Fuel cell system having two reformation reactors and method for operating same

Abstract

A fuel cell system includes a fuel cell unit and a gas-generating system containing at least one reforming unit for obtaining a hydrogen-rich reformate from a fuel. It is possible to supply the reformate at least partly to the anode side of the fuel cell unit. The system may include a first reforming reactor for producing a first reformate with a high outlet temperature; a second reforming reactor for producing a second reformate with a second outlet temperature which is below the first outlet temperature; a mixing element for mixing the first reformate with at least one fuel and located between an outlet of the first reforming reactor and an inlet of the second reforming reactor. The second reformate may be supplied to a gas-purification system and the purified reformate supplied to the fuel cell unit.

What is claimed is:  
     
         1 . A fuel cell system, comprising: 
 a fuel cell unit and a gas-generating system, said gas generating system comprising:    a first reforming reactor for producing a first reformate (R 1 ) with an outlet temperature (T 1, out );    a second reforming reactor for producing a second reformate (R 2 ) with a second outlet temperature (T 2, out ) that is below the first outlet temperature (T 1, out ); and    an device that supplies at least one fuel to the first reformate (R 1 ) between an outlet of the first reforming reactor and an inlet of the second reforming reactor.    
     
     
         2 . A fuel cell system according to  claim 1 , wherein the at least one fuel comprises methanol.  
     
     
         3 . A fuel cell system according to  claim 1 , wherein the device is a mixing element.  
     
     
         4 . A fuel cell system according to  claim 1 , further comprising a first heat exchanger upstream from the first reforming reactor.  
     
     
         5 . A fuel cell system according to  claim 1 , wherein the first reforming reactor is an auto-thermal reactor.  
     
     
         6 . A fuel cell system according to  claim 1 , wherein the second reforming reactor is an adiabatic reactor.  
     
     
         7 . A fuel cell system according to  claim 1 , further comprising a gas purification system that can be cooled with waste gas from at least one of an anode and a cathode of the fuel cell unit.  
     
     
         8 . A fuel cell system according to  claim 7 , wherein the gas purification system is a one-step system.  
     
     
         9 . A fuel cell system according to  claim 7 , wherein the gas purification system is a two-step system, comprising: 
 a first device in which the second reformate can be cooled with waste gas from the cathode; and    a second device in which the second reformate can be cooled with waste gas from the anode of the fuel cell unit.    
     
     
         10 . A fuel cell system according to  claim 1 , further comprising a gas purification system, an afterburner and a first heat exchanger located downstream from the afterburner, 
 wherein the gas purification system, the afterburner, and the first heat exchanger are disposed one after the other in the direction of waste gas flow from the fuel cell unit.    
     
     
         11 . A fuel cell system according to  claim 10 , further comprising an expander disposed between the afterburner and the first heat exchanger.  
     
     
         12 . A fuel cell system according to  claim 10 , further comprising an expander disposed in the waste gas downstream from the first heat exchanger.  
     
     
         13 . A fuel cell system according to  claim 11 , wherein the expander is coupled with a compressor in an air supply for the fuel cell unit.  
     
     
         14 . A fuel cell system according to  claim 1 , further comprising a reformate cooling unit disposed downstream from a gas purification system.  
     
     
         15 . A fuel cell system according to claim in  14 , wherein the reformate cooling unit can be cooled by a cooling medium of the fuel cell unit.  
     
     
         16 . A fuel cell system according to  claim 1 , wherein the first reforming reactor has a non-selective catalyst and the second reforming reactor has a selective catalyst.  
     
     
         17 . A method for operating a fuel cell system, comprising: 
 supplying at least one fuel with a first inlet temperature (T 1, in ) to a first reforming reactor;    carrying out an auto-thermal reforming reaction in the first reforming reactor, wherein the reaction proceeds in thermodynamic equilibrium, thereby forming a first reformate (R 1 ) with a first outlet temperature (T 1, out ) that is higher than the first inlet temperature (T 1, in );    mixing the first reformate with a fuel having a lower temperature than the first outlet temperature (T 1, out ), thereby forming a mixture having a second, lower inlet temperature (T 2, in ); and    supplying the mixture to a second reforming reactor in which, under adiabatic conditions, steam reforming and a hydrogen shift reaction take place, thereby producing a second reformate (R 2 ) with a second outlet temperature (T 2, out ) that is below the first outlet temperature (T 1, out ) of the first reformate (R 1 ).    
     
     
         18 . A method according to  claim 17 , wherein the at least one fuel comprises methanol.  
     
     
         19 . A method according to  claim 17 , wherein the fuel having a lower temperature than the first outlet temperature (T 1, out ) comprises methanol.  
     
     
         20 . A method according to  claim 17 , wherein the second outlet temperature (T 2, out ) of the second reformate (R 2 ) is equal to the first inlet temperature (T 1, in ).  
     
     
         21 . A method according to  claim 17 , wherein the second outlet temperature (T 2, out ) of the second reformate (R 2 ) is less than the first inlet temperature (T 1, in ).  
     
     
         22 . A method according to  claim 17 , wherein the first outlet temperature (T 1, out ) from the first reforming reactor ( 4 ) is between 600° C. and 900° C.  
     
     
         23 . A method according to  claim 17 , wherein the first inlet temperature (T 1, in ) in the first reforming reactor is between 200° C. and 300° C.  
     
     
         24 . A method according to  claim 17 , wherein the second outlet temperature (T 2, out ) of the second reforming reactor is between 150° C. and 250° C.  
     
     
         25 . A method according to  claim 17 , wherein the second inlet temperature (T 2, in ) in the second reforming reactor is between 200° C. and 400° C.