WO2020244801A1

WO2020244801A1 - Method and system for low-temperature air separation

Info

Publication number: WO2020244801A1
Application number: PCT/EP2020/025207
Authority: WO
Inventors: Dimitri GOLUBEV
Original assignee: Linde Gmbh
Priority date: 2019-06-04
Filing date: 2020-05-06
Publication date: 2020-12-10
Also published as: US20220228804A1; EP3980705A1; TW202108222A; KR20220015406A; CN113874669A

Abstract

The invention relates to a method for low-temperature air separation, in which an air separation system (100-500) with a column system (10) is used which has a first column (11), a second column (12), a third column (13) and a fourth column (14), wherein fluid from the first column (11) is fed at least into the second column (12), fluid from the second column (12) is fed at least into the third column (13), fluid from the third column (13) is fed at least into the fourth column (14), and fluid from the fourth column (14) is fed at least into the third column (13), and wherein the fluid fed from the third column (13) into the fourth column (14) comprises at least part of a side flow which is drawn from the third column (13) and has a lower oxygen content and a higher argon content than the third sump liquid. According to the invention, a return liquid is formed by condensing head gas from the first column (11) and is fed back flowingly to the first column (11). In order to condense the head gas from the first column (11), a liquid cooling flow is provided and is evaporated or partially evaporated in indirect heat exchange with the head gas, and gas formed during the evaporation or partial evaporation of the cooling stream is expanded to a pressure in the second pressure range such that work is performed and is fed into the second column (12). The present invention also relates to a corresponding system (100-500).

Description

description

Process and system for the cryogenic separation of air

The present invention relates to a method and a system for

Cryogenic decomposition of air according to the generic terms of the independent

Claims.

State of the art

The production of air products in the liquid or gaseous state by the low-temperature decomposition of air in air separation plants is known and

for example at H.-W. Häring (Ed.), Industrial Gases Processing, Wiley-VCH,

2006, especially Section 2.2.5, "Cryogenic Rectification".

Air separation plants have rectification column systems that

conventionally, for example, as two-column systems, in particular as classic Linde double-column systems, but also as three- or

Multi-column systems can be formed. In addition to the rectification columns for obtaining nitrogen and / or oxygen in liquid and / or gaseous state, i.e. the rectification columns for nitrogen-oxygen separation, rectification columns can be provided for obtaining further air components, in particular the noble gases krypton, xenon and / or argon. The terms “rectification” and “distillation” and “column” and “column” or terms composed of these are often used synonymously.

The rectification columns of the mentioned rectification column systems are operated at different pressure levels. Known double column systems have a so-called high pressure column (also referred to as a pressure column, medium pressure column or lower column) and a so-called low pressure column (also referred to as an upper column). The high pressure column is typically on a

Pressure level of 4 to 7 bar, in particular about 5.3 bar, operated. The

The low-pressure column is operated at a pressure level of typically 1 to 2 bar, in particular about 1.4 bar. In certain cases, both

Rectification columns can also be used at higher pressure levels. With the here and The pressures given below are absolute pressures at the top of the columns given.

In particular for the supply of semiconductor plants (so-called fabs), in addition to gaseous, high-purity nitrogen and, if possible, oxygen, which is as free of particles as possible, the supply of comparatively small amounts of

gaseous argon desired. For this purpose, either liquid argon can be delivered or evaporated on site, or gaseous argon can be obtained on site. The delivery of liquid argon not only brings economic disadvantages (transport costs, refueling losses, cold losses when evaporating against ambient air), but also makes high demands on the

Logistics chain reliability. For this reason, there is an increasing demand for systems for the low-temperature separation of air which, in addition to larger amounts of gaseous, high-purity nitrogen, can also supply smaller amounts of gaseous argon. The nitrogen produced should typically only contain about 1 ppb, a maximum of 1000 ppb, oxygen, be essentially free of particles, and be able to be supplied at a pressure level that is clearly above atmospheric. Figures in ppb or ppm relate to the molar proportion.

Air separation plants are typically used to extract argon

Double column systems and so-called raw and possibly so-called

Pure argon columns used. An example is illustrated by Häring (see above) in Figure 2.3A and described from page 26 in the section "Rectification in the Low-pressure, Crude and Pure Argon Column" and from page 29 in the section "Cryogenic Production of Pure Argon". In principle, a pure argon column can also be dispensed with in corresponding plants if the relevant

Rectification columns are designed accordingly. Pure argon can then be withdrawn from the crude argon column or a comparable column typically somewhat further below than the fluid conventionally transferred into the pure argon column.

Even if only comparatively small amounts of argon are in demand, conventionally a complete air separation plant with a double column and argon rectification (ie equipped with a classic low pressure column for oxygen production) is still required for the production of the gaseous argon installed as explained earlier. The generation of nitrogen at a pressure level that is significantly above atmospheric and at the same time large

Production quantities with reasonable yields are not possible in such plants. Most of the nitrogen is produced here as a low-pressure product and has to be compressed. The remaining part can be obtained under pressure column pressure, but in most cases must also be recompressed. In alternative

Plant configurations in which only the high pressure column is used

If nitrogen production is used, the compression of nitrogen from the low-pressure column can be omitted, but not the booster. In addition, there are generally poor nitrogen yields and corresponding systems are not well suited for argon production

The present invention therefore sets itself the task of specifying a method and an air separation plant by means of which, in addition to larger amounts of high-purity, gaseous nitrogen on a clearly

Above atmospheric pressure level, argon can also be advantageously provided.

Disclosure of the invention

Against this background, the present invention proposes a method and a system for the low-temperature separation of air with the features of the independent patent claims. Preferred configurations are the subject matter of the subclaims and the description below.

Before explaining the features and advantages of the present invention, some principles of the present invention are explained in more detail and the terms used below are defined.

The devices used in an air separation plant are described in the cited specialist literature, for example by Häring (see above) in Section 2.2.5.6, "Apparatus". Insofar as the following definitions do not deviate from this, express reference is therefore made to the technical literature cited for the language used in the context of the present application. Liquids and gases can be rich or poor in one or more components in the parlance used here, with "rich" for a content of at least 75%, 90%, 95%, 99%, 99.5%, 99.9% or 99.99% and "poor" can mean a content of no more than 25%, 10%, 5%, 1%, 0.1% or 0.01% on a mole, weight or volume basis. The term "predominantly" can match the definition of "rich". Liquids and gases can also be enriched or depleted in one or more components, these terms referring to a content in a starting liquid or a starting gas from which the liquid or the gas was obtained. Be the liquid or the gas

"Enriched" if this or this is at least 1, 1-fold, 1, 5-fold, 2-fold, 5-fold, 10-fold 100-fold or 1,000-fold salary, and "depleted" if this or this contains at most 0.9 times, 0, 5 times, 0.1 times, 0.01 times or 0.001 times the content of a corresponding component, based on the starting liquid or the starting gas. If, for example, “oxygen”, “nitrogen” or “argon” is used here, this also includes a liquid or a gas that is rich in oxygen, nitrogen or argon, but does not necessarily have to consist exclusively of these.

The present application uses the terms "pressure range" and "temperature range" to characterize pressures and temperatures, which is intended to express that corresponding pressures and temperatures in a corresponding system do not have to be used in the form of exact pressure or temperature values to realize the inventive concept. However, such pressures and temperatures typically move in certain ranges, for example ± 1%, 5%, 10% or 20% around a mean value. Corresponding pressure ranges and temperature ranges can be in disjoint areas or in areas that overlap one another. In particular, pressure ranges include, for example, unavoidable or expected pressure losses. The same applies to temperature ranges. The values specified in bar for the pressure ranges are absolute pressures.

If "expansion machines" are mentioned here, this is typically understood to mean known turboexpander. These expansion machines can in particular also be coupled to compressors. These compressors can in particular be turbo compressors. A corresponding combination of Turboexpander and turbo-compressor is typically also referred to as "turbine booster". In a turbine booster, the turbo-expander and the turbo-compressor are mechanically coupled, the coupling being able to take place at the same speed (for example via a common shaft) or at different speeds (for example via a suitable transmission gear). The term "compressor" is used here in general. A “cold compressor” here denotes a compressor to which a fluid flow is fed in a temperature range well below 0 ° C, in particular below -50, -75 or -100 ° C and down to -150 or -200 ° C. A corresponding fluid flow is particularly cooled to a temperature in this temperature range by means of a main heat exchanger (see below).

A "main air compressor" is characterized by the fact that it compresses all of the air that is fed to the air separation plant and separated there. In contrast, in one or more optionally provided further compressors, for example booster compressors, only a portion of this air that has already been previously compressed in the main air compressor is further compressed. Correspondingly, the "main heat exchanger" of an air separation plant represents the heat exchanger in which at least the

the majority of the air supplied to the air separation plant and separated there is cooled. This takes place at least partly in countercurrent to the material flows that are discharged from the air separation plant. Such "diverted" material flows or "products" are fluids in the parlance used here, which no longer participate in system-internal circuits, but are permanently withdrawn from them.

A “heat exchanger” for use in the context of the present invention can be designed in a manner customary in the art. It serves for the indirect transfer of heat between at least two e.g. fluid flows guided in countercurrent to one another, for example a warm compressed air flow and one or more cold ones

Fluid flows or a cryogenic liquid air product and one or more warm or warmer, but possibly also cryogenic fluid flows. One

Heat exchanger can be formed from a single or several heat exchanger sections connected in parallel and / or in series, e.g. from one or more plate heat exchanger blocks. For example, it is one

Plate Fin Heat Exchanger. Such a heat exchanger has "passages" which are separated from each other as fluid channels

Heat exchange surfaces formed and separated in parallel and by other passages are united to "passage groups". A heat exchanger is characterized by the fact that heat is exchanged between two mobile media in it at a time, namely at least one fluid flow to be cooled and at least one fluid flow to be heated.

A “condenser evaporator” is a heat exchanger in which a first, condensing fluid flow enters into indirect heat exchange with a second, evaporating fluid flow. Each condenser evaporator has one

Liquefaction space and an evaporation space. Liquefaction and

Evaporation chambers have liquefaction or evaporation passages. The condensation (liquefaction) of the first fluid flow is carried out in the liquefaction space, and the evaporation of the second fluid flow in the vaporization space. The evaporation and the liquefaction space are formed by groups of passages which are in a heat exchange relationship with one another.

In a "forced flow" condenser evaporator is a liquid or

Two-phase flow pressed through the evaporation chamber by means of its own pressure and partially or completely evaporated there. This pressure can be generated, for example, by a column of liquid in the feed line to the evaporation chamber. The height of this liquid column corresponds to the pressure loss in the

Evaporation room. The gas-liquid mixture emerging from the evaporation chamber is separated according to phases in a "once through" condenser evaporator of this type directly to the next process step or to one

downstream device forwarded and in particular not in a

Introduced liquid bath of the condenser evaporator, of which the remaining liquid portion would be sucked in again.

The relative spatial terms "above", "below", "above", "below", "above",

"Below", "next to", "next to each other", "vertical", "horizontal" etc. refer here to the spatial orientation of the rectification columns of an air separation plant or other components in normal operation. Under an arrangement of two

Components "one above the other" is understood here to mean that the upper end of the lower of the two components is at a lower or the same geodetic height as the lower end of the upper of the two components and that the projections of the two apparatus parts intersect in a horizontal plane. In particular, the two components are arranged exactly one above the other, that is, the axes of the two components run vertically on the same

Straight lines. However, the axes of the two components do not have to be exactly perpendicular, but can also be offset from one another, especially if one of the two components, for example a rectification column or a column part with a smaller diameter, is to have the same distance from the sheet metal jacket of a coldbox as another with a larger one Diameter.

Advantages of the invention

Against this background, the present invention proposes a method for

Cryogenic separation of air, in which an air separation plant is used with a column system comprising a first column, a second column, a third column and a fourth column.

The first to third columns in the air separation plant according to the invention emerge in particular from the expansion of a classic double column system known from the prior art by an additional column operated at a higher pressure than the conventionally present high pressure column.

In the context of the present invention, as also explained in more detail with reference to the accompanying drawings, the first column can be provided in particular structurally separate from the second and third column, wherein the second and third column can in particular be part of a double column and by means of a corresponding one Condenser evaporator, the so-called main condenser, can be in heat-exchanging connection with one another. However, different arrangements can also be made; the present invention is not limited by the explanations just given.

In particular, the second and the third column, which are part of a

Double columns are formed, can also be supplemented by an additional column in a corresponding multiple column system, or the second and third columns can be provided as separate columns. The one mentioned

The main capacitor can be provided as an internal or external main capacitor, as is basically known from the prior art. At Using an internal main condenser, this is at least partially submerged in a bottom liquid in the bottom of the third column and an overhead gas to be condensed from the second column is passed through a

Condensation chamber of the main condenser out.

As is also known and common in the field of air separation, a first bottom liquid is formed in the first column, a second bottom liquid is formed in the second column, and a third is formed in the third column

Bottom liquid is formed and a fourth bottom liquid is formed in the fourth column. Unlike the first to third columns, the fourth column in the context of the present invention is used in particular for argon production or

Argon discharge from a gas mixture taken from the third column. The fourth column can in particular be a conventional crude argon column of a known arrangement with crude and pure argon column, but it can also be a modified argon column from which argon is withdrawn in the pure state below the top without using an additional pure argon column.

Other variants are also possible within the scope of the present invention.

In the context of the present invention, the first column is in a first

Operated pressure range, the second column is operated in a second pressure range below the first pressure range and the third column is operated in a third pressure range below the second (and thus also the first) pressure range. The fourth column can in particular be operated in the third pressure range or in a pressure range which is slightly below this and which can result in particular from pressure losses via the lines connecting the third and fourth columns.

In the context of the present invention, the second sump liquid with a higher oxygen content and a higher argon content than the first

Sump liquid is formed and the third sump liquid is formed with a higher oxygen content and a lower argon content than the second sump liquid. The higher argon content of the second sump liquid compared to that of the first sump liquid results from the different

Operating conditions, in particular the different pressures used to operate the first and second columns, as well as different ones Compositions of streams in the first and second column

be fed in. In contrast, the lower argon content in the third column results in particular from the fact that an argon-enriched gas is withdrawn from this third column, as will be explained below.

In particular, within the scope of the present invention, the first oxygen content can be at 28 to 40%, in particular at approx. 34%, the second oxygen content at approx. 45 to 65%, in particular at approx. 55%, and the third oxygen content at approx. 0 to 99.9%, in particular around 99.5%. The respective percentages relate to the molar content of oxygen in a corresponding one

Component mixture. The third column is therefore used in the context of the present invention as a pure oxygen column and a corresponding pure oxygen product can be withdrawn from it. In contrast, the first and the second sump liquid are typically not used as a product, but are further processed in the plant.

In the context of the present invention, fluid is generally fed from the first column at least into the second column. The fluid fed into the second column from the first column can in particular comprise bottom liquid from the first column, which is evaporated, expanded and introduced into the second column.

In particular, fluid can be fed from the first column into the second and into the third column. Fluid from the second column is fed into at least the third column, fluid from the third column is fed into at least the fourth column, and fluid from the fourth column is fed into at least the third column.

If it is mentioned here that “fluid” is “at least” fed into another column from one column, in particular a direct or indirect one

Understood transfer of a corresponding fluid flow. In particular, the transfer of the corresponding fluids can initially also be carried out in one feed

Include condenser evaporator or its evaporation chamber, from which liquid and / or gaseous components are then transferred into the other column. This fluid flow also falls under the transfer of a fluid from one column to the other. The same also applies if a corresponding fluid is only is partially transferred, for example when it is enriched or depleted in certain components and / or divided into partial flows.

The transferred fluids can include overhead gases, bottom liquids and / or side streams of corresponding columns. Under a "side stream" is a

Understood stream that is taken from a corresponding column between different dividing trays or separating sections, whereas the top gas denotes a gas mixture that is taken from the column above the uppermost dividing tray or dividing area and a bottom liquid denotes the liquid that comes from a corresponding column below the lowest Separation bottom or separation area is removed. A sump liquid is discharged in particular in the form of a liquid substance flow, and an overhead gas in particular in the form of a gaseous substance flow. However, liquid or gaseous material flows can also be withdrawn, for example, directly above the sump, but still below the lowest separating section or the lowest separating tray. One

Sidestream can be in the liquid or gaseous state. A liquid side stream can, for example, be removed from a liquid retention device or from a storage floor.

In the context of the present invention, the fluid fed into the fourth column from the third column comprises at least part of a side stream which is withdrawn from the third column with a lower oxygen content and a higher argon content than the third bottom liquid. The side stream is withdrawn from the third column in particular in the area of the argon transition already explained above, but it can also be withdrawn below the argon transition. A corresponding side stream represents a gas mixture in particular, which has a higher argon content than the bottom liquid and a lower argon content than the top gas.

An essential aspect of the present invention is that a reflux liquid is formed by condensing top gas of the first column, and that this reflux liquid is returned in liquid form to the first column. The formation of the reflux liquid “using” the top gas can in particular include removing top gas in gaseous form from the first column, at least this in a condenser evaporator which is also explained in detail below partially liquefied, and a liquid portion at least partially returned to the first column.

According to the invention, for the explained condensation of the top gas of the first column, a liquid cooling stream is evaporated or partially evaporated in indirect heat exchange with the top gas. With evaporation or partial evaporation of the

Gas formed in the cooling stream (any remaining liquid can be separated off beforehand) is furthermore, according to the invention, work-producing to a pressure in the second pressure range, ie the operating pressure of the second column, expanded and fed into the second column. The correspondingly expanded gas can be part of the gas formed during the evaporation or partial evaporation or also only a part thereof. The liquid cooling stream can in particular be provided at a pressure in the first pressure range and before evaporation or

Partial evaporation, for example by means of a valve, can be expanded to a somewhat lower pressure, for example in a region between the first pressure range and the second pressure range. Another relaxation after the

Evaporation to a pressure in the second pressure range before being fed into the second column then takes place downstream of the evaporation in the column mentioned

labor-performing form.

As an alternative, the present invention creates a method with lower energy consumption than methods currently under development. This applies in particular in comparison to known so-called SPECTRA processes and variants thereof. The present invention can, however, as explained for example in connection with FIG. 4, be used in connection with such a SPECTRA method or a variant thereof.

A SPECTRA method is known, for example, from EP 2 789 958 A1 and the patent literature cited there. In its simplest form, it is a single-column process. A SPECTRA process can also be expanded to include oxygen and argon production by providing additional columns. SPECTRA processes enable a relatively high nitrogen yield.

From the rectification column for nitrogen production, which is also fed with the main amount of the feed air, cryogenic air, compared to atmospheric air, is generated Oxygen-enriched liquid taken in the form of one or more streams and heated in the condenser evaporator, which is used for cooling and

Condensation of at least a portion of the top gas of the same column is used. Correspondingly condensed top gas is at least partially returned to the column from which it was previously taken. In conventional SPECTRA processes, the fluid to be evaporated can be passed through the condenser evaporator in the form of just one material flow or in the form of two or more separate first material flows.

The correspondingly vaporized fluid is partially cold, i.e. using one or more compressors. at a temperature level well below 0 ° C, in particular at a temperature level of -50 ° C or less, compressed and then fed back into the column from which it was previously removed. The one or more compressors can or can with one or more

Relaxation machines, in particular with one of two relaxation machines arranged in parallel, be coupled and at least partially driven using them. In the expansion machine or machines, a further part of the evaporated fluid is expanded and discharged from the air separation plant.

In particular, the present invention is based on the knowledge that the potential of a method of the generic type cannot be fully exploited without the measures proposed according to the invention. An indicator for this is or was a still relatively high temperature difference present in such generic processes in a condenser which condenses overhead gas of the first rectification column operating under the highest pressure. In previous concepts, this condenser was used as a bath condenser with a relatively high hydrostatic level because of the requirements for the nitrogen product pressure and thus the first pressure level (for example 11 bar; the feed air is correspondingly highly compressed)

Pressure loss of approx. 150-200 mbar and an average temperature difference of 2.5 K (or more). As a result, a relatively large amount of exergy is "destroyed" in a corresponding process, which is not the case within the scope of the present invention.

Another point (to be seen as a disadvantage) in the case of alternative concepts that are not according to the invention and which are based on one of the SPECTRA methods

The process topology with several rectification columns is based on the generation Injection of air (approx. 10-15% of the amount of air used) into the medium-pressure unit, provided for the cooling capacity

working second rectification column. This amount of air is not subjected to rectification in the first (main) rectification column to obtain high-pressure nitrogen product, so that a corresponding solution is inevitably associated with corresponding disadvantages in terms of nitrogen yield.

As a result of the measures proposed according to the invention, a corresponding injection of feed air, which is essentially provided for obtaining cold, is no longer necessary, since the cooling fluid evaporated in the condenser evaporator can be used instead. This advantageously originates from the bottom liquid of the first rectification column and has therefore already taken part in the rectification taking place there. This increases the efficiency and

Yield in the process proposed according to the invention.

In other words, the present invention proposes that not (or at least not exclusively) a feed air stream into the second rectification column is used to generate the process cooling capacity, but rather one in one

Condenser evaporator (top condenser) of the first rectification column evaporating stream, namely the stream referred to here as "cooling stream". An essential aspect of the present invention consists inter alia in the utilization of the differential pressure between the operating pressure of the second

Rectification column (i.e. the corresponding to the second pressure range) and the evaporation pressure in the one used for condensing the top gas

Condenser for generating the cold and reducing the air "blown amount" into the second rectification column.

The evaporation pressure in the condenser mentioned becomes higher (and thus the better for the process of refrigeration), the lower the temperature difference in the condenser. The capacitor is therefore advantageously not as

Bath condenser, but in particular designed as a forced flow condenser with the lowest possible minimum temperature difference.

In other words, in order to achieve the advantages mentioned, the previously mentioned cooling flow (which is expanded for cooling performance instead of air) advantageously formed using at least a portion of the first bottom liquid and / or to condense the top gas of the first column and to evaporate the cooling stream, a forced flow condenser evaporator is advantageously used. Regarding the term “forced-flow condenser evaporator”, express reference is made to the explanations above.

In a particularly preferred embodiment of the invention, which is part of a SPECTRA process in this way, a further liquid cooling stream is evaporated or partially evaporated in indirect heat exchange against the top gas to condense the top gas of the first column, with the further cooling stream coming out above the bottom taken from the first column and after evaporation or

Partial evaporation is at least partially compressed and returned to the first column. The vaporized further cooling flow or a part thereof is compressed in particular in one or more compressors that are mechanically coupled to one or more expansion machines and, in particular, are additionally braked. The compression takes place in particular on one

Temperature level below 0 ° C, especially below -50 ° C,

for example at -100 to -150 ° C. One or more

Expansion machines compress, in particular, a remainder of the cooling flow formed from the bottom liquid of the first column, which is not compressed and is returned to the second column. This compressed remainder is in particular compressed to a pressure in the first pressure range and into the first column

returned.

In the context of the present invention, the mentioned first pressure range is in particular from 9 to 12 bar, the second pressure range in particular from 4 to 6.5 bar and the third pressure range in particular from 1 to 2 bar. The third pressure range can, however, also be reduced further, in particular by 50 to 200 mbar, for example compared to the pressure value of 1.4 bar mentioned at the beginning with regard to conventional air separation plants. Accordingly, the second pressure range can also be reduced by 120 to 500 mbar, for example compared to the value of 5.3 bar mentioned at the beginning. A corresponding pressure reduction is possible in particular when, as explained below, gas from an evaporation chamber

Condenser evaporator, the top gas of the fourth column condensed as Regeneration gas is used. The driving temperature difference in this condenser evaporator is also reduced.

When the pressure is reduced to the values mentioned or the pressure is further reduced, the refrigeration capacity can be increased accordingly by increasing the pressure difference between the first pressure range and the second pressure range or lowering the outlet pressure during expansion. As mentioned, the pressure specifications here denote absolute pressures at the top of the columns. The first pressure range is thus above a pressure which is conventionally used for a high pressure column in an air separation plant. In the context of the present invention, the second column can in particular be operated at a lower pressure range than that conventionally in one

High pressure column used in the air separation plant. In principle, however, it can also be the same pressure.

By using the present invention, in particular, when the for condensing the top gas of the first column and for evaporating the

Cooling stream used cooling stream is formed using the first bottom liquid of the first column, no pump is necessary for pumping liquid nitrogen due to the existing pressure conditions. This means that there is less heat input into the low-temperature system and, in contrast to the use of a fluid that is more oxygen-rich, there is a higher driving temperature difference due to the lower oxygen content in the evaporating liquid. This enables a higher evaporation pressure and the turbine output is increased accordingly.

The turbine output (process cooling output) achieved with the measures according to the invention is particularly sufficient for "gas" systems with a

relatively small liquid production, for example with a required nitrogen product pressure of 11 bar (which is then also the pressure in the first

Pressure range). No further turbine is required in such a configuration. In this constellation, moreover, no air is required to be blown into the second column or no bypass of the first column is required. An additional turbine can, however, be used in an operating case with a relatively high liquid production. In the method proposed according to the invention, in particular a nitrogen-rich gas is withdrawn as product from the first rectification column, heated and discharged from the plant at a pressure in the first pressure range. In this way, a nitrogen product can be provided in a corresponding pressure range without further compression.

Overall, in the context of the present invention, an energy advantage of 5-6%, based on the performance of the main air compressor, can be achieved by increasing the yield of nitrogen product and the recovery of turbine power compared to the aforementioned, likewise possible expansion of feed air instead of the evaporated cooling stream . This can correspond to a reduced energy consumption of, for example, approx. 500 kW and thus a TCO (Total Cost of Ownership) cost reduction of over EUR 1 million. As a result of the measures proposed according to the invention, a smaller amount of air is required overall, which leads to a smaller “warm” part of the system. This means that a smaller main heat exchanger can also be used (the kF value is approx. 6% lower with the same MTD value). If a forced flow condenser evaporator is used, there is no enrichment of flammable hydrocarbons due to the relatively high evaporation pressure (typically more than 7 bar).

The present invention can provide different possibilities for temperature control or non-temperature control of the cooling stream, each of which can offer certain energetic advantages. This can be done with the evaporation or partial evaporation of the

Cooling stream formed gas, which is expanded to perform work and fed into the second column, are heated before the expansion. In particular, the main heat exchanger of the air separation plant can be used for this purpose. In this way, the feed streams can be cooled by means of appropriate cold and the heat exchanger profile can be adapted accordingly. That at the

Evaporation or partial evaporation of the cooling stream, which is expanded to perform work and is fed into the second column, but can also be supplied to the expansion at a temperature at which it is present after the evaporation or partial evaporation; so there is no further temperature control in this embodiment. In one embodiment of the present invention that is given below

Boundary conditions can also offer energetic advantages, the gas formed during the evaporation or partial evaporation of the cooling stream, which is expanded to perform work and fed into the second column, can be fed into the second column at a temperature at which it is taken from an expansion machine used for expansion will. Alternatively, you can warm up after relaxation.

Overhead gas of the fourth column is particularly preferred in the context of a

Embodiment of the present invention at least in part in one

Condensation space of a condenser evaporator condenses, its

A gas mixture is removed from the evaporation chamber.

Part of this gas mixture and / or also at least part of the residual gas from the upper region of the third column, i.e. at least part of a gas mixture which is withdrawn from the third column, can be used in one embodiment of the present invention to form a recycle stream and thereby heated, compressed, cooled and fed into the second column. In the context of the present invention, in particular the main heat exchanger can be used for heating and cooling the recycle stream mentioned

Air separation plant can be used.

In particular, a (further) part of the gas mixture from the evaporation chamber of the condenser evaporator can also be used as a regeneration gas for an adsorber, in which feed air that is fed to the column system is processed. This can take place in particular with a corresponding evaporation pressure. The aforementioned adsorber is operated in particular without the use of regeneration gas, which is taken from the third column and fed to the adsorber in the same composition as there. For example, however, gas from the upper region of the third column and gas from the lower region of this column can be combined and heated as a common stream in the main heat exchanger and as

Regeneration gas can be used.

In a particularly preferred embodiment of the invention, at least part of the gas mixture that is in the evaporation space of the condenser evaporator is taken, used as a first regeneration gas portion, and at least part of the gas or the gas mixture mentioned, which is withdrawn from the third column, is used as a second regeneration gas portion. In this case, in particular, the second regeneration gas component is provided at a lower pressure than the first, compressed and combined with the first regeneration gas component before it is fed to the adsorber. So it is combined residual gas from the third column and gas from a top condenser of the argon column.

The embodiment just explained has advantages in particular when no refrigeration machine is used for pre-cooling and therefore the need for regeneration gas is comparatively high. In such cases it can happen that the amount of gas from the condenser evaporator is insufficient as the amount of regeneration gas. Therefore, a partial flow of the residual gas from the low-pressure column (i.e. the third column) is recompressed (the pressure difference is approx. 50 to 200 mbar) and combined with the other flow. There are also advantages if the

Requirements for the hydrogen content in the gaseous nitrogen product

are comparatively high. In such cases, the air inlet temperature into the molecular sieve (i.e. the adsorber) cannot be selected as low as desired, since otherwise the hydrogen removal (on the special layer provided for this with a catalyst in the adsorber) is less complete. In such cases, too, the amount of gas from the condenser evaporator is not sufficient as the amount of regeneration gas.

In a particularly preferred embodiment of the present invention, the evaporation chamber of the condenser evaporator, in whose condensation chamber the top gas of the fourth column is at least partially condensed, is supplied with a portion of the first bottom liquid and subjected to partial evaporation, the aforementioned gas mixture being formed in this partial evaporation. In other words, in this embodiment, a top condenser of a crude argon column or the only existing argon column is cooled using bottom liquid from the first column. If a pure argon column is available as the fifth column, its top condenser can also be cooled using a corresponding bottom liquid, as explained below.

In general, evaporated and non-evaporated portions of the bottom liquid from the first column, which are in the condenser evaporator or evaporators of the fourth or fourth column and fifth column were used, then also at least partially transferred into the third column (possibly minus the portion used in the adsorber), namely at a position which corresponds to the oxygen content and argon content of these fluids. The vaporized and non-vaporized fractions can therefore be fed into the third column at essentially the same point. The streams mentioned can be combined or transferred separately from one another into the third column. The fluid transferred from the first column to the third column thus comprises corresponding liquid, ie at least part of the first bottom liquid which was used to cool the top condenser or condensers of the fourth or fourth and fifth columns. If necessary, it is also possible to dispense with feeding vaporized fractions from the top condenser or condensers and these vaporized fractions are carried out from the process without being fed into the third column, as mentioned for the case of the recycle stream and the fraction used in the adsorber. In this case, too, part of the first bottom liquid is fed into the third column with the non-evaporated liquid.

According to one embodiment of the present invention, the fluid fed from the second column into the third column can comprise at least part of the second bottom liquid which is transferred from the second column to the third column without using a pump. According to this embodiment, corresponding bottom liquid can be transferred into the third column only on the basis of the pressure difference between the second and the third column. However, it can be subcooled beforehand or during the transfer against further currents using a subcooling countercurrent.

Top gas can be withdrawn from the first column at a defined withdrawal position and discharged from the air separation plant as a nitrogen pressure product in a corresponding pressure range.

As already mentioned, the present invention can be used in combination with a

Pure argon column can be used, that is to say a fifth column into which the fluid from the fourth column is transferred, the fluid transferred from the fourth column having an argon content which is higher than that from the third column

withdrawn and at least a portion transferred to the fourth column Gas mixture is. The fifth column is therefore used in the context of the present invention, as is fundamentally known from the field of air separation technology, to obtain a corresponding argon product.

Advantageously, the top gas of the fifth column is condensed by means of a further condenser evaporator, in which a further portion of the second

Bottom liquid is subjected to partial evaporation. On the above

Explanations are expressly referred to.

The side stream, which in the context of the present invention is formed with a lower oxygen content and a higher argon content than the third bottom liquid and is withdrawn from the third column, can, in particular, obtain an oxygen-depleted gas mixture and an oxygen-rich one

Liquid are subjected to processing in a further column, with at least a portion of the oxygen-depleted gas mixture from the further column being able to be fed into the fourth column. In this way, part of the side stream reaches the fourth column via the detour of the further column. The further column is in particular designed in two parts and comprises two parts arranged one above the other, which are separated by a fluid-tight separating tray, the oxygen-depleted gas mixture at least at the top of the upper part, but possibly also at the top of the lower part, and the oxygen-rich liquid is taken from the sump of the lower part. The side stream from the third column is fed, in particular in gaseous form, into a lower region of the upper part. In particular, liquid is withdrawn from the bottom of the upper part and returned to the third column. Bottom liquid from the fourth column is given up as reflux, in particular at the top of the upper part, but can also be partly given up as reflux on the lower part. In such an arrangement, the lower part fulfills the function of a (high-purity) oxygen column. Different configurations are shown in the figures

illustrated.

Finally, the present invention also extends to a

Air separation plant, for the features of which reference is expressly made to the corresponding independent patent claim. In particular, such is

Air separation plant set up to carry out a process as previously described in different configurations has been explained, and this has each set up means. On features and advantages of a corresponding

Air separation plant is expressly referred to the explanations relating to the method according to the invention.

The invention is explained in more detail below with reference to the accompanying drawings, and not the embodiments of the present invention

illustrate embodiments of the invention.

Figure description

In FIGS. 1 to 4, air separation plants are shown which each correspond to configurations of the present invention insofar as they fall under the scope of the patent claims and otherwise relate to the technical background and / or configurations not according to the invention. The air separation plants according to FIGS. 1 to 4 are each designated as a whole with the reference numerals 100 to 400. Although the following explanations refer to the corresponding

Refer to air separation plants 100 to 400, these relate accordingly

Procedure in the same way. The air separation plant 500 illustrated in FIG. 5 is shown as a variant of the air separation plant 100 illustrated in FIG. 1. The aspects illustrated here can nevertheless also be implemented in other systems, in particular systems 200 to 400. The following

Explanations, in particular regarding the system 100 according to FIG. 1, relate to the system 500 in the same way, even if no specific reference is made to it.

All of the air separation plants 100 to 400 shown in FIGS. 1 to 4 are equipped with a column system which, regardless of the different design and possibly different number of columns, is each designated overall by 10. The column systems 10 each have a first column 11, a second column 12, a third column 13 and a fourth column 14.

The second column 12 and the third column 13 are each part of one

Double column basically of a known type. To the technical literature on air separation systems cited at the beginning, in particular to the explanations relating to FIG 2.3A at Häring (see above), in which a corresponding double column is shown, is expressly referred to in this context.

The first column 11 is formed separately from the second column 12 and the third column 13. The first column 11 is equipped with a condenser-evaporator 111 which is used for the condensation of top gas from the first column 11 and, in the configurations according to FIGS. 1 to 3, is more classic

Head capacitor is formed. In each case, bottom liquid from the first column 11 is fed into the condenser evaporator 111, which is designed as a forced flow condenser evaporator in the illustrated examples, and is conveyed without the use of a pump.

An essential aspect of the embodiments of the invention illustrated here is in each case that by condensing top gas of the first column 11 a

Return liquid is formed and that the return liquid is returned to the first column 11. In order to condense the top gas of the first column 11, a liquid cooling stream, which is produced using the aforementioned

Bottom liquid is formed from the first column 11, evaporated against the top gas of the first column 11 or partially evaporated. When evaporating or

Partial evaporation of the cooling flow is formed by means of a

Expansion machine 5 expanded to a pressure in the second pressure range, performing work, and fed into the second column 12.

The second column 12 and the third column 13 stand in via an internal condenser-evaporator 121, the so-called main condenser

heat-exchanging connection with each other. The main condenser 121 serves on the one hand to condense an overhead gas of the second column 12 and

on the other hand, for the evaporation of a bottom liquid of the third column 13. As an alternative to the embodiment illustrated here, the second column 12 and the third column 13 can also be formed separately. The main capacitor 121 can alternatively also be formed on the outside. Different types of

Condenser evaporators can be used as the main condensers 121.

The fourth column 14 is used in all air separation plants 100 to 400 according to FIGS. 1 to 4 for the extraction of argon. In the examples shown there is none Crude argon column is present, but the systems 100 to 400 are each designed to remove an argon product from the fourth column 14. For crude and pure argon columns and corresponding modifications, reference is also made to the above citations from the specialist literature.

The fourth column is equipped with a condenser-evaporator (top condenser) 141 which condenses top gas. In the configurations according to FIGS. 1 to 3, this is cooled with part of the bottom liquid from the first column 11, whereas in the configuration according to FIG. 4, bottom liquid from the second column 12 is used for this purpose. The sump liquid used in each case is subcooled beforehand by a subcooling countercurrent 18. One in that

Head condenser 141 unevaporated portion is illustrated in the here

Examples at least partially fed into the third column 13. In contrast, in the examples illustrated here, a vaporized portion is used to regenerate an adsorber and, in the case of the air separation plant 300 according to FIG. 3, to form a return flow, as will be explained below.

In all air separation plants 100 to 400 according to Figures 1 to 4, a further column 15 is provided in which a mass transfer between a portion of a bottom stream from the fourth column 14 and a side stream from the third column 13 and a portion of the bottom stream from the fourth Column 14 is depleted in more volatile components. The further column 15 has an upper and a lower area which are functionally completely separated from one another. Further details are explained below. The further column 15 is designed with a condenser evaporator 152, which is heated with top gas from the second column 12.

As a component directly assigned to the column system 10, all

Air separation plants 100 to 300 according to FIGS. 1 to 3 have a pump 19 which conveys bottom liquid from the fourth column 14 back into the further column 15.

In all of the air separation plants 100 to 400 according to FIGS. 1 to 4, a bottom liquid is formed in the first column 11, which here is the first

Sump liquid is called. In the second column 12 are accordingly a second bottom liquid, a third bottom liquid in the third column 13 and a fourth bottom liquid in the fourth column 14. The first column 11 is in a first pressure range, the second column 12 in a second

Pressure range below the first pressure range and the third column 13 operated in a third pressure range below the second pressure range. The second sump liquid will have a higher oxygen content and a higher one

Argon content as the first sump liquid and the third sump liquid with a higher oxygen content and a lower argon content than the second

Sump liquid formed. For the pressure ranges and oxygen or argon contents, reference is made to the above explanations.

In the manner explained below, in all air separation plants 100 to 400 according to FIGS. 1 to 4, fluid is transferred from the first column 11 into the second column 12 (and in the air separation plants 100 to 300 according to FIGS. 1 to 3 also into the third column 13) fed in. Furthermore, fluid is fed from the second column 12 into the third column 13 and fluid is fed from the fourth column 14 into the third column 13. In all air separation plants 100 to 400 according to FIGS. 1 to 4, the fluid fed from the third column 13 into the fourth column 14 comprises at least a part of a side stream which has a lower oxygen content and a higher argon content than the second bottom liquid from the third column 13 is removed. The other fluids mentioned, at least in the embodiments illustrated here, each comprise at least parts of the respective sump fluids. In all cases, a direct feed or a feed via an interposed top capacitor or the like and a corresponding partial feed can take place.

In the following, the air separation plant 100 according to FIG. 1 will first be explained in more detail. For the sake of clarity, the explanations relating to the air separation plants 200, 300 and 400 according to FIGS. 2 to 4 only relate to the features that differ therefrom. In Figures 2, 3 and 4 are identical

Features also only partially provided with corresponding reference symbols.

In the air separation plant 100 according to FIG. 1, a feed air stream a is sucked in from the atmosphere generally designated here by A by means of a main air compressor 1 via a filter which is not separately designated and is shown hatched, in FIG an aftercooler, also not separately designated, and fed to a direct contact cooler 2, which is operated with cooling water W.

After the precooling which has taken place in the direct contact cooler 2, the feed air stream, further designated by a, is freed from water and carbon dioxide in an adsorption device 3 in a manner which has been described many times in the literature. The

Adsorption device 3, previously also generally referred to as "adsorber", can be regenerated by means of a regeneration gas flow z. The formation of the

Regenerating gas flow z is explained below.

The correspondingly treated and thus purified feed air stream, further designated with a, is fed to a main heat exchanger 4 on the warm side. The feed air stream a is withdrawn from the main heat exchanger 4 on the cold side or near its cold end and fed into the first column 11.

The bottom liquid of the first column 11 is withdrawn from this and divided into two substreams d and e in the air separation plants 100 to 300 according to FIGS. 1 to 3. The substream d is fed into the condenser evaporator 111 and evaporated in the process. The vaporized substream d is then partially heated in the main heat exchanger 4 and then expanded to the operating pressure of the second column 12 in an expansion machine 5, which is coupled to a generator G, and fed into this second column 12 in a lower region. The treatment of the sump liquid in the air separation plant 400 according to FIG. 4 differs from this. Please refer to the specific explanations below.

The partial flow e, on the other hand, is conducted in the air separation plants 100 to 300 according to FIGS. 1 to 3 through the subcooling countercurrent 18 and then through the condenser evaporator 141. A part can also, as in the form of a

Linkage f illustrated, are fed into the second column 12. Gas generated in the top condenser 141 may be different from that already mentioned

Regeneration gas stream z can be used. This is done first in the

Subcooling countercurrent 18 and then heated in the main heat exchanger 4. A portion that remains liquid is fed into the third column 13, as illustrated here in the form of a stream g. In the air separation plant 400 according to FIG. 4 no corresponding partial flow e or f is formed. Here, too, express reference is made to the specific explanations below.

The top gas of the first column 11 is partly conducted in the form of a stream h through the condensation space of the top condenser 111 and returned to the first column 11 as a liquid reflux. Another portion is in the form of a

Material flow i heated in the main heat exchanger 4 and as a gaseous

Nitrogen pressurized product discharged from the air separation unit 100 or otherwise used.

The bottom liquid of the second column 12 is withdrawn therefrom in the form of a stream j, passed through the subcooling countercurrent 18, and fed into the third column 13. In the air separation plant 400 according to FIG. 4, the material flow j is passed through the condenser evaporator 141 for cooling as an alternative to the material flow e (see above). In the top capacitor 141 of FIG

Gas formed in the air separation plant 400 can also be used here as a regeneration gas stream, which is also designated with z for the sake of simplicity. In the air separation plant 400 according to FIG. 4, gas from the top condenser 141 or its evaporation space is also fed into the third column 13. A portion which remains liquid is fed into the third column 13, as also illustrated in FIG. 4 in the form of a stream g.

The top gas of the second column 12 is partly conducted in the form of a stream k through the condensation space of the main condenser 121, liquefied there and partly returned to the second column 12 as a liquid reflux. Another part is in the form of a material flow I in the condensation chamber of the

Condenser evaporator 152 liquefied. This further share is in the

Air separation plants 100 to 300 according to Figures 1 to 3 with the im

Condensation chamber of the main condenser 121 combined liquefied portion, as illustrated in the form of link I. Corresponding liquid can also be fed into the first column 11 as return flow by means of a pump 6. In the configurations according to FIGS. 1 to 3, the pump 6 conveys a liquid, nitrogen-rich stream b, which is withdrawn from the second column 12 in an upper region. Another portion of overhead gas from the second column 12 is in the examples according to Figures 1 to 3 carried out in the form of a stream c from the plant.

In the embodiment of the air separation plant 400 according to FIG. 3, the liquefied portion of the stream k and the stream I are not combined. Rather, portions of the stream k are fed separately to the second column 12 and the third column 13 after liquefaction. The stream I is fed into the third column 13 separately.

The bottom liquid of the third column 13 is withdrawn from this in the form of a material flow o, brought to liquid pressure by means of an internal compression pump 7, converted into the gaseous or critical state by heating in the main heat exchanger 4 and as a gaseous oxygen pressure product from the

Air separation unit 100 diverted or otherwise used. On the other hand, gas withdrawn from the third column 13 in the form of a stream p above the sump becomes one with residual gas from the third column 13 (see below)

Collective flow q combined, which is then heated in the main heat exchanger 4 and discharged from the air separation unit 100 or used in some other way.

The top gas of the third column 13 is passed in the form of a stream r through the subcooling countercurrent 18 and combined in the air separation plants 100 to 300 according to FIGS. 1 to 3 with the stream o, as mentioned, to form the collective stream q. In the air separation plant 400 according to FIG. 4, a separate one takes place

Diversion.

A side stream t is also withdrawn in gaseous form from the third column 13 and initially fed into an upper part of the further column 15. From the upper part of the further column 15, on the other hand, a material flow u is returned in liquid form to the third column 13. In the upper part of the further column 15 is a

Substance exchange is carried out with bottom liquid from the fourth column 14, which is applied in liquid form in the air separation plants 100 to 300 according to FIGS. 1 to 3 in the form of a mass flow v into the upper and lower part of the further column 15. In the air separation plant 400 according to FIG

Feeding of the stream v only into the upper part of the further column 15. In the lower part of the further column 15, more volatile components are expelled by heating by means of the condenser evaporator 152. Gas is withdrawn from the upper and the lower part of the further column 15 in each case, which in the air separation plants 100 to 300 according to FIGS. 1 to 3 in the form of a

Stream w is fed into the fourth column 14. In contrast, in the air separation plant 400 according to FIG. 4, the fourth column 14 is only fed with a gas stream w ′ from the upper part of the further column 15. A gas and

Liquid exchange between the upper and lower part of the further column 15 takes place here in the form of the streams w "and w '". Thus, part of the side stream t is ultimately fed into the fourth column 14 and from this part of the bottom liquid is ultimately returned to the third column 13. In all of the examples illustrated here, the further column 15 can, for example, also be arranged above the top condenser 111 of the first column 11.

Bottom liquid from the lower part of the further column 15 is drawn off in the form of a material flow x and, in the example shown, into a tank system T

fed in. If necessary, a material flow, also designated by x for the sake of clarity, is taken from the tank system T, evaporated in the main heat exchanger 4 and implemented as a highly pure, gaseous oxygen product.

From the fourth column 14, argon-rich liquid is withdrawn in the form of a substance flow y by means of a further internal compression pump 8, brought to liquid pressure, converted into the gaseous or critical state by heating in the main heat exchanger 4, and as a gaseous argon pressure product from

Air separation unit 100 diverted or otherwise used. In the

Air separation plant 400 according to FIG. 4 also shows a corresponding tank system T ′ in this context.

Liquid nitrogen, liquid oxygen (possibly also with different purities) and liquid argon can be provided as further products of the system 100, as is known in principle and shown for example in the form of a partial flow of the liquefied top gas h of the first column 11. In the design of the

Air separation plant 400 according to FIG. 4 also shows a liquid nitrogen feed into the condenser evaporator 111 based on a material flow h '. The illustrated in Figure 2, according to an embodiment of the invention

The air separation plant 200 constructed in this way differs from the air separation plant shown in FIG. 1 essentially in that the material flow d is not heated before it is expanded in the expansion machine 8.

The air separation plant 300 illustrated in FIG. 3 differs from the air separation plant 200 shown in FIG Main heat exchanger 4 is cooled and fed into the second column 12. The air separation plant 300 can otherwise also be the same as the air separation plant 100 illustrated in FIG. 1.

The air separation plant 400 shown in FIG. 4 illustrates the

measures proposed according to the invention in connection with a known SPECTRA process. This is the first column 11 next to the

Bottom stream d, which has already been explained above, a further stream d 'is withdrawn above the sump and, like stream d, is cooled again in the main heat exchanger 4. Evaporation then takes place in the

Condenser Evaporator 111.

Part of the stream d is expanded in the expansion machine 5, which is coupled to a generator G, and, as mentioned (see link D), is fed into the second column 12. The remainder of the material flow d is partially heated in the main heat exchanger 4 and then in another

Relaxation machine 401, which is coupled to a compressor 402 and a brake 403, relaxes. Subsequently, a diversion from the

Air separation plant 400. Part of the liquefied material flow h is discharged in liquid form and, if necessary, subcooled against part of the same material flow in a subcooler 404. The portion used for subcooling can be combined with the relaxed remainder of the stream d.

The stream d ', however, after its evaporation in the

Condenser evaporator 111, at least in part, a compression in the compressor 402 subjected, cooled again in the main heat exchanger 4 and returned to the first column 11.

As mentioned, the air separation plant 500 shown in FIG. 5 is illustrated as a variant of the air separation plant 100 according to FIG. She stands out

in particular through the use of a blower 501, by means of which part of the material flow q, here denoted by q ', is brought to the pressure of the material flow z and is fed to the latter. As mentioned, such a configuration is particularly advantageous when no refrigeration machine is used to precool the feed air and the need for regeneration gas is therefore comparatively high. There are also advantages when the hydrogen content in the nitrogen product is comparatively high. Reference is made to the corresponding explanations above.

Claims

1. Process for the cryogenic separation of air, in which a

Air separation plant (100-500) is used with a column system (10) which has a first column (11), a second column (12), a third column (13) and a fourth column (14), wherein a) in the a first bottom liquid is formed in the first column (11), a second bottom liquid is formed in the second column (12), a third bottom liquid is formed in the third column (13) and a fourth bottom liquid is formed in the fourth column (14), b) the first column (11) is operated in a first pressure range, the second column (12) in a second pressure range below the first

Pressure range is operated and the third column (13) is operated in a third pressure range below the second pressure range, c) the second sump liquid is formed with a higher oxygen content and a higher argon content than the first sump liquid and the third sump liquid with a higher oxygen content and a lower argon content than the second bottom liquid is formed, d) fluid from the first column (11) at least into the second column (12), fluid from the second column (12) at least into the third column (13), fluid from the third column (13) is fed into the fourth column (14) and fluid from the fourth column (14) is fed into at least the third column (13), and e) the fluid fed from the third column (13) into the fourth column (14) comprises at least part of a side stream which has a lower oxygen content and a higher argon content than the third

Bottom liquid is removed from the third column (13), characterized in that f) a reflux liquid is formed by condensing the top gas of the first column (11) and the liquid reflux liquid is returned to the first column (11), g) a liquid for condensing the top gas of the first column (11)

Cooling stream is evaporated or partially evaporated in indirect heat exchange against the top gas, and h) gas formed during the evaporation or partial evaporation of the cooling stream is expanded to a pressure in the second pressure range and is fed into the second column (12).

2. The method of claim 1, wherein the cooling stream is formed using at least a portion of the first sump liquid.

3. The method according to claim 2, wherein for condensing the top gas of the first column (11) a further liquid cooling stream is evaporated or partially evaporated in indirect heat exchange against the top gas, the further cooling stream being taken from the first column (11) above the bottom and after the evaporation or partial evaporation is at least partially compressed and returned to the first column (11).

4. The method according to any one of claims 1 to 3, in which a forced-flow condenser-evaporator is used to condense the top gas of the first column (11) and to evaporate the cooling stream.

5. The method according to any one of the preceding claims, wherein the in the

Evaporation or partial evaporation of the cooling stream formed gas, which is expanded and fed into the second column (12), is heated before the expansion.

6. The method according to any one of claims 1 to 3, in which the gas formed during evaporation or partial evaporation of the cooling stream, which is expanded to provide work and is fed into the second column (12), at a temperature in which it is present after evaporation or partial evaporation, is supplied to the relaxation.

7. The method according to any one of claims 1 to 3, in which the gas formed during the evaporation or partial evaporation of the cooling stream, which expands to perform work and is fed into the second column (12), at a temperature at which it is an expansion machine used for expansion (5) is removed, is fed into the second column (12).

8. The method according to any one of the preceding claims, wherein the top gas of the fourth column (14) at least partially in a condensation chamber

Condenser evaporator (141) is condensed, the evaporation chamber of which a gas mixture is removed, with at least part of the gas mixture that is removed from the evaporation chamber of the condenser evaporator (141) is used to form a recycle stream, which heats, compresses, cools and enters the second column (12) is fed in and / or as

Regenerating gas for an adsorber (3) is used, in which feed air is processed, which is fed to the column system (10) is processed.

9. The method according to any one of claims 1 to 7, in which at least part of a gas mixture which is removed from an upper region of the third column (13) is used to form a recycle stream, which is heated, compressed, cooled and into the second Column (12) is fed.

10. The method according to claim 8 or 9, wherein the adsorber (3) in which the

Feed air is processed, which is fed to the column system (10), is operated without the use of regeneration gas, which is taken from the third column (12) and fed to the adsorber (3) in an unchanged material composition.

11. The method according to claim 8, in which at least part of the gas mixture which is taken from the evaporation space of the condenser evaporator (141) is used as a first regeneration gas portion, and in which at least a portion of the gas which is from the third column (13 ) is removed, is used as a second regeneration gas component, the second regeneration gas component on a lower pressure than the first is provided, compressed and combined with the first regeneration gas portion before it is fed to the adsorber (3).

12. The method according to any one of the preceding claims, wherein the

work-producing relaxation of the evaporated or partially evaporated cooling stream or at least its portion, which is work-producing relaxed and is fed into the second column (12), the power released is used to operate an electrical generator.

13. The method according to any one of the preceding claims, wherein the second

Pressure range is 4 to 6.5 bar.

14. The method according to any one of the preceding claims, in which the side stream which is formed with a lower oxygen content and a higher argon content than the third bottom liquid and is withdrawn from the third column (13) to obtain an oxygen-depleted gas mixture and a

Bottom liquid is subjected to processing in a further column (16), at least a portion of the oxygen-depleted gas mixture from the further column (16) being fed into the fourth column (14).

15. Air separation plant (100-500) which has a column system (10) with a first column (11), a second column (12), a third column (13) and a fourth column (14) and which is set up for this purpose, a) to form a first bottom liquid in the first column (11) in which

second column (12) to form a second bottom liquid, in the third column (13) to form a third bottom liquid and in the fourth

Column (14) to form a fourth bottom liquid, b) to operate the first column (11) in a first pressure range, the second column (12) in a second pressure range below the first

To operate the pressure range and to operate the third column (13) in a third pressure range below the second pressure range, c) to form the second sump liquid with a higher oxygen content and a higher argon content than the first sump liquid and to form the third sump liquid with a higher oxygen content and a lower argon content than the second sump liquid, d) fluid from the first column (11) at least in the second column (13), fluid from the second column (12) at least into the third column (13), fluid from the third column (13) at least into the fourth column (14) and fluid from the fourth column (14) at least feed into the third column (13), and e) as the fluid fed from the third column (13) into the fourth column (14) to use at least a part of a side stream which has a lower oxygen content and a higher argon content than the third Bottom liquid withdrawn from the third column (13) is characterized by means which are set up f) by condensing top gas from the first column (11) ei no

Form reflux liquid and return the liquid reflux liquid to the first column (11), g) to condense the top gas of the first column (11) to evaporate or partially evaporate a liquid cooling stream in indirect heat exchange against the top gas, and h) in the evaporation or partial evaporation the gas formed in the cooling stream to work to expand to a pressure in the second pressure range and feed it into the second column (12).