U.S. patent application number 12/404431 was filed with the patent office on 2010-09-16 for hydrocarbon scr aftertreatment system.
This patent application is currently assigned to Caterpillar Inc.. Invention is credited to JAMES J. DRISCOLL, JOHN P. TIMMONS, ZHIYONG WEI.
Application Number | 20100229539 12/404431 |
Document ID | / |
Family ID | 42729565 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100229539 |
Kind Code |
A1 |
TIMMONS; JOHN P. ; et
al. |
September 16, 2010 |
HYDROCARBON SCR AFTERTREATMENT SYSTEM
Abstract
An engine exhaust aftertreatment system including a selective
catalytic reduction (SCR) device. The system contains no
significant amount of catalyzed material upstream of the SCR
device.
Inventors: |
TIMMONS; JOHN P.;
(Chillicothe, IL) ; DRISCOLL; JAMES J.; (Dunlap,
IL) ; WEI; ZHIYONG; (Chicago, IL) |
Correspondence
Address: |
Caterpillar Inc.;Intellectual Property Dept.
AH 9510, 100 N.E. Adams Street
PEORIA
IL
61629-9510
US
|
Assignee: |
Caterpillar Inc.
Peoria
IL
|
Family ID: |
42729565 |
Appl. No.: |
12/404431 |
Filed: |
March 16, 2009 |
Current U.S.
Class: |
60/297 ;
60/301 |
Current CPC
Class: |
Y02T 10/24 20130101;
F01N 2570/14 20130101; Y02T 10/12 20130101; F01N 3/2066
20130101 |
Class at
Publication: |
60/297 ;
60/301 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Claims
1. An engine exhaust aftertreatment system comprising: a selective
catalytic reduction (SCR) device in an exhaust stream of an engine,
the SCR device including a composition that reduces an amount of
NOx in the presence of a reductant; and wherein no significant
amount of catalyzed material is present in the exhaust stream
upstream of the SCR device.
2. The engine exhaust aftertreatment system of claim 1 wherein the
SCR device is not sensitive to the ratio of NO to NO2 in the
exhaust stream.
3. The engine exhaust aftertreatment system of claim 1 wherein the
composition of the SCR device includes silver tungstate.
4. The engine exhaust aftertreatment system of claim 1 wherein the
reductant is a hydrocarbon.
5. The engine exhaust aftertreatment system of claim 1 further
including: a clean-up catalyst downstream of the SCR device.
6. The engine exhaust aftertreatment system of claim 1 further
including: a diesel particulate filter present in the exhaust
stream upstream of the SCR device.
7. The engine exhaust aftertreatment system of claim 6 further
including: a heat source present in the exhaust stream upstream of
the diesel particulate filter.
8. The engine exhaust aftertreatment system of claim 7 wherein the
heat source is a fuel fired burner.
9. An engine exhaust aftertreatment system comprising: a selective
catalytic reduction (SCR) device in an exhaust stream of an engine,
the SCR device including a composition that reduces an amount of
NOx in the presence of a reductant; and wherein a ratio of NO to
NO2 exiting the engine is substantially the same as a ratio of NO
to NO2 entering the SCR device.
10. The engine exhaust aftertreatment system of claim 9 wherein no
significant amount of catalyzed material is present in the exhaust
stream upstream of the SCR device.
11. The engine exhaust aftertreatment system of claim 9 wherein the
SCR device is not sensitive to the ratio of NO to NO2 in the
exhaust stream.
12. The engine exhaust aftertreatment system of claim 9 wherein the
composition of the SCR device includes silver tungstate.
13. The engine exhaust aftertreatment system of claim 9 wherein the
reductant is a hydrocarbon.
14. The engine exhaust aftertreatment system of claim 9 further
including: a clean-up catalyst downstream of the SCR device.
15. The engine exhaust aftertreatment system of claim 9 further
including: a diesel particulate filter present in the exhaust
stream upstream of the SCR device.
16. The engine exhaust aftertreatment system of claim 15 further
including: a heat source present in the exhaust stream upstream of
the diesel particulate filter.
17. The engine exhaust aftertreatment system of claim 16 wherein
the heat source is a fuel fired burner.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to engine exhaust
aftertreatment systems, and more particularly to exhaust
aftertreatment systems employing NOx reduction technologies.
BACKGROUND
[0002] Systems may be included in an exhaust treatment or
aftertreatment system for a power system to remove or reduce
nitrous oxide (NOx or NO) emissions coming from the exhaust of an
engine. Two systems that may be used to reduce NOx are ammonia
selective catalytic reduction (NH3-SCR) and hydrocarbon selective
catalytic reduction (HC-SCR) systems. NH3 SCR systems use ammonia,
commonly from urea, as a reductant while HC-SCR systems use
hydrocarbon, commonly from fuel, as a reductant.
[0003] U.S. Patent Publication No. 2008/0155972 (the '972 publn)
describes multiple exhaust treatment systems. The '972 publn
discloses in FIG. 4 a system including a filter having a catalyzed
substrate upstream of an NH3-SCR and a clean-up catalyst.
SUMMARY
[0004] The present disclosure provides an engine exhaust
aftertreatment system including a selective catalytic reduction
(SCR) device. In one aspect, the system includes no significant
amount of catalyzed material upstream of the SCR device. In another
aspect, the present disclosure provides a ratio of NO to NO2
exiting the engine that is substantially the same as a ratio of NO
to NO2 entering the SCR device.
[0005] Other features and aspects of this disclosure will be
apparent from the following description and the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a diagrammatic view of a power system including an
engine and an aftertreatment system.
DETAILED DESCRIPTION
[0007] As seen in FIG. 1, a power system 10 includes an engine 12,
a fuel system 14, and an aftertreatment system 16 to treat an
exhaust stream 18 produced by the engine 12. The engine 12 may
include other features not shown, such as controllers, air systems,
cooling systems, peripheries, drivetrain components, turbochargers,
exhaust gas recirculation systems, etc. The engine 12 may be any
type of engine (internal combustion, gas, diesel, gaseous fuel,
natural gas, propane, etc.), may be of any size, with any number of
cylinders, and in any configuration ("V," in-line, radial, etc.).
The engine 12 may be used to power any machine or other device,
including on-highway trucks or vehicles, off-highway trucks or
machines, earth moving equipment, generators, aerospace
applications, locomotive applications, marine applications, pumps,
stationary equipment, or other engine powered applications.
[0008] The aftertreatment system 16 includes a heat source 20, a
bare diesel particulate filter (DPF) 22, a hydrocarbon selective
catalytic reduction (HC-SCR) system 24, a clean-up catalyst 26, and
an exhaust pipe 28. The exhaust stream 18 exits the engine 12,
passes by the heat source 20, passes through the bare DPF 22, then
passes through the HC-SCR system 24, and then passes through the
clean-up catalyst 26 via the exhaust pipe 28.
[0009] The engine's 12 fuel system 14 includes a fuel tank 30
holding fuel 32. The fuel 32 may be supplied to engine 12, heat
source 20, and HC-SCR system 24 via fuel lines 34 and fuel pumps
36. In certain embodiments, the fuel system may have more than one
fuel tank 30. More than one type of fuel 32 may also be used. The
heat source 20 and HC-SCR system 24 may also not need to be
supplied by fuel 32 in certain embodiments.
[0010] The heat source 20 regenerates the bare DPF 22. During
operation, the bare DPF 22 collects particulate matter or soot. The
heat source 20 heats the soot, typically in excess of 600 degrees
Celsius, and burns it away.
[0011] The heat source 20 may include a housing 38 and a burner 40.
The housing 38 may contain a flame 41 generated by the burner 40.
The housing 38 may also route the exhaust stream 18 to be heated by
the burner 40. The burner 40 may receive a supply of fuel 32 and
may also include an ignition source and air supply to generate the
flame 41. In alternative embodiments the heat source may not employ
a fuel-fired burner 40. The heat source 20 may embody an electric
heating element or microwave device. The heat source 20 may also
embody operating the engine 12 under conditions to generate
elevated exhaust stream 18 temperatures.
[0012] The bare DPF 22 removes particulate matter from the exhaust
stream 18. The bare DPF 22 may be made from cordierite, silicon
carbide, or other material to remove the particulate matter. The
bare DPF 22 may be wall flow with a honeycomb cross-section. The
bare DPF 22 contains no significant amount of catalyzed
material.
[0013] The HC-SCR system 24 may include a reductant system 42,
mixer 44, and a HC-SCR 46. The reductant system 42 is shown to
include a valve 48 and injector 50. The fuel 32 may serve as a
reductant for the HC-SCR 46 and the fuel tank 30 may serve as the
reductant source. The reductant is drawn from the fuel tank 30 via
the pump 36 and delivery is controlled via the valve 48. In other
embodiments, the reductant may be a different source of
hydrocarbons than the fuel 32. The reductant source may also be
different and separate form the engine's 12 fuel system 14.
[0014] The injector 50 creates a reductant spray 52 or otherwise
introduces the reductant or fuel 32 into the exhaust stream 18 or
HC-SCR 46. The injector may or may not be air assisted. The mixer
44 may be added to aid mixing of the reductant with the exhaust
stream 18.
[0015] The HC-SCR 46 includes a catalyst disposed on a substrate.
The catalyst is configured to reduce an amount of NOx in the
exhaust stream 18 by using a hydrocarbon as a reductant. One such
HC-SCR uses silver tungstate as described in US Patent Application
2008/0069743.
[0016] The clean-up catalyst 26 may be included downstream of the
HC-SCR 46. The clean-up catalyst 26 may be configured to capture,
store, oxidize, reduce, and/or convert reductant that may slip past
or breakthrough the HC-SCR 46. The clean-up catalyst may also
convert carbon monoxide (CO) into carbon dioxide (CO2). The
clean-up catalyst 26 may also reduce ammonia (NH3) that may be
produced by the HC-SCR or otherwise present into nitrogen (N2). The
clean-up catalyst may consist of an ammonia catalyst (AMOx), diesel
oxidation catalyst (DOC), NH3-SCR, or a combination of catalyst
types. The clean-up catalyst 26 may also be a new catalyst design
configured to capture, store, oxidize, reduce, and/or convert the
constituents present.
[0017] Controllers and sensors may also be added to the
aftertreatment system 16. The sensors may measure parameters such
as temperature, soot quantity, NOx level, etc. The controllers may
receive data from the sensors and control the operation of the heat
source 20, reductant system 42, and/or engine 12 to achieve a
desired performance.
INDUSTRIAL APPLICABILITY
[0018] As described above, the disclosed aftertreatment system 16
does not contain a significant amount of catalyzed material
upstream of the HC-SCR 46. The absent catalyzed material may
represent an oxidation or other non-NOx reduction catalysts, such
as a DOC. Removing the catalyzed material may enhance the operation
of the aftertreatment system 16 as described below.
[0019] Avoiding a significant amount of catalyzed material or
bodies upstream of the HC-SCR 46 may prevent sulfate poisoning that
would deactivate the HC-SCR 46. A significant amount of catalyzed
material may be the amount needed to generate a quantity of
sulfates from the exhaust stream 18 that would deactivate the
HC-SCR 46. Catalysts transform sulfur dioxide SO2 into sulfur
trioxide SO3, which then becomes sulfuric acid via reaction with
water (SO3+H2O.fwdarw.H2SO4) or a sulfate (such as AgSO4) on the
HC-SCR catalyst.
[0020] Applicants have found that the HC-SCR 46 is negatively
impacted and deactivated from exposure to these sulfates. The
negative impacts have even been experienced as a result of even
small amounts of sulfates, such as levels generated by even
ultra-low sulfur fuels. By removing the catalyzed bodies upstream
of the HC-SCR 46, sulfur poisoning can be avoided.
[0021] Because the disclosed aftertreatment system 16 avoids
catalyzed bodies upstream of the HC-SCR 46, heat source 20 is
needed to regenerate the bare DPF 22. Other aftertreatment systems
may use catalyzed bodies upstream of or integrated with the DPF to
achieve full or partial passive regeneration. Passive regeneration
uses the catalyst to convert nitrogen monoxide (NO) into nitrogen
dioxide (NO2). The NO2 is used by the DPF to oxidize the soot and
regenerate the DPF at a lower temperature. The disclosed
aftertreatment system 16, however, does not convert NO to NO2
upstream of the HC-SCR 46. Therefore, no substantial passive
regeneration is achieved and heat source 20 may need to be capable
of reaching high temperatures in a robust manner. This need for a
heat source 20 capable of reaching high temperatures in a robust
manner may be met through the use of a fuel fired burner 40.
[0022] In addition to achieving passive regeneration, other
aftertreatment systems include catalyzed bodies upstream of the SCR
to achieve a desired NO to NO2 ratio entering the SCR to improve
the efficiency of the SCR. As mentioned above, in contrast to other
SCR aftertreatment systems, the disclosed aftertreatment system 16
does not convert NO to NO2 upstream of the HC-SCR 46. In the
disclosed aftertreatment system 16, the NO to NO2 ratio is
substantially the same entering the HC-SCR 46 as it is exiting the
engine 12. Applicants realized that the HC-SCR 46 is not sensitive
to the NO to NO2 ratio like other SCR systems may be and therefore
the catalyzed bodies upstream of the HC-SCR 46 are not needed to
achieve this ratio.
[0023] The disclosed aftertreatment system 16 may also provide
additional reductant to be used by the HC-SCR 46 in the form of
engine out hydrocarbons and soluble organic fraction (SOF) long
chain alkanes. The bare DPF 22 may store or trap SOF at low
temperatures when the HC-SCR 46 is not active and release the SOF
at higher temperatures when the HC-SCR 46 is active and the
reductant is needed. This additional source of reductant may reduce
the quantity needing to be supplied by the reductant system 42 and
may reduce fuel consumption. In other aftertreatment systems, this
additional source of reductant may be, at least partially, consumed
by the upstream catalyzed bodies.
[0024] Avoiding the catalyst bodies upstream of the HC-SCR 46 may
also reduce backpressure in the aftertreatment system 16. Packaging
of the aftertreatment system 16 may also be easier without the
catalyzed body upstream of the HC-SCR 46.
[0025] Although the embodiments of this disclosure as described
herein may be incorporated without departing from the scope of the
following claims, it will be apparent to those skilled in the art
that various modifications and variations can be made. Other
embodiments will be apparent to those skilled in the art from
consideration of the specification and practice of the disclosure.
It is intended that the specification and examples be considered as
exemplary only, with a true scope being indicated by the following
claims and their equivalents.
* * * * *