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Flow Phenomena, Heat and Mass Transfer in Microchannel Reactors

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Flow Phenomena, Heat and Mass Transfer in Microchannel Reactors LAPPEENRANTA UNIVERSITY OF TECHNOLOGY Faculty of Technology The Degree Program of Chemical Technology Master’s Thesis Flow phenomena, heat and mass transfer in microchannel reactors Examiners: Professor Ilkka Turunen D.Sc. Jukka Koskinen Supervisors: M.Sc. Isto Eilos M.Sc. Steven Gust D.Sc. Azita Soleymani Lappeenranta 12.09.2007 Warin Ratchananusorn Liesharjunkatu 5 C10 53850 Lappeenranta Finland Tel. +358 50 9365742 Acknowledgement I am exceptionally grateful to Professor Ilkka Turunen for giving me an opportunity to complete this Master’s Thesis with Neste Oil Oyj and for his valuable advice. I would like to thank Jukka Koskinen, Isto Eilos, and Steven Gust for their suggestions during my stay at Neste Oil Oyj. Also, I would like to thank Azita Soleymani who greatly helps me on the simulation work. Without her guidance, I would not have been able to complete my Master’s Thesis. Finally, I would like to thank to my family and all my friends who help me get through two years of study. ABSTRACT Lappeenranta University of Technology Faculty of Technology Author: Warin Ratchananusorn Title: Flow phenomena, heat and mass transfer in microchannel reactors Year: 2007 The studies of flow phenomena, heat and mass transfer in microchannel reactors are beneficial to estimate and evaluate the ability of microchannel reactors to be operated for a given process reaction such as Fischer-Tropsch synthesis. The flow phenomena, for example, the flow regimes and flow patterns in microchannel reactors for both single phase and multiphase flow are affected by the configuration of the flow channel. The reviews of the previous works about the analysis of related parameters that affect the flow phenomena are shown in this report. In order to predict the phenomena of Fischer-Tropsch synthesis in microchannel reactors, the 3-dimensional computational fluid dynamic simulation with commercial software package FLUENT was done to study the flow phenomena and heat transfer for gas phase Fischer-Tropsch products flow in rectangular microchannel with hydraulic diameter 500 µm and length 15 cm. Numerical solution with slip boundary condition was used in the simulation and the flow phenomena and heat transfer were determined. Examiner: Professor Ilkka Turunen D.Sc. Jukka Koskinen Keywords: Rectangular microchannel; Slip flow; Heat transfer coefficient; Fischer-Tropsch synthesis Table of content Nomenclature ...............................................................................................................1 1. Introduction ..........................................................................................................5 1.1 Microchannel reactor......................................................................................5 1.2 Fischer-Tropsch synthesis ..............................................................................6 1.3 Goals...............................................................................................................7 2. Flow phenomena in microchannel reactors..........................................................8 2.1 Single phase flow ...........................................................................................9 2.2 Two-phase flow............................................................................................10 2.2.1 Contacting principles..........................................................................10 2.2.2 Flow regimes ......................................................................................11 2.2.2.1 Stratified flow regime...........................................................11 2.2.2.2 Intermittent flow regime.......................................................12 2.2.2.3 Annular flow regime ............................................................13 2.2.2.4 Dispersed flow regime..........................................................13 2.3 Trickle bed flow ...........................................................................................15 2.3.1 Flow regimes ......................................................................................16 2.3.2 Liquid distribution..............................................................................19 2.4 Slip flow .......................................................................................................19 2.4.1 Knudsen number.................................................................................21 2.4.2 Numerical models for gas phase slip flow .........................................23 2.5 Friction factor and pressure drop..................................................................27 3. Heat transfer in microchannel reactors...............................................................31 3.1 Effects of the geometry of the flow channels...............................................32 3.2 Thermal entrance length...............................................................................35 3.2 Heat transfer coefficient in rectangular microchannels................................36 3.2.1 Effect of the Reynolds number...........................................................38 3.2.2 Heat transfer coefficient in microchannel ..........................................40 3.3 Heat transfer in two-phase flow ...................................................................42 4. Mass transfer in microchannel reactors..............................................................44 4.1 Sherwood correlation ...................................................................................45 4.2 Mass transfer limitation in microchannels ...................................................47 4.3 Mass transfer model for catalyst coated microchannel ................................48 5. Fischer-Tropsch synthesis..................................................................................51 5.1 Influence of process conditions on the selectivity........................................53 5.1.1 Temperature........................................................................................53 5.1.2 Partial pressure of H2 and CO ............................................................54 5.1.3 Space velocity.....................................................................................55 5.1.4 Time on stream...................................................................................55 5.2 Anderson-Schulz-Flory distribution.............................................................56 6. Simulation of the flow in microchannel.............................................................59 6.1 ASPEN PLUS simulation on Fischer-Tropsch synthesis.............................59 6.2 CFD Simulation of Fischer-Tropsch products .............................................60 6.2.1 Domain and grid.................................................................................62 6.2.2 Boundary conditions...........................................................................63 6.2.3 Model consideration...........................................................................64 6.2.4 Results and discussion........................................................................66 6.2.4.1 Flow phenomena in microchannel .......................................66 6.2.4.2 Heat transfer in microchannel ..............................................70 6.3 Conclusion....................................................................................................76 References ..................................................................................................................78 Appendices .................................................................................................................83 1 Nomenclature A convection heat transfer area [m2] 2 AC heat transfer area at control channel [m ] 2 AR heat transfer area at reaction channel [m ] 2 ARC heat transfer area between two flows [m ] a constant value, 0.2332 [-] b constant value, 0.6330 [-] C1 first-order slip coefficient [-] C2 second-order slip coefficient [-] C f friction coefficient [-] -1 -1 cp specific heat of the fluid [J kg K ] K Da Dämkohler number, [-] V Dh hydraulic diameter [m] 2 -1 Dv volumetric diffusivity [m s ] d molecular diameter [m] e roughness parameter [m] v -2 -2 F external body forces [kg m s ] f Darcy friction factor [-] G1 non-dimensional constant [-] G2 non-dimensional constant [-] D Gz Graetz number, RePr h [-] L H height of the channel [m] h convective heat transfer coefficient [W m-2 K-1] -2 -1 hc convective heat transfer coefficient of the controlling fluid [W m K ] -2 -1 J mass flux [kg m s ] v -2 -1 J j diffusion flux of species j [kg m s ] L pipe length [m] 2 K first order chemical reaction rate constant [m s-1] λ Kn Knudsen number, [-] Dh k thermal conductivity of the flow channel wall [W m-1 K-1] 2 -2 -1 kB Boltzmann constant, 1.3806503E-23 [m kg s K ] -1 -1 kc thermal conductivity of coated catalyst layer [W m K ] -1 -1 keff effective conductivity [W m K ] k HC1 constant value, 1.22E-05 [-] kHC5 constant value, 1.05E-06 [-] kHC6 constant value, 2.36E-06 [-] -1 km mass transfer coefficient [m s ] -1 kp propagation rate [m s ] -1 kt termination rate [m s ] -1 -1 kw thermal conductivity of the wall [W m K ] hD Nu Nusselt number, h [-] k NuG Nusselt number for gas flow [-] NuL Nusselt number for liquid flow [-] n number of carbon atom [-] PCO partial pressure of carbon monoxide [Pa] P partial pressure of hydrogen [Pa] H 2 Pe Peclet number, RePr [-] V Pem mass Peclet number, [-] kc c μ Pr Prandt number, p [-] k p Pressure [Pa] p0 Pressure
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