WO2013045051A1

WO2013045051A1 - Gas jet pump for conveying a main gas stream

Info

Publication number: WO2013045051A1
Application number: PCT/EP2012/003936
Authority: WO
Inventors: Cosimo Mazzotta
Original assignee: Daimler Ag
Priority date: 2011-10-01
Filing date: 2012-09-20
Publication date: 2013-04-04
Also published as: DE102011114735A1

Abstract

The invention relates to a gas jet pump (9) for conveying a main gas stream (A) through a propellant gas stream (14), wherein in an axial direction, the propellant gas stream (14) flows into a Venturi tube (12) having a cross-sectional narrowing, to which the main gas stream (A) also flows. The invention is characterized in that the propellant gas stream (14) is configured in the form of at least two separate partial propellant gas streams (14.1, 14.2), which jointly flow into the one Venturi tube (12), wherein the volume flow of at least one of the two separate partial propellant gas streams (14.1, 14.2) can be manipulated by way of a valve unit (16). The invention further relates to a fuel cell system (1) having such a gas jet pump (9) for exhaust gas recirculation.

Description

Gas jet pump for conveying a main gas flow

The invention relates to a gas jet pump for promoting a main gas flow through a propellant gas stream according to the closer defined in the preamble of claim 1.

Moreover, the invention relates to a fuel cell system with such

Gas jet pump.

Gas jet pumps are known from the general state of the art. The most widespread design of gas jet pumps uses a propellant jet, which flows into a so-called Venturi tube, which has a cross-sectional constriction. In addition to the propellant gas stream, the main gas stream to be conveyed is supplied to the venturi, in such a way that it comes into contact with the propellant gas stream in the flow device before or at the latest in the region of the cross-sectional constriction. Due to the cross-sectional constriction and a before and after further developed cross-section, there is an increase in the flow velocity of the propellant gas stream in the region of this cross-sectional constriction due to

Continuity Act. This creates a negative pressure in the area of

Cross-sectional constriction, which sucks the main gas stream and mixed with the propellant gas flow promotes.

This structure is known from the general state of the art. It can be used in many ways. For example, gas jet pumps in fuel cell systems are used, for example, to reclaim exhaust gas from the anode region to the anode region region within the scope of so-called anode recirculation. The fresh metered fuel, typically hydrogen, then serves as a propellant gas stream to appropriately draw the anode exhaust gas. This is advantageous in terms of the energy expenditure for the recirculation of the anode exhaust gas. In addition or alternatively, can be Insert hydrogen circulation fan. However, these are comparatively energy-intensive and expensive. For example, reference is made to DE 102 51 878 C5 for such a structure. The problem of the comparatively difficult design of a gas jet pump over the entire occurring load range of

Fuel cell system is counteracted here by the additional hydrogen pump in the form of a hydrogen circulation fan. This structure is very complex and expensive because it also requires the hydrogen recirculation fan in addition to the gas jet pump.

An alternative construction is known from DE 10 2007 004 590 A1. In order to achieve an adjustment of the delivery rate of the gas jet pump, two gas jet pumps, integrated into one housing, are combined here. Each of the gas jet pumps has its typical Venturi tube and the supply of a propellant gas stream. The

Propellant gas streams are divided accordingly and switchable via valve devices. They can be switched so that either one or the other or both propellant gas streams flow into the respective Venturi tube. As a result, one or the other gas jet pump or both gas jet pumps can be operated together. The structure is relatively complex, large and heavy due to the double existing gas jet pump, which must each have a venturi and the corresponding gas connections, despite the integration into a housing.

Furthermore, DE 2006 019 077 A1 describes a structure in which a

Nozzle opening for the propulsion jet can be changed. This is mechanical

extraordinarily complex. The structure is thus very expensive and prone to failure.

The object of the present invention is now to provide a gas jet pump or a fuel cell system with such a gas jet pump, which avoids these disadvantages and offers a simple and compact design, which is sufficiently flexible in terms of the required delivery capacity.

According to the invention this object is achieved by the features in the characterizing part of claim 1. Further advantageous embodiments of the gas jet pump are specified in the dependent claims. It also redeems

Fuel cell system with the features in the characterizing part of claim 4 the Task. Advantageous developments thereof will become apparent from the dependent claims.

The gas jet pump according to the invention utilizes a common Venturi tube, to which a propellant gas stream divided into at least two separate partial propellant gas streams can be fed. At least one of the two separate Teiltreibgasströme is via a

Valve device influenced in its flow. The structure can therefore be similar to a structure with two own gas jet pumps on the division of the

Propellant gas stream can be used in two Teiltreibgasströme either only with one or the other or both of the Teiltreibgasströme. This results in a simple and very compact construction of a gas jet pump which can be switched in its performance, at least in two stages, which manages with a single Venturi tube. Of course, this venturi tube must then be designed so that it is designed to be optimized for an average volume flow of the propellant gas stream, so that the functionality is given both with one and also with a plurality of the partial propellant gas streams.

The fineness in the regulation of the delivery rate of the gas jet pump can be easily influenced by the number of individual Teiltreibgasströme. In practice, certainly two to three partial propellant gas flows will result in a meaningful variation in performance. In principle, however, any number of individual partial gas streams are possible, so that a quasi-continuous power adjustment is possible.

In a very favorable and advantageous development of the construction according to the invention, it is provided that the at least one valve device is designed as a 2/2-way valve, in particular as a solenoid valve. Such a design of the at least one valve device as a 2/2-way valve is correspondingly simple and efficient. This can be realized in particular in the form of a solenoid valve, which is easily controllable and inexpensive available on the market. The disadvantage of such a solenoid valve, however, lies in the fact that the flow cross-section is typically released comparatively abruptly. Thus, the flow rate breaks down briefly, since the Teiltreibgasströme split when opening one of the solenoid valves differently and a reduced flow of the already open

Flow cross sections occurs. According to a particularly favorable and advantageous development of the gas jet pump according to the invention, it is therefore provided that the at least one valve device is designed as a proportional valve. Such a proportional valve allows a continuous increase in the flow-through cross-section, so that a collapse of the pressure and the flow rate can be avoided. The structure thus allows a better control of the required delivery rate of the gas jet pump, since when opening the valve means the delivery rate does not collapse for a short time, but by the continuous opening of the valve device accordingly

can be maintained.

The above object is also achieved by a fuel cell system with an exhaust gas recirculation, wherein the exhaust gas recirculation at least one flowing from a fuel cell exhaust gas stream together with a dosed

Eduktgasstrom recirculates to the fuel cell, wherein in the anode recirculation, a gas jet pump is provided according to the invention with the exhaust stream as the main gas stream and the Eduktgasstrom as a propellant gas stream.

The gas jet pump according to the invention, which with a simple, small, compact and lightweight construction yet a high variability in terms of

Capacity allows, in particular for the exhaust gas recirculation in one

Fuel cell system of particular advantage. In such an exhaust gas recirculation, the recirculation rate must be adjusted accordingly as a function of the electric power delivered by the fuel cell. This results in a structure in which a high variability in the flow rate of the gas jet pump is needed. On the other hand, a pressurized or compressed educt gas is supplied to the fuel cell anyway, so that a sufficiently pressurized

Propellant gas flow is available. The use of a gas jet pump compared to a recirculation fan therefore also has decisive advantages in terms of the energy efficiency of the overall system.

In an advantageous development of the fuel cell system according to the invention, it is provided that the exhaust gas recirculation is designed as an anode exhaust gas recirculation. Particularly in the field of anode exhaust gas, the use of a gas jet pump according to the invention is of particular advantage. Here, hydrogen is typically available as the reactant gas stream for the anode compartment of the fuel cell. Since this hydrogen is generally stored under high pressure in a compressed gas storage, the energy required for the hydrogen as propellant gas flow is available anyway, so that here particularly energy efficient with the

Gas jet pump according to the invention, the anode recirculation can be operated.

In a particularly favorable and advantageous development thereof, it is provided that the propellant gas stream is branched in the direction of flow after a metering valve into the at least two partial propellant gas streams. The metering valve, which is often designed in combination with a pressure regulating valve, is comparatively complex and expensive, since it must realize an exact metering of the hydrogen under very high pressure and, if appropriate, the relaxation of this hydrogen to a lower pressure level. This component is in the

The structure according to the invention therefore exists only once, after which the branching of the propellant gas stream takes place into the at least two partial propellant gas streams. The metering valve can be designed both as a proportional valve, which has advantages in terms of noise emissions, as well as a clock valve, which by a

Pulse width modulation is operated so that the desired gas flow

or can set the desired dosage of hydrogen accordingly.

In a particularly favorable and advantageous development of the fuel cell system according to the invention, it is provided that at least one of the separate Teiltreibgasströme between the metering valve and the Venturi tube is formed free of a valve device. This one Teiltreibgasstrom without valve device is of particular advantage to a continuous with open metering valve

To realize basic flow of hydrogen in the area of the fuel cell. This basic flow can be designed in a particularly favorable and advantageous development in particular so that it is designed in its amount to the idling operation of the fuel cell system.- idle operation can therefore without the

Control of valve devices in the separate Teiltreibgasströmen the operation of the fuel cell can be realized very energy efficient and with minimal control effort. With increasing load then one or more additional Teiltreibgasströme is connected by opening the corresponding valve device, so that adjusts the required capacity in the gas jet pump accordingly. Further advantageous embodiments of the gas jet pump according to the invention, the fuel cell system and the operating method for this result from the remaining dependent claims and the embodiment, which will be described below with reference to the figures.

Showing:

1 shows an exemplary fuel cell system in a vehicle.

Fig. 2 is a schematic diagram of a gas jet pump according to the invention in a first embodiment;

FIG. 3 shows a diagram of the pressure buildup over the load achieved with the gas jet pump according to FIG. 2; FIG.

4 is a schematic diagram of a gas jet pump according to the invention in a

second embodiment; and

5 shows a diagram of the pressure build-up over the load achieved with the gas jet pump according to FIG. 4.

In the representation of FIG. 1, a fuel cell system 1 in an indicated vehicle 2 can be seen purely by way of example and in a very highly schematic manner. The

Fuel cell system 1 essentially has a fuel cell 3, which in turn has an anode compartment 4 and a cathode compartment 5. The fuel cell 3 should be designed as a stack of PEM fuel cells. The cathode compartment 5 of the fuel cell 3 is supplied via an air conveyor 6 with air as an oxygen supplier. The exhaust air from the cathode chamber 5 passes in the illustrated here

Embodiment to the environment. Here, in principle, a post-processing, for example, an afterburner, a turbine or the like could be arranged. However, this is for the present invention is not of interest, so on a

Representation has been omitted.

The anode chamber 4 of the fuel cell 3 is supplied with hydrogen H ₂ , which originates from a compressed gas reservoir 7. It passes via a pressure control device 8 and a later explained in more detail gas jet pump 9 in the anode compartment 4. From the region of the anode compartment 4 exhaust gas A passes from the anode compartment 4 via a

Recirculation line 10 back into the region of the gas jet pump 9, and is sucked from this as a secondary gas stream and fed back into the anode chamber 4. This principle of an anode recirculation is from the general state of Technique known. It serves to the anode chamber 4 with an excess

Hydrogen H ₂ supply in order to make the best possible use of its active area. The remaining in the exhaust gas from the anode chamber 4 residual hydrogen is then together with inert gases, which through the membranes from the cathode compartment 5 in the

Anode space 4 are diffused and a small part of the product water, which is formed in the anode chamber 4, fed back via the recirculation line 10 and the anode chamber 4 mixed with the fresh hydrogen H ₂ supplied again. 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. For this purpose, a drain valve 11 is indicated in principle in the illustration of FIG.

In order now to the pressure losses in the region of the anode compartment 4 and in the region of

It is necessary to compensate a recirculation line 10

Provide recirculation conveyor for the recirculated exhaust gas from the anode compartment 4. As a recirculation conveyor is shown in the here

Embodiment of Figure 1, the aforementioned gas jet pump 9 is provided.

The gas jet pump 9 is again shown in detail in the illustration of FIG. It consists essentially of a principle indicated Venturi tube 12, which the exhaust gas A is supplied. In addition, the hydrogen flows H ₂ as

Propellant gas flow 14 via a metering valve 15, which may be formed, for example integrated in the region of the pressure control device 8, to the venturi 12. The metering valve 15 may be formed, for example, as a clock valve or preferably as a proportional valve to minimize noise emissions. After the metering valve 15, the propellant gas stream 14 branches off into two partial propellant gas streams 14.1 and 14.2, which are fed separately to the venturi tube 12. This setup with the two

Propellant gas streams 14.1, 14.2 is to be understood as an example. It would be

Of course, also conceivable to form a plurality of individual Teiltreibgasströme 14.1 to 14 n accordingly. However, the following explanations will be described in each case using the example of two such partial gas streams 14.1, 14.2. Of course, those skilled in the art the explanations and structures to more than two

Partial propellant gas streams 14.1 to 14.n expand. In the representation of FIG. 2, the first of the partial propellant gas streams 14.1 does not have any valve device. The second partial gas stream 14.2, which is guided parallel thereto, has a valve device 16, which in the embodiment illustrated here should be designed as a comparatively simple, economical and efficient 2/2 way valve. This is indicated in the illustration of the valve device 16 by the symbolized opening characteristic. In particular, the valve device 16 should be designed as a solenoid valve, which can be easily and efficiently switched between an open position and a closed position.

The situation in the area of the fuel cell system 1 is now that in the

Idle operation of the fuel cell system 1 to a certain volume flow

Hydrogen is needed. Accordingly, a small volume flow of anode exhaust gas A must be recirculated. For this case, the partial propellant gas stream 14.1 is provided, which flows continuously into the venturi tube 12 and provides a certain delivery rate. In the diagram of the possible pressure build-up dp over the load L in FIG. 3, this is shown in the section labeled I. The valve device 16 in the second Teiltreibgasstrom 14.2 is closed. It is achieved at relatively low load, a comparatively low pressure build-up by the gas jet pump 9. With higher load, the valve 16 is opened. Since this is designed as a 2/2-way valve, the opening is released suddenly. As a result, the delivery pressure built up via the first partial propellant gas stream 14.1 is first lost once before the delivery pressure at the common flow of the two partial propellant gas streams 14.1 and 14.2 adjusts accordingly in the diagram of FIG.

If there are still other partial gas streams in addition to the two mentioned, then a further and finer power adjustment can take place.

In the illustration of Figure 4, a comparable structure of the gas jet pump 9 is shown again. The only difference is the training of the

Valve device 16. This is in the embodiment of Figure 4 of

Gas jet pump 9 designed as a proportional valve. This is in turn indicated by the opening characteristic in the representation of the valve device 16. Thus, it releases a continuously increasing flow-through cross-section when opening. This has the consequence that the delivery between the designated I and II Regions of the diagram of the pressure build dp over the load L no longer breaks, but the applied from the first part of the propellant gas flow 14.1 delivery pressure remains. This is shown by way of example on the diagram to be understood in analogy to the diagram in FIG. 3 in FIG. Again, the corresponding areas are again denoted by I and II.

It has been found that the formation of the metering valve 15 has no appreciable influence on the pressure build-up, but that this depends primarily on the design of the valve device 16. Thus, in the area of the metering valve 8, the desired valve technology can continue to be used comparatively independently of the design of the gas jet pump 9. For example, a timing valve offers corresponding advantages in terms of cost and controllability, while a proportional valve allows for a more continuous flow and has advantages over the timing valve in terms of noise emissions caused.

Claims

claims

1. Gas jet pump (9) for conveying a main gas stream (A) by a

Propellant gas stream (14), wherein the propellant gas stream (14) in the axial direction in a

Venturi tube (12) flows with a cross-sectional constriction, which also flows in the main gas stream (A),

characterized in that

the propellant gas stream (14) in the form of at least two separate

Teiltreibgasströmen (14.1, 14.2) is formed, which together flow into the one Venturi tube (12), wherein at least one of the two separate

Teiltreibgasströme (14.1, 14.2) via a valve device (16) in his

Volume flow can be influenced.

2. gas jet pump (9) according to claim 1,

characterized in that

the at least one valve device (16) is designed as a 2/2-way valve, in particular as a solenoid valve.

3. gas jet pump (9) according to claim 1,

characterized in that

the at least one valve device (16) is designed as a proportional valve.

4. Fuel cell system (1) with an exhaust gas recirculation, which feeds a from a fuel cell (3) exhaust gas together with a metered Eduktgasstrom to the fuel cell (3), wherein in the exhaust gas recirculation, a gas jet pump according to one of claims 1 to 3 with the exhaust stream (A ) is provided as the main gas stream and the Eduktgasstrom as propellant gas stream (14).

5. Fuel cell system (1) according to claim 4,

characterized in that

the exhaust gas recirculation is designed as an anode exhaust gas recirculation.

6. Fuel cell system (1) according to claim 4 or 5,

characterized in that

the propellant gas stream (14) of the gas jet pump (9) is branched in the flow direction downstream of a metering valve (15) into the at least two partial propellant gas streams (14.1, 14.2).

7. Fuel cell system (1) according to claim 6,

characterized in that

the metering valve (15) is designed as a proportional valve.

8. Fuel cell system (1) according to claim 6,

characterized in that

the metering valve (15) is designed as a clock valve.

9. Fuel cell system (1) according to claim 6, 7 or 8,

characterized in that

at least one of the separate Teiltreibgasströme (1 .1, 14.2) between the metering valve (15) and the Venturi tube (12) is formed free of a valve device.

10. Fuel cell system (1) according to claim 9,

characterized in that

the partial propellant gas stream (14.1) designed free of a valve device is designed in its volumetric flow in such a way that it is optimized for idling operation of the fuel cell (3).