Braga, M.

Brunet-Errard, L

De Bellefon, C.

Fonte, C,

Lopes, Jcb

Pitault, I.

Rolland, M.

Santos-Moreau, V.

Simoëns, Serge

Vasile, R.

Fonte, C, P

de Bellefon, C.

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Renewable energies | Eco-friendly production | Innovative transport | Eco-efficient processes | Sustainable resources©2013 -IFP Energies nouvellesCFD for the Study of the Multiphase Flow and Mass Transfer in a Stirred Tank Reactor for the Screening of Shaped CatalystsCP Fonte1, M Braga1,2, R Vasile1, M Rolland1, L Brunet-Errard1, I Pitault2,S Simoëns3, C De Bellefon2, V Santos-Moreau1 and JCB Lopes4(1) IFP Energies nouvelles, Solaize, France (2) Laboratoire de Génie des Procédés Catalytiques, UCB Lyon, Villeurbanne, France(3) Laboratoire de Mécanique des Fluides et d'Acoustique, UCB Lyon, Écully, France(4) Laboratory of Separation and Reaction Engineering, Fac. Eng., Univ. Porto, Porto, Portugal©2013 -IFP Energies nouvelles2The Company IFP Energies NouvellesPublic interest missions:• providing solutions to face society’s challenges in  terms of energy and the climate change , promoting a sustainable use of energy sources• creating wealth and employment by supporting the French and European economic activity, and its competitiveness in related indust rial sectorsPublic research and training institute with interna tional scope, covering the fields of energy , transports and the environment Transposing research to industry, technological innovation is central to all its activitiesLyon Site©2013 -IFP Energies nouvelles3Evaluation of commercially shaped catalysts Petrochemical, Refining and New Biological Green industrial Processes Catalysts are evaluated/tested in its commercial shape to maintain the spatial distribution of its active sitesParticles (1-3 mm)ExtrudatesBeads©2013 -IFP Energies nouvelles4Evaluation of commercially shaped catalysts Possible choice at IFPEN:Stirred reactor with stationary catalytic basketCatalytic basket Lab-scale baffled stirred tank reactor (STR) Volume = 300 cm3 Stationary catalytic basket Perforated metal walls Support the catalyst particles (fixed bed) Gap between basket walls = 9 mm Diam. catalyst = 1 – 3 mm Self-inducing radial flow impeller Hollow shaft with orifices Recirculation of gas in a closed loop without the need for additional equipment Mixing of the gas/liquid phases D=20-25 mm, 800-2000 rpmHollow self-inducing impellerHighly complex gas-liquid turbulent flow (2 000 < Re < 20 000)©2013 -IFP Energies nouvelles5Characteristic time scales[1]1 10 100 1000 (s)Mixing timeG-L mass transferS-L mass transfer Constant development of catalysts with higher performance Faster reactions Mass transport limitations between the phases can compromise kinetic testsReaction[1] - Braga, M., 2013. Etude des phénomènes de trans fert et de l’hydrodynamique dans des réacteurs agit és à panier catalytique (Study of transport phenomen a and hydrodynamics in stirred reactors with a catalytic basket). Université Claude Bernard Lyon 1, Lyon, Fra nce.©2013 -IFP Energies nouvelles6General objectives of the project Having deeper knowledge on the hydrodynamics of STRs with stationary catalytic baskets Complex multiphase flow Difficult to observe experimentally the flow inside the catalytic basket Only a few papers exist in the literature (for similar, but different, setups) Knowing the conditions for which the reaction kinetics is the controlling rate for fast reactions (no mixing or mass transfer limitations). Propose more efficient and robust reactor/basket designs: More homogeneous dispersion of the gas in the liquid phase Optimize gas absorption rate into the liquid phase (↑kLa) Increase velocity of the liquid through the catalyst porous medium (↑kS)©2013 -IFP Energies nouvelles7Strategy Development of a “simple” parametric 3D Computational Fluid Dynamics (CFD) model of the reactor, describing the most significant aspects of: Turbulent mixing Flow through the porous media (catalyst particles in the basket) Gas dispersion from the self inducing impeller Computational working tool, to be used internally, for the selection of correct operating conditions and for the design of new reactors, reducing the need for experimentationEnsure regimes of kinetic controlComputational Model ©2013 -IFP Energies nouvellesSolid-Liquid Mass transfer©2013 -IFP Energies nouvelles9S-L CFD Model ANSYS Fluent Steady state Multiple Reference Frame approach to deal with impeller motion D = 19 mm N = 800-2000 rpm Working fluid: Heptane Reynolds Averaged Navier-Stokes equations Standard k-ε turbulence model to deal with the closure problem Standard Wall Functions Homogeneous porous media model inside the basket(momentum source terms from Ergun equation). Particles of 3 mm Porosity 47% Porous jump model to simulate the perforated basket wallsbasket walls0.5 mm9 mmSimulated as a homogeneous medium©2013 -IFP Energies nouvelles10Homogeneous Porous Medium Hypothesis verification A Discrete Elements Method code (GRAINS 3D)[2] was used to simulate a random packing of particles representative of the packing inside the basket Estimation of the pressure drop across the shallow packed bed inside the basket from CFD simulations at the particle scale using COMSOL MultiphysicsThe numerical results support the use of the Ergun equation to model the pressure drop inside the basket[2] Wachs A., Girolami L., Vinay G., Ferrer G., Powder Technology 224 (2012) 374–3891E+01E+11E+21E+31E+41E+50.001 0.01 0.1 1V  (m/s)P (Pa)Grains3D + COMSOLErgun Eq.©2013 -IFP Energies nouvellesGrid of the catalytic basketPerforated Plate ModelEmpty catalytic basketCatalytic basket walls simulated as a semi-permeable zero-thickness surface with pressure drop (porous jump model)( ) ( )2212pCxµ ρα∆  = − ⋅ + ⋅ ∆  v n v n0.8 mm1.5 mmRepeatingperiodic unit1.5 mmFlow direction(θ = 0°,ϕ = 0°)(θ = 30°,ϕ = 0°)[3]Simulations of the flow through a repeating periodic unit of the perforated plateDifferent velocity angles of attack [3] Perry's Chemical Engineer's Handbook, 14-30Parameters α and C2 from fitting to CFD results©2013 -IFP Energies nouvelles12Flow field N = 2000 rpmV/Vtip0.0 0.5 1.0Basketz = 28 mmθ = 30°Top view Side view Flow in the basket is not homogeneous Fluid pumped by the impeller blades traverses the basket radially at the height of the impeller Porous media promotes a rapid dissipation of velocity gradients by spreading the pumped jet in the axial direction  Fluid reenters the basket at the bottomBasket©2013 -IFP Energies nouvelles13Particle Image Velocimetry (PIV) Validation80°60°20° 40°Black discontinuous lines: range for the 8 impeller/baffle orientations in CFD00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V axial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V axial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V axial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V axial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V radial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V radial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V radial/V Tipz/HCFDPIV TopPIV Bottom00.10.20.30.40.50.60.70.80.91-0.04 -0.02 0 0.02 0.04V radial/V Tipz/HCFDPIV TopPIV Bottom20°40°60°80°2.25 mm from the wall©2013 -IFP Energies nouvelles14S-L mass transfer coefficient0%10%20%30%40%50%60%70%80%90%100%0.1% 1.0% 10.0% 100.0%V /V tipCumulative frequency distribution50%90%Ranz-Marshall correlation to estimate the spatial distribution of ShVelocity distribution in the catalyst volume can be used to estimate the solid-liquid mass transport rateAverage S-L mass transfer rateBroad distribution of velocities inside the basket0.5 0.33pSh( ) 2 1.8Re ( ) Sc= +x xcatalyst3S pappm catalystSh( )dShVk dD V= =∫∫∫ x x©2013 -IFP Energies nouvelles15S-L mass transfer coefficient CFD values show good agreement with experimental values reported in Braga’s PhD thesis[1] Assumed simplification of homogeneous porous medium proven acceptable Ranz-Marshall correlation also proven suited for the determination of the mass transfer coefficient[1] - Braga, M., 2013. Etude des phénomènes de trans fert et de l’hydrodynamique dans des réacteurs agit és à panier catalytique (Study of transport phenomena and hydrodynamics in stirred  reactors with a catalytic basket). Université Claud e Bernard Lyon 1, Lyon, France.Impeller Reynolds number, ρND2/μCharacteristic time (s)Solid-liquidLiquid-gasMixing©2013 -IFP Energies nouvellesGas-Liquid Mass transfer©2013 -IFP Energies nouvelles17G-L CFD Model ANSYS Fluent Steady state Eulerian-Eulerian multiphase flow model Heptane-Hydrogen binary system Gas inlet flow rate as a function of impeller rotational speed [4] Multiple Reference Frame approach to deal with impeller motion Reynolds Averaged Navier-Stokes equations Per-phase Realizable k-ε turbulence model to deal with the closure problem Standard Wall Functions A turbulence dispersive force modeled as a dispersive term in the phases mass conservation equations (Scturb=0.75) Spatially invariant bubble diameter of 2 mm (experimental ) Bubble drag coefficient from Schiller-Naumann correlation Different drag correction correlations for turbulent flows have been testedgas inlet from the impeller orificesPressure outlet(only liquid is allowed to re-enter the domain)[4] – C. P. Fonte et al., Chem Eng Technol (2014)©2013 -IFP Energies nouvellesDrag Modification Correlation Different correlations exist for taking into account the apparent decrease of the bubbles rising time due to constant accelerations and decelerations by turbulent velocities fluctuations.34 b,0 K1 8.76 10DDC dC λ−  = + ×    36 b,0 K1 6.5 10DDC dC λ−  = + ×    2K,0 b0.4 tanh 16 1 0.6DDCC dλ−     = − +       Brucato(Brucato et al., 1998)Modified Brucato(Lane et al., 2000)Pinelli(Pinelli et al., 2001)Different mechanism for bubbles and solid particles?©2013 -IFP Energies nouvellesDrag Modification correlation0204060801001201401601802002000 4000 6000 8000 10000 12000 14000Impeller Reynolds numberdb/λKBulk regionImpeller regionBubbles of 2 mm of diameter Brucato et al., Chem Eng Journal (1998)Values need to be extrapolated(high db/λK values) Approx. 50% of energy dissipation occurs in the impeller region Dissipation rate is ~100x less in the bulk region3impellerV D∼impeller0.25 0.75KP imp1.2 ReNDλ − −∼bulk impellerK K3λ λ∼©2013 -IFP Energies nouvellesDrag Modification correlation Approx. 50% of energy dissipation occurs in the impeller region Dissipation rate is ~100x less in the bulk regionBulk region Impeller regionBubbles of 2 mm of diameter3impellerV D∼impeller0.25 0.75KP imp1.2 ReNDλ − −∼bulk impellerK K3λ λ∼1101001000100002000 4000 6000 8000 10000 12000 14000Impeller Reynolds numberDrag correction factorBrucatoModified BrucatoPinelli1101001000100002000 4000 6000 8000 10000 12000 14000Impeller Reynolds numberDrag correction factorBrucatoModified BrucatoPinelliThe correlations predict quite different correction factors ©2013 -IFP Energies nouvellesDrag Modification Correlation (N = 1600 rpm)No modification PinelliBrucato Modified BrucatoGas vol. fraction1%10%100%<0.1%High speed camera©2013 -IFP Energies nouvelles22Gas phase distribution(Modified Brucato)N = 1000 rpm N = 2000 rpmN = 1600 rpmCFDHigh speed cameraGas vol. fraction1%10%100%<0.1%©2013 -IFP Energies nouvelles23G-L mass transfer coefficientGas Volume Fraction<0.1%1%10%100%Turbulent EnergyDissipation Rate (m 2/s3)10-210010-1101102Danckwerts bubble surface renewal model021.5Specific surface area(symmetric model)Spatial distribution of kLa (s-1)1/4L m0.4cck Dεν  =    b6(1 )adα α= −0.51©2013 -IFP Energies nouvelles24G-L mass transfer coefficient Global G-L mass transfer coefficients fairly well predicted by CFD in the studied range The curves trend is not the same, however Need for considering a bubble size distribution in the flow? Multi-zonal bubble size model Population balance modeling More accurate drag coefficient correction correlations?G-L mass transfer coefficient as a function of the impeller rotational speed00.10.20.30.45000 10000 15000Reimp<kLa> (s-1)ExperimentalCFD Model©2013 -IFP Energies nouvelles25Conclusions A CFD model has been proposed for simulating the flow in a STR for the testing of shaped catalysts Still a work in progress, but the developed CFD model is proving to be a valuable tool for the characterization of STR with stationary catalytic baskets Defining maps of operational regimes for existing devices, reducing experimentation Parametric design tool leading to intensified reactor designs Main difficulties have been due to dealing with phase interaction in turbulent multiphase flows Available correlations for drag correction do not seem universal Extrapolation of the correlations is needed Joint effort has been creating awareness and showing that the present testing reactor configurations and operational conditions may not be suited for measuring the kinetic constants of faster reactions Limited by the mass transfer rate between the phases Not always taken into consideration in laboratory tests©2013 -IFP Energies nouvellesRenewable energies | Eco-friendly production | Innovative transport | Eco-efficient processes | Sustainable resourcesclaudio.fonte@ifpen.frThank you for your attention.Questions? 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CFD for the Study of the Multiphase Flow and Mass Transfer in a Stirred Tank Reactor for the Screening of               Shaped Catalysts

https://hal.archives-ouvertes.fr/hal-02383095/file/Two-PhaseFlowMahoneyRobinson2015.pdf

CFD for the Study of the Multiphase Flow and Mass Transfer in a Stirred Tank Reactor for the Screening of Shaped Catalysts

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