HC-SCR System for Lean Burn Engines

Abstract

Systems and methods for abating NOx emission in an exhaust stream are provided. Systems comprising hydrocarbon conversion over a partial oxidation catalyst in a slip stream and a hydrocarbon selective catalytic reduction catalyst are described. The emissions treatment system is advantageously used for the treatment of exhaust streams from lean burn engines including diesel engines, lean burn gasoline engines and locomotive engines.

1 . An emissions treatment system for NOx abatement in an exhaust stream from a lean burn engine, comprising:
 a main exhaust conduit in flow communication with the engine exhaust stream, and a hydrocarbon selective catalytic reduction catalyst (HC-SCR) in flow communication with the main exhaust conduit;   a slip exhaust stream conduit branched off of the main exhaust conduit connected to the main exhaust conduit by a first junction to divert a portion of the exhaust stream from the main exhaust conduit into the slip exhaust stream conduit to provide a slip exhaust stream to flow through a catalytic partial oxidation (CPO) catalyst in flow communication with the slip exhaust stream conduit, and second junction downstream from the first junction to reintroduce the slip exhaust stream to the main exhaust conduit upstream of the HC-SCR; and   a hydrocarbon injector upstream of the CPO, wherein the CPO is effective to convert a portion of the hydrocarbons to carbon monoxide and hydrogen.   
     
     
         2 . The emissions treatment system of  claim 1 , wherein the CPO is designed to provide sufficient hydrogen and adequate amount of hydrocarbons for the downstream HC-SCR catalyst. 
     
     
         3 . The emissions treatment system of  claim 1 , wherein the hydrocarbon injector device includes a metering device adapted to control the amount of hydrocarbon injected into the slip exhaust stream conduit. 
     
     
         4 . The emissions treatment system of  claim 1 , wherein the hydrocarbon is fuel. 
     
     
         5 . The emissions treatment system of  claim 1 , wherein the portion of the exhaust gas diverted into the slip exhaust stream conduit is up to about 10% of the total exhaust flow. 
     
     
         6 . The emissions treatment system of  claim 1 , further comprising a metering device at the first junction of the slip exhaust stream conduit to regulate the percentage of exhaust gas diverted to the slip exhaust stream conduit. 
     
     
         7 . The emissions treatment system of  claim 6 , wherein the percentage of exhaust gas diverted to the slip exhaust stream conduit is regulated up to about 10% of the total exhaust flow. 
     
     
         8 . The emissions treatment system of  claim 1 , wherein the CPO catalyst contains platinum group metals. 
     
     
         9 . The emissions treatment system of  claim 8 , where the platinum group metals of CPO catalyst are selected from of platinum, palladium, rhodium and mixtures thereof. 
     
     
         10 . The emissions treatment system of  claim 1 , wherein one or both of the CPO catalyst and the HC-SCR are disposed on a flow through monolith. 
     
     
         11 . The emissions treatment system of  claim 1 , further comprising a diesel particulate filter (DPF) downstream of the HC-SCR catalyst. 
     
     
         12 . The emissions treatment system of  claim 1 , further comprising a diesel particulate filter (DPF) upstream of the HC-SCR catalyst. 
     
     
         13 . The emissions treatment system of  claim 12 , wherein the diesel particulate filter (DPF) is located between the first junction and the second junction in flow communication of the main exhaust conduit. 
     
     
         14 . The emissions treatment system of  claim 11 , further comprising a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. 
     
     
         15 . The emissions treatment system of  claim 12 , further comprising a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. 
     
     
         16 . The emissions treatment system of  claim 13 , further comprising a diesel oxidation catalyst (DOC) upstream of the DPF and HC-SCR catalyst. 
     
     
         17 . The emissions treatment system of  claim 14 , wherein the diesel oxidation catalyst (DOC) is located downstream of the first junction in flow communication with the main exhaust conduit. 
     
     
         18 . The emissions treatment system of  claim 15 , wherein the diesel oxidation catalyst (DOC) is located downstream of the first junction in flow communication with the main exhaust conduit. 
     
     
         19 . The emissions treatment system of  claim 16 , wherein the diesel oxidation catalyst (DOC) is located downstream of the first junction in flow communication with the main exhaust conduit. 
     
     
         20 . The emissions treatment system of  claim 13 , wherein the diesel oxidation catalyst (DOC) is located downstream of the first junction and upstream of the DPF and in flow communication with the main exhaust conduit. 
     
     
         21 . The emissions treatment system of  claim 20 , wherein the DOC and DPF are integrated into a single component. 
     
     
         22 . The emissions treatment system of  claim 1 , further comprising a NH3-SCR catalyst downstream of the HC-SCR catalyst. 
     
     
         23 . The emissions treatment system of  claim 1 , further comprising an oxidation catalyst downstream of the HC-SCR catalyst. 
     
     
         24 . A method of treating an exhaust stream comprising:
 passing the exhaust stream through a main exhaust conduit and a portion of the exhaust stream through a slip exhaust stream conduit, the main exhaust conduit comprising a hydrocarbon selective catalytic reduction catalyst (HC-SCR), the slip exhaust stream conduit comprising a catalytic partial oxidation (CPO) catalyst, the slip exhaust stream conduit branching-off of the main exhaust conduit at a first junction and in flow communication with the CPO, the slip exhaust stream conduit rejoining the main exhaust conduit at a second junction upstream of the HC-SCR, a hydrocarbon injector upstream of the CPO, where the CPO is adapted to convert a portion of the hydrocarbons to carbon monoxide and hydrogen.