DE102011118688A1 - Flow-driven device - Google Patents

Abstract

The invention relates to a flow-driven device with a metering device (16) for a propellant gas stream, wherein the metering device (16) has a plurality of valves (15). The invention is characterized in that at least three valves (15) are arranged in parallel in the influx of propellant gas stream (H2), wherein the valves (15) are designed as untacted switching valves.

Description

The invention relates to a flow-driven device according to the closer defined in the preamble of claim 1. The invention also relates to a fuel cell system with such a flow-driven device.

Flow-driven devices are well known in the art. For the purposes of the present invention, these are preferably gas jet pumps or turbines, which are each driven by a metered flow of propellant gas.

For the example of the gas jet pump as a flow-driven device is intended to the German Offenlegungsschrift DE 10 2007 057 451 A1 be pointed out. This shows a fuel cell system with a metering unit, which has two parallel valves. The metering unit can preferably be designed as a jet pump. Such a jet pump or gas jet pump uses a propellant gas stream which is injected through at least one nozzle into a mixing zone and into a so-called catching nozzle in order to suck in a second gas stream by pulse exchange and / or negative pressure and to convey the two gas streams in a mixed manner. This is done on the example of the prior art shown in the example of the fuel cell so that in this way an exhaust gas stream is recirculated and returned to the fuel cell. Since the propellant gas flow in this case is at the same time the fuel flow metered to the fuel cell, the metering of the propellant gas flow is crucial in order to achieve the operation of the fuel cell in the desired manner and to provide the requested power. The metering is achieved via the valves specified in the cited prior art. These valves are typically designed as proportional valves or particularly preferably as timing valves, which are driven, for example, as solenoid valves with a pulse-width-modulated timing to produce a pulsating gas flow, which corresponds to the desired gas flow to be metered in the time average. Such timing valves have the disadvantage that they are relatively loud, since the valve body is typically switched at high frequency between an open position and a closed position back and forth.

A comparable structure, in which a conveyor for the exhaust gas is driven by a turbine, is known from DE 10 2006 003 799 A1 known. Again, a propellant gas stream for the turbine is the metered fuel stream to the fuel cell, so its dosage must be regulated accordingly. This is also done via a proportional valve or via clock valves.

The advantage with this technology is that the drive uses the energy from the fuel typically stored in a pressurized gas tank. It is therefore in each case a flow-driven device in the sense described above.

A crucial point for this flow-driven device is now to convert the pressure energy into kinetic energy with the highest possible efficiency. In order to achieve this, the highest possible flow velocity in the propellant gas flow should be achieved. In particular when constructing a gas jet pump, the flow velocity in the nozzle or its nozzle openings should reach the speed of sound. This is easily possible by appropriate flow cross sections in principle. The use of tact or proportional valves for hydrogen metering, however, is a problem here because it either "chops" the flow or, if necessary, doses it down to a low flow value, so that in this case the required speeds for the best possible use of energy are no longer met ,

The object of the present invention is to provide a flow-driven device which allows a high conversion accuracy of the propellant gas flow a good implementation of the introduced energy.

According to the invention this object is achieved by the features in the characterizing part of claim 1 and the features in the characterizing part of the independent claim 2. Advantageous embodiments of the solution will become apparent from the dependent claims. Further, a fuel cell system is specified, which also solves the problem.

The propellant gas stream for the flow-driven device is metered via at least three valves in the influx of the propellant gas stream, which are arranged there in parallel and are designed as untacted switching valves. The advantage of this design is that the non-clocked switching valves, which only know the valve position "open" or "closed", are switched only when needed. This means that depending on the required propellant gas flow, more or less of the valves arranged in parallel are open. These are therefore not clocked, so that the problem of noise emissions, as it is known from dosing with clock valves ago, can not arise here. In addition, the decisive advantage that no pulsating propellant gas flow is generated, but a continuously flowing propellant gas flow. This can then by selecting a suitable nozzle or nozzle openings the required very high Flow rate of ideally reach approximately the speed of sound, so as to realize the best possible energy input into the gas stream to be pumped.

The flow-driven device according to the first embodiment of the invention may be designed as a gas jet pump. The second variant of the invention provides that the flow-driven device is designed as a turbine. The propellant gas stream is particularly suitable for such turbines, which can be driven by a gas stream, for example a Pelton turbine or a Tesla turbine. However, other turbine types, for example a conventional radial turbine, are also conceivable.

In a particularly favorable and advantageous development of the flow-driven device, all valves have the same cross-section through which they can flow. This structure is particularly simple and efficient, since it manages with several parallel identical valves. However, it requires a correspondingly large number of valves, especially if a comparatively fine regulation of the metering is to take place, since the flow-through cross section of each individual valve then counts as a switching step for the increase of the metering volume flow.

In a particularly favorable and advantageous development of the flow-driven device according to the invention, it is therefore provided that the number of valves is reduced to a minimum by a skillful choice of valve cross-sections. For doing so, the cross sections of the valves double from valve to valve.

If, for example, a number of only five valves are used in this connection, then dosing differential amounts of approx. 3.2% based on the total flow. This means that the required dosage can be set in 3.2% increments.

Now, in particular, when used in gas jet pumps as a flow-driven device, metering in the partial load range and in the area of small loads is particularly important. Therefore, it is crucial to have the smallest possible differential dosing here in order to realize a quasi-continuous dosing. For larger volume flows, this is not so important. According to a particularly favorable and particularly advantageous development of the flow-driven device, it is therefore provided that the flow-through cross-sections of the valves with a small flow cross-section be doubled, wherein the flow-through cross-sections of the valves with increasing cross-section by a larger cross-sectional with the increasing factor of more as two enlarge. This particularly favorable embodiment of the flow-driven device according to the invention thus uses the doubling in the area of the valves for the small dosing quantities, while with increasing diameter of the valves the factor of the increasing flow-through cross section increases by more than two. As a result, comparatively fine metering steps are possible in the lower load range without the number of valves required thereby increasing very sharply. The differential metering amounts are thus provided at lower loads with a narrower grading than at higher loads. However, this is typically not critical. With this construction, with a total number of still less than, for example, eight to ten valves, a very exact and fine dosage, a "quasi-continuous" dosage, can be achieved in the relevant areas.

According to a particularly favorable and advantageous development of the flow-driven device, it is further provided that each valve is connected to its own nozzle opening for the propellant gas stream. This is conceivable and possible both in a gas jet pump and in nozzles through which a turbine with a propellant gas stream is applied. In the gas jet pump, the nozzle openings can be realized, for example, as a field of nozzle openings in a nozzle body. In a construction as a turbine, the nozzles can be arranged, for example, uniformly distributed around the circumference, each with a nozzle opening and depending on the flow-through valves, only a few of the nozzles would then be correspondingly supplied. The advantage lies in the fact that the nozzle openings can be designed to match the respective valve diameter so that the required high velocity of the propellant gas stream, in this case in particular the speed of sound of the propellant gas stream, is achieved in all load situations. As a result, the efficiency of the gas jet pump or the drive of the turbine is improved.

Furthermore, a fuel cell system with such a flow-driven device solves the problem. It is provided in particular that the fuel cell system has at least one fuel cell, wherein at least one exhaust gas from the fuel cell is returned from an output of the fuel cell via a recirculation line to an input of the fuel cell. The fuel cell has as either an anode recirculation and / or a cathode recirculation. In the recirculation line at least one recirculation conveyor is arranged to compensate for the pressure losses. The recirculation conveyor can by the flow-driven device according to the invention according to one of the embodiments described above at least partially driven. This preferred structure of a fuel cell system in which the flow-driven device at least partially drives the recirculation conveyor allows very efficient recirculation of exhaust gas to provide the advantages such as recirculation of exhaust gas in fuel cells, such as improving humidification, improving the utilization of exhaust gas To reach available active surface in the anode compartment or the like.

In a particularly favorable development thereof, it is further provided that the exhaust gas is exhaust gas from an anode chamber of the fuel cell, fresh fuel supplied to the fuel cell forming the propellant gas flow for the flow-driven device. In particular, this use in an anode recirculation is of decisive advantage, since typically as a fresh fuel fuel or hydrogen is available under high pressure anyway. This can be used without additional energy consumption within the fuel cell system as a propellant gas flow, so that the fuel cell system itself is very energy efficient.

Further advantageous embodiments of the flow-driven device according to the invention and the fuel cell system according to the invention will become apparent from the remaining dependent claims and will become apparent from the embodiment, which will be described below with reference to the figures.

Showing:

1 an exemplary fuel cell system in a vehicle;

2 a schematic diagram of a gas jet pump as a flow-driven device according to the invention;

3 a diagram of the metered hydrogen flow as a function of the load-dependent setpoint at the in 2 illustrated gas jet pump; and

4 an exemplary embodiment of the flow-driven device according to the invention as a turbine.

In the presentation of the 1 is purely exemplary and very highly schematized a fuel cell system 1 in an indicated vehicle 2 to recognize. The fuel cell system 1 essentially comprises a fuel cell 3 which in turn has an anode compartment 4 and a cathode compartment 5 shows. The fuel cell 3 should be designed as a stack of PEM fuel cells. The cathode compartment 5 the fuel cell 3 is via an air conveyor 6 supplied with air as an oxygen supplier. The exhaust air from the cathode compartment 5 arrives in the embodiment shown here to the environment. Here, in principle, a post-processing, for example, an afterburner, a turbine or the like could be arranged. However, this is not of interest for the present invention, so that a representation has been omitted.

The anode compartment 4 the fuel cell 3 is supplied with hydrogen H ₂ , which consists of a compressed gas storage 7 comes. He comes through a shut-off valve 8th and a recirculation conveyor later explained in more detail 9 in the anode compartment 4 , From the area of the anode compartment 4 exhaust gas A comes out of the anode compartment 4 via a recirculation line 10 back into the area of the recirculation conveyor 9 , and is sucked by this and back into the anode compartment 4 promoted. This principle of an anode recirculation is known from the general state of the art. It serves to the anode space 4 to supply an excess of hydrogen H ₂ in order to make the best possible use of its active area. The in the exhaust from the anode compartment 4 Residual hydrogen remaining is then together with inert gases passing through the membranes from the cathode compartment 5 in the anode compartment 4 are diffused and a small portion of the product water, which in the anode compartment 4 arises, via the recirculation line 10 fed back and the anode room 4 fed again mixed with the fresh hydrogen H ₂ . Since in such an anode recirculation over time, inert gases and water accumulate and thereby the hydrogen concentration decreases, it is necessary, for example from time to time, to discharge water and gas from the anode recirculation. This is in the presentation of the 1 a drain valve 11 indicated in principle.

Now to the pressure losses in the region of the anode compartment 4 and in the area of the recirculation line 10 It is necessary to be able to compensate for the recirculation conveyor 9 for the recirculated exhaust gas from the anode compartment 4 provided. As a recirculation conveyor 9 can according to the embodiment of the 2 a gas jet pump 12 be. The gas jet pump 12 is a possible example of a flow-driven device according to the invention.

The gas jet pump 12 is in the representation of 2 again shown in detail cut. It consists essentially of a nozzle 13 , which as primary gas stream of hydrogen H ₂ via a line 14 is supplied. The gas flow is then split over several pipe elements. In each of the parallel line elements is a switching valve 15 , The switching valves 15 , in the illustrated embodiment, there are four such switching valves, which below with 15.1 . 15.2 . 15.3 and 15.4 be designated. The switching valves 15 lie parallel to each other in the parallel conduit elements. Now it is so that the switching valves 15 are designed as non-clocked switching valves. As switching valves they can only have two positions, namely an open position and a closed position. The entirety of the individual switching valves 15 in the parallel line elements thereby constitutes a metering device 16 for the gas jet pump 12 This metering device now works in such a way that, depending on the desired volume flow, one or more of the switching valves 15 be opened. This turns on through the switching valves 15 flowing volume flow in the desired size. Now it is so that the switching valves 15 in principle could be formed with the same diameter which can be flowed through. However, this leads to the fact that the metering proceeds in comparatively large steps, for example in the case of four similar switching valves 15 in four individual dosing steps of 25% each. This makes the dosage very inaccurate.

By a clever choice of the flow-through diameter of the switching valves 15 However, it is possible, a much finer dosage with a still very small number of valves 15 to realize. The structure then typically functions such that the flow-through cross section of the second switching valve 15.2 twice as large as that of the first switching valve 15.1 , The flow-through cross section of the third switching valve 15.3 is then again twice as large as the flow-through cross section of the second switching valve 15.2 , Ultimately, the flow-through cross section of the switching valve is also 15.4 twice as large as that of the third switching valve 15.3 , This makes it possible to achieve a very fine grading, in which the so-called differential metering amount D, ie the step size between the individual possible metered quantities, is about 6.66% of the maximum total metering. The Dosiermengendifferenz D results according to the formula D = 1001 (2 ^N - 1), where N is the number of valves used 15 is. With a number of four valves, the difference metering amount, as already mentioned, results in D = 6.66%, for five switching valves D = 3.2% and for six switching valves D = 1.58%. This shows that with very few valves already a comparatively exact dosage is possible.

In the presentation of the 3 this connection is for the example of in 2 shown gas jet pump 12 with its metering device 16 shown. The four switching valves 15 allow differential doses D of about 6.66%. In the presentation of the 3 this stepped functionality of the metered mass flow of hydrogen applied to the y-axis is plotted against the load-dependent setpoint value. The switching valves 15 are switched from the bottom starting in individual stages so that the first stage, only the first switching valve 15.1 is open. In the second stage, the second switching valve 15.2 opened, in the third stage, the first and the second switching valve 15.1 and 15.2 together. In the fourth stage then the third switching valve 15.3 opened alone, in the fifth stage, the third switching valve 15.3 together with the first switching valve 15.1 , in the sixth stage, the third switching valve 15.3 together with the second switching valve 15.2 , and so on. This results in a small number of only four switching valves nevertheless a comparatively exact way to meter the desired hydrogen mass flow.

Now, if a load point is set, which is between two differential doses D, it will inevitably lead to small fluctuations in the anode pressure, because because then typically between the two valve circuits "back and forth" is switched. In order to avoid this, it is possible to use a hysteresis loop which is customary in control technology in order to counteract this problem. This hysteresis loop is designated by the reference H and in the illustration of 3 drawn by way of example.

About the switching valves 15 is the volume flow of the primary gas flow through each of the parallel line elements separately adjustable. The line elements open in the region of the nozzle 13 each in individual nozzle openings 17 , which individually addressed below as nozzle openings 17.1 . 17.2 . 17.3 and 17.4 be designated. From these nozzle openings 17 in each case a part of the primary gas stream flows out, provided that the respective associated switching valve 15 is open. The outflowing primary gas stream then flows into a suction region of the gas jet pump designated I. 12 , which laterally from the recirculation line 10 an exhaust gas A from the anode compartment 4 the fuel cell 3 is supplied. The gases then mix in a mixing zone designated II and flow back to the anode compartment 4 ,

Now it is so that the use of multiple orifices 17 offers decisive advantages in the maximum utilization of the pressure energy to promote the exhaust gas A. The nozzle openings 17 can each on the flow-through cross section of their associated switching valves 15 be adjusted. For example, the nozzle opening 17.1 formed with the smallest diameter, as well as the switching valve 15.1 , By this adaptation of the nozzle openings 17 to the Diameter of the switching valves 15 can achieve that the nozzle openings 17 always be flowed through ideally. This means that they are flowed through at a very high flow rate, preferably sound velocity. As a result, the maximum energy exchange between the propellant gas stream H ₂ and the exhaust gas flow A is ensured. The potential energy used for the recirculation of the exhaust gas A from the pressurized hydrogen can thus be maximally converted into kinetic energy for the promotion of the exhaust gas flow A. At the same time, the metering is via the uncontacted switching valves 15 very quiet and can be with comparatively small number of valves 15 realize with a sufficiently small Differenzdosiermenge, as has been described above.

Another possibility for improvement lies in the fact that in fuel cell systems 1 Typically, a relatively accurate dosage of hydrogen is crucial, especially at low and medium loads. For larger loads, this plays a minor role. To still with very small number of switching valves 15 To be able to realize an exact dosage as needed, it can now be provided that the switching valves 15.1 . 15.2 with the smaller diameter corresponding to the above type with the factor 2 are equipped between their permeable diameters. The larger the diameter of the switching valves, so for example, the jump from the diameter of the switching valve 15.2 on the diameter of the switching valve 15.3 , the factor slightly larger than 2 can be selected here. The factor can then be between the switching valve 15.3 and 15.4 enlarge again. This allows, for example, when using six switching valves 15 the structure so that the first three switching valves each with the factor 2, the subsequent switching valve with a factor of, for example, 2.2, the following are formed by a factor of 2.6, and so on. In the range of small and lower loads then a more exact dosage than in the described construction is possible, while the dosing difference amount D to "up" out to be larger. As a result, a very exact dosage can be realized in the range of small and medium loads, in the area of the upper loads, where this is no longer so crucial, the differential doses D are correspondingly larger. The design allows for optimum dosing accuracy in the area where it is needed and a minimum number of required switching valves 15 ,

This advantageous construction with the metering device 16 can not be just for a gas jet pump 12 realize as a flow-driven device. It is rather conceivable to use these for other flow-driven devices, such as a turbine 18 , In the presentation of the 4 is such a turbine 18 illustrated by the example of a Pelton turbine. The turbine 18 as Pelton turbine is symbolized in the plan view only as a circular Peltonrad. The typical and known blades 19 on the outer diameter were merely indicated in principle to simplify the presentation. The construction of the turbine 18 has analogous to the representation in 2 via a metering device 16 which in turn has four individual switching valves 15 having. Again, the individual line elements lead to individual over the circumference of the Pelton turbine 18 distributed in principle known per se arranged principle indicated nozzles 20 , which each have a nozzle opening 17 exhibit. The structure can be so with respect to the dosage of the propellant gas stream analogous to the gas jet pump described in detail above 12 realize. About the Pelton turbine 18 For example, a recirculation fan as Rezirkulationsfördereinrichtung 9 be driven, as is known from the above DE 10 2006 003 799 A1 known per se.

As an alternative to the Pelton turbine, of course, the use of a Tesla turbine or radial turbine would be conceivable and possible.

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 102007057451 A1 [0003]
• DE 102006003799 A1 [0004, 0034]

Claims (10)

Flow-driven device with a metering device ( 16 ) for a propellant gas stream, wherein the metering device ( 16 ) several valves ( 15 ), characterized in that at least three valves ( 15 ) are arranged in parallel in the influx of propellant gas stream (H ₂ ), the valves ( 15 ) as non-clocked switching valves ( 15 ) are formed. Flow-driven device according to claim 1, characterized by its design as a gas jet pump. Flow-driven device according to claim 1, characterized by its design as a turbine, in particular as a Pelton, Tesla or radial turbine. Flow-driven device according to claim 1, 2 or 3, characterized in that all valves ( 15 ) have the same cross-section through. Flow-driven device according to claim 1, 2 or 3, characterized in that the flow-through cross-sections of the valves ( 15 ) away from valve ( 15 ) to valve ( 15 ) each double. Flow-driven device according to claim 1, 2 or 3, characterized in that the flow-through cross-sections of the valves ( 15 ) with a small cross-section through which valve ( 15 ) to valve ( 15 ), whereby the flow-through cross-sections of the valves ( 15 ) with increasing cross-section through a larger by the flow-through cross-section factor of more than 2 of valve ( 15 ) to valve ( 15 ) enlarge. Flow-driven device according to one of claims 1 to 6, characterized in that each valve ( 15 ) with its own nozzle opening ( 17 ) is connected to the propellant gas stream (H ₂ ). Flow-driven device according to one of claims 1 to 6, characterized in that in each case several or all of the valves ( 15 ) are each connected to a nozzle opening for the propellant gas stream (H ₂ ). Fuel cell system ( 1 ) with at least one fuel cell ( 3 ), wherein at least one exhaust gas from the fuel cell ( 3 ) from an output of the fuel cell ( 3 ) via a recirculation line ( 10 ) to an input of the fuel cell ( 3 ), wherein in the recirculation line ( 10 ) at least one recirculation conveyor ( 9 ), characterized in that the flow-driven device according to one of claims 1 to 8, the recirculation conveyor ( 9 ) at least partially drives. Fuel cell system ( 1 ) according to claim 9, characterized in that the exhaust gas exhaust (A) from an anode compartment ( 4 ) of the fuel cell ( 3 ), wherein freshen the fuel cell ( 3 ) supplied fuel (H ₂ ) forms the propellant gas flow for the flow-driven device.

Images