Abstract:
Apparatus and method is provided for capturing centrifugally-liberated liquid from a gas stream including separator components installed in a cyclonic vessel. A plurality of concentric shells supported on a base form annular cavities arranged about a gas outlet for capturing separated liquids from a spinning gas stream. The shells can be suspended from an insert manufactured with or retrofit to a vessel. Helical vanes aid in maintaining the spinning gas stream. In low moisture conditions, liquid removal through annular cavities can be supplemented with an annular layer of packing adjacent the vessel wall.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority of U.S. Provisional Patent Application Ser. No. 60/445,450, filed on Feb. 7, 2003, the entirety of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The invention relates generally to apparatus for removing small amounts of liquids from a gas stream. More particularly, cyclonic operation aids in the removal of moisture from compressed air and moisture and mists from gas streams such as wellhead gas effluent. 
   BACKGROUND OF THE INVENTION 
   Downstream condensation and formation of hydrates can be a serious problem in gas processing. Liquids include water vapor (moisture) and liquid hydrocarbon mist. In some cases, simple centrifugal separator vessels are implemented which are capable of gross removal but result in substantial moisture or liquid re-entrainment. Dehydrators are applied for the removal of water vapor from hydrocarbon gas streams. Dehydrators, such as those implementing glycol, are capable of greater moisture removal, however they are also associated with a large cost and negative environmental impact including a large energy cost associated with heating to separate water and glycol and the exhaust emissions. 
   Applicant has determined that there is a novel approach to the removal of liquids which demonstrates improved efficiency without the need for additional energy consumption and emissions. 
   SUMMARY OF THE INVENTION 
   Methodology and apparatus are applied for the removal of liquids from gas streams including compressed air and gas from gas wells. 
   Apparatus is provided for better capturing centrifugally-liberated liquid from such gas streams so as to prevent re-entrainment and thereby achieve greater removal. In one embodiment, the present invention comprises components for a cyclonic vessel. The components can be conveniently provided as an insert to a manufactured vessel or as a retrofit to an existing vessel. 
   In one form of the present invention, a tangential gas inlet imparts a cyclonic spin to incoming wet gas. A plurality of concentric shells are placed adjacent the gas outlet at the discharge of the cyclonic vessel for capturing separated liquids before re-entrainment. Liquid collects in annular cavities for draining out of the vessel. Helical vanes can be added for enhancing or maintaining the spinning of the gas stream. In low moisture conditions, the shells can be supplemented with an annular layer of high surface area contacting material at the vessel wall. 
   In a broad embodiment, apparatus for treating a gas stream containing liquid is adapted to a vessel having cylindrical side walls, a bottom end, and a tangential gas inlet adjacent a top end. The apparatus comprises: a base plate positioned below the tangential gas inlet; at one least cylindrical shell arranged on the base plate and adjacent the wall portion for forming at least one annular cavity extending upwardly from the base plate and having an open upper end for receiving liquid therein; an opening in the base plate at each annular cavity for draining liquid from the at least one annular cavity; an outlet for the gas stream positioned adjacent the base plate and within the annular shells; and a plate above the gas outlet for directing the gas stream over the one or more annular cavities before the gas stream is removed through the gas outlet. 
   Preferably the base plate and shells are includes as part of an insert installed into a sectional vessel having a tangential gas inlet. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a substantially conventional prior art surge vessel for primary separation of wet gas from solids; 
       FIG. 2   a  is a cross-sectional view of a separator according to one embodiment of the invention which illustrates a separation insert installed in a gas processing vessel. An optional annular blanket is only shown partially to improve clarity of the other components; 
       FIG. 2   b  is a cross sectional view of the insert of  FIG. 2   a , illustrated isolated from the vessel prior to insertion into the vessel and having optional helical vanes thereon for spinning the downcoming wet gas stream. The optional mist pad has been omitted for clarity; 
       FIGS. 3   a  and  3   b  are side and top cross-sectional views respectively of a top portion of the vessel of  FIG. 2   a  illustrating the dry gas discharge conduit, dry gas exit, the tangential wet gas inlet, and the top of the vessel being flanged for enabling installation and maintenance of the insert of  FIG. 2   b  as required; 
       FIGS. 4   a  and  4   b  are cross-sectional views of the base of the vessel of  FIG. 2   a  and illustrating a side and a top views respectively of the concentric shells section and the dry gas discharge conduit; 
       FIG. 5  is a partial cross-sectional view of another embodiment of the concentric shells section and the dry gas discharge conduit; and 
       FIG. 6  is a cross-sectional view of a separator according to another embodiment of the invention which illustrates cyclone separation apparatus having a lower end gas outlet from the vessel. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   One embodiment of the separator  20  is shown in  FIGS. 2   a – 4   b . The separator  20  is particularly well adapted to treatment of wellhead gas streams containing hydrocarbon mists and moisture. Typically, the incoming gas stream is initially and conventionally treated in a surge separator  10  ( FIG. 1 ) where gross removal of impurities and solids from the wet gas stream is required. 
   The wet gas stream containing liquid is then directed tangentially through one or more separators  20  of the present invention. 
   Each separator  20  comprises a cylindrical vessel  21  having a top end  22 , a bottom end  23  and side walls  25 . As shown in  FIGS. 3   a  and  3   b , a tangential gas inlet  24  is fit to the top end  22  for imparting cyclonic action to the incoming wet gas stream. 
   A base plate  29 , spaced downstream and below the tangential gas inlet  24 , divides the vessel  21  into a cyclonic upper separation section G and a lower liquid storage section L. 
   The upper separation section G comprises a centrifugal or cyclonic section C above a liquid trapping section T. The wet gas stream travels downwardly through the upper separation section G from the gas inlet  24  in a spinning motion towards the bottom end  23  of the vessel  21  and base plate  29 . Liquid contained therein concentrates adjacent the side walls  25 . As necessary, the spinning motion of the gas stream is further encouraged using one or more helical vanes  26  spaced along the cyclonic section C. 
   Optionally, and typically where liquid loading is light, a thin layer or annular blanket  50  of high surface area contacting material or packing  51 , such as felt, resides adjacent the side walls  25  for capturing released liquid and conducting the liquid to the liquid trapping section T. The blanket  50  extends upwardly from the liquid trapping section T and along the vessel side walls  25 . The packing  51  is retained adjacent the vessel side wall by a mesh frame  52  which enables maximal communication between the wet gas stream and the packing. Cyclonic action engages the majority of moisture and mists with the annular packing  51  which then drains down the packing to the liquid trapping section T. The mesh frame  52  can be suspended from the helical vanes  26  or additionally upon the liquid trapping section T. 
   The liquid trapping section T comprises one or more cylindrical shells  42 , 42  . . . which extend upwardly from the base plate  29  and which are spaced from each other  42 , 42  and can also be spaced from the side walls  25  for forming one or more annular cavities  43  therebetween. A substantially dry gas entrance  31  is located generally centrally and adjacent the base plate  29 . The dry gas entrance  31  is shielded from the upper separation section G by a laterally extending barrier or deflector  40  having gas flow bypass  41  formed about its periphery. The deflector  40  maximizes exposure of the gas stream and separated liquids remain outwardly and maximally exposed to the annular cavities  42 , 42  . . . before a substantially dry gas is re-directed radially inwardly to the dry gas entrance. 
   The shells  42  are spaced from the vessel side walls  25  and from one another  42 , 42 , 42  . . . , each of the one or more shells  42  being arranged successively from an outermost shell adjacent the vessel&#39;s side walls  25  to an innermost shell spaced from the gas inlet  31 . As stated, the cyclonic action concentrates liquids from the gas stream radially outwards towards the vessel&#39;s side walls  25 . Liquids adjacent the vessel side walls  25 , and those which may diminish in a gradient radially inward, are captured in the successive annular cavities  43 , 43  . . . . 
   In embodiment applied in operation on light loadings, few shells  42  are required. For the treatment of moist air, one may use a solitary cylindrical shell forming a single annular cavity between the side walls  25  and the shell  42 . 
   In another the embodiment, as shown, each successively and radially inwardly spaced shell  42 , having an ever decreasing radius, has a corresponding diminishing height. Accordingly a gas stream, having released much of its liquid content, approaches the gas outlet  31  and is more-and-more constricted radially by a conical and reducing vessel volume, the gas stream traversing each annular cavity  43  for additional liquid capture therein and wherein a drier gas stream results with is discharged through the gas outlet  31  and out of the vessel. 
   In one embodiment shown in  FIG. 2   a , a discharge conduit  30  extends out of the top end  22  of the vessel  21  such as for transfer of the drier gas stream to additional stages of separators  20  or collection. The discharge conduit  30  extends along the axis of the vessel  21  between a bottom end  33  at the gas outlet  31  adjacent the base plate  29  and a top end  32  at the vessel&#39;s top end  22 . In another embodiment shown in  FIG. 6 , the drier gas stream is discharged from the bottom end  23  of the vessel  21 . In this case the discharge conduit  30  is directed downwardly. If helical vanes are employed, a dummy support member  35  extends upwardly from the liquid trapping section T. 
   Various embodiments of the shells  42  are shown in  FIGS. 4   a , 4   b  and in  FIG. 5 . As shown in  FIGS. 4   a  and  4   b , each shell  42  extends upwards from the base plate  29 . Typically, the shells  42  would be nested concentrically. Each annular cavity  43  is formed between each adjacent pair of shells  42  and has an open end  46 . In one aspect, the annular cavities  43  result in a quieting of the gas stream and permit the centrifugally separated liquids to fall-out of suspension and avoid re-entrainment. As the separation of liquids by centrifugal force is a continuum, occurring at a maximum at the vessel side  25  wall and a minimum at the central axis, the series of shells  42 , 42  and annular cavities  25 , 43  and  43 , 43  collect liquid from a plurality of radial locations in the spinning gas stream, The base plate  29  adjacent each annular cavities  43  is lit with a plurality of drain holes  45  to enable the emptying of each cavities into the liquid collection section L below the shells  42  and base plate  29 . 
   With reference to  FIG. 5 , an alternate embodiment of the gas outlet  31  is shown. The deflector  40  is incorporated into a sump affixed to the base plate  29 . A plurality of entrances  55  are formed in the sump, below the deflector  40 . An variation on the number of cylindrical shells is also illustrated, having three concentric shells  42 , 42 , 42  and having spacer elements  56  between the vessel  21  and between adjacent shells  42 , 42 . 
   The separator of the present invention can be manufactured as a component of a custom vessel or a retrofit to an existing vessel  21 . With reference to  FIG. 2   b , the base plate  29 , concentric shells  42 , 42 , and discharge conduit  30  can be fabricated as an insert  49  for installation into a typical gas processing vessel having a tangential gas inlet  24 . The base plate  29  is supported from the bottom end  33  of the discharge conduit  30 . Further, as shown only in  FIG. 2   a , the helical vanes  26  and mesh  50  can be manufactured as part of the insert  49 . A vessel  21  can include a connection  60  between the top end  22  and the bottom end  23  which enables opening the vessel  21  for installation of the insert  49 . Typically, for pressure vessels, a flanged connection  61  can be employed. Further, connection  60  enables insertion of an additional cylindrical spool (not shown) which can be provided as desired to increase separation distance above the base plate  29 . 
   Accordingly, one can retrofit an approved or regulated vessel with the apparatus of the invention without a need for manufacture of a custom vessel which may require re-certification. 
   With reference to  FIG. 2   a , the illustrated separator is suitable for ASME code up to 1440 psi service and was designed for processing up to 6 million cubic feet of natural gas per day and has the following specifications: 12 inch inside diameter pipe having hemispherical heads for an overall height of about 10 feet. As shown, five cylindrical shells of 12 gauge material have the following diameters spaced sequentially from the side walls: 11, 10, 9, 8, and 6 inch. Each shell  42 , 42 , 42 , 42 , 42  has a different height measured from the base plate  26 , respectively: 16, 14, 12, 10, and 8 inches. A seven inch diameter deflector plate  40  is supported on a 2 inch discharge conduit  30 . The gas outlet  31  can be formed of approximately forty-eight ⅜ inch holes drilled in the discharge conduit  30  adjacent the base plate  29 . An annular blanket  50  is formed of ½ inch of felt  51  supported in a 20 gauge expanded metal mesh frame  52 . A plurality of ¼ inch drain holes  45  were provided along radial quadrants in the base plate  29  outside the outermost of the shells  42 , between each shell  42 , 42  and inside the innermost of the shells  42 . 
   EXAMPLES 
   A smaller yet similarly proportioned separator according to  FIG. 2   a , was tested for removing air from compressed air. Such a separator, being 7 foot tall and 6⅝ inch diameter was tested on 185 scfm air at 100 psig. Only one shell adjacent the side walls was utilized and a felt annular blanket was installed. Ambient air at 43 F and 74–82% humidity was compressed to 100 psig and 84 F and treated through the separator. A drier gas stream exited the vessel at 5% relative humidity and 55 F. The liquid recovery was 29 ounces in 2 hours. 
   In another test on the same unit, drier ambient air was tested with the addition of supplementary water. Ambient air at 56 F and 54% humidity was compressed to 100 psig and 90 F. Over a two hour period, 72 ounces of water were added to the compressed gas stream and treated through the separator. The liquid recovery was 98 ounces in 2 hours or a recovery of 26 ounces from the air stream. A drier gas stream exited the vessel at 65 F. 
   Application of the apparatus and methodology disclosed herein results in significant savings over known dehydrator technology.