EP2914913A2 - Process for the low-temperature separation of air in an air separation plant and air separation plant - Google Patents

Abstract

The invention relates to a process for the separation of air (AIR), in which cooled air (AIR) at a first separation pressure is separated in a first separation column (S1) at least into a nitrogen-enriched top fraction and an oxygen-enriched bottom fraction, and in which further cooled air (AIR) in a mixing column (M) is liquefied at a mixing column pressure by means of direct heat exchange against a liquid oxygen-enriched stream, which is at least partly obtained from the oxygen-enriched bottom fraction from the first separation column (S1), to form a mixing column bottom fraction. According to the invention further cooled air (AIR) at a second separation pressure is likewise separated in a second separation column (S2) into a nitrogen-enriched top fraction and an oxygen-enriched bottom fraction, wherein the nitrogen-enriched top fraction from the second separation column (S2) is at least partly cooled by using the mixing column bottom fraction from the mixing column (M). To this end, the nitrogen-enriched top fraction from the second separation column (S2) is at least partly guided through the liquefaction chamber of a top condenser (E2) of the second separation column (S2), which is constructed as a condenser evaporator and the evaporation chamber of which is operated at an evaporation chamber pressure which lies between the mixing column pressure and a third separation pressure, at which the liquid oxygen-rich stream is obtained in a third separation column (S3), and in which at least part of the mixing column bottom fraction from the mixing column (M) is fed in in liquid form at the evaporation chamber pressure. The invention further relates to a corresponding air separation plant.

Description

 description

Process for the cryogenic decomposition of air in an air separation plant and

 The invention relates to a process for the cryogenic separation of air using a mixing column and to an air separation plant set up to carry out a corresponding process.

State of the art

The production of oxygen or of oxygen-rich mixtures, hereinafter referred to as oxygen products, is usually carried out by cryogenic separation of air in air separation plants with distillation column systems known per se. These can be designed as two-column systems, in particular as classical double-column systems, but also as three-column or multi-column systems. Furthermore, devices for obtaining further air components, in particular the noble gases krypton, xenon and / or argon, may be provided.

At least not exclusively pure oxygen is needed for a number of industrial applications. This opens up the possibility of optimizing air separation plants with regard to their production and operating costs, in particular their energy consumption (see, for example, Chapter 3.8 in Kerry, F.G.: Industrial Gas Handbook: Gas Separation and Purification, Boca Raton: CRC Press, 2006). For this purpose, inter alia, air separation plants can be used with so-called mixing columns, as they have been known for some time. Corresponding systems and methods are described, for example, in DE 2 204 376 A1 (corresponding to US Pat. No. 4,022,030 A) US Pat. No. 5,454,227 A, US Pat. No. 5,490,391 A, DE 198 03 437 A1, DE 199 51 521 A1, US Pat.

EP 1 139 046 B1 (US 2001/052244 A1), EP 1 284 404 A1 (US Pat. No. 6,662,595 B2), DE 102 09 421 A1, DE 102 17 093 A1, EP 1 376 037 B1 (US Pat. No. 6,776,004 B2) .

EP 1 387 136 A1 and EP 1 666 824 A1. Further air separation plants, which can be designed as three-column systems and have mixing columns, are described, for example, in US Pat. No. 4,818,262 A, US Pat. No. 5,715,706 A, EP 1 139 046 B1 and US Pat US 4,783,208 A discloses. An air separation plant with a three-pillar system is also disclosed in DE 10 2009 023 900 A1.

In a mixing column, a liquid, oxygen-rich stream in a top region and a gaseous air stream are fed in a lower region and sent towards each other. Through intensive contact, a certain proportion of the more volatile nitrogen from the air stream passes into the oxygen-rich stream. The oxygen-rich stream is vaporized in the mixing column and withdrawn at the upper end as gaseous, so-called impure oxygen. The impure oxygen can be taken from the air separation plant as a gaseous oxygen product.

The air stream in turn is liquified, enriched to some extent with oxygen, and can be withdrawn at the bottom of the mixing column. The liquefied stream can then be fed into the distillation column system used at an energetically and / or separation-appropriate location. By using a mixing column, the energy required for material separation can be significantly reduced at the expense of the purity of the gaseous oxygen product.

In air separation plants, especially in air separation plants with mixing columns, there is a need for improvements that increase overall efficiency and reduce power consumption.

DISCLOSURE OF THE INVENTION Against this background, the invention proposes a method for the cryogenic separation of air using a mixing column and an air separation plant adapted for carrying out a corresponding method with the features of the independent claims. Preferred embodiments are subject of the dependent claims and the following description.

Advantages of the invention

The present invention is based on a method for the decomposition of air, wherein the cooled air at a first separation pressure in a first separation column of a Distillationssäulensystems at least in a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction is separated.

As mentioned, air separation may, for example, be done using double column systems. Such double column systems include a so-called high pressure separation column and a low pressure separation column. In the high-pressure separation column is compressed and cooled to a temperature near its condensation temperature cooled air is fed. In the high-pressure separation column, this air is separated into a nitrogen-enriched top fraction and into an oxygen-enriched bottoms fraction. The oxygen enriched bottoms fraction is at least partially withdrawn from the high pressure separation column and transferred to the low pressure separation column.

In the low-pressure separation column, an oxygen-rich liquid fraction which separates out in the bottom of the low-pressure separation column is obtained at least from the oxygen-enriched bottom fraction from the high-pressure separation column. In the low-pressure separation column but also other streams can be fed, for example, a sump fraction from the mixing column.

In the present application substances and mixtures are also referred to as streams and fractions. A stream is usually routed as fluid in a conduit designed for this purpose. A fraction usually denotes a portion of a starting mixture separated from a starting mixture. A political group can generate a corresponding current at any time if it is managed accordingly. Conversely, for example, a stream may serve to provide a starting mixture from which a fraction can be separated.

A stream or fraction may be rich or poor in one or more of its constituents, with "rich" accounting for greater than 75%, 80%, 85%, 90%, 95%, 99%, 99.5%. or 99.9% and "poor" for less than 25%, 20%, 15%, 10%, 5%, 1%, 0.5% or 0.1%, respectively, in molar, weight and% / or volume basis, can stand. A stream or fraction may also be enriched or depleted of a component over a starting mixture, "enriched" for at least 1.5, 2x, 3, 5, 10, or 100 times Content and "depleted" for not more than 0.75 times, 0.5 times, 0.25 times, 0.1 times or 0.01 times the content, in each case based on the appropriate content in each Aüsgangsgemisch, may be. The terms also include ranges of values, for example, with the stated values as upper and lower limits. Conventional high-pressure separation columns operate at a separation pressure of for example 5 to 7.5 bar, in particular from 5.5 to 6 bar. Conventional low-pressure separation columns operate at a separation pressure of for example 1, 3 to 1, 8 bar, in particular from 1, 3 to 1, 6 bar. These and the following are absolute pressures. The high-pressure separation column and the low-pressure separation column can also be at least structurally separated from one another. In this case, it is the aforementioned two-pillar systems. The high pressure separation column is sometimes referred to as medium pressure separation column. Also Ehrsäulensysteme and / or distillation column systems, which are adapted to obtain further components from air, can be used in the context of the present invention.

However, all such systems have at least one column in which cooled air at a defined operating pressure, referred to herein as separation pressure, is separated at least into a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction. Such a separation column is referred to in this application as the first separation column, the corresponding pressure as the first separation pressure.

In the context of the present invention, a mixing column is furthermore used, in which cooled air, which is fed in gaseous form into the mixing column, is liquefied by direct heat exchange against a liquid, oxygen-rich stream. The cooled air is fed into a lower area of the mixing column, the liquid oxygen-rich stream in an upper area. Both streams are sent to each other. As mentioned, enriched by the intense exchange between the two streams of oxygen from the liquid, oxygen-rich stream in the air, conversely, the liquid oxygen-rich stream is contaminated with particular nitrogen from the air. This is also done at a defined pressure, which is referred to herein as mixing column pressure. In the bottom of the mixing column, the liquefied and oxygen-enriched air separates as Mischsäulensumpfffraktion. The liquid, oxygen-rich stream fed to the mixing column is usually recovered using the oxygen-enriched bottom fraction of at least the first separation column. For this purpose, as mentioned, at least partially transferred into the low-pressure separation column and from this a corresponding liquid, oxygen-rich fraction deposited.

The distillation columns of distillation column systems in air separation plants are at least partially equipped with a so-called top condenser. This applies at least to the high-pressure separation column of classic double-column systems. The top condenser of the high-pressure separation column, which is typically designed as a condenser evaporator, is also commonly referred to as a main condenser. In a top condenser, gaseous fluid is withdrawn from the top of the corresponding column and passed through the top condenser. The gaseous fluid liquefies thereby at least partially. In conventional air separation plants, a gaseous top product (so-called head nitrogen) of the high-pressure separation column is at least partially liquefied in the main condenser (ie the top condenser of the high-pressure separation column) and a bottom product of the low-pressure separation column, which is arranged above the high-pressure column, evaporates. The main condenser is often placed inside the low pressure separation column (internal main condenser) alternatively it can be placed in a separate container outside the low pressure column and connected via lines to the low pressure separation column (external main condenser).

In a condenser evaporator, as is typically used as a top condenser, a liquid to be evaporated (also referred to as cooling medium) in an evaporation space is at least partially vaporized against a gaseous fluid in a liquefaction space. The gaseous fluid, which is passed through the liquefaction space, liquefies thereby at least partially. A condenser evaporator thus has a liquefaction space and an evaporation space. Evaporation and liquefaction space are each formed by groups of passages (liquefaction or evaporation passages) which are in fluid communication with each other. In the liquefaction space, the condensation of a first fluid flow is performed, in the evaporation space, the evaporation of a second fluid flow. The two fluid streams are in indirect heat exchange. Condenser evaporators are also referred to as bath evaporators. According to the invention, it is now provided to use a second separation column with a corresponding overhead condenser designed as a condenser evaporator, into which cooled air is also fed. This is operated at a second separation pressure. In the second separation column, the air is also separated at least into a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction. It is therefore a second separation column, which can be operated with respect to the first separation column at a different second separation pressure. The second separation pressure may be less than the first separation pressure. The second separation column can therefore also be referred to, for example, as a second high-pressure separation column or as a medium-pressure separation column.

In order to distinguish this from the present application, the separation column in which the liquid, oxygen-rich stream is obtained, which is fed into the mixing column, referred to as the third separation column. The pressure used in the third separation column is referred to as the third separation pressure. As mentioned, this is typically a low pressure separation column.

According to the invention, it is further provided to cool the nitrogen-enriched top fraction of the second separation column with the mixed column sump fraction, that is to say the air liquefied in the mixing column and enriched with oxygen. By cooling the nitrogen-rich overhead fraction of the second separation column, it can be liquefied, so that it can be applied again to the second separation column. In the context of the present invention, the second separation column is equipped for this purpose with the mentioned top condenser, which is designed in the form of a condenser evaporator whose evaporation space is operated at a pressure which lies between the mixing column pressure and the third separation pressure, at which the liquid oxygen-rich stream in the third separation column is recovered. The pressure at which this evaporation space is operated is referred to herein as evaporation space pressure. At least part of the mixed column sump fraction at the evaporation space pressure in liquid form is fed into the evaporation space. The mixing column sump fraction forms a liquid bath in the evaporation space of the top condenser of the second separation column. The top fraction of the second separation column is guided at least in part through the liquefaction space of the overhead condenser and warms the liquid bath with it. The latter is thereby continuously evaporated, the top fraction of the second separation column is at least partially liquefied.

As also explained below, the present invention, by using the mixing column scum fraction to cool the top fraction of the second separation column, allows separation of feed air with the natural contents of its individual air components at a comparatively low or even very low second separation pressure. Correspondingly low separation pressures are conventionally used only in medium-pressure separation columns, which, however, are fed at least in part with air fractions already pre-separated in a high-pressure separation column. The mixed column scum fraction is particularly suitable for cooling the top fraction of the second separation column due to its composition and low boiling point as discussed below. The correspondingly vaporized mixed column sump fraction can be fed in gaseous form into the third separation column, for example the mentioned low-pressure separation column. A small proportion of the Mischsäulensumpffraktion can also be withdrawn in liquid form as a flushing.

Due to the low separation pressure that can be used in the second separation column, only a comparatively small part of the air used in an air separation plant according to the invention needs to be compressed to higher pressures, which saves compressor performance and thus results in improved efficiency.

Advantageously, a pressure which is at least 0.5 bar higher than the pressure used as the second separation pressure is used as the first separation pressure. Further, as the second separation pressure, it is preferable to use a pressure which differs by at most 0.5 bar from the pressure used as the mixing column pressure. As the third separation pressure, it is advantageous to use a pressure which is at least 2 bar below the pressure used as the first and / or the second separation pressure. Here, as the first separation pressure is a pressure of 4 to 6 bar, in particular from 5.0 to 5.5 bar, and / or as the second separation pressure, a pressure of 3 to 5 bar, in particular from 4.0 to 4.5 bar , and / or as the third separation pressure, a pressure of 1 to 2 bar, in particular from 1, 2 to 1, 6 bar, and / or as the mixing column pressure, a pressure of 2 to 5 bar, in particular from 4.0 to 4.5 bar, particularly advantageous, as explained below. The advantages of a method using said pressures and providing each of the cooled air at the first separation pressure, the second separation pressure and the mixing column pressure and fed to the first separation column, the second separation column and the mixing column are explained below ,

By the method proposed according to the invention, or in a corresponding air separation plant, energy can be saved in particular by not having to compress all the air to the pressure level of the first separation pressure, that is, the pressure used in the first separation column. As mentioned, the first separation pressure is usually higher than the second separation pressure.

However, even at the low pressure in the second separation column, similar to the first separation column, an oxygen-enriched bottom fraction can be obtained. This can be transferred together with the oxygen-enriched bottoms fraction from the first separation column in a third separation column, for example, the so-called low-pressure separation column. In the third separation column, an oxygen-rich liquid fraction can be obtained from the two bottom fractions, ie from the bottom fraction of the first separation column and from the bottom fraction of the second separation column. However, the energy required for this purpose is much lower.

Advantageously, a pressure which is at most 0.5 bar higher than the pressure which is used as the third separation pressure is used as the evaporation space pressure. Here, the Mischsäulensumpffraktion is relaxed via a valve in the evaporation chamber of the top condenser of the second separation column. The vaporization space pressure is adjusted as far as possible so that on the one hand a maximum amount of cold can be provided by the evaporating mixed column sump fraction and on the other hand the vaporized portion of the mixed column sump fraction can flow into the third separation column without further measures. The evaporation space pressure is thus advantageously at least slightly above the third separation pressure at which the third separation column is operated.

The invention thus provides an energy-optimized mixed column method with a second separation column. The proposed mixed column method is particularly suitable for producing an oxygen product which is obtained in gaseous form and which has between 80 and 98% purity. Appropriate products can can be obtained with conventional mixing column methods, but the proposed method is optimized in terms of its power consumption due to the lower pressure requirement. The inventive method is particularly suitable for a discharge pressure of the oxygen product of about 4 bar.

In the method according to the invention, for example, a main air compressor compresses the total amount of air required, here also referred to as total air, to a pressure of, for example, 4.6 bar. The compressed air is dried and purified, for example, in a molecular sieve adsorber.

A portion of the air, for example, about half, is in this example in a booster to a higher pressure, for example, to 5.6 bar, recompressed. The rest will not be re-compressed. The recompressed air and the non-compressed air are cooled in a main heat exchanger. Different parts or partial flows of the after-compressed and / or the non-compressed air can also be cooled to different temperatures. By cooling and by line losses results in each case a slight pressure drop of, for example, 0, 1 to 0.2 bar. As a result, the post-compressed, cooled air is present at the first separation pressure, for example at 5.4 bar, the non-compressed, cooled air at the second separation pressure, for example at 4.3 bar.

The recompressed, cooled air can now be partially fed into the first separation column and separated there. Another fraction which has not necessarily been cooled to the same temperature as the fraction fed into the first separation column can be expanded for cooling by means of a so-called injection turbine. The correspondingly relaxed air can be fed, for example, at a defined height into a third separation column, for example the low-pressure separation column.

Alternatively, however, the post-compressed, cooled air can be completely fed into and separated from the first separation column, especially when a mixed-column turbine explained below is used.

The non-densified, cooled air can be fed to one part in the second separation column and to another part in the mixing column. As explained, a mixed column scum fraction is recovered in the mixing column. In the second separation le, the feed air is separated at the second separation pressure. In order to enable separation at the low second separation pressure, for example at 4.3 bar, the top fraction from the second separation column is cooled, as mentioned, in a top condenser designed as a condenser evaporator with a part of the mixing column sump fraction. The Mischsäulensumpffraktion is suitable for this purpose in a special way. It evaporates, for example, at about 1.4 bar (ie at the third separation pressure or slightly above it) and has about 65% oxygen.

However, the air fed into the mixing column need not be provided, or not exclusively, in the form of non-compressed and cooled air. For example, it is also possible to use a mixing column turbine, is fed into the air at a pressure higher than the mixing column pressure, and can be obtained in accordance with the cold. The air which is fed into the mixing column turbine can be made available as a further proportion of the recompressed and cooled air, but it is also possible for example to carry out a separate recompression, for example in a booster coupled to the mixing column turbine.

The expanded in the mixing column turbine air can then be fed at the mixing column pressure in the mixing column. This is particularly advantageous if no injection turbine, as explained above, is provided. In certain cases, however, both an injection turbine and a mixing column turbine may be provided. If a mixing column turbine is provided, the non-compressed and cooled air can also be fed completely into the second separation column. In other words, it is possible to provide process variants in which alternative to one another or in a respectively suitable combination

the cooled air at the second separation pressure and / or with the mixing column pressure is provided by compression in a main compressor and subsequent cooling in a heat exchanger,

- The cooled air is provided with the mixing column pressure by compression in a main compressor, subsequent recompression in a secondary compressor, subsequent cooling in a heat exchanger and subsequent expansion in a relaxation machine, or - The cooled air is provided with the first separation pressure by compression in a main compressor, subsequent recompression in a secondary compressor and subsequent cooling in a heat exchanger.

Instead of a supplied with cooled air injection and / or mixing column turbine and a so-called PGAN turbine can be used. For this purpose, a nitrogen-containing top product can be withdrawn in gaseous form from the first separation column, heated in the main heat exchanger to 130 to 200 K, and then in a so-called PGAN turbine, for example. be relaxed from about 5.3 to about 1, 1 bar work.

Compared to conventional methods in which mixed-column turbines are used, the measures according to the invention result in energy savings of up to 5%, compared to conventional methods in which injection turbines are used, energy savings of up to 10%. As explained, these advantages result inter alia from the use of the low second separation pressure which, in turn, can be used with the bottom product of the mixing column owing to the inventively proposed cooling of the top fraction of the second separation column. In summary, it can thus advantageously be provided to provide the cooled air with the second separation pressure and / or the mixing column pressure by compression in a main compressor and cooling in a heat exchanger. This is very easy to implement in cases in which the second separation pressure corresponds to the mixing column pressure, because thus an air stream compressed to a corresponding pressure has to be divided only into partial streams. Alternatively, however, it is also possible to provide the cooled air with the mixing column pressure by compression in a main compressor, after-compression in a secondary compressor, cooling in a heat exchanger and venting in a expansion machine, namely the illustrated mixed-gas turbine. The advantages of this embodiment lie in a more flexible refrigeration production. Furthermore, the mixing column can also be operated at a mixing column pressure which deviates to a certain extent from the second separation pressure. Since the mixing column pressure essentially corresponds to the discharge pressure of the oxygen product produced in the mixing column, there is also the possibility of a more flexible adaptation. The mixing column can thereby be operated at a lower mixing column pressure. The cooled air with the first separation pressure becomes finally advantageously provided by compression in a main compressor and a secondary compressor and subsequent cooling.

As already explained, in conventional mixed column processes the oxygen-rich, liquid stream fed into the mixing column is obtained by separating an oxygen-rich bottoms fraction from the separation column enriched in an oxygen-enriched bottoms fraction in a further separation column, for example the low-pressure separation column, and removing them from the separation column becomes. In the context of the method proposed here, the oxygen-enriched bottom fraction of the first and / or second separation column, in particular both, is advantageously used. The oxygen-rich bottoms fraction is deposited in the third separation column already mentioned. This results in the explained savings. In this case, the third separation pressure is advantageously at least 2 bar below the first and / or the second separation pressure.

Cooled air, which has been compressed to a pressure above the third separation pressure, can advantageously also be blown into the third separation column. For this purpose, the already explained injection turbine is used. An air separation plant according to the invention is set up for carrying out a method as explained above and has corresponding means.

In particular, the means which are designed to cool the nitrogen-enriched top fraction of the second separation column with the Mischsäulensumpffraktion, a top condenser of the second separation column, which is designed as a condenser evaporator whose liquefaction space flows through the nitrogen-enriched overhead fraction and its evaporation space are cooled with the Mischsäulensumpfffraktion can, and in which the Mischsäulensumpfffraktion is liquid. In a corresponding system, the mixing column is advantageously arranged above the second separation column. This allows a particularly compact design of corresponding air separation plants. By an arrangement "above" is meant that overlap the projections of the mixing column and the second separation column to a horizontal plane at least partially. The horizontal plane It speaks a plane perpendicular to the longitudinal axis of corresponding columns. In operation, the longitudinal axis is aligned perpendicular to the earth's surface.

Furthermore, in the context of the present invention, the mixing column and the second separation column are advantageously designed together in the form of a one-part column. A one-piece column is surrounded by a common metal shell, which encloses the respective column parts, and within which the column parts can be provided as compartments. An example of a one-piece column with two column sections is the classic Linde double column with the high and low pressure separation column. Also, the mixing column and the second separation column can thus form a double column in the context of the present invention.

The top condenser of the second separation column is advantageously arranged inside or below the mixing column in a corresponding one-part column (corresponding to an internal main condenser of a Linde double column).

The invention will be explained in more detail with reference to the accompanying drawing, which shows a preferred embodiment of the invention. Brief description of the drawings

Figure 1 shows an air separation plant according to a particularly preferred embodiment of the invention in a schematic representation. Embodiment of the invention

1 shows an air separation plant according to a particularly preferred embodiment of the invention is shown and designated 10 in total. In FIG. 1, pressures used in particular lines are indicated in dashed lines. These pressures merely represent non-limiting example values. The pressure values and value ranges which can be used in a corresponding air separation plant 10 have been explained above.

The air separation plant 10 is fed, inter alia, via a line a and b via a line compressed and purified air AIR. The compaction and Cleaning is carried out in a known manner, for example in a main compressor, the filter plants upstream and air scrubber or adsorption devices are followed. A corresponding air separation plant 10 can be operated using main and secondary compressors, so that the supplied air AIR with different pressures, here for example 5.6 bar in the line a and 4.4 bar in the line b, can be provided ,

The fed via the line a in the system 10 air is fed to a heat exchanger E1 and cooled in this. Via a line c, this air can be taken from the heat exchanger E1 to a part at the cold end and via a line d to another part at an intermediate temperature. The air is present in the lines c and d due to the cooling and due to pressure losses each at a pressure which is slightly lower than the pressure in the line a. The pressure in line c corresponds to the separation pressure of a first separation column S1 and in the example shown is 5.4 bar. The corresponding air is fed via the line c into a lower region of the first separation column S1. In this, the feed air can be separated in a known manner into a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction.

In line d, the air removed at the intermediate temperature from the heat exchanger E1 can be fed to an expansion machine X1, which is coupled to an energy converter B, for example an oil brake. The correspondingly relaxed air leaves the expansion machine X1 via a line e.

The fed via the line b in the system 10 air is also fed to the heat exchanger E1 and cooled in this. It can via a line f at a relation to the pressure in line b also slightly reduced pressure, for example 4.3 bar, via a line f to a part in a lower region of a second separation column S2 and via a line g to another part be fed into a lower region of a mixing column M.

The second separation column S2 and the mixing column M can also be designed as a structural unit (one-part column). The second separation column S2 and the mixing column are operated in the example shown at the pressure of 4.3 bar. Into the mixing column M is fed via a line h an oxygen-rich liquid stream in an upper region and fed against the fed via the line g air at the mixing column pressure. Due to the intensive contact of the air from the line g and the oxygen-rich liquid stream from the line h, part of the nitrogen in the air passes into the oxygen-rich stream. The oxygen-rich stream is vaporized, the air liquefies, is at the same time enriched to some extent with oxygen, and separates out as Mischsäulensumpffraktion in a lower region of the mixing column M. From the lower region of the mixing column M, the mixing column scum fraction can be removed via lines i and k.

Via the line i, the mixing column sump fraction can be fed via an unillustrated valve into an underlying evaporation space of a top condenser E2 of the second separation column S2, which is designed as a condenser evaporator. The liquefaction space of the top condenser E2 can be flowed through via a line system I with the nitrogen-enriched overhead fraction from the second separation column S2. The condensate obtained in the liquefaction space of the top condenser E2 can be partly supplied as reflux to the second separation column S2 and fed to another part via a line m to a heat exchanger E3 designed as a subcooler and subsequently via a line n to an upper region of a third separation column S3 are fed. The third separation column S3 is designed as a low-pressure separation column.

The proportion of Mischsäulensumpffraktion in the line k passes through the heat exchanger E3 and can then be fed via a line o, in a defined height in the third separation column S3. A vaporized portion of the mixing column scum fraction used to cool the top condenser E2 can also be supplied to the third separation column S3 via a line p. Since the evaporation space of the top condenser E2 is operated at an evaporation space pressure between the mixing column pressure at which the mixing column M is operated and the third separation pressure at which the third separation column S3 is operated, fluid can escape from the evaporation space of the top condenser E2 discharge further measures in the third separation column S3. On the top side of the mixing column M, a gaseous oxygen-rich stream obtained by evaporating the liquid oxygen-rich stream from the line h and exchanging it with the air from the line g can be withdrawn via a line q and a valve V1. The gaseous oxygen-rich stream is heated in the heat exchanger E1 and discharged via a valve V2 at a pressure of, for example, 4.0 bar as gaseous oxygen product GOX. Another portion of the liquid oxygen-rich stream can be discharged via a valve V3 as the purge fraction LOX. This discharge takes place in small quantities, the liquid oxygen is therefore not a product of a corresponding air separation plant 10. Its removal is used primarily the removal of components contained therein such as methane.

The oxygen-enriched bottom fraction from the second separation column S2 can be removed via a line r, cooled in the heat exchanger E3 and fed via a line s and a valve V4 in the third separation column S3.

From the first separation column S1, the nitrogen-enriched overhead fraction can be removed and condensed via a line system t to a part in a heat exchanger E4 and be charged in liquid form back to the first separation column S1. The heat exchanger E4 is designed as a top condenser and is cooled with a liquid, oxygen-rich sump fraction of the third separation column S3.

Via a line u, another part of the nitrogen-enriched top fraction can be taken from the first separation column S1, passed through the heat exchanger E1, and discharged via a valve V5 as purge gas SG.

The oxygen-enriched bottoms fraction may be withdrawn via a line v from the first separation column S1, passed through the heat exchanger E3 and fed together with the oxygen-rich bottom fraction from the second separation column S2 via the line s in the third separation column S3. Another fraction can be removed from the first separation column via a line w and after passing through the heat exchanger E3 via the explained line n also be fed into the third separation column S3.

In the third separation column S3 is from the oxygen-enriched bottom fraction of the first and second separation column S1, S2 and using the other fed streams deposited an oxygen-rich sump fraction. The air released from the line e via the expansion machine X1 is also fed into the third separation column (blown in). The oxygen-rich bottom fraction can be removed via a line x and fed by means of a pump P1 to the heat exchanger E3. After a first heating there, the oxygen-rich bottom fraction can be fed via a line y to the heat exchanger E1, where it is further heated and finally fed via the illustrated line h into the upper region of the mixing column M.

Via a line z, a gaseous fraction can be withdrawn from the top of the third separation column, heated by the heat exchangers E3 and E1 and discharged from the air separation plant 10. This fraction can be used in the upstream air purification and / or delivered to the atmosphere ATM.

As mentioned, air can also be fed into the mixing column M via a flash-down machine, then called a mixing column turbine. This can be provided additionally or alternatively to the expansion machine X1, which is also referred to as injection turbine.

Claims

claims A process for the separation of air (AIR), wherein the cooled air (AIR) at a first separation pressure in a first separation column (S1) at least in a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction is separated, and in the further cooled air (AIR) in one Mixed column (M) at a mixing column pressure by direct heat exchange against a liquid oxygen-rich stream, which is at least partially recovered from the oxygen-enriched bottoms fraction from the first separation column (S1) is liquefied to a Mischsäulen- sumpffraktion, characterized in that further cooled air (AIR ) is also separated in a second separation column (S2) at a second separation pressure at least in a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction, wherein the nitrogen-enriched top fraction of the second separation column (S2) at least partially with the mixing column sumpffraktion from the mixing column (M) is cooled by the nitrogen-enriched overhead fraction of the second separation column (S2) at least partially through the liquefaction space of a top condenser (E2) of the second separation column (S2) is formed, which is designed as a condenser evaporator whose evaporation space is operated at an evaporation space pressure between the mixing column pressure and a third separation pressure at which the liquid oxygen-rich stream is recovered in a third separation column (S3) and to which at least a portion of the mixing column sump fraction from the mixing column (M) is liquidly fed at the evaporation space pressure. The method of claim 1, wherein the pressure used as the first separation pressure is at least 0.5 bar, in particular at least 1 bar, higher than the pressure used as the second separation pressure. The method of claim 1 or 2, wherein the pressure used as the second separation pressure is at most 0.5 bar different from the pressure used as the mixing column pressure. A method according to any one of the preceding claims, wherein the pressure used as the third separation pressure is at least 2 bar below the pressure used as the first and / or the second separation pressure. A method according to any one of the preceding claims, wherein as the evaporation space pressure, a pressure which is at most 0.5 bar higher than the pressure used as the third separation pressure is used. Method according to one of the preceding claims, wherein as the first separation pressure, a pressure of 4 to 6 bar, in particular from 5.0 to 5.5 bar, and / or as the second separation pressure, a pressure of 3 to 5 bar, in particular of 4 , 0 to 4.5 bar, and / or as the third separation pressure, a pressure of 1 to 2 bar, in particular from 1, 2 to 1, 6 bar, and / or as the mixing column pressure, a pressure of 2 to 5 bar, in particular of 4.0 to 4.5 bar, is used. Method according to one of the preceding claims, wherein each of the cooled air (AIR) provided with the first separation pressure, the second separation pressure and the mixing column pressure and in the first separation column (S1), the second separation column (52) and the mixing column (M) is fed. A process according to any one of the preceding claims, wherein the oxygen-rich liquid stream is recovered by passing from the oxygen-enriched bottom fraction of the first and / or second separation column (S1, S2) in the third separation column (53) at the third separation pressure an oxygen-rich bottoms fraction is deposited and removed from the third separation column (S3). Process according to Claim 8, in which air (AIR), which has been compressed and cooled to a pressure above the third separation pressure, is expanded in at least one expansion machine (X1) to the third separation pressure and fed to the third separation column (S3). 0. Air separation plant (10), which is adapted to carry out a method according to any one of the preceding claims, with  a first separation column (S1) adapted to separate cooled air (AIR) at least at a first separation pressure into a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction, a mixing column (M), which is adapted to supply further cooled air (AIR) at a mixing column pressure by direct heat exchange against a liquid column to liquefy oxygen-rich stream to a mixed column bottoms fraction,  - A second separation column (S2) having a top condenser (E2), which is designed as a condenser evaporator, and which is adapted, further cooled air (AIR) at a second separation pressure also at least in a nitrogen-enriched overhead fraction and an oxygen-enriched bottom fraction to separate, and  - a third separation column (S3), which is adapted to at least partially extract the liquid oxygen-rich stream at a third separation pressure from the oxygen-enriched bottom fraction from the first separation column (S1),  wherein means are provided which are adapted to at least partially cool the nitrogen-enriched overhead fraction of the second separation column (S2) with the mixed column scum fraction from the mixing column (M) by at least partially transferring the nitrogen-enriched overhead fraction of the second separation column (S2) Lead the liquefaction space of the top condenser (E2) of the second separation column (S2),  • Operate the evaporation space of the top condenser (E2) at an evaporative space pressure between the mixing column pressure and the third separation pressure, and  • In the evaporation space of the top condenser (E2) at least a portion of the Mischsäulensumpfffraktion from the mixing column (M) at the evaporation space pressure liquid feed. 1 1. Air separation plant (10) according to claim 10, wherein the mixing column (M) together with the second separation column (S2) in the form of a one-piece column and / or the mixing column (M) above the second separation column (S2) is arranged.