The two phase separation can be divided in:
1 - Gas/liquid separation
2 - Liquid/liquid separation
3 - Gas/solid separation
In all these cases both wire mesh separators and vane pack separators can be used to eliminate liquid droplets, solid particles or separate two liquids. The choice of the separator must be taken considering the working conditions, cross velocity and requested performances.
GAS/LIQUID SEPARATION
Wire mesh pads and vane packs are the mostly used separators to eliminate liquid droplets from a gas flow.
Wire mesh pads: the metallic wire mesh layers form a very dense cellular structure. Crossing through it, the liquid droplets impact on the filaments of the net and are captured. During the process the droplets are reached by other liquid particles and increase their mass until they reach and exceed the point of equilibrium with the force of gravity which, at that point, causes them to fall towards the lower part of the vessel where they will be drained. The aeriform, on the other hand, continues its path purified from the liquid that, without the demister, it would have dragged with it.
Separation of liquid droplets from a gas flow using a wire mesh demister
- Vane packs: these separators are made up of a box containing a variable number of vanes that can be provided with nails or flat. Vanes and nails intercept and separate the liquid droplets carried by the aeriform flow that pass through the pack. Once captured, the drops leach downwards.
Separation of liquid droplets from a gas flow using vane pack separator
- Separation efficiency: wire mesh demisters can separate droplets with diameter approximately around 3 microns, while the vane packs can separate droplets around 10 microns. Referring to a target diameter of the droplets for both devices, the separation efficiency can be very high, even reaching over 99.9% of separated liquid particles.
- Speed: on the other hand, wire mesh demisters usually work with a very low speed while vane packs can reach much higher speed. When the working conditions include a high separation efficiency and high crossing speed, it is possible to mesh a wire mesh pad and a vane separator. In this case the wire mesh pad works as “droplet agglomerator” increasing the droplets diameter at the inlet of the vane pack.
LIQUID/LIQUID SEPARATION
In this case the internals provide the separation of two immiscible liquids. This operation can be performed by two different kinds of internal:
- Wire mesh coalescer: made by wire mesh as the demisters but with different kinds of layer and a higher thickness.
- Plate pack separators: made by parallel plates crossed by the liquid flow.
- Speed and performances: as in the case of gas/liquid separation, considering same working conditions, the wire mesh coalescer needs a crossing speed lower than the plate but, considering the efficiency of separation, higher performances.
ADVANTAGIES: the liquid/liquid separation provides the following advantages:
- reduction of dimensions and costs of vessels
- increase of the purification and quality of products
- reduction of loss of glicol, ammine and other expensive chemical elements
GAS/SOLID SEPARATION
In this case wire mesh demisters are used to eliminate solid particulate from a aeriform flowrate.
Some common applications are:
- desalination plants, where salt is separated from the water vapour flow. The intercepted droplets of salt solidify inside the mesh pad and are separated from the vapour.
- air filtration and purification used in many different industrial and food processes.
- filtration of solid particulate from mechanical processes like, for example, drawing of metallic wire.
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