GB2424379A

GB2424379A - Gas reactor electrode connections

Info

Publication number: GB2424379A
Application number: GB0502301A
Authority: GB
Inventors: Peter James Andrews; Michael Inman; David Michael Weeks
Original assignee: IPSOLUTIONS; Accentus Medical PLC
Current assignee: IPSOLUTIONS; Accentus Medical PLC
Priority date: 2005-02-04
Filing date: 2005-02-04
Publication date: 2006-09-27
Also published as: GB0502301D0

Abstract

Dielectric plates 11,12,13,14,15 are stacked one upon another with spacer strips 16,17,18,19 in between to provide gas channels 25. Layers 26 of electrically conducting material are printed onto the plates to provide electrodes on each side of a gas channel 25 with dielectric material intervening as a barrier layer between the electrodes. Peninsular extensions 27 of each electrode are arranged to project in the opposite direction relative to its neighbouring electrode. Apertures 28 extend through the peninsular extensions 27 transversely of the electrodes. Symmetrically positioned apertures 29 extend through the dielectric material clear of the electrode on the opposite side to the apertures 28. Apertures 28 in one layer align with apertures 29 in the neighbouring layers to provide a socket for receiving a plug connector to contact the electrodes (in each alternate layer) traversed by the aperture.

Description

fl - 1 - 2424379 Gas reactor electrode connections The invention relates

to the provision of electrode connections in a gas reactor and in particular in a non- thermal plasma reactor.

U.S. patent publication 2001/0016179 Al discloses a non-thermal plasma reactor fabricated from a stacked arrangement of dielectric building blocks providing an array of gas channels therethrough. Flat surfaces of the dielectric building blocks which abut neighbouring building blocks in the stack are provided, by a printing process, with layer electrodes. A part of each electrode layer extends to an edge of the building block on which it is printed. The arrangement and stacking of the blocks is such that this part of an electrode layer, which extends to the edge, is on the opposite side of the block from the corresponding part of its neighbouring electrode layers. Electrical terminal connection can then be made down one side of the stack to each alternate electrode layer, and down the other side of the stack to each alternate intervening electrode layer.

A problem with this configuration is that thermal expansion and contraction may lead to a break or high resistance in the connection between the electrical terminals and the electrode layers. Also, electrical insulation has to be provided for the side terminal connections.

It is an object of the present invention to address these problems with an improved form of terminal connection for electrode layers in a reactor of this type.

The invention provides a reactor comprising an assembly of components of dielectric material stacked one upon another and providing gas channels for the passage of gas therethrough, there being at least two components supporting a layer of electrically conducting material to provide electrodes on each side of a gas channel, preferably with dielectric material intervening as a barrier layer between the electrodes, the shape and position of each layer of electrically conducting material relative to its neighbouring layer or layers of electrically conducting material being such as to provide a region in each electrically conducting layer which overlies a region of dielectric material component from which neighbouring electrically conducting layer or layers is or are absent, and at least one aperture extending through the said region transversely of the electrically conducting layers, the aperture being adapted for receiving a connector to contact the or each electrically conducting layer traversed by the aperture.

It will be appreciated that the aperture, and thus a connector received therein, will extend through, and provide for electrical contact with, the electrically conducting layer or layers through which the aperture passes, but will be insulated from the neighbouring electrically conducting layer, or the intervening neighbouring electrically conducting layers, because this or these are arranged to be absent from the region through which the aperture passes. Conveniently the aperture forms a socket for receiving a plug connector.

Given appropriate dimensions and a trapping capability within the aperture, the "plug" connector may be constituted by a bare wire. Alternatively, the aperture may receive a wire connector therein glued into the aperture by means of an electrically conducting glue.

Preferably a second aperture is provided which extends through the region of the said neighbouring electrically conducting layer, or the intervening neighbouring electrically conducting layers, which overlies the region or regions from which the first mentioned electrically conducting layer or layers is or are absent.

Preferably the components of dielectric material comprise flat plates stacked in the form of a sandwich with ceramic spacers to provide gas channels between the plates. Electrodes may be provided on the plates by screen printing, but are not printed up to the edges of the plates. The gas channels may contain permeable filler material which can be polymeric, ceramic or metallic in the form of particles such as spheres, pellets, extrudates, sheets, coils, granules, wafers, frits, foams, membrane, meshes, or fibres or may contain a multiplicity of cells in the form of a ceramic honeycomb, a flowthrough filter or wallflow filter. The filler material may comprise catalytic material or may be coated with catalytic material, as also may the channel walls.

In a preferred arrangement, a double dielectric barrier configuration is achieved by providing, for example by printing, an electrically conducting layer on at least one of two dielectric material partial thickness plates and bonding, through a firing step, the partial thickness plates together to form a single plate with the electrically conducting layer sandwiched in the middle.

The invention includes a method of manufacturing a reactor, which method comprises forming a plurality of components of dielectric material, providing electrically conducting layers, stacking the components and the electrically conducting layers to form at least one gas channel through dielectric material, with an electrically conducting layer on opposed sides of the gas channel and preferably at least one dielectric barrier layer between the electrically conducting layers, so shaping and positioning the layers of electrically conducting material relative to the neighbouring layer or layers of electrically conducting material that there is a region in each electrically conducting layer which overlies a region of dielectric material component from which neighbouring electrically conducting layer or layers is or are absent, and providing at least one aperture extending through the said region transversely of the electrically conducting layers, the aperture being adapted for receiving a connector to contact the or each electrically conducting layer traversed by the aperture.

Preferably a second aperture is provided which extends through the region of the said neighbouring electrically conducting layer, or the intervening neighbouring electrically conducting layers, which overlies the region or regions from which the first mentioned electrically conducting layer or layers is or are absent. The apertures may be provided by drilling through the assembled stack of components and electrically conducting layers. Apertures can also be provided by cutting with a water jet or by laser cutting or by diamond hole saw cutting.

A specific construction of reactor and method of manufacture embodying the invention will now be described by way of example and with reference to the drawings filed herewith, in which: Figure 1 is a diagrammatic perspective view of a reactor, Figure 2 is a diagrammatic perspective exploded view of a plurality of components for assembly into a reactor as shown in Figure 1, Figure 3 is a diagrammatic perspective exploded view of part of some components for assembly into a modified form of reactor, Figure 4 illustrates diagrammatically how a plurality of reactors such as shown in Figure 1 may be combined in a vertical (Figure 4a) array, or a horizontal (Figure 4b) array, and Figure 5 illustrates an alternative method of providing electrically conducting layers.

Figure 1 shows a non-thermal plasma reactor module formed by a stack of rectangular plates 11,12, 13, 14,15 made of dielectric material, alumina in this example, but which may be any suitable dielectric material such as cordierite, zirconia, non- conducting silicon carbide, barium titanate or diamond. Spacer strips 16, 17, 18, 19 and 21,22, 23,24 of the same dielectric material are positioned between the plates 11,12,13,14,15 along opposite sides of the stack to provide four gas channels 25 extending through the stack.

The spacer strips can be made from a different dielectric material to that used for the plate material as long as the mechanical and electrical properties are assessed as suitable for the construction of the reactor.

Each plate 11,12, 13, 14 has formed thereon, by a screen printing process, a layer of electrically conducting material 26. This layer of electrically conducting material is generally rectangular, but does not extend right up to the edges of the plate and, in particular, a wide margin is allowed on the sides of the plates which overlie the spacer strips 16-24. The layer of electrically conducting material 26 is formed with a peninsular extension 27 into this wide margin on one side only of the plate.

As may best be seen from Figure 2 (which shows only four plates rather than the five assembled into the stack shown in Figure 1), the shape of the electrically conducting layer 26 with its peninsular extension 27 is identical on each plate, but for assembly into the stack, each successive layer is rotated through 180 degrees so that the peninsular extension 27 on one plate projects on the opposite side to that of the peninsular extension 27 on its neighbouring plates.

Figure 2 shows each plate provided with a circular aperture 28 through the peninsular extension 27 and a symmetrically positioned circular aperture 29 on the opposite side. The circular aperture may conveniently be provided by drilling, but ceramic dielectric material such as alumina may be difficult to drill, in which case a preferred method would be to use laser cutting or water jet cutting or a diamond hole saw. When the plates are assembled into the stack, the apertures 28 in plates 11,13 and 15 line up with the apertures 29 in the plates 12 and 14. The apertures 28 in plates 12 and 14 line up with the apertures 29 in plates 11,13, and 15.

The aligned apertures provide a pair of sockets 31, 32 into which plug connectors 33, 34 are received. Plug connector 33 will make electrical contact with the electrically conducting layers on plates 12 and 14, but will be insulated from the electrically conducting layers on plates 11,13 and 15. Plug connector 34 will make electrical contact with the electrically conducting layers on plates 11, 13 and 15, but will be insulated from the electrically conducting layers on plates 12 and 14. Connection may be made by these plug connectors 33,34 to a power supply unit (not shown) Figure 3 illustrates diagrammatically a modification. Three dielectric material plates ha, 12a, 13a are shown and may be assembled, with appropriate spacer strips (not shown in Figure 3) into a stack as described with reference to Figure 1. However, Figure 3 shows plates ha, 12a, 13a with an embedded electrically conducting layer 26a formed by a screen printing process onto a half thickness plate, which in all other respects corresponds to the arrangement shown in Figure 1. This half thickness plate, with an electrically conducting layer 26a printed thereon, is then sandwiched together with another plain half thickness plate and glued or fused together by a firing process to form the plates ha, 12a, 13a as shown in Figure 3. When assembled into a stack with spacer strips, the electrodes formed by the electrically conducting layers 26a will have double dielectric barriers between them. Electrically conducting layers can be printed or vacuum or plasma sprayed onto the first half thickness dielectric plate with good molecular contact so that there are substantially no voids (air spaces) . However a problem with this method of manufacture is that it is difficult to avoid the formation of small voids (air spaces) between the electrically conducting layer and the plain half thickness plate of dielectric to which it is secured by gluing or fusing. In use plasma is likely to form in such voids with deleterious effects, in particular damage to the bond between the two half thickness plates. A solution is to provide both half thickness plates with an electrically conducting layer, applied by printing or vacuum or plasma spraying. The two half thickness plates 0 -8- are glued together or fused together by a firing process with the two electrically conducting layers facing and in intimate, and good electrical contact, with one another.

There may be voids formed between the two electrically conducting layers in this joining process, but there will be no possibility of plasma forming in such voids. This is because the two electrically conducting layers, being in electrical contact will necessarily always be at the same electrical potential.

A further improvement, shown in Figure 3, which may also be applied to the Figure 1 embodiment, is provision of a printed electrically conducting layer 35 onto the inside surfaces of the apertures which form the sockets 31a, 32a. This is fused with the electrically conducting layers 26a, where the apertures pass through them, and serves to improve electrical connection between the electrically conducting layers 26a and a plug connector (such as 33, 34 in Figure 1) inserted into the sockets.

Figure 4a illustrates how several (three are shown in the Figure) reactor modules 10 may be arranged together in a vertical stack and connected to power supply unit 36. Figure 4b illustrates a connection arrangement for reactor modules 10 in a horizontal stack.

It will be appreciated that any convenient number of reactor modules 10 may be assembled together in this way, including a combination of vertical and horizontal stacking. Modules can be constructed by the use of larger electrode/dielectric plate material. Thus Figure 4b, which illustrates three modules that have been combined together, can be replaced by one module of the same overall dimensions or two modules also of the same overall dimension so that a common high voltage connection and earthy connection can be used to power up the enlarged assembly. The use of larger plates allows 0 -9- the high voltage connection to be positioned towards the centre of the plate and this allows a greater creepage distance for preventing electrical breakdown of the high voltage connection. By creepage we mean the distance from a high voltage connection to an earth connection as measured along the surface of a component.

Figure 5 illustrates an alternative method for providing an electrically conducting layer 26b embedded, sandwich fashion, between two half thickness plates 37,38. The electrically conducting layer 26b is preformed as a rectangular electrode plate, approximately 0.5 mm thick, with a small rectangular projection on one side and received within a spacer 39, similar in form to a picture frame. The spacer 39 has a cut out at 41 for receiving the small rectangular projection on one side of the electrode plate forming the electrically conducting layer 26b. The small rectangular projection serves the same purpose as the peninsular extensions 27, and is provided with an aperture extending therethrough in the same way as described for the example of Figure 1.

The invention is not restricted to the details of the foregoing examples. For instance, instead of peninsular extensions 27, the electrically conducting layers 26 may simply be rectangular, but arranged to extend closer to one of the sides which is to overlie the spacer strips, leaving a wide margin on the opposite side.

In plates with an electrically conducting layer embedded, as shown in Figure 3, the embedded electrically conducting layer need not necessarily he embedded in the middle. By using partial thickness plates of different thickness from one another, the embedded layer can be nearer to one surface than the other.

C - 10 - The reactor can be used for treatment of gaseous media, in particular for the reduction of the emissions of nitrogen oxides and carbon combustion products in the exhaust gases from internal combustion engines. Examples of catalysts that can be used for the reduction of such emissions are given in WO 00/43102 and WO 00/71866, WO 01/59270 and WO 01/76733. The reactor can also be used for the plasma reforming of hydrocarbons into hydrogen.

The shape of the assembled module can be changed in order to provide an improved gas seal. For example the cross section of the assembly perpendicular to the gas flow can be altered from one where all of the plates have the same dimension to an elliptical or oval section where the length of the plates decreases towards the top and bottom of the module. 0 -11

Claims

Claims 1. A reactor comprising an assembly of components of dielectric

material stacked one upon another and providing gas channels for the passage of gas therethrough, there being at least two components supporting a layer of electrically conducting material to provide electrodes on each side of a gas channel, the shape and position of each layer of electrically conducting material relative to its neighbouring layer or layers of electrically conducting material being such as to provide a region in each electrically conducting layer which overlies a region of dielectric material component from which neighbouring electrically conducting layer or layers is or are absent, and at least one aperture extending through the said region transversely of the electrically conducting layers, the aperture being adapted for receiving a connector to contact the or each electrically conducting layer traversed by the aperture.
2. A reactor as claimed in claim 1, wherein a second aperture is provided which extends through the region of the said neighbouring electrically conducting layer, or the intervening neighbouring electrically conducting layers, which overlies the region or regions from which the first mentioned electrically conducting layer or layers is or are absent.
3. A reactor as claimed in claim 1 or claim 2, wherein the components of dielectric material comprise flat plates stacked in the form of a sandwich with ceramic spacers to provide gas channels between the plates.
4. A reactor as claimed in claim 3, wherein the electrodes are provided on the plates by screen printing, but are not printed up to the edges of the plates.
5. A reactor as claimed in any of the preceding claims, wherein the gas channels contain permeable filler material in the form of particles, meshes, or fibres or a multiplicity of cells in the form of a ceramic honeycomb, a flowthrough filter or wallflow filter.
6. A reactor as claimed in claim 5, wherein the filler material comprises catalytic material or is coated with catalytic material.
7. A reactor as claimed in any of the preceding claims, wherein the channel walls are coated with catalytic material.
8. A reactor as claimed in any of the preceding claims, wherein the components of dielectric material and the layers of electrically conducting material are arranged so that there is dielectric material intervening as a barrier layer between the electrodes.
9. A reactor as claimed in claim 8, having a double dielectric barrier configuration.
10. A method of manufacturing a reactor, which method comprises forming a plurality of components of dielectric material, providing electrically conducting layers, stacking the components and the electrically conducting layers to form at least one gas channel through dielectric material with an electrically conducting layer on opposed sides of the gas channel, so shaping and positioning the layers of electrically conducting material relative to the neighbouring layer or layers of electrically conducting material that there is a region in each electrically conducting layer which overlies a region of dielectric material component from which neighbouring electrically conducting layer or layers is or are absent, and providing at least one aperture extending through the said region transversely of the electrically conducting layers, the aperture being adapted for receiving a connector to contact the or each electrically conducting layer traversed by the aperture.
11. A method as claimed in claim 10, wherein a second aperture is provided which extends through the region of the said neighbouring electrically conducting layer, or the intervening neighbouring electrically conducting layers, which overlies the region or regions from which the first mentioned electrically conducting layer or layers is or are absent.
12. A method as claimed in claim 10 or claim 11, wherein the apertures are provided by drilling through the assembled stack of components and electrically conducting layers.
13. A method as claimed in any of claims 10 to 12, wherein the components of dielectric material and the layers of electrically conducting material are arranged so that there is dielectric material intervening as a barrier layer between the electrodes.
14. A method as claimed in any of claims 10 to 13, wherein the said components comprise plates of dielectric material and a double dielectric barrier configuration is achieved by providing an electrically conducting layer on at least one of two dielectric material partial thickness plates and bonding the partial thickness plates together to form a single plate with the electrically conducting layer sandwiched inside.
15. A method as claimed in any of claims 9 to 14, wherein the electrically conducting layers are formed by printing onto the component or components of dielectric material.
16. A reactor substantially as hereinbefore described with reference to, and illustrated in, Figures 1 and 2, or Figure 3, or Figure 4, or Figure 5 of the drawings filed herewith.
17. A method of manufacturing a reactor substantially as hereinbefore described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 5 of the drawings filed herewith.