How does it work?
Depth filters are designed to retain particles throughout the entire media, not only on the surface. They therefore capture contaminants across the full cross-section of the filter. Larger particles are retained near the surface, while finer particles progressively penetrate the media and are gradually captured as their size decreases, thanks to the graded density of the filter.
What are the advantages?
The main advantage of depth filters is their high filtration capacity and their good resistance to clogging, as opposed to filters that operate only on the surface. They are also very useful when the particles to be removed vary greatly in size.
They also have a good capacity to absorb gelatinous particles and generally offer a longer service life than surface filters, thanks to their three-dimensional structure.
Among their potential drawbacks are the possible migration of media particles into the fluid and the release of retained particles.
FOR WHICH INDUSTRIAL SECTORS?
Industries using depth filtration are numerous: food & beverage, APIs, pigments, petrochemicals, automotive industry, etc.
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Which media should be used?
To perform depth filtration, porous filter media with variable porosity are generally used. As the fluid to be treated enters the filter, the largest particles are trapped and cannot pass through. As the fluid progresses through the media, increasingly smaller pores gradually prevent the passage of all particles, except those whose diameter remains smaller than the pore size. Depth filtration is not achieved solely by mechanical separation of particles at the surface, but through a combination of mechanical filtration and adsorption within the media.
Filter media made from natural or synthetic fibers can be used: cellulosic filters, melt-blown polypropylene media, polyester media, or metal filters. Some depth filters also contain activated carbon, used to decolorize or deodorize the fluid to be treated.
In certain cases (such as filter plates, for example), the media also contains natural diatomaceous earth and perlite, used as filter aids, or moisture-resistance agents, such as polyamidoamine.
Which geometries?
Depending on requirements and industrial applications, filter cartridges, bag filters, lenticular module filters, as well as candles or filter plates can be used to perform depth filtration. The geometry of the filtration devices to be implemented depends on the pressure conditions within your production line and on the configuration of your installation.
In addition to filter geometry, it is also necessary to specify in your specifications the required filtration ratings, based on the impurities to be removed and your final product requirements.
Focus on filter plates
Unlike membranes, filter plates provide filtration throughout the entire depth of the media, ensuring a high impurity retention capacity. With a thickness generally ranging from 2.5 to 4.5 mm, they are available in various dimensions and grades suitable for microbial reduction and for applications requiring fine filtration, clarifying filtration, or coarser filtration. Filter plates are used in the food & beverage sector, the chemical and pharmaceutical industries, and in cosmetics and perfumery.
Their ability to retain contaminating agents is particularly high, as they combine surface filtration, depth filtration, and adsorption. During the filtration process, the liquid to be purified flows, under the effect of a differential pressure, through the fibers of the plate. The largest particles to be removed are stopped at the inlet surface by a sieving effect. Intermediate-sized particles are mechanically retained within increasingly smaller pores. The finest particles, whose size is smaller than that of the smallest pores, are retained by adsorption on the outlet face of the plate.
Discover examples of depth filter implementations:
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