SELF-SUPPORTING INDUSTRIAL AIR FILTER

A self-supporting filter media as well filter element and filtration system including the same is provided. A method of manufacturing the self-supporting filter media is also provided. The self-supporting filter media is formed such that it has a rigidity which permits the omission of filter support cage or other internal media support structure.

FIELD OF THE INVENTION

This invention generally relates to filtration, and more particularly to industrial air filters.

BACKGROUND OF THE INVENTION

Filters are commonly used to remove particulate matter from an air stream in an industrial air filtration system. For example, such filters are often used in known baghouses. At least some known baghouses include a housing that has an inlet that receives dirty, particulate-containing air, and an outlet through which clean air is discharged from the baghouse. In such baghouses, often the interior of the housing is divided, by a tube sheet, into a dirty air or upstream plenum, and a clean air or downstream plenum. Air flows through the inlet into the dirty air plenum, through the filters, and into the clean air plenum before clean air is discharged through the outlet of the clean air plenum.

One particular type of filter used in such industrial applications utilizes what is referred to as a filter bag installed on a cage. The filter bag is made of a porous material through which air passes. Dust and other contaminants in the air stream are trapped by the porous filter media material. The filter bag is supported on its interior side by the cage, which is a generally rigid assembly.

For the typical bag and cage installation, the bag is applied to the tube sheet and the welded cage is then installed into the bag in one or more pieces. This method of installation necessitates that there is clearance designed between the bag and cage to allow for field assembly. If this clearance is too small, the bags will be difficult to install. If the clearance is too large, the bags will wear prematurely.

Because the cages have useful life longer than bags, they are retained and re-fit to new bags when filters need to be replaced. After months or years of operation, the removal of the bag from the cage and re-installation of an old cage into a new bag requires significant labor, and handling of the old bag may require significant precautions to protect the health of the individuals changing filters if the filtered dust is hazardous.

Accordingly, there is a need in the art for a rigid, self-supporting filter media and associated filter which does not require a support cage and is suitable for application in baghouse systems. The invention provides such a filter media, filter, and system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

BRIEF SUMMARY OF THE INVENTION

A self-supporting filter media according to the teachings herein may be made from one or more layers of a fiber-reinforced composite material. The composite material is designed so that multiple layers of fibers create a structure that is porous, allowing air flow through the material. A binder is used to attach the fibers together so that they provide the necessary structure to withstand differential pressure created by air flow through the fibrous medium.

Choice of fiber materials, fiber sizes, and binder systems may be driven by the filtration application were the filters are intended to be used. Fibers may be glass, thermoplastic, or other fibers such as metal, carbon or silica. The sizing of the fibers may be dictated by the size of the particulate to be filtered from the air stream with larger fibers being used to create a larger pore size for larger dust. Likewise, finer fibers may be used to create a smaller pore size for smaller dust. Fibers may also be blended homogeneously or layered in a gradient fashion to create the desired pore structure, temperature and chemical resistance. The binder systems may be thermosetting, thermoplastic, or epoxy systems. They type of binder system used may be driven by application considerations such as temperature or chemical resistance, or commercial considerations such as cost. Binders may also be blended or layered as needed to create the support structure for the fibers.

Heat treatment or chemical treatment could also be used to modify the characteristics of the fibers and/or binders used to create the air filter pore structure. These treatments may be used in impart superior mechanical properties, alter surface properties such as water or oil repellency, enhance chemical resistance, or improve dust release.

For air filters which are to be back-pulsed, surface filtration is a desired characteristic. This surface filtration may be accomplished by creating a surface with a finer pore size on the “dirty” side of the filter. This finer pore structure may be created using small diameter fibers suspended in a binder or it may be achieved by a surface coating of fine fibers deposited by electro-spinning or force-spinning. A membrane of expanded polytetrafluoroethylene (ePTFE) or other materials may also be laminated to the dirty side of the filter to provide fine filtration. A blend of surface filtration materials may be used homogeneously or in a gradient fashion. Surface filtration layers may also be heat treated or chemically treated to impart mechanical properties, alter surface properties such as water or oil repellency, enhance chemical resistance, or improve dust release.

The self-supporting filter may be manufactured in a variety of geometries due to the elimination of the support cage and cage clearance. The filters may have a constant cross section over its length, or it may be rotated, blended or swept through varying cross sections. These filter cross-sections may include a simple, circular shape, or a shape designed to increase the filter cross-sectional area including pleated, lobed, or star-shaped. Other configurations designed to increase filtration area such as using concentric cylinders would also be possible with the self-supporting tube.

The self-supporting filter must have a means of attachment to the tube sheet which divides the clean side from the dirty side of the dust collector. Self-supporting filters may be attached to the tube sheet using elastomeric gaskets, felt or woven gaskets, or felt or woven cuffs applied to the ID of the tube sheet opening or to the face of either side of the tube sheet. Stepped, tapered, or expandable features may be incorporated to extend the range of tube sheet holes that may be fit with a single filter.

Like the tube sheet attachment feature, filters may be joined one or more other filters to extend the total length of the combined filter element. Self-supporting filters may be attached to the other self-supporting filter elements end-to-end using elastomeric gaskets, felt or woven gaskets, or felt or woven cuffs applied to the ID or OD of the filter element. They may also use the face of either filter element. Stepped, tapered, or expandable features may be incorporated to extend the range of filters that may be connected to another filter element.

In one aspect, the invention provides a method for manufacturing a self-supporting filter media. An embodiment of such a method includes providing a forming device, placing a deactivated filter media on the forming device, activating the deactivated filter media to form an activated filter media, removing the forming device from the activated filter media.

In certain embodiments, the forming device is a mandrel which has a circular cross section. In other embodiments, the forming device may be a mandrel which has a non-circular cross section.

In certain embodiments, the deactivated filter media comprises a fibrous material and a binder. The fibrous material may comprise at least one of glass fibers, thermoplastic fibers, and metal fibers, polymer fibers.

In certain embodiments, activating includes curing in a curing oven. Activating may also include chemical curing.

In certain embodiments, the fibrous material has a fiber diameter of 0.2 micron to 30 micron. In certain embodiments, filter media has a mean flow pore size of 0.1 micron to 100 micron. The filter media may comprise multiple layers of filter media, wherein the multiple layers of filter media have differing compositions from one another.

In certain embodiments, the method may also include applying a coating to at least one of an interior or exterior surface of the filter media prior to curing. Additionally or in the alternative, the method may also include applying a coating to at least one of an interior or exterior surface of the cured filter media after curing.

In certain embodiments, the filter media comprises at least one of a high efficiency filtration layer and a surface filtration layer.

In another aspect, a self-supporting filter media is provided. An embodiment according to this aspect includes at least one layer of filter media, the at least one layer of filter media including a binder and a fibrous material.

In certain embodiments, the fibrous material may include at least one of glass fibers, thermoplastic fibers, metal fibers, and polymer fibers. The fibrous material may have a fiber diameter of 0.2 micron to 20 micron. The binder may comprise one of a phenolic, polyester, polyurethane, vinyl ester, epoxy, silicone, melamine, diallyl phthalate, polypropylene, polyethylene, nylon, polyphenylene sulfide, polyvinylidene fluoride, or polytetrafluoroethylene polymer.

In certain embodiments, the at least one layer of the filter media has a mean flow pore size of 0.1 micron to 100 micron. The at least one layer of filter media may include a plurality of filter media layers, wherein the plurality of filter media layers have differing compositions from one another.

In certain embodiments, a coating on at least one of an interior and exterior surface of the at least one layer filter media may be provided.

In certain embodiments, the at least one layer of filter media comprises at least one of a high efficiency filtration layer and a surface filtration layer.

In yet another aspect, the invention provides a filter element. An embodiment of a filter element according to this aspect includes at least one layer of filter media, the at least one layer of filter media including a binder and a fibrous material. The filter element also includes a first end cap, the first end cap configured to form a seal with a tube sheet of a filtration housing. The filter element is free of an internal support structure such that only the at least one layer of filter media is situated between the end caps.

In certain embodiments, the filter element also includes a second end cap, the first and second end caps respectively positioned at first and second ends of the at least one layer of filter media. In certain embodiments, the fibrous material comprises at least one of glass fibers, thermoplastic fibers, metal fibers, and polymer fibers. The fibrous material has a fiber diameter of 0.2 micron to 20 micron.

In certain embodiments, the at least one layer of filter media has a mean flow pore size of 0.1 micron to 100 micron. In certain embodiments, the at least one layer of filter media includes a plurality of deactivated cured filter media layers, wherein the plurality of deactivated cured filter media layers have differing compositions from one another.

In certain embodiments, the filter element also includes a coating on at least one of an interior and exterior surface of the at least one layer of deactivated cured filter media.

In certain embodiments, the filter element also includes at least one of a high efficiency filtration layer and a surface filtration layer.

In certain embodiments, the high efficiency filtration layer comprises at least one of electro-spun, force-spun, nano, fine, spunbonded, ePTFE or meltblown fibers, or ePTFE membrane.

In yet another aspect, the invention provides a filtration system. An embodiment of a filtration system according to this aspect includes a housing having an inlet and an outlet, the inlet separated from the outlet by a tube sheet. The system also includes at least one filter element mounted to the tube sheet, the filter element comprising at least one layer of filter media, the at least one layer of filter media including a binder and a fibrous material.

In certain embodiments, the at least one filter element comprises a plurality of filter elements arranged in an array relative to the tube sheet.

In certain embodiments, less than 70 pulses are required during 2 hour performance testing using Pural NF dust per ASTM D6830, and less than 200 pulses are required during 6 hour performance testing using Pural NF dust per ASTM D6830.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, a self-supporting filter media as well as a filter element incorporating the same are shown and described. Also shown is an exemplary embodiment of a filtration system employing the aforementioned filter element. As will be understood from the following, the self-supporting media described herein advantageously allows for the provision of a filter element which does not require any support structure to support the filter media. The filter media itself is self-supporting and strong enough to maintain its shape under typical pressure differentials seen in a variety of filtration applications. Such a configuration leads to a filter element which lasts longer, and is less costly to produce. As a result, the invention achieves a substantial cost and labor reduction in the maintenance and operation of a baghouse filtration system.

With particular reference now toFIG. 1, a filtration system20is illustrated. This filtration system20includes a schematically illustrated housing22which carries a filter element24that employs a self-supporting filter media according to the teachings herein. Housing22includes an inlet26and an outlet28. Filter element24is situated within housing22such that it is sealingly mounted within an opening30of a tube sheet32. Tube sheet32divides the interior of filter housing22into a dirty side which opens to inlet26, and a clean side which opens to outlet28. Air entering inlet26passes through the aforementioned self-supporting filter media of filter element24and then exits housing22via outlet28. It will be recognized by those of skill in the art thatFIG. 1represents a generally schematic exemplary configuration of a typical baghouse filtration system. However, the self-supporting media described herein may be incorporated into filter elements which are utilized in applications not associated with a baghouse. Further, although a single filter element24is illustrated, it will be recognized that in a typical configuration multiple filter elements24are mounted to tube sheet32within the interior of housing22.

Turning now toFIG. 2, the same illustrates a cross-section of filter element24. Filter element24includes a ring of self-supporting filter media40. Filter element24also includes an open end cap as a first end cap34at one end of filter element24. A closed end cap in the form of a second end cap36is positioned opposite first end cap34. First end cap34may incorporate a variety of contemporary tube sheet sealing configurations including gaskets, radial or annular seals, etc. Further, a cap of self-supporting filter media may be utilized in place of second end cap36to increase overall filtration area.

As will be understood in from the following, filter media40may be a deactivated filter media which may be activated to transition the same from a deactivated filter media to an activated filter media. Such activation includes, but is not limited to, activing a binder interspersed with the fibers of the filter media and/or curing a resin interspersed with the fibers of the filter media.

Turning now toFIG. 3, the same illustrates a schematic cross-section of the self-supporting filter media according to the teachings herein. As can be seen in this view, filter media40includes at least one layer48of filter media. This layer48includes a fibrous material represented by fibers52and a binder, resin, or other substance (collectively referred to as binder50) interspersed throughout fibers52. This binder50has been activated such that it has hardened to provide the needed strength and rigidity to filter media40. As a result, and with momentary reference back toFIG. 2, an interior support structure such as a support cage or other rigid structure is not within the interior42of filter element24to support the same. Filter media40is thus self-supporting. Put differently, because the media itself is responsible for providing support, additional filtration depth is provided by this embodiment which would otherwise not be available. The increased filtration depth increases the filter dust holding capacity and helps to manage differential pressure over the life of the filter. Indeed, the support cage or structure in prior designs takes up a substantial portion of the filter element with which it is incorporated in, yet provides no filtration capabilities.

Still referring toFIG. 3, filter media40may also include additional layers54,56on the interior and exterior surfaces of filter element24. These additional layers54,56may be other fibrous layers similar to or the same as layer48, or alternatively, may have different properties. For example, either or both of additional layers54,56may be a high efficiency filtration layer. As non-limiting examples, this high efficiency filtration layer may comprise at least one of electro-spun, nano, fine, spun-bonded, meltblown, melt-spun, or force-spun fibers, or ePTFE membrane. Such a high efficiency layer may present a mean flow pore size of 0.2 to 40 microns. Alternatively or in addition, layers54,56may also be coatings such as fire, moisture, or acid-resistant coatings.

Further, the outer layer54may be designed as a surface filtration layer, having a mean flow pore size of 0.5 to 40 microns. This will allow a dust cake to form on the inlet side of filter media40and enhance the filtration efficiency of filter element24. As non-limiting examples, this surface filtration layer may comprise at least one of electro-spun, nano, fine, spun-bonded, meltblown, melt-spun, or force-spun fibers, or ePTFE membrane. Although only a single layer54,56is shown on the clean and dirty side, respectively, multiple layers may be presented on the inlet side of layer48, and multiple layers may be presented on the outlet side of layer48. Use of such a surface filtration layer as described above also allows filter element24to be back-pulsed for cleaning purposes. Advantageously, filter media40is of a strong enough construction to permit such back pulsing without the need of the support structure of prior designs.

Layer48may present a generally uniform mean flow pore size of 0.1 micron to 100 micron. Alternatively, layer48may be constructed by utilizing fibers of different diameter or different spacing to achieve a variable pore size as air moves through filter media40to achieve a desired filtration gradient. One example of such a configuration may be to use a very small pore size near the inlet side of filter media40to provide for fine filtration at the surface thereof as mentioned above. Alternatively, filter media40may utilize a variable pore size which begins large near the inlet side of filter media40and progressively becomes smaller towards the outlet side of filter media40. Still further, layer48may in its entirety, or in at least a portion, be provided as a high-efficiency filtration layer as provided above. Accordingly, it is contemplated herein that the filter media40includes at least one layer of filter media, which may include those layers48,54,56, described above, as well as fewer or additional layers, as also described above.

As used above, the terms inlet side and outlet side of the filter media are made relative to the direction of air flow through the filter media. The inlet side is that side of the filter media40which air encounters first. The outlet side is that side of filter media40which air encounters after encountering the inlet side.

Various fiber types and fiber sizes may be utilized in layer48. As non-limiting examples, the fibrous material52which makes up layer48may be made of one or more of glass fibers, thermoplastic fibers, metal fibers, and/or polymer fibers. Further, such fibers may have an exemplary fiber diameter of 0.2 micron to 30 micron. It will be recognized, however, that other fiber diameter may be utilized and are contemplated herein.

The binder50employed may take on a variety of forms depending upon application. As non-limiting examples, the binder may be one of a phenolic, polyester, polyurethane, vinyl ester, epoxy, silicone, melamine, diallyl phthalate, polypropylene, polyethylene, nylon, polyphenylene sulfide, polyvinylidene fluoride, or polytetrafluoroethylene polymer.

Such a binder may be a resin which may be activated, i.e. cured via heat, chemically, or via any other known cure methodology based on the resin utilized. Other processing may also be employed. For example, additional chemical and heat treatments may be employed before or after curing. Further, electrostatic charging may also be employed. These processing steps will largely depend upon the application of filter media40. It will be understood, however, where the binder is not a resin, other activations steps will be utilized outside of curing used with a resin system. For example, the binder may be chemically activated, heat activated, pressure activated, etc. Accordingly, terms such as “activating” and “activate” and their derivatives are used herein to mean any operation which transitions a binder into a state which provides the required strength and rigidity to filter media40so as to not require an additional support structure.

Turning now toFIG. 4, the same illustrates a generally schematic view of the formation of filter media40into a desired shape. As can be seen in this figure, filter media40is in its deactivated state and is wrapped around a mandrel60. In the illustrated embodiment, filter media40is generally very flexible prior to activation allowing it to be shaped around mandrel60. Once wrapped about mandrel60, the mandrel is then placed into an activating device. In the illustrated embodiment, this activating device is a curing oven62used to cure a resin which constitutes binder50in the illustrated example. However, this activating device will vary depending upon the activating method utilized. This curing step is necessary to cure the resin contained within filter media40to transform the same from its deactivated state to its activated state. By doing so, filter media40becomes rigid and assumes the overall shape of the mandrel60upon which it was wrapped.

Although a cylindrical mandrel60is utilized, other shapes are contemplated. For example, mandrel60may have a non-circular cross-section. An example of such a configuration may be a triangular or star-shaped cross-section. A star shape is particularly useful as it could be utilized to form pleats to increase the overall surface area of filter media40. Further, mandrel60may be shaped such that filter media40follows a twist, i.e. helical axis, along its length. It will be recognized that relatively complex geometries may be achieved based on the shape of mandrel60.

Although not shown inFIG. 4, it will be recognized that a conveyor or feeding device may also be used for moving mandrel60into curing device62. Such a system may include a conveyor, rollers, or any combination thereof. The particular system used will depend largely upon the curing device selected. It will be recognized that where multiple layers48of filter media are employed, each will be wrapped around mandrel60as illustrated inFIG. 4. Further, a pre-cure coating or treatment may be applied to media40prior to or after it has been wrapped around mandrel60. Likewise after curing a post-cure coating may also be applied.

Broadly, forming a self-supporting filter media for incorporation into a filter element according to the teachings herein includes first providing a forming device. Thereafter, a deactivated layer or layers of filter media is/are applied to the forming device. Thereafter, the layer or layers is/are activated in an activating device. This cases the layer or layers of media to become structurally rigid. The forming device is then removed, and subsequent operations such as end cap installation, etc., may ensue. The forming device may be a mandrel, form, or mold, or any structure which functions to hold a general shape of the deactivated media while transitioning the same form a deactivated state to an activated state. The activating device may be any device used to transition the media from its deactivated to its activated state by interacting with the binder provided within the media.

Turning now toFIG. 5, the same illustrates one exemplary schematic process of forming the self-supporting media as described herein. At step70, a forming device in the form of a mandrel is provided. At step72, the mandrel is wrapped with one or more layers of filter media40. These layers may have identical or different properties including but not limited to the types of fibers used, or the binders contained therein. This wrapping continues at steps72,74until wrapping is complete.

Once wrapping is complete, a pre-cure coating may be applied at steps76and78. Whether utilizing a pre-cure coating or not, process then moves to step80where the wrapped mandrel is placed in the curing device and the filter media40is cured. After curing at step80, a post-cure coating may be applied at steps82and86. The mandrel84is then removed and the self-supporting filter media is formed.

As discussed above, post-processing steps may also include other treatment such as chemical or heat treating steps. Further electrostatic charges may be applied to enhance the filtration capabilities of the self-supporting media. Also as described above, a high efficiency filtration layer may also be applied to the exterior surface of the cured filter media40. This high efficiency layer may be formed concurrently during curing step80by wrapping mandrel60with an outermost wrap of very fine fibers suitable for high efficiency filtration which become rigid after curing. Alternatively, this high efficiency filtration layer may be applied after curing via another process as described above, e.g. electrospinning.

After being formed and after any additional post-processing, cured filter media40may be utilized in the manufacture of a filter element such as that shown inFIGS. 1 and 2. Indeed, first and second end caps34,36may be attached. As discussed above, however, second end cap36may be omitted where the same is formed via cured filter media. Additionally, although a basic cylindrical filter element24is shown herein, it is contemplated that the self-supporting media described may be utilized to multiple filter elements which nest into one another to form a concentric primary/secondary filtration configuration. It will be recognized that while filter media40is cured it can be utilized to form a variety of filter elements not limited to the exemplary configuration shown herein. Indeed, the self-supporting media may be utilized in a variety of applications and advantageously allow for the omission of an internal support structure which is otherwise typically required.

Other formation methodologies are also contemplated by the teachings herein. For example, the fibers52of filter media40may be coated with a binder and air-laid in a web, or the fibers52may be treated with a binder after the web is formed. As another example, the fibers may be chopped, mixed with a binder, and then sprayed into a sheet or onto a form such as a mandrel or mold for subsequent activation. Still further, the fibers may be wet laid into a sheet, or onto a form such as a mandrel or mold. Still further, sheets, molds and mandrels treated with fiber and binder may have subsequent forming operations performed on them to achieve the targeted size, shape and density of fibers appropriate for filtration. These operations may include compressing in molds, expanding in molds, compressing using consumable components, thermal forming, hydroforming, rotational molding, or blow molding.

Media40according to the invention as described above performs exceedingly well in surface filtration applications. For example, testing of the media40per ASTM D6830-02 revealed very good results. According to this test, a dust concentration 8+−1.6 gr/dscf, filtration velocity 6.6+−0.5 ft/min, pulse pressure 75 psi, pulse duration 50 ms, air temperature 78+−4 F and relative humidity 50+−10%, were used. Per this test, a conditioning phase 10,000 pulses at 3-5 second intervals was employed, then a recovery phase at 30 pulses was employed after the pressure differential across a test sample of media40reaches 4″ w.c. Thereafter performance test phase was conducted During this phase, the number of pulses required during the performance test phase of ASTM were measured at two and six hour time intervals were measured. The results were less than 70 pulses during 2 hour performance test using Pural NF dust per ASTM D6830-02 for the two hour test, and less than 200 pulses during 6 hour performance test using Pural NF dust per ASTM D6830-02 for the six hour test.