Patent Publication Number: US-8986431-B2

Title: Purification arrangements and methods for gas pipeline systems

Description:
DISCLOSURE OF THE INVENTION 
     Natural gas and other gases transmitted through pipeline systems may carry many types of particulates, including liquid droplets and/or solid particles. The gas may be the source of the particulates. For example, gas entering the pipeline system from a gas treatment facility after it has been extracted from a well may still be laden with particulates. Or the particulates may be generated within the pipeline system itself. For example, solid particles may be generated by corrosion and abrasion within the pipeline system. Liquid droplets may arise from condensation or as residues of liquid cleaners for the pipeline system. Many of these particulates are harmful to the components of the pipeline system and the personnel who operate and service the pipeline system. For example, the gas may carry black powder, a general term used to describe a host corrosion-related particulate contaminants, that can be erosive, toxic, and/or chemically reactive with air, i.e., pyrophoric. 
     The present invention relates to purification arrangements and methods thr removing particulates from gas flowing through the pipeline system. Embodiments of the invention may include a pressure vessel having an inlet and an outlet connected to the pipeline system. The pressure vessel may contain at least two purification assemblies, and the gas may be directed through the pressure vessel, where the purification assemblies remove particulates from the gas. 
     A wide variety of purification assemblies may be used to remove the particulates. For example, one or more of the purification assemblies may comprise a filter assembly. Each filter assembly may include one or more filter elements, and each filter element may include a porous filter medium. As the gas flows through the pressure vessel, it passes through the filter medium, and the particulates carried by the gas are trapped on the surface of and/or within the filter medium. Alternatively or additionally, one or more of the purification assemblies may comprise a separator assembly. Each separator assembly may include one or more separators which remove particulates from the gas without the use of a porous filter medium. For example, a separator may slow the velocity of the gas and allow the particulates to settle from the gas, or a separator may deflect the particulates from the principal gas flow stream, causing the gas and the particulates to separate from one another. In any event, the purification assemblies remove a significant portion of the particulates, and gas leaving the pressure vessel has significantly fewer particulates than gas entering the pressure vessel. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, purification arrangements for a gas pipeline system may comprise a pressure vessel, a modular filter assembly, and a modular separator assembly. The pressure vessel may include an interior, a gas inlet, and a gas outlet and may define a gas flow path through the interior of the pressure vessel between the gas inlet and the gas outlet. The pressure vessel may have an elongate configuration including a horizontal axis and first and second axial ends. The pressure vessel may also have a cover moveably mounted to the first axial end, the cover being movable between a first position and a second position. In the first position, the cover may be sealed to the first axial end of the pressure vessel, and in the second position the cover may provide an opening at the first axial end of the pressure vessel. The modular filter assembly may be removeably located in the gas flow path in the interior of the pressure vessel and may comprise a plurality of filter elements. Each filter element may have a filter medium positioned across the gas flow path to filter particulates from gas flowing through the filter element. The modular separator assembly may be removeably located in the gas flow path in the interior of the pressure vessel between modular filter assembly and the gas inlet. The modular separator assembly may have one or more separators positioned in the gas flow path to remove particulates from gas flowing along the gas flow path. The modular filter assembly and the modular separator assembly may each be removable from and moveable into the interior of the pressure vessel as an integral unit. The modular separator assembly may be removable from and moveable into the pressure vessel via the opening at the first axial end of the pressure vessel when the cover is in the second position. 
     In accordance with another aspect of the invention, methods for removing particulates from a gas flowing in a gas pipeline system may comprise establishing a flow of gas through the interior of a horizontal pressure vessel from a gas inlet to a gas outlet, including directing the gas through one or more separators of a modular separator assembly and through one or more filter elements of a modular filter assembly to remove particulates from the gas. The methods may also comprise terminating the flow of gas through the pressure vessel; removing the modular separator assembly as an integral unit from the pressure vessel through an opening in a first axial end of the pressure vessel; and installing a cleaned or new modular separator assembly as an integral unit into the pressure vessel through the opening in the first axial end of the pressure vessel. The methods may further comprise reestablishing a flow of gas through the interior of the pressure vessel from the gas inlet to the gas outlet and through the new or cleaned modular separator assembly in the interior of the pressure vessel. 
     Purification arrangements and methods embodying one or more aspects of the invention have many advantageous features, including features that are highly effective for removing particulates from the gas. For example, by including both a filter assembly and a separator assembly, purification arrangements and methods embodying the invention remove most particulates, especially black powder, so the gas returning to the pipeline system from the pressure vessel has far fewer particulates, e.g., may be largely free of solid particles and liquid droplets, compared to the gas entering the pressure vessel from the pipeline system. Further, the modular separator assembly, as well as the modular filter assembly, may quickly and easily be removed and installed in the horizontal pressure vessel. Each assembly is modular in that it can be removed from, and installed into, the horizontal pressure vessel as an integral unit. For example, once the modular separator assembly becomes loaded with particulates, it may be removed from the horizontal pressure vessel in a very short period of time as an integral unit through the opening in the first axial end of the pressure vessel when the cover is open. Similarly, a cleaned or new modular separator assembly may be installed in the horizontal pressure vessel even more quickly as an integral unit through the opening in the first axial end of the pressure vessel. For many embodiments, a modular filter assembly loaded with particulates and a cleaned or new modular filter assembly may also be quickly and easily removed/installed as an integral unit, for example, through the same opening in the first axial end of the horizontal pressure vessel. The modular nature of the filter and separator assemblies thus greatly reduces the downtime required to remove and replace each assembly, thereby enhancing the efficiency of the purification process. Further, the purification assemblies, e.g., the modular filter assembly and the modular separator assembly, may be adjusted or restructured to accommodate varying gas flow conditions in the pipeline without modification of the pressure vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of purification arrangement with portions of the pressure vessel and shell cut away. 
         FIG. 2  is an oblique view of a filter assembly. 
         FIGS. 3   a  and  3   b  are oblique top and bottom views of a separator assembly. 
         FIG. 4  is an oblique view of a casing for the separator assembly of  FIG. 3 . 
         FIG. 5  is an exploded oblique view of an openable/closeable barrier. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Purification arrangements embodying the invention may be configured in a wide variety of different ways. For example, the purification arrangement  10  shown in  FIG. 1  may comprise a pressure vessel  11  and two or more purification assemblies  12 ,  13  located in the interior of the pressure vessel  11 . The pressure vessel  11  may have a gas inlet  15  and a gas outlet  16  coupled to a gas pipeline system (not shown) and may define a gas flow path through the interior of the pressure vessel between the gas inlet  15  and the gas outlet  16 . The purification assemblies  12 ,  13 , one a modular separator assembly and the other a modular filter assembly, may be positioned in the gas flow path between the gas inlet  15  and the gas outlet  16 . Natural gas or any other gas passing through the gas pipeline system is directed through the pressure vessel  11  from the gas inlet  15  through the purification assemblies  12 ,  13  to the gas outlet  16 . A significant portion of the particulates, e.g., almost all solid particles and most of the liquid droplets, entrained in the gas as it enters the gas inlet  15  is removed by the purification assemblies  12 ,  13 , so the gas leaving the pressure vessel  11  is largely free of particulates. 
     The pressure vessel may be configured in any of numerous ways. For example, the pressure vessel may have a configuration similar to a scraper trap/launcher vessel used to service the interior of the pipeline. The pressure vessel may have an elongate, generally cylindrical structure and the axis may extend horizontally, or it may extend vertically or at any angle between horizontal and vertical. The pressure vessel may be formed as a unitary structure or in a plurality of sections joined together in a fluid-tight manner. Further, the pressure vessel may be constructed to withstand the design pressures and temperatures appropriate for the pipelines of the pipeline system. For example, for many natural gas pipeline systems, the design pressure may be in the range from about 30 barg or less to about 75 barg or more, e.g., about 60 barg, and the design temperature may be in the range from about minus 40° C. to about 100° C., e.g., about 70° C. For many embodiments, the pressure vessel may be formed from a metal and is quite large and heavy. The gas inlet and the gas outlet of the pressure vessel may be on opposite axial ends of the vessel, or one may be on an end and the other may be on the side of the vessel, or both may be on the side of the vessel facing in the same or different directions. In addition to the gas inlet and the gas outlet, a variety of other ports may be provided at various locations on the vessel, including ports for pressure protection, purging, flooding, depressurization, and/or draining and for pressure drop and level control. Further, the pressure vessel may include one or more hatches or other covers on the ends or side of the pressure vessel to allow access to the interior for service personnel and/or equipment, including removal and installation of the purification assemblies. In the embodiment of  FIG. 1 , the pressure vessel  11  may be oriented horizontally and supported by two or more stands  17  and may include a gas outlet  16  at one axial end of the pressure vessel  11 , a gas inlet  15  in the side of the pressure vessel  11 , e.g., at the top and nearer the other axial end, and a cover such as a quick opening hatch  20  hinged at the other axial end of the pressure vessel  11 . The hatch  20  may be large enough to swing open and provide access along the entire inner diameter of the pressure vessel  11 , facilitating installation and removal of the purification assemblies. Alternatively, any other cover may be bolted to the end of the pressure vessel, again providing access along the entire inner diameter when the cover is removed and facilitating removal and installation of one or more of the purification assemblies. The pressure vessel  11  may also be provided with one or more purge gas inlets  21  and one or more gas discharge outlets  22  communicating between the interior and exterior of the pressure vessel  11 . 
     The purification assemblies may be configured in a wide variety of ways to remove particulates, including liquid particulates and/or solid particulates, entrained in the gas. For example, depending on the specific type of particulates present in the gas of the pipeline system, at least one of the purification assemblies in the pressure vessel may be a modular filter assembly and at least one of the purification assemblies in the pressure vessel may be a modular separator assembly. For many pipeline systems, black powder may be a typical particulate entrained in the gas. Black powder is a general term used to describe a host of corrosion related contaminants in pipelines that transport natural gas, hydrocarbon condensates, liquefied petroleum gas, and other gases. The chemical and physical composition of black powder may vary significantly. It can be a dry powder, a liquid suspension, and/or an intermediate sticky sludge. The dry powder may include iron oxides, iron sulfides, and iron carbonates and may be fine, even submicron in size. For example, about 70% of the dry black powder particles may be about 10 microns or less in size, and the total loading may be in the range of about 5 to 30 grams/MMSCF during normal operation of the pipeline, although after a scraping operation the total loading may increase by a factor of up to 20 or more. Binder material present in the pipelines, e.g., parafins, asphaltenes, glycols, and/or lubricants, may hold some of the black powder particles together to form larger agglomerates. Additional solids, e.g., sand and/or silt, frequently accompany the black powder entrained in the gas. Consequently, for many of the embodiments, one of the purification assemblies, e.g., the most downstream purification assembly in the pressure vessel, may be a modular filter assembly arranged to remove finer particulates, and another purification assembly, e.g., the most upstream purification assembly, may be a modular separator assembly arranged to remove liquid particulates and/or larger solid particulates and agglomerates. For example, in the purification arrangement  10  shown in  FIG. 1 , the purification assembly  12  coupled more closely to the gas inlet  15  may be a modular separator assembly  23  and the purification assembly  13  coupled more closely to the gas outlet  16  may be a modular filter assembly  24 . A modular assembly is an assembly that can be removed from or moved into the pressure vessel as an integral unit. 
     The modular filter assembly may be configured in any of numerous ways and may include one or more filter elements. For many embodiments, the modular filter assembly  24  may comprise a filter bundle assembly having an array of filter elements  25 , as shown in  FIG. 2 . The filter elements may have any of a wide variety of shapes and sizes. For example, each filter element  25  may have a hollow, generally cylindrical shape, may include a blind end and an open end fluidly communicating with the interior of the hollow element, and may be arranged for gas flow outside-in or inside-out through the element. The filter elements  25  may include a wide variety of porous filter media  26  for removing particulates from the gas. The porous filter medium may, for example, include a porous metal medium, a porous ceramic medium, or a porous polymeric medium and may, for example, be in the form of a spirally wound or pleated membrane or sheet, e.g., a fibrous sheet, or a hollow, cylindrical mass, e.g., a fibrous mass. Further, the filter medium may have any of a variety of removal ratings. For embodiments targeting black powder, the filter medium may comprise a high-efficiency, high-dirt capacity, tapered-pore, absolute-rated gas depth filter medium. Examples of filter elements that are particularly effective for removing black powder include filter elements rated 0.3 micron in gas and available under the trade designation Coreless from Pall Corporation of Port Washington, N.Y. USA. 
     The modular filter assembly  24  may also include a frame  30  for supporting the filter assembly, including the array of filter elements  25 , as an integral unit. The frame may be configured in any of numerous ways and may support the array for gas flow outside-in or inside-out through the hollow filter elements. For example, the frame  30  may support the array for outside-in gas flow and may include a tube sheet  31  at the end of the array nearer the gas outlet  16 , a support plate  32  closer to, or at, the opposite end of the array, and one or more struts  33  that connect the tube sheet  31  and the support plate  32 . The tube sheet  31  and the support plate  32  may have a shape that generally conforms to the cross-sectional shape of the interior of the pressure vessel and a dimension, e.g., an outer diameter, that closely corresponds to the inner diameter of the pressure vessel. The tube sheet  31  may have a plurality of openings, and the open end of each filter element  25  may be sealed to an opening in the tube sheet  31 , either directly or via a stand-off tube, as shown in  FIG. 2 . The tube sheet  31  thus defines an unfiltered region of the filter assembly around the filter elements  25  on one side of the tube sheet  31  and a filtrate region on the opposite side of the tube sheet  31 . The filtrate side of the tube sheet  31  may be sealed to a header  34  which, in turn, may be sealed to the gas outlet.  16  of the pressure vessel  11 . For example, the header  34  may taper to an open outlet end that may be sealed to the gas outlet  16 . Alternatively, the tube sheet may be sealed to the interior of the pressure vessel, e.g., along the outer edge of the tube sheet. The support plate  32 , which may be connected to the filter elements  25 , for example, at the blind ends of the filter elements  25 , may also have a plurality of openings, allowing the unfiltered gas to flow from the gas inlet  15  along the exterior of the filter elements  25 . 
     The modular filter assembly may include one or more additional components. For example, the filter assembly may or may not further include a shell surrounding the array of filter elements and/or a transit mechanism facilitating the removal and installation of the modular filter assembly within the pressure vessel. In the embodiment shown in  FIG. 2 , the filter assembly  24  may not include a shell but may include a transit mechanism  35 . The transit mechanism may be configured in any of numerous ways including, for example, as slides on the modular filter assembly and/or rails along the interior of the pressure vessel. In  2 , the transit mechanism  35  may comprise a plurality of wheels  36 , e.g., spring loaded wheels, connected to the frame  30  and/or the header  34  and distributed around the modular filter assembly  24 , allowing the modular filter assembly  2 . 4  to be quickly and conveniently rolled out of and into the interior of the pressure vessel  11 . 
     The modular separator assembly may be configured in any of numerous ways and may include one or more separators, including, for example, one or more inertial separators. For many embodiments, the modular separator assembly may comprise a multi-stage separator assembly, and at least one stage may include any type of centrifugal or dynamic separator. One of many different examples of a modular separator assembly is the two-stage separator assembly  23  shown in  FIG. 3  The first stage may include an impact separator, e.g., a downwardly angled impact plate  40 , directly in the gas flow path from the gas inlet  15  and a large settling region  41  below the impact plate  40 . The second stage may include one or more higher efficiency separators  42 , e.g., a bank of cyclone separators  42  supported by a top plate  43 . For some embodiments, the cyclone separators  42  may have a cut off of down to 8 microns or less at rated gas flow and a cut off of down to 10 microns or less at 50% of rated gas flow. Any number of cyclone separators may be provided, e.g., four or more, six or more, eight or more, or ten or more, and the cyclone separators may be variously configured. In the embodiment of  FIG. 3 , each cyclone separator  42  may include an outer can  44  mounted around an inner can  45 . The outer can  44  may be closed at the inlet end, e.g., by the top plate  43 , and open at the lower outlet end, and the inner can  45  may be open at both the inlet and outlet ends, the outlet end of the inner can opening through the top plate  43 . The axes of the cyclone separators may be oriented parallel to, perpendicular to, or at any angle to the axis of the pressure vessel. In the illustrated embodiment, the axes are generally perpendicular to the axis of the pressure vessel  11 . Additional traps may be arranged at and/or below the lower outlet of the outer can to enhance the retention of particulates. 
     The modular separator assembly may also include a frame supporting the multi-stage separators as an integral unit in the pressure vessel, and the frame may be configured in any of numerous ways. For example, the frame may comprise a plurality of support plates  50 - 52  connected by one or more struts  53 , as well as the top plate  43  and the impact plate  40 . A downstream support plate  50  may be positioned at the outlet end of the separator assembly  23 , an upstream support plate  51  maybe positioned at the opposite end of the separator assembly  23 , and an intermediate support plate  52  may be positioned between the upstream and downstream support plates  50 ,  51 . Each support plate  50 - 52  may have a dimension, e.g., an outer diameter, that closely corresponds to the inner diameter of the pressure vessel  11 , enabling the support plates  50 - 52  to fit closely against the pressure vessel  11  and inhibit bypass of any gas around the entire separator assembly  23  or any of the stages of the separator assembly  23 . For some embodiments, one or more of the support plates  50 - 52  may be sealed to the pressure vessel  11 . The first stage of the separator assembly  23  may be defined between the upstream support plate  51  and the intermediate support plate  52 , while the second stage may be defined between the intermediate support plate  52  and the downstream support plate  50 . An opening in the intermediate support plate  52  beneath the angled impact plate  40  may open into a duct  54  that extends below the top plate  43 , allowing gas to flow from the first stage into the second stage. The duct  54  may feed the gas to each cyclone separator  42 , for example, through an inlet opening in the side of the outer can  44  near the inlet end. An opening in the downstream support plate  50  above the top plate  43  allows gas to exit the second stage of the modular separator assembly  23  and enter the modular filter assembly  24 . 
     The modular separator assembly may include one or more additional components. For example, for many embodiments the modular separator assembly may include a shell mounted to one or more of the separators and/or stages of the separator assembly to contain the particulates removed by the separators. The shell may be variously configured and may or may not be connected and/or sealed to the remainder of the separation assembly. For example, the shell  55  may be generally cylindrical and open on both ends and may surround one or more or all of the separators  40 - 42  or stages. The shell  55  may be dimensioned to fit within the interior of the pressure vessel  11  and around the separators and support plates  50 - 52  of the separator assembly  23 . For example, the shell  55  may be dimensioned to closely correspond to the inner diameter of the pressure vessel  11  and the outer diameter of the support plates  50 - 52 , enabling the shell  55  to inhibit bypass of any gas between the pressure vessel  11  and the shell  55  or between the shell  55  and the support plates  50 - 52 . For many embodiments, the shell  55  may be sealed to the support plates  50 - 52  in any suitable manner, e.g., permanently or releasably, to contain any particulates removed from the gas by the modular separator assembly  23 . For example, the shell  55  may be welded to the outer rims of the separator plates  50 - 52  to form a liquid-tight container containing the solids and liquids removed from the gas by the modular separator assembly  23 . The shell  55  may have a significant liquid and/or solids holding capacity which allows all of the particulates removed by the modular separator assembly  23  over an extended period, even after scraping operations, to be conveniently and safely stored within the shell  55 . The shell may have one or more openings. For example, the shell  55  may include an inlet opening  57  in the side, e.g., at the top, of the shell  55  that fluidly communicates with the gas inlet  15  in the pressure vessel  11 , allowing gas to flow through the gas inlet  15  into the first stage of the separator assembly  23 . The inlet opening  57  in the shell  55  may fit closely against the gas inlet  15  and/or may be sealed to the gas inlet  15  to prevent bypass of gas around the modular separator assembly  23 . Other openings in the shell  55  may include sealable side openings  58  that facilitate emptying and cleaning of the interior of the shell  55  and another top opening  59  that allows the shell to be filled with water and/or any other suitable inhibitor. For many embodiments, the shell  55  need not be a pressure vessel capable of withstanding the difference in pressure between the interior and the exterior of the pressure vessel  11 . Instead, the shell  55  may be formed from a much lighter gauge material, e.g., a lighter gauge metal, that can contain solids and liquids removed by the modular separator assembly  23 . 
     The modular separator assembly may or may not further include a transit mechanism facilitating removal and insertion of the separator assembly within the pressure vessel or the shell. The transit mechanism may be configured in any of numerous ways, including, for example, as slides on the frame or the shell of the filter assembly and/or rails along the pressure vessel. In the illustrated embodiment, the transit mechanism may comprise a plurality of wheels  56 . For embodiments without a shell, the transit mechanism, e.g., the wheels, may be distributed around the frame of the separator assembly and may be arranged to move, e.g., roll, along the inner periphery of the pressure vessel  11  in a manner similar to the filter assembly wheels  36 . The modular separator assembly may then be quickly and easily rolled along the pressure vessel to remove and install the modular separator assembly, e.g., via the open hatch. Once it is installed, the modular separator assembly may be locked in place in the pressure vessel by a locking mechanism. For embodiments with a shell  55 , a transit mechanism, e.g., the wheels  56 , may be attached to the frame of the separator assembly  23  and may be arranged to move along the interior of the shell  55 . For example, outside of the pressure vessel lithe separators  40 ,  42  and the frame of the separator assembly  23  may be moved, e.g., rolled, along the interior of the shell  55  and permanently or removably fixed in place in the shell  55 , for example, by welding the support plates  50 - 52  to the shell  55 . Then the entire modular separator assembly  23  including the shell  55  may be moved as an integral unit into the pressure vessel  11 , e.g., through the open hatch  20 , and fixed in place in any suitable manner with the gas inlet  15  of the pressure vessel  11  fluidly communicating with the inlet opening  57  in the shell  55 . The shell may further include a transit mechanism, e.g., wheels, to facilitate movement along the pressure vessel, or the shell with the remainder of the separator assembly inside may be guided along the pressure vessel, for example, by a push/pull table similar to the push/pull tables used for scrapers. 
     The purification arrangement may include one or more additional components. For example, for some embodiments the purification arrangement  10  may include an openable/closeable barrier  14  positioned in the interior of the pressure vessel  11  between the modular separator and filter assemblies  23 ,  24 . The openable/closeable barrier may be configured in a variety of ways to alternately provide fluid communication between the modular filter assembly and the modular separator assembly and fluidly isolate the modular assemblies. For example, the barrier  14  may comprise a pair of coaxially mounted plates  60 ,  61 , at least one of the plates  61  being rotatable. For many embodiments, one plate  60  may be stationary and the other plate  61  may be rotatable. The plates  60 ,  61  may have a shape that generally conforms to the cross-sectional shape of the interior of the pressure vessel  11  and a dimension, e.g., an outer diameter, that closely corresponds to the inner diameter of the pressure vessel  11 , providing a close fit between the outer edge of the plates  60 ,  61  and the interior of the pressure vessel  11  to inhibit gas flow when the barrier  14  is closed. The plates  60 ,  61  may extend generally perpendicular to the axis of the pressure vessel  11  and may or may not be sealed to the pressure vessel  11 . Each plate  60 ,  61  may have one or more apertures extending around a significant portion, e.g., about 50% or less, of the circumference of the plate  60 ,  61 , the remainder of the plate  60 ,  61  being imperforate. Alternatively, one of the plates  60 ,  61 , e.g., a rotatable plate  61 , may be a partial plate having only an imperforate portion large enough to obstruct the aperture on the other plate  60  in the closed position. The barrier  14  may be movable between an open position and a closed position. For example, at least one of the plates  61  may rotate with respect to the other plate  60  between the open position and the closed position. In the open position, the aperture(s) of the plates  60 ,  61  are aligned and unobstructed, the barrier  14  is open, and gas may flow through the open barrier  14  between the modular assemblies  23 ,  24 . For many embodiments, the imperforate portion of the rotatable plate(s) may be oriented gravitationally below the aperture(s). The greater weight of the imperforate portion may “lock” the barrier in the open position during normal operation when gas flows between the purification assemblies. Alternatively or additionally, the plates  60 ,  61  may be locked in the open position by a locking mechanism (not shown). In the closed position, the imperforate portions of the plates  60 ,  61  obstruct the apertures of the plates  60 ,  61 , the barrier  14  is closed, and the modular assemblies  23 ,  24  are fluidly isolated from one another. The plates  60 ,  61  may be sealed to one another or may be positioned sufficiently close to one another to substantially inhibit gas flow through the obstructed apertures of the closed barrier. 
     The barrier  14  may be mounted in the gas flow path between the modular separator and filter assemblies in a wide variety of ways. For example, the barrier  14  may include a mount  62  for supporting the barrier  14  in the gas flow path between the modular assemblies  23 ,  24 . The mount  62  may be variously configured and the plates  60 ,  61  may be supported by the mount  62  in a variety of ways, e.g., rotatably supported. The mount may be attached to a variety of structures to support the barrier in the interior of the pressure vessel. For some embodiments, the mount may be attached to the pressure vessel itself. For example, the mount may be attached, e.g., removably attached, to the interior of the pressure vessel, supporting the barrier between the modular filter assembly and the modular separator assembly. For other embodiments, the mount may be attached to the modular separator assembly. For example, the mount may be attached to the struts or the downstream support plate of the frame or to the shell of the separator assembly, supporting the barrier just beyond and downstream of the separator assembly. For still other embodiments, the mount may be attached directly to the modular filter assembly  24 . For example, the mount  62  may be attached to the frame  30  of the filter assembly  24 , e.g., the support plate  32  and/or the struts  33 , supporting the barrier  14  just behind and upstream of the filter assembly  24 . 
     Methods for removing particulates from a gas flowing in a gas pipeline system may be embodied in a wide variety of ways. For example, during normal operation a flow of gas may be established through the pipeline system and through the pressure vessel  11  connected to the pipeline. As the gas flows along the gas flow path through the interior of the pressure vessel  11 , the gas is directed through the gas inlet  15 , the modular separator assembly  23  and the modular filter assembly  24  before exiting the pressure vessel  11  via the gas outlet  16 . As the gas flows through the modular separator and filter assemblies  23 ,  24 , a significant portion of the particulates, both liquid and solids, is removed from the gas by the modular assemblies  23 ,  24 . The upstream modular separator assembly  23  may remove liquid and larger solids particulates and the downstream modular filter assembly  24  may remove finer solids particulates. This arrangement of a modular separator assembly  23  upstream and a modular filter assembly  24  downstream in the pressure vessel  11  is particularly effective for removing black powder from the gas. 
     As shown in  FIG. 1 , gas may enter the pressure vessel  11  and pass along the gas flow path first through the modular separator assembly  23  and then through the modular filter assembly  24 . As the gas passes through the separator assembly  23 , it may be first directed through the first stage of the separator assembly to remove liquid and larger solids particulates and then through the second stage to remove additional liquids and finer solids particulates. For example, gas may pass from the gas inlet  15  directly to the first stage, impinging against an impact separator, e.g., the angled impact plate  40 . Liquid particulates may coalesce along the impact plate  40  and then flow to the bottom of the first stage. The larger solids particulates may be deflected by the impact plate  40  to the side and then fall to the bottom of the first stage. After moving quickly past the edges of the angled impact plate  40 , the gas may slow in the larger settling region  41  below the angled impact plate  41 , allowing additional particulates to settle to the bottom of the first stage. Particulates removed in the first stage may be contained between the upstream support plate  51  and the intermediate support plate  52 . 
     The gas may then enter the second stage from the settling region  41  of the first stage, for example, passing through an aperture located closely under the apex of the angled impact plate  40  and into the duct  54  of the second stage. From the duct  54 , the gas may enter a cyclone separator  42 , for example, through an inlet opening in the side of each outer can  44 , where the gas and remaining liquid and solids particulates are swirled within the outer can  44  toward the outlet end of the can  44 . Liquid and solids particulates are deflected from the principal gas flow stream by the cyclonic movement of the gas in the outer can  44  and fall to the bottom of the second stage through the outlet end of the outer can  44 . Additional traps (not shown) beneath the outer cans may enhance the retention of liquid and solid particulates between the intermediate and downstream support plates  52 ,  50 . The gas may pass from the outlet end of the outer can  44  and into the inlet end of the inner can  45 , where it may pass along the inner can  45  and through the outlet end of the inner can  45  into the space above the top plate  43 . From the space above the top plate  43 , the gas, substantially depleted in particulates, may exit the modular separation assembly  23 , for example, through the opening in the downstream support plate  50  above the top plate  43 . Particulates removed in the second stage may be contained between the intermediate support plate  52  and the downstream support plate  50 . 
     For embodiments having a shell  55  around the separators or stages of the modular separation assembly  23 , e.g., the first and/or second stages of the separation assembly  23 , the removed liquid and solid particulates are conveniently and safely contained in the modular separation assembly  23  by the shell  55  and isolated from the pressure vessel  11 . For example, the particulates removed in the first stage may be contained between the upstream support plate  51  and the intermediate support plate  52  by the shell  55 . The particulates removed in the second stage may be contained between the intermediate support plate  52  and the downstream support plate  50  by the shell  55 . For embodiments without a shell, the removed particulates may be contained in the separation assembly by the support plates and the pressure vessel. 
     From the modular separator assembly  23 , the gas may flow along the gas flow path to the modular filter assembly  24 . For embodiments having an openable/closable barrier  14 , the gas may flow between the modular assemblies  23 ,  24  through an open barrier  14 . For example, the gas may flow through the aligned apertures in the plates  60 ,  61  of the open barrier  14  between the modular separator assembly  23  and the modular filter assembly  24  with little or no pressure drop. For embodiments without an openable/closable barrier, the gas may flow directly to the modular filter assembly. 
     The gas may then pass along the gas flow path through the modular filter assembly  24 , where any finer particulates remaining in the gas may be removed by the filter medium  26 . For example, for embodiments arranged for outside-in flow through the filter elements  25 , the gas may flow into the unfiltered region along the exterior of the filter elements  25 . The gas then passes outside-in through the porous filter medium  26  of each filter element  25 , where the finer particulates are removed by the filter medium  26 , and into the interior of the hollow filter element  25 . From the interiors of the filter elements  25 , the filtered gas may pass to the gas outlet  16  of the pressure vessel  11  substantially free of liquid and solids particulates. For example, the gas may pass along the interiors of the filter elements  25  through the apertures in the tube sheet  31  into the header  34  and through the header  34  to the gas outlet  16 . 
     After an extended period of time, one or both of the modular separator assembly  23  and the modular filter assembly  24  may become loaded with particulates. Various sensors, e.g., pressure sensors and/or weight sensors, associated with the modular assemblies  12 ,  13  may provide an indication that a design parameter, e.g., the pressure drop across or the particulate weight within the modular assembly, has been exceeded. Gas flow through the pressure vessel  11  may then be terminated. For example, the pipeline system may be shut down or the purification arrangement  10  may be bypassed or taken off line in favor of a parallel purification arrangement  10 . Upon termination of the gas flow one or both of the modular separator and filter assemblies  23 ,  24  may be serviced, e.g., cleaned and/or replaced. 
     The modular structure of the separator assembly, as well as the filter assembly, greatly facilitates removal and replacement. After the modular separator assembly becomes loaded with particulates, the pressure vessel may be opened and the modular separator assembly, including at least the frame and the separators, may be quickly and easily removed from the pressure vessel as an integral unit. For example, the pressure vessel  11  may be opened by removing the cover, e.g., swinging open the hatch  20  at the first axial end of the horizontal pressure vessel  11 . The opening provided when the cover is removed may be large enough to accommodate removal of the entire modular separator assembly  23  as a single integral unit through the first axial end of the pressure vessel. The modular separator assembly  23  may be removed, fir example, via a push/pull table and/or a transit mechanism. Because the modular separator assembly  23  is removed as a single integral unit, the downtime required to extract the modular separator assembly from the pressure vessel  11  is far less than the downtime required to disassemble a separator assembly within the pressure vessel and remove it piece-by-piece. 
     For embodiments having a shell  55 , the shell  55  of the modular separator assembly  23  also facilitates servicing of the purification arrangement  10 . Many particulates, including black powder, may be toxic and/or may be chemically reactive, e.g., pyrophoric, when exposed to air and, therefore, present a serious safety hazard to the service personnel. The shell  55  collects and contains the particulates removed by the separators  40 ,  42  and isolates the service personnel from many of the hazards of these particulates. For example, in the illustrated embodiment, when the pressure vessel  11  is opened, e.g., by swinging the hatch  20  open, and the modular separator assembly  23  is removed through the open hatch  20 , all of the collected liquid and solid particulates contained within the shell  55  are removed with the modular separator assembly  23  and are isolated from the service personnel. To even further ensure the safety of the service personnel, the shell may be filled with water and/or any other suitable inhibitor. For example, water may dilute the liquid contaminants in the shell and prevent any solid contaminants in the shell from reacting with air. The water may be supplied to the shell  55  through a water inlet in the pressure vessel  11  and the top opening  59  in the shell  55  before the modular separator assembly  23  is removed. 
     In addition to protecting the service personnel, the shell  55  of the modular separator assembly  23  further reduces the downtime required for removing a separator assembly  23  fully loaded with particulates and replacing it with a cleaned/new modular separator assembly  23  empty of particulates. Not only does the shell  55  isolate the particulates from the service personnel, it also isolates the particulates from the pressure vessel  11 . When the loaded modular separator assembly  23  with all of the removed particulates contained within the shell  55  is removed, the pressure vessel remains relatively clean, requiring far less time to clean the interior of the pressure vessel  11  in the vicinity of the removed modular separator assembly  23  and install the cleaned/new modular separator assembly  23 . 
     For embodiments having an openable/closeable barrier, service personnel may be further protected by the openable/closeable barrier  14 . For example, after the gas flow is terminated, the open barrier may be closed, isolating the modular separator and filter assemblies from one another and allowing at least one of the modular assemblies e.g., the modular separator assembly  23 , to be serviced without exposing the service personnel to the particulates in the other assembly, e.g., the modular filter assembly  24 . For example, the hatch  20  of the pressure vessel  11  may be opened and the open barrier  14  may be moved to the closed position in any of a variety of ways. For example, one of the modular assemblies, e.g., the modular separator assembly  23 , may have a hollow guide  63  which extends through the separator assembly  23  and allows a tool  64 , e.g., an elongate T-bar, to be coupled to the open barrier  14  to move it to the closed position. For some embodiments, the tool  64  may have a fitting on one end that engages the rotatable plate  61  of the barrier  14  and rotates the plate  61  until the imperforate portions of the plates  61 ,  62  obstruct the apertures in the plates  61 ,  62 , closing the barrier  14 . The closed barrier  14  defines first and second isolated chambers  65 ,  66  within the pressure vessel  11  around the modular separator and filter assemblies  23 ,  24 , respectively, allowing the service personnel to service one of the modular assemblies  12 ,  13  free of the risks from the particulates in the other modular assembly  13 ,  12 . 
     For many embodiments, the service personnel may be even further protected by flooding one or both of the first and second chambers  65 ,  66  with an inert gas, e.g., nitrogen. For some embodiments, before the hatch  20  is opened, the entire pressure vessel  11 , the first and second chambers  65 ,  66 , or at least the second chamber  66  may be flooded with the inert gas via an inert gas inlet in the pressure vessel  11 . The hatch  20  may then be opened and the barrier  14  may be moved to the closed position, maintaining the inert gas in the second chamber  66  around the filter elements  25  of the modular filter assembly  24 . Additionally, a small flow of inert, gas may be directed into the second chamber  66  to maintain a small positive pressure of inert gas in the second chamber  66  while barrier  14  is closed and the modular separator assembly  23  is removed and/or serviced. Maintaining the inert gas around the modular filter assembly  24  ensures that the fine particulates removed by the filter assembly  24  are not exposed to air and subject to the possibility of a pyrophoric reaction. 
     If the modular filter assembly  24  is not in need of servicing, the region of the pressure vessel  11  containing the modular separator assembly  23  may be cleaned, a task made much easier and faster if the modular separator assembly  23  includes a shell  55  containing the removed particulates. A cleaned/new modular separator assembly  23 , with or without a shell, may then be installed in the pressure vessel  11 , for example, through the open hatch  20  in the pressure vessel  11 , e.g., via a transit mechanism and/or push/pull table. The modular separator assembly  23  may be installed quickly and easily as a single integral unit, further reducing downtime for many reasons similar to those previously described. For embodiments having an openable/closeable barrier  14 , the closed barrier  14  may be opened, either before or after the cleaned/new modular separator assembly is installed. For example, a cleaned/new modular separator assembly  23  with a shell  55  may be installed in the pressure vessel  11 . The T-bar  65  may then be inserted through the guide  63  and engaged with the rotatable plate  61 , and the plate  61  may be rotated until the apertures in the plates  60 ,  61  are aligned, opening the barrier  14  for normal operation. The cover, e.g., the hatch  20 , may be closed, and gas flow may again be established through the purification arrangement  10 . 
     If the modular filter assembly  24  is also in need of servicing, it too may be removed from the pressure vessel  11 . For some embodiments, the pressure vessel may include a separate opening, e.g., a separate hatch or cover, for removing the modular filter assembly, allowing the modular filter assembly to be removed before or at the same time as the modular separator assembly. In the illustrated embodiment, the modular filter assembly  24  may be removed from the pressure vessel  11  after the modular separator assembly  23  through the same opening, e.g., the hatch  20 , as the modular separator assembly  23 . For embodiments in which an openable/closeable barrier is attached directly to the pressure vessel, the barrier and/or the barrier mount may be removed from the pressure vessel before the modular filter assembly follows the modular separator assembly through the hatch. For embodiments in which the barrier  14  is attached to the modular separator or filter assembly  23 ,  24  or no barrier is provided, the modular filter assembly  24  may be quickly and easily removed as an integral unit from the pressure vessel  11  for cleaning or replacement in a variety of ways, similar to those previously described with respect to the modular separator assembly  23 . In the illustrated embodiment, the modular filter assembly  24  may be disengaged from the gas outlet  16  of the pressure vessel  11 , for example, by disengaging the header  34  from the gas outlet  16 . The modular filter assembly, including at least the frame and the array of filter elements, may then be extracted from the pressure vessel as a single integral unit. For example, the opening provided when the cover is removed may be large enough to accommodate removal of the entire modular filter assembly  24 , for example, through the first axial end of the pressure vessel by means of a push/pull table and/or a transit mechanism. For embodiments with a transit mechanism, e.g., the wheels  36 , the modular filter assembly  24  may be quickly and easily rolled along the pressure vessel  11 , e.g., through the open hatch  20 . Again, because the modular filter assembly  24  is removed as a single integral unit, the downtime required to extract the modular filter assembly  24  from the pressure vessel  11  is far less than the downtime required to disassemble a filter assembly within the pressure vessel and remove the filter assembly piece-by-piece. The hairier  14  may be removed from the pressure vessel  11 , for example, along with the modular filter assembly  24 . The individual filter elements  25  may be cleaned or replaced. Alternatively, an entirely new filter assembly  24 , including new filter elements  25 , with or without a barrier  14 , may replace the spent modular filter assembly  24 . 
     Once the pressure vessel  11  is empty, it may be cleaned and a cleaned/new modular filter assembly  24  may be installed in the pressure vessel  11  as an integral unit. For example, the cleaned/new modular filter assembly  24 , with or without an attached barrier  14 , may be moved into the pressure vessel  11  through the open axial end and along the pressure vessel  11  and fitted into sealed engagement with the gas outlet  16  at the opposite axial end of the pressure vessel  11 . For embodiments with a transit mechanism, e.g., the wheels  36 , the modular filter assembly  24  may be quickly and easily rolled toward the gas outlet  16  until the header  34  engages and is sealed to the gas inlet  16 . The modular filter assembly  24  may be installed quickly and easily as a single integral unit, further reducing the downtime as previously described. 
     Before or after the cleaned/new modular filter assembly  24  is installed, any barrier  14  may be moved to the open position. The cleaned/new modular separator assembly  23  may then be installed as a single integral unit as previously described. The cover, e.g., the hatch  20 , may be closed. And a gas flow may again be established through the purification arrangement  10 , including the modular separator assembly  23  and the modular filter assembly  24 . 
     Although the invention has been disclosed in the embodiments previously described and illustrated, the invention is not limited to those embodiments. For instance, one or more features of an embodiment may be eliminated or modified, one or more features of one embodiment may be combined with one or more features of other embodiments, or embodiments with very different features may be envisioned without departing from the scope of the invention. For example, for some embodiments the openable/closeable barrier may comprise a single plate including one section hinged to another section. The hinged section may be moved between a closed position and an open position. In the closed position, the two sections of the plate may be co-planar and the plate may have a shape that closely fits across the cross section of the pressure vessel, inhibiting gas flow and isolating the modular separator and filter assemblies. In the open section, the hinged sections may extend at an angle to one another, creating an aperture through which gas may flow between the modular separator and filter assemblies. A tool similar to the T-bar may be used to open and close the hinged barrier. For some embodiments, the barrier may comprise a shuttered or louvered plate. The shutter(s) or louver(s) may be moved to an open or closed position in a variety of ways, including fir example, as previously described with respect to the T-bar. Alternatively, the shutter(s) or louver(s) may be biased toward a closed position, e.g., by springs, but forced to the open position, for example, when the modular separator assembly is inserted in the pressure vessel. For example, a member on the modular separator assembly may contact the barrier and force the shutter(s) or louver(s) open when the modular separator assembly is properly positioned in the pressure vessel. 
     For some embodiments, the array of filter elements of the modular filter assembly may be arranged for gas flow inside-out. The tube sheet may be positioned at the end of the array closest to the barrier and may be sealed to the pressure vessel or to a housing surrounding the array of filter elements. The open ends of the filter elements may be sealed to the apertures in the tube sheet, while the support plate may be located at or near the opposite end of the array. Gas flowing through the open barrier may pass into the interiors of the hollow filter elements through the apertures in the tube sheet and then pass inside-out through the filter medium of the filter elements, where the finer particulates are removed, to the exterior of the filter elements. From the exterior of the filter elements, the gas may pass to the gas outlet of the pressure vessel. 
     The present invention thus encompasses innumerable embodiments and is not restricted to the particular embodiments that have been described, illustrated, and/or suggested herein. Rather, the present invention includes all embodiments and modifications that may fall within the scope of the claims. 
     The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.