U.S. patent application number 17/229923 was filed with the patent office on 2021-11-18 for enhancements to a moderate pressure nitrogen and argon producing cryogenic air separation unit.
The applicant listed for this patent is James R. Handley, Henry E. Howard, Brian R. Kromer, Neil M. Prosser, Zhengrong Xu. Invention is credited to James R. Handley, Henry E. Howard, Brian R. Kromer, Neil M. Prosser, Zhengrong Xu.
Application Number | 20210356205 17/229923 |
Document ID | / |
Family ID | 1000005579059 |
Filed Date | 2021-11-18 |
United States Patent
Application |
20210356205 |
Kind Code |
A1 |
Kromer; Brian R. ; et
al. |
November 18, 2021 |
ENHANCEMENTS TO A MODERATE PRESSURE NITROGEN AND ARGON PRODUCING
CRYOGENIC AIR SEPARATION UNIT
Abstract
Enhancements to the distillation column system and cycles for an
argon and nitrogen producing cryogenic air separation unit are
provided. The enhancements include systems and methods for: (i)
recovery of xenon and krypton; (ii) production of oxygen product
substantially free of hydrocarbons; and (iii) improvement in the
design and performance of the super-stage argon column. The present
systems and methods are further characterized in an oxygen enriched
stream from the lower pressure column of the air separation unit is
an oxygen enriched condensing medium used in the argon
condenser.
Inventors: |
Kromer; Brian R.; (Buffalo,
NY) ; Prosser; Neil M.; (Lockport, NY) ;
Handley; James R.; (East Amherst, NY) ; Xu;
Zhengrong; (East Amherst, NY) ; Howard; Henry E.;
(Grand Island, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kromer; Brian R.
Prosser; Neil M.
Handley; James R.
Xu; Zhengrong
Howard; Henry E. |
Buffalo
Lockport
East Amherst
East Amherst
Grand Island |
NY
NY
NY
NY
NY |
US
US
US
US
US |
|
|
Family ID: |
1000005579059 |
Appl. No.: |
17/229923 |
Filed: |
April 14, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
63025347 |
May 15, 2020 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 3/04412 20130101;
F25J 3/04715 20130101; F25J 3/04303 20130101; F25J 3/028 20130101;
F25J 2215/36 20130101; F25J 2215/42 20130101; F25J 2215/40
20130101; F25J 3/04212 20130101; F25J 2215/50 20130101; F25J
2210/40 20130101; F25J 2215/58 20130101 |
International
Class: |
F25J 3/04 20060101
F25J003/04; F25J 3/02 20060101 F25J003/02 |
Claims
1. An air separation unit comprising: a main air compression system
configured for receiving a stream of incoming feed air and
producing a compressed air stream; an adsorption based pre-purifier
unit configured for removing water vapor, carbon dioxide, nitrous
oxide, and hydrocarbons from the compressed air stream and
producing a compressed and purified air stream; a main heat
exchange system configured to cool the compressed and purified air
stream to temperatures suitable for fractional distillation; a
distillation column system having a higher pressure column and a
lower pressure column linked in a heat transfer relationship via a
condenser-reboiler, the distillation column system further includes
an argon column arrangement operatively coupled with the lower
pressure column, the argon column arrangement having at least one
argon column and an argon condenser, the distillation column system
configured for receiving the cooled, compressed and purified air
stream and produce at least two or more oxygen enriched streams
from the lower pressure column; an argon product stream, a gaseous
nitrogen product stream; and wherein the distillation column system
further comprises a rare gas rectification system configured to
receive an argon-oxygen enriched stream from the lower pressure
column and to produce a crude rare gas stream.
2. The air separation unit of claim 1, wherein at least one of the
oxygen enriched streams from the lower pressure column is an oxygen
product stream and at least one of the oxygen enriched streams from
the lower pressure column is an oxygen enriched condensing medium
directed to the argon condenser.
3. The air separation unit of claim 1, wherein the rare gas
rectification system further comprises between 2 and 6 theoretical
stages of separation.
4. The air separation unit of claim 1, wherein the rare gas
rectification system is configured to recover between about 90% to
99% of the xenon and between about 10% to 90% of the krypton in the
compressed and purified air stream.
5. The air separation unit of claim 1, wherein the rare gas
rectification system further comprises an additional separation
section of trays disposed in the lower pressure column just above
the condenser-reboiler and the crude rare gas stream is extracted
from the bottom of the lower pressure column.
6. The air separation unit of claim 1, wherein the rare gas
rectification system further comprises an additional separation
section of trays disposed in an argon condenser vessel just above
the argon condenser and the crude rare gas stream is extracted from
the bottom of the argon condenser vessel.
7. The air separation unit of claim 1, wherein the rare gas
rectification system further comprises a bifurcated separation
section of trays with a first part of the separation section
disposed in an argon condenser vessel just above the argon
condenser and a second part of the of the separation section
disposed in the lower pressure column just above the
condenser-reboiler and the crude rare gas stream is extracted from
the bottom of the lower pressure column.
8. The air separation unit of claim 1, wherein the rare gas
rectification system further comprises a bifurcated separation
section of trays with a first part of the separation section
disposed in an argon condenser vessel just above the argon
condenser and a second part of the of the separation section
disposed in a stand-alone rare gas column and the crude rare gas
stream is extracted from the bottom of the stand-alone rare gas
column.
9. The air separation unit of claim 8, wherein the crude rare gas
stream is bifurcated into a first crude rare gas stream directed to
an upper location of the stand-alone rare gas column and a second
crude rare gas stream directed to an intermediate location of the
stand-alone rare gas column.
10. An air separation unit comprising: a main air compression
system configured for receiving a stream of incoming feed air and
producing a compressed air stream; an adsorption based pre-purifier
unit configured for removing water vapor, carbon dioxide, nitrous
oxide, and hydrocarbons from the compressed air stream and
producing a compressed and purified air stream; a main heat
exchange system configured to cool the compressed and purified air
stream to temperatures suitable for fractional distillation; a
distillation column system having a higher pressure column and a
lower pressure column linked in a heat transfer relationship via a
condenser-reboiler, the distillation column system further includes
an argon column arrangement operatively coupled with the lower
pressure column, the argon column arrangement having an argon
column, an argon condenser, and a reboiler; wherein the
distillation column system configured for receiving the cooled,
compressed and purified air stream and produce a first oxygen
enriched stream from the bottom of the lower pressure column; an
argon product stream, a gaseous nitrogen product stream; wherein
the argon column arrangement is configured to receive an
argon-oxygen enriched stream from the lower pressure column at the
reboiler and produce a condensed argon-oxygen enriched stream that
is let down in pressure and directed to an intermediate location of
the argon column; wherein the argon column arrangement is further
configured to produce another oxygen enriched stream that is
returned to or released into the lower pressure column and an
argon-enriched overhead that is directed to the argon condenser;
and wherein the argon condenser is configured to condense the
argon-enriched overhead against the oxygen enriched stream taken
from the bottom of the lower pressure column to produce a crude
argon stream, an argon reflux stream and an oxygen enriched waste
stream.
11. The air separation unit of claim 10, wherein the argon
condenser is configured to condense the argon-enriched overhead
against a mixture of the oxygen enriched stream taken from the
bottom of the lower pressure column and a source of liquid nitrogen
to produce the crude argon stream, the argon reflux stream and the
oxygen enriched waste stream.
12. The air separation unit of claim 10, wherein the oxygen
enriched waste stream is warmed in the main heat exchange system
and used to regenerate the adsorption based pre-purification
unit.
13. An air separation unit comprising: a main air compression
system configured for receiving a stream of incoming feed air and
producing a compressed air stream; an adsorption based pre-purifier
unit configured for removing water vapor, carbon dioxide, nitrous
oxide, and hydrocarbons from the compressed air stream and
producing a compressed and purified air stream; a main heat
exchange system configured to cool the compressed and purified air
stream to temperatures suitable for fractional distillation; a
distillation column system having a higher pressure column and a
lower pressure column linked in a heat transfer relationship via a
condenser-reboiler, the distillation column system further includes
an argon column arrangement operatively coupled with the lower
pressure column, the argon column arrangement having an argon
column and an argon condenser, the distillation column system
configured for receiving the cooled, compressed and purified air
stream and a first oxygen enriched stream from the lower pressure
column; an argon product stream, a gaseous nitrogen product stream;
wherein the argon column arrangement is configured to receive an
argon-oxygen enriched stream from the lower pressure column and
produce a second oxygen enriched stream that is returned to or
released into the lower pressure column and an argon-enriched
overhead that is directed to the argon condenser; wherein the
distillation column system further comprises a supplemental oxygen
column configured to receive another oxygen enriched stream from
the argon column and rectify the received another oxygen enriched
stream to produce an oxygen enriched overhead stream that is
returned to the argon column and a hydrocarbon-free oxygen liquid
stream; wherein the supplemental oxygen column includes a reboiler
disposed proximate the bottom of the supplemental oxygen column and
configured to boil oxygen in the supplemental oxygen column against
a stream of nitrogen received from the higher pressure column or a
portion of the compressed and purified air stream to produce an
ascending oxygen vapor in the supplemental oxygen column and a
condensed nitrogen stream; and wherein all or a portion of the
first oxygen enriched stream from the lower pressure column is an
oxygen enriched condensing medium directed to the argon
condenser.
14. The air separation unit of claim 13, wherein the another oxygen
enriched stream from the argon column received by the supplemental
oxygen column is a diverted portion of the second oxygen enriched
stream and the oxygen enriched overhead stream is returned to the
argon column.
15. The air separation unit of claim 13, wherein the another oxygen
enriched stream from the argon column received by the supplemental
oxygen column is taken from an intermediate location of the argon
column and the oxygen enriched overhead stream is returned to
another intermediate location of the argon column just below the
intermediate location of the argon column where the oxygen enriched
stream is taken.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of and priority to U.S.
provisional patent application Ser. No. 63/025,347 filed May 15,
2020 the disclosure of which is incorporated by reference.
TECHNICAL FIELD
[0002] The present inventions relates to enhancements to a moderate
pressure nitrogen and argon producing cryogenic air separation
unit, and more particularly, to improvements to the distillation
column system in the nitrogen and argon producing cryogenic air
separation unit for (i) recovery of xenon and krypton; (ii)
production of an oxygen product substantially free of hydrocarbons;
and (iii) improvement in the design and performance of the
super-stage argon column.
BACKGROUND
[0003] Industrial gas customers often seek argon and nitrogen
product slates at volumes and pressures that are typically produced
from a cryogenic air separation unit as disclosed in the technical
publication Cheung, Moderate Pressure Cryogenic Air Separation
Process, Gas Separation & Purification, Vol 5, March 1991 and
U.S. Pat. No. 4,822,395 issued to Cheung. Similarly, U.S. patent
application Ser. Nos. 15/962,205; 15/962,245; 15/962,292; and Ser.
No. 15/962,358 filed on Apr. 25, 2018 as well as U.S. patent
application Ser. No. 16/662,193 filed on Oct. 24, 2019, the
disclosures of which are incorporated by reference herein, disclose
new air separation systems and cycles that represent improvements
over the system disclosed by Cheung. Such improvements to moderate
pressure argon and nitrogen producing air separation units use an
oxygen enriched stream taken from the lower pressure column as the
condensing medium in the argon condenser to condense the argon-rich
stream thus improving argon and nitrogen recoveries.
[0004] What is needed are further enhancements to the moderate
pressure argon and nitrogen producing cryogenic air separation unit
originally developed by Cheung and subsequently improved by the
advancements disclosed in the above-identified U.S. patent
application Ser. Nos. to expand the product slates or improve the
performance and flexibility of such cryogenic air separation unit
to meet customer requirements.
SUMMARY OF THE INVENTION
[0005] The present invention may be characterized as an air
separation unit comprising: (i) a main air compression system
configured for receiving a stream of incoming feed air and
producing a compressed air stream; (ii) an adsorption based
pre-purifier unit configured for removing water vapor, carbon
dioxide, nitrous oxide, and hydrocarbons from the compressed air
stream and producing a compressed and purified air stream; (iii) a
main heat exchange system configured to cool the compressed and
purified air stream to temperatures suitable for fractional
distillation; (iv) a distillation column system having a higher
pressure column and a lower pressure column linked in a heat
transfer relationship via a condenser-reboiler, the distillation
column system further includes an argon column arrangement
operatively coupled with the lower pressure column, the argon
column arrangement having an argon column and an argon condenser,
the distillation column system configured for receiving the cooled,
compressed and purified air stream and produce one or more oxygen
enriched streams from the lower pressure column; an argon product
stream, a gaseous nitrogen product stream; and (v) wherein the
distillation column system further comprises a rare gas
rectification system configured to receive an argon-oxygen enriched
stream from the lower pressure column and to produce a crude rare
gas stream. At least one of the oxygen enriched streams from the
lower pressure column is an oxygen product stream and at least one
of the oxygen enriched streams from the lower pressure column is an
oxygen enriched condensing medium directed to the argon condenser.
The rare gas rectification system preferably has between 2 and 6
theoretical stages of separation and is configured to recover
between 90% to 99% of the xenon and between about 10% to 90% of the
krypton in the compressed and purified air stream.
[0006] In one embodiment, the rare gas rectification system further
comprises an additional separation section of trays disposed in the
lower pressure column just above the condenser-reboiler and the
crude rare gas stream is extracted from the bottom of the lower
pressure column whereas I another embodiment the rare gas
rectification system further comprises an additional separation
section of trays disposed in the argon condenser vessel just above
the argon condenser and the crude rare gas stream is extracted from
the bottom of the argon condenser vessel.
[0007] In still other embodiments of the air separation unit the
rare gas rectification system further comprises a bifurcated
separation section of trays with a first part of the separation
section disposed in an argon condenser vessel just above the argon
condenser and a second part of the of the separation section
disposed either in in the lower pressure column just above the
condenser-reboiler or in a stand-alone rare gas column.
[0008] The present invention may also be characterized as an air
separation unit comprising: (i) a main air compression system
configured for receiving a stream of incoming feed air and
producing a compressed air stream; (ii) an adsorption based
pre-purifier unit configured for removing water vapor, carbon
dioxide, nitrous oxide, and hydrocarbons from the compressed air
stream and producing a compressed and purified air stream; (iii) a
main heat exchange system configured to cool the compressed and
purified air stream to temperatures suitable for fractional
distillation; and (iv) a distillation column system having a higher
pressure column and a lower pressure column linked in a heat
transfer relationship via a condenser-reboiler, the distillation
column system further includes an argon column arrangement
operatively coupled with the lower pressure column, the argon
column arrangement having an argon column, an argon condenser, and
a reboiler. The distillation column system is configured for
receiving the cooled, compressed and purified air stream and
produce a first oxygen enriched stream from the bottom of the lower
pressure column; an argon product stream, a gaseous nitrogen
product stream wherein all or a portion of the oxygen enriched
streams from the bottom of lower pressure column is directed to the
argon condenser to be used as an oxygen enriched condensing medium.
The argon condenser is configured to condense the argon-enriched
overhead against the oxygen enriched condensing medium to produce a
crude argon stream, an argon reflux stream, an oxygen enriched
waste stream, and optionally an oxygen product stream.
[0009] The argon column arrangement is configured to receive an
argon-oxygen enriched stream from the lower pressure column at the
reboiler and produce a condensed argon-oxygen enriched stream that
is let down in pressure and directed to an intermediate location of
the argon column. The argon column arrangement is further
configured to produce another oxygen enriched stream that is
returned to or released into the lower pressure column and an
argon-enriched overhead that is directed to the argon
condenser.
[0010] Lastly, the present invention may also be characterized as
an air separation unit comprising: (i) a main air compression
system configured for receiving a stream of incoming feed air and
producing a compressed air stream; (ii) an adsorption based
pre-purifier unit configured for removing water vapor, carbon
dioxide, nitrous oxide, and hydrocarbons from the compressed air
stream and producing a compressed and purified air stream; (iii) a
main heat exchange system configured to cool the compressed and
purified air stream to temperatures suitable for fractional
distillation; (iv) a distillation column system having a higher
pressure column and a lower pressure column linked in a heat
transfer relationship via a condenser-reboiler, the distillation
column system further includes an argon column arrangement
operatively coupled with the lower pressure column, the argon
column arrangement having an argon column and an argon condenser,
the distillation column system configured for receiving the cooled,
compressed and purified air stream and a first oxygen enriched
stream from the lower pressure column to be used as the condensing
medium in the argon condenser; an argon product stream, a gaseous
nitrogen product stream; and (v) a supplemental oxygen column. The
argon column arrangement is configured to receive an argon-oxygen
enriched stream from the lower pressure column and produce a second
oxygen enriched stream that is returned to or released into the
lower pressure column and an argon-enriched overhead that is
directed to the argon condenser. The supplemental oxygen column is
configured to receive an oxygen enriched stream from the argon
column, either as a portion of the oxygen enriched stream to be
returned to the lower pressure column or as a separate oxygen
enriched stream taken from an intermediate location of the argon
column. The supplemental oxygen column is configured to rectify the
received oxygen enriched stream to produce an oxygen enriched
overhead stream that is returned to the argon column and a
hydrocarbon-free oxygen liquid stream. The supplemental oxygen
column includes a reboiler disposed proximate the bottom of the
supplemental oxygen column and is configured to boil oxygen in the
supplemental oxygen column against a stream of nitrogen received
from the higher pressure column or a portion of the compressed and
purified air stream to produce an ascending oxygen vapor in the
supplemental oxygen column and a condensed nitrogen stream.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] While the present invention concludes with claims distinctly
pointing out the subject matter that Applicants regard as their
invention, it is believed that the invention will be better
understood when taken in connection with the accompanying drawings
in which:
[0012] FIG. 1 is a schematic process flow diagram of a cryogenic
air separation unit capable of operating at moderate pressure and
having high nitrogen recovery and high argon recovery;
[0013] FIG. 2 is a schematic process flow diagram of an alternate
embodiment of a cryogenic air separation unit capable of operating
at moderate pressure and having high nitrogen recovery and high
argon recovery;
[0014] FIG. 3 is a schematic process flow diagram of a yet another
embodiment of a cryogenic air separation unit capable of operating
at moderate pressure and having high nitrogen recovery and high
argon recovery;
[0015] FIG. 4 is a schematic process flow diagram of still another
embodiment of a cryogenic air separation unit capable of operating
at moderate pressure and having high nitrogen recovery and high
argon recovery;
[0016] FIG. 5 is a partial schematic diagram of a modified lower
pressure column of the distillation column system of FIGS. 1-4
suitable for the recovery of xenon and krypton in accordance with
an aspect or embodiment of the present invention;
[0017] FIG. 6 is a partial schematic diagram of a modified argon
condenser vessel of the distillation column system of FIGS. 1-4
suitable for the recovery of xenon and krypton in accordance with
another aspect or embodiment of the present invention;
[0018] FIG. 7 is a partial schematic diagram of a modified lower
pressure column and modified argon condenser vessel of the
distillation column system shown in FIGS. 1-4 that is suitable for
the recovery of xenon and krypton in accordance with yet another
aspect or embodiment of the present invention;
[0019] FIG. 8 is another partial schematic diagram of a modified
lower pressure column and modified argon condenser vessel of the
distillation column system shown in FIGS. 1-4 that is suitable for
the recovery of xenon and krypton in accordance with still another
aspect or embodiment of the present invention;
[0020] FIGS. 9A and 9B depict graphs showing the expected xenon and
krypton recoveries as a function of argon condenser recirculation
for the air separation unit of FIGS. 1-4 with the modified
distillation column systems;
[0021] FIG. 10 is a partial schematic diagram of a modified lower
pressure column, higher pressure column and argon column
arrangement of the distillation column system of FIGS. 1-4 suitable
for the recovery of an oxygen product substantially free of
hydrocarbon impurities;
[0022] FIG. 11 is a partial schematic diagram of a modified column
arrangement of the distillation column system of FIGS. 1-4 suitable
for the recovery of an oxygen product substantially free of
hydrocarbon impurities; and
[0023] FIG. 12 is a schematic diagram of a of a cryogenic air
separation unit similar to those shown in FIGS. 1-4 but with a
modified distillation column system suitable for the enhanced
design and performance of the super-staged argon column.
DETAILED DESCRIPTION
[0024] The presently disclosed systems and methods provides for
enhancements to the distillation column system in a moderate
pressure nitrogen and argon producing cryogenic air separation
unit, including (i) enhancements for the recovery of xenon and
krypton; (ii) enhancements for the production of a hydrocarbon free
oxygen product; (iii) enhancements to the argon super-stage column;
and (iv) enhancements to the air separation cycles. Each of these
enhancements together with the baseline moderate pressure nitrogen
and argon producing cryogenic air separation unit will be described
in the sections that follow.
Moderate Pressure Argon and Nitrogen Producing Cryogenic Air
Separation Unit
[0025] As discussed in more detail below, the disclosed moderate
pressure argon and nitrogen producing cryogenic air separation unit
comprises a multi-column arrangement and achieves the high argon
and nitrogen recoveries by using a portion of an oxygen enriched
stream taken from the lower pressure column as the condensing
medium in the argon condenser to condense the argon-rich stream.
The oxygen rich boil-off from the argon condenser is then used as a
purge gas to regenerate the adsorbent beds in the adsorption based
pre-purifier unit. The disclosed cryogenic air separation system
and methods are further capable of limited oxygen production.
[0026] Turning to FIG. 1, there is shown a schematic illustration
of the baseline argon and nitrogen producing cryogenic air
separation unit 10 having high nitrogen and argon recoveries. In a
broad sense, the depicted air separation unit includes a main feed
air compression train or system, a turbine air circuit, an optional
booster air circuit, a primary heat exchanger system, and a
distillation column system. As used herein, the main feed air
compression train, the turbine air circuit, and the booster air
circuit, collectively comprise the `warm-end` air compression
circuit. Similarly, main heat exchanger, portions of the turbine
based refrigeration circuit and portions of distillation column
system are referred to as `cold-end` equipment that are typically
housed in insulated cold boxes.
[0027] In the main feed compression train shown in FIG. 1 the
incoming feed air 22 is typically drawn through an air suction
filter house and is compressed in a multi-stage, intercooled main
air compressor arrangement 24 to a pressure that can be between
about 6.5 bar(a) and about 11 bar(a). This main air compressor
arrangement 24 may include integrally geared compressor stages or a
direct drive compressor stages, arranged in series or in parallel.
The compressed air stream 26 exiting the main air compressor
arrangement 24 is fed to an aftercooler (not shown) with integral
demister to remove the free moisture in the incoming feed air
stream. The heat of compression from the final stages of
compression for the main air compressor arrangement 24 is removed
in aftercoolers by cooling the compressed feed air with cooling
tower water. The condensate from this aftercooler as well as some
of the intercoolers in the main air compression arrangement 24 is
preferably piped to a condensate tank and used to supply water to
other portions of the air separation plant.
[0028] The cool, dry compressed air stream 26 is then purified in a
pre-purification unit 28 to remove high boiling contaminants from
the cool, dry compressed air feed. A pre-purification unit 28, as
is well known in the art, typically contains two beds of alumina
and/or molecular sieve operating in accordance with a temperature
swing adsorption cycle in which moisture and other impurities, such
as carbon dioxide, water vapor and hydrocarbons, are adsorbed.
While one of the beds is used for pre-purification of the cool, dry
compressed air feed while the other bed is regenerated, preferably
with a portion of the waste nitrogen from the air separation unit.
The two beds switch service periodically. Particulates are removed
from the compressed, pre-purified feed air in a dust filter
disposed downstream of the pre-purification unit 28 to produce the
compressed, purified air stream 29.
[0029] The compressed and purified air stream 29 is separated into
oxygen-rich, nitrogen-rich, and argon-rich fractions in a plurality
of distillation columns including at least a higher pressure column
72, a lower pressure column 74, and an argon column 129. Prior to
such distillation however, the compressed and pre-purified air
stream 29 is typically split into a plurality of feed air streams,
which may include a boiler air stream 32, a turbine air stream 31,
and a non-boosted air stream 33.
[0030] As shown in FIG. 1, the boiler air stream 32 may be further
compressed in a booster compressor 34 and subsequently cooled in an
aftercooler 39 to form a boosted pressure air stream 36 which is
then further cooled in the main heat exchanger 52. Likewise,
turbine air stream 31 may be further compressed in a turbine air
booster compressor 37 and subsequently cooled in an aftercooler 39
to form a boosted pressure turbine air stream 38 which is then
further cooled in the main heat exchanger 52.
[0031] Cooling the booster air stream 36 and non-booster air stream
33 and partially cooling the boosted turbine air stream 38 in the
main heat exchanger 52 is preferably accomplished by way of
indirect heat exchange with the warming streams which include the
oxygen streams 197, 386 as well as nitrogen streams 195 from the
distillation column system to produce cooled air streams at
temperatures suitable for rectification in the distillation column
systems.
[0032] The partially cooled turbine air stream 38 is expanded in
turbine 35 to produce exhaust stream 64 that is directed to the
lower pressure column 74. In this manner, a portion of the
refrigeration for the air separation unit 10 is thus provided by
the expansion of the turbine air stream 38 in turbine 35. The
boosted pressure air stream is fully cooled and exits the cold end
of main heat exchanger 52 as elevated pressure air stream 48. The
non-boosted air stream 31 is also fully cooled in the main heat
exchanger 52 to produce a fully cooled air stream 47. The fully
cooled non-boosted air stream 47 as well as the elevated pressure
air stream 48 are introduced into higher pressure column 72.
Preferably, the boosted pressure stream 48 is preferably let down
in pressure in valve 49 and fed to higher pressure column 72 at a
location several stages above the bottom where the non-boosted air
stream 47 is introduced into the higher pressure column 72.
[0033] The main heat exchanger 52 is preferably a brazed aluminum
plate-fin type heat exchanger. Such heat exchangers are
advantageous due to their compact design, high heat transfer rates
and their ability to process multiple streams. They are
manufactured as fully brazed and welded pressure vessels. For small
air separation unit units, a heat exchanger comprising a single
core may be sufficient. For larger air separation unit units
handling higher flows, the heat exchanger may be constructed from
several cores which must be connected in parallel or series.
[0034] Alternate arrangements for processing the air streams that
do not include booster compressor 34 are shown in FIGS. 2-4. As
seen in FIG. 4, the turbine air stream 31 and boiler air stream 32
remain combined are further compressed in compressor 37, cooled in
aftercooler 39 and then split into the boosted pressure air stream
36 and the booster turbine air stream 38 both of which are directed
to separate heat exchange passages within the main heat exchanger
52. The boosted turbine air stream 38 is partially cooled and
extracted from an intermediate location of the main heat exchanger
52 and then expanded in turbine 35 to produce exhaust stream 64
that is directed to the lower pressure column 74. The boosted air
stream 36 as well as the non-boosted air stream 33 are fully cooled
in the main heat exchanger 52 and then directed to the higher
pressure column 74 as described above with reference to FIG. 1.
[0035] In the embodiment illustrated in FIG. 3, the turbine air
stream 31 and boiler air stream 32 also remain combined are further
compressed in compressor 37, cooled in aftercooler 39 and then
directed to a common heat exchange passage within the main heat
exchanger 52. The stream is then split within the main heat
exchanger such that the boosted turbine air stream 38 is partially
cooled and extracted from an intermediate location of the main heat
exchanger 52 while the boosted air stream 36 continues through the
main heat exchanger where it is fully cooled and directed to the
higher pressure column 74 as described above with reference to FIG.
1. The partially cooled turbine air stream 38 is expanded in
turbine 35 to produce exhaust stream 64 that is directed to the
lower pressure column 74. The non-boosted air stream 33 is fully
cooled in a separate heat exchange passage of the main heat
exchanger 52 and then also directed to the higher pressure column
74 as described above.
[0036] The embodiment of FIG. 2 shows a further arrangement where
the turbine air stream 31 is not boosted, so there is no need for
the turbine air compressor. In this embodiment, the boiler air
stream 32 is further compressed in booster compressor 34 and cooled
in aftercooler 39 and directed to main heat exchanger 52 where it
is fully cooled and then directed to the higher pressure column 74
as described above with reference to FIG. 1. Similarly, the
non-booster air stream 33 is also directed to main heat exchanger
52 where it is fully cooled and then directed to the higher
pressure column 74 as described above with reference to FIG. 1. The
non-boosted turbine air stream 38 is partially cooled and extracted
from an intermediate location of the main heat exchanger 52 and
then expanded in turbine 35 to produce exhaust stream 64 that is
directed to the lower pressure column 74.
[0037] The turbine based refrigeration circuits used in cryogenic
air separation units are often referred to as either a lower column
turbine (LCT) arrangement or an upper column turbine (UCT)
arrangement which are used to provide refrigeration to a two-column
or three column cryogenic air distillation column systems. In the
UCT arrangements shown in FIGS. 1-3, the boosted turbine air stream
is preferably at a pressure in the range from between about 6
bar(a) to about 10.7 bar(a) and partially cooled to a temperature
in a range of between about 140 K and about 220 K. This cooled,
compressed turbine air stream that is introduced into the turbine
to produce a cold exhaust stream 64 that is then introduced into
the lower pressure column of the distillation column system. The
supplemental refrigeration created by the expansion of the turbine
air stream is thus imparted directly to the lower pressure column
thereby alleviating some of the cooling duty of the main heat
exchanger. In some embodiments, the turbine may be coupled with a
compressor, either directly or by appropriate gearing.
[0038] While the turbine based refrigeration circuit illustrated in
the FIGS. 1-4 is shown as an upper column turbine (UCT) circuit
where the turbine exhaust stream is directed to the lower pressure
column, it is contemplated that the turbine based refrigeration
circuit alternatively may be a lower column turbine (LCT) circuit
or a partial lower column (PLCT) where the expanded exhaust stream
is fed to the higher pressure column of the distillation column
system. Still further, turbine based refrigeration circuits may be
some variant or combination of LCT arrangement, UCT arrangement
and/or a warm recycle turbine (WRT) arrangement, generally known to
those persons skilled in the art.
[0039] The aforementioned components of the incoming feed air
stream, namely oxygen, nitrogen, and argon are separated within the
distillation column system that includes a higher pressure column
72, a lower pressure column 74, an argon column 129, a
condenser-reboiler 75 and an argon condenser 78. The higher
pressure column 72 typically operates in the range from between
about 6 bar(a) to about 10 bar(a) whereas lower pressure column 74
operates at pressures between about 1.5 bar(a) to about 2.8 bar(a).
The higher pressure column 72 and the lower pressure column 74 are
preferably linked in a heat transfer relationship such that all or
a portion of the nitrogen-rich vapor column overhead, extracted
from proximate the top of higher pressure column 72 as stream 73,
is condensed within a condenser-reboiler 75 located in the base of
lower pressure column 74 against the oxygen-rich liquid column
bottoms 77 residing in the bottom of the lower pressure column 74.
The boiling of oxygen-rich liquid column bottoms 77 initiates the
formation of an ascending vapor phase within lower pressure column
74. The condensation produces a liquid nitrogen containing stream
81 that is divided into a clean shelf reflux stream 83 that may be
used to reflux the lower pressure column 74 to initiate the
formation of descending liquid phase therein and a nitrogen-rich
stream 85 that is used as reflux to the higher pressure column
72.
[0040] Cooled feed air stream 47 is preferably a vapor air stream
slightly above its dew point, although it may be at or slightly
below its dew point, that is fed into the higher pressure column
for rectification resulting from mass transfer between an ascending
vapor phase and a descending liquid phase that is initiated by a
nitrogen based reflux stream 85. The mass transfer occurs within a
plurality of mass transfer contacting elements, illustrated as
distillation trays 71. This produces crude liquid oxygen column
bottoms 86, also known as kettle liquid which is taken as stream
88, and the nitrogen-rich column overhead 89, taken as clean shelf
liquid stream 83.
[0041] In the lower pressure column, the ascending vapor phase
includes the boil-off from the condenser-reboiler as well as the
exhaust stream 64 from the turbine 35 which is subcooled in
subcooling unit 99B and introduced as a vapor stream at an
intermediate location of the lower pressure column 72. The
descending liquid is initiated by nitrogen reflux stream 83, which
is sent to subcooling unit 99A, where it is subcooled and
subsequently expanded in valve 96 prior to introduction to the
lower pressure column 74 at a location proximate the top of the
lower pressure column.
[0042] Lower pressure column 74 is also provided with a plurality
of mass transfer contacting elements, that can be trays or
structured packing or other known elements in the art of cryogenic
air separation. The contacting elements in the lower pressure
column 74 are illustrated as structured packing 79. The separation
occurring within lower pressure column 74 produces an oxygen-rich
liquid column bottoms 77 extracted as a high purity oxygen enriched
liquid stream 377 having an oxygen concentration of greater than
99.5%. In addition, a lower purity oxygen enriched stream 90 is
also extracted from the lower pressure column several stages above
the condenser 75 as the condensing medium to condense the
argon-rich stream. The lower pressure column further produces a
nitrogen-rich vapor column overhead that is extracted as a gaseous
nitrogen product stream 95. If needed, a small portion of the
subcooled nitrogen reflux stream 83 may be taken via valve 101 as
liquid nitrogen product 98.
[0043] The high purity oxygen enriched liquid stream 377 can be
separated into a first oxygen enriched liquid stream 380 that is
pumped in pump 385 and the resulting pumped oxygen stream 386 is
directed to the main heat exchanger 52 where it is warmed to
produce a high purity gaseous oxygen product stream 390. A second
portion of the high purity oxygen enriched liquid stream 377 may be
taken as a liquid oxygen product 185. The lower purity oxygen
enriched liquid stream 90 is preferably subcooled in subcooling
unit 99B via indirect heat exchange with the oxygen enriched waste
stream 196 and then pumped via pump 180 to argon condenser 78 where
it is used to condense argon-rich stream 126 taken from the
overhead 123 of argon column.
[0044] The vaporized oxygen stream that is boiled off from the
argon condenser 78 is an oxygen enriched waste stream 196 that is
warmed within subcooler 99B. The warmed oxygen enriched waste
stream 197 is directed to the main or primary heat exchanger and
then used as a purge gas to regenerate the adsorption based
prepurifier unit 28. Additionally, a waste nitrogen stream 93 may
be extracted from the lower pressure column to control the purity
of the gaseous nitrogen product stream 95. The waste nitrogen
stream 93 is preferably combined with the oxygen enriched waste
stream 196 upstream of subcooler 99B. Also, vapor waste oxygen
stream 97 may be needed in some cases when more oxygen is available
than is needed to operate argon condenser 78, typically when argon
production is reduced.
[0045] A liquid stream is withdrawn from argon condenser vessel,
may be passed through gel trap and returned to the base or near the
base of lower pressure column. The gel trap serves to remove carbon
dioxide, nitrous oxide, and certain heavy hydrocarbons that might
otherwise accumulate in the system. Alternatively, a small flow can
be withdrawn via stream as a drain from the system such that gel
trap is eliminated.
[0046] Conventionally, the argon condenser shown in FIGS. 1-4 is of
a pool boiler (i.e. thermosyphon) design. Alternatively, the argon
condenser can be of a once through upflow design. These are well
known. Optionally, the argon condenser shown in FIGS. 1-4 is a
downflow argon condenser. The downflow configuration makes the
effective delta temperature (.DELTA.T) between the condensing
stream and the boiling stream smaller. As indicated above, the
smaller .DELTA.T may result in reduced operating pressures within
the argon column, lower pressure column, and higher pressure
column, which translates to a reduction in power required to
produce the various product streams as well as improved argon
recovery. The use of the downflow argon condenser also enables a
potential reduction in the number of column stages, particularly
for the argon column. Use of an argon downflow condenser is also
benefitted from a capital standpoint, in part, because pump 180 is
already required in the presently disclosed air separation cycles.
Also, since liquid stream 130 already provides a continuous liquid
stream exiting the argon condenser shell which also provides the
necessary wetting of the reboiling surfaces to prevent the argon
condenser from `boiling to dryness` and maintain safe
operation.
[0047] Nitrogen product stream 95 is passed through subcooling unit
99A to subcool the nitrogen reflux stream 83 and kettle liquid
stream 88 via indirect heat exchange. As indicated above, the
subcooled nitrogen reflux stream 83 is expanded in valve 96 and
introduced into an uppermost location of the lower pressure column
74 while the subcooled the kettle liquid stream 88 is expanded in
valve 107 and introduced to an intermediate location of the lower
pressure column 74. After passage through subcooling units 99A, the
warmed nitrogen stream 195 is further warmed within main heat
exchanger 52 to produce a warmed gaseous nitrogen product stream
295.
[0048] The flow of the first oxygen enriched liquid stream 380 may
be up to about 20% of the total oxygen enriched streams exiting the
system. The argon recovery of this arrangement is between about 75%
and 96% or higher which is greater than the prior art moderate
pressure air separation systems. Although not shown, a stream of
liquid nitrogen taken from a nitrogen liquefier or from an external
source may be combined with the oxygen enriched liquid stream 90 to
condense the argon-rich stream 126 in the argon condenser 78, to
enhance argon recovery.
[0049] With liquid nitrogen add, the boiling refrigerant in the
argon condenser is a mix of liquid oxygen and liquid nitrogen and
will be generally colder than the boiling refrigerant disclosed in
U.S. patent application Ser. Nos. referenced above. As a result,
the distillation column system pressures may be naturally lower. In
other words, the cryogenic air separation unit, and specifically
the compressors and distillation column system, may be designed to
take advantage of this lower operating pressure which would result
in an overall power savings. Alternatively, if it is not feasible
or desirable to design the compressors and distillation columns of
cryogenic air separation unit for the required pressure ranges, the
vaporized waste gas from the argon condenser may be back pressured
at the warm end of the main heat exchanger. By doing this back
pressuring in combination with liquid nitrogen add, the boiling
fluid temperature in the argon condenser is not altered and the
distillation column system pressures will also remain the same.
Employing this alternate back pressuring method would be the likely
method of operation if the higher liquid oxygen production is
expected to be infrequent or non-continuous.
Recovery of Xenon and Krypton
[0050] Turning now to FIGS. 5-8 there are shown partial schematic
diagrams of selected portions of the distillation column system.
Many of the features, components and streams associated with the
lower pressure column arrangement shown in FIGS. 5-8 are similar or
identical to those described above with reference to FIGS. 1-4 and
for sake of brevity will not be repeated here.
[0051] The key difference between the lower pressure column
arrangement illustrated in FIG. 5 compared to the lower pressure
column arrangements shown in FIGS. 1-4 is the inclusion of an
additional separation section 502 at the bottom region of the lower
pressure column 74 just above the condenser-reboiler 75. The
additional separation section 502 preferably consists of between 2
and 6 theoretical stages of separation, which could be in the form
of 2 to 6 trays or an equivalent height of structured packing
elements.
[0052] The oxygen enriched stream 90 is extracted from the lower
pressure column 74 several stages above the additional separation
section 502 and directed to the argon condenser 78 to be used as
the condensing medium to condense the argon-rich stream. The
product oxygen stream 377, if any, is also preferably withdrawn
from the lower pressure column 74 at a location just above the
additional separation section 502 while a crude rare gas liquid
stream 510 is extracted from the bottom section or base of lower
pressure column 74.
[0053] Turning now to FIG. 6, the difference between the
distillation column system arrangement shown in FIG. 6 compared to
the distillation column system arrangements shown in FIGS. 1-4 is
the inclusion of an additional separation section 504 in the argon
condenser vessel 120 at the upper region of the vessel just above
the argon condenser 78. The additional separation section 504 in
the argon condenser vessel 120 also preferably consists of between
2 and 6 theoretical stages of separation, which could be in the
form of 2 to 6 trays. The differences further include the
extraction of the crude rare gas liquid stream 510 from the bottom
section or base of the argon condenser vessel 120 and extraction of
a recirculation liquid stream 515 from an intermediate location of
the argon condenser vessel 120 that, if needed, is returned to an
intermediate location of the lower pressure column 74.
[0054] Turning now to FIGS. 7-8, the notable differences between
the illustrated distillation column system arrangements compared to
the distillation column system arrangements shown in FIGS. 1-4 are
the inclusion of a split or bifurcated separation section 506A and
506B to facilitate the recovery of xenon and krypton. A first part
of the bifurcated separation section 506A is disposed in the argon
condenser vessel 120 at the uppermost region of the vessel just
above the argon condenser 78 while the second part of the
bifurcated separation section 506B is disposed in the bottom region
of the lower pressure column 74 just above the condenser-reboiler
75. Collectively, the bifurcated separation section 506A, 506B
preferably consists of between 2 and 6 theoretical stages of
separation.
[0055] In the embodiment depicted in FIG. 7, the oxygen enriched
liquid stream 190 containing rare gas is extracted from the lower
pressure column 74 at a location just above the second part of the
bifurcated separation section 506B and fed into the argon condenser
vessel 120. Pumping and subcooling of analogous stream 90, as shown
in FIGS. 1-4 is employed for stream 190, but not shown for
simplicity. The fed stream undergoes some further separation in the
first part of the bifurcated separation section 506A with the
resulting oxygen enriched waste gas 196 removed from the overhead
of the argon condensing vessel 120 and the descending liquid used
as the condensing medium to the argon condenser with the bottoms
liquid extracted as a rare gas containing liquid stream 508 which
is returned to the lower pressure column 74. The rare gas
containing liquid stream 508 is fed into the lower pressure column
74 at a location just above the second part of the bifurcated
separation section 506B where it undergoes further separation while
the crude rare gas stream 510 is extracted from the bottom section
or base of lower pressure column 74. This arrangement improves the
potential recovery of krypton that would otherwise be lost in the
oxygen enriched waste stream leaving the argon condenser.
[0056] The embodiment depicted in FIG. 8 is similar to the
embodiment in FIG. 7 except that the part of the bifurcated
separation section that was incorporated into the lower pressure
column is now embodied as a separation section 506C in separate
column 570. The separate column 570 preferably includes several
xenon and krypton separation stages 506 as well as a reboiler 525
that receives a liquid nitrogen stream 526 from the higher pressure
column and returns the vaporized nitrogen stream 528 to the higher
pressure column. The entire liquid feed stream can be supplied via
stream 511. Preferably, though, about 25% of the feed is supplied
via stream 511 and 75% is supplied via stream 512. This enables
considerably increased Kr and Xe enrichment before the constraining
concentrations of other contaminants are reached. Separate column
570 enables this, as this result is entirely dependent on reducing
the internal reflux ratio in the rare gas separation. The
previously described embodiments do not have this capability
because the influence of the rare gas feed has only a very small
effect on the internal reflux ratio when the rare gas separation is
part of the low pressure column. Furthermore, separate column 570
is preferably smaller in diameter than the lower pressure column 74
and is advantageous in that it reduces the height of the lower
pressure column compared to the previously described embodiments.
The separate column 570 also may reduce the capital costs
associated with the structured packing or large trays used in the
additional stages of separation in the embodiment in FIG. 7 as it
is likely less costly to add stages of separation in the small
diameter column 570 to improve krypton recovery. By moving the rare
gas enrichment stages 506C out of lower pressure column 74 a small
reduction in compression power is also realized.
[0057] As depicted in FIGS. 9A and 9B, xenon recovery of between
about 90% to 99% or more and krypton recovery of between about 10%
to 90% or more was shown for the contemplated distillation column
system modifications. The expected xenon and krypton recoveries are
based on computer simulations of the present modifications to the
distillation column system and very much depend on how many stages
of separation are included in the additional separation section how
much oxygen is recirculated back to the lower pressure column from
the argon condenser. Without being bound by any particular theory,
the high recoveries of xenon and krypton using the present
modifications to the distillation column system is likely due to
the back pressure of the air separation cycle which has a tendency
to keep the heavy components in the liquid phase.
Production of a Hydrocarbon Free Oxygen Stream
[0058] Turning now to FIGS. 10-11, there are shown partial
schematic diagrams of selected portions of the modified
distillation column system. Many of the features, components and
streams associated with the lower pressure column arrangement shown
in FIG. 10 and FIG. 11 are similar or identical to those described
above with reference to FIGS. 1-4 and for sake of brevity will not
be repeated here.
[0059] The key difference between the modified distillation column
systems shown in FIGS. 10-11 compared to the distillation column
systems shown in FIGS. 1-4 is the inclusion of a supplemental
oxygen column 600. The supplemental oxygen column 600 is configured
to produce a liquid oxygen product 610 substantially free of
hydrocarbons, preferably less than about 50 ppm hydrocarbon
impurities and more preferably less than or equal to about 10 ppm
hydrocarbon impurities.
[0060] Hydrocarbon impurities are generally introduced to the lower
pressure column of the distillation column system primarily through
the kettle liquid feed to the lower pressure column. All of the
hydrocarbons work their way down the lower pressure column with the
descending liquid where the hydrocarbons are concentrated. The
ascending vapor is in equilibrium with the descending liquid but
contains much lower concentrations of hydrocarbon impurities
because of the high relative volatilities. In fact, the ascending
vapor in the lower pressure column at the argon column takeoff
point generally contains only about 1 ppb of the heavy hydrocarbons
(i.e. heavier than methane) and about 4 ppm methane or other light
hydrocarbons. Given the low content of hydrocarbon impurities in
the ascending vapor in the lower pressure column, the vapor feed
from the intermediate location of lower pressure column to the
argon column also contains the same hydrocarbon impurity content as
the ascending vapor in the lower pressure column. Consequently, the
liquid streams in the argon column as well as the liquid stream
returned to the lower pressure column from the argon column are
also very low in hydrocarbon impurities.
[0061] In the embodiment illustrated in FIG. 10, the supplemental
oxygen column 600 is configured to receive a liquid stream 602,
enriched in oxygen, from the argon column 129 and rectify the
received oxygen enriched stream 602 to produce an oxygen enriched
overhead vapor stream 604 that is returned to the argon column and
a hydrocarbon-free oxygen liquid stream 610. The illustrated
supplemental oxygen column preferably has about 32 theoretical
stages of separation and is configured as a re-boiled oxygen
column. The reboiler 615 is disposed proximate the bottom of the
supplemental oxygen column and is configured to boil oxygen against
a stream of nitrogen 606 received from the higher pressure column
to produce an ascending oxygen vapor in the supplemental oxygen
column 600 and a condensed nitrogen stream 608. Condensed nitrogen
stream 608 is returned to the high pressure column. Alternatively,
a diverted stream of compressed and purified air may be used in
lieu of the nitrogen streams.
[0062] In the embodiment illustrated in FIG. 11, the supplemental
oxygen column 600 is configured to receive a liquid stream 612,
enriched in oxygen, from an intermediate location of the argon
column 129 and rectify the received oxygen enriched stream 612 to
produce an oxygen enriched overhead vapor stream 614 that is
returned to the argon column and a hydrocarbon-free oxygen liquid
stream 610. In the illustrated embodiment, oxygen enriched stream
612 is taken from a location about 8 stages from the bottom of the
argon column 129 and the oxygen enriched overhead vapor stream 614
is returned to an intermediate location of the argon column,
preferably the same location or just below the extraction point of
the oxygen enriched stream 612. As with the embodiment of FIG. 10,
this embodiment also has about 32 stages of separation and includes
reboiler 615 is disposed proximate the bottom of the supplemental
oxygen column and configured to boil oxygen against a stream of
nitrogen 606 received from the higher pressure column to produce an
ascending oxygen vapor in the supplemental oxygen column 600 and a
condensed nitrogen stream 608. As was the case for FIG. 10,
alternatively a diverted stream of compressed and purified air may
be used in lieu of the nitrogen streams.
[0063] In lieu of the separate stand-alone supplemental oxygen
column vessel as illustrated in FIGS. 10 and 11, contemplated
alternative arrangements include disposing or integrating the
supplemental oxygen column within the lower pressure column shell,
perhaps as a divided wall type column configuration such as an
annular divided column annular wall arrangement or a split divided
column annular wall arrangement in the lower portions of the column
shell. Alternatively, the supplemental oxygen column may be
combined or integrated with the argon column shell.
Super-Stage Argon Column with Reboiler
[0064] Turning now to FIG. 12 there is shown a schematic diagram of
a cryogenic air separation unit similar to those shown in FIGS. 1-4
but with a modified distillation column system. Many of the
features, components and streams associated with the distillation
column system arrangement shown in FIG. 12 are similar or identical
to those described above with reference to FIGS. 1-4 and for sake
of brevity will not be repeated here.
[0065] The key differences between the distillation column system
arrangement for a cryogenic argon and nitrogen producing air
separation unit shown in FIG. 12 compared to the lower pressure
column arrangements shown in FIGS. 1-4 are found in the super-stage
argon column arrangement where the argon rectifier produces
merchant grade argon directly from the columns. Specifically, the
key difference is the use of a reboiler 199 positioned at the base
of the argon super-stage column 129 to condense the argon column
feed stream. U.S. Pat. No. 5,305,611, the disclosure of which is
incorporated by reference herein, provides a similar super-stage
reboiling concept for an oxygen producing plant that uses a kettle
stream from the higher pressure column as the condensing medium in
the argon condenser in lieu of the oxygen enriched stream from the
lower pressure column.
[0066] The feed stream to the argon column 121 taken from the lower
pressure column 74 is substantially condensed within a reboiler 200
positioned at the base of the argon column 129, as shown in the
embodiment of FIG. 12. The condensed stream 201 exiting the
reboiler 200 is then depressurized in valve 198 and fed as stream
199 to an intermediate location of the argon column 129. In so
doing, the relative recovery of the argon column is increased. In
other words, a greater fraction of the argon contained in the feed
stream that is fed to the argon column is obtained as argon
product. Use of the reboiler at the base of the argon super-stage
column, reduces the net volume occupied by the argon column. While
the illustrated embodiment shows all of the condensed feed stream
being fed to the intermediate location of the argon column, it is
contemplated that a portion of this condensed feed stream may be
returned directly to the lower pressure column.
[0067] Mechanical pump 180 may be used to motivate the oxygen
liquid from the lower pressure column while pump 188 may be used to
motivate the argon depleted bottoms from the argon column to/from
the other columns. The argon depleted bottoms 123 of the argon
column may be directed via a pump to a location in the lower
pressure column below the argon column feed draw point. Although
not shown, pumps may also be used to split the argon column into
two or more sections as necessary to reduce the overall physical
height of the argon super-stage column. FIG. 12 also contemplates
the use of a waste nitrogen expansion cycle including the expansion
of a partially cooled waste nitrogen stream in turboexpander 193
and the resulting expanded stream 194 cooled in a separate passage
of the main heat exchanger 52 to yield the warmed waste nitrogen
stream 191 in lieu of combining the waste nitrogen stream with the
waste oxygen stream into a single waste stream as shown in FIGS.
1-4.
[0068] While the present enhancements has been described with
reference to a preferred embodiment or embodiments, it is
understood that numerous additions, changes and omissions can be
made without departing from the spirit and scope of the present
inventions as set forth in the appended claims.
* * * * *