DE102012007375A1 - Fuel cell system i.e. proton-conducting membrane fuel cell system, for use in vehicle, has pulsation device comprising movable element, which is automatically moved by variable force caused over flow and reaction force - Google Patents

Abstract

The system (1) has an anode circuit (10) for returning exhaust gas from an anode region (4) with a pulsation device (14). The pulsation device comprises a movable element, which narrows a flow throughable cross-section for flow of gas. The movable element is automatically moved by variable force caused over flow and a reaction force. The moving element is designed as a flap. The pulsation device comprises an exhaust nozzle and a detour element as the movable element. A retainer i.e. electromagnet, is utilized for fixing the movable element.

Description

The invention relates to a fuel cell system with an anode circuit for the return of exhaust gases from an anode compartment in the input region of the anode compartment, according to the closer defined in the preamble of claim 1.

Fuel cell systems with an anode circuit are known from the general state of the art. This is exemplified on the JP 2007-200725 A directed. In Japanese Script, a fuel cell system with a fuel cell is shown. In addition, the fuel cell system comprises a so-called anode circuit, which connects the output of the anode to the input of the anode. In this so-called recirculation line of the anode circuit, a Rezirkulationsgasfördereinrichtung is arranged to promote the exhaust gas from the exit of the anode compartment to the input of the anode compartment. The exhaust gas is then fed to the inlet of the anode compartment again mixed with fresh gas, for example from a compressed gas storage.

It is known from the general state of the art that a better utilization of the available active area of the fuel cell in the anode space is achieved by this anode circuit, since an excess of fuel, for example hydrogen, can be used. As a result, the available area is ideally utilized. The excess of, for example, 10 to several hundred percent of the required fuel is returned via the recirculation line, so it is not lost. The recirculated fuel also contains moisture, so that the membranes in the fuel cell, which is typically constructed as a PEM fuel cell, are ideally humidified. From time to time, in the anode cycle, an undesirably large amount of water and inert gases, which, like nitrogen, z. B. diffuse through the membranes of the fuel cell from a cathode compartment in the anode compartment, or be present as impurities in the fuel itself. These can be drained from time to time via a water separator and / or a valve.

Now it is the case that product water collects in the area of the fuel cell, which at high loads and a high volumetric flow of fuel and recirculated exhaust gas is easily discharged from the comparatively narrow gas distribution channels of the anode compartment. At lower loads, however, this can possibly lead to problems, since liquid water can block channels and / or parts of the membranes or the so-called gas diffusion electrodes due to the low volume flow of the gas flowing through. As a result, active cell area is lost and the performance of the fuel cell decreases.

In order to improve the discharge of water, it is in the above-mentioned Japanese writing JP 2007-200725 A proposed to create over a pulsating operation of a fan as Rezirkulationsgasfördereinrichtung larger pressure differences in the anode compartment and the recirculation line, so that the discharge of liquid water is improved from the anode compartment. The structure is comparatively complex because it requires a targeted control of the recirculation fan. In addition, due to the inertia of the recirculation blower, which is typically driven by an electric motor, the pressure will increase and decrease only comparatively slowly, so that the discharge of water by the device described in the JP publication is not optimal.

Another problem lies in the fact that an increased demand for energy in the region of the recirculation fan occurs due to constant braking and re-acceleration of the recirculation fan, as a result of which the efficiency of the fuel cell system deteriorates.

Furthermore, from the JP 2010-044911 A a fuel cell system with an anode circuit known. In the anode circuit of this fuel cell system, a buffer for the recirculated exhaust gas is arranged. Via valve devices, which are opened and closed accordingly, a pressure pulsation in the anode circuit is generated for the same reasons as in the aforementioned prior art. Again, the structure is relatively complex, as it requires a lot of space and many components required, all of which must be dense compared to the hydrogen present in the exhaust. This is known to be complicated and expensive. In addition, the control of the valve means for generating the pulsation requires a complex control system. Furthermore, energy is needed to control the valve devices.

The object of the present invention is now to provide a fuel cell system with an anode recirculation, in which a pulsation device is arranged, which circumvents the disadvantages mentioned above and ensures a simple, inexpensive and energy-efficient system.

According to the invention this object is achieved by the features in the characterizing part of claim 3. Advantageous embodiments and further developments of the invention Fuel cell system resulting from the remaining dependent therefrom dependent claims.

The pulsation device according to the invention is thus constructed so that it has a movable element. The movable element influences the flow-through cross section for the gas flow more or less strongly. As a result of the arrangement at any point in the anode circuit, this gas stream can either be the recirculated exhaust gas alone or the exhaust gas that has already been mixed again with fresh fuel. As far as the pulsation device corresponds to a valve device which is opened and closed, as is carried out in the prior art.

However, the solution according to the invention now provides that the movable element automatically moves in a pulsating manner by means of a variable force and a counterforce caused by the flow. The pulsation device thus allows the generation of a pulsating gas flow without having to actively intervene by a control or regulation in the flow of the gas stream. The pulsating gas flow is generated via a movable element which, due to a variable force caused by the flow and a counterforce acting against each other and causing a fluctuating force or pressure difference once in the direction of a force and once in the direction of the other force.

The pulsation device with the self-moving element according to the invention is extremely simple and efficient. It requires no additional control and can thus be installed as a passive pulsation device very space-saving at any point in the anode circuit.

According to a particularly favorable and advantageous development of the fuel cell system according to the invention, it is provided that the movable element is designed as a flap which is rotatably mounted on a front in the flow direction of the gas flow outside the center of the flow of the gas stream. Such an eccentrically mounted flap will always experience a resultant force due to the inflow or flow in one direction. As a result, the flap is first deflected in one direction until an equilibrium of forces sets in. From inertia, it is moved slightly beyond this balance of power. Then she experiences a resultant force in the other direction and moves back again. According to a particularly favorable and advantageous development, the weight of the flap and / or the force of a spring can additionally be designed as a counterforce in order to press the flap into the flow. In both cases results in a pulsating movement of the flap. It thereby alternately releases the flow-through cross-section more or less so that this results in a pulsating gas flow.

In an alternative embodiment of the fuel cell system according to the invention, it may be provided that the pulsation device has an outlet nozzle and a deflecting element which is freely movable in its distance from the outlet nozzle at least between a position closing the outlet nozzle and a position spaced from the outlet nozzle, the outlet nozzle being an outlet opening and having a projection corresponding to the deflection element, so that a more or less large flowed-through gap is formed between the deflection element and the projection of the outlet nozzle as a function of the automatically changing position of the deflection element.

This embodiment of the passive pulsation device uses the so-called hydrodynamic paradox to achieve a pulsating flow. The deflecting element is arranged in front of the outlet nozzle, that it deflects the flow, whereby it flows through a narrow gap between the deflecting element and the outlet nozzle. The narrower this gap is, the higher the flow velocity. This results in the region between the gap and the extension of the outlet nozzle, a lower pressure than in the environment. The deflecting element is thereby moved in the direction of the outlet opening of the outlet nozzle, whereby the gap is even smaller and the effect is further enhanced. At some point, the deflecting element closes the outlet nozzle. The flow then abruptly breaks off, it sets everywhere the ambient pressure, whereby the deflecting element is lifted again from the extension of the outlet nozzle. The re-forming flow gap is then again traversed by gas, the process described begins again. The process thereby causes a pulsating flow of the propellant gas stream, which becomes high-frequency as the flow rate of the gas increases.

In a particularly favorable and advantageous development of the fuel cell system according to the invention, it can be provided for both embodiments of the pulsation device described above that a locking device is provided for fixing the movable element. About such a locking device, which can be equipped in particular actively switchable, the movable element can be fixed. This is a shutdown of the pulsation possible. This can, for example, at higher loads or higher flow rates in the anode circuit be useful.

In a very advantageous embodiment thereof, it is accordingly provided that the fixation of the movable element takes place in a position largely releasing the flow. The fixation is thus carried out so that the movable element is preferably fixed in its maximum flow cross-section releasing end position, so as to be able to change from a pulsating gas flow to a continuous gas flow.

Further advantageous embodiments of the fuel cell system according to the invention will become apparent from the remaining dependent subclaims and will be apparent from the embodiments, which are described in more detail below with reference to the figures.

Showing:

1 a detail of a fuel cell system according to the invention in a first embodiment;

2 a detail of a fuel cell system according to the invention in a second embodiment;

3 a possible embodiment of a pulsation device of a gas jet pump according to the invention;

4 a possible alternative embodiment of a pulsation device of a gas jet pump according to the invention; and

5 a possible embodiment of a locking device.

In the presentation of the 1 is a fuel cell system 1 shown in a first possible embodiment. It is intended in an example indicated vehicle 2 be arranged. The core of the fuel cell system 1 forms a fuel cell 3 , This is designed as a PEM fuel cell stack. The fuel cell 3 includes an anode compartment 4 and a cathode compartment 5 , About an indicated air conveyor 6 should the cathode compartment 5 Air can be supplied as an oxygen supplier in a conventional manner. The exhaust air from the cathode compartment 5 then gets to the environment. This is very much simplified and purely exemplary to understand. Of course, a module for exchanging heat and / or moisture could still be arranged between supply air and exhaust air, or a turbine may be arranged in the region of the exhaust air in order to recover energy from the exhaust air. The anode compartment 4 the fuel cell 3 is used as fuel hydrogen from a compressed gas storage 7 fed. The hydrogen passes through a pressure regulating and metering valve 8th in the anode compartment 4 the fuel cell 3 , Unconsumed hydrogen passes along with inert gas, in particular nitrogen, which passes through the membranes of the fuel cell 3 from the cathode compartment 5 in the anode compartment 4 diffused, and together with a part of the product water of the fuel cell 3 via a recirculation line 9 back to the entrance of the anode room 4 to which the recirculated exhaust gas is recycled together with fresh hydrogen. This structure is also referred to as anode circuit and is in the representation of 1 with the reference number 10 Mistake.

To the pressure losses in the anode space 4 and in the anode circuit 10 compensate, is in a conventional manner a Rezirkulationsgasfördereinrichtung 11 intended. This is in the embodiment shown here as a recirculation fan 12 educated. Now it is like that in the anode cycle 10 accumulate water and inert gases over time. These must be drained, for example, from time to time or depending on the quantities of substances and / or substance concentrations produced. This is in the presentation of the 1 a water separator 13 provided with a drain valve. In the anode cycle 10 is also a pulsation device 14 arranged, which will be discussed later.

In the presentation of the 2 is a comparable fuel cell system 1 in a vehicle 2 shown. As far as the components are the same, they also carry the same reference numerals. The following therefore only on the differences in the structure of the fuel cell system 1 again in detail. The first difference is in the area of the recirculation gas delivery device 11 to find. The recirculation gas conveyor 11 is in the in 2 illustrated embodiment as a so-called jet pump or gas jet pump 15 executed. The gas jet pump 15 is doing of the hydrogen from the compressed gas storage 7 Driven as a propellant gas stream and ensures by pulse exchange and / or a negative pressure generated by the propellant gas flow that the exhaust gas from the recirculation line 9 together with the propellant gas flow to the anode compartment 4 the fuel cell 3 is fed again. In addition to the use of a recirculation fan 12 or a gas jet pump 15 as Rezirkulationsgasfärdereinrichtung 11 would also be the use of a combination of these two embodiments conceivable.

Another difference of in 2 illustrated fuel cell system 1 is in the area of the recirculation line 9 to recognize. This is divided according to the output of the anode compartment 4 in two with 9.1 and 9.2 designated flow branches on. These two flow branches 9.1 and 9.2 then run in front of the gas jet pump 15 together again with the fresh serving as propellant gas hydrogen to the entrance of the anode compartment 4 to be fed again. The two flow branches 9.1 and 9.2 are now designed so that the water separator 13 with its drain valve in the region of a flow branch 9.1 is arranged while the pulsation device 14 is placed in the parallel flow branch.

This causes the pulsations in the area of the water separator 13 even to the pulsations in the remainder of the anode circuit 10 reduced, which in particular the functionality when discharging water and / or gas from the water 13 is improved, since in its area then less pulsations occur.

For the present invention, in particular the already mentioned and in the 1 and 2 illustrated pulsation device 14 crucial. It serves to convert the gas stream in the anode circuit into a pulsating gas stream, to the discharge of water from the anode compartment 4 to improve. The embodiment of the pulsation device 14 is designed so that a movable element moves automatically by a force caused by the flow variable force and then building up opposing force pulsating. It is therefore a passive pulsation device 14 ,

In the presentation of the 3 is a first possible embodiment of such a pulsation device 14 to recognize. The pulsation device 14 in the embodiment according to 3 consists essentially of a flap 16 which forms the movable element. The flap 16 is ideally mounted on one side, namely from the direction of the inflowing gas flow forward, ball-mounted rotatably mounted. About her weight and possibly the power of an example here indicated spring 17 , which is preferably designed as a torsion spring in the storage area, is the flap 16 at standstill of the fuel cell system 1 move down. It then protrudes from the surge chamber 18 in which it is arranged, via the connection to the conduit element 19 for the gas flow into the flow of the gas stream. It accumulates the flow of the gas flow through it. With higher forming dynamic pressure takes the force on the flap 16 against the weight and the spring force corresponding to, so the flap 16 , as indicated by the double arrow, in the direction of the shock pressure chamber 18 is moved up and into it. This allows the gas flow freely through the conduit element 19 flow and the back pressure, which is in the flow direction in front of the flap 16 has built up accordingly. As a result, the opposing force, in this case the weight force and the spring force on the flap, regains the upper hand, so that the flap is in turn pushed into the flow and the process begins again. This results in a pulsating gas flow. At low loads, this works great and the flap 16 Performs a pulsating motion, which achieves the pulsating gas flow. At higher loads, where a pulsation of the gas flow is no longer necessary and sometimes even undesirable, the flap 16 largely kept open by the flow pressure and remains predominantly in the region of the shock pressure chamber 18 , It then only minimally influences the flow of the gas stream, so that the pressure pulsations with higher flow velocity and higher volume flow of the recirculated gas stream decrease in a self-regulating manner. The pulsation device 14 is self-acting and requires no influence via a control or regulation from the outside. Only spring force and weight of the flap 16 must be based on the particular application in the construction of the pulsation device 14 be tuned and designed.

In the presentation of the 4 is another embodiment of a pulsation device 14 to recognize. This uses the so-called hydrodynamic paradox. To the pipe element 19 for the inflowing gas flow in this case an outlet nozzle closes 20 at. This consists of a nozzle opening 21 , here practically the end of the conduit element 19 , as well as an extension 22 designated part. This can be formed for example as an annular disc. It would also be conceivable that the extension 22 another form, for example in the form of a funnel, has. Following in the direction of flow to the outlet opening is a deflecting element 23 , This corresponds in its shape with the extension 22 , So is formed in the embodiment shown here as a circular disc. In principle also possible embodiment of the extension 22 in the manner of the aforementioned funnel would have the deflection 23 then be formed accordingly in the manner of a cone.

The functionality of the pulsation device 14 is now the one through the deflector 23 the flow after exiting the outlet 22 is deflected accordingly. The deflected flow then flows through the in 4 recognizable gap 24 between the deflecting element 23 and the extension 22 the outlet nozzle 21 therethrough. Due to the high flow velocity in the gap 24 prevails in the area of the gap 24 a smaller pressure than in the vicinity of the structure, and in particular in the region of the deflecting element 23 on its the outlet 21 opposite side. The deflecting element 23 As a result, as the flow velocity increases, it is increasingly in the direction of the outlet opening 21 pressed. As soon as the pressure becomes so high that the deflection element 23 the extension 22 touched, it closes the outlet 21 and the gap 24 falls away. This equalizes the pressure between the extension 22 and the deflecting element 23 Immediately to the prevailing pressure in the environment. The deflecting element 23 This will no longer be in the direction of the extension 22 pressed so that the gap 24 again arises and the flow through the gap 24 starts again. As the flow increases, the pressure in the gap is reduced 24 again, this is correspondingly smaller and the process described is repeated. The result is one after the pulsation device 14 pulsating gas flow.

in both described embodiments of the pulsation device 14 It is conceivable and possible, a locking device 25 provide over which the movable element, so the flap 16 or the deflecting element 23 , let fix. For example, the locking device could 25 be designed as an electromagnet when the movable element 16 . 23 consists of a magnetizable material. For example, the flap could 16 be held in its upper position, or the deflecting element 23 in the maximum permeable gap 24 releasing position. Alternatively to such a locking device 25 is in the representation of 5 a possible embodiment of a mechanical locking device 25 shown. Such a locking device 25 For example, in the embodiment of the movable element as a flap 16 on the rotatable mounting of the flap 16 opposite side of the shock pressure chamber 18 be arranged. In the embodiment of the movable element as a deflecting element 23 ideally would be three or more evenly over the circumference of the diverting element 23 distributed locking devices 25 possible. In the presentation of the 5 the orientation of the representation is chosen so that it is essentially the representation in 3 equivalent. When used with the deflector 23 as a moving element would be the gap 24 in the in 5 illustrated embodiment below there drawn in its final position movable element 16 . 23 to understand. The pulsation of the moving element 16 . 23 is indicated by the double arrow. The locking device 25 has a pawl 26 on which, for example, by the force of a spring 27 in the direction of the movable element 16 . 23 is pressed when the movable element 16 . 23 should be fixed. As typically the position of the movable element 16 . 23 at the time of activation of the locking device 25 not known, is the in 5 illustrated structure of particular advantage. Is the moving element 16 . 23 already above the pawl 26 then it will stay there. If it is still below the pawl 26 , then it will be up against a sloping surface 28 the pawl 26 emotional. The pawl 26 is against the force of the spring 27 pushed back and the movable element 16 . 23 can the pawl 26 happen. By the force of the spring 27 the pawl is then back in the in 5 shown position pressed and the movable element 23 is above the pawl 26 recorded. In addition, via an actuator 29 an active control of the pawl 26 done so that they, for example, against the force of the spring 27 from the engagement area of the movable element 16 . 23 can be moved if the pulsation should not be interrupted. Also a move in the 5 shown position by the actuator 29 if necessary is possible.

The locking device 25 can now preferably be used so that from a certain predetermined volume flow, which typically a predetermined load of the fuel cell system 1 corresponds to the in 5 shown position is moved. Once the moving element 16 . 23 the pawl 26 happens, the movable element is fixed and can not fall back into the area of flow. The pulsation of the flow in the conduit element 19 is then canceled and there is a continuous flow through the pipe element 19 , The volume flow in the line element drops 19 or the load of the fuel cell 3 again off, then can over the actuator 29 the movable element 16 . 23 be released again and it can again a pulsed propellant gas flow through the pulsation device 14 in the conduit element 19 to be provided.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2007-200725 A [0002, 0005]
• JP 2010-044911 A [0007]

Claims (9)

Fuel cell system ( 1 ) with an anode circuit ( 10 ) for the recirculation of exhaust gas from an anode compartment ( 4 ) in the entrance area of the anode space ( 4 ) with a pulsation device ( 14 ), wherein the pulsation device ( 14 ) a movable element ( 16 . 23 ), which by its movement more or less narrows a flow-through cross section for the gas stream, characterized in that the movable element ( 16 . 23 ) automatically moves in a pulsating manner by means of a variable force caused by the flow and a counterforce to it. Fuel cell system ( 1 ) according to claim 1, characterized in that the movable element as a flap ( 16 ), which is rotatably mounted at a front end in the flow direction of the propellant gas flow outside the center of the flow of propellant gas stream. Fuel cell system ( 1 ) according to claim 2, characterized in that, the flap ( 16 ) by their weight and / or the force of a spring ( 17 ) is pressed as counterforce in the flow is. Fuel cell system ( 1 ) according to claim 2 or 3, characterized in that the flap ( 16 ) in a chamber which is connected to the flow-through cross-section and adjacent to the flow ( 18 ), wherein the flap ( 16 ) protrudes into the flow at least in its one end position, in which it is pressed by the counterforce. Fuel cell system ( 1 ) according to claim 1, characterized in that the pulsation device ( 14 ) an outlet nozzle ( 20 ) and a deflecting element ( 23 ) as a movable element, which in its distance from the outlet nozzle ( 20 ) at least between one of the outlet nozzle and one of the outlet nozzle ( 20 ) spaced position is freely movable, wherein the outlet nozzle ( 20 ) an outlet opening ( 22 ) and one with the deflecting element ( 23 ) corresponding extension ( 22 ), so that between the deflecting element ( 23 ) and the extension ( 22 ) of the outlet nozzle ( 20 ) depending on the automatically changing position of the deflecting element ( 23 ) more or less large gap ( 24 ) trains. Fuel cell system ( 1 ) according to claim 5, characterized in that the deflecting element ( 24 ) and the extension ( 22 ) of the outlet nozzle ( 20 ) are formed flat in each case in a plane and arranged parallel to each other. Fuel cell system ( 1 ) according to one of claims 1 to 6, characterized in that a locking device ( 25 ) for fixing the movable element ( 16 . 23 ) is provided. Fuel cell system ( 1 ) according to claim 7, characterized in that the fixation of the movable element ( 16 . 23 ) by the detention facility ( 25 ) takes place in a position largely releasing the flow. Fuel cell system ( 1 ) according to one of claims 1 to 8, characterized in that in the anode circuit ( 10 ) a water separator ( 13 ), wherein the pulsation device ( 14 ) in a parallel to the flow branch ( 9.1 ) with the water separator ( 13 ) extending flow branch ( 9.2 ) is arranged.

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