Exhaust gas treatment system with emission control during filter regeneration

Abstract

An exhaust gas treatment system for an engine includes an exhaust gas inlet tube configured to receive an exhaust gas from the engine. A particulate filter, a heat exchange system and first and second selective catalytic reduction (SCR) devices are in fluid communication with the exhaust gas inlet tube. The particulate filter is configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature. The controller is configured to control a temperature difference, between a present temperature of the second SCR device and a predefined optimal second SCR temperature, to be within a predefined threshold during the thermal regeneration of the particulate filter. The controller may be configured to direct an injector to inject a reductant into the first SCR device when the temperature difference is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.

1 . An exhaust gas treatment system for an engine producing an exhaust gas, the system comprising:
 an exhaust gas inlet tube configured to receive the exhaust gas;   a particulate filter in fluid communication with the exhaust gas inlet tube and configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature;   a heat exchange system in fluid communication with the exhaust gas inlet tube and positioned downstream of the particulate filter;   a first selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned upstream of the heat exchange system;   a second selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned downstream of the heat exchange system;   a first temperature sensor operatively connected to and configured to determine a present second SCR temperature (T S2 ) of the second SCR device;   a controller operatively connected to the first temperature sensor and configured to determine whether the thermal regeneration is taking place in the particulate filter; and   wherein the controller is configured to control a temperature difference (T S2 −T O ) between the present second SCR temperature (T S2 ) and a predefined optimal second SCR temperature (T O ) to be within a predefined threshold during the thermal regeneration of the particulate filter.   
     
     
         2 . The exhaust gas treatment system of  claim 1 , further comprising:
 an injector operatively connected to and configured to selectively inject a reductant into the first SCR device, the reductant being configured to travel to the second SCR device; and   wherein the controller is configured to direct the injector to inject the reductant when the temperature difference (T S2 −T O ) is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.   
     
     
         3 . The exhaust gas treatment system of  claim 1 , wherein the predefined optimal second SCR temperature (T O ) is between approximately 200 and 220° Celsius. 
     
     
         4 . The exhaust gas treatment system of  claim 1 , wherein the predefined optimal second SCR temperature (T O ) is approximately 220° Celsius and the predefined threshold is approximately 10° Celsius. 
     
     
         5 . The exhaust gas treatment system of  claim 1 , wherein the controller being configured to control the temperature difference (T S2 −T O ) to be within a predefined threshold includes:
 the controller being configured to direct the heat exchange system to transfer heat from the exhaust gas when the temperature difference (T S2 −T O ) is above the predefined threshold. 
 
     
     
         6 . The exhaust gas treatment system of  claim 1 , further comprising:
 first and second pressure sensors positioned upstream and downstream of the particulate filter, respectively, and configured to determine a differential pressure across the particulate filter; and   wherein the controller is configured to determine whether the thermal regeneration is taking place in the particulate filter by determining when the differential pressure across the particulate filter is above a predefined threshold pressure.   
     
     
         7 . The exhaust gas treatment system of  claim 1 , further comprising:
 a second temperature sensor operatively connected to and configured to determine a present filter temperature (T F ) of the particulate filter; and   wherein the controller is configured to determine whether the thermal regeneration is taking place in the particulate filter by determining whether the present filter temperature (T F ) of the particulate filter has elapsed a predefined amount of time at a predefined temperature.   
     
     
         8 . The exhaust gas treatment system of  claim 7 , wherein the predefined amount of time is 30 minutes and the predefined temperature is 550 Celsius. 
     
     
         9 . The exhaust gas treatment system of  claim 1 , wherein:
 the first SCR device includes a first catalyst;   the particulate filter includes a plurality of channels having respective walls; and   the first SCR device and the particulate filter are disposed in a common housing such that the first catalyst is coated on the respective walls of the plurality of channels of the particulate filter.   
     
     
         10 . The exhaust gas treatment system of  claim 1 , further comprising:
 first and second NOx sensors positioned upstream and downstream of the particulate filter, respectively; and   wherein the first and the second NOx sensors are configured to determine respective amounts of the NOx emission in the exhaust gas upstream and downstream of the particulate filter.   
     
     
         11 . The exhaust gas treatment system of  claim 1 , wherein the heat exchange system includes:
 an inlet portion configured to receive the exhaust gas from the particulate filter;   an outlet portion configured to transmit the exhaust gas to the second SCR device;   an interior cavity connecting the inlet and outlet portions and defining a central passageway and a bypass passageway;   a heat exchange device positioned within the bypass passageway and configured to transfer heat from the exhaust gas; and   a bypass valve selectively movable between a plurality of positions to selectively permit the exhaust gas entering the second SCR device to include a first portion from the central passageway and a second portion from the bypass passageway.   
     
     
         12 . The exhaust gas treatment system of  claim 11 , wherein the bypass valve is positioned such that the first portion is approximately 100% and the second portion is approximately 0% when the temperature difference (T S2 −T O ) is below the predefined threshold. 
     
     
         13 . The exhaust gas treatment system of  claim 11 , wherein the bypass valve is positioned such that the first portion is approximately 60% and the second portion is approximately 40% when the temperature difference (T S2 −T O ) is above the predefined threshold. 
     
     
         14 . The exhaust gas treatment system of  claim 11 , wherein the heat exchange device includes:
 a plurality of plates having respective spaces between the plurality of plates, the respective spaces defining a first flow path for the exhaust gas;   wherein the plurality of plates each define at least one respective slot, the at least one respective slot being aligned to fit at least one tube configured for flow of a coolant.   
     
     
         15 . The exhaust gas treatment system of  claim 8 , further comprising:
 a coolant circuit operatively connected to the heat exchange system; and   wherein the heat exchange device is configured to selectively transfer heat from the exhaust gas to the coolant circuit.   
     
     
         16 . A vehicle comprising:
 an engine;   an exhaust gas inlet tube in fluid communication with and configured to receive an exhaust gas from the engine;   a particulate filter in fluid communication with the exhaust gas inlet tube and configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature;   a heat exchange system in fluid communication with the exhaust gas inlet tube and positioned downstream of the particulate filter;   a first selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned upstream of the heat exchange system;   a second selective catalytic reduction (SCR) device in fluid communication with the exhaust gas inlet tube and positioned downstream of the heat exchange system;   an injector operatively connected to and configured to selectively inject a reductant into the first SCR device, the reductant being configured to travel to the second SCR device;   a first temperature sensor operatively connected to the second SCR device and configured to determine a present temperature of the second SCR device;   a controller operatively connected to the first temperature sensor and configured to determine whether the thermal regeneration is taking place in the particulate filter;   wherein the controller is configured to control a temperature difference (T S2 −T O ) between the present second SCR temperature (T S2 ) and a predefined optimal second SCR temperature (T O ) to be within a predefined threshold during the thermal regeneration of the particulate filter; and   wherein the controller is configured to direct the injector to inject the reductant when the temperature difference is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.   
     
     
         17 . A method for controlling operation of an exhaust gas treatment system in an engine producing exhaust gas, the method comprising:
 operatively connecting an exhaust gas inlet tube to the engine for receiving the exhaust gas;   operatively connecting a particulate filter and heat exchange system for fluid communication with the exhaust gas inlet tube, the particulate filter being configured to undergo thermal regeneration when the exhaust gas in the particulate filter is heated above a regeneration temperature;   operatively connecting first and second selective catalytic reduction (SCR) devices for fluid communication with the exhaust gas inlet tube, the first and second SCR devices being positioned upstream and downstream of the heat exchange system, respectively;   operatively connecting an injector to the first SCR device for selective injection of a reductant into the first SCR device;   detecting when the thermal regeneration is taking place in the particulate filter;   controlling the temperature difference between the present SCR temperature and a predefined optimal SCR temperature to be within a predefined threshold during the thermal regeneration of the particulate filter; and   directing the injector to inject the reductant when the temperature difference is below the predefined threshold, thereby controlling a NOx emission in the exhaust gas.   
     
     
         18 . The method of  claim 17 , wherein controlling the temperature difference to be within a predefined threshold during the thermal regeneration of the particulate filter includes:
 determining a present second SCR temperature of the second SCR device based on a first temperature sensor operatively connected to the second SCR device;   determining whether the temperature difference between the present SCR temperature and a predefined optimal SCR temperature is above or below the predefined threshold when the thermal regeneration is taking place in the particulate filter; and   directing the heat exchange system to transfer heat from the exhaust gas when the temperature difference is above the predefined threshold.   
     
     
         19 . The method of  claim 16 , further comprising:
 positioning first and second pressure sensors upstream and downstream of the particulate filter, respectively, for determining a differential pressure across the particulate filter; and   wherein said detecting when the thermal regeneration is taking place in the particulate filter includes determining when the differential pressure is above a predefined threshold pressure.