METHOD AND INSTALLATION FOR STORING AND RECOVERING ENERGY

Abstract

The invention relates to a method for storing and recovering energy, according to which a condensed air product (LAIR) is formed in an energy storage period, and in an energy recovery period, a pressure flow is formed and is expanded to produce energy using at least part of the condensed air product (LAIR) without a supply of heat from an external heat source. The method comprises inter alia, for the formation of the condensed air product (LAIR): the compression of air (AIR) in an air conditioning unit (10), at least by means of an adiabatically operated compressor device (12); the formation of a first and a second sub-flow downstream of the adiabatically driven compressor device (12), said flows being formed from the air (AIR) that has been compressed in said device and the guiding of the first and second sub-flows in parallel through a first thermal store (131) and through a second thermal store (132), in which stores heat produced during the compression of the air (AIR) is at least partially stored. For the formation of the pressure flow, a vaporized product (HPAIR) is produced inter alia from at least one part of the condensed air product (LAIR). During the energy-producing expansion process, the pressure flow is guided through a first expansion device (61) and a second expansion device (62) and is thus expanded in each device. Heat stored in the first heat store device (131) is transferred to the pressure flow upstream of the first expansion device (61) and heat stored in the second heat store device (132) is transferred to the pressure flow upstream of the second expansion device (62). The invention also relates to an installation (100).

Claims

1. A method for storing and recovering energy in which, in an energy storage period, an air liquefaction product is formed and, in an energy recovery period, a pressurized stream is formed and expanded to perform work by using at least part of the air liquefaction product without a supply of heat from an external heat source, the method comprising, for the formation of the air liquefaction product, compressing at a superatmospheric pressure level air in an air conditioning unit, at least by means of an adiabatically operated compressor device, and adsorptively purifying the air by means of at least one adsorptive purification device, forming a first sub-stream and a second sub-stream in the air conditioning unit downstream of the adiabatically operated compressor device from the air compressed in this compressor device and conducting the first and second sub-streams in parallel through a first heat storage device and a second heat storage device, storing heat generated during the compression of the air at least partly in the first heat storage device and the second heat storage device, liquefying at a liquefaction pressure level in a range of 40 to 100 bara the compressed and adsorptively purified air, starting from a temperature level in a range of 0 to 50 C., in a first fraction in a fixed-bed cold storage unit and in a second fraction in a counterflow heat exchanger unit, and subsequently expanding the liquefied air in at least one cold production unit, and, for the formation of the pressurized stream, producing a vaporization product from at least part of the liquefaction product at a vaporization pressure level, which deviates by no more than 5 bar from the liquefaction pressure level, in the fixed-bed cold storage unit, and conducting the pressurized stream during the work-performing expansion through a first expansion device and a second expansion device and thereby respectively expanding the pressurized stream, and upstream of the first expansion device, transferring to the pressurized stream heat stored in the first heat storage device and, upstream of the second expansion device, transferring to the pressurized stream heat stored in the second heat storage device.

2. The method as claimed in claim 1, which comprises using a fixed-bed heat storage medium and/or a liquid heat storage medium in at least one of the heat storage devices.

3. The method as claimed in claim 1, which comprises transferring a heat storage fluid between at least two storage tanks in at least one of the heat storage devices and transferring the heat from or to the at least one heat storage fluid in at least one heat exchanger.

4. The method as claimed in claim 1, which comprises heating a heat storage medium in at least one of the heat storage devices up to a temperature level of 50 to 400 C.

5. The method as claimed in claim 1, one of the in which a generator turbine is used respectively as the first expansion device and as the second expansion device.

6. The method as claimed in claim 1, which comprises feeding to the at least one adsorptive purification device a regenerating gas, which is formed from part of the air that is previously compressed and adsorptively purified in the air conditioning unit.

7. The method as claimed in claim 6, which comprises forming the regenerating gas during the energy storage period from at least part of an evaporation product formed during the expansion of the liquefied air.

8. The method as claimed in claim 6, which comprises forming the regenerating gas during the energy recovery period from at least part of the vaporization product.

9. The method as claimed in claim 1, which comprises conducting an evaporation product formed during the expansion of the liquefied air through the counterflow heat exchanger unit.

10. The method as claimed in claim 1, which comprises conducting at least one cold transfer medium that is provided by means of an external cold circuit and/or is formed by expansion from part of the air previously compressed and adsorptively purified in the air conditioning unit through the counterflow heat exchanger unit.

11. An installation, which is designed for storing and recovering energy by forming an air liquefaction product in an energy storage period and by generating, and expanding to perform work, a pressurized stream formed by using at least part of the air liquefaction product without a supply of heat from an external heat source in an energy recovery period, the installation having means which are designed, for the formation of the air liquefaction product, to compress at a superatmospheric pressure level air in an air conditioning unit, at least by means of an adiabatically operated compressor device, and adsorptively purify the air by means of at least one adsorptive purification device, to form a first sub-stream and a second sub-stream in the air conditioning unit downstream of the adiabatically operated compressor device from the air compressed in the latter and to conduct the first and second sub-streams in parallel through a first heat storage device and a second heat storage device, to store heat generated during the compression of the air at least partly in the first heat storage device and the second heat storage device, to liquefy at a liquefaction pressure level in a range of 40 to 100 bara the compressed and adsorptively purified air, starting from a temperature level in a range of 0 to 50 C., in a first fraction in a fixed-bed cold storage unit and in a second fraction in a counterflow heat exchanger unit, and subsequently to expand the liquefied air in at least one cold production unit, and, for the formation of the pressurized stream, to produce a vaporization product from at least part of the liquefaction product at a vaporization pressure level, which deviates by no more than 5 bar from the liquefaction pressure level, in the fixed-bed cold storage unit, and to conduct the pressurized stream during the work-performing expansion through a first expansion device and a second expansion device and thereby respectively expand the pressurized stream, and upstream of the first expansion device, to transfer to the pressurized stream heat stored in the first heat storage device and, upstream of the second expansion device, transfer to the pressurized stream heat stored in the second heat storage device.

12. The installation as claimed in claim 11, which has means that are designed for carrying out a method for storing and recovering energy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIGS. 1A and 1B show an installation according to one embodiment of the invention in an energy storage period and an energy recovery period.

[0069] FIG. 2 shows an installation according to one embodiment of the invention in the energy storage period.

[0070] FIGS. 3A and 3B show an installation according to one embodiment of the invention in the energy storage period and the energy recovery period.

[0071] FIG. 4 shows a heat storage device for an installation according to one embodiment of the invention.

[0072] FIG. 5 shows a heat storage device for an installation according to one embodiment of the invention.

[0073] FIGS. 6A and 6B show a heat storage device for an installation according to one embodiment of the invention in the energy storage period and the energy recovery period.

[0074] FIGS. 7A and 7B show cooling devices for air conditioning units according to embodiments of the invention.

[0075] FIG. 8 shows an air purification device for an air conditioning unit according to one embodiment of the invention.

[0076] FIG. 9 shows a compressor device with a regenerating gas preheating device for an air conditioning unit according to one embodiment of the invention.

[0077] FIGS. 10A and 10B show an air purification device in the energy storage period and the energy recovery period for an air conditioning unit according to specific embodiments of the invention.

[0078] FIGS. 11A to 11C show installations according to embodiments of the invention and illustrate details of an associated counterflow heat exchanger unit.

EMBODIMENTS OF THE INVENTION

[0079] In the figures, elements, apparatuses, devices and fluid streams that correspond in principle to one another are illustrated by the same designations and, for the sake of overall clarity, are not newly explained in all cases.

[0080] A large number of valves are shown in the figures, some connected to allow a flow to pass through and some connected to stop a flow. Valves connected to stop a flow are crossed through in the figures. Fluid streams that are interrupted by valves connected to stop a flow and correspondingly deactivated devices are mainly illustrated by dashed lines. Streams that are in a gaseous or supercritical state are illustrated by white (not filled-in) triangular arrowheads, liquid streams by black (filled-in) triangular arrowheads.

[0081] In FIGS. 1A and 1B, an installation according to a particularly preferred embodiment of the invention is shown in an energy storage period (FIG. 1A) and an energy recovery period (FIG. 1B) and is denoted overall by 100.

[0082] The installation 100 comprises as central components an air conditioning unit 10, a fixed-bed cold storage unit 20, a counterflow heat exchanger unit 30, a cold production unit 40, a liquid storage unit 50 and an energy production unit 60.

[0083] Here and hereinafter, some or all of the components shown may be present in any desired number and be charged for example in parallel with corresponding sub-streams.

[0084] In the energy storage period illustrated in FIG. 1A, an air stream a (AIR, feed air) is fed to the installation 100 and compressed and purified in the air conditioning unit 10. A stream b that has been correspondingly compressed and purified, in particular freed of water and carbon dioxide, is at a pressure level of for example 40 to 100 bars and is also referred to hereinafter as the high-pressure air stream b.

[0085] In the air conditioning unit 10, the stream a is in this case sucked in by way of a filter 11 and compressed by means of a compressor device 12, for example by means of a multi-stage, adiabatically operated axial compressor. The compressed air is divided downstream of the compressor device 12 in the example represented into two sub-streams, each of which is fed to a heat storage device 131, 132 of a heat storage unit 13. The heat storage devices 131, 132, described a number of times, may be operated for example by using a fixed-bed storage medium and/or a liquid heat storage medium, as also illustrated for example in the subsequent FIGS. 4, 5, 6A and 6B. In the heat storage unit 13, or its heat storage devices 131, 132, the compression heat or compressor waste heat produced in the compressor device 12 can be at least partly stored.

[0086] Downstream of the heat storage unit 13, the stream a that has been compressed and conducted through the heat storage unit 13 is fed to a cooling device 14 and subsequently to an air purification device 15. Examples of corresponding cooling devices 14 and air purification devices 15 are illustrated more specifically inter alia in the subsequent FIGS. 7A, 7B and 8. For operating or regenerating the air purification device 15, a regenerating gas stream k explained below may be fed to it and a stream l discharged from it.

[0087] Downstream of the air purification device 15, a sub-stream of the air of the stream a is removed as stream j, which is at an (intermediate) pressure level of for example 5 to 20 bars. This stream j is also referred to hereinafter as the medium-pressure air stream (MPAIR). Air of the stream a that is not discharged as medium-pressure air stream j is compressed further in a further compressor device 16, for example an isothermally operated compressor device 16. The compressor device 16 may also be formed as a multi-stage axial compressor. An aftercooling device 17 may be arranged downstream of the compressor device 16. Air compressed in the compressor device 16 and cooled in the aftercooling device 17 is provided as the mentioned high-pressure air stream b.

[0088] As already mentioned, the high-pressure air stream b and the medium-pressure air stream j through the air conditioning unit 10 are typically only provided in the energy storage period. In this energy storage period, the energy production unit 60 is typically not in operation. Conversely, in the energy recovery period, typically only the energy production unit 60 is in operation, but not the air conditioning unit 10.

[0089] In the energy storage period of the installation 100 that is illustrated in FIG. 1A, the high-pressure air stream b is divided into a first sub-stream c and a second sub-stream d. It goes without saying that, in corresponding installations, it may also be provided that a corresponding high-pressure air stream b is divided into more than two sub-streams.

[0090] The air of the sub-streams c and d (HPAIR) is fed on the one hand to the fixed-bed cold storage unit 20 and on the other hand to the counterflow heat exchanger unit 30 at the already mentioned pressure level of the high-pressure air stream b and respectively liquefied in the fixed-bed cold storage unit 20 and the counterflow heat exchanger unit 30. The air of the correspondingly liquefied streams e and f (HPLAIR) is combined to form a collective stream g. The pressure level of the streams e, f and g corresponds substantially, i.e. apart from line losses and cooling losses, to the pressure level of the high-pressure air stream b.

[0091] The liquefied air of the stream g, that is to say an air liquefaction product, is expanded in the cold production unit 20, which may for example comprise a generator turbine 41. The expanded air may be transferred for example into a separator vessel 42, in the lower part of which a liquid phase is separated and in the upper part of which there is a gas phase.

[0092] The liquid phase can be drawn off from the separator vessel 42 as stream h (LAIR) and transferred into the liquid storage unit 50, which may for example comprise one or more isolated storage tanks. The pressure level of the stream h is for example at 1 to 16 bara. The gas phase drawn off from the upper part of the separator vessel 42 as stream i (flash) may be conducted in counterflow to the stream f through the counterflow heat exchanger unit 30 and subsequently, in the form of the stream k (LPAIR, reggas) already referred to, be used in the air conditioning unit 10 as regenerating gas. The pressure level of the stream k is for example at atmospheric pressure to about 2 bara. Downstream, a corresponding stream l is typically at atmospheric pressure (amb) and may for example be discharged into the surroundings.

[0093] During the energy storage period illustrated in FIG. 1A, the cold stored in the fixed-bed cold storage unit 20 is used for liquefying the air of the sub-stream c. Additionally provided is the counterflow heat exchanger unit 30, in which additional air, specifically air of the sub-stream d, can be liquefied in counterflow to for example a cold stream i, which can be obtained from expanded, and thereby evaporated, air of the stream g. Use of the counterflow heat exchanger unit 30 makes more flexible operation of the installation 100 possible than would be the case when using only the fixed-bed cold storage unit 20. Furthermore, the already mentioned medium-pressure air stream j (MPAIR) is provided by the counterflow heat exchanger unit 30.

[0094] In the energy recovery period illustrated in FIG. 1B, liquefied air (LAIR) previously stored in the energy storage period, that is to say the air liquefaction product, is removed from the liquid storage unit 50 and increased in pressure by means of a pump 51. A stream m (HPLAIR) obtained in this way is conducted through the fixed-bed cold storage unit 20 and thereby evaporated or transformed from the liquid state into the supercritical state (vaporized). A vaporization product is therefore formed, from which a fluid stream is formed completely, as shown here, or else only partially. The stream m is in this case at a comparable pressure level to the already previously explained high-pressure air stream b. The pressurized stream n obtained by the evaporation or the transformation from the liquid state into the supercritical state in the fixed-bed cold storage unit 20 is consequently also a high-pressure air stream.

[0095] In the energy recovery period illustrated in FIG. 1B, the pressurized stream n is first heated in the energy production unit 60 by means of heat stored in the first heat storage device 131 of the heat storage unit 13 in the energy storage period (cf. FIG. 1A) and then expanded in a first expansion device 61, which is formed here as a generator turbine. Subsequently, the pressurized stream n is heated in the energy production unit 60 by means of heat stored in the second heat storage device 132 of the heat storage unit 13 in the energy storage period (cf. FIG. 1A) and then expanded further in a second expansion device 62, which is likewise formed here as a generator turbine. A correspondingly expanded stream o is for example at atmospheric pressure (amb) and can be discharged into the surroundings.

[0096] In the installation 100 shown in FIGS. 1A and 1B, the cooling device 14 and the air purification device 15 are arranged upstream of the compressor device 16 and downstream of the heat storage device 13. However, it is similarly possible to arrange the cooling device 14 and the air purification device 15 downstream of the compressor device 16 and the aftercooling device 17, as is shown in FIG. 2. FIG. 2 illustrates a corresponding installation in the energy storage period, which however is not separately denoted. The cooling device 14 and the air purification device 15 are therefore provided here in a region of higher pressure, and consequently can be made to be of a smaller size. In the installation shown in FIG. 2, furthermore, no medium-pressure air stream j is formed.

[0097] In the installations shown in FIGS. 1A, 1B and 2, a regenerating gas stream k is provided in the energy storage period, in which the air purification device 15 must at the same time produce a purifying capacity. Therefore, in corresponding installations, the air purification devices 15 must necessarily be formed with alternately operable adsorber vessels, as also illustrated in FIG. 8. Provision of a regenerating gas stream k during the energy recovery period, in which the air purification device 15 is in any case not needed, makes it possible on the other hand to use only one adsorber vessel (cf. FIGS. 10A and 10B) and consequently to design and operate a corresponding installation in a simpler and lower-cost form.

[0098] As can be seen from viewing FIGS. 3A and 3B together, in a corresponding installation the regenerating gas stream k can therefore also be formed in the energy recovery period (FIG. 3B). For this purpose, it is preferably provided as a high-pressure stream k, in that it is branched off from the high-pressure stream n. After being used in the air purification device 15, the regenerating gas stream k can, as stream l, be reunited with the high-pressure air stream n. Components contained in the stream l downstream of the air purification device 15, such as water and carbon dioxide, generally prove to be unproblematic on account of the temperatures that prevail in the energy production unit 60. The variant illustrated in FIGS. 3A and 3B has the advantage that less compressed air is lost.

[0099] Shown in FIG. 4 is a heat storage device for an installation according to one embodiment of the invention. As in the previous figures, the heat storage device is denoted here by 131 and 132. The heat storage device 131, 132 shown in FIG. 4 is formed as a fixed-bed heat storage device 131 132 and has a heat storage medium in the form of a fixed bed 1. The fixed bed 1 is arranged in a pressure vessel 2 with inlet and outlet connectors 3 and in this way can be flowed through by air compressed by means of the compressor device 12. The pressure vessel 2 is surrounded by a thermal insulating layer 4.

[0100] Also in FIG. 5, a heat storage device for an installation according to one embodiment of the invention is illustrated and denoted overall by 131 and 132. A fixed-bed heat storage medium may be arranged here in an only schematically illustrated vessel 5, which is flowed through by a heat transfer fluid 6, which can be delivered by means of a pump 7. The heat transfer from the air of the stream a compressed by means of the compressor device 12 to the heat transfer fluid 6 may take place by means of a suitable heat exchanger 8.

[0101] By contrast with the heat storage device 131, 132 shown in FIG. 4, the heat storage device 131, 132 shown in FIG. 5 therefore comprises an indirect heat transfer to the heat storage medium (not shown).

[0102] In FIGS. 6A and 6B, a heat storage device 131, 132, which is formed as a liquid heat storage device, is shown in an energy storage period (FIG. 6A) and an energy recovery period (FIG. 6B).

[0103] In the energy storage period illustrated in FIG. 6A, the stream a, explained a number of times (after a first compression in the compressor device 12) is in this case conducted through a heat exchanger 71 in counterflow to a cold heat storage fluid from a storage tank 72. The heat storage fluid from the storage tank 72 is in this case delivered through the heat exchanger 71 by means of a pump 73 and, correspondingly heated, transferred into a further storage tank 74.

[0104] In the energy recovery period illustrated in FIG. 6B, on the other hand, a stream to be heated, here the high-pressure air stream n, is conducted through the heat exchanger 71 in the opposite direction to the stream a and heated by means of a warm heat storage medium that is then likewise delivered in the opposite direction.

[0105] In FIG. 7A, a cooling device 14 for use in an air conditioning unit 10, such as that illustrated for example in the previously shown FIGS. 1A, 1B, 2, 3A and 3B, is shown in detail, The cooling device 14 may be arranged with a downstream of the heat storage unit 13 (cf. FIGS. 1A, 1B and 2) or downstream of the aftercooling device 17 (cf. FIGS. 3A and 3B). A corresponding stream, here denoted by r, is fed into a lower region of a direct contact cooler 141. The stream r corresponds to the stream a previously compressed in the compressor device 12 and cooled in the heat storage unit 13. In an upper region of the direct contact cooler 141, a water stream (H2O), which is conducted through an (optional) cooling device 143 by means of a pump 142, is introduced. Water may be drawn off from a lower region of the direct contact cooler 141. A correspondingly cooled stream s is drawn off from the head of the direct contact cooler 141 and can subsequently be transferred into an air purification device 15 (cf. FIGS. 1A, 1B, 2, 3A and 3B).

[0106] As a departure, according to the variant of the cooling device 14 that is illustrated in FIG. 7B, a direct contact cooler 141 is not provided, but instead a heat exchanger 144. This heat exchanger 144 may also be operated with a water stream, which is conducted through an (optional) cooling device 143 by means of a pump 142.

[0107] In FIG. 8, an air purification device 15, which is suitable in particular for use in an air conditioning unit 10, such as that shown in FIGS. 1A, 1B and 2, is illustrated in detail. A cooled stream s, originating there for example from a cooling device 14, may be conducted here alternately through two adsorber vessels 151, which for example comprise a molecular sieve. The stream s corresponds in this case to the stream a treated as explained above. In the adsorber vessels 151, water and carbon dioxide in particular are removed from the stream s. A correspondingly obtained stream t, which for example in the case of the embodiments illustrated in FIG. 2 may correspond to the stream b, is fed to the device respectively arranged downstream of it, for example the next compressor device (cf. FIGS. 1A and 1B) or the fixed-bed cold storage unit 20 or the counterflow heat exchanger unit 30 (cf. FIG. 3).

[0108] The adsorber vessel 151 that is respectively not being used for purifying the stream s may be regenerated by means of the already explained regenerating gas stream k. The regenerating gas stream k may in this case first be fed to an optional regenerating gas preheating device 152, which is illustrated in an example in the subsequent FIG. 9. In a downstream regenerating gas heating device 153, which may for example be operated electrically and/or with hot steam, the regenerating gas stream k is heated further and conducted through the adsorber vessel 151 that is respectively to be regenerated. Downstream of the adsorber vessel 151 to be regenerated there is a corresponding stream l. The same applies if no regenerating gas is needed at the time shown, because in this case a corresponding stream l is discharged directly from the air purification device 15 (see stream l in the upper part of FIG. 8).

[0109] In FIG. 9, the operation of a regenerating gas preheating device 152 according to one embodiment of the invention is illustrated in particular. The regenerating gas preheating device 152 may for example replace or supplement an aftercooling device 17, and consequently be arranged downstream of an air compressor device 16. An air stream heated as a result of a corresponding compression may be conducted through a heat exchanger 152a of the regenerating gas preheating device 152 or past it, and thereby transfer heat to a regenerating gas stream k.

[0110] Shown in FIGS. 10A and 10B are air purification devices 15, which are suitable in particular for the embodiments of the present invention illustrated in FIGS. 3A and 3B and the air conditioning devices shown in them. In FIGS. 10A and 10B, the energy storage period (FIG. 10A) and the energy recovery period (FIG. 10B) are illustrated, the purification of a corresponding stream s taking place in the energy storage period. Because in the energy recovery period a corresponding installation 100 is not fed air in the form of the stream a, and consequently the air conditioning device 10 is not in operation, at such times (FIG. 10B) a corresponding adsorber vessel 151 is available for regeneration. The embodiment illustrated in FIGS. 10A and 10B therefore has the particular advantage that only one corresponding adsorber vessel 151 has to be provided, and not two, which according to FIG. 8 are operated alternately.

[0111] Here, too, a regenerating gas stream k may be preheated in an optional regenerating gas preheating device (not shown), and heated in a regenerating gas heating device 153. The regenerating gas heating device 153 may be operated in particular also by means of heat stored in the heat storage unit 13 (not shown).

[0112] In the energy recovery period illustrated in FIG. 10B, correspondingly heated regenerating gas is consequently conducted through the adsorber vessel 151; in the energy storage period (FIG. 10A), this regenerating gas vessel 151 is available for purifying the stream s.

[0113] FIGS. 11A to 11C illustrate installations according to preferred embodiments of the invention in each case in the energy storage period. The installations correspond substantially to the previously explained embodiments with respect to the fixed-bed cold storage unit 20, the cold production unit 40, the liquid storage unit 50 and the energy production unit 60, but differ in particular with regard to the counterflow heat exchanger unit 30, which is therefore explained below.

[0114] According to the embodiment illustrated in FIG. 11A, the counterflow heat exchanger unit 30 may for example be operated by means of a stream u, which is conducted from the cold end to the warm end through one or more heat exchangers 31 of the counterflow heat exchanger unit 30.

[0115] To provide the stream u, a separate liquefaction process 32, operated by means of dedicated compressors, i.e. compressors provided in addition to the air conditioning unit 10, may for example be implemented.

[0116] In the embodiment shown in FIG. 11B, which corresponds substantially to the embodiment shown in FIGS. 1A and 1B, on the other hand, a medium-pressure air stream j may be fed to the the counterflow heat exchanger unit 10 and fed into the heat exchanger 31 at the warm end. The stream j may be removed from the heat exchanger 31 at an intermediate temperature and expanded in a generator turbine 33. A further sub-stream of the high-pressure air stream b, or its sub-stream d, may likewise be removed from the heat exchanger 131 at an intermediate temperature and expanded in a further generator turbine 34. Said flows may be combined and conducted together through the generator turbine 33. Cold released by the expansion is used for the liquefaction of the stream c (see FIGS. 1A and 1B), in that corresponding streams are fed on the cold side to the heat exchanger 31 together with the already explained stream i.

[0117] In a variant shown in FIG. 11C, the stream i is fed on the cold side to the heat exchanger 31 of the counterflow heat exchanger unit 30, removed at an intermediate temperature, combined with the medium-pressure air stream j, which has likewise been conducted through the heat exchanger 31 up to an intermediate temperature, and subsequently expanded in the generator turbine 33. Previously, corresponding air may be combined with a sub-stream of the stream c, as already shown in FIG. 11B.

[0118] The embodiments illustrated in FIGS. 11B and 11C are suitable in particular for the use of streams i at different pressure levels.