DE102009048247A1 - Method for operating fuel cell system of e.g. ship in water, involves operating valve device in opened condition when pressure within anode area of valve device is larger or equal to pressure in cathode area of valve device - Google Patents

Abstract

The method involves supplying fuel to an anode area (3) of a fuel cell (2), and supplying an oxidant to a cathode area (4) of the fuel cell. Anode exhaust gas is recirculated by a recirculation line from an anode output to an anode input. A valve device (14) is operated in an opened condition when mass flow of the oxidant exceeds a preset value and pressure within an anode area of the valve device is larger or equal to the pressure in a cathode area of the valve device.

Description

The invention relates to a method for operating a fuel cell system having at least one fuel cell according to the type defined in greater detail in the preamble of claim 1. Further, the invention relates to a use of the method.

Such a structure of a fuel cell system with a recirculation line for returning the anode exhaust gas in the anode input is for example from DE 101 15 336 A1 known. In such systems with a so-called anode loop, nitrogen and water accumulate in the recirculated anode exhaust gas over time. Therefore, it is known from the general state of the art and described in the above-mentioned document that in the region of the recirculation line valve devices are arranged, which are opened from time to time to the nitrogen from the area of the recirculation line and the area of the anode space to blow off accordingly. According to the DE 101 15 336 A1 For example, the "disposal" of this exhaust gas from the region of the anode loop can be effected in different regions, which typically each have a catalytic surface or are in connection with another component which has such a catalytic surface. This structure is common because, together with the nitrogen, there will always be a small amount of hydrogen in the vented gas, which can be rendered harmless in this way. In order to be able to dissipate the product water of the fuel cell arising in the region of the anode exhaust gas, is in the DE 101 15 336 A1 Furthermore, a water separator described in the recirculation line.

From the international application WO 2008/052578 A1 Also known is a fuel cell system having an anode loop, referred to herein as a fuel loop. The special feature of this design is that the functionality of the water separator with a drain valve to drain the water (drain) and the functionality of the blow-off valve for blowing off the nitrogen-containing gas (purge) are combined. The structure provides that a water separator is provided with a valve device. Whenever a correspondingly large amount of water has accumulated, it is drained from the water separator via the valve device. In addition, after the water is drained, gas exits the anode loop via the valve means of the water separator before it is closed again. The functionality, which was distributed in the above-mentioned writing on two separate components, is thereby integrated into a single component. The structure is still relatively complex and vulnerable, since it requires a large number of sensors for controlling the common valve device. In particular, the level sensors of a water separator described here are in practice very susceptible to dirt and therefore often cause disturbances which complicate the use of the method described in the WO document.

From the further general state of the art is also the DE 103 11 785 A1 known. Therein a connection of the cathode region to the anode region of a fuel cell is described, in particular a fuel cell, which is operated with a hydrogen-containing gas from a gas generating device. Such hydrogen usually has some contamination with carbon monoxide, which damages the catalyst in the region of the anode space. Therefore, if necessary, air is introduced into the hydrogen via the compound, which oxidizes this carbon monoxide to carbon dioxide and thus minimizes the amount of carbon monoxide harmful to the catalyst. The control takes place via a corresponding pressure difference between the region of the anode and the region of the cathode, so that at lower pressure in the region of the anode air flows through the opening in the region of the anode (Airbleed). On the other hand, this structure can also be used to allow gas to flow from the region of the anode into the region of the cathode, namely whenever the pressure conditions are reversed (purge). This is also in the structure according to the DE 103 11 785 A1 used, for example, to blow off the resulting carbon dioxide, or in the case of an anode loop, the accumulating nitrogen together with the carbon dioxide in the region of the cathode.

For further general state of the art is also still the WO 2008/052577 A1 known. In this, a structure is described in which from the area of the anode recirculation, a gas stream is introduced into the region of the cathode input. In this case, the supply can take place at different locations and / or via different types of treatment devices.

It is now the object of the present invention to provide a method for operating a fuel cell system according to the preamble of claim 1, in which the discharge of water and gas from the area of the recirculation line can be realized safely and reliably with minimal effort.

According to the invention this object is achieved by the features mentioned in the characterizing part of claim 1. The dependent claims describe advantageous embodiments and developments of the invention.

The method according to the invention ensures that the valve device can only ever be opened when predetermined operating conditions of the fuel cell system are present. The valve device thus only assumes its open state when the fuel cell system is in operation and no pressure difference or a pressure drop that falls in the direction of the anode side is given across the valve device. This reliably and reliably prevents the passage of oxygen into the region of the recirculation line and thus ultimately into the anode region, which would then lead to corresponding reactions with the fuel, typically hydrogen. Such a reaction would possibly adversely affect the life of the fuel cell. In addition, the valve device only changes to its open state if, in addition to the conditions already described, a mass flow of the oxidizing agent to the cathode region is present, which is above a predetermined limit. The limit value is to be set in such a way that the entire fuel remaining in the discharged gas, typically hydrogen, can react with the oxygen excessively stoichiometrically or at least stoichiometrically, so that it is ensured that no fuel passes through the cathode space with the exhaust gas from the cathode space to the surroundings arrives. Only when all three conditions are met will the valve device be allowed to change to the open state. This allows safe and reliable avoidance of unwanted emissions and potentially damaging gas flows to the fuel cell.

In a very favorable and advantageous embodiment of the structure according to the invention, it is so that the valve device is kept open in the open state.

Whenever the above three conditions are present, the valve device is thus kept in the open state. This means that accumulating water can be removed via the valve device from the region of the recirculation line to the anode region. In addition, once this water has been removed, a small amount of gas will be removed with it until new water has accumulated. This leads to a continuous or quasi-continuous outflow of gases from the area of the recirculation line. This inert gases are safely and reliably discharged, so that the concentration of the fuel does not fall below a meaningful for the operation of the fuel cell value.

The permanently open valve device has the decisive advantage that it ensures a continuous drain and purge without the need for their control sensors, such as a fuel concentration sensor in the recirculation line and / or very vulnerable water level sensors in the range of a water separator or the like , The method according to the invention thus makes possible a very simple and thus cost-effective and reliable fuel cell system.

In a particularly favorable and advantageous alternative embodiment of the method according to the invention, on the other hand, it is provided that the valve device is opened in clocked fashion in the opened state.

This structure, in which are also checked by the three conditions mentioned above, before the valve device changes to the open state, is now designed so that whenever the open state is allowed, the valve device is opened in clocked and thus closed again , This clocked operation of the valve device allows the use of a simple and inexpensive valve device, which knows only an open and a closed state. By appropriate timing can still volume or mass flow of the media flowing through the valve device set by these flow for a predetermined period and then again can not flow for a predetermined period. This structure then makes it possible to control or regulate the drain and the purge via a further dependency, for example by modulating a pulse width of the clocking as a function of the current load state of the fuel cell system.

Regardless of how the valve device is operated in the open state, the amount of water and gas which is discharged via the valve device can be controlled in an advantageous development of the method according to the invention on the basis of the pressure in the anode region.

By appropriate control of the pressure in the anode region or the differential pressure between the anode region and the cathode region, the mass flow of the discharged media can thus be influenced correspondingly by controlling the pressures.

In a very favorable and advantageous alternative to such a control, it may also be provided that, for example, the concentration of the fuel contained in the gas in the input region of the cathode region is regulated by means of the pressure in the anode region.

This can be done via a comparatively simple sensor a very detailed control be realized so that very constant operating conditions can be adjusted via a tracking of the anode pressure or the differential pressure between the cathode and anode.

In a further very advantageous embodiment of the method according to the invention, it can also be provided that a flow factor of the valve device in the open state is predetermined based on the size of the fuel cell system.

By a specific design of the valve device with regard to its flow factor or flow coefficient (kv value) can be realized suitable flow to the respective fuel cell system, so that accumulating water and accumulating inert gas (quasi) can flow off continuously. By choosing the appropriate kv value appropriate for the system and the volume of reactants reacted there, a loss of fuel can be limited to a tolerable minimum.

A particularly suitable use of the method according to the invention provides that the method is used for operating the fuel cell system in a means of transport on land, in the water or in the air. In particular, in such means of transport, such as vehicles, ships, aircraft or the like, it is important to realize a simple, compact and lightweight construction of the fuel cell system and safe and reliable operation, since additional weight always additional, generally difficult to build space needed, and because additional weight always requires additional energy to move. In addition, with a correspondingly high number of items, as can be considered, for example, for motor vehicles, a decisive advantage can be seen in the fact that the method according to the invention requires only minimal effort with regard to the control. In particular, a very safe and reliable operation is possible because no sensor technology is necessary, which under extreme conditions, such as shocks, vibrations, temperature fluctuations, as they occur very often in such means of transport could possibly fail.

Further advantageous embodiments of the invention will become apparent from the remaining dependent claims and will be apparent from the embodiment, which is explained below with reference to the reference to the figures.

Showing:

1 a schematic representation of a fuel cell system in a first embodiment for use with the inventive method;

2 a schematic representation of a fuel cell system in a second embodiment for use with the method according to the invention; and

3 a logic diagram for the course of the method according to the invention.

In the illustration according to 1 is a fuel cell system 1 in a relevant to the present invention section highly schematized indicated. Most important component of the fuel cell system 1 is a fuel cell 2 which is typically designed as a stack of individual fuel cells, as a so-called fuel cell stack. The fuel cell 2 has an anode area 3 and a cathode region 4 on, which should be separated from each other in the embodiments shown here by a proton-conducting membrane. At the fuel cell 2 So it is a so-called PEM fuel cell stack. The fuel cell 2 in the form of a PEM fuel cell stack is now supplied with fuel, here for example hydrogen, and an oxidizing agent, in particular air here. In the exemplary embodiments, the invention is based on such a PEM fuel cell operated with air and hydrogen 2 described, without the inventive method on the operation of such a fuel cell 2 to be restricted with the mentioned material flows.

The anode area 3 the fuel cell 2 is now using hydrogen as fuel from a storage device 5 provided. There is a valve 6 provided, which the influx of hydrogen to the anode area 3 controls, and which generally also in the memory device 5 stored under a very high pressure hydrogen to one for the anode area 3 appropriate pressure decreases. In the fuel cell 2 This hydrogen then reacts with a mass flow of oxidizing agent, which via a conveyor 7 the cathode area 4 the fuel cell 2 is supplied. An exhaust gas flow of the oxidant, in this case an exhaust gas flow with respect to the oxygen content depleted air, is then via an exhaust pipe 8th to the environment of the fuel cell system 1 issued. The exhaust gas from the cathode area 4 it also performs a part of the fuel cell 2 resulting product water with him. It is therefore a typically moist exhaust gas stream. To now dry out the PEM membranes of the fuel cell 2 it can avoid it optionally be provided that this humid exhaust gas flow in a gas-gas humidifier 9 , which is optionally indicated here, that to the cathode region 4 flowing mass flow of air humidifies. Such a humidifier 9 may consist of membranes, which are continuous for vaporous water, but not for the gas stream itself. Flows on one side of the membrane now the hot dry mass flow of air to the cathode area 4 and on the other side of the membrane, the moist exhaust gas stream, the moisture is transferred from the exhaust stream to the mass flow of the oxidant and drying of the membranes can be prevented.

On the side of the anode area 3 It is now so that the hydrogen from the storage device 5 in the anode area 3 not fully implemented. Typically, exhaust gas remains, which in addition to residual hydrogen in the anode area 3 resulting product water and through the membranes diffused through inert gas, in particular nitrogen. This exhaust gas flow is to use the residual hydrogen remaining in it via a recirculation line 10 and a recirculation conveyor 11 recirculates and passes out of the storage device together with fresh hydrogen 5 back to the anode area 3 , In the area of the recirculation line 10 accumulating water can thereby via a water separator 12 be separated and collected.

In the embodiment of the fuel cell system shown here 1 It is now so that this water separator 12 over a connecting line 13 and a valve device located therein 14 is connected to the influx of air mass flow accordingly. Water, which is in the water separator 12 collects when the valve device is open 14 So over the connection line 13 introduced into the region of the air mass flow and passes together with this on the conveyor 7 in the cathode area 4 , Once in the water separator 12 no liquid water is present, is also a certain amount of gas from the area of the recirculation line 10 , and here is as a gas predominantly nitrogen with a certain proportion of residual hydrogen, in the range of the air mass flow and thus in the cathode area 4 reach. Residual hydrogen is then added to the electrocatalysts of the cathode region 4 react with oxygen from the air mass flow, so that no emissions of hydrogen through the exhaust pipe 8th from the fuel cell system 1 to occur out.

In the presentation of the 2 is another embodiment to recognize, in which the only difference from the embodiment of the fuel cell system 1 according to 1 it consists in that the connecting line 13 between the air conveyor 7 and the cathode area 4 flows into the air mass flow, and not in front of the conveyor 7 , It also focused on the appearance of the optional humidifier 9 waived.

In addition to these two illustrated embodiments, it would of course also conceivable to realize a structure in which the connecting line 13 between two air conveyors or between the stages of a two-stage air conveyor opens and previously possibly further components, such as a housing of the fuel cell 2 , flows through.

The core of the method according to the invention is now in the control of the valve device 14 , This is done according to the in 3 displayed logic diagram driven. First, it is checked if the fuel cell system 1 (BZS) is in operation. Only if this check yields a true statement does a true value arrive at a first AND operation 15 , In addition, the mass flow dm / dt of the air as an oxidant is constantly monitored. This can be done for example by means of an air mass sensor or very simply based on the speed of the air conveyor 7 and possibly a map. The thus-detected air mass flow dm / dt is then compared with a predetermined value of an air mass flow dm / dt. As soon as the current air mass flow is above this predetermined value, a true value is created, which continues to a second AND gate 16 arrives.

In addition, a pressure drop across the valve device 14 or the pressure difference between the pressure p _A in the anode region 3 and the pressure p _K in the cathode region 4 monitored accordingly. Only if there is a pressure difference which is 0 or greater does this monitoring give rise to a true value. The two values from the monitoring of the mass flow dm / dt and the pressure p _K arrive after the AND operation in the AND gate 16 also to the AND gate 15 and be with the test, whether the fuel cell system 1 is in operation, also linked to an AND operation. As soon as all three values give a true value, permission is given to the valve device 14 to change to an open state.

This construction ensures that the valve device 14 only opened when the fuel cell system 1 is in operation. This is important, for example, an open valve device 14 then to prevent when the fuel cell system is not in operation and via the valve means oxygen in the region of the recirculation line 10 and thus into the anode area 3 penetration could. Upon restart of the fuel cell system, this would result in a mixture of fuel and oxygen in the anode region 3 lead, which in Abreagieren the life of the fuel cell 2 adversely affected and in extreme cases could lead to the formation of explosive mixtures of hydrogen and oxygen.

In addition, the comparison of the mass flows dm / dt and dm ₀ / dt ensures that a sufficient air mass flow to the cathode region 4 flows before the valve device 14 is opened. This has the advantage that always a sufficient amount of air and thus a sufficient amount of oxygen in the cathode area 4 present to over with the valve device 14 Abreacted gas and it contained residual hydrogen to react. The value of the mass flow dm ₀ / dt is therefore specified so that always in all operating states an at least stoichiometric - in particular superstoichiometric - amount of oxygen in relation to the registered hydrogen is present. The value of the air mass flow dm ₀ / dt given in this way is typically of the order of magnitude of approximately 30-60% of the air mass flow during idling operation of the fuel cell system 1 selected. In a fuel cell system with an electrical rating of 80 kW and an air mass flow of approximately 17 kg / h in idling mode, this would result in a value dm ₀ / dt of less than 10 kg / h.

The last query regarding the pressure P again ensures that in the anode area 3 and in the cathode area 4 at least the same pressure P prevails, so that at least ensures that no oxygen or no air from the cathode area 4 conveyed air mass flow into the anode area 3 penetrates. Such an intrusion of air and in particular a mixing of this air with the hydrogen in the anode region 3 would have similar adverse consequences on the life of the fuel cell 2 and would in extreme cases lead to the formation of explosive mixtures of hydrogen and oxygen, such as the above-described penetration of air into the anode region 3 in the case of standstill.

Only when all these conditions are present and an opening of the valve device 14 is possible for a combined drain / purge, the inventive method allows an open state of the valve device 14 ,

In a particularly simple and favorable variant, it may be provided that the valve device 14 is always kept open. Then there is a continuous drain, so a continuous discharge of the accumulating water. Once in the area of the valve device 14 and the connection line 13 no water is present, there is also a discharge of gas from the area of the recirculation line 10 , the purge. This structure has the advantage that it can do without further sensors. The outflowing rate of the gas from the region of the recirculation line can be determined by a suitable choice of the flow factor, the so-called kv value, depending on the power and size of the fuel cell system. This allows an optimal drain and purge to be realized without additional sensors, such as level sensors in the area of the water separator 12 , would be necessary. Such functionality is also in the earlier application with the file number DE 10 2009 014 592.3 the applicant described.

As in this embodiment, the flow factor of the valve device 14 as a value once based on the size of the fuel cell system 1 In its planning and dimensioning is given, this is in principle no variation of the purge discharged amount of gas possible. Nevertheless, in order to be able to influence the amount differently during operation, it may be provided that the one in the anode area 3 for example via the valve device 6 adjusted pressure is varied accordingly. This results in a variable pressure difference between the anode region 3 facing side of the valve device 14 and the cathode area 4 facing side of the valve device 14 , About this pressure difference or the pressure in the anode region 3 can then control the amount of purged gas accordingly.

In order to improve the functionality even further, it can also be provided that in the input area of the cathode area 4 a sensor for the hydrogen is attached. Then it is conceivable, via a corresponding change in the pressure in the anode region 3 or the pressure difference between the anode region 3 and cathode area 4 the flow through the valve device 14 to regulate. For example, it could be a constant concentration of hydrogen in the entrance area of the cathode area 4 be managed. Then it would always be ensured that, due to the constant concentration, a quasi-continuous purge takes place, which otherwise leaves the regulation and control of the system unaffected.

In an alternative or supplementary variant used, the open state of the valve device 14 by a timed operation of the valve device 14 be designed. The valve device 14 will only switch to this clocked operation, if it has been signaled via the logic explained above, that an open Condition of the valve device 14 is allowed. The valve device 14 However, it is then not fully opened and kept open as long as the conditions are present, but is operated in a clocked manner while the conditions are present. This makes it possible, without a proportional valve should be used by the valve device 14 influence flowing volume flow or mass flow. The timing can be specified by a controller with modulatable pulse width. About this modulated pulse width so different times of open and closed states of the valve device 14 realized in quick succession to each other. The modulation of the pulse width can, for example, in dependence on the performance of the fuel cell system or as a function of the fuel cell 2 retrieved and measured anyway electrical power done. Since the power is approximately associated with the consumption of hydrogen and oxygen, the power is also about the amount of accumulating water and / or accumulating inert gases in the anode region 3 predictable. Will now the mass flow through the valve device 14 Controlled by the power, so it can be ensured here without further sensor or the like that no more hydrogen is lost as necessary in the purge and on the other hand, the accumulated water is safely and reliably dissipated. Also this clocked operation of the valve device 14 is, as already mentioned, the in 3 shown upstream or higher, so that even in the pulsed operation no operating conditions can occur which the performance and the life of the fuel cell 2 would adversely affect.

With the method according to the invention, the operation of a fuel cell system 1 be realized so that this can be minimized in terms of the sensor and maximized in terms of reliability. Such a system is now particularly well suited to be used in means of transport, for example in motor vehicles, in order to generate electrical drive energy.

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

• DE 10115336 A1 [0002, 0002, 0002]
• WO 2008/052578 A1 [0003]
• DE 10311785 A1 [0004, 0004]
• WO 2008/052577 A1 [0005]
• DE 102009014592 [0038]

Claims (14)

A method for operating a fuel cell system having at least one fuel cell, wherein an anode region of the fuel cell, a fuel and a cathode region of the fuel cell is supplied to an oxidizing agent, wherein anode exhaust gas is recirculated from an anode outlet via a recirculation line to an anode inlet, and wherein water and / or gas via a Valve device is discharged from the region of the recirculation line in the cathode region, characterized in that the valve device ( 14 ) is operated only in an open state, when the fuel cell system ( 1 ) is in operation and the mass flow (dm / dt) of the oxidant exceeds a predetermined value (dm ₀ / dt), and when the pressure (p _A ) in the anode-side region of the valve device ( 14 ) greater than or equal to the pressure (p _K ) in the cathode-side region of the valve device ( 14 ). Method according to claim 1, characterized in that the valve device ( 14 ) is kept constantly open in the open state. Method according to claim 1, characterized in that the valve device ( 14 ) is opened clocked in the open state. A method according to claim 3, characterized in that the timing is predetermined by a controller with modulatable pulse width. A method according to claim 4, characterized in that in a modulation of the pulse width of the current load state of the fuel cell system ( 1 ). Method according to one of claims 1 to 5, characterized in that the amount of water and gas passing through the valve device ( 14 ) is discharged, based on the pressure (p _A ) in the anode region ( 3 ) is controlled. Method according to one of claims 1 to 5, characterized in that the amount of water and gas passing through the valve device ( 14 ) is discharged, based on the pressure (p _A ) in the anode region ( 3 ) to a constant concentration of the fuel contained in the gas in the input region of the cathode region ( 4 ) is regulated. Method according to one of claims 1 to 7, characterized in that the predetermined value of the mass flow (dm ₀ / dt) of the oxidizing agent at 30-60% of the idle mode of the fuel cell system ( 1 ) present mass flow (dm / dt) of the oxidizing agent is selected. Method according to one of claims 1 to 8, characterized in that in the region of the recirculation line ( 10 ) liquid water in a water separator ( 12 ) is collected. Method according to one of claims 1 to 9, characterized in that a flow factor (kv value) of the valve device ( 14 ) in the open state on the basis of the size of the fuel cell system ( 1 ) is given. Method according to one of claims 1 to 10, characterized in that the discharged water and gas is supplied to the cathode region in such a way that it with the mass flow (dm / dt) of the oxidizing agent according to at least a first conveyor ( 7 ) is mixed for the mass flow (dm / dt) of the oxidizing agent. Method according to one of claims 1 to 11, characterized in that the discharged water and gas to the cathode region 4 is fed in such a way that it is mixed with the mass flow (dm / dt) of the oxidizing agent before at least one first conveying device ( 7 ) is mixed for the mass flow (dm / dt) of the oxidizing agent. Use of a method according to one of claims 1 to 12 in a fuel cell system ( 1 ) in a means of transport on land, in the water or in the air. Use according to claim 13, characterized in that via the fuel cell system ( 1 ) electrical energy is generated for the drive.

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