WO2023051946A1

WO2023051946A1 - Method for the cryogenic separation of air, and air separation plant

Info

Publication number: WO2023051946A1
Application number: PCT/EP2022/025406
Authority: WO
Inventors: Daniel OTTE
Original assignee: Linde Gmbh
Priority date: 2021-09-29
Filing date: 2022-09-01
Publication date: 2023-04-06

Abstract

The invention relates to an air separation plant (100) for cryogenic separation, said plant being designed to carry out a high-air-pressure process, wherein nitrogen is removed from the pressure column (11), expanded in a turbine (9) that is coupled to a cold booster (8), and heated. Separately from the nitrogen which is removed from the pressure column (11), nitrogen is removed from the low-pressure column (12) and heated to the same temperature. Before expansion in the turbine (9) that is coupled to the cold booster (8), the nitrogen removed from the pressure column (11) is heated to a temperature in a temperature range of -100 to 50°C. During expansion, the nitrogen cools down to a temperature in a temperature range of -150 to -40 °C and is then heated again. The invention also relates to a corresponding air separation plant (100).

Description

Process for the cryogenic separation of air and air separation plant

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

background

The production of air products in a liquid or gaseous state by low-temperature separation of air in air separation plants is known and is described, for example, by H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5, "Cryogenic Rectification". Unless expressly defined otherwise, the terms used below have the usual meaning in the specialist literature.

As is known, so-called main (air) compressor/boost compressor methods (MAC/BAC) or so-called high air pressure methods (high air pressure, HAP) can be used for air separation. The main air compressor/boosting processes are the more conventional processes, high air pressure processes are increasingly being used as alternatives in recent times. Reference is made to the further explanations below.

As also explained below, despite their advantages, in particular the reduction in the number of rotating machines and thus the lower construction costs, high-air pressure processes prove to be disadvantageous compared to main air compressor/boost processes for certain product constellations.

The object of the invention is therefore to improve the process switching in high-air pressure processes in such a way that the main advantage of the high-air pressure process mentioned is retained, but advantages over main air compressor/post-compressor processes also result overall. Disclosure of Invention

Against this background, the invention proposes a method for the low-temperature separation of air and an air separation plant according to the preambles of the independent patent claims. Refinements of the invention are the subject of the dependent patent claims and the following description.

First of all, further principles of the invention are explained in more detail and terms used to describe the invention are defined.

In particular, the term air product is intended herein to refer to a fluid provided at least in part by the cryogenic decomposition of atmospheric air. An air product according to the understanding on which this is based has one or more air gases contained in the atmospheric air in a different composition than in the atmospheric air. In principle, an air product can exist or be provided in a gaseous, liquid or supercritical state and can be converted from one of these states of aggregation to another. In particular, a liquid air product can be converted to the gaseous state (vaporized) or converted to the supercritical state (pseudo-vaporized) by heating to a certain pressure, depending on whether the pressure at the time of heating is below or above the critical pressure. If “vaporization” is mentioned below, this should also include a corresponding pseudo-vaporization.

Air separation plants have rectification column arrangements that can be designed in different ways. In addition to rectification columns for obtaining nitrogen and/or oxygen in the liquid and/or gaseous state, i.e. rectification columns for nitrogen-oxygen separation, which can be combined in particular in a known double column, rectification columns for obtaining other air components, in particular noble gases, or from be provided pure oxygen.

The rectification columns of typical rectification column arrangements are operated at different pressure levels. Known double columns have a so-called pressure column (also referred to as high-pressure column, medium-pressure column or lower column) and a so-called low-pressure column (upper column). The high-pressure column is typically operated in a pressure range from 4 to 7 bar, in particular to about 5.3 bar, whereas the low-pressure column is operated in a pressure range from typically 1 to 2 bar, in particular about 1.4 bar.

In air separation plants, multi-stage turbo compressors are used to compress the input air, which are referred to here as main air compressors. The mechanical structure of turbo compressors is known in principle to those skilled in the art. In a turbo compressor, the medium to be compressed is compressed by means of turbine blades, which are arranged on a turbine wheel or directly on a shaft. A turbo compressor forms a structural unit which, however, can have several compressor stages in the case of a multi-stage turbo compressor. A compressor stage generally includes a turbine wheel or a corresponding arrangement of turbine blades. All of these airends can be driven by a common shaft. However, it can also be provided that the compressor stages are driven in groups with different shafts, in which case the shafts can also be connected to one another via gears.

The main air compressor is further distinguished by the fact that it compresses the entire amount of air fed into the rectification column arrangement and used for the production of air products, ie the entire amount of feed air. Correspondingly, an after-compressor can also be provided, in which, however, only part of the input air quantity compressed in the main air compressor is brought to an even higher pressure. This can also be designed as a turbo compressor. Additional turbo compressors are typically provided for compressing partial quantities of air, which are also referred to as boosters, but compared to the main air compressor or the secondary compressor, they typically only compress to a relatively small extent, in particular in relation to the compressed quantity of air. A booster can also be present in a high-air pressure process (see below), but this then compresses a subset of the input air quantity, starting from a higher pressure.

A cold compressor or cold booster is to be understood here as a compressor or booster, the fluid at a temperature in a temperature range is supplied significantly below the ambient temperature of the air separation plant, in particular at a temperature of less than -50 °C or -100 °C and in particular more than -150 °C or -200 °C. In contrast, a warm compressor or warm booster is supplied with fluid at a temperature in a temperature range of more than −30° C., 0° C., 20° C. or 50° C. and in particular up to 100° C. or 200° C.

Air can also be expanded at several points in air separation plants, for which purpose, among other things, expansion machines in the form of turboexpanders, also referred to here as expansion turbines or turbines for short, can be used. Turboexpanders can also be coupled to and drive turbocompressors. If one or more turbo compressors are driven without externally supplied energy, i.e. only via one or more turbo expanders, the term turbine booster is also used for such an arrangement. In a turbine booster, the turboexpander (the expansion turbine) and the turbocompressor (the booster) are mechanically coupled, with the coupling being able to take place at the same speed (e.g. via a common shaft) or at different speeds (e.g. via an intermediate gearbox). If a turbine unit is discussed here, this should be understood to mean in particular an arrangement with at least one expansion turbine.

Main air compressor/recompressor processes are characterized in that only part of the total amount of feed air fed to the rectification column arrangement is compressed to a pressure level that is significantly, i.e. by at least 3, 4, 5, 6, 7, 8, 9 or 10 bar, above of the pressure level of the pressure column, and thus above the highest pressure level used in the rectification column arrangement. A further portion of the feed air quantity is only compressed to the pressure level of the pressure column or at most to a pressure level which differs therefrom by no more than 1 to 2 bar, and is fed into the pressure column at this level without expansion. An example of such a main air compressor/post-compressor process is shown by Häring (see above) in Figure 2.3A.

In a high-air pressure process, on the other hand, the entire amount of feed air fed to the rectification column arrangement is typically compressed to a pressure level that is significantly, ie by 3, 4, 5, 6, 7, 8, 9 or 10 bar or more above the pressure level of the pressure column and thus above the highest in the pressure level used in the rectification column arrangement. The pressure difference can be up to 14, 16, 18 or 20 bar or more, for example. High-air pressure processes have been described many times and are known, for example, from EP 2 980 514 A1 and EP 2 963 367 A1.

High-air pressure processes are typically used with so-called internal compression (IV, Internal Compression, IC). In the case of internal compression, at least one gaseous, pressurized air product, which is provided by the air separation plant, is formed by taking a cryogenic, liquid air product from the rectification column arrangement, subjecting it to a pressure increase to a product pressure, and subjecting it to the product pressure by heating it to the gaseous or supercritical state is transferred. For example, gaseous pressurized oxygen (GOX IV, GOX IC), gaseous pressurized nitrogen (GAN IV, GAN IC) and/or gaseous pressurized argon (GAR IV, GAR IC) can be produced by internal compression. Internal compression offers a number of advantages over external compression, which is also possible as an alternative, and is explained, for example, by Häring (see above) in Section 2.2.5.2, "Internal Compression".

In typical air separation plants, corresponding expansion turbines are present at different points for the generation of cold and the liquefaction of material flows. These are in particular Claude turbines and Lachmann turbines and possibly Joule-Thomson turbines. For the function and purpose of corresponding turbines, reference is made to the specialist literature, for example F.G. Kerry, Industrial Gas Handbook: Gas Separation and Purification, CRC Press, 2006, particularly Sections 2.4, "Contemporary Liquefaction Cycles", 2.6, "Theoretical Analysis of the Claude Cycle" and 3.8.1, "The Lachmann Principle".

In particular, high-air pressure processes are known, in which the Lachmann turbines mentioned are used. The air expanded in a Lachmann turbine is fed (blown) into the low-pressure column, which is why it is also referred to as an upper column expander. The Lachmann turbine can be provided as a further turbine unit in addition to a turbine unit, by means of which gaseous compressed air is expanded into the pressure column, ie a Claude turbine. The term blown-in air quantity refers to the compressed air that has been expanded using a typical Lachmann turbine (blow-in turbine) and fed (blown-in) into the low-pressure column. The air expanded in this way into the low-pressure column disturbs the rectification, which is why the amount of air that can be expanded in the injection turbine and thus the cold that can be generated in this way for a corresponding installation are limited. Nitrogen-rich air products, which are taken from the pressure column as pressurized nitrogen and taken out of the air separation plant, and also liquid nitrogen taken out of the air separation plant and internally compressed nitrogen taken out of the air separation plant, influence the rectification accordingly and/or and have common effects.

The amount of air blown into the low-pressure column by means of a Lachmann turbine plus the nitrogen taken from the pressure column and discharged from the air separation plant, plus the liquid nitrogen discharged from the air separation plant and plus the internally compressed nitrogen discharged from the air separation plant (if any) can be increased in relation to the total amount of air supplied to the rectification column arrangement. The value obtained in this way is called the injection equivalent.

A throttle flow or Joule-Thomson flow is understood to mean an amount of air which, at least for the most part, liquefies under pressure in the main heat exchanger of an air separation plant and is then fed, in particular via a throttle valve, into the pressure column in particular. A Joule-Thomson turbine can also be used instead of a throttle valve.

Liquid, gaseous or fluids in the supercritical state can be rich or poor in one or more components in the language used here, with "rich" for a content of at least 75%, 90%, 95%, 99%, 99.5% , 99.9% or 99.99% and "poor" can stand for a content of at most 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" just given, but in particular denotes a content of more than 90%. Is here For example, when we talk about "nitrogen", it can be a pure gas, but it can also be a gas rich in nitrogen.

Features and advantages of the invention

High-air pressure methods can be used in different configurations. These are often classified and differentiated according to the liquid output of the system, i.e. according to the quantity of air products provided in liquid form and removed from the system in liquid form (here also referred to as liquid products), or according to the ratio of internally compressed air products to liquid products.

When the amount of liquid products is low or when no liquid products are formed and at certain internal compressions, a high air pressure process with a warm booster (driven by a turbine) and a cold booster (also driven by a turbine) provides a cost-effective An alternative to a main air compressor / booster process. However, the maximum achievable pressure achieved by hot and cold boosters connected in series may not be high enough to optimally balance the hot and cold flows in the main heat exchanger without the pressure excessive lift at the main air compressor (resulting in an energy penalty over main air compressor/boost processes) or jeopardizing the buildability of the turbine booster assemblies.

With a conventional main air compressor / booster process, the process can be adapted relatively well to different product constellations, since both compressors used (main air compressor and booster) are "responsible" for functionally separate tasks. In principle, the main air compressor only supplies the input air for the separation and the booster the energy for internal compression and liquid production. Very good energy efficiency can be achieved through the clever connection of turbines and boosters (with/without intermediate extraction) and the use of additional throttle currents. In general, however, a large number of airends are necessary, which increases the investment costs. The present invention provides a remedy here. In a high-air pressure process, the tasks mentioned are fulfilled by just one compressor (supply of decomposition air and energy for internal compression and liquid production). Thus, all feed air must be compressed to a high pressure to achieve a good match between cold and warm flows in the main heat exchanger. The high pressure must be provided by the turbine boosters and main air compressors. In some cases, especially in the case of product constellations with little or no liquid production, efficient balancing is difficult to achieve without jeopardizing the buildability of the booster turbines or raising the pressure on the main air compressor very sharply.

High-air pressure methods are known in which a throttle current can be generated with the aid of a cold booster and the pressure on the main air compressor can be lowered. However, the energy efficiency is still not equivalent to that of the main air compressor/boost process. Here, the cold booster follows the warm booster. Since the warm booster usually has to compress a large quantity or the quantity ratios between the turbines and boosters have to be set in such a way that the machines can be built, the stage pressure ratio is generally less than 1.4. With cold boosters, a stage pressure ratio of up to 2 or slightly higher can be achieved. The specific speed for the turbine and booster must be within the buildable range and the speed of the machine must not be too high. A corresponding process with two cold compressors connected in series is also known from US 2013/0255313 A1.

The invention unfolds its advantages in particular in the case of low liquid production (with less than 10% liquid withdrawal from the plant based on internal compression products), and in processes where the use of a cold compressor is reasonable and the injection equivalent is very low, but the nitrogen recovery in proportion to the oxygen product is very high

The solution according to the invention makes use of the fact that the injection equivalent in the sense explained above is not fully utilized in many systems and operating cases. It is known that increasing the injection equivalent can improve energy capture (using a Lachmann turbine in high air pressure and main air compressor/supercharger processes). By increasing the injection equivalent, the amount of air required to provide the required products increased exponentially, but the necessary pressure on the main air compressor reduced and thus the total energy consumption reduced. Furthermore, increasing the injection equivalent reduces the argon yield. For optimization, there is an optimum up to which the injection equivalent should (only) be exhausted.

For plants with high nitrogen production, the optimum injection equivalent is lower, as increasing the injection equivalent decreases the nitrogen recovery.

The idea on which the invention is based is now that of exhausting the injection equivalent in that an additional quantity of compressed nitrogen is removed from the pressure column at its operating pressure. This amount of pressurized nitrogen is fed to the turbine, which drives a cold booster (after it has been previously heated in the main heat exchanger) and expanded to the pressure below the low-pressure column (or to the pressure of pure nitrogen taken from the top of the low-pressure column). The stream of nitrogen expanded in this way is now heated in the main heat exchanger and fed to the pure nitrogen from the top of the low-pressure column, in particular before it is compressed in an external nitrogen compressor.

The cold booster, in turn, is supplied with a partial flow of compressed and then cooled air in a warm booster. A partial flow of the air compressed in the main air compressor is fed to the warm booster. The partial flow compressed in the cold booster is used as high-pressure throttle flow or high-pressure Joule-Thomson flow. Thus, part of the air from the main air compressor is post-compressed twice to provide the high-pressure Joule-Thomson current. In this way, the injection equivalent is set optimally for the system so that the required nitrogen production can be provided.

In an overall view (Total Cost of Ownership, TCO), the present invention leads to an improvement in the efficiency of high-air pressure circuits without loss of cost advantages or great complexity of the method. Above all, a reduction in costs can be achieved:

By increasing the injection equivalent (here by removing compressed nitrogen from the pressure column), the gas load in the Low-pressure column can be reduced, which means that it can optionally be designed with a smaller column diameter.

• Compared to a possibly energetically equivalent cold booster process with a self-boosted turbine, the required cold booster turbine machine is one size class smaller, since significantly less air is driven through the machines.

• A process with a cold booster driven by a Lachmann turbine, which may be equivalent in terms of energy and also has the advantage of increasing the injection equivalent, results in a turbine of the appropriate size that cannot be built, since the required speed is more than 75,000 rpm lies (less air volume on the turbine, larger pressure drop of the relaxed air).

In a conservative calculation of the proposed process compared to the conventional high-air pressure cold booster process, the energy consumption is the same. Depending on the argon and energy evaluation and the necessary air products, the proposed process is very to moderately beneficial. It is very advantageous for systems without argon production.

The process according to the invention for the low-temperature separation of air is carried out using an air separation plant which has a rectification column arrangement with a pressure column and a low-pressure column, the pressure column being operated in a first pressure range and the low-pressure column being operated in a second pressure range which is below the first pressure range, and at least 90% of a total quantity of air separated in the rectification column arrangement is compressed to a pressure in a third pressure range which is more than 5 bar above the first pressure range. A high-air pressure process is therefore carried out, as has been explained in detail before.

A subset of the total amount of air that has been separated is successively fed at a temperature in a first temperature range from -30 to 100 °C to a first booster driven by a first turbine, using the first booster from the pressure in the third pressure range to a pressure in one fourth Pressure range that is above the third pressure range, compressed, cooled to a temperature in a second temperature range of -160 to -60 °C, fed to a second booster driven with a second turbine at the temperature in the second temperature range, using the second booster compressed from the pressure in the fourth pressure range to a pressure in a fifth pressure range, which is above the fourth pressure range, cooled to a temperature in a third temperature range of -200 to -150 °C, in particular at least partially liquefied, and in fed into the pressure column. This is in particular a high-pressure Joule-Thomson current, which can be used in addition to a further Joule-Thomson current provided on the pressure in the third pressure range. All of the cooling steps explained here and below can be carried out using the main heat exchanger—provided that cooling does not already result from expansion.

In the context of the present invention, gaseous nitrogen is removed from the pressure column at a pressure in the first pressure range and successively heated to a temperature in a fourth temperature range of in particular -100 °C to 50 °C, in the second turbine with cooling to a temperature in a fifth temperature range of in particular -150 °C to -40 °C relaxed to a pressure in the second pressure range, and heated to a temperature in a sixth temperature range of 0 °C to 50 °C °C. Furthermore, gaseous nitrogen is also removed from the low-pressure column and heated to the temperature in the sixth temperature range.

According to the invention, and for example in contrast to the prior art such as US Pat. and the fourth temperature range is -100 to 50°C and the fifth temperature range is -140°C to -40°C.

In the context of the present invention, in other words, nitrogen for the nitrogen turbine used (ie the second turbine) is set to the comparatively high Temperature of the fourth temperature range is heated, then relaxed, so that the temperature is set in the fifth temperature range, and then heated in particular in a separate passage in the main heat exchanger and mixed together only downstream of this heating with the low-pressure nitrogen from the low-pressure column. The advantage here is that the high inlet temperature of the turbine leads to lower consumption of nitrogen to provide the necessary power for the cold booster and thus to better energy efficiency than if this expansion were carried out at a lower temperature and previously mixed with the low-pressure nitrogen .

Due to the higher turbine inlet temperature and the reduction in quantity, the necessary turbine becomes smaller and also easier to build due to the improvement in the specific speed. The higher turbine inlet temperature also reduces the amount of compressed nitrogen required, resulting in a lower injection equivalent and therefore a lower air factor than a Lachmann turbine or a compressed nitrogen turbine with a lower inlet temperature. This leads to a reduction in the required amount of air and higher air pressure, which leads to energy and cost savings in pre-cooling and the molecular sieve adsorber or regeneration capacity.

The main heat exchanger volume is reduced by the proposed process since the passage for low pressure nitrogen is from about 200K to 300K and not from 96 to 300K. In contrast to a process with a Lachmann or cold compressed nitrogen turbine, the main heat exchanger can be made significantly smaller with the same performance, since less air has to be used for the process. An additional Joule-Thomson current on the main air compressor pressure, as provided according to an embodiment of the invention, leads to an improvement in the matching of the heat exchanger temperature profile and thus to better energy efficiency. A smaller amount of air has to be compressed in the warm booster so that it can be operated with a higher pressure difference. The additional throttle flows have a very large energetic advantage, especially in processes with two or more different internal compression pressures of, for example, 30 bar (abs.) for gaseous oxygen and 15 bar (abs.) for gaseous oxygen or nitrogen. In the context of the present invention, the first pressure range is in particular 4 to 7 bar, the second pressure range is in particular 1 to 2 bar, the third pressure range is in particular 10 to 18 bar, the fourth pressure range is in particular in a pressure range from 1.2 times to 1.5 times the third pressure range and the fifth pressure range in particular in a pressure range of 1.6 times to 2.5 times the fourth pressure range.

Advantageously, a further subset of the total separated air quantity is successively fed to the first booster at the temperature in the first temperature range, compressed using the first booster from the pressure in the third pressure range to the pressure in the fourth pressure range, to the temperature in the second temperature range or a further temperature range, expanded in the first turbine to a pressure in the first pressure range and fed into the pressure column. In other words, a turbine flow is advantageously formed, which is first subjected to a common compression with the high-pressure throttle flow in the warm booster. The subsequent cooling can take place to the same or a different temperature level than the cooling of the high-pressure throttle flow.

As mentioned, in a particularly preferred embodiment, a method according to the present invention can also include cooling a further subset of the total amount of air separated at the pressure in the third pressure range to the temperature in the third temperature range and (as a further throttle flow) into the pressure column is fed. Benefits have already been explained.

The gaseous nitrogen taken from the low-pressure column and the gaseous nitrogen taken from the pressure column can be combined with one another after separate heating to the temperature in the sixth temperature range. The advantages of this combination downstream of the heating have also already been explained above.

In the process, one or more liquids are or are advantageously removed from the rectification column arrangement, subjected to one or more internal compression, and discharged from the air separation plant in the form of one or more gaseous internal compression products. Advantageously, the one or more gaseous internal compression products is or comprise a gaseous internal compression product produced using oxygen-rich liquid from the low pressure column.

Advantageously, no liquid products are removed from the air separation plant or one or more liquid products are removed from the air separation plant in a total amount that does not exceed 10% of a total amount of the one or more gaseous internal compression products. As mentioned, the present invention is particularly useful in such cases of low liquid production.

In one embodiment of the present invention, an argon-rich liquid can be removed from the low pressure column and fed to an argon recovery system for the recovery of argon. However, an embodiment without argon extraction can also be provided in an embodiment of the invention.

The air separation plant according to the invention for the low-temperature separation of air has a rectification column arrangement with a pressure column and a low-pressure column, the air separation plant being set up to operate the pressure column in a first pressure range and the low-pressure column in a second pressure range, which is below the first pressure range, and at least to compress 90% of a total amount of air separated in the rectification column arrangement to a pressure in a third pressure range which is more than 5 bar above the first pressure range.

The air separation plant is also set up to supply a partial quantity of the total quantity of separated air successively at a temperature in a first temperature range of -30 to 100 °C to a first booster driven by a first turbine, using the first booster from the pressure in the third pressure range to compress to a pressure in a fourth pressure range, which is above the third pressure range, to cool to a temperature in a second temperature range of -160 to -60 °C, to the temperature in the second temperature range with a second booster driven by a second turbine to deliver, using the second booster of the pressure in the to compress the fourth pressure range to a pressure in a fifth pressure range which is above the fourth pressure range, to cool it to a temperature in a third temperature range of -200 to -150° C., and to feed it into the pressure column.

Furthermore, the air separation plant according to the invention is set up to remove gaseous nitrogen from the pressure column at a pressure in the first pressure range and successively heat it to a temperature in a fourth temperature range, in the second turbine with cooling to a temperature in a fifth temperature range to a pressure in to expand the second pressure range and to heat to a temperature in a sixth temperature range of 0 to 50°C, and to withdraw gaseous nitrogen from the low-pressure column and to heat to the temperature in the sixth temperature range.

According to the invention, the air separation plant is set up to heat the gaseous nitrogen removed from the low-pressure column separately from the gaseous nitrogen removed from the pressure column to the temperature in the sixth temperature range, with the fourth temperature range being from -100 to 50 °C and the fifth temperature range from -150 to -40 °C.

The air separation plant proposed according to the invention is set up in particular to carry out a method as has been explained above in the configurations. Reference is therefore expressly made to the above explanations regarding the methods according to the invention and their advantageous configurations.

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

character description

FIG. 1 illustrates an air separation plant according to an advantageous embodiment of the present invention. Elements that correspond structurally or functionally to one another are indicated in the figure with identical reference symbols and are not explained again for the sake of clarity. Explanations relating to plants and plant components apply in the same way to corresponding processes and process steps.

In FIG. 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 denoted overall by 100 .

In the air separation plant 100, air is sucked in by means of a main air compressor 2 via a filter 1 and is compressed to a suitable pressure level. After pre-cooling in a pre-cooling device 3, the compressed air stream A formed in this way is freed from residual water and carbon dioxide in a pre-cleaning unit 4, which can be configured in a manner known per se. For the design of the components mentioned, reference is made to the specialist literature cited at the outset.

In the example illustrated here, the compressed air flow, which is also designated A, is now divided into two partial flows B and C, of which partial flow B is fed as a Joule-Thomson flow from the warm to the cold end through a main heat exchanger 4 and fed into the pressure column 11 of a rectification column arrangement 10 becomes. The partial flow C is first boosted in a warm booster 6 (previously described as the "first" booster), to which it is fed at a temperature in a corresponding temperature range (previously "first" temperature range), and then cooled in the main heat exchanger 4 . In the embodiment according to FIG. 1, partial streams D and E are formed after removal from the main heat exchanger 4 at a temperature in a corresponding temperature range (previously “second” temperature range). However, extraction from the main heat exchanger 4 can also take place at different temperatures.

The partial stream D is now pressure-increased further in a cold booster (previously "second" booster), then cooled in the main heat exchanger 4 to a temperature in a cold-side temperature range (previously "third" temperature range) and fed into the pressure column as a high-pressure Joule-Thomson stream 11 fed. The partial flow E is expanded in the turbine coupled to the first booster 6 (previously “first” turbine) and is also fed into the pressure column 11 . Also a Substream F of substream C is fed into the pressure column 11 (as a further Joule-Thomson stream).

Nitrogen is withdrawn from the pressure column 11 in the form of a substance stream G, heated in the main heat exchanger 4 to a temperature in a suitable or advantageous temperature range (previously "fourth" temperature range), in the turbine coupled to the second booster 8 (previously "second" Turbine) with cooling to a temperature in a corresponding temperature range (previously "fifth" temperature range) and then heated again in the main heat exchanger 4 to a temperature in a temperature range on the warm side of the main heat exchanger 4 (previously "sixth" temperature range).

Gaseous nitrogen in the form of a stream H is removed from the low-pressure column 12 and heated to the temperature in the sixth temperature range. After heating, it is combined with material flow H to form a corresponding collective flow I.

The pressure column 11 is connected in the rectification column arrangement 10 to the low-pressure column 12 via a main condenser 13 in a heat-exchanging manner. The rectification column system 10 is associated with a supercooling counterflow 14 . Denoted at 15 is an internal compression pump. The air separation plant 100 can have an argon recovery unit (not shown here) designed in a known manner.

As explained, the pressure column 11 is fed here with cooled, pressurized and optionally liquefied air from streams B, D, E and F. Liquid in the form of a stream K is withdrawn from the pressure column 11 immediately downstream of the feed point of the stream F, passed through the supercooling countercurrent 14 and fed into the low-pressure column 12 . The low-pressure column 12 is also fed with liquid that is enriched in oxygen compared to the feed in the form of a bottoms liquid stream L from the pressure column 11, which has also previously been passed through the subcooling countercurrent flow device 14. Additional top gas from the pressure column 11 is passed through the main condenser 13 . The main condenser 13 is operated in a known manner, with a stream M in particular also being transferred to the low-pressure column 12 . Impure nitrogen can from the low-pressure column 12 in the form of a stream h, pure low-pressure nitrogen can be drawn off in the form of a stream g.

Oxygen-rich bottom liquid is withdrawn from the low-pressure column 12 in the form of a stream N and pressurized in the internal compression pump 15 as a liquid. After evaporation in the main heat exchanger, a partial flow O can be provided as a gaseous internal compression product. Another partial flow P can be supercooled in the supercooling counterflow 14 and discharged from the air separation plant 100 in liquid form.

Liquid can also be collected at the top of the low-pressure column 12 and discharged in the form of a stream Q as a liquid nitrogen product. An impure nitrogen stream R can be withdrawn from the low pressure column 12 and used in a known manner.

Claims

Claims Method for low-temperature separation of air using an air separation plant (100) having a rectification column arrangement (10) with a pressure column (11) and a low-pressure column (12), wherein

- the pressure column (11) is operated in a first pressure range and the low-pressure column (12) is operated in a second pressure range, which is below the first pressure range, and at least 90% of a total amount of air separated in the rectification column arrangement (10) to a pressure in one third pressure range, which is more than 4 bar above the first pressure range, is compressed,

- a subset of the total amount of air separated is fed successively at a temperature in a first temperature range from -30 to 100 °C to a first booster (6) driven by a first turbine (7), using the first booster (6) from the pressure in compressed in the third pressure range to a pressure in a fourth pressure range, which is above the third pressure range, cooled to a temperature in a second temperature range of -160 to -60 °C, to the temperature in the second temperature range with a second turbine ( 9) driven second booster (8), compressed using the second booster (6) from the pressure in the fourth pressure range to a pressure in a fifth pressure range, which is above the fourth pressure range, to a temperature in a third temperature range from -200 to -150 °C is cooled and fed into the pressure column (11),

- Gaseous nitrogen is removed from the pressure column (11) at a pressure in the first pressure range and successively heated to a temperature in a fourth temperature range, expanded in the second turbine to a pressure in the second pressure range while cooling to a temperature in a fifth temperature range, and is heated to a temperature in a sixth temperature range of 0 to 50°C, and - Gaseous nitrogen is removed from the low-pressure column (12) and heated to the temperature in the sixth temperature range, characterized in that

- the gaseous nitrogen taken from the low-pressure column (12) is heated separately from the gaseous nitrogen taken from the pressure column (11) to the temperature in the sixth temperature range, and

- the fourth temperature range is -100 to 50 °C and the fifth temperature range is -150 to -40 °C. Method according to Claim 1, in which the first pressure range is 4 to 7 bar, the second pressure range is 1 to 2 bar, the third pressure range is 10 to 18 bar, the fourth pressure range is in a pressure range from 1.2 times to 1.5 times the third pressure range and the fifth pressure range is in a pressure range from 1.6 times to 2.5 times the fourth pressure range. Method according to Claim 1 or according to Claim 2, in which a further subset of the total separated air quantity is successively supplied to the first booster (6) at the temperature in the first temperature range, using the first booster (6) from the pressure in the third pressure range up the pressure in the fourth pressure range is compressed, cooled to the temperature in the second temperature range or a further temperature range, expanded in the first turbine (7) to a pressure in the first pressure range and fed into the pressure column (11). Method according to one of the preceding claims, in which a further partial quantity of the total quantity of air separated at the pressure in the third pressure range is cooled to the temperature in the third temperature range and fed into the pressure column (11). The method according to any one of the preceding claims, wherein the low-pressure column (12) withdrawn gaseous nitrogen and the pressure column (11) withdrawn gaseous nitrogen at the temperature in the after being separately heated to the temperature in the sixth temperature range.

6. The method as claimed in one of the preceding claims, in which one or more liquids are removed from the rectification column arrangement (10), subjected to one or more internal compression, and discharged from the air separation plant (100) in the form of one or more gaseous internal compression products.

7. The method of claim 6, wherein the one or more gaseous internal compression products is or comprises a gaseous internal compression product produced using oxygen-rich liquid from the low pressure column.

8. The method according to claim 6 or according to claim 7, in which no liquid products are taken from the air separation plant (100) or in which one or more liquid products are taken from the air separation plant (100) in a total amount that accounts for 10% of a total amount of the one or more gaseous internal compression products.

9. The method according to any one of the preceding claims, wherein an argon-rich liquid is removed from the low pressure column and fed to an argon recovery system for the recovery of argon.

10. The method according to any one of the preceding claims, in which the pressure column (11) removed gaseous nitrogen, heated to a temperature in the sixth temperature range and obtained at a pressure in the first pressure range as a nitrogen-rich air product.

11 . Air separation plant (100) for the low-temperature separation of air, which has a rectification column arrangement (10) with a pressure column (11) and a low-pressure column (12), the air separation plant (100) being set up, 22

- to operate the pressure column (11) in a first pressure range and the low-pressure column (12) in a second pressure range, which is below the first pressure range, and at least 90% of a total amount of air separated in the rectification column arrangement (10) to a pressure in one to compress the third pressure range, which is more than 5 bar above the first pressure range,

- to supply a subset of the total amount of air separated successively at a temperature in a first temperature range from -30 to 100 °C to a first booster (6) driven by a first turbine (7), using the first booster (6) from the pressure in to compress the third pressure range to a pressure in a fourth pressure range that is above the third pressure range, to cool to a temperature in a second temperature range of -160 to -60 °C, to the temperature in the second temperature range with a second turbine (9) to supply driven second booster (8), to compress using the second booster (6) from the pressure in the fourth pressure range to a pressure in a fifth pressure range, which is above the fourth pressure range, to a temperature in a third cooled in the temperature range from -200 to -150 °C and fed into the pressure column (11),

- to remove gaseous nitrogen from the pressure column (11) at a pressure in the first pressure range and to successively heat it to a temperature in a fourth temperature range, in the second turbine with cooling to a temperature in a fifth temperature range towards a pressure in the second pressure range relaxing and heating to a temperature in a sixth temperature range of 0 to 50°C, and

- removing gaseous nitrogen from the low-pressure column (12) and heating it to the temperature in the sixth temperature range, characterized in that the air separation plant (100) is set up, - to heat the gaseous nitrogen taken from the low-pressure column (12) separately from the gaseous nitrogen taken from the pressure column (11) to the temperature in the sixth temperature range, wherein - the fourth temperature range at -100 to 50 °C and the fifth

temperature range is -150 to -40 °C.