Treatment of nox sorber regeneration gas

Abstract

A method of treating an exhaust gas of a lean-burn reciprocating engine includes sorbing NO x on at least one NO x sorber when the exhaust gas is lean, intermittently contacting the at least one NO x sorber with an agent effective to convert NO x to N 2 , thereby to regenerate the at least one NO x sorber and feeding effluent of said intermittent contacting step to the engine inlet.

1 . A method of treating an exhaust gas of a lean-burn reciprocating engine containing NO x , which method comprising sorbing NO x  on at least one NO x  sorber when the exhaust gas is lean, intermittently contacting the at least one NO x  sorber with an agent effective to convert NO x  to N 2  thereby to regenerate the at least one NO x  sorber and feeding effluent from said intermittent contacting step to an engine inlet.  
     
     
         2 . A method according to  claim 1 , wherein the sorbing step comprises simultaneously contacting the lean exhaust gas with at least two NO x  sorbers arranged in parallel, and wherein the intermittently contacting step comprises intermittently contacting fewer than all of the at least two NO x  sorbers simultaneously with said agent.  
     
     
         3 . A method according to  claim 1 , wherein an exhaust gas flow through the at least one NO x  sorber being regenerated during the intermittently contacting step is less than in a NO x  sorber not being regenerated, wherein substantially all of the effluent from the at least one NO x  sorber being regenerated by said intermittent contacting step is fed to the engine inlet.  
     
     
         4 . A method according to  claim 1 , wherein the agent is a non-selective reductant.  
     
     
         5 . A method according to  claim 4 , wherein the non-selective reductant is engine fuel.  
     
     
         6 . A method according to  claim 1 , wherein the agent is a nitrogen hydride.  
     
     
         7 . A method according to  claim 1 , further comprising of catalytically oxidizing HC and CO to steam (H 2 O (g) ), CO 2  and/or NO to NO 2  upstream of the at least one NO x  sorber.  
     
     
         8 . A method according to  claim 7 , further comprising collecting particulate matter (PM) between the step of NO oxidation and the step of NO x  sorption.  
     
     
         9 . A lean-burn reciprocating engine emitting exhaust gas containing NO x  and having a treatment system comprising at least one NO x  sorber for sorbing NO x  when the exhaust gas is lean, means for intermittently contacting the at least one NO x  sorber with an agent effective to convert NO x  to N 2  to regenerate the at least one NO x  sorber and means for feeding effluents from said intermittently contacting step to an engine inlet.  
     
     
         10 . An engine according to  claim 9 , further comprising exhaust gas recirculation (EGR) means for use in normal or occasional modes of operation.  
     
     
         11 . An engine according to  claim 9 , wherein the at least one NO x  sorber comprises at least two NO x  sorbers arranged in parallel, and further comprising a means for selectively contacting fewer than all of the at least two NO x  sorbers with the agent.  
     
     
         12 . An engine according to  claim 11 , further comprising means for reducing an exhaust gas flow to one of the at least two NO x  sorbers when the one of the at least two NO x  sorbers is being regenerated relative to an exhaust gas flow to another NO x  sorber not being regenerated, and means for feeding to the engine inlet substantially all of an effluent from the one of the at least two NO x  sorbers being regenerated.  
     
     
         13 . An engine according to  claim 9 , wherein the at least one NO x  sorber is associated with injector means for introducing the agent to the exhaust gas at an inlet of the at least one NO x  sorber during regeneration.  
     
     
         14 . An engine according to  claim 9 , wherein the agent comprises a supply of agent.  
     
     
         15 . An engine according to  claim 14 , wherein the agent is a non-selective reductant.  
     
     
         16 . An engine according to  claim 14 , wherein the agent is engine fuel.  
     
     
         17 . An engine according to  claim 13 , further comprising a common-rail fuel injection system with a branch to the injector of the at least one NO x  sorber.  
     
     
         18 . An engine according to  claim 14 , wherein the agent is a nitrogen hydride.  
     
     
         19 . An engine according to  claim 9 , further comprising means for controlling the intermittent regeneration of the at least one NO x  sorber and a means for feeding the effluent from the at least one NO x  sorber being regenerated to the engine inlet, wherein the amount of regeneration agent released into the atmosphere is reduced relative to a similar engine lacking the means for feeding the effluent from the at least one NO x  sorber being regenerated to the engine inlet.  
     
     
         20 . An engine according to  claim 9 , wherein the system further comprises an oxidation catalyst disposed upstream of the at least one NO x  sorber for catalysing the oxidation of HC and CO to steam and CO 2  and/or NO to NO 2 .  
     
     
         21 . An engine according to  claim 20 , wherein the system further comprises a particulate matter (PM) filter located between the NO oxidation catalyst and the at least one NO x  sorber.  
     
     
         22 . A method according to  claim 4 , wherein the non-selective reductant is selected from the group consisting of hydrocarbon (HC), CO, and hydrogen.  
     
     
         23 . An engine according to  claim 10 , wherein the EGR means comprises a pump.  
     
     
         24 . A engine according to  claim 15 , wherein the non-selective reductant is selected from the group consisting of hydrocarbon (HC), CO, and hydrogen.