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

Multi-phase modelling is required when the liquid-gas interface plays an important role for the scale-up – e.g. for powder dissolution. Some powders tend to form lumps as they get wetted, and the dissolution rate decreases significantly leading to unreasonably long dissolution times. A suitable powder addition strategy is therefore essential. This involves choosing the correct stirring conditions and powder addition location.

Simulation insights and recommendations

Observations of transient effects in animation:

  • Periodic local turbulence zones.
  • Upward pointing axial velocity UZ (red).

Recommended actions:

  • Determine required turbulence levels in the lab.
  • Simulate large scale reactor and set conditions well above determined turbulence.

Instruct process operators:

  • Avoid addition close to the wall: low turbulence levels and axial velocities pointing upwards, can cause powder to stay at the surface (red zones).
  • Add powder within the vortex: high turbulence levels and downward pointing axial velocity, higher dissolution rates and powder transport into bulk.

Simulation metrics

The simulation is performed with OpenFOAM v9:

  • Solver: interFoam
  • Turbulence model: RNGkEpsilon
  • Impeller rotation model: sliding mesh
  • Gas-liquid system: Air-water
  • Mesh size: ~ 1.5Mio

References

  1. Frank Delvigne, Ralf Takors, Rob Mudde, Walter van Gulik and Henk Noorman, TERRA Research Center, Microbial Processes and Interactions (MiPI), University of Liege, Li ege, Belgium. Institute of Biochemical Engineering, University of Stuttgart, Stuttgart, Germany 2017
  2. V. Atiemo-Obeng, S. Kresta, E. Paul. Handbook of Industrial Mixing Science and Practice (Wiley, Hoboken, NJ, 2004)
  3. Li, H.; Li, X.; Zhan, J.; Chen,W.; Zong,W. Study of Turbulent Kinetic Energy and Dissipation Based on Fractal Impeller. Sustainability 2023, 15, 7772.https://doi.org/10.3390/su15107772
  4. Schober, J.J.Fitzpatrick, Journal of Food Engineering, Volume 71, Issue 1, November 2005, Pages 1-8: Effect of vortex formation on powder sinkability for reconstituting milk powders in water to high solids content in a stirred-tank
  5. Thomas Hörmann, Daniele Suzzi, and Johannes G. Khinast, Ind. Eng. Chem. Res. 2011, 50, 21, 12011–12025 Publication Date: September 23, 2011 https://doi.org/10.1021/ie2002523: Mixing and Dissolution Processes of Pharmaceutical Bulk Materials in Stirred Tanks: Experimental and Numerical Investigations