Abstract:
A gas recovery system designed to recover vent gas emanating from a gas processing system and return the gas to the processing system. The gas recovery system includes a pressurized motive gas that is directed through a vacuum generating apparatus. The vacuum suctions the vent gas into the vacuum generating apparatus and mixes the vent gas with the motive gas to create a mixed gas stream. The mixed gas stream is transported away from the vacuum generating apparatus by a mixed gas outlet line. A vent gas pressure regulator is fluidly connected between the vent gas supply line and the mixed gas outlet line. The vent gas pressure regulator maintains the vent gas supply line pressure above a predetermined pressure.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a gas recovery and re-injection method and apparatus. Specifically, the invention relates to a system for recovering gas emanating from the seals of a reciprocating gas compressor. 
   BACKGROUND OF THE INVENTION 
   The prior art includes various systems designed to recover unpreassurized excess gas (i.e. “vent gas”) for re-injection or collection. In earlier gas processing systems, vent gas was either ignored, burned-off as a flare, or vented to the atmosphere away from the main processing system. Although these methods are relatively inexpensive, they have adverse environmental impacts and may create a safety hazard. 
   Some existing and prior-art systems use electrical power to vacuum vent gas from a low pressure or gas leakage area and pump the gas back into a host system. While these systems are effective, they require a source of electrical power and an electrical pumping mechanism, which could fail and/or create a safety hazard. Other systems have a separate dedicated mechanical compressor that scavenges, pressurizes and re-injects the vent gas back into the host system. Both of these types of systems are relatively complex and employ comparatively elaborate sensing and pumping mechanisms with multiple moving parts. 
   More recently gas recovery systems have been introduced that direct a relatively high pressure gas (known as “motive gas”) through a vacuum generating apparatus, such as a jet compressor, to create a vacuum. The vacuum is then used to suction the vent gas into the jet compressor. The suctioned gas is mixed with the motive gas to create a mixed gas stream, which is then injected back into the system. Although these systems do not require electrical or mechanical pumping mechanisms, they lack a simple and effective control system to maintain the various pressures and flow rates within predetermined limits and prevent the entry of air into the system. 
   The gas that is being processed preferably is recovered for the above reasons. Recovery of the gas requires that contamination be minimized, in order to preserve subsequent usability of the gas and also due to costs. Natural gas, for example, is priced based upon BTU value. Should the natural gas be contaminated during the recovery process with air, then the BTU value of the gas will be reduced and its value lowered. Other gases which are to be reacted, for example, should have minimal contamination in order to preserve reactivity. 
   The need exists for a self-contained gas recovery method and apparatus that has a reliable pressure regulating capability. The present invention provides a gas recovery system that includes a self-powered gas recovery device with no moving parts. The invention has a pressure regulation system that continuously monitors and adjusts a jet compressor inlet vent gas supply line pressure to ensure that the pressure in the vent gas supply line does not go below a pre-defined pressure, and thereby allow air gas to enter the system. 
   SUMMARY OF THE INVENTION 
   The present invention is a gas recovery system comprising a vent gas supply line for transporting a vent gas, and a motive gas supply line for transporting a motive gas. The motive gas and vent gas are directed through a vacuum generating apparatus so that a vacuum is generated. The vacuum suctions the vent gas into the vacuum generating apparatus and mixes the vent gas with the motive gas to create a mixed gas stream. The mixed gas stream is transported away from the vacuum generating apparatus by a mixed gas outlet line. A vent gas pressure regulator is fluidly connected between the vent gas supply line and the mixed gas outline. The vent gas pressure regulator maintains the vent gas supply line pressure above a predetermined pressure. 
   The invention also comprises a gas recovery system operatively associated with a compressor. The system includes a compressor that leaks a vent gas and discharges a motive gas. A vent gas supply line transports the vent gas, and a motive gas supply line transports the motive gas. Both the motive gas and the vent gas are directed through a vacuum generating apparatus so that a vacuum is generated to suction the vent gas into the vacuum generating apparatus. The vent gas and the motive gas mix in the vacuum generating apparatus and thereby produce a mixed gas stream. The mixed gas stream is transported in a mixed gas outlet line. The pressure of the vent gas supply line is controlled by using a pressure regulator to direct the mixed gas through the pressure regulator and into the vent gas supply line if a pressure in the vent gas supply line pressure falls below a predetermined pressure. The mixed gas is then directed back into the compressor system. 
   The present invention also comprises a gas recovery system that includes a reciprocating compressor that discharges a motive gas and has a packing gland that is operatively associated with the compressor. The packing gland emanates a vent gas. The vent gas is transported by a vent gas supply line, and the motive gas is transported by a motive gas supply line. The vent gas supply line includes a liquid knockout vessel with a pressure relief valve. The motive gas supply line includes a motive gas pressure regulator and a filter mechanism that filters the motive gas before it reaches the pressure regulator. The system also includes a jet compressor that receives the vent gas supply line and the motive gas supply line. The motive gas is directed through a venturi nozzle in the jet compressor. The jet compressor generates a vacuum to suction vent gas from the packing gland into the jet compressor. The vent gas and the motive gas are mixed within the jet compressor to form a mixed gas. The mixed gas is transported away from the jet compressor by a mixed gas outlet line. 
   A directional flow valve is connected to the vent gas supply line between the liquid knockout vessel and the jet compressor. A vent gas supply line pressure monitoring apparatus is connected to the vent gas supply line between the directional flow valve and the liquid knockout vessel. A vent gas pressure regulator monitors the vent gas supply line pressure at the liquid knockout vessel. The vent gas pressure regulator regulates the pressure in the vent gas supply line so that when the vent gas supply line pressure goes below a predetermined pressure, the pressure regulator directs the mixed gas from the mixed gas outlet line through the vent gas pressure regulator to a mixed gas injection point on the vent gas supply line. The mixed gas injection point is positioned between the directional flow valve and the jet compressor. The pressure regulator causes the mixed gas to flow into the vent gas supply line so that the vent gas supply line pressure is moderated. The mixed gas that is not re-directed by the pressure regulator flows into a gas suction intake for the compressor. 
   The present invention also discloses a method for recovering vent gas from a gas processing operation. The vent gas is collected in a containment area associated with gas processing equipment. The vent gas is suctioned from the containment area by a vacuum generating apparatus. The vent gas is mixed with a motive gas that has been compressed by the gas processing equipment so that a mixed gas is produced. The mixed gas is then injected back into a lower pressure intake operatively associated with the gas processing equipment. 
   The present invention further discloses a method of recovering leaking vent gas from a gas compressor operation. Gas leaking from a compressor packing gland is contained in a gas containment area. Motive gas from the compressor is directed through a jet compressor to generate a vacuum. The vacuum created by the jet compressor is used to suction vent gas from the gas containment area through a vent gas supply line and into the jet compressor. In the jet compressor, the vent gas is mixed with the motive gas to create a mixed gas. The mixed gas is transported by a mixed gas outlet line. A pressure regulator controls the pressure in the vent gas supply line. When the pressure in the vent gas supply line falls below a predetermined pressure, the pressure regulator directs mixed gas from the mixed gas outlet line through the pressure regulator and into the vent gas supply line. The mixed gas produced by the process is injected back into an intake of the compressor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view of a compressor system according to the invention with portions shown in section of the gas compressor cylinder and associated equipment. 
       FIG. 2  is a schematic of the gas recovery device of the present invention. 
       FIG. 3  is an elevational view of the front side of the gas recovery device. 
       FIG. 4  is an elevational view of the rear of the gas recovery device. 
       FIG. 5  is an elevational view of an alternative embodiment of the gas compressor system with portions shown in section of the gas compressor cylinder and associated equipment. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention comprises a system designed to recover vent gas from a compressor  12 . Specifically, the current invention is designed to recover gas emanating from the seals of a reciprocating gas compressor  12 . The gas recovery device  10  of the invention maintains the pressure in a vent gas line sufficiently high to prevent ingress of air or other gaseous contaminants into the supply line. 
   As best shown in  FIG. 1 , a reciprocating compressor  12  includes a gas compression cylinder  14  and a compressing piston  16 . Gas, such as natural gas, is compressed within the cylinder  14  through the reciprocating movement of the piston  16 . In the double-acting compressor  12  shown in  FIG. 1 , each time the piston  16  extends (moves to the left in  FIG. 1 ), gas is suctioned into the compressor  12  through a suction line  18 , and discharged through a discharge line  20 . When the piston  16  retracts (moves to the right in  FIG. 1 ), gas is suctioned into the cylinder  14  through a second suction line  22  and discharged through a second discharge line  24 . A portion of the relatively high pressure discharged gas is directed to a motive gas supply line  38 . The motive gas supply line  38  directs the motive gas to a gas recovery device  10 . 
   The compressor piston  16  is driven by a piston rod  26  that extends through an aperture  28  in the wall of gas cylinder  14 . A packing gland  30  seals the aperture  28  during compressor  12  operations. Although the packing gland  30  may initially function as an effective seal, as the packing gland  30  wears, an increasing amount of vent gas escapes through the packing gland  30 . The escaping vent gas is collected in a gas containment area  32 , such as provided by a surrounding housing. 
   As best shown in  FIG. 1 , both the motive gas and the vent gas are directed to the gas recovery device  10  of the present invention. The vent gas is transported to the gas recovery device  10  through a vent gas supply line  34  in the direction indicated by the arrow  36 , and the motive gas is transported to the gas recovery device  10  through the motive gas supply line  38  in the direction of the arrow  40 . The vent gas supply line  34  is connected to a liquid knockout vessel  35  positioned below the gas recovery device  10 . A vent gas pressure sensing line  37  extends from the gas recovery device  10  to sense the pressure of the vent gas supply line  34  at the liquid knockout vessel  35 . The motive gas and the vent gas are combined within the gas recovery device  10  in a manner discussed below to produce a “mixed gas”. The mixed gas is transported away from the gas recovery device  10  through a mixed gas outlet line  42  in the direction indicated by the arrow  44 . In the preferred embodiment, the mixed gas is directed into a compressor suction line  18 . 
   As schematically shown in  FIG. 2 , the motive gas enters the gas recovery unit  10  through the motive gas supply line  38 . The motive gas is directed through a motive gas supply line isolation valve  46  so that an operator can selectively isolate the motive gas from the gas recovery device  10 . The motive gas then flows through a filter  48 , preferably a “Y-strainer”, and a motive gas pressure regulator  50  to ensure that all debris is removed from the gas and the motive gas is maintained at a constant pressure. A motive gas supply monitoring line  52  extends from the motive gas supply line  38 . A motive gas pressure gauge  56  and a gauge isolation valve  54  are connected to the motive gas monitoring line  52 . 
   The motive gas is then directed through a jet compressor-type eductor  58  having a venturi nozzle. When the relatively high-pressure motive gas is directed through the jet compressor  58 , a vacuum is created in the attached vent gas supply line  34 . The vacuum draws vent gas from the vent gas containment area  32  shown in  FIG. 1 , up through the vent gas supply line  34  and into the jet compressor  58 . A vent gas supply line isolation valve  60  allows an operator to selectively cut-off the vent gas from the gas recovery device  10 . 
   In the jet compressor  58 , the relatively high-pressure motive gas is mixed with the low pressure vent gas to create a mixed gas having a pressure intermediate the motive gas and vent gas. The mixed gas is directed away from the jet compressor  58  through the mixed gas outlet line  42 . A mixed gas isolation valve  62  and a mixed gas monitoring line  64  are connected to the mixed gas outlet line  42 . The mixed gas isolation valve  62  allows an operator to selectively cut off the mixed gas leaving the gas recovery device  10 . The mixed gas pressure gauge  70 , a gauge saver  66  and a gauge isolation valve  68  are connected to the mixed gas monitoring line  64 . As shown in  FIG. 1 , in the preferred embodiment, after leaving the gas recovery device  10 , the mixed gas is directed back in to a suction intake line  18  for the compressor  12 . 
   As best shown in  FIGS. 1 and 2 , the vent gas is drawn up through the vent gas supply line  34  to the liquid knockout vessel  35 . Liquids that condense within the vent gas recovery device  10  are collected in the liquid knockout vessel  35 . Liquids condensing within the jet compressor  58  are allowed to drain freely in the direction of the arrows  72 . The liquid knockout vessel  35  also collects lubricating oils from the piston rod  26  and other liquids and debris associated with the operation of the compressor  10 . The liquid knockout vessel  35  includes a pressure relief valve  74  that protects the system from over pressurization. 
   As best shown in  FIG. 2 , the pressure within the vent gas recovery device  10  is regulated by a vent gas pressure regulator  76 . The pressure within the vent gas supply line  34  is sensed by the pressure regulator  76  through a sensing line  37  that extends from the pressure regulator  76  to the liquid knockout vessel  35 . The vent gas pressure is measured at the liquid knockout vessel  35  because the liquid knockout vessel provides the largest volume sensing point within the vent gas system. When the pressure regulator  76  detects a vent gas supply line  34  pressure that is below a predetermined pressure, mixed gas is directed from the mixed gas outlet line  42  through a pressure regulation line  78  connected to the vent gas pressure regulator  76 . The mixed gas is directed through the pressure regulator  76  and into the vent gas supply line  34  at a mixed gas injection point  80 . The injected mixed gas raises the pressure in the vent gas supply line  34  above the predetermined minimum pressure to ensure that no air is ingested into the system. A vent gas supply line directional valve  82  prevents the injected mixed gas from flowing away from the jet compressor  58 . 
   In the preferred embodiment, the vent gas pressure regulator  76  is a diaphragm-type regulator valve, and the directional valve  82  is a check valve, preferably a ball check valve. However, other types of pressure regulators and directional valves should be considered within the scope of the invention. 
   As best shown in  FIG. 2 , pressure within the vent gas supply line  34  is monitored by monitoring equipment in fluid communication with a vent gas monitoring line  84 . A vent gas pressure gauge  86  is connected to the vent gas monitoring line  84  so that an operator can monitor visually the vent gas supply line  34  pressure. A remote transmitter  88  may also be attached to the vent gas monitoring line  84  so that the vent gas pressure may be monitored from remote locations. A gauge isolation valve  90 , and a gauge saver  92  are also connected to the vent gas monitoring line  84 . The vent gas monitoring line  84  is connected to the vent gas supply line  34  between the vent gas isolation valve  60  and the directional flow valve  82 . 
   As best shown in  FIG. 3 , the front face  94  of the housing containing the gas recovery device  10  includes the vent gas inlet supply line pressure gauge  86 , the motive gas inlet supply line pressure gauge  56 , and the mixed gas outlet line pressure gauge  70 . Additionally the front face  94  also includes a valve control handle  96  for controlling the motive gas inlet supply line isolation valve  46 , a valve control handle  98  for controlling the mixed gas outlet line isolation valve  62 , and a control handle  100  for controlling the vent gas supply line isolation valve  60 . 
     FIG. 4  shows a rear view of the housing containing the gas recovery device  10 . As shown in  FIG. 4 , the jet compressor  58  is positioned at the intersection of the motive  38 , vent  34 , and mixed gas  42  lines. As described above, the motive, vent, and mixed gas pressure gauges  56 ,  86 ,  70  monitor the pressure in their respective lines  38 ,  34 ,  42 . A pressure transmitter  88  can also monitor the pressure of the vent gas inlet line  34 . The vent gas pressure regulator  76  is in fluid communication with the mixed gas outlet line  42  and the vent gas inlet line  34 . As described above, the vent gas pressure regulator  76  introduces mixed gas to the vent gas supply line  34 , if needed, to maintain the vent gas supply line  34  pressure above a predetermined minimum pressure. Leakage past packing gland  30  is not necessarily at a constant rate, so the gas being suctioned through vent gas line  34  is not at a constant flow rate and the pressure regulator  76  therefore assures sufficient pressure in vent gas line  34  to prevent ingress of contaminants. 
   An alternative embodiment of the present invention is best shown in  FIG. 5 . The alternative embodiment is essentially identical to the preferred embodiment shown in  FIG. 1 , however, in the alternate embodiment, a mixed gas outlet line  102  directs mixed gas leaving the gas recovery device  10  in a direction indicated by the arrow  104 . The mixed gas is directed into a fuel manifold  106  operatively associated with the compressor  12  so that the mixed gas is burned as fuel to power the compressor  12 . Additional alternative embodiments may include other applications for the mixed gas flowing from the vent gas recovery device. 
   As best shown in  FIGS. 1–4 , in operation, a relatively high-pressure motive gas is discharged from a reciprocating compressor  12  and directed to a gas jet compressor  58  within a vent gas recovery device  10 . A vacuum is generated within the jet compressor  58  to suction a low pressure vent gas from a gas containment area  32  operatively associated with a compressor packing gland  30 . The collected vent gas is mixed with the motive gas within the jet compressor  58  to produce a mixed gas having a pressure intermediate the vent gas and the motive gas. The pressure of the vent gas supply line  34  is controlled by a pressure regulator  76 . If the vent gas supply line pressure falls below a predetermined pressure, mixed gas is directed from a mixed gas outlet line  42  through the pressure regulator  76  and into the vent gas supply line  34 , thereby moderating the pressure of the vent gas supply line  34 . In the preferred embodiment, the mixed gas flowing from the mixed gas supply line  44  is directed into a suction intake line  18  for the compressor  12 . In an alternative embodiment, the mixed gas is directed into a compressor fuel manifold  106 . 
   The present invention may be modified in multiple ways and applied in various technological applications. The current invention may be modified and customized as required by a specific operation or application, and the individual components may be modified and defined, as required, to achieve the desired result. Although the materials of construction are not described, they may include a variety of compositions consistent with the function of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.