Patent Publication Number: US-2007107396-A1

Title: Method and apparatus for a gas-liquid separator

Description:
RELATED APPLICATIONS  
      This application is a continuation-in-part of U.S. patent application Ser. No. 11/322,777, filed Dec. 30, 2005, entitled “Process for Extruding a Porous Substrate”, which claims priority to U.S. provisional patent application Ser. No. 60/737,237, filed Nov. 16, 2005, and entitled “System for Extruding a Porous Substrate”; both of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND  
      The present invention relates generally to a device for separating a liquid from a gas, and in one example, to an air-oil separator using a ceramic honeycomb structure for effecting the separation.  
     DESCRIPTION OF RELATED ART  
      A liquid-gas separator is used in many industrial, commercial, and residential applications. Other applications may exist in other fields such as in military applications. A liquid gas separator is typically attached to an exhaust line for removing a liquid content from a gas. In one particular example, a gas liquid separator may be an air oil separator. An air oil separator may advantageously be used on internal combustion engines for removing oil from the crank case vent system, or may be used on other industrial equipment such as compressors for removing oil mist from a compressed air stream. In the case of air-oil filtration system for compressors, a coalescence filter can be used as a first stage filter with a trapping filter as a second stage. Smaller droplets, such as fine mist of diameters from 10 nm -10 microns, are trapped onto the first stage filter element, where they coalesce to form larger droplets and then any large droplets that escape from the first stage filter are trapped with a second stage filter.  
      To facilitate description of the liquid gas separator, this application will describe in detail an air oil separator, although other implementations may be used. In one example, an air oil separator is used on internal combustion engines for removing oil from a crank case ventilation system. In an internal combustion engine, the exhaust from the crank case vent may account for 10% to 40% of particulate exhaust or other VOC or noxious emission. Accordingly, it is important for environmental considerations to effectively remove oil or other particular matter from crank case vent exhausts for reducing oil consumption, for environmental concerns as well as for performance and durability of other engine components, such as turbo and inter-coolers. In engine design, two considerations drive the design and implementation of the crank case vents filters. First, the crank case vent filter must be able to sufficiently clean the exhaust according to environmental requirements. This is especially necessary for open crank case filters where the crank case emissions are vented to the environment, however, in the case of closed crank case ventilation, trapping of oil and other debris, including soot and fine dust, is equally important to prevent engine component wear downstream. Second, the filter needs to be as small as possible, as space is at a premium in the design of current engine systems. However, these design considerations are in conflict. For example, a filter system which removes a large quantity of oil and particulate may have to be large (in order to last a long enough period before needing a replacement or regeneration) , or if the filter is made compact, it may generate an unacceptable back pressure to the engine or may not trap sufficiently.  
      In current designs, a crank case filter may be a mesh filter made out of metal gauze. Such a filter is quite coarse, and relatively ineffective for removal of oil or particulate matter. Due to the ineffectiveness of such mesh filters, newer filters have been developed using a fiberglass filter. Here, the fiberglass is a term used to broadly classify filters made of fiber-based papers, where the fibers can constitute a variety of plastic, polymeric, ceramic or metal compositions. Sometimes these fiberglass filters are complimented by a secondary stage filter which may be made of a metal wire mesh. These fiberglass filters have fiberglass matting, in paper form wrapped multiple times around a central cylinder, for coalescing oil, as well as for trapping some particulate matter. In some cases, very thin diameter fibers are deployed, such as nano-fibers (made of fibers with diameters from 50 nm to 1000 nm). However, these nano-fiber filters are typically expensive, present a risk of secondary emissions of nanofiber particles, and produce higher backpressures. Consequently, standard fiberglass filters (wrapped or pleated paper honeycomb) must be relatively large to adequately filter exhaust gas, and are subject to easy clogging and high backpressures. Developments are occurring in the field of new fiber chemistries and fiber diameters, in order to better trap and coalesce the liquid media in a fluid stream, but the basic geometry, form, and structure of the filters remains a problem. However, none of the fibrous systems in the mat, i.e., paper wrapped around a central spindle, or pleated in the form of a honeycomb, or pleated in the form of a donut design, have provided adequate filtration in the desired filter size range. Accordingly, the industry has attempted to use non-fiber based techniques to separate air and oil from an admixture of the components. An example of such a technique is electrostatic precipitation. An electrostatic precipitator requires external power for separating oil from the air, and provides acceptable filtration and oil removal results. Further, electrostatic precipitator may be made very small, so is advantageously used in space-constrained designs. However, the electrostatic precipitator is very expensive, and requires external power and external control systems, complicating the integration of electrostatic precipitator into existing engine systems. Other exotic systems, such as centrifuge systems, may also be used in highly specialized applications, but do not provide cost-effective filtration for mass production. Accordingly, all known technologies suffer either from inadequate filtration, excessive back pressure, excessive size, or excessive of cost. Therefore, there exists a need for a cost-effective filter that may be compactly implemented, and still provide effective and efficient air oil separation.  
     SUMMARY OF THE INVENTION  
      The present invention provides an inexpensive and efficient filter for the separation of gas and oil to trap and coalesce liquid and particulate matter in a fluid stream. The filter of the present invention is composed of bonded fibers in a porous ceramic substrate housed within a housing. The housing provides an inlet for a mixture of gas and liquid, and an outlet for the gas that has been filtered by the porous ceramic substrate. A liquid collection area receives the liquid that has been coalesced from within the porous substrate. In an embodiment of the invention, the porous substrate has channels that form a honeycomb configuration. The honeycomb substrate can be provided in a wall-flow configuration with a set of inlet channels and outlet channels arranged in an alternating pattern.  
      In a more specific example, the air-oil separator of the present invention is used in a crank case ventilation system. In this embodiment, the porous ceramic substrate is mounted in a housing that is connected to a crank case vent on an engine. The system has an inlet connecting the crank case vent to the filter with an exhaust line for the filtered vent gas and an oil return line for the oil that has been coalesced and collected by the filter. In another embodiment, a second stage filter can be used to collect coalesced oil droplets that pass through the filter into the exhaust stream. These escaped particles can be easily trapped and collected by conventional pleated paper, or fiberglass filters.  
      These and other features of the present invention will become apparent from a reading of the following description, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The drawings constitute a part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.  
       FIG. 1  is a diagram of an air-oil separator in accordance with the present invention.  
       FIG. 2  is a diagram of a honeycomb substrate for an air-oil separator in accordance with the present invention.  
       FIG. 3  is a diagram of a ventilation system using an air-oil separator in accordance with the present invention.  
       FIG. 4  is a flowchart of a process of using of an air-oil separator in accordance with the present invention.  
       FIG. 5  is a flowchart of a process of using of an air-oil separator in accordance with the present invention.  
       FIG. 6  is an enlarged illustration of an oil coalescence using an air-oil separator in accordance with the present invention.  
       FIG. 7  is a diagram of a ventilation system using an air-oil separator in accordance with the present invention.  
       FIG. 8  is a diagram of a ventilation system using an air-oil separator in accordance with the present invention.  
       FIG. 9  is a diagram of an air-oil separator in accordance with the present invention.  
       FIG. 10  is a diagram of an air compressor system using an air-oil separator in accordance with the present invention.  
       FIG. 11  is a flowchart of a process using an air compressor system having an air-oil separator in accordance with the present invention.  
       FIG. 12  is a diagram showing the alumina-silica phase relationship. 
    
    
     DETAILED DESCRIPTION  
      Detailed descriptions of examples of the invention are provided herein. It is to be understood, however, that the present invention may be exemplified in various forms. Therefore, the specific details disclosed herein are not to be interpreted as limiting, but rather as a representative basis for teaching one skilled in the art how to employ the present invention in virtually any detailed system, structure, or manner.  
      Referring now to  FIG. 1 , a gas-liquid filter is illustrated. The gas-liquid filter is illustrated as a crank case ventilation filter  10  for separating oil from a gas exhausted from the crank case of an engine. One skilled in the art will appreciate that while the illustrative embodiment of  FIG. 1  is directed toward a crank case ventilation of an internal combustion engine, such as a diesel or gasoline engine, the filter  10  can be used for a variety of gas-liquid separation applications, such as, for example, in an air compressor. Crank case ventilation filter  10  is intended to be installed with an internal combustion engine, and more particularly connected to the crank case ventilation output port. Filter  10  has a can  12  for holding the filter substrate  21  and for mechanically positioning the filter  10 . The can  12  has an air oil admixture inlet  14  for receiving a mixture of exhaust air and oil being exhausted from the crank case event. As used herein, the term “admixture” generally describes a mixture of gases, solids, and/or liquids. It is understood that the oil may also contain other impurities such as ash particulates, unburned hydrocarbons, soot particles, dust particles, etc. The air oil admixture is received into an inlet manifold  16  which distributes and routes the air oil admixture into a set of input channels  23 . It will be appreciated that more complex manifold arrangements may be used. The input channels are formed in a porous substrate  21 . The porous substrate  21  may, in one example, be formed in the shape of a honeycomb. The honeycomb porous substrate may be a ceramic fiber substrate as described in co-pending patent application Ser. No. 11/322,777, herein incorporated by reference. It will be appreciated that other porous honeycomb filters may be used, including those extruded as a single monolithic substrate, or segmented by the fabrication of a plurality of honeycomb substrate sections into a single substrate.  
      In an exemplary embodiment the honeycomb porous substrate is composed of mullite fibers having a porosity of about 85%. Mullite is the mineralogical name given to the only chemically stable intermediate phase in the Al 2 O 3  —SiO 2  system. The natural mineral is rare, naturally occurring on the Isle of Mull off the west coast of Scotland. Mullite is commonly denoted as 3Al 2 O 3 .2SiO 2 (i.e., 60 mol % Al 2 O 3  and 40 mol % SiO 2 ), though mullite fibers, in this exemplary embodiment, can include a metastable phase of 2Al 2 O 3 .SiO 2  or compositions from 60 mol % to 67 mol % alumina. An alumina-silica phase diagram showing the mullite composition is shown as  FIG. 12 .  
      The porosity of the porous substrate can range between 50% and 85% depending upon the selection of fiber characteristics and additives. In other embodiments, the material of the porous substrate can be fiberglass (i.e., silica-based material). Alternative fiber compositions, including alumina-zirconia-silica can alternatively be used. The fibers can have diameters that characterize the fibers as microfibers, with diameter larger than 0.2 microns but not larger than 10 microns. Alternatively, the fiber can be characterized as nanofibers, with a diameter less than about 0.2 micron. In an embodiment, the fiber diameter is in the range of 0.05 microns to about 100 microns. In another embodiment, the fiber diameter is 1 micron to about 25 microns. In still other embodiments, the porous honeycomb substrate can be composed of a mixture of fiber materials and/or of varying diameters, to form a composite porous substrate. The two fiber materials and/or fiber materials having varying diameters can be mixed or they can be layered as a gradient substrate. Substrates or portions of substrates composed of nanofibers have a high trapping efficiency for the smallest drops, which result in effective coalescing. However, a substrate composed essentially of nanofibers may exceed backpressure requirements. By mixing the fibers of varying materials and/or diameters, or by layering the two types of fibers, the nanofiber portion performs effective coalescing, while the larger diameter fibers or material traps larger particles, or coalesced material, without increasing backpressure in the flow or stream.  
      The admixture is received in to the set of input channels, and the gas and oil mixture is forced through walls in the channels. In this way, air from an input channel  23  is routed into an exhaust channel  25 . As the air oil mixture passes through the porous walls, oil is trapped onto the fibers in the filter, coalescing from small droplets and mist to form larger droplets in the wall  33  and falls as oil droplets  39  into an oil collection area  41 . As gas passes through the wall, particulate matter in the gas is also captured in the porous ceramic wall  32 . The filtered gas then exits the open channels  43  into an output manifold.  27 , and passes through an air return line  29 . The air return line may couple to a turbocharger, to an air input for the engine, or may be exhausted to the atmosphere. In another example, the air exit couples to a second stage filter. This may be advantageous as a single air oil filter may not sufficiently remove enough oil or particulate matter from the air oil admixture. It will be appreciated that multiple stages may be used. Larger droplets of oil that may escape the filter (and thus, not fall below in the oil collection area  41 ) can be trapped by means of a secondary stage filter. At this stage, since the particles have already coalesced and are larger in diameter, conventional methods for trapping can be applied through the use of a secondary fibrous honeycomb filter, or any other type of existing coalescing filters (such as fiber mesh filter, wire mesh filters, pleated paper filters). To form a honeycomb pattern, a plug  44  is provided at alternating input and output channels for the porous substrate  21 . This alternate arrangement of plugging creates a set of input channels  21  where and air oil mixture is received, and all gas is forced through a channel wall to be received in an adjacent exhaust channel  25 . This honeycomb construction is typically referred to as a wall flow filter. It will be appreciated that several modifications may be made to the positioning of the plugs, sizing up the channels, and arrangements of the honeycomb, as well as shape of channels, thickness of walls, design and arrangement of the checkerboard pattern, arrangement of channels, and overall geometry of the filter.  
      The honeycomb configuration of the porous substrate provides high surface area for filtration to facilitate coalescence of the admixture stream that improves the effective utilization of filter volume. In this honeycomb configuration, the porous substrate can provide increased effective filtration with a minimum overall filter size. Further, the honeycomb configuration of the porous substrate provides sufficient strength in the filtration material to avoid the telescoping phenomenon seen in conventional pleated paper honeycomb substrates. Accordingly, the honeycomb configuration of the porous substrate is a robust and effective mechanism for filtration and coalescence of admixture streams.  
      Advantageously, air oil separator  10  efficiently removes oil from the air, and also filters particulate matter from the exhaust gas. Due to the highly effective and efficient removal of oil and particulate matter, the filter may be made relatively small, thereby saving valuable space in engine design. Further, it has been found that filter  10  may be constructed to provide acceptably low back pressures, even when compactly arranged.  
      Referring now to  FIG. 2 , an air oil filter  50  is illustrated. Air oil filter  50  has a housing  51  holding a porous substrate arranged in a honeycomb pattern  55 . The porous substrate, in one example, may be a ceramic porous substrate comprising bonded ceramic fibers. The filter  50  has an input end  53  for receiving an air oil admixture, and an exhaust end  54  for exhausting a filtered gas. It will be understood that an oil collection area may be positioned at the input end  53 , or in an alternate position, and that design variations, such as the flow direction and inlet position, as well as the location and position of the housing  51 , can be made without departing from the scope of the invention. The honeycomb  55  has alternating open channels  57  and closed channels having plugs  59 . In this way, the air oil admixture entering any open channel will pass through a wall such as wall  61  as the air moves through the filter. The wall  61  acts to both coalesce oil, and to trap particulate matter from the gas.  
      Referring now to  FIG. 3 , a closed crank case ventilation system  100  is illustrated. Closed crank case ventilation system  100  has an engine  102 . Internal combustion engine  102  will not be described in detail, but major components relevant to the filtration system will be described. Engine  102  has a crank case  103  having a set of pistons  105 . The pistons are sealed  107  from the crank case  103 , however the seals provide an imperfect seal, so the higher-pressure gas from the crank case may escape into the crank case. The crank case  103  also contains a pool of oil  113 . The oil  113  is used for lubricating the engine, including the piston and drive mechanism for the engine. The engine gases that escape into the low-pressure area  111  are exhausted through the crank case exhaust line  115 . The exhaust line couples to a crank case filter  120 , which may be similar to crank case filter  10  described with reference to  FIG. 1 . Crank case filter  120  is preferably a honeycomb structure having porous walls. These porous walls may be constructed using bonded ceramic fibrous material, with the structure of the wall being defined by ceramic bonds. The exhaust line  115  receives a mixture of exhaust gas and oil, which passes through the honeycomb substrate  121 . Oil coalesces in the walls of the honeycomb substrate, and is collected and returned through oil return line  122  to the crank case  103 . Air continues through the honeycomb substrate  121 , where particulate matter is also captured either on the surface of the walls or inside the thickness of the walls. The air continues through an air return line  121  and may be received into, for example, a turbocharger  125 . It will be appreciated the other connections and components may be used in the construction of a closed crank case ventilation system. To ensure the flow of gas in an intended direction, it is presumed that the inlet side will have slightly higher pressure than the outlet side.  
      Referring now to  FIG. 4 , a process for using a crank case filter is illustrated. Process  150  starts with a filter receiving an air oil admixture from a crank case vent as shown in block  152 . This air oil admixture may include gases, air, soot, particles, and oil. The admixture is routed to input channels of a honeycomb filter as shown in block  154 . The admixture is passed through walls as shown in block  156 , thereby providing a wall flow filtering. Oil is coalesced as the admixture passes through the honeycomb as shown in block  159 , while soot and other particular matter is captured as shown in block  161 . Depending upon the type of soot or particular matter, the particulate matter may be captured through impaction, diffusion, or depth filtering. In some cases, another stage of filtering may be provided as shown in block  165 . This secondary filtration may include, for example, another air oil filter separator, or may include additional filtering specific for the oil or gas. In another example, the primary or the secondary or both filters may be coated with catalyst materials for conversion of species entrained in the fluid flow. The oil is returned to the crank case as shown in block  167 , and the gases are returned to the engine as shown in block  171 . In this way, process  150  operates as a closed crank case system.  
      Referring now to  FIG. 5 , another air oil process is illustrated. Process  200  has a crank case filter receiving an air oil admixture from a crank case as shown in block  202 . This gas admixture may include air, exhaust gases, soot, particles, and oil. The admixture is routed to the inlet channels of a honeycomb filter as shown in block  204 . The honeycomb filter, as previously described, provides for wall flow filtering as shown in block  206 . The wall flow filtering acts to coalesce the oil as shown in block  209 . The coalesced oil is returned to the crank case as shown in block  217 . The gases are passed through the honeycomb wall, which acts to trap particulates  211  as previously described. A low temperature catalyst may also be provided of the filter as shown in block  215 . This low temperature catalyst acts to convert noxious components in the gas to less harmful and less polluting gases. For example, a low temperature catalyst may be provided for converting carbon monoxide to carbon dioxide. The low temperature catalyst may also act to reduce the VOC emissions, as well as provided for NOx reduction. The catalyzed gases may then be returned to the engine as shown in block  219 . Alternatively a secondary device, such as microwave discharge, plasma or external heating may also be used to burnoff any volatile or refractory material so the filter can be cleaned via regeneration to the highest possible extent.  
      Referring now to  FIG. 6 , additional detail is illustrated for a crank case filter. Crank case filter portion  250  shows a honeycomb substrate  252  having an inlet channel  456  that receives an admixture  458 . The admixture contains a mixture of air and oil. The admixture is received into inlet channel  456  and passes through one or more honeycomb walls. The honeycomb wall is shown with an enlarged area  254 . As illustrated, the substrate wall has overlapping and bonded fibers, which may be ceramic fibers. The ceramic fibers are arranged and bonded to construct a rigid filtration media, which is porous to the passage of air, but is able to capture particulate and soot, as well as coalesce oil. The structure of the overlapping and bonded fibers creates small interconnected spaces, or pores, that typically range between 1 and 30 microns, depending on the diameter of the fiber. Sub-micron spaces can be attained through the use of nano-fiber sizes. Further, as the air oil admixture passes through the filter, the oil mist  475  contacts fibers, and begins to coalesce in the pores  465  of the channel walls. Through the coalescing process, oil coalesces into progressively larger drops, until large enough oil drops  475  are created that gravity or other mechanical force causes the oil to move to an oil collection area. In this way, oil may be efficiently removed from an air oil admixture, while enabling air to pass through the honeycomb wall without undue back pressure. It will be appreciated that the thickness of the cell wall, porosity of the cell wall, and sizes and shapes of pores may be adjusted for different removal of requirements.  
      Referring now to  FIG. 7 , another closed crank case filter system is illustrated. Crank case system  300  has an engine  302  which includes a crank case  303 . Pistons  305  have seals to isolate a high pressure area  310  from a low pressure area  311 . Although seals  307  provided some isolation between high-pressure area  310  and low pressure area  311 , some exhaust gases from high-pressure area  310  escapes into low pressure area  311 . Gases that escape into low pressure area  311  mix with oil  313  to form an admixture of air and oil. This air oil admixture is exhausted to exhaust line  315  and received into crank case filter  320 . Crank case filter  320  may be similar to filter  10  described with reference to  FIG. 1 . Crank case filter  320  has a honeycomb substrate  321  as described earlier. As the air oil admixture passes through crank case filter  320 , oil is coalesced and returned to the crank case  303  through oil return line  322 . Air exiting crank case filter  320  may still contain some amount of oil or particulate matter. The next stage filter  322  is used to further clean the exhaust gas. In one example, the second stage filter  322  is another crank case filter as described with reference to  FIG. 1 . The diameter of the fibers, the chemical composition of the fibers, the cell density of the substrate, wall thickness, cellular structure, porosity, permeability, or pore size of filter  322 , as well as overall dimensions of the filter may be adjusted to trap different size particles, or coalesce a finer mist of oil. For example, the honeycomb substrate  321  of the crank case filter  320  can be composed of mullite fibers, and the second stage filter  320  can be composed of fiberglass. The air exhausted from the next stage filter  322  is returned to the engine  302 . In one example, the air is simply returned to an air intake  325 , although the air may be returned to a turbocharger, for example.  
      Referring now to  FIG. 8 , an open crank case filter system  350  is illustrated. System  350  has an engine  352  having a crank case, high-pressure area, low-pressure area, piston, and seals as previously described. An air oil admixture is exhausted through an exhaust line into a honeycomb substrate. The honeycomb substrate may be, for example, a filter  10  as described with reference to  FIG. 1 . Air passing through the honeycomb substrate has its oil mist coalesced into larger drops, which are collected and returned to the crank case. Particulate matter, such as soot, is also trapped in the honeycomb walls. The air is returned to the atmosphere through an air exit  370 . Although less environmentally friendly than previously described closed systems, the open system may be used in some applications, such as for small engines used in gardening equipment.  
       FIG. 9  shows another application for an oil-gas separator. In  FIG. 9 , the air-oil separator  400  is used as part of an air compression system. Such systems are typically used in industrial applications for generating compressed air, for example, to operate pneumatic equipment. A compressor is a device used to take air at atmospheric pressure and increase its pressure for pneumatic purposes. In this process, the compression system injects a fine mist of oil into the compressed air. This compressed air, if the oil were not removed, might damage pneumatic equipment. Therefore, it is important to remove oil from the compressed air. Trapping the oil and recycling it also reduces the oil loss and extends the time before re-filling of oil by operator is required. The air oil separator  400  has an air oil admixture inlet  414  for receiving compressed air. The compressed air has a mixture of air and oil, which is received into the input manifold  416 . The compressed air is received into the honeycomb  418 , and more particularly into the input channels  423 . The air oil admixture is passed through honeycomb walls into the exhaust channels  425 . Input channels  423  are separated from exhaust channels  425  using plugs  444 . In this way, a wall flow filtering system is designed. As the air oil admixture passes through the honeycomb walls, the oil coalesces in the porous substrate  421  of the wall, causing oil droplets  439  to fall into the oil return area and be returned through an oil return line  441 . The compressed air also passes through the wall, where particulate matter  432  may be captured on the surface of the wall or inside the thickness of the wall. The clean air exits output channel  443  and is received into output  427 . The outlook manifold  427  then couples to attached pneumatic equipment through its output  429 . Advantageously, the air oil separator  400  is able to efficiently remove particulate matter and oil from compressed pneumatic air, while causing little reduction in air pressure. Further, the ceramic honeycomb structure provides high efficiency, enabling a relatively small filter  400  to be used. Alternatively, a second stage filter can be used to capture any material, oil droplets, or particulate matter that may escape the porous substrate  421 . For example, a secondary stage filter, as described above with regard to other embodiments, can be used as a separate filter, or within the outlet port  429  of the separator  400 .  
      Referring now to  FIG. 10 , and overall structure for a compressor system  450  is illustrated. A compressor system  450  has an air compressor  452  having an oil reservoir  453 . As the air compressor operates to compress air, the compressor apparatus injects a fine mist of oil into the compressed air. In this way, a compressed admixture  452  of air and oil is generated by the air compressor. The compressed admixture  452  is received into an air oil separator  454 . The air oil separator  454  may be, for example, similar to air oil separator  400  discussed with reference to  FIG. 9 . The air oil admixture passes through a honeycomb substrate  456 , so that oil coalesces into an oil collection area  463  and is returned to the oil reservoir  453 , and clean air is received into an output manifold  461 . The clean air has also had particular matter removed. The cleaned air is then sent through output line  465  to attached pneumatic equipment.  
      Referring now to  FIG. 11 , a process for removing oil is illustrated. Process  500  has a compressor generating an air oil admixture as shown in block  502 . The admixture may include air, particulate matter (debris such as soot, dust, engine wear particles, etc), and lubrication and coolant oil. The air oil admixture is routed into a set of inlet channels in a honeycomb filter as shown in block  504 . The honeycomb filter is preferably constructed of bonded ceramic fibers, thereby providing highly porous ceramic walls. The filter is further constructed as a wall flow filter, such that alternate channels are plugged. Since the filter is a wall flow filter as shown in block  506 , the air oil admixture is routed through the highly porous walls. Oil is coalesced in the wall as shown in block  519 , which then may be returned to an oil reservoir as shown in block  517 . As the air flows through the porous wall, particulate matter may also be captured. The particular matter may be captured through impaction, diffusion, or depth filtering as shown in block  511 . In some applications, a secondary filtration may be used to further clean particulate matter from the air, or remove additional oil as shown in block  515 . The air is then provided to pneumatic equipment as shown in block  521 .  
      The filters of the present invention can be used to separate oil and particulate matter from air flow in stationary applications, for example, power generation, pumping equipment, and the like, and mobile applications over land, sea, and air, including, but not limited to automobiles, motorcycles, and farm and commercial vehicles.  
      While particular preferred and alternative embodiments of the present intention have been disclosed, it will be apparent to one of ordinary skill in the art that many various modifications and extensions of the above described technology may be implemented using the teaching of this invention described herein. All such modifications and extensions are intended to be included within the true spirit and scope of the invention as discussed in the appended claims.