Method of operating a fuel cell to provide a heated and humidified oxidant
A method and apparatus are provided for humidifying fuel, and optionally oxidant, supplied to a fuel cell system, which can be a single fuel cell or a multiplicity of fuel cells. A catalytic reactor is provided, which is supplied with a portion of the fuel and the oxidant. The fuel is supplied in excess of the oxidant to the catalytic reactor, so as to generate a stream of fuel which is both heated and humidified. For a closed system, a heated and humidified fuel flow, and optionally a heated and humidified oxidant flow, are mixed with additional flows of these gases supplied to the fuel cell.
1. A method of operating a fuel cell system comprising a plurality of fuel cells, each fuel cell comprising a fuel inlet for fuel, an anode having a catalyst associated therewith for producing cations from the fuel, a fuel manifold connected between the fuel inlet and the anode for distributing the fuel to the anode, an oxidant inlet means for supplying oxidant, a cathode having a catalyst associated therewith and connected to the oxidant inlet means for producing anions from the oxidant, said anions reacting with said cations to form water on said cathode and an ion exchange membrane disposed between the anode and the cathode, for facilitating migration of cations from the anode to the cathode, while isolating the fuel and oxidant from one another, the method comprising:
(a) supplying one part of the fuel to the fuel inlet of the fuel cell for reaction at the anode to generate electrical power and heat;
(b) providing a catalytic reactor for promoting reaction of the fuel and the oxidant, supplying another part of the fuel to the catalytic reactor and supplying the oxidant to the catalytic reactor in an amount greater than the stoichiometic amount required for the combustion of the other part of the fuel to ensure complete consumption of the other part of the fuel, and thereby to generate a flow of heated and humidified oxidant; and
(c) supplying the heated and humidified oxidant to the oxidant inlet of the fuel cell system, for reaction at the cathode with the one part of the fuel to generate electricity and heat; and
(d) supplying the oxidant and the other part of the fuel to the catalytic reactor, prior to supply thereof to the oxidant inlet.
2. A method as claimed in claim 1 , for which it comprises, for initial start-up below a preset temperature, initially supplying fuel and oxidant only to the catalytic reactor to generate a flow of heated and humidified oxidant, and passing the heated and humidified oxidant through the fuel cells to pre-heat the fuel cells, and commencing supply of fuel to the fuel cells, once the fuel cells reach a desired temperature.
3. A method as claimed in claim 1 or 2 , which includes providing the catalytic reactor as a tubular reactor.
4. A method as claimed in claim 1 or 2 , which includes:
supplying air as the oxidant
providing the fuel cell system as an air-breathing system including vertical channels for flow of air as the oxidant;
and providing only a portion of the air required as the oxidant through the catalytic reactor, with additional air flowing directly through the channels of the fuel cell system.
5. A method as claimed in claim 1 or 2 , which includes supplying one part of the oxidant directly to the fuel cells and supplying another part of the oxidant to the catalytic reactor for heating and humidification, and mixing the one part and the heated and humidified other part of the oxidant together prior to supply to the fuel cells.