Abstract
Coalescence filtration is a mechanical filtration process, which is used for the removal of liquid droplets from a gas stream. A numerical model is proposed using an Euler-Euler multi-phase formulation to model the macro-scale filtration process. The model is implemented for a 2D case using the commercial CFD software ANSYS© CFX. The capture of the dispersed phase is modelled using the penetration approach for single fiber capture efficiency which is extrapolated to multiple fibers, resulting in an exponentially-decaying interpolation scheme. To model the flow of gas through the dry filter, an empirical pressure-drop correlation is developed based on fiber-scale flow simulations for varied flow parameters. For the fiber-scale simulations, three-dimensional fibers are generated with random position, thickness and orientation using algorithms developed in house, ensuring that all fibers remain in the filter bed and that the fibers do not intersect. The correlation is extended to a wet filter by adapting the correlation parameters, with the assumption that the oil completely wets the fibers and results in a homogeneous increase in net packing density. The local velocity of the fiber-wetting oil is estimated analytically using the local oil saturation and gas velocity using a thin-film approach, taking into account the effect of the mean fiber orientation (determined using three-dimensional micro-CT scans) on the absorbed oil residence time in the filter bed. An analytical model is used to approximate the thickness of the oil film formed at the back of the filter surface and the pressure drop caused by the gas flow through it.Both steady-state and transient simulations are run and validated against measurement data provided by the Institute for Energy and Environmental Technology (IUTA), Germany. The steady-state pressure drop and oil-saturation predictions from the simulations follow the same trend as the experimental data albeit showing a stronger influence on air flow velocity. The transient simulations show the expected three-stage process with an initial gradual increase of the pressure drop, followed by a drastic increase, and finally, an approach to an equilibrium state.
Published Version
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