Patent Application
20060053774
In order to meet exhaust fluid emission standards, the exhaust fluid emitted from internal combustion engines is treated prior to emission into the atmosphere. Exhaust fluids can be routed through an exhaust treatment device disposed in fluid communication with the exhaust outlet system of the engine, wherein the exhaust fluid can be treated, for example, by reactions employing a catalyst. Examples of exhaust treatment devices include catalytic converters, catalytic absorbers, diesel particulate traps, non-thermal plasma conversion devices, and the like. The exhaust fluid generally comprises undesirable emission components including carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). In addition to the gaseous components, exhaust fluid can also comprise particulate matter such as carbon-containing particles or soot.
In order to maintain the desired operability of the exhaust treatment devices, the exhaust treatment devices need to be periodically regenerated. For example, a NOx adsorber, which can also be referred to as a “lean NOx trap,” can be regenerated by periodically introducing a reducing agent into the NOx adsorber such that the NOx trapped (stored) in the NOx adsorber can be converted to nitrogen. Suitable reducing agents include hydrogen gas, synthesis gas (i.e., a gas comprising primarily carbon monoxide and hydrogen gas), and the like. Hydrogen gas can also be employed in the regeneration of other exhaust treatment devices.
The hydrogen employed in regenerating various exhaust treatment devices can be obtained, for example, using a reformer (also referred to as a fuel processor), wherein a hydrocarbon fuel (methane, propane, natural gas, gasoline, diesel, and the like) can be converted to hydrogen or to a less complex hydrocarbon. More particularly, fuel reforming can comprise mixing a hydrocarbon fuel with an oxygen source (e.g., air, exhaust gas recycle (EGR), and the like), water, and/or steam in a mixing zone of the reformer prior to entering a reforming zone of the reformer, and converting the hydrocarbon fuel into, for example, hydrogen (H2), byproducts (e.g., carbon monoxide (CO), methane (CH4), inert materials (e.g., nitrogen (N2), carbon dioxide (CO2), and water (H2O)). Common approaches include steam reforming, partial oxidation, and dry reforming.
Steam reforming involves the use of a fuel and steam (H2O) that is reacted in heated tubes filled with a catalyst(s) to convert the hydrocarbons into principally hydrogen and carbon monoxide. The steam reforming reactions are endothermic, thus the steam reformers are designed to transfer heat into the catalytic process. An example of the steam reforming reaction is as follows:
CH4+H2O→CO+3H2
Partial oxidation reformers are based on substoichiometric combustion to achieve the temperatures sufficient to reform the hydrocarbon fuel. Decomposition of the fuel to primarily hydrogen and carbon monoxide occurs through thermal reactions at high temperatures, e.g., about 700° C. to about 1,000° C. Catalysts have been used with partial oxidation systems (catalytic partial oxidation) to promote conversion of various fuels, such as ethanol, into synthesis gas. The use of a catalyst can result in acceleration of the reforming reactions and can provide this effect at lower reaction temperatures than those that would otherwise be required in the absence of a catalyst. An example of the partial oxidation reforming reaction is as follows:
CH4+½O2→CO+2H2
Dry reforming involves the creation of hydrogen and carbon monoxide in the absence of water, for example, using carbon dioxide as the oxidant. Dry reforming reactions, like steam reforming reactions, are endothermic processes. An example of the dry reforming reaction is depicted in the following reaction:
CH4+CO2→2CO+2H2
Practical reformers can comprise a combination of these idealized processes. Thus, a combination of air, water, and/or recycled exhaust fluid can be used as the oxidant in the fuel reforming process.
What is needed in the art is an overall less complex exhaust treatment system compared to traditional exhaust treatment systems and exhaust treatment systems, wherein exhaust fluid can be directed to a reformer without significantly coking or clogging the reformer and/or valve(s) in fluid communication with the reformer.
Disclosed herein are exhaust treatment systems and methods of using the same.
One embodiment of an exhaust treatment system comprises an exhaust fluid source; a particulate filter disposed downstream of and in fluid communication with the exhaust fluid source; a valve disposed downstream of and in fluid communication with the particulate filter; and a reformer disposed in fluid communication with and downstream of the valve such that the valve is capable of directing exhaust fluid from the exhaust fluid source to the reformer.
Another embodiment of an exhaust treatment system comprises an exhaust fluid source; a proportioning valve in fluid communication with the exhaust fluid source; an exhaust treatment device disposed downstream of the proportioning valve; and a reformer disposed in fluid communication with the proportioning valve, wherein the proportioning valve is capable of selectively directing exhaust fluid from the exhaust fluid source to both the reformer and the exhaust treatment device.
A third embodiment of an exhaust treatment system comprises an exhaust fluid source; an oxidation catalyst disposed downstream of and in direct fluid communication with the exhaust fluid source; a NOx adsorber disposed downstream of and in direct fluid communication with the oxidation catalyst; a particulate filter disposed downstream of and in direct fluid communication with the NOx adsorber; a reformer disposed in selective fluid communication with at least one of the oxidation catalyst, the NOx adsorber, and the particulate filter; and a valve disposed downstream of and in fluid communication with the particulate filter, and disposed in fluid communication the reformer such that the valve is capable of directing exhaust fluid from the exhaust fluid source to the reformer.
One embodiment of a method of treating an exhaust fluid comprises passing an exhaust fluid through a particulate filter; removing particulate matter from the exhaust fluid to produce a treated exhaust fluid; and periodically directing a portion of the treated exhaust fluid to a reformer.
Another embodiment of a method of treating an exhaust fluid, the method comprises directing an exhaust fluid to a reformer during a regeneration mode of operation using a proportioning valve, wherein the proportioning valve is disposed upstream of and in fluid communication with the reformer; directing the exhaust fluid to an exhaust treatment device during the regeneration mode of operation and during an exhaust treatment mode of operation using the proportioning valve, wherein the proportioning valve is disposed upstream of and in fluid communication with, and treating the exhaust fluid using the exhaust treatment device to remove a component from the exhaust fluid.
The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.
Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
It should first be noted that the system comprising a reformer disclosed herein can readily be adapted for use in any system where hydrocarbon fuels are processed to hydrogen or less complex hydrocarbons, such as a fuel cell system (e.g., solid oxide fuel cell (SOFC) system, proton exchange membrane (PEM) system, and the like), an exhaust treatment of a vehicle system (e.g., diesel, gasoline, and the like), and the like. It is briefly noted that in those embodiments comprising a fuel cell, the fuel cell is disposed in fluid communication with the reformer such that reformate (e.g., hydrogen gas) from the reformer can be directed to the fuel cell. For convenience in discussion, however, the system comprising the reformer is discussed below in relation to an exhaust treatment system for a vehicle system.
The terms “first,” “second,” and the like herein do not denote any order or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Furthermore, all ranges disclosed herein are inclusive and combinable (e.g., ranges of “up to about 25 weight percent (wt. %), with about 5 wt. % to about 20 wt. % desired, and about 10 wt. % to about 15 wt. % more desired,” are inclusive of the endpoints and all intermediate values of the ranges, e.g., “about 5 wt. % to about 25 wt. %, about 5 wt. % to about 15 wt. %”, etc.).
In describing the arrangement of exhaust treatment devices within the system, the terms “upstream” and “downstream” are used. These terms have their ordinary meaning. Additionally, it is noted that embodiments are envisioned, wherein a device can be both “upstream” and “downstream” of the same device in certain configurations, e.g., a system comprising a recycle loop.
The term “direct” fluid communication is also used throughout this disclosure. The term “direct” as used herein refers to a communication between a first point and a second point in a system that is uninterrupted by the presence of reaction devices, such as, a reactor, converter, and the like, but can have other components such as valves, mixers, flow regulators, and the like, that are generally not used for purposes of reacting exhaust fluids or removing components from an exhaust fluid.
Combinations of exhaust treatment devices are discussed hereunder with reference to individual figures. One of skill in the art will easily recognize that many of the components of each of the embodiments are similar or identical to the others. These various components can be added or omitted based on various design choices. As such, various elements and/or features can be introduced in a given figure, but it is understood that the systems can be modified as taught herein to include features illustrated in other embodiments. Each of these elements is first introduced in the discussion of a given figure, but is not repeated for each embodiment. Rather, distinct structure is discussed relative to each figure/embodiment.
Referring to
Referring to
An exhaust conduit 32 allows fluid communication between the various system devices. Disposed in fluid communication with exhaust conduit 32 is a reformer 18, which produces reformate that can periodically be introduced into exhaust conduit 32, via, for example, valves 24, 26, and 28 to selectively regenerate the exhaust treatment devices. Valves 24, 26, and 28 can comprise a spool valve, butterfly valve, ball valve, or similar configurations capable of selectively allowing and inhibiting flow. During a regeneration mode of operation, these valves can direct reformate from the reformer 18 to a location upstream of and/or a location in fluid communication with oxidation catalyst 12, NOx adsorber 14, and/or particulate filter 16. A discussion of using reformate to selectively regenerate an oxidation catalyst(s), particulate filter(s), and/or NOx adsorber(s) can be found, for example, in U.S. Published Patent Application No. 2004/0098977.
The system 200 further comprises a proportioning valve 30, which can direct exhaust fluid to the exhaust treatment devices and/or reformer 18. More particularly, during an exhaust treatment mode, proportioning valve 30 can direct the exhaust fluid to exhaust treatment devices. During a regeneration mode, proportioning valve 30 can direct at least a portion of the exhaust fluid to reformer 18, wherein the exhaust fluid can act as an oxygen source for the reforming reactions. Advantageously, proportioning valve 30 allows a fluid stream to be simultaneously directed to two locations (e.g., to an exhaust treatment device and reformer 18), while having to control only one valve. As such, exhaust fluid can continually be treated, while a portion of the exhaust fluid can be employed in the reformer 18.
Proportioning valve 30 (as well as valves 24, 26, and 28) can be disposed in information/command (e.g., electrical) communication with a controller (not shown). The controller can be programmed to divert at least a portion of exhaust fluid to reformer 18 based upon NOx slip (i.e., the NOx remaining in the exhaust fluid after exiting a system component, e.g., NOx adsorber 14), engine management (e.g., RPM, air-to-fuel ratio, and the like), time, and the like, as well as combinations of the foregoing. Similarly, having produced reformate from the reformer 18, valves 24, 26, and 28 can be manipulated to provide intermittent flow, for example, a pulse, of hydrogen and carbon monoxide from the reformer 18 to oxidation catalyst 12, NOx adsorber 14, particulate filter 16, and/or other exhaust treatment devices.
Further, it is noted that the complexity of the exhaust treatment system is reduced by employing proportioning valve 30 compared to system 100 employing multiple valves (20 and 22 (
In other embodiments, further advantageous can be recognized by first passing the exhaust fluid through particulate filter 16 before directing it to reformer 18. By passing the exhaust fluid first through particulate filter 16, soot and other particulates are removed from the exhaust fluid. Since soot and particulates can coke and/or clog filters and/or reformer 18, embodiments that remove soot and particles prior to directing the exhaust fluid to a valve or reformer 18 can have an increased operating life.
Referring to
During an exhaust treatment mode of operation, exhaust fluid can pass through each exhaust treatment device in series and then can be vented to the atmosphere via the tail pipe. Proportioning valve 34 can be disposed downstream of particulate filter 16 proximate to the tail pipe. It is noted that the temperature of the exhaust fluid generally decreases as it progresses downstream from engine 10. Without being bound by theory, this temperature decrease can be attributed to heat loss to the environment as the exhaust fluid travels along conduit 32 and through the various exhaust treatment devices. Since valve 34 is disposed downstream of particulate filter 16, the exhaust fluid passing through valve 34 is at a lower temperature compared to valves 20 and 22 (
Other embodiments are envisioned wherein exhaust treatment components are added to or removed from the system. In those embodiments, a proportioning valve (e.g. 30, 34) can be employed to direct exhaust fluid to an exhaust treatment device and/or reformer. Additionally/alternatively, the proportioning valve can be disposed downstream of a particulate filter. It is further noted that various types of traditional valves can be used in addition to or alternative to the proportioning valve. In other words, any valve disposed downstream of a particulate filter, wherein exhaust fluid is directed using the valve to a reformer is envisioned to be with the scope of this disclosure. Moreover, it is understood that various other exhaust treatment devices can be disposed in series between the particulate filter and the proportioning valve. For example, referring again to
Oxidation catalyst 12 comprises a catalytic metal(s), support material(s), and a substrate(s) disposed within in a housing. Optionally, a retention material can be disposed between the substrate and the housing. The catalytic metal and support material can be disposed on/in/throughout the substrate (hereinafter “on” the substrate for convenience in discussion). For example, the catalytic metal and support material can be washcoated, imbibed, impregnated, physisorbed, chemisorbed, precipitated, or otherwise applied onto and/or within the substrate. Examples of catalytic metals include, but are not limited to, platinum, palladium, ruthenium, rhodium, iridium, gold, and silver, as well as oxides, alloys, salts, and mixtures comprising at least one of the foregoing metals.
Suitable support materials for oxidation catalyst 12 include, but are not limited to, gamma aluminum oxide, delta aluminum oxide, theta aluminum oxide, stabilized aluminum oxides, titanium oxides, zirconium oxides, yttrium oxides, lanthanum oxides, cerium oxides, scandium oxides, and the like, as well as combinations comprising at least one of the foregoing.
The substrate can comprise any material designed for use in a spark ignition or diesel engine environment having the following characteristics: (1) capable of operating at temperatures up to about 600° C.; (2) capable of withstanding exposure to hydrocarbons, nitrogen oxides, carbon monoxide, particulate matter (e.g., soot and the like), carbon dioxide, and/or sulfur; and (3) having sufficient surface area and structural integrity to support a catalyst. Suitable materials for the substrate include, but are not limited to, cordierite, mullite, alpha-aluminum oxide, aluminum phosphate, aluminum titanate, aluminosilicate, zirconium oxide, titanium oxide, titanium phosphate and/or magnesium silicate. Additionally, it is noted that the substrate can be metallic, ceramic, or combinations of the foregoing, and be in a physical form as extrudates, foams, pellets, wire assemblies, filters, meshes, foils, and the like.
The choice of material for the housing depends upon the type of exhaust fluid, the maximum temperature reached by the substrate, the maximum temperature of the exhaust fluid stream, and the like. Suitable materials for the housing can comprise any material that is capable of resisting under-car salt, temperature, and corrosion. For example, ferrous materials can be employed such as ferritic stainless steels. Ferritic stainless steels can include stainless steels such as, e.g., the 400-Series such as SS-409, SS-439, and SS-441.
Located between the substrate and the housing can optionally be a retention material that insulates the housing from both the exhaust fluid temperatures and the exothermic catalytic reaction(s) occurring within the catalyst substrate. The retention material, which enhances the structural integrity of the substrate by applying compressive radial forces about it, reducing its axial movement and retaining it in place, can be concentrically disposed around the substrate to form a retention material/substrate subassembly.
The retention material, which can be in the form of a mat, particulates, or the like, can be an intumescent material (e.g., a material that comprises vermiculite component, i.e., a component that expands upon the application of heat,) a non-intumescent material, or a combination thereof. These materials can comprise ceramic materials (e.g., ceramic fibers) and other materials such as organic and inorganic binders and the like, or combinations comprising at least one of the foregoing materials. Non-intumescent materials include materials such as those sold under the trademarks “NEXTEL” and “INTERAM 1101HT” by the “3M” Company, Minneapolis, Minn., or those sold under the trademark, “FIBERFRAX” and “CC-MAX” by the Unifrax Co., Niagara Falls, N.Y., and the like. Intumescent materials include materials sold under the trademark “INTERAM” by the “3M” Company, Minneapolis, Minn., as well as those intumescents which are also sold under the aforementioned “FIBERFRAX” trademark, as well as combinations thereof and others.
The NOx adsorber 14 generally comprises a substrate comprising catalytic metal(s), NOx trapping material(s), and optional catalyst support material(s) disposed thereon, wherein the substrate is disposed within a housing. The NOx adsorber 14 can also comprise a retention material disposed between the substrate and the housing. The catalytic metal component, the catalytic metal support, and the NOx trapping materials can be disposed on the substrate by those methods discussed above with regard to oxidation catalyst 12.
The housing, the catalytic metal, catalyst support material, and the retention material for NOx adsorber 14 can comprise materials similar to those listed above with regard to oxidation catalyst 12. Some possible substrate materials for NOx adsorber 14 include cordierite, mullite, metallic foils, zirconium toughened aluminum oxide, silicon carbide, and the like, and mixtures comprising at least one of the foregoing materials.
In addition to the catalytic metal, the support material is further loaded with NOx trapping material(s), such as alkali metal oxides, alkaline earth metal oxides, and mixtures comprising at least one of the foregoing metal oxides. Suitable trapping materials include oxides of barium, strontium, calcium, magnesium, cesium, lithium, sodium, potassium, magnesium, rubidium, and the like, and combinations comprising at least one of the foregoing, and more particularly a mixture of oxides of barium and potassium.
The particulate filter 16 can comprise any filter design capable of removing particulate matter from the exhaust stream and preventing the emission of such particulate matter into the atmosphere. The particulate filter 16 generally comprises, a filter element (e.g., substrate) disposed within in a housing and can also comprise a retention material disposed between the filter element and the housing. The housing and the retention material can comprise geometries and materials similar to those listed above with regard to oxidation catalyst 12.
The filter element of the particulate filter 16 can comprises a gas permeable ceramic material having a honeycomb structure comprising a plurality of channels. The channels can be divided into alternating inlet channels and exit channels. For example, the inlet channels are open at an inlet end of the filter element and are plugged at the exit end of the filter. Conversely, exit channels are plugged at the inlet end and open at the exit end of the filter. The inlet and exit channels are separated by porous sidewalls that permit the exhaust gases to pass from the inlet channels to the exit channels along their length.
The filter element is generally desired to filter out the particulate matter present in the exhaust. It can generally be manufactured from materials such as ceramics, which can include cordierite, metallics such as sintered stainless steel powder, carbides (such as silicon carbide), nitrides (such as silicon nitride), and the like, as well as combinations comprising at least one of the foregoing materials. Such materials can comprise a sufficient porosity to permit the passage of exhaust fluids and reformate through the element walls, yet filter out a substantial portion, if not all of the particulate matter present in the exhaust fluid. For example, the filter element can have a porosity greater than or equal to about 20%, particularly greater than or equal to about 40%. Furthermore, the filter element pores can have a pore sized measured along a major diameter of about 0.1 micrometers to about 30 micrometer, particularly a pore size of about 0.4 to 20 micrometer. The particulate filter element can optionally include a catalyst on the filter element (e.g., a coating of a catalyst material). Suitable catalysts and support materials include those discussed above with respect to oxidation catalyst 12.
As discussed above, reformer 18 can be configured for partial oxidation, steam reforming, or dry reforming. In various embodiments, the reformer 18 is configured primarily for partial oxidation reforming. However, it is noted that steam reforming and dry reforming can also occur to the extent of the water and carbon dioxide present during the reforming reaction.
Reformer 18 comprises a substrate(s), a catalytic metal(s), and a support material (s). The reformer 18 can also comprise retention material disposed between the substrate and a housing. The retention material can comprise the same materials listed above with respect to oxidation catalyst 12. Possible catalyst materials for the reformer 18 include metals, such as platinum, palladium, rhodium, iridium, osmium, ruthenium, tantalum, zirconium, yttrium, cerium, nickel, copper, and the like, and oxides, mixtures, and alloys comprising at least one of the foregoing metals. In an embodiment, the catalytic metal component of the reformer 18 is a combination of rhodium with other metals, wherein the other metals, e.g., platinum, and the like, can be present in an amount less than the rhodium.
The support materials can include those materials listed above with respect to oxidation catalyst 12. The support materials for the reformer 18, include, but are not limited to, hexaaluminates, aluminates, aluminum oxides (e.g., gamma-aluminum oxide, theta-aluminum oxide, delta-aluminum oxide), gallium oxides, zirconium oxides and titanium oxides. Since the reformer is generally subjected to temperatures greater than or equal to 1,200° C., the reformer support can be a hexaaluminate. Hexaaluminates are crystalline, porous structures that are able to withstand high temperatures e.g., temperatures of about 1,200° C. to about 1,350° C., without sintering. Even at temperatures of up to about 1,600° C., hexaaluminates can have a surface area as high as 20 square meters per gram (m2/g).
The reformer substrate is capable of withstanding strong reducing environments in the presence of water containing, for example, hydrocarbons, hydrogen, carbon monoxide, water, oxygen, sulfur and sulfur-containing compounds, combustion radicals, such as hydrogen and hydroxyl ions, and the like, and carbon particulate matter; and has sufficient surface area and structural integrity to support the desired catalytic metal component and support material. Materials that can be used as the reformer substrate include, zirconium toughened aluminum oxide, titanium toughened aluminum oxide, aluminum oxide, zirconium oxide, titanium oxide, as well as oxides, alloys, cermets, and the like, as well as combinations comprising at least one of the foregoing materials.
Referring now to
For example, the proportioning valve 30 can operate to vary the proportion of exhaust fluid directed to the reformer 18. More particularly, during a regeneration mode of operation first throttle plate 44 can actuate to an open position, i.e., to open the reformer port 42, such that exhaust fluid can be directed to the reformer 18 (
Advantageously, embodiments are disclosed herein where a single controlled valve (e.g., proportioning valve) can direct exhaust fluid to a reformer, which can simplify the exhaust treatment system compared to exhaust treatment designs that employ multiple valves. Further, embodiments are discussed herein where particulate matter, and the like is removed from the exhaust fluid prior to be directed to the valve and/or reforming system. Since soot and particulates can coke and/or clog valves and/or the reformer, embodiments that remove soot and particles prior to directing the exhaust fluid to a valve or reformer can increase the operating life of the valve, reformer, and the like. It is further noted that disposing the valve at a location that minimizes the exhaust fluid temperature, e.g., a location proximate to a tail pipe outlet, can further extend operating life of the valve directing exhaust fluid.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
