Deeper process understanding and large cost savings through CFD

In 2017 Delvigne et al. [1] reported in their paper that the use of computational fluid dynamics (CFD) can reduce the number of scale-up trials by 80% with cost savings per trial from $40k to $80k. V. Atiemo-Obeng and S. Kresta, E. Paul reported in their Book “Handbook of Industrial Mixing: Science and Practice” [2], that “for each individual process test, the cost savings from using CFD were estimated to be between $500k –$1 million.”

These are only two examples that report the benefit of using CFD for scale-up and tech transfer in stirred reactors. The present use case shows one specific application of CFD and how it can help gaining deeper insights of the process and deriving conclusions for an informed decision making in the context of scale-up and tech transfer.

Problem statement

In many cases, steady-state, single-phase CFD modelling and scale-up is sufficient.

However, single-phase simulations are not sufficient when spatial and temporal information about particles in the reactor are needed. This is the case for sedimentation and homogeneity considerations.

The “brute force” approach is setting the impeller speed at the machine or process maximum. However, this can lead to particle attrition, aeration, and other adverse effects.

Also, the power consumption scales approx. to the power of 3 with respect to the impeller speed. For large reactors running almost 24/7, setting a CFD-optimized impeller speed can lead to significant power savings.

To obtain an optimized impeller speed for particle laden reactors with volumetric solids fractions of up to 15%, a solid-liquid, 2-way-coupled Lagrange approach can be used.

Simulation metrics

The simulation is performed with OpenFOAM v9:

  • Solver: denseParticleFoam
  • Dispersion Model: stochasticDispersionRAS
  • Turbulence model: kEpsilon
  • Impeller rotation model: sliding mesh
  • Two-phase system: water-solids
  • Mesh size: ~ 1 Mio

References

  1. Christian Weiland, Eike Steuwe, Jürgen Fitschen, Marko Hoffmann, Michael Schlüter, Kathrin Padberg-Gehle, Alexandra von Kameke, Chemical Engineering Journal Advances Volume 14, 15 May 2023, 100448: Computational study of three-dimensional Lagrangian transport and mixing in a stirred tank reactor.
  2. Ananda J. Jadhav, Mostafa Barigou, International Journal of Multiphase Flow, Volume 155, October 2022, 104191: Eulerian-Lagrangian Modelling of Turbulent Two-Phase Particle-Liquid
    Flow in a Stirred Vessel: CFD and Experiments Compared.
  3. V. Atiemo-Obeng, S. Kresta, E. Paul. Handbook of Industrial Mixing Science and Practice (Wiley, Hoboken, NJ, 2004)