The invention relates to a fuel cell system in which anode exhaust gas is recirculated to the anode inlet.
This fuel cell system comprises an anode circuit having a gas jet pump with two inlets and one outlet, for conveying surplus hydrogen from the anode outlet to the anode inlet. A “motive jet” under elevated pressure is introduced at one inlet, and passes through the gas jet pump to its outlet. A further inlet of the gas jet pump is arranged such that the motive jet flowing through the gas jet pump produces a low pressure at the further inlet, and is thereby able to draw in gas via the further inlet and entrain it as far as the outlet.
It is known in particular from fuel cell systems to utilize the high pressure which hydrogen is conventionally under in a hydrogen tank to form a motive jet for a gas jet pump. The gas jet pump is thus arranged between the hydrogen tank and the anode inlet. As a result, the quantity of anode waste gas that is drawn in via the further inlet of the gas jet pump is directly dependent on the quantity of hydrogen gas supplied from the tank and forming the motive jet, which in turn depends on the fuel cell system load.
This known arrangement is problematic under low load. In particular, it would then be desirable for somewhat more anode waste gas to be recirculated than is possible with the gas jet pump. Satisfactory recirculation under low loads has heretofore been made possible, if need be, by using a blower. However, a blower is a complex and expensive component, which is susceptible to failure in particular at cold temperatures due to icing.
It is therefore an object of the present invention to provide a fuel cell system which operates reliably, even under low loads, and is nonetheless inexpensive.
This and other objects and advantages are achieved by the fuel cell system according to the invention, in which a part of the anode waste gas is supplied to a compressor, which comprises it and supplies it to the motive jet side of a gas jet pump. In this way it is ensured that a sufficient quantity of gas in particular a quantity sufficient for low loads, is always available on the motive jet side. In practice only very small quantities of anode waste gas need to be compressed, such that the power of the compressor may be so low that it can be operated with a 12 volt power supply. Expenditure is therefore low, while the solution is nevertheless effective.
It is advantageous, first of all, for hydrogen from a tank also to be supplied to the same gas jet pump to which the compressed waste gas is supplied, as in the prior art. This may be achieved by bringing the compressed waste gas and the hydrogen from the tank together upstream of the gas jet pump. It needs to be ensured that the compressed waste gas and the hydrogen are at roughly the same pressure. The compressed waste gas and the hydrogen may however also be supplied directly to the gas jet pump independently of one another, using different inlet nozzles.
Another embodiment of the invention has two gas jet pumps, to one of which the compressed waste is supplied, with hydrogen from the tank being supplied to the other. Each gas jet pump then has a part of the uncompressed waste gas supplied to it as gas to be drawn in. With this embodiment too it is ensured that the fuel cell system functions under low loads.
To prevent flow in undesired directions, all the gas jet pumps in this embodiment need to have a nonreturn valve on the anode inlet side.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
As shown in the Figures, a fuel cell 10 comprises an anode 12, which has an anode inlet 14, via which hydrogen is supplied. The majority of the hydrogen comes from a tank 16. Arranged downstream of the tank 16 are a valve 18 and a gas jet pump 20. The hydrogen jet coming from the tank 16 functions as the motive jet for the gas jet pump 20, this being supplied to a motive jet inlet (normally a nozzle) 22 of the gas jet pump 20, and exiting at an outlet 24. As a result of the low pressure generated by the motive jet, further gas may be drawn in via a further inlet 26 of the gas jet pump 20. In the present case, the waste gas emerging from the anode 12 via an anode outlet 28 is supplied in part to the further inlet 26. According to the invention, provision is then made for a further part of the waste gas to be supplied from a branch point 30, which also leads to the further inlet 26, to a compressor 32, there to be compressed to the pressure of the hydrogen coming from the tank 16 downstream of the valve 18 and also to be introduced into the hydrogen stream downstream of the valve 18 at a point 34 which lies upstream of the inlet nozzle 22 in the first embodiment according to
In a modification of the embodiment of
The invention also works if the hydrogen from the tank 16 and the compressed waste gas are supplied to different gas jet pumps 20 and 38 respectively. Different parts of the waste gas from the anode 12 are supplied to each gas jet pump 20 and 38, the two gas jet pumps 20 and 38 operating mutually independently. (See
In accordance with the stated object, the compressor 32 serves in particular to recirculate a sufficient stream of waste gas when the fuel cell 10 is under low loads. The quantity of waste gas compressed by the compressor 32 may here be relatively small. The compressor 32 does not therefore need to be of a high power and may for example be operated with a 12 V voltage. It is significantly less expensive to provide the compressor 32 than a blower, as is occasionally used in the anode circuit in the prior art.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
Number | Date | Country | Kind |
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10 2008 014 783.4 | Mar 2008 | DE | national |
This application is a national stage of PCT International Application No. PCT/EP2009/001494, filed Mar. 3, 2009, which claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2008 014 783.4, filed Mar. 18, 2008, the entire disclosure of which is herein expressly incorporated by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/001484 | 3/3/2009 | WO | 00 | 9/16/2010 |