Method and device for generating electric energy

Abstract

A method for generating electrical energy by a fuel cell system operated with a reformate gas is provided. According to this method, a fuel cell system is provided. The fuel cell system has a first reactor and a second reactor. A gas separation unit is also provided. A portion of a first fuel gas is fed to the gas separation unit. A target gas including N.sub.2 or CO.sub.2 is separated by the gas separation unit. The separated target gas is fed into a protective housing of the fuel cell system. An H.sub.2-enriched tail gas formed in the gas separation unit is fed as a second fuel gas for operation of the fuel cell.

Claims

1. A method of generating electrical energy through a fuel cell system operated with a reformate gas, comprising: providing a fuel cell system having a first reactor for conversion of a fuel to a first fuel gas and a second reactor connected downstream of the first reactor, wherein the second reactor forms a fuel cell for generation of electrical energy with formation of a cathode offgas and an anode offgas, and wherein at least the second reactor is surrounded by a protective housing, providing a gas separation unit, wherein the gas separation unit is configured to separate a target gas from the first fuel gas or a further gas mixture formed from the first fuel gas, wherein the target gas comprises at least one of CO.sub.2, N.sub.2 and a partial gas mixture comprising CO.sub.2 and N.sub.2, feeding a portion of the first fuel gas or the further gas mixture to the gas separation unit, wherein the remaining portion of the first fuel gas or further gas mixture is led to the second reactor, separating the target gas from the first fuel gas or the further gas mixture, feeding the separated target gas as an inert gas into the protective housing, and feeding an H.sub.2-enriched tail gas formed in the gas separation unit as a second fuel gas to the fuel cell.

2. The method as claimed in claim 1, wherein the gas separated off by the gas separation unit comprises H.sub.2 and is used as the second fuel gas for operation of the fuel cell or the further fuel cell.

3. The method as claimed in claim 1, wherein a proportion of CO in the first fuel gas is reduced by a third reactor designed as a water-gas shift stage and connected downstream of the first reactor and/or of a fourth reactor configured as a PrOx stage.

4. The method as claimed in claim 1, wherein at least one of the cathode offgas and anode offgas is supplied at least partly as another further gas mixture to the gas separation unit.

5. The method as claimed in claim 1, wherein a fifth reactor for conversion of the cathode offgas and/or anode offgas is connected downstream of the second reactor, and wherein an offgas formed in the fifth reactor is used as another inert gas and/or supplied as another further gas mixture to the gas separation unit.

6. The method as claimed in claim 1, wherein the first fuel gas or the further gas mixture comprises gaseous H.sub.2O separatable by the gas separation unit, and wherein the separated gaseous H.sub.2O is used as another inert gas.

7. The method as claimed in claim 6, wherein the gaseous H.sub.2O is converted to liquid H.sub.2O and discharged for external and/or internal use.

8. The method as claimed in claim 1, wherein the first fuel gas or the further gas mixture comprises gaseous H.sub.2O, and wherein the gaseous H.sub.2O is converted by a condenser to liquid H.sub.2O and discharged for external and/or internal use.

9. The method as claimed in claim 8, wherein heat released in the conversion of the gaseous H.sub.2O to the liquid H.sub.2O is discharged for external use.

10. The method as claimed in claim 1, wherein the first fuel gas or the further gas mixture is separated in the gas separation unit using membranes.

11. The method as claimed in claim 1, wherein the fuel used is a hydrocarbon of the general formula C.sub.xH.sub.yO.sub.z or a mixture of different hydrocarbons, including kerosene, natural gas and alcohol.

12. The method as claimed in claim 1, wherein CO.sub.2 and/or N.sub.2 separated off by the gas separation unit is discharged for external use, including for inertization of a cargo hold and/or a tank hold in an aircraft.

13. The method as claimed in claim 1, wherein CO.sub.2 and/or N.sub.2 separated off by the gas separation unit is used mixed with gaseous H.sub.2O as extinguishant for a cargo hold in an aircraft.

14. The method as claimed in claim 1, wherein a portion of the first fuel gas is branched off and discharged for external use, said external use including for operation of the further fuel cell or another fuel cell.

15. The method as claimed in claim 1, wherein the anode offgas is discharged for use as a further fuel gas for external use.

16. The method as claimed in claim 1, wherein all reactors, the gas separation unit, one or more conduits that connect the reactors to one another, feeds connected to the gas separation unit and/or control valves inserted into the conduits and feeds are surrounded by the protective housing.

17. The method as claimed in claim 11, wherein said alcohol is methanol.

18. A fuel cell system comprising: a first reactor for conversion of a fuel to a first fuel gas, a second reactor connected downstream of the first reactor, wherein the second reactor forms a fuel cell for generation of electrical energy using a cathode offgas and an anode offgas, and wherein at least the second reactor is surrounded by a protective housing, a gas separation unit configured to separate a target gas from the first fuel gas or a further gas mixture formed, wherein the target gas comprises at least one of CO.sub.2, N.sub.2 and a partial gas mixture comprising CO.sub.2 and N.sub.2, a first feed unit for feeding a portion of the first fuel gas or the further gas mixture to the gas separation unit, wherein the remaining portion of the first fuel gas or further gas mixture is led to the second reactor, a second feed unit for feeding the target gas separated by the gas separation unit as an inert gas into the protective housing, and a third feed unit for feeding an H.sub.2-enriched tail gas formed in the gas separation unit as a second fuel gas to the second reactor or to a sixth reactor comprising a further fuel cell.

19. The fuel cell system as claimed in claim 18, wherein the gas separation unit is configured to separate H.sub.2 from the first fuel gas or the further gas mixture.

20. The fuel cell system as claimed in claim 18, wherein at least one of a third reactor in the form of a water-gas shift stage and a fourth reactor in the form of a PrOx stage is connected downstream of the first reactor.

21. The fuel cell system as claimed in claim 18, wherein a fourth feed unit is provided for feeding at least a portion of the cathode offgas and/or the anode offgas as another further gas mixture to the gas separation unit.

22. The fuel cell system as claimed in claim 18, wherein a fifth reactor for conversion of the cathode offgas and/or anode offgas is connected downstream of the second reactor.

23. The fuel cell system as claimed in claim 18, wherein a unit for conversion of gaseous H.sub.2O separated off by the gas separation unit to liquid H.sub.2O is provided.

24. The fuel cell system as claimed in claim 23, wherein a unit for discharge of heat released in the conversion of gaseous H.sub.2O to liquid H.sub.2O is provided.

25. The fuel cell system as claimed in claim 18, wherein a condenser for separating gaseous H.sub.2O present in the first fuel gas or in the further gas mixture is provided.

26. The fuel cell system as claimed in claim 18, wherein the gas separation unit comprises at least one membrane for separation of the gases present in the first fuel gas or in the further gas mixture.

27. The fuel cell system as claimed in claim 18, wherein all reactors, the gas separation unit, one or more conduits that connect the reactors to one another, feeds connected to the gas separation unit and/or control valves inserted into the conduits and feeds are surrounded by the protective housing.

Description

(1) There follows a detailed elucidation of configurations of the invention with reference to the drawings. The drawings show:

(2) FIG. 1A a first fuel cell system,

(3) FIG. 1B a modification of the first fuel cell system according to FIG. 1A,

(4) FIG. 2 a second fuel cell system,

(5) FIG. 3 a third fuel cell system,

(6) FIG. 4 a fourth fuel cell system and

(7) FIG. 5 a fifth fuel cell system.

(8) FIG. 1A shows a schematic view of a first fuel cell system. A first conduit L1 for supply of a fuel B opens into a first reactor R1. The fuel B may, for example, be methanol, kerosene or the like. The first reactor R1 comprises a reformer. It is connected at the outlet end via a second conduit L2 to a downstream second reactor R2. The second reactor R2 comprises at least one fuel cell, for example a solid oxide fuel cell, NTPEM, HTPEM or the like. A first feed Z1 branches off from the second conduit L2 and is connected to a gas separation unit 1. Reference numeral 2 denotes a first barrier or control valve with which an amount of a stream of a first fuel gas BG1 exiting from the first reactor R1 is controllable such that the stream can be fed partly or else entirely to the first feed Z1.

(9) At the outlet end, a second feed Z2 for removal of N.sub.2 and/or CO.sub.2 and/or H.sub.2O extends from the gas separation unit 1. The second feed Z2 can be shut off by means of a second barrier or control valve 3. A third feed Z3 that extends from the gas separation unit 1 at the outlet end opens into the second conduit L2. The third feed Z3 can be shut off by means of a third barrier or control valve 4. Reference numeral 5 denotes a protective housing which surrounds the first reactor R1, the second reactor R2, the gas separation unit 1 and conduits L1, L2, L3 and feeds Z1, Z2, Z3 at least in sections here. It may of course also be the case that the protective housing 5 surrounds the second reactor R2 only. In that case, the second feed Z2 opens into the protective housing 5.

(10) Cathode offgas KA and anode offgas AA exits from a third conduit L3 or conduits (not shown here) from the second reactor R2 at the outlet end.

(11) Reference numeral L4 denotes a fourth conduit that opens into the second conduit L2 upstream of the second reactor R2. A fourth barrier or control valve 6 is inserted into the fourth conduit L4, with which a mass flow of a gas supplied by the fourth conduit L4 can be controlled by open- or closed-loop control. If air or oxygen, for example, is supplied through the fourth conduit L4, the fourth conduit L4 may also be connected directly to the respective reactor. According to the nature of the gas supplied to the fourth conduit L4, according to the desired reaction, the gas may be fed directly to the reactor or else fed into a feed conduit to the reactor.

(12) Reference numeral 8 denotes an outlet that penetrates the housing 5. The outlet 8 may be provided with a valve for elective opening or closing. The valve provided in the outlet may also be controllable by means of the controller.

(13) The function of the first fuel system is as follows:

(14) A first reactor R1, in the form of a reformer here, is supplied via the first conduit L1 with fuel B, for example methanol. In the first reactor R1, the fuel B is converted to a gaseous first fuel gas BG1 and discharged at the outlet end via the second conduit L2.

(15) At least a portion of the first fuel gas BG1 is branched off by means of the first control valve 2 and fed via the first feed Z1 to the gas separation unit 1. The first fuel gas BG1 especially contains N.sub.2, CO.sub.2, H.sub.2 and further gases. By means of the gas separation unit 1 at least N.sub.2 and/or CO.sub.2 and/or H.sub.2O is separated from the first fuel gas BG1. The gases separated off or a partial gas mixture of N.sub.2, CO.sub.2 and H.sub.2O are then guided by means of the second feed Z2 into the protective housing 5. The protective housing 5 is thus flooded with an inert gas atmosphere. The tail gas formed or remaining in the gas separation unit 1, formed from H.sub.2 or enriched with H.sub.2, forms a second fuel gas BG2 which is fed via the third feed Z3 to the second reactor R2 at the inlet end. The second reactor R2 is one or more fuel cells.

(16) The second fuel gas BG2 or a mixture of the first fuel gas BG1 and the second fuel gas BG2 is converted to electrical current in the second reactor R2. This forms a cathode offgas KA and an anode offgas AA that are removed by the third conduit L3 or third conduits L3 (not shown here).

(17) FIG. 1B shows a simplified, modified configuration of the first fuel cell system according to FIG. 1A. The first feed Z1 is omitted here. The second conduit L2 opens into the gas separation unit 1. At the outlet end, the third feed Z3 extends directly from the gas separation unit 1 to the inlet of the second reactor R2. The second feed Z2 that extends from the outlet side of the gas separation unit 1 can be shut off with the second barrier or control valve 3.

(18) In the modified configuration of FIG. 1B, the first fuel gas BG1 produced by the first reactor R1 is fed via the second conduit L2 to the gas separation unit 1. By means of the gas separation unit 1, at least N.sub.2 and/or CO.sub.2 and/or H.sub.2O is separated from the first fuel gas BG1. The gases separated off are then—as in the case of the first fuel cell system according to FIG. 1A—guided into the protective housing 5. The tail gas enriched with H.sub.2 which is formed or remaining in the gas separation unit 1 forms the second fuel gas BG2, which is fed via the third feed Z3 to the second reactor R2 at the inlet end.

(19) FIG. 2 shows a second configuration of the fuel cell system of the invention. In this case, a third reactor R3 is provided downstream of the first reactor R1 and, downstream of the third reactor R3, a fourth reactor R4 with the second reactor R2 downstream thereof.

(20) The third reactor R3 is a water-gas shift stage and the fourth reactor R4 is a PrOx stage. Both the third reactor R3 and the fourth reactor R4 are used to remove CO from the first fuel gas BG1 or a further gas mixture formed therefrom. Between the reactors, via fourth conduits L4 that may open into the second conduit L2, further hydrocarbons, air or other substances may electively be supplied to the stream of the first fuel gas BG1 or the further gas mixture, such that it is electively possible to influence the molar proportions between the reactors. If exclusively air is fed in via the fourth conduit L4, this may also be connected directly to the reactor that falls downstream. In other words, in this case, the fourth conduit L4 need not necessarily open into the feed to the downstream reactor.

(21) At the inlet of the fourth reactor R4, it is possible to supply air for example. At the inlet of the second reactor R2, it is likewise possible to supply air. Downstream of the third reactor R3, a further first feed Z1 is provided, with which a further gas mixture exiting from the third reactor R3 can be supplied to the gas separation unit 1. Reference numeral 7 denotes a fifth barrier or control valve with which a gas stream through the further first conduit Z1 can be enabled, shut off or controlled in terms of amount.

(22) In the first fuel cell system shown in FIG. 3, a fifth reactor R5 is connected downstream of the second reactor R2. The offgas from the fifth reactor R5 may—given suitable gas supply via the fourth conduit L4 connected directly upstream of the fifth reactor R5—be or become an inert gas which can be introduced into the protective housing 5 or discharged from the process and used elsewhere. The fifth reactor R5 may comprise a condenser. It is thus possible to separate water vapor from the offgas and provide it as liquid water for in-process use, for example in the reactor R1. The water can also be discharged from the process and used elsewhere. The fourth reactor R4 may also comprise a condenser for removal of water in order to remove water upstream of the second reactor R2.

(23) FIG. 4 shows a fourth fuel cell system. In this case, a fourth feed Z4 is provided at the outlet end of the second reactor R2, with which cathode offgas KA and/or anode offgas AA exiting from the second reactor R2 is supplied to the gas separation unit 1. It is thus possible to separate residual hydrogen from the cathode offgas KA and/or anode offgas AA and supply it again via the third feed Z3 to the second reactor R2.

(24) In the fifth fuel cell system shown in FIG. 5, the second fuel gas BG2 separated off with the gas separation unit 1, hydrogen in this case, is fed via the third feed Z3 to a sixth reactor R6. This may be a further fuel cell, for example an LTPEM. In this case, the second reactor R2 preferably comprises an HTPEM as fuel cell.

(25) The gas separation unit 1 is additionally connected by means of further first feeds Z1 that branch off downstream of the third reactor R3 and the second reactor R2. It is thus possible to branch off first fuel gas BG1 and/or further gas mixture at any points from the second conduit L2 or the main stream and feed them to the gas separation unit 1.

(26) A sixth reactor R6 is inserted into the third feed Z3. The sixth reactor R6 may comprise an LTPEM as fuel cell. At the outlet end, the sixth reactor R6 has a fourth conduit L4 with a fourth barrier or control valve 6, with which a mass flow of a gas supplied through the fourth conduit L4 can be controlled under open- or closed-loop control.

(27) A further fourth conduit L4 can branch off from the third conduit Z3 a further fourth conduit L4 with a barrier or control valve 6.

(28) In a modification of the fifth fuel cell system, the third reactor R3 can also be omitted. In this case, the second reactor R2 comprises an SOFC as fuel cell. The sixth reactor R6 comprises an LTPEM as fuel cell.

(29) A portion of the hydrogen that forms the second fuel gas BG2 may also be discharged from the process and used elsewhere. With the gas separation unit 1 it is also possible to feed external loads outside the fuel cell system.

(30) Although it is not shown in the figures, it may also be the case that the protective housing 5 surrounds only those reactors that comprise fuel cells.

(31) The fuel cell system proposed is especially suitable for use in a vehicle, especially an aircraft. The invention also relates to an aircraft comprising the fuel cell system described above.

LIST OF REFERENCE NUMERALS

(32) 1 gas separation unit

(33) 2 first control valve

(34) 3 second control valve

(35) 4 third control valve

(36) 5 protective housing

(37) 6 fourth control valve

(38) 7 fifth control valve

(39) AA anode offgas

(40) B fuel

(41) BG1 first fuel gas

(42) BG2 second fuel gas

(43) KA cathode offgas

(44) L1 first conduit

(45) L2 second conduit

(46) L3 third conduit

(47) L4 fourth conduit

(48) R1 first reactor

(49) R2 second reactor

(50) R3 third reactor

(51) R4 fourth reactor

(52) R5 fifth reactor

(53) R6 sixth reactor

(54) Z1 first feed

(55) Z2 second feed

(56) Z3 third feed

(57) Z4 fourth feed