Apparatus and method for fuel cell start from freezing without melting ice

Abstract

Fuel cell systems ( 100, 400 ) and related methods involving accumulators ( 106, 200, 300, 406 ) with multiple regions (R 1 , R 2 ; R 1 ′, R 2 ′) of differing water fill rates are provided. At least one accumulator region with a relatively more-rapid fill rate (R 2 ; R 2 ′) than another accumulator region (R 1 ; R 1 ′) is drained of water at shutdown under freezing conditions to allow at least that region to be free of water and ice. That region is then available to receive water from and supply water to, a fuel cell ( 102; 402 ) nominally upon start-up. The region having the relatively more-rapid fill rate (R 2 ; R 2 ′) may typically be of relatively lesser volume, and may be positioned either relatively below or relatively above the other region(s).

1 . A fuel cell system ( 100 ,  400 ) subject to operation under freezing conditions, comprising:
 at least one fuel cell ( 102 ,  402 ); and   an accumulator ( 106 ,  200 ,  300 ,  406 ) operative to receive water from and supply water to, the at least one fuel cell, the accumulator having structure ( 202 ,  204 ;  310 ,  312 ,  314 ,  316 ;  410 ) defining a first region (R 1 , R 1 ′) having a first volume configured to contain a volume of water during steady state operation of the at least one fuel cell and configured to fill with water vertically at a first rate for an arbitrary fill water flow rate, and structure ( 206 ,  204 ;  310 ,  312 ,  314 ,  316 ;  414 ) defining a second region (R 2 , R 2 ′) having a second volume and configured to fill with water vertically at a second rate greater than said first rate for said same arbitrary fill water flow rate, the accumulator including a drain ( 121 ,  234 ,  320 ,  440 ) in the second region, said drain being configured and operative to allow water to drain substantially entirely from at least said second region following shutdown of the at least one fuel cell, thereby to prevent water from freezing in at least said second region.   
     
     
         2 . The fuel cell system ( 100 ) of  claim 1  wherein the accumulator second region (R 2 ) is positioned below the accumulator first region (R 1 ), the accumulator first region (R 1 ) and the accumulator second region (R 2 ) each having respective vertical extents and having sidewalls that define respective cross-sectional areas along the respective vertical extents, and wherein the cross-sectional areas of the accumulator second region are less than those of the accumulator first region. 
     
     
         3 . The fuel cell system ( 100 ) of  claim 2  wherein the sidewalls defining at least one of the accumulator first region (R 1 ) and the accumulator second region (R 2 ) are inclined downwardly inward. 
     
     
         4 . The fuel cell system ( 100 ;  400 ) of  claim 1  wherein the accumulator first region (R 1 ) and the accumulator second region (R 2 ) each having respective volumes, the volume of the accumulator first region being greater than the volume of the accumulator second region. 
     
     
         5 . The fuel cell system ( 100 ) of  claim 1  wherein said drain in said accumulator second region (R 2 ) includes a valve ( 121 ;  234 ;  320 ) that is operative to permit selective drainage of the accumulator. 
     
     
         6 . The fuel cell system ( 100 ) of  claim 5  wherein said valve of said drain is automatically controlled by a controller ( 119 ). 
     
     
         7 . The fuel cell system ( 100 ;  400 ) of  claim 1  wherein a water conduit ( 126 ;  450 ,  450 A) is operatively connected from at least the accumulator second region (R 2 ) to the at least one fuel cell to return water to the at least one fuel cell. 
     
     
         8 . The fuel cell system ( 100 ;  400 ) of  claim 1  further including a condenser ( 104 ;  404 ) and a variable speed condenser fan ( 117 ;  417 ), said condenser fan being operative at a maximum fan speed responsive to a start-up condition of the at least one fuel cell. 
     
     
         9 . The fuel cell system ( 100 ;  400 ) of  claim 1  wherein the at least one fuel cell comprises a stack ( 102 ;  402 ) of multiple Proton Exchange Membrane fuel cells. 
     
     
         10 . The fuel cell system ( 400 ) of  claim 1  wherein the accumulator second region (R 2 ′) is positioned above the accumulator first region (R 1 ′), the accumulator first region (R 1 ′) and the accumulator second region (R 2 ′) each having respective vertical extents and sidewalls that define respective cross-sectional areas along the respective vertical extents, and wherein the cross-sectional areas of the accumulator second region are less than those of the accumulator first region. 
     
     
         11 . The fuel cell system ( 100 ) of  claim 10  wherein water from the at least one fuel cell ( 402 ) is directed to the accumulator ( 406 ), and the accumulator includes structure ( 430 ) to direct most of said water from said at least one fuel cell to said accumulator second region (R 2 ) prior to said accumulator first region (R 1 ′). 
     
     
         12 . The fuel cell system ( 100 ) of  claim 11  wherein said drain in said accumulator second region (R 2 ′) comprises a passive device ( 440 ) allowing a continuous restricted flow there through to said accumulator first region (R 1 ′). 
     
     
         13 . The fuel cell system ( 100 ) of  claim 12  wherein said passive device comprising said drain comprises a porous plug ( 440 ). 
     
     
         14 . The fuel cell system ( 100 ) of  claim 12  wherein the structure of said accumulator second region (R 2 ′) further includes an overflow arrangement configured to discharge water from the accumulator second region to the accumulator first region (R 1 ′) at a rate greater than said continuous restricted flow via said passive device ( 440 ) when water in said accumulator second region exceeds a predetermined level. 
     
     
         15 . The fuel cell system ( 100 ) of  claim 10  wherein water conduits ( 450 ,  450 A) extend from each of the accumulator first region (R 1 ′) and the accumulator second region (R 2 ′), and are each operative to return water to the at least one fuel cell. 
     
     
         16 . The fuel cell system ( 100 ) of  claim 10  wherein the at least one fuel cell comprises a stack ( 402 ) of multiple Proton Exchange Membrane fuel cells, and further including a condenser ( 404 ) and a variable speed condenser fan ( 417 ), said condenser fan being operative at a maximum fan speed responsive to a start-up condition of the fuel cell stack ( 402 ). 
     
     
         17 . A fuel cell system ( 100 ,  400 ) subject to operation under freezing conditions, comprising:
 an accumulator ( 106 ;  200 ;  300 ;  406 ) operative to receive water from a fuel cell ( 102 ,  402 ), the accumulator having structure ( 202 ,  204 ;  310 ,  312 ,  314 ,  316 ;  410 ) defining a first region (R 1 ; R 1 ′) having a first volume configured to contain a volume of water during steady state operation of the fuel cell and configured to fill with water vertically at a first rate for an arbitrary fill water flow rate, and structure ( 206 ,  204 ;  310 ,  312 ,  314 ,  316 ;  414 ) defining a second region (R 2 ; R 2 ′) having a second volume and configured to fill with water vertically at a second rate greater than said first rate for said same arbitrary fill water flow rate, said first volume of said first region (R 1 ; R 1 ′) being greater than said second volume of said second region (R 2 ; R 2 ′), and the accumulator including a drain ( 121 ;  234 ;  320 ;  440 ) in the second region, said drain being configured and operative to allow water to drain substantially entirely from at least said second region following shutdown of the at least one fuel cell, thereby to prevent water from freezing in at least said second region.   
     
     
         18 . A method of operating a fuel cell system at shutdown under freezing conditions, the fuel cell system having a fuel cell stack, and an accumulator for receiving water from and supplying water to the fuel cell stack, comprising the step of:
 draining water from at least a region of the of the accumulator at shutdown to allow the region to be nominally water and ice-free during shutdown, whereby said region of the accumulator may receive water from and supply water to the fuel cell stack nominally upon start up.   
     
     
         19 . The method of  claim 18  including the step of providing the accumulator with at least two regions, one of the at least two regions filling with water vertically more rapidly than an other of the at least two regions for the same arbitrary fill flow rate, and wherein the step of draining at least a region of the accumulator comprises draining at least said one more-rapidly filling region. 
     
     
         20 . The method of  claim 19  wherein said one more-rapidly filling region is positioned relatively above the other of the at least two regions, and the step of draining the more-rapidly filling region is continuous via a passive drain discharging into at least the other of the at least two regions.