WO2022179748A1

WO2022179748A1 - Process and plant for providing compressed nitrogen

Info

Publication number: WO2022179748A1
Application number: PCT/EP2022/025032
Authority: WO
Inventors: Tobias Lautenschlager
Original assignee: Linde Gmbh
Priority date: 2021-02-25
Filing date: 2022-02-02
Publication date: 2022-09-01

Abstract

The present invention relates to a process for producing a compressed-nitrogen product by the cryogenic separation of air, in which process an air separation plant (100-500) having a main heat exchanger (3) and having a rectifying column (5) with a top condenser (5.1) is used, wherein: in the rectifying column (5), a top gas and a bottom liquid are formed by the use of compressed air which is at a pressure in a first pressure range, the compressed air being fed into the rectifying column (5) and being cooled in the main heat exchanger (3); in the top condenser (5.1), a first part of the top gas is condensed at a pressure in the first pressure range such that a first condensate is obtained, and at least part of the bottom liquid is evaporated at a pressure in a second pressure range below the first pressure range; and nitrogen-rich liquid is withdrawn at a pressure in the first pressure range, in a product amount, from an upper region of the rectifying column (5), is subjected to internal compression and is used to provide the compressed-nitrogen product. According to the present invention, the nitrogen-rich liquid is subjected, in the liquid state, to a pressure increase to a pressure in a third pressure range of 50 to 110 bar absolute pressure during the internal compression and is put into the supercritical state in the main heat exchanger (3), and a second part of the top gas, in a feedback amount, is heated in the main heat exchanger (3), is subjected, on the hot side of the main heat exchanger (3), to compression to a pressure in a fourth pressure range, is condensed in the main heat exchanger (3) such that a second condensate is obtained, and is at least partly fed back into the rectifying column (5). The pressure in the third pressure range is higher than the pressure in the fourth pressure range at least by a factor of 1.5, and an amount ratio between the feedback amount and the product amount is 2:1 to 1.3:1. The present invention also relates to a corresponding air separation plant (100-500).

Description

description

Methods and systems for providing pressurized nitrogen

The invention relates to a method and a system for providing a compressed nitrogen product according to the preambles of the independent patent claims.

Technical 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".

GB 870349 A discloses a process for separating a gas mixture, for example air, in a rectification column to provide at least one component. The mixture is cooled by passing it through a first passage in heat exchange relationship with a cold refrigerant flowing through a second passage and causing contaminants with a higher freezing point to be deposited in the first passage. Thereafter, the flows of the mixture and cold coolant are discontinued and a cold fluid (e.g., waste fluid) is passed through the first passage in heat exchange relationship with a warm coolant capable of heating the cold fluid to remove the deposited contaminants sublimate and transport away, then stopping the flow of warm coolant, then stopping the flow of cold fluid in the first passage, and restoring the flow of the mixture and cold coolant in the first and second passages, respectively.

From US 5303 556 A a cryogenic rectification process for the production of nitrogen gas under elevated pressure is known, which comprises compressing a feedstock containing nitrogen and oxygen, cooling the compressed feedstock and introducing the resulting cooled feedstock into a column, separating the feedstock within the column by cryogenic rectification into nitrogen-rich vapor and oxygen-enriched liquid, the vaporization of the oxygen-enriched liquid by indirect heat exchange with nitrogen-rich vapor to produce nitrogen-rich liquid and oxygen-enriched vapor, pressurizing the nitrogen-rich liquid to produce an elevated pressure nitrogen-rich liquid, evaporating the nitrogen-rich elevated liquid by indirect heat exchange with compressed fluid to produce elevated pressure nitrogen gas and recovering elevated pressure nitrogen gas as product.

Air separation plants of the classic type have rectification column systems which can be designed, for example, as two-column systems, in particular as double-column systems, but also as three-column or multi-column systems. In addition to rectification columns for obtaining nitrogen and/or oxygen in the liquid and/or gaseous state, ie rectification columns for nitrogen-oxygen separation, rectification columns for obtaining further air components, in particular inert gases, can be provided.

The rectification columns of the rectification column systems mentioned are operated at pressures in different pressure ranges. 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 (upper column). The high-pressure column is typically operated at a pressure in a pressure range of 4 to 7 bar, in particular approx. 5.3 bar, while the low-pressure column is operated at a pressure in a pressure range of typically 1 to 2 bar, in particular approx. 1.4 bar. In certain cases, higher pressures can also be used in both rectification columns. The pressures or pressure ranges specified here and below are absolute pressures at the top of the columns specified in each case.

Depending on the required product spectrum (ie the absolute and relative quantities of liquid and gaseous air products to be produced), different plant configurations of air separation plants are of different suitability. Thus, instead of the two- and multi-column processes mentioned, single-column processes can also be used to generate nitrogen. In these, only one rectification column is used, which can be operated at a pressure comparable to that of a known high-pressure column, but can also be operated at a higher pressure. A rectification column used in accordance with a conventional low-pressure column for nitrogen-oxygen separation and operated under lower pressure, however, is missing. However, this does not preclude the rectification column system from being able to have further rectification columns in addition to the rectification column mentioned, for example for obtaining high-purity oxygen.

Corresponding single-column processes can be carried out in particular as so-called single-column single-condenser processes (SCSC) using so-called residual gas turbines. In this case, the rectification column is operated with a top condenser, in which bottom liquid from the rectification column is evaporated and top gas from the rectification column is condensed to form a reflux. A sump reboiler, on the other hand, is typically absent. In the residual gas turbine, at least part of the bottom liquid evaporated in the top condenser, the residual gas, is expanded to obtain cold.

For example, EP 3 521 739 A1 discloses a process for obtaining nitrogen in which the low-pressure column of a double column system, or more generally a second rectification column for nitrogen-oxygen separation, has a first rectification column for nitrogen-oxygen separation and the second rectification column Column system, is operated with a top condenser (also referred to as "double condenser, double reboiler" or "double column, double condenser" or DCDC process).

Particularly in liquefied natural gas terminals, in which liquefied natural gas (LNG) is vaporized and fed into supply lines in gaseous form, gaseous nitrogen under comparatively high pressure (typically 50 to 130 bar) is required to adjust caloric parameters (Wobbe index, etc.). The same applies to certain applications for tertiary oil recovery (enhanced oil recovery, EOR), or the provision of nitrogen for ammonia synthesis, where higher pressures tend to be required.

Classically, for such applications, the gaseous nitrogen is obtained from a system designed as explained above at 5 to 10 bar (abs.) and then further compressed in a complex manner. With quantities below 20 kNm ³ /h (the unit Nm ³ denotes standard cubic meters here), the nitrogen is compressed to pressures of over 80 bar (abs.) typically in piston compressors, which have considerable disadvantages due to their design (high investment costs, low efficiency, no partial load behavior, high maintenance costs).

The present invention therefore sets itself the task of improving the provision of compressed nitrogen, in particular in the pressure range mentioned and in particular for the applications mentioned, and making it more efficient.

Disclosure of Invention

Against this background, a method and a system for providing a compressed nitrogen product with the features of the independent patent claims are proposed. Refinements of the invention are the subject matter of the dependent claims and the following description.

Some of the terms used in the description of the present invention and its advantages, as well as the underlying technical background, are explained in more detail below.

The devices used in an air separation plant are described in the technical literature cited, for example in Häring in Section 2.2.5.6, "Apparatus". Unless the following definitions deviate from this, reference is therefore expressly made to the technical literature cited for the language used in the context of the present application.

A "condenser evaporator" refers to a heat exchanger in which a first, condensing fluid stream enters into indirect heat exchange with a second, evaporating fluid stream. Each condenser evaporator has a condensing space and an evaporating space. Condensation and evaporation chambers have liquefaction and evaporation passages. The condensation (liquefaction) of the first fluid stream is carried out in the liquefaction chamber, and the evaporation of the second fluid stream is carried out in the evaporation chamber. The evaporating and condensing spaces are formed by groups of passages which are in heat exchange relationship with each other. Condenser evaporators are also called "top condenser" and referred to as "bottom reboiler", where a top condenser is a condenser evaporator in which top gas of a rectification column is condensed and a bottom evaporator is a condenser evaporator in which bottom liquid of a rectification column is evaporated.

In a "forced-flow" condenser evaporator, a liquid flow is pushed through the evaporation chamber by its own pressure and partially evaporated there. This pressure is generated, for example, by a liquid column in the feed line to the evaporation space. The fleas of this liquid column corresponds to the pressure loss in the evaporation space. In a once-through condenser evaporator of this type, the gas-liquid mixture emerging from the evaporation chamber is separated according to phases and forwarded directly to the next process step or to a downstream device and, in particular, is not introduced into a liquid bath of the condenser evaporator, from which the portion that remains liquid is fed again would be sucked in.

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 set up to expand a gaseous or at least partially liquid stream. In particular, expansion turbines for use in the present invention can be designed as turboexpanders. If a compressor is driven with one or more expansion turbines, but without energy supplied externally, 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 in the following it is mentioned that an expansion takes place in a booster turbine or a turbine booster, this should 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.

In air separation plants, multi-stage turbo compressors are used to compress the feed air to be separated, 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. The compression of the to takes place in a turbo compressor compressing medium by means of turbine blades, which are arranged on a turbine wheel or impeller 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 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 also distinguished by the fact that it compresses the entire amount of air fed into the rectification column system and used for the production of air products, ie the entire feed air. Correspondingly, a "post-compressor" can also be provided, in which, however, only part of the air quantity compressed in the main air compressor is brought to an even higher pressure. This can also be designed as a turbo compressor. The use of a common compressor or compressor stages of such a compressor as the main air compressor and booster can also be provided. In order to compress partial quantities of air, additional turbo compressors in the form of the boosters mentioned are typically provided in air separation plants, but these usually only perform compression to a relatively small extent compared to the main air compressor or the secondary compressor.

Liquids and gases, as used herein, can be rich or poor in one or more components, where "rich" means a content of at least 50%, 75%, 90%, 95%, 99%, 99.5%, 99, 9% or 99.99% and "poor" can stand for 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 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 gas was obtained. The liquid or the gas is "enriched" if this or this at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1,000 times the content, and "depleted" if this or this has at most 0.9 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of a corresponding one Component based on the starting liquid or the starting gas contains. If, for example, “oxygen” or “nitrogen” is mentioned 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 them.

As mentioned, air separation plants can be designed differently depending on the air products to be delivered and their required aggregate and pressure states. So-called internal compression is known for providing gaseous pressure products. In this case, a cryogenic liquid is removed from the rectification column system, subjected to an increase in pressure in the liquid state and converted to the gaseous or supercritical state by heating. For example, internally compressed gaseous oxygen, internally compressed gaseous nitrogen or internally compressed gaseous argon can be produced in this way. Internal compression offers a number of advantages over external compression, which is also possible as an alternative, and is explained, for example, in Häring (see above), Section 2.2.5.2, "Internal Compression".

Features and advantages of the invention

The present invention proposes a method and a system for providing pressurized nitrogen in the above-mentioned single-column single-condenser configuration, in which up to 100% of the total pressurized nitrogen to be provided is internally compressed to pressures of 60 bar (abs.) up to 150 bar (abs.) can be compressed. Optionally, however, a double-column double-condenser configuration can also be used, as was also explained above.

In order to be able to remove the large amounts of liquid nitrogen required for this from the rectification column used, gaseous nitrogen from the rectification column used is further compressed and liquefied in the main heat exchanger, with available combination machines being able to be used in a particularly advantageous manner.

Overall, the invention proposes a process for producing a compressed nitrogen product by cryogenic separation of air, in which an air separation plant with a main heat exchanger and a rectification column used with a head condenser. The top condenser can be designed as a bath, cascade or forced flow condenser, as explained.

In particular when using a single column (i.e. the rectification column is the only rectification column), the process is investment-optimized, the pressure energy contained in the top gas of the condenser is used within the scope of the present invention, in particular in a residual gas turbine.

In the rectification column, a top gas and a bottom liquid are formed at a pressure in a first pressure range, as is known in principle, using compressed air fed into the rectification column and cooled in the top heat exchanger.

In the top condenser, a first part of the top gas is condensed to obtain a first condensate at a pressure in the first pressure range and at least part of the bottom liquid is evaporated at a pressure in a second pressure range below the first pressure range, as also in particular for the mentioned single-column - Single condenser and double column double condenser configurations are known.

From an upper section of the rectification column, nitrogen-rich liquid is withdrawn in a product quantity at a pressure in the first pressure section, subjected to internal compression and used to provide the compressed nitrogen product. During internal compression in the liquid state, the nitrogen-rich liquid is subjected to a pressure increase to a pressure in a third pressure range of 50 to 110 bar absolute pressure and is converted to the supercritical state in the Flaupt heat exchanger, so that the pressure requirements mentioned at the outset are met by the use of the present invention can become.

According to the invention, a second part of the top gas is heated in a recirculation amount in the main heat exchanger, subjected to compression on the warm side of the main heat exchanger to a pressure in a fourth pressure range, condensed in the main heat exchanger to obtain a second condensate, and fed back into the rectification column. According to the invention, the pressure in the third pressure range is at least a factor of 1.5, in particular at least a factor of 1.6 and up to a factor of 2 higher than the pressure in the fourth pressure range, and a ratio between the feed-back quantity and the product quantity is 2:1 up to 1.3:1.

The internal compression of nitrogen (in the product quantity) against nitrogen (in the recirculation quantity) proposed according to the invention makes little sense without knowledge of the present invention, since gaseous nitrogen can in principle be conveniently compressed in an external compressor. There is a clear difference here compared to oxygen, where an expensive oxygen compressor is replaced by a cheap booster (BAC) for internal compression. The measures according to the invention are therefore not obvious. However, if the internal compression pressures of the gaseous nitrogen increase (in particular to more than 70 bar) and the quantity is also rather small (e.g. less than 20,000 standard cubic meters per hour), external compression becomes increasingly complex and expensive, since piston compressors have to be used The invention relates in particular to such cases As has been recognized according to the invention, precisely in this configuration the internal compression of nitrogen versus nitrogen can offer advantages which do not result from other methods and are also not to be expected here.

A "procedural transmission" is created by the present invention, so to speak. The compressor used for the second portion of the top gas, or corresponding compressor stages, compresses a large quantity of compressed nitrogen to a comparatively low pressure and thus drives the internal compression of a small quantity of liquid nitrogen under high pressure. The analogy in a gearbox is high speed with low torque converted to low speed with high torque. The combination of large volume and low pressure enables the corresponding compressor or compressor stages to be designed as turbo compressors (stages), which brings advantages in the areas of investment costs, efficiency, part-load behavior and maintenance. The piston compressors mentioned at the outset can be dispensed with.

The first pressure range, in which the operating pressure of the rectification column lies, can be in particular from 7 to 15 bar (absolute), for example about 10.5 bar (absolute). the for feeding the rectification column can be at a pressure in a pressure range above this, which depends on the specific configuration. The second pressure range, in which the evaporation pressure in the top condenser lies, can be in particular from 3 to 7 bar (abs.), in particular about 5.6 bar (abs.). The fourth pressure range, in which the pressure lies to which the second part of the top gas is compressed, is in particular 30 to 70 bar (abs.), for example approx. 36 bar (abs.).

A quantity ratio between the second part of the top gas, which is treated accordingly, i.e. the recirculation quantity, and the nitrogen-rich liquid subjected to internal compression, i.e. the product quantity, can in particular be in a range from 2:1 to 1.5:1 or from 1.5:1 to 1.3:1, in each case based on normalized mass flows.

If required, compressed nitrogen can also be taken off at a pressure range below the third pressure range, in the form of overhead gas, before or after compression to the pressure in the third pressure range, i.e. to the pressure in the first or the third pressure range.

At least part of the first condensate can be fed back to the rectification column and/or used to provide a liquid nitrogen product, if required, within the scope of the present invention.

During the evaporation of at least part of the bottoms liquid in the top condenser, a gas phase can be formed which is used at least in part to form a residual gas stream, the residual gas stream being subjected to a first heating in the main heat exchanger at the pressure in the second pressure range, and then being expanded to a pressure in a fifth pressure range in a booster turbine arrangement, and thereafter at the pressure in the fifth pressure range may be subjected to a second heating in the main heat exchanger.

In this case, in particular, a residual gas turbine can be used to cover the cold balance, with the residual gas turbine being braked by a booster, oil or generator can be executed. The residual gas turbine can be self-boosted or braked by a booster which further compresses the previously compressed second part of the overhead gas before it is liquefied in the main heat exchanger.

In other words, in the embodiment with a self-boosted residual gas turbine, after the first heating, the residual gas stream can be subjected to compression to a pressure in a sixth pressure range in the booster turbine arrangement, then to the pressure in the sixth pressure range, to intermediate cooling in the main heat exchanger, and thereafter being subjected to the expansion to the pressure in the fifth pressure range in the booster turbine arrangement, and thereafter being subjected to the second heating.

As an alternative to the configuration just explained, however, the second part of the head gas in particular can also be subjected to a pressure in a seventh pressure range after compression on the warm side of the main heat exchanger to the pressure in the fourth pressure range and before condensation in the main heat exchanger to further compression in the booster turbine arrangement . The seventh pressure range can in particular be 40 to 70 bar (abs.), for example about 48 bar (abs.).

In the embodiment just explained, the second part of the top gas can, after further compression in the booster turbine arrangement to the pressure in the seventh pressure range and before condensation in the main heat exchanger, also undergo (again) further compression in a further

Booster turbine assembly is subjected to a pressure in an eighth pressure range. Due to the double further compression of the second part of the top gas, the first compressor used can be designed with fewer stages, which improves the buildability, especially in combination with the main air compressor.

In this embodiment, the further booster turbine arrangement (or its booster) can be used as a warm or cold booster. The second part of the top gas can therefore in particular after further compression in the booster turbine arrangement to the pressure in the seventh pressure range and before further compression in the further booster turbine arrangement to the pressure in the eighth printing range may be subjected to cooling to a temperature in a temperature range from 0 to -170 °C.

When the compressed air is compressed to higher values than those in the first pressure range, for example to a pressure in a pressure range of 15 to 25 bar (abs.), in particular 16 to 24 bar (abs.), the compressed air can be brought to the main heat exchanger at a temperature in a first

Removed intermediate temperature range, expanded in the further booster turbine arrangement to a pressure in a tenth pressure range, fed back to the main heat exchanger at a temperature in a second intermediate temperature range, and further cooled in the main heat exchanger. A corresponding configuration can alternatively also include the use of an oil or generator-braked turbine instead of the further booster turbine arrangement for expanding the compressed air.

Depending on requirements, another turbine can also be used. The main heat exchanger can also be provided in several parts (e.g. set up for higher and lower pressures), for example to meet requirements for design pressures, thermal stresses and the like.

The compressed air fed into the rectification column and cooled in the main heat exchanger can also represent only part of a compressed total amount of air, with a further part of the compressed total amount of air being cooled in the main heat exchanger, an expansion to a pressure in a ninth, in particular slightly above atmospheric pressure range of, for example, 1, 1 to 1.5 bar (abs.), Subject to heating in the main heat exchanger to the pressure in the ninth pressure range and discharged from the air separation plant.

This corresponds to the known use of an excess air flow or a corresponding turbine (Excess Air Turbine).

As mentioned several times, one or more first compressor stages can be used to provide the compressed air, and one or more (in particular two or three) second compressor stages can be used to compress the second part of the overhead gas on the hot side of the main heat exchanger, with the one or more first and the one or more second Compressor stages are provided in a common compressor. The second portion of the overhead gas can be driven to the compressor stage(s) 5 to 35° C. colder than the other streams, if there is excess cold.

With regard to the features of the system also proposed according to the invention, reference is expressly made to the corresponding independent patent claim. This system 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 method according to the invention and its 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.

Brief description of the drawings

FIGS. 1 to 5 show systems according to preferred embodiments of the invention in a simplified, schematic representation.

In the figures, structurally and/or functionally corresponding components and identical or comparable material flows are indicated with identical reference numbers and are not explained again for the sake of clarity. Explanations regarding process steps also relate to corresponding devices or components of plants and vice versa.

In FIG. 1, an air separation plant according to one embodiment of the invention is illustrated and denoted overall by 100.

In the air separation plant 100, feed air is sucked in by means of a main air compressor 1 or one or more corresponding compressor stages and compressed to a pressure in a pressure range of 7 to 15 bar (abs.), for example approx. 11 bar (abs.). A compressed air flow formed in this way is in a warm part 2 of the air separation plant 100, which can have components known per se and in particular with a pre-cleaning unit 2.1 (Prepurification Unit, PPU) can be equipped in a known way, conditioned to obtain a compressed air stream b. After the compressed air stream b has been divided into two partial streams c and d, these are fed to a main heat exchanger 3 of the air separation plant 100 on the hot side.

The partial flow c is taken from the main heat exchanger 3 of the air separation plant 100 at an intermediate temperature and expanded in a turbine arrangement 4 with an expansion turbine, for example oil-braked. The partial flow c is then heated in the main heat exchanger 3 and discharged, for example, into the atmosphere (so-called excess air). Partial stream d is taken from the cold side of main heat exchanger 3 of air separation plant 100 and fed into a rectification column 5, in which a top gas and a bottom liquid are formed using the air fed in. The rectification column 5 is operated, in particular at the top, at a pressure in a pressure range which, apart from pressure losses, corresponds to that of the compressed air stream a, for example at approx. 10.5 bar (abs.).

The top gas is withdrawn from the rectification column 5 in the form of a stream e. A substream f of stream e is condensed in a top condenser 5.1 of the rectification column 5 and, again in portions, used in the form of a stream g to form a reflux stream h to the rectification column 5 and in the form of a stream i optionally in an optionally provided subcooler 6 supercooled and provided as a liquid nitrogen product. Another part of the top gas of stream e is heated in the main heat exchanger 3 in the form of stream k.

A part of the heated material flow k is recompressed in the form of a material flow I in a compressor 7 or one or more compressor stages, which can also be installed in a common machine with the compressor stage(s) of the main air compressor 1 . The recompression can take place, for example, to a pressure in a pressure range from 40 to 70 bar (abs.), for example approx. 44 bar (abs.). After recompression, the stream I is cooled again in the main heat exchanger 3 and condensed in the process, expanded at a throttle valve 8 and used to form the return stream h already mentioned. In the top condenser 5.1 of the rectification column 5, bottom liquid from the rectification column 5, which is removed from this in the form of a stream m, is supercooled in a subcooler 9 and expanded at a throttle valve 10, evaporated. A purge stream n is removed from the top condenser 5.1 of the rectification column 5 to avoid the accumulation of less volatile components. Residual gas, which is formed by the evaporation of the bottom liquid of the rectification column 5, is carried out in gaseous form in the form of a stream o from the top condenser 5.1 and passed through the subcoolers 6 (if present) and 9. The removal takes place at a pressure in a pressure range at which the bottom liquid of the rectification column 5 is also evaporated in the top condenser 5.1, in particular at 3 to 6 bar (abs.), for example at approx. 5.6 bar (abs.).

After further heating in the main heat exchanger 3, the material flow o is then brought to a higher pressure in a booster turbine arrangement 11, fed back to the main heat exchanger 3 on the hot side, removed from it at an intermediate temperature, expanded in the booster turbine arrangement 11, completely heated in the main heat exchanger 3, and discharged from the air separation plant 100 or used in the pre-cleaning unit 2.1 in a known manner as regeneration gas.

Liquid nitrogen is removed from the rectification column 5 in the form of a liquid nitrogen stream p, pressurized in liquid form in an internal compression pump 12, heated in the main heat exchanger 3 and discharged as compressed nitrogen product from the air separation plant (100).

In FIG. 2, an air separation plant according to a further embodiment of the invention is illustrated and denoted overall by 200.

In contrast to the air separation plant 100 according to FIG. 1, in the air separation plant 200 according to FIG. 2 there is no removal of liquid nitrogen in the form of the material flow i. Furthermore, there is no formation of the material flow c and its use as an excess air flow. Rather, in the air separation plant 200 according to FIG. 2, the entire stream b is fed into the rectification column 5, as described above for the stream d in the air separation plant 100 according to FIG. In FIG. 3, an air separation plant according to a further embodiment of the invention is illustrated and denoted overall by 300.

In contrast to air separation plant 100 according to FIG. 1 and air separation plant 200 according to FIG. 2, in air separation plant 300 according to FIG brought higher pressure, whereas the flow o experiences no such increase in pressure. The material flow o is only heated to an intermediate temperature in the auxiliary heat exchanger 3 , then expanded in the booster turbine arrangement 11 and then completely heated in the auxiliary heat exchanger 3 .

Otherwise, the air separation plant 300 according to FIG. 3 can essentially correspond to the air separation plant 200 according to FIG.

In FIG. 4, an air separation plant according to a further embodiment of the invention is illustrated and denoted overall by 400.

In contrast to the air separation plant 300 according to FIG. 3, a further booster turbine arrangement 13 is used in the air separation plant 400 according to FIG. The further booster turbine arrangement 13 is driven by the material flow b provided here as in the air separation plant 200 according to FIG. 2 and in the air separation plant 300 according to FIG. The material stream b is cooled to an intermediate temperature in the Flaupt heat exchanger 3, then expanded in the further booster turbine arrangement 13 and, after being fed back into the Flaupt heat exchanger 3, further cooled to a further intermediate temperature.

In FIG. 5, an air separation plant according to a further embodiment of the invention is illustrated and denoted overall by 500. In contrast to the air separation plant 400 according to FIG. 4, the booster of the further booster turbine arrangement 13 is operated as a cold booster in the air separation plant 500 according to FIG. For this purpose, the material flow I (see also connection point L) is cooled further in the booster turbine arrangement 11 after its compression in the booster turbine arrangement 11 and before further compression in the further booster turbine arrangement 13 .

Claims

patent claims

1. A method of making a compressed nitrogen product by

Low-temperature separation of air, in which an air separation plant (100-500) with a main heat exchanger (3) and a rectification column (5) with a

Top condenser (5.1) is used, wherein

- in the rectification column (5) using compressed air fed into the rectification column (5) and cooled in the main heat exchanger (3) at a pressure in a first pressure range, a top gas and a bottom liquid are formed, in the top condenser (5.1) a first part the top gas is condensed to obtain a first condensate at a pressure in the first pressure range and at least part of the bottoms liquid is vaporized at a pressure in a second pressure range below the first pressure range,

- nitrogen-rich liquid is withdrawn from an upper region of the rectification column (5) in a product quantity at a pressure in the first pressure region, subjected to internal compression, and used to provide the compressed nitrogen product, characterized in that

- the nitrogen-rich liquid is subjected to a pressure increase in the internal compression in the liquid state to a pressure in a third pressure range of 50 to 110 bar absolute pressure and is converted into the supercritical state in the main heat exchanger (3),

- a second part of the overhead gas in a recycle amount heated in the main heat exchanger (3), subjected to compression on the hot side of the main heat exchanger (3) to a pressure in a fourth pressure range, condensed in the main heat exchanger (3) to obtain a second condensate, and into the Rectification column (5) is fed back, and the pressure in the third pressure range is at least a factor of 1.5 higher than the pressure in the fourth pressure range and a ratio between the feed back quantity and the product quantity is 2:1 to 1.3:1.

2. The method of claim 1, in which parts of the first condensate are fed back into the rectification column (5) and used to provide a liquid nitrogen product.

3. Process according to Claim 1 or Claim 2, in which during the evaporation of at least part of the bottom liquid in the top condenser (5.1), a gas phase is formed which is used at least in part to form a residual gas stream, the residual gas stream being at the pressure in the second pressure range is subjected to a first heating in the main heat exchanger (3), thereafter being subjected to expansion to a pressure in a fifth pressure range in a booster turbine assembly (11), and thereafter to the pressure in the fifth pressure range to a second heating in the main heat exchanger ( 3) being subjected.

4. The method of claim 3, wherein the residual gas stream after the first heating is subjected to compression to a pressure in a sixth pressure range in the booster turbine assembly (11), then to the pressure in the sixth pressure range to intermediate cooling in the main heat exchanger (3). is thereafter subjected to the expansion to the pressure in the fifth pressure range in the booster turbine assembly (11), and thereafter is subjected to the second heating.

5. The method according to claim 3, in which the second part of the head gas is subjected to further compression in the booster turbine arrangement (11) after compression on the warm side of the main heat exchanger (3) to the pressure in the fourth pressure range and before condensation in the main heat exchanger (3). is subjected to a pressure in a seventh pressure range.

6. The method of claim 5, wherein the second portion of the overhead gas after further compression in the booster turbine assembly (11) to the pressure in the seventh pressure range and prior to condensation in the main heat exchanger (3) is subjected to a further compression in a further booster turbine arrangement (13) to a pressure in an eighth pressure range.

7. The method of claim 6, wherein the second portion of the head gas after further compression in the booster turbine assembly (11) to the pressure in the seventh pressure range and before further compression in the further booster turbine assembly (13) to the pressure in the eighth pressure range is subjected to cooling to a temperature in a temperature range of 0 to -150°C.

8. The method according to claim 7, in which the compressed air taken from the main heat exchanger (3) at a temperature in a first intermediate temperature range, expanded in the further booster turbine arrangement (13) to a pressure in a tenth pressure range, the main heat exchanger (3) at a temperature in fed back to a second intermediate temperature range, and further cooled in the main heat exchanger (3).

9. Process according to one of Claims 1 to 5, in which the compressed air fed into the rectification column (5) and cooled in the main heat exchanger (3) is part of a compressed total amount of air, with a further part of the compressed total amount of air in the main heat exchanger (3) cooled, subjected to expansion to a pressure in a ninth pressure range, heated in the main heat exchanger (3) to the pressure in the ninth pressure range and discharged from the air separation plant (100).

10. The method according to any one of the preceding claims, in which one or more first compressor stages are used to provide the compressed air, and in which one or more second compressor stages are used on the warm side of the main heat exchanger (3) to compress the second part of the overhead gas, the one or more first and one or more second compressor stages are provided in a common compressor.

11. Air separation plant (100-500) for producing a compressed nitrogen product by low-temperature separation of air, a main heat exchanger (3) and a rectification column (5) with a top condenser (5.1), wherein the

air separation plant (100-500) is set up to

- in the rectification column (5) using compressed air fed into the rectification column (5) and cooled in the main heat exchanger (3) at a pressure in a first pressure range to form a top gas and a bottom liquid, in the top condenser (5.1) a first part condensing the top gas to obtain a first condensate at a pressure in the first pressure range and evaporating at least part of the bottoms liquid at a pressure in a second pressure range which is below the first pressure range,

- withdrawing from an upper region of the rectification column (5) in a product amount of nitrogen-rich liquid at a pressure in the first pressure region, subjecting it to internal compression and using it to provide the compressed nitrogen product, characterized in that

- the air separation plant (100-500) is set up to subject the nitrogen-rich liquid during internal compression in the liquid state to a pressure increase to a pressure in a third pressure range of 50 to 110 bar absolute pressure and in the main heat exchanger (3) to the supercritical state convict,

- the air separation plant (100-500) is set up to heat a second part of the top gas in a feed-back quantity in the main heat exchanger (3), to subject the warm side of the main heat exchanger (3) to a pressure in a fourth pressure range in the main heat exchanger (3) to condense to obtain a second condensate and then to feed it back into the rectification column (5), and the pressure in the third pressure range is at least a factor of 1.5 higher than the pressure in the fourth pressure range and a ratio between the feed back quantity and the product quantity is 2:1 to 1.3:1.