POST THERMAL CONTROL DEVICE FOR USE WITH A NOx SLIP CATALYST

Abstract

A system and method for treating diesel exhaust in a diesel exhaust system, and specifically for improved NO x conversion efficiency during particulate filter regeneration, is disclosed. The exhaust gas treatment system includes a diesel oxidation catalyst (DOC); a diesel particulate filter (DPF) fluidly coupled to the DOC; a mixer fluidly coupled to the DOC and DPF, a thermal control device (TCD) positioned after the DPF, a NO x slip catalyst (NSC), at least one temperature sensor (TS), wherein the thermal control device reduces the temperature of the exhaust gas stream. The thermal control device used in conjunction with the NO x slip catalyst provides for improved overall exhaust system NO x conversion efficiency during active DPF regeneration.

What is claimed is: 
     
         1 . A method for reducing NO x  in an exhaust gas stream of a diesel-engine vehicle, the method comprising the steps of:
 fluidly coupling components of an exhaust gas treatment system package to an engine exhaust gas system;   flowing a heated exhaust stream through the exhaust gas treatment system package;   injecting gaseous ammonia into the exhaust gas treatment system package;   reducing an outgoing temperature of engine exhaust gas after the exhaust passes through the system package; and, reducing the NO x  to an acceptable level.   
     
     
         2 . The method of  claim 1 , wherein the components of the exhaust gas treatment system package comprise a mixing chamber for reacting the gaseous ammonia with the exhaust gas stream to reduce NO x  in the exhaust gas. 
     
     
         3 . The method of  claim 2 , wherein the components of the exhaust gas treatment system package further comprise:
 a diesel oxidation catalyst (DOC);   a diesel particulate filter (DPF);   a thermal control device (TCD);   a NO x  slip catalyst (NSC); and, at least one temperature sensor (TS);   wherein the DOC, DPF, TCD, TS and NSC are all fluidly coupled together and to the mixing chamber, and wherein the TCD operates in conjunction with the NSC to effectively reduce the amount of NO x  in the exhaust stream.   
     
     
         4 . The method of  claim 3 , wherein the thermal control device is positioned before the NSC. 
     
     
         5 . The method of  claim 3 , wherein at least one of the temperature sensors is positioned after the thermal control device and before the NSC. 
     
     
         6 . The method of  claim 3 , wherein at least one of the temperature sensors is positioned before the thermal control device. 
     
     
         7 . The method of  claim 1 , wherein the step of reducing an outgoing temperature of engine exhaust gas prior to entry into a NO x  slip catalyst (NSC) includes installation of a thermal control device (TCD) before the NSC. 
     
     
         8 . The method of  claim 7 , wherein the step of reducing an outgoing temperature of engine exhaust gas prior to entry into a NO x  slip catalyst (NSC) includes installation of a thermal control device (TCD) after the DPF. 
     
     
         9 . An exhaust gas treatment system for use in reducing NO x  in an exhaust gas stream of a diesel-engine vehicle, the system comprising:
 a diesel oxidation catalyst (DOC);   a mixer fluidly coupled to the DOC;   a diesel particulate filter (DPF) fluidly coupled to the mixer and DOC;   a thermal control device (TCD) positioned after the DPF;   a NO x  slip catalyst (NSC) positioned downstream from the DPF; and,   at least one temperature sensor (TS) positioned in conjunction with one of the TCD and NSC, wherein the TCD operates in conjunction with the at least one temperature sensor to reduce the temperature of the exhaust gas stream prior to entry into the NSC.   
     
     
         10 . The exhaust gas treatment system of  claim 9 , wherein the temperature sensor is positioned after the NSC. 
     
     
         11 . The exhaust gas treatment system of  claim 9 , wherein a first temperature sensor is positioned before the NSC, and a second temperature sensor is located after the NSC. 
     
     
         12 . The exhaust gas treatment system of  claim 9 , wherein the thermal control device is an exhaust temperature reducing device. 
     
     
         13 . The exhaust gas treatment system of  claim 9 , wherein the temperature sensor interacts with the thermal control device to reduce exhaust temperatures to a desired level. 
     
     
         14 . A method for reducing NO x  in an exhaust gas stream in a diesel-engine vehicle after particulate filter regeneration, the method comprising:
 fluidly coupling components of an exhaust gas treatment system package to an engine exhaust gas system;   applying superheated exhaust gas into the exhaust gas treatment system package for filter regeneration;   injecting gaseous ammonia into the exhaust gas treatment system package for NO x  reduction;   incorporating a NO x  slip catalyst (NSC) into the exhaust gas treatment system;   reducing the temperature of the exhaust gas prior to entry into the NSC; and,   further reducing the level of NO x  to an acceptable level.   
     
     
         15 . The method of  claim 14 , wherein the components of the exhaust gas treatment system package further comprise:
 a diesel oxidation catalyst (DOC);   a diesel particulate filter (DPF);   a thermal control device (TCD); and,   at least one temperature sensor (TS);   wherein the DOC, DPF, TCD, TS and NSC are all fluidly coupled together and to the mixing chamber, and wherein the TCD operates to reduce the temperature of the superheated exhaust gas.   
     
     
         16 . The method of  claim 15 , wherein the TCD operates in conjunction with the NSC to effectively reduce the amount of NO x  in the exhaust stream.