Coalescence filter

Abstract

The present invention relates to a filter unit for filtering a compressed gas contaminated with oil, in particular compressed air, wherein the filter unit contains a coalescence filter for coalescing the contaminant contained in the compressed gas, in particular oil. The coalescence filter comprises a housing with a gas supply for supplying the gas to a primary coalescence medium disposed in the housing, the gas flowing in a flow direction, wherein the primary coalescence medium contains at least one first layer of a first porous coalescence medium and a second layer of a second porous coalescence medium adjacent to the first layer, wherein the primary coalescence medium has a total thickness of at least 3.5 mm, measured at a pressure of 2 N/cm.sup.2.

Claims

1. A filter unit for filtering a compressed gas contaminated with oil, wherein the filter unit comprises a coalescence filter for coalescing the contaminant contained in the compressed gas, wherein the coalescence filter comprises a housing with a gas supply for supplying the gas to a primary coalescence medium disposed in the housing, the gas flowing in a flow direction, wherein the primary coalescence medium comprises at least one first layer of a first porous coalescence medium and a second layer of a second porous coalescence medium wrapped around and adjacent to the first layer, wherein the primary coalescence medium has a total thickness of at least 3.5 mm measured at a pressure of 2 N/cm.sup.2, wherein the primary coalescence medium has an air permeability of at least 100 l/m.sup.2.Math.s, and wherein pores of the primary coalescence medium and the second porous coalescence medium have the same average pore diameter of between 5 and 30 m wherein the primary coalescence medium has a density of between 0.05 and 0.90 g/cm.sup.3.

2. The filter unit according to claim 1, wherein the primary coalescence medium has a thickness of maximum 50 mm.

3. The filter unit according to claim 1, wherein the primary coalescence medium is made of a plurality of layers of a material that is wetting for the contaminant which is to be coalesced, or of a plurality of layers of a material that is non-wetting for the contaminant to be coalesced.

4. The filter unit according to claim 3, wherein the primary coalescence medium is made up of a plurality of layers of an oleophilic or oleophobic material.

5. The filter unit according to claim 1, wherein the primary coalescence medium contains, at a position upstream with respect to the gas supply, a plurality of layers of a material which is wetting for the compound to be coalesced and at a downstream position, a plurality of layers of a material which is non-wetting for the compound to be coalesced.

6. The filter unit according to claim 5, wherein the primary coalescence medium contains, at a position upstream with respect to the gas supply, a plurality of layers of an oleophilic material, and downstream of the gas supply a plurality of layers of an oleophobic material.

7. The filter unit according to claim 1, wherein the gas is compressed air.

8. The filter unit according to claim 1, wherein the contaminant is oil.

9. The filter unit according to claim 1, wherein the primary coalescence medium has an air permeability of maximum 20001/m.sup.2.Math.s.

10. The filter unit according to claim 1, wherein the coalescence filter contains at a position adjacent to a surface of the primary coalescence medium, along a surface of the primary coalescence medium positioned downstream with respect to the gas supply, through which the coalesced contaminant leaves the primary coalescence medium, a layer of drainage material, for receiving and draining of coalesced contaminant.

11. The filter unit according to claim 1, wherein in the coalescence filter downstream of the coalescence medium, one or more layers are provided of a filter material for removing oil vapor.

12. The filter unit according to claim 1 which further comprises a water filter for removing water.

13. The filter unit according to claim 12, wherein the filter for removing water is a refrigerant dryer, a dryer provided with a drying agent, a membrane dryer, or a combination of two or more hereof.

14. The filter unit according to claim 1 which further comprises a filter for removing solid particles.

15. A compressor for compressing one or more gases, wherein the compressor is provided with an outlet for releasing the one or more gases, wherein the outlet is connected to a filter unit according to claim 1 for the purification of the one or more gases.

16. A coalescence filter for coalescing the contaminant contained in the compressed gas comprising a housing with a gas supply for supplying the gas to a primary coalescence medium disposed in the housing, the gas flowing in a flow direction, wherein the primary coalescence medium contains at least one first layer of a first porous coalescence medium and a second layer of a second porous coalescence medium wrapped around and adjacent to the first layer, wherein the primary coalescence medium has a total thickness of at least 3.5 mm at a pressure of 2 N/cm.sup.2, as a part of a filter unit, and wherein the primary coalescence medium has an air permeability of at least 100 l/m.sup.2.Math.s, and wherein pores of the primary coalescence medium and the second porous coalescence medium have the same average pore diameter of between 5 and 30 m wherein the primary coalescence medium has a density of between 0.05 and 0.90 g/cm.sup.3.

17. The filter unit according to claim 1, wherein the primary coalescence medium has a density of between 0.12 and 0.17 g/cm.sup.3.

18. The filter unit according to claim 1, wherein the compressed gas is air, and wherein the primary coalescence medium has a total thickness of at least 5 mm.

19. The filter unit according to claim 18, wherein the primary coalescence medium has a density of between 0.12 and 0.17 g/cm.sup.3, and wherein the primary coalescence medium has a total thickness of at least 7.5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is further explained below in the attached figures and description of these figures.

(2) FIG. 1 shows a view of the inner volume of a representative coalescence filter for the purification of compressed gas.

(3) FIG. 2 shows a schematic view of a coalescence filter of this invention.

(4) FIG. 3 shows the pressure drop measured over a coalescence filter.

(5) FIG. 3a shows the pressure drop measured over a conventional filter system, with a first housing in which a first coalescence filter is made of an oleophilic filter material, and a second housing in which a second coalescence filter is made of an oleophobic filter material.

(6) FIG. 3b shows the pressure drop measured over a coalescentiefiler of this invention, with a first filter coalescence medium made of an oleophilic material, and a second coalescence medium made of an oleophobic filter material.

(7) FIG. 3c shows the pressure drop measured over a coalescentiefiler of this invention, with one type of coalescence medium.

DETAILED DESCRIPTION OF THE INVENTION

(8) The filter unit of this invention contains a coalescence filter 10 as shown in FIGS. 1 and 2. The coalescence filter 10 includes a closed housing 24 with a filter head 12 at the top. Filter head 12 includes an inlet 16 through which a fluid comprising a support and at least one contaminant is introduced into the coalescence filter, for example, a gas with an contaminant, in particular air or compressed air contaminated with oil. The housing 24 contains an outlet 18 for discharging a fluid and/or carrier liquid, which has moved through the coalescence filter 22, for example compressed air. Filter head 12 is removably connected to housing 24, so that the interior of the coalescence filter 10 is accessible for the replacement of the coalescence medium 22, if necessary. The releasable connection may be established in any manner considered suitable by the skilled person, for example by means of a screw connection, by means of pressure, friction, clamps etc. Inlet 16 is connected to the interior of the coalescence filter 10 in such a manner that a fluid, for example a compressed gas, may be fed to the coalescence medium 22, The coalescence medium 22 is preferably releasably connected with the filter head 12, so that the coalescence medium 22 may be replaced periodically, or can be replaced if necessary.

(9) The coalescence medium 22 includes a primary coalescence medium. As shown in FIG. 2 the primary coalescence medium contains at least a first layer 1 of a first porous coalescence medium, and a second layer 2 of a second porous coalescence medium positioned adjacent to the first layer. The gas to be purified flows in the direction of the arrow, i.e., from and through the first coalescence medium 1 to and through the second coalescence medium 2. The first coalescence medium 1 has a surface 3 situated upstream relative to the gas supply or air supply and a surface 4 situated downstream with respect to the compressed air supply which forms the contact surface with the second coalescence medium 2. The second coalescence medium 2 has an upstream surface 5 which forms the contact surface with the first coalescence medium 1 and a downstream surface 6.

(10) If so desired, the primary coalescence medium may further contain additional layers of one or more porous coalescence media, for example, a third and/or fourth layer or a further additional layers. The choice of the number of layers and the nature of the material for these layers can be tailored by the skilled person taking into account the removal of contaminant, and the concentration thereof.

(11) The primary coalescence medium 10 preferably has a total thickness of at least 3.5 mm, preferably at least 4 mm, preferably at least 5 mm, more preferably at least 6 mm, most preferably at least 7 mm, in particular at least 7.5 mm measured at a pressure of 2 N/cm.sup.2. The thickness of the primary coalescence medium will usually not exceed 50 mm, preferably up to 40 mm, more preferably up to 30 mm, most preferably up to 25 mm, in particular at most 20 mm.

(12) The coalescence filter shown in FIG. 1 is intended for coalescence one or more liquid contaminants present in a carrier of a fluid. The one or more contaminants may for example be an inert or reactive substance. The one or more contaminants may, for example, belong to the group of liquids, aerosols, drops or macro-mixtures of two or more of these materials. An example of a fluidum suitable for use with the coalescence filter of this invention is compressed air contaminated with an oil aerosol.

(13) Suitable materials for use as a primary coalescence medium, in particular suitable for use as the first layer of the first coalescence medium and as a second layer of the second coalescence medium, include sheet-shaped or layer-shaped substrates or materials composed of fibers having a finite length, continuous filaments, and combinations thereof. The primary coalescence medium preferably contains suitable materials that can withstand the pressure exerted in order to permit displacement of the fluid through the primary coalescence medium, against the liquid contaminants present in the fluid and the static and dynamic load to which the material is subjected during the manufacture of the filter, the assembling thereof and the use thereof. Examples of suitable layer-shaped fibrous materials include woven or non-woven fibrous materials, knitted fabrics, mesh, film, and combinations of the above materials or laminates or composites thereof.

(14) The primary coalescence medium is preferably a multilayered material, which preferably includes at least 4 layers, more preferably at least 6 layers, most preferably at least 10 layers. Mostly, the number of layers of fibrous material will not be higher than 20. The thickness of the individual layers of the coalescence medium is not critical for this invention and may vary within wide limits. The thickness of a layer can be, for instance, a thickness of 0.4 mm, 0.5 mm, 0.6 mm, 0.75 mm or 1 mm. On the other hand, the primary coalescence medium may also be made up of one layer of the desired material, in the desired thickness.

(15) In a first embodiment of this invention, the primary coalescence medium is made up of a plurality of layers of a material that is wetting for the contaminant to be coalesced, or non-wetting. The primary coalescence medium is preferably composed of a plurality of layers of an oleophilic or oleophobic porous filter medium. Successive layers of coalescence medium with wetting properties may be the same or different, successive layers may be more or less wetting, have the same density or different, have the same air permeability or a different, fibers substantially have the same dimensions and/or different physical properties or different, etc. In the same way, successive layers of a coalescence medium with non-wetting properties may be the same or different, i.e. successive layers may be more or less wetting, have the same or a different density, the same air permeability or a different one, fibers of substantially the same dimensions and/or the same or different physical properties, etc. The number of layers of material in the first coalescence medium may be the same as or different from the number of layers of material in the second coalescence medium.

(16) In another embodiment of this invention, the layer of the first coalescence medium built of a coalescence medium that wetting is for the coalescing contaminant, and is the layer of the second coalescence medium built from a material that is non-wetting for the coalescing contaminant. The first layer of the coalescence medium may be built of one single layer, or of a plurality of layers of material that is wetting for the contaminant to be coalesced. The second coalescence medium may be comprised of one single layer, or of a plurality of layers of material which is non-wetting for the contaminant to be coalesced. The number of layers of material in the first coalescence medium may be the same as or different from the number of layers of material in the second coalescence medium.

(17) Examples of fibrous materials that are particularly suitable for manufacturing a layered material for use in the primary coalescence medium of this invention comprise thermoplastic materials, thermosetting materials, organic or inorganic materials, metallic materials or alloys, admixtures, blends and chemically modified materials, for instance manufactured by drawing, spinning, needling, hydroentanglement, melt spinning (for instance, spin bonding, nanofibers, melt blowing), wet-laying, electro-spinning, solvent spinning, point bonding, adhesive bonding, continuous weave/knit, casting, co-extrusion, etc. Materials of particular preference comprise glass fibers, silicate-based wet-laid thermosetting adhesive bond nonwoven fabrics, for instance, a borosilicate glass fiber of finite length, because of their thermal and hydrothermal resistance to loading by the fluid, the carrier liquid and the contaminant, without the need of chemical modification, for instance by a fluorocarbon surface treatment.

(18) A multi-layered primary coalescence medium can be produced in different ways, for instance, by stacking, pleating, rolling or wrapping a plurality of layers of a fibrous material, so that the desired number of layers is obtained. However, any other method can be suitably used. The layers of the fibrous material are preferably arranged adjacently relative to each other, such that a layer of air of a least possible layer thickness is present between adjacent layers. Preferably, adjacent layers are so arranged that no layer of air is present between them. This can be obtained, for instance, by pressing a plurality of stacked layers together or clamping them, for instance along one or more sides of the fibrous material. Preferably, however, the fibrous material is wrapped, to keep the risk of damage minimal.

(19) Adjacent to a surface of the primary coalescence medium 22 positioned downstream in relation to the air supply, a drainage layer 30 may be provided, preferably along a downstream surface of the primary coalescence medium through which coalesced contamination leaves the primary coalescence medium, for receiving and discharging of coalesced contaminants and promoting their discharge. This downstream positioned drainage layer 30 is also intended to provide a barrier which counteracts back flow of coalesced contaminants to the coalescence medium, and/or, in particular, to the carrier of the fluid. Without being bound to this hypothesis it is assumed that the drainage layer forms an interface or transition zone along the interface of the primary coalescence medium along which drainage occurs, as a result of which accumulation of the contaminant: along the interface or transition layer is counteracted, by the formation of large droplets which are driven by the driving force of gravitation and which settle in the filter housing prior to being discharged from the filter. If so desired, also upstream of the primary coalescence medium a protective layer can be arranged, adjacent to a surface of the primary coalescence medium through which fluid is supplied to the primary coalescence medium, in such a way that both materials contact each other. Downstream of the coalescence filter also a protective layer can be added adjacent to a surface of the primary coalescence medium, which except to a protective effect may also have an additional drainage function.

(20) Materials for use in the drainage layer 30 can be, for instance, woven or nonwoven materials, knitted materials, films, open cell foams, cast or spun scrims, open meshes and combinations of laminates or composites of the aforementioned materials. Materials for use in the drainage layer 30 may be chosen, for instance, from the group of thermoplastic or thermosetting plastics, organic or inorganic substances, metallic materials or alloys, blends of the aforementioned materials and chemically modified forms thereof. The aforementioned materials can be manufactured in any manner considered suitable by the skilled person, for instance by drawing, spinning, needling, hydroentanglement, melt spinning (for instance, spin bonding, nanofibers, melt blowing), wet-laying, electro-spinning, solvent spinning, point bonding, through-air bonding, adhesive bonding, continuous weave/knit, casting, coextrusion, expansion, solvent cast and the like. Particularly preferred are polyurethane foams, since they are well resistant, to thermal loading by the fluid and/or the carrier and contaminant liquid present in the fluid, but at the same time counteract return of the contaminants, for instance hydrocarbon-based contaminants, to the coalescence medium, without the necessity of pretreating one or more parts of the coalescence filter or the drainage layer with fluorine-containing substances.

(21) The primary coalescence medium 22, the drainage layer 30 and the barrier layer can be assembled in the coalescence filter 10 as separate layer-form materials. It is also possible, however, to unite the aforementioned materials in a laminate, so that they form a whole, and optimum contact between adjacent layers is ensured and optimum flow of fluid from one layer to the next can take place.

(22) If desired, upstream but also downstream of the primary coalescence medium 22, a protective layer 25 may be provided. This protective layer 25 can also serve as a drainage layer, or direct the fluid flow in a desired direction. An example of a suitable material for use as a protective layer 25 is an open polypropylene layer, but other materials can also be used. Preferably, the filter element also includes a core 20. The at least one primary coalescence medium 22 is arranged downstream of the filter core 20.

(23) The coalescence filter 10 preferably includes one or more internal support structures 26, which support integration of the filter element into one mechanical whole, which minimize the risk of mechanical deformation of the filter materials including the coalescence medium 22, under the influence of loading by the fluid, and protect same against the action of unexpected or momentary impact.

(24) Downstream of the coalescence medium 22 in the direction of the discharge, further a layer of a filter material may be provided which is capable of adsorbing oil vapors and vapors of other hydrocarbons, for example, a layer of activated carbon.

(25) Upstream with respect to the coalescence medium 22, for example, a particle filter may be provided for the removal of solid particles.

(26) The housing 24 may further include a drainage mechanism 32. A suitable drainage mechanism 32 may include automatic, semi-automatic or manually controlled valves, along which a contaminant which has been coalesced and retained and drained in the housing, may be removed.

(27) The coalescence filter 10 can further include optional components, which further improve the use and the yield of the filter. Filter head 12 can include, for instance, a status indicator 14, which gives an indication about the status of the coalescence filter, including the potential necessity for a periodic replacement. The status indicator 14 may be provided for directly or indirectly measuring the yield of the coalescence filter and may include an indicator providing indicia of the condition of the coalescence filter 10, by means of, for instance, a visual, auditory or electronic signal or a combination thereof. The indicator 14 may work pneumatically or electrically or according to any principle considered suitable by the skilled person.

(28) The invention further relates to a filter unit for the filtering of compressed gas, in particular a compressed air filter unit, which contains a coalescence filter as described above, and which further comprises a filter for removing water. The filter for removing water may be any filter known to the skilled person, for example, a refrigerant dryer, a dryer provided with a drying agent, a membrane dryer, or a combination of two or more of them. The compressed air filter unit may also contain a filter to remove solid particles.

(29) The invention also relates to a coalescence filter as described above, as part of a filter unit as described above.

(30) The invention further relates to a compressor for the compression of one or more gases, wherein the compressor is provided with an outlet for releasing one or more compressed gases, wherein the outlet is connected to a filter unit as described above for purification of the one or more gases. The invention relates in particular to an air compressor provided with an outlet for releasing compressed air, wherein the outlet is connected to a filter unit as described above.

(31) In a particular embodiment, the compressor is built into a housing, and the housing further includes a coalescence filter as described above, and one or more filters fib the removal of water, water vapor and water aerosol as described above. Preferably, the filter unit as described above and the water filter built into a separate housing, so that they are removed together in the separate housing and can be replaced.

(32) The invention also relates to a primary coalescence medium 22, as described above, as part of a compressed air filter unit 10 as described above.

(33) FIG. 3, in particular FIG. 3a, shows the pressure drop measured over a conventional filter system, with a first housing comprising a first coalescence filter made of an oleophilic filter material, and a second housing with a second coalescence filter made of an oleophobic filter material. Approximately half of the total pressure drop across both coalescence filters is due to the pressure drop caused by housing by the first and second housing. The oil contaminant present in the compressed air easily penetrates the oleophilic material in at the surface located upstream with respect to the supply, and moves easily through the oleophilic material. Upon reaching the surface located downstream with respect to the supply, capillary forces will tend to keep the oil in the filter material, so that a capillary pressure must be able to be built up before the coalesced oil will be capable of leaving the filter material. On entering the second filter the oil in the compressed air has to overcome a capillary pressure to penetrate the oleophobic filter material. Finally, the oil is moved through the oleophilic and the oleophobic filter medium and reorganization may take place.

(34) FIG. 3b shows the pressure drop measured over a compressed air filter unit according to the invention, wherein the primary coalescence medium contains a plurality of layers of an oleophilic material upstream with respect to the air inlet, and a plurality of layers of an oleophobic material downstream with respect to the air supply. The number of layers is the same as in FIG. 3. Because only one housing is provided, the pressure drop caused by the housing is almost halved when compared to the situation of FIG. 3. The dry pressure drop caused by the filter material remains the same as in FIG. 3, since also two filters are present. The pressure drop due to the channel pressure is the same as in FIG. 3, since the same number of layers are present. However, the pressure drop due to the capillary pressure is considerably lower: the film which is pushed out of the oleophilic medium, into the oleophobic medium, needs only be formed once and not twice as in the case in FIG. 3.

(35) FIG. 3c shows the pressure drop measured across a compressed air filter unit according to the invention, wherein the primary coalescence medium comprises a plurality of layers of an oleophilic material. The number of layers is higher than in FIGS. 3a and 3b. Because only one single housing is present, the pressure drop caused by the housing is almost halved compared with the situation in FIG. 3. The dry pressure drop caused by the filter material is higher as in FIGS. 3a and 3b because of the higher number of layers of filter medium. Also, to the pressure drop due to the channel pressure is somewhat higher as in FIGS. 3a and 3b due to the larger number of layers.

(36) The invention is further elucidated with reference to the examples below.

(37) The fibrous materials described below were tested as a coalescence filter for the purification of oil-polluted air, as described in ISO 125004, and ISO 8573-2. The initial oil concentration in the air was 10 mg/m.sup.3.

COMPARATIVE EXPERIMENTS A-B

(38) Compressed air with an oil concentration of 10 mg/m.sup.3 was passed through a pre-filter containing 6 layers of an oleophilic material. The air which had been purified by pre-filter was then passed through a second coalescence filter, containing 6 layers of an oleophobic material. The compressed air that left the filter contained 0.001 mg/m.sup.3 of oil.

(39) The total pressure drop across the pre-filter and the coalescence filter was 400 mbar.

Example 1

(40) Compressed air with an oil concentration of 10 mg/m.sup.3 was sent through one single coalescence filter, made up of 15 layers of an oleophilic material, which are cylindrically wound in such a way that successive layers are adjacently positioned. The pressure drop across the filter was 250 mbar. The compressed air that left the filter contained 0.001 mg/m.sup.3 of oil.

Example 2

(41) Compressed air with an oil concentration or 10 mg/m.sup.3 was controlled by only one coalescence filter, made up of six layers of an oleophilic material, which are cylindrically wound in such a way that successive layers are adjacently positioned, followed by 6 layers of an oleophobic material which are also wound in such a way that successive cylindrical layers adjacent are positioned. The pressure drop across the filter was 330 mbar. The compressed air that has left the filter contained 0.001 mg/m.sup.3 of oil.

(42) From the comparison of Examples 1 and 2 with Comparative Experiment A shows that the pressure drop across the housing may considerably be reduced by omitting one housing.

(43) Furthermore, it appears that the pressure drop across a coalescence filter with a larger layer thickness is less than the pressure drop formed when compressed air is guided over a successive pre-filter and coalescence filter as is shown by comparative experiment A.