DE2537104A1 - LONG TERM FILTER MEDIUM - Google Patents

Description

Patent attorney

Dipl-Ing. Gerhard Schwan

aooo M «as,«. «». sä ^

FDN-754

GAF Corporation 140 West 51st Street, New York, N.Y. 1OO2O, V.St.A.

Long-term filter medium

It is known to use non-woven felts for filtering purposes. Filters made from such materials can generally be divided into two main groups. With one it is are surface filters on which a cake of dirt particles is placed is being built. The second main group are the depth filters, which collect dirt particles over their full thickness and hold on. Both types of filters are designed for special filtration systems widely used.

In the case of surface filters, the pore size can usually be determined master quite precisely. As a result, such filters are often used in fluid systems in which dirt particles predetermined size and distribution occur. In such cases, filters with desired pore sizes can be selected to remove all or a predetermined portion of the dirt particles. If there is a filter cake on a surface filter As is well known, the cake itself reduces the effective pore size of the filter. This increases the pressure difference, the fluid that passes through the filter

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electricity is due; ultimately, this limits the flow capacity of the entire system. The service life or dirt holding capacity of a surface filter is normally calculated by determining the amount of filtrate that can flow through a predetermined area of the filter in question at a predetermined flow rate until a predetermined maximum differential pressure is reached at the filter. After exceeding this point, the flow in the system can be hindered; the filter must either be cleaned or replaced. As a result, there has long been a need for a surface filter with increased pollutant capacity in order to keep the shutdown time of such filtration systems as short as possible. In an effort to find improvements in this direction, an increase in the surface area of the filter has often been made without, however, extending its service life per unit area. However, the size of the filter area that can be used in a given system is limited by the physical properties of the system. As a result, an increase in the filter surface does not always lead to the desired service life.

Other attempts to extend filter life include the roughening or pimpling of the surface of the filter medium and the use of a layer of a coarser surface filter medium on the upstream side of a finer filter. It was assumed that in this way larger pollutants

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particles on the roughened surface of the filter medium or accumulated on the coarser upstream filter media, while the finer particles are passed through and captured by the finer filter media. In some special use cases This procedure proved to be useful; there were some advantages over a conventional surface filter achieved. In most cases, however, these attempted solutions were inadequate and often even with marked disadvantages tied together. For example, dimpled or roughened filter media can increase the life expectancy of the filter in practice when used in conjunction with a fluid that has a viscosity greater than 400 cps. This is upon it attributed to the fact that the nub has no firm cohesion and tends to become matted and the surface to which it is applied is to clog. If roughened or knobbed media are used to filter gels or tapioca-like particles, such particles also tend to clog the surface. In the case of multi-layer filters with coarser upstream ones Filter media it was found that when filtering out spherical particles from liquids, the service life of the multilayer Filter is no larger than that of the finer filter medium alone. This is due to the fact that the in The larger particles retained by the coarser layer tend to block the flow to the finer filter.

Depth filters often have a longer service life than surface filters, however, have the disadvantage that the

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Pore size cannot be effectively controlled and, as a result, fine dirt particles often pass through in full get through the filter.

The present invention provides an improved multilayer, nonwoven filter media which, by comparison has a significantly increased dirt absorption capacity compared to the known filters discussed above, while the pore size can be controlled well and the surface of the filter does not need to be increased. At the filter medium after of the invention are the most favorable properties of a surface filter and a depth filter combined. In particular, it is on the upstream side of a conventional one Surface filter a loose fiber mat lower Density provided. It has been found that the filter medium according to the invention in many cases leads to an increase in contaminants on absorption capacity by a factor of 4 compared to the same conventional surface filter medium, if this one without the upstream fiber mat is used.

The long term filter medium according to the invention generally comprises a Support with a large number of fibers with a predetermined titer and / or diameter, which has a surface main filter Form a given pore size, thickness and density. On the upstream side of the pad and in contact with it also arranged a loose, non-woven fiber mat, which consists of a plurality of fibers that are within a tolerance

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range of approximately - 40 % have a titer and / or diameter that corresponds to the titer and / or diameter of the fibers of the main filter and form a depth prefilter whose thickness is at least ten times greater and whose density is at least ten times smaller than the thickness or density of the base are

The fibers forming the main filter pad are preferred so intertwined that a non-woven felt-like product is created. The fibers are wrapped in a textile card Processed into a pile and aligned in both the machine and cross directions for uniformity To ensure strength. In addition, some of the fibers are left run in the direction of the depth of the pile to increase the abrasion resistance to increase the felt. This is controlled by an accordingly mechanical engulfing achieved. A woven lattice-shaped insert is preferably inside the batt as Support structure is provided to support the individual fibers and to give the filter material increased strength. the Openings between the threads forming the mesh are generally large enough to allow for the filtering properties of the fabric to have no adverse influence. The known manufacturing processes used to make such felt filter media allow effective control of the pore size, so that media with a range of target pollutant removal values be available. As a result, surface filter media used as a base can be selected in the present case, the nominal elimination values in the range of about 5 yum or less

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ger have to about 2OO μ m or more. The term “nominal separation value” is to be understood in the present case as the mean smallest particle size that is retained by the filter medium in question. The filtration properties of felts are such that the nominal separation value is considerably smaller than the absolute separation value, which represents the size of the largest pore that extends completely through the filter. This is due to the forces of attraction between the dirt particles and the fibers making up the filter, as well as the curved paths formed by the intertwined fibers. These attractive forces, combined with the curved paths, prevent the passage of small particles through the filter, although these particles can be smaller than the maximum pore size.

It is also known that the pore size of a particular felt filter media is in direct relation to the fiber denier and the fiber diameter and that the fiber diameter inversely proportional for a given titer or degree of fineness to the specific gravity of the fiber changes. Consequently The selection of fibers with a certain diameter and titer for the construction of a filter medium with the desired pore size and with the desired separation value is very important. Generally are fibers with a denier in the range from about 1.5 to about 22.00 and corresponding diameters in the range from about 11 to 45 / Jm suitable to cover a wide range To achieve elimination values. The fiber volume of the filter

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mediums is critical in controlling pore size. That Fiber volume depends on the density, the relative density or the Unit weight of the filter medium. Usually one of these latter parameters is used when developing a particular Filter medium used because the pore size is inversely proportional to this parameter. In this regard, filter media with nominal rejection values in the range of about 5 to 200 / µm, relative densities in the range of about O.O50 to about Have O, 5O.

The thickness of the main filter is also an important parameter, as it is directly related to the flow capacity or the permeability of the material. It was found, that main filter materials with a thickness in the range of about 1.3 mm to about 25.4 mm for the one discussed herein Long-term filter media are suitable. Preferably with Thicknesses in the range of about 1.6 mm to about 6.4 mm worked.

If a main filter medium of the type described above is used in the to filtering current is applied, a filter cake forms on its surface, which only minimally penetrates the surface. It was therefore found that using the above-described conventional filter media that of a given filter flow rate Differential pressure caused by the filter medium increases almost instantly when the filter cake is on the Surface builds up. This is due to the fact that the

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cake clogs certain parts of the filter medium. With the The build-up of the filter cake on the surface of the filter medium also reduces the final separation value of the filter medium almost immediately, so that smaller particles that would normally pass through the filter medium without clogging it from the Filter cake are collected to further build up the filter cake contribute and thus worsen the flow properties of the filter and shorten its service life.

By using the fiber mat on the upstream On the side of the conventional main filter medium, dirt particles become accumulated and retained over the full thickness of the fiber mat. When a filter cake tries to form on the main filter medium, the fiber mat mixes with the cake, whereby a mirror image of the original filter medium begins to form and continues to develop. It is believed that this The phenomenon is due to the fact that the low-density fiber mat has substantially the same fiber structure like the main filter medium, while its density is essential is lower. As a result, the particles penetrate through the fiber mat and form the fiber mat inside comprehensive depth filter, the filter properties of the main filter medium the end. It was found that the differential pressure across the long-term filter medium does not increase significantly as long as particles are present be retained across the depth of the fiber mat, and that the fiber mat, like the main filter, essentially retains the original porosity of the main filter medium,

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while the cake continues to build. It was also shown
that the maximum service life is achieved when the fiber mat
consists of fibers whose titer and / or diameter with the
Titer and / or diameter of the main filter medium largely
to match. The best results have been achieved when the titer and diameter of the fibers of the mat and the main filter medium are not more than -40% apart. For the fiber mat there are fibers with a titer in the range of approximately
1 to about 30 and diameters in the range of about 6.6 µm to about 60 µm are suitable, provided they correspond to the denier and diameter of the fibers of the backing with the above tolerance. Further, the density or specific gravity of the mat should be at least smaller by a factor of 1O than that
Be the density or relative density of the main filter medium in order to ensure the lowest possible flow resistance. the
Thickness of the mat should be at least ten times greater than the thickness
of the main filter media to provide sufficient filter depth within which the particles can be retained. For example, fiber mats with a specific gravity in the range from about 0.05 to about 0.05 and a thickness in the range from about 13 mm to about 250 mm can be used. It is preferable to work with a relative density of the fiber mat of approximately 0.010 to approximately 0.03 and a mat thickness of approximately 25 mm to approximately 80 mm
to simplify handling and processing into suitable filter bodies. It has been found that multilayer filters constructed within the above parameters compared to

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conventional filter media for a significantly longer service life result in all types of filtrates containing various types of dirt particles.

It is of particular importance that the original porosity of the main filter medium is maintained until the loose Fiber mat is almost completely loaded with dirt particles. In other words, the normal filter properties, namely decreased Porosity and increased differential pressure, which occur almost immediately, if a conventional filter enters the fiI stream go I <. "\) f. will remain with the long-term filter medium described here until the fiber mat is almost completely loaded. University predetermined flow rate and predetermined differential pressure is hence the service life of the filter medium explained here until a given differential pressure is reached by the factor 4 longer than the service life of a conventional surface filter material, this with the same flow and pollutant conditions is used.

Any fibers can be used to form both the main filter medium and the fiber mat, from which a felt-like one can be used Material can be made. These fibers include natural fibers such as wool, cotton, silk and the like, synthetic fibers such as acetate silk, viscous silk, nylon, polypropylene, polyethylene, polyester fibers, polytetrafluoride, Acrylic fibers, glass fibers and the like, and stainless steel metal fibers and the like. It doesn't come

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on that the fiber material of the backing is the same as is the fiber material of the mat. However, since the relative densities of the available fibers differ from each other, it is it is generally expedient to choose fibers which have relatively little different specific gravity. This is important, because, as discussed above, fiber diameter is a function of denier and specific gravity. As the present explained Long-term filter media largely depends on the ability to the titer and / or the diameter of the fibers of the substrate and Matching the mat makes it easier to select Fibers with largely the same relative density this adaptation.

That it depends, for a mutual adjustment of the titre and / or the diameter of the fibers that form the fiber mat or the backing has been determined experimentally. The degree of fineness of the fiber mat was 40% above that of the degree of fineness of the fibers of the main filter medium a 15 to 40% increase in lifespan over one conventional filter medium when using a particulate Pollutant, such as A C road dust, in the form of a aqueous sludge was present. However, the same fiber mat with a coarser degree of fineness and a standard main filter were used used to filter gels and tapioca-like particles, the life expectancy was increased by a factor of more than 4 compared to the standard filter medium. This is due to, that the gel and tapioca-like particles are successfully removed by means of the low density fiber mat

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- 12 were kept away from the surface of the main filter medium.

When using a main filter medium of the same type in conjunction with a fiber mat whose titer was 40 % below the titer of the basic filter medium, a 30 to 60% increase in service life compared to conventional filter media was determined for a filter that was also made from a sludge from A. C-road dust in water. The same increase in service life by a factor of 4 was obtained when this filter was used in conjunction with gel or tapioca-like particles.

If the titer of the fiber mat was almost exactly the same as the titer of the main filter medium, there was a minimum increase in service life of 100% compared to the standard filter medium when filtering a sludge from A C road dust in water. In other tests, in which the density and the thickness of the fiber mat were varied, an increase in the service life of at least 300 % was achieved.

The long-term filter medium explained here can be used to filter any desired type and shape can be processed. For example, it can be used to make filter bags, plates or frames, Manufacture cylindrical filter bodies or filter bodies with a different shape. The invention is described below with reference to the drawings explained in more detail. Show it:

Figure 1 shows a cross section through an embodiment dos

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- 1 3 long-term filter media, and

Figure 2 is a graph showing the results

of lifetime tests carried out under the same conditions with a conventional filter medium and the improved long term filter media of the invention.

In the preferred embodiment illustrated in FIG of the long-term filter medium is a main filter pad 1 and a a non-woven, loose fiber mat forming a depth filter provided, which is arranged on the upstream side of the pad 1 and is in intimate contact with this. In the Pad 1 is a surface filter from a non-woven felt with a nominal separation value of 25 yum. The base 1 consists of a large number of viscose staple fibers 3 with a denier of 8, a staple length of approximately 80 mm and a relative density of approximately 1.50. It follows that the diameter of the fibers is approximately 27.5 / .mu.m. Every fiber is provided with approximately 2.36 to 3.15 corrugations per cm length in order to improve the mutual mechanical entanglement. To the To increase the rigidity of the base 1, an insert in the form of a woven nylon mesh 4 is inserted between the fibers 3.

2 The grid has 5.5 χ 5.5 fibers per cm; the fibers have a titre of 840 and a specific gravity of 1.14. The base including the grid 4 has a total thickness of about 1.6 mm; the relative density of the base is in particular

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total 0.21; the weight per unit area is 34O g / m 2.

The fiber mat 2 consists of a large number of polyester fibers 5 with a titer of 6, a staple length of 80 mm and a relative density of the fibers of 1.3. As in the case of the base, the fibers 5 are also provided with approximately 2.36 to 1.35 corrugations per cm in order to ensure improved mechanical entanglement. From the denier and the specific gravity of the fibers 5 it can be calculated that the fibers have a diameter of about 25 µm . The fiber mat 2 is approximately 51 mm thick and has an overall specific gravity of 0.011; their weight per unit area is 120 g / m. Since the base 1 serving as the main filter is arranged downstream of the fiber mat 2, the base determines the separation value or the filter properties of the overall medium. Due to the use of the fiber mat 2, however, particles 6 are collected and retained over the full depth of the fiber mat without the total differential pressure on the filter medium increasing significantly until the fiber mat is fully loaded with particles.

FIG. 2 shows service life comparison tests for the main filter pad illustrated in FIG. 1 and explained above 1 and the entire long-term filter medium that has the same main filter pad 1 and the fiber mat 2 according to FIG. 1 and the above explanation. The samples of both the standard filter medium as well as the long-term filter medium according to the invention were processed into a filter bag, which is an effective

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It had a surface of 25.5 dm and was arranged in this way in the test facility was that the filter bags were flown through from the inside to the outside. Each filter was a constant flow of water with a Flow rate of 38 l / min exposed, with the water as Test contaminant contained 2.65 g fly ash / l.

The fly ash had a particle size distribution accordingly the following table:

Particle size in ^ m ■ Share in %

O - 7.5 38.2

7.5-20 27.0

20-60 24.6

6O - 2OO 1O, 2

1OO.O

In the graphical representation according to FIG. 2, the abscissa represents represents the volume of water containing the test contaminant and passed through the filters, while in the direction of the The ordinate shows the differential pressure across the filters was established at a flow rate of 38 l / min after predetermined amounts of water and test contaminant through the Filters had been passed through. Curve A shows the dependence of the differential pressure on the volume of the test liquid for the standard filter medium, while curve B shows the dependence of the differential pressure on the test liquid volume for reveals the long-term filter medium according to the invention. It it can be clearly seen that the standard filter medium has a dif-

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2
differential pressure of 0.35 kp / cm developed after approximately 1 32 1 test liquid has flowed through, while with the long-term filter medium according to the invention a differential pressure of 0.35 kp /

cm only occurs after approximately 398 liters of test liquid have passed through. After a total test liquid amount of 1 7O 1 it builds conventional filter medium according to curve A a differential pressure of 0.7 kp / cm. In contrast, with the long-term filter medium according to curve B, a differential pressure of 0.7 kp /

cm only reached after approximately 473 1 test liquid has flowed through are. The curves A and B of Figure 2 thus show that the long-term filter medium according to the invention and in particular the embodiment of this medium explained in connection with FIG. 1 in comparison with a conventional surface filter made of felt with a nominal separation value of 25 μm has approximately three times the dirt absorption capacity. The curve FIG. 2 also shows that the initial differential pressure across the long-term filter medium, which occurs at a flow rate of 38 l / min is approximately 0.21 kgf / cm, remains essentially constant until approximately 341 l of test liquid passes through have flowed through the filter. In contrast, with the conventional filter medium, the differential pressure increases according to curve A. almost instantly. The structure of the filter cake on the conventional filter medium, which leads to an increase in the differential pressure also results in a reduced flow capacity and a reduction in the nominal pore size of the filter. This is not the case with the long-term filter medium according to the invention, which follows from the fact that the differential pressure is

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remains moderately constant until that on the upstream side
the main filter arranged, a depth filter forming a fiber mat begins to be clogged. Results similar to those illustrated in FIG. 2 were also achieved with the long-term filter medium according to the invention with other separation values and different fiber arrangements under the same test conditions as in FIG. Similar results were also obtained for other test fluids containing other test contaminants.

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Claims (17)

- 18 claims 1.) Long-term filter medium, characterized by a pad (1) from a plurality of fibers provided with a predetermined titer (3), which form a main surface filter with a predetermined pore size, thickness and density, and a nonwoven fiber mat (2) made of a plurality of Fibers (5) which, within a tolerance range of approximately -4O %, have a titer that corresponds to the titer of the fibers of the main filter and which form a depth prefilter whose thickness is at least ten times greater and whose density is at least ten times smaller than the thickness or density of the base are. 2. Filter medium according to claim 1, characterized in that the fibers (3) of the base (1) form a non-woven felt. 3. Filter medium according to claim 1 or 2, characterized in that the base (1) serves to increase the rigidity has coarse woven insert (4) located between the fibers (3). 4. Filter medium according to one of claims 1 to 3, characterized in that that the fiber mat (2) on the upstream Side of the base (1) is arranged and designed in such a way that 609811/0647 that it collects dirt particles over its full thickness and holding back. 5. Filter medium according to claim 4, characterized in that the base (1) has a differential pressure for a predetermined flow rate developed during the collection and retention of the dirt particles by the fiber mat (2) essentially remains constant. 6. Filter medium according to one of the preceding claims, characterized characterized in that the fibers (3) of the base (1) are crimped are. 7. Filter medium according to one of the preceding claims, characterized in that the diameter of the fibers (5) of the fiber mat (2) is within a range of - 40 % equal to the diameter of the fibers (3) of the base (1). 8. Filter medium according to one of the preceding claims, characterized in that the relative density of the fibers (5) forming the fiber mat (2) is within a range of -4O % equal to the relative density of the fibers (3) forming the base (1) . 9. Filter medium according to claim 5, characterized in that the dirt particle absorption capacity of the base (1) and fiber mat (2) together for a given area and flow rate 609811/0647 25371 as well as the specified differential pressure at least twice
the dirt particle absorption capacity of the base alone
is. 10. Filter medium according to one of the preceding claims, characterized characterized in that the fibers (3) of the base (1) have an im substantially uniform titers in the range of about 1.5 to about 22 denier. 11. Filter medium according to claim 10, characterized in that
the fibers (5) of the fiber mat (2) have a uniform titer
ranging from about 1 to about 30 deniers. 12. Filter medium according to one of the preceding claims, characterized characterized in that the fibers (3) of the base (1) have a substantially uniform diameter in the range of approximately 11 yum to about 45 / um. 13. Filter medium according to one of the preceding claims, characterized in that the fibers (5) of the fiber mat (2) one
have substantially uniform diameters ranging from about 6.6 µm to about 60 µm. 14. Filter medium according to one of the preceding claims, characterized in that the base (1) has a substantially
has a uniform thickness ranging from about 1.6 mm to about 6.4 mm. 60981 1/0647 15. Filter medium according to claim 14, characterized in that the fiber mat (2) has a substantially uniform thickness in the range of about 25 mm to about 80 mm. 16. Filter medium according to one of the preceding claims, characterized characterized in that the base (1) has a substantially uniform specific gravity in the range of about 0.050 until about 0.50. 17. Filter medium according to claim 16, characterized in that the fiber mat (2) has a substantially uniform relative Density in the range of about 0.05 to about 0.050 Has. 609811/0647 Blank page