GB2119291A

GB2119291A - Insulator for an electrostatic precipitator

Info

Publication number: GB2119291A
Application number: GB08308929A
Authority: GB
Inventors: Erik Moe Bojsen; Lars Gronnegaard Pedersen
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 1982-04-05
Filing date: 1983-03-31
Publication date: 1983-11-16
Also published as: GB2119291B

Abstract

An insulator assembly for carrying an emission electrode system of an electrostatic precipitator comprises a tubular insulator body (4) for mounting on and extending through an opening in a casing (1) of an electrostatic precipitator. A rod (6) for carrying an emission electrode system is supported by and extends through the insulator body (4) and is spaced from an inner wall of the tubular insulator body. At least part of the inner wall of the tubular insulator body (4) is electrically connected to the carrying rod (6) via an electrically conductive material, which may be a coating (8) on the inner wall of the insulator body, or a resilient conductive material filling the gap between the insulator body and the carrying rod. <IMAGE>

Description

SPECIFICATION Insulator for an electrostatic precipitator The invention relates to an insulator assembly for carrying an emission electrode system of an electrostatic precipitator, the assembly comprising a tubular insulator body for mounting on an opening in a casing of an electrostatic precipitator; and a rod for carrying an emission electrode system, the rod being supported by and extending through the insulator body and being spaced from an inner wall of the tubular insulator body. Such an assembly is hereinafter referred to as of the kind described.

It is the object of assemblies of the kind described to keep the emission electrode system, which is powered by high-voltage, insulated from the framework and wall construction of the precipitator casing, which is at earth potential.

Usually the emission electrode system is suspended from carrying rods projecting through a wall of the precipitator or electro-filter casing, the rods simultaneously acting to supply current to the emission system from a high-voltage generator situated outside the casing.

When these carrying rods project through the roof of the filter casing the opening in the roof is normally of such a size that the distance from a carrying rod to an edge of the opening alone ensures that no flash-over occurs and the rods are insulated from the casing. Each insulator body normally has the shape of a cylindrical or cone-shaped tube which at its lower end rests on the edge of the opening, while the carrying rod is secured to a plate resting on the top edge of the insulator body so that the rod is vertically mounted to extend down through the centre of the insulator tube and the opening in the roof of the filter casing. The height of the insulator tube is such that flash-overs from the plate resting on its upper end to the filter casing are avoided.

Usually the carrying insulator body is positioned in an insulator chamber built on the filter casing.

Also the walls of this chamber must be positioned at such a distance from the live parts that flash-overs are averted. Because of the high voltages used in a modern electrofilter, particularly when the pulse technique is used, the distances needed to avert flash-overs through air will be considerable, and the increased material consumption alone for the chambers will be appreciable.

By shaping the tubular insulator body in such a way that it projects down into the space between the edge of the filter casing and the rod carrying the emission electrode it is made possible to reduce the size of the opening through which the rod penetrates as the insulator material has a greater break-down strength than air.

As the carrying rod must be able freely to carry out the small bending movements to which it is exposed through the vibrations to which the emission system is exposed, partly by the rapping of the electrodes and partly as a consequence of the gas flowing by, it is necessary that it is freely suspended down through the carrying insulator body. Had it been cast integral with the latter, the transmitted bending forces could cause the insulator body to rupture.

Similarly, any difference in the degree of heat expansion between the carrying rod and the insulator body material could make the comparatively brittle insulator material fracture.

Consequently, the insulation between the edge of the opening in the filter casing through which the carrying rod passes and the carrying rod proper is not only constituted by the material used for manufacturing the carrying insulator, but also by a narrow air gap. As the radius of curvature of the carrying rod is comparatively small and as the carrying insulator material has a higher dielectric constant than air, a powerful electric field will occur in the air gap around the carrying rod, which will cause a corona discharge which in time will decompose the insulation material of the opposite insulator body wall, and subsequent break-down thereof.

In accordance with the present invention, in an insulator assembly of the kind described the insulator body extends through the opening in the casing, and at least part of the inner wall of the tubular insulator body is electrically connected to the carrying rod via an electrically conductive material.

With this arrangement corona discharge around the carrying rod is avoided.

At least part of the inner wall of the tubular insulator body may be coated with an electrically conductive material, an electrical connection being made between this coating and the rod.

Alternatively or additionally at least part of the gap between the rod and the tubular insulator body may be filled with a temperature resistant, electrically conductive, resilient material. The material will be partly in contact with the inner surface of the insulator body and partly in contact with the rod to form a conductive connection therebetween. The temperature resistant, resilient, conductive material may be for example compressed powdered graphite or metal sponge.

Examples of conventional assemblies are illustrated in Figures 1 and 2 of the accompanying drawings which are diagrammatic views.

Some examples of assemblies in accordance with the present invention are illustrated in Figures 3 to 5 of the accompanying drawings, which are diagram maticviews similarto Figures 1 and 2.

In Figures 1 and 2 a roof 1 of an electrostatic precipitator or electrofilter casing (not otherwise shown) has an opening 2, along the edge of which a carrying flange 3 is provided. Resting on the carrying flange 3 is a tubular insulator body 4, which is frusto-conical in Figure 1 and cylindrical in Figure 2.

The upper end of the body 4 is covered by a carrying plate 5 from which a carrying rod 6 carrying an emission electrode system (not shown) is suspended down through the opening 2. It is one object of the insulator body 4 to create a sufficient distance between the carrying rod 6 and the filter casing, which is at earth potential, so that flash-overs are averted. This is done partly by making the insulator body 4 of a sufficient height, and partly by making the distance a between the carrying rod 6 and the carrying flange 3 and consequently the edge of the opening 2 sufficiently large. Normally, the insulator bodywill be encased in an insulator chamber, diagrammatically indicated by the dashed line 7.The insulator chamber must also everywhere have such a distance from the detached parts of the carrying rod 6 and the parts connected thereto that flashovers from such parts to the chamber walls are avoided.

Examples of insulator assemblies according to the invention are shown in Figures 3 to 5 in which the same reference numerals are used as for corresponding parts in Figures 1 and 2. The insulator body 4 here projects through the opening 2 in the roof 1 of the filter casing, and constitutes the insulation between the edge of the roof and the carrying rod 6.

As the insulator body 4 is made from a material the break-down strength of which is several times larger than that of air, the distance a can be reduced significantly more than according to the known art. It should be noted that the insulator body 4 must encase the carrying rod 6 far enough into the filter casing that flash-overs between the carrying rod 6 and the filter casing are avoided. In order to avert large electric field strengths in the air gap between the insulator body 4 and the carrying rod 6, the inner surface of the tubular insulator body 4 is provided, in the example shown in Figure 3, with a coating 8 of conductive material being electrically connected to the carrying rod 6 through the carrying plate 5.

Figure 4 shows another example, which differs from the one shown in Figure 3 in that the air gap between the carrying rod 6 and the insulator body 4 is filled out with a resilient, conductive material 9, e.g. powdered graphite or metal sponge.

In the example shown in Figure 5 only part of the air gap is filled out with conductive material 9, viz.

the part in alignment with the roof 1 of the filter casing and the carrying flange 3, at which locality the largest field strengths occur.

Combinations of the examples shown could be used e.g. an arrangement in which part of the inner surface of the insulator body 4 is coated with conductive material to which connection is made from the carrying rod 6 by filling out a smaller or larger part of the air gap with a resilient, conductive material.

Typically, the distance a in the conventional construction shown in Figures 1 and 2 is about 200 mm whereas with the invention this value is decreased by a factor of 10 to about 25 mm although the exact size depends on the tension to which the rod 6 is raised.

The insulator body 4 shown in Figures 3 to 5 may be made from aluminium oxide (alumina). Previously the insulator body 4 has been made from steatite.

Claims

1. An insulator assembly for carrying an emission electrode system of an electrostatic precipitator, the assembly comprising a tubular insulator body for mounting on an opening in a casing of an electrostatic precipitator; and a rod for carrying an emission electrode system, the rod being supported by and extending through the insulator body and being spaced from an inner wall of the tubular insulator body, wherein the insulator body extends through the opening in the casing, and at least part of the inner wall of the tubular insulator body is electrically connected to the carrying rod via an electrically conductive material.

2. An assembly according to claim 1, characterised in that at least part of the inner wall of the tubular insulator body is coated with an electrically conductive material and an electrical connection is made between this coating and the rod.

3. An assembly according to claim 1 or claim 2, characterised in that at least part of the gap between the tubular insulator body and the rod is fiiled with an electrically conductive, resilient, temperature resistant material.

4. An assembly according to any of the claims 1 to 3, wherein the insulator body comprises an outwardly extending, integral support portion which rests on the precipitator casing in use.

5. An assembly according to claim 1, substantially as described with reference to any of the examples shown in Figures 3 to 5 of the accompanying drawings.

6. An electrostatic precipitator having a casing with an opening in which is mounted an insulator assembly according to any of the preceding claims.