AU643232B2 - Cryogenic air separation process and apparatus - Google Patents

Cryogenic air separation process and apparatus Download PDF

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Publication number
AU643232B2
AU643232B2 AU62375/90A AU6237590A AU643232B2 AU 643232 B2 AU643232 B2 AU 643232B2 AU 62375/90 A AU62375/90 A AU 62375/90A AU 6237590 A AU6237590 A AU 6237590A AU 643232 B2 AU643232 B2 AU 643232B2
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Prior art keywords
pressure column
oxygen
nitrogen
feed air
low pressure
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AU6237590A (en
Inventor
Bao V. Ha
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Liquid Air Engineering Corp Canada
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Liquid Air Engineering Corp Canada
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes 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
    • F25J3/04—Processes 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
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284—Generation 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
    • F25J3/04309—Generation 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 nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes 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
    • F25J3/04—Processes 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
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284—Generation 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
    • F25J3/0429—Generation 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
    • F25J3/04303—Lachmann expansion, i.e. expanded into oxygen producing or low pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes 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
    • F25J3/04—Processes 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
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04284—Generation 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
    • F25J3/04321—Generation 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 oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes 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
    • F25J3/04—Processes 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
    • F25J3/04406—Processes 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
    • F25J3/04424—Processes 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 without thermally coupled high and low pressure columns, i.e. a so-called split columns
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/20—Processes or apparatus using separation by rectification in an elevated pressure multiple column system wherein the lowest pressure column is at a pressure well above the minimum pressure needed to overcome pressure drop to reject the products to atmosphere
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/50—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column
    • F25J2200/54—Processes or apparatus using separation by rectification using multiple (re-)boiler-condensers at different heights of the column in the low pressure column of a double pressure main column system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2215/00—Processes characterised by the type or other details of the product stream
    • F25J2215/50—Oxygen or special cases, e.g. isotope-mixtures or low purity O2
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2240/00—Processes or apparatus involving steps for expanding of process streams
    • F25J2240/40—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
    • F25J2240/42—Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval the fluid being air

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Emergency Medicine (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Description

AUSTRALIA
Patents Act 2 COMPLETE SPECIFICATION
(ORIGINAL)
Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: C 1* Applicant(s): Liquid Air Engineering Corporation 1155, rue Sherbrooke Ouest, Montreal H3A 1H8. CANADA Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Complete Specification for the invention entitled: CRYOGENIC AIR SEPARATION PROCESS AND APPARATUS Our Ref 182496 POF Code: 1290/120218 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 6006 6006 la
TITLE:
CRYOGENIC AIR SEPARATION PROCESS AND APPARATUS TECHNICAL FIELD OF THE INVENTION This invention relates to the field of air separation processes and particularly to a process and apparatus for the production of nitrogen, oxygen and/or argon from air wherein liquefied air is used as the heat exchange medium for the high pressure column condenser to provide an energy efficient process.
BACKGROUND ART Standard cryogenic air separation processes involve filtering of feed air to remove particulate matter followed by compression of the air to supply energy for separation. Generally the feed air stream is then cooled and passed through absorbents to remove contaminants such as carbon dioxide and water vapor. The resulting stream is subjected to •cryogenic distillation.
Cryogenic distillation or air separation includes feeding the high pressure air into one or more separation columns which are operated at cryogenic temperatures whereby the air components including oxygen, nitrogen, argon, and the rare gases can be separated by distillation.
Cryogenic separation processes involving vapor and liquid 5* contact depend on the differences in vapor pressure for the respective components. The component having the higher vapor pressuce, meaning that it is more volatile or lower boiling, has a tendency to concentrate in the vapor phase. The component having the lower vapor pressure meaning that it is less volatile or higher boiling tends to concentrate
S
in the liquid phase.
The separation process in which there is heating of a liquid mixture to concentrate the volatile components in the vapor phase and the less volatile components in the liquid phase defines distillation.
Partial condensation is a separation process in which a vapor mixture is cooled to concentrate the volatile component or components in the vapor phase and at the same time concentrate the less volatile component or components in the liquid phase.
A process which combines successive partial vaporizations and condensations involving countercurrent treatment of the vapor in liquid phases is called rectification or sometimes called continuous distillation. The countercurrent contacting of the vapor and liquid phases is adiabatic and can include integral or differential contact between the phases.
Apparatus used to achieve separation processes utilizing the principles of rectification to separate mixtures are often called rectification columns, distillation columns, or fractionation columns.
When used herein and in the claims, the term "column" designates a distillation or fractionation column or zone. It can also be described as a contacting column or zone wherein liquid or vapor phases are countercurrently contacted for purposes of separating a fluid mixture. By way of example this would include contacting of the vapor and liquid phases on a series of vertically spaced trays or plates which are often perforated and corrugated and which extend crosswise of the column, perpendicular to the central axis. In place of the trays or plates there can be used packing elements to fill the column.
"Double column" as used herein refers to a higher pressure column having its upper end in heat exchange relation with the lower end of a lower pressure column.
The term "a standard air separation process or apparatus" as used herein is meant to describe that process and apparatus as above described as well as other air separation processes well known to those skilled in the art.
As used herein and in the appended claims, the term "indirect heat exchange" means the bringing of two fluid streams into heat exchange relation without any physical contact or intermixing of the fluids with each other.
Historically, nitrogen, oxygen and/or argon have been produced by one of two basic process schemes including the single column process and the double column process.
With respect to nitrogen, the single column process produces good quality gaseous and liquid nitrogen at pressures of approximately 6-10 bar. The recovery of nitrogen is limited by the equilibrium at the bottom of the column. Typically, the process can produce nitrogen at a rate of approximately 50-60% of the nitrogen in the initial air feed.
With the double column process, nitrogen is produced at pressures of about 1-4 bar. It is more efficient than the single column process, and approximately 90% or more of nitrogen can be recovered from the nitrogen present in the initial air feed. Typically the columns are stacked with a condenser-reboiler separating the two columns. Since the process produces nitrogen at relatively low pressures, further compression of nitrogen is frequently needed adding to the cost of production and use.
In the prior art double column process, air is separated by cryogenic distillation or rectification to produce a nitrogen-rich stream or fraction at the top of the high pressure column and oxygen-rich stream or fraction at the bottom. The nitrogen-rich stream S. is sent to the top of the low pressure column to provide the reflux for this column. The bottom oxygen-rich stream is fed to the low pressure column for further separation.
In the low pressure column the feed stream is further separated by cryogenic distillation into an oxygen-rich stream or fraction at the bottom and a nitrogen-rich stream or fraction at the top. The top stream can then be recovered as nitrogen product. In the double column arrangement, the high pressure column and the low pressure column are thermally linked through the condenser-reboiler arrangement. Thus, in the prior art double column process the nitrogen-rich fraction of the high pressure column is condensed against the vaporizing oxygen-rich fraction of the low pressure column.
For a given pressure in the low pressure column, the pressure of the air feed to the high pressure column is dictated by the composition of the vaporizing oxygen-enriched stream, the temperature difference of the high pressure column condenser and the low pressure column reboiler, and to some extent the composition of the condensing nitrogen-enriched stream which is relatively pure in nitrogen.
Other prior art process schemes are variations of the above described single or double column process with additional features such as an additional overhead condenser or bottom reboiler.
SUMMARY OF THE INVENTION The process of the invention can be utilized for the energy efficient production of nitrogen, oxygen and argon.
Essentially, the invention lies in using vaporized and liquefied air as the heating and cooling medium between the high pressure and the low pressure columns. Formerly nitrogen has been used.
The invention will be explained in particular detail with respect to nitrogen but it should be understood that the invention is equally applicable to the production of oxygen and argon. It will be obvious to those skilled in the art how to optimize temperature, pressure and other operating conditions to optimize output of oxygen and/or argon as primary product.
The particular advantage in the use of air for the heating and cooling medium is that less energy is required to condense the air than to condense a nitrogen rich stream. Since the main energy cost involves o compression of the gases, the lower pressure which is required to condense air at a given temperature is less costly than to condense .fe' nitrogen.
For example, nitrogen condenses at 7 bar pressure at -180 0
C.
By contrast, only 6 bar pressure at -178 0 C is required to condense air.
Thus the 2 0 C difference in temperature and the 1 bar pressure provides the reduced energy expenditure in the invention process.
In prior art processes wherein nitrogen is used for the heating and cooling medium between the high pressure and low pressure columns, it is necessary to compress the feed air to a higher feed air pressure as required by the nitrogen. Thus, the primary energy savings come from the reduced requirement for compression of the feed air.
The process of the invention makes possible the production of high purity nitrogen to the extent of more than 90% of the nitrogen contained in the initial feed air. It can be produced at a pressure range within about 3 bar to about 15 bar. Both high pressure and low pressure nitrogen can be produced. This can be done separately or together. Moreover, the process is energy efficient compared with prior art processes.
5 According to the invention process, feed air, which has been treated to remove moisture and impurities such as
CO
2 and methane by passage through molecular sieves, alumina, silica gel and the like is compressed and fed to a heat exchanger to exchange heat with outgoing products. In particular, the invention provides a cryogenic process for producing nitrogen from air including: dividing cooled compressed feed air substantially free of moisture and impurities into a first feed air fraction and a second feed air fraction; feeding said first feed air fraction into a high pressure column equipped with a top condenser; separating said first feed air fraction within said high pressure column by cryogenic distallation into a first nitrogen-rich fraction and a first oxygen-rich fraction; withdrawing at least a portion of said first oxygenrich fraction from said high pressure column; introducing at least a portion of, said first oxygenrich fraction into a low pressure column equipped wiLh a bottom condenser/reboiler and an overhead evaporator/ condenser for cryogenic separation into a second nitrogen-rich fraction and a second oxygen-rich fraction; introducing said second feed air fraction into said condenser/reboiler in said low pressure column; condensing said second feed air fraction by indirect heat exchange with said second oxygen-rich fraction in said low pressure column thereby vaporizing at least a portion of said second oxygen-rich fraction; introducing at least a portion of said condensed 30 second feed air fraction into said top condenser of said high pressure column; vaporizing at least a portion of said second condensed feed air fraction within said top condenser of said high pressure column by indirect heat exchange with at least a portion of said first nitrogen-rich fraction in said high pressure column to condense at least a portion of said first nitrogen-rich fraction; introducing into said low pressure column at least a 9 1 portion of said second feed air fraction vaporized by
II
*5
C
4* 4 4 *44 4 3 i
I*-
indirect heat exchange contact with said first nitrogen-rich fraction in said top condenser of said high pressure column for cryogenic separation together with at least a portion of said first oxygen-rich fraction into a second nitrogen-rich fraction and a second oxygen-rich fraction; removing at least a portion of said second nitrogenrich fraction as low pressure nitrogen product from said low pressure column; withdrawing at least a portion of said condensed second oxygen-rich fraction from said low pressure column; introducing at least a portion of said withdrawn oxygen-rich fraction into said overhead condenser of said low pressure column; vaporizing at least a portion of said second oxygenrich fraction in said overhead condenser by indirect heat exchange with at least a portion of said second nitrogenrich fraction within said low pressure column thereby causing said second nitrogen-rich fraction to be condensed and providing reflux for said low pressure column; and withdrawing at least a portion of said vaporized second oxygen-rich fraction from said overhead condenser as waste oxygen.
int According to another embodiment, the feed air is split into three fractions. Two of the feed air fractions are fed 25 to the high pressure column and the condenser/reboiler at S. the base of the low pressure column as above described. The third air fraction is expanded to provide plant cooling and then introduced into the low pressure column for cryogenic separation.
30 According to a further embodiment, part of the condensed nitrogen-rich fraction in the high pressure column is separated and fed to the low pressure column to provide extra reflux. At the same time the second feed air fraction which has been vaporized by indirect heat exchange contact with nitrogen in the top condenser of the high pressure column is then introduced into the low pressure column for cryogenic separation.
Within the low pressure column, the second feed air 77L U, fraction 13~ .E along with a portion of the first oxygen-rich fraction from the high pressure column are then separated into a second nitrogen-rich stream and a second oxygen-rich stream.
According to another embodiment, a portion of the second nitrogen-rich stream can be removed as high pressure nitrogen product while the remaining portion is used to provide reflux for the low pressure column.
According to another embodiment, a portion of the high pressure nitrogen product can be expanded to provide plant cooling and added to the low pressure nitrogen product stream.
The second oxygen-rich stream which falls to the bottom of the low pressure column is vaporized by indirect heat exchange contact with the incoming second feed air fraction which is thereby condensed. By another embodiment, the second oxygen-rich fraction can also include a third feed air fraction which has been expanded prior to being introduced into the low pressure column.
A portion of the second oxygen-rich stream is fed to the overhead condenser of the low pressure column where it is vaporized by heat exchange contact with rising nitrogen which is thereby condensed.
The thus vaporized second oxygen-rich stream can be removed from the overhead condenser as waste and warmed in subcoolers and in the heat 'exchanger by indirect heat exchange with process streams and feed air.
If desired the waste oxygen can be expanded to provide plant cooling. Alternately, the waste oxygen which has about 70% purity can be utilized as product in applications where high purity oxygen is not required.
Apparatus for the above described process are also provided.
The apparatus !Aud in combination, air compression means for compressing air from an outside source, purification means for removing carbon dioxide and water vapor from the air compressed by the air compression means, and heat exchange means for cooling the compressed air from the purification means to a cryogenic temperature, A first distillation column equipped with a top column or overhead evaporator/condenser is included for cryogenic separation of a portion S 'N of the feed air from the heat exchanger.
7 A second distillation column equipped with a top column condenser and a bottom column reboiler is provided for separation by fractionation of at least a portion of the cooled compressed feed air after circulation through the bottom column reboiler of the second distillation column and the top column condenser of the first distillation column together with at least a portion of the oxygen-rich liquid obtained from the first distillation column into a second oxygen-rich fraction and a second nitrogen-rich fraction.
Means are provided for withdrawal of oxygen liquid at the base of the second distillation column for introduction into the overhead condenser of the second distillation column to provide indirect heat exchange with vapors rising within the second distillation column.
Expansion means are provided for expansion of compressed air prior to introduction in the second distillation column, of oxygen withdrawn from the overhead condenser of the second distillation column, and/or for expansion of nitrogen product to provide cooling.
In particular the invention provides apparatus for producing nitrogen from cooled condensed feed air including: a high pressure distillation column equipped with a top condenser for cryogenic separation by fractionation of cooled compressed feed air into a first nitrogen-rich i 25 fraction and a first oxygen-rich fraction; a low pressure distillation column with an overhead condenser and a bottom reboiler for separation by S: fractionation of cooled compressed feed air and at least a portion of said first oxygen-rich fraction to produce second 30 nitrogen-rich and oxygen--ich fractions; conduit means for supplying cooled compressed feed air to said reboiler; conduit means for transferring said portion of said first oxygen-rich fraction from said high pressure column to 35 said low pressure column for cryogenic separation therein; conduit means for transferring condensed feed air from said reboiler to said top condenser; conduit means for transferring vaporized air from said 3 top condenser to said low pressure column;
V."
7qcconduit means for withdrawal of said second oxygenrich fraction as waste oxygen following vaporization of said second oxygen-rich fraction in said overhead condenser and conduit means for withdrawal of said second nitrogen-rich fraction from said low pressure column as a product, characterized in that said apparatus further includes: conduit means for introducing cooled compressed feed air directly into said high pressure column.
BRIEF DESCRIPTION OF THE DRAWING Figure 1 shows a schematic flow diagram of the process and apparatus of the invention in which low pressure nitrogen is produced; Figure 2 shows a schematic flow diagram of the process and apparatus of the invention similar to Figure 1 except that air expansion is provided in place of waste expansion; Figure 3 shows a schematic flow diagram of the process and apparatus of the invention wherein high pree~ure and low pressure nitrogen are produced; and, Figure 4 shows a schematic flow diagram of the process and apparatus of the invention similar to Figure 3 wherein part of the high pressure nitrogen is expanded to low pressure nitrogen.
DETAILED DESCRIPTION OF THE INVENTION Referring now to the flow diagram of Figure 1, compressed feed air free of impurities is introduced by means of conduit 20 into a heat e 4 4 4 exchanger 30. The air is preferably introduced into the heat exchanger at a pressure in the range of about k bar to about 20 bar where the temperature of the air is cooled to cryogenic temperature by indirect heat exchange with outgoing waste and product streams.
Next the feed air is split into two fractions. Good results have beer obtained with equal fractions or streams of feed air but other ratios can be used. The first fraction of the feed air is sent to the high pressure column 32 through lines 22 and 62 and the remaining second fraction of feed air is sent to the reboiler 58 of the low pressure column 34 through lines 22 and At the high pressure column 32 the pressure is preferably in the range of about Ikbar to 20 bar.
The first feed air fraction is introduced into the lower part of column 32 below the bottom distillation tray as indicated at 36.
Here, the first feed air fraction is separated into a first nitrogen-rich vapor fraction which rises to the top of the column 32 and a first oxygen-rich liquid fraction which falls to the bottom of the column 32.
4 At least a portion of the first oxygen-rich liquid is withdrawn from the bottom of the high pressure column at 38. It is comprised of about 35% to about 40% oxygen which is about the same proportion as for the prior art processej.
The first oxygen-rich liquid which is removed from the bottom of the high pressure column 32 through line 54 is passed through subcooler 46 where the temperature is further reduced by indirect heat exchange with product nitroqen which exits from the upper part of the low pressure column 34 through line 48 and with waste which exits through line 52 from the )verhead condenser/evaporator 70 of the low pressure column 34.
The cooled first oxygen rich liquid from the subcooler 46 is then introduced into the low pressure column 34 above the bottom tray after expansion through valve 76.
The second feed air fraction which enters the condenser/reboiler 58 in the base of the low pressure column 34 is condensed by indirect heat exchange with oxygen-rich liquid at the bottom of the low pressure column 34. This causes the second feed air fraction to be condensed and the oxygen-rich liquid to be vaporized.
The condensed second feed air fraction leaves the condenser/reboiler 58 of the low pressure column 34 via line 82 where it enters subcooler 46. The liquefied air exits subcooler 46 via line 84 and expands through valve 44 into the condenser/reboiler 40 of the high pressure column 32. If needed, a portion of the condensed second feed air fraction can be introduced into the low pressure column 34 via line after expansion through valve 92 to control the balance of air between the high pressure and low pressure columns.
The first nitrogen-rich vapor fraction rises to the top of the high pressure column 32 where it enters the condenser/reboiler 40. Here the nitrogen vapor is brought into indirect heat exchange contact with the condensed second feed air fraction which enters through valve 44 from the condenser/reboiler 58 of the low pressure column 34. This causes the liquefied air to vaporize and the nitrogen vapor to be condensed. As shown in Figures 3 and 4, part or all of the condensed nitrogen portion is returned to the high pressure column 32 to provide reflux as required.
Any nitrogen vapor which is not condensed by indirect heat exchange with the condensed second feed air fraction can be recovered as high pressure nitrogen by removal from the upper part of the high pressure column 32 for example, through line 67 as shown in Figure 3.
Part of the condensed nitrogen can be sent to the low pressure column 34 for extra reflux if the high pressure nitrogen flow is small or not needed. This part of the condensed nitrogen is removed from the upper part of the high pressure column 32 through line 68 as shown in Fiqures 1 and The condensed nitrogen is then passed through subcooler 66 where it is brought into indirect heat exchange contact with outgoing nitrogen product and waste. From the subcooler 66, the condensed nitrogen passes through a continuation of line 68 and is introduced into the low pressure column 34 after expansion through valve 78.
At the same time, the vaporized air exitirg via line 56 from the condenser/reboiler 40 at the top of the high pressure column 32 is separated by introduction into the low pressure column 34 through line 64 at about the same level as for the introduction of the first oxygen-rich liquid which enters through line 54.
The first oxygen-rich liquid withdrawn from the base of column 32 and the vaporized air withdrawn from the condenser/reboiler 40 at the top of the high pressure column 32 through line 56 a-e further separated within column 34 into a second nitrogen-rich vapor fraction and a second oxygen-rich fraction.
The second nitrogen-rich vapor fraction rises to the top of the low pressure column 34 while the second oxygen-rich fraction falls to the bottom of the low pressure column 34.
A portion of the second oxygen-enriched liquid fraction at the bottom of the low pressure column 34 is withdrawn through line 74 and passed through a first subcooler 46. Here the second oxygen-enriched liquid is further cooled by indirect heat exchange with nitrogen gas removed from the upper part of the low pressure column 34 through line 48 and with the waste stream exiting through line 52 from the overhead *condenser 70 of the low pressure column 34.
S" The second oxygen-enriched liquid is passed by means of a continuation of line 74 to a second subcooler 66 for further cooling by indirect heat exchange with nitrogen gas removed from the top of the high pressure column 32 through line 68 and with the waste oxygen stream which exits from the overhead condenser 70 through line 52.
*4 The resulting cooled second oxygen-rich liquid is passed through an extension of line 74 where the liquid is introduced into the overhead condenser 70 in the top of the low pressure column 34 after expansion through a valve 72 to further cool the second oxygen enriched stream.
A major part of the second nitrogen-rich stream is recovered as nitrogen product from the upper part of the low pressure column 34 through line 48. The gaseous nitrogen stream is warmed by passage through subcoolers 66 and 46 and heat exchanger 30 before exiting the system.
The remaining portion of the second nitrogen-rich stveam within the low pressure column 34 is condensed by heat excha, ge with the second oxygen-enriched liquid in the overhead evapora,:or/condenser 70 of the low pressure column 34 which causes the second oxygen-enriched liquid to 11 be vaporized. The condensation of the nitrogen provides reflux for the low pressure column 34. The vaporizing oxygen-enriched liquid exits overhead evaporator/condenser 70 via line 52 and is subsequently warmed by passage through subcoolers 66 and 46 and heat exchanger After warming in the heat exchanger 30, the waste oxygen stream is passed through a turbo expander 78 where the stream can be expanded to provide plant cooling.
it can seen that the above described process utilizes air as a heating and cooling medium between the high pcessure and low pressure columns. Conventionally in prior art processes, the nitrogen-rich stream has been used to transfer heat to the bottom of the low pressure column. Keeping in mind that for a given nitrogen recovery, that is, having the same composition of oxygen-rich stream, more energy is required to condense the nitrogen-rich stream than to condense air.
what this means is that for a given nitrogen recovery, using air as thle heat transfer medium, the high pressure column can function at a lower pressure than for conventional prior art processes. Also, for th.4. same pressure in the high pressure column, according to the invention process, the low pressure column can function at a higher pressure.
4 4 044 4 4* 4.4 a. *9 a 44 4 a.
aa *4 4 4 Table 1 below shows the expected performance process shown in Figure 1 and above described for the nitrogen as product.
of the invention products of 494 4 S 'e.G a S .5 5 44.9 a *4 a
S
9**SS* a
S
Total Feed Air Flow Feed Air Pressure Nitrogen Product Flow Nitrogen Pressure Nitrogen Purity Waste (oxygen-Rich) Flow Waste Pressure Compressed Air Column 32 Column 32 Column 32 oxygen-Rich Liquid Condensed Second Feed Air Fraction Table 1 Line 20 Line 20 Line 48 Line 18 Line 52 Line 16 Line 22 Top Bottom Line 38 15462 Nm 3 /h 10.2 bar abs.
10514 Nm 3 /h 5.5 bar abs.
18 vpm 02 4948 Nm 3 /'h 1.3 bar abs.
-1600 c 10.2 bar abs.
-170o C -160o C -165.6 0
C
Line 82 Li 82-167. 5 0
C
12 Table I continued Condensed Second Feed Air Fraction Line 82 Condensed Second Feed Air Fraction Line 84 Vaporized Second Feed Air Fraction from Condenser/ Reboiler 40 Line 56 Nitrogen Exiting Column 32 Line 68 Condensed Nitrogen Exiting Subcooler 66 Line 68 Column 34 Oxygen-Rich Liquid from Column 34 Line 74 Oxygen-Rich Liquid Exiting from Cooler 66 Line 74 Oxygen-Rich Liquid after Expansion Valve 72 Nitrogen Product Exiting Column -167.50 C -171 C -172.6 0
C
-170.6 0 -174.4 0
C
5.5. bar abs.
-168.80 C -174.40 C -1790 C -177.6 C 5 bar abs.
-178.90 C 0464
S
:0.
*D S r S 0 0.
0 S4 045.
34 Nitrogen Product Exiting Column 34 Oxygen Waste Stream from Condenser 70 Line 48 Line 48 Line 52 When the embodiment shown in Figure 3 or Figure 4 is followed, a feed air pressure of 21 bar abs. would produce a pressure of about bar abs. within the high pressure column 32 and a pressure of about 14 bic abs. within the low pressure column 34.
Various modifications of the invention process and apparatus as above described will be apparent to those skilled in the art and can be resorted to without departing from the spirit and scope of the invention as defined by the following appended claims.
S
4* 5. 0

Claims (15)

  1. 2. A process as claimed in rlaim 1, further including: withdrawing at least a portion of said condensed first nitrogen-rich fraction from said high pressure column as high pressure nitrogen product.
  2. 3. A process as claimed in claim 1, further including: withdrawing at least a portion of said condensed first 25 nitrogen-rich fraction from said high pressure column; and, introducing at least a portion of said withdrawn condensed first nitrogen-rich fraction into said low 6 pressure column.
  3. 4. A process as claimed in one of claims 1 to 3, further including: fe afurther dividing said compressed feed air into a third feed air fraction; expanding at least a portion of said third feed air fraction to provide cooling; and, 35 introducing at least a portion of said expanded feed air fraction into said low pressure column. A process as claimed in claim 2, further including: expanding at least a portion of said waste oxygen 39 withdrawn from said overhead condenser to provide plant 15 cooling.
  4. 6. A process as claimed in claim 2, further including: expanding at least a portion of said high pressure nitrogen product prior to discharge with said low pressure nitrogen product.
  5. 7. A process as claimed in one of claims 2 to 6, further including: cooling said feed air by indirect heat exchange contact with at least one of said waste oxygen and high and low pressure nitrogen product streams; and compressing said feed air to provide a pressure in the high pressure column in the range of about 2 bar to abour bar.
  6. 8. A process as claimed in one of claims 1 to 7, wherein: said first feed air fraction in step is fed into the lower half of said high pressure column; and, said first oxygen-rich fraction in step is withdrawn from the base of said high pressure column.
  7. 9. A process as claimed in one of claims 1 to 8, wherein: said first oxygen-rich fraction of step is introduced into the lower half of said low pressure column; and said second oxygen-rich fraction of step is withdrawn from the base of said low pressure column. 25 10. A process as claimed in one of claims 1 to 9, further S. including: passing said waste oxygen obtained in step through i: a turbo expander to provide cooling; and warming said cooled waste oxygen from said turbo 30 expander by indirect heat exchange contact with feed air S which is thereby cooled.
  8. 11. Apparatus for producing nitrogen from cooled condensed. feed air including: a high pressure distillation column equipped with a S" 35 top condenser for cryogenic separation by fractionation of cooled compressed feed air into a first nitrogen-rich fraction and a first oxygen-rich fraction; a low pressure distillation column with an overhead 39 condenser and a bottom reboiler for separation by .4/ 16 fractionation of cooled compressed feed air and at least a portion of said first oxygen-rich fraction to produce second nitrogen-rich and oxygen-rich fractions; conduit means for supplying cooled compressed feed air to said reboiler; conduit means for transferring said portion of said first oxygen-rich fraction from said high pressure column to said low pressure column for cryogenic separation therein; conduit means for transferring condensed feed air from said reboiler to said top condenser; conduit means for transferring vaporized air from said top condenser to said low pressure column; conduit means for withdrawal of said second oxygen- rich fraction as waste oxygen following vaporization of said second oxygen-rich fraction in said overhead condenser and conduit means for withdrawal of said second nitrogen-rich fraction from said low pressure column as a product, characterized in that said apparatus further includes: conduit means for introducing cooled compressed feed air directly into said high pressure column.
  9. 12. Apparatus as claimed in claim 11, including means for ensuring total condensation of feed air introduced into said low pressure column.
  10. 13. Apparatus as claimed in claim 11 or 12, including conduit means for withdrawal of said first nitrogen-rich product from said high pressure column and introduction thereof into said low pressure column to provide reflux.
  11. 14. Apparatus as claimed in claims 11, 12 or 13, including: compression means for compressing feed air; 30 purification means for removing carbon dioxide, water vapour and other impurities from air compressed by said air compression means; heat exchange means for cooling the compressed air from said purification means to a cryogenic temperature; two 35 conduit means in communication with said overhead condenser for the introduction and withdrawal of liquids and vapors; conduit means in communication with said heat exchange 39 means and said high and low pressure column for the %c 17 introduction of cooled compressed feed air; and, valve means within at least one of said conduit means for metering of vapours and liquids and for expansion therethrough.
  12. 15. Apparatus as claimed in one of claims 11 to 14, further including: expansion means for expansion of at least a portion of nitrogen product to provide cooling.
  13. 16. Apparatus as claimed in one of claims 11 to further including: expansion means for expansion of oxygen waste.
  14. 17. Apparatus as claimed in one of claims 11 to 16, further including: expansion means for expansion of cooled compressed air prior to introduction into said low pressure column to provide cooling.
  15. 18. Apparatus as claimed in claim 11 substantially as hereinbefore described with reference to any one of the accompanying drawings. DATED: 13 August, 1993 LIQUID AIR ENGINEERING CORPORATION By their Patent Attorneys: PHILLIPS ORMONDE FITZPATRIC, e- r :00.0- 9 e* 39
AU62375/90A 1989-09-12 1990-09-11 Cryogenic air separation process and apparatus Ceased AU643232B2 (en)

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US5396269A (en) * 1991-02-20 1995-03-07 Hitachi, Ltd. Television telephone
US5257504A (en) * 1992-02-18 1993-11-02 Air Products And Chemicals, Inc. Multiple reboiler, double column, elevated pressure air separation cycles and their integration with gas turbines
US5251450A (en) * 1992-08-28 1993-10-12 Air Products And Chemicals, Inc. Efficient single column air separation cycle and its integration with gas turbines
US5251451A (en) * 1992-08-28 1993-10-12 Air Products And Chemicals, Inc. Multiple reboiler, double column, air boosted, elevated pressure air separation cycle and its integration with gas turbines
DE19819263C2 (en) * 1998-04-30 2003-08-21 Linde Ag Process and device for the production of pressurized nitrogen
EP2312247A1 (en) * 2009-10-09 2011-04-20 Linde AG Method and device for generating liquid nitrogen from low temperature air separation
EP3159648B1 (en) * 2015-10-20 2018-09-19 Linde Aktiengesellschaft Plate heat exchanger capacitor evaporator and method for cryogenic decomposition of air
WO2020074120A1 (en) * 2018-10-09 2020-04-16 Linde Aktiengesellschaft Method for obtaining one or more air products and air separation system
CN109297260A (en) * 2018-10-17 2019-02-01 浙江海天气体有限公司 A kind of full nitrogen space division waste gas recovering device processed

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US4530708A (en) * 1982-05-14 1985-07-23 Hitachi, Ltd. Air separation method and apparatus therefor
AU3469689A (en) * 1988-01-14 1990-11-29 Boc Group Plc, The Air separation

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WO1993013373A1 (en) 1993-07-08
DE69004647D1 (en) 1993-12-23

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