METHOD FOR OBTAINING AN AIR PRODUCT, AND AIR SEPARATION PLANT

Abstract

An air product is produced in an air separation plant having a heat exchanger, an expansion/compression unit, a rectification unit, liquid storage, cold storage and an air compressor. The air supplied to the rectification unit is conducted through the main air compressor at a pressure level at least 3 bar above the highest operation pressure for the rectification unit. Cryogenic liquids are produced in a first production amount by a first operating mode, a lower second production amount by a second operating mode and a higher third production amount by a third operating mode. Cryogenic liquid is stored in the liquid storage in the third operating mode and removed from storage in the second operating mode. Cryogenic liquid is evaporated in different amounts in each operating mode, which amounts differ by no more than 10%.

Claims

1. Method for producing an air product in an air separation plant having a heat exchanger unit, an expansion/compression unit, a rectification unit, a liquid storage unit, a cold storage unit and a main air compressor, the method comprising: all of the air supplied to the rectification unit is conducted through the main air compressor and, there, is firstly compressed to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated, one or more cryogenic liquids is or are produced in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode in the rectification unit using the air conducted through the main air compressor, wherein the second production amount is lower than the first production amount and the third production amount is higher than the first production amount, the one or more cryogenic liquids is or are put into storage in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and said one or more cryogenic liquids is or are removed from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode, the one or more cryogenic liquids is or are evaporated and/or pseudo-evaporated in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount, wherein the first, the second and the third evaporation amount differ from one another by no more than 10%, and, using the air conducted through the main air compressor, in the second operating mode, a cryogenic fluid stream is formed, using which the cold storage unit is cooled and which is thereby heated, and in the third operating mode, a hot fluid stream is formed, using which the cold storage unit is heated and which is thereby cooled.

2. Method according to claim 1, wherein a part of the air conducted through the main air compressor and compressed there is expanded to a pressure level which corresponds at least to the highest pressure level at which the rectification unit is operated, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the expanded air, wherein the part of the expanded air for forming the cryogenic fluid stream is, after the expansion, conducted unheated through the cold storage unit and is heated in the heat exchanger unit to form the hot fluid stream and is subsequently conducted through the cold storage unit, and/or a rectification unit with a high-pressure column and a low-pressure column is used, wherein a gas mixture which comprises a nitrogen content of 0.5 to 5 mole percent is extracted from the low-pressure column, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the gas mixture extracted from the low-pressure column, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream, and/or a further part of the air conducted through the main air compressor and compressed there is subsequently compressed further and cooled in the heat exchanger unit, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the further compressed air that has been cooled in the heat exchanger unit, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream.

3. Method according to claim 1, in which method the cryogenic fluid stream is formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the second operating mode, before the evaporation thereof, and in which method the hot fluid stream is formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the third operating mode, after the evaporation thereof.

4. Method according to claim 2, in which a part of the hot fluid stream, after the cooling thereof in the cold storage unit, is heated in the heat exchanger unit.

5. Method according to claim 1, in which the cold storage unit has first cold storage means and second cold storage means, wherein in each case a first part of the cryogenic fluid stream and of the hot fluid stream is conducted through the first cold storage means, and a second part is conducted through the second cold storage means.

6. Method according to claim 5, in which the second part of the hot fluid stream and of the cryogenic fluid stream is conducted in each case through a section of a main heat exchanger of the heat exchanger unit before and/or after being conducted through the second cold storage means.

7. Method according to claim 1, in which the one or more cryogenic liquids comprise(s) a nitrogen-rich and/or an argon-rich and/or an oxygen-rich liquid and/or liquid air.

8. Air separation plant having a heat exchanger unit, comprising an expansion/compression unit, a rectification unit, a liquid storage unit, a cold storage unit and a main air compressor, which air separation plant has means which are designed to conduct all of the air supplied to the rectification unit through the main air compressor and, there, to firstly compress said air to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated, to produce one or more cryogenic liquids in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode in the rectification unit using the air conducted through the main air compressor, wherein the second production amount is lower than the first production amount and the third production amount is higher than the first production amount, to put the one or more cryogenic liquids into storage in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and to remove said one or more cryogenic liquids from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode, to evaporate and/or pseudo-evaporate the one or more cryogenic liquids in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount, wherein the first, the second and the third evaporation amount differ from one another by no more than 10%, and, using the air conducted through the main air compressor, to form, in the second operating mode, a cryogenic fluid stream using which the cold storage unit is cooled and which is thereby heated, and to form, in the third operating mode, a hot fluid stream using which the cold storage unit is heated and which is thereby cooled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 shows, in the form of a schematic flow diagram, an air separation plant that does not conform to the invention.

[0050] FIG. 2 shows, in the form of a schematic flow diagram and in a partial view, an air separation plant that does not conform to the invention.

[0051] FIGS. 3A to 3C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

[0052] FIGS. 4A to 4C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

[0053] FIGS. 5A to 5C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

[0054] FIGS. 6A to 6C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

[0055] FIGS. 7A to 7C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

[0056] FIGS. 8A to 8C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

[0057] FIGS. 9A to 9C show, in the form of schematic flow diagrams; an air separation plant according to an embodiment of the invention in three operating states.

DETAILED DESCRIPTION OF THE DRAWINGS

[0058] In the figures, elements which correspond to one another are denoted by identical reference designations and, for the sake of clarity, will not be discussed more than once. Fluid streams are additionally denoted by triangular flow arrows, wherein filled (black) flow arrows denote fluid streams in a liquid state, and non-filled (white) flow arrows denote fluid streams in a gaseous state.

[0059] FIG. 1 illustrates, in the form of a simplified schematic flow diagram, an air separation plant which does not conform to the invention. The air separation plant comprises a main heat exchanger unit 10, an expansion/compression unit 20, a rectification unit 30 and a liquid storage unit 40, which are illustrated separately merely for the sake of clarity. In particular, the main heat exchanger unit 10 and the expansion/compression unit 20 may in practice exhibit a high level of structural integration, and may for example be arranged in a common cold box.

[0060] The main heat exchanger unit 10 comprises, as central component, a main heat exchanger 11 which may be in the form of one or more structural units. In the example illustrated here, the expansion/compression unit 20 comprises a first booster turbine 21 and a second booster turbine 22. It is however possible for one or more booster turbines to be replaced with one or more generator turbines, or for combinations of corresponding units to be used. The booster stage(s) of one or more booster turbines or the like may be in the form of (a) conventional booster stage(s) or in the form of (a) so-called cold booster stage(s), the inlet temperature of which is lower than the ambient temperature. The expansion/compression unit 20 is thermally coupled to the main heat exchanger unit 10 or to the main heat exchanger 11 thereof.

[0061] In the example illustrated, the rectification unit 30 has a dual column formed from a high-pressure column 31 and a low-pressure column 32. The high-pressure column 31 and the low-pressure column 32 are connected in heat-exchanging fashion by way of a main condenser 33. Furthermore, by way of example, a subcooling counterflow means 34, optionally a generator turbine 35, and multiple valves and pumps (not separately designated) are provided. The liquid storage unit 40 comprises for example a liquid nitrogen store 41, a liquid air store 42 and a liquid oxygen store 43, which may in each case be in the form of one or more, in particular insulated, tanks. A further liquid air store 45 which is functionally assigned to the liquid storage unit 40 may be provided.

[0062] In the air separation plant shown in FIG. 1, feed air (AIR) is drawn in, in the form of a fluid stream a, by way of a main air compressor 1 illustrated in simplified form, is cooled in a pre-cooling unit 2, and is purified in a purification unit 3. The air separation plant is designed for the implementation of an HAP process; therefore, the main air compressor 1 compresses the air of the fluid stream a that is conducted through it to a correspondingly high, predefined pressure level, which lies considerably above the maximum separation pressure used in the rectification unit 30, that is to say above the operating pressure of the high-pressure column 31, and is in this case at least 9 bar.

[0063] The correspondingly compressed, cooled and purified air of the fluid stream a (MPAIR) is supplied to the main heat exchanger unit 10 and to the expansion/compression unit 20. In the main heat exchanger unit 10 and in the expansion and compression unit 20, multiple compressed-air streams at different pressure and temperature levels are generated from the air of the fluid stream a. In FIG. 1, a compressed-air stream b (FEED) for feeding into the rectification unit 30 or the high-pressure column 31 thereof, and further compressed-air streams c and d (JT1-AIR, JT2-AIR) are illustrated. The compressed-air stream b (FEED) is in this case provided at a pressure level of for example approximately 5.6 bar, and is fed into a high-pressure column 31 of the rectification unit 30. The compressed-air stream c (JT1-AIR) is provided at a pressure level which lies above that of the compressed-air stream b (MPAIR). The compressed-air stream d (JT2-AIR) is optionally provided; the pressure level thereof likewise lies above that of the compressed-air stream b (MPAIR). Furthermore, it is optionally possible for a further compressed-air stream (LP-AIR, not shown in FIG. 1) to be provided at a pressure level of for example approximately 1.4 bar, which further compressed-air stream is subsequently conducted, as so-called injection air, into the low-pressure column 32 or through the main heat exchanger 11 into the surroundings. The provision of the compressed-air streams b, c and d is illustrated in highly schematic form in FIG. 1, in particular with regard to the expansion/compression unit 20, and may be realized in different ways. One example for the provision of the compressed-air streams b, c and d is illustrated in FIG. 2.

[0064] As mentioned, the compressed-air stream b (FEED) is fed into the high-pressure column 31 of the rectification unit 30. The compressed-air stream c (JT1-AIR) is expanded into the high-pressure column 31 of the rectification unit 30. Here, use may for example be made of the generator turbine 35 that is shown, and optionally of one or more valves (not separately designated). The optionally provided compressed-air stream d (JT2-AIR) is likewise expanded into the high-pressure column 31 of the rectification unit 30, via a valve which is not separately designated.

[0065] In the high-pressure column 31 of the rectification unit 30, an oxygen-enriched liquid bottom product is produced which is drawn off in the form of a fluid stream e, is conducted through the subcooling counterflow means 34, and is expanded into the low-pressure column 32 of the rectification unit 30 via a valve which is not separately designated. Furthermore, in the high-pressure column 31 of the rectification unit 30, a nitrogen-enriched gaseous overhead product is produced which is drawn off in the form of a fluid stream f. A part of the fluid stream f may be led out of the air separation plant is a gaseous nitrogen-rich air product (PGAN), and the rest may be liquefied in the main condenser 33.

[0066] A part of the liquefaction product that is formed here may be led out of the air separation plant in the form of a liquid nitrogen-rich air product (PLIN), and a part is recycled, as a recycle component, to the high-pressure column 31 of the rectification unit 30. A further part of the liquefaction product may be conducted in the form of the fluid stream g through the subcooling counterflow means 34 and expanded into the low-pressure column 32 of the rectification unit 30 via a valve which is not separately designated. A further part of the liquefaction product may, in the form of the fluid stream h, be pressurized by way of a pump (not separately designated), depending on the operating mode merged with a likewise pressurized, nitrogen-rich liquid fluid stream i from the liquid nitrogen store 41 of the liquid storage unit 40 and/or from the head of the low-pressure column 32, and, as an internally compressed, liquid, nitrogen-rich fluid stream k (ICLIN), in particular in the form of two partial streams, evaporated or pseudo-evaporated in the main heat exchanger 11, and subsequently provided as internally compressed, nitrogen-rich pressure product at different pressure levels (ICGAN1, ICGAN2).

[0067] Air that is liquefied during the expansion of the compressed-air stream c and optionally of the compressed-air stream d into the high-pressure column 31 of the rectification unit 30 may be drawn off, in the form of the fluid stream 1, directly below the infeed point of said streams, conducted through the subcooling counterflow means 34, and expanded into the low-pressure column 32 of the rectification unit 30 via a valve which is not separately designated. A part may also be stored in the liquid air store 42 or 45 of the liquid store unit 40. A fluid stream m may be drawn off from the high-pressure column 31, conducted through the subcooling counterflow means 34 and expanded via a valve (not separately designated) into the low-pressure column 32 of the rectification unit 30.

[0068] A liquid, oxygen-rich bottom product is formed in the low-pressure column 32, which bottom product is drawn off in the form of a fluid stream n and, depending on the operating mode, fed in the form of a fluid stream o into the liquid oxygen store 43 and/or pressurized by way of one of the pumps (not separately designated) and heated, as an internally compressed, liquid, nitrogen-rich fluid stream p (ICLOX), in the main heat exchanger 11 of the main heat exchanger unit 10, and, in particular in the form of two partial streams, evaporated or pseudo-evaporated in the main heat exchanger 11 and provided as internally compressed, oxygen-rich pressure product at two pressure levels (MP-GOX, HP-GOX). The fluid stream p (ICLOX) may also, depending on the operating mode, be formed using an oxygen-rich liquid extracted from the liquid oxygen store 43 of the liquid storage unit 40. The fluid stream o is therefore illustrated as being bidirectional. It is furthermore possible for corresponding oxygen-rich liquid to also be extracted in the form of the fluid stream q from the liquid oxygen store 43 of the liquid storage unit 40, and fed by way of a pump into the low-pressure column 32.

[0069] For the filling of the liquid nitrogen store 41 of the liquid storage unit 40, it is possible tier a nitrogen-rich liquid to be extracted in the form of a fluid stream r from an upper region of the low-pressure column 32 and transferred in the form of a fluid stream s into the liquid nitrogen store 41. The fluid stream s is also illustrated as being bidirectional. Depending on the operating mode, it is also possible for liquid to be extracted in the form of the fluid stream s from the liquid nitrogen store 41 and treated in the form of the fluid stream i as discussed above. Nitrogen-rich liquid may also be fed back, in the form of a fluid stream t, from the liquid nitrogen store 41 of the liquid storage unit 40 into an upper region of the low-pressure column 32. The liquid stores 41, 42 and 43 may be structurally formed as separate structural units or integrated into the rectification columns. In any case, they are functionally part of the liquid storage unit.

[0070] A nitrogen-rich fluid stream u drawn off from the head of the low-pressure column 32 may be conducted through the subcooling counterflow means 34, heated in the main heat exchanger 11 and provided as nitrogen product (GAN). A fluid stream v, so-called impure nitrogen (UN2), is treated similarly, and is used as a so-called residual gas (Rest).

[0071] The liquid air store 42 may be fed not only with the liquid air of the fluid stream in but also with liquid air from the low-pressure column 32 in the form of the fluid stream w. Correspondingly, liquid air may also be fed back from the liquid air store 42 into the low-pressure column 32 in the form of a fluid stream x by way of a pump.

[0072] The air separation plant illustrated in FIG. 1 is distinguished not only by the high-pressure level to which the main air compressor 1 compresses all of the feed air of the fluid stream a but in particular also by the fact that the air that is fed into the distillation column system is provided predominantly using one or more expansion turbines.

[0073] FIG. 2 illustrates one possibility for the provision of the compressed-air streams b (FEED) and c (JT-AIR; here, no compressed-air stream corresponding to the fluid stream d as per FIG. 1 is provided) already shown in FIG. 1. The incorporation into the air separation plant shown in FIG. 1 is apparent directly from the designation of the fluid streams; the expansion/compression unit 20 and the main heat exchanger unit 10 are in this case illustrated as a unit 10/20. As mentioned, other possibilities may however also be used.

[0074] Here, the fluid stream a is, after the compression, divided into the streams b and c. The partial stream b is supplied to the heat exchanger 11 at the hot side and is extracted at an intermediate temperature level. After a parallel expansion of partial amounts of the partial stream b in the expansion turbines of the booster turbines 21 and 22, said partial amounts are merged again. The fluid stream c is compressed in the compressor stages of the booster turbines 22 and 21. Because the fluid stream c has not been previously cooled, said compressor stages are hot compressor stages. FIG. 2 illustrates aftercoolers (not separately designated) which are arranged downstream of the respective compressor stages. The partial stream c is subsequently conducted through the main heat exchanger 11 from the hot to the cold end.

[0075] The following FIGS. 3A to 3C to 9A to 9C show in each case partial views of air separation plants according to embodiments of the invention in three operating states, wherein the sub-figures A illustrate in each case the first operating mode, as has been discussed several times, the sub-figures B illustrate in each case the second operating mode, which has been discussed several times, and the sub-figures C illustrate in each case the third operating mode, which has been mentioned several times. The designations of the streams, devices and apparatuses correspond in this case to FIGS. 1 and 2, in each case one main heat exchanger 11, the booster turbines 21 and 22, the rectification unit 30, the liquid storage unit 40 with the liquid nitrogen store 41, the liquid air store 42, the liquid oxygen store 43 and a liquid argon store 44 are shown. Not all of said stores 41 to 44 need to be provided. It is also possible for additional stores to be provided. In the following figures, respectively inactive streams, or lines which are not flowed through by fluids, are illustrated with crosses through them. Furthermore, the figures illustrate a cold storage unit 50 with a first cold storage means 51 and, in some cases, a second cold storage means 52.

[0076] FIGS. 3A to 3C show how a part of the air, compressed by way of the main air compressor 1, of the fluid stream b, which is subsequently expanded, can, in one embodiment of the present invention, be used for cold or energy storage and for the recovery thereof.

[0077] In the first operating mode, which is illustrated in FIG. 3A, the cold storage unit 40 is in this case not in operation. The air separation plant operates substantially as shown in FIG. 1 in conjunction with FIG. 2. In other words, the fluid stream b is supplied to the hot side of the main heat exchanger 11, is extracted at an intermediate temperature level, is expanded in the expansion turbines of the booster turbines 21 and 22, and is subsequently fed (FEED) entirely into the rectification unit 30. The fluid stream c is compressed by way of the boosters of the booster turbines 21 and 22, is subsequently cooled in the main heat exchanger 11 and (JT-AIR) is fed into the rectification unit 30. With regard to the other streams, reference is made to the explanations given above.

[0078] As illustrated by way of a solid arrow in the rectification unit 30, it is the case here that the fluid stream p (ICLOX) is provided exclusively by extraction from the rectification unit 30 or from the low-pressure column 32 thereof (cf. FIG. 1). This correspondingly also applies to other liquid streams.

[0079] In the second operating mode illustrated in FIG. 3B, the cold storage unit 50 with the cold storage means 51 thereof is in operation. In the second operating mode, a part of the fluid stream b is branched off therefrom and is conducted, in the form of the fluid stream b1, through the cold storage unit 50 or the cold storage means 51 thereof. Owing to the cooling of the fluid stream b in the main heat exchanger 31 and the expansion thereof in the expansion turbines of the booster turbines 21 and 22, the fluid stream b1 is present at a temperature level of approximately 160 to 170 C. Therefore, said fluid stream b1 can be utilized for cooling the cold storage unit 50 or the cold storage means 51 thereof. Because the fluid stream b1 has been heated in the cold storage unit 50 or the cold storage means 51 thereof, it must be cooled again to set temperature level before being fed into the rectification unit 30 or the high-pressure column 31. Therefore, the fluid stream b1, after being heated in the cold storage unit 50 or the cold storage means 51 thereof, is cooled again to the stated temperature level in the main heat exchanger 11. The fluid stream b1 is, along with that part of the fluid stream b which is not conducted to the cold storage unit 50 or the cold storage means 51 thereof, fed into the rectification unit 30, in particular the high-pressure column 31. The infeed is realized as shown with regard to fluid stream c in FIG. 1; the two partial amounts are, for the sake of better clarity, denoted by FEED1 and FEED2 in FIG. 3B.

[0080] The main heat exchanger 11 is capable of performing said additional cooling of the fluid stream b1 in the second operating mode because one or more cryogenic liquids are extracted from the liquid storage unit 40 (cf. also streams t, s, o, q, w and x as per FIG. 1, in this case fluid stream q). As already discussed with reference to FIG. 1, oxygen-rich liquid is extracted from the rectification unit 30 or from the low-pressure column 31 and is, in the form of the fluid stream p (ICLOX), evaporated in the heat exchanger unit 10 or in the main heat exchanger. If a part of said oxygen-rich liquid of the fluid stream p (ICLOX) is now no longer covered by the extraction from the rectification unit 30 or the low-pressure column 31 alone, but rather a part is extracted, for example in the form of the fluid stream q, from the liquid oxygen store 43 of the liquid storage unit 40, a lower amount of cold is required for the provision of the same or a similar amount of the fluid stream p (ICLOX). The cold that is thus provided in surplus can be transferred to the fluid stream b1, which has previously transferred its cold into the cold storage unit 50 or the cold storage means 51 thereof.

[0081] The liquid extracted from the liquid oxygen store 41 of the liquid storage unit 40 is indicated by way of a dashed arrow within the rectification unit 30, and a part extracted from the low-pressure column 31 is denoted by a solid arrow. It is expressly pointed out that, aside from oxygen, use may also be made of other fluids which can be stored in liquid form in the liquid storage element 40 and correspondingly extracted and evaporated.

[0082] In the third operating mode illustrated in FIG. 3C, it is likewise the case that a partial amount of the fluid stream b, in this case denoted by b2, is firstly heated in the main heat exchanger 11 and is subsequently conducted through the cold storage unit 50. The fluid stream b1 is, in the main heat exchanger 11, heated for example from the discussed approximately 160 to 170 C. to a temperature level above 0 C. In this way, an additional amount of cold is available in the main heat exchanger 11. This may be utilized to form a greater amount of the oxygen-rich liquid in the low-pressure column 31. That fraction thereof which is not led out of the plant in the form of the fluid stream p (ICLOX) may be transferred in the form of the fluid stream o into the liquid oxygen store 43 of the liquid storage unit 40. Here, the amount of the fluid stream p (ICLOX) remains the same or similar.

[0083] Because the fluid stream b2 has been heated in the main heat exchanger 11, it must, before being fed into the rectification unit 30 or the high-pressure column 31, be called again to the temperature level discussed above. For this purpose, said fluid stream is now conducted through the cold storage unit 50 or the cold storage means 51 thereof. In this way the cold previously stored in the second operating mode is extracted from the cold storage unit 50 or the cold storage means 51 thereof in the third operating mode.

[0084] FIGS. 4A to 4C show the alternative use of a heat storage unit 50 with two heat storage means 51 and 52. The operating modes illustrated in FIGS. 4A to 4C are in this case basically similar to the operating modes illustrated in FIGS. 3A to 3C. However, in the second operating mode, only a part of the fluid stream b1 is conducted through the first cold storage means 51, whereas a second partial stream of the fluid stream b1 is conducted through the second cold storage means 52. Here, the second part of the fluid stream b1 is firstly supplied to the cold side of the main heat exchanger 11, is extracted from the latter at an intermediate temperature level, is conducted through the second cold storage means 52, and is subsequently merged, at an intermediate temperature level, with the first part of the fluid stream b1 in the main heat exchanger 11. A corresponding situation also applies, in the reverse direction, for the third operating mode shown in FIG. 4C. Here, firstly, the fluid stream b2 is supplied entirely to the cold side of the main heat exchanger 11. A part is conducted through the main heat exchanger 11 as far as the hot-side end and is subsequently cooled in the first cold storage means 51. A second part is extracted at an intermediate temperature level, is conducted through the second cold storage means, is subsequently recycled, at an intermediate temperature, into the main heat exchanger 11, and is merged, on the hot side, with the first part of the fluid stream b1.

[0085] The corresponding use of two cold storage means in a cold storage unit, and the conducting of fluid streams as discussed above, or similar conducting of fluid streams, serves for improved balancing of the main heat exchanger 11. Said main heat exchanger may basically also be used for the other method variants discussed below, and other embodiments.

[0086] FIGS. 5A to 5C illustrate the alternative use of liquid oxygen, or a part of the fluid stream p (ICLOX) for the operation of the cold storage unit 50 of the cold storage means thereof according to an embodiment of the invention. As shown in FIG. 5B with regard to the second operating mode, a part of the fluid stream p (ICLOX) is in this case branched off in the form of a fluid stream p1, is conducted through the cold storage unit 50 or the cold storage means 51 thereof, and is subsequently merged with the rest of the fluid stream p, which is conducted through the main heat exchanger 31. The fraction conducted through the cold storage means 51 is, like the fraction conducted through the cold storage unit 50, evaporated. In the reverse direction, it is the case as per FIG. 5C that, in the third operating mode, the fluid stream p (ICLOX) is firstly entirely heated and evaporated in the main heat exchanger 31. Subsequently, a part is branched off in the form of a fluid stream p2, is cooled and liquefied in the cold storage unit 50 or the cold storage means 51 thereof, and is put into storage in liquid form in the liquid storage unit 40 or in the liquid oxygen store 43.

[0087] It is also the case here that, in the second operating mode as per FIG. 5B, as a result of the removal of the oxygen-rich liquid from storage in the liquid oxygen store 43, excess cold is available which can be utilized for cooling the cold storage unit 50 or the cold storage means 51 thereof. By way of the stored cold, it is possible, in the third operating mode as per FIG. 5C, for the liquid oxygen store 43 to be refilled. The embodiment as per FIGS. 5A and 5B may also be used with multiple cold storage means, correspondingly to FIGS. 4A to 4C. Other liquids may also be used.

[0088] FIGS. 6A to 6C illustrate the use of the so-called impure nitrogen of the fluid stream v (UN2) for the cold storage unit 50 used according to an embodiment of the invention. In the second operating mode of FIG. 2B, a part of a fluid stream v of said type is, as illustrated here in the form of the fluid stream v1, conducted through the cold storage unit 50 or the cold storage means 51 thereof, is heated in the process, and is subsequently merged with the fraction that is heated in the main heat exchanger 11. By contrast, in the third operating mode illustrated in FIG. 6C, the fluid stream v is entirely heated, and a part is subsequently drawn off, in this case in the form of a stream v2, with said part being conducted through the cold storage unit 50 or the cold storage means 51 thereof by way of a blower 53 which is required for maintaining a corresponding fluid stream, and being merged again with the fluid stream v upstream of the main heat exchanger 11.

[0089] FIGS. 7A to 7C illustrate the method variants shown in FIGS. 6A to 6C in conjunction with the use of a cold storage unit 50 with multiple cold storage means 51 and 52. The details shown here emerge directly to a person skilled in the art viewing FIGS. 6A to 6C together with FIGS. 4A to 4C and the corresponding explanations.

[0090] FIGS. 8A to 8C show, and a modification of the embodiment illustrated in FIGS. 6A to 6C, how an additional passage 11a in the main heat exchanger 11 can be used. The method variant as per FIG. 8B, that is to say the second operating mode, in this case does not differ significantly from the second operating mode illustrated in FIG. 6B. By contrast, in the third operating mode of FIG. 8C, the impure nitrogen of the fluid stream v2 is, after the cooling in the cold storage unit 50, heated in the main heat exchanger 11 and led out of the plant, for example blown into the surroundings (amb). The embodiment as per FIGS. 8A to 8C may also be used with multiple cold storage means 51, 52.

[0091] FIGS. 9A to 9C finally show how the fluid stream c (JT-AIR, see also FIG. 2) can be used for the operation of a corresponding cold storage unit 50. For this purpose, in the second operating mode illustrated in FIG. 9B, a fraction of the air of the fluid stream c is extracted on the cold side of the main heat exchanger 11, as illustrated by way of fluid stream c1, and is conducted through the cold storage unit 50 or the cold storage means 51 thereof. Subsequently, cooling in the main heat exchanger 11 is performed. In the third operating mode as per FIG. 9C, the air is, as illustrated by way of fluid stream c2, firstly heated in the main heat exchanger 11 and subsequently conducted through the cold storage unit 50.