U.S. patent application number 12/858454 was filed with the patent office on 2012-02-23 for tall vertical scr.
This patent application is currently assigned to Caterpillar Inc.. Invention is credited to Andrew J. Kieser, Stephan D. Roozenboom.
Application Number | 20120042637 12/858454 |
Document ID | / |
Family ID | 45592963 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120042637 |
Kind Code |
A1 |
Roozenboom; Stephan D. ; et
al. |
February 23, 2012 |
TALL VERTICAL SCR
Abstract
An exhaust aftertreatment system including an exhaust conduit
transmitting exhaust from an engine, a reductant introduction
system introducing a reductant into the exhaust, and a selective
catalytic reduction catalyst (SCR) receiving the exhaust and
reductant. A SCR length divided by a SCR width is greater than 4. A
SCR cell density is less than 180 cells per square inch of
cross-sectional area of the SCR. The SCR is vertically mounted
adjacent a corner of a cab of a machine.
Inventors: |
Roozenboom; Stephan D.;
(Washington, IL) ; Kieser; Andrew J.;
(Peterborough, GB) |
Assignee: |
Caterpillar Inc.
Peoria
IL
|
Family ID: |
45592963 |
Appl. No.: |
12/858454 |
Filed: |
August 18, 2010 |
Current U.S.
Class: |
60/297 ;
60/301 |
Current CPC
Class: |
F01N 2590/08 20130101;
Y02T 10/12 20130101; Y02T 10/24 20130101; F01N 3/035 20130101; F01N
2340/00 20130101; F01N 2340/04 20130101; F01N 2490/18 20130101;
F01N 3/2066 20130101; F01N 2330/48 20130101 |
Class at
Publication: |
60/297 ;
60/301 |
International
Class: |
F01N 3/035 20060101
F01N003/035; F01N 3/10 20060101 F01N003/10 |
Claims
1. A exhaust aftertreatment system comprising: an exhaust conduit
transmitting exhaust from an engine; a reductant introduction
system introducing a reductant into the exhaust; and a selective
catalytic reduction catalyst (SCR) receiving the exhaust and
reductant, wherein a SCR length divided by a SCR width is greater
than 4.
2. The exhaust aftertreatment system of claim 1 wherein the SCR
includes a plurality of cells with a cell density of less than 180
cells per square inch of cross-sectional area of the SCR.
3. The exhaust aftertreatment system of claim 1 wherein the SCR
includes a plurality of cells with a cell density of between 130
and 180 cells per square inch of cross-sectional area of the
SCR.
4. The exhaust aftertreatment system of claim 3 wherein the SCR
length is between 3 and 4 feet.
5. The exhaust aftertreatment system of claim 1 wherein the SCR is
vertically mounted on a machine.
6. The exhaust aftertreatment system of claim 5 wherein the
reductant introduction system introduces the reductant into a
horizontal section of the exhaust conduit.
7. The exhaust aftertreatment system of claim 5 wherein the SCR is
mounted adjacent a corner of a cab.
8. The exhaust aftertreatment system of claim 5 wherein the SCR
includes a metallic substrate.
9. The exhaust aftertreatment system of claim 5 further including a
diesel oxidation catalyst (DOC) and a diesel particulate filter
(DPF) upstream of the SCR and a clean-up catalyst downstream of the
SCR.
10. A exhaust aftertreatment system comprising: an exhaust conduit
transmitting exhaust from an engine; a reductant introduction
system introducing a reductant into the exhaust; and a selective
catalytic reduction catalyst (SCR) receiving the exhaust and
reductant, wherein the SCR includes a plurality of cells with a
cell density of less than 180 cells per square inch of
cross-sectional area of the SCR.
11. The exhaust aftertreatment system of claim 1 wherein a SCR
length divided by a SCR width is greater than 4.
12. The exhaust aftertreatment system of claim 11 wherein the SCR
includes a plurality of cells with a cell density of between 130
and 180 cells per square inch of cross-sectional area of the
SCR.
13. The exhaust aftertreatment system of claim 11 wherein the SCR
length is between 3 and 4 feet.
14. The exhaust aftertreatment system of claim 11 wherein the SCR
is vertically mounted on a machine.
15. The exhaust aftertreatment system of claim 14 wherein the
reductant introduction system introduces the reductant into a
horizontal section of the exhaust conduit.
16. The exhaust aftertreatment system of claim 14 wherein the SCR
is mounted adjacent a corner of a cab.
17. The exhaust aftertreatment system of claim 14 wherein the SCR
includes a metallic substrate.
18. The exhaust aftertreatment system of claim 14 further including
a diesel oxidation catalyst (DOC) and a diesel particulate filter
(DPF) upstream of the SCR and a clean-up catalyst downstream of the
SCR.
19. A machine comprising: an exhaust conduit transmitting exhaust
from an engine; a reductant introduction system introducing a
reductant into the exhaust; and a selective catalytic reduction
catalyst (SCR) receiving the exhaust and reductant, wherein the SCR
is vertically mounted adjacent a corner of a cab of the
machine.
20. The exhaust aftertreatment system of claim 19 wherein a SCR
length divided by a SCR width is greater than 4 and the SCR
includes a plurality of cells with a cell density of less than 180
cells per square inch of cross-sectional area of the SCR.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to engine exhaust
aftertreatment systems and more particularly to the size,
orientation, and locations of components in exhaust aftertreatment
systems.
BACKGROUND
[0002] A selective catalytic reduction (SCR) system 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. SCR systems use reductants, such as urea,
that are introduced into the exhaust stream.
[0003] U.S. Pat. No. 6,182,443 (the '443 patent) discloses an
aftertreatment system including an SCR system. The SCR includes a
monolithic structure with a catalyst applied. The monolithic
structure has channels or cells through which the exhaust passes
and interacts with the applied catalyst. According to the '443
patent, the "[c]ell density should be maximized consistent with
pressure drop limitations and is preferably in the range of 200-800
cells per square inch of cross-sectional area of the
structure."
SUMMARY
[0004] The present disclosure provides an exhaust aftertreatment
system including an exhaust conduit transmitting exhaust from an
engine, a reductant introduction system introducing a reductant
into the exhaust, and a selective catalytic reduction catalyst
(SCR) receiving the exhaust and reductant. In one aspect a SCR
length divided by a SCR width is greater than 4. In another aspect
a SCR cell density is less than 180 cells per square inch of
cross-sectional area of the SCR. In yet another aspect the SCR is
vertically mounted adjacent a corner of a cab of a machine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a diagrammatic view of a machine including a power
system with an engine and an aftertreatment system.
[0006] FIG. 2 is a side view of a SCR known in the prior art.
[0007] FIG. 3 is a side view of a SCR from FIG. 1.
[0008] FIG. 4 is a side view of an alternative SCR from FIG. 1.
[0009] FIG. 5 is a cross-sectional view of the alternative SCR from
FIG. 3.
[0010] FIG. 6 is another cross-sectional view of the alternative
SCR from FIG. 3.
DETAILED DESCRIPTION
[0011] FIG. 1 shows a machine 1 including a cab 2 where an operator
3 sits and a power system 10. The machine 1 might be a tractor (as
illustrated), on-highway truck, car, vehicle, off-highway truck,
earth moving equipment, material handler, logging machine,
compactor, construction equipment, generator, pump, aerospace
application, locomotive application, marine application, or any
other device or application requiring a power system 10.
[0012] The power system 10 includes an engine 12 and an
aftertreatment system 14 to treat an exhaust stream 16 produced by
the engine 12. The engine 12 may include other features not shown,
such as controllers, fuel systems, 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.).
[0013] The aftertreatment system 14 includes an engine exhaust
conduit 18 delivering the exhaust stream 16. The aftertreatment
system 14 includes an exhaust conduit 18 and a Selective Catalytic
Reduction (SCR) system 20. The SCR system 20 includes an SCR 22,
and a reductant supply system 24.
[0014] In some embodiments, the aftertreatment system 14 may also
include a diesel oxidation catalyst (DOC) 26, a diesel particulate
filter (DPF) 28, and a clean-up catalyst 30. The DOC 26, DPF 28,
SCR 22, and clean-up catalyst 30 involve the appropriate catalyst
or other material disposed on a substrate. The substrate may
consist of cordierite, silicon carbide, other ceramic, or metal
structure. The substrates may form a honeycomb structure with a
plurality of through going channels or cells for the exhaust stream
16 to pass through. The DOC 26, DPF 28, SCR 22, and clean-up
catalyst 30 substrates may be housed in canisters 31. The DOC 26
and DPF 28 may be in the same canister 31, as shown, or separate.
Likewise, the SCR catalyst 22 and clean-up catalyst 30 may also be
in the same canister 31, as shown, or separate.
[0015] The aftertreatment system 14 is configured to remove,
collect, or convert undesired constituents from the exhaust stream
16. The DOC 26 oxidizes Carbon Monoxide (CO) and unburnt
hydrocarbons (HC) into Carbon Dioxide (CO2). The DPF 28 collects
particulate matter or soot. The SCR catalyst 22 is configured to
reduce an amount of NOx in the exhaust stream 16 in the presence of
a reductant.
[0016] The clean-up catalyst 30 may embody an ammonia oxidation
catalyst (AMOX). The clean-up catalyst 30 is configured to capture,
store, oxidize, reduce, and/or convert reductant that may slip past
or breakthrough the SCR catalyst 22. The clean-up catalyst 30 may
also be configured to capture, store, oxidize, reduce, and/or
convert other constituents present.
[0017] In the illustrated embodiment, the exhaust stream 16 exits
the engine 12, passes through the DOC 46, DPF 48, then passes
through the SCR system 20, and then passes through the clean-up
catalyst 30 via the exhaust conduit 18. The SCR system 20 is
downstream of the DPF 28 and the DOC 26 is upstream of the DPF 28.
The clean-up catalyst 30 is downstream of the SCR system 20. In
other embodiments, these devices may be arranged in a variety of
orders and may be combined together. In one embodiment, the SCR
catalyst 22 may be combined with the DPF 48 with the catalyst
material deposited on the DPF 48. Other exhaust treatment devices
may also be located upstream, downstream, or within the SCR system
20.
[0018] The reductant supply system 24 is configured to introduce
the reductant in to the exhaust upstream of the SCR 22. The
reductant supply system 24 may include a reductant source 32,
reductant line 34, and an injector 36. The reductant supply system
24 may also include a pump and one or more valves to achieve and
control the delivery of the reductant. Reductant may also be
provided to the SCR 22 from the engine 12 or in a variety of other
ways.
[0019] The reductant supply system 24 may also include a thermal
management system to thaw frozen reductant, prevent reductant from
freezing, or preventing reductant from overheating. Components of
the reductant supply system 24 may also be insulated to prevent
overheating of the reductant. The reductant supply system 24 may
also include an air assist system for introducing compressed air.
The air assist system may also be used to purge the reductant line
34 and other reductant supply system 24 components of reductant
when not in use.
[0020] The injector 36 injects reductant in a mixing section 37 of
the exhaust conduit 18 where the reductant may be converted and mix
with the exhaust stream 16. A mixer may also be included in the
mixing section 37 to help the conversion and mixing. While other
reductants are possible, urea is the most common reductant. The
urea reductant converts, decomposes, or hydrolyzes into ammonia
(NH3) and is then adsorbed or otherwise stored in the SCR catalyst
22. The NH3 is then consumed in the SCR Catalyst 22 through a
reduction of NOx into Nitrogen gas (N2).
[0021] A heat source may also be included to remove the soot from
or regenerate the DPF 28, thermally manage the SCR catalyst 22, DOC
26, or clean-up catalyst 30, to remove sulfur from the DOC 26, DPF
28, or SCR catalyst 22, or to remove deposits of reductant that may
have formed. The heat source may embody a burner, hydrocarbon
dosing system to create an exothermic reaction on the DOC 46,
electric heating element, microwave device, or other heat source.
The heat source may also embody operating the engine 12 under
conditions to generate elevated exhaust stream 16 temperatures. The
heat source may also embody a backpressure valve or another
restriction in the exhaust conduit 18 to cause elevated exhaust
stream 16 temperatures.
[0022] The aftertreatment system 14 may also include a control
system with NOX sensors. The control system may use the NOX sensor
or engine maps to control the introduction of reductant from the
reductant supply system 24 to achieve the level of NOX reduction
required while controlling ammonia slip. The control system may
also include soot sensors associated with the DPF 28 to control
regeneration of the DPF 28.
INDUSTRIAL APPLICABILITY
[0023] Emission regulations have only recently necessitated the
need for SCR systems 20. Prior art SCR systems utilize horizontally
mounted, short and wide SCRs 38 with high cell densities, as shown
in FIG. 2. The short and wide dimensions limit backpressure losses
while the high cell densities provide high NOX conversion
efficiencies by exposing the exhaust to a greater surface area of
catalyst material. The horizontal mounting is utilized for
structural reasons. Ceramic substrates are often used which may be
heavy, especially when cell densities are high. The horizontal
mounting allows the heavy substrate to be supported. The horizontal
mounting is also conducive to receive the reductant, which is often
injected in a horizontal section of the exhaust pipe.
[0024] However, many existing machines 1 were not designed to
accommodate a short and wide SCR 38. The design changes required to
accommodate such a short and wide SCR 38 may impact an operator's 3
visibility. Such design changes may include larger hoods or engine
compartments. Such design changes are also expensive.
[0025] The disclosed SCR 22 is suited to be located in certain
mounting locations of the machine 1. The mounting location may be
selected for a number of different reasons. For example, the
mounting location may be a location where the impact on operator 3
visibility is reduced or a location where the machine 1 was already
designed to have a muffler located. Because an SCR often provides
the level of sound dampening required, the SCR 22 may replace the
muffler and therefore only limited design changes to the machine 1
would be required
[0026] An example of one such mounting location is shown in FIG. 1.
FIG. 1 shows a tractor with the SCR 22 mounted along or adjacent a
corner of the cab 2. While adjacent, the SCR 22 may still be spaced
apart from the corner of the cab, which a common location for a
muffler. The corner of the cab 2 provides the operator 3 with a
greater degree of visibility than other solutions and is a location
where a muffler is commonly located.
[0027] Many other mounting locations for mounting of the SCR 22 are
also possible. For example, with a bulldozer or track-type tractor
side visibility is important and the SCR 22 may be mounted more
toward the front center of the cab 2 over the engine compartment.
Other machines, such as motor graders, compactors, excavators, and
wheel loaders often have rear-mounted engines so the SCR 22 may be
vertically mounted behind the cab 2. Yet other machines, such as
large mining trucks and wheel tractor-scrapers have side-mounted
engines so the SCR 22 may be vertically mounted to the side of the
cab 2. In another example, the mounting location for an on-highway
truck may be the back corner of the cab 2, despite a front engine
mounted design. The mounting location does not necessary require a
vertical orientation, for many automotive applications the mounting
location is a horizontal mounting along the length and underneath
the vehicle.
[0028] Many of the mounting locations described above require the
SCR not to be too wide. A wide SCR 38 could limit visibility in
vertical mounting situations outside the cab 2. A wide SCR 38 could
also be a clearance issue in horizontal mounted situations
underneath the machine 1.
[0029] However, while the mounting locations described above often
do not facilitate a wide SCR 38, they do often allow the SCR 22 to
be long. In vertical mounting locations, the SCR 22 may also need
to be light because the vertical mounting provides limited support.
Meanwhile the SCR 22 must still achieve the level of NOX conversion
needed without creating too much backpressure.
[0030] FIG. 3 illustrates an SCR 22 configured to meet the needs
listed above. The illustrated SCR 22 has a SCR length 40 and a SCR
width 42. The SCR width 42 may represent a diameter if the SCR 22
is circular. The SCR length 40 and SCR width 42 establish an aspect
ratio of SCR length 40 divided by SCR width 42 of greater than 4.
In other embodiments the aspect ratio of SCR length 40 divided by
SCR width 42 may be greater than 3.5. In yet other embodiments the
aspect ratio of SCR length 40 divided by SCR width 42 may be
greater than 5, between 4 and 8, or between 5 and 8. By way of
comparison, prior art wide SCRs 38, as shown in FIG. 2, may have
lower aspect ratios of typically between 1 and 2.
[0031] In contrast to the prior art's teachings of higher cell
densities, the long SCR length 40 enables lower cell density and
larger cells or channels. Because of the long SCR length 40, high
cell densities are not needed to create the surface area for
exhaust stream 16 contact needed for high NOX conversion
efficiencies. The long SCR length 40 creates the high amount of
surface area for exhaust stream 16 contact for high NOX conversion
efficiencies. The larger cells prevent excessive amounts of
backpressure created from small cells which block exhaust stream 16
flow. The larger cells enable a narrower SCR width 42 while still
limiting backpressure.
[0032] The SCR 22 cell density may be less than 180 cells per
square inch of cross-sectional area. In other embodiments, The SCR
22 cell density may be between 50 and 180. By way of comparison,
prior art wide SCRs 38, as shown in FIG. 2, may have cell densities
between 200 and 800 cells per square inch of cross-sectional
area.
[0033] The SCR cell density may be a function of SCR length 40 and
the power system's 10 characteristics. The longer the SCR length
40, the less the cell density may need to be to achieve the desired
SCR efficiency. The SCR length 40 may be between 2 and 8 feet. When
the SCR length 40 is between 4 and 5 feet the SCR cell density may
be between 100 and 150 cells per square inch of cross-sectional
area. When the SCR length 40 is between 5 and 6 feet the SCR cell
density may be between 60 and 120 cells per square inch of
cross-sectional area. When the SCR length 40 is between 3 and 4
feet the SCR cell density may be between 130 and 180 cells per
square inch of cross-sectional area.
[0034] The SCR 22 substrate may also be metallic, which is often
lighter than ceramic. The lightweight achieved by the low cells per
square inch of cross-sectional area and lighter metallic material
helps enable vertical mounting because less weight needs to be
supported. The long SCR length 40 also helps provide greater
surface area between the canister 31 and the SCR 22 to help achieve
the vertical mounting. Metallic substrates may also be able to be
formed in longer structures with through going cells than ceramic
can be extruded into.
[0035] A support 44 may also be needed to achieve the vertical
mounting. The support 44 may be located underneath the SCR 22 to
help support the weight of the SCR 22. The support 44 may be
configured to allow the exhaust stream 16 to pass and not block the
SCR 22. As seen in FIG. 3, the support 44 may embody tabs or a thin
ring welded or otherwise secured to the inside wall of the canister
31. The support 44 may also be thick ring with openings, as seen in
FIG. 5. The support 44 could also be thin cross-members extending
from one side of the canister 31 to another side.
[0036] The reductant mixing section 37 may need to be sufficiently
long and may need to be horizontal. Spraying a liquid reductant
vertically upward may be problematic due to gravity. In the current
configuration the injector 36 is mounted horizontal and most of the
reductant is gaseous before turning vertical to pass through the
SCR 22. The reductant mixing section 37 length allows a majority of
the urea reductant to convert into gaseous ammonia before turning
vertical. If the reductant were injected in the gaseous form these
limitations on the reductant mixing section 37 could be removed or
decreased.
[0037] FIGS. 4-6 illustrate a split SCR 50 as an alternative
embodiment for the SCR 22 while still achieving the same aspect
ratios described above. Unlike the SCR 22 in FIG. 3, the split SCR
50 includes multiple SCR 22 bodies with the exhaust stream 16 being
split. The split SCR 50 includes an interior SCR 52, exterior SCR
54, exterior passage 56, and an interior passage 58. The split SCR
50 configuration allows for individual split SCRs 52 and 54 to have
shorter lengths and larger cell densities, like prior art wide SCRs
38.
[0038] The interior SCR 52 has a cross-section area that is smaller
than the cross-sectional area of the canister 31. The space between
the interior SCR 52 and the canister forms a lower portion 60 of
the exterior passage 56. An upper portion 62 of the exterior
passage 56 widens in a transition zone 64 between the interior and
exterior SCRs 52 and 54 to meet with the exterior SCR 54. The
exterior SCR 54 has cross-section with a through-going opening that
forms an upper portion 66 of the interior passage 58. A lower
portion 68 of the interior passage 58 mates between the interior
SCR 52 and the upper portion of the interior passage 58 in the
transition zone 64. A dividing wall 70 isolates the flow of exhaust
in the interior passage 58 from the exterior passage 56 in the
transition zone 64. The support 44 for the SCR 52 may extend across
yet still allow the exhaust stream 16 to pass through or around to
enter the lower portion 60 of the exterior passage 56.
[0039] A portion of the exhaust stream 16 passes through the
interior SCR 52 and then through the interior passage 58. The other
portion of the exhaust stream 16 passes through the exterior
passage 56 and then through the exterior SCR 54. The exhaust stream
16 then exits the split SCR 50 and may pass through the clean-up
catalyst 30.
[0040] Others configurations of the split SCR 50 are possible. For
example, the order of interior and exterior SCRs and passages 52,
54, 56, 58 may be reversed. The clean-up catalyst 30 may also be
split in a similar manner as the split SCR 50.
[0041] 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.
* * * * *