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