EP3620739A1 - Method for the low-temperature decomposition of air and air separation plant - Google Patents

Abstract

The present invention proposes a method for extracting an air product using an air separation plant (100) with a rectification column system (10), which has a high pressure column (11) which is operated at a first pressure level and a low pressure column (12) which is operated on a second Has operated pressure level below the first pressure level, before. It is provided that a first compressed air flow at a first pressure level and a second compressed air flow at a third pressure level above the first pressure level are provided and subjected to cooling, the first compressed air flow is fed into the rectification column system (11) and the second compressed air flow using an expansion turbine (5) relaxed to the first pressure level is fed into the rectification column system (11), and a liquid material flow from the rectification column system (10) is carried out and pressure-increased in the liquid state, converted into the gaseous or supercritical state and as the at least one air product from the air separation plant (100) is derived. The invention is characterized in that the expansion turbine (5), which is used when the second compressed air stream is expanded to the first pressure level, is operated in such a way that a two-phase mixture is formed at its outlet, which has a gas content of 5 to 25 at the outlet %, based on the total two-phase mixture. A corresponding air separation plant (100) is also the subject of the invention.

Description

The invention relates to a method and a plant for obtaining an air product according to the respective preambles of the independent claims.

State of the art

The production of air products in a liquid or gaseous state by low-temperature separation of air in air separation plants is known and, for example, at H.-W. Häring (ed.), Industrial Gases Processing, Wiley-VCH, 2006, in particular Section 2.2.5, "Cryogenic Rectification ", described.

Air separation plants have rectification column systems which can be designed, for example, as two-column systems, in particular as classic Linde double-column systems, but also as three- or multi-column systems. In addition to the rectification columns for the production of nitrogen and / or oxygen in the liquid and / or gaseous state, i.e. the rectification columns for the nitrogen-oxygen separation, rectification columns for the production of further air components, in particular the noble gases krypton, xenon and / or argon, can be provided. Even if corresponding rectification columns for the extraction of further air components are not specifically discussed below, they can also be the subject of the present invention.

The rectification columns of the rectification column systems mentioned are operated at different pressure levels. Double column systems have a so-called high pressure column (also referred to as a pressure column, medium pressure column or lower column) and a so-called low pressure column (also referred to as an upper column). The pressure level of the high pressure column is, for example, 4 to 6 bar, preferably about 5.5 bar. The low pressure column is operated at a pressure level of, for example, 1.3 to 1.7 bar, preferably approximately 1.5 bar. The pressure levels given here and below are absolute pressures which are present at the top of the columns mentioned. The values mentioned are only examples that can be changed if necessary.

So-called main compressors / post-compressors (Main Air Compressor / Booster Air Compressor, MAC-BAC) processes or so-called high air pressure (HAP) processes can be used for air separation. The main compressor / post-compressor processes are the more conventional processes, and high-air pressure processes have been used more and more recently as alternatives.

The main compressor / post-compressor process is characterized by the fact that only part of the total amount of feed air supplied to the rectification column system is compressed to a pressure level that is significantly higher, i.e. by at least 3, 4, 5, 6, 7, 8, 9 or 10 bar the pressure level of the high pressure column. Another part of the quantity of feed air is merely compressed to the pressure level of the high-pressure column or a pressure level that does not differ by more than 1 to 2 bar from the pressure level of the high-pressure column, and is fed into the high-pressure column at this lower pressure level. An example of a main compressor / post-compressor process is at Häring (see above) in Figure 2 .3A shown.

In the case of a high-air pressure process, on the other hand, the total amount of feed air supplied to the rectification column system is compressed to a pressure level that is substantially, ie at least 3, 4, 5, 6, 7, 8, 9 or 10 bar above the pressure level of the high-pressure column. The pressure difference can be up to 14, 16, 18 or 20 bar, for example. High air pressure processes are for example from the EP 2 980 514 A1 and the EP 2 963 367 A1 known.

The present invention is used in particular in air separation plants with so-called internal compression (IV, internal compression, IC). Here, at least one product, which is provided by means of the air separation plant, is formed by removing a cryogenic liquid from the rectification column system, subjecting it to a pressure increase in the liquid state, and, depending on the pressure present, by heating either in the gaseous or in the supercritical state is transferred. For example, internally compressed gaseous oxygen (GOX IV, GOX IC), internally compressed gaseous nitrogen (GAN IV, GAN IC) or internally compressed gaseous argon (GAR IV, GAR IC) can be generated by means of internal compression. The internal compression offers a number of technical advantages over an external compression of corresponding products, which is also possible in principle, and is explained in the specialist literature, for example from Häring (see above), Section 2.2.5.2, "Internal Compression".

The object of the present invention is to improve the extraction of air products using air separation plants which are set up for internal compression and to make them simpler and less expensive.

Disclosure of the invention

This object is achieved by a method and a plant for obtaining an air product with the respective features of the independent claims. Advantageous embodiments are the subject of the respective dependent claims and the description below.

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

As explained with reference to the below Figure 1 illustrated, turbo expanders, also known as "turbines" for short, can be used in typical air separation plants set up for internal compression for the refrigeration and liquefaction of material flows, as is known in principle to the person skilled in the art. In the following, we speak in particular of "Joule-Thomson turbines", "Claude turbines", "Lachmann turbines" and "pressure nitrogen turbines". In addition to the explanations below, reference is made to the specialist literature on the function and purpose of corresponding turbines, for example FG Kerry, Industrial Gas Handbook: Gas Separation and Purification, CRC Press, 2006, in particular sections 2.4, "Contemporary Liquefaction Cycles", 2.6, "Theoretical Analysis of the Claude Cycle" and 3.8.1, "The Lachmann Principle" , referred.

In a Joule-Thomson turbine, a high-pressure air stream is expanded in an air separation plant. This current is necessary for the evaporation and heating of internally compressed products. In most cases, this compressed air is noticeably supercooled before relaxation or cooled relatively deep in the supercritical state and after relaxation into the high pressure column of a double column system. The Joule-Thomson turbine thus takes on the role of an expansion valve, by means of which a so-called throttle flow is expanded into the high-pressure column in conventional systems.

In the case of a double-column system, a Claude turbine is used to release compressed air that has cooled down from a higher pressure level to the pressure level of the high-pressure column and feed it into it. By means of a Lachmann turbine, however, cooled compressed air is expanded to the pressure level of the low pressure column and fed into it. A Claude turbine is also referred to as a medium pressure turbine and a Lachmann turbine is also referred to as a low pressure turbine. Claude and Lachmann turbines are supplied with compressed air at higher temperature levels than Joule-Thomson turbines, so that no (significant) liquefaction occurs during expansion. The two turbines are also referred to as "gas turbines" in connection with air separation plants. Finally, nitrogen or a nitrogen-rich fluid is released from the high-pressure column by means of a pressure nitrogen turbine.

Typically, a Joule-Thomson turbine is used in conjunction with either a Claude turbine or a Lachmann turbine in air separation plants designed for internal compression. Even without a Joule-Thomson turbine, only a Claude or a Lachmann turbine can be used. In all cases, the use of appropriate turbines serves to compensate for exergy losses and heat leaks. The use of a Joule-Thomson turbine together with either a Claude turbine or a Lachmann turbine has energetic advantages, but obviously leads to significantly higher investment costs compared to an arrangement in which only a Claude turbine or a Lachmann turbine is used .

The air liquefaction process proposed by F. Linde at the beginning of the 20th century does not require any turbines and only uses the Joule-Thomson effect. However, there is no internal compression here and the process requires pressures of over 100 bar. Details are given in Kerry (see above), Section 2.5, "Linde Cycle (Free Expansion through a Valve)".

The other devices used in an air separation plant are described in the technical literature cited, for example from Haering (see above) in Section 2.2.5.6, "Apparatus". If the following definitions do not deviate from this, express reference is made to the cited technical literature for the language used in the context of the present application.

Liquids and gases can be rich or poor in one or more components in the language used here, "rich" for a content of at least 90%, 95%, 99%, 99.5%, 99.9% or 99.99 % and "poor" may represent 10%, 5%, 1%, 0.1% or 0.01% on a mole, weight or volume basis. The term "predominantly" can correspond to the definition of "rich". Liquids and gases can be enriched or depleted in one or more components, these terms refer to a content in a starting liquid or gas from which the liquid or gas in question was obtained. The liquid or gas is "enriched" if it contains at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times 100 times or 1,000 times the content, and " depleted "if this or this contains at most 0.9 times, 0.5 times, 0.1 times, 0.01 times or 0.001 times the content of a corresponding component, based on the starting liquid or the starting gas. If, for example, "oxygen" or "nitrogen" is used here, this should also be understood to mean a liquid or a gas which is rich in oxygen or nitrogen, but does not necessarily have to consist exclusively of it.

The present application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, which is intended to express that pressures and temperatures in a corresponding system do not have to be used in the form of exact pressure or temperature values in order to to realize inventive concept. However, such pressures and temperatures are typically in certain ranges, for example ± 1%, 5%, 10% or 20% around an average. Corresponding pressure levels and temperature levels can lie in disjoint areas or in areas that overlap one another. In particular, pressure levels include, for example, unavoidable or expected pressure drops. Corresponding applies to temperature levels. The pressure levels given here in bar are absolute pressures.

Advantages of the invention

Turbines contribute significantly to the construction costs of an air separation plant. Therefore, the number of turbines should be as low as possible from a manufacturing cost perspective. However, due to the energy savings that can be achieved, turbines reduce the operating costs of a corresponding system, so that there is a conflict of objectives. This is solved by the measures proposed according to the invention. The use of the present invention makes it possible to reduce the number of turbines without significantly negatively influencing the energy consumption of a corresponding system in this way.

The design of corresponding processes is traditionally limited by the required outlet conditions at the turbines: The required minimum gas or steam content at the outlet of a Claude turbine or a Lachmann turbine is typically at least 90% (there is therefore a maximum of 10% liquid content) . Joule-Thomson turbines specifically designed as liquid turbines, on the other hand, are typically operated without any gas or steam at the outlet, i.e. they are completely liquefied.

An essential aspect of the present invention is to use the Joule-Thomson turbine as the only turbine in a corresponding process, but to use it to expand into the two-phase area. In this way, the present invention achieves the advantages already mentioned. The present invention is particularly suitable for applications with a comparatively low cooling requirement, that is to say those processes in which comparatively small quantities of liquid products are provided and in which comparatively low internal compression pressures are present. Furthermore, the present invention can be used in particular when forced rectification conditions are used, for example when comparatively large amounts of nitrogen-rich fluids are withdrawn from the high-pressure column.

Corresponding "forced rectification conditions" exist in the language used here in particular when a so-called blowing equivalent is more than 10 or more than 15%. The blowing-in equivalent denotes the amount (in particular in mole fractions) of the air fed into the low-pressure column plus the nitrogen removed from the high-pressure column and discharged from the air separation unit, in relation to the total air supplied to the distillation column system.

The blowing-in equivalent is therefore defined as the amount of compressed air compressed and expanded into the low-pressure column of an air separation plant by means of a blowing turbine, plus the amount of nitrogen that may have been taken from the high-pressure column and neither returned to the high-pressure column itself as a liquid return, nor as a liquid return to the low-pressure column is given, based on the total compressed air fed into the distillation column system. It goes without saying that either the amount of compressed air expanded into the low-pressure column of an air separation plant or the amount of nitrogen that is taken from the high-pressure column and neither returned to the high-pressure column itself as a liquid return nor fed to the low-pressure column as a liquid return is also zero in each case can. The nitrogen withdrawn from the high pressure column may be pure or substantially pure nitrogen from the top of the high pressure column, but may also be a nitrogen enriched gas or liquid which is withdrawn from the area below the head from the high pressure column with a lower nitrogen content can be.

If a blowing-in turbine is used in a corresponding air separation plant and a quantity M1 of compressed air is expanded in this, a quantity M2 nitrogen is removed from the high-pressure column and removed as a liquid and / or gaseous nitrogen product from the air separation plant, i.e. not used as a return to the high and / or low pressure column, and a quantity M3 of compressed air supplied to the distillation column system as a whole, the blowing-in equivalent E in a corresponding system results in E = (M1 + M2) / M3. Basically, increasing the blowing-in equivalent in an air separation plant enables a reduction in energy consumption.

The present invention proposes a method for obtaining an air product using an air separation plant with a rectification column system, which comprises a high pressure column which is operated at a first pressure level, and has a low pressure column which is operated at a second pressure level below the first pressure level. The rectification column system can be designed in a basically known manner, in particular as a double column, or can comprise a corresponding double column. The high and low pressure columns are connected via a main condenser, the top gas of the high pressure column is partially liquefied so that it can be returned to the high pressure column as a return line, and the bottom liquid of the low pressure column evaporates. The main capacitor can be designed as an internal or external main capacitor. Other configurations of the rectification column system are also possible in principle. In particular, the rectification column system can have further rectification columns, in particular for the production of argon. For details, reference is made to the cited specialist literature.

In the method according to the invention, a first stream of compressed air at a first pressure level and a second stream of compressed air at a third pressure level which is above the first pressure level are provided and are each cooled to the first and third pressure levels. The usable pressure levels are explained in detail below. The cooling can be carried out in particular in a main heat exchanger of the air separation plant, to which the first and second compressed air streams are supplied on the warm side and removed on the cold side. The cooling takes place in particular at different temperature levels and in different passages of the main heat exchanger. Here too, details are given below. In particular, the first compressed air flow at the first pressure level can be subjected to cooling to a lower pressure level than the second compressed air flow at the third pressure level. The first and the second compressed air stream are compressed in particular by means of a main air compressor on the one hand or by means of the main air compressor and a secondary compressor on the other hand, as also explained in detail below. The first and the second compressed air stream consist of purified compressed air, which has been dried in a known manner and in particular has been freed from carbon dioxide and possibly other impurities.

In the context of the present invention, the first compressed air stream is fed into the rectification column system. The feed is particularly in the high pressure column. The second stream of compressed air is used using a Expansion turbine relaxed to the first pressure level and fed into the rectification column system.

If there is talk here of a material flow, for example a compressed air flow, being subjected to certain process steps, this does not rule out that this material flow can also be subjected to part of these process steps as part of a material flow with a larger volume or volume flow. The material flow mentioned in each case can be branched off at any point from the material flow with the larger volume or quantity flow or can be combined at any point with a further material flow to form the material flow with the larger volume or quantity flow. It is also possible, for example, that a material flow with a larger volume or volume flow is first divided to form the material flow mentioned and the material flow mentioned is then combined again with further material flows to form a material flow with a larger volume or volume flow. In other words, at least one further material flow can be subjected to part of the specified process steps together with the material flow mentioned in each case.

Thus, as mentioned, the first compressed air flow is fed into the rectification column system, which does not exclude that this first compressed air flow is initially part of a compressed air flow provided at the first pressure level with a larger volume or volume flow, of which the first compressed air flow before or after cooling is branched off. As mentioned further, the first compressed air flow is fed in particular into the high-pressure column, but this does not rule out that further compressed air at the first pressure level is also fed into the low-pressure column, even after a corresponding cooling. As mentioned, the second compressed air stream is expanded to the first pressure level using an expansion turbine and fed into the rectification column system. This in turn does not preclude further compressed air from being treated in a similar manner and fed into the rectification column system.

As also explained below, in particular a part of the second compressed air flow can be relaxed by means of the expansion turbine and another part by means of an expansion valve. This should be covered by the statement that the second compressed air stream "using" an expansion turbine is relaxed, since this formulation does not indicate that the relaxation takes place using only the relaxation machine. In particular, however, the entire second compressed air stream is expanded to the second pressure level by means of an expansion turbine. However, this does not rule out that parts of it can then be further relaxed. In particular, the entire second compressed air stream can be fed into the rectification column system, in particular completely into the high-pressure column, but also partly into the high-pressure column and partly, after further relaxation, into the low-pressure column, previously also in particular in the high-pressure column Phase separation can take place and a liquid phase that is formed immediately, ie in particular in unchanged material composition as in the two-phase mixture of the second compressed air stream or after mixing with the liquid flowing down in the high-pressure column at the same point in the high-pressure column, again drawn off, supercooled and into the low-pressure column can be relaxed. This can already be the case in the prior art, as is shown, for example, in Figure 1 is illustrated, even if this is in Figure 1 is not explicitly shown. The expansion turbine, which is used in the context of the present invention for expanding the second compressed air stream, can in particular be coupled or braked to a generator in order to be able to obtain electrical current in this way. However, it goes without saying that, within the scope of the present invention, other options for braking a corresponding expansion turbine, for example oil brakes, can in principle also be used.

As already mentioned, the present invention is particularly suitable for use in processes by means of which internally compressed air products are provided. The present invention therefore encompasses that a liquid stream of material from the rectification column system (the high-pressure column, the low-pressure column or a possibly existing crude or crude and pure argon column) is carried out, then increased in pressure in the liquid state, converted to the gaseous or supercritical state by heating, and as the air product is discharged from the air separation plant. Here, too, it goes without saying that the liquid material flow can initially be part of a liquid material flow with a larger volume or volume flow, for example. In this way, so-called internally compressed oxygen, internally compressed nitrogen or internally compressed argon can be provided. As mentioned, a corresponding air separation plant can in particular also have units for known types of argon. Provision of internally compressed air products of the same composition but different pressures is also fundamentally possible within the scope of the present invention, for example by pressurizing them to different extents. The conversion into the gaseous or supercritical state takes place in particular in the main heat exchanger of the air separation plant in countercurrent to a stream of material to be cooled, in particular the first and / or second air pressure stream. If, after the pressure increase, the liquid flow (s) is at a supercritical pressure level, there is no evaporation in the classical sense when heated accordingly, but instead it is converted to the supercritical state, ie a "pseudo evaporation".

In the context of the present invention, it was recognized as particularly advantageous if the expansion of the second compressed air stream or a corresponding portion thereof is carried out using the expansion turbine in such a way that a two-phase mixture with the gas portion mentioned below forms at the outlet thereof. The expansion turbine, the second compressed air stream or its relaxed portion here is supplied in particular in a purely liquid or supercritical state. The two-phase mixture formed comprises a liquid phase and a gaseous phase. In principle, these phases can be separated from one another, for example after a settling in a separator. In the context of the present invention, the expansion turbine mentioned, which is otherwise basically comparable to a known so-called liquid turbine, as can be used for expanding a throttle flow in a conventional system, is therefore not operated with complete liquefaction of the expanded fluid, but only with partial liquefaction of the fluid. Such operation was recognized as particularly advantageous in the context of the present invention. In other words, the expansion of a choke current into the two-phase region is provided in the context of the present invention, whereas in conventional systems a corresponding expansion takes place with complete liquefaction.

In particular, in the context of the present invention, the expansion turbine, which is used for expanding the second compressed air stream or its portion, is the only expansion turbine used in an appropriate air separation plant. In other words, no other expansion turbine is advantageously used in addition to the expansion turbine in the context of the present invention. In particular, in the context of the invention, however, no classic "gas turbines" are used as expansion turbines, so advantageously no expansion turbines are used which are operated in such a way that a pure gas phase or a two-phase mixture with a gas fraction of more than 80% is present at their outlet. By dispensing with corresponding additional turbines, an air separation plant designed according to the invention can be constructed and operated particularly cost-effectively.

The percentage given with regard to the gas fraction is expressed here and below in particular in standard volume or mass fractions and relates to the total flow (which comprises the gas fraction and the liquid fraction). A corresponding percentage is calculated, for example, from the quotient of gas flow and total flow (each in standard cubic meters per hour) multiplied by 100%.

In the context of the present invention, it was recognized as particularly advantageous to operate the expansion turbine in such a way that the two-phase mixture at the outlet of the expansion turbine has a gas fraction of 5 to 25%, in the above sense based on the entire two-phase mixture, in particular 10 to 20%. This is therefore provided according to the invention. The operation of a corresponding expansion turbine, which relaxes in the two-phase region in the context of the present invention, requires a certain (extremely low) temperature at the turbine inlet. This can only be achieved by means of the Joule-Thomson effect during slow cooling of the system with reduced air flow and without the internal compression pumps being operated.

Within the scope of the present invention, a corresponding plant without gas turbines can nevertheless be operated using comparatively moderate pressures, for example a maximum of 80 bar, whereas the classic Linde air separation plants from the beginning of the 20th century had to be operated at pressures of significantly more than 100 bar. Please refer to the explanations above for details. In particular, a method or a corresponding system can be created within the scope of the present invention, which or the significantly lower investment costs with comparable energy requirements. This is especially true when compared to a system with two turbines, namely a gas turbine (Claude or Lachmann turbine) in combination with a Joule-Thomson turbine that replaces the classic Joule-Thomson valve. In comparison with a conventional configuration with only one gas turbine and one Joule-Thomson valve (ie without a Joule-Thomson turbine), there are even significant energy savings within the scope of the present invention.

As also mentioned above, the method proposed according to the invention is particularly suitable for cases in which comparatively small amounts of liquid air products are provided. Thus, a method according to a particularly preferred embodiment of the invention comprises either no liquid air products or liquid air products in an amount of not more than 1 mole percent, in particular not more than 0.5 mole percent, of the total air supplied to the rectification column system from the air separation plant . Such a comparatively low level of liquid production means that comparatively small amounts of cold are "withdrawn" from the air system in question by these air products, and therefore the process or the system manages with relatively small amounts of additionally produced cold.

In the context of the present application, an “air product that is discharged from an air separation plant” is understood to mean a fluid that no longer participates in internal circuits, but rather leaves the plant completely. In particular, such a fluid is no longer, even partially, fed into the rectification column system.

If there is talk here of the fact that no liquid air products are discharged in a corresponding system, this does not exclude the fact that small amounts of substance can be discharged from certain apparatus or areas of the system, in particular temporarily, for example in order to prevent the accumulation of undesired components , for example the accumulation of methane in a sump of the low pressure column. However, the amount of appropriately designed material flows is clearly below the mentioned or 0.5 mol percent of the total air supplied to the rectification column system.

Furthermore, the present invention is particularly suitable for processes in which internally compressed air products are provided at comparatively moderate pressure levels. A particularly advantageous embodiment of the present invention therefore includes that the air product which is provided in the internal compression method explained is discharged from the air separation plant at a pressure level of not more than 50 bar, in particular not more than 40 or not more than 30 bar.

The present invention is used in particular in so-called main compressor-post-compressor processes, as have also been explained above. In such a method, the first compressed air flow is compressed to the first pressure level by means of a first compression device, or the air is provided at this first pressure level from the outside of the air separation system, for example by means of a so-called air rail at the installation site. The second compressed air stream is first brought to the first pressure level by means of the first compression device or likewise made available externally at the first pressure level and then further compressed to the third pressure level by means of a second compression device. In the context of the present invention, the first and the second compression device, if present, can in particular be separate compressors in the form of a main air compressor and a post-compressor.

However, the main air compressor and the post-compressor or the first compression device and the second compression device can also be integrated together in one machine. In particular, a multi-stage compressor can be used within the scope of the present invention, from which the first compressed air flow at an intermediate pressure level and the second compressed air flow at an end pressure level can be taken. In this case, the first compression device is part of the compression stages of the common machine, and the second compression device is a further part of the compression stages of this machine. The compressor stages can in particular be driven in synchronism with speed or at different speeds using a common drive. In principle, however, any combination of compression devices or compressors is possible within the scope of the present invention, by means of which a corresponding compression can be carried out. A temperature level to which the second compressed air stream is cooled is advantageously within the scope of the present invention at the outlet from the main heat exchanger at -150 to -180 ° C. This temperature level is advantageously in particular from −155 to −170 ° C. The second compressed air stream is cooled to a temperature level below the condensing temperature at a corresponding pressure level or to a temperature level significantly below the critical temperature for supercritical pressures. The first compressed air stream is cooled in particular near the liquefaction temperature of air at the first pressure level, but at a certain distance, for example from 0.5 to 10 K above it. In other words, due to its higher pressure, the second compressed air stream already experiences a liquefaction or a temperature drop significantly below the critical point, whereas the first compressed air stream remains in the gaseous state. The first compressed air flow at the first pressure level is cooled in particular more deeply than the second compressed air flow at the third pressure level.

In the context of the present invention, the first pressure level is in particular 5 to 7 bar absolute pressure. The second pressure level can be in particular 1.1 to 2 bar absolute pressure. The third pressure level can be, for example, approximately 50 to 90 bar absolute pressure, in particular approximately 80 bar absolute pressure. The first and second pressure levels are typical pressure levels as they exist in the high and low pressure columns of known double column systems of air separation plants; the third pressure level corresponds to a typically used post-compressor pressure in a corresponding system.

In the context of the present invention, in particular a part of the second compressed air stream which has been expanded to the first pressure level using the expansion turbine is fed into the low-pressure column. In particular, it can be provided that the two-phase mixture that forms at the outlet of the expansion turbine, which is used in the at least partial expansion of the second compressed air flow to the first pressure level, is partially or completely fed into the high-pressure column and a liquid fraction is separated from it in the high-pressure column and that the liquid fraction is partially or completely passed through a countercooling countercurrent, expanded to the second pressure level, and fed into the low pressure column.

According to a particularly preferred embodiment of the present invention, the second compressed air stream is expanded to the first pressure level partly using the expansion turbine and partly using an expansion valve. The respective relaxation of different proportions of the first pressure level in corresponding expansion devices arranged in parallel can in particular also take place in different, variable proportions as required.

With particular advantage in the context of the present invention, the first and the second compressed air stream are completely fed into the rectification column system of the air separation plant and, in addition to the first and second compressed air stream, no further air is conducted into the rectification column system. This also underlines that in the context of the present invention, apart from the expansion turbine, which is used to expand the first compressed air stream, no further expansion turbines, in particular none of the gas turbines mentioned, are used.

With particular advantage, the first compressed air stream in the context of the present invention can comprise 60 to 80 mole percent and the second compressed air stream can comprise the rest of the total air fed into the rectification column system.

The present invention also extends to an air separation plant for obtaining an air product, comprising a rectification column system comprising a high pressure column configured to operate at a first pressure level and a low pressure column configured to operate at a second pressure level below the first pressure level is. For the features of a corresponding air separation plant, reference is expressly made to the corresponding independent patent claim.

Regarding the advantages of a corresponding air separation plant and configurations according to the invention, the above explanations regarding the method according to the invention and its different advantageous configurations are express referred. An air separation plant provided according to the invention is in particular set up to carry out corresponding methods and has specifically designed means for this in each case.

The invention is explained in more detail below with reference to the accompanying drawings, which show an air separation plant according to an embodiment of the invention compared to an air separation plant not according to the invention.

• Figur 1 zeigt eine Luftzerlegungsanlage gemäß einer nicht erfindungsgemäßen Ausgestaltung in Form eines vereinfachten Prozessflussdiagramms.
• Figur 2 zeigt eine Luftzerlegungsanlage gemäß einer Ausführungsform der Erfindung in Form eines vereinfachten Prozessflussdiagramms.

Brief description of the drawings

• Figure 1 shows an air separation plant according to an embodiment not in accordance with the invention in the form of a simplified process flow diagram.
• Figure 2 shows an air separation plant according to an embodiment of the invention in the form of a simplified process flow diagram.

Detailed description of the drawings

In the figures, elements that correspond to one another structurally or functionally are given identical reference numerals and are not repeated for the sake of clarity. Air separation plants are illustrated using the figures. However, the corresponding explanations relate to corresponding methods in the same way, so that if components of corresponding systems are described below, the respective explanations apply to the method steps carried out by these components. In the figures, liquid material flows are illustrated by means of filled (black) and gaseous material flows by means of unfilled (white) flow arrows.

In Figure 1 an air separation plant according to an embodiment not according to the invention is illustrated and designated by 200 in total. In the air separation plant 200, a compressed air flow a is provided and divided into two partial flows b and c.

After dividing the partial flow b into partial flows d and e, these are fed to a main heat exchanger 3 of the air separation plant 200 on the warm side. The Partial stream d is taken from the main heat exchanger 3 at an intermediate temperature level, expanded in a expansion turbine 210, which can in particular be mechanically coupled to a generator or an oil brake, and into a low-pressure column 12 of a rectification column system 10, which also has a high-pressure column and a high-pressure column 11 and Low pressure column 12 has heat-exchanging connecting main capacitor 13, fed. The expansion turbine 210 is therefore a typical Lachmann turbine, for which reference is made to the introductory explanations.

The partial stream e is led to the cold end through the main heat exchanger of the air separation plant 200 and then fed into a lower region of the high-pressure column 11. The partial flow c is subjected to a post-compression in a post-compressor 4, which is followed by an after-cooler (not designated separately). Sub-stream c is then divided into further sub-streams f and g, which are each fed to the main heat exchanger 3 on the warm side.

The partial flow f is led to the cold end through the main heat exchanger 3 and expanded by means of an expansion turbine 5 or an expansion valve 6. The expansion turbine 5 is a so-called Joule-Thomson expansion turbine, for which reference is also made to the above explanations. As a classic Joule-Thomson expansion turbine, expansion is carried out in this, in which the fluid at the outlet is in the completely or almost completely liquid state. The stream f released in the expansion turbine 5 and in the expansion valve 6 is likewise fed into the high-pressure column 11. The partial flow f is a typical choke current.

The partial stream g is taken from the main heat exchanger 3 at an intermediate temperature level, which, however, in the example shown is below the intermediate temperature level at which the material stream d is taken from the main heat exchanger, and is expanded in an expansion turbine 220. The expansion turbine 220 is a classic Claude expansion turbine and is operated in the illustrated conventional air separation plant 200 with little or no liquid at the turbine outlet. The stream of matter g is after its relaxation in the Expansion turbine 220 combined with the stream e and fed into the lower region of the high pressure column 11.

A material flow h is removed from the bottom of the high-pressure column 11, passed through a supercooling counterflow 8, and expanded into the low-pressure column 12. Nitrogen-rich head gas in the form of a stream i is drawn off from the top of the high-pressure column 11, which is partly passed through the main condenser 11 in the form of a stream k and is at least partially liquefied in the process. Again a part of it is fed back in the form of a material flow I to the high pressure column 11, a further part is led in the form of a material flow m through the supercooling countercurrent 8 and fed in at the top of the low pressure column 12 as a return.

A portion of the stream i, which is not liquefied in the main condenser 11, here designated n, is heated and evaporated in the main heat exchanger 3 and is carried out as compressed nitrogen (PGAN) from the air separation plant 200. An oxygen-rich liquid in the form of a stream o is drawn off from the bottom of the low-pressure column 12, the pressure is raised by means of a pump 9, and is heated in the main heat exchanger 3 and thereby converted into the gaseous or supercritical state. In this way, an internally compressed compressed oxygen product (PGOX) can be provided. A gaseous stream p is discharged from an intermediate region of the low-pressure column 12, passed through the supercooling counterflow 8 and heated in the main heat exchanger 3. This is so-called impure nitrogen (UN2), which can be used for different purposes in the air separation plant 200.

A liquid retention device in the head region of the low-pressure column 12 separates out nitrogen-rich liquid, which can be drawn off in the form of a material flow r and made available as a liquid nitrogen product (LIN). A gaseous fluid drawn off from the top of the high-pressure column 12 can be conducted in the form of a material flow s through the supercooling countercurrent and through the main heat exchanger 3, heated, and provided as a low-pressure nitrogen product (LPGAN).

As already explained, the operation of a corresponding system, which in conventional configurations as illustrated in FIG. typically comprise at least two expansion turbines, as complex and in particular the creation is associated with high investment costs.

In Figure 2 is an air separation plant according to an embodiment of the invention schematically illustrated and generally designated 100. Already in Figure 1 Components illustrated and present here for a comparable purpose are in Figure 2 indicated with identical reference numerals and are only partially explained again for the sake of clarity.

As in Figure 2 illustrated, ambient air (A) is drawn in here by means of a main air compressor 1 via a filter 2 and compressed to a pressure level, which is referred to here as the "first" pressure level. After one or more processing steps 20, which may in particular include cooling and purification, the correspondingly compressed compressed air, which is here as in FIG Figure 1 is illustrated in the form of a stream a, divided into partial streams b and c, the first partial stream b being referred to here consistently as the "first" compressed air stream and the partial stream c being referred to throughout as the "second" compressed air stream.

In contrast to the air separation plant 200 according to Figure 2 the first compressed air flow b is passed through the main heat exchanger 3 without further division into two partial flows. The same applies to the partial flow c, which is also compressed here in the post-compressor 4, to a pressure level referred to here as "third" pressure level of, for example, approximately 80 bar. This second compressed air stream c is also led from the warm end to the cold end through the main heat exchanger 3. The first compressed air flow b and the second compressed air flow c are thus cooled in the main heat exchanger 3 in separate passages, as explained above.

In the example shown, the first compressed air stream b is fed into the lower region of the high-pressure column 11 of the rectification column system 10, the second compressed air stream c is expanded to the first pressure level using the expansion turbine 5 and the expansion valve 6. The relaxed compressed air flow c, here denoted by t, is fed here into the high-pressure column 11 as a two-phase mixture which forms at the outlet of the at least one expansion turbine 5. In the high-pressure column 11, this becomes a suitable one Liquid retention device separated a liquid fraction. This liquid fraction, referred to here as u, is at least partially withdrawn from the high-pressure column 11, passed through the supercooling counterflow 3 and expanded into the low-pressure column 12 of the rectification column system 10.

Operation of the in Figure 2 Air separation plant 100 illustrated otherwise corresponds to the operation of FIG Figure 1 Air separation plant 100 illustrated. However, no further expansion turbines 210 and 220 are used, and expansion takes place in the expansion turbine 5 in such a way that a considerable proportion of gas is present at the outlet of the expansion turbine. In the air separation plant 100 according to Figure 2 In particular, low-oxygen nitrogen can be drawn off at a pressure level of 5 to 6 bar in the form of stream i and partially made available as a product.

In the air separation plant 100 according to Figure 2 the pump 9 of the material flow o is increased in particular to a pressure level of 20 to 40 bar, for example approx. 30 bar. From the top of the low pressure column 12, impure nitrogen (UN2) is drawn off in the form of a material flow, the low pressure column 12 is thereby forced to operate.

Claims (14)

Method for extracting an air product using an air separation plant (100) with a rectification column system (10) which has a high pressure column (11) which is operated at a first pressure level and a low pressure column (12) which is at a second pressure level below the first pressure level is operated, wherein a first compressed air flow at the first pressure level and a second compressed air flow at a third pressure level above the first pressure level are provided and subjected to cooling, - The first compressed air stream is fed into the rectification column system (11) and the second compressed air stream is expanded to the first pressure level and fed into the rectification column system (11) using a decompression turbine (5), and a liquid stream of material from the rectification column system (10) is carried out, the pressure is increased in the liquid state, it is converted into the gaseous or supercritical state and the air product is discharged from the air separation plant (100), characterized in that - The expansion turbine (5), which is used in the expansion of the second compressed air flow to the first pressure level, is operated such that a two-phase mixture is formed at the outlet, which has a gas content of 5 to 25% at the outlet, based on the entire two-phase mixture , having. Method according to Claim 1, in which no further expansion turbines are used in addition to the expansion turbine (5), which is used when the second compressed air flow is expanded to the first pressure level. Method according to one of the preceding claims, in which no expansion turbines are used which are operated in such a way that at their outlet there is a pure gas phase or a two-phase mixture with a gas fraction of more than 80%. Method according to one of the preceding claims, in which no liquid air products or liquid air products in an amount of not more than 1 mole percent of the total air supplied to the rectification column system (10) are discharged from the air separation plant (100). Method according to one of the preceding claims, in which the air product is discharged from the air separation plant (100) at a pressure level of not more than 50 bar. Method according to one of the preceding claims, in which the first compressed air flow is compressed to the first pressure level by means of a first compression device (1) or is provided externally at the first pressure level, and in which the second compressed air flow is first applied to the by means of the first compression device (1) is brought to the first pressure level or is likewise provided externally at the first pressure level and is then further compressed to the third pressure level by means of a second compression device (4). Method according to one of the preceding claims, in which a temperature level to which the first compressed air stream is cooled is from -150 to -180 ° C. Method according to one of the preceding claims, in which the first pressure level is 5 to 7 bar and the second pressure level is 1.1 to 2 bar and the third pressure level is 50 to 90 bar. Method according to one of the preceding claims, in which a part of the first compressed air stream expanded to the first pressure level in the expansion turbine (5) is fed into the low-pressure column (12). Method according to one of Claims 1 to 8, in which the two-phase mixture which forms at the outlet of the expansion turbine (5), which is used when the second compressed air stream is expanded to the first pressure level, is partly or completely fed into the high-pressure column (11) , a liquid fraction is separated therefrom in the high-pressure column (11), and the liquid fraction is partially or completely passed through a subcooling countercurrent (8), expanded to the second pressure level and fed into the low-pressure column (12). Method according to one of the preceding claims, in which the second compressed air stream is expanded to the first pressure level partly using the expansion turbine (5) and partly using an expansion valve (6). Method according to one of the preceding claims, in which the first and the second compressed air stream are completely fed into the rectification column system (10) and in addition to the first and the second compressed air stream no further air is fed into the rectification column system (10). The method of claim 12, wherein the first stream of compressed air comprises 60 to 80 mole percent and the second stream of compressed air comprises the remainder of the total air fed into the rectification column system (10). Air separation plant (100) for extracting an air product, with a rectification column system (10) which has a high pressure column (11) which is set up for operation at a first pressure level and a low pressure column (12) which is set up for operation at a second pressure level below of the first pressure level is established, wherein Means are provided which are set up to provide a first compressed air flow at the first pressure level and a second compressed air flow at a third pressure level above the first pressure level and to subject them to cooling, - Means are provided which are set up to feed the first compressed air stream into the rectification column system (11) and to relax the second compressed air stream using at least one expansion turbine (5) to the first pressure level and to feed into the rectification column system (11), and Means are provided which are set up to carry out a liquid stream from the rectification column system (10), to increase the pressure in the liquid state, to convert it to the gaseous or supercritical state and to discharge it as the air product from the air separation plant (100), characterized in that - The air separation plant (100) is set up to operate the expansion turbine (5), which is used in the expansion of the second compressed air flow to the first pressure level, in such a way that a two-phase mixture forms at its outlet, which has a gas fraction of 5 at the outlet up to 25%, based on the total two-phase mixture.

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