U.S. patent application number 11/646514 was filed with the patent office on 2008-07-03 for exhaust treatment system.
Invention is credited to Praveen Shivshankar Chavannavar, James Joshua Driscoll, Cho Y. Liang, Thomas Edward Paulson, Michael L. Woods.
Application Number | 20080155972 11/646514 |
Document ID | / |
Family ID | 39126588 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080155972 |
Kind Code |
A1 |
Driscoll; James Joshua ; et
al. |
July 3, 2008 |
Exhaust treatment system
Abstract
An exhaust gas treatment system of an internal combustion engine
includes a selective catalytic reduction catalyst fluidly connected
to the internal combustion engine, an oxidation catalyst fluidly
connected upstream of the selective catalytic reduction catalyst,
and a particulate filter fluidly connected upstream of the
selective catalytic reduction catalyst. The exhaust gas treatment
system further includes a recirculation line configured to direct a
portion of an exhaust flow of the internal combustion engine toward
an inlet of the engine.
Inventors: |
Driscoll; James Joshua;
(Dunlap, IL) ; Chavannavar; Praveen Shivshankar;
(Dunlap, IL) ; Liang; Cho Y.; (Henderson, NV)
; Paulson; Thomas Edward; (Groveland, IL) ; Woods;
Michael L.; (Austin, TX) |
Correspondence
Address: |
CATERPILLAR/FINNEGAN, HENDERSON, L.L.P.
901 New York Avenue, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39126588 |
Appl. No.: |
11/646514 |
Filed: |
December 28, 2006 |
Current U.S.
Class: |
60/299 |
Current CPC
Class: |
F01N 3/0821 20130101;
F01N 3/0814 20130101; F02B 37/013 20130101; Y02T 10/47 20130101;
Y02T 10/12 20130101; Y02T 10/24 20130101; F01N 3/023 20130101; F01N
3/206 20130101; F01N 13/009 20140601; Y02T 10/40 20130101; F02M
26/06 20160201; F01N 3/035 20130101; F01N 9/002 20130101 |
Class at
Publication: |
60/299 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Claims
1. An exhaust gas treatment system of an internal combustion
engine, comprising: a selective catalytic reduction catalyst
fluidly connected to the internal combustion engine; an oxidation
catalyst fluidly connected upstream of the selective catalytic
reduction catalyst; a particulate filter fluidly connected upstream
of the selective catalytic reduction catalyst; and a recirculation
line configured to direct a portion of an exhaust flow of the
internal combustion engine toward an inlet of the engine.
2. The system of claim 1, further including at least one component
configured to inject a flow of reductant upstream of the selective
catalytic reduction catalyst.
3. The system of claim 1, wherein the recirculation line is fluidly
connected one of downstream of the oxidation catalyst, downstream
of the particulate filter, or downstream of the selective catalytic
reduction catalyst.
4. The system of claim 1, wherein the recirculation line is fluidly
connected downstream of an energy extraction assembly of the
exhaust gas treatment system.
5. The system of claim 1, wherein the oxidation catalyst is
disposed on a substrate of the particulate filter.
6. The system of claim 1, wherein the oxidation catalyst is
configured to maintain a desired ratio of NO to NO.sub.2 in an
exhaust flow of the internal combustion engine.
7. The system of claim 1, further including an NOx trap fluidly
connected upstream of the oxidation catalyst.
8. The system of claim 7, wherein the NOx trap is disposed between
an outlet of the internal combustion engine and an energy
extraction assembly of the exhaust gas treatment system.
9. The system of claim 1, further including a catalyst fluidly
connected downstream of the SCR catalyst.
10. The system of claim 1, further including a ventilation line
fluidly connected to a crankcase of the internal combustion
engine.
11. The system of claim 1, further including an energy extraction
assembly configured to reduce the pressure of an exhaust flow of
the internal combustion engine.
12. An exhaust gas treatment system of an internal combustion
engine, comprising: a selective catalytic reduction catalyst
fluidly connected to the internal combustion engine; an oxidation
catalyst fluidly connected upstream of the selective catalytic
reduction catalyst; a particulate filter fluidly connected upstream
of the selective catalytic reduction catalyst; and a low pressure
exhaust gas recirculation loop.
13. The system of claim 12, wherein a component of the low pressure
exhaust gas recirculation loop is fluidly connected one of
downstream of the oxidation catalyst, downstream of the particulate
filter, or downstream of the selective catalytic reduction
catalyst, and the component is configured to direct a portion of an
exhaust flow of the internal combustion engine toward an inlet of
the internal combustion engine.
14. The system of claim 12, wherein the oxidation catalyst is
disposed on a substrate of the particulate filter.
15. The system of claim 12, wherein the oxidation catalyst is
configured to maintain a desired ratio of NO to NO.sub.2 in an
exhaust flow of the internal combustion engine.
16. The system of claim 12, further including an NOx trap fluidly
connected upstream of the oxidation catalyst.
17. The system of claim 12, further including a catalyst fluidly
connected downstream of the selective catalytic reduction
catalyst.
18. A method of an exhaust flow of an internal combustion engine,
comprising: filtering the exhaust flow with a particulate filter;
oxidizing the exhaust flow with an oxidation catalyst;
catalytically reducing NOx contained in the filtered oxidized flow
with a selective catalytic reduction catalyst; and directing a
portion of the exhaust flow to an inlet of the internal combustion
engine.
19. The method of claim 18, further including collecting NOx
contained within the exhaust flow with an NOx trap fluidly
connected upstream of the selective catalytic reduction
catalyst.
20. The method of claim 18, further including removing reductant
from the exhaust flow with a catalyst fluidly connected downstream
of the selective catalytic reduction catalyst.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to an exhaust
treatment system and, more particularly, to an exhaust treatment
system having a selective catalytic reduction ("SCR") catalyst.
BACKGROUND
[0002] Internal combustion engines, including diesel engines,
gasoline engines, natural gas engines, and other engines known in
the art, may emit an exhaust flow containing a complex mixture of
solid, liquid, and gaseous components. For example, the gaseous
components of the exhaust flow may include compounds such as
nitrous oxides ("NOx") and CO, and the solid and/or liquid
components of the flow may include soluble organic fraction, soot,
and/or unburned hydrocarbons. Together, the soluble organic
fraction, soot, and unburned hydrocarbons emitted by internal
combustion engines is generally referred to as particulate
matter.
[0003] The Environmental Protection Agency regulates the emissions
released into the atmosphere from such engines based on the type,
size, and/or class of engine. These exhaust emission standards
continue to become more stringent, and engine manufacturers have
begun to use catalytic exhaust treatment systems to comply with
these regulations. In such systems, a reductant, such as urea or
ammonia, may be injected into the exhaust gas upstream of an SCR
catalyst, and the catalyst materials within the SCR catalyst may
reduce NOx carried by the exhaust gas in the presence of the
reductant. In addition, a particulate filter may capture a portion
of the particulate matter carried by the exhaust.
[0004] The effectiveness of an SCR catalyst is based on its ability
to convert NOx carried in the exhaust gas to N.sub.2 and other
gaseous species such as O.sub.2 and H.sub.2O. Maintaining the SCR
catalyst within a desired temperature range and providing it with a
flow of exhaust gas having approximately a one-to-one ratio of NO
to NO.sub.2 are both factors that assist in maximizing the NOx
conversion rate of the SCR catalyst. The exhaust gas leaving the
engine, however, typically contains a much higher percentage of NO
than NO.sub.2. Thus, exhaust treatment systems often include an
oxidation catalyst disposed upstream of the SCR catalyst to assist
in oxidizing the NO present in the exhaust gas. Oxidizing the NO
may increase the amount of NO.sub.2 present in the exhaust gas
entering the SCR catalyst and may facilitate achieving a one-to-one
ratio of NO to NO.sub.2.
[0005] An exhaust treatment system for controlling the NOx and
particulate matter emissions of an internal combustion engine is
illustrated in U.S. Pat. No. 6,928,806 ("the '806 patent").
Specifically, the '806 patent discloses an oxidation catalyst, an
SCR catalyst coupled downstream of the oxidation catalyst, and a
particulate filter coupled downstream of the SCR catalyst.
[0006] Although the system disclosed in the '806 patent may assist
in removing particulate matter and reducing the NOx content of the
exhaust gas, the SCR catalyst of the '806 patent is disposed
upstream of the particulate filter and is, therefore, particularly
susceptible to fouling from, for example, particulate matter
carried in the exhaust flow.
[0007] In addition, the system of the '806 patent fails to take
advantage of the benefits associated with the use of exhaust gas
recirculation ("EGR") to direct at least a portion of the exhaust
gas into the intake air supply of the engine. The use of EGR may
assist in reducing the concentration of oxygen within the cylinder
and increasing the specific heat of the air/fuel mixture, thereby
reducing the amount of NOx produced by the engine. The use of EGR
in combination with SCR catalyst technology may also assist in
improving the fuel economy of the engine system and may increase
the amount of NO.sub.2 produced by the engine relative to NO. The
system of the '806 patent is not configured to direct any portion
of the exhaust gas back to the intake of the engine to reduce NOx
formation, improve fuel economy, or increase the quantity of
NO.sub.2 produced by the engine.
[0008] The disclosed exhaust treatment system is directed to
overcoming one or more of the problems set forth above.
SUMMARY OF THE INVENTION
[0009] In one embodiment of the present disclosure, an exhaust gas
treatment system of an internal combustion engine includes an SCR
catalyst fluidly connected to the internal combustion engine, an
oxidation catalyst fluidly connected upstream of the SCR catalyst,
and a particulate filter fluidly connected upstream of the SCR
catalyst. The exhaust gas treatment system further includes a
recirculation line configured to direct a portion of an exhaust
flow of the internal combustion engine toward an inlet of the
engine.
[0010] In another embodiment of the present disclosure, an exhaust
gas treatment system of an internal combustion engine includes an
SCR catalyst fluidly connected to the internal combustion engine,
an oxidation catalyst fluidly connected upstream of the SCR
catalyst, and a particulate filter fluidly connected upstream of
the SCR catalyst. The system further includes a low pressure
exhaust gas recirculation loop.
[0011] In yet another embodiment of the present disclosure, a
method of an exhaust flow of an internal combustion engine includes
filtering the exhaust flow with a particulate filter, oxidizing the
exhaust flow with an oxidation catalyst, catalytically reducing NOx
contained in the filtered oxidized flow with an SCR catalyst, and
directing a portion of the exhaust flow to an inlet of the internal
combustion engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagrammatic illustration of an engine having an
exhaust treatment system according to an exemplary embodiment of
the present disclosure.
[0013] FIG. 2 is a diagrammatic illustration of an engine having an
exhaust treatment system according to another exemplary embodiment
of the present disclosure.
[0014] FIG. 3 is a diagrammatic illustration of an engine having an
exhaust treatment system according to still another exemplary
embodiment of the present disclosure.
[0015] FIG. 4 is a diagrammatic illustration of an engine having an
exhaust treatment system according to yet another exemplary
embodiment of the present disclosure.
DETAILED DESCRIPTION
[0016] FIG. 1 illustrates a power source 12 having an exemplary
exhaust treatment system 10. The power source 12 may include an
engine, such as, for example, a diesel engine, a gasoline engine, a
natural gas engine, or any other engine apparent to one skilled in
the art. The power source 12 may alternatively include another
source of power, such as a furnace or any other source of power
known in the art.
[0017] The exhaust treatment system 10 may be configured to direct
exhaust gases out of the power source 12, treat the gases, and
introduce a portion of the treated gases into an inlet 21 of the
power source 12. The exhaust treatment system 10 may include, for
example, an NOx trap 35, an energy extraction assembly 22, a
regeneration device 20, an oxidation catalyst 18, a filter 16, an
SCR catalyst 19, and/or a clean-up catalyst 33. The exhaust
treatment system 10 may further include a recirculation line 24
fluidly connected between the filter 16 and the SCR catalyst 19.
Alternatively, the recirculation line 24 may be fluidly connected
between the oxidation catalyst 18 and the filter 16, between the
SCR catalyst 19 and the clean-up catalyst 33, or downstream of the
clean-up catalyst 33. The exhaust treatment system 10 may still
further include a flow cooler 26, a flow sensor 28, a mixing valve
30, a compression assembly 32, and an aftercooler 34.
[0018] A flow of exhaust produced by the power source 12 may be
directed from the power source 12 to components of the exhaust
treatment system 10 by flow lines 15. It is understood that the
power source 12 may include one or more combustion chambers (not
shown) fluidly connected to an exhaust manifold. In such an
exemplary embodiment, the flow lines 15 may be configured to
transmit a flow of exhaust from the combustion chambers to the
components of the exhaust treatment system 10 via the exhaust
manifold. The flow lines 15 may include pipes, tubing, and/or other
exhaust flow carrying means known in the art. The flow lines 15 may
be made of alloys of steel, aluminum, and/or other materials known
in the art. The flow lines 15 may be rigid or flexible, and may be
capable of safely carrying high temperature exhaust flows, such as
flows having temperatures in excess of 700 degrees Celsius
(approximately 1,292 degrees Fahrenheit).
[0019] The NOx trap 35 may be any type of NOx adsorber or absorber
known in the art, such as, for example, a lean NOx trap, and may
contain catalyst materials capable of absorbing, adsorbing, and/or
otherwise storing oxides of nitrogen. Such catalyst materials may
include, for example, aluminum, platinum, rhodium, barium, cerium,
and/or alkali metals, alkaline-earth metals, rare-earth metals, or
combinations thereof. The catalyst materials may be situated within
the NOx trap 35 so as to maximize the surface area available for
NOx absorption, and the catalyst materials may be located on a
substrate of the NOx trap 35. Substrate configurations may include,
for example, a honeycomb, mesh, or any other configuration known in
the art. The NOx trap 35 may be capable of storing NOx over a wide
range of exhaust temperatures and may be configured to store NOx at
relatively low exhaust temperatures, such as, for example, below
200 degrees Celsius. Such exhaust temperatures may occur during
power source start-up or in low-load operating conditions. For
example, it may be difficult for the SCR catalyst 19 to reduce or
otherwise convert NOx at such low temperatures; thus, the NOx trap
35 may be particularly helpful in meeting government NOx emissions
regulations at low temperatures. The NOx trap 35 may, however,
store NOx more effectively at elevated exhaust temperatures. For
example, the ability of the NOx trap 35 to adsorb NOx may be
maximized when the exhaust gas temperatures between approximately
300 degrees Celsius and approximately 400 degrees Celsius.
Accordingly, in an exemplary embodiment, the NOx trap 35 may be
fluidly connected proximate an outlet 43 of the power source 12
such that the exhaust gases entering the NOx trap 35 may undergo
relatively little convective cooling. It is understood that the
outlet 43 may be an outlet of an exhaust manifold of the power
source 12.
[0020] The energy extraction assembly 22 may be configured to
extract energy from, and reduce the pressure of, the exhaust gases
produced by the power source 12. The energy extraction assembly 22
may be fluidly connected to the power source 12 by one or more flow
lines 15 and may reduce the pressure of the exhaust gases to any
desired pressure. The energy extraction assembly 22 may include one
or more turbines 14, diffusers, or other energy extraction devices
known in the art. In an exemplary embodiment wherein the energy
extraction assembly 22 includes more than one turbine 14, the
multiple turbines 14 may be disposed in parallel or in series
relationship. It is also understood that in an embodiment of the
present disclosure, the energy extraction assembly 22 may
alternatively be omitted. In such an embodiment, the power source
12 may include, for example, a naturally aspirated engine. As will
be described in greater detail below, a component of the energy
extraction assembly 22 may be configured in certain embodiments to
drive a component of the compression assembly 32. It is understood
that, in an exemplary embodiment, the energy extraction assembly 22
may include a heat exchanger and/or other components required to
form and/or facilitate, for example, a Rankine cycle or a Brayton
cycle.
[0021] In an exemplary embodiment, the regeneration device 20 of
the exhaust treatment system 10 may be fluidly connected to the
energy extraction assembly 22 via flow line 15 and may be
configured to increase the temperature of an entire flow of exhaust
produced by the power source 12 to a desired temperature. The
desired temperature may be, for example, a regeneration temperature
of the filter 16. Accordingly, the regeneration device 20 may be
configured to assist in actively regenerating the filter 16.
Alternatively, in another exemplary embodiment, the regeneration
device 20 may be configured to increase the temperature of only a
portion of the entire flow of exhaust produced by the power source
12. The regeneration device 20 may include, for example, a fuel
injector and an ignitor (not shown), heat coils (not shown), and/or
other heat sources known in the art. Such heat sources may be
disposed within the regeneration device 20 and may be configured to
assist in increasing the temperature of the flow of exhaust through
convection, combustion, and/or other methods.
[0022] As shown in FIG. 1, the filter 16 of the exhaust treatment
system 10 may be connected downstream of the regeneration device
20. The filter 16 may have a housing 25 including an inlet 23 and
an outlet 31. In an exemplary embodiment, the regeneration device
20 may be disposed outside of the housing 25 and may be fluidly
connected to the inlet 23 of the housing 25. In another exemplary
embodiment, the regeneration device 20 may be disposed within the
housing 25 of the filter 16. The filter 16 may be any type of
filter known in the art capable of extracting matter from a flow of
gas. In an embodiment of the present disclosure, the filter 16 may
be, for example, a particulate matter filter positioned to extract
particulates from an exhaust flow of the power source 12. The
filter 16 may include, for example, a ceramic substrate, a metallic
mesh, foam, or any other porous material known in the art. These
materials may form, for example, a honeycomb structure within the
housing 25 of the filter 16 to facilitate the removal of
particulates. As discussed above, the particulates may be, for
example, soluble organic fraction, hydrocarbons, and/or soot.
[0023] In an exemplary embodiment of the present disclosure, a
portion of the exhaust produced by the combustion process may leak
past piston seal rings within a crankcase 45 of the power source
12. This portion of the exhaust, often called "blow-by gases" or
simply "blow-by," may contain one or more of the exhaust gas
components discussed above. In addition, because the crankcase 45
is partially filled with lubricating oil being agitated at high
temperatures, the blow-by gases may also contain oil droplets and
oil vapor. The blow-by gases may build up within the crankcase 45
over time, thereby increasing the pressure within the crankcase 45.
In such an embodiment, a ventilation line 42 may be fluidly
connected to the crankcase 45 of the power source 12.
[0024] The ventilation line 42 may comprise piping, tubing, and/or
other exhaust flow carrying means known in the art and may be
structurally similar to the flow lines 15 described above. The
ventilation line 42 may include, for example, a check valve 44
and/or any other valve assembly known in the art. The check valve
44 may be configured to assist in controllably regulating a flow of
fluid through the ventilation line 42. The ventilation line 42 may
be configured to direct the blow-by gases from the crankcase 45 to
a location upstream of the filter 16, such as, for example, a port
46 of the flow line 15. For example, the ventilation line 42 may
assist in directing the portion of exhaust gas from the crankcase
45 to a port 46 disposed upstream of the regeneration device 20. By
directing the blow-by gases upstream of the filter 16 and/or the
regeneration device 20, the contaminants contained in the blow-by
gases may be substantially removed without contaminating the
supercharger, turbocharger, or various power source components.
[0025] The oxidation catalyst 18 of the exhaust treatment system 10
may be located between the regeneration device 20 and the filter
16, and may contain catalyst materials useful in collecting,
absorbing, adsorbing, and/or converting hydrocarbons, carbon
monoxide, and/or oxides of nitrogen contained in a flow. Such
catalyst materials may include, for example, aluminum, platinum,
palladium, rhodium, barium, cerium, and/or alkali metals,
alkaline-earth metals, rare-earth metals, or combinations thereof.
The catalyst materials may be situated within the oxidation
catalyst 18 so as to maximize the surface area available for the
collection and/or conversion of the flow components discussed
above. The oxidation catalyst 18 may include, for example, a
ceramic substrate, a metallic mesh, foam, or any other porous
material known in the art, and the catalyst materials may be
located on, for example, a substrate of the oxidation catalyst 18.
The oxidation catalyst 18 may, for example, assist in oxidizing one
or more components of the exhaust flow, such as, for example,
particulate matter, hydrocarbons, and/or carbon monoxide. The
oxidation catalyst 18 may also be configured to oxidize NO
contained in the exhaust gas, thereby converting it to NO.sub.2.
Thus, the oxidation catalyst 18 may assist in achieving a desired
ratio of NO to NO.sub.2 upstream of the SCR catalyst 19. As
mentioned above, this desired ratio may be, for example,
approximately one to one.
[0026] As illustrated in FIG. 2, in an additional exemplary
embodiment of the present disclosure, a filter 36 of the exhaust
treatment system 100 may include catalyst materials useful in
collecting, absorbing, adsorbing, and/or converting hydrocarbons,
carbon monoxide, and/or oxides of nitrogen contained in a flow. In
such an embodiment, the oxidation catalyst 18 (FIG. 1) may be
omitted. The catalyst materials may include, for example, any of
the catalyst materials discussed above with respect to the
oxidation catalyst 18 (FIG. 1). The catalyst materials may be
situated within the filter 36 so as to maximize the surface area
available for collection and/or conversion. For example, the
catalyst materials may be located on a substrate of the filter 36.
The catalyst materials may be added to the filter 36 by any
conventional means, such as, for example, coating or spraying, and
the substrate of the filter 36 may be partially or completely
coated with the materials.
[0027] In the embodiment shown in FIG. 2, the catalyst materials
disposed on the substrate of the filter 36 may assist in passively
regenerating the filter 36 during power source operation. As the
power source 12 operates, particulates and other components of the
power source exhaust may be trapped by the filter substrate. The
exhaust flow may reach temperatures in excess of, for example, 300
degrees Celsius during normal operation of the power source 12
(i.e., without operating the power source 12 in a manner so as to
increase the temperature of the exhaust by, for example,
wastegating or other conventional methods), and the exhaust gas may
increase the temperature of at least a portion of the filter
substrate through convective heat transfer. At such temperatures,
the components of the power source exhaust trapped by the substrate
of the filter 36 may begin to react with the catalyst material
located on the substrate. In particular, the catalyst material may
passively regenerate a portion of the filter 36 by oxidizing
particulate matter trapped by the filter substrate as well as
carbon monoxide and/or hydrocarbons contained in the exhaust flow.
Oxidation may occur at a passive regeneration temperature of the
filter 36 in which the catalyst material is hot enough to react
with the components of the exhaust flow without additional heat
being provided by, for example, the regeneration device 20. Such
passive regeneration temperatures may be below the active
regeneration temperature of the filter 36.
[0028] Although at least a portion of the particulate matter
contained within the filter 36 may be oxidized and/or removed
therefrom through passive regeneration, it is understood that, as
shown in FIG. 2, an exemplary exhaust treatment system 100 of the
present disclosure may, nonetheless, include a regeneration device
20. Utilizing a catalyzed filter 36 in conjunction with a
regeneration device 20 may assist in increasing the interval
between active regenerations. Increasing this interval may reduce
the amount of, for example, fuel burned during operation of the
power source 12 and, thus, may reduce the cost of operating the
machine to which the power source 12 is connected. An exhaust
treatment system 100 including both a catalyzed filter 36 and a
regeneration device 20 may also enable filter manufacturers to
include less catalyst material (such as, for example, precious
metals) in the filter 36, thereby reducing the cost of the filter
36 and the overall cost of the exhaust treatment system 100.
[0029] Referring again to FIG. 1, the SCR catalyst 19 of the
exhaust treatment system 10 may be any selective catalytic
reduction catalyst known in the art and may be, for example, a
urea-based or an ammonia-based catalyst. The SCR catalyst 19 may
be, for example, a vanadium and titanium-type, a platinum-type, or
a zeolite-type SCR catalyst, and may include a substrate containing
one or more of these metals and configured to assist in reducing
NOx. For example, the SCR catalyst 19 may be capable of maintaining
the NOx emissions of the exhaust treatment system 10 below
approximately 0.2 grams/horsepower-hour, in compliance with future
government regulations. The SCR catalyst 19 may have an optimum or
peak NOx conversion rate when the ratio of NO to NO.sub.2 entering
the SCR catalyst 19 is approximately one to one. The SCR catalyst
19 may be most effective at temperatures between approximately 200
degrees Celsius and approximately 500 degrees Celsius. As used
herein, the term "conversion rate" is defined as the rate at which
NOx is catalytically converted to N.sub.2 through a reduction
reaction.
[0030] As mentioned above, the SCR catalyst 19 may be configured to
reduce NOx in the presence of a reductant, such as, for example,
urea or ammonia. Accordingly, the exhaust treatment system 10 may
include an injector 37, a pump 39, a storage device 41, and/or any
other components required to deliver reductant upstream of the SCR
catalyst 19 and/or otherwise facilitate NOx reduction. In an
exemplary embodiment, the injector 37 may be any type of fluid
injector configured to deliver a flow of aqueous reductant. The
injector 37 may be configured to at least partially atomize the
flow of reductant as it is delivered, thereby facilitating mixing
of the reductant with, for example, an exhaust flow of the power
source 12. The pump 39 may be configured to draw reductant from the
storage device 41 and pressurize the reductant upstream of the
injector 37. Although not shown in FIG. 1, it is understood that
one or more control valves maybe used in conjunction with the pump
39 to meter the flow of reductant supplied to the injector 37.
Moreover, the control valves, pump 39, and/or the injector 37 may
be electrically connected to and controlled by a controller (not
shown).
[0031] As shown in FIG. 1, the clean-up catalyst 33 may be fluidly
connected downstream of the SCR catalyst 19. The clean-up catalyst
33 may be configured to capture, store, and/or convert unreacted
reductants that may slip past the SCR catalyst 19. In addition, it
is understood that in some operating conditions, a quantity of NOx
carried by the exhaust flow may not be converted to N.sub.2 by the
SCR catalyst 19. Such conditions may include, for example, when the
SCR catalyst 19 is below the optimum NOx conversion temperature
range discussed above (between approximately 200 degrees Celsius
and approximately 500 degrees Celsius), when the ratio of NO to
NO.sub.2 is not approximately one to one, and when substantially
all of the NOx conversion sites of the SCR catalyst substrate are
occupied. In such conditions, the clean-up catalyst 33 may also
assist in, for example, collecting and/or storing NOx. In an
exemplary embodiment, the clean-up catalyst 33 may be an NOx trap
similar to the NOx trap 35 discussed above.
[0032] The recirculation line 24 may be disposed between the filter
16 and the SCR catalyst 19, and may be configured to assist in
directing a portion of the exhaust flow from the filter 16 to the
inlet 21 of the power source 12. As discussed above, the
recirculation line 24 may alternatively be fluidly connected
between the oxidation catalyst 18 and the filter 16, between the
SCR catalyst 19 and the clean-up catalyst 33, or downstream of the
clean-up catalyst 33. The recirculation line 24 may comprise
piping, tubing, and/or other exhaust flow carrying means known in
the art, and may be structurally similar to the flow lines 15
described above. The portion of the exhaust flow directed to the
power source 12 by the recirculation line 24 may assist in reducing
the concentration of oxygen within, for example, one or more
combustion chambers of the power source 12 and may assist in
increasing the specific heat of the air/fuel mixture therein,
thereby lowering the maximum combustion temperature within the one
or more combustion chambers. The lowered maximum combustion
temperature and reduced oxygen concentration may slow the chemical
reaction of the combustion process and decrease the formation of
NOx by the power source 12.
[0033] The flow cooler 26 may be fluidly connected to the filter 16
via the recirculation line 24 and may be configured to cool the
portion of the exhaust flow passing through the recirculation line
24. The flow cooler 26 may include a liquid-to-air heat exchanger,
an air-to-air heat exchanger, or any other type of heat exchanger
known in the art for cooling an exhaust flow. In an alternative
exemplary embodiment of the present disclosure, the flow cooler 26
may be omitted.
[0034] The mixing valve 30 may be fluidly connected to the flow
cooler 26 via the recirculation line 24 and may be configured to
assist in regulating the flow of exhaust through the recirculation
line 24. It is understood that in an exemplary embodiment, a check
valve (not shown) may be fluidly connected upstream of the flow
cooler 26 to further assist in regulating the flow of exhaust
through the recirculation line 24. The mixing valve 30 may be a
spool valve, a shutter valve, a butterfly valve, a check valve, a
diaphragm valve, a gate valve, a shuttle valve, a ball valve, a
globe valve, or any other valve known in the art. The mixing valve
30 may be actuated manually, electrically, hydraulically,
pneumatically, or in any other manner known in the art. The mixing
valve 30 may be in communication with the controller mentioned
above (not shown) and may be selectively actuated in response to
one or more predetermined conditions.
[0035] The mixing valve 30 may also be fluidly connected to an
ambient air intake 29 of the exhaust treatment system 10. Thus, the
mixing valve 30 may be configured to control the amount of exhaust
flow entering a flow line 27 relative to the amount of ambient air
flow entering the flow line 27. For example, as the amount of
exhaust flow passing through the mixing valve 30 is desirably
increased, the amount of ambient air flow passing through the
mixing valve 30 may be proportionally decreased and vice versa.
[0036] As shown in FIG. 1, the flow sensor 28 may be fluidly
connected to the recirculation line 24 downstream of the flow
cooler 26. The flow sensor 28 may be any type of mass air flow
sensor, such as, for example, a hot wire anemometer or a
venturi-type sensor. The flow sensor 28 may be configured to sense
the amount of exhaust flow passing through the recirculation line
24. It is understood that the flow cooler 26 may assist in reducing
fluctuations in the temperature of the portion of the exhaust flow
passing through the recirculation line 24. Reducing temperature
fluctuations may also assist in reducing fluctuations in the volume
occupied by a flow of exhaust gas since a high temperature mass of
gas occupies a greater volume than the same mass of gas at a low
temperature. Thus, sensing the amount of exhaust flow through the
recirculation line 24 at positions downstream of the flow cooler 26
(i.e., at a relatively controlled temperature) may result in more
accurate flow measurements than measurements taken upstream of the
flow cooler 26. It is further understood that the flow sensor 28
may also include, for example, a thermocouple (not shown) or other
device configured to sense the temperature of the exhaust flow.
[0037] The flow line 27 downstream of the mixing valve 30 may
direct the ambient air/exhaust flow mixture to the compression
assembly 32. The compression assembly 32 may include a compressor
13 configured to increase the pressure of a flow of gas to a
desired pressure. The compressor 13 may include a fixed geometry
type compressor, a variable geometry type compressor, or any other
type of compressor known in the art. In the exemplary embodiment
shown in FIG. 1, the compression assembly 32 may include more than
one compressor 13, and the multiple compressors 13 may be disposed
in parallel or in series relationship. A compressor 13 of the
compression assembly 32 may be connected to a turbine 14 of the
energy extraction assembly 22, and the turbine 14 may be configured
to drive the compressor 13. In particular, as hot exhaust gases
exit the power source 12 and expand against the blades (not shown)
of the turbine 14, components of the turbine 14 may rotate and
drive the connected compressor 13. Alternatively, in an embodiment
in which the turbine 14 is omitted, the compressor 13 may be driven
by, for example, the power source 12, or by any other drive known
in the art. It is also understood that in a nonpressurized air
induction system, the compression assembly 32 may be omitted.
[0038] The aftercooler 34 may be fluidly connected to the power
source 12 via the flow line 27 and may be configured to cool a flow
of gas passing through the flow line 27. In an exemplary
embodiment, this flow of gas may be the ambient air/exhaust flow
mixture discussed above. The aftercooler 34 may include a
liquid-to-air heat exchanger, an air-to-air heat exchanger, or any
other type of flow cooler or heat exchanger known in the art. In an
exemplary embodiment of the present disclosure, the aftercooler 34
may be omitted if desired.
[0039] The exhaust treatment system 10 may further include a
condensate drain 38 fluidly connected to the aftercooler 34. The
condensate drain 38 may be configured to collect a fluid, such as,
for example, water or other condensate formed at the aftercooler
34. It is understood that such fluids may consist of, for example,
condensed water vapor contained in recycled exhaust gas and/or
ambient air. In such an exemplary embodiment, the condensate drain
38 may include a removably attachable fluid tank (not shown)
capable of safely storing the condensed fluid. The fluid tank may
be configured to be removed, safely emptied, and reconnected to the
condensate drain 38. In another exemplary embodiment, the
condensate drain 38 may be configured to direct the condensed fluid
to a fluid container (not shown) and/or other component or location
on the machine. Alternatively, the condensate drain 38 may be
configured to direct the fluid to the atmosphere or to the surface
by which the machine is supported.
[0040] As shown in FIGS. 1 and 2, the recirculation line 24 may
form a low pressure EGR loop in which a portion of the exhaust gas
is extracted downstream of the energy extraction assembly 22 and
directed to the inlet 21. It is understood, however, that in an
exemplary embodiment, the recirculation line 24 may form a high
pressure EGR loop. In such an embodiment, the portion of the
exhaust gas may be extracted upstream of the energy extraction
assembly 22. For example, as shown in FIGS. 3 and 4, in additional
exemplary embodiments, the recirculation line 24 may be connected
downstream of the NOx trap 35 and upstream of the energy extraction
assembly 22. FIG. 3 illustrates an exemplary embodiment including
an oxidation catalyst separate from and upstream of a filter 36,
and FIG. 4 illustrates an exemplary embodiment in which a filter 36
includes a catalyzed substrate and in which the oxidation catalyst
18 is omitted.
[0041] In the high pressure EGR loop embodiments of FIGS. 3 and 4,
the recirculated exhaust gas may pass through the flow cooler 26
upstream of the flow sensor 28. The recirculated exhaust gas may
then be combined with a compressed flow of ambient air at the
mixing valve 30, and the combined flow may be directed to the
aftercooler 34. It is understood that, in the high pressure EGR
loop embodiments of FIGS. 3 and 4, one or more components of the
exhaust treatment system 200, 300 may be omitted. In another
exemplary embodiment of a high pressure EGR loop (not shown), the
recirculation line 24 may be internal to the power source 12,
thereby creating an internal EGR loop. In such an embodiment, at
least the flow cooler 26 may be omitted. In still another high
pressure EGR loop embodiment, the recirculation line 24 may be
fluidly connected downstream of the power source 12 and upstream of
the NOx trap 35.
INDUSTRIAL APPLICABILITY
[0042] The exhaust treatment systems 10, 100, 200, 300 of the
present disclosure may be used with any combustion-type device,
such as, for example, an engine, a furnace, or any other device
known in the art, where the reduction of NOx emissions, the
reduction of particulate matter emissions, and/or the recirculation
of treated exhaust into an inlet of the device is desired. The
exhaust treatment systems 10, 100, 200, 300 may be useful in
reducing the amount of engine emissions (such as, for example, NOx
and particulate matter) discharged into the environment. The
exhaust treatment systems 10, 100, 200, 300 may also be capable of
purging the portions of the exhaust gas captured by components of
the system through a regeneration process.
[0043] The operation of the exhaust treatment systems 10, 100, 200,
300 will now be explained in detail. Unless otherwise noted, the
exhaust treatment system 10 of FIG. 1 will be referred to for the
duration of the disclosure.
[0044] The power source 12 may combust a mixture of fuel,
recirculated exhaust gas, and ambient air to produce mechanical
work and an exhaust flow. As discussed above, the exhaust flow
includes a complex mixture of solid, liquid, and/or gaseous
components. In general, the solid and liquid components of the
exhaust flow may consist of soot, soluble organic fraction, and
unburned hydrocarbons. The soot produced during combustion may
include carbonaceous materials, and the soluble organic fraction
may include unburned hydrocarbons that are deposited on or
otherwise chemically combined with the soot. The gaseous components
of the exhaust flow may consist of, among other things, NOx and
CO.
[0045] The exhaust flow may be directed, via flow line 15, from the
power source 12 through the NOx trap 35. The NOx trap 35 may store,
absorb, adsorb, collect, and/or otherwise store NOx carried by the
exhaust flow. The NOx trap 35 may be useful in removing NOx in, for
example, low load or low temperature (start-up) operating
conditions in which the SCR catalyst 19 may be less effective in
catalytically reducing NOx. The reduced NOx exhaust may then be
directed to the energy extraction assembly 22. The hot exhaust flow
may expand on the blades of the turbines 14 of the energy
extraction assembly 22, and this expansion may reduce the pressure
of the exhaust flow while assisting in rotating the turbine
blades.
[0046] The reduced pressure exhaust flow may pass through the
regeneration device 20 to the oxidation catalyst 18. The
regeneration device 20 may be deactivated during the normal
operation of the power source 12. As the exhaust flow passes
through the oxidation catalyst 18, the catalyst materials contained
therein may assist in oxidizing the particulate matter,
hydrocarbons, and/or carbon monoxide carried by the flow. The
catalyst materials may also assist in oxidizing gaseous NO
contained in the flow, thereby converting the NO to NO.sub.2. The
oxidation catalyst 18 may be coated and/or otherwise configured to
yield a treated flow of exhaust having a desired ratio of NO to
NO.sub.2 to optimize the NOx conversion rate of the SCR catalyst
19. As discussed above, this desired ratio may be approximately one
to one.
[0047] As the exhaust flow exits the oxidation catalyst 18 and
passes through the filter 16, at least a portion of the particulate
matter entrained with the exhaust flow may be captured by the
substrate, mesh, and/or other structures within the filter 16. As
discussed above with respect to FIG. 2, in an exemplary embodiment,
the catalyst materials of the oxidation catalyst 18 may be disposed
on the substrate of the filter 36 and, in such an embodiment, the
oxidation catalyst 18 may be omitted. Such a configuration may also
allow for the passive regeneration of the filter 36 during
operation of the power source 12.
[0048] With continued reference to FIG. 1, a portion of the
filtered exhaust flow may be extracted downstream of the filter 16
and the remainder of the filtered exhaust flow may be directed to
the SCR catalyst 19. Disposing the filter 16 upstream of the SCR
catalyst 19 minimizes the amount of, for example, particulate
matter entering the SCR catalyst 19, thereby reducing the fouling
thereof. The injector 37 may inject a desirable quantity of
reductant into the exhaust flow upstream of the SCR catalyst 19,
and the amount of reductant injected may depend on, among other
things, the mass flow, temperature, and NOx concentration of the
filtered flow. The injection amount may be calculated and otherwise
controlled by the controller mentioned above (not shown). The
injected reductant may be substantially atomized and may mix
substantially uniformly with the filtered flow upstream of the SCR
catalyst 19.
[0049] The NOx carried by the filtered flow may be catalytically
reduced by the SCR catalyst 19 in the presence of the injected
reductant. In particular, the NOx molecules may be substantially
entirely converted to, for example, N.sub.2, CO.sub.2, H.sub.2O,
and O.sub.2 by the SCR catalyst 19, and the SCR catalyst 19 may be
configured to reduce the overall NOx emissions of the exhaust
treatment system 10 to below 0.2 grams/horsepower-hour. The SCR
catalyst 19 reduces NOx most effectively at temperatures between
approximately 200 degrees Celsius and approximately 500 degrees
Celsius, and the conversion rate of the SCR catalyst 19 will be
maximized when the ratio of NO to NO.sub.2 is approximately one to
one.
[0050] The clean-up catalyst 33 downstream of the SCR catalyst 19
may remove any unreacted reductant from the flow exiting the SCR
catalyst 19. After passing through the clean-up catalyst 33, the
treated exhaust flow may exit the exhaust treatment system 10
through an exhaust system outlet 17.
[0051] In the low pressure EGR loop embodiments of FIGS. 1 and 2,
the extracted portion of the exhaust flow discussed above may enter
the recirculation line 24 downstream of the energy extraction
assembly 22 and may be recirculated back to the power source 12.
Alternatively, with reference to FIGS. 3 and 4, in the exemplary
high pressure EGR loop embodiments disclosed herein, a portion of
the exhaust flow may be extracted upstream of the energy extraction
assembly 22. With reference to FIG. 1, the recirculated portion of
the exhaust flow may pass through the flow cooler 26. The flow
cooler 26 may reduce the temperature of the portion of the exhaust
flow before the portion enters the flow line 27. The mixing valve
30 may be configured to regulate the ratio of recirculated exhaust
flow to ambient inlet air passing through flow line 27. As
described above, the flow sensor 28 may assist in regulating this
ratio.
[0052] The mixing valve 30 may permit the ambient air/exhaust flow
mixture to pass to the compression assembly 32 where the
compressors 13 may increase the pressure of the flow, thereby
increasing the temperature of the flow. The compressed flow may
pass through the flow line 27 to the aftercooler 34, which may
reduce the temperature of the flow before the flow enters the inlet
21 of the power source 12. As discussed above, recirculating a
portion of the exhaust flow back to the power source 12 assists in
reducing the overall NOx produce thereby.
[0053] Over time, soot produced by the combustion process may
collect in the filter 16 and may begin to impair the ability of the
filter 16 to store particulates. The flow sensor 28 and other
sensors (not shown) sense parameters of the power source 12 and/or
the exhaust treatment system 10. Such parameters may include, for
example, engine speed, engine temperature, exhaust flow
temperature, exhaust flow pressure, and particulate matter content.
The controller (not shown) may use the information sent from the
sensors in conjunction with an algorithm or other preset criteria
to determine whether the filter 16 has become saturated and is in
need of regeneration. Once this saturation point has been reached,
the controller may send appropriate signals to components of the
exhaust treatment system 10 to begin the regeneration process. A
preset algorithm stored in the controller may assist in this
determination and may use the sensed parameters as inputs.
Alternatively, regeneration may commence according to a set
schedule based on fuel consumption, hours of operation, and/or
other variables.
[0054] The signals sent by the controller may alter the position of
the mixing valve 30 to desirably alter the ratio of the ambient
air/exhaust flow mixture. These signals may also activate the
regeneration device 20. Upon activation, oxygen and a combustible
substance, such as, for example, fuel, may be directed to the
regeneration device 20. The regeneration device 20 may ignite the
fuel and may increase the temperature of the exhaust flow passing
to the filter 16 to a desired temperature for regeneration. This
temperature may be in excess of 700 degrees Celsius (approximately
1,292 degrees Fahrenheit) in some applications, depending on the
type and size of the filter 16. At these temperatures, soot
contained within the filter 16 may be burned away to restore the
storage capabilities of the filter 16.
[0055] As discussed above, disposing the filter 36 upstream of the
SCR catalyst 19 may reduce or substantially eliminate fouling of
the SCR catalyst 19 caused by, for example, particulate matter
carried by the exhaust flow. Minimizing SCR catalyst fouling may
assist in maximizing the number of available NOx conversion sites
on the substrate of the SCR catalyst 19, thereby maximizing the
ability of the SCR catalyst 19 to convert NOx carried by the
exhaust flow to, for example, N.sub.2.
[0056] It is understood that systems employing an SCR catalyst for
NOx conversion may provide for reduced NOx emissions to the
environment. For example, as mentioned above, the SCR catalyst 19
may be capable of maintaining the NOx emissions of the exhaust
treatment system 10 described herein below approximately 0.2
grams/horsepower-hour, in compliance with future government
regulations. Because the SCR catalyst 19 is capable of obtaining
such low levels of NOx emissions, reducing the amount of NOx
produced by the power source 12 by, for example, recirculating at
least a portion of the exhaust gas, may no longer be necessary.
Thus, due to the presence of the SCR catalyst 19, the EGR loop may
instead be used to assist in improving, for example, the fuel
economy of the power source 12 and/or the exhaust treatment system
10, generally. In particular, a system combining an SCR catalyst
with EGR methods and components may enable the user to employ, for
example, power source control techniques to improve fuel economy.
Such techniques may include, for example, advancing fuel injection
timing, modifying the actuation of combustion chamber intake
valves, and/or altering fuel (rail) pressure.
[0057] In addition, recirculating a portion of the exhaust flow
back to the power source 12 may increase the amount of NO.sub.2
produced by the power source 12 during combustion. Such an increase
may result in an exhaust flow having a higher ratio of NO.sub.2 to
NO at the outlet 43 of the power source 12 than an exhaust flow
produced by a power source of an exhaust treatment system not
utilizing EGR. Obtaining this higher ratio of NO.sub.2 to NO
through combustion may reduce the oxidation requirements of the
oxidation catalyst 18 during operation. As a result, a smaller,
less expensive oxidation catalyst 18 having less precious metals,
may be used. The use of such an oxidation catalyst 18 may, thus,
reduce the overall cost of the exhaust treatment system 10 and may
reduce the overall footprint of the system 10 within, for example,
a crowded engine compartment of a machine to which the power source
12 is connected. In addition, obtaining this higher ratio of
NO.sub.2 to NO may be particularly advantageous at low temperatures
(such as those occurring at start-up or during low load conditions)
where the ability of the oxidation catalyst 18 to oxidize NO to
NO.sub.2 is diminished.
[0058] Other embodiments of the disclosed exhaust treatment system
10, 100, 200, 300 will be apparent to those skilled in the art from
consideration of the specification. For example, the system 10,
100, 200, 300 may include additional filters, such as, for example,
a sulfur trap, disposed upstream of the filter 16. The sulfur trap
may be useful in capturing sulfur molecules carried by the exhaust
flow. It is intended that the specification and examples be
considered as exemplary only, with the true scope of the invention
being indicated by the following claims.
* * * * *