Euler-Euler based simulations on multiphase flows in porous media

Chemical industries are always in search of new catalyst supports to improve the energy efficiency of the chemical process. Metallic and ceramic foam packing, due to their high porosity, high specific surface area and low pressure drop are promising alternatives for packing internals used in chemical engineering processes. They can serve as new support for catalyst deposition. The long term goal of this work is to perform three-dimensional Computational Fluid Dynamics (3D CFD) simulations of the evolving gas-liquid flow patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies. MRI Image of ceramic foam is shown in Figure 1.

Figure 1 REM image of 10 ppi foam

The problem is approached as explained in Figure 2. There are not many work performed with ceramic foams as reactor internal using CFD. On the other hand, there are many closures available for trickle bed reactor studies where spherical particles are considered as reactor internals. So, the closures available in trickle bed reactor will be extended for ceramic foams studies. It is also very tedious to characterize the structural parameters of ceramic foams. Ceramic foams with different pore density are analyzed using MRI technique and characterized for different geometrical parameters. There are few works available in the literature with ceramic foams as reactor internals using experimental technique. Few empirical equations have been proposed for the same. These empirical equations will be studied in detail and validated with in house experiments performed using X-ray tomographic studies.

Figure 2 Methodology for the problem

A two-phase Eulerian model is used considering the flow domain as porous. The influence of the liquid and gas drag is added as external source terms to liquid and gas momentum equations separately. The drag forces between the phases have been taken into account using the relative permeability approach, which was developed by Saez and Carbonell (1985) and Fluid-Fluid model developed by Attou and Forschneider (1999). The advantage and disadvantage of both the closures will be studied in detail. The major hydrodynamic parameters such as dynamic liquid holdup, liquid distribution in different heights of the column, pressure drop will be studied and validated with experimental studies. The liquid is fed through single orifice at the top and gas through 4 orifices around as shown in Figure 3.

Figure 3 Geometry used in the simulation

The liquid distribution at the different heights can be seen in Figure 4. The comparison between experiment and two different closures from simulation in terms of percentage of liquid distribution at the outlet is shown in Figure 5. The flow behavior is in good agreement between experiments and simulations. There is a possibility to improve the radial distribution of the liquid flow. The closures for the dispersion forces will be further included in order to improve the agreement and accuracy of the simulation. These closures will be further modified to study the liquid flow behavior in the reactor with solid ceramic foams as internals.

Figure 4 Liquid Distribution at different heights. ul = 0.006 m/s, ug = 0.051 m/s

Figure 5 Comparison of percentage of liquid distribution at the outlet (a) Experiment - Marcandelli et. al. (2000) ; (b) Relative Permeability model ; (c) Fluid-Fluid model

Acknowledgement

This work was funded by the Helmholtz Association within the frame of the Helmholtz Energy Alliance "Energy Efficient Chemical Multiphase Processes".

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References

• K. Subramanian, M. Schubert, E.Krepper, D.Lucas, U. Hampel (2013), Three-dimensional simulation of multiphase flows in porous solid foam structures, Poster, International conference on Porous media (Interpore), Prague, 21. - 24.May 2013

• K. Subramanian, M. Schubert, D.Lucas, U. Hampel (2014), Closures for simulation of Gas-Liquid flows in Solid foam structures, Oral Talk, International Symposium on Chemical Reaction Engineering (ISCRE 23) , Bangkok, Thailand, 07 – 10th September 2014