Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1997-02-19
1999-02-23
Reifsnyder, David A.
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
210505, 2105101, B01D 2400, B01D 3902
Patent
active
058740007
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a filter element having an inherently stable, porous supporting body and, on its afflux surface for fluid to be filtered, a fibrous coating of the supporting body which is finer-pored than the supporting body, the fibrous coating being bound to the supporting body in part by a fiber/fiber bond and in part by a fiber/supporting body bond.
In a known filter element of this type (WO 87/01610) the fibrous coating consists of fibers which are considerably longer than the average pore size of the supporting body, and fine-grain particles distributed in the fibrous coating and bound to the fibers. During the work in connection with this invention, however, it was found that such a filter element with high fine filtering ability can be created only if the fibrous coating is rather thick; this increases the pressure loss which the medium to be filtered suffers when flowing through the filter element.
The invention is based on the problem of providing a filter element of the abovementioned type which is characterized by a good compromise between the particular degree of fine filtering ability desired and a low pressure loss for the medium to be filtered flowing through the filter element. Methods are furthermore to be provided for producing such filter elements.
Several solutions to this problem are described in the following.
According to a first aspect of the invention the filter element is characterized in that the fibrous coating has first fibers whose length is greater than the average pore size of the supporting body, and second fibers whose length is clearly smaller than the length of the first fibers to create the fine porosity of the fibrous coating.
This realizes the principle of filling or covering the spaces between the first fibers with the shorter second fibers.
The first fibers generally have a length which is clearly greater than the average pore size of the supporting body, in particular more than twice as great as the average pore size of the supporting body. The second fibers generally have a length smaller than the average pore size of the supporting body, in particular less than half the average pore size of the supporting body. The fibrous coating preferably contains more second fibers than first fibers (measured as part by weight), the weight ratio of second fibers to first fibers especially preferably being greater than 2:1. The first fibers and second fibers are preferably fibers made of the same material and/or fibers of approximately the same diameter class. It is frequently sufficient if less than 10% by weight of the fibrous coating is first fibers.
According to a second aspect of the invention the filter element is characterized in that any fine-grained particles distributed in the fibrous coating are contained with under 30% by weight, preferably under 20% by weight, more preferably under 10% by weight, most preferably 0 to 3% by weight, based on the total weight of fibers and fine-grained particles.
This goes in a direction contrary to the relevant prior art (WO 87/01610) in that one very considerably reduces the proportion of fine-grained particles distributed in the fibrous coating, in extreme cases even to zero or near zero. The desired degree of fine filtering ability is thus provided essentially by the fibers and not by fine-grained particles distributed in the fibrous coating. In the second aspect of the invention the described first fibers and the described second fibers need not be present, but they can be.
The invention can be realized with filter elements made of a multitude of materials. As far the supporting body is concerned, plastic or synthetic resin materials, ceramic materials and metallic materials are especially pointed out. To produce the porous supporting body efficiently one can sinter particles of the stated materials together or inter-connect them by other bonding mechanisms, e.g. using a binder. As far the material of the fibers is concerned, ceramic fibers are preferred, in particular from aluminum silicate. However one can also use
REFERENCES:
patent: 5290449 (1994-03-01), Haegle et al.
patent: 5552049 (1996-09-01), Gray
patent: 5591335 (1997-01-01), Barboza et al.
patent: 5681469 (1997-10-01), Barboza et al.
Herding GmbH Filtertechnik
Reifsnyder David A.
Spencer George H.
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