Abstract
The present invention relates to a fuel cell system (100) for generating electrical energy, comprising a fuel cell stack (110) with an anode section (120) and a cathode section (130), the anode section (120) comprising an anode feed section (122) for supplying anode feed gas (AZG) and an anode discharge section (124) for discharging anode exhaust gas (AAG), wherein the anode discharge section (124) transitions into an anode recirculation section (140) for recirculating the anode exhaust gas (AAG) as anode recirculation gas (ARG) to the anode feed section (122), the cathode section (130) comprising a cathode feed section (132) for supplying cathode feed gas (KZG) and a cathode discharge section (134) for discharging cathode exhaust gas (KAG), wherein an active cooling device (180) is arranged in the anode recirculation section (140) for cooling the anode recirculation gas (ARG), wherein a water outlet (128) is arranged downstream of the active cooling device (180) to discharge the condensation water (KW) condensed in the active cooling device (180), wherein a mixing section (123) is arranged downstream of the water outlet (128) for mixing the anode recirculation gas (ARG) with fuel gas (BRG) and for supplying this, as anode feed gas (AZG), into the anode feed section (122).
Claims
1. Fuel cell system for generating electrical energy, comprising a fuel cell stack with an anode section and a cathode section the anode section comprising an anode feed section for supplying anode feed gas (AZG) and an anode discharge section for discharging anode exhaust gas (AAG), wherein the anode discharge section transitions into an anode recirculation section for recirculating the anode exhaust gas (AAG) as anode recirculation gas (ARG) to the anode feed section, the cathode section comprising a cathode feed section for supplying cathode feed gas (KZG) and a cathode discharge section for discharging cathode exhaust gas, wherein an active cooling device is arranged in the anode recirculation section for cooling the anode recirculation gas (ARG), wherein a water outlet is arranged downstream of the active cooling device to discharge the condensation water (KW) condensed in the active cooling device, wherein a mixing section is arranged downstream of the water outlet for mixing the anode recirculation gas (ARG) with fuel gas (BRG) and for supplying this, as anode feed gas (AZG), into the anode feed section, characterised in that the active cooling device comprises a thermally activated cooling device, in particular comprising an absorption heat pump, wherein the active cooling device is arranged in heat-transferring contact with the cathode discharge section for thermal activation by means of the heat contained in the cathode exhaust gas (KAG).
2. (canceled)
3. Fuel cell system according to claim 1, wherein the active cooling device comprises an electrically activated cooling device.
4. Fuel cell system according to claim 1, wherein the anode recirculation section has a condenser device in heat-transferring contact with the cathode feed section for cooling the anode recirculation gas (ARG) by heating the cathode feed gas (KZG), wherein a water outlet is arranged downstream of the condenser device and upstream of the active cooling device to discharge the condensation water (KW) condensed in the condenser device.
5. Fuel cell system according to claim 1, wherein the cathode discharge section is designed without a catalyst device and/or a burner.
6. Fuel cell system according to claim 1, wherein the anode discharge section and the anode recirculation section are designed without a divider section to enable a complete or substantially complete recirculation of the anode exhaust gas (AAG) as anode recirculation gas (RZG).
7. Fuel cell system according to claim 1, wherein a discharge valve is arranged in the anode recirculation section downstream of the active cooling device and downstream of the water outlet to enable a controlled discharge of at least part of the recirculation gas (RZG).
8. Fuel cell system according to claim 1, wherein the anode discharge section has an anode feed heat exchanger in heat-transferring contact with the anode feed section to transfer heat from the anode exhaust gas (AAG) to the anode feed gas (AZG).
9. Fuel cell system according to claim 1, wherein the mixing section is designed as an ejector device, with a fuel feed of fuel gas (BRG) at a primary connection of the ejector device and the anode recirculation section at the secondary connection of the ejector device.
10. Fuel cell system according to claim 1, wherein the cathode feed section has a cathode feed heat exchanger in heat-transferring contact with the cathode discharge section to transfer heat from the cathode exhaust gas (KAG) to the cathode feed gas (KZG).
11. Fuel cell system according to claim 1, wherein a cathode discharge heat exchanger is arranged in the anode feed section, preferably downstream of an anode feed heat exchanger, to transfer heat from the cathode exhaust gas (KAG) to the anode feed gas (AZG).
12. Fuel cell system according to claim 1, wherein a control valve is located in the anode feed section upstream of the mixing section to control the volume flow of fuel gas (BRG) through the mixing section.
13. Fuel cell system according to claim 1, wherein the anode discharge section is designed without an external cooling circuit.
14. Fuel cell system according to claim 1, wherein a cathode mixing section, in particular in the form of an ejector device, is arranged in the cathode feed section, a cathode recirculation section being connected in a fluid-communicating manner to the secondary connection thereof to recirculate part of the cathode exhaust gas (KZG) as cathode recirculation gas (KRG).
15. Method for recirculating anode exhaust gas (AZG) in a fuel cell system having the features of claim 1 as anode recirculation gas (ARG), comprising the following steps: cooling the anode recirculation gas (ARG) to below the boiling temperature of water by active cooling by means of the active cooling device, separating the condensed condensation water (KW) from the anode recirculation gas (ARG), mixing the dried anode recirculation gas (ARG) with a fuel gas (BRG) to form anode feed gas (AZG).
Description
[0040] Further advantages, features and details of the invention are explained in the following description, in which embodiments of the invention are described in detail with reference to the drawings. In each case schematically:
[0041] FIG. 1 shows an embodiment of a fuel cell system according to the invention,
[0042] FIG. 2 shows a further embodiment of a fuel cell system according to the invention,
[0043] FIG. 3 shows a further embodiment of a fuel cell system according to the invention,
[0044] FIG. 4a shows a further embodiment of a fuel cell system according to the invention,
[0045] FIG. 4b shows a further embodiment of a fuel cell system according to the invention,
[0046] FIG. 5 shows a further embodiment of a fuel cell system according to the invention,
[0047] FIG. 6 shows a further embodiment of a fuel cell system according to the invention.
[0048] FIG. 7 shows a further embodiment of a fuel cell system according to the invention.
[0049] FIG. 1 shows schematically a fuel cell system 100 which has a fuel cell stack 110 with an anode section 120 [and] a cathode section 130. The anode section is supplied with anode feed gas AZG via an anode feed section 122 and the anode exhaust gas AAG is discharged via the anode discharge section 124. In the same way, the cathode section 130 is supplied with cathode feed gas KZG, here in the form of air LU, via a cathode feed section 132, and the cathode exhaust gas KAG is discharged via the cathode discharge section 134. As can be clearly seen in FIG. 1, the anode section is a so-called dead-end design, since 100%, i.e. all of the anode exhaust gas AAG is also recirculated as anode recirculation gas ARG. In terms of construction design, this is achieved in that the anode discharge section 124 transitions into the anode recirculation section 140. In order to provide the desired drying for this recirculation of the anode exhaust gas AAG, an active cooling device 180 is arranged in the further course of the anode recirculation section 140 which actively provides a heat sink for cooling the anode recirculation gas ARG at this point, and thus without any external cooling connections. The cooling function is designed as a condensation function, so that the anode recirculation gas ARG is cooled below the boiling temperature of water, which depends on the partial pressure, e.g., for the sake of simplicity, 100 degrees Celsius. The cooled anode circulation gas ARG is thus condensed with regard to the water content and the now liquefied condensation water KW is discharged via a separator into the water outlet 128 from the anode recirculation section 140. The dried anode recirculation gas ARG is fed here into an injector device as mixing section 123, where it is mixed with fuel gas BRG, whereby this mixed gas is then fed back into the anode section 120 as anode feed gas AZG. It is easy to see here that the one hundred percent recirculation rate allows maximum efficiency to be achieved in the use of the fuel gas BRG, also from the anode exhaust gas AAG. The reduction in the Nernst voltage due to the water content of the anode recirculation gas ARG which would otherwise have to be accepted can be avoided or at least reduced here, since the water contained can be at least partially condensed out and discharged via the water outlet 128 cost-effectively and easily with the help of an active cooling device 180.
[0050] FIG. 2 shows a further development of the embodiment of FIG. 1. Here, upstream heat transfer systems are provided to supplement the active cooling device 180 and thus further increase the efficiency of the overall system. The individual components of this additional temperature control system can of course be freely combined with each other, where technically expedient.
[0051] Thus, FIG. 2 shows an anode feed heat exchanger 121 which is able to ensure a heat exchange from the hot anode exhaust gas AAG to the anode feed gas AZG which is to be heated. This allows the anode feed gas AZG to be conditioned and pre-heated in order to have a desired higher inlet temperature into the anode section 120. At the same time, the anode exhaust gas AAG is pre-cooled here, so that the necessary cooling capacity, in particular at the active cooling device 180, is further reduced in this way. The dimensioning of the active cooling device 180 can accordingly be smaller. In addition, in order to provide further pre-cooling, in particular to already provide partial condensation, a condenser device 126 is integrated into the cathode feed section 132. A heat exchange takes place there between the anode exhaust gas AAG and the air LU supplied as cathode feed gas KZG. The air is thus sucked in from the environment and warmed up here through the transfer of heat from the hot anode exhaust gas AAG. In the same way, in particular in combination with the anode feed heat exchanger 121 already explained, a first condensation step is already created here, the anode exhaust gas AAG, in this case as anode recirculation gas ARG, is thus cooled to a temperature of less than 100 Celsius. This means that at least part of the water from the anode recirculation gas ARG condenses out here and is discharged as condensation water KW via a separate water outlet 128. The active cooling device 180, which makes possible even further cooling and thus an even more effective drying of the anode recirculation gas, is arranged downstream. The effect according to the invention is further enhanced in this case by the three-stage cooling of the anode exhaust gas as anode recirculation gas ARG.
[0052] FIG. 2 also shows an additional detail variant of the activity of the active cooling device 180. In this case, this is designed as a thermally activated cooling device 180. The thermal activation is provided by the fuel cell system itself, since hot cathode exhaust gas KAG is also directed from the cathode discharge section 134 to the activation area of the active cooling device 180. As already indicated, such a thermally activated cooling device 180 can for example be designed as an absorption heat pump, whereby the necessary heat activation is provided by the increased temperature of the cathode exhaust gas KAG. Since the cathode exhaust gas KAG also usually has a very high temperature and the cathode feed gas KZG can also be preconditioned to an elevated temperature, in the embodiment of FIG. 2 an air-heat exchanger 190 is also provided in the overall temperature control system of the fuel cell system 100. This allows the very hot cathode exhaust gas KAG to be used, in a first step, for the preconditioning of the cathode feed gas KZG and then allows the remaining residual heat to be used for the thermal activation of the active cooling device. In the opposite direction, for the supplied air LU as cathode feed gas KZG, this means that two heating stages are provided here, namely through the compensator device 126 and the aforementioned air-heat exchanger 190.
[0053] FIG. 3 also shows a further development of the embodiment of FIGS. 1 and 2. Here too, further additional components have been added which can be used individually or in combination with the other components of the temperature control system. One of these components is a cathode feed heat exchanger 131, which is used here as a third heating stage for heating up the cathode feed gas 132. In addition, a discharge valve 129 is also provided here which provides additional flexibility due to the one hundred percent recirculation rate of the anode exhaust gas.
[0054] In special situations in which the amount of anode recirculation gas ARG is greater than required, such a discharge valve 129, also referred to as a blowout valve, can provide a discharge function for part or all of the anode recirculation gas ARG.
[0055] FIG. 4a also shows further components of a temperature control system, in particular with regard to additional temperature control of the anode feed gas AZG by means of the heated cathode exhaust gas KAG. For this purpose, a cathode discharge heat exchanger 133 is arranged in the anode feed section 122 to ensure the aforementioned heat transfer.
[0056] FIG. 4b shows a fuel cell system 100 which largely corresponds to that of FIG. 4a. However, in FIG. 4b, the one cathode discharge heat exchanger 133 is arranged with the cold side downstream of the anode feed heat exchanger 121. The hot anode exhaust gas AAG is thus passed through a warm side of the anode feed heat exchanger 121, which brings the anode feed gas AZG further up to operating temperature. Here, the cathode exhaust gas KAG is passed through the warm side of the cathode discharge heat exchanger 133, whereby the anode feed gas AZG is first heated by the cathode exhaust gas KAG in the cathode discharge heat exchanger 133 and then by the anode discharge gas AAG in the anode feed heat exchanger 121. In contrast, in the design according to FIG. 4a, the anode feed gas AZG is first heated by the anode discharge gas AAG in the anode feed heat exchanger 121 and then by the cathode exhaust gas KAG in the cathode discharge heat exchanger 133.
[0057] FIG. 5 also shows further components with which the fuel cell system 100 can be further developed. On the one hand, these are a cathode recirculation fan 171 and a cathode divider section 137 which allow a part of the cathode exhaust gas KAG to be diverted into a cathode recirculation section 170. This means that this diverted part of the cathode exhaust gas KAG can be fed as cathode recirculation gas KRG into an ejector device as cathode mixing section 135 and cathode recirculation can be guaranteed. Thus, a variable recirculation fraction at the cathode is possible, whereby higher recirculation rates can be set under partial load operation. The remaining cathode exhaust gas KAG is fed to the catalyst device 136 in the way already explained several times.
[0058] Also shown in FIG. 5 is a control valve 160 in the fuel gas feed for the fuel gas BRG. This is in particular designed to be quantitatively controllable, so that different volume flows of fuel gas BRG can be set and different quantities of fuel gas can also actually be added to the anode recirculation gas ARG for different operating situations.
[0059] FIG. 6 shows another component with which the fuel cell system 100 can be further developed. Thus, in the embodiment shown in FIG. 6, a further air-heat exchanger 192 is additionally provided in the overall temperature control system of the fuel cell system 100 which, in a further step for the preconditioning of the cathode feed gas KZG, allows residual heat from the cathode exhaust gas KAG to be used before it is discharged into the environment. In the opposite direction, for the supplied air LU as cathode feed gas KZG, this means that three heating stages are provided here, namely through the condenser device 126, the air heat exchanger 192 and the air heat exchanger 190.
[0060] FIG. 7 shows another fuel cell system 100. Those elements which have the same reference sign as in the previous embodiments correspond to these and are not described further. A discharge valve 195 is provided here, via which anode exhaust gas AAG can be discharged from the anode recirculation section 140. The dashed representation of the discharge valve 195 shows a further possible arrangement of the same. The discharge valve 195 may be necessary when a fuel such as hydrogen or ammonia contains impurities such as nitrogen or carbon dioxide in order to prevent an accumulation of the inert and non-condensable gases in the anode path. The discharge valve 195 can be opened periodically or a continuous discharge can also take place. In order to chemically convert anode exhaust gas, an exhaust gas conversion device 194 is provided which is for example designed as an oxidation catalyst. In addition, a post-treatment unit 193 is provided here which is arranged downstream of the air-heat exchanger 190. The post-treatment unit 193 is particularly advantageous when operating the fuel cell system 100 with ammonia, in order to convert traces of ammonia once again before the exhaust gas is released into the environment. For this purpose, the post-treatment unit 193 can for example be designed as an ammonia slip catalyst (ASC) which functions at temperatures between 200 C. and 500 C.
[0061] The individual components, in particular the system consisting of a large number of heat exchangers, can be freely combined with each other and, in particular, can be freely switched via control valve systems in order to be able to react as flexibly as possible to a wide variety of operating situations of the fuel cell system 100.
[0062] In this context, further alternative features and combinations of features are explicitly suggested below.
[0063] For example, the component of the ejector device as cathode mixing section 135 from the embodiment of the fuel cell system 100 shown in FIG. 5 can also be combined with the embodiments of the fuel cell system 100 from FIG. 6 which include the component of the further air-heat exchanger 192.
[0064] Furthermore, in an embodiment which includes the aforementioned components of the ejector device as cathode mixing section 135 from FIG. 5 and the further air-heat exchanger 192 from FIG. 6, the cooling device 180 can be supported by a water cooling system which may be usable in a system environment involving use of the fuel cell system 100.
[0065] In addition, in an embodiment which includes the aforementioned component of the further air-heat exchanger 192 from FIG. 6, a blower may be used as cathode mixing section 135 instead of the ejector device shown in FIG. 5.
[0066] Alternatively, in an embodiment comprising said component of the further air-heat exchanger 192 from FIG. 6, and in which said blower is used as cathode mixing section 135 instead of the ejector device from FIG. 5, the cooling device 180 can be supported by said water cooling system which may be usable in a system environment involving use of the fuel cell system 100.
[0067] The above explanation of the embodiments describes the present invention exclusively in the context of examples.
LIST OF REFERENCE SIGNS
[0068] 100 fuel cell system [0069] 110 fuel cell stack [0070] 120 anode section [0071] 121 anode feed heat exchanger [0072] 122 anode feed section [0073] 123 mixing section [0074] 124 anode discharge section [0075] 126 condenser device [0076] 128 water outlet [0077] 129 discharge valve [0078] 130 cathode section [0079] 131 cathode feed heat exchanger [0080] 132 cathode feed section [0081] 133 cathode discharge heat exchanger [0082] 134 cathode discharge section [0083] 135 cathode mixing section [0084] 140 anode recirculation section [0085] 160 control valve [0086] 170 cathode recirculation section [0087] 171 cathode recirculation fan [0088] 180 active cooling device [0089] 192 air-heat exchanger [0090] 193 post-treatment unit [0091] 194 exhaust gas conversion device [0092] 195 discharge valve [0093] AZG anode feed gas [0094] AAG anode exhaust gas [0095] ARG anode recirculation gas [0096] KZG cathode feed gas [0097] KAG cathode exhaust gas [0098] KRG cathode recirculation gas [0099] BRG fuel gas [0100] LU air [0101] KW condensation water
