Abstract:
A cryogenic nitrogen production plant wherein all the heat transfer steps, and preferably all the heat transfer and separation steps, are carried out in a brazement which receives feed air and from which is recovered product nitrogen.

Description:
TECHNICAL FIELD 
     This invention relates generally to the cryogenic separation of feed air for the production of nitrogen and, more particularly, to an improved plant for the production of same. 
     BACKGROUND ART 
     In the production of nitrogen by the cryogenic rectification of feed air, the feed air, after being pressurized and cleaned of high boiling impurities, undergoes cooling to the proper temperature prior to being introduced into a cryogenic rectification column. Fluids from the column undergo one or more subcooling, condensation, vaporization and heating steps, and the product nitrogen is heated prior to recovery. These separation and heat exchange operations require the use of an extensive piping network as fluids are passed from one piece of equipment to another in order to carry out these operations. Such a network is complicated, expensive to construct, and inefficient to operate. A cryogenic nitrogen production plant which reduces the complexity of heretofore necessary piping networks would be highly desirable. 
     Accordingly, it is an object of this invention to provide a cryogenic nitrogen production plant which for comparable production capability is less complex than heretofore available cryogenic nitrogen production plants. 
     SUMMARY OF THE INVENTION 
     The above and other objects, which will become apparent to one skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is: 
     Apparatus for producing product nitrogen by the cryogenic separation of feed air comprising: 
     (A) a brazement containing a heat exchange section, a condenser, and a separation section; 
     (B) means for passing feed air from outside the brazement into the heat exchange section, and means for passing feed air from the heat exchange section to the separation section; 
     (C) means for passing waste fluid from the separation section to the condenser, means for passing waste fluid from the condenser to the heat exchange section, and means for passing waste fluid from the heat exchange section to outside the brazement; and 
     (D) means for passing product nitrogen from the separation section to the heat exchange section, and means for passing product nitrogen from the heat exchange section to outside the brazement for recovery. 
     Another aspect of the invention is: 
     Apparatus for producing product nitrogen by the cryogenic separation of feed air comprising: 
     (A) a brazement containing a heat exchange section and a condenser, and a separation section outside of the brazement; 
     (B) means for passing feed air from outside the brazement into the heat exchange section, and means for passing feed air from the heat exchange section to the separation section; 
     (C) means for passing waste fluid from the separation section to the condenser, means for passing waste fluid from the condenser to the heat exchange section, and means for passing waste fluid from the heat exchange section to outside the brazement; and 
     (D) means for passing product nitrogen from the separation section to the heat exchange section, and means for passing product nitrogen from the heat exchange section to outside the brazement for recovery. 
     As used herein, the term “feed air” means a mixture comprising primarily nitrogen and oxygen, such as ambient air. 
     As used herein, the term “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 thereby generating refrigeration. 
     As used herein, the term “column” means a distillation of fractionation column or zone, i.e. a contacting column or zone wherein liquid and vapor phases are counter currently contacted to effect separation of a fluid mixture, as for example, by contacting or the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements which may be structured packing and/or random packing elements. For a further discussion of distillation columns, see the Chemical Engineer&#39;s Handbook fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13 , The Continuous Distillation Process.    
     Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phase is adiabatic and can include integral or differential contact between the phases. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin. 
     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 “subcool” means to cool a liquid to be at a temperature lower than the saturation temperature of that liquid for the existing pressure. 
     As used herein, the term “phase separator” means a vessel wherein incoming feed is separated into individual vapor and liquid fractions. Typically, the vessel has sufficient cross-sectional area so that the vapor and liquid are separated by gravity. 
     As used herein, the term “product nitrogen” means a fluid having a nitrogen concentration of at least 90 mole percent. 
     As used herein, the term “waste fluid” means a fluid having a nitrogen concentration which is less than the nitrogen concentration of the product nitrogen produced using the invention. 
     As used herein, the term “brazement” means a structure for carrying out heat and/or mass transfer processes having a complex internal arrangement and being put together by brazing, soldering, welding and/or flange connections. 
     As used herein, the term “condenser” means a device which generates reflux for use in cryogenic rectification. 
     As used herein, the term “reflux condenser” means a structure that enables simultaneous heat and mass transfer while condensing a vapor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of one preferred embodiment of the nitrogen production facility of the invention. 
     FIG. 2 is a schematic representation of another preferred embodiment of the nitrogen production facility of the invention employing a reflux condenser. 
     FIG. 3 is a schematic representation of another preferred embodiment of the nitrogen production facility of the invention wherein the separation section is outside the brazement. 
    
    
     DETAILED DESCRIPTION 
     The invention will be described in detail with reference to the Drawings. Referring now to FIG. 1, brazement  50  contain heat exchange section  1  condenser  3 , and separation section  10 . Feed air  60 , which has been cleaned of high boiling impurities, is cooled to near saturation temperature by indirect heat exchange in heat exchange section  1  with return streams, and the resulting cooled feed is passed in line  61  to separation section  10 . Within separation section  10  the feed air is separated by cryogenic rectification into product nitrogen and waste fluid. Waste fluid is passed in line  62  from separation section  10  through valve  63  and as stream  64  to condenser  3  wherein it is vaporized thereby serving to condense a portion of the product nitrogen rising from the separation section. The condensed product nitrogen falls back from condenser  3  into the separation section to serve as reflux for the cryogenic rectification. 
     A portion of the product nitrogen Vapor rising from the separation section is passed from separation section  10  in line  69  to heat exchange section  1  wherein it is warmed and from which it is passed out of brazement  50  in line  70  for recovery as product nitrogen. Waste fluid from condenser  3  is passed in line  65  to heat exchange section  1  wherein it is warmed to an intermediate temperature. It is then passed as stream  66  to turboexpander  30  wherein it is turboexpanded to generate refrigeration. Resulting refrigeration bearing stream  67  is passed back to heat exchange section  1  wherein it is warmed. The warmed waste fluid stream is then passed out of brazement  50  in line  68 . 
     In the practice of this invention, all of the heat transfer steps associated with the system, including heating, cooling, condensation, vaporization and subcooling steps, take place within the brazement. The only heat transfer steps that take place outside the brazement are extraprocess heat transfer steps such as cooling of compressor discharge to remove heat of compression. 
     FIG. 2 illustrates another embodiment of the invention wherein the condenser includes a reflux condenser. Referring now to FIG. 2, brazement  7  contain heat exchange section  31 , condenser  32 , and separation section  4 . Feed air  54  is compressed to a pressure generally within the range of from 50 to 250 pounds per square inch absolute (psia) by passage through compressor  55 . Compressed feed air  56  is cooled of the heat of compression by passage through cooler  57  and resulting feed air  58  is passed to purifier  59  wherein it is cleaned of high boiling impurities such as water vapor, carbon dioxide and hydrocarbons. 
     Cleaned, compressed feed air  51  is passed into brazement  7  and is cooled in heat exchange section  31  by indirect heat exchange with return streams. The cooled feed air is then passed in line  21  to separation section  4  wherein it is separated by cryogenic rectification into product nitrogen and into waste fluid. Waste fluid is passed in line  22  from separation section  4  to heat exchange section  31  wherein it is subcooled and from there is passed in line  23  to valve  24  and from there in line  25  to phase separator  5 . Liquid waste fluid is passed from phase separator  5  in line  34  to condenser  32  wherein it is at least partially vaporized by indirect heat exchange with product nitrogen which is passing through reflux condenser portion  33  of condenser  32 . The resulting waste fluid from condenser  32  is passed back into phase separator  5  using line  35 . 
     Product nitrogen vapor passes out from separation section  4  in line  26  in reflux condenser  33  and is partially condensed as it rises. The liquid portion of the resulting product nitrogen is passed back down reflux condenser  33  and returned in line  28  to separation section  4  wherein it serves as reflux for the cryogenic rectification. The remaining vapor portion of the product nitrogen is passed in line  27  to heat exchange section  31  wherein it is warmed. It is then removed from brazement  7  in line  29  for recovery as product nitrogen. 
     Waste fluid vapor is passed out of phase separator  5  in stream  36  and divided into portion  37  and portion  43 . Portion  37  is further divided into part  38  which is warmed by partial traverse of heat exchange section  31  to form stream  40 , and into part  39  which bypasses heat exchange section  31  and unites with stream  40  to form combined stream  41 . The partial traverse of the heat exchange section may include countercurrent flow, cocurrent flow, and/or crossflow. Stream  41  is turboexpanded by passage through turboexpander  6  to form refrigeration bearing stream  42  which is then combined with portion  43  to form waste fluid stream  44 . Stream  44  is then warmed by passage through heat exchange section  31  and is withdrawn from brazement  7  as waste fluid stream  45 . 
     FIG. 3 illustrates another embodiment of the invention wherein the separation section is outside of the brazement. The numerals in FIG. 3 are the same as those of FIG. 2 for the common elements, and these common elements will not be described again in detail. 
     Referring now to FIG. 3, brazement  17  contains heat exchange section  31  and condenser  32 . The separation section, in the form of column  14 , is outside brazement  17 . The feed air from heat exchange section  31  is passed in stream  21  to column  14  and is separated therein by cryogenic rectification into product nitrogen, which is then processed as previously described, and into waste fluid. 
     Waste fluid in stream  25  is passed to module  19  of condenser  32  wherein it is partially vaporized with a portion passed in stream  81  to phase separator  15  and a portion passed in stream  85  to phase separator  11 . Vapor from phase separator  15  is passed in stream  12  to compressor  18  wherein it is compressed to a pressure generally within the range of from 60 to 250 psia, and resulting pressurized waste fluid is passed in stream  77  from compressor  18  to column  14  to serve as vapor upflow for the cryogenic rectification. Liquid from phase separator  15  is passed in stream  86  through valve  100  and as stream  101  into phase separator  11 . 
     Liquid from phase separator  11  is passed in line  102  to condenser  32  wherein it is at least partially vaporized and from there passed in stream  103  into phase separator  11 . As shown in FIG. 3, stream  103  may be combined with aforesaid stream  85  to form stream,  105  for passage into phase separator  11 . Waste fluid vapor from phase separator  11  is passed in line  95  to heat exchange section  31  wherein it is warmed to an intermediate temperature and then passed in stream  86  to turboexpander  16  wherein it is turboexpanded. In the embodiment of the invention illustrated in FIG. 3, turboexpander  16  is coupled to compressor  18  thus serving to drive compressor  18 . Refrigeration bearing waste fluid stream  88  is passed from turboexpander  16  to heat exchange section  31  wherein it is warmed. The warmed waste fluid is then passed out of brazement  17  it in line  96 . 
     Although the invention has been discussed 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.