Catalytic humidifier and heater, primarily for humidification of the oxidant stream for a fuel cell

Abstract

A method and apparatus are provided for humidifying 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 oxidant is supplied in excess of the fuel to the reactor, so as to generate a stream of oxidant which is both heated and humidified. For an air breathing stack, this heated oxidant can simply be mixed with air flowing through the fuel cell stack. For a closed system, a heated and humidified oxidant flow, and optionally a fuel flow are mixed with additional flows of these gases supplied to the fuel cell.

1 . A tubular reactor, for catalyzing the reaction of hydrogen and a gaseous oxidant, the tubular reactor comprising: 
 an elongated housing,    a catalyst formed from a material adapted to promote catalytic combustion of the fuel and the oxidant, being formed into an elongated body substantially filling the elongated housing and being porous, a first inlet for a gaseous fuel and a second inlet for a gaseous oxidant, both first and second inlets being provided at one end of the elongated housing; and    an outlet at the other end of the housing, whereby, in use, the catalyst promotes combustion between the fuel and the oxidant to generate heat and moisture, whereby a heated and humidified gas flow exits through the outlet.    
     
     
         2 . A tubular reactor as claimed in  claim 1 , wherein the housing and the body of the catalyst are both generally cylindrical and have a length substantially longer than the diameter thereof.  
     
     
         3 . A tubular reactor as claimed in  claim 1  or  2 , which includes, for the first and second inlets, fittings for connection to supply lines for fuel and the oxidant, and for the outlet, a fitting for connection to a conduit for receiving the heated, humidified gas flow.  
     
     
         4 . A fuel cell system comprising: 
 at least one fuel cell, each fuel cell comprising: 
 an inlet for a fuel;  
 an anode having a catalyst associated therewith for producing cations from the fuel;  
 a fuel manifold, connected between the inlet and the anode, for distributing 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;  
 an ion exchange membrane deposed between said anode and said cathode, said membrane facilitating migration of cations from said anode to said cathode, while isolating the fuel and the oxidant from one another; and  
 a catalytic reactor having a first inlet for fuel and a second inlet for an oxidant, and an outlet for heated and humidified oxidant, the catalytic reactor being mounted to supply the heated and humidified oxidant to the fuel cell.  
   
     
     
         5 . A fuel cell system as claimed in  claim 4 , which includes a plurality of fuel cells forming a fuel cell stack, which includes a main fuel inlet connected to all of the inlets of the fuel cells.  
     
     
         6 . A fuel cell system as claimed in  claim 5 , wherein the fuel cell stack is an air-breathing stack, including a plurality of channels extending upwardly through the fuel cell stack for permitting free flow of ambient air as the oxidant through the fuel cell stack, there being at least one channel for each fuel cell and the oxidant inlet means being provided by the lower ends of the channels, wherein the catalytic reactor is mounted below the fuel cell stack and is configured to receive air as an oxidant through the second inlet thereof in excess of the stoichiometric quantity of air required for combustion of fuel within the catalytic reactor, whereby heated and humidified air is discharged from the outlet of the catalytic reactor, and wherein the outlet of the catalytic reactor is mounted below the channels of the fuel cell stack, whereby, heated and moistened air flows upwardly through the channels of the fuel cell stack from the catalytic reactor.  
     
     
         7 . A fuel cell system as claimed in  claim 6  which includes a supply line for fuel connected to both the main fuel inlet of the fuel cell stack and the first inlet of the catalytic reactor, and which includes an air supply line including an air delivery device connected to the second inlet of the catalytic reactor.  
     
     
         8 . A fuel cell system as claimed in  claim 6  or  7  wherein the catalytic reactor is generally tubular.  
     
     
         9 . A fuel cell system as claimed in  claim 6  or  7 , wherein the catalytic reactor includes a generally disc shaped reactor element, configured for flow of fuel and oxidant, generally along a central axis thereof.  
     
     
         10 . A fuel cell system as claimed in  claim 5  wherein the outlet of the catalytic reactor is connected by a first control valve to the main fuel inlet of the fuel cell stack and by a second control valve to the oxidant inlet means whereby, in use, the outlet of the catalytic reactor can be selectively connected to one of the main fuel inlet and the oxidant inlet means, with supply of the oxidant as the fuel to the catalytic reactor adjusted so that the heated and humidified gas at the outlet of the catalytic reactor includes an excess of gas corresponding to said one of the main fuel inlet and the oxidant inlet means.  
     
     
         11 . A fuel cell system as claimed in  claim 10 , wherein each of the fuel supply line and the air supply line include at least one of a pressure gauge, a flow meter and a non-return valve.  
     
     
         12 . A fuel cell system as claimed in  claim 5 , wherein the oxidant inlet means comprises an air distribution manifold within the fuel cell stack for distributing air, as the oxidant, to individual fuel cells, wherein a main air supply line is provided connected to the air distribution manifold, and a main fuel line is connected to the fuel inlet, and wherein a secondary fuel line branches off from the main fuel supply line and is connected to the catalytic reactor for supplying fuel.  
     
     
         13 . A fuel cell system as claimed in  claim 12 , wherein the fuel cell stack includes a fuel outlet and means for recirculating fuel from the fuel outlet to the fuel inlet.  
     
     
         14 . A fuel cell system as claimed in  claim 12 , wherein the catalytic reactor is provided in the main air supply line, and wherein a second catalytic reactor is provided in the fuel cell line and a secondary air supply line connects the main air supply line to the secondary catalytic reactor, for a supply of air in an amount less than the stoichiometric amount required for combustion of fuel, whereby, the secondary catalytic reactor generates heated and humidified fuel.  
     
     
         15 . A fuel cell system as claimed in  claim 14 , where each of the first and second catalytic reactors is generally tubular.  
     
     
         16 . A method of operating a fuel cell system comprising a plurality of fuel cells, each fuel cell comprising an inlet for fuel, an anode having a catalyst associated therewith for producing cations from fuel, a fuel manifold connected between the inlet and the anode for distributing 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 fuel to the fuel cell for reaction to generate electrical power and heat;    (b) providing a catalytic reactor, supplying fuel to the catalytic reactor and supplying oxidant to the catalytic reactor, in an amount greater than the stoichiometric amount required for the combustion of the fuel, to ensure complete combustion of the fuel, thereby generating a flow of heated and humidified oxidant;    (c) supplying the heated and humidified oxidant to the fuel cell, for reaction with the fuel to generate electricity and heat.    
     
     
         17 . A method as claimed in  claim 16 , which 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 cell to preheat the fuel cell, and commencing supply of fuel to the fuel cell, once the fuel cell reaches a desired temperature.  
     
     
         18 . A method as claimed in  claim 16 , which includes providing the catalytic reactor in a main oxidant supply line for supplying oxidant to the fuel cell stack.  
     
     
         19 . A method as claimed in  claim 17 , which includes, after start-up and after the cell has reached the desired temperature, supplying a sufficient quantity of the oxidant and the fuel to the catalytic reactor, to maintain the oxidant supplied to the fuel cell system at a desired humidity level.  
     
     
         20 . A method as claimed in  claim 19 , which includes supplying air as the oxidant; where the fuel cell system is an air-breathing system including vertical channels for flow of air as the oxidant; and providing only a portion of air required as the oxidant through the catalytic reactor, with additional air flowing directly through the channels of the fuel cell system.  
     
     
         21 . A method as claimed in  claim 16 , which includes: 
 (a) providing a second catalytic reactor;    (b) supplying the second reactor with fuel and oxidant in an amount less than the stoichiometric amount required for combustion of fuel, thereby generating a flow of heated and humidified fuel;    (c) supplying the heated and humidified fuel to the inlet for fuel of the fuel cell.    
     
     
         22 . A method as claimed in any one of  claims 16  to  21 , which includes providing the fuel cell system with proton exchange membranes.