EP2980514A1 - Method for the low-temperature decomposition of air and air separation plant - Google Patents

Abstract

It is a method for the cryogenic separation of air (AIR) in an air separation plant (100) with a main air compressor (2), a main heat exchanger (4) and a distillation column system (10) operated at a first pressure level low pressure column (11) and one on a proposed second pressure level operated high-pressure column (12), in which a feed air stream (a), the total, the air separation plant (100, 200) supplied feed air, in the main air compressor (2) is compressed to a third pressure level, which is at least 2 bar above of the second pressure level, wherein of the compressed feed air stream (b) a first portion (c) is cooled at least once in the main heat exchanger (4) and relaxed by the third pressure level in a first expansion turbine (5), a second portion (d) at least Once cooled in the main heat exchanger (4) and starting from the third pressure level in a second expansion is cooled and a third portion (e) is further compressed to a fourth pressure level, cooled at least once in the main heat exchanger (4) and expanded from the fourth pressure level, wherein air of the first portion (c) and / or of the second portion (d) and / or the third portion (e) at the first and / or at the second pressure level in the distillation column system (10) is fed. It is envisaged that the third portion (e) is further compressed successively in a booster (7), a first turbine booster and a second turbine booster to the fourth pressure level, and a Dichtfluidexpander (8) is used to relax the third portion (e) to which the third portion (e) is supplied in the liquid state and at the fourth pressure level. An air separation plant (100) is also the subject of the invention.

Description

The invention relates to a method for the cryogenic separation of air in an air separation plant and a corresponding air separation plant according to the preambles of the independent claims.

State of the art

The production of air products in the liquid or gaseous state by cryogenic separation of air in air separation plants is known and in the literature, for example in H.-W. Haring (ed.), Industrial Gas Processing, Wiley-VCH 2006 , in particular Section 2.2.5, "Cryogenic Rectification" described. Air separation plants have distillation column systems which can be designed, for example, as two-column systems, in particular as classic Linde double-column systems, but also as three-column or multi-column systems. In addition to the distillation columns for the recovery of nitrogen and / or oxygen in the liquid and / or gaseous state (for example, liquid oxygen, LOX, gaseous oxygen, GOX, liquid nitrogen, LIN and / or gaseous nitrogen, GAN), so the distillation columns for nitrogen-oxygen Separation, distillation columns can be provided for obtaining further air components, in particular the noble gases krypton, xenon and / or argon.

The distillation column systems are operated at different operating pressures in their respective distillation columns. Known double column systems have, for example, a so-called high-pressure column (sometimes also referred to merely as a pressure column) and a so-called low-pressure column. The operating pressure of the high-pressure column is, for example, 4.3 to 6.9 bar, preferably about 5.0 bar. The low-pressure column is operated at an operating pressure of, for example, 1.3 to 1.7 bar, preferably about 1.5 bar. The pressures given here and below are absolute pressures.

In air separation, so-called high-air pressure (HAP) processes can be used. In a HAP process, the entire, the Air separation plant supplied or used in a corresponding process total air (referred to as feed air) compressed in a main air compressor to a pressure which is well above the highest operating pressure of the distillation column system, typically well above the operating pressure of the high pressure column. The pressure difference is at least 2 or 4 bar and preferably between 6 and 16 bar. For example, the pressure is at least twice as high as the operating pressure of the high-pressure column. HAP processes are eg from the EP 2 466 236 A1 , of the EP 2 458 311 A1 and the US 5,329,776 A known.

With HAP processes, the increased compaction can reduce the container and pipe dimensions required for air purification. Furthermore, the absolute water content of the compressed air decreases. Depending on the existing boundary conditions can be dispensed with a refrigeration system for air purification.

In HAP processes, the compressed air quantity in the main air compressor can also be decoupled from the process air quantity. In such a case, only a portion of the compressed to the said pressure feed air is used as so-called process air, so used for the actual rectification and fed into the high-pressure column. Another part is relaxed to recover cold, whereby the amount of cold can be adjusted independently of the process air. However, such decoupling is not provided in all HAP methods.

Further, methods are known in which the feed air in the main air compressor only to the highest operating pressure of the distillation column system, typically only the operating pressure of the high pressure column or slightly above, is compressed. A portion of the feed air can therefore be fed after cooling without further relaxation in the distillation column system. Only certain proportions, which are required, for example, for additional cooling production or also for heating liquid streams (see below), are further compressed in one or more secondary compressors. Such methods with main and Nachverdichter (s) are also referred to as MAC / BAC (Main Air Compressor / Booster Air Compressor). In a MAC / BAC process, therefore, not all of the feed air, but only a part is compressed to a pressure well above the highest operating pressure of the distillation column system.

In air separation, the so-called internal compression can be used. In the internal compression, a liquid stream is taken from the distillation column system and at least partially brought to liquid pressure. The liquid brought to pressure is heated in a main heat exchanger of the air separation plant against a heat transfer medium and evaporated or, in the presence of appropriate pressures, transferred from the liquid to the supercritical state. The liquid stream may in particular be liquid oxygen, but also nitrogen or argon. The internal compression is thus used to obtain appropriate gaseous printed products. Amongst other things, the advantage of internal compression processes is that corresponding fluids do not have to be compressed outside the air separation plant in a gaseous state, which often proves to be very complicated and / or requires considerable safety measures. The internal compression is described in the literature cited above.

Subsequently, the collective term "liquefaction" is used for the transfer from the liquid to the supercritical or gaseous state. The transition from the supercritical or gaseous to the liquid state, whose product is a clearly defined liquid, is referred to as "liquefaction".

Against the stream to be liquefied, a heat transfer fluid is liquefied. The heat carrier is usually formed by a part of the air separation plant supplied air. In order to efficiently heat and liquefy the stream brought to liquid pressure, this heat transfer medium must have a higher pressure than the liquid that is being pressurized due to thermodynamic conditions. Therefore, a correspondingly high-density power must be provided. This is also referred to as "throttle flow" because it is conventionally expanded by means of a flash valve ("throttle"), thereby at least partially liquefied and fed into the distillation column system used.

The production of internally compressed, gaseous oxygen by means of the HAP process is comparatively cost-effective and can be implemented in different embodiments, in particular due to the omission of a secondary compressor for providing a correspondingly highly compressed stream. In certain cases, however, MAC / BAC methods may prove to be more energetically favorable, which is particularly the case the use of a turbine (instead of the conventional expansion valve) is due to which the inductor flow is supplied in the liquid state at supercritical pressure and taken in a further liquid state at subcritical pressure. In the context of this application, such a turbine is referred to as a sealing fluid expander (Dense Liquid Expander or Dense Fluid Expander, DLE). The energetic advantages of such a sealing fluid expander are likewise described in the specialist literature cited at the beginning, for example Section 2.2.5.6, "Apparatus", pages 48 and 49.

The aim of the present invention is to combine the low investment costs associated with HAP processes with the efficiency advantages of conventional MAC / BAC processes.

Disclosure of the invention

Against this background, the present invention proposes a method for the cryogenic separation of feed air in an air separation plant and a corresponding air separation plant with the features of the independent claims. Preferred embodiments are the subject of the dependent claims and the following description.

Before explaining the features and advantages of the present invention, its principles and the terms used will be explained.

An "expansion turbine" or "expansion machine", which can be coupled via a common shaft with further expansion turbines or energy converters such as oil brakes, generators or compressors, is set up to relax a gaseous or at least partially liquid stream. In particular, expansion turbines may be designed for use in the present invention as a turboexpander. If a compressor is driven by one or more expansion turbines, but without externally, for example by means of an electric motor, supplied energy, the term "turbine-driven compressor" or alternatively "turbine booster" is used.

A "compressor" is a device designed to compress at least one gaseous stream from at least one inlet pressure at which it is fed to the compressor to at least one final pressure at which it is taken from the compressor. A compressor forms a structural unit, which, however, can have a plurality of "compressor stages" in the form of piston, screw and / or Schaufelrad- or turbine assemblies (ie axial or radial compressor stages). This also applies in particular to the "main (air) compressor" of an air separation plant, which is characterized by the fact that all or most of the amount of air fed into the air separation plant, ie the total feed air flow, is compressed by this. A "secondary compressor", in which a part of the air quantity compressed in the main air compressor is brought to an even higher pressure in the MAC / BAC process, is often also of multi-stage design. In particular, corresponding compressor stages are driven by means of a common drive, for example via a common shaft.

Conventionally, MAC / BAC processes use recompressors that are driven by externally supplied energy; in HAP processes, such recompressors are not. However, turbine boosters are typically present in both cases, in particular in order to be able to make sensible use of shaft power released during the expansion for cooling purposes.

A "heat exchanger" serves to indirectly transfer heat between at least two e.g. in countercurrent flow, such as a warm compressed air stream and one or more cold streams or a cryogenic liquid air product and one or more hot streams. A heat exchanger may be formed from a single or multiple heat exchanger sections connected in parallel and / or in series, e.g. from one or more plate heat exchanger blocks. A heat exchanger, for example, the "main heat exchanger" used in an air separation plant, which is characterized in that the main part of the streams to be cooled or heated to be cooled or heated by him, has "passages", which are as separate fluid channels with heat exchange surfaces are formed.

The present application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, thereby providing for the It should be stated that appropriate pressures and temperatures in a corresponding plant need not be used in the form of exact pressure or temperature values in order to realize the inventive concept. However, such pressures and temperatures typically range in certain ranges that are, for example, ± 1%, 5%, 10%, 20% or even 50% about an average. Corresponding pressure levels and temperature levels can be in disjoint areas or in areas that overlap one another. In particular, for example, pressure levels include unavoidable or expected pressure drops, for example, due to cooling effects. The same applies to temperature levels.

Advantages of the invention

The inventive method uses an air separation plant with a main air compressor, a main heat exchanger and a distillation column system with a operated at a first pressure level low pressure column and operated at a second pressure level high pressure column. The above and other used pressure levels are given below in detail.

In the method according to the invention, a feed air stream which comprises the entire feed air supplied to the air separation plant is compressed in the main air compressor to a third pressure level which is at least 2 bar, in particular at least 4 bar, above the second pressure level. The third pressure level may for example also be twice the second pressure level. Thus, a HAP method is performed.

From the compressed feed air stream, a first portion is cooled at least once in the main heat exchanger and expanded in a first expansion turbine, starting from the third pressure level. By "cooled at least once" is understood here and below that a corresponding current before and / or after the relaxation at least once at least through a section of the main heat exchanger is performed.

A second portion is treated similarly, ie also cooled at least once in the main heat exchanger and starting in a second expansion turbine relaxed from the third pressure level. The second part is the so-called turbine flow, its relaxation takes place in order to provide additional cooling in a corresponding system and to be able to regulate this.

A third portion is further compressed to a fourth pressure level and then also cooled at least once in the main heat exchanger and expanded from the fourth pressure level. The third portion is the so-called inductor flow, which, as explained above, in particular allows internal compression.

Air of the first portion and / or the second portion and / or the third portion is then fed at the first and / or at the second pressure level in the distillation column system. Typically, the entire air of the first portion is fed to the second pressure level in the high-pressure column. All or part of the air of the second portion may be fed to the low pressure column at the first pressure level and / or to the high pressure column at the second pressure level. The same applies to the third share.

The present invention is based on the recognition that a combination of a HAP process associated with the energy efficiency of a MAC / BAC process is particularly advantageous both in terms of the creation and in the operating costs of an air separation plant. As explained, in particular the use of a sealing fluid expander from an energetic point of view (ie in terms of operating costs) is particularly favorable, whereas the use of a HAP method allows low creation costs. However, the use of a sealing fluid expander is not advantageous in conventional HAP processes because the energy saving achievable by a sealing fluid expander is coupled to the pressure difference occurring at the sealing fluid expander. At lower inlet pressures and thus lower pressure differences, the use is less rewarding overall. Also, improved by the increased pressures of a MAC / BAC process Q, T-profiles can not be conventionally achieved by a HAP method.

In HAP process, the final pressure of the main air compressor (in this case the "third pressure level") is determined both by the internal compression pressures, ie the pressures of the gaseous air products to be provided by internal compression, and by the amount of liquid air products to be extracted. The first dependence results from the vaporization capacity of a corresponding stream, which is essentially set by the pressure, the latter from the amount of cold "withdrawn" by the removal of the liquid air products, which must be compensated for by relaxation of another stream.

Since the amount of air of the feed air stream, that is, the amount of air of the entire, compressed by the main air compressor feed air is determined by the amount of air products generated, but the system can be fed more or less exergy only via a variation of the discharge pressure of the main air compressor. Due to technical-economical limits (used pipe classes) this is typically limited to approx. 23 bar.

Under these conditions, sufficient pressure can not be provided in conventional HAP processes which makes the use of a liquid turbine appear advantageous. As mentioned, the use of a liquid turbine is only technically advantageous if a sufficient pressure difference can be achieved over this.

The present invention therefore proposes to further densify the third portion successively in a booster compressor, a first turbine booster and a second turbine booster to the fourth pressure level. Thus, instead of the usual maximum of two compression steps, which are typically realized by two turbine boosters, at least three compression steps are used, two of which are implemented by a respective turbine booster and one by a secondary compressor. As a result, a significantly higher fourth pressure level can be achieved.

As mentioned, although in MAC / BAC processes, but not in HAP processes, recompressors which are driven by externally supplied energy are conventionally used. However, the present invention proposes the same. The booster used in the context of the present invention is a compressor driven by external energy, which is thus not or at least not exclusively driven by expansion of a fluid which has previously been compressed in the air separation plant. To the different possibilities, one In accordance with the invention, to drive additional compressors with external energy, reference is made to the explanations below.

The invention makes it possible by the said compression to provide the third portion (throttle flow) at a significantly increased fourth pressure level, which makes the use of a sealing fluid expander energetically meaningful. Therefore, it is provided according to the invention to use a corresponding Dichtfluidexpander to relax the third portion to which the third portion is supplied in the liquid state and at the fourth (supercritical) pressure level.

The third portion (throttle flow) may be supplied to the second turbine booster in particular depending on the amount of liquid or liquid products that are obtained in a corresponding air separation plant and to be removed, at different temperature levels.

For a provision of larger amounts of one or more liquid air products, it has proven to be particularly advantageous to supply the third portion of the first turbine booster at a temperature level of 0 to 50 ° C and the second turbine booster at a temperature level of -40 to 50 ° C. The second turbine booster is therefore not a typical cold compressor, so no "cold" turbine booster. Although this is the third portion (throttle current) possibly supplied well below the ambient temperature, downstream of the second turbine booster, however, its temperature is above the ambient temperature.

If a corresponding air separation plant larger quantities of air products are removed liquid, "cold" turbine boosters are less advantageous because the entire available cooling capacity is used to provide these liquid air products. However, a cold turbine booster inevitably introduces heat into the system since the heat of compression from the compressed stream typically can not be dissipated in an aftercooler, but only in the main heat exchanger, coupled with a corresponding input of heat. A turbine booster operated at higher inlet temperatures, in which the compressed stream has significantly higher temperatures than, for example, existing cooling water, enables effective heat removal in a conventional aftercooler. By dissipating the heat of compression downstream of the second turbine booster is the compression in this largely neutral in terms of heat, since the compression work is compensated here by the aftercooler.

Overall, the use of a second turbine booster operated at the above-mentioned higher inlet temperatures therefore makes it possible to take off a comparatively large amount of from 3 to 10 mol% of the feed air stream in the form of liquid air products, for example liquid oxygen (LOX), liquid nitrogen (LIN) and / or liquid argon (LAR).

For an air separation plant, however, the predominantly or exclusively provide gaseous air products (but can also be obtained, for example by means of internal compression of liquid intermediates), it is advantageous to the third portion of the first turbine booster at a temperature level of 0 to 50 ° C and the second turbine booster at a temperature level of -140 to -20 ° C supply. The second turbine booster is in this case a typical cold compressor, so a "cold" turbine booster. This is the third portion (inductor current) supplied below the ambient temperature, downstream of the second turbine booster, its temperature is still (significantly) below the ambient temperature. The temperature of the third portion compressed in the second turbine booster may be, for example, at -90 to 20 ° C. directly downstream of the second turbine booster.

A cold turbine booster adds heat to the system because the heat of compression from the compressed stream is typically not dissipated in an aftercooler operating with cooling water but only in the main heat exchanger itself, with associated heat input. By means of this heat input, which is intended in the present case, a cold turbine booster permits particularly good heating and liquefaction of internal compression products and is suitable for air separation plants for generating large quantities of corresponding gaseous printed products and comparatively small amounts of liquid air products.

Overall, therefore, the use of a second turbine booster operated at the mentioned low inlet temperatures permits removal of a comparatively small amount of up to 3 mol% of the feed air stream in Form of liquid air products, for example liquid oxygen (LOX), liquid nitrogen (LIN) and / or liquid argon (LAR).
The invention advantageously provides for driving the turbine boosters in each case with one of the expansion turbines, for example, the first turbine booster with the second expansion turbine and the second turbine booster with the first expansion turbine.

The additional compressor used in addition to the compression of the third portion (throttle flow), however, is driven by external energy, so not via associated expansion turbines, each relax the air portions of the feed air stream. It can be advantageous, for example, to drive the secondary compressor with high-pressure fluid and / or electrically and / or together with a compressor stage of the main air compressor. In the latter case, at least one compressor stage of the main air compressor and at least one compressor stage of the secondary compressor are arranged, for example, on a common shaft. Even a use of several appropriate measures can be done simultaneously.

It is particularly advantageous to cool the third portion before and after the further compression in the second turbine booster in the main heat exchanger. The third portion is taken from or fed to the main heat exchanger at appropriate temperature levels. As explained above, in cases where the second turbine booster is operated at the higher temperatures mentioned, additional after-cooling may be provided downstream of the second turbine booster and before being reintroduced into the main heat exchanger. If, however, the second turbine booster operated at the lower temperatures mentioned, this is, as explained, not the case.

The cooling in the main heat exchanger after the recompression in the second turbine booster is advantageously carried out by a temperature level that depends on the inlet and outlet temperature of the second turbine booster and a possible aftercooling, ie, for example, 10 to 50 ° C or -90 to 20 ° C to a temperature level of -140 to -180 ° C.

It may also be advantageous if the first portion before relaxing in the first expansion turbine in the main heat exchanger to a temperature level of 0 to -150 ° C is cooled. Advantageously, the first portion is cooled to a temperature level of -130 to -180 ° C after relaxing in the first expansion turbine in the main heat exchanger. In other words, after the expansion in the first expansion turbine, the first portion is again passed through the main heat exchanger.

The second portion is advantageously cooled to a temperature level of -50 to -150 ° C before relaxing in the second expansion turbine in the main heat exchanger.

In the context of the present invention is advantageously the first pressure level 1 to 2 bar and / or the second pressure level 5 to 6 bar and / or the third pressure level 8 to 23 bar and / or the fourth pressure level 50 to 70 bar absolute pressure, if the second turbine booster is operated at the higher temperatures mentioned. If the second turbine booster is operated at the lower temperatures mentioned, the first pressure level is advantageously 1 to 2 bar and / or the second pressure level 5 to 6 bar and / or the third pressure level 8 to 23 bar and / or the fourth pressure level 50 to 70 bar absolute pressure. The third pressure level can be achieved in each case with conventional HAP main air compressors, the fourth, in particular achieved with the help of said compressor the pressure level allows the use of a Dichtfluidexpanders. The fourth pressure level is at supercritical pressure.

The process according to the invention makes it possible, in particular, to remove at least one liquid air product from the distillation column system, to pressurize it in the main heat exchanger or to convert it into the supercritical state (to "liquefy") and to carry out at least one internal compression product from the air separation plant. So as mentioned several times for use with a Innenverdichtungsverfahren.

The at least one internal compression product can be carried out at a pressure of 6 bar to 100 bar from the air separation plant. Due to the additional heat input explained above, the method according to the invention is particularly suitable for providing internal compaction products in comparison high pressure, ie at least 30 bar, when the second turbine booster is operated at the mentioned lower temperatures.

For the features of the air separation plant according to the invention, reference is made to the corresponding device claim. In particular, such an air separation plant has all the means which enable it to carry out a previously explained method. The features and advantages discussed above are therefore expressly referred to.

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

• Figur 1 zeigt eine Luftzerlegungsanlage gemäß einer Ausführungsform der Erfindung in Form eines schematischen Anlagendiagramms.
• Figur 2 zeigt eine Luftzerlegungsanlage gemäß einer Ausführungsform der Erfindung in Form eines schematischen Anlagendiagramms.

Short description of the drawing

• FIG. 1 shows an air separation plant according to an embodiment of the invention in the form of a schematic diagram of the system.
• FIG. 2 shows an air separation plant according to an embodiment of the invention in the form of a schematic diagram of the system.

Detailed description of the drawing

In FIG. 1 an air separation plant according to a particularly preferred embodiment of the invention is shown schematically and designated 100 in total. The air separation plant 100 is supplied to feed air (AIR) in the form of an input air flow a, pre-cleaned by a filter 1 and then fed to a main air compressor 2. The main air compressor 2 is illustrated very schematically. The main air compressor 2 typically has a plurality of compressor stages, which can be driven via a common shaft with one or more electric motors.

Downstream of the main air compressor 2 is compressed in this compressed feed air flow a, which is here the entire, in the air separation plant treated feed air 100, a cleaning device 3, not shown, and there free of residual moisture and carbon dioxide, for example. It will be a compressed (and purified) feed air stream b obtained downstream of the cleaning device 3 at a pressure level of, for example, 15 to 23 bar, referred to in this application as the third pressure level, is present. The third pressure level in the illustrated example is well above the operating pressure of a typical high-pressure column of an air separation plant, as explained above. This is a HAP procedure.

The feed air stream b is successively divided into the streams c, d and e. In the context of this application, the current c is referred to as the first portion, the current d as the second portion, and the current e as the third portion of the feed air flow b.

The streams c and d are separated from each other warmly supplied to a main heat exchanger 4 of the air separation plant 100 and this removed again at different intermediate temperature levels. The stream c is after removal from the main heat exchanger 4 in an expansion turbine 5, which is referred to in the context of this application as the first expansion turbine to a pressure level of for example 5 to 6 bar, which is referred to in the context of this application as a second pressure level, relaxed, and again passed through a section of the main heat exchanger 4. The stream d is also released to the second pressure level after removal from the main heat exchanger 4 in an expansion turbine 6, which is referred to in the context of this application as a second expansion turbine.

The current e is the so-called inductor current, which in particular enables internal compression. The current e is for this purpose first in a booster 7 and then in two turbine booster, which are each driven by the first expansion turbine 5 and the second expansion turbine 6 (not separately designated), re-compressed. The turbine booster driven by the second expansion turbine 6 is referred to here as the first turbine booster, whereas the turbine booster driven by the first expansion turbine 5 is referred to as the second turbine booster. In principle, the assignment of the turbine boosters to the expansion turbines 5, 6 can also be reversed. The recompression takes place at a pressure level of for example 50 to 70 bar, which is referred to in the context of this application as the fourth pressure level. Downstream of the booster 7 and upstream of the turbine booster is the power e at a pressure level of for example 26 to 36 bar. The secondary compressor 7 is driven by external energy, ie not by a relaxation of compressed air portions of the feed air stream b.

After the recompression steps in the two turbine boosters, the current e is recooled in each case in non-separately designated aftercoolers of the turbine boosters to a temperature which corresponds approximately to the cooling water temperature. A further cooling takes place as shown by means of the main heat exchanger 4 as needed. At the fourth pressure level, the current e is thus again passed through an aftercooler and then through the main heat exchanger 4 and then expanded in a sealing fluid expander 8. The fourth pressure level is well above the critical pressure for nitrogen and above the critical pressure for oxygen.

After cooling in the main heat exchanger 4 and upstream of the sealing fluid expander 8, the flow e is in the liquid state at supercritical pressure. The sealing fluid expander 8 is coupled, for example, with a generator or an oil brake (without designation). After relaxation, the current e is here at the second pressure level. He is still liquid, but is at a subcritical pressure.

The distillation column system 10 is shown greatly simplified. It comprises at least one at a pressure level of 1 to 2 bar (referred to here as the first pressure level) operated low pressure column 11 and operated at the second pressure level high pressure column 12 of a double column system in which the low pressure column 11 and the high pressure column 12 via a main condenser 13 in heat exchanging connection stand. On the specific presentation of the low pressure column 11 and the high pressure column 12 feeding and connecting them and the main capacitor 13 lines, valves, pumps, other heat exchangers and the like has been omitted for clarity.

The streams c, d and e are fed into the high pressure column 12 in the example shown. However, it can also be provided, for example, not to feed the stream d and / or the stream e into the distillation column system after appropriate expansion into the low-pressure column 11 and / or portions.

The distillation column system 10, the currents f, g and h can be removed in the example shown. The air separation plant 100 is set up to carry out an internal compression process, as explained in more detail. In the example shown, the streams f and g, which may be a liquid, oxygen-rich stream f and a liquid, nitrogen-rich stream g, are therefore pressurized by means of pumps 9 in the liquid state and vaporized in the main heat exchanger 4 or, depending on the pressure , transferred from the liquid to the supercritical state. Fluid of the flows f and g can be taken from the air separation plant 100 as internally compressed oxygen (GOX-IC) or internally compressed nitrogen (GAN-IC). Stream h illustrates one or more streams taken from the distillation column system 10 in the gaseous state at the first pressure level.

In FIG. 2 an air separation plant according to a particularly preferred embodiment of the invention is shown schematically and indicated generally at 200. Equal or comparable plant components and currents as in FIG. 1 shown air separation unit 100 are given identical reference numerals and will not be explained repeatedly.

The feed air stream b is also present downstream of the cleaning device 3 at a third pressure level, which, however, here is for example 9 to 17 bar. The fourth pressure level, to which the current e (inductor current) is compressed, is for example 30 to 80 bar here. While the stream e here after the Nachverdichtungsschritt in the first turbine booster in a not separately designated aftercooler is cooled back to a temperature which corresponds approximately to the cooling water temperature, cooling takes place downstream of the second turbine booster only by means of the main heat exchanger 4, but not by means of an aftercooler such in the air separation plant 100 according to FIG. 1 , Since the second turbine booster is operated as a "cold" turbine booster, the current e downstream of this second turbine booster is at a correspondingly low temperature level well below the ambient temperature.

In the example shown, the air separation plant 100, the drive of the booster 7 is carried out together with one or more compressor stages of the Main air compressor 2 and using a pressurized fluid, such as pressure steam, which is in an expansion turbine (not separately referred to) relaxed. As mentioned, an air separation plant 100 is suitable according to FIG. 1 in which the second turbine booster is operated as a "warm" turbine booster, especially for the provision of larger quantities of liquid air products (not shown), an air separation plant 200 according to FIG FIG. 2 whereas the second turbine booster operates as a "cold" turbine booster, especially for providing high pressure gaseous internal compression products.

Claims (15)

Process for the cryogenic separation of air (AIR) in an air separation plant (100, 200) comprising a main air compressor (2), a main heat exchanger (4) and a distillation column system (10) with a low pressure column (11) operated at a first pressure level and one on a second one Pressure level operated high pressure column (12), in which a feed air stream (a) comprising the total feed air supplied to the air separation plant (100, 200) is compressed in the main air compressor (2) to a third pressure level which is at least 2 bar above the second pressure level, the compressed feed air stream (b) a first portion (c) is cooled at least once in the main heat exchanger (4) and expanded from the third pressure level in a first expansion turbine (5), - a second portion (d) is cooled at least once in the main heat exchanger (4) and expanded from the third pressure level in a second expansion turbine (6), and - a third portion (e) is further compressed to a fourth pressure level, cooled at least once in the main heat exchanger (4) and expanded from the fourth pressure level, wherein - air of the first portion (c) and / or the second portion (d) and / or the third portion (s) at the first and / or at the second pressure level in the distillation column system (10) is fed
characterized in that - The third portion (e) successively in a booster (7), a first turbine booster and a second turbine booster to the fourth pressure level is further compressed, and - To relax the third portion (e) a Dichtfluidexpander (8) is used, to which the third portion (s) is supplied in the liquid state and at the fourth pressure level. The method of claim 1, wherein the third portion (e) is supplied to the first turbine booster at a temperature level of 0 to 50 ° C and the second turbine booster at a temperature level of -40 to 50 ° C. The method of claim 2, wherein the air separation plant (100, 200) at least one liquid air product in a proportion of 3 to 10 mol .-% of the feed air stream (a) is removed. The method of claim 2 or 3, wherein the third portion (e) after the recompression in the second turbine booster in an aftercooler from a temperature level above the ambient temperature and then in the main heat exchanger (4) from a temperature level of 10 to 50 ° C. a temperature level of -140 to -180 ° C is cooled. Method according to one of claims 1 to 4, wherein the first pressure level at 1 to 2 bar, the second pressure level at 5 to 6 bar, the third pressure level at 8 to 23 bar and / or the fourth pressure level at 50 to 70 bar absolute pressure , The method of claim 1, wherein the third portion (e) is supplied to the first turbine booster at a temperature level of 0 to 50 ° C and the second turbine booster at a temperature level of -140 to -20 ° C. The method of claim 6, wherein the air separation plant (100, 200) at least one liquid air product in a proportion of up to 3 mol .-% of the feed air stream (a) is removed. The method of claim 6 or 7, wherein the third portion (e) after the recompression in the second turbine booster in the main heat exchanger (4) from a temperature level of -90 to 20 ° C to a temperature level of -140 to -180 ° C. is cooled. Method according to one of claims 6 to 8, wherein the first pressure level at 1 to 2 bar, the second pressure level at 5 to 6 bar, the third pressure level at 9 to 17 bar and / or the fourth pressure level at 30 to 80 bar absolute pressure , Method according to one of the preceding claims, in which the turbine boosters are each driven by one of the expansion turbines (5, 6). Method according to one of the preceding claims, in which the after-compressor (7) is driven with high-pressure fluid and / or electrically and / or together with a compressor stage of the main air compressor (2). Method according to one of the preceding claims, wherein the first portion (c) in the main heat exchanger (4) is cooled to a temperature level of 0 to 150 ° C before being expanded. Method according to one of the preceding claims, wherein the first portion (c) is cooled in the main heat exchanger (4) after relaxing to a temperature level of -150 to -180 ° C. A method according to any preceding claim, wherein the second portion (d) in the main heat exchanger (4) is cooled to a temperature level of -100 to -160 ° C prior to expansion. An air separation plant (100) adapted for cryogenic separation of air (AIR) according to a method of any one of claims 1 to 14 and a main air compressor (2), a main heat exchanger (4) and a distillation column system (10) operated at a first pressure level Low pressure column (11) and a operated at a second pressure level high-pressure column (12), wherein the air separation plant (100) has means which are adapted to a feed air stream (a) comprising all the feed air supplied to the air separation plant (100, 200) to compress in the main air compressor (2) to a third pressure level which is at least 2 bar above the second pressure level and from the compressed feed air stream (b) to cool a first portion (c) at least once in the main heat exchanger (4) and to relax from the third pressure level in a first expansion turbine (5), to cool a second portion (d) at least once in the main heat exchanger (4) and to relax it from the third pressure level in a second expansion turbine (6), to further compress a third portion (e) to a fourth pressure level, to cool at least once in the main heat exchanger (4) and to relax from the fourth pressure level, and To feed air of the first portion (c) and / or the second portion (d) and / or the third portion (s) at the first and / or at the second pressure level into the distillate column system (10),
characterized by means adapted for - The third portion (e) successively in a booster (7), a first turbine booster and a second turbine booster to the fourth pressure level to further compress, and to relax the third portion (e) in a sealing fluid expander (8) and to supply the third portion (e) thereof in the liquid state and at the fourth pressure level.

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