CN112710125A - Method and apparatus for separating air by cryogenic distillation - Google Patents

Method and apparatus for separating air by cryogenic distillation Download PDF

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Publication number
CN112710125A
CN112710125A CN202011154571.2A CN202011154571A CN112710125A CN 112710125 A CN112710125 A CN 112710125A CN 202011154571 A CN202011154571 A CN 202011154571A CN 112710125 A CN112710125 A CN 112710125A
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Prior art keywords
column
oxygen
argon
rich
liquid
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CN202011154571.2A
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Chinese (zh)
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B·德蒙莱恩斯
P·勒博特
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Publication of CN112710125A publication Critical patent/CN112710125A/en
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    • 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
    • F25J3/04642—Recovering noble gases from air
    • F25J3/04648—Recovering noble gases from air argon
    • F25J3/04654—Producing crude argon in a crude argon column
    • F25J3/04709—Producing crude argon in a crude argon column as an auxiliary column system in at least a dual pressure main column system
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    • 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
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    • 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
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    • F25J2220/50—Separating low boiling, i.e. more volatile components from oxygen, e.g. N2, Ar
    • 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
    • F25J2235/00—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams
    • F25J2235/58—Processes or apparatus involving steps for increasing the pressure or for conveying of liquid process streams the fluid being argon or crude argon
    • 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
    • F25J2240/02—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
    • F25J2240/10—Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream the fluid being air
    • 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
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/58—Processes or apparatus involving steps for recycling of process streams the recycled stream being argon or crude argon
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/20—Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/50—One fluid being 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/52—One fluid being oxygen enriched compared to air, e.g. "crude 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/58—One fluid being argon or crude argon
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/44—Particular materials used, e.g. copper, steel or alloys thereof or surface treatments used, e.g. enhanced surface
    • 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
    • F25J3/04642—Recovering noble gases from air
    • F25J3/04648—Recovering noble gases from air argon
    • F25J3/04721—Producing pure argon, e.g. recovered from a crude argon column
    • F25J3/04727—Producing pure argon, e.g. recovered from a crude argon column using an auxiliary pure argon column for nitrogen rejection

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

Abstract

The invention relates to a method for separating air by cryogenic distillation, in which method cooled air (1) purified of water is sent to a first column (K1) operating at a first pressure, where the cooled air is separated into a nitrogen-rich gas and an oxygen-rich liquid (3); extracting from the second column an argon-rich gas (7) enriched with argon with respect to air; at least a portion of the oxygen-rich liquid is vaporized by heat exchange with the argon-rich gas; and feeding the vaporized oxygen-enriched liquid (5) to the second column at an intermediate level. The invention also relates to a device for separating air by cryogenic distillation.

Description

Method and apparatus for separating air by cryogenic distillation
Technical Field
According to the present invention, a method and apparatus for separating air by cryogenic distillation is provided. The process is carried out using a double air distillation column, known per se, which may or may not be combined with an argon separation column.
Background
Conventionally, in an air separation plant, air that has been purified and cooled is sent to a first column operating at cryogenic temperatures to be separated into a nitrogen-rich gas and an oxygen-rich liquid.
After expansion in the valve, the liquid is withdrawn from the first column and sent to a second column, which operates at a lower pressure than the first column.
In addition to the double column, the air separation plant typically includes an argon separation column. The argon separation column can obviously be used for the production of argon, although in some cases it is installed with the main purpose of increasing the production of oxygen and/or of nitrogen at high pressure and/or of expanding the large volume of air intended for the second column, in order to increase the kilocalorie production and therefore the production of liquids, or in order to increase the energy efficiency.
Disclosure of Invention
It is an object of the present invention to improve the energy performance of an air separation unit with or without the presence of an argon separation column.
In the presence of an argon separation column, even if no argon is produced and/or the column contains only few stages, it is an object of the present invention to reduce the additional costs associated with the presence of this column. Thus, the gain in energy performance provided by the present invention can be achieved in whole or in part to a lesser extent.
ｃA method according to the characterizing part of claim 1 is known from EP- ｃA-0860670. In this process, the liquid fed to the overhead condenser of the argon column is not directly from the first column but is previously partially vaporized in order to condense the argon mixture. As the oxygen concentration in the liquid becomes higher, the vaporization temperature thereof also increases accordingly. Thus, the temperature differential in the argon column condenser is extremely low and requires a very large exchanger volume. The result of this is an increase in the size of the cold box.
According to one subject of the invention, a process is provided for separating air by cryogenic distillation, in which
a) Passing cooled air purified of water removal to a first column operating at a first pressure, said cooled air being separated in said first column into a nitrogen-rich gas and an oxygen-rich liquid;
b) withdrawing from said first column a liquid enriched in nitrogen relative to air and sending it to the top of a second column thermally connected to the first column and operating at a second pressure lower than the first pressure;
c) extracting from the first column a liquid enriched in oxygen with respect to air and optionally sending a first portion of the oxygen-enriched liquid to an intermediate level of the second column, optionally after the first portion of the oxygen-enriched liquid has undergone a partial vaporization step in which it has undergone an oxygen-enrichment treatment;
d) extracting from the second column a gas enriched in argon with respect to air;
e) at least partially vaporizing at least a portion of the oxygen-rich liquid by heat exchanging the at least a portion of the oxygen-rich liquid with an argon-rich gas and sending the vaporized oxygen-rich liquid to an intermediate level of the second column, optionally after the step of subjecting the vaporized oxygen-rich liquid to oxygen enrichment;
f) returning at least one condensed portion of the argon-rich gas to the third column, which is also fed with an argon-rich gas stream originating from the second column, extracting an argon-rich stream at the top of the third column, returning an argon-depleted liquid from the third column to the second column;
g) sending a portion of the oxygen-enriched liquid to an overhead condenser of a third column;
h) vaporizing the oxygen-rich liquid sent to the overhead condenser in the overhead condenser and sending the resulting vapor to the second column,
characterised in that the portion of the oxygen-rich liquid sent to the overhead condenser of the third column is not reheated by the argon-rich gas stream.
According to other aspects, said other aspects are optional and can be combined with each other:
the vaporized oxygen-rich liquid is at a pressure of at least 1bar greater than the pressure of the second column and is expanded in a turbine before being sent to the second column at an intermediate height;
at least one condensed portion of the argon-rich gas is fed back to the second column;
at least one condensed portion of the argon-rich gas is fed back to the third column, which is also fed with an argon-rich gas stream originating from the second column, the argon-rich stream being extracted at the top of the third column and the argon-depleted liquid being returned from the third column to the second column;
the part of the oxygen-rich liquid sent to the top condenser of the third column is not subjected to oxygen-enrichment;
the third column is arranged within the second column and the at least part of the oxygen-rich liquid is vaporized by heat exchange with the argon-rich gas inside the second column;
the condensation temperature of the argon-rich gas sent to the exchanger is higher than the vaporization temperature of the oxygen-rich liquid in the exchanger;
all the oxygen-rich liquid is sent to the heat exchanger from the bottom of the first column; vaporizing only a portion of the liquid and then feeding this portion to the second column;
in this case, the unvaporised fraction is separated off in a phase separator, expanded and sent to the second column;
a portion of the oxygen-rich liquid is sent from the bottom of the first column to the heat exchanger, is at least partially vaporized in the heat exchanger, and a portion of the oxygen-rich liquid is sent from the bottom of the first column to the second column without passing through the heat exchanger.
All of the oxygen-rich liquid sent to the heat exchanger undergoes vaporization in the heat exchanger.
According to another subject of the present invention, there is provided an apparatus for separating air by cryogenic distillation, the apparatus comprising a first column operated at a first pressure; a second column thermally connected to the first column and operating at a second pressure lower than the first pressure; a heat exchanger; means for passing the cooled air purified of water to a first column operating at a first pressure where it is separated into a nitrogen-rich gas and an oxygen-rich liquid; means for extracting from the first column a liquid enriched in nitrogen relative to air; means for feeding a nitrogen-rich liquid to the top of the second column; means for extracting from the first column a liquid enriched in oxygen relative to air; optionally means for sending a first portion of the oxygen-rich liquid to an intermediate height of the second column, optionally after subjecting the first portion of the oxygen-rich liquid to oxygen enrichment; means for extracting from the second column a gas enriched in argon with respect to air; means for sending the portion of the oxygen-rich liquid to a heat exchanger for at least partially vaporizing the portion of the oxygen-rich liquid by heat exchanging the portion of the oxygen-rich liquid with an argon-rich gas; and means for feeding the oxygen-rich liquid vaporized in the heat exchanger to an intermediate level of the second column, optionally after the step of subjecting the vaporized liquid to oxygen enrichment; a third tower; means for feeding at least a condensed portion of the argon-rich gas in the heat exchanger to the third column; and means for passing the argon-rich gas stream from the second column to a third column; means for withdrawing an argon-rich stream at the top of the third column; means for passing argon-depleted liquid from the third column to the second column; means for sending a portion of the oxygen-enriched liquid to the overhead condenser of the third column; and means for sending vapor produced by vaporizing an oxygen-rich liquid in the overhead condenser to the second column, characterized in that the means for sending the portion of the oxygen-rich liquid to the overhead condenser is directly connected to the first column without passing through an exchanger.
According to other optional aspects:
the plant comprises a turbine connected to the second column at an intermediate height, the turbine being fed with the vaporized oxygen-enriched liquid;
the plant comprises means for feeding back at least one condensed portion of the argon-rich gas to the second column;
the plant comprises means for sending said produced vapour to the second column by mixing it with a stream expanded in a turbine;
the third column is arranged inside the second column;
the apparatus comprises means for vaporizing said at least part of the oxygen-rich liquid by heat exchange with argon-rich gas inside the second column;
the third column contains less than 50 or even less than 10 theoretical stages.
Drawings
The invention will be described in more detail with reference to the accompanying drawings:
fig. 1, which is composed of fig. 1a and 1b, shows a comparison method.
Fig. 2 shows a method according to the invention.
Fig. 3 shows a method according to the invention.
Fig. 4 shows a variant of fig. 2 and 3.
Fig. 5 also shows a variant of fig. 2 and 3.
Detailed Description
Fig. 1a shows a dual air separation column comprising a first column K1 operating at a first pressure and a second column K2 operating at a second pressure lower than the first pressure. Both columns are thermally connected to each other, for example by a condenser-reboiler C which vaporizes the bottom oxygen from the second column K2 by heat exchange with gaseous nitrogen from the first column K1.
Nitrogen-rich liquid 11 is sent from the top of the first column K1 to the top of the second column K2. By already purifying to remove water and CO2To feed gaseous air to the first tower. Air may also be supplied to the second column K2.
The oxygen-rich liquid is withdrawn at the bottom of the first column K1 and split into two portions. One portion 3 is sent to a heat exchanger E where it is totally vaporized to form a gas 5. The gas 5 is expanded in the turbine T and sent to an intermediate position of the second column K2. The cold energy produced at very low temperatures by this expansion thus provides a gain in the energy consumption of the unit compared to the consumption that would be produced without this expansion.
The remainder 10 of the oxygen-rich liquid extracted at the bottom is expanded in a valve and sent as stream 12 above the entry point of streams 5 and 9.
The exchanger E contained in the chamber B is also used to liquefy the flow of intermediate gas 7 coming from the second column K2. The gas 7 is extracted at a position such that the condensation temperature (bubble point) of the gas 7 is higher than the vaporization temperature of the oxygen-rich liquid 3 in the exchanger E. The composition of the gas 7 is typically that of the feed gas to the argon production column. After having undergone condensation in exchanger E, this stream is then optionally conveyed by means of a pump P to a position at least above its extraction position and below the position of the expanded gas inlet of turbine T.
An oxygen-rich liquid 15 is withdrawn from the bottom of the second column K2 and a nitrogen-rich overhead gas 13 is withdrawn from the top of the same column.
As a variant, all the bottom liquid can be sent to exchanger E, where it is partially vaporized, as shown in fig. 1 b. The partially condensed stream is separated in phase separator 8 to produce gas 5 and liquid 10 enriched in oxygen relative to liquid 3. The resulting gas 5 is expanded in a turbine T and the remaining liquid 10 is expanded and sent to the column as stream 12. In this case, the liquid enters column K2 at a higher or lower level than the gas from turbine T, since it is already enriched with oxygen. Fig. 1b shows only a modified part of fig. 1 a.
Unlike fig. 2 and 3, fig. 1a and 1b do not include an argon separation column.
In fig. 2, which is a variant of fig. 1, the oxygen-rich liquid 3 is split into three portions 3, 17 and 19.
One portion 17 is sent directly in liquid form to the second column K2.
With respect to fig. 1, portion 3 is subjected to heat exchange with an argon-rich gas stream 7, argon-rich gas stream 7 being a portion of the argon-rich gas extracted from the second column; the remaining part 7A of the gas is fed directly to an argon separation column K3.
Portion 3 is vaporized at 2.1 bar to form stream 5, then expanded in turbine T and sent to column K2. Stream 7 undergoes condensation in exchanger E housed in chamber B and the resulting liquid 9 is fed to column K3, preferably in multiple stages above the inlet of gas 7A.
Chamber B is preferably arranged above the entry point of liquid 9 in column K3.
A portion 19 of the oxygen-rich liquid is fed without being enriched with oxygen to the overhead condenser N of column K3 and vaporized to form gas 23. The gas 23 is mixed with the gas expanded in the turbine T to form a gas 25, which gas 25 is fed to the second column K2.
Thus, the oxygen-rich liquid is fed in parallel to the exchanger E and the overhead condenser N.
If argon purified to remove oxygen (stream 21) is recovered as the product, the yield of argon is about 80%. If stream 21 is not recovered in pure product form, column K3 may be very small because it contains only tens of theoretical stages (<50), or even less than 10 theoretical stages.
In fig. 3, the oxygen-enriched liquid is split into two portions 3 and 3A only. Part 3A is fed to column K2 and part 3 is partially vaporized in heat exchanger E. The remaining liquid 3B was fed to the overhead condenser N of column K3, and the gas 23 formed in the condenser was fed to column K2.
The gas 5 formed in the exchanger E feeds the turbine T with an inlet pressure of 2.7 bar.
If argon is recovered (stream 21), the argon yield is about 75-76%.
In the case of fig. 2 and 3, the argon column has a liquid feed in addition to the normally gaseous feed. Thus, for the section above the inlet of liquid 9, the diameter of column K3 can be reduced by about 20%, which reduces its cost.
Given that the argon column is the highest column in the plant, it is important to be able to reduce its volume and therefore the size of the cold box (not shown) that houses it.
In a variant, column K3 of fig. 2 and 3 can be located inside column K2, column K3 being arranged concentrically with the shell of column K2. Column K3 may contain structured packing or loose packing.
The gas rising in column K2 will enter column K3 or into the annular section surrounding column K2.
In this case, the overhead condenser N of column K3 will be used to heat the liquid bath located at the mid-height of column K2. Gas from the top of column K3 will enter the overhead condenser N via a pipe through a barrier forming a storage tank located in column K2 at an intermediate height, and liquid condensed in condenser N will enter another pipe in the same way, passing through the barrier to return to column K2. A valve can regulate the amount of liquid returned from condenser N to column K2.
Column K3 is surrounded by an annular section of column K2 in which the packing is located. The gas separated at the top of the annular section is sent to this section of column K2, enters the pipe through the barrier, or will be sent outside the column below the barrier to return to the column above the barrier. The bottom liquid accumulated above the barrier will be sent to the top of the annular section via a pipe passing through the barrier or via a pipe connected to the outside of the column.
In this case, exchanger E, in its chamber B, is still located outside column K2 and outside column K3. In this case, stream 7 is extracted directly from column K2 without being split, since the stream equivalent to 7A rises directly in column K2 to column K3.
Similarly, liquid 3B is injected in column K2 to be directed to condenser N.
For concentric column K3 inside another column K2, heat exchange takes place between the inside of column K2 and the annular section through the wall of column K2, due to the difference in composition of the fluid mixture on both sides of the internal column K3. Distillation is promoted by heat exchange at the top of column K2, not at the bottom of the column.
It is therefore suggested to increase the heat exchange surface area by adding fins on the shell of the upper section of column K3, thereby improving the exchange in the upper section of column K3.
Alternatively, the material for the upper portion of the shell may be a metal that is more conductive than the lower portion (e.g., made of aluminum at the top of the shell of tower K3 and stainless steel at the bottom of the tower). Another possibility is to use a casing made entirely of aluminium for the tower K3 and to apply a coating in the lower section to reduce the heat exchange.
It has previously been proposed to arrange an argon separation column with an overhead condenser in the second column (low-pressure column). One possibility is to place the top column such that the top gas from the argon column undergoes partial condensation in the top condenser of the argon column and partial condensation in the top condenser of the low-pressure column by heat exchange with the oxygen-rich liquid from the bottom of the first column (medium-pressure column). The liquid formed in the overhead condenser of the second column is sent to the top of the second column and the vaporized liquid is sent to a level above the overhead condenser of the argon column. The overhead condenser may be a thin film evaporator.
In fig. 2 and 3, the turbine T can be replaced by a mixing column K4, for example operating at 2.2 to 2.7 bar, as shown in fig. 4. The mixing column will be fed at the bottom with the vaporized rich liquid 5 vaporized through exchanger E. The inlet at the top of column K4 is an impure liquid oxygen stream having an oxygen content of about 90 mol%. In the case of fig. 2, the oxygen content of the vaporized rich liquid is 34% and in the case of fig. 3 the oxygen content of the vaporized rich liquid is 20%. Liquid 31 is withdrawn at the bottom of column K4, liquid 31 having an oxygen content of 65% (in the case of fig. 2) or 50% (in the case of fig. 3). Stream 43 is withdrawn in the middle of column K4.
Column K4 produces stream 35 at the top of the column, stream 35 having an oxygen content of 75% (fig. 2) or 65% (fig. 3) at 2.1 bar to 2.7 bar. This stream is condensed in a condenser C, which may be the bottom condenser of the second column K2 or any evaporator external to the column. It condenses by heat exchange with pure liquid oxygen 39 to produce pure gaseous oxygen 41.
Thus, the gas 35 may replace the gaseous nitrogen from the first column in the condenser C of fig. 2 or 3. This results in an increase in the argon yield of about 5%, or an increase in the production of gaseous nitrogen at the top of the first column.
In contrast, the energy gain will be reduced relative to fig. 2 and 3; however, the turbine T is omitted.
Fig. 5 also shows a variation of fig. 2 and 3, wherein the oxygen-rich liquid 3 from the bottom of the first column is enriched with oxygen in the etianne column K5, with the bottom reboiler E corresponding to exchanger 3 in the previous figures.
Thus, reboiler E is reheated by argon-rich stream 7 from the second argon column. In addition to the gaseous feed, the liquid stream 9 produced is also fed as a second feed to the argon column K3.
Liquid 3 expanded in the valve descends along the stages of column K5 becoming oxygen-enriched to produce oxygen-enriched stream 53 (75% oxygen), a bottoms stream, and an overhead gas containing only 16% oxygen. Stream 53 is fed to column K2 and allows for a 3% increase in argon yield.

Claims (13)

1. A process for separating air by cryogenic distillation wherein:
a) sending the cooled air (1) purified of water to a first column (K1) operating at a first pressure, said cooled air being separated in said first column into a nitrogen-rich gas and an oxygen-rich liquid (3);
b) extracting a nitrogen-rich liquid (11) enriched in nitrogen with respect to air from the first column and sending the nitrogen-rich liquid to the top of a second column (K2) thermally connected to the first column and operating at a second pressure lower than the first pressure;
c) extracting an oxygen-rich liquid (3) enriched in oxygen with respect to air from the first column and optionally sending a first portion (10, 17) of the oxygen-rich liquid to the second column at an intermediate level, optionally after the first portion of the oxygen-rich liquid has undergone a partial vaporization step in which it has undergone an oxygen enrichment treatment;
d) extracting from the second column an argon-rich gas (7) enriched with argon with respect to air;
e) at least partially vaporizing at least a portion of the oxygen-rich liquid by heat exchanging the at least a portion of the oxygen-rich liquid with the argon-rich gas and sending the vaporized oxygen-rich liquid (5) to an intermediate level of the second column, optionally after the step of subjecting the vaporized oxygen-rich liquid to oxygen enrichment;
f) returning at least one condensed portion (9) of the argon-rich gas to a third column (K3), the third column (K3) being also fed with an argon-rich gas stream (7A) originating from the second column (K2), extracting an argon-rich stream (21) at the top of the third column, returning argon-depleted liquid from the third column to the second column;
g) sending a portion (19) of the oxygen-enriched liquid to the overhead condenser (N) of the third column (K3);
h) subjecting the oxygen-rich liquid sent to the overhead condenser to vaporization in the overhead condenser and sending the resulting vapor (23) to the second column,
characterized in that said portion (19) of the oxygen-rich liquid sent to the overhead condenser (N) of the third column (K3) is not reheated by the flow of argon-rich gas (7).
2. The process according to claim 1, wherein the vaporized oxygen-rich liquid (5) is at a pressure of at least 1bar greater than the pressure of the second column (K2) and expanded in a turbine (T) before being sent to the second column at an intermediate height.
3. The method according to claim 1 or 2, wherein at least one condensed portion (9) of the argon-rich gas is fed back to the second column (K2).
4. A process according to claim 1 or 2, wherein the generated vapour (23) is sent to the second column by mixing with a stream expanded in the turbine (T).
5. The process according to claim 1, wherein the third column (K3) is arranged inside the second column (K2), the at least part of the oxygen-rich liquid being vaporized by heat exchange with argon-rich gas inside the second column.
6. Method according to any of the previous claims, wherein the condensation temperature of the argon-rich gas (7) sent to the exchanger (E) where the heat exchange takes place is higher than the vaporization temperature of the oxygen-rich liquid (3) in said exchanger.
7. An apparatus for separating air by cryogenic distillation, the apparatus comprising: a first column (K1) operating at a first pressure; a second column (K2) thermally connected to the first column and operating at a second pressure lower than the first pressure; a heat exchanger (E); means for sending cooled air (1) purified of water to said first column operating at a first pressure, the cooled air being separated in the first column into a nitrogen-rich gas and an oxygen-rich liquid; means for extracting from the first column a nitrogen-rich liquid (11) enriched in nitrogen relative to air; means for passing the nitrogen-rich liquid to the top of the second column; means for extracting from the first column an oxygen-enriched liquid enriched in oxygen relative to air; optionally means for sending a first portion of the oxygen-rich liquid to an intermediate height of the second column, optionally after subjecting the first portion (10, 17) of the oxygen-rich liquid to oxygen enrichment; means for extracting from said second column an argon-rich gas (7) enriched with argon with respect to air; means for sending a portion (3) of the oxygen-rich liquid to the heat exchanger for at least partially vaporizing the portion (3) of the oxygen-rich liquid by heat exchanging the portion (3) of the oxygen-rich liquid with the argon-rich gas; and means for feeding the oxygen-rich liquid (5) vaporized in the heat exchanger to an intermediate level of the second column, optionally after the step of subjecting the vaporized oxygen-rich liquid to oxygen enrichment; a third column (K3); means for sending at least one condensed portion (9) of the argon-rich gas in the heat exchanger to the third column; and means for sending an argon-rich gas stream (7A) originating from the second column to the third column; means for withdrawing an argon-rich stream (21) at the top of the third column; means for passing argon-depleted liquid from the third column to the second column; means for sending a portion (19) of the oxygen-enriched liquid to the overhead condenser (N) of the third column (K3); and means for sending to the second column a vapor (23) produced by vaporizing an oxygen-rich liquid in the overhead condenser, characterized in that the means for sending the portion of the oxygen-rich liquid to the overhead condenser is directly connected to the first column without passing through the heat exchanger (E).
8. Plant according to claim 7, comprising a turbine (T) connected to the second column (K2) at an intermediate height, fed with the vaporized oxygen-enriched liquid (5).
9. Plant according to claim 7 or 8, comprising means for feeding back at least one condensed portion (9) of the argon-rich gas to the second column (K2).
10. Plant according to claims 7 and 8, comprising means for sending the generated vapour (23) to the second column by mixing it (23) with a stream expanded in the turbine (T).
11. The plant according to any one of claims 7 to 10, wherein the third column (K3) is arranged inside the second column (K2), the third column comprising means for vaporizing at least part of the oxygen-rich liquid by heat exchange with argon-rich gas inside the second column.
12. The apparatus of any one of claims 7 to 11, wherein the third column contains less than 50 theoretical stages.
13. The apparatus of claim 12, wherein the third column contains less than 10 theoretical stages.
CN202011154571.2A 2019-10-24 2020-10-26 Method and apparatus for separating air by cryogenic distillation Pending CN112710125A (en)

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