Abstract:
A cryogenic separation arrangement wherein feed air is processed simultaneously through two regenerator systems and then separated in a reflux condenser, with product and waste from the reflux condenser processed through one and the other respectively of the regenerator systems.

Description:
TECHNICAL FIELD 
     This invention relates generally to air separation for the production of lower purity products wherein a column is not employed. 
     BACKGROUND ART 
     Oxygen-enriched air is widely used in a number of applications such as in furnace operations and chemical oxidation processes. While lower purity oxygen may be produced with a system using distillation columns, such systems are generally not economical for producing oxygen-enriched air. Oxygen-enriched air may be produced with a system employing reflux condensers, and it is desirable to produce oxygen-enriched air with a reflux condenser system with improved efficiency over known such systems. 
     Accordingly, it is an object of this invention to provide a reflux condenser system for producing oxygen-enriched air which operates with improved efficiency compared to conventional reflux condenser systems. 
     Often it is desirable to also produce lower purity nitrogen in addition to oxygen-enriched air in the production facility so as to use the lower purity nitrogen for inerting, drying or blanketing at the same location where the oxygen-enriched air is used. 
     Accordingly, it is a further object of this invention to provide a reflux condenser system for producing oxygen-enriched air which operates with improved efficiency compared to conventional reflux condenser systems and which can also effectively produce lower purity nitrogen. 
     SUMMARY OF THE INVENTION 
     The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is: 
     A method for producing oxygen-enriched air comprising: 
     (A) dividing feed air into a first portion comprising from 25 to 45 percent of the feed air and into a second portion comprising from 55 to 75 percent of the feed air; 
     (B) passing the first portion of the feed air through a first regenerator wherein said first portion is cooled and cleaned of high boiling impurities, and passing the second portion of the feed air through a second regenerator wherein said second portion is cooled and cleaned of high boiling impurities; 
     (C) passing the cooled and cleaned first and second portions of the feed air into and up the condensing side of a reflux condenser having a condensing side and a vaporizing side and condensing a portion of said upwardly flowing feed air to form a first vapor portion and a first liquid portion; 
     (D) passing the first liquid portion into and down the vaporizing side of the reflux condenser and vaporizing a portion of said downwardly flowing first liquid portion to form a second vapor portion and a second liquid portion; and 
     (E) vaporizing said second liquid portion and recovering the resulting vaporized second liquid portion as product oxygen-enriched air. 
     Another aspect of the invention is: 
     Apparatus for producing oxygen-enriched air comprising: 
     (A) at least two first regenerators, at least two second regenerators, means for providing feed air to the first regenerators, and means for providing feed air to the second regenerators; 
     (B) a primary heat exchanger, means for passing feed air from the first regenerators to the primary heat exchanger, and means for passing feed air from the second regenerators to the primary heat exchanger; 
     (C) a reflux condenser having a vaporizing side and a condensing side, means for passing feed air from the primary heat exchanger into the condensing side of the reflux condenser, and means for passing fluid from the condensing side of the reflux condenser into the vaporizing side of the reflux condenser; 
     (D) means for passing fluid from the condensing side of the reflux condenser to the primary heat exchanger and from the primary heat exchanger to the second regenerators; and 
     (E) means for passing fluid from the vaporizing side of the reflux condenser to the primary heat exchanger and from the primary heat exchanger to the first regenerators, and means for recovering product oxygen-enriched air from the first regenerators. 
     As used herein, the term “feed air” means a mixture comprising primarily nitrogen and oxygen, such as ambient air. 
     As used herein, the terms “turboexpansion” and “turboexpander” mean respectively method and apparatus for the flow of high pressure gas through a turbine to reduce the pressure and the temperature of the gas. 
     As used herein, the term “indirect heat exchange” means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other. 
     As used herein, the term “regenerator” means a reversible periodic heat exchanger through which gases flow in an alternating fashion and in which heat in transit is temporarily stored in a packing material of high thermal capacity. 
     As used herein, the term “reflux condenser” means a heat exchange device containing a plurality of vertically oriented finned tubes or passages for the flow of vapor from the bottom to the top of the tubes or passages, collectively termed the condensing side of the reflux condenser, and a plurality of vertically oriented finned tubes or passages for the flow of liquid from the top to the bottom of the tubes or passages, collectively termed the vaporizing side of the reflux condenser. Each condensing tube or passage is in heat exchange relationship with at least one vaporizing tube or passage such that the vapor rising through the condensing tubes or passages is partially condensed by indirect heat exchange with the liquid flowing down the vaporizing tubes or passages which is partially vaporized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of one preferred embodiment of the invention wherein feed air turboexpansion is employed to provide the requisite cryogenic temperatures. 
     FIG. 2 is a schematic representation of another preferred embodiment of the invention wherein waste fluid turboexpansion is employed to provide the requisite cryogenic temperatures. 
    
    
     DETAILED DESCRIPTION 
     The invention will be described in greater detail with reference to the Drawings. Referring now to FIG. 1, feed air  60  is compressed to a pressure generally within the range of from 45 to 70 pounds per square inch absolute (psia) by passage through compressor  30 . Resulting compressed feed air  61  is cooled of the heat of compression by passage through aftercooler  1 , and the resulting feed air  62  is divided into a first portion  64  comprising from 25 to 45 percent, preferably from 30 to 40 percent, of feed air  62 , and into second portion  63  comprising from 55 to 75 percent, preferably from 60 to 70 percent, of feed air  62 . First feed air portion  64  is passed through one of at least two first regenerators which in the embodiment of the invention illustrated in FIG. 1 are regenerators  2  and  3 , and second feed air portion  63  is passed through one of at least two second regenerators which in the embodiment of the invention illustrated in FIG. 1 are regenerators  4  and  5 . For purposes of this discussion of the invention it will be assumed that the feed air is passing through regenerators  2  and  4  while the return streams are passing through regenerators  3  and  5 , with the understanding that these flows are periodically changed so that the feed air passes through regenerators  3  and  5  while the return streams pass through regenerators  2  and  4 . 
     Referring back now to FIG. 1, first feed air portion  64  is passed in piping  65  through valve  66  and piping  67  and  68  to first regenerator  2 . In the aforesaid alternate operating mode, first feed air portion  64  would be passed in piping  73  through valve  74  and through piping  75  and  76  into first regenerator  3 . Within the first regenerator the first feed air portion is cooled and cleaned of high boiling impurities such as carbon dioxide and water vapor which condense and plate out on the internals of the first regenerator. Cooled, cleaned feed air first portion  95  is then passed through piping  96 , valve  108  and piping  107  to form feed air stream  109 . In the alternate operating mode, cooled, cleaned feed air first portion  100  would be passed through piping  104 , valve  105  and piping  106  to form feed air stream  109 . Second feed air portion  63  is passed in piping  21  through valve  81  and piping  82  and  84  to second regenerator  4 . In the alternate operating mode, second feed air portion  63  would be passed in piping  86  through valve  87  and piping  88  and  93  to second regenerator  5 . Within the second regenerator the second feed air portion is cooled and cleaned of high boiling impurities such as carbon dioxide and water vapor which condense and plate out on the internals of the second regenerator. Cooled, cleaned feed air second portion  110  is then passed through piping  111 , valve  118  and piping  119  to form feed air stream  123 . In the alternate operating mode, cooled cleaned feed air second portion  115  would be passed through piping  120 , valve  121  and piping  122  to form feed air stream  123 . 
     The first feed air portion  109  and the second feed air portion  123  are passed, at least in part, through primary heat exchanger  6  and then the entire feed air is passed into reflux condenser  7  which has a condensing side and a vaporizing side illustrated in representational fashion in FIG. 1 as condensing side  22  and vaporizing side  23 . In the preferred embodiment of the invention illustrated in FIG. 1, first feed air portion  109  and second feed air portion  123  are combined to form feed air stream  124 . A portion  125  of feed air stream  124  is passed through primary heat exchanger  6  wherein it is cooled and partially condensed by indirect heat exchange with return streams, emerging from primary heat exchanger  6  as stream  128  which is passed through valve  129  to form stream  130 . Another portion  126  of feed air stream  124  is turboexpanded by passage through turboexpander  31  to generate refrigeration. Resulting refrigeration bearing feed air stream  127  is combined with stream  130  to form stream  131  which comprises the first and second portions of the feed air and which is passed into the condensing side of reflux condenser  7 . 
     The liquid portion of feed air stream  131  passes to the bottom of condensing side  22  while the vapor portion passes up condensing side  22  and is progressively partially condensed by indirect heat exchange with downflowing liquid in the vaporizing side  23  of reflux condenser  7  to form a first vapor portion and a first liquid portion. The first liquid portion passes to the bottom of condensing side  22  where it is combined with the existing liquid and passed in stream  132  through valve  133  and piping  134  into the vaporizing side  23  of reflux condenser  7  wherein it forms the aforesaid downflowing liquid. 
     The first vapor portion is withdrawn from the condensing side  22  of reflux condenser  7  in stream  24  and passed through piping  136 , valve  137 , and piping  138  and  139  to and through primary heat exchanger  6  wherein it is warmed by indirect heat exchange with the cooling feed air. 
     Resulting stream  140  is passed through valve  117  and piping  116  and  115  to second regenerator  5  wherein it serves to pick up plated out low boiling impurities and to cool the second regenerator so as to make it ready to receive feed air in the alternate operating mode. The resulting impurity-containing vapor emerges from second regenerator  5  in piping  93  and is passed in piping  89  through valve  90  and piping  91  and  92  out of the system. In the alternate operating mode, stream  140  would be passed in piping  114  through valve  113  and piping  112  and  110  into second regenerator  4 , emerging as impurity-containing vapor in piping  84  and then passed in piping  83  through valve  85  and piping  94  and  92  out of the system. 
     The embodiment illustrated in FIG. 1 is a preferred embodiment wherein a portion of the first vapor portion is recovered as product lower purity nitrogen. Referring back now to FIG. 1, a portion of the first vapor portion is passed in stream  144  through primary heat exchanger  6  wherein it is warmed by indirect heat exchange with feed air, emerging therefrom as stream  145  which is passed through embedded coils within the second regenerators. In the embodiment of the invention illustrated in FIG. 1 a portion  146  of stream  145  passes through second regenerator  4  emerging therefrom as stream  147  which combines with the remaining portion of stream  145  which passes through second regenerator  5  to form stream  148  which is recovered as product lower purity nitrogen fluid having a nitrogen concentration generally within the range of from 95 to 99.9 mole percent. 
     The liquid passed in stream  134  into vaporizing side  23  of reflux condenser  7  flows downwardly in vaporizing side  23  and is partially vaporized to effect the aforesaid partial condensation in condensing side  22 , resulting in the formation of a second vapor portion and a second liquid portion. The second vapor portion is withdrawn from vaporizing side  23  in stream  135  and, as illustrated in FIG. 1, preferably combined with stream  138  to form stream  139  for further processing as previously described. 
     The second liquid portion is withdrawn from vaporizing side  23  of reflux condenser  7  in stream  141  and passed through primary heat exchanger  6  wherein it is vaporized by indirect heat exchange with feed air. Resulting vapor stream  142  is passed in piping  103  through valve  102  and piping  101  and  100  to first regenerator  3  wherein it picks up previously plated out low boiling impurities, emerging in piping  76 . From there it is passed through piping  77 , valve  78  and piping  79  to piping  72  from where it is recovered as product oxygen-enriched air being a fluid having an oxygen concentration generally within the range of from 35 to 65 mole percent. If desired, some or all of stream  72  may be combined with air to produce oxygen-enriched air having a somewhat lower oxygen concentration than that of the fluid in stream  72 . In the alternate operating mode stream  142  would be passed in piping  99  through valve  98  and piping  97  and  95  into first regenerator  2  wherein it picks up low boiling impurities and from which it emerges in piping  68  and passed in piping  69  through valve  70  and piping  71  to become stream  72  for recovery as product. 
     FIG. 2 illustrates another embodiment of the invention wherein refrigeration for the cryogenic processing of the feed air is generated by turboexpansion of a waste stream. The numerals in FIG. 2 are the same as those in FIG. 1 for the common elements and these common elements will not be described again in detail. Referring now to FIG. 2, all of feed air stream  124  is passed through primary heat exchanger  6  wherein it is cooled and partially condensed by indirect heat exchange with return streams. Resulting feed air stream  128  is passed into the condensing side  22  of reflux condenser  7 . First vapor portion  136  is warmed by passage through primary heat exchanger  6 , emerging therefrom as stream  25  which is turboexpanded by passage through turboexpander  26  to generate refrigeration. Resulting refrigeration bearing turboexpanded stream  27  is combined with stream  135  to form stream  28 . Stream  28  is passed through primary heat exchanger  6  wherein it is warmed thereby transferring refrigeration for the process to the incoming feed air. The resulting first vapor stream  140  is then processed as previously described in connection with the embodiment of the invention illustrated in FIG.  1 . 
     Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims.