CN117940727A - Method and air separation plant for the cryogenic separation of air - Google Patents

Abstract

For cryogenic separation, an air separation plant (100) is used for carrying out the high-pressure method, wherein nitrogen is removed from the pressure column (11), expanded in a turbine (9) connected to a cold booster (8) and heated. The nitrogen withdrawn from the low pressure column (12) is heated to the same temperature separately from the nitrogen withdrawn from the pressure column (11). The nitrogen taken out of the pressure column (11) is heated to a temperature in the range of-100 ℃ to 50 ℃ before expansion in a turbine (9) connected to the cold booster (8). During expansion, the nitrogen is cooled to a temperature in the temperature range of-150 ℃ to-40 ℃ and then reheated. The invention also relates to a corresponding air separation plant (100).

Description

Method and air separation plant for the cryogenic separation of air

The present invention relates to a method for the cryogenic separation of air and an air separation plant according to the preamble of the independent claim.

Background

It is known to produce liquid or gaseous air products by cryogenic separation of air in an air separation plant and is described, for example, by h.Editing the published "Industrial Gases Processing" is described in one book, particularly in section 2.2.5"Cryogenic Rectification". Unless explicitly defined otherwise, the terms used hereinafter have meanings commonly used in the technical literature.

For air separation, a known so-called primary (air) compressor/secondary compressor (Main Air Compressor/Booster Air Compressor, MAC/BAC) method or a so-called high-pressure (High Air Pressure, HAP) method may be used. The main air compressor/secondary compressor approach is a more traditional approach, and in recent years, the high pressure approach is increasingly used as an alternative. Please refer to the explanation below in more detail.

As described below, while the high pressure method has its advantages, particularly a reduced number of rotating machines, thereby reducing construction costs, the high pressure method has drawbacks in terms of certain product settings as compared to the main air compressor/secondary compressor method.

The object of the present invention is therefore to improve the process connection of the high-pressure process in such a way that the above-mentioned main advantages of the high-pressure process are retained, but that they also have advantages over the main air compressor/secondary compressor process as a whole.

Disclosure of Invention

Against this background, the invention proposes a method for the cryogenic separation of air and an air separation plant according to the preambles of the independent claims. Embodiments of the invention are subject matter of the dependent claims and of the following description.

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

The term "air product" shall in particular refer here to a fluid which is provided at least partly by cryogenic separation of atmospheric air. According to the basic understanding herein, an air product has one or more air gases contained in the atmosphere, which have a composition that differs from the composition in the atmosphere. The air product may in principle be present or provided in a gaseous, liquid or supercritical state and may be converted from one of these polymerization states to the other. In particular, by heating at a specific pressure, the liquid air product can be converted to a gaseous state ("vaporisation") or to a supercritical state ("pseudo-vaporisation"), depending on whether the pressure during heating is below or above the critical pressure. If "evaporation" is mentioned hereinafter, corresponding pseudo-evaporation should also be included.

The air separation plant has rectifying column assemblies, which may be of different designs. In addition to the rectification columns for extracting nitrogen and/or oxygen in liquid and/or gaseous form, i.e. for separating nitrogen from oxygen, in particular rectification columns which can be combined in known double columns, rectification columns for extracting other air components, in particular noble gases, or pure oxygen, can also be provided.

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

In air separation plants, a multistage turbocompressor, referred to herein as a "main air compressor", is used to compress the intake air amount. The mechanical construction of turbocompressors is generally known to those skilled in the art. In a turbo compressor, the medium to be compressed is compressed by means of turbine blades arranged on a turbine or directly on a shaft. The turbocompressor forms a structural unit, but the structural unit may have a plurality of compression stages in a multistage turbocompressor. The compression stage here generally comprises a corresponding arrangement of turbines or turbine blades. All of these compression stages may be driven by the same shaft. However, it is also possible to arrange for the compression stages to be driven in different groups of shafts, which shafts can also be coupled to one another via a reduction gear.

Furthermore, the main air compressor is characterized in that the total air quantity fed to the rectifying column assembly and used for producing the air product is compressed by the main air compressor, i.e. the total air intake quantity is compressed. A "secondary compressor" may correspondingly be provided, in which, however, only the partial intake air quantity compressed in the main air compressor is increased to a higher pressure. The compressor may also be designed as a turbo compressor. For compressing a part of the air quantity, a further turbo compressor, also called booster compressor, is usually provided, which is however typically compressed only to a relatively small extent compared to the main air compressor or the secondary compressor, in particular for the compressed air quantity. In the high-pressure method (see below), there may also be a secondary compressor, which, however, compresses a part of the intake air amount starting from a higher pressure.

"Cold compressor" or "cold booster" refers herein to a compressor or booster for which a fluid is delivered at a temperature, in particular below-50℃or-100℃and in particular above-150℃or-200℃within a temperature range significantly below the ambient temperature of the air separation plant. Whereas the fluid is fed to the thermo-compressor or thermo-booster at a temperature in a temperature range above-30 ℃, 0 ℃,20 ℃ or 50 ℃, in particular up to 100 ℃ or 200 ℃.

The air can also be expanded at several points in the air separation plant, for which purpose an expander in the form of a turboexpander, also referred to herein as an "expansion turbine" or simply a turbine, can be used, among other things. The turboexpander may also be coupled to and drive a turbocompressor. The term "turbocharger" may also be used for such an arrangement if one or several turbocompressors are driven without externally supplied energy, i.e. via one or several turboexpanders only. In a turbocharger, a turbo-expander (expansion turbine) and a turbo-compressor (supercharger) are mechanically coupled, wherein the coupling can be effected at the same rotational speed (e.g. via a common shaft) or at different rotational speeds (e.g. via an intermediate transmission gear). If we refer here to a "turbine unit", it is in particular a device with at least one expansion turbine.

The main air compressor/secondary compressor method is characterized in that only a part of the intake air amount supplied in its entirety to the rectifying column assembly is compressed to a pressure level that is significantly higher than the pressure level of the pressure column, i.e. at least 3 bar, 4 bar, 5 bar, 6 bar, 7 bar, 8 bar, 9 bar or 10 bar higher than the pressure level of the pressure column, and in turn higher than the highest pressure level used in the rectifying column assembly. The other part of the intake air amount is compressed only to the pressure level of the pressure column, or up to a pressure level not differing from the pressure level of the pressure column by more than 1 bar to 2 bar, and is fed into the pressure column at the pressure level without expansion. An example of such a primary air compressor/secondary compressor approach is inShown in fig. 2.3A in the book (see above).

In contrast, typically in high pressure processes, the total amount of intake air supplied to the rectifying column assembly as a whole is compressed to a pressure level that is significantly higher than the pressure level of the pressure column, i.e., 3 bar, 4 bar, 5 bar, 6 bar, 7 bar, 8 bar, 9 bar or 10 bar or more, and further higher than the pressure level of the highest pressure level used in the rectifying column assembly. The pressure difference may for example be up to 14 bar, 16 bar, 18 bar or 20 bar or more. The high-pressure process has been described several times and is known, for example, from EP 2 980 A1 and EP 2 963 367 A1.

The high pressure process is typically used in combination with so-called internal compression (IV, internal Compression, IC). In internal compression, a gaseous pressurized air product is formed by extracting a low temperature liquid air product from a rectifying column assembly, subjecting the air product to a pressure increase to a product pressure, and converting to a gaseous or supercritical state at the product pressure by heating, thereby forming at least one gaseous pressurized air product provided by means of an air separation plant. For example, gaseous pressurized oxygen (GOX IV, GOX IC), gaseous pressurized nitrogen (GAN IV, GAN IC) or gaseous pressurized argon (GAR IV, GAR IC) can be produced by means of internal compression. Compression offers a range of technical advantages over alternative, equally possible external compression and is used, for example, inThe "compression" in section 2.2.5.2 of the book (see above) has been explained.

In a typical air separation plant, corresponding expansion turbines are present at various points for refrigerating and liquefying the stream. In particular, the claude turbines and the raman turbines are referred to, and the joule-thomson turbines may be referred to as such. Reference is made to the specialized literature concerning the functioning and use of the corresponding turbines, for example in the book "Industrial Gas Handbook: gas Separation and Purification", in particular chapter 2.4, "Contemporary Liquefaction Cycles", chapter 2.6, "Theoretical Analysis of the Claude Cycle" and chapter 3.8.1, "THE LACHMANN PRINCIPLE", published by CRC Press in 2006.

Particularly well known are high pressure processes in which the above described raman turbines are employed. The air expanded in the Raschmann turbine is fed (blown) into the low pressure column and is therefore also referred to as a blow-in turbine (English: upper column expander). The raman turbine may be provided as a further turbine unit, outside the turbine unit, by means of which the gaseous compressed air, i.e. the claude turbine, is expanded into the pressure column.

The term "amount of air blown in" refers to compressed air that is expanded by a typical Raschmann turbine (blown-in turbine) and then fed (blown in) to a low pressure column. The air which expands into the low-pressure column in this way interferes with the rectification, so that the amount of air which can be expanded in the blowing-in turbine and the amount of cold which is produced in this way for a corresponding plant are limited. The nitrogen-enriched air product withdrawn from the pressure column as pressurized nitrogen and output from the air separation plant, as well as the liquid nitrogen output from the air separation plant and the internal compressed nitrogen output from the air separation plant, may also have a corresponding impact and/or co-action on the rectification.

The amount of air blown into the lower pressure column by the raman turbine, including the amount of nitrogen withdrawn from the pressure column and output from the air separation unit, and also including the amount of liquid nitrogen output from the air separation unit and the amount of internal compressed nitrogen output from the air separation unit (if any) may be determined based on the total amount of air input to the rectifying column assembly. The values thus obtained are referred to as blowing equivalents.

"Throttling flow" or "Joule-Thomson flow" refers to the amount of air that is at least largely liquefied under pressure in the main heat exchanger of the air separation plant and then, in particular, fed to the pressure column (in particular, via a throttle valve). Instead of a throttle valve, a joule-thomson turbine may also be used.

In the language used herein, a liquid, gaseous or liquid also present in a supercritical state may be enriched or deficient in one or several components, wherein "enriched" may denote a content of at least 75%, 90%, 95%, 99%, 99.5%, 99.9% or 99.99% on a molar, weight or volume basis, and "deficient" may denote a content of at most 25%, 10%, 5%, 1%, 0.1% or 0.01%. The term "mainly" may correspond to the definition of "enriched" just given, however in particular refers to a content above 90%. For example, if "nitrogen" is referred to herein, it may refer to pure gas, but may also refer to nitrogen-enriched gas.

Features and advantages of the invention

High pressure processes may be used in different embodiments. These are generally classified and distinguished by the liquid output of the apparatus, i.e. by the amount of air product (also referred to herein as liquid product) provided in liquid form and extracted from the apparatus in liquid form, or by the ratio of internally compressed air product to liquid product.

The high pressure process using a hot booster (driven by a turbine) and a cold booster (also driven by a turbine) is an economical and efficient alternative to the main air compressor/secondary compressor process with little or no liquid product and some internal compression. However, the maximum pressure achievable by the series connected cold and hot superchargers may not be high enough to optimally balance the cold and hot flows in the main heat exchanger without excessively increasing the main air compressor pressure (which may result in energy disadvantages compared to the main air compressor/secondary compressor approach) or affecting the manufacturability of the turbocharger assembly.

In the conventional main air compressor/secondary compressor approach, the approach is well suited to different product settings, since both compressors (main air compressor and secondary compressor) are used to "handle" the tasks of different functions. In principle, the main air compressor provides only intake air for separation, while the booster provides energy for internal compression and liquid production. By skillfully connecting the turbine and the secondary compressor (with/without intermediate extraction) and using additional throttle flows, a very high energy efficiency can be achieved. However, a large number of compressor stages is typically required, thereby increasing investment costs. The invention herein provides a remedy.

In the high pressure process, the above-described tasks (providing separate air and energy for internal compression and liquid production) are accomplished by only one compressor. Therefore, the total intake air must be compressed to a high pressure to achieve a good balance of cold and warm flows in the main heat exchanger. The high pressure must be provided by the turbocharger and the main air compressor. In some cases, particularly in product settings where there is little or no liquid product, it is difficult to achieve effective balancing without affecting the manufacturability of the booster turbine or significantly increasing the main air compressor pressure.

In the known high-pressure process, it is possible to generate a throttle flow by means of a cold booster and to reduce the pressure of the main air compressor. However, its energy efficiency is still not comparable to the main air compressor/secondary compressor approach. In this case, the cold booster is connected downstream of the hot booster. Since thermal superchargers generally require a larger volume to be compressed, or the volume ratio between the turbine and the supercharger must be set in order to be able to build the machine, the stage pressure ratio is generally less than 1.4. When using a cold booster, the step ratio may be up to 2 or slightly higher. The specific rotational speeds of the turbine and supercharger must be within a constructable range and the rotational speed of the machine must not be too high. Furthermore, a corresponding process using two cold compressors connected in series is known from US2013/0255313 A1.

The advantages of the invention are particularly reflected in the low liquid production (less than 10% of the liquid withdrawn from the plant based on the internal compressed product) and in the process where a cold compressor is used and the blowing equivalent is very low, but the nitrogen production is very high relative to the oxygen production.

The solution of the invention exploits the fact that in many equipment and operating situations the blowing equivalent in the above sense is not fully utilized. It is well known that increasing the blow-in equivalent weight can increase energy absorption (using a Lahim turbine in the high pressure and main air compressor/secondary compressor process). By increasing the blowing equivalent, the amount of air needed to provide the desired product is multiplied, but the pressure needed for the main air compressor is reduced, thereby reducing the overall energy consumption. Furthermore, increasing the blowing equivalent reduces argon production. To achieve the optimization, there is an optimum value at which (only) the blowing equivalents should be exhausted.

For plants with higher nitrogen production, the optimum of blowing equivalent is lower, as an increase in blowing equivalent reduces nitrogen production.

The current concept of the present invention is to utilize the blowing equivalent by withdrawing additional compressed nitrogen from the pressure column at operating pressure. This pressurized nitrogen is sent to a turbine which drives a cold booster (after heating in the main heat exchanger) and expands to a pressure below the low pressure column (or to a pressure of pure nitrogen withdrawn at the top of the low pressure column). The nitrogen stream expanded in this way is now heated in the main heat exchanger and fed with pure nitrogen from the top of the lower pressure column, in particular before the pure nitrogen is compressed in an external nitrogen compressor.

While a partial flow of air cooled after compression in the hot booster is fed into the cold booster. While a partial flow of the air compressed in the main air compressor is fed into the hot booster. The compressed part of the gas stream in the cold booster is used as a high pressure throttling stream or a high pressure joule-thomson stream. This means that part of the air from the main air compressor is recompressed twice to provide a high pressure joule-thomson flow. In this way, the blowing equivalent of the apparatus can be optimized to provide the desired nitrogen production.

From a Total Cost of Ownership (TCO) perspective, the present invention increases the efficiency of high pressure air wiring without losing any cost effectiveness or increasing the complexity of the process. Most importantly, the cost can be reduced:

● By increasing the blowing equivalent (in this case by withdrawing compressed nitrogen from the pressure column), the gas load in the lower pressure column can be reduced, so that alternatively the lower pressure column can be designed with a smaller column diameter.

● The required cold charge turbine is one level smaller than if a self-charge turbine were used in an energy efficient cold charge method, because the amount of air passing through the turbine is much smaller.

● The method of using a cold booster driven by a raman turbine may be comparable in energy efficiency and have the advantage of increasing the blowing equivalent, but in the case of corresponding system sizes, the turbine cannot be built because the required rotational speed exceeds 75,000 revolutions per minute (less air volume on the turbine, greater pressure gradient of the expanding air).

Based on conservative calculations, the energy consumption of the proposed method is the same compared to the traditional high-pressure cold-pressurization method. The proposed method is very advantageous in terms of argon and energy assessment and the required air production. This method is very advantageous for plants that do not produce argon.

The method for cryogenically separating air according to the invention is carried out with an air separation plant having a rectifying column assembly comprising a pressure column and a low pressure column, wherein the pressure column is operated in a first pressure range, the low pressure column is operated in a second pressure range which is lower than the first pressure range, and at least 90% of the total amount of air separated in the rectifying column assembly is compressed to a certain pressure in a third pressure range which is 5 bar higher than the first pressure range. Thus, as described in detail above, the high-pressure method is performed.

Continuously feeding a portion of the total amount of separated air into a first booster driven by a first turbine at a temperature in a first temperature range of-30 ℃ to 100 ℃, compressing the portion with the first booster from a pressure in a third pressure range to a pressure in a fourth pressure range higher than the third pressure range, cooling the portion to a temperature in a second temperature range of-160 ℃ to-60 ℃, feeding the portion into a second booster driven by a second turbine at a temperature in the second temperature range, compressing the portion with the second booster from a pressure in the fourth pressure range to a pressure in a fifth pressure range higher than the fourth pressure range, cooling the portion to a temperature in the third temperature range of-200 ℃ to-150 ℃, wherein in particular the portion is at least partially liquefied and feeding it into a pressure column. In particular a high pressure joule-thomson flow, which may be used with another joule-thomson flow provided at a pressure in the third pressure range. All cooling steps explained herein and below can be performed using the main heat exchanger, provided that cooling has not been achieved by expansion.

In the context of the present invention, gaseous nitrogen is taken from the pressure column at a pressure in the first pressure range and is continuously heated to a temperature in the fourth temperature range, in particular-100 ℃ to 50 ℃, expanded in the second turbine to a pressure in the second pressure range while being cooled to a temperature in the fifth temperature range, in particular-150 ℃ to-40 ℃, and heated to a temperature in the sixth temperature range, in particular 0 ℃ to 50 ℃. In addition, gaseous nitrogen is also withdrawn from the low pressure column and heated to a temperature in a sixth temperature range.

According to the invention, the gaseous nitrogen withdrawn from the low pressure column is heated separately from the gaseous nitrogen withdrawn from the pressure column, i.e. in particular in a separate heat exchange channel of the main heat exchanger, to a temperature in the sixth temperature range, and the fourth temperature range is-100 ℃ to 50 ℃ and the fifth temperature range is-140 ℃ to-40 ℃, for example in the range of the prior art, such as in particular in the range of US 9,945,606 B2.

In other words, within the scope of the present invention, the nitrogen for the nitrogen turbine (i.e. the second turbine) is heated to a relatively high temperature in the fourth temperature range and then expanded, thereby adjusting the temperature in the fifth temperature range, and then this nitrogen is heated in particular in a separate channel in the main heat exchanger and is mixed with the low pressure nitrogen from the low pressure column only downstream of the heating. This has the advantage that the higher turbine inlet temperature reduces nitrogen consumption and provides the necessary power for the cold booster to increase energy efficiency, as compared to expansion at lower temperatures and prior to mixing with low pressure nitrogen.

Higher turbine inlet temperatures or lower intake air amounts may result in smaller turbines being required and easier construction by increasing specific speed. In addition, the higher turbine inlet temperature also reduces the amount of compressed nitrogen required compared to a lower inlet temperature Raschmann turbine or pressure nitrogen turbine nozzle, which results in a lower blowing equivalent and thus a lower air factor. This reduces the amount of air required and increases the air pressure, thereby saving energy and cost in terms of pre-cooling and molecular sieve adsorbers or regeneration capacity.

The proposed process reduces the volume of the main heat exchanger since the passage of low pressure nitrogen is from about 200K to 300K, rather than from 96K to 300K. The main heat exchanger can be designed to be significantly smaller in volume at the same output as compared to methods using a raman or cold pressure nitrogen turbine, as the process requires a smaller amount of air to be used. Additional joule-thomson flow at the pressure of the main air compressor, provided according to embodiments of the present invention, may improve the balance of the heat exchanger temperature profile, thereby improving energy efficiency. The amount of air that needs to be compressed in the thermal booster is small and therefore can be operated at a high pressure differential. The additional throttling has a very great energy advantage, especially in processes with two or more different internal compression pressures, for example 30 bar (absolute) for gaseous oxygen, 15 bar (absolute) for gaseous oxygen or nitrogen.

Within the scope of the invention, the first pressure range is in particular 4 bar to 7 bar, the second pressure range is in particular 1 bar to 2 bar, the third pressure range is in particular 10 bar to 18 bar, the fourth pressure range is in particular in a pressure range of 1.2 times to 1.5 times the third pressure range, and the fifth pressure range is in particular in a pressure range of 1.6 times to 2.5 times the fourth pressure range.

Advantageously, a further portion of the total amount of separated air is fed continuously to the first booster at a temperature in the first temperature range, the further portion is compressed from a pressure in the third pressure range to a pressure in the fourth pressure range by means of the first booster, the further portion is cooled to a temperature in the second temperature range or in a further temperature range, the further portion is expanded in the first turbine to a pressure in the first pressure range, and the further portion is fed to the pressure column. In other words, the formation of the turbine wheel is advantageous, which is first compressed in the thermal booster together with the high-pressure throttle flow. Subsequent cooling may be to the same or different temperature levels as compared to cooling of the high pressure throttling stream.

As previously mentioned, in a particularly preferred embodiment, the method according to the invention may further comprise: at a pressure in the third pressure range, a further part of the total amount of separated air is cooled to a temperature in the third temperature range and fed (as a further throttling stream) to the pressure column. The advantages have already been described.

The gaseous nitrogen withdrawn from the low pressure column and the gaseous nitrogen withdrawn from the pressure column may be joined to each other after being separately heated to a temperature in the sixth temperature range. The advantages of such joining downstream of heating have also been described above.

In this process, one or more liquids are advantageously withdrawn from the rectification column assembly, either internally compressed separately or discharged from the air separation plant as one or more gaseous internally compressed products.

Advantageously, the one or more gaseous internal compression products are or include gaseous internal compression products produced using an oxygen-rich liquid from a low pressure column.

Advantageously, the liquid product is not withdrawn from the air separation plant, or the one or more liquid products are withdrawn from the air separation plant in a total amount of no more than 10% of the total amount of the one or more gaseous internal compressed products. As previously mentioned, the present invention is particularly useful in situations where such liquid yields are low.

In an embodiment of the invention, an argon-rich liquid may be withdrawn from the low pressure column and fed to an argon extraction system to extract argon. However, in embodiments of the present invention, embodiments without argon extraction may also be provided.

An air separation plant for the cryogenic separation of air according to the present invention has a rectifying column assembly comprising a pressure column and a low pressure column, wherein the air separation plant is arranged to: the pressure column is operated in a first pressure range, the low pressure column is operated in a second pressure range lower than the first pressure range, and at least 90% of the total amount of air separated in the rectifying column assembly is compressed to a pressure in a third pressure range, the third pressure range being 5 bar higher than the first pressure range.

Furthermore, the air separation apparatus is provided for: continuously feeding a portion of the total amount of separated air into a first booster driven by a first turbine at a temperature in a first temperature range of-30 ℃ to 100 ℃, compressing the portion with the first booster from a pressure in a third pressure range to a pressure in a fourth pressure range higher than the third pressure range, cooling the portion to a temperature in a second temperature range of-160 ℃ to-60 ℃, feeding the portion into a second booster driven by a second turbine at a temperature in the second temperature range, compressing the portion with the second booster from a pressure in the fourth pressure range to a pressure in a fifth pressure range higher than the fourth pressure range, cooling the portion to a temperature in the third temperature range of-200 ℃ to-150 ℃, and feeding the portion into a pressure tower.

Furthermore, the air separation apparatus according to the present invention is provided for: gaseous nitrogen is withdrawn from the pressure column at a pressure in the first pressure range and continuously heated to a temperature in the fourth temperature range, the gaseous nitrogen is expanded in the second turbine to a pressure in the second pressure range while cooling to a temperature in the fifth temperature range and heating the gaseous nitrogen to a temperature in the sixth temperature range of 0 ℃ to 50 ℃, and gaseous nitrogen is withdrawn from the low pressure column and heated to a temperature in the sixth temperature range.

According to the invention, the air separation plant is arranged for: the gaseous nitrogen withdrawn from the low pressure column is heated separately from the gaseous nitrogen withdrawn from the pressure column to a temperature in a sixth temperature range, wherein the fourth temperature range is-100 ℃ to 50 ℃ and the fifth temperature range is-150 ℃ to-40 ℃.

The air separation plant proposed according to the invention is particularly adapted for carrying out the method as set forth in the embodiments previously. Thus, reference should be explicitly made to the above description of the process according to the invention and its advantageous embodiments.

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

Drawings

Fig. 1 shows an air separation plant according to an advantageous embodiment of the invention.

In the figures, elements that correspond to each other structurally or functionally are given the same reference numerals and are not repeated for the sake of clarity. The statements made with respect to apparatuses and apparatus components apply equally to the respective methods and method steps.

An air separation plant according to an embodiment of the present invention is shown in simplified flow diagram form in fig. 1 and is generally designated 100.

In the air separation plant 100, air is sucked in through the filter 1 by means of the main air compressor 2 and compressed to a suitable pressure level. After precooling in the precooling apparatus 3, the compressed air stream a formed in this way removes residual water and carbon dioxide in a precleaning unit 4, which can be designed in a known manner. The structure of the relevant components is referred to in the literature at the outset.

In this example, the compressed air stream a is split into two partial streams B and C, wherein the partial stream B passes from the warm end through the main heat exchanger 4 to the cold end as a joule-thomson stream and is fed to the pressure column 11 of the rectifying column assembly 10. The partial gas flow C is first boosted in a thermal booster 6 (previously referred to as "first" booster), is fed into this booster at a temperature within the respective temperature range (previously referred to as "first" temperature range), and is then cooled in the main heat exchanger 4. In the embodiment shown in fig. 1, the partial streams D and E are formed after removal from the main heat exchanger 4 at temperatures within the respective temperature ranges (the "second" temperature ranges previously). However, it is also possible to take it out of the main heat exchanger 4 at a different temperature.

Now, part of the gas stream D is further pressurized in a cold booster (the previous "second" booster) and then cooled in the main heat exchanger 4 to a temperature in the cold side temperature range (the previous "third" temperature range) and fed as a high pressure joule-thomson stream to the pressure column 11. Part of the gas stream E is expanded in a turbine (the "first" turbine before) connected to the first booster 6 and is also fed to the pressure column 11. A partial stream F of the partial stream C (as another joule-thomson stream) is also fed to the pressure column 11.

Nitrogen in the form of stream G is withdrawn from pressure column 11 and heated in main heat exchanger 4 to a temperature in the appropriate or advantageous temperature range (the previous "fourth" temperature range), expanded in a turbine (the previous "second" turbine) connected to second booster 8, cooled to a temperature in the corresponding temperature range (the previous "fifth" temperature range), and then again heated in main heat exchanger 4 to a temperature in the warm side temperature range (the previous "sixth" temperature range) of main heat exchanger 4.

Gaseous nitrogen in the form of stream H is withdrawn from lower pressure column 12 and heated to a temperature in the sixth temperature range. After heating, it is combined with stream H to form the corresponding aggregate stream I.

In the rectifying column assembly 10, a pressure column 11 is connected in heat exchange with a low pressure column 12 through a main condenser 13. Subcooled reflux 14 is distributed to rectifying column assembly 10. An internal compression pump is indicated at 15. The air separation plant 100 may have an argon extraction unit (not shown here) designed in a known manner.

As previously described, the feed to pressure column 11 is cooled, pressurized, and optionally liquefied air for streams B, D, E and F. Directly downstream of the feed point for stream F, liquid in the form of stream K is withdrawn from pressure column 11 and directed through subcooled reflux 14 before being fed to low pressure column 12. In addition, the low pressure column 12 is fed with an oxygen-rich liquid in the form of a bottom liquid stream L from the pressure column 11, which is also led beforehand through a subcooling countercurrent device 14. The top gas of the pressure column 11 further passes through a main condenser 13. The main condenser 13 is operated in a known manner, in particular the material stream M is also transferred to the low-pressure column 12. Impure nitrogen is withdrawn from the lower pressure column 12 as stream h and pure lower pressure nitrogen is withdrawn from the lower pressure column as stream g.

The oxygen-rich column bottoms liquid is withdrawn from lower pressure column 12 in stream N and pressurized in liquid form in internal compression pump 15. Part of the gas stream O may be provided as gaseous internal compression product after evaporation in the main heat exchanger. Another portion of the airflow P may be subcooled in the subcooled counter-flow 14 and discharged from the air separation plant 100 in liquid form.

Liquid may also be collected at the top of low pressure column 12 and withdrawn as liquid nitrogen product in stream Q. An impure nitrogen stream R may be withdrawn from the lower pressure column 12 and utilized in a known manner.

Claims (11)

1. A method for cryogenically separating air using an air separation plant (100) having a rectifying column assembly (10) comprising a pressure column (11) and a low pressure column (12), wherein

Operating the pressure column (11) in a first pressure range, operating the low pressure column (12) in a second pressure range lower than the first pressure range, and compressing at least 90% of the total amount of air separated in the rectifying column assembly (10) to a pressure in a third pressure range, the third pressure range being 4 bar higher than the first pressure range,

Continuously feeding a portion of the total amount of separated air into a first booster (6) driven by a first turbine (7) at a temperature in a first temperature range of-30 ℃ to 100 ℃, compressing the portion with the first booster (6) from a pressure in the third pressure range to a pressure in a fourth pressure range higher than the third pressure range, cooling the portion to a temperature in a second temperature range of-160 ℃ to-60 ℃, feeding the portion into a second booster (8) driven by a second turbine (9) at a temperature in the second temperature range, compressing the portion with the second booster (6) from a pressure in the fourth pressure range to a pressure in a fifth pressure range higher than the fourth pressure range, cooling the portion to a temperature in the third temperature range of-200 ℃ to-150 ℃, and feeding the portion into the pressure column (11),

-Withdrawing gaseous nitrogen from the pressure column (11) at a pressure in the first pressure range and continuously heating it to a temperature in a fourth temperature range, expanding the gaseous nitrogen in the second turbine to a pressure in a second pressure range while cooling to a temperature in a fifth temperature range and heating the gaseous nitrogen to a temperature in a sixth temperature range of 0 ℃ to 50 ℃, and

Gaseous nitrogen is withdrawn from the low pressure column (12) and heated to a temperature in a sixth temperature range,

It is characterized in that the method comprises the steps of,

-Heating the gaseous nitrogen withdrawn from the low pressure column (12) separately from the gaseous nitrogen withdrawn from the pressure column (11) to a temperature in a sixth temperature range, and

-The fourth temperature range is-100 ℃ to 50 ℃ and the fifth temperature range is-150 ℃ to-40 ℃.

2. The method of claim 1, wherein the first pressure range is 4 bar to 7 bar, the second pressure range is 1 bar to 2 bar, the third pressure range is 10 bar to 18 bar, the fourth pressure range is within a pressure range of 1.2 to 1.5 times the third pressure range, and the fifth pressure range is within a pressure range of 1.6 to 2.5 times the fourth pressure range.

3. A method according to claim 1 or claim 2, wherein a further portion of the total amount of separated air is fed continuously to the first booster (6) at a temperature in the first temperature range, the further portion is compressed from a pressure in the third pressure range to a pressure in the fourth pressure range by means of the first booster (6), the further portion is cooled to a temperature in the second temperature range or a further temperature range, the further portion is expanded in the first turbine (7) to a pressure in the first pressure range, and the further portion is fed to the pressure column (11).

4. A method according to any of the preceding claims, wherein a further portion of the total amount of separated air is cooled to a temperature in the third temperature range at a pressure in the third pressure range and is fed to the pressure column (11).

5. The method according to any of the preceding claims, wherein the gaseous nitrogen withdrawn from the low pressure column (12) and the gaseous nitrogen withdrawn from the pressure column (11) merge with each other after separate heating to a temperature in the sixth temperature range.

6. A method according to any one of the preceding claims, wherein one or more liquids are withdrawn from the rectifying column assembly (10), either internally compressed separately or as one or more gaseous internal compressed products, and discharged from the air separation plant (100).

7. The method of claim 6, wherein the one or more gaseous internal compression products are or include gaseous internal compression products produced with an oxygen-rich liquid from the low pressure column.

8. The method of claim 6 or claim 7, wherein no liquid product is withdrawn from the air separation plant (100) or one or more liquid products are withdrawn from the air separation plant (100) in a total amount of no more than 10% of the total amount of the one or more gaseous internal compressed products.

9. The process of any one of the preceding claims, wherein an argon-rich liquid is withdrawn from the low pressure column and fed to an argon extraction system to extract argon.

10. A method according to any of the preceding claims, wherein gaseous nitrogen is taken from the pressure column (11), heated to a temperature in the sixth temperature range and extracted as nitrogen-enriched air product at a pressure in the first pressure range.

11. An air separation apparatus (100) for cryogenically separating air, the air separation apparatus having a rectifying column assembly (10) comprising a pressure column (11) and a low pressure column (12), wherein the air separation apparatus (100) is arranged to:

Operating the pressure column (11) in a first pressure range, operating the low pressure column (12) in a second pressure range lower than the first pressure range, and compressing at least 90% of the total amount of air separated in the rectifying column assembly (10) to a pressure in a third pressure range, the third pressure range being 5 bar higher than the first pressure range,

Continuously feeding a portion of the total amount of separated air into a first booster (6) driven by a first turbine (7) at a temperature in a first temperature range of-30 ℃ to 100 ℃, compressing the portion with the first booster (6) from a pressure in the third pressure range to a pressure in a fourth pressure range higher than the third pressure range, cooling the portion to a temperature in a second temperature range of-160 ℃ to-60 ℃, feeding the portion into a second booster (8) driven by a second turbine (9) at a temperature in the second temperature range, compressing the portion with the second booster (6) from a pressure in the fourth pressure range to a pressure in a fifth pressure range higher than the fourth pressure range, cooling the portion to a temperature in the third temperature range of-200 ℃ to-150 ℃, and feeding the portion into the pressure column (11),

-Withdrawing gaseous nitrogen from the pressure column (11) at a pressure in the first pressure range and continuously heating it to a temperature in a fourth temperature range, expanding the gaseous nitrogen in the second turbine to a pressure in a second pressure range while cooling to a temperature in a fifth temperature range and heating the gaseous nitrogen to a temperature in a sixth temperature range of 0 ℃ to 50 ℃, and

Gaseous nitrogen is withdrawn from the low pressure column (12) and heated to a temperature in the sixth temperature range,

Characterized in that the air separation plant (100) is arranged to,

-Heating the gaseous nitrogen withdrawn from the low pressure column (12) separately from the gaseous nitrogen withdrawn from the pressure column (11) to a temperature in the sixth temperature range, wherein

-The fourth temperature range is-100 ℃ to 50 ℃ and the fifth temperature range is-150 ℃ to-40 ℃.