Bubble column reactors multiphase flow

Bertola F, Grundseth J, Hagesaether L, Dorao C, Luo H, Hjarbo KW, Svend-sen HF, Vanni M, Baldi G, Jakobsen HA (2005) Numerical Analysis and Experimental Validation of Bubble Size Distribution in Two-Phase Bubble Column Reactors. Multiphase Science Technology 17(1-2) 123-145 Breim G, Braeske H, Durst F (2002) Investigation of the unsteady two-phase flow with small bubbles in a model bubble column using phase-Doppler anemometry. Chem Eng Sci 57(24) 5143-5159... 

Slurry Bubble Column Reactors As in the case of gas-liquid slurry agitated reactors, bubble column reactors may also be used when solids are present. Most issues associated with multiphase bubble columns are analogous to the gas-liquid bubble columns. In addition, the gas flow and/or the liquid flow have to be sufficient to maintain the solid phase suspended. In the case of a bubble column fermenter, the sparged oxygen is partly used to grow biomass that serves as the catalyst in the system. Many bubble columns operate in semibatch mode with gas sparged continuously and liquid and catalyst in batch mode. 

For multiphase flows, it is possible to encounter a boundary of the solution domain through which one of the phases exits the domain but not the other (for example, the top surface of the bubble column reactor). Special boundary conditions need to be developed to represent such cases. These are discussed in Chapter 5. 

The other situation which may require special treatment is a boundary of multiphase dispersion through which dispersed phase particles are allowed to escape, but not the continuous phase (for example, the top surface of gas-liquid dispersion in a bubble column reactor). The standard outlet boundary conditions need to be suitably modified to represent the observed flow processes. It is possible to simulate the actual behavior by specifying appropriate sink near the top surface (see Ranade, 1998 and Chapter 11). 

The recent progress in experimental techniques and applications of DNS and LES for turbulent multiphase flows may lead to new insights necessary to develop better computational models to simulate dispersed multiphase flows with wide particle size distribution in turbulent regimes. Until then, the simulations of such complex turbulent multiphase flow processes have to be accompanied by careful validation (to assess errors due to modeling) and error estimation (due to numerical issues) exercise. Applications of these models to simulate multiphase stirred reactors, bubble column reactors and fluidized bed reactors, are discussed in Part IV of this book. 

The fluid dynamics of bubble column reactors is very complex and several different CFD models may have to be used to address critical reactor engineering issues. The application of various approaches to modeling dispersed multiphase flows, namely, Eulerian-Eulerian, Eulerian-Lagrangian and VOF approaches to simulate flow in a loop reactor, is discussed in Chapter 9 (Section 9.4). In this chapter, some examples of the application of these three approaches to simulating gas-liquid flow bubble columns are discussed. Before that, basic equations and boundary conditions used to simulate flow in bubble columns are briefly discussed. 

The list is merely suggestive. Complexity of reactive flows may greatly expand the list of issues on which further research is required. Another area which deserves mention here is modeling of inherently unsteady flows. Most flows in engineering equipment are unsteady (gas-liquid flow in a bubble column reactor, gas-solid flow in a riser reactor and so on). However, for most engineering purposes, all the details of these unsteady flows are not required to be known. Further work is necessary to evolve adequate representation of such flows within the CFD framework without resorting to full, unsteady simulations. This development is especially necessary to simulate inherently unsteady flows in large industrial reactors where full, unsteady simulations may require unaffordable resources (and therefore, may not be cost effective). Different reactor types and different classes of multiphase flows will have different research requirements based on current and future applications under consideration. 

Olmos E, Centric C, Vial C, Wild G, Midoux N (2001) Numerical simulation of multiphase flow in bubble column reactors. Influence of bubble coalescence and breakup. Chem Eng Sci 56(21-22) 6359-6365. 

Shah YT, Kelkar BG, Godbole SP, Deckwer W-D (1982) Design parameter estimations for bubble column reactors. AlChE J 28(3) 353-379 Shi J, Zwart P, Frank T, Rohde U, Prasser H (2004). Development of a multiple velocity multiple size group model for poly-dispersed multiphase flows. Aimual Report 2004. Institute of Safety Research, Forschungszentrum Rossendorf, Germany... 

Guillen DP, Grimmett T, Gandrik AM, Antal SP. Development of a computational multiphase flow model for Fischer Tropsch synthesis in a slurry bubble column reactor. Chem. Eng. J. 2011 176-177 83-94. 

Shnip AI, Kolhatkar RV, Swamy D, Joshi JB. Criteria for the transition from the homogeneous to the heterogeneous regime in two-dimensional bubble column reactors. Int J Multiphase Flow 18 705-726, 1992. 

In this chapter, we focus on our efforts to model dispersed multiphase flows in which a discrete phase (consisting of solid particles, gas bubbles, or liquid droplets) is moving through, or is moved by, a continuous Newtonian fluid phase. Such flows appear frequendy in process equipment in the chemical, metallurgical, pharmaceutical, and food industries. Examples include fluidized bed reactors, spouted bed reactors, pneumatic conveyors, bubble column reactors, slurry reactors, and spray driers. Figure 1 shows a schematic overview of typical dispersed multiphase systems. 

Pareek, V., M.P. Brungs, and A.A. Adesina, Photocausticization of Spent Bayer liquor A Pilot-Scale Study. Advances in Environmental Research, 2003. 7(2) p. 411-420. Bertola, F., M. Vanni, and G. Baldi, Application of Computational Fluid Dynamics to Multiphase Flow in Bubble Columns. International journal of Chemical Reactor Engineering, 2003. 1 p. A3. 

Computational fluid dynamics (CFD) is rapidly becoming a standard tool for the analysis of chemically reacting flows. For single-phase reactors, such as stirred tanks and empty tubes, it is already well-established. For multiphase reactors such as fixed beds, bubble columns, trickle beds and fluidized beds, its use is relatively new, and methods are still under development. The aim of this chapter is to present the application of CFD to the simulation of three-dimensional interstitial flow in packed tubes, with and without catalytic reaction. Although the use of... 

This situation describes an emulsion reactor in which reacting drops (such as oil drops in water or water drops in oil) flow through the CSTR with stirring to make the residence time of each drop obey the CSTR equation. A spray tower (liquid drops in vapor) or bubble column or sparger (vapor bubbles in a continuous liquid phase) are also segregated-flow situations, but these are not always mixed. We wiU consider these and other multiphase reactors in Chapter 12. 

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