Abstract:
A hybrid system which utilizes high purity oxygen from a local pipeline, which is blended with low purity oxygen from an on-site or local cryogenic distillation system, thus resulting in a blend of intermediate quality which satisfies the needs of the customer. In order to offset the operating and energy costs associated with this fairly low profit margin intermediate purity oxygen, high purity nitrogen at high pressure is simultaneously exported to the local pipeline, thereby acting as a credit to the overall system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/831,170, filed Jul. 14, 2006, the entire contents of which are incorporated herein by reference. 
     
     BACKGROUND 
       [0002]    For typical industrial applications, high purity oxygen is typically produced and supplied at a purity of about 99.5% or higher. This high purity oxygen may be produced on-site, provided to the site by means of a pipeline network, or brought into the site in liquid form, and stored in tanks. For pipeline applications, typically, the pipeline operating pressure is 40 bar or higher. However, there are numerous applications, such as combustion, that require neither this purity level, nor a delivery pressure this high. 
         [0003]    Applications, such as glassmaking, steelmaking and gasification for energy production can use low purity oxygen. Typically, for glassmaking or steelmaking applications, the acceptable oxygen purity level may be as low as about 90%. Typically, for gasification applications, the required oxygen purity level may be as low as about 95%, or even about 85%. 
         [0004]    The power required to compress the gaseous oxygen to such high pressure contributes significantly to the production and supply cost of the product oxygen. This cost of compression can account for more than about 50% of the energy required to perform the separation of oxygen from air. As applications develop and are identified that require relatively impure, low pressure oxygen, a solution is required that will allow such a product to be provided to the customer in a cost-effective way. 
         [0005]    The person skilled in the art would recognize that there are currently five basic solutions to the above problem. 
         [0006]    The first solution would be to use a VSA or PSA based system. Vacuum swing adsorption (VSA) or pressure swing adsorption (PSA) processes use a non-cryogenic technology based on nitrogen adsorption through a molecular sieve. These types of units produce low purity oxygen, typically between about 90% and about 95% purity. Typically, the VSA produces oxygen at around 1.03 bar, and the PSA produces oxygen at between about 2 bar and 4 bar. These technologies tend to be moderately cost effective, however, the reliability of this technology requires that expensive liquid backup systems be installed. Other non-cryogenic adsorption processes, such as temperature swing adsorption (TSA), temperature-pressure swing adsorption (TPSA) process may also be used, but suffer from similar disadvantages. The adsorption solution is described in several technical papers, such as U.S. Pat. Nos. 5,114,440, 5,679,134, and 6,332,915. 
         [0007]    The second solution would be to use a small, standardized, pre-designed and modularized cryogenic air separation unit. These units produce moderately low purity oxygen, typically between about 95% and about 98.5%. This technology is more reliable than the adsorption based technologies, however, a liquid backup system would typically still be required. This cryogenic process is usually the basic double column process and is widely used in the air separation industry. 
         [0008]    The third solution would be to co-produce low purity and low pressure oxygen from a liquid production plant and utilize the existing storage facilities as the backup source 
         [0009]    The fourth solution would be to install an air separation plant that would provide oxygen at two purity levels. Typically, if all the oxygen is removed at a lower purity level, the energy requirement of the plant may be reduced on the order of about 10%. A basic cryogenic air separation plant is actually more efficient if, for example, one half of the oxygen is extracted at a high purity level, and the other half of the oxygen is extracted at a lower purity level, and if a traditional power usage is assigned to the high purity portion then the resulting power usage for low purity oxygen portion can be reduced on the order of about 20%. 
         [0010]    This sort of bi-purity arrangement is advantageous, for example, for iron metallurgy applications. The blast furnace may require a lower purity oxygen, while the steelworks may require a higher purity oxygen. While this type of solution works well in theory, practical considerations, such as customer demand changes, fluctuations in the different loads, etc. make this solution marginal at best. 
         [0011]    The fifth, and final, solution would be to utilize an oxygen pipeline. This solution is only available should the consumer be in close proximity to an existing pipeline. Typically, these pipelines operate at pressures of about 40 bar or higher. Such a solution would require taking high value added, high purity and high pressure oxygen and reducing the pressure to provide low pressure oxygen at a much higher purity than required by the customer. This solution is not efficient since high purity and high pressure oxygen is used to supply a demand for low purity and low pressure. Its first investment cost is low and can only be used for short term needs but not for long term operations. 
         [0012]    For the foregoing reasons, a need exists within the industry for a system that will provide low purity and low pressure oxygen to a customer at an economically attractive price. 
       SUMMARY 
       [0013]    The present invention is directed to a method and apparatus that satisfies the need in general for a system that will provide a means for providing low pressure and low purity oxygen to customers, while minimizing the installed cost and operating cost associated with large, on-site facilities. The present invention represents a hybrid system which utilizes high purity oxygen from a local pipeline, which is blended with low purity oxygen from an on-site or local cryogenic distillation system, thus resulting in a blend of intermediate quality which satisfies the needs of the customer. In order to offset the operating and energy costs associated with the intermediate purity oxygen, high purity nitrogen at high pressure is simultaneously exported to the local pipeline, thereby acting as a credit to the overall system (in general, there usually is a nitrogen pipeline in the same trench as the oxygen pipeline). 
         [0014]    In one aspect of the present invention, a method for providing low pressure and intermediate purity oxygen is provided. The method includes the steps of:
       a) providing a cryogenic distillation system, wherein said cryogenic distillation system produces a first liquid oxygen;   b) increasing the pressure of the first pressure oxygen to a first pressure;   c) providing a high purity oxygen vapor stream from a pipeline at a second pressure, wherein said second pressure is greater than said first pressure;   d) cooling and at least partially condensing said high purity oxygen vapor stream and reducing its pressure to approximately said first pressure, through a pressure reducing device;   e) combining said at least partially condensed high purity oxygen stream and said first liquid oxygen stream to produce an intermediate purity liquid oxygen;   f) vaporizing said intermediate purity liquid oxygen thereby producing an intermediate purity oxygen vapor stream; and   g) warming the intermediate purity oxygen vapor stream, thereby producing a warm intermediate purity oxygen vapor stream.       
 
         [0022]    In another aspect of the present invention, an apparatus for providing low pressure and intermediate purity oxygen is provided. The apparatus includes:
       a) a cryogenic distillation system, wherein said cryogenic distillation system produces a first liquid oxygen stream;   b) a mean to increase the pressure of the first liquid oxygen stream to a first pressure;   c) a pressure reducing device for reducing the pressure of a high purity oxygen stream, at a second pressure, to approximately said first pressure; and   d) a first heat exchanging device for vaporizing said first liquid oxygen stream and a portion of said reduced pressure high purity oxygen stream, thereby producing an intermediate purity oxygen vapor stream.       
 
     
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0027]    For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein: 
           [0028]      FIG. 1  is a schematic representation of one embodiment of the present invention; 
           [0029]      FIG. 2  is a schematic representation of another embodiment of the present invention; 
           [0030]      FIG. 3  is a schematic representation of another embodiment of the present invention 
           [0031]      FIG. 4  is a schematic representation of another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
         [0033]    It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0034]    As used in this application, all the percentage purities mentioned are molar purities. 
         [0035]    As used in this application, intermediate purity is defined as a purity level of less than about 99.5%. Alternately, intermediate purity may be defined as having a purity level of 98% or less. Alternately, intermediate purity may be defined a having a purity level of 95% or less. Alternately, intermediate purity may be defined as having a purity level of between about 85% and about 99.5%. Alternately, intermediate purity may be defined as having a purity level of between about 85% and about 98%. Alternately, intermediate purity may be defined as having a purity level of between about 85% and about 95%. 
         [0036]    As used in this application high purity is defined as having a purity of greater than about 99.5%. Alternately, high purity may be defined as having a purity level of greater than about 98%. 
         [0037]    As used in this application, typical oxygen or nitrogen pipeline pressures are defined as being about 40 bar. Alternately, typical oxygen or nitrogen pipeline pressures may be between about 40 bar and about 65 bar. 
         [0038]    As used in this application, a typical cryogenic distillation system produces a nitrogen vapor stream that will typically have a pressure of between about 3.5 bar and about 11 bar. Alternately, the nitrogen vapor stream may have a pressure of between about 5 bar and about 7 bar. Alternately, the nitrogen vapor stream may have a pressure of between about 5.5 bar and about 6.6 bar. 
         [0039]    As used in this application, a typical cryogenic distillation system produces a liquid oxygen stream that will typically have a pressure of between about 1.3 bar and about 2 bar. Alternately, the liquid oxygen stream may have a pressure of between about 1.4 bar and about 1.8 bar. 
         [0040]    As used in this application, low pressure gaseous oxygen is defined as having a pressure of between about 2 bar and 2.5 bar. Alternately, low pressure gaseous oxygen is defined as having a pressure of between about 2.1 bar and 2.4 bar. 
         [0041]      FIG. 1  is a stylized diagram depicting an illustrative embodiment of an apparatus  100  in accordance with the present invention. The apparatus  100  comprises a cryogenic distillation system  101 , a pressure reducing device  105 , a first heat exchanging device  108 , a pressure increasing device  111 , and a second heat exchanging device  114 . 
         [0042]    The cryogenic distillation system  101  may be of any design known to the skilled artisan that is capable of producing a low purity liquid oxygen stream and a high purity nitrogen vapor stream. Such system may include fluid transfer devices, such as liquid pumps to provide liquid products above the pressures of the columns. For illustration purposes, a traditional double column distillation system is shown in  FIG. 1 . The pressure reducing device  105  may be of any design known to the skilled artisan that is capable of reducing the pressure of cooled or liquefied high purity oxygen from typical pipeline pressures down to the approximate pressure at which a cryogenic distillation system produces liquid oxygen. Such pressure reducing devices  105  may include, but are not limited to, Joule-Thompson valves and turboexpanders. The first heat exchanging device  108  and the second heat exchanging device  114  may be of any design known to the skilled artisan. The pressure increasing device  111  may be of any design known to the skilled artisan that is capable of increasing the working pressure of a cryogenic liquid. 
         [0043]    In one embodiment of the present invention a high purity oxygen vapor stream  104  is provided. This high purity oxygen vapor stream  104  has a pressure that is approximately equal to the typical pressure within an oxygen pipeline. This high purity oxygen vapor stream  104  is introduced into the second heat exchanging device  114 , wherein it will exchange heat with streams  112 ,  124  and  109  (hereinafter more fully described). The result of this heat transfer process within the second heat exchanger device  114  will be a cold high purity oxygen stream  117 , which may be at least partially condensed. If the oxygen pressure exceeds its critical pressure, there will be no phase change and stream  117  will be cooled to a temperature colder than its critical temperature. The cold high purity oxygen stream  117  is then directed to the pressure reduction device  105 , which results in an at least partially condensed high purity oxygen stream  106 . 
         [0044]    The at least partially condensed high purity oxygen stream  106  is then introduced into the first heat exchanging device  108 , wherein it will be combined with a first liquid oxygen stream  118 , which is being output from the cryogenic distillation system  101  via stream  102  and pumped by device  120  to the pressure of device  108 , thereby resulting in an intermediate purity oxygen. If the pressure increase of device  120  is low it may be possible to use hydraulic liquid head to increase the pressure of stream  102 . This intermediate purity oxygen will be vaporized against a condensing air stream  110 . The result of this heat transfer process within the first heat exchange device  108  will be an intermediate purity oxygen vapor stream  109 . This intermediate purity oxygen vapor stream  109  is then introduced into the second heat exchange device  114 , wherein it will be warmed by exchanging heat with other streams to yield the warm intermediate purity low pressure gaseous oxygen stream  115 , which may then be sent to the end user. 
         [0045]    In another embodiment, the high purity oxygen stream  141  is first combined with a first liquid oxygen stream  118 , thereby resulting in an intermediate purity oxygen stream. The intermediate purity oxygen stream is then introduced into the first heat exchanging device  108 , wherein it will exchange heat with stream  110  to yield an intermediate purity oxygen vapor stream  109   
         [0046]    A gaseous feed air stream  113  is pretreated using methods and devices well known to those skilled in the art, then introduced into the second heat exchange device  114 , wherein it exchanges heat with streams  109 ,  124  and  112  (hereinafter more fully described). A portion of stream  113  may be sent via stream  128  to a system of compressor-expander  130  and  131  to provide the necessary refrigeration for the cryogenic unit. As a result of this heat transfer, the gaseous feed air stream  126  is cooled and introduced into the cryogenic distillation system  101 . The cryogenic distillation system  101  produces a low purity liquid oxygen stream  102 , and a liquid nitrogen stream  150 . The pressure of the low purity liquid oxygen stream  102  is increased then combined with the at least partially condensed high purity oxygen  106  inside the first heat exchanging device  108 , resulting in an intermediate purity oxygen. The intermediate purity oxygen will exchange heat with the air stream  110  inside the first heat exchanging device  108 . The result of this heat transfer is that the intermediate purity oxygen will at least partially vaporize into an intermediate purity oxygen vapor stream  109 . The liquid nitrogen stream  150  is extracted from the distillation system and then be introduced to pressure increasing device  111 , resulting in a high pressure liquid nitrogen stream  112 . This high pressure liquid nitrogen stream  112  is then introduced to second heat exchange device  114 , wherein it exchanges heat with streams  126  and  104 , resulting in a vaporized high pressure nitrogen stream  116 , which may then be sent to an end user or introduced into a pipeline. 
         [0047]    As illustrated in  FIG. 1 , in one embodiment some or all of stream  113  may be passed through a pressure reduction device  150  prior to admission into second heat exchange device  114 . 
         [0048]    As illustrated in  FIG. 1 , in one embodiment a portion  140  of the high purity oxygen stream  117  may be sent via stream  140  to the cryogenic distillation system  101 . It is possible to send the totality of the high purity oxygen stream  117  to the column system  101 , in this situation the mixing of high purity and low purity oxygen takes place in the sump of one column of the distillation system  101 . This configuration would result in slightly warmer sump temperature which results in slightly higher system pressure, however, the richer vapor generated at the sump is slightly favorable for the distillation. 
         [0049]      FIG. 2  is similar to  FIG. 1  but the distillation system  101 , instead of being a traditional double column system, is a triple column system. The mixture of high purity oxygen  206  and low purity oxygen  218  is vaporized into an intermediate purity oxygen vapor stream  209  by exchanging heat with a nitrogen vapor stream  203  originated from a column of the distillation system  201 . This arrangement can maximize the flow of the high purity nitrogen  203 . A portion of the condensed nitrogen stream  210  can feed the pressure increasing device  211  and vaporized in exchanger  214  to yield the vaporized high pressure stream  216 . Of course, this liquid nitrogen feeding the device  211  can also be extracted from the cryogenic distillation system  201  if so desired. 
         [0050]      FIG. 2  is also a stylized diagram depicting an illustrative embodiment of an apparatus  200  in accordance with the present invention. The apparatus  200  comprises a cryogenic distillation system  201 , a first pressure reducing device  205 , a second pressure reducing device  233 , a first heat exchanging device  208 , a pressure increasing device  211 , and a second heat exchanging device  214 . 
         [0051]    The cryogenic distillation system  201  may be of any design known to the skilled artisan that is capable of producing a low purity liquid oxygen stream and a high purity nitrogen vapor stream. The pressure reducing device  205  may be of any design known to the skilled artisan that is capable of reducing the pressure of cooled or liquefied high purity oxygen from typical pipeline pressures down to the approximate pressure at which liquid oxygen can be vaporized against condensing air or condensing nitrogen vapor of the high pressure column. The pressure at which the liquid oxygen can be vaporized is higher for the triple column than the corresponding pressure for the double column. Such pressure reducing devices  205  include, but are not limited to, Joule-Thompson valves and turboexpanders. The first heat exchanging device  208  and the second heat exchanging device  214  may be of any design known to the skilled artisan. The pressure increasing device  211  may be of any design known to the skilled artisan that is capable of increasing the working pressure of a cryogenic liquid. 
         [0052]    In one embodiment of the present invention a high purity oxygen vapor stream  204  is provided. This high purity oxygen vapor stream  204  has a pressure that is approximately equal to the typical pressure within an oxygen pipeline. This high purity oxygen vapor stream  204  is introduced into the second heat exchanging device  214 , wherein it will exchange heat with other streams. The result of this heat transfer process within the second heat exchanger device  214 , will be a cold high purity oxygen stream  217 , which may be at least partially condensed or at below its critical temperature if its pressure is above its critical pressure. A portion or all of this cold high purity oxygen stream  217  may be directed toward a second pressure reducing device  233  the outlet pressure of the second pressure reducing device  233  will be approximately equal to the pressure of the low pressure column in the cryogenic distillation system  201 . The cold low pressure pure oxygen stream  240  may then be introduced into column  255  of the cryogenic distillation system  201 . The cold high purity oxygen stream  217  can be directed to the first pressure reduction device  205 , which results in an at least partially condensed high purity oxygen stream  206 . 
         [0053]    The at least partially condensed high purity oxygen stream  206  is then introduced into the first heat exchanging device  208 , wherein it will be combined with a low purity liquid oxygen stream  218  resulting in an intermediate purity oxygen. This intermediate purity oxygen will exchange heat with stream  203 , which will be discussed later. The result of this heat transfer process within the first heat exchange device  208  will be an intermediate purity oxygen vapor stream  209 . This intermediate purity oxygen vapor stream  209  is then introduced into the second heat exchange device  214 . As a result of this heat transfer, the cool intermediate purity oxygen vapor stream  209  will be heated and become a warm intermediate purity low pressure gaseous oxygen stream  215 , which may then be sent to the end user. 
         [0054]    In another embodiment, the at least partially condensed high purity oxygen stream  206  is first combined with a low purity liquid oxygen stream  218 , thereby resulting in an intermediate purity oxygen stream. The intermediate purity oxygen stream is then introduced into the first heat exchanging device  208 , wherein it will exchange heat with stream  203 , which will be discussed later. The result of this heat transfer process within the first heat exchange device  208  will be an intermediate purity oxygen vapor stream  209 . 
         [0055]    A gaseous feed air stream  213  is pretreated using methods and devices well known to those skilled in the art then introduced into the second heat exchange device  214 , wherein it exchanges heat with streams  212 ,  209  and  224 . A portion of stream  213  may be sent via stream  228  to a system of compressor-expander  230  and  231  to provide the necessary refrigeration for the cryogenic unit. As a result of this heat transfer, the gaseous feed air stream  227  is cooled and introduced into the cryogenic distillation system  201 . 
         [0056]    The cooled feed air stream is sent to the bottom of the high pressure column  253  of the cryogenic distillation system  201 , where it separates into an oxygen-enriched bottom fraction  222  and a nitrogen-enriched top fraction  260 . A portion of the oxygen enriched bottom fraction  222  then enters the medium pressure column  254 . A portion of the oxygen enriched bottom fraction  222  may also enter the low pressure column  255 A portion of the nitrogen-enriched is removed as a high purity nitrogen vapor stream  203  at the top of the column  253 . Nitrogen gas at the top of the column  253  is condensed in condenser by heat exchange with the bottom liquid of the medium pressure column  254 . The nitrogen-enriched top fraction  260  feeds the low pressure column as reflux. A nitrogen-enriched liquid is optionally extracted at the top of the column  254  and sent to the column  255  as another feed. If its purity is equivalent with stream  260  it can also serve as reflux. An impure nitrogen stream  224  is removed from low pressure column  255 , warmed in the second heat exchanging device  214 , and removed from the system as waste  225 . From the above description, the cryogenic distillation system  201  produces a low purity liquid oxygen stream  202 , and a high purity nitrogen vapor stream  203 . 
         [0057]    In one embodiment, a portion of gaseous feed air stream  228  is sent to a compression device  230 , which results in a warm compressed feed air stream  234 . The compression device  230  may be of any design known to the skilled artisan that is capable of compressing pre-treated feed air to a cryogenic distillation system. Such compression devices  230  may include, but are not limited to, compressors. The warm compressed feed air stream  234  is then introduced into second heat exchanging device  214 , where it will exchange heat with streams  209 ,  212  and  224 . As a result of this heat transfer, the warm compressed feed air stream  234  is cooled into a cool compressed feed air stream  235 . The cool compressed feed air stream  235  is then sent to an expansion device  231 , which results in a cold feed air stream  229 . The expansion device  231  may be of any design known to the skilled artisan that is capable of expanding compressed feed air to a cryogenic distillation system. Such expansion devices  231  may include, but are not limited to, turboexpanders. This cold feed air stream  229  is then introduced into the low pressure column  255  of the cryogenic distillation system  201 . This cold feed air stream can also be fed to the medium pressure column  254 . 
         [0058]    The low purity liquid oxygen stream  202  is combined with the at least partially condensed high purity oxygen  206  inside the first heat exchanging device  208 , resulting in an intermediate purity oxygen. The intermediate purity oxygen will exchange heat with the warmer high purity nitrogen vapor stream  203  The result of this heat transfer is that the warm high purity nitrogen vapor stream  203  will condense into a high purity liquid nitrogen stream  210 , and the intermediate purity oxygen will at least partially vaporize into an intermediate purity oxygen vapor stream  209 . The high purity liquid nitrogen stream will then be introduced at least in part to pressure increasing device  211 , resulting in a warm high pressure liquid nitrogen stream  212 . It is useful to note the high purity liquid nitrogen stream can also be extracted from the column  253  or any column of the distillation system  201  and sent to the pressure increasing device  211 . This high pressure liquid nitrogen stream  212  is then introduced to second heat exchange device  214 , wherein it exchanges heat with streams  226 ,  204  and  234 , resulting in a vaporized high pressure nitrogen stream  216 , which may then be sent to an end user or introduced into a pipeline. 
         [0059]    The high purity oxygen is normally being provided by a pipeline, but it can also be derived from other sources, such as a pumped vaporized liquid from a tank. 
         [0060]    The high purity liquid nitrogen is needed when the vaporized liquid feed a nitrogen pipeline, it is possible however to use an impure liquid nitrogen stream, then pressurize, vaporize and warm to yield a pressurized gaseous nitrogen stream which could be expanded at a warm temperature or injected into a gas turbine for power recovery (not shown). 
         [0061]      FIG. 3  is a stylized diagram depicting an illustrative embodiment of an apparatus  300  in accordance with the present invention. The apparatus  300  comprises a cryogenic distillation system  301 , a pressure reducing device  305 , a first heat exchanging device  308 , a pressure increasing device  311 , and a second heat exchanging device  314 . 
         [0062]    The cryogenic distillation system  301  may be of any design known to the skilled artisan that is capable of producing a low purity liquid oxygen stream and a high purity nitrogen vapor stream. Such system may include fluid transfer devices, such as liquid pumps to provide liquid products above the pressures of the columns. For illustration purposes, a traditional double column distillation system is shown in  FIG. 3 . The pressure reducing device  305  may be of any design known to the skilled artisan that is capable of reducing the pressure of cooled or liquefied high purity oxygen from typical pipeline pressures down to the approximate pressure at which a cryogenic distillation system produces liquid oxygen. Such pressure reducing devices  305  may include, but are not limited to, Joule-Thompson valves and turboexpanders. The first heat exchanging device  308  and the second heat exchanging device  314  may be of any design known to the skilled artisan. The pressure increasing device  311  may be of any design known to the skilled artisan that is capable of increasing the working pressure of a cryogenic liquid. 
         [0063]    In one embodiment of the present invention a high purity oxygen vapor stream  304  is provided. This high purity oxygen vapor stream  304  has a pressure that is approximately equal to the typical pressure within an oxygen pipeline. This high purity oxygen vapor stream  304  is introduced into the second heat exchanging device  314 , wherein it will exchange heat with streams  312 ,  324  and  309  (hereinafter more fully described). The result of this heat transfer process within the second heat exchanger device  314  will be a cold high purity oxygen stream  317 , which may be at least partially condensed. If the oxygen pressure exceeds its critical pressure, there will be no phase change and stream  317  will be cooled to a temperature colder than its critical temperature. The cold high purity oxygen stream  317  is then directed to the pressure reduction device  305 , which results in an at least partially condensed high purity oxygen stream  306 . 
         [0064]    The at least partially condensed high purity oxygen stream  306  is then combined with a first liquid oxygen stream  318 , which is being output from the cryogenic distillation system  301  via stream  302  and pumped by device  320  to the pressure of device  308 , thereby resulting in an intermediate purity oxygen  307 . The intermediate purity oxygen stream  307  is then introduced into the first heat exchanging device  308 , wherein it will be vaporized against a condensing air stream  310 . The result of this heat transfer process within the first heat exchange device  308  will be an intermediate purity oxygen vapor stream  309 . This intermediate purity oxygen vapor stream  309  is then introduced into the second heat exchange device  314 , wherein it will be warmed by exchanging heat with other streams to yield the warm intermediate purity low pressure gaseous oxygen stream  315 , which may then be sent to the end user. 
         [0065]    In another embodiment, the high purity oxygen stream  341  is first combined with a first liquid oxygen stream  318 , thereby resulting in an intermediate purity oxygen stream. The intermediate purity oxygen stream is then introduced into the first heat exchanging device  308 , wherein it will exchange heat with stream  310  to yield an intermediate purity oxygen vapor stream  309   
         [0066]    A gaseous feed air stream  313  is pretreated using methods and devices well known to those skilled in the art, then introduced into the second heat exchange device  314 , wherein it exchanges heat with streams  309 ,  324  and  312  (hereinafter more fully described). A portion of stream  313  may be sent via stream  328  to a system of compressor-expander  330  and  331  to provide the necessary refrigeration for the cryogenic unit. As a result of this heat transfer, the gaseous feed air stream  326  is cooled and introduced into the cryogenic distillation system  301 . The cryogenic distillation system  301  produces a low purity liquid oxygen stream  302 , and a liquid nitrogen stream  350 . The pressure of the low purity liquid oxygen stream  302  is increased then combined with the at least partially condensed high purity oxygen  306  inside the first heat exchanging device  308 , resulting in an intermediate purity oxygen. The intermediate purity oxygen will exchange heat with the air stream  310  inside the first heat exchanging device  308 . The result of this heat transfer is that the intermediate purity oxygen will at least partially vaporize into an intermediate purity oxygen vapor stream  309 . The liquid nitrogen stream  350  is extracted from the distillation system and then be introduced to pressure increasing device  311 , resulting in a high pressure liquid nitrogen stream  312 . This high pressure liquid nitrogen stream  312  is then introduced to second heat exchange device  314 , wherein it exchanges heat with streams  326  and  304 , resulting in a vaporized high pressure nitrogen stream  316 , which may then be sent to an end user or introduced into a pipeline. 
         [0067]    As illustrated in  FIG. 3 , in one embodiment a portion  340  of the high purity oxygen stream  317  may be sent via stream  340  to the cryogenic distillation system  301 . It is possible to send the totality of the high purity oxygen stream  317  to the column system  301 , in this situation the mixing of high purity and low purity oxygen takes place in the sump of one column of the distillation system  301 . This configuration would result in slightly warmer sump temperature which results in slightly higher system pressure, however, the richer vapor generated at the sump is slightly favorable for the distillation. 
         [0068]      FIG. 4  is a stylized diagram depicting an illustrative embodiment of an apparatus  400  in accordance with the present invention. The apparatus  400  comprises a cryogenic distillation system  401 , a pressure reducing device  405 , a first heat exchanging device  408 , a pressure increasing device  411 , and a second heat exchanging device  414 . 
         [0069]    The cryogenic distillation system  401  may be of any design known to the skilled artisan that is capable of producing a low purity liquid oxygen stream and a high purity nitrogen vapor stream. Such system may include fluid transfer devices, such as liquid pumps to provide liquid products above the pressures of the columns. For illustration purposes, a traditional double column distillation system is shown in  FIG. 4 . The pressure reducing device  405  may be of any design known to the skilled artisan that is capable of reducing the pressure of cooled or liquefied high purity oxygen from typical pipeline pressures down to the approximate pressure at which a cryogenic distillation system produces liquid oxygen. Such pressure reducing devices  405  may include, but are not limited to, Joule-Thompson valves and turboexpanders. The first heat exchanging device  408  and the second heat exchanging device  414  may be of any design known to the skilled artisan. The pressure increasing device  411  may be of any design known to the skilled artisan that is capable of increasing the working pressure of a cryogenic liquid. 
         [0070]    In one embodiment of the present invention a high purity oxygen vapor stream  404  is provided. This high purity oxygen vapor stream  404  has a pressure that is approximately equal to the typical pressure within an oxygen pipeline. This high purity oxygen vapor stream  404  is introduced into the second heat exchanging device  414 , wherein it will exchange heat with streams  412 ,  424  and  409  (hereinafter more fully described). The result of this heat transfer process within the second heat exchanger device  414  will be a cold high purity oxygen stream  417 , which may be at least partially condensed. If the oxygen pressure exceeds its critical pressure, there will be no phase change and stream  417  will be cooled to a temperature colder than its critical temperature. The cold high purity oxygen stream  417  is then directed to the pressure reduction device  405 , which results in an at least partially condensed high purity oxygen stream  440 . 
         [0071]    The at least partially condensed high purity oxygen stream  440  is then introduced into cryogenic distillation system  401 . A first liquid oxygen stream  418  is output from the cryogenic distillation system  401  via stream  402  and pumped by device  420  to the pressure of device  408 . The first liquid oxygen stream  418  is then introduced into the first heat exchanging device  408 , wherein it will be vaporized against a condensing air stream  410 . The result of this heat transfer process within the first heat exchange device  408  will be an oxygen vapor stream  409 . This oxygen vapor stream  409  is then introduced into the second heat exchange device  414 , wherein it will be warmed by exchanging heat with other streams to yield the warm low pressure gaseous oxygen stream  415 , which may then be sent to the end user. 
         [0072]      FIG. 5  is a stylized diagram depicting an illustrative embodiment of an apparatus  500  in accordance with the present invention. The apparatus  500  comprises a cryogenic distillation system  501 , a pressure reducing device  505 , a pressure increasing device  511 , and a heat exchanging device  514 . 
         [0073]    The cryogenic distillation system  501  may be of any design known to the skilled artisan that is capable of producing a low purity liquid oxygen stream and a high purity nitrogen vapor stream. Such system may include fluid transfer devices, such as liquid pumps to provide liquid products above the pressures of the columns. For illustration purposes, a traditional double column distillation system is shown in  FIG. 3 . The pressure reducing device  505  may be of any design known to the skilled artisan that is capable of reducing the pressure of cooled or liquefied high purity oxygen from typical pipeline pressures down to the approximate pressure at which a cryogenic distillation system produces liquid oxygen. Such pressure reducing devices  505  may include, but are not limited to, Joule-Thompson valves and turboexpanders. The heat exchanging device  514  may be of any design known to the skilled artisan. The pressure increasing device  511  may be of any design known to the skilled artisan that is capable of increasing the working pressure of a cryogenic liquid. 
         [0074]    In one embodiment of the present invention a high purity oxygen vapor stream  504  is provided. This high purity oxygen vapor stream  504  has a pressure that is approximately equal to the typical pressure within an oxygen pipeline. This high purity oxygen vapor stream  504  is introduced into the heat exchanging device  514 , wherein it will exchange heat with streams  512 ,  524 ,  517  and  509  (hereinafter more fully described). The result of this heat transfer process within the heat exchanger device  514  will be a cold high purity oxygen stream  517 , which may be at least partially condensed. If the oxygen pressure exceeds its critical pressure, there will be no phase change and stream  517  will be cooled to a temperature colder than its critical temperature. The cold high purity oxygen stream  517  is then directed to the pressure reduction device  505 , which results in an at least partially condensed high purity oxygen stream  506 . 
         [0075]    The at least partially condensed high purity oxygen stream  506  is combined with a first liquid oxygen stream  518 , which is being output from the cryogenic distillation system  501  via stream  502  and pumped by device  520  to a pressure of between about 2 bar and about 2.5 bar (alternately, between about 2.1 bar and about 2.4 bar), thereby resulting in an intermediate purity oxygen  509 . The intermediate purity oxygen stream  509  is then introduced into the heat exchanging device  314 , wherein it will be vaporized by exchanging heat with other streams to yield a warm intermediate purity low pressure gaseous oxygen stream  515 , which may then be sent to the end user. 
         [0076]    A gaseous feed air stream  513  is pretreated using methods and devices well known to those skilled in the art, then introduced into the heat exchange device  514 , wherein it exchanges heat with streams  509 ,  524  and  512  (hereinafter more fully described). A portion of stream  513  may be sent via stream  528  to a system of compressor-expander  530  and  531  to provide the necessary refrigeration for the cryogenic unit. As a result of this heat transfer, the gaseous feed air stream  526  is cooled and introduced into the cryogenic distillation system  501 . The cryogenic distillation system  501  produces a low purity liquid oxygen stream  502 , and a liquid nitrogen stream  550 . The pressure of the low purity liquid oxygen stream  502  is increased then combined with the at least partially condensed high purity oxygen  506  resulting in an intermediate purity oxygen. The liquid nitrogen stream  550  is extracted from the distillation system and then be introduced to pressure increasing device  511 , resulting in a high pressure liquid nitrogen stream  512 . This high pressure liquid nitrogen stream  512  is then introduced to heat exchange device  514 , wherein it exchanges heat with streams  526  and  504 , resulting in a vaporized high pressure nitrogen stream  516 , which may then be sent to an end user or introduced into a pipeline. 
         [0077]    As illustrated in  FIG. 5 , in one embodiment a portion  540  of the high purity oxygen stream  517  may be sent via stream  540  to the cryogenic distillation system  501 . It is possible to send the totality of the high purity oxygen stream  517  to the column system  501 , in this situation the mixing of high purity and low purity oxygen takes place in the sump of one column of the distillation system  501 . This configuration would result in slightly warmer sump temperature which results in slightly higher system pressure, however, the richer vapor generated at the sump is slightly favorable for the distillation.