EP4435364A1 - Method for the low-temperature separation of air, and air separation plant - Google Patents

Abstract

The invention relates to a method for the low-temperature separation of air using an air separation plant (100-300) with a main heat exchanger (4) and a subcooling countercurrent device (18) and a rectification column system (10) which has a first rectification column (11), a second rectification column (12) and a third rectification column (13), in which the first rectification column (11) is operated at a first pressure level and is fed using gaseous compressed air cooled in the main heat exchanger (4), the second rectification column (12) is operated at a second pressure level and is fed using bottom liquid from the first rectification column (11), the third rectification column (13) is operated at a third pressure level and is fed using fluid which is taken from the second rectification column (12), the first pressure level is at 9 to 14.5 bar at the top of the first rectification column (11) and the second pressure level is 2 to 5 bar at the top of the second rectification column (12), and top gas from the second rectification column (12) is used to form a turbine cycle stream which is cyclically and successively subjected to a first heating in the countercurrent subcooling device (18), a second heating in the main heat exchanger (4), compression, cooling and expansion. It is provided that the top gas from the second rectification column (12) used to form the turbine cycle stream is partially or completely combined with the turbine cycle stream downstream of the expansion and upstream of the first heating of the turbine cycle stream. A corresponding system (100-400) is also the subject of the present invention.

Description

The invention relates to a process for the low-temperature separation of air and an air separation plant according to the respective preambles of the independent patent claims.

Background of the invention

The production of air products in liquid or gaseous state by low-temperature separation of air in air separation plants is well known and is used, for example, in H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 2006 , in particular Section 2.2.5, "Cryogenic Rectification". In the following, the terms known from the specialist literature are used for the components and plant parts used in an air separation plant.

From the WO 2021/204424 A2 A process for the low-temperature separation of air is known in which the top gas of the low-pressure column is heated in the main heat exchanger, compressed, cooled again and, after partial or complete liquefaction or in an unliquefied state, is partially or completely or in portions returned to the pressure column and/or to the low-pressure column.

According to this publication, such a process has proven to be particularly advantageous for a requirement profile that includes the production of gaseous pressure nitrogen at a certain pressure level and an additional production of argon. A double column system formed from the pressure column and the low-pressure column is operated at an increased pressure level. The low-pressure column is designed to provide a very nitrogen-rich top gas by using a suitable nitrogen section in the upper area.

There is still a need for processes that allow the provision of air products, in particular using top gas from the low-pressure column as just explained, to be further improved and made more efficient and simpler.

Disclosure of the invention

Against this background, the present invention proposes a method for the low-temperature separation of air and an air separation plant with the features of the respective independent patent claims. Embodiments are the subject of the dependent patent claims and the following description.

In the following, some of the terms used to describe the present invention and its advantages as well as the underlying technical background are explained in more detail.

An "expansion turbine" or "expansion machine", which can be coupled to other expansion turbines or energy converters such as oil brakes, generators or compressors via a common shaft, is designed to expand a gaseous or at least partially liquid stream. In particular, expansion turbines for use in the present invention can be designed as turbo expanders. If a compressor is driven by one or more expansion turbines, but without externally supplied energy, for example by means of an electric motor, the term "turbine-driven" compressor or alternatively "booster" is used. Arrangements of turbine-driven compressors and expansion turbines are also referred to as "booster turbines" or alternatively as "turbine boosters". If it is mentioned below that expansion takes place in a booster turbine, this is to mean the turbine part. The same applies to the compression, which then takes place in the compressor part of the booster turbine or the turbine booster.

Liquids and gases, as used herein, may be rich or poor in one or more components, where "rich" may mean a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9% or 99.99% and "poor" may mean a content of at most 50%, 25%, 10%, 5%, 1%, 0.1% or 0.01% on a mole, weight or volume basis. The term "predominantly" may correspond to the definition of "rich". Liquids and gases may also be enriched or depleted in one or more components, where these terms refer to a content in a starting liquid or gas from which the liquid or gas was derived. The A liquid or gas is "enriched" if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1,000 times the content of a corresponding component, and "depleted" if it 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 original liquid or gas. If, for example, "oxygen" or "nitrogen" is mentioned here, this also includes a liquid or gas that is rich in oxygen or nitrogen, but does not necessarily have to consist exclusively of these.

The present disclosure uses the terms "pressure level" and "temperature level" 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 in order to implement the inventive concept. However, such pressures and temperatures typically move in certain ranges that are, for example, 1%, 5%, 10%, 20% or even 50% around a mean value. Corresponding pressure levels and temperature levels can lie in disjoint ranges or in ranges that overlap one another. In particular, pressure levels, for example, include unavoidable or expected pressure losses. The same applies to temperature levels.

Advantages of the invention

Just to avoid misunderstandings, it should be emphasized that when we talk about a turbine cycle stream below, we are talking about a material stream that is used to generate additional cold and is circulated, and not a material stream that is also known or used and is circulated and used to improve rectification in the low-pressure column. The latter represents a rectification cycle stream in the language used here. Turbine and rectification cycle streams can, however, be run together in certain sections. The rectification cycle stream is not expanded in the turbine, but is typically returned to the rectification column arrangement after cooling in the main heat exchanger.

The turbine cycle flow referred to as such below does not have to correspond to the state of the art, e.g. WO 2021/204424 A2 , material flow referred to as the circulating flow. In the following, the term "turbine circulating flow" refers to fluid that is cyclically compressed on the warm side of the main heat exchanger, boosted if necessary, cooled, expanded in the turbine, passed through a subcooling counterflow, heated in the main heat exchanger and then compressed again on the warm side of the main heat exchanger when the circuit is closed.

In conventional processes of the type explained at the beginning, a partial liquefaction of the process air flow, i.e. at least part of the air fed into the pressure column, also referred to as "feed air", is typically required in order to close the enthalpy balance around the rectification system. This partial liquefaction is also referred to below as "pre-liquefaction". The reason for this is in particular that the typically occurring removal of a comparatively large amount of liquid products from the air separation plant leads to a comparatively low enthalpy value of the incoming process air flow. In the context of the present invention, it has now been recognized that this pre-liquefaction has negative effects on the rectification process and should advantageously be avoided or reduced in order to improve the efficiency of the air separation process. The negative effects conventionally arise from the fact that the liquefied portion bypasses the separation process in the pressure column and is not condensed in the main condenser. The resulting lack of power in the main condenser must be compensated for.

As has now been recognized within the scope of the present invention, this problem can be addressed by guiding a turbine cycle stream or a portion thereof after its expansion through a subcooling countercurrent device, which is part of the air separation plant and through which certain material streams are guided in the manner explained below. The turbine cycle stream is combined with top gas from the low-pressure column upstream of this subcooling countercurrent device. Since a temperature level of approx. 90 K is reached here, the enthalpy of the process air stream can be increased and the pre-liquefaction of the same at approx. 110 K can be avoided or significantly reduced.

The present invention proposes a method for the low-temperature separation of air using an air separation plant with a main heat exchanger and a counter-current subcooling device and a rectification column system that has a first rectification column, a second rectification column and a third rectification column. The first and second rectification columns are in particular rectification columns that can be designed according to a pressure column and a low-pressure column of a known double column system and are basically connected in a comparable way. However, these are operated at an increased pressure level. The third rectification column is in particular a crude argon column or a single column for obtaining an argon product, which partially combines the functions of the crude and pure argon columns by having a further section intended for the separation of nitrogen.

The first rectification column provided within the scope of the present invention is operated at a first pressure level, the first rectification column is fed using compressed air cooled in the main heat exchanger, and in the first rectification column, in particular, a bottom liquid enriched in oxygen and argon compared to the first feed stream and a nitrogen-rich top gas are formed. By means of the measures proposed according to the invention, the first feed stream can be fed into the first rectification column in particular in a completely or essentially completely gaseous state, which can therefore represent a feature of embodiments of the invention, wherein an "essentially" completely gaseous state is intended to denote a gas content of more than 90%, 95% or 99% in the molar fraction.

The bottom liquid of the first rectification column can in particular have a content of 28 to 38% oxygen as well as argon and nitrogen. The top gas of the first rectification column can in particular have a content of 0.1 to 100 ppb (billionths of a part), for example approx. 10 ppb, of oxygen, 1 to 100 ppm (millionths of a part), for example approx. 30 ppm, of argon, and otherwise essentially nitrogen and possibly lighter components.

The second rectification column is operated in the context of the present invention at a second pressure level, and the second rectification column is (at least) using bottom liquid from the first rectification column. As also explained below, the bottom liquid from the first rectification column, or a corresponding part thereof, can also be used in particular to cool one or more top condensers of the argon recovery column(s), ie in particular also of the third rectification column, whereby evaporated and unevaporated portions may be formed, which are then fed into the second rectification column as a feed stream or feed streams. In the second rectification column, in particular an oxygen-rich bottom liquid and a nitrogen-rich top gas are formed.

The top gas of the second rectification column can be formed in particular with a content of 1 to 1000 ppb, for example about 100 ppb, of oxygen and 3 to 300 ppm, for example about 90 ppm, of argon. In certain cases, the top gas of the first and second rectification columns can also have essentially the same contents of the components mentioned.

The third rectification column is operated at a third pressure level, which can in particular be slightly lower than the second pressure level, and is fed using fluid which in particular has a higher argon content than the second bottom liquid and the second top gas and is taken from the second rectification column, typically at the so-called argon belly or below. In the third rectification column, in particular, a third top gas enriched in argon compared to the third feed stream is formed. The feeding does not have to be carried out with the fluid from the second rectification column, but can also be carried out using fluid taken from another rectification column or another separation apparatus, which in turn is fed with the fluid taken from the second rectification column. The corresponding can be the case in particular if, in one embodiment of the invention, a fourth rectification column is used to obtain high-purity oxygen.

In the context of the present invention, the first rectification column can in particular have 80 to 110, for example 90, theoretical plates, the second rectification column with 90 to 150, for example 110, theoretical plates and the A third rectification column with 210 to 320, for example 250, theoretical plates can be formed.

In the context of the present invention, the first pressure level is 9 to 14.5 bar, for example about 11.6 bar, at the top of the first rectification column and the second pressure level is 2 to 5 bar, for example about 3.5 bar, at the top of the second rectification column.

In the proposed process, top gas from the second rectification column is combined with a turbine cycle stream, which is cyclically and successively subjected to a first heating in the countercurrent subcooling device, a second heating in the main heat exchanger, compression, cooling and expansion using an expansion turbine. For the meaning of the term "turbine cycle stream", reference is also made to the above explanations. To avoid misunderstandings, it should be emphasized that the fact that we are talking about a combination of top gas with a turbine cycle stream says nothing about the quantitative ratios. In other words, the amount of top gas combined with the turbine cycle stream can also be significantly larger than the turbine cycle stream at the point of combination. A combination of top gas with the turbine cycle stream means that gas molecules of the top gas become part of the turbine cycle stream.

The term "cyclically and one after the other" is to be understood as meaning that the turbine cycle stream is guided in a cycle through the corresponding equipment used and in each cycle undergoes the processing steps mentioned. A cycle stream is present because a portion of the individual gas molecules are subjected to the processing steps mentioned several times, even if portions are removed from the turbine cycle stream at certain points or additional gas is fed into the turbine cycle stream or the turbine cycle stream is guided in sections together with other cycle streams. The efficiency of the proposed air separation process can be significantly increased simply by forming the turbine cycle stream described above.

Such a process is further improved within the scope of the present invention in that the top gas of the second rectification column, which is combined with the turbine cycle stream, is combined partially or completely with the turbine cycle stream downstream of the expansion and upstream of the first heating. As mentioned, the present invention thereby makes it possible to dispense with pre-liquefaction of the feed air which is fed to the first rectification column.

The combination of the top gas with the turbine cycle stream can also take place at the top of the second rectification column, i.e. within the second rectification column and in an upper region thereof, the "upper region" being in particular a region above the uppermost separation section. This is particularly advantageous in the case when the expansion turbine used to expand the turbine cycle stream expands strongly into the pre-liquefaction, since in this case the second rectification column can practically serve as a liquid separator for the turbine cycle stream. In such a case, it is understood that liquid formed during the expansion is initially removed from the turbine cycle stream by remaining in the second rectification column. In this case, the turbine cycle stream is closed via the top of the second rectification column.

In embodiments of the invention, a bypass of the turbine circuit stream around the subcooling countercurrent can also be provided, i.e. the top gas of the second rectification column combined with the turbine circuit stream can be combined partially or completely with the turbine circuit stream downstream of the expansion and then in particular adjustable proportions upstream and downstream of the first heating.

The advantages of the present invention arise, as also mentioned, in particular when, as is the case in embodiments of the present invention, the turbine circuit flow is brought to a temperature level of 80 to 100 K, in particular approximately 90 K, by cooling and relaxation.

In embodiments of the present invention, fluid is conducted together with the turbine cycle stream, which downstream of the second heating, upstream and/or downstream of the compression and upstream of the cooling in the form of one or several partial streams are branched off again and discharged from the air separation plant. In this way, gases can be advantageously provided for specific purposes and a rectification cycle stream can also be formed which is returned to the rectification column system.

In particular, the one partial stream or at least one of the several partial streams can be used to provide a gaseous, pressurized air product with the desired specifications.

In embodiments of the present invention, the turbine cycle stream downstream of its turbine expansion can, for example, comprise a certain amount of fluid per unit of time, which is also referred to here as the turbine cycle flow amount. The overhead gas removed from the low-pressure column per unit of time, also referred to below as the overhead gas amount, can be 1.2 to 3 times the turbine cycle flow amount. As mentioned, within the scope of the present invention, gas can also be fed back into the rectification column arrangement in a rectification cycle stream, the amount of which is also referred to here as the rectification cycle flow amount. This is typically no more than 0.6 times the turbine cycle flow amount.

In the context of the present invention, in the countercurrent subcooling device, in particular a residual gas discharged from the second rectification column is also heated and/or one or more liquids formed using top gas from the first rectification column and/or bottom liquid from the first rectification column and/or an argon product are subcooled. In this way, the heat balance can be balanced in a particularly advantageous manner.

Furthermore, a significant reduction in the amount of recirculated gas can be achieved (due to the increased steam loading in the pressure column). This results in significant advantages in terms of energy consumption, which can, for example, lead to a reduction of up to 0.8% of the total energy consumption of the plant.

In one embodiment of the present invention, the compression of the turbine cycle stream may comprise a first compression step and a second compression step, wherein the second compression step is carried out using a booster which is mechanically coupled to an expansion turbine used to carry out the expansion. In this way, the mechanical energy released during the expansion can be used in a particularly advantageous manner during the compression. The first compression step can be carried out in particular using a single- or multi-stage compressor of any type.

In specific embodiments, a further compression step can be inserted between the first and second compression steps, which can in particular also be carried out with a separate, in particular single-stage, nitrogen compressor. This makes it possible in particular to achieve a higher liquid production.

In a process according to an embodiment of the present invention, a residual gas turbine can be used in particular. In this, residual gas from the second rectification column, which is taken from below an uppermost separation section thereof and is significantly richer in oxygen than the top gas of the second rectification column, can be withdrawn.

In certain embodiments, as already mentioned, the present invention can in particular comprise the third rectification column being operated alone or together with a pure argon column to produce argon. For information on argon production, reference is made to the specialist literature cited at the beginning.

Any other rectification columns can be used in embodiments of the present invention, in particular a further rectification column for obtaining an oxygen product and/or a further rectification column for obtaining a crude krypton/xenon mixture and/or a further rectification column for obtaining a crude helium/neon mixture, wherein reference is also made to the cited specialist literature for the formation of crude krypton/xenon mixtures or crude helium/neon mixtures. In corresponding embodiments, the turbine cycle stream or a part thereof can be used as a heating medium for the bottom evaporators of corresponding columns.

By means of the measures proposed within the scope of the present invention, the air fed into the first rectification column can be completely gaseous or more than 90%, 95% or 99% gaseous, thus pre-liquefaction can be dispensed with.

Further features of embodiments according to the invention and non-invention are explained below.

Within the scope of the present invention, in particular significantly more than 85%, for example approximately 90%, of the argon from the second rectification column can be transferred to the argon recovery system, and thus the third rectification column, and used to recover an argon product. When recovering argon, an argon yield of more than 85%, for example approximately 90%, can also be achieved. A yield of more than 90% is also possible.

Within the scope of the present invention, in certain embodiments, compression of a nitrogen product can be dispensed with by operating the first rectification column at the first pressure level. For a compressor that compresses the turbine cycle stream and possibly other gas, a simple design, for example with only two compression stages, can be used. This compressor can also be designed in the form of a so-called combination compressor, which for example also comprises four stages that fulfill the function of the main air compressor. In other words, the compression of the compressed air and the second top gas used to form the turbine cycle stream or a corresponding part thereof can be carried out using a jointly driven compressor arrangement.

In a particularly preferred embodiment of the present invention, the fluid taken from the second rectification column to feed the third rectification column can, as already mentioned, be fed into a further rectification column, and a corresponding feed stream can be formed using fluid taken from this further rectification column. The further rectification column is set up in particular to form a high-purity oxygen product and is operated as explained below.

The further rectification column has in particular a first (upper) part and a second (lower) part, with a "barrier plate" rectification section, which serves in particular to retain hydrocarbons, being arranged between the first and the second part. In particular, the first part of the further rectification column can be functionally designed as the lowest part of a crude argon column and can be coupled accordingly to the actual crude argon column, i.e. the third rectification column. A corresponding design is carried out in particular for reasons of installation space in order to reduce the overall height of the air separation plant. The fluid which is taken from the second rectification column and used to feed the third rectification column is fed into a lower region of the first part. Gas is taken from an upper region of the first part and used to feed the third rectification column. Bottom liquid formed in the third rectification column is at least partially transferred to the upper region of the first part.

Liquid is taken from an intermediate area of the first part and fed into an upper area of the second part, where the actual pure oxygen production takes place. Gas is taken from the upper area of the second part and fed into the intermediate area of the first part, and pure oxygen is formed in a lower area of the second part and discharged from the air separation plant. The pure oxygen can be formed in particular with a residual content of 5 to 500 ppb, for example approx. 10 ppb, of argon.

If no corresponding additional or further two-part column is available, the fluid from the second rectification column can also be fed directly into the third rectification column, i.e. a crude argon column.

In the context of the present invention, the lower region of the second part of the further rectification column just described can be heated in particular using a condenser evaporator in which part of the top gas of the first rectification column is used as heating fluid. The part of the top gas of the first rectification column used as heating fluid can then be fed into the first rectification column or into the second rectification column, in particular in a liquefied state.

The bottom liquid of the first rectification column or at least the part thereof that is used to feed the second rectification column can, as mentioned several times, be used to condense top gas from at least the third rectification column. This top gas can in particular, as is known from the prior art, be purified to pure argon in a pure argon column.

With regard to the features of the air separation plant also proposed according to the invention, express reference is made to the corresponding independent patent claim. The air separation plant is set up in particular to carry out a process as previously explained in embodiments. Express reference is therefore made to the above explanations regarding the process according to the invention and its advantageous embodiments.

The invention is explained in more detail below with reference to the accompanying drawings, which illustrate the preferred embodiments of the present invention.

Character description

The Figures 1 to 3 illustrate air separation plants according to different embodiments of the present invention.

In the figures, structurally or functionally corresponding elements are indicated with identical reference symbols and are not explained repeatedly for the sake of clarity. Explanations relating to systems and system components apply equally to corresponding processes and process steps.

In Figure 1 An air separation plant according to an embodiment of the present invention is illustrated in the form of a simplified process flow diagram and is designated overall by 100.

In the air separation plant 100, air is sucked in by means of a main air compressor 1 through a filter 2 and compressed to a pressure level of, for example, approximately 12.5 bar. The correspondingly compressed air is cooled and separated from Water is freed from residual water and carbon dioxide in an adsorber station 3, which can be designed in a known manner. For the design of the components mentioned, reference is made to the specialist literature cited at the beginning.

A correspondingly formed compressed air stream a is guided from the warm to the cold end through a main heat exchanger 4 and fed here in a substantially gaseous state into a pressure column 11 ("first rectification column") of a rectification column system 10. In the example shown, the rectification column system 10 has, in addition to the pressure column 11, a low-pressure column 12 ("second rectification column"), a two-part crude argon column 13 ("third rectification column") with two column parts 13a (upper part) and 13b (lower part) and a pure argon column 14. Furthermore, a rectification column 15 for obtaining a crude krypton/xenon mixture and a rectification column 16 for obtaining a crude helium/neon mixture are provided. The pressure column 11 is connected to the low-pressure column 12 via a main condenser 11a in a heat-exchanging manner, which can be designed, for example, as a multi-level bath evaporator, and a bottom evaporator 15a is arranged in the bottom of the rectification column 15 for obtaining the krypton/xenon raw mixture. In the example shown, a subcooling countercurrent device 18 is also assigned to the rectification column system 10.

A top gas is formed at the top of the pressure column 11. In the example shown, this is partly passed in the form of a material flow b through the main condenser 11a and another part in the form of a material flow c through the bottom evaporator 15a of the rectification column 15 to obtain the crude krypton/xenon mixture. Condensate formed in the main condenser 11a is returned to the pressure column 11. A non-condensed portion is fed into the rectification column 16 to obtain the crude helium/neon mixture. Further condensate that forms in the bottom evaporator 15a of the rectification column 15 to obtain a crude krypton/xenon mixture can be passed in the form of a liquid nitrogen flow m through the subcooling countercurrent 18 and fed into the low-pressure column 12 at the top. Condensate b1 removed via a liquid extraction point at the top of the pressure column can be treated in this way. A material stream d that has been cooled in the main heat exchanger 4 can be fed to the top gas of the pressure column 11. Its origin is explained below.

A bottom liquid is formed in the bottom of the pressure column 11 and is withdrawn from it in the form of a material stream e. The material stream e is first passed through the countercurrent subcooler 18 and then used in a manner known per se to cool top condensers (not separately designated) of the crude argon column 13 and the pure argon column 14. Vaporized and unvaporized portions are fed into the low-pressure column 12 in the form of material streams f or are used to form the material stream k explained below.

In the low-pressure column 12, bottom liquid ("second bottom liquid") is formed, which is fed into an evaporation space of the main condenser 11a, and gas is fed from the main condenser 11a into the low-pressure column 11 at the bottom. Above the bottom, liquid h is withdrawn from the low-pressure column 11. A first part of this is increased in pressure in a pump 5 in the form of a material flow h1, heated in the main heat exchanger 4 and discharged as an internally compressed oxygen product. A second part of the liquid h is fed into the rectification column 15 in the form of a material flow h2 to obtain the krypton/xenon raw mixture, and a third part is discharged in the form of a material flow h3, in particular as a liquid product from the air separation plant 100.

Above the sump, gas is withdrawn from the low-pressure column 12 in the form of a material stream i, combined with material streams k and o explained below to form a collective stream I with a content of, for example, approx. 90% oxygen, partially heated in the main heat exchanger 4, expanded in a generator turbine or residual gas turbine 6, heated again in the main heat exchanger 4, and used, for example, as regeneration gas in the adsorber station 3.

A gaseous pressurized nitrogen stream is withdrawn in the form of a material stream n from the top of the low-pressure column 12. This is present, for example, at a pressure level of approximately 3.5 bar and has a content of approximately 50 ppb oxygen, for example. It is used to form a turbine cycle stream, which is first heated in the subcooling counterflow 18 ("first heating"), then heated in the main heat exchanger 4 ("second heating"), compressed in a compressor 7 and then in a booster of a booster turbine arrangement 9, in the Main heat exchanger 4 is cooled again and expanded in an expansion turbine of the booster turbine arrangement 9. The circuit is closed by feeding into the subcooling counterflow 18. The mentioned material flow n is branched off downstream of the compressor 7 and cooled in the main heat exchanger 4. Upstream and downstream of the compressor 7, further partial flows can be branched off and used, for example, as compressed nitrogen product, blow-off gas and sealing gas. Any combination is possible. A rectification circuit flow is fed partly together with the turbine circuit flow, but this is not subjected to the second compression and expansion, but is cooled in the main heat exchanger 4 and then used as explained.

Argon-enriched gas is withdrawn from the low-pressure column 11 in the form of a stream o and fed into the crude argon column 13. Bottom liquid is returned from the crude argon column 13 in the form of a stream p to the low-pressure column 11 by means of a pump not specifically designated.

The operation of the crude argon column 13 and the pure argon column 14 essentially corresponds to that known in the prior art and is not explained separately. A pure argon stream v is withdrawn from the pure argon column 15, which, in particular after supercooling in the supercooling countercurrent 18, now designated w, is partly stored or temporarily stored in a tank T, for example, the pressure is increased by pressure build-up evaporation and after heating in the main heat exchanger 4 can be provided with a content of, for example, approx. 200 ppb oxygen.

The mentioned material stream k is formed using gas which is taken from the top condenser of the crude argon column 13. The material stream o comes from the top of the rectification column 15 for obtaining the crude krypton/xenon mixture, from the bottom of which the crude krypton/xenon mixture is taken in the form of a material stream not separately designated.

At the top of the low-pressure column 12, liquid is withdrawn and partly subcooled in the form of a stream x and provided as a liquid nitrogen product, and a further part y is fed into an evaporation chamber of the rectification column 16 to obtain the raw helium/neon mixture, which is withdrawn therefrom in the form of a material stream z.

A dashed line illustrates a temperature-insulated area whose enthalpy balance is essentially closed by the use of the measures proposed according to the illustrated design.

In Figure 2 an air separation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and designated overall by 200.

The Figure 2 The air separation plant 200 illustrated has, in contrast to the air separation plant 100 according to Figure 1 a one-piece crude argon column 13. A pure oxygen column 7 is also present. This is operated with a bottom evaporator 17a and has an upper region and a lower region which are separated from one another by a partition wall 17b. The upper region is fed with the material flow o and the material flow p is taken from this. Functionally, it is a "separated oxygen section" of the low-pressure column. The bottom evaporator 17a is operated with the material flow d. A condensate u formed is treated like the material flow m. The upper and lower parts of the pure oxygen column 17 are operated with bottom liquid r from the crude argon column as reflux, and top gas s from the parts of the pure oxygen column 17 is fed into the crude argon column 13. Pure oxygen is withdrawn in the form of a material flow t from the pure oxygen column 17, for example by means of a pressure build-up evaporation using a tank system T2, and discharged from the plant. A liquid argon tank system T3 is also shown here.

In Figure 3 an air separation plant according to a further embodiment of the present invention is illustrated in the form of a simplified process flow diagram and designated overall by 300.

The Figure 3 The air separation plant 300 illustrated in FIG. 1 has, in contrast to the air separation plant 200 according to Figure 2 a bypass around the subcooling counterflow 18, so that the material flow n after its Expansion can be fed back into portions n1 and/or n2 upstream or downstream of the subcooling countercurrent device 18.

Claims (14)

Process for the low-temperature separation of air using an air separation plant (100-300) with a main heat exchanger (4) and a subcooling countercurrent (18) and a rectification column system (10) which has a first rectification column (11), a second rectification column (12) and a third rectification column (13), in which - the first rectification column (11) is operated at a first pressure level and is fed using gaseous compressed air cooled in the main heat exchanger (4), - the second rectification column (12) is operated at a second pressure level and is fed using bottom liquid from the first rectification column (11), - the third rectification column (13) is operated at a third pressure level and is fed using fluid taken from the second rectification column (12), - the first pressure level is 9 to 14.5 bar at the top of the first rectification column (11) and the second pressure level is 2 to 5 bar at the top of the second rectification column (12), and - top gas of the second rectification column (12) is combined with a turbine cycle stream which is cyclically and successively subjected to a first heating in the subcooling countercurrent device (18), a second heating in the main heat exchanger (4), a compression, a cooling and an expansion,
characterized in that - the top gas of the second rectification column (12) combined with the turbine cycle stream is partially or completely combined with the turbine cycle stream downstream of the expansion and upstream of the first heating of the turbine cycle stream. A process according to claim 1, wherein the combining of the overhead gas with the turbine cycle stream occurs in an upper region and within the second rectification column (12). A process according to claim 1 or claim 2, wherein the top gas of the second rectification column (12) combined with the turbine cycle stream is combined partially or completely with the turbine cycle stream downstream of the expansion and then in portions upstream and downstream of the first heating. Method according to one of the preceding claims, in which the turbine cycle stream is brought to a temperature level of 80 to 100 K by cooling and expansion. Method according to one of the preceding claims, in which fluid is conducted together with the turbine circuit stream and is branched off again downstream of the second heating, upstream and/or downstream of the compression and upstream of the cooling in the form of one or more partial streams and is discharged from the air separation plant (100-300). A method according to claim 5, wherein the one partial stream or at least one of the plurality of partial streams is used to provide a gaseous, pressurized air product. Process according to one of the preceding claims, in which a residual gas discharged from the second rectification column (12) is heated in the subcooling countercurrent device (18) and/or one or more liquids formed using top gas from the first rectification column (11) and/or bottom liquid of the first rectification column (11) and/or an argon product are subcooled. A method according to any preceding claim, wherein the compression of the turbine cycle stream comprises a first compression step and a second compression step, the second compression step being carried out using a booster which is mechanically coupled to an expansion turbine used to carry out the expansion. Method according to one of the preceding claims, in which a residual gas turbine (9) is used. Process according to one of the preceding claims, in which the third rectification column (13) is operated alone or together with a pure argon column for argon recovery. Process according to one of the preceding claims, in which a further rectification column (17) is or are used to obtain an oxygen product and/or a further rectification column (15) is or are used to obtain a crude krypton/xenon mixture and/or a further rectification column (16) is or are used to obtain a crude helium/neon mixture. A process according to claim 10, wherein the air fed into the first rectification column (11) is completely or more than 90%, 95% or 99% gaseous. Air separation plant (100-300) with a main heat exchanger (4) and a subcooling countercurrent (18) and a rectification column system (10) which has a first rectification column (11), a second rectification column (12) and a third rectification column (13), and which is designed to - operating the first rectification column (11) at a first pressure level and feeding it using compressed air cooled in the main heat exchanger (4), - operating the second rectification column (12) at a second pressure level and feeding it using bottom liquid from the first rectification column (11), - operating the third rectification column (13) at a third pressure level and feeding it using fluid from the second rectification column (12), - the first pressure level is 9 to 14.5 bar at the top of the first rectification column (11) and the second pressure level is 2 to 5 bar at the top of the second rectification column (12), and - to combine top gas of the second rectification column (12) with a turbine circulation stream and to subject the turbine circulation stream cyclically and in each case successively to a first heating in the subcooling countercurrent device (18), a second heating in the main heat exchanger (4), a compression, a cooling and an expansion,
characterized in that - the air separation plant (100) is designed to combine the top gas of the second rectification column combined with the turbine cycle stream partially or completely downstream of the expansion and upstream of the first heating with the turbine cycle stream. Air separation plant (100-300) according to claim 13, which is arranged to carry out a process according to one of claims 1 to 12.

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