US20100170225A1

US20100170225A1 - Exhaust treatment system having a reductant supply system

Info

Publication number: US20100170225A1
Application number: US12/318,816
Authority: US
Inventors: Cornelius N. Opris; Anthony C. Rodman
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2009-01-08
Filing date: 2009-01-08
Publication date: 2010-07-08

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.

Description

TECHNICAL FIELD

The present disclosure relates generally to an exhaust treatment system, and more particularly, to an exhaust treatment system having a reductant supply system.

BACKGROUND

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.
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.
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.
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.
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.
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

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.
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.
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

FIG. 1 is a diagrammatic illustration of a power source having an exhaust system according to an exemplary disclosed embodiment; and

FIG. 2 is a diagrammatic illustration of an SCR device of the exhaust system of FIG. 1.

DETAILED DESCRIPTION

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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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.