Method and apparatus for vaporizing fuel for a reformer fuel cell system

Abstract

Rapid response to a fuel cell system of the type including a reformer ( 32 ) in response to a change in load is achieved in a system that includes a fuel tank ( 24 ), a water tank ( 20 ) and a source ( 42 ) of a fluid at an elevated temperature. A heat exchanger ( 28 ) is provided for vaporizing fuel and water and delivering the resulting vapor to the system reformer ( 32 ) and includes an inlet ( 64 ) and an outlet ( 66 ) for the fluid. It includes a plurality of fluid flow paths ( 100 ), ( 102 ), ( 104 ) extending between the inlet ( 64 ) and outlet ( 66 ) as well as a fuel inlet ( 56 ) and a fuel outlet ( 58 ) spaced therefrom. The fuel inlet ( 56 ) and outlet ( 58 ) are connected by a plurality of fuel flow paths ( 52 ) that are in heat exchange relation with the fluid flow paths ( 100 ), ( 102 ), ( 104 ) and the fuel water inlet ( 56 ) is located adjacent the upstream ends of the fluid flow paths ( 100 ), ( 102 ), ( 104 ).

1 . A fuel cell system including. 
 a fuel reservoir for storing a liquid fuel for a fuel cell;    a fuel cell for consuming a fuel and generating electricity therefrom;    a fuel reformer for receiving fuel in a vaporized state and connected to the fuel cell for providing a fuel thereto for consumption therein; and    a fuel vaporizer interposed between the fuel reservoir and the fuel reformer for receiving liquid fuel from the fuel reservoir and vaporizing the liquid fuel to the vaporized state for delivery to the fuel reformer, and including a heat exchanger having a hot fluid inlet, a hot fluid outlet and a core interconnecting said inlet and said outlet, said core having alternating hot fluid passages extending between said hot fluid inlet and said hot fluid outlet and in heat exchange relation with liquid/vaporized fuel passages, said hot fluid passages each being defined by two, elongated spaced, generally parallel bars, a fin or fins between said bars and extending the length thereof and two separator plates bonded to and sandwiching said bars and said fin(s), said heat exchanger further including a liquid fuel inlet and a vaporized fuel outlet, each said liquid/vaporized fuel passage extending between said liquid fuel inlet and said vaporized fuel outlet and including an undulating spacer nested between generally parallel bar sections and separator plates bonded to and sandwiching said spacer to define a plurality of flow ports of relatively small hydraulic diameter.    
   
   
       2 . The fuel cell system of  claim 1  wherein most, but not all, of the separator plates are located within said core and each of said most separator sheets is common to adjacent ones of said hot fluid passages and said liquid/vaporized fuel passages.  
   
   
       3 . The fuel cell system of  claim 2  wherein said bars, said bar sections, said fins, said separator plates and said undulating spacers are bonded together by braze metal.  
   
   
       4 . The fuel cell system of  claim 1  wherein said core is a stack of said bars, said bar sections, said fins, said separator plates and said undulating spacers arranged to define said alternating hot fluid passages in heat exchange relation with liquid/vaporized fuel passages.  
   
   
       5 . The fuel cell system of  claim 1  wherein said undulating spacer is in plural sections and said bar sections are oriented with respect to said undulating spacer sections to define multipass liquid/vaporized flow passages, at least one pass of said multipass liquid/vaporized flow passages being in countercurrent relation to said hot fluid passage.  
   
   
       6 . The fuel cell system of  claim 5  wherein at least one another pass of said multipass liquid/vaporized flow passages is in concurrent relation to said hot fluid passages.  
   
   
       7 . The fuel cell system of  claim 6  wherein said at least one pass is connected to said vaporized fuel outlet and said at least one another pass of said multipass liquid/vaporized fuel flow passages is connected to said liquid fuel inlet.  
   
   
       8 . The fuel cell system of  claim 7  wherein the cross-sectional area of said at least one pass is greater than the cross-sectional area of said at least one another pass.  
   
   
       9 . The fuel cell system of  claim 7  wherein said at least one pass has an increasing cross-sectional area as said vaporized fuel outlet is approached.  
   
   
       10 . The fuel cell system of  claim 9  wherein said increasing cross-sectional area is provided by a step-wise increase.  
   
   
       11 . The fuel cell system of  claim 9  wherein said increasing cross-sectional area is provided by a continuous increase.  
   
   
       12 . The fuel cell system of  claim 7  wherein said at least one another pass has an increasing cross-section in the direction of flow away from liquid fuel inlet.  
   
   
       13 . The fuel cell system of  claim 12  wherein said increasing cross-sectional area is provided by a step-wise increase.  
   
   
       14 . The fuel cell system of  claim 12  wherein said increasing cross-sectional area is provided by a continuous increase.  
   
   
       15 . The fuel cell system of  claim 7  wherein said at least one path and said at least one another pass are separate by an elongated divider having one end closer to said liquid fuel inlet than said vaporized fuel outlet and an opposite approximately midway between said liquid fuel inlet and said vaporized fuel outlet.  
   
   
       16 . The fuel cell system of  claim 15  wherein said divider is straight.  
   
   
       17 . The fuel cell system of  claim 15  wherein said divider is stepped.  
   
   
       18 . The fuel cell system of  claim 1  wherein said undulating spacer includes a plurality of spacer sections separated by gaps.  
   
   
       19 . A method of vaporizing liquid fuel and water prior to its introduction into a reformer in a fuel cell system, comprising the steps of: 
 a) causing a stream of hot fluid to traverse a flow path such that the fluid is at maximum temperature at the beginning of the flow path and at a lower temperature at a location downstream of said beginning;    b) vaporizing the liquid water and fuel by bringing liquid water and liquid fuel into heat exchange relation with said stream at said beginning and flowing the water and fuel concurrently with said stream and in heat exchange relation therewith to said location; and    c) subsequently flowing the vaporized water and fuel in heat exchange relation and countercurrent with said stream back to said beginning and out of contact with the flow of water and fuel occurring during the performance of step b) to superheat the vaporized water and fuel;    steps a), b) and c) being performed in a continuous operation.    
   
   
       20 . The method of  claim 19  wherein step c) is followed by the step of directing the vaporized and superheated water and fuel to a reformer in a fuel cell system.  
   
   
       21 . The method of  claim 19  wherein said fuel is methanol.  
   
   
       22 . A fuel cell system including: 
 a fuel reservoir for storing a liquid fuel for a fuel cell;    a fuel cell for consuming a fuel and generating electricity therefrom;    a fuel reformer for receiving fuel in a vaporized state and connected to the fuel cell for providing a fuel thereto for consumption therein; and    a fuel vaporizer interposed between the fuel reservoir and the fuel reformer for receiving liquid fuel from the fuel reservoir and vaporizing the liquid fuel to the vaporized state for delivery to the fuel reformer, and including a heat exchanger having a hot fluid inlet, a hot fluid outlet and a core interconnecting said inlet and said outlet, said core having alternating hot fluid passages extending between said hot fluid inlet and said hot fluid outlet and in heat exchange relation with liquid/vaporized fuel passages, a fin or fins in said hot fluid passages, said heat exchanger further including a liquid fuel inlet and a vaporized fuel outlet, each said liquid/vaporized fuel passage extending between said liquid fuel inlet and said vaporized fuel outlet and including an undulating spacer to define a plurality of flow ports of relatively small hydraulic diameter, said spacer being formed of a plurality of spacer sections, each separated by a gap.