# Patent

## Title
Filter element and mounting method

## Abstract

The present invention relates to an apparatus for filtering a gas or liquid stream such as a natural gas stream. The apparatus includes a closed vessel having a longitudinally extending length, an initially open interior, an input port at one extent and an output port at an opposite extent thereof. A partition located within the vessel interior divides the vessel interior into a first stage and a second stage. At least one opening is provided in the partition. A filter element is disposed within the vessel to extend from within the first stage. The filter element is easily mounted or removed from the vessel by rotating a J-slot engagement surface on the element which mates with a mounting structure provided in the vessel interior.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of earlier filed Ser. No. 10/775,892, filed Feb. 10, 2004, entitled “Filter Element and Mounting Method,” now issued U.S. Pat. No. 7,014,685, issued Mar. 21, 2006.


BACKGROUND ART
1. Field of the Invention
The invention relates to filter vessels used to filter gas and liquid streams and to filter elements for such vessels, and, more specifically, to an improved structure and method for mounting the filter elements within the interior of the associated filter vessel.
2. Description of Related Art
Gas filter elements for filtering dry gas streams as well as for separating solids and liquids from contaminated gas streams are well known, as are gas filter elements for coalescing entrained liquids from a gas stream. Often these types of gas filter elements are installed in multi-stage vessels, which are in turn installed in a gas pipeline, to perform these filtering functions. U.S. Pat. Nos. 5,919,284, issued Jul. 6, 1999, and 6,168,647, issued Jan. 2, 2001, both to Perry, Jr., and assigned to the assignee of the present invention, disclose multi-stage vessels using individual separator/coalescer filter elements to separate solids, filter liquids, and coalesce liquids. The foregoing multi-stage vessels, as well as a multitude of other similar filtration vessels used in industry utilize solid or hollow core tubular elements, typically formed at least partially a porous filtration media. For example, porous filtration elements useful in the above type of filtration vessels are of the same general type as those that are described in U.S. Pat. No. 5,827,430, issued Oct. 27, 1998 to Perry, Jr., et al., and assigned to the assignee of the present invention.
It is periodically necessary to perform maintenance on the filtration vessels, including replacement of the porous filter elements. This task has been labor intensive and time consuming in the past because of the mounting structure used to mount the filter elements within the filtration vessel interior. Often, it was necessary to unscrew and end cap or nut to free the filter element from its associated structural mounting within the vessel interior. Not only was this time consuming, but the location of the mounting structure was sometimes inconvenient to access, making filter replacement a difficult or inconvenient chore. The same type of inconveniences were present in the initial filter installation process for new filtration vessels.
Thus, despite various advances which have been made in overall filtration vessel design, there continues to be a need for improvements which simplify the process of mounting and replacing filter elements within the filtration vessel, thereby decreasing the cost of vessel installation and maintenance.
BRIEF SUMMARY OF THE INVENTION
An apparatus is shown for filtering a gas or liquid stream such as a natural gas stream or a natural gas processing liquid stream. The apparatus includes a closed vessel having a length and an initially open interior. A partition is disposed within the vessel interior. The partition has a planar inner and planar outer side, respectively, dividing the vessel interior into a first stage and a second stage. At least one opening is provided in the partition. An inlet port is provided in fluid communication with the first stage. An outlet port also provides fluid communication from the second stage. At least one tubular filter element is disposed within the vessel to sealingly extend within the first stage. Each filter element has a locking end, a tubular length and an opposite end. A mounting structure is located on a selected planar side of the partition. Rotational mounting means are provided on the locking end of at least selected filter elements which means cooperate with the mounting structure of the vessel for rotationally locking the filter element with respect to the partition upon rotational movement of the filter element.
In one form of the invention, the locking end of the filter elements is a generally cylindrical surface which forms an end opening and the mounting means provided on the locking end of the filter elements is a slot provided in the cylindrical surface. The most preferred mounting means provided on the locking end of the filter element is a J-slot. The generally cylindrical locking end of the filter elements joins the tubular length of the filter elements at a neck region of each filter element. The neck region forms a region of increased external diameter along the tubular length of the filter element. A seal means is located at the neck region for sealing against the partition when the filter element is locked in a fully engaged position. The preferred seal means can comprise a chevron-shaped seal or an O-ring seal. The preferred mounting structure for this form of the invention is located on a selected side of the partition and comprises a continuous post, or a pair of spaced post elements, aligned with respect to the partition opening, wherein the J-slot receives and engages the post or pair of post elements as the filter element is rotated.
The filter elements each have a filter wall and can have hollow cores. The input port, vessel interior, tubular filter elements and output port together define a flow passage within the apparatus. The gas stream flows into the first stage through the input port and through the outer filter wall of the filter element and through the hollow filter core, thereby separating impurities out of the gas stream. The gas stream then flows out of the second stage through the outlet port. A particularly preferred form of the filter element consists of multi-overlapped layers of non-woven fabric strips.
In another form of the invention, the J-slot is located on the mounting structure of the vessel. The filter element carries a T-bar which extends from the interior of the filter element and engages the J-slot on the mounting structure to rotationally lock the filter element with respect to the partition upon rotational movement of the filter element.
In yet another form of the invention, the J-slot is located within an end cap of the filter element. The mounting structure of the vessel includes a riser which supports a T-bar. The T-bar passes through the interior of the filter element and engages the J-slot in the end cap to rotationally lock the filter element with respect to the partition upon rotational movement of the filter element.
A method is also shown for installing a filter element within a filtration vessel used to filter gas, liquid and gas/liquid streams. A filter vessel is provided as previously described having a first and second stage divided by a partition. At least one replaceable filter element is installed within the filter vessel. The filter element is provided with one of the previously described locking ends for engaging a respective mounting structure of the vessel. The filter element is installed within the vessel by rotationally locking the filter element with respect to the partition upon rotational movement of the filter element.
The above as well as additional objects, features, and advantages of the invention will become apparent in the following detailed description.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view in partial section of a filter vessel having a filter element of the invention installed therein.
FIG. 2A is partial, end view of a filter element of the invention showing the element engaged within the vessel mounting structure.
FIG. 2B is an isolated view of the handle end of the filter element of the invention.
FIG. 3A is a side, sectional view of a filter element of the invention shown disengaged from the associated vessel mounting structure, the filter element having a chevron-shaped seal.
FIG. 3B is a view similar to FIG. 3A but with the filter element shown in the engaged position with respect to the vessel mounting structure.
FIG. 4A is a view of an alternative filter element design showing an O-ring type seal for engaging the associated vessel mounting structure.
FIG. 4B is a view of the filter element of FIG. 4A engaged with the vessel mounting structure.
FIG. 5 is a view of a prior art filtration vessel showing the method of mounting the filter elements therein.
FIG. 6 is a simplified, side view of a conventional filter element which is used in retrofit fashion within the filter vessel of the invention.
FIG. 7 is an exploded view showing another form of the filter element of the invention, showing the T-bar which is carried by the element and the mating mounting structure of the vessel.
FIG. 8 is an isolated view of the mounting structure of the vessel which is used with the filter element of FIG. 7.
FIG. 9 is another view of the mounting structure of FIG. 8, partly broken away, showing the T-bar engaging the J-slot of the mounting structure.
FIG. 10 is an isolated view of another form of the filter element of the invention in which the J-slot is located within an end cap of the filter element and in which the mounting structure of the vessel includes a riser which supports a T-bar.
FIG. 11 is an isolated view of the end cap of the filter element of FIG. 10, showing the J-slot with the T-bar engaged.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning to FIG. 1 there as shown a filter vessel of the invention designated generally as 13. The apparatus 13 is shown in its simplest form as a dry-gas filter. The internals or filter element shown in unit 13, illustrated in FIG. 1, can be followed by a second stage mist extractor of the type commercially available in the industry. While FIG. 1 illustrates one embodiment of a natural gas filtration vessel, it will be understood by those skilled in the art that the filter elements and method of mounting covered by the present invention can be applied to a variety of such vessels used in the industry. For example, the filter elements of the invention might be employed in vessels which are used for simultaneously filtering solids, separating liquids, pre-coalescing liquids, and coalescing liquids out of a gas stream. The filter elements might also be utilized in vessels used for coalescing and separating two liquids and for filtering solids out of liquids. Also, while the vessel shown in FIG. 1 illustrates one filter element mounted within the vessel for simplicity of illustration, it will be understood that some vessel designs will employ multiple elements utilizing the attachment means of the invention in a single vessel.
Referring again to FIG. 1, it should be understood that although the vessel 13 is shown in a generally horizontal configuration, it may also be configured in a generally vertical embodiment. The vessel 13 has a generally tubular shell 15 having an initially open interior 17. The shell 15 is enclosed at an inlet end 19 by means of a closure member 21 which, in this case, is a bolted flange. The shell 15 is permanently enclosed at an outlet end 23 by a cap 25, preferably elliptical. The flanged closure 21 provides a fluid tight seal with respect to the inlet end 19. In the embodiment of FIG. 1, a single filter element 27 is supported within the vessel open interior 17 by means of a vessel partition 29 and support element 31. The support element 31 can comprise a flat bar or expanded metal.
The partition 29 divides the hull interior into a first stage 35 and a second stage 33. The vessel 13 is preferably manufactured of steel materials which conform to published pressure-vessel standards, such as ASME Boiler and Pressure Vessel Code, Section VIII, Division 1.
The partition 29 which divides the vessel interior into the first and second filtration stages has a planar inner and planar outer opposing sides 37, 39, respectfully. At least one opening 41 is provided in the partition for receiving an end of the filter element. An inlet port 45 is in fluid communication with the first stage and an outlet port 43 is in communication with the second stage. The tubular filter element 27 is disposed within the vessel to sealingly extend within the first stage 35 through one of the openings 41 in the partition 29 into the second stage 33. Gas flow is through the inlet port 45, through the filter wall, of the filter element, through the hollow core 47 of the filter element, and through the second stage to the outlet 43. The direction of the gas flow is indicated by the arrows in FIG. 1.
As best seen in FIGS. 3A and 3B, each tubular filter element 27 has a locking end 49, a tubular length and an opposite, handle end 51. As shown in FIG. 3A, a mounting structure is located on a selected planar side of the partition 29. A rotational mounting means is provided on the locking end 49 of the filter element 27 which cooperates with the mounting structure of the vessel for rotationally locking the filter element with respect to the partition 29 upon rotational movement of the filter element 27 from the handle end 51.
Preferably, the filter element is provided with a generally cylindrical locking end 53 and the rotational mounting means on the locking end of the filter element is a slot 55 provided in the cylindrical surface of the locking end 53. The preferred mounting means on the locking end of the filter element is a J-slot, as illustrated in the drawings. The generally cylindrical locking end 53 of the filter element joins the tubular length of the filter element at a neck region 57. The neck region 57 forms a region of increased external diameter along the tubular length of the filter element. A seal means is located at the neck region for sealing against the partition 29 when the filter element 27 is locked in position. In the embodiment of the invention illustrated in FIGS. 3A and 3B, the seal means is an elastomeric chevron-shaped member 59. The chevron-shaped seal 59 is shown engaged against the partition planar inner side 37 in FIG. 3B. The exposed lip 60 of the seal member 59 acts as a resilient spring in holding the overall filter element in a “locked” or “seal engaged” position (illustrated in FIG. 3B).
FIGS. 4A and 4B illustrate another sealing arrangement of the previously described filter element in which the neck region 57 carries an O-ring seal 61, the O-ring seal being received within a mating groove provided on the planar surface of the neck region. FIG. 4B shows the O-ring seal in engagement with the planar inner side 37 of the partition 29 when the element is in the locked in position.
As shown in FIG. 3A, the mounting structure which is provided on the partition 29 can comprise a continuous post 63 which is aligned with respect to a partition opening 41. As shown in FIG. 3B, the J-slot 55 provided in the cylindrical end 53 of the filter element receives and engages the post 63 as the filter element is rotated from the handle end 51. The post 63 is, in this case, supported between opposing side flanges 65, 67 which are arranged to generally perpendicular to the planar face 39 of the partition 29. In this way, the post 63 extends in a plane generally parallel to the plane of the selected planar face of the partition.
As illustrated in FIGS. 4A and 4B, the mounting means which is provided on the partition 29 can also comprise two spaced-apart post elements 62, 64, with one post element being attached to each opposing side flange 65, 67. The discontinuity in the post 63 (shown in FIG. 3A) helps to reduce the flow restriction in the filter element outlet end caused by the presence of the mounting structure.
FIGS. 2A and 2B illustrate the respective locking and handle ends of the filter element 27. FIG. 2A illustrates the rotational mounting means (J-slot 55) fully engaged with the mounting post 63. In this case, the post 63 is a continuous post which is supported between the opposing side flanges 65, 67, as described with respect to FIGS. 3A and 3B.
The filter elements of the invention can be easily installed or removed from within the filter vessel 13. As shown in FIG. 1, the initially open interior 17 can be accessed by means of the closure 21. The filter element 27 can removed by simply turning the handle end 51. Rotational movement of the handle 51 causes the locking end 49 to rotate, whereby the J-slot rides about the post 63 (FIG. 2A), thereby releasing the element. The element can then be withdrawn from the vessel interior 17 by sliding the element longitudinally along the horizontal axis of the vessel and out the closure opening. A replacement filter element can then be easily installed by repeating the above steps in the reverse order.
The filter vessel 13 having the previously described mounting structure can also be retrofitted with an existing, conventional filter element, such as the element 201 shown in FIG. 6. In the example illustrated, a single or double open end filter element 201 is provided with a sealing plate 203 at one extent. An element attachment rod 205 is secured to the sealing plate 203 by means of external nut 207 on one end and is supported within an opening 209 in the partition or tubesheet (29 in FIG. 1) by means of a flat bar (shown in dotted lines as 211 in FIG. 6) which fits across the tubesheet opening.
It will be understood by one skilled in the art that other mounting means could also be utilized to mount a conventional filter element within the vessel of the invention. For example, the element attachment rod (205 in FIG. 6) could carry a transverse pipe in place of the flat bar 211 which pipe would have end openings which could be received over the spaced-apart posts (62 and 64 in FIG. 4A). Other types of engagement means could also be carried on the element attachment rod 205. All of these means could be utilized to mount a conventional filter element within a vessel having the special mounting structure used with the rotationally mounted filter elements of the invention.
Turning now to FIGS. 7-9, there is shown another form of the present invention in which a filter element 311 has a generally cylindrical exterior 313, an end cap 315 and an opposite initially open end 317. A T-bar 319 supported on the end cap 315 by means of nut 321 passes within the filter interior and extends slightly therefrom. The T-bar outer extent 323 is matingly engaged within a J-slot 325 provided within the mounting structure of the vessel. An O-ring 327 located within a groove provided in the mounting structure seals against the filter exterior once the filter element is installed within the mounting structure. FIG. 9 shows the T-bar being engaged within the J-slot provided in the mounting structure.
FIGS. 10 and 11 illustrate another form of the invention in which the vessel structure includes either horizontal or vertical risers 329. The risers 329, in turn, support T-bars 331 of the type previously described. Each T-bar 331 has an outer extent 333 which is received within a J-slot 335 provided within an outer end cap 337 of a filter element 339. As best seen in FIG. 11, the outer end cap 337 has a base 341 which supports the cylindrical mounting member 343. The cylindrical sidewalls of the mounting member 343 has portions removed to form the J-slot. In the embodiment of the end cap shown in FIG. 11, a biasing means, such as coil spring 345 is located within the interior of the mounting member 343 and is held in position by means of tabs 347 located on the interior sidewalls of the mounting member 343. As shown in FIG. 11, movement of the outer extent 333 of the T-bar within the J-slot 335 causes the T-bar to contact the coil spring, thereby compressing the coil spring. This biasing force serves to securely retain the T-bar within the J-slot 335. Also, while a coil spring 345 has been illustrated as the biasing means, other types of biasing elements could also be utilized. For example, a spring steel element could be tack welded on the interior of the base 341 to replace the coil spring. The filter element 339 in FIG. 10 also includes an inner end cap 342 which seals against the exterior of the riser 329 by means of a suitable O-ring seal, or the like (not shown). The inner and outer end caps 342, 337, respectively, are typically formed of a metal while the remainder of the filter body is formed of a porous filtration material.
The embodiment of the invention illustrated in FIGS. 10 and 11 has an advantage in applications where flow is from the inside of the filter element to the outside. Holding the filter element by the outer end cap makes it easier to hold the element in place where the flow is from the inside of the element to the outside. Such an arrangement reduces or eliminates tension on the connection from the outer end cap to the body of the element and from the inner end cap to the body of the element. This is true because the element is being held at a point where all of those forces are in compression against the outer end cap, instead of in tension from the inner end cap. This may allow the outer end cap to be made using less metal while still maintaining the necessary strength.
The bodies, or tubular filter walls of the filter elements of the invention can be formed of any material conventionally used in the art. The construction of the filter elements will vary depending upon the particular end application of the filtration vessel. By way of example, the filter elements can be constructed in the manner and of the materials disclosed in U.S. Pat. No. 5,827,430, issued Oct. 27, 1998 to Perry, Jr., et al. Such filter elements are sold commercially under the PEACH® trademark by Perry Equipment Corporation of Mineral Wells, Texas. In a typical application, the filter elements consist of four multi-overlapped layers of non-woven fabric strips of varying composition. The first layer is composed of equal amounts by volume of fibers purchased from Hoechst Celanese of Charlotte, N.C., United States, sold under the fiber designation “252,” “271,” and “224,”has a basis weight of 0.576 ounces per square foot, is ten inches wide, and is overlapped upon itself five times. The denier of fiber “252” is 3 and its length is 1.500 inches. The denier of fiber “271” is 15 and its length is 3.000 inches. The denier of fiber “224” is 6 and it is 2.000 inches.
The second layer is composed of equal amounts by volume of “252,” “271,” and “224,” has a basis weight of 0.576 ounces per square foot, is eight inches wide, and is overlapped upon itself four times. The third layer is composed of equal amounts by volume of “252,” “271,” and “224,” has a basis weight of 0.576 ounces per square foot, is eight inches wide, and is overlapped upon itself four times. The fourth layer is composed of equal amounts by volume of “252” and a fiber sold under the name “Tairilin,” has a basis weight of 0.576 ounces per square foot, is six inches wide, and is overlapped upon itself three times. Fiber “252” being of the core and shell type serves as the binder fiber in each of the aforementioned blends.
The above example of particular types of material, fabric denier, number of wrapping layers, etc., is intended to be illustrative only of one type of filter material useful in the practice of the present invention. The rotational lock and release feature of the elements of the invention could be used with a variety of other conventional filter materials, as well.
The advantages of the improved filter elements and method of mounting thereof can perhaps best be understood with reference to the prior art filtration unit shown in FIG. 5 of the drawings. This vessel is described in issued U.S. Pat. No. 6,168,647, issued Jan. 2, 2001, and assigned to the assignee of the present invention. The discussion which follows also describes the filtration process in greater detail. The vessel 111, shown in FIG. 5, is best suited for mist collection. In addition, multi-stage vessel 111 is well suited for applications involving immiscible fluids, and as such, can be used in applications requiring the separation and filtration of two immiscible liquids or immiscible liquids and gases. The flow of the gas stream is indicated below as arrow G. Multi-stage vessel 111 has a generally tubular hull 112 having an initially open interior. Hull 112 is releasably enclosed on an upper inlet end 112a by a conventional closure member 115, preferably a quick-opening closure. Hull 112 is permanently enclosed on a lower outlet end 112b by a cap 113, preferably elliptical. Closure member 115 consists of a conventional head member 116 and a conventional clamping member 117. Head member 116 is releasably sealed to multi-stage vessel 111 by clamping member 117. Clamping member 117 maybe released, and head member 116 may be opened to allow access to the interior of hull 112. Clamping member 117 provides a fluid-tight seal between hull 112 and head member 116, preferably with a conventional O-ring (not shown). A plurality of separator/coalescer filter elements 118 are disposed within hull 112. Separator/coalescer filter elements 118 are constructed as described above with respect to the vessel of the invention. Hull 112 is supported by support members 119. A conventional davit assembly supports head 116 when head 116 so that head 116 may be swung open to allow access to multi-stage vessel 111.
The interior of hull 112 is divided into a first stage 121a and a second stage 121b by a generally transverse partition 123. Partition 123 includes a plurality of openings 125. A tubular filter guide 127 is aligned with each opening 125. Each filter guide 127 extends longitudinally a selected distance from partition 123 into first stage 121a. An inlet port 129 is disposed on hull 112 and opens into first stage 121a. Inlet port 129 terminates with an inlet flange 131. Inlet port 129 is located near partition 123 so that as a gas stream flows through the inlet port 129 into first stage 121a, the gas stream impinges upon filter guides 127. An outlet port 133 is disposed on hull 112 and opens into second stage 121b. Outlet port 133 terminates with an outlet flange 135. Outlet flange 135 is adapted to allow multi-stage vessel 111 to be connected to a conventional gas pipeline. An annular collar 136 is aligned with outlet port 133 and extends into second stage 121b. 
Disposed underneath portion 112c of hull 112 is a sump 139 for collecting the filtered solids, the separated liquids, the pre-coalesced liquids, and the coalesced liquids, that are removed from the gas stream. Sump 139 is divided into a first stage sump 139a and a second stage sump 139b by an impermeable sump partition 141. A first stage downcomer 143a provides fluid communication between first stage 121a and first stage sump 139a. The second stage downcomer 143b similarly provides fluid communication between second stage 121b and second stage sump 139b. 
A plurality of first stage support straps 165 are disposed in first stage 121a to support separator/coalescer filter elements 118. First stage support straps 165 generally extend transversely across first stage 121a and are connected to the interior of hull 112 by a snap fit or any suitable holding clip member. First stage support straps 165 include a plurality of apertures 166 to receive separator/coalescer filter elements 118 firmly in place without longitudinal compression. Likewise, a plurality of second stage support straps 167 are disposed in second stage 121b to support separator/coalescer filter elements 118. Second stage support straps 167 generally extend transversely across second stage 121b and are connected to the interior of hull 112. Second stage support straps 167 include a plurality of apertures 168 to receive separator/coalescer filter elements 118. The filter elements include filter cap posts 193a and 193b. 
A plurality of louvered impingement baffles 171 are disposed in second stage 121b to prevent coalesced liquids and fine liquids from becoming re-entrained in the gas stream as the gas stream flows through second stage 121b toward outlet port 133. A separate louvered impingement baffle 171 is associated with each separator/coalescer filter element 118 and each corresponding opening 125 in partition 123. Each louvered impingement baffle 171 includes a basket body portion 173 coupled to a basket cap portion 175. Each louvered impingement baffle 171 includes a plurality of annular louvers disposed along the extent of basket body portion 173.
It will be appreciated from the foregoing discussion that a more complicated mounting and support structure are required in the prior art device. The improved filter element and mounting method of the invention provides several advantages over such a structure. The improved filter elements of the invention utilize a rotational locking feature which allows the filter element to be easily installed or removed from the filter vessel interior. The simplicity of the J-slot locking mechanism simplifies the design of the element and associated mounting structure and provides improved efficiency during installation and maintenance operations. The filter locking design is simple in design and economical to manufacture. The locking mechanism is extremely reliable in operation.
While the invention is shown in only one of its forms, it is not just limited but is susceptible to various changes and modifications without departing from the spirit thereof.

## Claims

1. An apparatus for filtering a natural gas stream, the apparatus comprising:
a closed vessel having a length and an initially open interior;
a partition disposed within the vessel interior, the partition having a planar inner and planar outer side, respectively, dividing the vessel interior into a first stage and a second stage;
at least one opening in the partition;
an inlet port in fluid communication with the first stage;
an outlet port in fluid communication with the second stage;
at least one tubular filter element, the tubular filter element being disposed within the vessel to sealingly extend from within the first stage to within the second stage, the filter element having a locking end, a tubular length, and an opposite end;
a mounting structure located on a selected planar side of the partition within the vessel interior;
a rotational mounting means on the locking end of the at least one filter element which cooperates with the mounting structure of the vessel for rotationally locking the filter element with respect to the partition upon rotational movement of the filter element;
wherein a J-slot is provided in the mounting structure of the vessel and wherein the filter element carries a T-bar with an outer extent which matingly engages the J-slot in the mounting structure.

2. An apparatus for filtering a natural gas stream, the apparatus comprising:
a closed vessel having a length and an initially open interior;
a partition disposed within the vessel interior, the partition having a planar inner and planar outer side, respectively, dividing the vessel interior into a first stage and a second stage;
at least one opening in the partition;
an inlet port in fluid communication with the first stage;
an outlet port in fluid communication with the second stage;
at least one tubular filter element, the tubular filter element being disposed within the vessel to sealingly extend from within the first stage to within the second stage, the filter element having a locking end, a tubular length, and an opposite end;
a mounting structure located on a selected planar side of the partition within the vessel interior;
a rotational mounting means on the locking end of the at least one filter element which cooperates with the mounting structure of the vessel for rotationally locking the filter element with respect to the partition upon rotational movement of the filter element; and
wherein the mounting structure includes an outwardly extending T-bar and wherein the filter element has an outer end cap provided with a mounting member, the mounting member having a J-slot for receiving a mating portion of the T-bar, thereby securing the filter element to the mounting structure.

3. The apparatus of claim 2, wherein the mounting member has cylindrical sidewalls, a portion of which have been removed to form the J-slot and wherein a biasing means is contained within the cylindrical sidewalls of the mounting member for contacting and biasing the T-bar when the T-bar is engaged within the J-slot of the outer end cap.

4. The apparatus of claim 3, wherein the biasing means is a coil spring.

5. The apparatus of claim 2, wherein the filter elements each have a filter wall and a hollow core.

6. The apparatus of claim 5, wherein the input port, the vessel interior, the tubular filter elements, and the output port together define a flow passage within the apparatus, whereby the gas stream flows into the first stage through the input port, through the filter wall of the filter element and out the hollow core thereof, thereby separating impurities out of the gas stream, and whereby the gas stream then flows out of the second stage through the outlet port.

7. The apparatus according to claim 5, wherein each of the tubular filter elements consists of multi-overlapped layers of non-woven fabric strips.

8. A tubular filter element for filtering a natural gas stream passing through a filter vessel, the filter element comprising:
a body having a locking end, a tubular length and an opposite end;
the tubular length of the filter body comprising a filter wall formed of a porous material, the filter body also having a hollow core;
a rotational mounting means on the locking end of the filter element which cooperates with a mating mounting structure provided within the filter vessel for rotationally locking the filter element with respect to the mounting structure upon rotational movement of the filter element; and
wherein a J-slot is provided in the mounting structure of the vessel and wherein the filter element carries a T-bar with an outer extent which matingly engages the J-slot in the mounting structure.

9. A tubular filter element for filtering a natural gas stream passing through a filter vessel, the filter element comprising:
a body having a locking end, a tubular length and an opposite end;
the tubular length of the filter body comprising a filter wall formed of a porous material, the filter body also having a hollow core;
a rotational mounting means on the locking end of the filter element which cooperates with a mating mounting structure provided within the filter vessel for rotationally locking the filter element with respect to the mounting structure upon rotational movement of the filter element; and
wherein the mounting structure includes an outwardly extending T-bar and wherein the filter element has an outer end cap provided with a mounting member, the mounting member having a J-slot for receiving a mating portion of the T-bar, thereby securing the filter element to the mounting structure.

10. The filter element of claim 9, wherein the mounting member has cylindrical sidewalls, a portion of which have been removed to form the J-slot and wherein a biasing means is contained within the cylindrical sidewalls of the mounting member for contacting and biasing the T-bar when the T-bar is engaged within the J-slot of the outer end cap.

11. The filter element of claim 10, wherein the biasing means is a coil spring.

12. A method of maintaining a filter vessel having associated tubular filter elements, the filter vessel having at least a first stage and a second stage, the first stage being separated from the second stage by a partition having oppositely arranged planar sides and having at least one opening through which the filter elements are sealingly disposed, the method comprising the steps of:
opening the multi-stage vessel;
removing at least one filter element from the filter vessel;
replacing the filter element with a replacement filter element;
creating a fluid-tight seal between the replacement filter element and the opening in the partition;
closing the multi-stage vessel; and wherein
the filter element is provided with a locking end, a tubular length, and an opposite end;
a mounting structure is located on a selected planar side of the partition;
a rotational mounting means is located on the locking end of at least selected filter elements which cooperates with the mounting structure of the vessel for rotationally locking the filter element with respect to the partition upon rotational movement of the filter element; and
wherein a J-slot is provided in the mounting structure of the vessel and wherein the filter element carries a T-bar with an outer extent which matingly engages the J-slot in the mounting structure.

13. The method of claim 12, wherein the rotational movement of the filter element is accomplished by turning the filter element by hand to align and engage J-slot with a mating mounting structure.

14. A method of maintaining a filter vessel having associated tubular filter elements, the filter vessel having at least a first stage and a second stage, the first stage being separated from the second stage by a partition having oppositely arranged planar sides and having at least one opening through which the filter elements are sealingly disposed, the method comprising the steps of:
opening the multi-stage vessel;
removing at least one filter element from the filter vessel;
replacing the filter element with a replacement filter element;
creating a fluid-tight seal between the replacement filter element and the opening in the partition;
closing the multi-stage vessel; and wherein
the filter element is provided with a locking end, a tubular length, and an opposite end;
a mounting structure is located on a selected planar side of the partition;
a rotational mounting means is located on the locking end of at least selected filter elements which cooperates with the mounting structure of the vessel for rotationally locking the filter element with respect to the partition upon rotational movement of the filter element; and
wherein the mounting structure includes an outwardly extending T-bar and wherein the filter element has an outer end cap provided with a mounting member, the mounting member having a J-slot for receiving a mating portion of the T-bar, thereby securing the filter element to the mounting structure.