Patent Abstract:
A feed gas conditioner includes a pressure vessel that encloses at least part of a pre-heater. The pre-heater has an inlet for connection to a source of feed gas and an outlet for delivering the feed gas into the interior of the pressure vessel. An electrical heater element located within the pre-heater increases the temperature of the feed gas as it flows through the pre-heater. An expansion valve reduces the pressure of the feed gas as it flows from the pre-heater so as to initiate condensation. A super heater is at least partially located within the pressure vessel and has an inlet within the interior of the pressure vessel. A filter is in a flow path in the pressure vessel leading from the pre-heater heater to the super heater for removing condensate from the feed gas. An electrical heater element is in the super heater for heating the feed gas.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. utility patent application Ser. No. 12/029,957, filed on Feb. 12, 2008, which claimed priority to provisional application 60/889,324, filed Feb. 12, 2007, the disclosures of which are incorporated herein by reference. 
    
    
     This application is also related to U.S. utility patent application Ser. No. 12/339,811, filed Mar. 6, 2009; U.S. utility patent application Ser. No. 12/553,808, filed on Sep. 3, 2009, U.S. utility patent application Ser. No. 12/553,823, filed Sep. 3, 2009, U.S. utility patent application Ser. No. 12/584,610; filed Sep. 9, 2009, U.S. utility patent application Ser. No. 12/584,626, filed Sep. 9, 2009, and U.S. utility patent application Ser. No. 12/584,640, filed Sep. 9, 2009. 
     FIELD OF THE INVENTION 
     This invention relates in general to an apparatus for converting a natural gas from a feed line to a superheated, clean and dry fuel gas for a gas turbine. 
     BACKGROUND OF THE INVENTION 
     Gas turbines are normally supplied with a dry gas that is superheated a selected level above its due point. The super heat avoids any liquids in the gas condensing as the temperature drops. 
     A typical conditioning system is made up of several pieces of equipment connected together by flowlines. This equipment may include a pre-heater to pre-heat the feed gas flowing into the system. An expansion valve is located in a flowline leading from the pre-heater to a gas scrubber. The expansion valve drops the temperature below the dew point of the gas. Typically, the gas scrubber comprises a cylindrical pressure vessel oriented upright, with the inlet at a lower portion and the outlet at an upper end. A coalescing filter is located between the inlet and the outlet for removing the condensate as the gas flows through. The gas flows then to a super heater, which heats the gas to a desired temperature above the dew point. The gas then flows through another filter to the gas turbine. 
     While this system works well, it takes up considerable space. Some facilities may lack adequate space. Also, the separate pieces of equipment add to the cost. 
     SUMMARY 
     In this invention, a gas conditioning system is provided that is substantially contained within a single pressure vessel. A pre-heater heater element housing is at least partially located within the pressure vessel. The pre-heater heater element housing has an inner passage with an inlet for connection to a source of feed gas and an outlet for delivering the feed gas into the interior of the pressure vessel. At least one electrical heater element is located within the inner passage of the pre-heater heater element housing for increasing the temperature of the feed gas as it flows through the pre-heater heater element housing. An expansion valve reduces the pressure of the feed gas as it flows from the pre-heater heater element housing so as to initiate condensation. A super heater housing is at least partially located within the pressure vessel and has an inlet within the interior of the pressure vessel. The super heater housing has an outlet leading exterior of the pressure vessel. A filter within the interior of the pressure vessel is in a flow path leading from the pre-heater heater element passage housing to the super heater housing for removing condensate from the feed gas. At least one electrical heater element is in the super heater housing for heating the feed gas. 
     In the preferred embodiment, the pre-heater heater element housing is located within an outer housing, defining an annular passage between the pre-heater heater element housing and the outer housing. The expansion valve is located at a junction between the outlet of the inner passage and an inlet of the annular passage. The expansion valve may be located exterior of the pressure vessel or within the pressure vessel. 
     The filter is preferably divided into a plurality of segments that are separately removable from the pressure vessel. Each of the segments has an outer edge that comprises a portion of a cylinder and which engages an inner cylindrical wall of the pressure vessel. Each of the segments has an inner edge that abuts an inner edge of another of the segments. Drains lead from the pressure vessel on opposite sides of the filter for draining condensate from the pressure vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of an apparatus constructed in accordance with this invention. 
         FIG. 2  is a sectional view of the apparatus of  FIG. 1  taken along the line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a sectional view of a portion of an alternate embodiment of an apparatus in accordance with this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , fuel gas conditioning system  11  includes a pressure vessel  13  having an interior chamber  12 . Pressure vessel  13  is preferably cylindrical and has two closed ends  14 ,  16 . The length of pressure vessel  13  considerably greater than its diameter. In this example, the longitudinal axis of pressure vessel  13  is horizontal. 
     A pre-heater unit  15  is mounted in pressure vessel  13  with its axis parallel and offset from the longitudinal axis of pressure vessel  13 . Pre-heater unit  15  has a length somewhat greater than the length of pressure vessel  13  in this example, with its ends protruding past ends  14 ,  16  of pressure vessel  13 . Pre-heater unit  15  has an outer tubular housing  17  and a concentric inner tubular housing  19 , defining an annulus  21  between housings  17 ,  19 . A plurality of electrical heater elements  23  extend longitudinally within inner housing  19 . 
     Heater elements  23  are conventional elements, each comprising a metal tube containing an electrical resistance wire electrically insulated from the tube. In this embodiment, heater elements  23  are U-shaped, each having its terminal ends mounted within a connector housing  25  located exterior of end  14  of pressure vessel  13 . The bent portions of heater elements  23  are located near the opposite end of pre-heater unit  15 . A power controller  27  supplies power via wires  29  to electrical heater elements  23 . Power controller  27  varies the power in response to temperature sensed by a temperature sensor  31  that is located within chamber  12  in pressure vessel  13 . 
     Pre-heater unit  15  has an inlet  33  that leads to the interior of inner housing  19  of pre-heater unit  15  in the portion of pre-heater unit  15  exterior of pressure vessel end  14 . In the embodiment of  FIG. 1 , an external conduit loop  35  is located on the opposite end of pre-heater unit  15 , exterior of pressure vessel end  16 . External loop  35  leads from the interior of inner housing  19  to annulus  21 . A variable expansion valve  37  is located in external loop  35  for reducing the pressure of the gas flowing through external loop  35 , which also results in cooling of the gas. Expansion valve  37  varies the amount of pressure drop in response to a pressure sensor  39  located within pressure vessel chamber  12 . 
     Annulus  21  has an outlet  41  located within pressure vessel chamber  12  near end  14 . A mist or coalescing filter  43  is located within pressure vessel chamber  12  approximately halfway between ends  14 ,  16  of pressure vessel  13 . Coalescing filter  43  collects liquid mist from the gas flowing from annulus outlet  41  towards the pressure vessel end  16 . 
     A super-heater  45  is mounted in pressure vessel chamber  12 . Super-heater  45  has an elongated tubular housing  47  that hag an axis parallel with the axis of pre-heater unit  15  and offset from the axis of pressure vessel  13 . Super-heater  45  is located above pre-heater unit  15  in this example and has a length that is less than the length of pre-heater unit  15 . Super-heater  45  has an inlet  49  in housing  47 , inlet  49  being within pressure vessel chamber  12  and closer to pressure vessel end  16  than end  14 . Super-heater  45  has a plurality of electrical resistance heater elements  51  located within housing  47 . 
     Electrical resistance heater elements  51  may be of the same type as electrical resistance heater elements  23  of pre-heater unit  15 . Preferably, each is U-shaped with both of its terminal ends mounted within an a connector housing  53 , which is external of end  14  of pressure vessel  13 . A power controller  55  supplies power to electrical resistance heater elements  51 . Power controller  55  controls the power in response to temperature sensed by a temperature sensor  57  located within an outlet  59  of super-heater  45 . In this embodiment, outlet  59  leads from a portion of super-heater housing  47  that is external of pressure vessel  13 . 
     Pressure vessel  13  has at least one drain  61  for draining liquid that condenses within chamber  13  upstream of filter  43  as a result of the pressure drop. A second drain  63  drains liquid that separates from the gas as a result of flowing through filter  43 . Drains  61 ,  63  are located on opposite sides of filter  43  and lead downward from a lower point on the sidewall of pressure vessel  13 . Each drain  61 ,  63  leads to a separate sump  65 ,  66 . In this example, sumps  65 ,  66  are compartments of a single tubular pressure vessel and separated from each other by a sealed plate  67 . Outlets  69 ,  71  lead from the bottom of sumps  65 ,  66  to liquid control valves  73 ,  75 . Each liquid control valve  73 ,  75  has a level controller  77 ,  79 , respectively. Level controllers  77 ,  79  are conventional devices to open valves  73 ,  75  when the levels of liquid within sumps  65 ,  66  reach a selected amount, so as to discharge the liquid from sumps  65 ,  66 . Other automatic drain arrangements are feasible. 
     Pressure vessel  13  has a pressure relief valve  81  in communication with its chamber  12 . Pressure relief valve  81  is a conventional device to relieve pressure in the event that it reaches an excessive amount. Preferably, pressure vessel  13  has an access port  82  with a removable cap. Access port  82  is located in its sidewall in this embodiment. Access port  82  is of a size selected to allow a worker to enter chamber  12  for maintenance, particularly for removing and installing coalescing filter  43 , which must be done periodically. 
     Referring to  FIG. 2 , coalescing filter  43  comprises an assembly of compressible pieces or segments that define an outer diameter that sealingly engages the inner diameter of pressure vessel  13 . The multiple pieces of coalescing filter  43  are sized so that each will pass through access port  82  ( FIG. 1 ). These pieces include in this example a pair of central segments  83 ,  85  having inner edges  87  and outer edges  89  that are straight and parallel with each other. Inner edges  87  sealingly abut each other. Each inner edge  87  has a semi-cylindrical recess  91  for engaging super-heater  45 . Each inner edge  87  has a semi-cylindrical recess  93  for fitting around pre-heater unit  15 . Each central segment  83 ,  85  has outer diameter portions  95  on opposite ends that are partially cylindrical and sealingly engage the inner diameter of pressure vessel  13 . 
     Coalescing filter  43  also has two side segments  97 ,  99  in this embodiment. Each side segment  97 ,  99  has a straight inner edge  101  that abuts one of the outer edges  89  of one of the central segments  83 ,  85 . Each side segment  97  has an outer diameter portion  103  that seals against the inner diameter of pressure vessel  13 . Segments  83 ,  85 ,  97  and  99  are compressible so as to exert retentive forces against each other and against pressure vessel  13  to hold them in place. Retainers (not shown) may also be employed to hold the segments of coalescing filter  43  in position. 
     Fuel gas conditioning system  11  serves to condition fuel gas for gas turbines. Gas turbines, particularly low pollution types, require a dry feed gas that has a selected amount of superheat, such as 50 degrees above its dew point curve. The term “superheat” is a conventional industry term to refer to a range where the pressure and temperature of the fuel gas are above a range where condensation can occur. Referring to  FIG. 1 , feed gas enters inlet  49  at a pressure that may be, for example, 1,000 to 1,300 psig and at a temperature from 60-80 degrees F. The feed gas flows through inner housing  19  of pre-heater unit  15 , which increases the temperature of the feed gas a selected amount over the temperature of the incoming gas. For example, the temperature may be approximately 100-120 degrees F. as it exits inner housing  19 , and the pressure would be approximately the same as at inlet  49 . 
     This preheated gas then flows through expansion valve  37 , causing a pressure drop to a selected level below the dew point curve, as monitored by pressure sensor  39 . For example, if the intake pressure is 1,000 to 1,300 psig, the pressure may drop to approximately 450-500 psig. The temperature will also drop to perhaps 60-80 degrees F., and at this temperature and pressure, the gas will be below its dew point curve. The lower pressure cooler gas flows back through annulus  21  in pre-heater unit  15 , which adds additional heat. At annulus outlet  41 , the pressure may still be around 450-550 psig and the temperature may be 70-100 degrees F., but still below the dew point. Controller  27  controls the power to heater elements  23  to maintain a desired temperature at outlet  41  as monitored by sensor  31 . 
     Because the drop in pressure at expansion valve  37  caused the gas to be below its dew point, some of the liquids contained within the gas will condense in chamber  14  upstream of filter  43 . Also, liquids will be separated from the gas by coalescing filter  43  as the gas flows through coalescing filter  43 . The liquids collect on the bottom of pressure vessel  13  and flow through outlets  61 ,  63  into sumps  65 ,  66  and out through valves  73 ,  75 . 
     After passing through filter  43 , the gas flows toward pressure vessel end  16  and enters inlet  49  of super-heater  45 . Electrical resistance heater elements  51  add heat to the dry gas in an amount that will place the temperature of the gas well above its dew point curve, such as by 50 degrees. The gas, now in a superheated condition, flows out outlet  59  at for example 110-130 degrees F. and 450-550 psig. The gas from outlet  59  flows into a conventional gas turbine (not shown). 
       FIG. 3  shows a portion of an alternate embodiment wherein pressure vessel  105  contains an expansion valve  107  within its interior. In the first embodiment, expansion valve  37  is located on the exterior of pressure vessel  13 . In  FIG. 3 , pre-heater inner housing  109  and outer housing  11  have one end within pressure vessel  105  instead of on the exterior as in the first embodiment. Heater elements  113  are contained within inner housing  109  as in the first embodiment. A valve actuator  115  controls the orifice of expansion valve  107 . Valve actuator  115  varies the pressure drop in response to pressure sensed by a pressure sensor  117  located within the interior of pressure vessel  105 . The second embodiment operates in the same manner as the first embodiment. 
     The gas conditioner is compact as the components are principally contained within a single pressure vessel. This arrangement reduces the amount of space required and the external flowlines connecting the various components. 
     While the invention has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.

Technology Classification (CPC): 8