Abstract:
A portable cryogenic nitrogen generator consists of an air preparation unit and a cryogenic distillation unit mounted inside separate standard-sized ISO containers that can be easily shipped to a drilling site and efficiently and quickly assembled into an operative state. The containers can be connected together at anchor points on the housings of both containers, making the nitrogen generator assembly more stable. The air preparation unit includes an absorption device and optionally includes one or a plurality of air compressor units. The cryogenic distillation unit includes a distillation column and associated heat exchangers. The air preparation and cryogenic distillation units connect through apertures in their respective containers and operate while being mounted in the containers.

Description:
RELATED CASES  
       [0001]    This application is based on and claims priority to U.S. Provisional Patent Application No. 60/402,878, filed Aug. 8, 2002, the entire contents of which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention is directed to nitrogen generators, and in particular, portable cryogenic nitrogen generators.  
           [0004]    2. Description of the Related Art  
           [0005]    Inert gases are widely used in many industrial processes. For example, nitrogen gas is commonly used in conjunction with operation of a drilling rig for oil, gas, or geothermal wells, as well as for post drilling operations. In particular, nitrogen is injected into the down-hole region during a drilling operation, to remove drill cuttings.  
           [0006]    In the art of well drilling, tubular casings are typically inserted into the wells so as to secure the perimeter of the wellbore. In some wells, multiple casings are secured at the surface of the well to lower down-hole locations. Other types of casings, called liners, are sometimes used to extend from the lower-most casing into the lower-most portion of the wellbore. Drilling fluids, such as drilling mud, are often used when large flows of water are present in the well. The drilling mud is circulated down the drill string, through the drill bit, and up the annular region between the drill string and the wellbore or casing. Gas, such as Nitrogen gas, may be injected into the down-hole region to provide faster drilling when substantial amounts of water are not present in the well.  
           [0007]    In the past, air has been used as the principal down-hole drilling fluid for lower water content drilling. The air can be combined with a surfactant, foaming agent, water, and/or mud for different applications. The primary advantages of straight air drilling are greatly increased penetration rates, greater bit footage, and fewer down-hole drilling problems.  
           [0008]    However, drilling with air does raise a number of disadvantages. For example, injection of high-pressure air into a down-hole during a drilling operation increases corrosion rates and raises the risk of explosions or fire due to the presence of high levels of oxygen in the pressurized air. In order to reduce the risk of explosions or fire, it has been known to reduce the temperature of the injected air, or to replace the air with an inert gas, such as Nitrogen.  
           [0009]    One option for supplying nitrogen gas to the down-hole region of a well during a drilling operation is to ship containerized nitrogen to the drilling site and pump the nitrogen gas into the well at a pressure from about 200 psig to 10,000 psig. However, the shipment of containerized nitrogen to a drilling site, which may be in a remote location, can be expensive. Thus, it is more desirable to generate nitrogen gas at the site of the drilling operation.  
           [0010]    One option for producing nitrogen gas at a drilling site is disclosed in U.S. Pat. No. 6,041,873 issued to Michael, the entire contents of which is hereby expressly incorporated by reference. The Michael patent discloses a portable unit that produces nitrogen gas through non-cryogenic systems including membrane separation units.  
         SUMMARY OF THE INVENTION  
         [0011]    One drawback of non-cryogenic devices is that efficiency drops off rapidly as purity increases. For example, it has been found that portable membrane separation units can provide 95% pure nitrogen gas at a flow rate sufficient for drilling operations. However, these units are not practical for generating an appropriate nitrogen flow at purities of above 95%, and in particular, purities above 99.0%.  
           [0012]    One aspect of the present invention includes the realization that cryogenic nitrogen generators can be made sufficiently portable to provide practicable sources of higher purity nitrogen gas for drilling operations.  
           [0013]    Another aspect of the present invention includes the realization that standard sized containers can be used to provide a protective housing during transportation and operation of the cryogenic nitrogen generator. By using standard size containers to form a housing for a cryogenic nitrogen generator, such as a cryogenic distillation and associated heat exchanger unit, the device can be shipped to a drilling site and efficiently and quickly assembled into an operative state. For example, a cryogenic nitrogen generator can include an air preparation unit and a cryogenic distillation and associated heat exchanger unit. The air preparation unit typically will include an absorption device, such as a Pressure Swing Absorption (PSA) or a Temperature Swing Absorption (TSA) unit. Optionally, the air preparation unit can also include one or a plurality of air compressor units. The air preparation unit can be configured to fit within a standard ISO container resting horizontally. However, a cryogenic distillation unit is quite tall. For example, typical cryogenic distillation units, also known as “cold boxes,” can be as tall as 30 feet or more to produce Nitrogen gas of better than 99% purity. Thus, the distillation unit can be separately housed in a standard ISO container. With these units separately housed as such, they can be transported to and through virtually any country in the world using standard sized trucks or via ocean-going ships. Additionally, once delivered to a drilling site, the separate components can be connected and operated while they remain in the separate containers.  
           [0014]    A further advantage in using ISO containers is that such containers include standard anchoring points which can be connected together. For example, anchoring points of each container can be connected together so as to provide further stability for plumbing connections between the containers and also to provide further stability to the container housing the distillation unit. For example, because the distillation unit is tall, connection to another container, and in particular another ISO container, provides further stability to the total system.  
           [0015]    Typical cryogenic air separation plants are designed to remove normal levels of carbon dioxide, hydrocarbons, sulfur containing compounds, and other acid gases in ambient feed air. However, ambient air contaminate levels at oil or gas exploration drilling and recovery sites can be higher than normal levels, making it necessary to use additional precautions to ensure safe air separation plant operation. Accordingly, in one embodiment, the air preparation unit also includes a catalytic converter to remove hydrocarbons from an ambient air stream, preferably before the air stream enters the absorption device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic illustration of a gas separation unit constructed in accordance with one aspect of the present invention;  
         [0017]    [0017]FIG. 2 is a schematic illustration of a modification of the gas separation unit illustrated in FIG. 1;  
         [0018]    [0018]FIG. 3 is a schematic illustration of the gas separation unit illustrated in FIG. 1 containing a catalytic reactor system.  
         [0019]    [0019]FIG. 4 is a front, top, and left side perspective view of a housing assembly for the gas separation units illustrated in FIGS. 1 and 2, the housing assembly including a generally horizontal portion and a generally vertical portion;  
         [0020]    [0020]FIG. 4A is a left side elevational view of the generally vertical portion of the housing assembly of FIG. 4;  
         [0021]    [0021]FIG. 5 is a front, top, and left side perspective view of the housing unit illustrated in FIG. 4, with components of the gas separation units illustrated in FIGS. 1 and 2 shown in phantom;  
         [0022]    [0022]FIG. 6 is a front, top, and left side perspective view of a modification of the housing assembly illustrated in FIG. 5;  
         [0023]    [0023]FIG. 6A is a rear elevational view of the horizontal portion of the housing assembly shown in FIG. 6; and  
         [0024]    [0024]FIG. 7 is a front, top, and left side perspective view of a further modification of the housing assembly illustrated in FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    With reference to FIG. 1, a gas separation unit, constructed in accordance with one aspect of the present invention, is illustrated therein identified by the reference numeral  10 . The gas separation unit  10  comprises an air source  12 , an absorption unit  14 , and a cryogenic distillation unit  16 .  
         [0026]    The air source  12  can be in the form of any source of air. Preferably, the air source  12  is an air compressor configured to pressurize air. Any commercially available air compressor can be used for the air source  12 . For example, the air source  12  can be a centrifugal, dry or lubricated screw, or reciprocating-type air compressor. If an oil-lubricated system is used, additional equipment can be used to remove oil droplets and vapors formed during the compression process.  
         [0027]    The absorption unit  14  can be in the form of a pressure swing absorption (PSA) or a temperature swing absorption (TSA) system. Preferably, the absorption unit  14  is configured to remove water vapor, carbon dioxide, and other air contaminants from a feed stream of air from the air source  12 . The illustrated absorption unit  14  is a pressure swing absorption unit and preferably includes at least two absorption beds  18 ,  20 . In the illustrated embodiment, the absorption unit  14  includes three absorption beds,  18 ,  20 , and  22 . The absorption unit  14  also includes a set of check valves  23  disposed downstream of the absorption beds  18 ,  20 ,  22  to prevent reverse flow into the absorption beds  18 ,  20 ,  22  during operation of the unit  14  and to allow flow into the beds  18 ,  20 ,  22  to reactivate the beds  18 ,  20 ,  22  by purging, described below. Those of ordinary skill in the art readily appreciate that the check valves can be in the form of passive mechanical check valves, or electronically controlled solenoid or switch controlled valves.  
         [0028]    The absorption unit  14  also includes the controller  24 . The controller  24  can be in the form of a programmable logic controller configured to emit electronic control signals via a plurality of connectors  25  to a plurality of electronic actuators  27  which control the operation of a plurality of valves  29  which, in turn, control the flow of gases in and out of the beds  18 ,  20 ,  22 . Alternatively, the controller  24  can be configured to selectively apply pneumatic pressure to a plurality of pneumatic actuators for controlling the valves  29 . The operation of the controller  24  and the associated valves  29  is well known in the art and thus will not be described further.  
         [0029]    The cryogenic distillation unit  16  includes a main heat exchanger  26 , a distillation column  28 , and preferably a sub-cooler  30 . The illustrated embodiment also includes a coolant reservoir  32 , a purge vaporizer  33 , and a defrosting circuit  34 . The operation of the defrosting circuit  34  is well known in the art, and thus is not described further.  
         [0030]    In operation, compressed air is delivered from the air source  12  to the absorption unit  14  through a compressed air conduit  36 . A condensate trap  37  is disposed inline with the conduit  36 . The trap  37  removes condensed water and oil from the air supplied by the air source  12  before it enters the absorption unit  14 . In the absorption unit  14 , water vapor, carbon dioxide, and a majority of other air contaminants are removed. As noted above, the illustrated absorption unit is a pressure swing absorption device.  
         [0031]    In the illustrated embodiment, the absorption unit can be configured to provide pre-purification of the compressed air from the air source  12 . As known in the art, the absorption unit  14 , operating under a pressure swing absorption principle, selectively pressurizes and depressurizes the beds  18 ,  20 ,  22  through the actuation of the valves  29  which are controlled by the controller  24 . Absorbent material in the beds  18 ,  20 ,  22  is used to absorb the water vapor, carbon dioxide, and other air contaminants. Once each bed is saturated with the waste products, the bed can be reactivated by purging, described below. The pre-purified air from the absorption unit  14  can be delivered to the cryogenic distillation unit  16  through a conduit  38 . Check valves  23  disposed downstream of the absorption beds  18 ,  20 ,  22  can prevent reverse flow along the conduit  38  during operation of the absorption unit  14 . A particulate filter  39  can be disposed in-line with the conduit  38 . The particulate filter  39  prevents dust from the absorption unit  14  from entering the cryogenic distillation unit  16 .  
         [0032]    The pre-purified and compressed air, which is predominately oxygen and nitrogen, is fed into the main heat exchanger  26 . The main heat exchanger  26  is configured to cool the incoming pre-purified air to its condensing temperature. Refrigeration for cooling the incoming pre-purified air is provided by purified nitrogen (i.e., product nitrogen) and waste gas discharged from the distillation unit  16 , described in greater detail below. A startup/defrost loop control  41  connects to the conduit  38  upstream of the heat exchanger  26 . The loop control  41  diverts a portion of the air stream through the defrosting circuit  34  and associated valves  43  during the initial activation of the absorption unit  14  and for periodic defrosting of the cryogenic distillation unit  16  to remove built-up contaminates. An instrument air supply line  45  can also be connected to the conduit  38  upstream of the heat exchanger  26  and diverts a portion of the pre-purified air stream to supply instrument air to plant controls and instruments.  
         [0033]    The cooled pre-purified air discharged from the main heat exchanger  26  is supplied to the distillation column  28  through a conduit  40 . A safety valve  47  can be connected to the conduit  40  to provide high-pressure safety relief to the heat exchanger  26  and distillation column  28 . The conduit  40  is connected to a lower end of the distillation column  28 . As the cooled and pre-purified air enters the distillation column  28 , it contacts a descending liquid reflux, described in greater detail below.  
         [0034]    As the pre-purified and cooled air rises within the distillation column  28 , the nitrogen concentration increases until it reaches the top of the column. Preferably, the pre-purified and cooled air rises through a series of distillation trays or packing material as it rises through the distillation column  28 .  
         [0035]    Above the distillation trays or packing material, a further heat exchanger, commonly known as a “condenser/reboiler,” can be disposed within the distillation column. The rising pre-purified and cooled air, which has been distilled into purified or “product nitrogen,” rises and thus flows into thermal communication with the reboiler/condenser where it is condensed against a boiling stream of oxygen-enriched reflux, described in greater detail below.  
         [0036]    The condensed liquid nitrogen then falls into the distillation column, and in particular through the distillation trays or packing material, and thus effects the desired separation on the rising pre-purified gas. As noted above, the falling condensed nitrogen is referred to as “liquid reflux.” As this liquid reflux falls through the distillation column, it causes oxygen to separate out of the rising pre-purified air and thus the liquid reflux itself becomes enriched with oxygen.  
         [0037]    At the bottom of the distillation column, the liquid reflux stream, which includes liquid nitrogen enriched with oxygen, pools. The pooled liquid reflux is discharged from the lower end of the distillation column through a conduit  42 . The liquid reflux, flowing through the conduit  42 , enters an optional subcooler  30 . After leaving the subcooler  30 , the liquid reflux flows through the pressure reduction valve  44 , which lowers pressure and thus lowers the boiling point of the liquid reflux to a temperature lower than the boiling point of the higher pressure nitrogen gas flowing upward toward the top of the distillation column  28 . Thus, as the liquid reflux boils, and thus changes phase, it absorbs heat from the higher-pressure nitrogen gas flowing up towards the top of the distillation column  28 .  
         [0038]    Optionally, a portion of the liquid reflux is diverted to the purge vaporizer  33  to prevent the build up of contaminates. In one embodiment, the vaporizer  33  comprises an external heat exchanger that vaporizes the liquid against compressed air. In another alternative, a portion of the liquid reflux can be mixed with waste stream entering the cold end of the vaporizer.  
         [0039]    In order to compensate for process and heat leak refrigeration losses, liquid nitrogen (LIN) from the liquid coolant reservoir  32  is introduced at the top of the distillation column where it is mixed with the reflux stream of oxygen enriched liquid nitrogen flowing downward through the distillation column  28  and is thus used in the distillation process to further aid and separation of oxygen from the rising pre-purified air. A liquid assist control valve  49  is disposed downstream of the reservoir  32  and regulates the flow of liquid nitrogen from the reservoir  32  into the distillation column  28 .  
         [0040]    The uncondensed gaseous nitrogen at the top of the distillation column is directed to the cold end of the main heat exchanger  26  through a conduit  46 . As the uncondensed nitrogen gas passes through the main heat exchanger  26 , it absorbs heat from the incoming pre-purified air, as noted above. As the flow of uncondensed nitrogen gas leaves the main heat exchanger  26 , it is approximately at ambient temperature. This flow of product nitrogen gas at ambient temperature is delivered to either a generator battery limits or to the suction of a booster compressor where it is raised to the desired delivery pressure. For a drilling operation, the pressure can be raised to from about 70 psig to about 10,000 psig. More typically, the pressure is raised from about 1,000 to 2,000 psig.  
         [0041]    With reference again to the reboiler/condenser and the distillation column  28 , as the liquid reflux is revaporized, it is discharged from the top of the distillation column  28  through a conduit  48 . The conduit  48  directs the vaporized oxygen enriched reflux through the optional subcooler  30 . In the subcooler  30 , heat from the liquid reflux flowing through the conduit  42  is absorbed by the flow of vaporized reflux flowing through the conduit  48 . After the subcooler, the vaporized reflux is directed through the cold end of the main heat exchanger  26 .  
         [0042]    Within the main heat exchanger  26 , the vaporized reflux absorbs additional heat from the incoming flow of pre-purified air. The vaporized reflux from the distillation column  28  can be used for reactivating the beds  18 ,  20 ,  22  in the absorption unit  14 . Thus, a conduit  50  guides the vaporized reflux back to the absorption unit  14  for purging of the beds  18 ,  20 ,  22 . The check valves  23  prevent reverse flow along the conduit  50  during the purging process. A cold box purge control  51  connects to the conduit  50  and diverts a portion of the vaporized reflux to maintain a slight positive pressure in the cryogenic distillation unit  16  to prevent moisture laden air from entering the unit  16 , where moisture would freeze and air condense upon contact with very cold vessels and/or piping.  
         [0043]    Although the various heat exchangers  26 ,  30 , and the condenser/reboiler are illustrated as separate units, all of the heat exchanges in the distillation unit  16 , including but not limited to the heat exchangers  26 ,  30 , and the condenser/reboiler, can be constructed as a single unit. Additionally, it is to be noted that the condenser/reboiler can be separate from the distillation unit  28 . However, the condenser/reboiler preferably is disposed above the top of the distillation column  28 .  
         [0044]    The gas separation unit  10  includes a number of thermocouples  53  and pressure sensors  55  for collecting data indications of temperature and pressure, respectively, throughout the system  10 . The system  10  also includes a number of drains  57  for draining fluids or purging air out of the system  10  for maintenance or repair purposes.  
         [0045]    With reference to FIG. 2, a modification of the separation unit  10  is illustrated therein and identified generally by the reference numeral  10 ′. Components of the gas separation unit  10 ′ that are similar to the corresponding components of the gas separation unit  10  are identified with the same reference numeral, except that a “′” has been added thereto. These components can be constructed identically to the correspondence components of the gas separation unit  10 , except as noted below.  
         [0046]    In the gas separation unit  10 ′, a centrifugal expander  52  communicates with the main heat exchanger  26 ′. The centrifugal expander  52  replaces the addition of liquid coolant from the liquid coolant reservoir  32  of the gas separation unit  10  (FIG. 1). In this modification, the centrifugal expander  52  compensates for process and heat leak refrigeration losses. Optionally, the additional refrigeration provided by the expander  52  can be used to liquefy part of the liquid nitrogen product as liquid or stored for later use, such as, for example, but without limitation, peak operation.  
         [0047]    In this modification, the pressure of the oxygen rich reflux vapor discharge from the distillation column  28 ′ is reduced through an expander so as to provide the additional compensating cooling effect. In particular, after the vaporized oxygen rich reflux has entered the cold end of the main heat exchanger  26 ′, the vapor is passed through the centrifugal expander, which reduces the pressure of the reflux vapor and thus the temperature. The expanded oxygen rich reflux is then rerouted through the cool end of the main heat exchanger  26 ′. As such, the vaporized oxygen rich reflux aids in cooling the incoming pre-purified compressed air. Thus, as noted above, the vaporized oxygen rich reflux can optionally be diverted or stored for any use, or for later use, such as during peak operation.  
         [0048]    After passing through the main heat exchanger  26 ′, the vaporized oxygen rich reflux is returned to the absorption unit  14 ′ through the conduit  50 ′. The expansion of the reflux in the centrifugal expander  52  produces energy. Preferably, the energy, in the form of a spinning shaft, is absorbed through an air or oil brake connected to the shaft of the centrifugal expander  52 .  
         [0049]    [0049]FIG. 3 illustrates a modification of the separation unit  10 , and is identified generally by the reference numeral  10 ″. Components of the gas separation unit  10 ″ that are similar to the corresponding components of the gas separation unit  10  are identified with the same reference numeral, except that a “″” has been added thereto. These components can be constructed identically to the correspondence components of the gas separation unit  10 , and can be used with or without the expander  52 , except as noted below.  
         [0050]    Preferably, the gas separation unit  10 ″ includes an additional device for removing hydrocarbons. In the illustrated embodiment, the unit  10 ″ includes a catalytic reactor system  54  configured to remove hydrocarbons from the air discharged from the air source  12 ″. An example of such a catalytic reactor system is known as a “Deoxo system.” 
         [0051]    Preferably, the reactor system  54  is located upstream of the absorption beds  18 ″,  20 ″,  22 ″ and is connected to the air source  12 ″ through the conduit  36 ″. The reactor system  54  preferably includes a housing containing a catalyst. For example, the catalyst can be Platinum or Palladium. The reactor system  54  is configured to receive a stream of air from the air source  12 ″ and an amount of oxygen, and to generate a reaction between the air stream and oxygen to form water and carbon dioxide. The reactor system  54  is further configured to remove the water and carbon dioxide from the air stream.  
         [0052]    During operation, a feed stream of air from the air source  12 ″ enters the system  54  through the conduit  36 ″. Inside the system  54 , hydrocarbons present in the air stream react with a measured amount of oxygen in the presence of a catalyst to form water and carbon dioxide. The water and carbon dioxide produced by the catalytic reaction are then removed from the air stream by the system  54  and the air stream continues onto the absorption beds  18 ″,  20 ″,  22 ″ essentially free of hydrocarbons. The operation of the system  54  is well known in the art and thus will not be described further.  
         [0053]    With reference to FIG. 4, a housing assembly  60  is illustrated therein. The housing assembly  60  can be used to house either of the gas separation units  10 ,  10 ′,  10 ″. Preferably, the housing assembly  60  comprises an air preparation unit housing  62  and a cryogenic distillation and associated heat exchanger housing  64 .  
         [0054]    Preferably, the air preparation unit housing  62  is comprised of a frame assembly  66  defining a rectangular prism. Additionally, the housing  62  preferably includes anchoring points  68  at each of its corners. Additionally, the housing  62  preferably includes one or a plurality of removable or openable panels  70 . For example, the panels  70  can be in the form of hinged doors, panels that are completely removable, scroll-type, or sliding doors.  
         [0055]    Preferably, the frame  66  is dimensioned so as to conform to a standard ISO size. For example, the frame  66  can be about five feet, seven feet, ten feet, twenty feet, forty, or forty-five feet long. As used herein, “length,” or “long,” refers to the longest dimension of the frame  66 , i.e., the major axis  72 . Additionally, the frame  66  can have a standard height, such as, for example, but without limitation, five feet, seven feet, eight feet, or nine and one-half feet. Additionally, the anchoring points  68  preferably conform to ISO standard anchoring points. Such anchoring points have at least two flat faces, each of which includes an aperture for connection to other anchoring points or other anchoring or connector devices.  
         [0056]    The housing  64  includes a frame  74 . The frame  74  preferably is configured and sized to conform to at least one standard ISO container dimension. For example, but without limitation, the frame  74  can have a length along its major axis  76  of five feet, six feet, seven feet, ten feet, twenty feet, or forty feet. Additionally, the frame  74  also preferably includes anchoring points  68  at each of its corners.  
         [0057]    With reference to FIG. 4A, one side of the housing  64  preferably includes an aperture  78  that can be aligned with an aperture on the housing  62 . Preferably, the aperture  78  includes a hinged, removable, scroll-type, or sliding door. Additionally, the frame  74  preferably includes two additional anchoring points  80  that are not positioned at a corner of the frame  74 . Rather, the additional mounting points  80  are disposed on a longitudinally-extending side of the frame  74  so as to be in alignment with two of the anchoring points  68  of the frame  66 .  
         [0058]    For example, as shown in FIG. 4, one end of the housing  62  abuts a lower end of the housing  64 . The standard anchoring points  68  on the housing  64  are in alignment with the lower anchoring points  68  of the housing  62 . Additionally, the mounting points  80  are in alignment with the upper anchoring points  68  of the housing  62 . Thus, when the housings  62 ,  64  are arranged as illustrated in FIG. 4, the mounting points  68 ,  80  can be connected together to ensure a secure connection between the housings  62 ,  64  and thus protect any plumbing connection between the absorption unit  14 ,  14 ′,  14 ″ and the distillation and heat exchanger unit  16 ,  16 ′,  16 ″. Additionally, by connecting the housings  62 ,  64  as such, the housing assembly  60  is more stable and thus less likely to fall over if struck by heavy machinery or exposed to a strong wind.  
         [0059]    For example, as shown in FIG. 5, the absorption unit  14 ,  14 ′,  14 ″ is mounted within the housing  62 . Optionally, the compressor  12  can also be mounted in the housing  62 . Further, another compressor can be mounted in the housing  62 . For example, as noted above with reference to FIG. 1, a booster compressor can be used to raise the pressure of the product Nitrogen. Thus, such a booster can be mounted in the housing  62 . Additionally, the cryogenic distillation unit  16 ,  16 ′,  16 ″ is mounted within the housing  64 . Preferably, the absorption unit  14 ,  14 ′,  14 ″ and cryogenic distillation unit  16 ,  16 ′,  16 ″ are rigidly mounted to the interior of the housings  62 ,  64 , respectively. Vibration isolation devices can be used for rigidly mounting the units  14 ,  14 ′,  14 ″,  16 ,  16 ′,  16 ″ to the housings  62 ,  64 .  
         [0060]    As schematically shown in FIG. 1, the conduits  38 ,  38 ′,  38 ″, and  50 ,  50 ′,  50 ″ preferably include flanges  59  which allow the conduits  38 ,  38 ′,  38 ″,  50 ,  50 ′,  50 ″ to be separated in proximity to the apertures in the housings  62 ,  64 . Preferably, the flanges  59  are located closer to the apertures in the housings  62 ,  64  than as depicted in FIG. 1. For example, the conduits  38 ,  38 ′,  38 ″,  50 ,  50 ′,  50 ″ can include flat flanges disposed in proximity to the apertures in the housings  62 ,  64 . Alternatively, the flanges  59  disposed on the conduits  38 ,  38 ′,  38 ″,  50 ,  50 ′,  50 ″ can be disposed so as to be spaced apart when the housings  62 ,  64  are juxtaposed to each other. In this modification, flexible or rigid intermediate conduits can be installed between the flanges so as to complete the conduits  38 ,  38 ′,  38 ″,  50 ,  50 ′,  50 ″.  
         [0061]    With reference to FIG. 6, a modification of the housing assembly  60  is illustrated therein and identified generally by the reference numeral  60 A. Components of the housing assembly  60 A similar to corresponding components of the housing assembly  60  are identified with the same reference numeral, except that a letter “A” has been added.  
         [0062]    As shown in FIG. 6, the lower portion of the housing  64 A is aligned with a central portion of the side of the housing  62 A. Preferably, in this modification, as shown in FIG. 6A, the frame  66 A of the housing  62 A includes additional anchoring points  80  on the side of the housing  62 A that faces the housing  64 A. The additional anchoring points  80  disposed on the frame  66 A can be connected to the anchoring points  68 A,  80 A of the housing  64 A.  
         [0063]    By connecting the housing  64 A to a central side portion of the housing  62 A, the housing assembly  60 A provides further stability and thus better protection against the risk of tip over of the housing  64 A.  
         [0064]    With reference to FIG. 7, a further modification of the housing assembly  60  is illustrated therein and identified generally by the reference numeral  60 B. Components of the housing assembly  60 B similar to the corresponding components of the housing assemblies  60 ,  60 A are identified with the same reference numeral, except that a letter “B” has been added.  
         [0065]    As shown in FIG. 7, the housing  64 B can be connected to a side of the housing  62 B adjacent a longitudinal end thereof. The connections between the housing  62 B and  64 B of the assembly  60 B can be the same as those described above with reference to FIG. 5.  
         [0066]    As noted above, by mounting an absorption unit in one container having standard ISO container dimensions and mounting a cryogenic distillation unit in a second container also including standard ISO container dimensions, an entire cryogenic gas separation unit can be conveniently shipped to a drilling location and quickly assembled. Additionally, because the units  14 ,  14 ′,  14 ″,  16 ,  16 ′,  16 ″ remain in the containers, they are well protected from hazards common at the site of a drilling operation.  
         [0067]    Additionally, by connecting the housings  62 ,  62 A,  62 B,  64 ,  64 A,  64 B together using the standard ISO anchoring point hardware, the entire housing assembly  60 ,  60 A,  60 B can be stabilized. This is particularly advantageous because the containers or housings  64 ,  64 A,  64 B which house the cryogenic distillation units, stand on their longitudinal end in operation. Thus, connecting the housing together provides additional stability thereby lowering the risk that the housing  64 ,  64 A,  64 B could tip over. Preferably, the housings  62 ,  62 A,  62 B are preferably connected to the housings  64 ,  64 A,  64 B with bridge fittings which provide a tension and can connect the containers so they touch each other.  
         [0068]    While a cryogenic process to produce Nitrogen from ambient air is disclosed herein, other similar cryogenic processes can be used to produce the desired product Nitrogen. In the systems described above, refrigeration is generated by either the injection of liquid Nitrogen or by the expansion of waste gas from the distillation process to compensate for heat leak and process losses.  
         [0069]    Other cryogenic processes can include the expansion of part or all of the inlet air to produce the required refrigeration. Such processes, including the processes disclosed above, are considered to be applicable to the present inventions.  
         [0070]    Although these inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. In addition, while several variations of the inventions have been shown and described in detail, other modifications, which are within the scope of the present inventions, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combination or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.