U.S. patent application number 12/318816 was filed with the patent office on 2010-07-08 for exhaust treatment system having a reductant supply system.
This patent application is currently assigned to CATERPILLAR INC.. Invention is credited to Cornelius N. Opris, Anthony C. Rodman.
Application Number | 20100170225 12/318816 |
Document ID | / |
Family ID | 42310811 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100170225 |
Kind Code |
A1 |
Opris; Cornelius N. ; et
al. |
July 8, 2010 |
Exhaust treatment system having a reductant supply system
Abstract
An exhaust treatment device is disclosed. The exhaust treatment
device includes a supply of reductant at a first pressure and an
exhaust passage. The device further includes a venturi located
within the exhaust passage and configured to facilitate reductant
entry into the exhaust passage by reducing a pressure of exhaust
flowing through the exhaust passage to a second pressure that is
less than the first pressure.
Inventors: |
Opris; Cornelius N.;
(Peoria, IL) ; Rodman; Anthony C.; (Chillicothe,
IL) |
Correspondence
Address: |
CATERPILLAR/FINNEGAN, HENDERSON, L.L.P.
901 New York Avenue, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
CATERPILLAR INC.
|
Family ID: |
42310811 |
Appl. No.: |
12/318816 |
Filed: |
January 8, 2009 |
Current U.S.
Class: |
60/286 ; 60/297;
60/324 |
Current CPC
Class: |
Y02T 10/12 20130101;
F01N 2610/1453 20130101; F01N 2610/02 20130101; Y02T 10/24
20130101; F01N 2470/30 20130101; F01N 2610/14 20130101; F01N 3/2066
20130101 |
Class at
Publication: |
60/286 ; 60/297;
60/324 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Claims
1. An exhaust treatment system comprising: a supply of reductant at
a first pressure; an exhaust passage; and a venturi located within
the exhaust passage and configured to facilitate reductant entry
into the exhaust passage by reducing a pressure of exhaust flowing
though the exhaust passage to a second pressure that is less than
the first pressure.
2. The exhaust treatment system of claim 1, further including at
least one orifice located at a throat of the venturi.
3. The exhaust treatment system of claim 2, wherein the supply of
reductant enters the exhaust passage through the at least one
orifice.
4. The exhaust treatment system of claim 1, further including a
temperature controlled valve.
5. The exhaust treatment system of claim 4, wherein the temperature
controlled valve is located upstream of the venturi and is
configured to control a flow of exhaust through the venturi.
6. The exhaust treatment system of claim 1, wherein the reductant
is urea.
7. The exhaust treatment system of claim 1, further including a
catalyst that is at least one of an alumina, elite,
aluminophosphate, hexaluminate, aluminosilicate, zirconate,
titanosilicate, or titanate.
8. The exhaust treatment system of claim 1, wherein the exhaust
passage is a first exhaust passage and the system further includes
a second exhaust passage in parallel with the first exhaust
passage.
9. The exhaust treatment system of claim 8, wherein the second
exhaust passage includes an inlet upstream of the venturi and an
outlet downstream of the venturi.
10. A method of operating an exhaust treatment system comprising:
controlling a flow of exhaust through exhaust passage as a function
of temperature; and injecting a reductant into the exhaust passage
based on a flow rate of exhaust through the exhaust passage.
11. The method of claim 10, wherein the injecting a reductant
includes passively injecting the reductant based on a pressure
difference between a reductant supply and the exhaust passage.
12. The method of claim 10, wherein the injecting a reductant
includes injecting a reductant into a venturi of the exhaust
passage.
13. The method of claim 10, wherein the controlling a flow of
exhaust includes controlling a temperature controlled valve in the
exhaust passage.
14. The method of claim 13, wherein the controlling a flow of
exhaust includes diverting flow around a portion of the exhaust
passage.
15. An exhaust passage comprising: a venturi configured to receive
a reductant and provide an atomized flow of the reductant to the
exhaust passage.
16. The exhaust passage of claim 15, further including at least one
orifice located at a throat of the venturi configured to atomize
the reductant.
17. The exhaust passage of claim 15, further including a valve
configured to control a flow of exhaust to the venturi.
18. The exhaust passage of claim 17, wherein the valve is
configured to control the flow of exhaust as a function of a
temperature of the exhaust.
19. The exhaust passage of claim 15, wherein an amount of flow of
the reductant is a function of a pressure of an exhaust flow
through the venturi.
20. The exhaust passage of claim 15, wherein an amount of flow of
the reductant is a function of temperature of an exhaust flow.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to an exhaust
treatment system, and more particularly, to an exhaust treatment
system having a reductant supply system.
BACKGROUND
[0002] Internal combustion engines, including diesel engines,
gasoline engines, gaseous fuel-powered engines, and other engines
known in the art exhaust a complex mixture of air pollutants. These
air pollutants may be composed of gaseous compounds such as, for
example, oxides of nitrogen (NOx). Due to increased awareness of
the environment, exhaust emission standards have become more
stringent, and the amount of NOx emitted from an engine may be
regulated depending on the type of engine, size of engine, and/or
class of engine.
[0003] One method implemented by engine manufacturers to comply
with the regulation of exhaust flow pollutants is the use of a
selective catalytic reduction (SCR) catalyst to reduce nitrogen
oxides (NOx) from the engine exhaust flow. In SCR systems, a
reductant is added to the exhaust stream and absorbed onto a
catalyst. As exhaust flows over or through the catalyst, adsorbed
reductant and NOx and are chemically reduced to compounds
relatively less harmful than NOx, such as nitrogen gas and
water.
[0004] Thorough mixing and absorption of the reactant into the
exhaust stream helps achieve maximum NOx reduction. In some SCR
systems, a mixer may be disposed within the exhaust stream to
increase turbulence and thereby encourage mixing and absorption. In
other SCR systems, the length of the exhaust pipe may be maximized
to aid mixing and absorption of reactant. These solutions may each
have disadvantages. For example, mixers and long exhaust pipes may
result in non-recoverable increases in backpressure, which may
reduce engine efficiency.
[0005] One method of mixing the reductant in an SCR process is
described in U.S. Pat. No. 6,526,746 (the '746 patent) issued to
Wu. Specifically, the '746 patent discloses an assembly for
delivering reductant into an exhaust line. The assembly includes a
reductant outlet fluidly connected with a mixing chamber. The
mixing chamber includes a venturi throat formed by a converging
portion and a diverging portion. The reductant outlet is positioned
to be in a converging portion of the venturi throat. An electric
metering pump controls the amount of reductant supplied into a NOx
containing exhaust gas stream from a combustion engine.
[0006] Although the '746 patent may direct a reductant into an
exhaust line without the use of a mixer or long exhaust pipe, it
relies on an external sources, such as metering pumps, to supply
the reductant to the exhaust line. External sources may be
expensive and/or heavy, and thus increase operating expenses.
Furthermore, the '746 patent may not adjust the amount of reductant
directed to an exhaust line based on exhaust temperatures.
Specifically, increased exhaust temperatures may increase a rate of
desorption of the reductant from the catalyst surface. The desorbed
reductant may not facilitate NOx conversion and may be considered
wasted. Thus, it may be desirable to reduce the amount of reductant
provided to the exhaust flow when exhaust flow temperature is
increased.
[0007] The disclosed exhaust system is directed to overcoming one
or more of the shortcomings set forth above and/or other problems
in the art.
SUMMARY
[0008] In one aspect, the present disclosure is directed to an
exhaust treatment device. The exhaust treatment device may include
a supply of reductant at a first pressure and an exhaust passage.
The device may further include a venturi located within the exhaust
passage and configured to facilitate reductant entry into the
exhaust passage by reducing a pressure of exhaust flowing through
the exhaust passage to a second pressure that is less than the
first pressure.
[0009] In another aspect, the present disclosure is directed to a
method of operating an exhaust treatment device. The method may
include controlling a flow through an exhaust passage based on
temperature. The method may further include injecting a reductant
into the exhaust passage as function of a flow rate through the
exhaust passage.
[0010] In yet another aspect, the present disclosure is directed to
an exhaust passage. The exhaust passage may include a venturi
configured to receive a reductant and provide an atomized flow of
the reductant to the exhaust passage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagrammatic illustration of a power source
having an exhaust system according to an exemplary disclosed
embodiment; and
[0012] FIG. 2 is a diagrammatic illustration of an SCR device of
the exhaust system of FIG. 1.
DETAILED DESCRIPTION
[0013] FIG. 1 illustrates an exemplary power source 10. The power
source 10 may include an engine 11 such as, for example, a diesel
engine. The power source 10 may also include an exhaust system 16
that directs exhaust away from the engine 11.
[0014] The exhaust system 16 may reduce emissions of harmful gases
and particulate matter emitted from the power source 10 after a
combustion process. The exhaust system 16 may include an emissions
control system 18 and an exhaust outlet 20. The emissions control
system 18 may include an SCR system 28. It is contemplated that the
emissions control system 18 may include other devices, such as, for
example, a diesel particulate filter, additional injectors and/or
filters, and other devices known in the art. The exhaust outlet 20
may be positioned downstream of the emissions control system 18 and
may be configured to discharge exhaust to the environment.
[0015] Referring to FIG. 2, the SCR system 28 may be a flow-through
device configured to catalyze a reaction between exhaust NOx and a
reduction agent. The SCR system 28 may include a first exhaust
passage 30, a second exhaust passage 32, a valve 40, a venturi 42,
a flow of a reductant 44, and a catalyst 46.
[0016] The first and second exhaust passages 30, 32 may be parallel
to each other and configured to receive exhaust flow from engine
11. The second exhaust passage 32 may be connected to the first
exhaust passage 30 at an inlet 50, upstream of the valve 40. The
second exhaust passage 32 may also be connected to the first
exhaust passage 30 at an outlet 52, upstream of the catalyst
46.
[0017] The valve 40 may be located within the first exhaust passage
30, and may be configured to control the flow of exhaust through
the venturi 42. The valve 40 may be a temperature controlled valve,
for example, a bimetallic butterfly or temperature sensor
controlled solenoid valve, so that the flow to the venturi 42 may
vary based on exhaust temperature. In an alternative arrangement,
the valve 40 may be located within the second exhaust passage 32,
rather than in the first exhaust passage 30.
[0018] The venturi 42 may be disposed in the first exhaust passage
30, downstream of the valve 40. The venturi 42 may be configured to
inject the reductant 44 into the first exhaust passage 30 via one
or more holes 60. The holes 60 may be orifices locates at a throat
of the venturi 42 and may be configured to atomize a flow of the
reductant 44. The venturi 42 may have substantially any
configuration known in the art that facilitates an increase in an
exhaust velocity and a decrease in pressure as the exhaust flows
though the venturi 42 in the direction of the arrow 62. For
example, as shown in FIG. 2, the venturi 42 may be formed by a
constriction within the first exhaust passage 30. It is further
considered that the venturi 42 may alternatively be formed by
protruding members (not shown) mounted on opposing walls of the
exhaust passage 30.
[0019] The size and configuration of the first and second exhaust
passages 30, 32 and the venturi 42 may be interdependent. For
example, the diameter of the second exhaust passage 32 may depend
upon the design parameters of the first exhaust passage 30 and the
venturi 42. Specifically, the diameter of the second exhaust
passage 32 may be small enough so that exhaust will flow primarily
though first exhaust passage 30 when the valve 40 is in an open
position, yet large enough to compensate for detrimental
backpressures that may result from the position of valve 40 and/or
the passage of exhaust through the venturi 42.
[0020] The reductant 44 may be, for example, aqueous urea, gaseous
ammonia, ammonia in aqueous solution, ammonia from an ammonia
generator (not shown), or any other reductant known in the art. The
reductant 44 may be contained in a supply tank (not shown)
configured to maintain a pressurized supply of the reductant 44 and
provide for repeated injections of the reductant 44 in a manner
discussed below.
[0021] The catalyst 46 may include a catalyst support material and
a metal promoter, for example, silver, dispersed within the
catalyst support material. The catalyst support material may
include at least one of alumina, elite, aluminophosphates,
hexaluminates, aluminosilicates, zirconates, titanosilicates, and
titanates. Combinations of these materials may be used, and the
catalyst materials may be chosen based on the type of fuel used,
engine operating parameters, and/or for conformity with
environmental standards.
[0022] It is also contemplated that the emissions control system 18
may be used to facilitate an operation of a diesel particulate
filter (not shown). The diesel particulate filter may include an
oxidation catalyst and a porous structure that catches NOx
particulate matter (i.e., soot) passing through the exhaust system
16. An injector (not shown) may inject the reductant 44, which may
be a fuel such as, for example, diesel fuel, into the diesel
particulate filter. The reductant 44 may be injected via the
venturi 42, where the venturi 42 may facilitate a mixing of the
reductant 44 and the catalyst within the diesel particulate
filter.
INDUSTRIAL APPLICABILITY
[0023] The disclosed exhaust treatment system may be applicable to
any combustion-type device, such as an engine or a furnace, where
the injection of a reductant into an SCR system thereof is desired.
The disclosed exhaust treatment system may provide an injection of
reductant without requiring metering pumps. Furthermore, the
disclosed exhaust treatment system may provide reductant to an
exhaust flow at a rate dependant upon the exhaust temperature.
Operation of the exhaust system 16 will now be explained.
[0024] Atmospheric air may be drawn into a combustion chamber of
the engine 11. Fuel may be mixed with the air before or after
entering the combustion chamber. This fuel-air mixture may be
combusted by the engine 11 to produce mechanical work and an
exhaust flow including, for example, hydrocarbon, CO, NOx, and
other solid and gaseous compounds. The exhaust flow may be directed
to the emissions control system 18 where particulate matter
entrained with the exhaust flow may be filtered and harmful gases
may be reduced.
[0025] In particular, the exhaust flow may be communicated to SCR
system 28 to reduce NOx in the exhaust flow. Based upon a
temperature of the exhaust flow, the valve 40 may adjust the amount
of exhaust directed to the first and second exhaust passages 30 and
32, respectively. For example, the valve 40 may be a bimetallic
butterfly valve, which responds to a decease in temperature of the
exhaust flow by increasing the flow of exhaust to the first exhaust
passage 30. The remainder of the exhaust flow may enter the second
exhaust passage 32 via the inlet 50.
[0026] Exhaust directed to the first exhaust passage 30 may flow
through the venturi 42. As the exhaust passes through the venturi
42, the pressure may drop to a pressure below the pressure of the
reductant 44. Because of the pressure difference, the reductant 44
may flow through the atomizing holes 60 and be drawn into the
exhaust stream. That is, the reductant may be injected into the
exhaust stream passively, without the use of a metering pump. The
rate at which the reductant 44 flows through the atomizing holes 60
may be controlled by changing the pressure in the exhaust line with
the valve 40.
[0027] The valve 40 may be configured to restrict flow to the
venturi 42 at one exhaust temperature and increase the flow to the
venturi 42 as the exhaust temperature decreases. For example, in an
embodiment where the valve 40 is located in the first exhaust
passage 30, the valve 40 may be configured to allow exhaust to flow
freely through the first exhaust passage 30 to the venturi 42 at a
first temperature. As the temperature increases, the valve 40 may
be configured to restrict flow to the first exhaust passage 30 and
venturi 42, so that a greater portion of the exhaust may be
directed away from the first exhaust passage 30, to the second
exhaust passage 32. It is further considered that in an embodiment
where the valve 40 is located in the second exhaust passage 32, the
valve 40 may be configured to achieve substantially the same
function. For example, the valve 40 may be configured to restrict
exhaust flow through the second exhaust passage 32 at the first
temperature, so that a greater portion of the exhaust may be
directed towards the first exhaust passage 30 and the venturi 42.
As the temperature increases, the valve 40 may be configured to
allow exhaust to flow freely through the second exhaust passage 32,
so that a greater portion of the exhaust may be directed away from
the first exhaust passage 30 and the venturi 42.
[0028] When the valve 40 increases the supply of exhaust to the
venturi 42, the speed of the exhaust through the venturi 42 may
increase, resulting in a decreased pressure of the exhaust as it
passes through the venturi 42. The decrease in pressure may result
in a greater pressure differential between the reductant 44 and the
exhaust, and thus a greater flow rate of reductant into the low
pressure exhaust.
[0029] As the temperature of the exhaust rises in response to a
change in an operating condition of the engine 11, the valve 40 may
restrict flow to the venturi 42, resulting in decreased speed and
increased pressure at the venturi 42. Because of the increased
pressure at the venturi 42, the pressure differential between the
reductant 44 and the exhaust may decrease, and thus a reduced flow
of reductant 44 is provided to the exhaust.
[0030] When the exhaust and atomized reductant 44 exit the venturi
42, they may expand and mix, thus reducing the need for a
downstream mixer. After the mixture exits the venturi 42, the
reductant 44 may be stored on the surface of the catalyst 46, where
it may be available for reaction with the NOx in the exhaust flow.
Because a reduced flow of reductant 44 is provided to the exhaust
when temperatures are elevated, the amount of reductant desorbed
from the catalyst 46 is decreased, and less reductant 44 may be
wasted.
[0031] In order to avoid creating an undesirable backpressure
upstream of the valve 40, exhaust restricted by the valve 40 may
enter the second exhaust passage 32 at the inlet 50, as discussed
above. Thus, instead of increasing the exhaust backpressure a
portion of the exhaust may bypass the venturi 42 via the second
exhaust passage 32. The exhaust flowing through exhaust passage 32
may be rejoined with the exhaust flowing through the first exhaust
passage 30 at the outlet 52. Thus, the second exhaust passage 32
may be configured to direct a flow of exhaust diverted from the
first exhaust passage 30, by the valve 40, to a location downstream
of the venturi 42 and reductant 44, and upstream of the catalyst
46.
[0032] The disclosed exhaust treatment system may provide a
reductant to an exhaust stream without the use of mixers, a long
exhaust pipe, or external sources. Furthermore, the disclosed
exhaust treatment system may provide a reduced supply of reductant
to the exhaust stream when temperature is increased. As a result,
the amount of reductant desorbed wasted by desorption at elevated
temperatures may be reduced.
[0033] It will be apparent to those skilled in the art that various
modifications and variations can be made to the exhaust treatment
system. Other embodiments will be apparent to those skilled in the
art from consideration of the specification and practice of the
disclosed exhaust treatment system. 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.
* * * * *