Process and apparatus for supplying air to a fuel cell system

DETAILED DESCRIPTION OF THE DRAWING The fuel cell system, identified generally by reference numeral 1, has a fuel cell 12 or a stack of fuel cells supplied via an air supply line 3 with process air which is discharged via an air discharge line 5 after passing through a conventional cathode chamber (not shown) of the fuel cell 12.
The conventional anode chamber (not shown) of the fuel cell 12 is supplied via a second gas supply line with combustible gas such as, for example, hydrogen.
Compressor 6 for compressing the process air is located in the air supply line 3.
During the reaction of the hydrogen in the fuel cell 12 with the oxygen that is contained in the process air, not only electrical energy but also product water and heat of reaction are generated.
The product water and the heat of reaction are largely discharged from the fuel cell 12 along with the process air.
At the same time, as the air volume flow V.
sub.
air leaves the fuel cell 12, it is reduced by the quantity of oxygen consumed.
To recover the pressure energy that is contained in the discharged process air, an expander 16 with a variable absorption capacity is located in the air discharge line 5.
The expander 16 is connected to the compressor 6 via a common shaft 20.
The common shaft 20 also holds an electric motor 30 in the form of a continuously excited synchronous motor, a starter motor 28 and, optionally, a pump 8.
To ensure that, under certain operating conditions, the expander 16 is unable to transmit a negative moment to the compressor 6, an air register 32 is provided between the fuel cell 12 and the expander 16 so as to, at reduced pressure, suck in ambient air.
As soon as a working pressure P.
sub.
L is reached, the expander 16 is allowed to again deliver energy to the compressor 6.
In conventional systems, the working pressure P.
sub.
L is generally set via a pressurizing valve which builds up the working pressure P.
sub.
L and discharges the waste air to the ambient air after leaving the fuel cell 12.
In that conventional process, however, the pressure energy that is supplied at considerable cost to the medium is not utilized but is lost and dissipated outside the system