Filter Definition

Candela Rocío Barbisan
Chemical engineer

An equipment filter belonging to the family of pressure vessels, which is made up of two easily identifiable components, from which the Case or enveloping, being the part that gives the structure and that contains the filter unitwho is inside it to remove specific impurities from the fluid that passes through it.

Filtration is one of the oldest methods of separating the components of a mixture, since the first inhabitants of the planet filtered their food and drinks with homemade mesh. For this reason, this method has evolved over the years, incorporating new technologies. It could be said that it is a separation method present in almost all chemical processes.

Each filter is specifically designed for the retention function it is used for. This implies that the designs are varied and very versatile, for example, if you want to retain solid impurities depending on the particle size, the filter unit and its mesh size will be designed. On the other hand, if the filter unit is made to retain mercury in a gas that comes from a reservoir, probably due to the work flow and conditions, its design is very different from the case of water purification.


One of the main characteristics at the time of design is the pressure drop generated on the fluid by the passage through a resistance such as a filter bed, therefore, the maximum load losses estimated by design for the filter are taken into account. design of the pressure profile throughout the entire process line. The pressure drop or DeltaP (in the world of Engineering) is the difference in pressure between the inlet and outlet of the fluid, however, it should be noted that as the filter becomes saturated, that is, it takes up its places. filtration and it becomes clogged, it generates a greater resistance to the passage of the fluid, therefore the discharge loss is greater. For this reason, it is said to be a dynamic pressure differential.

Another fundamental characteristic is that the filter unit must be made of a permeable material, so that the fluid can pass through it without complications and, in turn, retain the desired particles in the empty places. Therefore, when selecting a filter, it is essential to choose the material properly in order to increase its efficiency.

At the time of replacement, it is very difficult to estimate the service life of the filtering element, often speaking of work cycles. However, this characteristic is exclusive to each filter, it will depend on its size, the efficiency of the filtering material, the quality of the feed fluid and the operating flow. The higher the flow rate and the greater the contamination of the inlet fluid, the shorter the useful life of the filter will be. It should be noted that in industrial processes only the filter unit is replaced, while the casing and caps are not, since these components meet rigorous quality and safety standards and are expensive, being designed according to the design standards of Containers subjected to pressure.

When it is desired to incorporate a filter, the efficiency parameter is identified, which shows the relationship between the total number of particles of a certain size that enter the feed stream and the amount that are retained.

Examples in the case of water filters

There are many varieties of filters depending on the service. Next, the classic distinction between water filters will be mentioned.

One of the most common forms is the cartridge-type filter, formed by synthetic fibers that removes suspended particles and also pathogens. These filters have the capacity to retain particles down to the size of a micron (keep in mind that there are water filters with the capacity to retain nanometer-sized particles). These filters are the typical ones placed in homes or plants that work with low flow.

Another type of filter is that of granular media, which can be sand, gravel with quartz, zeolites, among others. In general, sand filters are used for larger flow rates and considerable particle sizes. On the other hand, those of gravel with quartz and those of zeolites are applied to industrial treatments, particularly those of zeolite have achieved a particular boom in the market due to their high efficiency.

Finally, we find disc-type filters where the filter unit is instead of being the typical mesh, it is a superposition of stacked discs and the fluid passes through the center of the annulus formed by the same perforated discs.