Patent Application
20090173058
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.
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. NO2 is 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.
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.
Referring to
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
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
Referring to
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
Structurally, the controllers 62 and 64, as shown in
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.
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:
