Patent Publication Number: US-2013239609-A1

Title: Krypton xenon recovery from pipeline oxygen

Description:
RELATED APPLICATIONS 
     This application is a divisional of prior U.S. application Ser. No. 12/629,408, filed on Dec. 2, 2009. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for producing a krypton-xenon-rich stream from oxygen flowing in an oxygen pipeline that can be further processed to produce krypton and xenon products. More particularly, the present invention relates to such a method in which an oxygen stream is removed from an oxygen pipeline and then introduced into a cryogenic rectification process that produces the krypton-xenon-rich stream from bottoms liquid within a distillation column. 
     BACKGROUND OF THE INVENTION 
     Krypton and xenon are rare gases that are used in a variety of industrial, commercial, and medical applications and are typically recovered from air. Air contains approximately 78.08 percent nitrogen, 20.95 percent oxygen and 0.93 percent argon, on a moisture-free basis. The remainder of the air contains carbon dioxide, heavier hydrocarbons and trace amounts of neon, helium, krypton, hydrogen and xenon. Typically, krypton is present in an amount of about 1.14 part per million by volume and xenon is present in an amount of about 0.087 parts per million by volume. 
     Krypton and xenon are recovered from the air by cryogenic distillation that involves the steps of compressing, cooling the air and then rectifying the air in distillation column having high and low pressure columns operatively associated with one another in a heat transfer relationship so that an oxygen-rich column bottoms collects in the low pressure column that is used to condense a nitrogen-rich vapor overhead produced in the higher pressure column. The resulting liquid nitrogen is used to reflux both the high and the low pressure column. The krypton and xenon will collect in the oxygen produced in the low pressure column due to the fact that both the krypton and xenon have a lower volatility than oxygen. Consequently, a liquid oxygen stream, removed from the low pressure column will initially be distilled in a distillation column to produce a krypton-xenon-rich stream that can be further processed through a series of distillation steps to produce krypton and xenon products. In such further processing, heavier hydrocarbons that will also collect in the oxygen are removed. 
     The distillation column used in connection with the initial concentrating of the krypton and xenon from the liquid oxygen stream is generally integrated into the air separation plant itself. An example of this is shown in U.S. Pat. No. 6,378,333 in which a liquid oxygen stream is removed from the low pressure column and then introduced into the top of a distillation column used to concentrate xenon in a bottoms liquid formed within such column. The distillation column is reboiled with nitrogen-rich vapor from the high pressure column that is in turn condensed to serve as reflux to the high pressure column. A portion of the bottoms liquid can be removed, sent to a trap to remove hydrocarbons and then reintroduced into the distillation column. In U.S. Pat. No. 6,694,775, a liquid oxygen stream is removed from the low pressure column and pumped to produce a pressurized liquid oxygen stream. Part of the pumped liquid oxygen stream is partially heated in a heat exchanger and vaporized. The resulting high pressure oxygen vapor is rectified in a distillation column that is refluxed with a remaining part of the pumped liquid oxygen stream. The heat exchanger is used to condense a compressed air stream that, after condensation, is fed into the double column unit. Part of the compressed air can be used to reboil the distillation column. In US Patent Appln. No. 2006/0021380 A1, unlike the other two patents, a stream of crude liquid oxygen derived from bottoms liquid produced in the high pressure column is further refined in an auxiliary distillation column that is reboiled by an argon condenser to condense argon for reflux purposes within an argon column. The residual liquid from the auxiliary distillation column is taken as the krypton-xenon-rich stream. 
     The need for krypton and xenon has increased over time due to increased demands for the use of such gas in lighting and laser applications. Xenon is also used as an anesthetic. Thus, there also exists the need to retrofit cryogenic air separation plants to recover the krypton and xenon for such applications. The difficulty with such a retrofit is that it is difficult to modify an existing plant with apparatus such as set forth above. 
     As will be discussed, the present invention solves this problem by providing a process for the production of a krypton-xenon-rich stream that can be effectuated in a free standing apparatus that utilizes oxygen flowing from the plant in an oxygen pipeline. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of producing a krypton-xenon-rich stream in which a pipeline oxygen stream, containing oxygen vapor, is removed from an oxygen pipeline at ambient temperature. The pipeline oxygen stream is introduced into a cryogenic rectification process to produce the krypton-xenon-rich stream. In the cryogenic rectification process, the pipeline oxygen stream is cooled to a temperature at or near a dew point temperature of the oxygen vapor contained in the pipeline oxygen stream. At least part of the pipeline oxygen stream, after having been cooled, is rectified in a distillation column to produce a krypton-xenon-rich liquid column bottoms. The krypton-xenon-rich stream is discharged from the distillation column and the krypton-xenon-rich stream composed of the krypton-xenon-rich liquid column bottoms. Refrigeration is imparted into the cryogenic rectification process. 
     The pipeline oxygen stream can be cooled in a main heat exchanger and the rectification of the pipeline oxygen stream produces an oxygen-rich vapor column overhead. An oxygen-rich vapor stream, composed of the oxygen-rich vapor column overhead, is removed from the distillation column and divided into a first oxygen-rich vapor stream and a second oxygen-rich vapor stream. The first oxygen-rich vapor stream is condensed in a condenser to produce a reflux stream and at least part of the reflux stream is introduced into the distillation column as reflux. The second oxygen-rich vapor stream is passed in indirect heat exchange with the pipeline oxygen stream from the oxygen pipeline in the main heat exchanger to assist in the cooling of the pipeline oxygen stream. The second oxygen-rich vapor stream is recycled back to the oxygen pipeline. 
     A heat exchange stream can be compressed and then cooled within the main heat exchanger. The heat exchange stream is condensed in a reboiler operatively associated with the distillation column to produce boil-up within the distillation column. The heat exchange stream, after having been condensed, is reduced in pressure and vaporized in the condenser in indirect heat exchange with the first oxygen-rich vapor stream, thereby to condense the first oxygen-rich vapor stream. The heat exchange stream, after having been vaporized, is partially warmed within the main heat exchanger and then expanded in a turboexpander to produce an exhaust stream and the turboexpander is coupled to a compressor used in compressing the heat exchange stream. The exhaust stream is fully warmed within the main heat exchanger to impart the refrigeration to the cryogenic rectification process and is recycled back to the compressor. 
     In another embodiment, a heat exchange stream can be cooled within the main heat exchanger and then, condensed in a reboiler located within the distillation column to produce boil-up within the distillation column. The heat exchange stream, after having been condensed, is vaporized in the condenser in indirect heat exchange with the first oxygen-rich vapor stream, thereby to condense the first oxygen-rich vapor stream and the heat exchange stream, after having been vaporized, is fully warmed within the main heat exchanger and then recycled back to the main heat exchanger. At least part of the reflux stream is introduced into the distillation column as part of the reflux thereof and an oxygen liquid stream is introduced into the distillation column to provide a further part of the reflux therefor and to impart the refrigeration into the cryogenic rectification process. 
     In another embodiment, the pipeline oxygen stream can be divided into a first oxygen vapor stream and a second oxygen vapor stream after having been cooled in the main heat exchanger. The first oxygen vapor stream can be expanded, introduced into the distillation column and rectified. The second oxygen vapor stream can be condensed in a reboiler operatively associated with the distillation column to produce boil-up for the distillation column and then expanded, after having been condensed and re-vaporized in the condenser in indirect heat exchange with the first oxygen-rich vapor stream. The second oxygen vapor stream, after having been re-vaporized, is fully warmed within the main heat exchanger, compressed and at least in part is recycled back into the oxygen pipeline. At least part of the reflux stream is passed into the distillation column as part of the reflux and an oxygen liquid stream is introduced into the distillation column as another part of the reflux and to introduce the refrigeration into the cryogenic rectification process. In yet another embodiment, the pipeline oxygen stream can be divided into a first oxygen vapor stream and a second oxygen vapor stream. The first oxygen vapor stream is fully cooled within the main heat exchanger, introduced into the distillation column and rectified. The second oxygen vapor stream is compressed and fully cooled within the main heat exchanger and then condensed in a reboiler operatively associated with the distillation column to produce boil-up for the distillation column. The second oxygen vapor stream is expanded after having been condensed and re-vaporized in the condenser in indirect heat exchange with the first oxygen-rich vapor stream. The second oxygen vapor stream, after having been re-vaporized, is fully warmed within the main heat exchanger, compressed and at least in part is recycled back into the oxygen pipeline. At least part of the reflux stream is passed into the distillation column as part of the reflux therefor and an oxygen liquid stream is passed into the column as another part of the reflux and to impart the refrigeration into the cryogenic rectification process. 
     In any embodiment of the present invention, the reflux stream can be passed in indirect heat exchange with the oxygen liquid stream within a subcooler, thereby to subcool the reflux stream. The oxygen liquid stream, after having passed through the subcooler, is expanded and introduced into the distillation column. A first part of the reflux stream after having been subcooled is passed into the distillation column as the part of the reflux therefore and a second part of the reflux stream, after having been subcooled, is discharged from the cryogenic rectification process. 
     The present invention also relates to an apparatus for producing a krypton-xenon-rich stream. In accordance with this aspect of the present invention, a cryogenic rectification plant is connected to an oxygen pipeline. The plant is configured to rectify a pipeline oxygen stream removed from an oxygen pipeline at ambient temperature and to produce the krypton-xenon-rich stream. The cryogenic rectification plant has a main heat exchanger connected to the oxygen pipeline so as to receive the pipeline oxygen stream and is configured to cool the pipeline oxygen stream to a temperature at or near a dew point temperature of oxygen vapor contained in the pipeline oxygen stream. A distillation column is connected to the main heat exchanger so as to receive at least part of the pipeline oxygen stream and is configured to rectify the at least part of the pipeline oxygen stream to produce a krypton-xenon-rich liquid column bottoms and an oxygen-rich vapor column overhead. The distillation column is provided with an outlet to discharge the krypton-xenon-rich stream from the distillation column such that the krypton-xenon-rich stream is composed of the krypton-xenon-rich liquid column bottoms. A condenser is connected to the distillation column so as to condense a first oxygen-rich vapor stream composed of the oxygen-rich vapor column overhead and thereby form a reflux stream and to return at least part of the reflux stream to the distillation column as reflux. The distillation column is also connected to the main heat exchanger so that a second oxygen-rich vapor stream, composed of the oxygen-rich vapor column overhead, is passed in indirect heat exchange with the pipeline oxygen stream from the oxygen pipeline to assist in the cooling of the pipeline oxygen stream. The main heat exchanger is also connected to the oxygen pipeline so that the second oxygen-rich vapor stream is recycled back to the oxygen pipeline. A means for imparting refrigeration to the cryogenic rectification plant is also provided. 
     In one embodiment, a compressor can be provided to compress a heat exchange stream and the main heat exchanger is connected to the compressor to receive the heat exchange stream, after having been compressed and then to cool the heat exchange stream. A reboiler is operatively associated with the distillation column to produce boil-up within the distillation column and is connected to the main heat exchanger so as to receive the heat exchange stream and to condense the heat exchange stream. The condenser is connected to the reboiler and is configured to vaporize the heat exchange stream, after having been condensed, through indirect heat exchange with the first oxygen-rich vapor stream, thereby to condense the first oxygen-rich vapor stream. The main heat exchanger is connected to the condenser and configured to receive the heat exchange stream after having been vaporized and to partially warm the heat exchange stream. An expansion valve is positioned between the condenser and the reboiler to expand the heat exchange stream after having been condensed and the refrigeration imparting means comprises a turboexpander connected to the main heat exchanger to receive the heat exchange stream after having been partially warmed and to expand the heat exchange stream, thereby to produce an exhaust stream. The turboexpander is coupled to the compressor used in compressing the heat exchange stream and the main heat exchanger is also connected to the turboexpander and is configured to fully warm the exhaust stream within the main heat exchanger to impart the refrigeration to the cryogenic rectification plant. A recycle compressor is positioned between the compressor and the heat exchanger to raise the pressure and recycle the heat exchange stream back to the compressor. 
     In another embodiment, the main heat exchanger can be configured to cool a heat exchange stream. A reboiler is operatively associated with the distillation column to produce boil-up within the distillation column and is connected to the main heat exchanger so as to receive the heat exchange stream and to condense the heat exchange stream. The condenser is connected to the reboiler and configured to vaporize the heat exchange stream, after having been condensed, through indirect heat exchange with the first oxygen-rich vapor stream, thereby to condense the first oxygen-rich vapor stream. An expansion valve is positioned between the condenser and the reboiler to expand the heat exchange stream after having been condensed and the main heat exchanger is connected to the condenser and is configured to receive the heat exchange stream after having been vaporized and to fully warm the heat exchange stream. A recycle compressor is connected to the main heat exchanger to receive the heat exchange stream after having been fully warmed such that the heat exchange stream is raised in pressure and recycled back into the main heat exchanger to fully cool the heat exchange stream. The refrigeration imparting means comprises the distillation column having an inlet positioned to receive an oxygen liquid stream as another part of the reflux. 
     In another embodiment, the distillation column can be connected to the main heat exchanger such that a first oxygen vapor stream composed of part of the pipeline oxygen stream is introduced into the distillation column and rectified. A reboiler is operatively associated with the distillation column to produce boil-up for the distillation column and is connected to the main heat exchanger so that a second oxygen vapor stream composed of another part of the pipeline oxygen stream is introduced into the reboiler and condensed. The reboiler is connected to the condenser so that the second oxygen vapor stream is introduced into the condenser and is re-vaporized through indirect heat exchange with the first oxygen-rich vapor stream, thereby to condense the first oxygen-rich vapor stream. Expansion valves are positioned between the main heat exchanger and the distillation column so that the first oxygen vapor stream is expanded prior to being introduced into the distillation column and between the reboiler and the condenser so that the second oxygen vapor stream after having been condensed is expanded. A compressor is connected between the main heat exchanger and the oxygen pipeline so that the second oxygen vapor stream after having been fully warmed is compressed back to pipeline pressure and at least in part is recycled back into the oxygen pipeline. The refrigeration imparting means comprises the distillation column having an inlet positioned to receive an oxygen liquid stream as another part of the reflux. 
     In yet another embodiment, the main heat exchanger and a compressor are connected to the oxygen pipeline so that a first oxygen vapor stream composed of part of the pipeline oxygen stream fully cools within the main heat exchanger and a second oxygen vapor stream composed of another part of the pipeline oxygen stream is compressed in the compressor and fully cools within the main heat exchanger. A reboiler is operatively associated with the distillation column to produce boil-up for the distillation column is connected to the main heat exchanger so that the second oxygen vapor stream is condensed in the reboiler. The condenser is connected to the reboiler so that the second oxygen vapor stream is re-vaporized after having been condensed through indirect heat exchange with the first oxygen-rich vapor stream. An expansion valve is positioned between the condenser and the reboiler to valve expand the second oxygen vapor stream after having been condensed in the reboiler. The main heat exchanger is connected to the condenser so that the second oxygen vapor stream is fully warmed within the main heat exchanger after having been re-vaporized. Another compressor is positioned between the main heat exchanger and the oxygen pipeline to compress the second oxygen vapor stream back to pipeline pressure and at least in part recycle the second oxygen vapor stream back into the oxygen pipeline. The refrigeration imparting means comprises the distillation column having an inlet positioned to receive an oxygen liquid stream as another part of the reflux. In such embodiment, the condenser can be connected to the distillation column so that a first part of the reflux stream is introduced into the distillation column as part of the reflux thereof. 
     In any embodiment of the present invention, a subcooler can be connected to the condenser. The subcooler is configured to receive the reflux stream and the oxygen liquid stream so that the reflux stream is subcooled within the subcooler. The subcooler is connected to the distillation column so that the oxygen liquid stream is introduced into the distillation column after having passed through the subcooler, a first part of the reflux stream is introduced into the distillation column and a second part of the reflux stream is discharged from the cryogenic rectification plant. A further expansion valve is positioned between the subcooler and the distillation column so that the oxygen liquid stream is valve expanded before introduction into the distillation column. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims distinctly pointing out the subject matter that Applicants regard as their invention, it is believed that the invention will be better understood when taken in connection with the accompanying drawings in which: 
         FIG. 1  is a schematic process flow diagram of an apparatus designed to carry out a method in accordance with the present invention; 
         FIG. 2  is a schematic process flow diagram of an alternative embodiment of the apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic process flow diagram of a further alternative embodiment of an apparatus designed to carry out a method in accordance with the present invention; and 
         FIG. 4  is a schematic process flow diagram of an alternative embodiment of the apparatus illustrated in  FIG. 3 . 
     
    
    
     In order to avoid needless repetition in the explanation of the various Figures, the same reference numbers are used for elements thereof having the same description. 
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a cryogenic rectification plant  1  is illustrated that is designed to process oxygen vapor flowing through an oxygen pipeline  2  and thereby produce a krypton-xenon-rich stream  3  that can be further processed to produce krypton and xenon products. Typical compositions of the stream flowing through oxygen pipeline  2 , on a percentile, volume basis are as follows: Oxygen: 0.9950-0.9995; Argon: 0.0050-0.0005; Nitrogen: 0.0; Krypton: 1.6-6.1 ppm; and Xenon: 0.12-0.46 ppm. Krypton-xenon-rich stream  3  will have the following composition: Oxygen: 0.9950-0.9995; Argon: 0.0050-0.0005; Nitrogen: 0.0; Krypton: 150-2600 ppm; and Xenon: 100-400 ppm. Cryogenic rectification plant  1  would be constructed as a retrofit to an existing air separation plant installation in which oxygen produced by such plant is being routed to an application utilizing such oxygen by means of an oxygen pipeline  2 . 
     An oxygen pipeline stream  10  is removed from the oxygen pipeline  2  at ambient temperature and is composed of the oxygen vapor flowing through the oxygen pipeline  2 . The oxygen pipeline stream  10  is introduced into a main heat exchanger  12  to cool the oxygen pipeline stream  10  to a temperature at or near its dewpoint. Main heat exchanger  12  can be of known braised aluminum plate-fin construction. 
     The resulting cooled oxygen pipeline stream  10  is then introduced into a distillation column  14  for rectification. Although not illustrated, distillation column  14  is provided with packing, either structured or random or a combination of the two type of packings or possibly sieve trays to contact an ascending vapor phase that becomes leaner in the krypton and xenon as it ascends and a descending liquid phase that become richer in the krypton and xenon as it descends such column. As a result, a krypton-xenon-rich column bottoms is produced at the bottom of distillation column  14  and an oxygen-rich vapor column overhead. 
     Distillation column  14  is provided with an outlet  16  to discharge the krypton-xenon-rich stream  3 . A condenser  18  is connected to the top of distillation column  14  so as to condense a first oxygen-rich vapor stream  20  that is composed of the oxygen-rich vapor column overhead. The condensation produces a reflux stream  22  that as will be described is reintroduced, at least in part, into distillation column  14  as reflux. The distillation column  14  is also connected to the main heat exchanger  12  so that a second oxygen-rich vapor stream  24  passes in indirect heat exchange with the pipeline oxygen stream  10  to assist in the cooling of the pipeline oxygen stream  10 . The second oxygen-rich vapor stream  24  is then recycled back to the oxygen pipeline  2  as a warm stream  26 . 
     Although in cryogenic rectification plant  1 , the reflux stream  22  in its entirety could be introduced into the top of distillation column  24 , it can advantageously be subcooled in a subcooling unit  28 . A first part  30  of the reflux stream  22  is introduced into the top of distillation column  14  as part of the reflux for such column. A second part  32  of the reflux stream  22  is discharged from the subcooling unit  14  as a subcooled, krypton and xenon depleted liquid oxygen stream. The heat exchange duty of the subcooling unit  28  is provided by a liquid oxygen stream  34  that after passing through the subcooling unit  28  is expanded to the pressure of distillation column  14  in an expansion valve  36  and then introduced as a remaining part of the reflux for distillation column  14 . 
     Liquid oxygen stream  34  can be obtained from the same installation where oxygen vapor is produced to feed oxygen pipeline  2 . In this regard, liquid oxygen stream  34  is derived from a pumped stream that is later vaporized and fed into the oxygen pipeline  2 . As such, in the illustrated embodiments it is reduced in pressure to column pressure. However, if it were obtained at a lower pressure, expansion might not be necessary. The part  32  of the reflux stream  22  could be reintroduced into the air separation plant or possibly back to the oxygen pipeline  2 . While optional in the cryogenic rectification plant  1 , the use of the liquid oxygen stream  34  is advantageous in that it allows the krypton and xenon within such liquid oxygen to be recovered and further, such stream also provides some of the refrigeration load of the cryogenic rectification plant  1 . 
     Cryogenic rectification plant  1  is designed to be a free standing plant and as such is also designed to produce its own refrigeration. This is done in a heat pump loop that uses nitrogen or suitable fluid as the heat exchange fluid. A heat exchange stream  38  is compressed by a compressor  40 . After removal of the heat of compression by means of an aftercooler  42 , the heat exchange stream is cooled in the main heat exchanger  12  to produce a cooled heat exchange stream  44 . A reboiler  46  located in the bottom of the distillation column  14  is connected to the main heat exchanger  12  to receive the cooled heat exchange stream  44  and to produce boil up within the distillation column  14  and thereby initiate formation of the ascending vapor phase from vaporized krypton-xenon-rich liquid column bottoms. This condenses the cooled heat exchange stream  44  and thereby produces a condensed heat exchange stream  48 . Condensed heat exchange stream  48  is then passed through an expansion valve  50  to cool such stream and thereby condense the first oxygen-rich vapor stream  20 . This re-vaporizes the heat exchange stream to produce a re-vaporized heat exchange stream  52  that is partially warmed within main heat exchanger  12  and then introduced into a turboexpander  54  to produce an exhaust stream  56 . As used herein and in the claims, the term “partially warmed” in such context means warmed to a temperature between the warm and cold end temperature of the main heat exchanger  12 . The refrigeration is imparted by warming the exhaust stream  56  in the main heat exchanger  12 . The exhaust stream is then introduced into a recycle compressor  58  and after cooling within an aftercooler  60  is recirculated back to the compressor  40  as the heat exchanger stream  38 . A makeup for the heat exchange fluid can also be introduced as a makeup stream  62  to replace heat exchange fluid that is lost due to leakage. As can be appreciated, the compression of the heat exchange stream represents an energy outlay and cost. This energy cost can be reduced if part of the refrigeration requirement for the plant is provided by liquid oxygen stream  34 . 
     With reference to  FIG. 2 , a cryogenic rectification plant  2  is illustrated that is an alternative embodiment of the cryogenic rectification plant  1 . Unlike cryogenic rectification plant  1 , cryogenic rectification plant  2  is not designed to be free-standing and hence, is not provided with a means to self-generate refrigeration. It does, however, employ a heat exchange loop in which heat exchange stream is cooled in a main heat exchanger  12 ′ that differs from main heat exchanger  12  in that it is not provided with passages to partially warm the re-vaporized heat exchange stream  52 . The resulting cool heat exchanger stream  44  is again introduced into reboiler  46  and condensed to produce a condensed heat exchange stream  48 ′ that, after passage through expansion valve  50 , is re-vaporized to produce the re-vaporized heat exchange stream  52 . The re-vaporized heat exchange stream  52  is warmed within the main heat exchanger  12 ′ to produce a warm heat exchange stream  64  that is reintroduced into the compressor  58 . The refrigeration is imparted into the cryogenic rectification plant solely by liquid oxygen stream  34 . In this regard, liquid oxygen stream  34  could be introduced directly into distillation column  14  without subcooling the reflux stream  22  and the reflux stream could be introduced in its entirety into the distillation column  14 . 
     With reference to  FIG. 3 , a yet further embodiment of the present invention is illustrated that incorporates a cryogenic rectification plant  3 . Cryogenic rectification plant  3 , as cryogenic rectification plant  2 , is not designed to be self-standing and as such is refrigerated externally by liquid oxygen stream  34 . The rectification is driven, however, not be a heat pump loop, but rather by the pipeline oxygen stream  10 . In this regard, the oxygen produced in the air separation plant supplying oxygen pipeline  2  would be compressed or supplied at about 15 psi higher than the embodiments discussed above. Pipeline oxygen stream  10  is cooled in a main heat exchanger  12 ″ that has fewer heat exchange passages than main heat exchangers  12  or  12 ′ given that it does not include a recycled heat exchange stream. The cooled pipeline oxygen stream is divided into a first oxygen vapor stream  70  and a second oxygen vapor stream  72 . First oxygen vapor stream  70  is valve expanded in an expansion valve  74 , introduced into the distillation column  14  and rectified. The second oxygen vapor stream  72  is introduced into reboiler  46  and condensed. The resulting condensed oxygen vapor stream  76  is then reduced in pressure by an expansion valve  78  and introduced into condenser  18  where it is re-vaporized in the production of the reflux. The reduction in pressure, lowers the temperature of the condensed oxygen vapor stream  76  so that it can operate to condense reflux for the distillation column  14 . In a like manner the reduction in pressure of the first oxygen vapor stream  70  lowers its temperature so that second oxygen vapor stream  72  can be condensed in reboiler  46 . 
     The re-vaporized oxygen vapor stream  80  is warmed within main heat exchanger  12 ″, compressed back to pipeline pressure in a compressor  82 . After removal of the heat of compression in an aftercooler  84 , a resulting first compressed oxygen vapor stream  86  is reintroduced into the oxygen pipeline  2 . Optionally, a second compressed oxygen vapor stream  88  can be recycled back to the pipeline oxygen stream  10  given that such stream has a krypton and xenon content that can be recovered. 
       FIG. 4  illustrates a cryogenic rectification plant  4  that is an alternative embodiment of the cryogenic rectification plant  3 . In cryogenic rectification plant  4 , the pipeline oxygen stream  10  is divided into a first oxygen vapor stream  70 ′ and a second oxygen vapor stream  72 ′ prior to a main heat exchanger  12 ′″. First oxygen vapor stream  70 ′ is cooled within main heat exchanger  12 ′″ and then introduced into distillation column  14  for rectification. The second oxygen vapor stream  72 ′ is compressed by a compressor  90  and after removal of the heat of compression in an aftercooler  92 , is cooled, as a compressed oxygen vapor stream  94 . As is apparent, in such embodiment not all of the oxygen need be compressed to a higher pressure in order to drive the distillation as is the case in cryogenic rectification plant  3 . 
     Compressed oxygen vapor stream  94  is introduced into reboiler  46  after cooling in main heat exchanger  12 ′″ to form a condensed oxygen vapor stream  48 ″. The condensed oxygen vapor stream  48 ″ is re-vaporized within condenser  18  while condensing the reflux to form the revaporized oxygen vapor stream  80 . Cryogenic rectification plant  4  otherwise functions in the same manner as cryogenic rectification plant  3 . 
     In any of the embodiments illustrated above, the krypton-xenon-rich stream  3  could be further processed on site and near any of the cryogenic rectification plants discussed above in order to lessen the amount of liquid that would be necessary to be transported for final processing to produce the krypton and xenon products. This would be done by vaporizing the krypton-xenon-rich stream and then subjecting such stream to catalytic oxidation followed by carbon dioxide and water vapor removal. The resulting dry stream would then be cooled and distilled in a distillation column equipped with enough stages to increase the concentration of krypton in the krypton-xenon-rich stream  3  from 340 ppm to 55 percent and that of xenon from 260 ppm to 43 percent with an oxygen impurity of 1 percent. The refrigeration requirement for such column could be provided by a portion of the condensed heat transfer fluid  48 . 
     The following Table is a calculated example of the embodiment of the present invention illustrated in  FIG. 1  illustrating a stream summary and heat and mass balance of the various streams flowing within cryogenic rectification plant  1 . 
     
       
         
           
               
               
             
               
                   
                 TABLE 
               
               
                   
                   
               
             
            
               
                   
                 Stream 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 10 1   
                 10 2   
                 24 
                 20 
                 30 
               
               
                   
               
               
                 Vapour 
                 1 
                 1 
                 1 
                 1 
                 0 
               
               
                 Fraction 
               
               
                 Temperature 
                 310.0 
                 122.0 
                 120.9 
                 120.9 
                 104.8 
               
               
                 [K] 
               
               
                 Pressure [psia] 
                 159.7 
                 157.2 
                 157.2 
                 157.2 
                 156.2 
               
               
                 Flow 
                 1000 
                 1000 
                 999 
                 51 
                 7 
               
               
                 [moles/hr] 
               
               
                 Enthalpy 
                 115.7 
                 −2417.7 
                 −2436.8 
                 −2436.8 
                 −5200.5 
               
               
                 [Btu/mol] 
               
               
                 Mole Frac 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 (Nitrogen) 
               
               
                 Mole Frac 
                 0.00398 
                 0.00398 
                 0.00398 
                 0.00398 
                 0.00398 
               
               
                 (Argon) 
               
               
                 Mole Frac 
                 0.996 
                 0.996 
                 0.996 
                 0.996 
                 0.996 
               
               
                 (Oxygen) 
               
               
                 Mole Frac 
                 5.59E−06 
                 5.59E−06 
                 5.11E−06 
                 5.11E−06 
                 5.11E−06 
               
               
                 (Krypton) 
               
               
                 Mole Frac 
                 4.26E−07 
                 4.26E−07 
                 5.39E−08 
                 5.39E−08 
                 5.39E−08 
               
               
                 (Xenon) 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Stream 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 32 
                 34 
                 38 
                 44 
                 48 
                 52 
               
               
                   
               
               
                 Vapour 
                 0 
                 0 
                 1 
                 1 
                 0 
                 1 
               
               
                 Fraction 
               
               
                 Temperature 
                 104.8 
                 93.7 
                 310.0 
                 124.0 
                 122.4 
                 119.0 
               
               
                 [K] 
               
               
                 Pressure [psia] 
                 156.2 
                 159.7 
                 253.0 
                 412.0 
                 412.0 
                 299.50 
               
               
                 Flow 
                 44 
                 44 
                 96 
                 96 
                 96 
                 96 
               
               
                 [moles/hr] 
               
               
                 Enthalpy 
                 −5200.5 
                 −5469.1 
                 108.0 
                 −2796.1 
                 −3827.0 
                 −2644.8 
               
               
                 [Btu/mol] 
               
               
                 Mole Frac 
                 0 
                 0 
                 1 
                 1 
                 1 
                 1 
               
               
                 (Nitrogen) 
               
               
                 Mole Frac 
                 0.00398 
                 0.00398 
                 0 
                 0 
                 0 
                 0 
               
               
                 (Argon) 
               
               
                 Mole Frac 
                 0.996 
                 0.996 
                 0 
                 0 
                 0 
                 0 
               
               
                 (Oxygen) 
               
               
                 Mole Frac 
                 5.11E−06 
                 5.59E−06 
                 0 
                 0 
                 0 
                 0 
               
               
                 (Krypton) 
               
               
                 Mole Frac 
                 5.39E−08 
                 4.26E−07 
                 0 
                 0 
                 0 
                 0 
               
               
                 (Xenon) 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Stream 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 52 3   
                 56 4   
                 56 5   
                 3 
               
               
                   
                   
               
               
                   
                 Vapour 
                 1 
                 1 
                 1 
                 0 
               
               
                   
                 Fraction 
               
               
                   
                 Temperature 
                 195.0 
                 126.4 
                 304.3 
                 121.0 
               
               
                   
                 [K] 
               
               
                   
                 Pressure [psia] 
                 296.5 
                 50.0 
                 46.0 
                 158.0 
               
               
                   
                 Flow 
                 96 
                 96 
                 96 
                 1.5 
               
               
                   
                 [moles/hr] 
               
               
                   
                 Enthalpy 
                 −1407.0 
                 −2165.8 
                 68.8 
                 −4811.3 
               
               
                   
                 [Btu/mol] 
               
               
                   
                 Mole Frac 
                 1 
                 1 
                 1 
                 0 
               
               
                   
                 (Nitrogen) 
               
               
                   
                 Mole Frac 
                 0 
                 0 
                 0 
                 0.00193 
               
               
                   
                 (Argon) 
               
               
                   
                 Mole Frac 
                 0 
                 0 
                 0 
                 0.9962 
               
               
                   
                 (Oxygen) 
               
               
                   
                 Mole Frac 
                 0 
                 0 
                 0 
                 3.42E−04 
               
               
                   
                 (Krypton) 
               
               
                   
                 Mole Frac 
                 0 
                 0 
                 0 
                 2.65E−04 
               
               
                   
                 (Xenon) 
               
               
                   
                   
               
               
                   
                   1 Pipeline oxygen stream before main heat exchanger 12 
               
               
                   
                   2 Pipeline oxygen stream after main heat exchanger 12 
               
               
                   
                   3 Re-vaporized heat exchange stream 52 after partial warming within main heat exchanger 12 
               
               
                   
                   4 Exhaust stream 56 prior to warming within main heat exchanger 12 
               
               
                   
                   5 Exhaust stream 56 after warming within main heat exchanger 12 
               
            
           
         
       
     
     While the present invention has been discussed with reference to preferred embodiments, as would occur to those skilled in the art, numerous changes and omission could be made in such embodiments without departing from the sprit and scope of the present invention as set forth in the appended claims.