble size becomes larger and the volume-averaged bubble size distribution is wider.
Nomenclature
- BB
birth rate of the bubble for the breakup of large bubbles
- BC
birth rate of the bubble due to the coalescence of small bubbles
- C
impeller clearance from the tank bottom, m
- C0
clearance of gas distributor from the tank bottom, m
turbulence model constants
- CD
drag coefficient
- d32
bubble Satuer diameter, m
- dmax
maximum diameter of the bubble in the size groups, m
- dmin
minimum diameter of the bubble in the size groups, m
- di
bubble diameter of group i, m
- D
diameter of the impeller, m
- D0
diameter of the disc, m
- DB
death rate for the bubble breakup into small bubbles
- DB
death rate due to the bubble coalescence with other bubbles
- Eo
Eotvos number
- fi
fraction of group i
Coriolis and centrifugal force caused by impeller rotation, N/m3
- Fl
gas flow number
- Fr
impeller Froude number
- g
gravitational force, m/s2
- h0
initial liquid film thickness, m
- hf
film thickness when rupture occurs, m
- H
unaerated liquid height, m
- H0
height of the stirred tank, m
- H1
parameter in Grace drag model
- Hs
submerge depth below the liquid level, m
- I
unit tensor
- J
parameter in Grace drag model
- k
turbulent kinetic energy, m2/s2
- k0
coefficient for Lopez de Bertodano model
- l
blade height, m
- mcell
liquid mass in a grid cell, kg
- M
number of the bubble size group
- Mo
Morton number
- N
impeller rotation speed, r/min
- Np
impeller power number
- p
static pressure, Pa
- P
correction exponent in eq. (30)
- P0
power consumption, W
- P1
potential energy due to gas sparging, W
- Pk,
turbulence production due to viscous and buoyancy force, kg/m s3
- Qg
gas inlet flow rate, L/min
- r
radial location in the tank, m
- R
radius of the tank, m
interphase forces, N/m3
- Re
Reynolds number in the stirred tank
- Reb
bubble Reynolds number
- t
time, s
- T
diameter of the tank, m
- T0
impeller torque in the rotation direction, N m
velocity vector, m/s
- Ug
superficial gas velocity, m/s
- UT
bubble terminal velocity, m/s
- w
width of the blade, m
- z
axial coordinate in the tank, m
- Greek Letters
phase hold up
- β
model constant in eq. (8)
- β0
model constant in eq. (35)
- ε
turbulent energy dissipation, m2/s3
dimensionless eddy size
eddy size, m
effective viscosity, kg/m s
molecular viscosity of gas phase, kg/m s
molecular viscosity of continuous phase, kg/m s
turbulent viscosity of continuous phase, kg/m s
- ρ
density, kg/m3
different of bubble diameter between two groups, m
density difference between continuous phase and dispersed phase, kg/m3
- σ
surface tension coefficient N/m
turbulence model constants
Reynolds stress tensor
- Subscripts
- i
number of phase, or bubble size group
- g
gas phase
- l
liquid phase
Acknowledgements
The authors would like to acknowledge the support by National Green Manufacturing System Integration Project(2016), Ministry of Industry and Information Technology of China. Key Scientific Research Project of Sichuan Provincial Education Department (15ZA0107)
References
Ahmed, S U, P Ranganathan, A Pandey, and S Sivaraman. 2010. “Computational Fluid Dynamics Modeling of Gas Dispersion in Multi Impeller Bioreactor.” Journal of Bioscience and Bioengineering 109: 588–597.10.1016/j.jbiosc.2009.11.014Search in Google Scholar
Alves, S S, C J Maid, J M T Vasconcelos, and A J Serralheiro. 2002. “Bubble Size in Aerated Stirred Tanks.” Chemical Engineering Journal (Lausanne, Switzerland : 1996) 89: 109–117.10.1016/S1385-8947(02)00008-6Search in Google Scholar
Armenante, P M, C Luo, C Chou, I Fort, and J Medek. 1997. “Velocity Profiles in a Closed Unbaffled Vessel: Comparison between Experimental LDV Data and Numerical CFD Predictions.” Chemical Engineering Science 52: 3483–3492.10.1016/S0009-2509(97)00150-4Search in Google Scholar
Aubin, J, N L Sauze, J Bertrand, D F Fletcher, and C Xuereb. 2004. “PIV Measurements of Flow in an Aerated Tank Stirred by a Down- and an Up-Pumping Axial Flow Impeller.” Experiments Thermal Fluid Sciences 28: 447–456.10.1016/j.expthermflusci.2001.12.001Search in Google Scholar
Bao, Y Y, B J Wang, M L Lin, Z M Gao, and J Yang. 2015a. “Influence of Impeller Diameter on Overall Gas Dispersion Properties in a Sparged Multi-Impeller Stirred Tank.” Chinese Journal Chemical Engineering 23: 890–896.10.1016/j.cjche.2014.11.030Search in Google Scholar
Bao, Y Y, B J Wang, M L Lin, Z M Gao, and J Yang. 2015b. “Influence of Impeller Diameter on Local Gas Dispersion Properties in a Sparged Multi-Impeller Stirred Tank.” Chinese Journal Chemical Engineering 23: 615–622.10.1016/j.cjche.2014.12.006Search in Google Scholar
Bertodano, M A L D. 1998. “Two Fluid Model for Two-Phase Turbulent Jets.” Nuclear Engineering Design 179: 65–74.10.1016/S0029-5493(97)00244-6Search in Google Scholar
Derksen, J J, M S Doelman, and H E A Van Den Akker. 1999. “Three-Dimensional LDA Measurements in the Impeller Region of a Turbulently Stirred Tank.” Experiments Fluids 27: 522–532.10.1007/s003480050376Search in Google Scholar
Devi, T T, and B Kumar. 2012. “CFD Simulation of Flow Patterns in Unbaffled Stirred Tank with CD-6 Impeller.” Chemical Industrial Chemical Engineering Quarterly 18: 535–546.10.2298/CICEQ111130029DSearch in Google Scholar
Dohi, N, T Takahashi, K Minekawa, and Y Kawase. 2004. “Power Consumption and Solid Suspension Performance of Large-Scale Impeller in Gas-Liquid-Solid Three-Phase Stirred Tank Reactors.” Chemical Engineering Journal (Lausanne, Switzerland : 1996) 97: 103–114.10.1016/S1385-8947(03)00148-7Search in Google Scholar
Gao, Z M, J M Smith, and H. Müller-Steinhagen. 2001. “Void Fraction Distribution in Sparged and Boiling Reactors with Modern Impeller Configuration.” Chemical Engineering and Processing 40: 489–497.10.1016/S0255-2701(00)00147-1Search in Google Scholar
Gimbun, J, C D Rielly, and Z K Nagy. 2009. “Modelling of Mass Transfer in Gas-Liquid Stirred Tanks Agitated by Rushton Turbine and CD-6 Impeller: A Scale-Up Study.” Chemical Engineering Researcher Design 87: 437–451.10.1016/j.cherd.2008.12.017Search in Google Scholar
Gimbun, J, C D Rielly, Z K Nagy, and J J Derksen. 2012. “Detached Eddy Simulation on the Turbulent Flow in a Stirred Tank.” AIChE Journal. American Institute of Chemical Engineers 58: 3224–3241.10.1002/aic.12807Search in Google Scholar
Grace, J R, T Wairegi, and T H Nguyen. 1976. “Shapes and Velocities of Single Drops and Bubbles Moving Freely through Immiscible Liquids.” Transactions Institute Chemical Engineering 54: 167–173.Search in Google Scholar
Hudcova, V, A W Nienow, H Z Wang, and H X. Liu. 1987. “On the Effect of Liquid Height on the Flooding/Loading Transition.” Chemical Engineering Science 2: 375–377.10.1016/0009-2509(87)85067-4Search in Google Scholar
Jahoda, M, L Tomášková, and M Moštĕk. 2009. “CFD Prediction of Liquid Homogenization in a Gas-Liquid Stirred Tank.” Chemical Engineering Researcher Design 87: 460–467.10.1016/j.cherd.2008.12.006Search in Google Scholar
Kasat, G R, A R Khopkar, V V Ranade, and A B Pandit. 2008. “CFD Simulation of Liquid Phase Mixing in Solid-Liquid Stirred Reactor.” Chemical Engineering Science 63: 3877–3885.10.1016/j.ces.2008.04.018Search in Google Scholar
Kerdouss, F, A Bannari, P Proulx, R Bannari, M Skrga, and Y Labrecque. 2008. “Two-Phase Mass Transfer Coefficient Prediction in Stirred Vessel with a CFD Model.” Computers & Chemical Engineering 32: 1943–1955.10.1016/j.compchemeng.2007.10.010Search in Google Scholar
Khopkar, A R, J Aubin, C Xureb, N Le Sauze, J Bertrand, and V V Ranade. 2003. “Gas–Liquid Flow Generated by a Pitched Blade Turbine: PIVmeasurements and CFD Simulations.” Industrial & Engineering Chemistry Research 42: 5318–5332.10.1021/ie020954tSearch in Google Scholar
Khopkar, A R, G R Kasat, A B Pandit, and V V Ranade. 2006. “CFD Simulation of Mixing in Tall Gas-Liquid Stirred Vessel: Role of Local Flow Pattern.” Chemical Engineering Science 61: 2921–2929.10.1016/j.ces.2005.09.023Search in Google Scholar
Laakkoen, M, V Alopaeus, and J Aittamas. 2006. “Validation of Bubble Breakage, Coalescence and Mass Transfer Models for Gas-Liquid Dispersion in Agitated Vessel.” Chemical Engineering Science 61: 218–228.10.1016/j.ces.2004.11.066Search in Google Scholar
Laakkoen, M, P Moilanen, V Alopaeus, and J Aittamas. 2007. “Modelling Local Bubble Size Distributions in Agitated Vessels.” Chemical Engineering Science 62: 721–740.10.1016/j.ces.2006.10.006Search in Google Scholar
Lane, G L, M P Schwarz, and G M Evans. 2005. “Numerical Modeling of Gas-Liquid Flow in Stirred Tanks.” Chemical Engineering Science 60: 2203–2214.10.1016/j.ces.2004.11.046Search in Google Scholar
Lehr, F, M Millies, and D Mewes. 2002. “Bubble Size Distribution and Flow Fields in Bubble Columns.” AIChE Journal. American Institute of Chemical Engineers 48: 2426–2443.10.1002/aic.690481103Search in Google Scholar
Li, G. Two-phase flow dynamical simulation and modeling of bubble column Reactors. PhD Thesis, Shanghai: East China University of Science and Technology. 2010.Search in Google Scholar
Li, L C, and B Xu. 2016. “Numerical Simulation of Flow Field Characteristics in a Gas-Liquid-Solid Agitated Tank.” The Korean Journal of Chemical Engineering 33: 2007–2017.10.1007/s11814-016-0105-7Search in Google Scholar
Luo, H, and H Svendsen. 1996. “Theoretical Model for Drop and Bubble Breakup in Turbulent Dispersions.” AIChE Journal. American Institute of Chemical Engineers 42: 1225–1233.10.1002/aic.690420505Search in Google Scholar
Min, J, Y Y Bao, L Chen, Z M Gao, and J M Smith. 2008. “Numerical Simulation of Gas Dispersion in an Aerated Stirred Reactor with Multiple Impellers.” Industrial & Engineering Chemistry Research 47: 7112–7117.10.1021/ie800490jSearch in Google Scholar
Min, J, and Z M Gao. 2006. “Large Eddy Simulation of Mixing Time in a Stirred Tank.” Chinese Journal Chemical Engineering 14: 1–7.10.1016/S1004-9541(06)60030-XSearch in Google Scholar
Montante, G, D Horn, and A Paglianti. 2008. “Gas-Liquid Flow and Bubble Size Distribution in Stirred Tanks.” Chemical Engineering Science 63: 2107–2118.10.1016/j.ces.2008.01.005Search in Google Scholar
Morud, K E, and B H Hjertager. 2008. “LDA Measurements and CFD Modeling of Gas-Liquid Flow in a Stirred Vessel.” Chemical Engineering Science 51: 233–249.10.1016/0009-2509(95)00270-7Search in Google Scholar
Murthy, B N, R B Kasundra, and J B Joshi. 2008. “Hollow Self-Inducing Impeller for Gas-Liquid-Solid Dispersion: Experimental and Computational Study.” Chemical Engineering Journal (Lausanne, Switzerland : 1996) 141: 332–345.10.1016/j.cej.2008.01.040Search in Google Scholar
Ng, K, and M Yianneskis. 2000. “Observation on the Distribution of Energy Dissipation in Stirred Vessels.” Chemical Engineering Researcher Design 78: 334–341.10.1205/026387600527446Search in Google Scholar
Nienow, A W. 1990. “Gas Dispersion Performance in Fermenter Operation.” Chemical Engineering Progress 86: 61–71.Search in Google Scholar
Nienow, A W. 1998. “Hydrodynamics of Stirred Bioreactors.” Applied Mechanics Review 51: 3–32.10.1115/1.3098990Search in Google Scholar
Ochieng, A, M S Onyango, A Kumar, K Kiriamiti, and P Musonge. 2008. “Mixing in a Tank Stirred by a Rushton Turbine at a Low Clearance.” Chemical Engineering and Processing 47: 842–851.10.1016/j.cep.2007.01.034Search in Google Scholar
Prince, M J, and H W Blanch. 1990. “Bubbly Coalescence and Break-Up in Air-Sparged Bubble Columns.” AIChE Journal. American Institute of Chemical Engineers 36: 1485–1499.10.1002/aic.690361004Search in Google Scholar
Qi, N N, GY Wu, H Wang, K Zhang, and H Zhang. 2010. “CFD Simulation of Mixing Characteristics in Stirred Tank by Smith Turbine.” CIESC Journal 61: 2305–2313.Search in Google Scholar
Qi, N N, H Zhang, K Zhang, G Xu, and Y P Yang. 2013. “CFD Simulation of Particle Suspension on a Stirred Tank.” Particuology 11: 317–326.10.1016/j.partic.2012.03.003Search in Google Scholar
Rewatkar, V B, and J B Joshi. 1992. “Effect of Addition of Alcohol on the Design Parameters of Mechanically Agitated Three-Phase Reactors.” The Chemical Engineering Journal 42: 107–117.10.1016/0300-9467(92)80044-BSearch in Google Scholar
Scargialio, F, F D'Orazio, F Grisafi, and Brucato. 2007. “Modeling and Simulation of Gas-Liquid Hydrodynamics in Mechanically Stirred Tanks.” Chemical Engineering Researcher Design 85: 637–646.10.1205/cherd06243Search in Google Scholar
Shewale, S D, and A B Pandit. 2006. “Studies in Multiple Impeller Agitated Gas-Liquid Contactors.” Chemical Engineering Science 61: 489–504.10.1016/j.ces.2005.04.078Search in Google Scholar
Wadnerkar, D, R P Utikar, M O Tade, and V K Pareek. 2012. “CFD Simulation of Solid-Liquid Stirred Tanks.” Advanced Powder Technology 23: 445–453.10.1016/j.apt.2012.03.007Search in Google Scholar
Wang, L C, Y F Zhang, X G Li, and Y Zhang. 2010. “Experiment Investigation and CFD Simulation of Liquid-Solid-Solid Dispersion in a Stirred Reactor.” Chemical Engineering Science 65: 5559–5572.10.1016/j.ces.2010.08.002Search in Google Scholar
Wang, T F, J F Wang, and Y. A Jin. 2006. “CFD-PBM Coupled Model for Gas-Liquid Flows.” AIChE Journal. American Institute of Chemical Engineers 52: 125–140.10.1002/aic.10611Search in Google Scholar
Wu, H, and G K Patterson. 1989. “Laser-Doppler Measurements of Turbulent Flow Parameters in a Stirred Mixer.” Chemical Engineering Science 44: 2207–2221.10.1016/0009-2509(89)85155-3Search in Google Scholar
Yeoh, S L, G Papadakis, and M Yianneskis. 2004. “Numerical Simulation of Turbulent Flow Characteristics in a Stirred Vessel Using the LES and RANS Approaches with the Sliding/Deforming Mesh Methodology.” Chemical Engineering Researcher Design 82: 834–848.10.1205/0263876041596751Search in Google Scholar
Zhang, Q H, Y Yong, Z S Mao, C Yang, and C Zhao. 2009. “Experimental Determination and Numerical Simulation of Mixing Time in a Gas-Liquid Stirred Tank.” Chemical Engineering Science 64: 2926–2933.10.1016/j.ces.2009.03.030Search in Google Scholar
Zhao, D L, Z M Gao, H Müller-Steinhagen, and J M Smith. 2001. “Liquid-Phase Mixing Time in Sparged and Boiling Agitated Reactors with High Gas Loading.” Industrial & Engineering Chemistry Research 40: 1482–1487.10.1021/ie000445wSearch in Google Scholar
© 2018 Walter de Gruyter GmbH, Berlin/Boston
Articles in the same Issue
- Review
- Modelling of Chemical Reactors: From Systemic Approach to Compartmental Modelling
- Articles
- Novel Solutions in Modeling of Anaerobic Digestion Process - Two-Phase AD Models Development and Comparison
- Characterization and Catalytic Performance of Modified SBA-16 in Liquid Phase Reaction
- Production of NMSBA from NMST Catalyzed by Co/Mn/Br and HPW@C Modified with ZnCl2 Solution
- Numerical Study on the Kinetic Effects of Hydrogen Addition on the Thermal Characteristics of Laminar Methane Diffusion Flames
- Transient Flow and Heat Transfer Characteristics of non-Newtonian Supercritical Third-Grade Fluid (CO2) past a Vertical Cylinder
- Synthesis of MgO/TiO2 Nanocomposite and Its Application in Photocatalytic Dye Degradation
- A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings
- Scrutinization of Chemical Reaction Effect on Flow and Mass Transfer of Prandtl Liquid over a Riga Plate in the Presence of Solutal Slip Effect
- Short Communications
- Edible Plant Oil Wastewater Treatment Using Electro-Fenton Technique: Experiment and Correlation
Articles in the same Issue
- Review
- Modelling of Chemical Reactors: From Systemic Approach to Compartmental Modelling
- Articles
- Novel Solutions in Modeling of Anaerobic Digestion Process - Two-Phase AD Models Development and Comparison
- Characterization and Catalytic Performance of Modified SBA-16 in Liquid Phase Reaction
- Production of NMSBA from NMST Catalyzed by Co/Mn/Br and HPW@C Modified with ZnCl2 Solution
- Numerical Study on the Kinetic Effects of Hydrogen Addition on the Thermal Characteristics of Laminar Methane Diffusion Flames
- Transient Flow and Heat Transfer Characteristics of non-Newtonian Supercritical Third-Grade Fluid (CO2) past a Vertical Cylinder
- Synthesis of MgO/TiO2 Nanocomposite and Its Application in Photocatalytic Dye Degradation
- A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings
- Scrutinization of Chemical Reaction Effect on Flow and Mass Transfer of Prandtl Liquid over a Riga Plate in the Presence of Solutal Slip Effect
- Short Communications
- Edible Plant Oil Wastewater Treatment Using Electro-Fenton Technique: Experiment and Correlation
