US20090173058A1

US20090173058A1 - System and method for the on-board production of reductants

Info

Publication number: US20090173058A1
Application number: US11/971,259
Authority: US
Inventors: Frederic Vitse; Dan Hancu; Benjamin Hale Winkler; Gregg Anthony Deluga
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2008-01-09
Filing date: 2008-01-09
Publication date: 2009-07-09
Also published as: WO2009088578A1

Abstract

A system is provided for the on-board production of reductants. The system comprises a fuel tank adapted to directly or indirectly supply a first fuel stream and a second fuel stream. An engine is in fluid communication with the fuel tank, and is configured to receive the first fuel stream and create an exhaust stream. The system further includes an emission treatment unit to treat the exhaust stream. A fuel conversion unit is configured to receive the second fuel stream, and also receive a stream comprising oxygen to partially oxidize at least a portion of the second fuel stream thereby forming reductants. In addition, the fuel conversion unit is configured to supply a reductant stream comprising the reductants to the exhaust stream. The invention further provides a method for the on-board production of reductants including supplying a first fuel stream to an engine, wherein the engine is configured to create an exhaust stream. A second fuel stream and a stream comprising oxygen are supplied to a fuel conversion unit. At least a portion of the second fuel stream is partially oxidized in the fuel conversion unit to form reductants, and a reductant stream comprising the reductants is supplied to the exhaust stream. The selective catalytic reduction of NOx present in the exhaust stream is performed.

Description

FIELD OF THE INVENTION

The invention includes embodiments that relate to an emission treatment system, and more particularly to the on-board production and supply of reductants to an emission treatment system.

BACKGROUND OF THE INVENTION

Current emission control regulations necessitate the reduction of pollutant species in diesel engine exhaust. NOx, principally NO and NO₂, contributes to smog, ground level ozone formation and acid rain. NO is produced in large quantities at the high combustion temperatures associated with diesel engines. NO₂is formed principally by the post oxidation of NO in the diesel exhaust stream. Exhaust aftertreatment devices achieve NOx reduction by using a reductant agent. The reductant agent is added to the exhaust gas entering the aftertreatment device and reacts with NOx over a catalyst in a process of selective catalytic reduction (SCR). Typical reducing agents may include light hydrocarbons and oxygen bearing compounds like alcohols.
Known methods of supplying the reductants may involve supplying the reducing agents and the fuel separately or may involve chemically producing the reducing agent in situ from the fuel itself. Such methods typically employ complex subsystems such as special purpose pumps, filters, storage tanks and the like. Additionally, these systems also require valuable space and specialized materials, thereby involving additional expenses. Accordingly, there is need for an improved system and method for producing and supplying reductants to provide better overall economy and ease of operation.

SUMMARY OF THE INVENTION

Embodiments of the invention provide systems and methods for the on-board production and supply of reducing agents for use in hydrocarbon based SCR treatment. Briefly stated, in accordance with one embodiment of the invention, there is provided a system for the on-board production of reductants comprising a fuel tank adapted to directly or indirectly supply a first fuel stream and a second fuel stream; an engine in fluid communication with the fuel tank, wherein the engine is configured to receive the first fuel stream and create an exhaust stream; an emission treatment unit to treat the exhaust stream; a fuel conversion unit configured to receive the second fuel stream, and also receive a stream comprising oxygen to partially oxidize at least a portion of the second fuel stream thereby forming reductants, the fuel conversion unit also configured to supply a reductant stream comprising the reductants to the exhaust stream.
In accordance with another embodiment of the invention, there is provided a method for the on-board production of reductants comprising supplying a first fuel stream to an engine, wherein the engine is configured to create an exhaust stream; supplying a second fuel stream and a stream comprising oxygen to a fuel conversion unit; partially oxidizing at least a portion of the second fuel stream in the fuel conversion unit to form reductants; supplying a reductant stream comprising the reductants to the exhaust stream; and performing a selective catalytic reduction of NOx present in the exhaust stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary system for the on-board production of reductants in accordance with an embodiment of the invention.

FIG. 2 is a schematic diagram of an exemplary system for the on-board production of reductants in accordance with an alternative embodiment of the invention.

FIG. 3 is a schematic diagram of an exemplary system for the on-board production of reductants in accordance with an alternative embodiment of the invention.

FIG. 4 illustrates a method for the on-board production of reductants in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an exemplary system 10 for the on-board production of reductants for treating NOx emissions from an engine. The system 10 includes an engine 12 that is directly supplied with a first fuel stream 14 from a fuel tank 16. An on-board fuel conversion unit 18 is directly supplied with a second fuel stream 20 from the fuel tank 16. If desired, the fuel tank 16 may be adapted to indirectly supply the first fuel stream 14 to the engine 12 and the second fuel stream 20 to the fuel conversion unit 18 via a single fuel stream 21 exiting the fuel tank that is split, or comprises a slip stream, to form the first and second fuel streams, as illustrated in FIG. 2.
Referring to FIGS. 1 and 2, the fuel tank 16 may be adapted to supply the first fuel stream 14 to a first fuel pump 22, wherein the first fuel pump is adapted to pump the first fuel stream to the engine 12. The fuel tank 16 is also adapted to supply the second fuel stream 20 to a second fuel pump 24. The second fuel pump 24 pumps the second fuel stream 20 to the fuel conversion unit 18. A portion of the first fuel stream 14 is burnt in the engine 12 during operation of the engine and an emission of exhaust gases containing NOx is produced thereby. The exhaust gases, thus produced, are discharged through an exhaust stream 30. The exhaust stream 30 carries the exhaust gases to an emission treatment unit 32 where the exhaust stream is treated by selective catalytic reduction. The resulting treated exhaust steam 38 is exhausted into the atmosphere.
The systems and methods of the invention allow for the use of one fuel tank 16 for carrying the fuel instead of requiring an extra storage tank for an SCR reductant. This is advantageous from an implementation and distribution point of view. For example, the system can be installed on existing locomotive engines.
The fuel conversion unit 18 converts at least a portion of the fuel entering the unit via the second fuel stream 20 into reductants. An oxygen supply stream 39 comprising oxygen is supplied to the fuel conversion unit 18 to partially oxidize the fuel within the unit. The oxygen supply stream 39 may be comprised of air from the surrounding atmosphere, an exhaust stream from the engine (not shown), or any other suitable oxygen source.
Any fuel conversion unit 18 known to those having skill in the art may be used in the system and methods of the invention, wherein the fuel conversion unit is capable of producing reductants effective for the selective catalytic reduction of NOx. In a preferred embodiment, the fuel conversion unit 18 is a catalytic partial oxidation unit. The fuel conversion unit 18 may produce reductants including, but not limited to hydrogen, as well as other hydrocarbon reductants such as diesel fuel, partially cracked diesel fuel, gasoline, olefins, paraffins, isoparaffins, olefinic esters, oxygenates, and aromatics such as napthalenes and naphtha. Hydrogen has been shown to be advantageous as a co-reductant with hydrocarbons, such as but not limited to oxygenates, alkanes, alkenes, acetylenes, aromatics, and naphthalenes.
Reductant stream 40 exiting the fuel conversion unit 18 supplies the reductants directly to exhaust stream 30, and subsequently to the emission treatment unit 32 wherein the reductants are used to perform the selective catalytic reduction of NOx. If desired, the fuel conversion unit 18 may supply the reductant stream 40 to a reductant pump 50, wherein the reductant pump is adapted to pump at least a portion of the reductant stream to the emission treatment unit 32 via exhaust stream 30, as shown in FIGS. 1 and 2. In another embodiment of the invention (not shown), a portion of the reductant stream 40 may be sent back to the fuel tank 16 or to the engine 12 directly. Complete conversion of the fuel in the fuel conversion unit 18, while desired, is not necessary because most fuels can also be used as reductants in hydrocarbon based SCR.
The first fuel pump 22, second fuel pump 24, and reductant pump 50 may each be an electrically actuated fuel pump. In another embodiment of the invention, the pumps 22, 24 and 50 may be a fuel injector.
Referring to FIG. 3, a condenser 54 may be disposed in fluid communication with the fuel conversion unit 18 for condensing at least a portion of the reductant stream 40 exiting the fuel conversion unit. The temperature of the condenser 54 is set so that the most active reductants and/or a higher concentration of reductants remain in the gaseous form and are supplied to the exhaust stream 30 and emission treatment unit 32 via gaseous reductant stream 58. Most active reductants mean those reductants which are most effective for the selective catalytic reduction of NOx. reduce NOx If desired, the reductant stream 58 may be supplied to pump 50. The condenser 54 also supplies a condensed reductant stream 56 which is recycled back to the fuel tank 16
Referring to FIGS. 1 and 2, the amount of reductant that is produced by the fuel conversion unit can be controlled using a NOx sensor 60 that is placed down stream of the emission treatment unit 32. The NOx sensor 60 measures the concentration of NOx in the treated exhaust steam 38 exiting the emission treatment unit 32. The NOx sensor 60 sends a signal representing the NOx concentration in the treated exhaust stream 38 to a second fuel controller 62. The second fuel controller 62 integrates the processed information and determines if the system parameters are indicative of proper control of the treated exhaust stream 38, and may further determine whether there is a need for supply of reductants to the emission treatment unit 32. Accordingly, the second fuel controller 62 regulates the flow of the second fuel stream 20, entering the fuel conversion unit 18, based on the signal received from the NOx sensor 60. The second fuel pump 24 is in communication with the second fuel controller 62, and the controller directly controls and monitors the operation of the second fuel pump to inject a portion of the second fuel stream 20 into the fuel conversion unit 18.
The NOx sensor 60 may alternatively be used to directly control the amount of reductant flow, i.e. the reductant stream 40 flow, into the exhaust stream 30 and emission treatment unit 32, as shown in FIGS. 1-3. The NOx sensor 60 sends a signal representing the NOx concentration in the treated exhaust stream 38 to a reductant controller 64. The reductant controller 64 regulates the flow of the reductant stream 40 entering the emission treatment unit 32, based on this signal. The reductant pump 50 is in communication with the reductant controller 64, and the controller 64 directly controls and monitors the operation of the reductant pump to inject at least a portion of the reductant stream 40 into the emission treatment unit 32 via exhaust stream 30.
Structurally, the controllers 62 and 64, as shown in FIGS. 1-3, may each be a conventional microcomputer, including conventional components such as a microprocessor unit, input/output ports, read-only memory, random access memory, read-out displays, and conventional data bus. Furthermore, the controllers 62 and 64 may each include a micro-controller or a solid-state switch to communicate with the sensor 60. In one embodiment, the controllers 62 and 64 may each be an electronic logic controller that is programmable by a user. In another embodiment, each controller 62 and 64 may include an analog-to-digital converter accessible through one or more analog input ports.
As will be recognized by those of ordinary skill in the art, the controllers 62 and 64 may be embodied in several other ways. In one embodiment, the controllers 62 and 64 may include a logical processor (not shown), a threshold detection circuitry (not shown) and an alerting system (not shown). Typically, the logical processor is a processing unit that performs computing tasks. It may be a software construct made up using software application programs or operating system resources.
The emission treatment unit 32, in one embodiment of the invention may include after-treatment devices in which NOx in the engine exhaust stream 30 is continuously removed by reacting with active reductants in the presence of a catalyst to produce N₂. In one embodiment of the invention, the catalysts may include oxidation catalysts that convert a portion of incoming NO to NO₂. In another embodiment of the invention, the catalysts may be lean NOx catalysts capable of reducing NOx in an oxygen rich environment. Efficiency of the reduction catalysts may be further increased in the presence of additional reductants. Such additional reductants may typically include hydrocarbon compounds. A number of hydrocarbon reductants may typically be disposed along with the fuel as an additive component, as described below herein.
The fuel used in the embodiments of the invention include any fuel suitable for operation of the engine 12, such as gasoline. In one embodiment of the invention, the fuel may be normal diesel fuel. In another embodiment of the invention, the fuel may be a renewable fuel. In one embodiment of the invention, the renewable fuel is green diesel fuel. In a preferred embodiment of the invention, the renewable fuel is biodiesel, which consists of fatty acid methyl esters and may be made from vegetable oil, animal fat, or waste grease. In another embodiment, the biodiesel is used as a blend with conventional diesel.
In yet another embodiment of the invention, Fischer-Tropsch diesel may be used as a renewable fuel that at times may be produced from biomass. Fischer-Tropsch or gas-to-liquid (GTL) fuels are typically created by a Fischer Tropsch process that makes liquid diesel fuel from a synthetic mix of gases including CO and H₂. Typical Fischer-Tropsch fuels may contain very low sulfur and aromatic content and very high cetane numbers. Fischer-Tropsch diesel fuels typically reduce regulated exhaust emissions from the engines and the vehicles where this fuel is used. Additionally, the low sulfur content of these fuels may enable use of advanced emission control devices.
In yet another embodiment of the invention, an additive component may be blended into the fuel before the fuel is supplied to the engine 12 and fuel conversion unit 18. For example, the additive component may be mixed with the fuel in fuel tank 16. Examples of additive components that may be used in the invention, include but are not limited to oxygenate reductants such as alcohols, aldehydes, ketones, ethers, esters, or combinations thereof. The alcohols may include methanol, ethanol, iso-propanol and the like. In addition, ethanol/diesel, ethanol/biodiesel and ethanol/gasoline fuel blends are readily available on the market, so no additional infrastructure would be required to mix the additive component with the fuel if desired. The concentration of the additive component in the fuel may typically be in the range of about 0.5 percent to about 20 percent by weight of the total fuel.
In one embodiment of the invention, hydrocarbon reductants may be used in order to aid in the production of oxygenated hydrocarbons, i.e. oxygenate reductants, as represented by equation (1) below.
Hydrocarbons (HC)+O₂=>oxygenated HC (1)
NOx+oxygenated HC+O₂=>N₂+CO₂+H₂O (2)
The hydrocarbon reductants may include propene, ethane, diesel fuel, partially cracked diesel fuel, gasoline, or any other suitable hydrocarbons and the oxygenated hydrocarbons may include methanol, ethanol, propanol, butanol, pentanol, hexanol, methanal, ethanal, propanal, butanal, propenal, acetone, 2-butanone, and 3-penten-2-one and any combination thereof. Although the lean-NOx reducing reaction is a complex process comprising many steps, one of the reaction mechanisms for lean NOx catalysts may be summarized as follows. A hydrocarbon-enriched reductant may be converted to an activated, oxygenated hydrocarbon that may interact with the NOx compounds to form organo-nitrogen containing compounds, which are then reduced to N₂. Through these or other mechanisms the NOx species are eventually reduced to N₂.
The principles of the invention are not limited to any particular type of engine. One of ordinary skill will recognize that other embodiments of the invention may be suited for many of the combustion-powered vehicles. For example, internal combustion engines that are used in railroad locomotives, in vehicles that run on roads such as trucks, municipal transport vehicles, city buses, cars and other passenger vehicles or in ships may be installed with this type of reductant supply system. The engine may also be a liquid fueled engine, a compression ignition engine, a gasoline engine, and any combination thereof. The gasoline engine may include a lean burn gasoline engine. A lean burn engine is one that produces an oxygen rich exhaust, which is defined as an exhaust having a higher molar ratio of oxygen than the total molar ratio of reductive compounds such as carbon-monoxide, hydrogen, hydrocarbons, and oxygenated hydrocarbons. Examples of such lean burn engine systems may include diesel engines, some natural gas or alternative fuel engines, liquid or gaseous-fueled turbine engines and various lean burn gasoline engine systems.
FIG. 4 illustrates an exemplary method for supplying reductants to an emission treatment unit in accordance with one embodiment of the invention. As will be appreciated by one of ordinary skill in the art, the method may represent one or more of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated herein may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features and advantages of the invention, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used.
To this end, beginning at block 102, a first fuel stream 14 is supplied to an engine 12, wherein the engine is configured to create an exhaust stream 30. A second fuel stream 20, and an oxygen supply stream 39 are supplied to a fuel conversion unit 18 as shown in block 104. Referring to block 106, at least a portion of the second fuel stream 20 is partially oxidized in a fuel conversion unit 18 to form reductants. A reductant stream 40 comprising the reductants is supplied to the exhaust stream 30 as shown in block 108. Referring to block 110, the selective catalytic reduction of NOx present in the exhaust stream 30 is performed.
All cited patents, patent applications, and other references are incorporated herein by reference in their entirety.
All ranges disclosed herein are inclusive of the endpoints, and the endpoints are combinable with each other.
It is to be noted that the terms “first,” “second,” and the like as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifiers “about” and “approximately” used in connection with a quantity are inclusive of the stated value and have the meaning dictated by the context (e.g., include the degree of error associated with measurement of the particular quantity). The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
What is claimed as new and desired to be protected by Letters Patent of the United States is:

Claims

1. A system for the on-board production of reductants comprising:

a fuel tank adapted to directly or indirectly supply a first fuel stream and a second fuel stream;

an engine in fluid communication with the fuel tank, wherein the engine is configured to receive the first fuel stream and create an exhaust stream;

an emission treatment unit to treat the exhaust stream;

a fuel conversion unit configured to receive the second fuel stream, and also receive a stream comprising oxygen to partially oxidize at least a portion of the second fuel stream thereby forming reductants, the fuel conversion unit also configured to supply a reductant stream comprising the reductants to the exhaust stream.

2. The system of claim 1, further comprising:

a first fuel pump adapted to pump the first fuel stream from the fuel tank to the engine.

3. The system of claim 1, further comprising:

a second fuel controller that receives a signal representing a concentration of NOx in a treated exhaust stream exiting the emission treatment unit, the controller regulates the flow of the second fuel stream into the fuel conversion unit in accordance with the received signal.

4. The system of claim 3, further comprising:

an NOx sensor located downstream of the emission treatment unit and in communication with the second fuel controller, the sensor measures the concentration of NOx in the treated emission stream and sends a signal to the second fuel controller representing the measured concentration.

5. The system of claim 3, further comprising:

a second fuel pump in communication with the second fuel controller to pump the second fuel stream to the fuel conversion unit.

6. The system of claim 1, further comprising:

a reductant controller that receives a signal representing a concentration of NOx in a treated exhaust stream exiting the emission treatment unit, the reductant controller regulates the flow of the reductant stream into the exhaust stream in accordance with the signal.

7. The system of claim 6, further comprising:

an NOx sensor located downstream of the emission treatment unit and in communication with the reductant controller, the sensor measures the concentration of NOx in the treated emission stream and sends a signal to the reductant controller representing the measured concentration.

8. The system according to claim 6, further comprising:

a reductant pump in communication with the reductant controller to pump at least a portion of the reductant stream into the exhaust stream.

9. The system according to claim 1, wherein the reductants comprise hydrogen, hydrocarbons, or a combination thereof.

10. The system according to claim 9, wherein the reductants comprise diesel fuel, partially cracked diesel fuel, gasoline, an olefin, paraffin, isoparaffin, olefinic ester, aromatic, oxygenate reductant, or a combination thereof.

11. The system according to claim 10, wherein the oxygenate reductant comprises an alcohol, aldehyde, or ketone, or a combination thereof.

12. The system according to claim 1, wherein the emission treatment unit is a selective catalytic reduction treatment unit.

13. The system according to claim 1, wherein the first and second fuel streams comprise diesel fuel, biodiesel fuel, green diesel fuel or Fischer-Tropsch fuel, or any combination thereof.

14. The system according to claim 13, wherein the first and second fuel streams comprise biodiesel fuel.

15. The system according to claim 1, wherein the engine is a liquid fueled engine, a compression ignition engine, or a gasoline engine, or any combination thereof.

16. The system according to claim 15, wherein the gasoline engine is a lean burn gasoline engine.

17. The system according to claim 1, wherein the first fuel stream and second fuel stream comprise an additive component.

18. The system according to claim 17, wherein the additive component is an alcohol, aldehyde, or ketone, or a combination thereof.

19. The system according to claim 1, wherein the reductant stream is a gaseous reductant stream, and the method further comprises:

a condenser configured to receive the gaseous reductant stream exiting the fuel conversion unit and condense at least a portion of the gaseous reductant stream.

20. The system according to claim 19, wherein the condenser unit is configured to supply the condensed portion of the reductant stream to the fuel tank, and supply the remaining gaseous reductant stream to the exhaust stream, and wherein the reductants present in the gaseous reductant stream are more active than the reductants present in the condensed portion of the reductant stream.

21. A method for the on-board production of reductants comprising:

supplying a first fuel stream to an engine, wherein the engine is configured to create an exhaust stream;

supplying a second fuel stream and a stream comprising oxygen to a fuel conversion unit;

partially oxidizing at least a portion of the second fuel stream in the fuel conversion unit to form reductants;

supplying a reductant stream comprising the reductants to the exhaust stream; and

performing a selective catalytic reduction of NOx present in the exhaust stream.

22. The method of claim 21, wherein the first and second fuel streams are supplied directly or indirectly from a fuel tank.

23. The method of claim 21, further comprising:

sensing a concentration of NOx in a treated exhaust stream exiting the emission treatment unit; and

regulating the flow of the second fuel stream into the fuel conversion unit in accordance with the sensed signal.

24. The method of claim 21, further comprising:

regulating the flow of the reductant stream into the exhaust stream in accordance with the sensed signal.

25. The method according to claim 21, wherein the reductants comprise hydrogen, hydrocarbons, or a combination thereof.

26. The method according to claim 25, wherein the reductants comprise diesel fuel, partially cracked diesel fuel, gasoline, an olefin, paraffin, isoparaffin, olefinic ester, aromatic, oxygenate reductant, or a combination thereof.

27. The method according to claim 26, wherein the oxygenate reductant comprises an alcohol, aldehyde, or ketone, or a combination thereof.

28. The method according to claim 21, wherein the first and second fuel streams comprise diesel fuel, biodiesel fuel, green diesel fuel, Fischer-Tropsch fuel, and any combination thereof.

29. The method according to claim 28, wherein the first and second fuel streams comprise biodiesel fuel.

30. The method according to claim 21, wherein the engine is a liquid fueled engine, a compression ignition engine, a gasoline engine, and any combination thereof.

31. The method according to claim 21, wherein the first fuel stream and second fuel stream comprise an additive component.

32. The method according to claim 31, wherein the additive component is an alcohol, aldehyde, or ketone, or a combination thereof.

33. The method according to claim 21, wherein the first and second fuels streams are supplied by a fuel tank, and the method further comprises:

condensing a portion of the reductants formed by the fuel conversion unit; and

supplying the condensed reductants to the fuel tank.