PEM-SOFC hybrid power generation systems

Abstract

A hybrid fuel cell system comprising a solid-oxide fuel cell system, a proton exchange membrane fuel cell system, a hydrocarbon reformer and a hydrogen separator. A large PEM provides output power, such as motive power for a vehicle, using hydrogen storage that may be resupplied from a separate hydrogen refilling station or from the onboard reformer. The SOFC is preferably small and provides heat and exhaust water that, when recycled into the reformer, allow the reformer to operate endothermically without requiring atmospheric air, thus excluding nitrogen from the reformate stream. Alternatively, the reformer and SOFC are stationary at a base station and the PEM is aboard the vehicle. The SOFC and reformer have sufficient capacity to recharge hydrogen storage in the vehicle in a relatively short period of time, such as overnight.

1 . A hybrid fuel cell system, comprising: 
 a) a catalytic hydrocarbon reformer for reforming hydrocarbon fuel to produce fuel gas;    b) a hydrogen separator for receiving said fuel gas from said reformer and forming a first fuel stream containing hydrogen and carbon monoxide and a second fuel stream containing hydrogen;    c) a solid-oxide fuel cell system for receiving said first fuel stream; and    d) a proton exchange membrane fuel cell system for receiving said second fuel stream.    
     
     
         2 . A hybrid fuel cell system in accordance with  claim 1  further comprising: 
 a) a compressor in said second fuel stream for compressing said second fuel stream; and    b) a first hydrogen storage tank in flow communication with said compressor and said proton exchange membrane fuel cell system for storing compressed hydrogen received from said compressor and for supplying hydrogen as fuel to said proton exchange membrane fuel cell system.    
     
     
         3 . A hybrid fuel cell system in accordance with  claim 2  wherein said reformer, said hydrogen separator, said solid-oxide fuel cell system, said proton exchange membrane fuel cell system, said compressor, and said hydrogen storage tank are all mounted on one of a platform selected from the group consisting of a motor vehicle, a boat, a ship, an aircraft, a spacecraft and a building.  
     
     
         4 . A hybrid fuel cell system in accordance with  claim 2  wherein said reformer, said hydrogen separator, said solid-oxide fuel cell system, and said first hydrogen storage tank define a stationary base station, and wherein said proton exchange membrane fuel cell system and a second hydrogen storage tank define a portable station mounted on one of a portable platform selected from the group consisting of a motor vehicle, a boat, a ship, an aircraft and a spacecraft.  
     
     
         5 . A hybrid fuel cell system in accordance with  claim 1  further comprising a first electrical storage device for receiving electrical power from said solid-oxide fuel cell system and a second electrical storage device for receiving electrical power from said proton exchange membrane fuel cell system.  
     
     
         6 . A hybrid fuel cell system in accordance with  claim 5  wherein said first electrical storage device has a voltage capacity of less than 50 volts and wherein said second electrical storage device has a voltage capacity greater than 50 volts.  
     
     
         7 . A hybrid fuel cell system in accordance with  claim 6  further comprising a bi-directional DC/DC converter connected between said first and second electrical storage devices.  
     
     
         8 . A hybrid fuel cell system in accordance with  claim 1  further comprising a first stream of anode effluent from said solid-oxide fuel cell system directed into an inlet of said reformer such that said reforming proceeds endothermically.  
     
     
         9 . A hybrid fuel cell system in accordance with  claim 1  further comprising a combustor for receiving a second stream of anode effluent from said solid-oxide fuel cell system and combusting said second stream to produce heat.  
     
     
         10 . A hybrid fuel cell system in accordance with  claim 1  wherein the electrical output capacity of said solid-oxide fuel cell system is less than the electrical output capacity of said proton exchange membrane fuel cell system.  
     
     
         11 . A hybrid fuel cell system in accordance with  claim 10  wherein a ratio of electrical output capacity of said solid-oxide fuel cell system to the electrical output capacity of said proton exchange membrane fuel cell system is between about 1:1 and about 1:100.  
     
     
         12 . A method for producing electricity, comprising the steps of: 
 a) providing a hybrid fuel cell system including a catalytic hydrocarbon reformer, a hydrogen separator, a solid-oxide fuel cell system, and a proton exchange membrane fuel cell system;    b) producing reformate fuel gas in said reformer;    c) separating said reformate fuel gas in said hydrogen separator into a first stream containing hydrogen and carbon monoxide and a second stream containing hydrogen;    d) directing said first stream into a SOFC fuel cell of said solid-oxide fuel cell system to produce a first electrical output and an anode exhaust stream; and    e) directing said second stream into said PEM fuel cell of a proton exchange membrane fuel cell system to produce a second electrical output and a cathode exhaust stream.    
     
     
         13 . A method in accordance with  claim 12  wherein said separating step is carried out by a separating apparatus selected from the group consisting of palladium membrane separator and pressure swing adsorption separator.  
     
     
         14 . A method in accordance with  claim 12  comprising the further steps of: 
 a) recovering water from said cathode exhaust stream; and    b) supplying said recovered water to said hydrocarbon reformer to assist in endothermic hydrocarbon reforming therein.    
     
     
         15 . A method in accordance with  claim 12  comprising the further step of directing at least a portion of said anode exhaust stream to an inlet of said hydrocarbon reformer.  
     
     
         16 . A vehicle comprising a hybrid fuel cell system including 
 a catalytic hydrocarbon reformer for reforming hydrocarbon fuel to produce fuel gas,    a hydrogen separator for receiving said fuel gas from said reformer and forming a first fuel stream containing hydrogen and carbon monoxide and a second fuel stream containing hydrogen,    a solid-oxide fuel cell system for receiving said first fuel stream and thereby producing a first electricity stream, and    a proton exchange membrane fuel cell system for receiving said second fuel stream.    
     
     
         17 . A vehicle in accordance with  claim 16  wherein said hybrid fuel cell system further comprises a first electrical storage device for receiving said first electricity stream and a second electrical storage device for receiving said second electricity stream, wherein said first electrical storage device has a voltage capacity of less than 50 volts and wherein said second storage battery has a voltage capacity greater than 50 volts.  
     
     
         18 . A vehicle in accordance with  claim 17  wherein said first electrical storage device supplies power to vehicle accessories and wherein said second electrical storage device supplies power to at least one electric drive motor for motivating said vehicle.