EP1231440B1 - Process and apparatus for air separation by cryogenic distillation - Google Patents

Abstract

Device for low temperature decomposition of air to recover nitrogen, oxygen and argon comprises a two-stage rectifier column comprising a high pressure column (1) and a low pressure column (3) which are thermally connected together using a condenser (2). Device for low temperature decomposition of air to recover nitrogen, oxygen and argon comprises a two-stage rectifier column comprising a high pressure column (1) and a low pressure column (3) which are thermally connected together using a condenser (2). The columns are connected to a heat exchange network, a crude argon column (10) and a liquefied air column (17) via lines including measuring, controlling, regulating and conveying devices. An Independent claim is also included for a process for the low temperature decomposition of air to recover nitrogen, oxygen and argon using a rectifier system consisting of a pressure column and a low pressure column thermally connected using a main condenser, a crude argon column, and a liquefied air column.

Description

The invention relates to a method and a device for the cryogenic separation of air for the production of nitrogen, oxygen and argon, according to the features of claims 1 and 17.

In the known air separation plants with internal compression rectified from the air products from the rectification are at least partially withdrawn as liquids, conveyed by means of conveyors, such as cryo pumps, to the desired final pressure and then in a connected to the rectification heat exchanger network in countercurrent with compressed Air to gaseous products, preferably to pressure nitrogen or pressure oxygen, evaporated.
The air separation plants designed with an internal compression circuit have the fundamental disadvantage that, depending on the product quantities taken off as liquid from the rectification system, a partial liquefaction of the process air used is accompanied by the amount of which the amount of air rectified in the pressure column of the rectification system decreases, with the result in that the separation effort and thus the structural complexity in the rectification columns connected to the pressure column increases and / or the product yields and in particular the argon yield decrease.

EP-A-0 752 565 discloses a process for the low temperature separation of air for the recovery of nitrogen, oxygen and argon in which, in a rectification system, at least one pressure and low pressure column thermally coupled together by the main condenser are connected to a crude argon column, a pure argon column and a liquid air column two-stage rectification column, wherein a further throttled air stream is withdrawn from the pressure column and fed into the liquid air column, and the oxygen-rich liquid bottom product of the pressure column fed into the liquid air column, and the liquid bottom product of the liquid air column is supplied as a cooling medium for a condenser of the pure argon column.

Out US 5,715,706 For example, a process is known in which the oxygen-rich bottom product of the pressure column is further rectified in an additional column, the RL flash column, and additionally oxygen-free reflux liquid is recovered, whereby the worsening of the reflux conditions associated with the internal compression can be at least partially reversed. For this purpose, compressed, purified of carbon dioxide and water (purified) and cooled air in a pressure column by means of conventional rectification under a pressure of about 5.3 bar rectified in an oxygen-rich fraction and a gaseous nitrogen stream. The resulting gaseous nitrogen stream is at least partially condensed and used as reflux for the pressure and low pressure column. The oxygen-enriched bottoms liquid of the pressure column is expanded into an RL-flash column equipped with or without rectifiers, a bottom evaporator and a top condenser, and the resulting in the expansion of the vapor in the RL-flash column under a between the pressure column and the the low pressure column rectified operating pressure. In the RL flash column is through with gaseous nitrogen from the pressure column resulting sump evaporation additionally produces oxygen-poor steam. In the case of the RL-flash column having no rectification units, the resulting bottoms liquid is merely throttled to form a two-phase mixture, which is subsequently further decomposed in the low-pressure column.
In addition, the throttled bottoms liquid or alternatively in a particularly advantageous embodiment of US 5,715,706 , liquid side draw from the low pressure column, as a condensation medium for the arranged at the top of the RL-flash column condenser use, by means of which the ascending in the RL-flash column vapor medium is at least partially condensed. The condensate is fed as reflux back into the RL-flash column and low pressure column and / or withdrawn as a liquid product from the liquid air column.

The disadvantage of this US 5,715,706 known method is that the crude argon capacitor must be significantly larger dimensions, since the oxygen concentration of the crude oxygen increases and thus the available temperature difference for heat exchange at the crude argon condenser reduced, if instead of the bottom product of the pressure column, the bottom product of the RL flash column is used for cooling the crude argon capacitor. In addition, the achievable yield of additional reflux is limited by the fact that only a relatively small proportion of the gaseous pressure nitrogen from the pressure column for heating the bottom evaporator of the RL flash column can be used without the buoyancy flow at the lower portions of the low pressure column so strong is lowered so that the nitrogen content in the argon gas side rises so much that the crude argon capacitor can no longer be operated.

The invention is therefore based on the object to provide a method and an apparatus of the type mentioned, by means of which a cost oxygen and nitrogen production with high product yields, in particular in a connected Argonrektifikation enabled.

This object is achieved by a method and an apparatus having the features of claims 1 and 17.

Further developments of the invention can be found in the dependent claims 2 to 16 and 18 to 23.

According to the invention, pre-cooled process air in a first partial flow predominantly vaporous process air directly from a heat exchanger network (all heat exchangers involved in the cooling of the incoming and outgoing process streams, such as high heat exchanger, subcooler and LOX evaporator) and in a second partial flow to the Pressure level of the pressure column throttled as predominantly liquid process air with the steam flow resulting from the throttling at least partially fed into the pressure column.

The remaining portion of liquid process air which is not supplied to the pressure column is throttled to the pressure level of the liquid-air column as liquid and vapor partial air stream is fed into the liquid-air column and as liquid reflux into the low-pressure column.

The process air fed into the rectification units in the form of differently arranged conventional trays and / or ordered packings or random packings and thermally coupled by means of a main condenser to the low pressure column is at a pressure of usually 4 to 6 bar in an oxygen-rich liquid bottom product and in decomposed a nitrogen-rich vaporous overhead fraction.

The nitrogen product present at the top of the pressure column with a residual oxygen content of up to less than 1 ppm is at least partially withdrawn from the rectification column as a vaporous and / or liquid product.

The rectified in the pressure column overhead vapor product is at least partially condensed by indirect heat exchange with thereby evaporating oxygen-rich liquid bottom fraction of the low pressure column by means of the main condenser and fed the resulting condensate at least partially as reflux of the pressure column.

The oxygen-rich liquid bottom product of the pressure column is at least partially fed as a cooling medium into the condenser of the crude argon column and / or as reflux into the low-pressure column.

The fed into the low-pressure column media are decomposed under a pressure of usually 1.1 to 1.6 bar by means of rectification in the form of differently arranged conventional trays and / or ordered packings or packing in a nitrogen-rich vaporous overhead product and in an oxygen-rich liquid bottom product.

If a pure nitrogen product with a residual oxygen content of 0.5 to 10 ppm is to be produced in the low-pressure column, then some gaseous nitrogen product contaminated with gaseous nitrogen contaminated with up to 2% by volume oxygen is withdrawn below the tap for the pure nitrogen.

The by means of the main condenser at least partially vaporized bottoms liquid rises in the low pressure column and is rectified in countercurrent with trickling down liquid.

To obtain crude argon, an argon-rich argon-oxygen side gas is withdrawn from the middle region of the low-pressure column, the so-called argon belly, and fed into the crude argon column equipped with rectification devices in the form of differently arranged ordered packings and / or random packings and overhead condenser, and at an operating pressure. which is only slightly below the operating pressure of the low pressure column, decomposed into a gaseous crude argon product and an oxygen-rich liquid bottom product.

The present at the top of the crude argon column gaseous oxygen poor Rohargonprodukt with a maximum of 6 vol .-% residual oxygen content is condensed by indirect heat exchange with liquid process medium, such as bottoms of the pressure column, at least partially to liquid crude argon and at least partially fed as reflux back to the crude argon column. At least a portion of the overhead product is withdrawn either as a vaporous product directly in front of head or as a liquid product from the crude argon condenser or possibly after further treatment steps, such as heating to ambient temperature of the gaseous crude argon product, compression to about 4 to 6 bar, catalytic conversion of im Crude argon remaining residual oxygen, with the aid of supplied hydrogen to steam, recooling to ambient temperature, adsorptive removal of hydrogen vapor formed in the reaction with hydrogen in a molecular sieve, recooling the oxygen-free crude argon in countercurrent with the extracted from the crude argon column crude argon, a pure argon column for the production of nitrogen-free Reinargonprodukt supplied.

The crude argon fed into the pure argon column equipped with rectification units in the form of differently arranged, ordered packings and / or random packings, overhead condenser and bottom evaporator is converted under an operating pressure of 1.1 to 5 bar into a largely oxygen and nitrogen-poor liquid bottom product, part of which is pure argon product With less than 1 ppm of residual oxygen content and residual nitrogen content is withdrawn from the pure argon column and the remaining fraction in the pure argon column is vaporized to maintain the rectification in the bottom evaporator, rectified to a nitrogen-rich overhead product.

The bottoms liquid rectified in the pure argon column is at least partially vaporized by means of a bottoms evaporator operated with gaseous process medium and the vaporous nitrogen-rich top product present in the pure argon column is condensed by means of bottom liquid fed from the liquid-air column.

The noncondensable gaseous inert portion of the nitrogen-rich overhead product of the pure argon column is blown off as purge gas into the plant environment.

The resulting on operation of the crude argon capacitor on the coolant side steam is fed into the low pressure column.

The vaporous and liquid process air fed into the liquid-air column in the manner described above is pressurized at a pressure which is between the operating pressure of the pressure and the low-pressure column and which, when liquid air is used, at about 2.3 to 2.6 bar , By means of both arranged above and below the feed point, designed as conventional trays and / or ordered packings or packing rectifying devices decomposed into a gaseous oxygen-poor top product and an oxygen-rich bottoms liquid.

The bottoms liquid rectified in the liquid air column is partially vaporized in a bottom evaporator in order to allow rectification below the feed point of the liquefied air and thereby to increase the oxygen content of the bottom liquid and thus the yield of top product.

Advantageously, the latent heat of a predominantly gaseous process medium and / or the sensible heat of a liquid coupled out of the process is used to heat the bottom evaporator.

As a heating medium for the at least partial vaporization of liquid present in the liquid column, a stream decoupled from the process, such as bottom liquid of the pressure column, a vaporous side gas stream or overhead product stream of the pressure column and particularly preferably a vaporous Side discharge of the crude argon column Use, which are fed individually or in combination into a bottom evaporator of the liquid air column.

The bottom liquid used as the heating medium in the bottom evaporator of the liquid column of the pressure column is then fed as a cooled liquid of the low pressure column and / or the condenser of the crude argon column.

The side gas stream or top product stream of the pressure column used as heating medium in the bottom evaporator of the liquid air column is then - at least partially condensed - fed as reflux liquid into the low pressure column and / or as cooling medium in the top condenser of the crude argon column.

In addition, liquid side draw is fed from the liquid air column as cooling medium into the condenser of the liquid air column and / or as reflux liquid into the pressure and low pressure column.

For vaporizing bottoms liquid in the liquid air column, the feedstock itself, so under pressure, deep-cold gaseous process air can be used by being passed before the throttling to the pressure levels of the liquid air column through the bottom evaporator of the liquid air column and there by dispensing contained in the gas stream sensitive heat generated by the boosting gas for the liquid air column.

The at least partially liquefied in the liquefaction of the vaporous overhead product in the condenser of the liquid air column process medium is fed as reflux in the pressure and low pressure column or withdrawn as a liquid nitrogen product.

In a further advantageous embodiment of the invention, the withdrawn from the heat exchanger network partial flow of the process air, which is present after throttling to the pressure level of the pressure or liquid air column in predominantly liquid form, throttled and fed as predominantly liquid process air directly and completely into the pressure column and deducted from the pressure column side discharges liquid as the cooling liquid for the condenser and as liquid for the liquid air column and withdrawn as reflux for the low pressure column.

If a strong evolution of steam is to be expected during the throttling, then it has proven to be favorable to pre-cool the process air before the throttling in an evaporator arranged in the bottom of the pressure column by indirect heat exchange with evaporating bottom liquid of the pressure column.

Furthermore, it has proven to be advantageous to feed the entire air to be liquefied directly into the liquid air column and provide liquid side fumes at the feed point to withdraw liquid air both as a cooling medium for the operation of the condenser of the liquid air column and as reflux liquid for the low pressure column when out For reasons of apparatus should be dispensed with a previous feed of the liquid air stream in the pressure column.

In a further advantageous embodiment of the invention, the entire withdrawn from the heat exchanger network and after the throttling predominantly liquid air flow in a operated at the operating pressure of the liquid air column separating vessel, which is connected via a gas line directly to the liquid air column, relaxed. From the separating vessel, the vapor produced during the throttling and a portion of the liquid air are fed as feed streams into the liquid air column, another part of the liquid air is passed as a cooling medium to the condenser of the liquid air column and the remaining part of the liquid air as reflux liquid in both the low pressure - fed as well as in the pressure column. The fact that the container is arranged at a sufficient height in the cold box, it is possible to feed liquid from the separating vessel alone by utilizing the geodetic height difference in the pressure column. This arrangement has proved to be particularly advantageous when larger amounts of process air are liquefied and / or when throttling with a high amount of steam is expected.

The invention further relates to a device according to the features of the claims 17 to 23.

The cryogenic separation of air according to the invention for the production of nitrogen, oxygen and argon has the following essential advantages over the known prior art:

According to the invention, a rectified, non-pretreated liquid air stream is used in the liquid air column, which has a higher nitrogen content than the previously described US 5,715,706 used bottoms liquid of the pressure column, whereby at the same oxygen content of the bottoms liquid in the liquid air column and RL flash column a higher yield of nitrogen and the resulting additional column reflux, a performance optimization of the liquid air column is achieved.

The invention is particularly advantageous when liquid products, preferably liquid oxygen or nitrogen, to be withdrawn from the rectification of the rectification to produce only liquid products or to evaporate the liquid products in countercurrent with compressed air (internal compression systems and liquid systems with integrated air liquefier).

The in the known methods for air separation also resulting pressurized, cryogenic air, which liquefied due to the throttling to the pressure level of the various rectification at least partially, would be fed in conventional process control as reflux liquid in the pressure or low pressure column and would thereby the reflux conditions improve only insignificantly in these columns.

As a result of the pre-separation of the liquefied air in the liquid-air column, an oxygen-poor top product is produced which can be fed into the low-pressure column as additional reflux above the feed point for the liquid air, thereby improving the argon yield achievable by the process according to the invention by 5 to 10%.

A further significant advantage of the liquid air column supplied according to the invention with liquid air is that a pure gaseous nitrogen product can be produced in the low-pressure column without having to generate a correspondingly low-oxygen washing liquid in the pressure column.

Characterized in that the required for the production of pure nitrogen product in the low pressure column reflux liquid is withdrawn from the top of the liquid air column, the pressure column can be provided with up to 15 to 20 separation stages less and accordingly reduces the height of the cold box and thus the system costs are substantially reduced.

Has proven to be a procedure in which - in contrast to US 5,715,706 - For the cooling of the top condenser of the liquid air column rectified untreated liquefied process air or a liquid side take the liquid air column, which is taken at the feed point of the liquid air column, is used. For this purpose, the liquefied process air or the liquid Side outlet of the liquid air column throttled directly or after further pre-cooling to the pressure level of the low-pressure column and fed to the top condenser of the liquid air column.

By operating the overhead condenser with liquefied air is achieved that the operating pressure of the liquid air column is only about 1 bar above that of the low pressure column, whereby compared to the pressure column, the separation effort, i. reduces the number of separation stages by up to 10 and / or reduces the amount of reflux required and thus correspondingly increases the nitrogen yield in the liquid-air column.

Advantageously, the reduced-pressure operation of the liquid-air column results in a multiplicity of integration possibilities for the liquid-air column that are optimally adapted to the particular specific rectification system.

Furthermore, it has proved to be particularly favorable, in addition to the known heating of the bottom evaporator of the liquid air column vaporous top product of the pressure column, including the sensible heat from the bottom product of the pressure column and / or withdrawn from the heat exchanger network, under pressure and in the throttling to use the pressure level of the pressure or the liquid air column liquefied, cryogenic partial air flow.

For this purpose, the decoupled from the plant process heat is coupled by means of the bottom evaporator in the liquid air column so that the oxygen concentration in the bottom liquid of the liquid air column is between 45 and 70 percent. In this way, the conversion in the liquid air column and thus the yield of low-oxygen overhead product in the liquid air column, especially in comparison to the pressure column, be increased so that up to 12% more reflux is available for the upper section of the low pressure column.

• Verringerung der Irreversibilitäten bei der Luftzerlegung aufgrund der geringen Temperaturunterschiede der beim erfindungsgemäßen Verfahren eingesetzten Heiz- und Kühlmedien;
• Variabilität hinsichtlich Anlagenkosten, Energieeinsatz und Produktausbeuten durch den einen optimalen Temperaturgradient in der Sumpfheizung der Flüssigluftsäule ermöglichenden Rohargonsäulen-Anstich;
• Senkung der Anlagenkosten für die Coldbox und für die Rektifiziersäule durch Verringerung der Rektifiziereinrichtungen und anderer Einbauten sowie Verringerung des Querschnitts der Rohargonsäule oberhalb des Seitengasabzugs;
• Verringerung der Anlagenkosten durch Einsatz eines Kopfkondensators mit kleinerer Abmessung in der Rohargonsäule.

Characterized in that deducted from the crude argon column, a vaporous side stream having an oxygen content of 30 to 90% and at least partially liquefied in the sump heating of the liquid air column by indirect heat exchange and fed back into the crude argon column, the following significant advantages can be achieved:

• Reduction of irreversibilities in the air separation due to the low temperature differences of the heating and cooling media used in the process according to the invention;
• Variability in terms of equipment costs, energy use and product yields by the crude argon column puncture enabling an optimal temperature gradient in the sump heater of the liquid air column;
• Reduction of equipment costs for the coldbox and for the rectification column by reducing the rectification units and other internals and reducing the cross section of the crude argon column above the side gas vent;
• Reduction of equipment costs by using a smaller condensing head condenser in the crude argon column.

Between 7 and 12% of the steam rising in the crude argon column can be used as the heating medium for the bottom heating of the liquid-air column, without the argon yield decreasing by more than 0.5% for the same number of theoretical plates in the crude argon column.

According to the invention, not only the yield of low-oxygen top product in the liquid air column is increased, but also reduces the irreversibilities in the crude argon column.

Another essential advantage of the invention is that a liquid side draw or part of the bottom product of the liquid air column can be used for cooling the top condenser of the pure argon column. By using the side draw or bottom product of the liquid air column as condensation medium in the pure argon column, the liquid overhead product used for this purpose in conventional process control can be substituted for the pressure column and instead be used as additional reflux liquid in the low pressure column, whereby the argon yield is increased even further and / / or the number of separation stages in the low pressure column can be reduced.

In addition, by taking place in the pure argon condenser additional separation of fed to a process-technically favorable place in the low-pressure column from the liquid column sump product further reduction of the separation effort and thus optimizing the separation process in the low-pressure column possible.

In a further preferred embodiment of the invention, the liquefied air is first completely or partially fed into the pressure column and from the pressure column in the form of liquid side draws as a feed medium for the liquid air column, and as a condensation medium for the top condenser Liquid air column used and fed the remaining portion of the liquid air as reflux liquid in the low pressure column.

Has proven particularly useful a procedure in which the liquefied air is passed before relaxation and division of the pressure, low pressure and liquid air column through a arranged in the bottom of the pressure column evaporator and there precooled by indirect heat exchange, thereby minimizing the irreversibilities of the throttle process let and by acting as a non-complete theoretical separation stage bottom evaporator, the yield of overhead product in the pressure column is increased.

In a further advantageous embodiment of the air separation according to the invention, the liquid-air column of the rectification system is preceded by a separation vessel arranged at as high a height as possible in the coldbox. In the separating tank operating at the same operating pressure as the liquid air column, the cryogenic pressurized liquid air stream is depressurized. The resulting in the expansion in the separation vessel steam is fed with a partial flow of the liquefied during throttling air in the downstream liquid air column.

It has proven to be beneficial to additionally cooled liquid air as a cooling medium to relax in the top condenser of the liquid air column into it. The liquid air not required in the liquid air column and as cooling medium for the top condenser of the liquid air column is fed into the pressure and low pressure column.

Since there is an additional source of reflux liquid for the low pressure column with the liquid air column, a pure nitrogen product with a residual oxygen content of 0.5 to 10 ppm can be generated in the low-pressure column without having to generate a correspondingly pure reflux liquid in the pressure column, thereby in the pressure column less separation stages to produce a top product with residual oxygen contents of 0.5 to 2 vol .-% are required without the argon and oxygen yield in the low pressure column is adversely affected.

The invention will be explained in more detail with reference to preferred embodiments shown in the drawing.

Fig. 1

eine schematische Darstellung eines erfindungsgemäßen Verfahrens zur Luftzerlegung mit einer zur Luftvorrektifizierung eingesetzten Flüssigluftsäule mit Rohargongewinnung;

Fig. 2

eine schematische Darstellung des erfindungsgemäßen Verfahrens zur Luftzerlegung mit einer zur Luftvorrektifizierung eingesetzten FLüssigluftsäule Rohargongewinnung;

Fig. 3

eine schematische Darstellung des erfindungsgemäßen Verfahrens zur Luftzerlegung mit aus Abscheider und Flüssigluftsäule bestehender Luftvorrektifizierung mit Roh- und Reinargongewinnung;

Fig. 4

eine graphische Darstellung der Irreversibilitäten in der Rohargonsäule bei Abzug eines dampfförmigen Teilstromes;

Show it:

Fig. 1

a schematic representation of a method according to the invention for the separation of air with a liquid air column with Rohargongewinnung used for air pre-rectification;

Fig. 2

a schematic representation of the process according to the invention for air separation with a liquid column used for air pre-rectification Rohargongewinnung;

Fig. 3

a schematic representation of the process according to the invention for the separation of air with existing from separator and liquid air column existing air pre-rectification with raw and pure argon extraction;

Fig. 4

a graphic representation of the irreversibilities in the crude argon column with deduction of a partial vapor stream;

In a in Fig. 1 schematically illustrated rectification with a consisting of pressure and low pressure column 1, 3 with common main condenser 2 rectification column, which is connected to a crude argon and liquid air column 10, 17, the entire process air before being fed into one of the Entire all arranged in the cold box heat exchanger, such as main heat exchanger, freezer and / or other separate heat exchanger existing heat exchanger network to a slightly higher pressure level than that of the pressure column 1, which usually moves between 4 and 6 bar, compressed and ambient temperature level of disturbing minor components such as water vapor and carbon dioxide, cleaned. A partial flow of the thus pre-cleaned air, the proportion of the total air depends on the amount of the liquid or internally compressed gaseous products before being fed into the heat exchanger network to a pressure which depends on the required pressure level of deducted from the system internally compressed product streams and usually between 10 and 80 bar, post-compacted. The compressed and purified process air available at the pressure level of the pressure column 1 is cooled in the heat exchanger network to near its dew point and as predominantly vaporous first partial stream 4 via a line 63 directly below rectification means 47 into the means of the main capacitor 2 with the Low-pressure column 3 thermally coupled pressure column 1 fed.

The second partial stream 5 of the process air, which is delivered to the higher pressure level, is likewise cooled in the heat exchanger network and expanded into a line 64 with throttle 45 to the pressure level of the pressure column and as liquid partial air flow 5b together with the resulting during expansion in the throttle 45 vapor partial air stream 5c fed via a line 65 above the lower rectification means 47 in the pressure column 1. In this connection, the term throttle is used to denote any device suitable for reducing pressure, such as, for example, a valve with moving parts, but also a simple cross-sectional tapering of the line. The predominantly vaporous process air 4 fed into the rectification units 47 in the form of differently arranged conventional trays and / or ordered packings or random packings below the lower rectification units 47 is used together with the liquid fed above the lower rectification units 47 of the pressure column 1 in the lower area Partial air stream 5b and the vaporous air stream 5c decomposed into an oxygen-rich liquid bottom product 6 and in a low-oxygen vaporous nitrogen product 7 having a residual oxygen content of usually 0.5 - 10 ppm. The resulting at the top of the pressure column 1 vaporous nitrogen product is partially withdrawn as vapor pressure nitrogen product 7a via a line 40 and condensed in the pressure column 1 product content in the condenser 2 by indirect heat exchange with thereby evaporating liquid bottom product 8 of the low pressure column 3. The condensate produced in this way is distributed via a line 9 as reflux liquid to the pressure and low pressure column 1, 3 or withdrawn as a liquid nitrogen product 7b via a line 41 with a residual oxygen content of 0.5 to 10 ppm.

The by the condenser 2 to the operating pressure of the low pressure column 3 of usually 1.2 to 1.6 bar coupled operating pressure of the pressure column 1 is between 4 and 6 bar. The rectified in the pressure column 1 bottoms liquid 6 is provided by a equipped with a throttle line 48a 48 as return to the low pressure column 3 and another with a throttle 49a provided line 49 as the cooling liquid in the operating at the same operating pressure as the low-pressure column 3, in usually designed as a thermosiphon head capacitor 11 of the crude argon column 10 into relaxed. The liquid and gaseous streams fed into the low-pressure column 3 equipped with rectification means 50 in the form of differently arranged conventional trays and / or ordered packings or packing are at an operating pressure of usually 1.2 to 1 with the aid of the sump-rich oxygen-rich liquid sump product 8. 6 bar in an oxygen-poor vaporous nitrogen product 12 with a residual oxygen content of 0.2 to 10 ppm and in the oxygen-rich liquid sump product 8 with an oxygen content of at least 99.5 vol .-% decomposed.

In order simultaneously to be able to remove both a pure nitrogen product 12 and a pure oxygen product 8a, b via line 43, 42 from the low-pressure column 3, in the upper section of the low-pressure column 3, a nitrogen-contaminated nitrogen stream 12a having an oxygen content of 0.1 to 12 is also contaminated with oxygen 2% deducted.

The rectified in the low-pressure column 3 liquid oxygen product 8a can be withdrawn via a line 43 and the present in the low-pressure column 3 vapor oxygen product 8b via a line 42 from the low-pressure column 3 for further use. The remaining in the low pressure column 3 residual content of bottoms liquid 8 is evaporated to maintain the rectification by indirect heat exchange in the usually designed as a thermosyphon, in special cases as a falling-film evaporator capacitor 2. From the low-pressure column 3, a proportion of about 30% of the ascending from the condenser 2 amount of vapor corresponding argon-oxygen mixture 13 with an argon content of usually 8 to 12 vol .-% deducted in the central column area, the so-called Argon belly and via a line 13a in the crude argon column 10 is fed. The gaseous argon-oxygen mixture fed into the crude argon column 10 equipped with rectification devices 51 in the form of differently arranged trays and / or ordered packings or packings is rectified into an oxygen-rich liquid bottom product 15 and into an oxygen-poor vaporous crude argon product 14. The crude argon product 14 is withdrawn as vaporous or liquid crude argon product 14a, b with a residual oxygen content of 0.2 to 5 vol .-% via a line 33a, 33b from the crude argon column 10 for further use. The vapor Rohargonstrom not withdrawn as a product before the top of the crude argon column 10 is condensed in the usually formed as a thermosiphon capacitor 11 by indirect heat exchange with evaporating thereby cooling medium, usually bottom liquid 6 of the pressure column 1, and fed as reflux back into the crude argon column 10. The vapor generated in the condensation on the coolant side in the condenser 11 is fed via a line 53 in the middle section of the low-pressure column 3. The oxygen-rich liquid bottom product 15 rectified in the crude argon column 10 is fed back into the low-pressure column 3 via a line 62. From the lower portion of the crude argon column 10 between 7 and 15% of the ascending in the crude argon side steam as side gas with an oxygen content of 20 to 90 vol .-% and taken over the Line 20 a sump evaporator 21 of the liquid air column 17 is supplied, in which the side gas is condensed by indirect heat exchange with evaporating sump liquid and fed as reflux liquid via line 52 again in crude argon column 10. The not directly fed into the pressure column 1 part of the liquid air stream 5b of the process air is by means disposed in a line 46 choke 46a on the operating pressure of the liquid air column 17, which is between the operating pressure of the pressure and low pressure column 1, 3, relaxed and at least partially as a liquid partial air stream 5 d together with the generated during the expansion of the vapor partial air stream 5 e, in which rectifying means 54 in the form of differently arranged conventional trays and / or ordered packings or packing equipped liquid air column 17 is fed. The partial air streams 5d, e fed into the liquid-air column 17 are rectified by means of the rectification units 54 into an oxygen-poor vaporous nitrogen product 18 having a residual oxygen content of 0.5 to 10 ppm and into an oxygen-rich liquid bottom product 19. The rectified in the liquid air column 17 liquid bottom product 19 has an oxygen content of 40 to 70 vol .-%.

The liquid partial air flow 5d fed into the liquid air column 17 is for the most part tapped again at the level of its feed point from the liquid air column 17 and fed via a line 23 with throttle 55 into a top condenser 22 of the liquid air column 17. The liquid air which is not fed into the top condenser 22 of the liquid-air column 17 is expanded as a liquid partial air flow 5f via a line 16 by means of throttle 56 into the region of the upper rectification devices 50 of the low-pressure column 3.

The coolant-side operating pressure of the condenser 22, which is usually designed as a thermosyphon, is only slightly above the operating pressure of the low-pressure column 3, so that the vapor produced during the evaporation of the liquid air can be fed via a line 25 into the low-pressure column 3.

By operating the top condenser 22 with the supplied via line 23 as the cooling medium, only an oxygen content of 15 to 23 vol .-% having liquid air, the liquid bath of the top condenser 22 in a temperature range of about 87 to 89 K, so that the liquid air column 17th can be operated at an operating pressure of 2.2 to 2.6 bar.

The low-oxygen vaporous nitrogen product 18 obtained in the liquid-air column 17 in front of the head is removed as a gaseous, oxygen-poor top product 18 c from the Withdrawn liquid air column 17 and / or condensed by indirect heat exchange in the top condenser 22 with evaporating liquid air and partially fed as reflux liquid back into the liquid air column 17. The condensate 18b which is not fed as reflux liquid into the liquid-air column 17 is fed via a line 24 by means of throttle 57 as an additional return above the rectification devices 50 into the low-pressure column 3.

The fraction of oxygen-rich liquid bottom product 19 which is not vaporized in a sump evaporator 21 of the liquid-air column 17 is fed via a line 58 to the low-pressure column 3.

In contrast to the embodiment of the invention shown in FIG. 1, FIG. 2 shows a rectification system in which a pure nitrogen product 12 having a residual oxygen content of 0.5 to 10 ppm is likewise withdrawn in the low-pressure column 1, but in which case the required one Return fluid 18b is withdrawn exclusively from the liquid air column 17.

In the pressure column 1, no more pressure nitrogen product is produced and reduced the number of separation stages and withdrawn before head a liquid nitrogen stream 9a via line 9 with a residual oxygen content of 0.5 to 3 vol .-% and fed as reflux liquid in the low pressure column 3.

Furthermore, in the rectification system according to the invention shown in FIG. 2, the second partial air stream 5 cooled from the heat exchanger network is not throttled to the pressure level of the pressure column as shown in FIG. 1, but before the pressure drop in the throttle 46a led by means of a line 66 to the bottom evaporator 21 and precooled by indirect heat exchange with thereby evaporating bottoms liquid and then passed via the line 46 to the throttle 46a and relaxed to the pressure level of the liquid air column 17. The liquefied air 5d is fed completely into the liquid-air column 17 together with the vapor stream 5e formed during the expansion. A partial flow of the liquefied air is withdrawn from a side draw liquid air column 17 again and used as a cooling liquid for the condenser 22 and as reflux liquid for the low-pressure column 3.

FIG. 3 shows a rectification system according to the invention, in which, contrary to the rectification system shown in FIG. 1, a portion of the bottom product 19 of the liquid air column 17 is fed via a conduit 59 as a cooling medium into a condenser 31 of a pure argon column equipped with conventional rectification means 39 32 is fed, wherein the coolant-side operating pressure of the normally formed as a thermosyphon pure argon capacitor 31 is only slightly above the operating pressure of the low pressure column 3, that the used evaporating bottom liquid 19 can be fed together with the vapor stream from the crude argon capacitor 11 back into the low pressure column 3. Into the pure argon column 32, via the line 33b, a liquid oxygen-free crude argon product 14b is fed, which is rectified into a nitrogen-free and oxygen-free bottom product 34 and a nitrogen-rich overhead product 35. The top product 35 is withdrawn as a gaseous inert stream 38 via a line provided with a throttle line 28a 29 and blown into the environment. Via a further line 69, the vapor arising on the coolant side of the condenser 31 is fed into the low-pressure column 3 at the level of the rectification devices 50. To produce the lift gas required for the rectification, bottoms liquid 34 is vaporized by indirect heat exchange in a bottom heater 37 with vaporous nitrogen 7a condensing thereinto, which is fed from the pressure column 1 via a pipeline 36. The non-evaporated part of bottoms liquid 34 is withdrawn via a line 68 as a liquid product and the liquid nitrogen condensed in the condensation in the bottom evaporator 37 is fed back into the pressure column 1 via a line 44.

The further difference between the rectification system shown in FIG. 3 and the rectification system of FIG. 1 is that the second partial air stream 5 withdrawn from the heat exchanger network is expanded directly and completely into a separation tank 27 via a conduit 67 provided with a throttle 67a, the operating pressure of which only so slightly above the liquid air column 17 is that the entire resulting in the throttling steam 5e can be fed from the separation vessel 27 via a line 28 directly into the liquid air column 17. The separation tank 27 is arranged so far up in the coldbox that a portion of the liquid air 5d can be fed via the conduit 59 into the pressure column 1 due to the geodetic height difference. Furthermore, at least one further part of the liquid partial air flow 5d is drawn off via the line 59 and fed into the liquid-air column 17 from the separating tank 27. The withdrawal of cooling medium for the condenser 22 of the liquid-air column 17 and of return liquid 5f takes place as already shown in FIG. 1 as a side draw from the liquid-air column 17 but could alternatively also take place directly from the separating tank 27.

FIG. 4 shows a graphic representation of the irreversibilities in the crude argon column 10 when operated with and without side condenser 11 individual soils and on the abscissa the exergy loss is plotted as a measure of the irreversibilities on each soil. It can be seen that the area under the curve for the exergy loss of the crude argon column 10 with side draw is significantly smaller than the curve for a crude argon column 10 without side draw.

Reference numeral lineup

1

pressure column

2

main condenser

3

Low-pressure column

4

first partial stream process air (predominantly vaporous)

5

second partial flow process air (10 to 80 bar)

5a

predominantly liquid partial air flow (from 5)

5b

liquid partial airflow

5c

vaporous partial air flow

5d

liquid air stream

5e

vaporous partial air flow

5f

liquid partial airflow

6

Oxygen-rich liquid bottom product (1)

7

low-oxygen vaporous nitrogen product (1)

7a

vapor withdrawn nitrogen product (1)

7b

liquid withdrawn nitrogen product (1)

8th

oxygen-rich liquid bottom product (3)

8a

vapor withdrawn oxygen product (3)

8b

liquid withdrawn oxygen product (3)

9

Liquid line (condensate of 7)

9a

liquid nitrogen flow

10

crude argon

11

Capacitor (10)

12

low-oxygen vaporous nitrogen product

12a ...

oxygen contaminated vaporous nitrogen product

13

gaseous argon rich argon-oxygen mixture

13a

Gas pipe (13)

14

low-oxygen vaporous crude argon product (10)

14a

vapor extracted crude argon product

14b

liquid withdrawn raw argon product (10)

15

Oxygen-rich liquid bottoms product (10)

16

Liquid line (5f)

17

Liquid air column

18

Gaseous low oxygen overhead product (17)

18a

Nitrogen product withdrawn as a liquid (17)

18b

liquid to low pressure column (1) withdrawn nitrogen product (17)

18c

vapor-depleted low-oxygen overhead product (17)

19

Liquid Oxygenated Bottom Product (17)

20

gaseous side draw (10-21)

21

Bottom evaporator (17)

22

Top condenser (17)

23

Liquid line (17-22)

24

Liquid line (17-3)

25

Vapor flow (22-3)

26

-

27

separating vessel

28

Gas line (27-17)

29

Gas pipe (32 environment)

30

-

31

Top condenser (32)

32

Pure argon column

33a

Gas line (14a)

33b

Liquid line (14b)

34

Bottom product (32)

35

Top product (32)

36

Gas line (1-32)

37

Bottom evaporator (32)

38

Peeled gaseous inert stream (32)

38a

Throttle (38)

39

Rectification equipment (32)

40

Gas line (7a)

41

Liquid line (7b)

42

Gas line (8b)

43

Liquid line (8a)

44

Liquid line (32-1)

45

Throttle (5)

46

Liquid line (5b)

46a

Throttle (in 46)

47

Rectification equipment (1)

48

Liquid line (6)

48a

Throttle (in 48)

49

Liquid line (6)

49a

Throttle (in 49)

50

Rectification equipment (3)

51

Rectifying equipment (10)

52

Liquid line (17-10)

53

Steam line (10-3)

54

Rectification equipment (17)

55

Throttle (23)

56

Throttle (16)

57

Choke (in 24)

58

Liquid line (17-3)

59

Liquid line (17-31)

59a

Throttle (59)

60

Liquid line (27-17)

61

-

62

Liquid line (15)

63

Liquid line (4)

64

Liquid line (5a, b,

65

Liquid line (5a, b, c)

66

Liquid line (5)

67

Liquid line (5)

67a

Throttle (in 67)

68

Liquid line (34)

69

Gas line (34-3)

Claims (23)

1. Process for the cryogenic separation of air to obtain nitrogen, oxygen and argon, wherein, in a rectifying system comprising a two-stage rectifying column connected to at least one pressure column (1) and a low-pressure column (3), thermally coupled to each other by means of a main condenser (2), to at least one crude argon column (10) and to a liquid air column (17):

   a) compressed, precleaned process air that has been precooled in a heat exchanger network is fed in a first predominantly gaseous partial stream (4) directly into the pressure column (1) and in a second partial stream (5), after throttling (45) to the operating pressure of the pressure column (1) predominantly liquid partial stream (5a), is fed at least partially as a liquid air partial stream (5b) into the pressure column (1), and a further part of the liquid air partial stream (5b), after further throttling (46a) to the operating pressure of the liquid air column (17), is fed at least partially as a liquid and gaseous air partial stream (5d, e) into the liquid air column (17) and from the liquid air column (17) as a predominantly liquid air partial stream (5f) after throttling (56) into the low-pressure column (3);

   b) the process air (4, 5a, b, c) fed into the pressure column (1) is rectified by means of rectifying devices (47) into an oxygen-rich liquid bottom product (6) and into an oxygen-poor vaporous nitrogen product (7);

   c) the vaporous nitrogen product (7) rectified in the pressure column (1) is at least partially condensed by means of the main condenser (2) in indirect heat exchange with thereby evaporating oxygen-rich liquid bottom product (8) of the low-pressure column (3), and the condensate occurring in the evaporation is at least partially fed back into the pressure column (1) and the low-pressure column (3) as runback (9);

   d) the oxygen-rich liquid bottom product (6) of the pressure column (1) is supplied to the crude argon column (10) as cooling medium for a condenser (11);

   e) from the media supplied to the low-pressure column (3), the oxygen-rich liquid bottom product (8) and an oxygen-poor vaporous nitrogen product (12) are rectified, and a vaporous and/or liquid oxygen product (8a, b) is drawn off from the bottom (8) of the low-pressure column (3);

   f) the bottom product (8) rectified in the low-pressure column (3) by means of rectifying devices (50) according to step 1c) is at least partially vaporized into rectification vapour for the low-pressure column (3) and drawn off from the top of the low-pressure column (3) as nitrogen product (12) ;

   g) a gaseous argon-rich argon-oxygen mixture is drawn off (13) from the low-pressure column (3) and fed into the crude argon column (10) and separated in the latter by means of rectifying devices (51) into an oxygen-poor vaporous crude argon product (14) and an oxygen-rich liquid bottom product (15);

   h) the oxygen-poor vaporous crude argon product (14) present at the top of the crude argon column (10) is at least partially condensed by indirect heat exchange with a liquid process medium, such as for example with liquid bottom product (6) of the pressure column (1), and at least partially fed to the crude argon column (10) as runback;

   i) the crude argon product (14) is drawn off at least partially as a vaporous or liquid product (14a, b) from the crude argon column (10) and/or at least partially fed into a pure argon column (32) for obtaining oxygen-free and nitrogen-free pure argon product (34);

   j) from the process air fed according to step 1 a) as a liquid or vaporous air partial stream (5d, e) into the liquid air column (17) that is equipped with rectifying devices (54) above and below the feeding-in point and is operated at an operating pressure lying between that of the pressure column (1) and the low-pressure column (3), an oxygen-poor vaporous top product (18) and an oxygen-rich liquid bottom product (19) are rectified;

   k) the oxygen-rich liquid bottom product (19) rectified in the liquid air column (17) is partially vaporized by indirect heat exchange by means of a bottom vaporizer (21) operated with predominantly gaseous process medium;

   l) the oxygen-poor vaporous top product (18) present in the liquid air column (17) is at least partially liquefied by means of a top condenser (22) operated with predominantly liquid process medium, and condensate occurring is fed at least partially into the liquid air column (17) and the low-pressure column (3) as runback;

   m) a vapour stream (25) produced in the condenser (22) of the liquid air column (17) on evaporation of the predominantly liquid process medium and at least part of the liquid bottom product (19) are fed into the low-pressure column (3).
2. Process according to Claim 1, wherein, in step d), the oxygen-rich liquid bottom product (6) of the pressure column (1) is supplied as runback liquid to the low-pressure column (3).
3. Process according to Claim 1 or 2, wherein, in step b), the oxygen-poor nitrogen product (7) present at the top of the pressure column (1) is at least partially drawn off as gaseous and/or liquid product (40, 41).
4. Process according to one of the preceding claims, wherein, in step a), in a second partial stream (5) after throttling (45) to the operating pressure of the pressure column (1), predominantly liquid partial stream (5a) is fed into the pressure column (1) at least partially as liquid air partial stream (5b) together with the gaseous air partial stream (5c) produced in the throttling (45).
5. Process according to one of the preceding claims, characterized in that a partial amount, preferably cooled and throttled to the pressure level of the low-pressure column (3), of the liquid partial air stream (5d) is used for the at least partial liquefaction of the oxygen-poor vaporous top product (18) of the liquid air column (17), the vapour (25) produced in the liquefaction of the top product (18) being fed into the low-pressure column (3).
6. Process according to one of the preceding claims, characterized in that the oxygen-poor vaporous top product (18) of the liquid air column (17) is drawn off as liquid or gaseous nitrogen product (18a, c).
7. Process according to one of Claims 1 to 4, characterized in that the oxygen-rich liquid bottom product (6) of the pressure column (1) is used as process medium for the partial vaporizing of liquid bottom product (19) of the liquid air column (17) and is subsequently supplied as cooled liquid to the low-pressure column (3) and/or to the condenser (11) of the crude argon column (10).
8. Process according to one of Claims 1 to 4, characterized in that a gaseous side draw-off (20) fed from the crude argon column (10) into the liquid air column (17) is used as the process medium for the partial vaporizing of liquid bottom product (19) of the liquid air column (17) and, on evaporation of the liquid bottom product (19), is fed back at least partially in condensed form as runback (52) into the crude argon column (10).
9. Process according to one of Claims 1 to 4, characterized in that a side gas stream tapped off from the pressure column (1), preferably the top product (7) of the pressure column (1) is used as process medium for the partial vaporizing of the bottom liquid (19) of the liquid air column (17) and is fed back in at least partially condensed form as runback liquid into the low-pressure column (3) and/or as cooling medium into the top condenser (11) of the crude argon column (10).
10. Process according to one of the preceding claims, characterized in that at least one liquid side draw-off (23) of the liquid air column (17) is fed into the pressure column (1) and/or low-pressure column (3) as cooling medium for the condenser (22) of the liquid air column (17) and/or as runback liquid.
11. Process according to one of Claims 1 to 4, characterized in that the predominantly liquid second partial stream (5) of the process air is fed at least partially as heating medium into the bottom vaporizer (21) of the liquid air column (17), is precooled there by indirect heat exchange with evaporating bottom liquid (19), throttled (46a) to the operating pressure of the liquid air column (17) and at least a partial stream of the liquefied air (5d) is fed into the liquid air column (17) together with the vapour (5e) produced in the throttling.
12. Process according to one of Claims 1 to 4, characterized in that the predominantly liquid second partial stream (5) of the process air is fed directly into the pressure column (1) and from the pressure column (1) at least one liquid side draw-off (46) is fed as cooling liquid into the condenser (22) of the liquid air column (17), as feed into the liquid air column (17) and a further partial stream (5f) as runback into the low-pressure column (3).
13. Process according to one of Claims 1 to 4, characterized in that the second partial stream (5) of the process air is cooled in a bottom vaporizer of the pressure column (1) by evaporating bottom product (6) and throttled (46a) to the pressure level of the liquid air column (17), and fed as liquid and vaporous air partial streams (5d, e) into the liquid air column (17) and from the liquid air column (17) at least partially as liquid air partial stream (5f) into the low-pressure column (3).
14. Process according to one of claims 1 to 4, characterized in that the predominantly liquid partial stream (5) is expanded directly into a separating tank (27) arranged upstream of the liquid air column (17), and the vapour (5e) produced in the expansion is fed into the liquid air column (17) together with at least one liquid air partial stream (5b) from the separating tank (27).
15. Process according to one of Claims 1 to 4, characterized in that a bottom product (34) that can be drawn off from the crude argon (14a, b) fed into the pure argon column (32) by means of rectifying devices (39) into the oxygen- and nitrogen-poor liquid pure argon product is partially vaporized by means of a bottom vaporizer (37) operated by means of a gaseous process medium (36) supplied from the pressure column (1), and the argon-poor vaporous top product (35) rectified from the crude argon (14a, b) is condensed by means of a partial stream of the liquid drawn off from the bottom product (19) of the liquid air column (17) and the gaseous inert fraction of the top product that cannot be condensed is blown off as scavenged discharge into the surroundings of the plant.
16. Process according to one of the preceding claims, characterized in that the liquid air column (17) is operated at an operating pressure lying between the pressure of the pressure column (1) and the low-pressure column (3), preferably at an operating pressure of less than 2.3 bar.
17. Apparatus for carrying out the process according to one of Claims 1 to 16, with at least one two-stage rectifying column, comprising a pressure column (1) and a low-pressure column (3) with a common condenser (2), which are connected to a heat exchanger network and at least one crude argon column (10) as well as at least one liquid air column (17) by means of lines equipped with measuring, controlling and conveying devices.
18. Apparatus according to Claim 17, characterized in that the liquid air column (17) connected to the heat exchanger network and equipped with rectifying devices (54), top condenser (22) and bottom vaporizer (21) as well as product lines is connected by means of lines (46, 20, 52, 25, 24, 16, 58) to the pressure column (1), the low-pressure column (3) and the crude argon column (10).
19. Apparatus according to Claim 17 or 18, characterized in that the bottom vaporizer (21) of the liquid air column (17) is connected by means of lines (20, 52, 66, 46) to the pressure column (1) and the crude argon column (10).
20. Apparatus according to Claim 17, characterized in that the crude argon column (10) equipped with rectifying devices (51), top condenser (11) and product lines is connected by means of line (33b) to a pure argon column (32) and by means of lines (13a, 49, 53, 62) to the pressure column (1), the low-pressure column (3) and the liquid air column (17).
21. Apparatus according to Claim 20, characterized in that the pure argon column (32), connected by means of line (33b) to the crude argon column (10) and having rectifying devices (39), a top condenser (31), a bottom vaporizer (37) and a product line (38), is connected by means of lines (44, 36, 54, 69) to the pressure column (1), the low-pressure column (3) and the liquid air column (17).
22. Apparatus according to Claim 21, characterized in that the top condenser (31) of the pure argon column (32) is connected by means of line (59) to the bottom of the liquid air column (17).
23. Apparatus according to Claim 17, characterized in that a separator (27) is connected by means of line (67) to the heat exchanger network and by means of lines (59, 28, 60) to the pressure column (1) and the liquid air column (17).

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