Non-thermal plasma reactor substrate design-E-shape with low...

Details Non-thermal plasma reactor substrate design-E-shape with low... Non-thermal plasma reactor substrate design-E-shape with low...

2002-03-28

2004-11-23

Mayekar, Kishor (Department: 1753)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

With means applying electromagnetic wave energy or...

C060S275000, C427S404000

Reexamination Certificate

active

06821493

ABSTRACT:

TECHNICAL FIELD
The present invention relates to reactors for chemical reduction of nitrogen oxide (NOx) emissions in the exhaust gases of automotive engines, particularly diesel and other engines operating with lean air fuel mixtures that produce relatively high emission of NOx and method of manufacturing the same. More particularly, the invention relates to a low-loss electrode-printed structural dielectric barrier for a non-thermal plasma reactor and to improved non-thermal plasma reactor multi-cell stacks having structural dielectric barriers printed with low-loss electrode patterns.
BACKGROUND OF THE INVENTION
In recent years, non-thermal plasma generated in a packed bed reactor has been shown to be effective in reducing oxides of nitrogen (NOx) produced by power plants and standby generators. These units usually have a reducing agent, such as urea, to enhance the conversion efficiency. The packed bed reactor consists essentially of a high voltage center electrode inserted into a cylinder of dielectric material, usually a form of glass or quartz. An outside or ground electrode is formed by a coating of metal in various forms, including, tape, flame spray, mesh, etc. The space between the center electrode and the inside diameter of the dielectric tube is filled or packed with small diameter glass beads. When high voltage alternating current is applied to the center electrode, the surfaces of the beads go into corona, producing a highly reactive and selective surface for inducing the desired reaction in the gas.
Unfortunately, the packed bed design with loose beads and glass dielectric is impractical for use in the conditions found in a mobile emitter, such as a car or truck. The vibration and wide temperature swings of the vehicle system would damage the packed bed and the necessary temperature and vibration isolation needed to make it survive would not be cost effective.
A non-thermal plasma reactor for use with diesel engines and other engines operating with lean air fuel mixtures is disclosed in commonly assigned U.S. patent application Ser. No. 09/465,073, filed Dec. 16, 1999, entitled “Non-thermal Plasma Exhaust NOx Reactor, which is hereby incorporated by reference herein in its entirety.” Disclosed therein is a reactor element comprising high dielectric, nonporous, high temperature insulating means defining a group of relatively thin stacked cells forming gas passages and separated by the insulating means. Alternate ground and charge carrying electrodes in the insulating means on opposite sides of the cells are disposed close to, but electrically insulated from, the cells by the insulating means. The electrodes may be silver or platinum material coated onto alumina plates. Conductive ink is sandwiched between two thin nonporous alumina plates or other suitable insulating plates to prevent arcing while providing a stable electrode spacing for a uniform electric field. The electrodes are coated onto alumina in a pattern that establishes a separation between the electrodes and the connectors of alternate electrodes suitable to prevent voltage leakage.
U.S. Pat. No. 6,338,827 to Nelson et al., commonly assigned, entitled “Stacked Shape Plasma Reactor Design for Treating Auto Emissions,” which is hereby incorporated by reference herein in its entirety, discloses a non-thermal plasma reactor element prepared from a planar arrangement of formed shapes of dielectric material. The shapes are used as building blocks for forming the region of the reactor wherein the plasma is generated. Individual cells are provided with a conductive print disposed on a formed shape to form electrodes and connectors. In a preferred embodiment, the conductive print comprises a continuous grid pattern having a cutout region disposed opposite the terminal connector for reducing potential charge leakage. Multiple cells are stacked and connected together to form a multi-cell reactor element.
Commonly assigned U.S. patent application Ser. No. 09/517,681, filed Mar. 2, 2000 entitled “Plasma Reactor Design for Treating Auto Emissions—Durable and Low Cost,” which is hereby incorporated by reference herein in its entirety, discloses a non-thermal plasma reactor element for conversion of exhaust gas constituents. The reactor comprises an element prepared from an extruded monolith of dense dielectric material having a plurality of channels separated by substantially planar dielectric barriers. Conductive material printed onto selected channels forms conductive channels that are connected along bus paths to form an alternating sequence of polarity, separated by exhaust channels. Conductive channels and channels not selected for exhaust flow are plugged at end portions of the monolith with a material suitable for excluding exhaust gases and preventing electrical charge leakage between conductive channels. Exhaust channels, disposed between opposite polarity conductive channels, are left uncoated and unplugged. During operation, exhaust gas flows through channels and is treated by the high voltage alternating current plasma field. The planar shape of the dielectric barriers provides a uniform electrical response throughout the exhaust channels.
U.S. Pat. No. 6,354,903 to Nelson et al., commonly assigned, entitled “Method of Manufacture of a Plasma Reactor with Curved Shape for Treating Auto Emissions,” which is hereby incorporated by reference herein in its entirety, discloses a non-thermal plasma reactor element wherein a swept shape substrate is formed and treated to create a non-thermal plasma reactor element. The substrate is formed via extrusion so that there is a series of nested, concentric dielectric barriers. Selected channels are coated with conductive material to form conductor channels capable of forming an electric field around exhaust channels. Conductive channels and channels not selected for exhaust flow are plugged at end portions of the monolith with a material suitable for excluding exhaust gases and preventing electrical charge leakage between conductive channels. Exhaust channels, disposed between opposite polarity conductive channels, are left uncoated and unplugged.
U.S. Provisional Application No. 60/249,231, of David E. Nelson, et al., filed Nov. 16, 2000, entitled “Edge-connected Non-thermal Plasma Exhaust After Treatment Device,” which is hereby incorporated by reference herein in its entirety, discloses an edge-connected non-thermal plasma reactor substrate including an edge-connected frame comprising a pair of dielectric edge connectors secured at opposite ends to first and second outer dielectric plates. The dielectric edge connectors comprise a backplane and a plurality of tines protruding along at least one major surface of the backplane, the plurality of tines being spaced apart from one another at regular intervals so as to form pockets between adjacent tines. A plurality of alternating polarity electrode plates are disposed within the edge-connected frame in an alternating polarity arrangement that defines the presence of at least one dielectric barrier next to a plasma cell with the pockets compliantly engaging opposite ends of the electrode plates.
While the above-described non-thermal plasma reactors meet some of the current needs and objectives in the art, there remain several issues that need to be more effectively addressed.
Current stacked planar designs without structural ligaments are prone to fracture during use in automotive exhaust applications if the unsupported span of the dielectric barrier becomes large (fracture is often observed when the length of unsupported span approaches about 30 millimeters for a 0.5 millimeter thick alumina dielectric barrier). This failure can be induced by gas flow and vibration induced stresses leading to deflection of the dielectric barriers. NOx conversion efficiency can be negatively affected even with slight deflection of the dielectric barriers due to gas by-pass between plates or from plasma field variation.
Current non-thermal plasma reactor elements having structural ligaments provide improved durability over ligament-fre

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