Cryogenic air separation system with integrated mass and heat transfer

Information

  • Patent Grant
  • 6295836
  • Patent Number
    6,295,836
  • Date Filed
    Friday, April 14, 2000
    24 years ago
  • Date Issued
    Tuesday, October 2, 2001
    23 years ago
Abstract
A cryogenic air separation system comprising an integrated core and typically including a double column wherein incoming feed air is cooled in the core which also processes a stream from the double column. A separating section of the core processes a stream from the double column to form product.
Description




FIELD OF THE INVENTION




This invention generally relates to cryogenic air separation and, more particularly, to the integration of various levels of heat-transfer and mass-transfer in order to enhance thermodynamic efficiency and to reduce capital costs.




BACKGROUND OF THE INVENTION




Cryogenic air separation systems are known in the art for separating gas mixtures into heavy components and light components, typically oxygen and nitrogen, respectively. Generally, the separation process takes place in plants that cool incoming mixed gas streams through heat exchange with other streams (either directly or indirectly) before separating the different components of the mixed gas through mass transfer methods such as distillation and/or reflux condensation (dephlegmation). Once separated to achieve desired purities, the different component streams are warmed back to ambient temperature. Typically, the different warming, cooling, and separating steps take place in separate pieces of equipment, which, along with the installation and piping, adds to the manufacturing costs for the plant.




Various air separation systems have been introduced that combine some of the separate heat transfer components in order to provide an integrated device that may perform a variety of functions. In particular, systems have been proposed that partially combine different heat exchangers for warming or cooling fluid streams and separation devices for separating out heavy and light components in the streams into a single heat exchange core in order to reduce the number of pieces of equipment needed in an air separation plant. This may reduce the overall cost of the plant.




SUMMARY OF THE INVENTION




The present invention is directed to an air separation system with a unique integration design that provides a single brazed core that can combine separation networks with a host of heat exchange functions.




Increasing the total cross section of a heat transfer core provides a greater opportunity for heat transfer between streams, thus increasing efficiency. This improvement may come at an attractive cost per unit area of heat transfer.




The present invention also reduces the capital costs associated with air separation systems (particularly the cold boxes of cryogenic air separation systems) and increases overall thermodynamic efficiency by utilizing designs that optimally combine mass-transfer functions with heat-transfer functions in a single core which results in the reduction or elimination of a significant amount of interconnecting piping and independent supporting structures and cold box volume thereby reducing piping and installation costs. Typically, the integrated core is used to (i) cool the process feed air down to a cryogenic temperature, (ii) boil the heavy component product (typically liquid oxygen), and (iii) superheat/subcool various process streams. Preferably, the integrated core is a brazed plate-fin core made of aluminum. The integrated core may include a plurality of passages arranged so as to effectively combine the various levels of heat-transfer, as well as different levels and types of mass-transfer (such as rectification and stripping).




In a preferred design of the present invention, an integrated core is provided in flow communication with a double column separation apparatus having a higher pressure column (generally termed the lower column) and a lower pressure column (generally termed the upper column). The double column separation apparatus may be of any conventional design that provides separation of heavy and light components from various vapor streams.




In a preferred design, the integrated core includes a first set of intake passages (although, it should be recognized that only one passage for each stream in the system is required to achieve the benefits of the present invention) in which an incoming feed air stream is cooled and then directed into the double column separation apparatus (typically the lower column). The cooling is preferably accomplished by positioning the first set of intake passages in a heat exchange relationship with at least one other passage in the integrated core. In variations of this embodiment, the first set of intake passages may include a section for mass transfer, in which a condensate in the passage serves as reflux to rectify the feed air stream. In this case, the first intake passages will form a condensate stream that may be directed into the upper column.




A first set of cooling passages cools a first bottom stream from the separation apparatus (typically the lower column) and feeds the cooled, first bottom stream back into the separation apparatus (typically the upper column). The first set of cooling passages may be in a heat exchange relationship with at least one other passage (or set of passages) in the integrated core.




A first set of warming passages warms a first overhead stream from the separation apparatus (preferably the upper column) and discharges the warmed first overhead stream from the integrated core. The first set of warming passages may be in a heat exchange relationship with at least one other set of passages in the integrated core.




A separating section (preferably a stripping column) in the integrated heat exchanger core separates a second bottom stream from the separation apparatus (preferably from the upper column external to the integrated heat exchanger core) to form an oxygen enriched stream and a nitrogen enriched stream. The nitrogen enriched stream may be directed back into the separation apparatus (preferably into the upper column). Preferably, the oxygen stream is separated into a vapor phase stream and a liquid phase stream by a phase separator. The vapor phase stream typically is directed back into the separating section. In preferred embodiments, the separating section is integrated within the integrated core and the separating apparatus is external to the integrated core. In addition, a pump may be provided to pump the liquid phase through the integrated core.




A set of vaporization passages vaporizes the liquid phase stream from the phase separator and discharges the vaporized liquid phase stream from the integrated core. The vaporization passages may be in heat exchange relationships with at least one other set of passages of the integrated core.




The integrated core may also include a second set of cooling passages that cools a condensed stream from the upper column and directs the cooled, condensed stream back into the separation apparatus (typically into the upper column). As with the first set of cooling passages, the second set is preferably in a heat exchange relationship with at least one other set of passages in the integrated core.




The integrated core may also include a second set of warming passages that warms a second overhead stream from the stripping apparatus (preferably from the lower pressure column) and discharges the warmed second overhead stream from the integrated core. The second set of warming passages may also be in a heat exchange relationship with at least one other set of passages in the integrated core.




A fourth set of warming passages may be provided to warm the oxygen enriched stream from the separating section and to direct the oxygen enriched stream into the phase separator. These passages may also be in heat exchange relationships with any number of other passages in the integrated core.




The integrated core may also include a second set of intake passages that cools a second incoming feed air stream and directs the cooled, second incoming feed air stream into the separation apparatus (preferably into the lower column). The second set of intake passages may be in a heat exchange relationship with at least one other set of passages in the integrated core.




The integrated core may also include a third set of intake passages that cools a third incoming feed air stream and directs the cooled, third incoming feed air stream into the separation apparatus (preferably into the lower pressure column). The third intake passages may be in heat exchange relationships with any number of other passages in the integrated core, but preferably exchange heat with the first set of warming passages and/or the second set of warming passages. In alternative embodiments, the third set of intake passages may cool a refrigerated air stream received from a refrigeration unit. In such an embodiment, the integrated core may also include a fourth set of warming passages to warm the refrigerated air stream cooled in the third set of intake passages against other passages in the integrated core and to discharge the refrigerated air stream from the integrated core back into the refrigerated unit.




Although the sets of passages may be designed so as to have various heat exchange interactions with other sets of passages within the integrated core, it is preferred that the first set of intake passages and the second set of intake passages share heat exchange relationships with any of the first set of warming passages, the second set of warming passages, the fourth set of warming passages, and the set of vaporization passages. Additionally, the first set of cooling passages and the second set of cooling passages may share heat exchange relationships with, at least, any of the first, second, and fourth sets of warming passages.




Generally, the integrated core is divided into a warm end, including openings in the integrated core for flow into and out of the intake passages and the warming passages, and a cold end, including the separation section. Typically, the warm end is the top end of the integrated core and the cold end is the bottom end; however, the integrated core may be designed so that the bottom end is the warm end (including the openings for the intake and warming passages) and the top end is the cold end (including the separation section).




In another embodiment of the present invention, the integrated core may stand alone, without using a double column separation system, in order to produce light component products. In this embodiment, the air separation system may include a rectification section (or other separation section) that rectifies an incoming feed air stream to form an overhead stream enriched in nitrogen, and a bottom stream enriched in oxygen. The rectification section may utilize any conventional design for rectifying mixed fluid streams. In more preferred embodiments, the rectification section is integrated within the integrated core; however, an air separation system may be designed such that the rectification section is outside of, but in flow communication with, the integrated core.




The integrated core of this embodiment includes a first set of cooling passages that cools the incoming feed air stream and feeds the cooled, incoming feed air stream into the rectification section. A second set of cooling passages cools the bottom stream from the rectification section. A first set of warming passages warms a first portion of the overhead stream and directs the warmed portion of the overhead stream back into the rectification section. The first set of warming passages may be in a heat exchange relationship with at least one of the sets of cooling passages. A second set of warming passages warms a second portion of the overhead stream and discharges the warmed second portion of the overhead stream from the integrated core. The second warming passages may also be in heat exchange relationships with any of the cooling passages. A set of vaporization passages vaporizes the cooled bottom stream from the second cooling passages and discharges the vaporized bottom stream from the integrated core. The vaporization passages may be in heat exchange relationships with any of the cooling passages. In preferred embodiments, the cooled bottom stream is expanded by a turboexpander.




In yet another embodiment of the present invention, an air separation system may include a double column separation apparatus, a rectification column (or other separation column), and an integrated core in which is included the lower column from the double column separation apparatus.




The integrated core of this embodiment includes a first set of intake passages that cools a first incoming feed air stream. The first incoming air stream may be directed into the separation apparatus of the lower column, depending on the design particulars. The integrated core may also include a second set of intake passages that cools a second incoming feed air stream and feeds the cooled, second incoming feed air stream into the double column separation apparatus (typically into the upper column). The lower column of the separating apparatus produces a first overhead stream enriched in nitrogen and a first bottom stream enriched in oxygen.




The integrated core may also include a first set of cooling passages that cools the first bottom stream from the lower column and feeds it back into the separation apparatus, typically into the upper column.




The upper column may separate streams it receives from the separation apparatus and/or the integrated core to produce a second bottom stream, which may be enriched in oxygen, and a second overhead stream enriched in nitrogen.




Preferably, a second set of cooling passages are provided in the integrated core to cool the second bottom stream from a condenser in the upper column and to feed the second bottom stream back into the double column separation apparatus (typically into the upper column). The second cooling passages may be in heat exchange relationships with any passages warming streams in the integrated core.




A first set of warming passages warms the first overhead stream from the lower column and discharges at least a portion of the warmed first overhead stream from the integrated core. The remainder of the warmed first overhead stream may be condensed by a condenser in the upper column. The first set of warming passages may be in heat exchange relationships with any passage for cooling a stream in the integrated core.




The integrated core may also include a second set of warming passages that warms a second overhead stream from the lower pressure column. The second warming passages may also be in heat exchange relationships with any of the cooling passages of the integrated core.




A third set of warming passages may be provided to warm a third bottom stream from the separating column (either upper column or integrated heat exchanger column) and to discharge that stream from the integrated core. Typically, the third warming passages are in heat exchange relationships with any of the cooling passages.




In another embodiment of the present invention, an air separation system may include two integrated cores in flow communication with each other. Preferably, the air separation system incorporates a double column arrangement, with the lower and upper pressure columns being integrated in the different integrated cores.




The first integrated core may include a first set of intake passages that cools a first feed air stream, although additional intake passages may be provided to receive other feed air streams as necessary. When a second set of intake passages is incorporated into the first integrated core, those passages may cool a second feed air stream. Typically, the second set of intake passages feeds its air stream into a first separation section (discussed below). In more preferred embodiments, a portion of the second feed air stream from the second intake passages may be expanded and fed into the first set of intake passages.




A first separation section may separate the cooled first feed air stream into a first overhead stream enriched in nitrogen and a first bottom stream enriched in oxygen. The first separation section is preferably the lower column of the double column separation system. A first set of cooling passages cools the first bottom stream from the first separation section.




A set of vaporization passages vaporizes a liquid phase stream from the second integrated core (discussed below) and discharges the vaporized liquid phase stream from the integrated core. The vaporization passages may be in heat exchange relationships with any of the intake passages and the first cooling passages.




A first set of warming passages warms a second overhead stream (preferably from the upper column in the second integrated core) and discharges the warmed second overhead stream from the first integrated core. The first warming passages may be in a heat exchange relationship with any of the intake passages and the first cooling passages.




The second integrated core may include a second set of warming passages that warms the first overhead stream from the first separation section and feeds the warmed first overhead stream back into the first separation section (i.e., reflux for the lower column). A second separation section (the upper column) receives at least one cooled stream and separates that stream into the second overhead stream enriched in nitrogen and a second bottom stream enriched in oxygen. A third set of warming passages warms the second overhead stream and feeds the warmed second overhead stream into the first warming passages. The third warming passages may be in heat exchange relationships with any cooling (including intake) passages of the integrated core.




A fourth set of warming passages may be provided to warm (and partially vaporize) the second bottom stream. The warmed second bottom stream may be separated, using a phase separator, into a vapor phase stream and the liquid phase stream. The liquid phase stream may be fed into the vaporization passages and the vapor phase stream may be fed back into the second separation section. Preferably, the liquid phase is pumped into the vaporization passages. The fourth warming passages may be in heat exchange relationships with any of cooling passages (including intake passages) of the integrated core.




The second integrated core may also include a fifth set of warming passages that warms a third overhead stream from the second separation section and discharges the warmed third overhead stream from the second integrated core. A sixth set of warming passages may be provided in the first integrated core to receive and to discharge from the first integrated core the third overhead stream from the fifth warming passages, while warming the stream against at least one other stream in the first integrated core.




In some embodiments, the second integrated core may also include a second set of cooling passages for cooling the first bottom stream from the first cooling passages. In addition, a third set of cooling passages may cool the second feed air stream from the second intake passages. A fourth set of cooling passages may receive and cool a portion of the warmed first overhead stream from the second warming passages before that portion is fed back into the first separation section. The second separation section (i.e., upper column) may separate any of the streams from the second, third, and fourth cooling passages. In addition, the second, third and fourth sets of cooling passages may provide cooling by being in heat exchange relationships with any of the warming passages in the second integrated core, particularly the second warming passages.




However, the air separation system may not necessarily include the second cooling passages, third cooling passages, or fourth cooling passages, at least as described above, if an additional separation section is incorporated into the second integrated core. For instance, the air separation system of this embodiment (having two integrated cores) may also incorporate an argon separation section, which preferably may be integrated into the second integrated core. When an argon rich stream is to be produced, the second separation section may be modified to produce a first argon-rich stream.




The argon separation section further separates the first argon-rich stream into a second argon-rich stream and an argon-depleted stream. At least a portion of the second argon-rich stream is discharged from the second integrated core as a first argon product stream.




A reboiler/condenser section may be provided in the second integrated core and includes a condensing passage in a heat exchange relationship with a boiling passage. A portion of the cooled first bottom stream may be condensed in the condensing passage. A portion of the second argon-rich stream typically is boiled in the boiling passage. At least a portion of the boiled second argon-rich stream may be fed back into the argon separation section for reflux. The remainder of the boiled second argon-rich stream may be discharged from the second integrated core as a second product argon stream.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1A

shows a first embodiment of an air separation system of the present invention that includes an integrated core with a side stripping column.





FIG. 1B

shows an air separation system similar to the one shown in

FIG. 1A

, but with a reverse orientation.





FIG. 1C

shows an air separation system similar to the one shown in

FIG. 1A

, but with the side stripping column positioned outside of the integrated core.





FIG. 1D

shows an air separation system similar to the one shown in

FIG. 1A

, but with a refrigeration unit.





FIG. 1E

shows an air separation system similar to the one shown in

FIG. 1D

, but without a second compensating incoming air stream.





FIG. 2A

shows another embodiment of an air separation system of the present invention that includes an integrated core designed for use as an air enriching/inerting grade light component plant.





FIG. 2B

shows an air separation system similar to the one shown in

FIG. 2B

, but with the separation section positioned outside of the integrated core.





FIG. 3A

shows another embodiment of the present invention in which the integrated core of the air separation system incorporates part of a double column stripping apparatus.





FIG. 3B

shows an air separation apparatus similar to the one shown in

FIG. 3A

, but with the incoming feed air being directed into the stripping column in the integrated core.





FIG. 4

shows another embodiment of an air separation system of the present invention that utilizes two integrated cores.





FIG. 5

shows an air separation system similar to the one shown in

FIG. 4

, but with an argon separation section incorporated into the second integrated core.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS





FIG. 1A

depicts a preferred embodiment of the present invention, and generally shows a cryogenic air separation system utilizing an integrated heat exchange core with a double column separation apparatus for producing low purity oxygen. The system is arranged with the cold end up. An auxiliary reboiled stripping section or side stripper


50


, used in an air separation process to produce a low purity oxygen product (preferably from about 50 to about 95% purity), is integrated within the heat exchange core. The double-column separation apparatus may be of any conventional type and, in this case, includes a lower column


20


and an upper column


40


, both of which are in flow communication with each other and integrated core


1


.




To facilitate heat transfer among various fluid streams in the system, the heat transfer section of integrated core


1


may utilize a plate-fin design, wherein passages throughout integrated core


1


have finned passages that allow fluid streams to flow through integrated core


1


in heat exchange relationships with fluid streams in other passages. It is preferred that the plate-fin system be constructed of aluminum to facilitate heat transfer and to keep costs low. Preferably, all of the heat exchange sections of integrated core


1


are incorporated in a single brazed aluminum core.




Integrated core


1


receives low pressure air stream


101


, high pressure boosted air stream


103


, and intermediate pressure turbine air stream


109


through passages in integrated core


1


, which are in heat exchange relationships with passages of integrated core


1


containing exiting process streams, including waste nitrogen stream


143


, gaseous oxygen stream


172


, and nitrogen product stream


124


in the section


2


(the warm end) of integrated core


1


. Through the heat exchange relationships, each of air streams


101


,


103


, and


109


is cooled as they travel through integrated core


1


.




Intermediate pressure air stream


109


, which typically ranges from about 125 to about 200 psia and comprises about 7 to about 15% of the total feed air flow, exits integrated core


1


as stream


110


after reaching a temperature that is preferably in the range of about 140 to about 160 K; however, the temperature may depend on the amount of refrigeration required in a particular design. Preferably, cooled air stream


110


is expanded in expander


10


to form stream


119


, which generates the refrigeration for the plant to compensate for various sources of refrigeration loss and heat leakage into the process. Stream


119


may also be used for additional refrigeration required to provide any liquid products (not shown). In this case, expanded turbine air stream


119


(typically in the range of about 19 to about 22 psia) is fed into upper column


40


to be separated.




Air stream


103


is further cooled along its passage(s) in integrated core


1


. In intermediate heat transfer section


3


of integrated core


1


, boosted air stream


103


, which is typically in the range from about 100 to about 450 psia and comprising about 25 to about 35% of the total feed air flow, may be condensed due to a heat exchange relationship with the passage(s) containing boiling liquid oxygen product stream


171


. In section


3


, stream


103


is preferably in a crossflow orientation with boiling liquid oxygen stream


171


. The resulting subcooled liquid boosted air stream


104


may exit integrated core


1


at a temperature typically in the range of about 95 to about 115 K.




In this embodiment, liquid air stream


104


is split into streams


105


and


107


and throttled in valves


10


A and


10


B, respectively. The resulting throttled liquid air streams


106


and


108


are fed into upper column


40


and lower column


20


, respectively. Stream


106


may range from 0 to 100% of the total subcooled liquid boosted air stream


104


.




Lower pressure air stream


101


(preferably in the range of about 45 to about 60 psia, and about 94 to about 96 K) contains the balance of the total feed air flow. Lower pressure air stream


101


is partially condensed against boiling liquid oxygen stream


152


exiting from the bottom of the separation section


50


in heat transfer section


4


of integrated core


1


. Lower pressure air stream


101


may be in a crossflow orientation with the boiling bottom liquid oxygen stream


153


. Resulting partially condensed air stream


101


exits integrated core


1


(at a temperature in the range of about 90 to about 105° K) as stream


102


, with its vapor fraction typically in the range from about 0.7 to about 0.8%. Stream


102


may be fed into higher pressure rectification column


20


.




The higher pressure column


20


separates partially condensed feed air stream


102


and throttled subcooled liquid feed air stream


108


into an almost-pure nitrogen vapor overhead stream


121


, and oxygen-rich bottom liquid stream


125


. A small fraction of overhead stream


121


, typically up to about 10%, may be taken as nitrogen product stream


123


. Product stream


123


may enter the cold end of integrated core


1


where it is then warmed to ambient temperature against one or more of incoming streams


101


,


103


and


109


, before exiting integrated core


1


as stream


124


.




Although an almost pure nitrogen vapor (about 90 to about 99.6% pure) product exits the top of lower column


20


, the nitrogen product may be withdrawn from elsewhere in the process. Although not depicted, the nitrogen product may also be drawn from upper column


40


. In that case, the high purity nitrogen product stream could be withdrawn from the top of upper column


40


, and the waste nitrogen could be withdrawn from a point somewhat lower in upper column


40


. Both of the nitrogen streams could then pass through integrated core


1


in separate passages.




The balance of overhead stream


121


from lower column


20


, the almost pure nitrogen, may be fed into the upper column


40


as stream


122


, where it is condensed in condenser/reboiler (main condenser)


30


against the bottom oxygen-rich liquid of upper column


40


. The condensed stream exits main condenser


30


as condensed overhead stream


131


. Stream


131


may be split into streams


132


and


133


. Stream


132


(typically in the range of about 40 to about 55% of the total condensed overhead stream


131


) is returned to lower column


20


for reflux.




Stream


133


, the remaining fraction of stream


132


, and kettle liquid stream


125


(typically about 35 mole percent oxygen), which exits the bottom of lower column


20


, are indirectly cooled (to a temperature of about 80 to about 95° K) against exiting gaseous streams


142


and


123


in heat transfer section


5


along the length of the integrated stripping separation section


50


of integrated core


1


. The corresponding subcooled streams


134


(corresponding to stream


133


) and


126


(corresponding to stream


125


) may be throttled in valves


10


C and


10


D, respectively, to form throttled liquid streams


135


and


127


, respectively. Streams


135


and


127


may be fed into upper column


40


to be further fractionated. Preferably, stream


135


is fed into the top of upper column


40


.




Upper column


40


separates streams


119


,


127


and


135


, into gaseous nitrogen stream


142


and bottom liquid oxygen stream


141


. Boilup vapor used in lower pressure column


40


may be provided by indirectly boiling the liquid oxygen at the bottom of upper column


40


against condensing overhead stream


122


of lower column


20


, as mentioned above with respect to the main condenser


30


.




Product liquid oxygen stream


141


from upper column


40


may be fed into section


50


of integrated core


1


. Section


50


preferably serves the function of a reboiled stripping separation column. Accordingly, a liquid fraction is further concentrated in oxygen as it flows down the length of stripping section


50


through crosscurrent contact with a stripping vapor. Vapor stream


151


exits the top of stripping section


50


and is fed into the bottom of upper column


40


. In upper column


40


, vapor stream


151


combines with the vapor generated by main condenser


30


and is further separated as it ascends the column.




The bottom liquid stream from stripping section


50


exits as stream


152


and then may be partially vaporized against low pressure feed air stream


102


in section


4


of integrated core


1


. The resulting two-phase (partially vaporized) bottom liquid oxygen stream


153


may exit integrated core


1


to be fed into phase separator


60


. Vapor stream


161


from phase separator


60


, typically comprising about 40 to about 60% of stream


153


, is returned to stripping section


50


to serve as the stripping vapor. The liquid fraction from phase separator


60


is pressurized using pump


70


to the desired pressure. The resulting higher pressure liquid oxygen stream


171


enters integrated core


1


at section


3


. Therein, it is vaporized primarily against the boosted air stream


103


and, along with the other exiting streams


127


and


143


, is warmed to ambient temperature against one or more of the other air streams


101


and


109


. Stream


171


exits integrated core


1


as product oxygen stream


172


.




It should be noted that phase separator


60


may be eliminated if proper process modifications are made to insure that safety issues are addressed related to boiling oxygen-rich streams to dryness in a plate-fin heat exchanger. If separator


60


is eliminated, liquid stream


152


may be taken from the bottom of stripping section


50


as the product stream, and the rest of the bottom liquid of stripping section


50


may be completely vaporized in heat transfer section


4


of integrated core


1


to provide stripping vapor to stripping section


50


(not shown). Although not depicted, liquid products can also be withdrawn from the integrated core with minimal changes in the process and design.





FIG. 1B

depicts an alternative arrangement of the integrated core depicted in

FIG. 1A

in which the directional orientation of integrated core


1


is reversed. The cold end, containing stripping section


50


, is positioned at the bottom of integrated core


1


, and the warm end is positioned at the top. In this configuration, air streams entering sections


2


and


3


transfer and mass transfer sections of integrated core


1


may be spatially arranged in this configuration to achieve the best overall thermodynamic characteristics with minimal labor and hardware. The remainder of the system is similar to that described with respect to the system of

FIG. 1A

, and will not be repeated herein.





FIG. 1C

depicts another slight modification to the integrated core depicted in FIG.


1


A. In this embodiment, stripping section


50


is positioned outside of integrated core


1


so as to be segregated from the heat transfer sections.




As depicted, integrated core


1


is vertically oriented, in terms of stream flow directions, with the cold end positioned above the warm end. However, the warm end may be situated above the cold end, as described with respect to the system in FIG.


1


B. In addition, with proper accommodations in the design, the integrated core


1


may be orientated with horizontal stream flow directions. The remainder of the heat transfer network of integrated core


1


is similar to that discussed with respect to FIG.


1


A.





FIG. 1D

depicts another slight modification to the air separation system depicted in FIG.


1


A. Specifically, in this embodiment, integrated core


1


accommodates mixed gas refrigeration system MGR10 for the plant refrigeration, instead of expanding feed air stream


109


in turbine


10


, as described with respect to the system in FIG.


1


A. Accordingly, turbine air streams


109


,


110


, and


119


are absent in this system.




Preferably, stream MG109, the working fluid of mixed gas refrigeration system MGR10 , which includes a mixture of gases suitably selected for the particular application, enters the warm end of integrated core


1


. Refrigerant stream MG109 is condensed and subcooled in section


2


of integrated core


1


against exiting process streams


123


,


142


, and


171


, as well as exiting throttled refrigerant stream MG119, discussed below. The resulting subcooled liquid refrigerant stream MG110 may be expanded in Joule-Thompson valve JT10, preferably after reaching a temperature in the range of about 80 to about 120° K. Resulting lower pressure refrigerant stream MG119 may be returned to integrated core


1


at a point along the length of the core which is colder than where stream MG110 exits integrated core


1


. The remainder of the air separation system is similar to the system described with respect to FIG.


1


A.





FIG. 1E

depicts yet another modification to the air separation system depicted in FIG.


1


A. This system incorporates a mixed gas refrigeration system similar to that described above with respect to

FIG. 1D

; however, refrigerant fluid stream MG109 also may be used to boil the pressurized liquid oxygen product (stream


171


). Accordingly, boosted feed air stream


103


and related streams used in the system in

FIG. 1A

are absent in this embodiment. Aside from the absence of boosted air streams


103


-


108


and the additional function of boiling stream


171


, the remainder of the system is similar to the system depicted in FIG.


1


D. It should be noted, however, that the exact flows and process conditions of this embodiment may differ from the other embodiments. In addition, the MGR system used to replace turbine


10


and stream


103


may include more than one refrigerant loop.





FIG. 2A

shows the application of the integrated core concept to an air separation system used to produce a nitrogen product and a very low purity oxygen product. Separation section


20


(preferably a rectification column) is used in the separation system and is incorporated in integrated core


1


. This system uses the expansion of the low purity oxygen to provide the required plant refrigeration; however, other process streams such as the nitrogen product stream, may be expanded for refrigeration purposes, if deemed optimal for the particular plant specifications.




As shown, pre-purified feed air stream


101


, typically having a pressure in the range from about 110 to about 150 psia, is cooled to a cryogenic temperature (preferably in the range from about 80 to about 120° K) against passage(s) containing exiting nitrogen product stream


123


/


124


and very low purity oxygen-rich stream


171


/


172


in section


2


of integrated core


1


. Separation section


20


of integrated core


1


separates cooled feed air stream


102


into an almost-pure nitrogen liquid overhead stream


121


, and oxygen-rich bottom stream


125


. A fraction of overhead stream


121


(typically about 40 to about 60%) may be taken as light component product stream


123


, which is warmed to ambient temperature against stream


101


and is discharged as stream


124


.




The remaining portion of stream


121


may be condensed against the throttled oxygen-rich stream


127


as overhead stream


122


in heat transfer section


30


of integrated core


1


. This condensation process serves a similar function as the condenser/reboiler


30


in the system of FIG.


1


A. The resulting condensed overhead stream is fed into separation section


20


for reflux, typically at a temperature of about 80 to about 90° K.




Bottom oxygen-rich liquid stream


125


exits separation section


20


and then may be indirectly cooled to a temperature of about 90 to about 120° K) against exiting gas stream


151


(preferably very low purity oxygen) in heat transfer section


5


. Stream


125


then exits integrated core


1


as stream


126


. Stream


126


may be throttled in valve


10


D to form stream


127


, which is returned to integrated core


1


at heat transfer section


30


as stream


151


. Stream


151


may be vaporized against stream


122


and superheated (to a temperature of about 80 to about 100° K) in section


5


. Superheated stream


151


exits the integrated core


1


as stream


170


, where it may be expanded in turbine/expander


10


to provide the required plant refrigeration. Resulting expanded stream


171


is returned to integrated core


1


and is warmed to ambient temperature against incoming feed air stream


101


.





FIG. 2B

depicts an alternative configuration of the process depicted in FIG.


2


A. In this embodiment, section


20


which is positioned outside of integrated core


1


(equivalent to separation section


20


of

FIG. 2A

) is used to separate the feed air into almost-pure nitrogen stream


121


and oxygen-rich bottom liquid stream


125


. Except for section


20


being positioned outside of integrated core


1


, the rest of the system is similar to the system depicted in

FIG. 2A

, although the placement of the various heat transfer sections of integrated core


1


may differ slightly.





FIG. 3A

depicts an alternative application of the integration concept to a cryogenic air separation system. Specifically,

FIG. 3A

shows a system in which higher pressure column


20


is integrated with the superheater, oxygen product boiler, and the primary heat exchanger in integrated core


1


, instead of stripping section


50


(as in the case of the system shown in FIG.


1


A). In addition, heat transfer section


4


, which typically serves as a reboiler for section


50


, is not present in the integrated core of this embodiment. Instead, auxiliary stripping section


50


and its reboiler


80


are situated outside of integrated core


1


. However, stripping section


50


may be eliminated altogether with some process modification. In such a modified system, the liquid stream from the bottom of upper column


40


would meet the oxygen product purity requirement without the need for further enrichment, which is typically provided by stripping section


50


. Other than the rearrangement of higher pressure column


20


and stripping section


50


, the system shown in

FIG. 3A

is similar to the system of FIG.


1


A.





FIG. 3B

depicts integrated core


1


in the case where stripping section


50


is eliminated. Lower pressure feed air stream


102


enters higher pressure section


20


of integrated core


1


directly from heat transfer section


3


of integrated core


1


as a slightly superheated vapor (typically having a temperature of about 90 to about 110° K) or a close to saturated vapor. Upper column


40


is not shown in

FIG. 3B

for sake of convenience. As in the case with the system depicted in

FIG. 1A

, integrated core


1


of

FIGS. 3A and 3B

may be modified to accommodate the most suitable directional orientation, as well as the optimal scheme to provide the plant refrigeration requirements.





FIG. 4

depicts yet another embodiment of the present invention. In this embodiment, lower pressure section


40


and higher pressure section


20


are integrated into separate integrated heat transfer cores


1


B and lA, respectively. Thus, in addition to integrated core


1


A, which is similar to integrated core


1


depicted in

FIG. 3B

, integrated core


1


B may also be utilized for heat and mass transfer by performing functions similar to those of main condenser


30


and upper column


40


of FIG.


1


A.




The air separation system of this embodiment does not use a side-stripping column or reboiler. Instead, the system operates so that the liquid stream at the bottom of lower pressure section


40


of integrated core


1


B is provided at the desired oxygen product purity. The remainder of the system is similar to that depicted in

FIG. 1A

except: (a) lower pressure separation section


40


(integrated in core


1


B) and higher pressure separation section


20


(integrated in core


1


A) take the place of upper column


40


and lower column


20


; (b) heat transfer section


30


of integrated core


1


B thermally links higher pressure separation section


20


and lower pressure separation section


40


, of integrated cores


1


A and


1


B, respectively, instead of using a typical reboiler/condenser; (c) kettle liquid stream


125


and condensed nitrogen stream


133


are subcooled against exiting gas streams in heat transfer zone


5


A of integrated core


1


A and in heat transfer section


5


B of integrated core


1


B, as opposed to being subcooled in a single heat transfer section; (d) phase separator


60


separates partially vaporized stream


153


, which exits from heat transfer section


30


of integrated core


1


B instead of heat transfer section


4


of integrated core


1


in FIG.


1


A.




Additionally, liquid stream


162


from phase separator


60


constitutes the liquid oxygen product and is fed to pump


70


, in the same manner as is depicted in

FIG. 1A

; however, vapor stream


161


is returned as stripping vapor to lower pressure section


40


, as opposed to the separation section


50


, as depicted in FIG.


1


A.





FIG. 5

illustrates the application of the integration concept of the present invention to an argon-producing cryogenic air separation system.

FIG. 5

shows a system containing three separation sections, although more may be used. Integrated core


1


B, with lower pressure separation section


40


, is similar to that depicted in

FIG. 4

, but is modified to incorporate argon rectification section


80


and its condenser. In addition, integrated core


1


A is similar to integrated core


1


A of the system depicted in FIG.


4


.




Pre-purified air streams


101


and


103


enter the warm end of heat exchanger core


1


A. Main air stream


101


may be cooled against nitrogen product stream


143




a


, waste nitrogen stream


142




a


, and oxygen product stream


171


G. Cooled air stream


110


is taken from an intermediate location along the length of integrated core


1


A and is fed through turbine/expander


10


. (The specific pressure and temperature at which air stream


110


is removed depends at least in part on the plant's particular refrigeration requirement.) Resulting expanded air stream


119


enters the section


3


of integrated core


1


A where it is further cooled before being fed into the bottom of section


20


, preferably at a temperature of about 85 to about 105° K. Section


20


functions as the lower column in FIG.


1


A.




Air stream


103


flows into integrated core


1


A and may be condensed mainly against boiling oxygen product stream


171


G and subcooled in heat transfer sections


3


and


5


A along the length of integrated core


1


A. Resulting subcooled liquid air stream


104


exits integrated core


1


A (preferably at a temperature of about 90 to about 110° K) where it may be divided into streams


105


and


107


. Stream


107


, which may comprise 0 to 100% of stream


104


, may be throttled in valve


10


B. Resulting throttled liquid air stream


108


is fed into section


20


at a position several stages above the feed point of lower pressure air stream


102


.




Stream


105


, including the remaining portion of liquid air stream


104


, is throttled in valve


10


A. Resulting throttled liquid air stream


106


is fed into section


40


below the stage from which waste nitrogen stream


142


is drawn. Section


40


serves as upper column


40


as in FIG.


1


A.




Feed air streams


102


and


108


, which both enter separation section


20


of integrated core


1


A, are separated into nearly pure nitrogen stream


121


, and kettle liquid stream


125


. Stream


121


may be condensed in main condenser


30


against boiling oxygen stream


152


from the bottom of separation section


40


to form stream


131


. Stream


131


, after exiting main condenser


30


, is divided into streams


132


and


133


. Stream


132


, which typically includes about 45 to about 60% of stream


131


, may be used as reflux for separation section


20


. Stream


133


, comprising the balance of stream


131


, may be subcooled against exiting gaseous nitrogen streams


143


and


142


in heat transfer section


5


B of integrated core


1


B to a temperature of about 80 to about 100° K. Resulting subcooled liquid nitrogen stream


134


may be divided into stream


134




a


and stream


134




b.






Stream


134




b


, preferably the major fraction of stream


134


, may be throttled in valve


10


C to form throttled stream


135


. Stream


135


preferably enters the top of separation section


40


as reflux. Stream


134




a


, the remainder of stream


134


, may be taken as product liquid nitrogen.




Kettle liquid stream


125


from separation section


20


may be subcooled against exiting gaseous streams


143




a


and


142




a


in heat transfer section


5


A at the cooler end of integrated core


1


A. Resulting stream


126


may be throttled in valve


10


D, outside of integrated core


1


A, and split into two streams. Preferably, stream


127




a


, a smaller fraction of stream


126


, enters section


40


a few stages below the feed point of stream


106


. The other fraction, stream


127




b


, which may include 0 to 100% of stream


126


, may be fed into heat transfer section


90


at the colder end of integrated core


1


B.




Heat transfer section


90


serves as an argon condenser. In heat transfer section


90


, stream


127




b


may be vaporized against condensing argon vapor overhead stream


180


from argon rectification section


80


of integrated core


1


B. Resulting, mostly-vapor stream


190


may be fed to phase separator


60


C and separated into stream


190


L and stream


190


V. Stream


190


V, which is less rich in oxygen, may be fed into separation section


40


a few stages below the feed position of stream


127




a


. Preferably, stream


190


L is fed into separation section


40


even lower than stream


190


V.




In separation section


40


, feed streams


106


,


127




a


,


190


L, and


190


V, along with liquid stream


185


from the bottom of argon rectification section


80


, are separated into high purity nitrogen product stream


142


, high purity liquid oxygen stream


152


, waste nitrogen stream


143


, and argon-rich vapor stream


145


, respectively. Argon-rich stream


145


, preferably containing about 10% to about 15% argon, feeds into argon rectification section


80


to be further separated.




Stream


142


typically contains less than 2 ppm of oxygen, and stream


152


typically is about 99.5% oxygen. Streams


143


and


142


may be superheated (to a temperature of about 80 to about 100° K) against almost-pure nitrogen stream


134


in integrated core


1


B, and then may be transferred into integrated core


1


A where those streams may be warmed to near ambient temperature.




In heat transfer section


30


of integrated core


1


B, stream


152


may be vaporized against stream


121


from separation section


20


. Resulting partially vaporized, almost-pure oxygen bottom stream


153


may be fed into separator


60


B, in which it may be separated into vapor stream


161


and liquid stream


162


. Vapor stream


161


may be returned as stripping vapor to the bottom of separation section


40


. Stream


162


may be pumped to the desired pressure through pump


70


to form stream


171


(which typically has a pressure in the range of about 60 to about 100 psia). A small fraction of the pressurized liquid oxygen stream


171


may be withdrawn as a product stream (not shown). The balance, stream


171


G, is fed through integrated core


1


A where it may be vaporized in heat transfer section


3


against condensing air stream


103


. Preferably, stream


171


G is warmed to near ambient temperature before being discharged from integrated cre


1


A.




Argon-rich vapor stream


145


, withdrawn at about 30 to about 40 stages from the bottom of the separation section


40


and typically containing about 10 to about 15% argon and nitrogen in ppm level, is sent to the bottom of separation section


80


of second integrated core


1


B. Argon separation section


80


further enriches vapor feed stream


145


in argon, resulting in an argon overhead product, typically containing about 1 to about 3% oxygen, and a less argon-rich bottom liquid stream


185


.




Bottom liquid stream


185


may be returned to separation section


40


. A portion of the overhead argon from separation section


80


may be taken as vapor argon product (stream


183


) and the rest (stream


182


) may be condensed against stream


127




b


in reboiler/condenser section


90


. A small fraction of the resulting condensed overhead stream may be taken as liquid crude argon product, as stream


193


. The balance of condensed overhead stream


182


preferably is returned as reflux to argon separation section


80


.




If the argon product from the rectification column is required to meet heavy component impurity specifications of a few ppm, another column (not shown) comprising higher stages (lower temperatures) than the single argon column featured in

FIG. 5

can be added to further rectify the argon-rich vapor. In this case, argon-rich vapor may flow from the top of section


80


to the bottom of the additional rectification section and then continue upward. Liquid from the bottom of the additional section may be pumped to the top of section


80


. Liquid argon may be withdrawn as product argon several stages from the top of the added section in order to meet the required ppm level of oxygen and nitrogen impurities.




A small vapor stream may be removed from the top of the added column section to prevent nitrogen buildup in the argon rectification sections. An overhead argon stream to be condensed in argon condenser


90


then may be taken from the top of the added column section instead of section


80


of integrated core


1


B. In any case, integrated cores


1


A and


1


B may be designed for optimal thermal interaction between the various heat transfer and mass transfer zones of the integrated cores.



Claims
  • 1. A cryogenic air separation system in flow communication with a double column separation apparatus having a higher pressure column and a lower pressure column, said air separation system comprising:an integrated core comprising: (i) a first intake passage cooling a first incoming feed air stream, and directing the cooled first incoming feed air stream into the separation apparatus, said first intake passage being in a heat exchange relationship with at least one other passage of said integrated core, (ii) a first cooling passage cooling a first bottom stream from the separation apparatus, and directing the cooled first bottom stream back into a separation section, said first cooling passage being in a heat exchange relationship with at least one other passage of said integrated core, (iii) a first warming passage warming a first overhead stream from the separation apparatus, and discharging the warmed first overhead stream from said integrated core, said first warming passage being in a heat exchange relationship with at least one other passage of said integrated core, and (iv) a vaporization passage vaporizing a liquid phase stream and discharging the vaporized liquid phase stream from said integrated core, said vaporization passage being in a heat exchange relationship with at least one other passage of said integrated core; and a separating section separating a second bottom stream from the separation apparatus to form an oxygen enriched stream and a nitrogen enriched stream, wherein the nitrogen enriched stream is directed back into the separation apparatus and the oxygen enriched stream is separated into a vapor phase stream and the liquid phase stream, the vapor phase stream being directed back into said separating section.
  • 2. The air separation system according to claim 1, wherein said separating section is integrated within said integrated core and wherein said integrated core further comprises a second cooling passage cooling a condensed stream from the lower pressure column, and directing the cooled condensed stream back into the separation apparatus, said second cooling passage being in a heat exchange relationship with at least one other passage of said integrated core.
  • 3. A method for separating air comprising the steps of:cooling, in an integrated core, a first incoming feed air stream against at least one other stream flowing through the integrated core, and directing the cooled incoming feed air stream into a separation apparatus; cooling, in the integrated core, a first bottom stream from the separation apparatus against at least one other stream flowing through the integrated core, and directing the cooled first bottom stream back into the separation apparatus; warming, in the integrated core, a first overhead stream from the separation apparatus against at least one other stream flowing through the integrated core, and discharging the warmed first overhead stream from the integrated core; vaporizing, in the integrated core, a liquid phase stream against at least one other stream in the integrated core, and discharging the vaporized liquid phase stream from the integrated core; separating a second bottom stream from the separation apparatus to form an oxygen enriched stream and a nitrogen enriched stream; and feeding the nitrogen enriched stream back into the separation apparatus; and further separating the oxygen enriched stream into a vapor phase stream and the liquid phase stream.
  • 4. The method according to claim 3, wherein the step of separating the second bottom stream is performed within the integrated core.
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5410885 Smolarek et al. May 1995
5463871 Cheung Nov 1995
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5596883 Bernhard et al. Jan 1997
5694790 Lavin Dec 1997
5699671 Lockett et al. Dec 1997
5724834 Srinivasan et al. Mar 1998
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