DEVICE FOR PLASMA PROCESSING OF GASES

Abstract: An apparatus (1) for the processing of gaseous media by means of a plasma wherein there is included at least one electrode (16, 14) which is maintained in position in relation to another by one or more insulating support structures (7, 8) made of a micaceous glass material.

Description: DEVICE FOR PLASMA PROCESSING OF GASES The present invention relates to devices for the processing of gaseous media by means of plasmas, and more particularly, to such devices in which one electrode is positioned axially within another electrode. Such devices, in particular for use in the treatment of exhaust gases from an internal combustion engine, operate in a very harsh environment. This represents a special problem for an insulating support structure for the electrodes in that the support structure must be chemically inert, able to withstand considerable thermal and mechanical shocks and also be able to withstand pulsed or continuous potentials of tens of kilovolts. Hitherto ceramic materials such as alumina have been used to make the support plates and although these are satisfactory in so far as their chemical inertness and insulating properties are concerned, they are brittle and prone to fracture. According to the present invention there is provided an apparatus for the processing of gaseous media by means of a plasma wherein there is included at least one electrode which is maintained in position in relation to another by one or more insulating support structures made of a micaceous glass material. Preferably the micaceous glass material is that manufactured by Morgan Matroc Limited, a subsidiary of the Morgan Crucible Company, under the Trade Mark MICATHERM. Preferably the electrode or a metal attachment member therefor is secured to a said insulating support by in situ moulding of the support material on to the said electrode or metal attachment member. In this way insulating supports and electrodes attached thereto directly or via metal attachment members can be formed as a self supporting removable and replaceable unit. Preferably, in such a unit, a pair of insulating supports and a pair of electrodes define a space therebetween which is filled with pellets of active material. The invention will now be described, by way of example, with reference to the accompanying drawing which is a schematic longitudinal section of a device for treating the exhaust gases from an internal combustion engine to remove pollutants therefrom. Referring to the drawing, a reactor 1 for removing pollutants, such as NO χ or carbonaceous combustion products, from the exhaust from an internal combustion engine consists of a cylindrical stainless steel chamber 2 which has an inlet stub 3 and an outlet stub 4 by means of which it can be connected into the exhaust system of an internal combustion engine. The chamber 2 is arranged, in use, to be connected to an earthing point 5. Perforated inner and outer cylindrical electrodes 6 and 14 respectively are positioned co-axially within the chamber 2 by means of two supports 7 and 8. The outer electrode 14 is held at earth potential by connection (not shown) to the earthed chamber 2. The upstream end of the inner electrode 6 is closed off and is arranged to be connected to a source 9 of a pulsed or continuous potential of the order of tens of kilovolts via an insulating feed through 10. Packed within the space 11 formed between the outer electrode 14, the inner electrode 6 and the supports 7 and 8 is a bed of pellets, represented diagramatically at 12, of an active material consisting of or incorporating ferroelectric material such as barium titanate. The upstream support 7 has a series of apertures 13 formed in it whereas the support 8 is impermeable. The exhaust gases therefore are constrained to flow through the reactor 1 in the manner shown in the figure. The selection of material composition of the pellets and the manner of operation of the reactor 1 are in this example based upon the considerations and examples described in our International Patent Application PCT/GB98/02569. The supports 7 and 8 are made of a lead-based glass with a dispersion of mica in it. The material which is marketed by Morgan Matroc Limited under the trade name MICATHERM, is particularly suitable for the purposes of the present invention because not only does it have the required electrical properties and can withstand the operating environment of an internal combustion engine exhaust system, but it is resistant to thermal shock and can be formed readily into required shapes by moulding techniques. In particular the material can be moulded directly on to metal components and in that way form a firmly adhered and sealed joint with the metal component. This is illustrated in the example shown in the drawing in which each of the supports 7 and 8 is moulded onto a concentric pair of cylindrical metal stubs 71, 72 and 81, 82 respectively. The stubs 71, 72 and 81, 82 are firmly fixed and sealed in the respective supports 7 and 8, and provide for attachment of the electrodes 6 and 14. Thus, inner electrode 6 is of slightly larger radius than the stubs 71 and 81 so that it can be pushed onto these stubs and fixedly attached to them in any suitable manner (e.g. welding) . Outer electrode 14 is similarly fixed on to stubs 72 and 82. In this way the complete set of components comprising the supports 7 and 8, the electrodes 6 and 14 and the pellet bed 12 form a self supporting removable and replaceable unit, conveniently referred to as a "cassette". Provision for filling, or refilling, with pellets may be made by incorporating one or more removable plugs (not shown) in the support 7 and/or support 8. The invention is not restricted to the details of the foregoing example. For instance, the feed through 10 need not necessarily be positioned on the side of the chamber 2 but may be positioned to extend through an end wall.

Claims: Claims 1. An apparatus for the processing of gaseous media by means of a plasma wherein there is included at least one electrode (6, 14) which is maintained in position in relation to another electrode (6, 14) by one or more insulating support structures (7, 8), characterised in that the support structure (7, 8) is made of a micaceous glass material. 2. An apparatus according to claim 1 further characterised in that the micaceous glass material is that marketed under the trade mark 'MICATHERM' by Morgan Matroc Limited. 3. An apparatus according to claim 1 or claim 2 adapted to form part of an exhaust system of an internal combustion engine. 4. An apparatus according to any of the preceding claims, further characterised in that the electrode (6, 14) or a metal attachment member (71, 72, 81, 82) therefor is secured to a said insulating support (7, 8) by in situ moulding of the support material on to the said electrode (6, 14) or metal attachment member (71, 72, 81, 82) . 5. An apparatus according to claim 4, further characterised in that insulating supports (7, 8) and electrodes (6, 14) attached thereto directly or via metal attachment members (71, 72, 81, 82) form a self supporting removable and replaceable unit. 6. An apparatus according to claim 5, further characterised in that a pair of insulating supports (7, 8) and a pair of electrodes (6, 14) define a space (11) therebetween which is filled with pellets (12) of active material.

Inventors: SEGAL DAVID LESLIE, WEEKS DAVID MICHAEL, SEGAL, DAVID, LESLIE, WEEKS, DAVID, MICHAEL
Applicants: AEA TECHNOLOGY PLC, SEGAL DAVID LESLIE, WEEKS DAVID MICHAEL, SEGAL, DAVID, LESLIE, WEEKS, DAVID, MICHAEL
Application year: 1998
Main classification: B01D53
IPC codes: B01D53, B01J19, F01N3