This application claims the priority of German patent document 100 55 106.8, filed Nov. 7, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fuel cell system having a reservoir for cryogenic media.
Hydrogen is used as a fuel for fuel cell systems. U.S. Pat. No. 5,728,483 discloses a stationary fuel cell system in which liquid hydrogen is stored in a tank and is vaporized to operate the fuel cell. To reduce hydrogen losses in the filling of the tank and storage of the liquid hydrogen, a hydrogen reservoir with a hydrogen absorption apparatus is provided, which absorbs hydrogen gas that leaks out of the liquid hydrogen tank. The hydrogen absorber serves as a buffer, to balance the considerable difference in demand for hydrogen between day and night operation. When necessary, the hydrogen absorber is acted upon by a heat transfer medium and is heated, creating hydrogen gas, which is then fed to the fuel cell. The heat transfer medium is also used to cool the fuel cell.
The object of the invention is to provide a fuel cell system which is especially suited for use in mobile fuel cell units.
This and other objects and advantages are achieved by the fuel cell system according to the invention, in which a heating circuit for heating and/or vaporizing the cryogenic medium (preferably liquid hydrogen) via a first heat exchanger, is coupled directly to a cooling circuit for the fuel cell unit. The heat exchanger is preferably designed to draw off the waste heat from the fuel cell system.
This arrangement has the specific advantage that the small amount of waste heat produced by a fuel cell having a low operating temperature is itself sufficient to vaporize the liquid hydrogen. In this manner, a favorable reduction in the size of the system, its weight, and the cost of the cooling device for the fuel cell system is achieved.
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.