Management of thermal fluctuations in lean NOx adsorber aftertreatment systems
A method and apparatus manage heat in exhaust gas in an aftertreatment system that employs a lean NOx adsorber. A de-sulfation hot line and cooling line are employed to control exhaust gas temperatures for adsorption, regeneration and de-sulfation cycles of the aftertreatment system where each cycle can require different chemical and exhaust gas temperatures independent of the engine operation. The method and apparatus include a SOx adsorber to provide greater system durability.
1 . An aftertreatment system for treating NOx found in exhaust gas produced during combustion of a fuel within a combustion chamber of an operating internal combustion engine, said aftertreatment system comprising:
an exhaust line for directing said exhaust gas from said engine and through said aftertreatment system, said exhaust line comprising a cooling line and a hot line for managing exhaust gas temperature during an adsorption cycle and a regeneration cycle;
a lean NOx adsorber disposed in said exhaust line;
a catalyst capable of oxidizing a reductant and directing said oxidized reductant into said exhaust gas;
a reductant line for delivering a reductant from a reductant store to said catalyst;
a reductant flow control disposed in said reductant line for controlling flow of said reductant into said exhaust line; and
a flow control for controlling flow of exhaust gas through said hot line and cooling line,
wherein said exhaust line is capable of delivering exhaust gas from said catalyst to said lean NOx adsorber.
2 . The aftertreatment system of claim 1 wherein said catalyst is disposed in said exhaust line.
3 . The aftertreatment system of claim 2 wherein said cooling line and said hot line are between said catalyst and said NOx adsorber.
4 . The aftertreatment system of claim 2 wherein said cooling line is longer than said hot line.
5 . The aftertreatment system of claim 2 further comprising a turbine disposed in said cooling line.
6 . The aftertreatment system of claim 5 wherein said turbine drives an air blower disposed in an air dilution line and connected to compress air and direct the compressed air into said cooling line.
7 . The aftertreatment system of claim 2 further comprising an air blower disposed in an air dilution line for compressing and directing air into said cooling line.
8 . The aftertreatment system of claim 2 further comprising a heat exchanger disposed in said cooling line.
9 . The aftertreatment system of claim 2 further comprising a close-coupled catalyst in said exhaust line upstream of said catalyst, said reductant line capable of delivering reductant to said exhaust line upstream of said close-coupled catalyst.
10 . The aftertreatment system of claim 2 wherein said reductant line delivers said reductant to said exhaust line upstream of said catalyst.
11 . The aftertreatment system of claim 2 wherein said exhaust line comprises a by-pass line capable of directing said exhaust gas around said catalyst.
12 . The aftertreatment system of claim 2 further comprising a SOx adsorber disposed in said exhaust line to remove SOx from said exhaust gas before said exhaust gas passes through said NOx adsorber during The adsorption cycle.
13 . The aftertreatment system of claim 12 wherein said exhaust line further comprises a sulfur line for bypassing said exhaust gas around said NOx adsorber when regenerating said SOx adsorber and a flow control for controlling flow of exhaust gas through said sulfur line.
14 . The aftertreatment system of claim 12 wherein said hot line is a reverse flow line capable of alternating flow of said exhaust gas where said NOx adsorber is upstream of said SOx adsorber.
15 . The aftertreatment system of claim 2 wherein a cooling line length is chosen relative to a hot line length such that more exhaust gas heat is dissipated through said cooling line than would occur through said hot line.
16 . The aftertreatment system of claim 2 wherein a cooling line material is chosen such that more exhaust gas heat is dissipated through said cooling line than would occur through said hot line.
17 . A method of operating an aftertreatment system for removing NOx from exhaust gas generated by combustion of a fuel in at least one combustion chamber of an internal combustion engine, said method comprising an adsorption cycle, a regeneration cycle and a de-sulfation cycle:
during said adsorption cycle:
cooling said exhaust gas to within a predetermined adsorption temperature range when said exhaust gas is above said adsorption temperature range,
directing said cooled exhaust gas through an exhaust line to a lean NOx adsorber disposed in said exhaust line,
during said regeneration cycle:
directing a first portion of said exhaust gas through a bypass line around said lean NOx adsorber;
oxidizing at least a second portion of said exhaust gas to a lambda value of less than or equal to 1,
heating said at least said second portion of said exhaust gas to within a predetermined regeneration temperature range when said at least said second portion of said exhaust gas is below said regeneration temperature range;
directing said oxidized and heated exhaust gas through said lean NOx adsorber,
during said de-sulfation cycle:
oxidizing said exhaust gas to a lambda value of less than or equal to 1,
heating said exhaust gas to within a predetermined de-sulfation temperature range when said exhaust gas is below said de-sulfation temperature range
directing said oxidized and heated exhaust gas through said lean NOx adsorber.
18 . The method of claim 17 wherein, during said adsorption cycle, said exhaust gas is cooled by introducing air into said exhaust gas.
19 . The method of claim 17 wherein, during said adsorption cycle, said exhaust gas is cooled by directing said exhaust gas through a turbine.
20 . The method of claim 19 wherein said turbine is employed to drive a blower for directing air into said exhaust line upstream of said NOx adsorber.
21 . The method of claim 17 wherein, during said adsorption cycle, said exhaust gas is cooled by expanding said exhaust gas.
22 . The method of claim 17 wherein, during said adsorption cycle, said exhaust gas is cooled by directing said exhaust gas through a heat exchanger.
23 . The method of claim 17 wherein, during said adsorption cycle, said exhaust gas is cooled by routing said exhaust line through a cooling line.
24 . The method of claim 17 wherein said at least said second portion of said exhaust gas does not include said first portion of said exhaust gas.
25 . The method of claim 17 wherein, during said de-sulfation cycle, a portion of said exhaust gas is directed through a bypass line around said lean NOx adsorber.
26 . The method of claim 17 wherein, during said adsorption cycle, said exhaust gas is directed through a SOx adsorber disposed in said exhaust line prior to directing said exhaust gas through said NOx adsorber.
27 . The method of claim 17 wherein said exhaust gas is heated and oxidized by passing said exhaust gas through a catalyst with a reductant introduced into said exhaust gas.
28 . The method of claim 17 wherein said reductant is selected from the group consisting of hydrocarbons, hydrogen, and combinations thereof.
29 . The method of claim 28 wherein said reductant includes a hydrocarbon selected from the group consisting of natural gas, diesel, methane, ethane, butane, propane, and combinations thereof.