Application of Computational Fluid Dynamics in the development and optimization of stock preparation equipment, 2011 PaperCon Conference

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Computational fluid dynamics (CFD) simulation has become a more powerful tool in the development of pulp and paper equipment and processes. But simulating pulp flow is still very challenging as it is multiphase (water, fibers, ash, air, etc), the shape factor of the fibers is large, and often there is high and non-isotropic turbulence in certain areas of the equipment, making the modeling effort very complex and difficult, sometimes to the point of even putting the validity of the results in question. For example, in a single piece of equipment, the vessel might be quite large but the actual process area of interest could be very small (e.g., refining gap vs. total refiner). In such cases, a complete and overarching simulation is not reasonable and not a good industrial application of CFD technology.

But by carefully selecting the area of interest, selecting the right simulation models and making further simplifications and approximations, the calculations can give insights into the flow and function of certain equipment that cannot (at a reasonable cost) be gained by physical experiment. To find the right balance between needed simplification and over-simplification (which would provide meaningless calculation results) a constant exchange of information between the simulation and the real world is vital. The application of this approach on selected equipment in the stock preparation area results in general guidelines that help to speed up development at minimal comparative costs.

Finally, and most importantly, equipment designed using CFD achieves a higher efficiency when finally installed and operating, thus validating the cost and effectiveness of the modeling tool.