WO2020169257A1

WO2020169257A1 - Method and system for low-temperature air separation

Info

Publication number: WO2020169257A1
Application number: PCT/EP2020/025083
Authority: WO
Inventors: Dimitri GOLUBEV
Original assignee: Linde Gmbh
Priority date: 2019-02-22
Filing date: 2020-02-21
Publication date: 2020-08-27

Abstract

The invention relates to a method for low-temperature air separation to obtain nitrogen at a pressure in a pressure range of 9 to 12 bar and to obtain argon, in which method an air-separation system (1001-1019) having a fractionating column system (10) is used, which fractionating column system comprises a first fractionating column (11), a second fractionating column (12), a third fractionating column (13) and a fourth fractionating column (14). In the first fractionating column (11) a first bottom liquid is formed, in the second fractionating column (12) a second bottom liquid is formed, in the third fractionating column (13) a third bottom liquid is formed, and in the fourth fractionating column (14) a fourth bottom liquid is formed. The first fractionating column (11) is operated in a first pressure range, the second fractionating column (12) is operated in a second pressure range below the first pressure range, and the third fractionating column (13) is operated in a third pressure range below the second pressure range. The second bottom liquid is formed having a greater oxygen content and a greater argon content than the first bottom liquid, and the third bottom liquid is formed having a greater oxygen content and a lower argon content than the second bottom liquid. Fluid is fed from the first fractionating column (11) into the second fractionating column (12) and into the third fractionating column (13), fluid is fed from the second fractionating column (12) into the third fractionating column (13), fluid is fed from the third fractionating column (13) into the fourth fractionating column (14), and fluid is fed from the fourth fractionating column (14) into the third fractionating column (13). The fluid fed from the third fractionating column (13) into the fourth fractionating column (14) comprises at least one portion of a side stream which, having a lower oxygen content and a greater argon content than the third bottom liquid, is removed from the third fractionating column (13). According to the invention, a backflow liquid is formed by condensing top gas of the second fractionating column (12). and the backflow liquid is fed in a liquid state into the first fractionating column (11) by means of a pump (8). The present invention also relates to a corresponding system (1001-1019).

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 the 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.

From DE 20 2009 004 099 U1 and US Pat. No. 3,079,759 A, air separation systems are known which have a further, at an even higher pressure level than the

Have a high pressure column operated column for the production of nitrogen at a correspondingly high pressure level.

In a column system with three columns, the third column comprises a first and a second condenser evaporator in an air separation process proposed in FR 3 011 916 A1 and nitrogen from a cold compressor is fed to one of the condenser evaporators.

In order to generate gaseous nitrogen under pressure, according to EP 1 653 183 A1, liquid nitrogen is pressurized and a heat exchange with a

subjected to oxygen-enriched fluid from an auxiliary column. In which

Heat exchange of non-evaporated liquid nitrogen is used as return.

According to JP 2000 009382 A, an improvement in the separation performance is to be achieved by withdrawing part of the gas rising through the low-pressure column, increasing its temperature and pressure and then feeding it into the

High pressure column take place after re-cooling.

EP 2 015 013 A2 proposes condensation and pseudocondensation of an air stream in the main heat exchanger with subsequent evaporation in an auxiliary condenser. The evaporated air stream is heated, recompressed and fed back into the feed air.

According to DE 101 52 356 A1, raw argon are made from a second

Rectification section and an oxygen fraction without volatile components for feeding into a pure oxygen column withdrawn from an intermediate point of a first rectification section of an argon column.

DE 199 33 558 A1 proposes a method for the low-temperature separation of air in a three-column system with an additional column, whereby from the upper area the high pressure and / or additional column withdrawn a pressure nitrogen product and the pressure of at least part of at least one oxygen or

nitrogen-enriched liquid fraction is increased.

According to EP 0 921 367 A2, nitrogen is separated from air by cryogenic rectification and the nitrogen separated in this way is condensed at three or more pressures. In the separation, at least part of the condensed nitrogen is used as reflux.

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 has to be installed for the production of the gaseous argon, as explained above. 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 in Häring (see above) in Section 2.2.5.6, "Apparatus", described. 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 or nitrogen, 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% or 10% 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 turbo expander and turbo compressor is typically also referred to as a "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 cooled to a temperature in this temperature range in particular 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. A

Heat exchanger can be formed from a single or from several parallel and / or serially connected heat exchanger sections, for example from one or more Plate heat exchanger blocks. It is, for example, a plate heat exchanger (plate fin heat exchanger). Such a heat exchanger has "passages" which are separated from each other as fluid channels

Heat exchange surfaces are formed and connected in parallel and separated by other passages to form "passage groups". Characteristic of a

The heat exchanger is that in it heat is exchanged between two mobile media 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 supply line to the evaporation chamber. The height of this liquid column corresponds to the pressure loss in the evaporation space. 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. 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 with the production of nitrogen at a pressure in a pressure range of 9 to 12 bar and with the recovery of argon, in which an air separation plant with a column system is used, which has a first column, a second column, a third column and a fourth Has column.

The first to third columns in the air separation plant according to the invention result 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, the second and third column in particular being 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. When 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. The first pressure range can in particular be 9 to 12 bar, for example approx. 10.5 bar, the first pressure range corresponding in particular to the pressure range in which nitrogen is also obtained within the scope of the present invention. The second pressure range is within the scope of the present Invention advantageously at 4 to 6 bar, in particular at approx. 5.5 bar, and the third pressure range is advantageously at 1 to 2 bar, in particular at approx. 1.4 bar. As mentioned, the pressure specifications here denote absolute pressures at the head of corresponding columns. The second and third columns are thus operated in the context of the present invention, as already mentioned above, in pressure ranges in which the high and low pressure columns conventionally used in air separation plants are also operated. The first column, on the other hand, is operated in a higher pressure range, in particular in order to be able to provide nitrogen in this pressure range without further compression, as is done by taking off from the first column.

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 oxygen content of the first sump liquid can be 28 to 40%, in particular about 34%

The oxygen content of the second sump liquid is approximately 45 to 65%, in particular approximately 55%, and the oxygen content of the third sump liquid is approximately 99.0 to 99.9%, in particular approximately 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 into the second column and into the third column, and fluid from the second

Column is fed to the third column, fluid from the third column is fed to the fourth column, and fluid from the fourth column is fed to the third column. If it is said here that “fluid” is fed from one column into another, this is to be understood in particular as a direct or indirect 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 when a corresponding fluid is only 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 material flow, and a top gas in particular in the form of a gaseous material 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. A

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 has a lower oxygen content and a higher argon content than the third Bottom liquid is withdrawn from the third column. 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 second column, and that this reflux liquid is fed into the first column in liquid form by means of a pump. The formation of the reflux liquid "using" the top gas can in particular include removing top gas in gaseous form from the second column, at least partially liquefying this in the main condenser, and at least partially returning a liquid portion to the first column. The liquid one

Return flow can be withdrawn from the second column, for example, directly below the feed point for a corresponding liquefied substance flow, or withdrawn directly from the main condenser and conveyed back to the first column by means of a pump. By means of the pump, the one between the first column and the second column can be used

Pressure difference can be overcome. A corresponding reflux stream can be used in particular to cool part of the bottom liquid of the first column, as will also be explained in detail below.

The return of reflux liquid from the second column to the first column in the form of the mentioned reflux liquid enables an increased removal of gaseous nitrogen or a corresponding nitrogen-rich gas mixture at a correspondingly high pressure, i.e. in the pressure range in which the first column is operated. In contrast to known methods of air separation, a corresponding material flow does not have to be compressed in gaseous form, but can be returned to the first column in the form of the liquid reflux and further purified there if necessary.

The use of the reflux liquid from the second column in the first column is precisely in connection with the further features proposed according to the invention or provided according to preferred embodiments of the invention advantageous and sensible, whereas the person skilled in the art based on differently designed air separation plants from the prior art one

corresponding use of a reflux liquid from the second column in the first column would not have been considered. This is illustrated below using two known methods.

In DE 20 2009 004 099 U1, which has already been cited, a three-column system with an additional column operated at a higher pressure to remove high-pressure nitrogen is already described. From the features shown there, however, it follows for the person skilled in the art that this additional column and that of the regular column

High pressure column corresponding column with almost identical

Bottom concentrations have to be operated, otherwise there would be noticeable thermodynamic losses when mixing the two bottom liquids. As can be seen from the figure there, in this document the bottom liquids of both columns are combined or the bottom liquid of the high-pressure nitrogen column (in the context of the present invention as "first

Column "referred to) in the" normal "high pressure column (in the context of the

present invention referred to as "second column") fed.

In the context of the present invention, the bottom liquid of the second column becomes significantly more oxygen-containing and therefore significantly warmer than the bottom liquid of the first column through the use of the reflux liquid from the second column (i.e. the described "pumping back" of part of the liquid formed in the top condenser of the second column) , since nitrogen is discharged from the second column via the substream removed in this way. For this reason, this bottom liquid of the second column cannot be used to cool one

Condenser in the argon part (for example, a top condenser of the fourth column, which can be designed as a crude argon column or modified crude argon column), since the driving temperature difference in such a condenser would otherwise be negative. The mixture provided in the prior art would also lead to a corresponding temperature reduction.

In other words, the person skilled in the art would not have used a return, as proposed in the context of the present invention, in DE 20 2009 004 099 U1, since in this way the process control as described in this publication is shown, would no longer have been possible, but inevitably further, extensive reconstruction would have been necessary.

Corresponding arguments also apply, for example, to the method as disclosed in US Pat. No. 3,079,759 A, since here too a (partial) unification of the

Bottom liquids and the cooling of the top condenser of the crude argon column with the combined bottom liquids takes place.

The nitrogen provided within the scope of the present invention at the initially mentioned pressure in the range from 9 to 12 bar (or in the first pressure) is advantageously provided with a residual oxygen content in the ppb range, i.e. in the range of 1 to 1,000 ppb. Its amount in standard cubic meters per hour is in particular in the range between 40 and 60%, further in particular between 45 and 55%, of the amount of air used, i.e. the total amount of air supplied to the column system, which is also specified here in standard cubic meters per hour. The oxygen contents of the respective bottom liquids of the columns which can be used here have already been mentioned above.

The amount of reflux of the repeatedly mentioned reflux liquid from the second column into the first column can in this embodiment, based in each case on standard cubic meters per hour, for example between 15 and 25%, for example between 20 and 22%, of the feed air amount. Without a corresponding return flow rate, the aforementioned nitrogen cannot be provided in the stated amount. Furthermore, in this embodiment, further products in particular can be produced in specific product quantities, again expressed in standard cubic meters per hour and based on the amount of air used. In particular, it can be internally compressed oxygen (0.5 to 5%, in particular 1 to 2% of the amount of air used), liquid nitrogen (0.1 to 0.5%, in particular 0.2 to 0.3% of the amount of air used), highly pure gaseous Oxygen (0.5 to 1%, in particular 0.6 to 0.8% of the feed air volume) and internally compressed argon (0.1 to 1%,

in particular 0.2 to 0.5% of the input air volume). A "product" leaves the air separation plant permanently and then no longer takes part in the plant-internal cycles etc.

In a particularly preferred embodiment of the present invention, gas at the top of the fourth column is released by means of a first condenser evaporator condensed, in which a portion of the first bottom liquid is subjected to partial evaporation. In other words, a head capacitor becomes one

Crude argon column or the only existing argon column cooled using bottom liquid from the first column. This top gas can in particular then be fed into the third 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.

The embodiment just explained is not suggested in particular on the basis of the prior art explained above, since this, as mentioned, is a

Combination of sump liquids teaches. As mentioned, the bottom liquid of the second column in the context of the present invention is significantly more oxygen-containing and therefore significantly warmer through the use of the reflux liquid from the second column (i.e. the described "pumping back" of part of the liquid formed in the top condenser of the second column), so that this is less suitable for cooling the top condenser.

According to an advantageous development of the method just explained, evaporated and non-evaporated portions of the bottom liquid from the first column, which were used in the top condenser or condensers of the fourth or fourth and fifth column, are then transferred to the third column, namely at a position which corresponds to the oxygen content and argon content of these fluids. The feed of vaporized and non-vaporized parts can therefore be im

Take place essentially at the same point in the third column. The mentioned

Streams 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 removed from the process without being fed into the third column. In this case, too, part of the first bottom liquid is fed into the third column with the non-evaporated liquid. According to a particularly preferred embodiment of the present invention, the fluid fed from the second column into the third column comprises 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.

Overhead gas can be withdrawn from the first column at a defined withdrawal position and discharged from the air separation plant. In a

Embodiment of the invention, the return liquid below the

Removal position of the top gas from the first column are fed into the first column. However, it is also possible to feed in at essentially the same point as the overhead gas is withdrawn. Feeding the reflux liquid below the removal position of the top gas from the first column is particularly advantageous in order to achieve high product purities. A simpler pump can be used here than with a feed at the same height, which can result in less contamination.

For example, by using this advantageously proposed

Measures a product purity of a nitrogen product can be achieved with a content of less than 1 ppb oxygen. With a feed at the same level, however, the entire thermodynamic potential can be used.

According to a preferred embodiment of the present invention, the reflux liquid is brought into a supercooled state by increasing the pressure by means of a pump, in particular the pump with which it is fed into the first column. Since it is not necessary to feed into the first column in the subcooled state, one or more liquid material flows can be cooled according to this embodiment of the invention by means of the reflux liquid, in particular in a subcooling countercurrent. For example, a first portion of the first bottom liquid can be subcooled in this context using the reflux stream and fed into the third column and a second portion can be fed into the second column without subcooling. The supercooled first portion can in particular after the supercooling in the explained manner for cooling the top condenser of the fourth or, if present, the fourth and fifth columns are used. The second fraction, which is not supercooled, can be fed into the second column directly or, if necessary, after being used for cooling in a top condenser of the first column. This enables the second and third columns to be advantageously fed with the fluids to be separated. However, as mentioned, other fluids can also be correspondingly supercooled.

In the context of the present invention, gas is advantageously withdrawn from the third column, heated, compressed, cooled and fed into the second column. In this way, a feed circuit is created in which gas essentially withdrawn from the third column and having an oxygen content of approx. 15% to 40% is transferred back to the second column. This configuration brings about a more advantageous separation and the achievement of higher product yields. The gas for such a feed circuit does not necessarily have to be taken directly from the third column, but gas can also be taken from the

Evaporation space of a top condenser of the fourth column (as a partial amount or as a whole stream) can be used accordingly before this gas is fed into the third column.

According to an alternative of the embodiment just explained, which can, however, also be combined with this, bottom liquid of the second or first column, which was used as a coolant in a top condenser of the first column and was partially evaporated in the process, can also be used in the evaporated portion to form a corresponding circulating flow can be used. In other words, the corresponding gas can be heated, compressed and cooled as explained above for the gas withdrawn from the third column. In contrast to the embodiment explained above, however, it is advantageously fed into the first column. The oxygen content can be comparable to that explained above with regard to the gas from the third column or it can be slightly higher. By doing

Top condenser of the first column, unevaporated bottom liquid from the first column can advantageously be transferred to the third column and given up there as reflux in a middle position.

In the context of the present invention, the fluid fed from the first column into the third column can, as already mentioned, at least a portion of a Gas phase, which is formed during partial evaporation in the first condenser evaporator, and at least a portion of a liquid phase which remains liquid during partial evaporation in the first condenser evaporator. As "first"

The condenser evaporator is only used for referencing reasons

Designated condenser evaporator of the fourth column. Further details on this have been explained above. Reference is therefore expressly made to the explanations.

In the method proposed according to the invention, top gas of the first column in particular can be condensed by means of a condenser evaporator, which is referred to here as a "second" condenser evaporator only for reference reasons, and in which a portion of the first and / or second bottom liquid, as also already mentioned, is a partial evaporation is subjected. The fluid fed into the third column from the first column can comprise at least a portion of a liquid phase which remains liquid during the partial evaporation in the second condenser evaporator. As mentioned, at least a portion of a gas phase that is formed during partial evaporation in the second condenser evaporator can be returned to the first column and in particular also be used partially in the form of the recycle stream already explained.

The fluid fed into the second column from the first column advantageously comprises a further portion of the first bottom liquid that has not been subjected to partial evaporation in the second condenser evaporator. In other words, the corresponding bottom liquid can be transferred directly from the first column to the second column.

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 of the gas mixture is transferred to the fourth column. 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, the fluid fed from the first column into the third column at least a portion of a

Gas phase, which is formed in the partial evaporation in the further condenser evaporator, and at least a portion of a liquid phase, which in the

Partial evaporation in the further condenser evaporator remains liquid includes. Reference is expressly made to the above explanations.

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 a top gas and a bottom liquid in a further column

Substance exchange with a portion of the fourth bottom liquid are subjected, with at least a portion of the gas phase being able to be fed into the fourth column from the further column. In this way there is another

Depletion of a corresponding bottom liquid or an oxygen section of a corresponding fourth column is transferred to the further column. A further proportion of the fourth bottom liquid can be depleted of higher-boiling components in the further column and returned to the fourth column, in particular a separate section of the further column being used.

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 an air separation plant is set up to carry out a method, as has been explained above in different configurations, and this has means set up in each case for this purpose. 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 the figures 1 to 19 air separation plants are shown, each

Refinements of the present invention correspond, insofar as they fall under the scope of protection of the patent claims, and otherwise the technical ones

Background and / or not relate to embodiments according to the invention. The latter is the case with regard to FIGS. 1 and 3. The air separation plants according to FIGS. 1 to 19 are each designated as a whole with the reference symbols 1001 to 1019. Although the following explanations refer to the corresponding

Relate air separation plants 1001 to 1019, these relate to corresponding processes in the same way.

All of the air separation plants 1001 to 1019 shown in FIGS. 1 to 19 are equipped with a column system which, regardless of the different configuration 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. In this context, express reference is made to the technical literature on air separation plants cited at the beginning, in particular to the explanations on Figure 2.3A in Häring (see above), in which a corresponding double column is shown.

The first column 11 is formed separately from the second column 12 and the third column 13. The first column 11 is equipped with an overhead condenser 111 which is used to condense overhead gas from the first column 11. Except for the air separation plants, in which this is explained differently (see there), bottom liquid from the second column 12, which is conveyed by means of a pump 17, is fed into the top condenser 111.

The second column 12 and the third column 13 are located above 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 1001 to 1019 according to FIGS. 1 to 19 for the extraction of argon. Except for the air separation plant 1018 according to FIG. 18, the fourth column 14 is in each case designed as a crude argon column and a separate pure argon column is provided as the fifth column 15. In the

Air separation plant 1018 according to FIG. 18, on the other hand, is not such a fifth column

15 available (see there). For crude and pure argon columns, reference is also made to the above citations from the specialist literature.

The fourth column 14 and the fifth column 15 are equipped with an overhead condenser 141 and 151, respectively, which in each case condenses overhead gas and, in all configurations, is cooled with a portion of the bottom liquid from the first column 11. In the air separation plant 1018 according to FIG. 18, only the fourth column 14 is designed accordingly because there is no fifth column 15. The bottom liquid used is subcooled beforehand by a subcooling countercurrent 18 and, apart from the cases in which this is explained differently below, is at least partially fed into the third column 13 in the evaporated and non-evaporated portions. If a fifth column 15 is present, bottom liquid is partially evaporated from this in a condenser evaporator 152, through which part of the bottom liquid from the first column 11 likewise flows.

In all air separation plants 1001 to 1019 according to Figures 1 to 19, a further further column 16 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

16 has an upper and a lower area which are functionally completely separated from one another. Further details are explained below. The further column 16 is designed with a condenser-evaporator 162 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 1001 to 1019 according to FIGS. 1 to 19 have a pump 19 which conveys bottom liquid from the fourth column 14 back into the third column 13.

In all the air separation plants 1001 to 1019 according to FIGS. 1 to 19, a bottom liquid is formed in the first column 11, which here is the first

Sump liquid is called. A second bottom liquid is correspondingly formed in the second column 12, 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 of the air separation plants 1001 to 1019 according to FIGS. 1 to 19, fluid is fed from the first column 11 into the second column 12 and into the third column 13. 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 1001 to 1019 according to FIGS. 1 to 16, the fluid fed from the third column 13 into the fourth column 14 comprises at least part of a side stream that has a lower oxygen content and a higher argon content than the second

Bottom liquid is withdrawn from the third column 13. 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. The air separation plant 1001 according to FIG. 1 is first explained in more detail below. For the sake of clarity, the explanations relating to the air separation plants 1002 to 1019 according to FIGS. 2 to 19 relate only to the features that differ therefrom. In FIGS. 2 to 19, identical features are only partially provided with corresponding reference symbols.

In the air separation plant 1001 according to Figure 1, a feed air stream a from the atmosphere generally designated here by A is sucked in by means of a main air compressor 1 through a filter, which is not separately designated and illustrated by hatching, aftercooled in an aftercooler, likewise not designated separately, and fed to a direct contact cooler 2, which is marked with Cooling water W is operated.

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 correspondingly treated and thus purified feed air flow, further designated with a, is then divided into two partial flows b and c, both of which are one on the warm side

Main heat exchanger 4 are supplied. The partial flow c is previously subjected to a further pressure increase in a booster of a booster turbine arrangement 5 and is cooled in an aftercooler, which is not specifically designated.

The substream b is withdrawn from the main heat exchanger 4 on the cold side and fed into the first column 11. The substream c, on the other hand, is withdrawn from the main heat exchanger 4 at an intermediate temperature level, then expanded in a turbine of the booster turbine arrangement 5 and fed into the second column 12.

The bottom liquid of the first column 11 is withdrawn from this and divided into two substreams d and e. The substream d is into the second column 12

fed in, the substream e, however, passed through the subcooling countercurrent 18 and then through the condenser evaporator 152. Again in the form of two substreams, which, however, are no longer designated separately after the subdivision of the material flow e, are then fed into the

Evaporation chambers of the top condensers 141 and 151. The gas formed here and portions remaining in liquid form are fed into the third column 13 individually or separately, as illustrated here with material flows f. The top gas of the first column 11 is partially passed through the condensation space of the top condenser 111 and returned to the first column 11 as liquid reflux. Another part is in the form of a stream g im

Main heat exchanger 4 heated and discharged as a gaseous nitrogen pressure product from the air separation plant 1001 or used in some other way.

The bottom liquid of the second column 12 is withdrawn from this in the form of a stream h and by means of the pump 17 into the evaporation chamber of the

Head capacitor 111 fed. A portion evaporated here is returned to the second column 12 in the form of a stream i. On the other hand, a portion that remains liquid is passed through the subcooling countercurrent 18 in the form of a stream k and then fed to the third column 13. An alternative feed position is shown in the form of a dotted material flow.

The top gas of the second column 12 is partly passed through the condensation space of the main condenser 121, liquefied there and partly returned to the second column 12 as a liquid reflux. A further portion is liquefied in the form of a material flow I in the condensation space of the condenser evaporator 162 and combined with the portion liquefied in the condensation space of the main condenser 121. As an alternative to this, the portion liquefied in the form of the stream I in the condensation space of the condenser-evaporator 162 can also be fed back to the first column 11 by means of a pump.

In the condensation space of the main condenser 121 and possibly in the condensation space of the condenser evaporator 162, liquefied overhead gas of the second column 12, if it is not used as reflux, is passed in the form of a stream m through the subcooling countercurrent 18 and fed into the third column 13. Non-liquefied top gas of the second column 12 is heated in the form of a stream n in the main heat exchanger 4 and discharged as a gaseous nitrogen pressure product from the air separation plant 1001 or used in some other way.

The bottom liquid of the third column 13 is withdrawn from this in the form of a stream o, brought to liquid pressure by means of an internal compression pump 6, in the main heat exchanger 4 by heating in the gaseous or critical State transferred and discharged as a gaseous oxygen pressure product from the air separation plant 1001 or used otherwise. Above the sump from the third column 13 in the form of a material flow p withdrawn gas is passed through the subcooling countercurrent 18 and combined with residual gas from the third column 13 (see below) to a collection flow q, which is then heated in the main heat exchanger 4 and as from

Air separation plant 1001 is diverted or used in some other way, in particular after further heating for the regeneration of the adsorption unit 3.

The top gas of the third column 12 is passed in the form of a stream r through the subcooling countercurrent 18, then heated in the main heat exchanger 4 and discharged from the air separation plant 1001 as a gaseous nitrogen product or used in some other way. A stream s withdrawn from the third column 13 with a lower nitrogen content below the stream r is combined with the stream o, as mentioned, to form the collective stream q.

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 16. From the upper part of the further column, on the other hand, a stream u is returned in liquid form to the third column 13. In the upper part of the further column 16 is a

Substance exchange is carried out with bottom liquid from the fourth column 15, which is applied in liquid form in the form of a substance flow v into the upper and lower part of the further column 16. In the lower part of the further column 16, more volatile components are expelled by heating by means of the condenser evaporator 162. Gas is withdrawn from the upper and the lower part of the further column 16 and is fed into the fourth column 14 in the form of a material flow w. Thus, part of the side stream t is fed into the fourth column 14 and from this part of the bottom liquid is returned to the third column 13. In all of the examples illustrated here, the further column 16 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 16 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, the tank system becomes a for the sake of clarity Also taken with x designated material flow, evaporated in the main heat exchanger 4 and executed as a highly pure, gaseous oxygen product.

Top gas of the fourth column 14 that is not liquefied in the condensation space of the top condenser 141 of the fourth column 14 is transferred into the fifth column 15 in the form of a stream y. Top gas of the fifth column 15 that is not liquefied in the condensation space of the top condenser 151 of the fifth column 15 is released into the atmosphere. The bottom liquid of the third column 13, if not evaporated in the condenser-evaporator 152, is brought to liquid pressure in the form of a stream z by means of an internal compression pump 7, in the

Main heat exchanger 4 converted into the gaseous or critical state by heating, and discharged as a gaseous argon pressure product from the air separation plant 1001 or used in some other way.

Liquid nitrogen, liquid oxygen (possibly also with different purities) and liquid argon can be provided as further products of the system 1001, as is generally known.

The illustrated in Figure 2, according to an embodiment of the invention

The air separation plant 1002 formed differs from the air separation plant shown in FIG. 1 essentially in that a liquid return flow R is carried out from an upper region of the second column 12 and fed into an upper region of the first column 11 by means of a pump 8. An alternative feed position below the removal position of the top gas from the first column is illustrated by dashed lines. An alternative embodiment, which represents a variant of the air separation plant 1002 according to FIG. 2, is illustrated in FIG. 19 in the form of the air separation plant 1019.

The air separation plant 1003 illustrated in FIG. 3 differs from the air separation plant 1001 shown in FIG. 1 essentially in that instead of dividing the feed air flow a into the two partial flows b and c and treating them separately, the entire input air flow a, as previously only the partial flow c , the further pressure increase in the booster

Booster turbine assembly 5 subjected, cooled in the not separately designated aftercooler, fed to the main heat exchanger 4 on the warm side, the Main heat exchanger 4 is taken at the intermediate temperature level, then expanded in the turbine of the booster turbine arrangement 5 and fed into the first column 11. Thus, the entire feed air in the air separation plant 1003 illustrated in FIG. 3 is brought to a significantly higher pressure level. No feed air is fed into the second column 12.

The air separation plant 1004 illustrated in FIG. 4 differs from the air separation plant 1002 shown in FIG. 2 essentially in the features already explained for the air separation plant 1003 according to FIG. The

Air separation plant 1004 is set up to carry out a high-air pressure process in which all of the feed air is in the booster

Booster turbine assembly 5 is compressed. As in the one in Figure 3

However, a turbine illustrated in the air separation plant 1003 can also be provided which is not coupled to a booster in a booster turbine arrangement 5, but, for example, to a generator or an oil brake.

The air separation plant 1005 illustrated in FIG. 5 differs from the air separation plant 1002 shown for example in FIG. 2 in that the material flow s, which is emphasized here for reasons of clarity, is not combined with the material flow p. The material flow s is instead routed to the warm side of the heat exchanger 4, as before the material flow q. There, a recycle stream designated here as S is branched off from the material stream s and fed back to the main heat exchanger 4 on the warm side by means of a circuit compressor 9 with a downstream but not separately designated aftercooler, removed from it on the cold side and fed into the second column 12. Gas is therefore taken from the third column 13, heated, compressed, cooled and fed into the second column 12. The material flow p is heated separately in the main heat exchanger 4 and provided as a gaseous oxygen product or used in some other way.

The air separation plant 1006 illustrated in FIG. 6 differs from the air separation plant 1005 shown in, for example, FIG. 5 in that the third column 13 is designed without a section which is used to provide

Low-pressure nitrogen in the form of the material flow r is used. A withdrawal of a corresponding material flow is therefore dispensed with, as is the feeding in of a material flow corresponding to the material flow m. The material flow n is here by means of a further compressor 91, which is advantageously provided in a common apparatus with the circulation compressor 9, is compressed.

The air separation plant 1007 illustrated in FIG. 7 differs from the air separation plant 1006 shown, for example, in FIG. 6 by the feed of external liquid nitrogen illustrated here in the form of a stream 11 into the second column 12 or optionally also the first column 11.

The air separation plant 1008 illustrated in FIG. 8 differs, for example, from the air separation plant 1005 shown in FIG. 5 in that the condenser evaporator 111 of the first column 11 is designed as a forced-flow condenser evaporator. A stream i from the condenser-evaporator 111, which can be a pure gas stream or a two-phase stream, is fed into the second column 12 as before. Since no stream corresponding to stream k is formed, instead liquid is removed from the bottom of the second column and treated accordingly in the form of stream K.

The air separation plant 1009 illustrated in FIG. 9 differs, for example, from the air separation plant 1005 shown in FIG. 5 in the absence of the pump 17. Instead of the previously in the form of the material flow h in the

The bottom liquid fed into the top condenser 111 of the first column 11 is the stream e used here, which is formed from the bottom liquid of the first column 11. The stream h is instead used as before the stream e, and the stream k is fed into the second column 12 instead of into the third column 13. One of the streams previously designated with f, which is now designated with F and is formed from liquid from the top condenser 151 of the fifth column 15, is fed into the third column 13 as before, or this third column 13 is equipped with an additional separating section and the Material flow F is fed in there in a suitable manner.

The air separation plant 1010 illustrated in FIG. 10 differs, for example, from the air separation plant 1005 shown in FIG. 5 in that the partial flow c, which is also here the main heat exchanger 4, is on a

Intermediate temperature level taken and in the turbine of the Booster turbine arrangement 5 is relaxed, is fed into the third column 13 instead of the second column 12. The turbine of the booster turbine arrangement 5 is thus operated here as a Lachmann or injection turbine.

The air separation plant 1011 illustrated in FIG. 11 differs, for example, from the air separation plant 1005 shown in FIG. 5 in that, in order to form the material flow denoted here by J, which is generated by means of the

Circulation pump 9 is fed back to the main heat exchanger 4, a partial flow of the material flow i is used. The stream J is returned here to the first column 11 instead of to the second column 12.

The air separation plant 1012 illustrated in FIG. 12 differs, for example, from the air separation plant 1005 shown in FIG. 5 in that, in addition to the material flow denoted by S in FIG

Air separation plant 1011 according to FIG. 11 labeled J and explained there is formed. These material flows S and J are by means of two

Circuit compressors 9a and 9b are supplied to the main heat exchanger 4. The

Circuit compressors 9a and 9b are preferably designed as part of a common machine. A connecting flow denoted by SJ can be omitted if the material flow J is formed in the manner shown. Instead, however, the material flow J upstream of the cycle compressor 9b can also completely pass through the

Connection stream SJ can be replaced.

The air separation plant 1013 illustrated in FIG. 13 differs, for example, from the air separation plant 1005 shown in FIG Adsorption unit 3 can be used.

The air separation plant 1014 illustrated in FIG. 14 differs, for example, from the air separation plant 1005 shown in FIG. 5 in that the partial flow c is recompressed by means of a booster 5a and that the partial flow b is expanded by means of a generator turbine 5b. The substreams present in particular at the same pressure are combined as shown and fed together into the first column 13. The air separation plant 1015 illustrated in FIG. 15 differs, for example, from the air separation plant 1002 shown in FIG. 2 in that the top condenser 111 of the first column 11 is fed with bottom liquid from the first column 11. For better differentiation, a corresponding material flow is designated here with h '. The bottom liquid of the second column 12, on the other hand, is only fed to the third column 13 here. A corresponding material flow is designated with k 'for the sake of better distinguishability. In addition, fluid evaporated in the form of a material flow f from the top condenser 141 of the fourth column 14 is partially combined with the material flow s. In the embodiment of the air separation plant 1015 illustrated here, a production ratio between gaseous low-pressure nitrogen and gaseous pressure nitrogen (cf. material flow g and material flow r) can in particular be 0 to approx. 15 to 20%.

The air separation plant 1016 illustrated in FIG. 16 represents a variant of the air separation plant 1015 illustrated in FIG. 15, in which a (small) pump 17 'is present, by means of which part of the bottom liquid from the second column 12 in the form of a material flow h ″ for compensation a possibly existing

Liquid deficit is pumped into the top condenser 111 of the first column 11 or into its evaporation chamber. In the embodiment of the air separation plant 1016 illustrated here, a production ratio between gaseous low-pressure nitrogen to gaseous pressure nitrogen (cf. material flow g and material flow r) can in particular be more than 15 to 20%.

The air separation plant 1017 illustrated in FIG. 17 represents a variant of the air separation plant 1016 illustrated in FIG. 16, in which in the

Top condenser 111 of the first column 11 or an additional separating section 112 is provided in its evaporation chamber. This functionally represents the lowermost separating section of the second column 12, which is present in the air separation plant 1016 illustrated in FIG. 16. The second column 12 of FIG

Air separation plant 1017 according to FIG. 17 therefore no longer has this separation section. In this embodiment, the pump 17 'can be made smaller.

A corresponding configuration is also possible in systems without the production of gaseous low-pressure nitrogen. The air separation plant 1018 illustrated in FIG. 18 differs from the air separation plants 1001 to 1017 previously shown in FIGS. 1 to 17 in that the fifth column 15 is not provided and that the third column 13, which is accordingly designed with one fewer separating section, does not the material flow corresponding to the material flow r is taken. However, these two features can also exist independently of one another. Liquid nitrogen can be implemented here in the form of a material flow L.

As mentioned, the air separation plant 1019 illustrated in FIG. 19 represents in particular a variant of the air separation plant 1002 according to FIG. 2. In the air separation plant 1019, part of the bottom liquid from the second column 12 is denoted by k 'as in FIGS Material flow in the third column 13 and a further part by means of a pump 17 'in the form of a

Material flow h ″ is fed into the evaporation space of the top condenser 111. Liquid from the evaporation space of the top condenser 111 is combined with the material flow i and fed into the second column 12 with this.

Claims

1. A method for the low-temperature separation of air with the production of nitrogen at a pressure in a pressure range of 9 to 12 bar and with the production of argon, in which an air separation plant (1001-1019) 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), a) in the first column (11) a first bottom liquid is formed, in the second column (12) a second bottom liquid is formed, in the third column (13) a third bottom liquid is formed 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) into the second column (12) and into the third column (13), fluid from the second column (12) 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) into the third column (13), and e) that from the third column (13) into the fourth column (14) fluid fed in comprises at least a portion of a side stream that has a lower oxygen content and a higher argon content than the third

Bottom liquid is withdrawn from the third column (13), characterized in that f) by condensing top gas of the second column (12) a

Return liquid is formed and the return liquid is fed into the first column (11) in liquid form by means of a pump (8).

2. The method according to claim 1, wherein the top gas of the fourth column (14) is condensed by means of a first condenser-evaporator (141) in which a portion of the first bottom liquid is subjected to partial evaporation.

3. The method according to claim 1 or 2, wherein the fluid fed from the second column (12) into the third column (13) comprises at least a portion of the second bottom liquid, which without the use of a pump from the second column (12) into the third column (13) is transferred.

4. The method according to any one of the preceding claims, in which the top gas is removed from the first column (11) at a removal position and from the

Air separation plant (1000-1019) is diverted, the reflux liquid being fed into the first column (11) below the removal position or at the same level as the removal position.

5. The method according to claim 3 or 4, wherein the return liquid through

The pressure increase is brought into a supercooled state by means of a pump (8) and is used in the supercooled state to cool one or more liquid material flows.

6. The method according to claim 2, in which gas is removed from the third column (13) or from the evaporation space of the first condenser evaporator (141), heated, compressed, cooled and fed into the second column (12).

7. The method according to claim 2, wherein the fluid fed from the first column (11) into the third column (13) has at least a portion of a gas phase that is formed during partial evaporation in the first condenser evaporator (141) and at least a portion a liquid phase which remains liquid during the partial evaporation in the first condenser evaporator (141).

8. The method of claim 2 or 7, wherein the top gas of the first column (11) is condensed by means of a second condenser evaporator (111), in which a portion of the first bottom liquid and / or a portion of the second

Bottom liquid is subjected to a partial evaporation, the fluid fed from the first column (11) into the third column (13) at least a portion of a liquid phase which, in the case of partial evaporation, in the second

Condenser evaporator (111) remains liquid, comprises.

9. The method according to claim 8, in which at least a portion of a gas phase that is formed in the partial evaporation in the second condenser evaporator (111) is returned to the first column (11), in particular after heating, compression and cooling.

10. The method according to claim 9, wherein the proportion of the gas phase in the

Partial evaporation in the second condenser evaporator (111) is formed and returned to the first column (11), the heating, compression and

Cooling is subjected, with the compaction of this proportion

Compressor (9) is used, which is provided in a common structural unit with a further compressor (91), by means of which gas withdrawn from the second column (12) is compressed after heating.

11. The method according to any one of claims 2 or 7 to 10, wherein the fluid fed from the first column (11) into the second column (12) comprises a further portion of the first bottom liquid which is not the partial evaporation in the first condenser evaporator (141 ) is subjected.

12. The method according to any one of claims 2 or 7 to 11, wherein a fifth

Column (15) is used, into which the fluid from the fourth column (14) is transferred, the fluid transferred from the fourth column (14) having an argon content which is higher than that in that removed from the third column (13) and at least to a portion in the fourth column (14) transferred gas mixture.

13. The method according to claim 13, in which the top gas of the fifth column (15) is condensed by means of a further condenser evaporator (141), in which a further portion of the second bottom liquid is subjected to partial evaporation, the fluid fed from the first column (11) into the third column (13) at least a portion of a gas phase which is formed in the further condenser evaporator (151) during partial evaporation, and at least a portion of a liquid phase that in the partial evaporation in the further

Condenser evaporator (151) remains liquid, comprises.

14. The method according to any one of the preceding claims, in which the side stream which is withdrawn from the third column (13) with the lower oxygen content and the higher argon content than the third bottom liquid, while obtaining a top gas and a bottom liquid in a further column (14) is subjected to a mass transfer with a portion of the fourth bottom liquid, at least a portion of the gas phase from the further column being fed into the fourth column (14).

15. Air separation plant (1001-1019), which has a column system (10) with a first column (11), a second column (12), a third column (13) and a fourth column (14) which, with the recovery of nitrogen can be operated at a pressure in a pressure range from 9 to 12 bar and with the production of argon, and which is set up to a) 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 the third sump liquid with a higher oxygen content and a to form a lower argon content than the second sump liquid, d) fluid from the first column (11) into the second column (12) and into the third column (13), fluid from the second column (12) into the third column (13), fluid from the third column (13) feed into the fourth column (14) and fluid from the fourth column (14) into the third column (13), and e) as the fluid fed from the third column (13) into the fourth column (14) at least part of a To use side stream which is withdrawn from the third column (13) with a lower oxygen content and a higher argon content than the third bottom liquid, characterized by means which are set up f) by condensing top gas of the second column (12) a

To form the return liquid and the return liquid by means of a

Feed the liquid pump (8) into the first column (11).