Rotary NOx trap

Abstract

One aspect of the invention relates to a NOx trapping device for a vehicle exhaust system having a plurality of NOx adsorbers. The device has a mobile framework configured to hold the NOx adsorbers and move them in sequence through a plurality of positions. A manifold channels exhaust to one or more of the NOx adsorber positions. The mobile framework is adapted to move the NOx adsorbers in and out of position to receive the exhaust. The adsorbers can be regenerated while they are not receiving any exhaust. The invention facilitates the use of multiple NOx adsorbers in an exhaust system, particularly the use of more than two adsorbers. The invention avoids complex exhaust valving, which is normally associated with multiple adsorber systems. In one embodiment, treated exhaust and exhaust from an adsorber undergoing regeneration are combined and supplied to an SCR reactor or an oxidation catalyst.

1 . An NOx trapping device for a vehicle exhaust system, comprising: 
 a plurality of NOx adsorbers;    a mobile framework configured to hold the NOx adsorbers and move them in sequence through a plurality of positions; and    a manifold adapted to couple a vehicle exhaust stream to the NOx adsorbers in a subset of the positions;    wherein a subset is at least one, but less than all;    whereby the mobile framework is adapted to move the NOx adsorbers in and out of position to receive a main exhaust flow and at any given time less than all of the NOx adsorbers are configured to receive the main exhaust flow.    
   
   
       2 . The NOx trapping device of  claim 1 , wherein the mobile framework holds the plurality of NOx adsorbers in a radial array and the mobile framework moves the NOx adsorbers by rotating the array.  
   
   
       3 . The NOx trapping device of  claim 1 , wherein the manifold is configured to channel the main exhaust flow to at least two of the NOx adsorbers at a time.  
   
   
       4 . The NOx trapping device of  claim 1 , further comprising: 
 a coupling for receiving a reducing agent;    wherein the device is configured to alternately place each of the NOx adsorbers into position to receive the reducing agent.    
   
   
       5 . The NOx trapping device of  claim 4 , further comprising: 
 a conduit configured to receive output flow from the NOx adsorbers while they are in position to receive the main exhaust flow; and    a conduit configured to receive output flow from the NOx adsorbers as they receive the reducing agent;    wherein, the two conduits join to combine the two output flows.    
   
   
       6 . The NOx trapping device of  claim 5 , further comprising an SCR reactor configured to receive the combined output flows.  
   
   
       7 . The NOx trapping device of  claim 5 , further comprising an oxidation catalyst configured to receive the combined output flows.  
   
   
       8 . The NOx trapping device of  claim 4 , further comprising: 
 a reducing catalyst bed configured to receive output from the NOx adsorbers while they are in position to receive the reducing agent;    wherein the device is adapted to reduce NOx by reaction with the reducing agent primarily in the reducing catalyst bed.    
   
   
       9 . The NOx trapping device of  claim 1 , wherein each of the NOx adsorbers comprises a molecular sieve adsorbant.  
   
   
       10 . The NOx trapping device of  claim 1 , wherein each of the NOx adsorbers comprises a precious metal catalyst.  
   
   
       11 . The NOx trapping device of  claim 1 , wherein the device comprises three or more NOx adsorbers.  
   
   
       12 . The NOx trapping device of  claim 1 , further comprising a housing that contains all the NOx adsorbers and that channels exhaust escaping from the manifold to join with treated exhaust from the NOx adsorbers.  
   
   
       13 . The NOx trapping device of  claim 1 , wherein the device is adapted to heat the NOx adsorbers in a second subset of the positions distinct from the subset of the positions in which the NOx adsorbers couple to the vehicle exhaust stream.  
   
   
       14 . The NOx trapping device of  claim 1 , wherein the device is adapted to cool the NOx adsorbers in a second subset of the positions distinct from the subset of the positions in which the NOx adsorbers couple to the vehicle exhaust stream.  
   
   
       15 . A vehicle comprising the NOx trapping device of  claim 1 .  
   
   
       16 . A method of trapping NOx in a vehicle exhaust system, comprising: 
 providing a plurality of NOx adsorbers; and    providing an indexing system that moves the NOx adsorbers whereby each of the NOx adsorbers alternates through a set of positions and in one or more of the positions the NOx adsorbers receive an exhaust flow and in one or more others of the positions the NOx adsorbers do not receive the exhaust flow.    
   
   
       17 . The method of  claim 16 , wherein moving the NOx adsorbers comprises rotating a radial array of the adsorbers.  
   
   
       18 . The method of  claim 16 , further comprising: 
 regenerating the adsorbers;    wherein the indexing system moves the NOx adsorbers into one or more positions where the NOx adsorbers are regenerated.    
   
   
       19 . The method of  claim 18 , wherein regenerating the adsorbers comprises heating the adsorbers.  
   
   
       20 . The method of  claim 19 , wherein the NOx adsorbers are heated in positions other than the positions in which they receive the exhaust flow.  
   
   
       21 . The method of  claim 16 , wherein regenerating the adsorbers comprises providing the adsorbers with a reducing atmosphere.  
   
   
       22 . The method of  claim 21 , wherein the desorbed NOx is reduced primarily in a catalyst bed shared by a plurality of the NOx adsorbers.  
   
   
       23 . The method of  claim 16 , wherein each of the NOx adsorbers comprises a molecular sieve adsorbant.  
   
   
       24 . The method of  claim 16 , wherein each of the NOx adsorbers comprises a precious metal catalyst.  
   
   
       25 . The method of  claim 18 , further comprising combining exhaust from the adsorbers receiving the exhaust flow and exhaust from the adsorbers undergoing regeneration.  
   
   
       26 . The method of  claim 25 , further comprising treating the combined flows in an SCR reactor.  
   
   
       27 . The method of  claim 25 , further comprising treating the combined flows with an oxidation catalyst.  
   
   
       28 . The method of  claim 16 , wherein the plurality of NOx adsorbers comprises three or more NOx adsorbers.