EP3034974A1 - Method and assembly for the liquefaction of air and for electrical energy storage and recovery - Google Patents

Abstract

The invention relates to a method for the liquefaction of air, in which a compressed air flow (b) is provided at a first pressure level and compressed by a compressor (11) to a second pressure level, from air of the compressed air flow (b) after compression to the second pressure level a first partial flow (b), a second partial flow (e) and a third partial flow (f) is formed, air of the first partial flow (c) using cold, by means of a relaxation of air of the second partial flow (e) and the third Partial flow (f) is generated, cooled and at least partially liquefied, and for providing the compressed air flow (b) at the first pressure level feed air (a), which is compressed to the first pressure level, and air of the second partial flow (e) and the third Partial flow (f), which is provided at the first pressure level, is used. It is provided that the air of the second partial flow (e) is cooled successively to a first temperature level, relaxed from the second pressure level to the first pressure level and heated against the first partial flow (c), and the air of the third partial flow (f) successively cooled to a second temperature level below the first temperature level, relaxed to a third pressure level below the first pressure level, heated against the first partial flow (c) and recompressed to the first pressure level. It is further provided that for recompression of the third partial flow (f) a first booster (5) and a second booster (6) are used, the first booster (5) having a relaxation machine (4) used for relaxation of the third partial flow (f) ) and is mechanically coupled, the second booster (6) is driven with a relaxation machine (3) used for relaxation of the second partial flow (e) and is mechanically coupled, and the first booster (5) and the second booster (6) with each other and with the compressor (11) are mechanically uncoupled. A method for storing and recovering electrical energy and a corresponding system (100, 200, 300, 400) are likewise provided by the present invention.

Description

The invention relates to a method and a plant for the liquefaction of air and for the storage and recovery of electrical energy according to the respective preambles of the independent claims.

State of the art

For example, from the DE 31 39 567 A1 and the EP 1 989 400 A1 It is known to use liquid air or liquid nitrogen, ie cryogenic air liquefaction products, for grid control and for the provision of control power in power grids.

At low-flow times or excess-current periods, air in an air liquefaction plant, which may also be part of an air separation plant, is liquefied in whole or in part to form such an air liquefaction product. The air liquefaction product is stored in a tank system with cryogenic tanks. This mode of operation occurs during a period of time, referred to herein as the energy storage period.

At peak load times, the air liquefaction product is withdrawn from the tank system, pressure increased by a pump and warmed to about ambient temperature or higher and thus converted to a gaseous or supercritical state. A pressure stream obtained in this way is decompressed to ambient pressure in a decompression machine or several expansion machines with intermediate heating. The thereby released mechanical power is converted into electrical energy in one or more generators and fed into an electrical grid. This mode of operation occurs during a period of time, referred to herein as the energy recovery period.

There are also known compressed air storage power plants in which the air is not liquefied, but compressed in a compressor and stored in an underground cavern. In times of high electricity demand, the compressed air from the cavern in passed the combustion chamber of a gas turbine. At the same time, the gas turbine is supplied via a gas line fuel, such as natural gas, and burned in the atmosphere formed by the compressed air. The formed exhaust gas is expanded in the gas turbine, thereby generating energy.

From the EP 1 205 721 A1 For example, a method and an apparatus for producing a cryogenic liquid are known in which a compressor arrangement is used in which two compressor stages each are arranged on a shaft. The shafts carry pinions, which are acted upon via a drive wheel with a torque.

The US 2011/0132032 A1 discloses a method and apparatus by which air may be liquefied and stored for later use. In later use, the liquefied air is pressurized, heated and relaxed liquid. Cold can be stored.

According to the US 6,666,048 B1 In order to be able to increase the formation of a specific product in a plant, for example an air separation plant, an additional plant or plant component, for example an absorption column, is integrated into the existing plant.

The WO 2014/006426 A2 relates to a liquefaction device comprising a heat exchanger, a first phase separator, a first expansion device, a first expansion turbine, a second expansion turbine and a refrigerant recovery line with a heat transfer fluid.

In particular, due to the large amounts of air to be liquefied known air liquefaction plants for the tasks mentioned often not sufficiently efficient, as also explained below, so that there is a need for improvement. The same applies to air liquefaction plants for purposes other than the storage and recovery of energy.

Disclosure of the invention

This object is achieved by a method and a plant for the liquefaction of air and for the storage and recovery of electrical energy with the characteristics the respective independent claims. Preferred embodiments are also subject matter of the dependent claims and the following description.

Before explaining the advantages that can be achieved within the scope of the present invention, its technical principles and some terms used in this application are explained in more detail.

A "relaxation machine", which can be coupled via a common shaft with other expansion machines or energy converters such as oil brakes, generators or compressor stages, is set up to relax a supercritical, gaseous or at least partially liquid stream. In particular, expansion machines may be designed for use in the present invention as a turboexpander. If one or more expansion machines designed as turboexpanders are coupled with one or more compressor stages (for example in the form of centrifugal compressor stages) and if necessary additionally mechanically braked, so that the compressor stage (s) are operated without externally supplied energy, for example by means of an electric motor In general, the term "booster turbine" is also used for this arrangement. The compressor stage (s) of a corresponding booster turbine is or are also referred to as a "booster". Such a booster turbine compresses at least one current by the relaxation of at least one other current, but without external, for example by means of an electric motor, supplied energy.

In this case, a "compressor" is understood here to mean an externally, typically electrically, driven device which is capable of compressing 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 , is set up. The entire compressor forms a structural unit, however, which may have a plurality of individual compressor units or "compressor stages" in the form of known piston, screw and / or Schaufelrad- or turbine assemblies (ie radial or Axialverdichterstufen). In particular, these compressor stages are driven by means of a common drive, for example via a common shaft or a common electric motor. Several compressor stages, eg compressor stages in one Air liquefaction plant used according to the invention can thus together form one or more compressors.

Rotating units, for example expansion machines or expansion turbines, compressors or compressor stages, booster turbines or booster, rotors of electric motors and the like, can be mechanically coupled to one another, wherein a "mechanical coupling" in the parlance of this application is understood that via mechanical elements such Gears, belts, gears and the like, a fixed or mechanically adjustable speed relationship between such rotating units can be produced. A mechanical coupling can generally be made by two or more elements, each engaging, such as in form-engagement or frictional engagement, such as gears or traction sheaves with belts, or a non-rotatable connection. A non-rotatable connection can in particular be effected via a common shaft, on which the rotating units are respectively secured against rotation. The rotational speed of the rotating units is the same in this case. By contrast, corresponding units are "mechanically uncoupled" if there is no fixed or mechanically adjustable speed relationship between corresponding elements. Of course, for example, between a plurality of electric motors, in particular by suitable electrical control, or between multiple turbines, in particular by the choice of suitable input and final pressures, certain speed relationships are given. However, these are not caused by two or more, in each case in engagement, for example in the form of engagement or frictional engagement, standing elements or by a rotationally fixed connection.

A "heat exchanger" is in the context of the present invention, in particular using one or more countercurrent heat exchange units, for example, one or more plate heat exchange units formed. In contrast to, for example, regenerators, cooling does not take place here by the release of heat to or from the absorption of heat from a solid medium, but indirectly to or from a heat or cold carrier conducted in countercurrent. All known heat exchange units, for example plate heat exchangers, tube bundle heat exchangers and the like, are suitable for use in the present invention. A heat exchanger is thus used for indirect transfer of heat between at least two countercurrently flowed streams, for example a warm compressed air stream and one or more cold streams or a cryogenic air liquefaction product and one or more warm streams. A heat exchanger may be formed from a single or multiple parallel and / or serially connected sections, eg, one or more plate heat exchanger blocks.

The present application uses the terms "pressure level" and "temperature level" to characterize pressures and temperatures, which is to express that pressures and temperatures in a given equipment need not be used in the form of exact pressure or temperature values to achieve this to realize innovative 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 pressure drops or expected pressure drops, for example, due to cooling effects or line losses. The same applies to temperature levels. The pressure levels indicated here in bar are absolute pressures.

Advantages of the invention

As previously discussed, for the purposes of storing and recovering electrical energy, air liquefaction may require specially adapted air liquefaction facilities or air liquefaction processes due to the large volumes of air to be liquefied. Conventional air liquefaction equipment is included as well as below with reference to FIGS FIG. 1 explained, built on the basis of two compressors and two booster turbines:

In a so-called feed compressor, the total amount of air to be liquefied, also referred to as feed air, is compressed to about 6 bar. A feed compressor downstream so-called closed-loop compressor compresses the feed air together with an amount of air recirculated downstream of the said about 6 bar to about 30 to 40 bar. Part of the compressed to the pressure of about 30 to 40 bar Feed air is cooled in the form of two partial streams in a heat exchanger to different low temperatures. The partial flows are relaxed in each case one of the relaxation machines of the booster turbines back to the pressure of about 6 bar, whereby liquefied a part of the cooled to the lower temperature air quantity. The non-liquefied portion of the two relaxed partial streams is heated in the heat exchanger and fed back to the input of the cycle compressor at the pressure of about 6 bar. The inlet temperature in one of the two expansion machines is at a temperature between 230 K and ambient temperature and the inlet temperature in the other expansion machine at about 140 to 180 K.

Another portion of the compressed to the pressure of about 30 to 40 bar feed air is further compressed by means of the said expansion machines driven booster to about 60 to 80 bar. The correspondingly highly compressed air flow is also cooled in the heat exchanger and expanded at a suitable temperature by means of a throttle. The air of this air flow liquefies at least partially. The total liquefied air is thus formed from air compressed to the pressure of about 60 to 80 bar air flow and from the air, which is fed to the expansion machine with the inlet temperature of about 140 to 180 K. The amount of air to be liquefied is at least partially cooled by the expanded air in the expansion machines.

A disadvantage of the method just described is that this is designed around the final pressure of the feed compressor and thus leaves little freedom. Both the inlet pressure of the cycle compressor and the pressure at the outlet of the two expansion machines are predetermined in this way, namely to the final pressure of the feed compressor or the inlet pressure of the cycle compressor.

However, feed compressors with a relatively high discharge pressure of about 12 to 20 bar would be of advantage in particular for energy storage or for air-liquefying equipment which can be used here. Accordingly, in the conventional method, the pressure as well as the minimum temperature at the outlet of the expansion machines would be determined, in particular the expansion machine operated at lower temperatures. This is due to the fact that the liquid content at the outlet of a corresponding Relaxation machine typically may not exceed 6 to 8 percent. This temperature would be higher than in the case of the above-described method, in which the outlet pressure of the feed compressor or the inlet pressure of the cycle compressor is about 6 bar. The air to be liquefied mainly, ie the air compressed to the even higher pressure of about 60 to 80 bar would be pre-cooled with the cold stream from the described expansion machine, but not as strong as in the conventional method due to the circumstances explained. Compared with the conventional method, the temperature of this stream at the coldest point would be significantly higher, namely at about 111 to 120 K instead of 101 K. After the subsequent relaxation in the described throttle would therefore significantly more steam and comparatively less air liquefaction product, resulting in larger Losses indicates.

The invention solves the problem to improve a corresponding method, characterized in that the outlet pressure of the explained, operated at a lower temperature expansion machine is reduced, so that this pressure is lower than the final pressure of the feed compressor or the inlet pressure of the cycle compressor. The amount of air expanded in this expansion machine is not led directly to the inlet of the cycle compressor (or via the heat exchanger to this), but first recompressed in two booster to the final pressure of the feed compressor or the inlet pressure of the cycle compressor.

In this way it is achieved that even at higher end pressures of a feed compressor or entry pressures of a cycle compressor relaxation to lower pressures is possible, so that an effective cooling for liquefaction of air is possible. In this way, losses in downstream devices are reduced within the scope of the present invention.

Against this background, the present invention is based on a method for liquefying air, in which a compressed air flow is provided at a first pressure level and compressed by means of a compressor, namely by means of the described cycle compressor, to a second pressure level, from air of the compressed air flow after compression formed on the second pressure level, a first partial flow, a second partial flow and a third partial flow, air of the first partial flow using cold, by means of a relaxation of air of the second Partial flow and the third partial flow is generated, cooled and at least partially liquefied, and in which for providing the compressed air flow at the first pressure level feed air, which is compressed to the first pressure level, and air of the second partial flow and the third partial flow, on the first Pressure level is provided is used.

The present invention provides that the air of the second partial flow is cooled successively to a first temperature level, expanded from the second pressure level to the first pressure level and heated against the first partial flow, and that the air of the third partial flow successively to a second temperature level below cooled to a third pressure level below the first pressure level, heated against the first partial flow and is recompressed to the first pressure level of the first temperature level. By relaxing to the third pressure level below the first pressure level, the advantages described above are achieved, namely an improved refrigeration, which is in the field of refrigeration in conventional systems with a corresponding final feed compressor pressure of about 6 bar or such a cycle compressor inlet pressure. At the same time, the advantages of a higher-density feed compressor can be used.

According to the invention, a first booster and a second booster are used for recompressing the third partial flow, wherein the first booster is driven with a relaxation machine used to relax the air of the second partial flow and is mechanically coupled and the second booster with one for relaxing the air of the third Partial flow used relaxation machine is driven and mechanically coupled. This makes it possible to effectively use energy released during the expansion of the partial flows for the recompression of the air of the third partial flow. There are no additional externally driven compressors required. According to the invention, the first booster and the second booster are mechanically uncoupled with one another and with the (circulatory) compressor in the sense explained above. Mechanically uncoupled are thus also the two mentioned relaxation machines with each other and with the compressor. In this way, the compressor, the first booster with the expansion machine used to relax the air of the second partial flow and the second booster with the used to relax the air of the third partial flow Relaxation machine each (within operational limits) are operated independently. In particular, the cold provided by the expansion of the second and the third partial flow as well as the discharge pressures of the booster can thereby be adjusted individually and independently of the compressor. In particular, the third pressure level can be set independently.

From the explained mechanical relationships of the booster and expansion machines with each other and with the compressor it follows that the recompression of the air of the partial flow to the first pressure level and the compression of the compressed air flow to the first pressure level independently, i. in different apparatuses (the first booster and the second booster on the one hand and in the compressor on the other hand) takes place. According to a particularly preferred embodiment of the present invention, as the air of the third partial flow, which is heated after cooling to the second temperature level and the relaxation to the third pressure level against the first partial flow and recompressed to the first pressure level, air of the third partial flow is used which remains gaseous at the third pressure level and a third temperature level generated by the relaxation to the third pressure level. In other words, according to this embodiment of the present invention, after the expansion of the third partial flow to the third pressure level, a liquid phase is separated and only the air of the third partial flow is passed through a corresponding heat exchanger and used to cool the first partial flow, which remains gaseous here.

According to this particularly preferred embodiment of the invention, it may be provided that air of the third partial flow, which has been cooled to the second temperature level and has been expanded to the third pressure level and is liquid at the third temperature level and the third pressure level, is combined with liquefied air of the first partial flow , Such air has already been liquefied, so that it can be used advantageously for obtaining the air liquefaction product according to the method according to the invention.

Advantageously, the air of the first partial flow is released after cooling to a fourth pressure level below the third pressure level. For this purpose, advantageously, a throttle device, such as a throttle valve or a Generator turbine, used in the Joule Thompson relaxation generated by further cold and thus a better liquefaction of the air is effected.

Advantageously, before the air of the first partial flow is released to the fourth pressure level, this air is first released to the previously described third pressure level. In this way, a combination of shares of the first partial flow with, for example, liquefied air of the third partial flow, which is present at the third pressure level, allows.

It is particularly advantageous, the air of the third partial flow, which is heated after cooling to the second temperature level and the relaxation to the third temperature level against the first partial flow and is recompressed to the first pressure level, after relaxing to the third pressure level on the to combine the third pressure level of relaxed and gaseous air of the first partial flow. Corresponding air can therefore be used effectively and returned to the entry of a cycle compressor.

Advantageously, the first pressure level in the context of the present invention at 5 to 25 bar, in particular 10 to 20 bar and / or the second pressure level at 50 to 100 bar, in particular at 60 to 80 bar. For example, about 17 bar can be used as the first pressure level and about 70 bar as the second pressure level. The method according to the invention is therefore particularly suitable for processes for the liquefaction of air which are used in processes for the storage and recovery of energy, where comparatively large amounts of air have to be liquefied, as explained above. In the same way, however, the method according to the invention is also suitable for other application scenarios in which corresponding requirements exist. In particular, feed compressors can be used by the use of the method according to the invention, which deliver correspondingly high first pressure levels.

Advantageously, the third pressure level is at least 1, 5 or 10 bar and up to 20 bar below the second pressure level and / or the fourth pressure level 1, 5 or 10 bar and up to 20 bar below the third pressure level, the fourth pressure level in particular at atmospheric pressure lies. An example of the third pressure level is about 6.5 bar. A corresponding relaxation on such a a low third pressure level corresponding to the feed compressor end compressor pressure in the previously discussed conventional methods enables particularly effective cooling.

Advantageously, the first temperature level is 230 to 330 K and / or the second temperature level is 140 to 180 K. Corresponding temperature levels correspond to those of conventional methods, as explained above, so that empirical values used here can be used further.

The invention further relates to a method for storing and recovering electrical energy, comprising a first mode of operation in which air is liquefied by means of electrical energy, and a second mode of operation in which electrical energy is obtained using the air liquefied in the first mode of operation , In this case, the first operating mode is the operating mode explained in the introduction in low-flow times or excess-current periods, that is to say in an energy storage period, the second operating mode is the operating mode which is used in peak load periods, that is to say in an energy recovery period. A corresponding method for storing and recovering electrical energy is inventively characterized in that in the first operating mode, a method is used, as previously explained. With respect to this method, therefore, express reference is made to the features and advantages discussed above.

The invention further relates to a plant for the liquefaction of air. This has means which are adapted to provide a compressed air flow at a first pressure level and by means of a compressor, the multiple-cycle compressor to compress to a second pressure level, from air of the compressed air stream after compression to the second pressure level, a first partial flow, a forming second partial flow and a third partial flow, to cool and at least partially liquefy air of the first partial flow using cold generated by a relaxation of air of the second partial flow and the third partial flow, and to provide the compressed air flow at the first pressure level Feed air, which is compressed to the first pressure level, and air of the second partial flow and the third partial flow, which is provided at the first pressure level to use.

Means are provided which are arranged to cool the air of the second partial flow successively to a first temperature level and to relax from the second pressure level to the first pressure level and to heat against the first partial flow, and which are further adapted to control the air of the first partial flow third sub-stream successively to a second temperature level below the first temperature level, to relax to a third pressure level below the first pressure level, to heat against the first partial flow and to recompress to the first pressure level.

According to the invention, a first booster and a second booster are provided for recompressing the third partial flow, wherein the first booster is drivably and mechanically coupled to a relaxation machine used for relaxation of the third partial flow, and the second booster can be driven and mechanically driven by a relaxation machine used for relaxation of the second partial flow is coupled, and the first booster and the second booster with each other and with the compressor are mechanically uncoupled.

For features and advantages of a corresponding system is also made to the features and advantages explained above. In particular, a corresponding system for implementing a method is set up, as explained above, so it can also be a system for storing and recovering electrical energy.

The invention will be explained in more detail below with reference to the accompanying drawings, in which embodiments of the invention over the prior art are illustrated.

Brief description of the drawings

• FIG. 1 illustrates a non-inventive system for the liquefaction of air in the form of a schematic process flow diagram.
• FIG. 2 FIG. 3 illustrates a system for liquefying air according to an embodiment of the invention in the form of a schematic process flow diagram.
• FIG. 3 FIG. 3 illustrates a system for liquefying air according to an embodiment of the invention in the form of a schematic process flow diagram.
• FIG. 4 FIG. 3 illustrates a system for liquefying air according to an embodiment of the invention in the form of a schematic process flow diagram.
• FIG. 5 FIG. 3 illustrates a system for liquefying air according to an embodiment of the invention in the form of a schematic process flow diagram.

In the figures, corresponding elements, currents and devices are given identical reference numerals and will not be explained repeatedly for the sake of clarity. Fluid flows are respectively indicated in uppercase and lowercase letters, predominantly or exclusively gaseous fluid streams further illustrated with unfilled (white), predominantly or exclusively liquid fluid streams with filled (black) flow arrows.

Detailed description of the drawings

FIG. 1 illustrates a non-inventive system for liquefying air, which is indicated generally at 500. For better distinctness, the fluid flows are indicated here in capital letters.

The plant 500 is fed feed air A at ambient pressure, and after combining with another air flow X in a compressor 12, the so-called feed compressor, compressed. The feed compressor 12 may be followed by a not separately designated aftercooler. A correspondingly obtained compressed air flow, now designated B, is fed to a second compressor 11, the so-called cyclone compressor, which may also be followed by an aftercooler which is not separately designated. Also, the cycle compressor 11, a current Y is supplied, which is formed as explained below. The streams B and Y are further compressed in the cycle compressor 11. Downstream of the cycle compressor 11, a current obtained by the compression, which is now denoted by C, is divided into a first partial flow D and a second partial flow E. The first partial flow D is fed to a heat exchanger 13 on the warm side and taken from this at an intermediate temperature level. The first partial stream D is subsequently expanded in a first expansion machine 14 to the pressure level provided by the feed compressor 12 and fed to the heat exchanger 13 at an intermediate temperature level.

The second partial flow E is first compressed in a ("first") booster 15 and then in a ("second") booster 16, each of which can not be separately designated aftercooler downstream, compressed to a higher pressure level. The correspondingly compressed second partial flow E is likewise fed to the heat exchanger 13 on the hot side and is partially removed at an intermediate temperature level in the form of the flow F. The stream F is expanded in a relaxation machine 17 and then transferred to a separation vessel 18. The relaxation in the expansion machine 17 also takes place on the provided by the feed compressor 12 pressure level.

Also supplied to the separation vessel 18 is a second portion of the second partial stream E, which is designated here by G and is guided almost to the cold end through the heat exchanger 13. In the bottom of the separation vessel 18 separated liquid air is withdrawn in the form of the stream H, undercooled in a part of the heat exchanger 13 and then partially transferred, for example in a tank. Among others, cooling is used for subcooling, which can be obtained from a relaxation of part of the flow H to the mentioned flow X. The latter is then passed from the cold to the warm end through the heat exchanger 13. The gaseous air remaining in the separation vessel 18 is drawn off in the form of the stream I, heated in the heat exchanger 13 and then combined in the form of the stream Y with the previously described compressed air stream B.

As mentioned previously, the in FIG. 1 illustrated air liquefaction plant 100 disadvantages. In the feed compressor 12, the feed air of the stream A is compressed to about 6 bar. The cycle compressor 11 further compresses the feed air of the stream A together with a recirculated air quantity of the stream Y from the cited approximately 6 bar to approximately 30 to 40 bar. In the expansion machine 14, the air compressed to the pressure of about 30 to 40 bar of the stream D is then again relaxed to the pressure of about 6 bar and at this pressure level as part of the current Y. led back to the input of the cycle compressor 11. In the expansion machine 17, the first compressed to the pressure of about 30 to 40 bar and then in the booster 15 and 16 further compressed to about 60 to 80 bar air of the stream F is also relaxed to the pressure of about 6 bar. A portion of it which remains gaseous in the separation vessel 18 is also conducted, as part of the flow Y, back to the inlet of the circulation compressor 11.

The expansion machines 14 and 17 are placed so that the inlet temperature is in the expansion machine 14 at a temperature level between 230 K and ambient temperature and the inlet temperature of the expansion machine 17 at about 140 to 180 K. This is achieved by passing the streams D and F through the heat exchanger 13 and removing it at the temperatures mentioned. The booster 15 and 16 driven by the mentioned expansion machines 14 and 17 compress the stream E to the said pressure level of about 60 to 80 bar. Part of the compressed to the pressure level of about 60 to 80 bar stream E is relaxed in the form of the current G via a throttle in the separating vessel 18. The air of this stream G liquefies at least partially. The liquefied air of the stream H is formed from the liquefied air of the stream G and from liquefied air of the stream F expanded in the expansion machine 17. The amount of air to be liquefied is cooled in each case by the relaxed in the expansion machines 14 and 17 air.

The disadvantage of this is that a corresponding method must be designed around the final pressure of the feed compressor 12 and thus leaves little freedom. Both the inlet pressure of the cycle compressor 11 and the pressure at the outlet of the two expansion machines 14 and 17 are set in this way, namely to the final pressure of the feed compressor 12 and the inlet pressure of the cycle compressor 11. Feed compressor 12 with higher final pressure of about 12 to 20 bar would be an advantage. Correspondingly, however, in the method implemented in the air liquefaction plant 500, the pressure and the minimum temperature at the outlet of the expansion machines 14 and 17 would be determined accordingly, in particular the expansion machine 17 operated at lower temperatures. The liquid fraction at the exit from such a relaxation machine 17 is typically no longer permitted than 6 to 8 percent. However, this temperature is then higher than in the case a method in which the outlet pressure of the feed compressor 12 and the inlet pressure of the cycle compressor 11 is about 6 bar. The air to be liquefied air, ie the compressed to the third pressure level of about 60 to 80 bar air of the stream E would be pre-cooled with the cold stream F from the expansion machine 17, but not as far as in a conventional method, due to the circumstances explained the outlet pressure of the feed compressor 12 or the inlet pressure of the cycle compressor 11 is about 6 bar. Compared with a conventional method, the final temperature would be significantly higher, namely at about 111 to 120 K instead of 101 K. After the subsequent relaxation in the described throttle would therefore produce significantly more steam and comparatively less air liquefaction product, indicating greater losses.

In FIG. 2 1, an air liquefaction plant according to an embodiment of the invention is illustrated in the form of a schematic process flow diagram and indicated generally at 100.

The system 100 is supplied to feed air a at a first pressure level. Here, too, the term "feed air" is understood to mean externally provided air which has been freed, for example, by means of suitable cleaning devices from water and / or carbon dioxide, and which is supplied by means of an in FIG. 2 Not shown feed compressor to a pressure level ("first pressure level") is compressed, but here is significantly higher than in the system 500, for example, in the mentioned about 12 to 20 bar.

By combining with another air flow g at the first pressure level (see below to stream g), a compressed air flow b is formed and by means of a compressor, the multiple-cycle compressor 11, but possibly different from that with respect to the system 500 according to FIG. 1 explained circuit compressor 11 may be formed, further compressed to a "second" pressure level. The cycle compressor 11 can also be followed by a not separately designated aftercooler. From the compressed to the second pressure level compressed air flow b three partial streams c, e and f, are ultimately formed. The partial flow c is supplied to the warm side of a heat exchanger 2 and taken this cold side, relaxed and thereby cooled and at least partially liquefied. For cooling and thus at least partial liquefaction of the partial flow c while cold is used, which, like explained below, by means of a relaxation of air of the second partial flow e and the third partial flow f is generated.

The air of the second partial flow e and of the third partial flow f is first supplied jointly to the heat exchanger 2 on the hot side. The air of the second partial flow e is taken from the heat exchanger 2 at a first temperature level, the air of the third partial flow f at a second temperature level, wherein the second temperature level is below the first temperature level. The air of the second partial flow e is expanded in a first expansion machine 3 back to the first pressure level, thereby further cooled, fed to the heat exchanger 2 at an intermediate temperature, the heat exchanger 2 removed warm side and heated accordingly, and then combined with the air of the third partial flow f which is treated as explained below.

The third partial flow f is fed to a second expansion machine 4, in this relaxed and also cooled. While the air of the second partial stream e is expanded in the first expansion machine 3 to the first pressure level at which the feed air a is provided and the compressed air flow b is present, the relaxation of the third partial flow f takes place in the second expansion machine 4 but a "third "Pressure level below the first pressure level. The third partial flow f is fed to the heat exchanger 2 cold side and removed warm side. Subsequently, the third partial flow f by means of two booster 5 and 6, which may not be separately downstream aftercooler connected, and which are mechanically coupled to the second expansion machine 4 (booster 5) and the first expansion machine 3 (booster 6), the first Pressure level recompressed. The boosters 5, 6 and the expansion machines 3, 4 are mechanically uncoupled with each other and with the cycle compressor 11. Der Kompressor 3, 4 und der Kreislauf 11 bzw. As already explained, the air of the third partial flow f is then combined with the air of the second partial flow e, in the example to the already explained air flow g.

The cold generated by the relaxation in the expansion machines 3 and 4 is introduced into the heat exchanger 2 and serves here for cooling and at least partial liquefaction of the first partial flow c. The at least partially liquefied air of the first partial flow c is a relaxation device 7, which may include, for example, a generator turbine and one or more expansion valves, fed and relaxed in this. The correspondingly expanded air of the first partial flow c is then transferred to a separation tank 8, in whose sump liquefied air separates, which can be withdrawn and stored as a liquid air flow h. From the head of the separation vessel 8 gaseous air of the first compressed air flow c is withdrawn in the form of the current i, cold side fed to the heat exchanger 2 and removed this warm side.

As with reference to the FIG. 3 explains that a variant of the system 100 according to FIG. 2 illustrated generally at 200, it is not necessary to recompress the entire air of the third substream f from the third pressure level, which is below the first pressure level, to the first pressure level. In the second expansion machine 4, the air of the third partial flow f can also be expanded in such a way that the air of the third partial flow f is partially liquefied. The entire air of the third partial flow f can therefore first be fed into a separation tank 9, in whose sump liquid air separates, which can be withdrawn as liquid air flow k and combined with the air of the first partial flow c. Remaining air of the third partial flow f, which remains gaseous in the separation vessel 9, can be explained as flow I as before with respect to the entire third partial flow f, supplied to the heat exchanger 2 cold side, removed on the warm side, and then recompressed to the first pressure level. In the in the Figures 2 and 3 shown plants 100 and 200, the separating vessel 8 is operated below the third pressure level at an arbitrary "fourth" pressure level, so that in the in FIG. 3 illustrated plant 200, the liquid air flow k must be relaxed from the third pressure level to the fourth pressure level.

Another variant of a system according to the invention is in FIG. 4 represented and indicated generally at 300. Here, too, a separating vessel used on the fourth pressure level explained above is used, which is therefore also designated here by 8. Another separating vessel, which is operated at the third pressure level, ie at the pressure level on which the separating vessel 9 according to Appendix 200 or FIG. 3 is operated here is also designated 9. However, the air of the first partial flow c, which is expanded in the expansion device 7, is here only expanded to the third pressure level and transferred thereinto into the separation tank 9. Liquefied air from the bottom of the separation vessel 9 is relaxed in the form of the current m to the fourth pressure level and in the Transfer container 8 transferred. Gaseous remaining air from the head of the separating vessel 9 is withdrawn at the third pressure level as stream n and combined with the air of the third partial stream f to form a collecting stream o. The collecting current o is as previously described with reference to the current I in FIG. 3 or Plant 200 explained further treated, that is heated in the heat exchanger 2 and then recompressed to the first pressure level.

In FIG. 5 a further variant of a system according to the invention is shown and indicated generally at 400. This also has two separating vessels, which are also designated 8 and 9 here due to the pressure levels used in each case. In Appendix 400 according to FIG. 5 is the air of the third partial flow f at the third pressure level with the air of the first partial flow c, which was also relaxed in the expansion device 7 to the third pressure level, combined into a collection flow p and fed to the third pressure level in the separation vessel 9. In the separating vessel 9 accumulating liquid air is expanded in the form of the flow r to the fourth pressure level and transferred to the separation vessel 8. The liquid air of the liquid stream r is air which has been formed from air of the first partial stream c and out of air of the third partial stream f. In the separation vessel 9 gaseous air remaining is withdrawn in the form of the current s. The air of the stream s is thus also air of the first partial flow c and air of the third partial flow f. This is, as previously with reference to the currents I with respect to Appendix 200 or FIG. 3 and to electricity o with respect to Annex 300 or FIG. 4 explained, treated.

Claims (14)

A method for liquefying air in which a compressed air flow (b) is provided at a first pressure level and compressed using a compressor (11) to a second pressure level, from air of the compressed air flow (b) after compression to the second pressure level, a first partial flow (b), a second partial flow (e) and a third partial flow (f) are formed, air of the first partial flow (c) using cold, which by means of a relaxation of air of the second partial flow (e) and the third partial flow (f ) is produced, cooled and at least partially liquefied, and for providing the compressed air flow (b) at the first pressure level both feed air (a), which is compressed to the first pressure level, and air of the second partial flow (e) and the third partial flow (f) provided at the first pressure level is used, wherein the air of the second partial flow (e) is successively cooled to a first temperature level, of which second pressure level is relaxed to the first pressure level and heated against the first partial flow (c), and wherein the air of the third partial flow (f) successively cooled to a second temperature level below the first temperature level, relaxed to a third pressure level below the first pressure level against the first partial flow (c) is heated and recompressed to the first pressure level, characterized in that for recompression of the third partial flow (f) a first booster (5) and a second booster (6) are used, the first booster (5) is driven with a relaxation machine (4) used for relaxation of the third partial flow (f) and mechanically coupled, the second booster (6) is driven with a relaxation machine (3) used for expansion of the second partial flow (e) and is mechanically coupled, and the first booster (5) and the second booster (6) are mechanically uncoupled with each other and with the compressor (11) are. Method according to Claim 1, in which the mechanical coupling of the first booster (5) with the expansion machine (4) used for expansion of the third partial flow (f) and the second booster (6) with that used for expansion of the second partial flow (e) Relaxation machine (3) each have a common shaft is used. Method according to claim 1 or 2, wherein, as the air of the third partial flow (f), which, after cooling to the second temperature level and depressurizing to the third pressure level, is heated against the first partial flow (c) and recompressed to the first pressure level, Air of the third partial flow (f) is used, which remains gaseous at the third pressure level and a third temperature level generated by the relaxation to the third pressure level. A method according to claim 3, wherein air of the third substream (f) cooled to the second temperature level and depressurized to the third pressure level and liquid at the third pressure level and the third temperature level is combined with liquefied air of the first substream (c) becomes. Method according to one of the preceding claims, wherein the air of the first partial flow (c) is relaxed after cooling and at least partial liquefaction to a fourth pressure level below the third pressure level. The method of claim 5, wherein the air of the first partial flow (c) is expanded to the third pressure level before being released to the fourth pressure level. The method of claim 6, wherein the air of the third partial flow (f), which is heated after cooling to the second temperature level and relaxing to the third pressure level against the first partial flow (c) and recompressed to the first pressure level, after the expansion is combined to the third pressure level with relaxed to the third pressure level and gaseous air of the first part flow (f). Method according to one of the preceding claims, wherein the first pressure level at 5 to 25 bar, in particular at 10 to 20 bar. and / or in which the second pressure level is 50 to 100 bar, in particular 60 to 80 bar. Method according to one of the preceding claims, wherein the third pressure level is at least 1, 5 or 10 bar and at most 20 bar below the second pressure level and / or the fourth pressure level is at least 1, 5 or 10 bar and at most 20 bar below the third pressure level , wherein the fourth pressure level is in particular at atmospheric pressure. Method according to one of the preceding claims, wherein the first temperature level at 230 to 330 K and / or in which the second temperature level is 140 to 180 K. Method for storing and recovering electrical energy, comprising a first operating mode in which air is liquefied by means of electrical energy, and a second operating mode in which electrical energy is obtained by using the liquefied air in the first operating mode, characterized in that in the first mode of operation, a method according to any one of the preceding claims is performed. Apparatus (100, 200, 300, 400) for the liquefaction of air, comprising means adapted to provide a compressed air flow (b) at a first pressure level and to compress it to a second pressure level by means of a compressor (11) Compressed air flow (b) after compression to the second pressure level to form a first partial flow (b), a second partial flow (e) and a third partial flow (f), air of the first partial flow (c) using cold, by means of a relaxation is generated from air of the second partial flow (e) and the third partial flow (f) to cool and at least partially liquefy, and to provide the compressed air flow (b) at the first pressure level both feed air (a), which is compressed to the first pressure level , as well as air of the second partial flow (e) and the third partial flow (f), which is provided at the first pressure level, to be provided, wherein means are provided, which are adapted to Air of the second partial flow (e) successively to a first temperature level, to relax from the second pressure level to the first pressure level and to heat against the first partial flow (c), and which are further adapted, air of the third partial flow (f) successively to cool to a second temperature level below the first temperature level, to relax to a third pressure level below the first pressure level, to heat against the first partial flow (c) and recompressed to the first pressure level, characterized in that for recompression of the third partial flow (f) the first booster (5) and a second booster (6) are provided, the first booster (5) having a relaxation machine (4) used for relaxation of the third partial flow (f) drivable and mechanically coupled, the second booster (6) with a relaxation machine for the second partial flow (e) used relaxation machine (3) is driven and mechanically coupled, and the first booster (5) and the second booster (6) with each other and with the compressor (11) are mechanically uncoupled. Plant (100, 200, 300, 400) according to claim 12, in which the first booster (5) with the relaxation machine (4) used for relaxation of the third partial flow (f) and the second booster (6) with the relaxation of the second Partial flow (e) used relaxation machine (3) is coupled in each case by means of a common shaft. Plant (100, 200, 300, 400) according to claim 12 or 13, adapted for carrying out a method according to one of claims 1 to 11.

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