Method and device for treating the exhaust gas of an internal combustion engine

Abstract

A device for treating exhaust gas of an internal combustion engine includes a reducing agent solution evaporator, a hydrolysis catalytic converter connected thereto for hydrolysis of urea to form ammonia and an SCR catalytic converter for selective catalytic reduction of nitrogen oxides. The evaporator includes an evaporator unit providing a gaseous substance mixture including at least one reducing agent precursor and/or reducing agent. The evaporator unit evaporates an aqueous solution including at least one reducing agent precursor. The SCR catalytic converter is in an exhaust line, and the evaporator and the hydrolysis catalytic converter are outside of and can be connected to the exhaust line. A sufficiently large quantity of reducing agent for selective catalytic reduction of nitrogen oxides in the SCR catalytic converter can be provided, while permitting a smaller volume of the hydrolysis catalytic converter than in the prior art, since it is not traversed by exhaust gas.

1 . A device for treating exhaust gas of an internal combustion engine passing through an exhaust line, the device comprising:
 a reducing agent solution evaporator disposed outside the exhaust line and to be connected to the exhaust line, said reducing agent solution evaporator including an evaporator unit configured for evaporating an aqueous solution including at least one reducing agent precursor and for providing a gaseous substance mixture including at least one of the following substances:   a) at least one reducing agent precursor, or   b) a reducing agent;   a hydrolysis catalytic converter connected to said reducing agent solution evaporator, disposed outside the exhaust line and to be connected to the exhaust line; and   an SCR catalytic converter disposed in the exhaust line for selective catalytic reduction of nitrogen oxides.   
     
     
         2 . The device according to  claim 1 , wherein said hydrolysis catalytic converter is configured for hydrolysis of urea to form ammonia. 
     
     
         3 . The device according to  claim 1 , which further comprises a reservoir for the aqueous solution, a delivery line connected to said reservoir, and a connecting unit connected between said delivery line and said evaporator unit. 
     
     
         4 . The device according to  claim 3 , wherein said connecting unit is formed at least in part of a material having a thermal conductivity of less than 10 W/m K (Watts per Meter and Kelvin). 
     
     
         5 . The device according to  claim 3 , wherein said connecting unit is formed of at least one substance including at least one of the following materials:
 a) a ceramic substance, or   b) polytetrafluoroethylene (PTFE).   
     
     
         6 . The device according to  claim 3 , wherein said connecting unit has a length and is configured for maintaining a temperature gradient of 40 K/mm (Kelvin per millimeter) and greater over said length. 
     
     
         7 . The device according to  claim 3 , which further comprises:
 a metering line for metering the gaseous substance mixture to said hydrolysis catalytic converter;   a dosing line for metering a generated reducing agent to the exhaust line;   a metering unit for connecting said hydrolysis catalytic converter to the exhaust line; and   a coating catalyzing the hydrolysis of urea, said coating disposed on at least one of:   a) at least parts of said connecting unit;   b) at least parts of said metering line;   c) at least parts of said evaporator unit;   d) at least parts of said dosing line; or   e) at least parts of said metering unit.   
     
     
         8 . The device according to  claim 1 , which further comprises thermal insulation disposed downstream of said hydrolysis catalytic converter. 
     
     
         9 . The device according to  claim 8 , wherein said thermal insulation directly adjoins said hydrolysis catalytic converter. 
     
     
         10 . A method for treating exhaust gas of an internal combustion engine, the method comprising the following steps:
 a) providing a gaseous substance mixture including at least one of the following substances:
 a1) a reducing agent, or 
 a2) at least one reducing agent precursor; 
   b) hydrolyzing the at least one reducing agent precursor to obtain a reducing agent substance mixture;   c) subjecting an SCR catalytic converter to the reducing agent substance mixture and the exhaust gas for at least partial selective catalytic reduction of nitrogen oxides contained in the exhaust gas; and   d) mixing the reducing agent substance mixture with at least parts of the exhaust gas after step b).   
     
     
         11 . The method according to  claim 10 , which further comprises carrying out step a) by evaporation of an aqueous solution including at least one reducing agent precursor, in an evaporator unit. 
     
     
         12 . The method according to  claim 11 , which further comprises at least partially carrying out step b) in a hydrolysis catalytic converter. 
     
     
         13 . The method according to  claim 12 , which further comprises:
 delivering the aqueous solution through a delivery line to the evaporator unit;   metering the gaseous substance mixture to the hydrolysis catalytic converter with a metering line;   metering a generated reducing agent to an exhaust line of the internal combustion engine with a dosing line;   flow-connecting the hydrolysis catalytic converter to the exhaust line with a metering unit; and   regulating a temperature of at least one of:   a) at least parts of the evaporator unit;   b) the hydrolysis catalytic converter;   c) the delivery line;   d) the metering line;   e) the dosing line; or   f) the metering unit.