LNT-SCR packaging

Abstract

A power generation system comprises a diesel engine and a fuel reformer configured to receive the engine exhaust. Two or more separate LNT bricks are configured in a parallel valveless arrangement wherein each simultaneously receives a separate portion of the exhaust leaving the fuel reformer. The LNTs are each adapted and configured to simultaneously store NO x when the exhaust from the fuel reformer is lean and to simultaneously reduce stored NO x and regenerate when the exhaust from the fuel reformer contains reformate. This parallel multi-brick arrangement reduces the effective length to width ratio of the LNTs as a group without the packaging difficulties associated with a single LNT having an equivalently reduced length to width ratio. Axial temperature gradients that develop in the LNTs during desulfation are thereby mitigated.

1 . A power generation system, comprising: 
 a diesel engine operative to produce an exhaust containing NO x      a fuel reformer configured to receive the exhaust and operative to produce reformate when the fuel reformer is sufficiently warm, the exhaust is rich, and the exhaust contains diesel fuel;    two or more separate LNT bricks configured in a parallel valveless;    arrangement wherein each simultaneously receives a separate portion of the exhaust leaving the fuel reformer, the LNTs each being adapted and configured to simultaneously store NO x  when the exhaust from the fuel reformer is lean and to simultaneously reduce stored NO x  and regenerate when the exhaust from the fuel reformer is rich and contains reformate.    
   
   
       2 . The power generation system of  claim 1 , wherein the two or more separate LNT bricks comprise at least three separate LNT bricks.  
   
   
       3 . The power generation system of  claim 1 , wherein each LNT brick is a monolith from about 7 cm to about 15 cm in length.  
   
   
       4 . The power generation system of  claim 1 , wherein: 
 an equivalent diameter to equivalent length ratio of the two or more separate LNT bricks is at least about two;    the equivalent diameter is obtained by dividing the total frontal area of the two or more separate LNT bricks by pi, taking the square root, and multiplying by two; and    the equivalent length is obtained by dividing the total volume of the two or more separate LNT bricks by the total frontal area of the two or more separate LNT bricks.    
   
   
       5 . The power generation system of  claim 4 , wherein the equivalent diameter to equivalent length ratio of the two or more separate LNT bricks is at least about three.  
   
   
       6 . The power generation system of  claim 4 , wherein the equivalent diameter to equivalent length ratio of the two or more separate LNT bricks is at least about four.  
   
   
       7 . A method of operating a power generation system, comprising: 
 operating a diesel engine to produce an exhaust containing NO x  and SO x ;    channeling the exhaust through a plurality of LNTs that adsorb and store a first portion of NO x  and a portion of the SO x  from the exhaust;    passing the exhaust from the plurality of LNTs through one or more SCR catalysts that reduce a second portion of NO x  in the exhaust by reaction with ammonia under lean conditions;    generating a first control signal to denitrate a first one or more of the LNTs;    in response to the control signal, supplying rich exhaust to the first one or more of the LNTs, whereby adsorbed NO x  in the first one or more LNTs is reduced producing ammonia-containing exhaust;    passing the ammonia containing exhaust through one or more of the SCR catalysts, whereby the one or more ammonia-SCR catalysts adsorb and store ammonia;    generating a second control signal to desulfate one or more of the LNTs; and    in response to the second control signal, desulfating a second one or more LNTs by heating the second one or more LNTs and making the exhaust supplying the second one or more LNTs rich such that over the course of the desulfation, the temperatures in the second one or more LNTs increase in the direction of the exhaust flow;    wherein the LNTs each comprise a separate brick and each LNT simultaneously receives a separate portion of the exhaust.    
   
   
       8 . The method of  claim 7 , wherein the exhaust is divided among the plurality of LNTs by static structures that do not move in response to either control signal.  
   
   
       9 . The method of  claim 7 , wherein the temperatures of the second one or more LNTs increase in the direction of flow during desulfation due to reactions involving residual oxygen carried by the exhaust during desulfation.  
   
   
       10 . The method of  claim 7 , wherein the temperatures of the second one or more LNTs increases in the direction of flow during desulfation by reactions between reductants and oxygen stored in the LNTs.  
   
   
       11 . The method of  claim 7 , wherein supplying rich exhaust to the first one or more of the LNTs comprises injecting hydrocarbons into the exhaust and passing the exhaust through a fuel reformer.  
   
   
       12 . The method of  claim 11 , further comprising heating the fuel reformer in response to the first control signal in preparation for supplying rich exhaust to the first one or more of the LNTs and wherein the fuel reformer comprises an effective amount of a steam reforming catalyst.  
   
   
       13 . The method of  claim 7 , wherein the first one or more LNTs and the second one or more LNTs each comprise all the LNTs.  
   
   
       14 . The method of  claim 13 , wherein a single fuel reformer is configured to supply rich exhaust to all the LNTs.  
   
   
       15 . The method of  claim 14 , wherein the fuel reformer is configured to receive all the exhaust from the diesel engine and the fuel reformer produces reformate by steam reforming reactions.  
   
   
       16 . The method of  claim 7 , wherein there are three or more LNTs each comprising a monolith brick from about 7 cm to about 15 cm in length.  
   
   
       17 . The method of  claim 7 , wherein the plurality of LNTs collectively have an equivalent diameter to equivalent length ratio of at least about three; 
 the equivalent diameter is obtained by dividing the total frontal area of the two or more separate LNT bricks by pi, taking the square root, and multiplying by two; and    the equivalent length is obtained by dividing the total volume of the two or more separate LNT bricks by the total frontal area of the two or more separate LNT bricks.    
   
   
       18 . The method of  claim 7 , wherein the equivalent diameter to equivalent length ratio of the two or more separate LNT bricks is at least about four.