Abstract:
The filter of the invention is a cartridge filter comprising a structure that can maintain a filter medium in an air stream to filter particulates to protect a gas turbine power system. The filter combines a mechanically adequate filter structure and an effective filter medium for to obtain a useful system.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 USC 119(e) from U.S. Provisional Application 61/061,408 filed on Jun. 13, 2008, to the extent appropriate. The entirety of the disclosure of U.S. Patent Application 61/061,408 is hereby incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to air filter systems. In certain applications it concerns air filters for use in the air intake stream of gas turbine systems. Methods of filtering to achieve such effect are also provided. 
       BACKGROUND 
       [0003]    Although the present disclosure may be applied in a variety of applications, it was developed for use with gas turbine filter systems. Gas turbine systems are useful in generating electricity. These types of systems are particularly convenient in that they can be constructed quickly; they are also desirable because they produce fewer harmful emissions than coal or oil based turbine systems. Gas turbines utilize air for combustion purposes. Due to the precision moving parts in these types of systems, the combustion air needs to be clean. To ensure clean air for combustion, air filters have been used to clean the air taken into the gas turbine system. 
         [0004]    Filters are used to purify the air intake for gas turbines. The filter media used for the purification, over time, will load with contaminant. Filters are used until they are plugged (contaminant blocks all flow through the media) or until a predetermined restriction level is reached. Both are associated with flow and the work necessary to move the flow. Either too little fluid is allowed to flow through, or too much work is required to move the desired flow due to the higher restriction. 
       SUMMARY 
       [0005]    The filter of the invention is a filter comprising a structure that can maintain a filter medium in an air stream to filter particulates to protect a gas turbine power system. The filter combines a mechanically adequate filter structure and an effective filter medium for to obtain a useful system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the invention and together with the description, serve to explain the principles of the invention. A brief description of the drawings is as follows: 
           [0007]      FIG. 1  is a schematic side elevational view of a first embodiment of an air intake for a gas turbine system with a plurality of filter elements, constructed in accordance with principles of this disclosure; 
           [0008]      FIG. 2  is a schematic side elevational view of second embodiment of an air intake for a gas turbine system with a plurality of filter elements, constructed in accordance with principles of this disclosure; 
           [0009]      FIG. 3  is a perspective view of one embodiment of a filter element usable in the air intake systems for gas turbines, constructed in accordance with principles of this disclosure; 
           [0010]      FIG. 4  is a perspective view of another embodiment of another element with the PTFE filter medium of the invention usable in gas turbine systems, constructed in accordance with principles of this disclosure; 
           [0011]      FIG. 5  is a top plan view of another filter element with the PTFE filter medium of the invention usable in an air intake for a gas turbine system, constructed in accordance with principles of this disclosure; 
           [0012]      FIG. 6  is a front elevational view of the element of  FIG. 5 ; 
           [0013]      FIG. 7  is a right side elevational view of the filter element of  FIG. 6 ; 
           [0014]      FIGS. 8-12  are schematic, cross-sectional views of further embodiments of filter elements usable in an air intake for a gas turbine system, constructed in accordance with principles of this disclosure; 
           [0015]      FIG. 13  is a perspective view of another embodiment of a filter element usable in an air intake for a gas turbine system, constructed in accordance with principles of this disclosure; and 
           [0016]      FIG. 14-18  are cross section views of the media of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    A durable, effective filter includes filtration media that is capable of being exposed to repeated exposures to particulate, water and other environmental conditions without degradation. A hydrophobic material that provides a barrier to particulate and liquid penetration is useful. Suitable filtration materials that can be used include expanded polytetrafluoroethylene (PTFE) membrane. 
         [0018]    An expanded PTFE filter is used with the present invention. Expanded PTFE is made in accordance with U.S. Pat. Nos. 3,953,566, 3,962,153, 4,096,227, and 4,187,390, all are specifically incorporated by reference herein for the disclosure of the polymer and its expansion. This material is formed by heating and rapidly expanding PTFE in at least one direction. When processed in this manner, the expanded PTFE forms a microscopic structure of polymeric nodes interconnected by fibrils. Space between the nodes and fibrils are micropores that allow the passage of air and water vapor, but are too small to permit passage of liquid water or even fine water droplets. The overall structure is a barrier to particulate. 
         [0019]    The expanded PTFE filter material for use with the present invention comprises a single layer of expanded PTFE membrane, the layer has a thickness greater than 0.1 mm or 0.1 to 1 mm thick. The final sheet ideally has the following properties. The pore size of greater than 0.1 micron to 10 micron, and a permeability range of 2 to 40 fpm. 
         [0020]    Pore size measurements may be made by ASTM f31 6-03 using a Capillary Flow Porometer (Model CFP 1500 AEXL from Porous Materials, Inc., Ithaca, N.Y.). 
         [0021]    The preferred expanded PTFE filter for use in the present invention provides a filtration efficiency of 60 to 99.9%, or more, at 0.3 microns. Ideally, the filter has an efficiency of 99.0 to 99.9% at 0.3 microns. 
         [0022]    Expanded PTFE materials are produced using processes that provide an expanded layer made of nodes of interconnecting fibrils, typically considered to be related to layer formation. The preferred fluorinated thermoplastic is polytetrafluoroethylene, however, other fluorinated materials can be used such as fluorinated ethylene propylene (FEP) and other fluorinated thermoplastic materials. Such materials include copolymers of tetrafluoroethylene, polychlorotrifluoroethylene and other fluorinated materials. Other suitable membranes include membrane materials made from polypropylene and polyethylene. 
         [0023]    The porous layer of expanded PTFE used in a fabric can be an expanded, porous PTFE layer that can satisfy the requirements of being waterproof while also being permeable to the flow of gases such as air and water vapor. Expanded porous PTFE layers are inherently hydrophobic and contain pores that resist the entry of liquid water even at substantial pressures or when rubbed or flexed, but readily allow the flow of gases. Unlike conventional PTFE layer fabric materials with sealed or closed pores that transport water through diffusion and are impermeable to bulk airflow, the permeability of the present invention is achieved by gaseous flow of air and water vapor through the layer to the clean side. 
         [0024]    The PTFE filter material is then layered or laminated to a porous backing material, such as a porous polyester nonwoven, paper, felt, sintered polypropelene, polyethylene, polyimide, polyamide, etc. In order to increase exposed surface area, the filter material can then be folded into multiple pleats and then installed in a “rippled” or “pleated” orientation into the filtration apparatus. The pleated material can be formed into a cylinder or “tube” and then bonded together such as through the use of an adhesive (urethane, hot-melt glue, etc.), or ultrasonic welding, for example. The structure typically comprises a PTFE layer that is substantially free of any agent that fills the pores created by stretching the PTFE into a stretched porous fabric. The hydrophobic PTFE layer, having small pore sizes, can act as a barrier to particulate and aerosols, or, using its hydrophobic nature, repel liquid agents. 
         [0025]    The filter can include an outer layer, either a woven or non-woven material that can act to protect the PTFE layer from damage, contamination or wear. Often the outer shell is combined with the PTFE layer using a variety of manufacturing techniques; however, such a combination is preferably manufactured using thermal bonding or adhesive lamination technology. Thermal bonding to the shell is the preferred method. In other multilayer constructions, the PTFE layer might be layered next to shell material, and not laminated. For example, the PTFE layer might be sewn together with the shell. 
         [0026]    The filter can further comprise a reactive layer that includes an absorbent or adsorbent material that is active in absorbing, adsorbing and/or deactivating gaseous chemical or biological warfare agents from the ambient atmosphere as it penetrates the fabric. A variety of active chemical treatment materials and active and/or passive adsorbents or absorbents can be present in such layer. 
       A. System, FIG. 1 
       [0027]    In  FIG. 1 , a schematic, cross-sectional, depiction of a gas turbine air intake system is depicted at  20 . The system  20  includes a chamber  21  having an air inlet side  22  and an air outlet side  23 . Air enters the chamber  21  through a plurality of vertically spaced inlet hoods  26  positioned along the air inlet side  22 . The inlet hoods  26 , although not required, function to protect internal filters of the system  20  from the effects of rain, snow and sun. Also, the inlet hoods  26  are configured such that air entering the inlet hoods  26  is first directed in an upward direction indicated by arrow  27 , and then deflected by deflector plates  28  in a downward direction indicated by arrow  29 . The initial upward movement of air causes some particulate material and moisture from the air stream to settle or accumulate on lower regions  30  of the inlet hoods  26 . The subsequent downward movement of air forces dust within the chamber  21  downward toward a dust collection hopper  32  located at the bottom of the chamber  21 . It should also be noted that air inlet side  22  may have vanes and other mechanical moisture separator inlets. 
         [0028]    The chamber  21  of the system  20  is divided into upstream and downstream volumes  34  and  36  by a tube sheet  38  (referred to also as partition  38 ). The upstream volume  34  generally represents the “dirty air section” of the air cleaner system  20 , while the downstream volume  36  generally represents the “clean air section” of the system  20 . The tubesheet  38  defines a plurality of apertures  40  for allowing air to flow from the upstream volume  34  to the downstream volume  36 . Each aperture  40  is covered by an air filter  42  or filter cartridge located in the upstream volume  34  of the chamber. The filters  42  have a filter medium comprising at least a PTFE layer as describe above or comprises a PTFE layer on a suitable support layer. The PTFE layer is on the upstream side of the medium. The filters  42  are arranged and configured such that air flowing from the upstream volume  34  to the downstream volume  36  passes through the filters  42  prior to passing through the apertures  40 . 
         [0029]    For the particular filter arrangement shown in  FIG. 1 , each air filter  42  includes a pair of filter elements. For example, each air filter  42  includes a cylindrical element  44  and, a somewhat truncated, conical, element  46 . Each truncated, conical element  46  includes one end having a major diameter and another end having a minor diameter. The cylindrical element  44  and the truncated, conical element  46  of each filter  42  are co-axially aligned and connected end-to-end with the minor diameter end of each conical element  46  being secured to one of the cylindrical elements  44  in a sealed manner. The major diameter end of each truncated, conical element  46  is secured to the partition  38  such that an annular seal is formed around its corresponding aperture  40 . Each filter  42  is generally co-axially aligned with respect to its corresponding aperture  40  and has a longitudinal axis that is generally horizontal. 
         [0030]    Other shapes and types of filter elements can be used, as described below. 
         [0031]    In general, during filtering, air is directed from the upstream volume  34  through the PTFE layer of the filter medium on air filters  42  into interior volumes  48  of the filters  42 . After being filtered, the air flows from the interior volumes  48  through the partition  38 , via apertures  40 , into the downstream clean air volume  36 . The clean air is then drawn out from the downstream volume  36  and into a gas turbine intake, not shown. 
         [0032]    In this embodiment, each aperture  40  of the partition  38  includes a pulse jet air cleaner  52  mounted in the downstream volume  36 . Periodically, the pulse jet air cleaner  52  is operated to direct a pulse jet of air backwardly through the associated air filter  42 , i.e. from the interior volume  48  of the filter element outwardly to shake or otherwise dislodge particular material trapped in or on the PTFE layer of filter media of the air filter  42 . The pulse jet air cleaners  52  can be sequentially operated from the top to the bottom of the chamber  21  to eventually direct the dust particulate material blown from the filters into the lower hopper  32 , for removal. In many air pulse jet cleaning applications, a useful air pressure is generally within the range of 60 to 1500 psi. A stream of liquid, such as water, soaps, degreasers, and solvents of any kind can also dislodge particulate from the PTFE layer alone or in conjunction with the reverse air. In many liquid jet applications, a useful liquid pressure is generally within the range of 0 to 120 psi. 
         [0033]    The properties of PTFE are such that captured particulate matter will not easily adhere to the PTFE layer in typical applications. By locating the PTFE layer on the upstream side of the filter medium, the layer is easily accessible for cleaning. As discussed previously, the cleaning of the PTFE layer can therefore be readily accomplished by various means such as air pulse cleaning or upstream washing with liquid or air. As a result, the useful service life of the filter medium can be significantly increased when the PTFE layer is located on the upstream side of the filter medium. Further, because a PTFE layer can be applied to virtually any size and style of filter medium, retrofit installations in existing systems can be readily accomplished without the need for extensive equipment modification. Thus, a gas turbine owner or operator can economically obtain a filter that has both a higher efficiency and better moisture removal characteristics than most typical filters. 
       B. System, FIG. 2 
       [0034]    In  FIG. 2 , a schematic, cross-sectional depiction of another embodiment of a gas turbine air intake system is depicted at  120 . In this embodiment, there are a plurality of filter elements  142  arranged vertically such that air to be filtered flows from a direction shown by arrows  143  upwardly, through the elements  142  and then into a clean air volume  144 . 
         [0035]    In this embodiment, because of the orientation of the elements  142  and the direction of air flow, if there was any moisture, the moisture will flow by gravity downwardly along the elements  142  to a position underneath the system  120 . In the embodiment shown in  FIG. 2 , each of the elements  142  is constructed of a cylinder of pleated media  146 . The pleats in the pleated media  146  run vertically with the direction of the orientation of the elements  142 . Therefore, any water or other types of moisture that contacts the media  146  will drain down along the pleats due to gravity.  FIG. 2  also depicts a reverse flow pulse cleaning system  150 . The reverse flow pulse cleaning system  150  emits a pulse of compressed gas periodically, such that the pulse of air will go from the downstream side through the media  146  to the upstream side. This helps to knock loose any particulate or other types of debris from the upstream side of the filter media, and periodically cleans the elements. 
         [0036]    In other embodiments, instead of using a reverse pulse cleaning system, the elements can be cleaned from the upstream side. In such systems, the elements can be sprayed with a jet of liquid or a jet of gas. In such systems, the upstream side of the filter media is at least partially cleaned of debris and particulate matter due to the spray or jet of liquid or air washing off the upstream side of the media. 
       C. Example Media Constructions, FIGS. 3-13 
       [0037]      FIGS. 3-13  depict various embodiments of filter elements using the PTFE medium that are usable in gas turbine air intake systems, such as systems  20 ,  120  characterized above. 
         [0038]    In  FIG. 3 , a pleated panel element  200  is shown in perspective view. The panel element  200  includes a media pack  202  of pleated media  204 . The pleated media  204  can comprise the filter medium having a layer of a support or substrate combined with a layer of the PTFE. In the embodiment shown, the media pack  202  is held within a frame  206 , with the examples shown being a rectangular frame  206 . The frame  206  typically will include a gasket (not shown) for permitting the element  200  to be sealed against a tube sheet, such as tube sheet  38 , in the intake system  20 ,  120 . In  FIG. 3 , the upstream side of the pleated media  204  with the exterior PTFE layer is shown at  205  on the same side as the incoming air shown at arrow  207 . The cleaned air is shown at arrow  208 , and emerges from the media  204  from a downstream side of the media. 
         [0039]      FIG. 4 , depicts a perspective view of pocket filter element  210 . The pocket element  210  includes a layer of filter media  212  that can comprise the filter medium having a layer of a support or substrate combined with a layer of the PTFE. In the embodiment shown, the pocket element  210  includes a plurality of panel pairs  213 ,  214 , with each panel pair  213 ,  214  forming a V-like shape. The PTFE media  212  is secured to a frame  216 . The frame  216  typically will carry a gasket for allowing the pocket element  210  to be sealed against a tube sheet, such as tube sheet  38 . In such an arrangement, the media  212  has an upstream PTFE side  217 , which is inside of the V&#39;s, and a downstream side  218 , which is on the outside of the V&#39;s. 
         [0040]      FIGS. 5-7  depict views of a mini-pleat or multi-V style element  220 . The element  220  includes a frame  222  holding a filter media pack  224  ( FIG. 7 ). The media pack  224  comprises a plurality of mini-pleats. The mini-pleats are arranged in a panel  226 , and the element  220  includes a plurality of mini-pleated panel pairs  227 ,  228  ( FIG. 5 ) of the media of the invention, each forming a V-like shape. In  FIG. 5 , the panel pairs  227 ,  228  are shown in hidden lines, since the top portion of the frame  222  obstructs the view of the panel pairs  227 ,  228 . The frame  222  defines a plurality of dirty air inlets  229  ( FIG. 6 ), which leads to the inside part of each V of each pleated panel pair  227 ,  228 . Each pleated panel pair  227 ,  228  includes an upstream side  230 , which is on the inside of the V, and a downstream side  231 , which is on the outside of the V. 
         [0041]      FIGS. 8-13  show various embodiments of tubular, pleated filter elements.  FIG. 8  shows a cylindrical pleated element  240  having a media pack  242  that can comprise the filter medium having a layer of a support or substrate combined with a layer of the PTFE with an upstream side  244  and a downstream side  246 . The downstream side  246  is inside of the interior volume of the element  240 . 
         [0042]      FIG. 9  depicts two of the cylindrical elements  240  axially aligned, such that they are stacked end to end. 
         [0043]      FIG. 10  depicts the arrangement shown in the example embodiment of  FIG. 1 . In  FIG. 10 , cylindrical element  240  is axially aligned with a partially conical element  250 . The partially conical element  250  is a tubular element having a media pack  252  that can comprise the filter medium having a layer of a support or substrate combined with a layer of the PTFE. The element has an upstream side  254  and a downstream side  256 . The conical element  250  has a first end  258  having a diameter that matches the diameter of the cylindrical element  240 . The conical element  250  includes a second end  260  having a diameter that is larger than the diameter of the first end  258 , thus forming the partial cone. 
         [0044]      FIG. 11  depicts two partially conical elements  270 ,  280  arranged axially, and engaged end to end. Each of the elements  270  includes a media pack  272 ,  282  forming a tube that can comprise the filter medium having a layer of a support or substrate combined with a layer of the PTFE. The media packs  272 ,  282  each has an upstream side  274 ,  284  and a downstream side  276 ,  286 . 
         [0045]      FIG. 12  shows a single conical element  270 . The element  270  can be used alone installed in the intake system for a gas turbine without being installed in element pairs, as shown in  FIGS. 10 and 11 . 
         [0046]      FIG. 13  is another embodiment of a filter element  290  having media pack  292  that can comprise the filter medium having a layer of a support or substrate combined with a layer of the PTFE. The media pack  292  is pleated and forms a tubular shape. In this embodiment, the tubular shape is an oval shape, and in one example embodiment, a ratio of the short axis compared to the long axis of the oval is about 0.7-0.9. The media  292  includes an upstream side  294  and a downstream side  296 . 
         [0047]    It should be understood that each of the filter elements characterized above and depicted in  FIGS. 3-13  can be flat media and/or operably installed in an intake or ventilation system for a gas turbine, such as system  20  or system  120  of  FIGS. 1 and 2 . 
         [0048]    In operation, air to be filtered will be directed through the upstream side, typically the PTFE layer and then through the downstream side of filter media in the respective filter element typically installed in a tube sheet. The filter media will remove at least some of the particulate from the air stream. After passing through the downstream side of the media, the filtered air is then directed to the gas turbine. 
         [0049]    The filter elements can be cleaned. In operation, a method of cleaning a filter element for a gas turbine air intake system includes removing at least some particulate material from the upstream side of the media pack of the filter element operably installed in the tube sheet of the gas turbine air intake system. The step of removing can include pulsing a jet of compressed gas from the downstream side to the upstream side. Alternatively, the step of removing can include spraying the upstream side with a jet of air or liquid. Alternatively, the cleaning step can use a reverse air step and a liquid stream, serially or in combination. 
       D. Example Media Formulations 
       [0050]    This invention provides improved PTFE filtration media and pulse cleanable filter elements thereof, to protect gas turbine systems from the deleterious effects of salt, moisture and hydrocarbons at the intake air of gas turbine systems. Furthermore, other outdoor filtration applications include the protection of electronic enclosures at cell base towers can benefits from the improved media technology. PTFE filtration layer is provided on a substrate. The substrate can be of any kind that can be laminated or otherwise combined with the PTFE layer. The substrate can have properties beyond its service as a surface for the PTFE. These properties can include coalescing, depth loading etc. It is also important to recognize that the substrate layer provides the necessary anchoring surface for not only the PTFE layer but also for any additional nanofiber media layer such as “electroblown” nanofiber layer/hybrid membrane (example DuPont HMT). The surface of such PTFE laminate media may be treated with oleophobic treatment to repel hydrocarbons in the air. 
       Example 1 
       [0051]      FIGS. 14 and 18  show a cross section of one embodiment of the media of the invention. In  FIGS. 14 and 18 , the media  150  includes a membrane layer, referred to as PTFE layer  152 . Media  150  also includes a substrate layer  153  for supporting PTFE layer  152 , and optionally for further filtering the air stream. Substrate layer  153  may be wet laid or air laid and may be comprised of spunbond media. On  FIG. 14  specifically, media  150  also includes first oleophobic coating  151  on the membrane layer  152 . Such oleophobic coatings can comprise any coating material that has substantial hydrophobicity. Such materials are often non-hydrophilic but repel oil and other organic substances. Such coatings are common and are well known to one of ordinary skill in the art. The oleophobic coating  151  covers the PTFE layer  152 . 
         [0052]      FIG. 15  shows a electron photomicrograph of the expanded PTFE layer of the invention. In the figure are fibers  155 . 
         [0053]    The final laminate will provide resistance to salt, water and hydrocarbons in the air. The minimum efficiency of the media will be Merv 14 or F9 (EN1822 standard). Also, the finished cartridge element using this type of media will have similar initial restrictions at same air flow as current media being used on existing system. This media further can be designed to have efficiency higher than HEPA and H12-H-13 (EN1822, MPP efficiency 99.95% @ 0.08 micron). 
       Example 2 
       [0054]    The media construction in  FIG. 16  is similar to Example #1, except that it will have another media downstream of the PTFE filtration layer. Similarly,  FIG. 16  shows a preferred media embodiment of the invention. Similarly, media layer  160  is a multilayer structure. The media comprises an oleophobic layer  151 , a PTFE layer  152 , a conventional melt blown substrate  153  and a hybrid membrane layer  154 . The downstream layer  154  can be another layer of membrane, more specifically but not limited to electroblown nanofiber membrane. A hybrid membrane layer is made by using a spinning process to create a membrane-like nonwoven sheet structure of continuous sub-micron polymeric filaments between 200-600 nanometers. Hybrid membranes are referred to as a nanofiber because the filtration industry, our predominant end use market, broadly uses the term “nanofiber” to describe any fiber between the size of 100 nm to about 800 nm. This is important because especially in environments with high humidity and abundance of salt particles, i.e. marine environments such as off shore or seaside environments, it is necessary to protect the critical equipment downstream of the filtration arrangement from the deleterious impact of nano-sized airborne salt that can be generated by wave breaking and is carried by the wind, which can in turn deliquesce or change physical state with varying humidity conditions and penetrate through the filtration arrangement and foul the equipment downstream. It is worth noting here that the particulates that can change physical state may not be limited to salt. It can include other forms of particulate matter. Also, it is important to recognize that conditions suitable for the particulate to change physical state can be realized in environments beyond marine environments described above. Certain localities or industrial processes can result in the right environmental conditions for the salt or other particulate types to deliquesce and penetration through the filter arrangement. 
         [0055]    The salt particles and other fine particles escaping through PTFE layer will have added protection to be captured in downstream media there by assuring 100% capture of such particles to prevent any blade erosion. 
       Example 3 
       [0056]    In this example, a wet laid media (See  FIG. 17 ) is used on the down stream side of the composite.  FIG. 17  shows a version of the media of the invention using a wet layer substrate material. In  FIG. 17  a media  170  is shown. The media comprises a wet laid substrate  156 , a conventional cellulosic or air layer substrate  153 , the PTFE layer  152  and an external upstream oleophobic layer  151 . The wet laid media can have a gradient density if needed but it is essentially intended to provide a depth loading structure and is used to increase the efficiency of the media by capturing any particles escaping through upstream filtration media. A suitable wet laid media that can be used in this application is Donaldson&#39;s Synteq XP technology. Donaldson&#39;s U.S. Pat. No. 7,314,497 which is incorporated, especially herein for its disclosure of a media layer that can be made by combining bicomponent fiber with other fiber sources including other filtration fibers, binder fibers, reinforcing fibers, reactive fibers and other components.