HEAT MANAGEMENT METHOD IN A HIGH-TEMPERATURE STEAM ELECTROLYSIS (SOEC), SOLID OXIDE FUEL CELL (SOFC) AND/OR REVERSIBLE HIGH-TEMPERATURE FUEL CELL (RSOC), AND HIGH-TEMPERATURE STEAM ELECTROLYSIS (SOEC), SOLID OXIDE FUEL CELL (SOFC) AND/OR REVERSIBLE HIGH-TEMPERATURE FUEL CELL (RSOC) ARRANGEMENT

Abstract

A heat management method in a high-temperature steam electrolysis [SOEC] (FIG. 1), to solid oxide fuel cells [SOFCs] (FIG. 2) and/or to a reversible high-temperature fuel cell having the SOEC and SOFC modes of operation [rSOC] (FIG. 1/2). The steam required (1) is supplied from at least one external source and at least one offgas stream (4, 12, 12a) is cooled at least once (3, 11, 18, 35) downstream of the cell [SOEC, SOFC, rSOC] (5, 5a). The internal generation of steam required (1, 38) is effected by internal recuperative heating of externally supplied water (47, 48, 51). The energy from the at least one cooling operation (3, 11, 18, 35) of the at least one offgas stream to be cooled (4, 4a, 12, 12a, 17, 20, 34, 36) is used for this purpose, and at the same time the external steam supply (1, 38) is reduced or shut down. Also a high-temperature steam electrolysis [SOEC] arrangement, solid oxide fuel cell [SOFC] arrangement and/or reversible high-temperature fuel cell arrangement with the SOEC and SOFC modes of operation [rSOC], each having an electrolysis/fuel cell (5, 5a), two gas supply conduits (8, 15), two gas outlet conduits (4, 12/12a), wherein at least one water evaporation arrangement (18, 35, 53), a steam generator and/or heat exchanger for steam generation is arranged in at least one gas outlet conduit (4, 12, 12a) in order to generate steam (1, 38) from water (47, 48, 51).

Claims

1. A heat management method in a high-temperature steam electrolysis [SOEC] (FIG. 1), solid oxide fuel cell [SOFC] (FIG. 2) and/or reversible high-temperature fuel cell having SOEC and SOFC [rSOC] operating modes (FIG. 1/2), wherein required steam (1) is supplied from at least one external source, and at least one exhaust gas stream (4, 12, 12a) is cooled at least once (3, 11, 18, 35) after the cell [SOEC, SOFC, rSOC] (5, 5a) wherein an internal generation of required steam (1, 8) takes place by internal recuperative heating of externally supplied water (47, 48, 51), for which purpose the energy from the at least one cooling system (3, 11, 18, 35) of at least one exhaust gas stream to be cooled (4, 4a, 12, 12a, 17, 20, 34, 36) is used, and thereby the external steam supply (1, 38) is switched off or reduced.

2. The heat management method according to claim 1, wherein the internally recuperatively produced steam (1, 49, 50) is stored, and time-delayed is used again in the SOEC or process mode SOEC (5) of the rSOC.

3. The heat management method according to claim 1, wherein the steam generated internally recuperatively (1, 49, 50) is supplied directly in the SOEC or the rSOC in SOEC process mode (5).

4. The heat management method according to claim 1, wherein heat from an air-oxygen exhaust-gas stream (12, 34, 36) and/or from a hydrogen and/or steam-gas stream (4, 4a, 17, 20) is used recuperatively for steam production (49, 50).

5. The heat management method according to claim 1, wherein heat sources with temperatures below 100 C. (54) are used for the internal steam production (1, 57), wherein evaporation of water is carried out at low pressure (56), in particular below 1 bar, and wherein the pressure of the steam produced (57) is subsequently boosted (55) to the operating pressure of the electrolysis or electrolysis occurs at low pressures (56), in particular below 1 bar, whereby the electrolysis products formed (61, 62), at least hydrogen (61), is subject to a pressure boost (59, 60) before further processing.

6. The heat management method according to claim 1, wherein heat sources with temperatures below 100 C. (54) are used internally for steam production (1, 57), wherein the temperature level of the heat source (54) is raised by means of a heat pump process (64) to a level useable for generating steam for the electrolysis.

7. The heat management method according to claim 1, wherein heat sources with temperatures below 100 C. (54) are used internally for steam production (1), wherein an internal recirculation of the products after the cell (5) are used as the carrier gas for the steam production.

8. The heat management method according to claim 1, wherein an additional recuperative heating of air (9) and/or hydrogen (1a, 2) is carried out with larger dimensioned recuperators (3, 11), wherein a bypass flow of the air (76) and/or the hydrogen (75) is guided temperature-controlled (73, 74) around the larger dimensioned recuperators (3, 11).

9. A high-temperature steam electrolysis [SOEC], solid oxide fuel cell [SOFC] and/or reversible high-temperature fuel cell having the operating modes SOEC and SOFC [rSOC] arrangement with a method according to claim 1, respectively comprising: electrolysis/fuel cell (5, 5a), two gas supply lines (8, 15), two gas discharge lines (4, 12/12a) wherein at least a water evaporation means (53), a steam generator and/or heat exchanger (3,11, 18, 35) for generation of steam is provided in at least one gas discharge pipe (4, 12, 12a) for production of steam (1, 8, 49, 50, 57).

10. SOEC, SOFC and/or rSOC, according to claim 9, wherein the water evaporation means (18, 35, 53, 70), the steam generator and/or the heat exchanger for steam generation is provided in at least one gas discharge pipe (4, 12, 12a) downstream of a recuperative preheater (3, 11) for preheating gas (8, 15) to be supplied to the electrolysis/fuel cell (5, 5a).

11. SOEC, SOFC and/or rSOC according to claim 9, wherein a heat storage, a Ruth accumulator (40, 91), a gas pressure accumulator with an upstream compressor (83), a high-temperature storage, a latent heat accumulator and/or a thermo-chemical heat accumulator is provided for the storage of steam generated (1, 39, 49, 50, 57).

12. SOEC, SOFC and/or rSOC according to claim 9, wherein a water evaporation means (53, 70) is provided with a supply of heat with low temperature (54) from the SOEC, SOFC and/or rSOC, wherein the pressure (56) of the therein occurring steam generation is at an under 1 bar, and wherein after the water evaporation means (53), a compressor (55) is provided, which increases the pressure of steam generated (57) to process pressure or the pressure in the subsequent electrolysis cell [SOEC] (5) in which the produced steam (57) is to be used, is under 1 bar, and after the electrolysis cell [SOEC] (5) at least one compressor (59, 60) is provided that increases the pressure of the obtained electrolysis gas or gases (61, 62) to at least ambient pressure.

13. SOEC, SOFC and/or rSOC according to claim 9, wherein a heat pump assembly (64) is provided, which with use of energy brings the low-temperature heat with T<100 C. (54) to a higher temperature level to be used as heat for a water evaporation (53, 1) at the process pressure of SOEC or the rSOC.

14. SOEC, SOFC and/or rSOC according to claim 9, wherein a hydrogen storage (31, 83), gas pressure accumulator to the internal storage of hydrogen (29, 77, 81, 87, 1a) and/or steam is provided.

15. SOEC, SOFC and/or rSOC according to claim 9, wherein the plant is part of a carbohydrate synthesis plant, particularly one involving regeneratively generated electric energy in the synthesis process, wherein the external steam (1, 38) is mainly derived from the carbohydrate synthesis plant.

16. The heat management method according to claim 1, wherein the internally recuperatively produced steam (1, 49, 50) is stored in a Ruth accumulator (40, 91) and time-delayed is used again in the SOEC or process mode SOEC (5) of the rSOC.

17. The heat management method according to claim 1, wherein heat sources with temperatures below 100 C. (54) are used internally for steam production (1), wherein an internal recirculation of hydrogen (2, 4, 87) after the cell (5) is used as the carrier gas for the steam production.

Description

[0069] In the following in the description of the figures embodiments of the invention will be described in detail on the basis of the accompanying drawings, which are intended to illustrate the invention and are not to be regarded as limiting:

[0070] Therein:

[0071] FIG. 1 shows a schematic representation of an exemplary embodiment of a SOEC (high-temperature water-vapor electrolysis);

[0072] FIG. 2 shows a schematic representation of an exemplary embodiment of an SOFC (fuel cell);

[0073] FIG. 3 shows a schematic representation of an exemplary embodiment of the SOEC with a Ruth accumulator for storing external steam and internal steam generation for reducing the external steam demand;

[0074] FIG. 4 shows a schematic representation of a first exemplary embodiment for the use of low-temperature heat for steam generation for a SOEC;

[0075] FIG. 5 shows a schematic representation of a second exemplary embodiment for utilizing low-temperature heat for steam generation for a SOEC;

[0076] FIG. 6 shows a schematic representation of a third exemplary embodiment for utilizing low-temperature heat for steam generation for a SOEC;

[0077] FIG. 7 shows a schematic representation of a fourth exemplary embodiment for the use of low-temperature heat for steam generation for a SOEC;

[0078] FIG. 8 shows a schematic representation of an exemplary embodiment for controlling the preheating temperature for the air and the hydrogen in an SOFC;

[0079] FIG. 9 shows a schematic representation of an exemplary embodiment of an rSOC (reversible high-temperature fuel cell) with an eternal steam supply and Ruth accumulator as well as controlled air and hydrogen preheating in the SOFC mode and

[0080] FIG. 10 shows a schematic representation of an exemplary embodiment of a storage of the steam or of the steam-hydrogen mixture from the fuel cells in the SOFC mode of an rSOC for later use in the SOEC mode.

[0081] In FIG. 1 is a schematic representation of a prior art embodiment of a SOEC (high-temperature steam electrolysis) is shown.

[0082] Steam 1 is mixed with a small amount of recirculated hydrogen 2 and preheated as high as possible in the recuperative preheater 3 against hot hydrogen-steam mixture 4 from the electrolysis cells 5 and subsequently heated in the heater 6 with electroenergy 7 up to electrolysis cell inlet temperature 8.

[0083] Purge air 9 is increased in pressure with a blower 10 and recuperatively preheated as high as possible in the air preheater 11 against the hot air-O.sub.2 mixture 12 from the electrolytic cell 5. In the heater 13, the further heating of the scavenging air with electric energy 14 takes place up to the electrolysis cell inlet temperature 15.

[0084] In the electrolysis cells 5, the hot steam 8 is decomposed into hydrogen and oxygen using electrical energy 16. The oxygen leaves the electrolysis cells 5 as an air-02 mixture 12 and the hydrogen with the unreacted residual steam as the hydrogen-steam mixture 4.

[0085] The hydrogen-steam mixture 17 cooled in the heat exchanger 3 is optionally further cooled in a heat exchanger 18. The dissipated heat can be supplied to an external heat utilization 19.

[0086] In the cooler 21, the gas mixture 20 from the heat exchanger 18 is cooled to such an extent that a large portion of the steam contained in the gas mixture 20 condenses and is deposited as condensate 23 in the subsequent phase separator 22.

[0087] A partial stream 24 of the hydrogen leaving the phase separator 22 is increased in pressure with the blower 26 and admixed as stream 2 to the steam 1.

[0088] Alternatively, if the blower 26 is suitable for higher temperatures, it can recirculate a partial stream of hydrogen-steam mixture downstream of the heat exchanger 3 or 18 instead of the stream 24. This also recirculates an increased proportion of unreacted steam, which reduces the external steam requirement 1.

[0089] The main quantity of hydrogen 27 is either transferred directly as a hydrogen stream 28 to a consumer or the entire quantity or a partial quantity 29 is compressed in a compressor 30 and buffered in the pressure accumulator 31, from which the hydrogen is withdrawn later in time as stream 32 via the pressure control valve 33 and sent to a consumer.

[0090] The air-O.sub.2 mixture 34 cooled in heat exchanger 11 is further cooled in optional heat exchanger 35 and discharged as exhaust gas 36 to the environment. The heat from the heat exchanger 35 can be supplied to an external heat user 37.

[0091] In FIG. 2 is a schematic representation of a prior art embodiment of a SOFC (fuel cell) is shown.

[0092] Hydrogen 1a is mixed with unreacted and recirculated hydrogen 2 and preheated in the recuperative preheater 3 against hot water/steam/hydrogen mixture 4 from the fuel cells 5a up to the fuel cell inlet temperature 8.

[0093] Air 9 is increased in pressure by means of a blower 10 and preheated recuperatively in the air preheater 11 against the hot air-nitrogen mixture 12a from the fuel cells 5a to the fuel cell inlet temperature 15.

[0094] In the fuel cells 5a, the hot hydrogen 8 reacts with a part of the air oxygen 15 to form steam. This produces electrical energy 16, which is delivered to the power supply grid or to consumers.

[0095] The formed steam and the unreacted hydrogen are contained in the hot stream 4 leaving the fuel cells 5a.

[0096] The steam-hydrogen mixture 17 cooled in the heat exchanger 3 is optionally further cooled in a heat exchanger 18. The dissipated heat can be supplied to an external heat utilization 19.

[0097] In the cooler 21, the gas mixture 20 from the heat exchanger 18 is cooled to such an extent that a large portion of the steam contained in the gas mixture 20 condenses and is deposited as condensate 23 in the subsequent phase separator 22.

[0098] The remaining hydrogen 24 from the phase separator 22 is increased in pressure with the blower 26 and admixed as a stream 2 to the hydrogen 1a for increasing the fuel utilization.

[0099] The hot gas stream 12a leaving the fuel cells 5a contains the residual air with a higher nitrogen content since a part of the air oxygen has bonded to the hydrogen.

[0100] After cooling this gas stream 12a in the heat exchanger 11, it is supplied as a stream 34a to the optional heat exchanger 35 for further cooling and then leaves the process as the exhaust stream 36.

[0101] The heat from the heat exchanger 35 can be supplied to an external heat supply 37.

[0102] The prior art for reversible high-temperature fuel cell (rSOC) corresponding to FIGS. 1 and 2:

[0103] The reversible high-temperature fuel cell (rSOC) corresponds to the diagram in FIG. 1, wherein the SOEC mode corresponds to the description of FIG. 1. The description of the SOFC mode essentially corresponds to the description of FIG. 2, wherein the electric heaters 6 and 13 are not in operation and are only flowed through in the SOFC mode.

[0104] The hydrogen discharge 27 and 28 as well as the hydrogen compressor 30 are likewise not in operation in the SOFC mode.

[0105] Reference is made to the descriptions of the FIGS. 1 (SOEC) and 2 (SOFC), which show the basic functions and conceptualities, as the basis for the following figures.

[0106] FIG. 3 shows a schematic representation of an embodiment of a SOEC of FIG. 1 with a Ruth accumulator for storing externally and internally generated steam for the reduction of the external steam requirements.

[0107] The pressure steam 38, which is produced in an external steam generator, is to be used as steam 1 for a SOEC. The load behavior of the external steam generation differs from the load behavior of the SOEC so that, with respect to the steam demand of the SOEC, there is at one time more and at another time less steam available from the external steam generation.

[0108] In order to balance to the steam demand for the SOEC, the excess pressure steam 39 supplied from the external steam generation is to be temporarily buffered in a heat accumulator 40.

[0109] The heat accumulator 40 is, for example, a sliding-pressure accumulator (Ruth accumulator) filled with boiling water and saturated steam. Other suitable heat accumulators are, for example, stratified storage tanks, liquid salt storage tanks and thermochemical storage tanks.

[0110] During the charging process the excess pressure steam 39 is added through the valve 41 into the accumulator 40. The remaining steam 42 is reduced via the throttle valve 43 to the pressure 44 and used as steam 1 for SOEC.

[0111] At the beginning of the charging process boiling water and saturated steam at the steam output pressure 44 are in the accumulator 40. Due to the additional introduction of pressurized steam 39, the boiling water in the accumulator 40 is heated and the pressure in the container increases. The maximum possible pressure corresponds to the pressure of the supplied pressure steam 39. Due to the pressure increase, the vapor portion is reduced and the water content increased in the container. The supplied heat is stored in the form of boiling water (principle of a Ruth accumulator).

[0112] If there is a steam deficiency in the SOEC, because the external steam generation directly provides too little steam, then the throttle valve 45 is opened at the accumulator 40 and the desired difference in amount of 46 steam is removed from the heat accumulator 40.

[0113] Through the removal of steam, the pressure in accumulator 40 is reduced, and boiling water is evaporated in the tank. A steam removal is possible up to the pressure 44.

[0114] After steam removal, the heat accumulator 40 can be recharged.

[0115] To reduce the external steam requirement 1, the heat exchangers 18 and 35 can be used, instead of providing heat for external users, to generating steam. For this purpose, feed water 47 and 48 is added to the respective heat exchangers 35 and 18. The generated steam 49 and 50 is mixed into the vapor stream 1 at A or B to the heat exchanger 3 resulting in a reduction of the required amount of steam 1.

[0116] In order to use lower temperature heat for evaporation of water and to supply of SOEC with steam, the following 4 embodiments are configured according to FIG. 4 to FIG. 7, wherein the illustrated evaporators are one possible embodiment, and other suitable evaporators may also be used.

[0117] FIG. 4 shows a schematic representation of a first embodiment for the use of low temperature heat to generate steam for a SOEC of FIG. 1.

[0118] The fill-level of feed water 51 introduced into an evaporator 53 is controlled by a throttle valve 52, which is heated with low-temperature heat 54. With a suction blower 55, a vacuum 56 is set in the evaporator 53, which is so high that the feedwater 51 heated with low temperature heat 54 is evaporated. The resulting low pressure steam 57 is sucked to the blower 55, is compressed and fed as process steam 1 with the required over-pressure to the SOEC 58 where it is separated with the electric energy 7, 14 and 16 into hydrogen 28 and oxygen, which via purge air 9 is discharged from the SOEC as an air-oxygen mixture 34.

[0119] FIG. 5 shows a schematic representation of a second embodiment for the use of low temperature heat to generate steam for a SOEC of FIG. 1.

[0120] Feed water 51, of which the level is controlled by a throttle valve 52, is introduced into an evaporator 53, which is heated with low-temperature heat 54. With the two suction fans 59 and 60, a vacuum 56 is set in the evaporator 53, which vacuum is so high, that the feedwater 51 with the low temperature heat 54 turns to steam. The resulting low pressure steam 57 is evaporated is sucked with the blowers 59 and 60 and supplied, at low pressure, to SOEC 58, which is operated at negative pressure.

[0121] In the SOEC 58 the steam 57 is decomposed with electrical energy 7, 14 and 16 into hydrogen 61 and oxygen 62. To flush the SOEC, purge air 9 is used, which is relaxed via the throttle valve 63 to the operating pressure of the SOEC 58. The blower 59 compresses the hydrogen 61 to the output state 28 and the blower 60 the oxygen 62 and the purge air to the discharge state 34.

[0122] In FIG. 6 is a schematic representation of a third embodiment is shown for the use of low temperature heat to generate steam for a SOEC according to FIG. 1.

[0123] To boost the temperature level of the low temperature heat 54 so that an evaporation of the feed water 51 is possible at temperatures >100 C., a heat pump 64 can be employed. Heat pumps are available as compact units consisting of evaporator 65, condenser 66, compressor 67 and throttle valve 68, and can be adapted to the respective requirements.

[0124] The steam 1 produced in the evaporator 53 is generated with the parameters required for the SOEC 58 and can be used directly in this.

[0125] FIG. 7 shows a schematic representation of a fourth embodiment for the use of low temperature heat to generate steam for a SOEC of FIG. 1.

[0126] Feed water 51 level-controlled by the control valve 52 is supplied to the steam generator 53, which is heated with low-temperature heat 54.

[0127] The recirculated quantity of hydrogen 2 is finely distributed through distributing elements 69, which are housed in a water bath 70 of the steam generator 53, into the water bath 70 heated with low-temperature heat 54. The hydrogen 2 flows through the water bath 70 and takes up steam 1 up to the saturation pressure of the respective water bath temperature. The hydrogen-steam mixture 1+2 is supplied to the following process stages of SOEC.

[0128] In order to supply the required amount of steam to the process, the recirculated amount of hydrogen 2 must be increased and adapted as a function of the temperature level 54 of the low temperature heat.

[0129] Alternatively, the blower 26, if it is suitable for higher temperatures, can recirculate a partial stream of hydrogen-steam mixture after the heat exchanger 3 or 18 rather than stream 24. Thus, an increased proportion of unreacted hydrogen is used again, reducing the heat demand 54 for the evaporation of water.

[0130] FIG. 8 shows a schematic representation of an embodiment for controlling the preheating temperature of the air and hydrogen at a SOFC of FIG. 2.

[0131] So that during SOFC operation in case of deviations from the operating parameters of the heat exchangers 3 and 11 the air 15 and the hydrogen 8 do not arrive in the fuel cell 5a too hot or too cold, where they lead due to thermal stresses occurring thereby to destruction of the cells, the heat exchangers 3 and 11 are so dimensioned so that they bring at maximum load (amount of gas 8, or 15) at least the desired minimum preheating temperature for the streams 8 and 15. In the design for partial load it must be observed that the heat transfer throughput does not decrease faster than the necessary heat transfer area, so that the desired preheating temperature of the streams 8 and 15 is at least provided, but is preferably exceeded.

[0132] To set the desired preheating temperature in all load conditions, the control valves 71 and 72 are installed before the heat exchangers 3 and 11 in the respective gas streams supplied to the heat exchangers, which, depending on the desired target temperatures 73 and 74, bypass a cold partial stream of hydrogen 75 or air 76 around the respective heat exchanger and thereafter intermix in the hot gas, so that the respectively resulting mixing temperature corresponds to the predetermined desired temperature.

[0133] In FIG. 9 is a schematic representation of an embodiment of an rSOC (reversible high temperature fuel cell) with own steam supply and Ruth accumulator and controlled air as well as hydrogen warming in SOFC mode.

[0134] Electrolysis mode (SOEC mMode):

[0135] Steam 1 is mixed with a small amount of recirculated hydrogen 2 and preheated in a recuperative preheater 3 with hot hydrogen-steam mixture 4 from the electrolytic cell 5, and then pre-heated in the heater 6 with electric power 7 to the electrolysis cell inlet temperature 8.

[0136] The control of the preheating temperature 73 is not in operation in SOEC mode, since a maximum preheating in heat exchanger 3 is desired for reducing the power requirements 7 for the heater 6. I.e., there is no hydrogen is passed around the heat exchanger 3 in the bypass 75.

[0137] Purge air 9 is increased in pressure with a blower 10 and recuperatively preheated in the air preheater 11 against the hot air-02 mixture 12 from the electrolysis cell 5. In the heater 13 the further heating of the gas mixture is effected with electric power 14 to the electrolysis cell inlet temperature 15.

[0138] The control of the preheating temperature 74 is also not in operation in SOEC mode, since a maximum preheating in heat exchanger 11 is desired to reduce the power demand 14 for the heater 13. I.e. no purge air passes around the heat exchanger 11 in the bypass 76.

[0139] In the electrolytic cell 5 the pre-heated steam 8 is decomposed under consumption of electrical energy 16 into hydrogen and oxygen. The oxygen leaves the electrolysis cell 5 with the scavenging air as an air-O.sub.2 mixture 12 and the hydrogen with the residual steam as hydrogen-steam mixture 4.

[0140] The hydrogen-steam mixture 17 cooled in the heat exchanger 3 is further cooled in a heat exchanger 18. For heat dissipation feedwater 48 is heated and subsequently transformed into steam 50.

[0141] In the cooler 21 the gas mixture 20 from the heat exchanger 18 is cooled to the extent that a large part of the steam contained in the gas mixture 20 condenses and is deposited in the subsequent phase separator 22 as condensate 23.

[0142] A partial stream 24 of the hydrogen 25 leaving the phase separator 22 is increased in pressure by the blower 26 and as a steam 2 is mixed with the steam 1.

[0143] Alternatively, the blower 26, if it is suitable for higher temperatures, rather than stream 24, can recirculate a partial hydrogen steam mixture after heat exchanger 3 or 18. Therewith, an increased proportion of unreacted steam is used again, reducing the external steam requirement 1.

[0144] The main amount of hydrogen 27 from the phase separator 22 is either directly output as the hydrogen stream 28 to a consumer or the entire amount or partial amount 29 is compressed in a compressor 30 and stored in the pressure accumulator 31, from which the hydrogen is removed time-shifted via the pressure control valve 33 and either supplied as a stream 32 to an external consumer, or returned as a stream 77 to the process as hydrogen for a time-shifted SOFC operation.

[0145] The air-O.sub.2 mixture 34 cooled in heat exchanger 11 is further cooled in heat exchanger 35 and discharged to the environment as exhaust gas 36.

[0146] The heat from the heat exchanger 35 is used to heat and evaporate feedwater 47. The generated steam 49 mixed together with the steam 50 (via B) is either supplied to an external user 88 or as a partial or total amount of 89 is I mixed with the steam supplied to the heat exchanger 3. Therewith, the steam 1 requirement is reduced for electrolysis cells 5. Storage as pressure steam 90 in a Ruth accumulator 91 is possible in principle, but not useful in the electrolysis operation case.

[0147] Steam 92, which has been previously stored in the operating mode fuel cell operation (SOFC mode) can be removed from the Ruth accumulator 91 via the throttle valve 93. This amount of steam 92 is mixed with the steam 1 and supplied to the heat exchanger 3 and reduces the steam demand for the electrolytic cell 5.

[0148] Fuel Cell Mode (SOFC Mode):

[0149] Hydrogen 1a is mixed with unreacted and recirculated hydrogen 2 and heated recuperatively in heat exchanger 3 with hot steam-hydrogen mixture 4 from the fuel cells 5a. To maintain a predetermined pre-heating temperature 73 under all load conditions, a bypass flow is guided through the control valve 71 around the heat exchanger 3 and mixed with the hot stream after the heat exchanger 3.

[0150] The subsequent heater 6 is not in operation and is therefore is not flowed through. The preheated hydrogen 8 reaches the fuel cell 5a.

[0151] Air 9 is increased in pressure with a blower 10 and in the air preheater 11 is recuperatively preheated against the hot air-N.sub.2 mixture 12a from the fuel cell 5a. To maintain a predetermined pre-heating temperature 74 at all load conditions, a bypass flow is guided through the control valve 72 around the heat exchanger 11 and mixed with the hot stream after the heat exchanger 11.

[0152] The heater 13 likewise is not in operation and is not flowed through. The preheated air 15 also enters to the fuel cell 5a.

[0153] In the fuel cell 5a the hydrogen 8 reacts with a portion of the oxygen of air 15 to form water vapor. This produces electric energy 16 that is delivered to the electric grid or to consumers.

[0154] In the hot stream after the fuel cell 4, the is the formed steam and the unreacted hydrogen.

[0155] The steam-hydrogen mixture 17 cooled in heat exchanger 3 is further cooled in heat exchanger 18. For heat dissipation feedwater 48 is heated and transformed into steam 50.

[0156] In the cooler 21 the gas mixture 20 from the heat exchanger 18 is cooled to the extent that a large part of the steam contained in the gas mixture 20 condenses and is deposited in the subsequent phase separator 22 as condensate 23.

[0157] The remaining hydrogen 24 from the phase separator 22 is fully raised in pressure by the blower 26 and mixed as stream 2 into the hydrogen 1a to increase the fuel utilization.

[0158] The hot gas stream 12a leaving the fuel cell 5a includes the remaining air with a higher nitrogen content, since a part of the atmospheric oxygen has bonded to the hydrogen. After cooling of this gas stream 12a in heat exchanger 11 it is fed as stream 34 to the heat exchanger 35 for further cooling and then leaves the process as waste gas stream 36.

[0159] The heat from the cooling of the gas in the heat exchanger 35 is used to heat and evaporate the feedwater stream 47. The generated steam 49 is supplied together with the steam 50 either to external users 88 or buffered as stream 90 in Ruth accumulator 91 for later use in the electrolysis mode.

[0160] The hydrogen stored in the pressure accumulator 31 in the electrolysis mode (SOEC) can be taken from the accumulator in the fuel cell mode, and be mixed as stream 77 into the hydrogen stream 1a. Therewith the required external amount of hydrogen 1a is reduced accordingly.

[0161] FIG. 10 shows a schematic representation of an embodiment of an accumulator for the steam or the steam-hydrogen mixture from the fuel cells in the SOFC mode of rSOC for later use in a SOEC mode.

[0162] Another possibility of storing heat (steam) from the fuel cell operation (SOFC) for the electrolysis operation (SOEC) ore a rSOC is the use of a gas pressure accumulator to store the steam or steam-hydrogen mixture from the SOFC operation. Here, two cases are conceivable:

a) compression of the steam before storage and
b) SOFC operating at a higher pressure than the operating SOEC.
A combination of cases a) and b) is also possible.

[0163] Fuel Cell Mode (SOEC):

[0164] If the fuel cell mode (SOEC) of the rSOC is operated at elevated pressure, then hydrogen 1 is fed as pressurized hydrogen to the rSOC and the blower 10 for increasing the pressure of the air 9 is designed for a larger pressure increase.

[0165] The steam-hydrogen mixture 17 cooled in heat exchanger 3 may go either the classical pathway via the heat recovery 18, cooling 21 and the recirculation 26 of residual hydrogen, or be routed via the valve 78 to an optional gas separation 79.

[0166] In the optional gas separation 79 the residual hydrogen 80 contained in the gas stream 17 is separated from the steam-hydrogen mixture and supplied to the blower 26 for recirculation and thus better hydrogen utilization in the SOFC process. After the pressure increase of the hydrogen is added as stream 2 to the hydrogen stream 1.

[0167] The remaining steam 81 or, in the case of omission of the gas separation 79, the steam-hydrogen mixture 17, can be increased in pressure by means of compressor 82 and goes into a gas pressure accumulator 83, where the gas or the gas mixture is buffered for the SOEC mode. The gas compressor 82 may be omitted if the SOFC operation of the rSOC is carried out at a higher pressure than the SOEC operation.

[0168] At this point a further possible configuration should be mentioned, namely that the compressor 82 can also be omitted if the SOEC operation takes place at a lower pressure than the SOFC operation.

[0169] The compressed gas reservoir is full when the SOFC operating pressure or the maximum compressor discharge pressure of the compressor is achieved 82.

[0170] During operation of the SOFC mode under elevated pressure, a pressure control valve 85 is located on the exhaust side of the SOFC process in the stream 36 to maintain the system pressure 84.

[0171] Electrolysis Mode (SOEC):

[0172] The electrolysis mode (SOEC) is carried out at a lower pressure than the pressure in the compressed gas storage 83.

[0173] By opening the throttle valve 86 on the compressed-gas accumulator 83 the steam/steam-hydrogen mixture 87 previously stored in the SOFC mode is fed to the SOEC process and may completely or partially replace the steam stream 1.

[0174] The gas pressure accumulator 83 is discharged when the pressure in the accumulator is equal to the pressure of the rSOC in SOEC mode.

Another Embodiment

[0175] In the following the invention will be described based on a concrete embodiment and with inclusion of the aforementioned figures as well as the following diagrams:

[0176] Numerical Example of an Inventive rSOC:

[0177] SOFC Mode

TABLE-US-00001 Hydrogen (1a): Mass flow 3.19 kg/h Power (Hu): 105.8 kW Air (9): Flow rate: 611.4 kg/h Heat exchanger (3): Power: 11.8 kW.sub.th Heat exchanger (11): Power: 105.1 kW.sub.th Heat exchanger (35): Power: 13.2 kW.sub.th Heat exchanger (18): not considered Heater (6): Power: 0 kW.sub.el Heater (13): Power: 0 kW.sub.el Fuel cell (16): Power: 72.6 kW.sub.el Feedwater (47): Flow rate 20.2 kg/h Pressure: 10 bar (a) Temperature: 100 C. Steam (90): Flow rate 20.2 kg/h Pressure: 10 bar (a) Saturated steam

[0178] SOEC Mode

[0179] A fuel cell with above listed performance parameters has according to experience the following parameters in the electrolysis mode:

TABLE-US-00002 Steam (1): Mass flow: 33.4 kg/h/h Pressure: 2 bar (a) Saturated steam Purge air (9): Mass flow: 62 kg/h Heat exchanger (3): Power: 15.1 kW.sub.th Heat exchanger (11): Power: 13.3 kW.sub.th Heat exchanger (35): Power: 6.0 kW.sub.th Heat exchanger (18): not considered Heater (6): Power: 5.0 kW.sub.el Heater (13): Power: 0.6 kW.sub.el Electrolytic cell (16): Power: 130.9 kW.sub.el Hydrogen (28): Mass flow: 3.85 kg/h Power (Hu): 127.6 kW Feed water (47): Mass flow: 9.4 kg/h Pressure: 3 bar (a) Temperature: 100 C. Steam (89): Mass flow: 9.4 kg/h Pressure: 3 bar (a) Saturated steam

[0180] The steam (90) generated in SOFC mode is to be stored in a Ruth accumulator (91). The Ruth accumulator has a usable volume of 1 m.sup.3 and at the beginning of storing the following condition:

TABLE-US-00003 Pressure: 2 bar (a) Degree of fill with boiling water: 70% (volume) Mass boiling water: 659.8 kg Mass saturated steam: 0.34 kg Total mass content: 660.14 kg

[0181] The store is charged up to a pressure of 10 bar(a) with saturated steam, and then has the following condition:

TABLE-US-00004 Pressure: 10 bar (a) Degree of fill with boiling water: 83.9% (volume) Mass boiling water: 744.4 kg Mass saturated steam: 0.83 kg Total mass content: 745.23 kg

[0182] It means, in the vessel with 1 m.sup.3 effective volume, with a beginning degree of filling of 70% 85.1 kg steam are stored, which corresponds to a charging time, when the amount of steam (90) as specified is 20.2 kg/h, of about 4.2 hours (about 252 min).

[0183] The stored amount of steam of 85.1 kg is sufficient in the SOEC mode, based on a required steam output of 33.4 kg/h, for 2.5 hours (about 152.9 min).

[0184] As H.sub.2-accumulator a gas pressure accumulator is assumed to have a volume of 5 m.sup.3. The lower pressure is due to the system pressure of the rSOC and should be, taking into consideration pressure losses, at 2 bar(a).

[0185] The boost pressure results from the H.sub.2 amount to be stored in the SOEC mode of 9.81 kg (3.85 kg/h in 152.9 min) and corresponds at 25 C in case 1 to about 25.8 bar(a).

[0186] For the production of 85.1 kg of steam in the SOFC mode but 13.4 kg of hydrogen are needed, I.e. there is a hydrogen deficit of 3.6 kg which has to be met in this case by an external supply.

[0187] Case 1:

TABLE-US-00005 TABLE 1 m.sub.D m.sub.H2 m.sub.D m.sub.H2 m.sub.D m.sub.H2 kg/h kg/h min kg kg kg kg min SOFC 20.23 3.19 252.40 85.10 13.42 0.00 3.61 67.89 SOEC 33.40 3.85 152.87 85.10 9.8

[0188] Case 2:

[0189] The SOEC mode could also be operated longer (209.1 min), so that the hydrogen demand of 13.4 kg for the subsequent SOFC operation is ensured. In this case, the charge pressure in the pressure gas accumulator increases to 34.6 bar(a). However, then the amount of steam stored in the Ruth accumulator is no longer sufficient to produce the hydrogen. For this, 31.3 kg steam must be provided by an external supply.

TABLE-US-00006 TABLE 2 m.sub.D m.sub.H2 m.sub.D m.sub.H2 m.sub.D m.sub.H2 kg/h kg/h min kg kg kg kg min SOFC 20.2 3.19 252.40 85.10 13.42 SOEC 33.40 3.85 209.13 116.42 13.42 31.32 0.00 56.26

TABLE-US-00007 LIST OF REFERENCE NUMBERS 1 steam 1a hydrogen 2 recirculated hydrogen 3 recuperative heat exchanger 4 hot hydrogen-steam mixture 5 electrolytic cell 5a fuel cell 6 electric heater 7 electricity 8 hot steam-hydrogen mixture 9 air 10 blower 11 recuperative heat exchanger 12 hot air-oxygen mixture 12a hot air-nitrogen mixture 13 electric heater 14 electric power 15 hot air 16 electric power 17 cooled hydrogen-steam mixture 18 heat exchanger 19 heat consumer 20 further cooled hydrogen-steam mixture 21 cooler 22 phase separator 23 condensate 24 hydrogen 25 hydrogen 26 blower 27 hydrogen 28 hydrogen for external consumer 29 hydrogen partial flow for storing 30 compressor 31 hydrogen-pressure accumulator 32 hydrogen for consumers 33 pressure control/throttle valve 34 air-oxygen mixture 34a air nitrogen mixture 35 heat exchanger 36 exhaust 37 heat consumer 38 external pressure steam/extrinsic steam 39 external steam 40 heat storage/Ruth accumulator 41 valve/valve 42 remaining external extrinsic steam 43 throttling/regulating valve 44 pressure measurement 45 throttling/regulating valve 46 required differential steam 47 feedwater 48 feedwater 49 internally generated steam 50 internally generated steam 51 feedwater 52 control valve 53 steam generator 54 low-temperature heat source 55 compressor/suction blower 56 pressure measurement 57 low pressure steam 58 SOEC 58 compressor/suction blower 59 compressur/suction fan 60 compressor/suction fan 61 hydrogen 62 air-O.sub.2 mixture 63 control/throttle valve 64 heat pump 65 evaporator 66 condenser 67 compressor 68 throttle valve 69 gas distributor elements 70 water 71 three-way valve/control valve 72 three-way valve/control valve 73 temperature measurement 74 temperature measurement 75 bypass flow hydrogen 76 bypass air stream 77 hydrogen 78 three-way valve 79 gas separation 80 hydrogen 81 steam/hydrogen-steam 82 compressor 83 gas storage 84 pressure measurement 85 throttling/control valve 86 control valve 87 steam/hydrogen-steam 88 steam for extenal consumers 89 steam 90 steam 91 Ruth accumulator 92 steam 93 thottle valve A internal steam production via heat exchanger 35 B internal steam production via heat exchanger 18