CA1280966C - Air separation process and apparatus for high argon recovery and moderate pressure nitrogen recovery - Google Patents

Air separation process and apparatus for high argon recovery and moderate pressure nitrogen recovery

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Publication number
CA1280966C
CA1280966C CA000595395A CA595395A CA1280966C CA 1280966 C CA1280966 C CA 1280966C CA 000595395 A CA000595395 A CA 000595395A CA 595395 A CA595395 A CA 595395A CA 1280966 C CA1280966 C CA 1280966C
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Prior art keywords
column
argon
richer
oxygen
vapor
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CA000595395A
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French (fr)
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Harry Cheung
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Union Carbide Corp
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Union Carbide Corp
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04412Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/04193Division of the main heat exchange line in consecutive sections having different functions
    • F25J3/04206Division of the main heat exchange line in consecutive sections having different functions including a so-called "auxiliary vaporiser" for vaporising and producing a gaseous product
    • F25J3/04212Division of the main heat exchange line in consecutive sections having different functions including a so-called "auxiliary vaporiser" for vaporising and producing a gaseous product and simultaneously condensing vapor from a column serving as reflux within the or another column
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/0429Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams of feed air, e.g. used as waste or product air or expanded into an auxiliary column
    • F25J3/04303Lachmann expansion, i.e. expanded into oxygen producing or low pressure column
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04642Recovering noble gases from air
    • F25J3/04648Recovering noble gases from air argon
    • F25J3/04654Producing crude argon in a crude argon column
    • F25J3/04666Producing crude argon in a crude argon column as a parallel working rectification column of the low pressure column in a dual pressure main column system
    • F25J3/04672Producing crude argon in a crude argon column as a parallel working rectification column of the low pressure column in a dual pressure main column system having a top condenser
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04642Recovering noble gases from air
    • F25J3/04648Recovering noble gases from air argon
    • F25J3/04654Producing crude argon in a crude argon column
    • F25J3/04709Producing crude argon in a crude argon column as an auxiliary column system in at least a dual pressure main column system
    • F25J3/04715The auxiliary column system simultaneously produces oxygen
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00Processes or apparatus using separation by rectification
    • F25J2200/08Processes or apparatus using separation by rectification in a triple pressure main column system
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00Processes or apparatus using separation by rectification
    • F25J2200/50Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2235/00Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/50Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being oxygen
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00Processes or apparatus involving steps for expanding of process streams
    • F25J2240/40Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00Details related to the use of reboiler-condensers
    • F25J2250/20Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S62/00Refrigeration
    • Y10S62/923Inert gas
    • Y10S62/924Argon

Abstract

Air Separation Process And Apparatus For High Argon Recovery And Moderate Pressure Nitrogen Recovery ABSTRACT

Process and apparatus to produce argon at high recovery with nitrogen at higher than conventional pressure comprising three columns wherein first column bottoms are passed into the second column, second column bottoms drive a third column top condenser, and argon-containing fluid is passed for separation into the third column from the second column at a point intermediate the points where first column bottoms enter and second column bottoms exit the second column.

Description

AIR SEPARATION PROCESS AND APPARATUS FOR HIGH ARGON
~ECOVERY ~ND MODERATE_PRESSURE NITROGEN RECOVERY
Technical Field This inven~ion relates generally to the cryogenic rectification of air and more par~icularly to the separation of air into its three major components.
Backqround Art The cryogenic separation of air is a well established industrial process. Cryogenic air separation involves the filtering of the feed air to remove particulate matter and compression of that clean air to supply the energy required for the separation. Following the air compression, the feed air ~tream is cooled and cleaned of the high boiling contaminants, such as carbon dioxide and water vapor, and then separated into its components by cryogenic distillation. The separation columns are operated at cryogenic temperatures to allow the gas and liquid contacting necessary for separation by distillation, and the separated products are then returned to ambient temperature conditions versus the cooling air stream, When argon recovery is desired in addition to separation of the air into nitrogen and oxygen, a commonly used system is one employing three columns wherein the air is separated into nitrogen and oxygen in the first two columns, a higher pressure and lower pressure column, which are generally in hea~ exchange relation at a main condenser, and wherein an argon containing stream is passed from ' .

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the lower pressure column into a third column for production o crude argon. A discussion of this conventional process is found in R.E. Latimer, "Distillation of Air", Chemical Engineering Progress, Volume 63, pages 35-59 (1967~.
The conventional three component air separation process is generally suitable for m~ny purposes but has a significant disadvantage if nitrogen recovery is desired at elevated pressure.
Of the three primary components of air, nitrogen is the most volatile, argon has intermediate volatility and oxygen is the least volatile. In order to enable high recovery of the individual components, the lower pressure column is operated at as low a pressure as possible, generally about 2 pounds per square inch (psi) a~ove atmospheric pressure. This low pressure enables ~he relative volatilities between argon and oxygen and between nitrogen and argon to be as large as possible thus maximizing the separation of the air into the three components.
If nitrogen at moderate pressure is desired, the lower pressure column could be operated at a pressure above the conventional low pressure.
However, this would result in a significant decrease in argon recovery hecause a significant amount of the argon would exit the process with the nitrogen rather than being passed to the crude argon column.
Moderate pressure nitrogen is b~coming in increasingly greater demand for such uses as blanketing, s~irring, and enhanced oil recovery.
Furthermore, production of moderate pressure nitrogen in conjunction with ar~on is increasing in ` ~'-' ' ` , '` . .' ' ' '' ` ~. ' :
-, . .

importance as oxygen-argon air separation plants, originally built for the steel industry, are experiencing reduced utilization.
It is therefore very desirable to have an air separation process which can produce nitrogen at higher than conventional pressures while also enabling high argon recovery.
Accordingly, it is an object of this invention to provide an air separation process and 10 apparatus for producing moderate pressure nitrogen while producing argon with high recovery.
SummarY of the Invention The above and other objects which will become apparent to one skilled in the art upon a 15 reading of this disclosure are attained by ~he present invention, one aspect of which is:
An air separation process comprising:
(A) introducing feed air into a first column operating at a pressure within the range of 20 from 60 to 300 psia and separating the feed within said first column into nitrogen-richer and oxygen-richer components;
(B) passing oxygen-richer and nitrogen-richer component from the first column into 25 a second column operating at a pressure less than that of the first column and within the range of from 20 to 90 psia, for separation into nitrogen-rich and oxygen-rich components;
(C) recovering nitrogen-rich component as ~ 30 moderate pressure nitrogen product;
- ~D) passing argon-containing fluid from an intermediate point of the second column into a third - , . , - .

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column and separating the argon-containing fluid within the third column into argon-richer vapor and oxygen-richer liquid:
~E~ recovering a first portion of the argon-richer vapor as crude argon product; and (F) condensing a second portion of the argon-richer vapor by indirect heat exchange with oxygen-rich component and passing resulting liquid down the third column as reflux liquid.
Another aspect of the present inve~tion is:
(A) a first column having feed introduction means;
~B) a second column having fluid recovery means;
(C) means to pass fluid from the first column into the second column;
(D) means to pass fluid from an intermediate point of the second column into a third column equipped with a top condenser and having fluid recovery means; and (E) means to pass fluid from the lower portion of the second column to the top condenser of the third column.
The term, "column", as used herein means a distillation or fractionation column or zone, i.e., a contacting colu~n or zone wherein liquid and vapor phases are countercurrently contacted to efect separation of a fluid mixture, as for example, by conta~ting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted - within the column or alternatively, on packing - elements with which the column is filled. For a ` , ~ .' ~ , ' ' ~ " ' '' ' ' ' ' ' . .
~ , , .

_ 5 further discussion of distillation columns see the Chemical ~ngineers' Mandbook. Fifth Edition, edited by R,H. Perry and C.H. Chilton, McGxaw Hill Book Company, New York, Section 13, "Distilla~ion" B.D.
Smith, et al., page 13-3 The Continuous Distillation Process. The term, double column is used to mean a higher pressure column having its upper end in heat exchange relation with the lower end of a lower pressure column. A further discussion of double columns appears in Ruheman ~The Separation of Gases~' Oxford University Press, 19~9, Chapter VII, Commercial Air Separation.
The term "indirect hea~ exchange", as used herein means the bringing of two fluid streams into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein, the term "reboiler" means a heat exchange device which generates column upflow vapor from column bottom liquid.
As used herein, the term "condenser" means a heat exchange device which generates column downflow liquid from column top vapor.
Brief DescriPtion of the Drawinqs Figure 1 is a schematic representation of one preferred embodiment of the invention wherein the argon-containing fluid is passed from the second column into the third column as a vapor.
Figure 2 is a schematic representation of one preferred embodiment of ~he invention wherein the argon-containing fluid is passed ~rom the second column into the third column as a liquid.

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~ 6 -Detailed Description The process and apparatus of the present invention will be described in detail with reference to the Drawings.
Referring now to Figure 1, cool, clean feed air 10 is is passed into first column 1 which is operating at a pressure within the range of from 60 to 300 pounds per square inch absolute (psia), preferably within the range of from 30 to ~50 psia.
Within first column 1 the feed is separated into nitrogen-richer and oxygen-richer components.
Oxygen-richer component is passed through conduit 21 and valve 50 into second column 2 which is operating at a pressure less than that of column 1 and within the range of from 20 to 90 psia, preferably within the range of from 20 to 60 psia, most preferably within the range of from 20 to 45 psia. Figure 1 illustrates a preferred embodiment wherein the first and second col D s are in heat exchange relation at main condènser 120 so as to form a double column.
In this arrangemen~ nitrogen-richer component 11 is passed as vapor to main condenser 120 and condensed by heat exchange with r~boiling second or lower pressure colu~n 2 bottoms . Optionally, a small, generally less than 15 percent, portion of stream ll may be removed from the column section and recovered as high pressure nitrogen product. The resulting condensed nitrogen richer component 12 is passed in part as stream 13 down column 1 as reflux and in part through conduit 22 and valve 51 into column 2.
If desired, additional feed air vapor 23, such as from a refrigeration-generating turbine expansion, may be added into second column 2.

:
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:
, Within col~n 2 the ni~rogen-richer and oxygen~richer componen~s and optional feed 23 are separated into nitrogen-rich and oxygen-rich components. Nitrogen-rich component 2~ is recovered from the upper portion of column 2 having a purity of at least 99.5 percent and at essentially the operating pressure of column 2. The percentages used herein are in mole percent unless otherwise specified. Small nitrogen waste stream 24 is also removed from column 2 for nitrogen puri~y control purposes.
Argon-containing fluid is passed as vapor from an intermediate point of column 2 though conduit 30 and into third column 3 having a top condenser 230 and which is operating at a pressure similar to that of column 2. The argon-containing fluid generally has an argon concentration within the range of from 8 to 20 percent, with the remainder comprised substantially of oxygen and with about 0.1 percent or less nitrogen. Within column 3 the argon-containing fluid is separated into argon-richer vapor and oxygen-richer liquid. A
first portion 32 of argon-richer vapor 31 is recovered as crude argon having an argon concentration generally within the range of from 95 to 99.5 percent. A second portion 33 of the argon-richer vapor is passed to top condenser 230 wherein it is condensed. Resulting liquid 34 is passed down column 3 as reflux. Oxygen-richer liquid is passed from the lower portion of column 3 as stream 35 into and down column 2.
Top condenser 230 is driven by vaporizing oxygen-rich component taken from the lower por~ion . ` : ~ , - ~ . . . .
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of lower pressure column 2. As shown in Figure 1, oxygen-rich component 40 is taken as liquid from column 2, expanded through valve 52 and passed into top condenser 230 wherein i~ vaporizes , at a temperature lower than the temperature at the bottom of column 2 due to its lower pressure, and condenses the argon-richer vapor 33. Depending on the pressure and elevation difference between the column 2 1iqui~ bottoms and the condensor 230 boiling side, the column 2 liquid bottoms pressure may be increased by liquid pump 100. Preferably s~ream 40 comprises at least ~0 percent of the oxygen product produced by the process.
The resulting vapor ~1 is passed out of the process and may be recovered as oxygen product 42.
Stream 40, prior to vaporization has an oxygen purity of at least 99 percent, preferably at least 99.5 percent. Conveniently stream 41 may be combined with oxygen stream 26 ~aken from column 2 ~0 and passed through valve 53 prior to recovery.
Oxygen stream 26 is employed for process control purposes and is typically within the range of from 3 to 10 percent, and preferably is about 5 percent, of the oxygen product 42. Optionally vapor stream 41 may be used to ~ubcool liquid s~ream 40 prior to the liquid expansion through valve 52 and the combination of stream 41 with stream 26.
The invention enables the recovery in -stream 32 of at least 70 percent and up to about 97 percent of the argon within the feed air while simultaneously enabling the recovery of high purity nitrogen at higher than conventional pressure. The invention accomplishes this very advantageous result ,, ~ ' : "
' .. ' ' '. . :
., '- :'. ' .. , ~, by driving the crude argon ~op condenser, not wi~h higher pressure column bottoms as with conven~ional processes, but with lower pressure column bottoms.
Since higher pressure column bottoms need not be used ~o drive condenser 230, a greater ~han conventional amount may be passed as stream 21 into the lower pressure column serving to favorably force argon downward toward ~he in~ermediate point from which argon-containing s~ream 30 is taken.
Essentially, the favorable effect on argon recovery is due to the added liquid downflow within the lower sections of col~mn 2.
Thus, in spite of the fact that the lower pressure column is operated at higher than conventional pressures thus making argon separation more difficult because of the reduction in relative vola~ilities, high argon production is achieved because the defined elements of the invention serve to drive argon out of the lower pressure column ~nd into the third column from which it is recovered as crude argon.
Generally more than 70 percent of the feed air introduced into the columns in stream 10 and optional stream 23 is recovered as high purity nitrogen in stream 25. Generally the vapor to liquid feed ratio for the lower pressure column, i.e. ths molar ratio of s~ream 23 ~o the combination of s~reams 21, 22 and 35 is less than 0.35 and preferably is within the range of from 0 to 0.15.
This further enables argon to be driven downward .. from the top portion of ~he lower pressure column where it would go with the nitrogen to ~h~

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intermediate point where it can be passed to the crude argon column.
As mentioned previously, the embodiment of the invsntion illustrated in Figure 1 is preferred when ~he argon-containing fluid is passed from the second to the ~hird column as vapor. When ~his fluid is passed as liquid, the embodiment of the invention illustrated in Figure 2 is preferred. The numerals of Figure 2 correspond to those of Figure 1 for the common elements and for the sake of simplicity only those aspects which differ from the previously discussed embodiment will be discussed in detail.
In the embodiment illustrated in Figure 2, third column 3 m~y be, and preferably is, operated at a pressure less ~han that of the lower pressure column 2. Argon-containing fluid is passed as liquid through conduit 30 and valve 54 into third column 3 wherein it is separated into argon-richer vapor and`oxygen-richer liquid. Column 3 additionally comprises bottom reboiler 130 which serves to reboil the column bot~oms to generate vapor upflow. Reboiler 130 is driven by a portion 14 of nitrogen-richer component 11 which condenses to effect the reboiling. The resulting condensed portion 15 is combined with stream 12 and passed into either column ~ as part of stream 22 or column 1 as part of stream 13. Oxygen-rich component is first expanded through valve 36 prior to passage to top condenser ?30. Finally, oxygen-rich liquid 35 - taken from the low~r portion of col~mn 3 is not passed into column 2 but rather i5 passed into the :. . . . : -, . - ' ,: ' , . . . . .

oxygen-rich component stream 40 downstream o valve 36 and upstream of pump lO0.
As can be seen, the liquid feed embodiment illustrated in Figure 2 retains the essential S elements of the invention whereby argon is driven out of column 2 and into column 3 despite ~he higher than conventional pressures at which column 2 is operated.
In Table 1 there is tabulated the results lQ of a computer simulation of the invention carried out with the embodiment illustrated in Figure 1 The stream numbers of Table 1 correspond to those of Figure 1, flow is reported in cubic feet per hour at normal temperature and pressure, pressure is in psia, temperature is in degrees Kelvin, and composition is in mole percent unless otherwise indicated. The vapor to liquid feed ratio to column 2, i.e. to mole ratio of stream 23 to ~he total of streams 21,22 and 35 was 0.065. The oxygen recovery was 99.9 percent, the nitrogen recovery was 94.6 percent and the argon recovery was 92.7 percent.
Blank spaces in the 'rable 1 indicate that the data was not available.

COMPOSI T ION
2 5 STREAM No. FLOW PRESSURE IE~ OXYGEN ARGON NITRoGEN
92.7 117.9 109.3 23 7,3 30.4 95.3 Ai r Feed 100 21,0 0.9 78.1 21 52.9 117.9 22 39.7 115.3 2 ppm 189 ppm 99.88 20.2 31.4 97.6 84.S0 15.45 0.05 - 35 19.3 31.4 97.6 73.9 27.7 83.2 1 ppm >99.98 ~ 32 0.9 27.3 93.6 1.9 97.3 0.8 42 21.0 lB.2 92.6 99.75 0.25 0 -' ' : ~ ' :
, ~ - ', ' :
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Now by the use of the present invention one can simultaneously produce high puri~y nitrogen at moderate pressure and crude argon wi~h high recovery.
Although the present invention has ~een discussed in de~ail with reference to two specific preferred embodiments, those skilled in ~he art will recognize that there are additional embodiments of the invention within the spirit and scope of the claims.

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Claims (20)

  1. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
    An air separation process comprising:
    (A) introducing feed air into a first column operating at a pressure within the range of from 60 to 300 psia and separating the feed within said first column into nitrogen-richer and oxygen-richer components;
    (B) passing oxygen-richer and nitrogen-richer component from the first column into a second column operating at a pressure less than that of the first column and within the range of from 20 to 90 psia, for separation into nitrogen-rich and oxygen-rich components;
    (C) recovering nitrogen-rich component as moderate pressure nitrogen product;
    (D) passing argon-containing fluid from an intermediate point of the second column into a third column and separating the argon-containing fluid within the third column into argon-richer vapor and oxygen-richer liquid;
    (E) recovering a first portion of the argon-richer vapor as crude argon product; and (F) condensing a second portion of the argon-richer vapor by indirect heat exchange with oxygen-rich component and passing resulting liquid down the third column as reflux liquid.
  2. 2. The process of Claim 1 wherein nitrogen-richer component from the first column is condensed to vaporize oxygen-rich liquid, a first part of the resulting nitrogen-richer component is passed into the first column and a second part is passed into the second column.
  3. 3. The process of Claim 1 further comprising introduction of feed vapor into the second column.
  4. 4. The process of Claim 1 wherein the molar ratio of the vapor to liquid feeds into the second column is less than 0.35.
  5. 5. The process of Claim 1 wherein the moderate pressure nitrogen product is recovered at a purity of at least 99.5 percent.
  6. 6. The process of Claim 1 wherein the crude argon product comprises at least 70 percent of the argon in the feed air.
  7. 7. The process of Claim 1 wherein the argon-containing fluid is passed from the second column into the third column as vapor.
  8. 8. The process of Claim 7 further comprising passing oxygen-rich liquid from the lower portion of the third column into the second column at an intermediate point of the second column.
  9. 9. The process of Claim 1 wherein the argon-containing fluid is passed from the second column into the third column as liquid.
  10. 10. The process of Claim 9 wherein the third column is operated at a pressure less than that at which the second column is operated.
  11. 11. The process of Claim 9 further comprising passing oxygen-rich liquid from the lower portion of the third column into heat exchange relation with argon-richer vapor.
  12. 12. The process of Claim 9 further comprising reboiling oxygen-rich liquid at the bottom of the third column by indirect heat exchange with condensing nitrogen-richer component from the first column.
  13. 13. The process of Claim 1 further comprising recovery of oxygen as product.
  14. 14. The process of Claim 13 wherein the product oxygen is taken from either or both of (a) the oxygen-rich component which serves to condense argon-richer vapor, or (b) the second column.
  15. 15. Apparatus for air separation comprising:
    (A) a first column having feed introduction means;
    (B) a second column having fluid recovery means;
    (C) means to pass fluid from the first column into the second column;
    (D) means to pass fluid from an intermediate point of the second column into a third column equipped with a top condenser and having fluid recovery means; and (E) means to pass fluid from the lower portion of the second column to the top condenser of the third column.
  16. 16. The apparatus of Claim 15 further comprising a main condenser within the lower portion of the second column, means to pass vapor from the upper portion of the first column to the main condenser, and means to pass liquid from the main condenser to the upper portion of the first column.
  17. 17. The apparatus of Claim 15 further comprising means to pass fluid from the lower portion of the third column into the second column at an intermediate point of the second column.
  18. 18. The apparatus of Claim 15 further comprising means to pass fluid from the lower portion of the third column to the top condenser.
  19. 19. The apparatus of Claim 18 further comprising a reboiler in the lower portion of the third column, means to pass vapor from the upper portion of the first column to the reboiler, and means to pass liquid from the reboiler to the upper portion of the first column.
  20. 20. The apparatus of Claim 15 further comprising means to introduce vapor feed into the second column.
CA000595395A 1988-06-02 1989-03-31 Air separation process and apparatus for high argon recovery and moderate pressure nitrogen recovery Expired - Lifetime CA1280966C (en)

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US203,264 1988-06-02
US07/203,264 US4822395A (en) 1988-06-02 1988-06-02 Air separation process and apparatus for high argon recovery and moderate pressure nitrogen recovery

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CN1046034A (en) 1990-10-10
CN1019689B (en) 1992-12-30
US4822395A (en) 1989-04-18
MX165349B (en) 1992-11-05
GB2219385B (en) 1992-09-16
GB8907259D0 (en) 1989-05-17
GB2219385A (en) 1989-12-06
BR8901507A (en) 1990-09-04

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