Sulfur control for fuel processing system for fuel cell power plant

Abstract

A fuel cell power plant ( 110 ) has a fuel cell stack assembly (CSA) ( 16 ) including an anode ( 18 ), and a fuel processing system (FPS) ( 120 ) providing a hydrogen-rich reformate/fuel stream ( 34, 134, 62 ) for the anode ( 18 ) of the CSA ( 16 ). A relatively active metal catalyst is associated with one or both of the anode ( 18 ) and the FPS ( 120 ), and is subject to degradation by the presence of even low levels, e.g. 100 ppb to 5 ppb-wt. reformate, of sulfur in the fuel stream. A guard bed ( 70 ) containing a guard material ( 72 ) is provided in the FPS ( 120 ) for protecting the relatively active metal catalysts by adsorbing, and further reducing the level of, sulfur in the fuel stream. The guard material ( 72 ) is a metal or metal oxide capable of forming a stable sulfide in the presence of low levels of H 2 S in the fuel stream ( 34 ), and is preferably selected from the group consisting of: ZnO, CuO on CeO 2 -based support, NiO on CeO 2 -based support, and Cu/ZnO. Provision is also made ( 80, 74, 75, 76, 78, 82 ) for regenerating the guard material ( 72 ) in situ.

What is claimed is:  
     
         1 . In a fuel cell power plant ( 110 ) having a fuel cell stack assembly (CSA)( 16 ), including an anode ( 18 ), and a fuel processing system (FPS) ( 120 ) for converting a hydrocarbon feedstock fuel ( 22 ) to a hydrogen-rich fuel stream ( 34 ,  134 ,  62 ) for the anode ( 18 ) of the CSA ( 16 ), the FPS ( 120 ) including at least a shift reactor ( 150 ,  152 ,  154 ) having a shift catalyst for converting CO in the fuel stream ( 34 ,  134 ) to CO 2  and increasing the yield of H 2 , the improvement comprising: 
 a) the shift catalyst comprising a relatively active metal; and    b) the FPS ( 120 ) including a guard bed ( 70 ) to protect at least the relatively active metal shift catalyst of the shift reactor ( 150 ,  152 ,  154 ), the guard bed ( 70 ) being positioned upstream of the relatively active metal catalyst of the shift reactor ( 150 ,  152 ,  154 ) and comprising a guard material ( 72 ) for at least adsorbing sulfur from the fuel stream ( 34 ).    
     
     
         2 . The fuel cell power plant ( 110 ) of  claim 1  wherein the guard material ( 72 ) is a metal or metal oxide capable of forming a stable sulfide in the presence of low levels of H 2 S in the fuel stream ( 34 ).  
     
     
         3 . The fuel cell power plant ( 110 ) of  claim 2  wherein the guard material ( 72 ) is selected from the group consisting of: ZnO, CuO, NiO, Cu/ZnO, Ce oxides, metal-doped Ce oxides, Mn oxide, Mg oxide, Mo oxide, Zr oxide, Co oxide, Fe oxide, Sn oxide and Zn/Ti oxide, either alone or in combination with a CeO 2 -based support.  
     
     
         4 . The fuel cell power plant ( 110 ) of  claim 3  wherein the guard material is selected from the group consisting of: ZnO, CuO on CeO 2 -based support, NiO on CeO 2 -based support, and Cu/ZnO.  
     
     
         5 . The fuel cell power plant ( 110 ) of  claim 2  wherein the relatively active metal of the shift catalyst comprises a noble metal, and the guard material ( 72 ) is other than a noble metal.  
     
     
         6 . The fuel cell power plant ( 110 ) of  claim 1  wherein the FPS ( 120 ) includes a desulfurizer ( 26 ) upstream of the guard bed ( 70 ), the desulfurizer ( 26 ) being capable of removing high levels of sulfur from the hydrocarbon feedstock ( 22 ).  
     
     
         7 . The fuel cell power plant ( 110 ) of  claim 6  wherein the FPS ( 120 ) includes a reformer ( 30 ) upstream of the guard bed ( 70 ) for reforming the hydrocarbon feedstock ( 22 ) to a reformate ( 34 ) comprising a H 2 -rich fuel stream.  
     
     
         8 . The fuel cell power plant ( 110 ) of  claim 1  further including means ( 80 ,  74 ,  75 ,  76 ,  78 ,  82 ) operatively connected to the guard bed ( 70 ) for regenerating the guard material ( 72 ) in situ.  
     
     
         9 . The fuel cell power plant ( 110 ) of  claim 8  wherein the means ( 80 ,  74 ,  75 ,  76 ,  78 ,  82 ) for regenerating the guard material ( 72 ) comprises first means ( 80 ,  74 ,  75 ) for selectively admitting an O 2 -containing fluid to the guard bed ( 70 ) to oxidize the adsorbed sulfur as SO 2  and second means ( 76 ,  78 ,  82 ) for discharging the SO 2  from the guard bed ( 70 ).  
     
     
         10 . The fuel cell power plant ( 110 ) of  claim 1  wherein the shift reactor ( 150 ,  152 ,  154 ) comprises a high temperature shift reactor ( 152 ) and a low temperature shift reactor ( 154 ) relatively downstream of the high temperature shift reactor ( 152 ), each of said high temperature and said low temperature shift reactors ( 152 ,  154 ) having a relatively active metal shift catalyst, and the guard bed ( 70 ) being upstream of the high temperature shift reactor ( 152 ).  
     
     
         11 . In a fuel cell power plant ( 110 ) having a fuel cell stack assembly (CSA) ( 16 ) including an anode ( 18 ), and a fuel processing system (FPS) ( 120 ) providing a hydrogen-rich fuel stream ( 34 ,  134 ,  62 ) for the anode ( 18 ) of the CSA ( 16 ), and a relatively active metal catalyst in at least one of the anode ( 18 ) and the FPS ( 120 ), the improvement comprising: 
 the FPS ( 120 ) including a guard bed ( 70 ) for said relatively active metal catalyst, the guard bed ( 70 ) being positioned upstream of said relatively active metal catalyst and comprising a guard material ( 72 ) for at least adsorbing sulfur from the fuel stream ( 34 ).    
     
     
         12 . The fuel cell power plant ( 110 ) of  claim 11  wherein the guard material ( 72 ) is a metal or metal oxide capable of forming a stable sulfide in the presence of low levels of H 2 S in the fuel stream ( 34 ).  
     
     
         13 . The fuel cell power plant ( 110 ) of  claim 12  wherein the fuel processing system (FPS) ( 120 ) includes a reformer ( 30 ) to provide a reformate as the hydrogen-rich fuel stream ( 34 ) and the level of sulfur in the reformate stream ( 34 ) just prior to the guard bed ( 70 ) is in the range of 100 ppb to 5 ppb-wt. reformate  
     
     
         14 . The fuel cell power plant ( 110 ) of  claim 11  wherein the relatively active metal of the shift catalyst comprises a noble metal, and the guard material ( 72 ) is other than a noble metal.  
     
     
         15 . The fuel cell power plant ( 110 ) of  claim 13  wherein the relatively active metal of the shift catalyst comprises a noble metal, and the guard material ( 72 ) is other than a noble metal.