Filtration

filter candlesFor over 45 years, Bekaert has developed and expanded its knowledge and experience of metal fiber filtration media and their applications. We are the world’s leading supplier of sintered metal fiber media. The filtration R&D team is supported by three global R&D competence centers, one of which focuses on metal fiber filtration media.

Metal fibers provide a solution for numerous filtration applications – including nano filtration – that other materials can’t match. They provide high temperature and corrosion resistance, a high mechanical strength, and high porosity for low pressure drops. Pleatable and flexible, they allow for small designs that can be easily customized for a small product footprint. Moreover, metal fiber filters are recyclable with no degradation in performance. This reusability enables metal fibers to support the circular economy.

 

Advantages of metal fibers for filtration:

High permeability

The combination of high porosity and thin filter layers at high mechanical strength provides unique permeability characteristics at levels unmatched by any other filter medium.

High porosity

Metal fibers produce media with a high fraction of void space and up to 90% porosity, resulting in low pressure drops, high flow rates and high permeability.

Mechanical strength

Metal fibers enable a mechanically strong 3D network of metal-to-metal connections. The media maintains its integrity under high vibration and pressure.

Thermal & corrosion resistance

Metal fibers in alloys 304, 316L, Fecralloy®, Inconel® 601 and Hastelloy® display high-temperature corrosion resistance at both the surface and the underlying steel.

A closer look at the two types of filtration

Bekaert’s metal fiber filtration media are suitable for both in-depth filtration and surface filtration. Here’s a short explanation of the main differences between these two types of filtration.

In-depth filtration

This is when the contaminants or particles that have to be removed from the fluid are captured within the structure of the filter medium. In other words, the particles penetrate the medium.

An in-depth filter has a 3D-structure and mostly consists of multiple layers. For the multiple layer media, the coarser fiber layers are placed at the flow-in side. Coarser particles are stopped by the coarser layer. Only small particles are held in the fine layer. This prevents premature blocking of the medium and increases the dirt holding capacity and on-stream lifetime.

In depth-filtration

In-depth filtration is mainly used for the filtration of liquids. A typical example is the filtration of polymers. 

Since the contaminants penetrate the filter medium, off-line cleaning will be required in order to clean the filter.

Surface filtration

As its name suggests, with surface filtration the particles are stopped at the surface layer of the filter medium. The pore size will determine the size of particles that are stopped.

In many cases, the filter medium will have a multi-layer structure, with the finer fiber layers at the upstream side of the flow. The particles will form a dense cake layer at the surface of the filter. This cake formation can increase the filtration efficiency, as finer particles are retained in the dense cake.

In surface filtration, the cake formation will cause an increasing pressure drop across the filter. In the case of liquids, when the pressure drop becomes too high, a reverse filtrate flow can be initiated to remove the cake. This is called backwashing or back-flushing. In the case of gases, the cake is blown off the candle with a short blow of gas against the hot gas flow. This is called back-pulsing. 

Surface filtration can be applied in both liquid and gas filtration, especially for fine filtration. Since the contaminants do not penetrate the filter medium, on-line cleaning (cleaning-in-place) of the filter is possible. This can be accomplished by initiating a reverse flow of the filtrate.

Surface filtration - cake formation

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