BACKGROUND TO THE INVENTION Electrostatic precipitators are widely used to remove suspended particulate matter from gaseous emissions.

In general, an electrostatic precipitator includes one or more high voltage discharge electrodes that have portions of their surfaces designed to facilitate corona discharge therefrom. The corona discharge produces an ionising electric field through which the suspended particles in the gaseous emissions are caused to flow, thereby becoming electrically charged, or ionised.

These discharge electrodes have corresponding collector electrodes, which are grounded, and are designed to eliminate the formation of corona discharge at the surfaces. These collector electrodes attract the ionised particles in the gaseous emissions and collect these particles on the surface thereof.

In most electrostatic precipitators, the discharge electrodes are arranged vertically and are secured to masts to form elongate discharge electrode assemblies. Each discharge assembly is attached, at its operatively upper end to a hanger, which is electrically connected to a high-voltage electrical supply, to form a discharge electrode"curtain"that is suspended in the gaseous emission.

Increasingly strict emission standards have led to a continuous demand for higher collection rates in electrostatic precipitators and this has, in turn, led to a general need for improvement in the performance of electrostatic precipitators. One of the ways of improving this performance is by increasing the charge imparted to particulate matter by the ionisation process described above. It is known that the design and shape of a discharge electrode affects the level of corona discharge necessary for the ionisation process.

OBJECT OF THE INVENTION It is an object of this invention to provide a discharge electrode which exhibits improved levels of corona discharge than prior art equivalents.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a discharge electrode for an electrostatic precipitator, comprising: a collar configured to receive a shaft therethrough; and a number of arms extending radially from the collar, each radially extending arm terminating in a number of tines at the free end thereof.

Further features of the invention provide for the collar to have two radially extending arms, for the two radially extending arms to be oppositely disposed, for the free end of each radially extending arm to terminate in four tines, for each tine to be pointed, for each tine to be curved relative to a plane of the oppositely disposed radially

extending arms, and for adjacent pairs of tines to be oppositely curved relative to the plane of the oppositely disposed radially extending arms.

Still further features of the invention provide for the collar to have a central ring formation, for the central ring formation to be arranged as two symmetric half loops which are axially offset from each other, for the discharge electrode to be a single pressing, for the discharge electrode to be made of metal, preferably stainless steel, for each radially extending arm of the collar to be indented along a portion of its length, and for each radially extending arm of the collar to have at least one aperture extending therethrough.

The invention extends to a discharge electrode assembly, comprising: an elongate shaft; and at least one discharge electrode, as described above, securable to the shaft.

There is also provided for the discharge electrode assembly to have a plurality of discharge electrodes securable to the elongate shaft along its length, for the plurality of discharge electrodes to be securable to the shaft along its length in an equidistant configuration, for the elongate shaft to have an engaging formation at one end thereof, for the engaging formation to be an attachment plate having an aperture extending therethrough, for each discharge electrode to be tack welded to the elongate shaft, alternatively for the discharge electrode to be securable to the elongate shaft by means of at least one screw engageable in a complementarily threaded aperture in the periphery of the collar.

The invention extends further to a discharge electrode curtain, comprising: a supporting frame; and at least one discharge electrode assembly, as described above, securable to the supporting frame.

The invention extends still further to an electrostatic precipitator having at least one discharge electrode curtain as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is described below, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a first embodiment of a discharge electrode according to the invention; Figure 2 is a perspective view of a second embodiment of a discharge electrode according to the invention; Figures 3a To 3d are further views of the discharge electrode of Figure 2; and Figures 4a to 4c are isometric views of three variations of a dischage electrode assembly according to the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figures 1 to 4, in which like features of the invention are indicated by like numerals, a discharge electrode is indicated generally by reference numeral (3).

The discharge electrode (3) is a single sheet metal pressing having a collar in the form of a central ring formation (6) arranged as two symmetric half loops that are axially offset from each other. Two oppositely disposed arms (8) extend radially from the ring formation (6) and the free end of each arm terminates in four tines (9).

Each radially extending arm (8) is indented, at (10), along a portion of its length, in order to provide rigidity of the entire discharge electrode (3). Further, each radially extending arm (8) has an oblong aperture (11) extending partway along its length, the function of which will be explained in the description that follows.

Each one of the four tines (9) at the free end of the radially extending arm (8) is tapered to a point and each tine is curved away from a plane defined by the two oppositely disposed radially extending arms (8). Each adjacent pair of tines (9) at the free end of a radially extending arm (8) is curved in opposing directions relative to the plane defined by the two oppositely disposed radially extending arms (6).

In use, a number of discharge electrodes (3) may be secured to an elongate shaft (2) to form a discharge electrode assembly, indicated generally by reference numeral (1) in Figures 4a, 4b and 4c.. The numbers of discharge electrodes (3) are securable to the shaft (2) at different positions along its length by receiving the shaft through the ring formation (6) of each of the discharge electrodes and tack welding each discharge electrode to the shaft (2) at each symmetric half-loop of the central ring formation (6). The discharge electrodes (3) are secured to the shaft (2) in an equidistant configuration along its length. Furthermore, the discharge electrodes (3) can be arranged such that the oppositely disposed radially extending arms of adjacent discharge electrodes (3) are normal to each other, as indicated in Figure 4a, or such that the radially extending arms of all of the discharge electrodes (3) are coplanar, as shown in Figures 4b and 4c.

The elongate shaft (2) has an engaging formation (4) in the form of an attachment plate with an aperture (5) therethrough, which is securable, to an operatively upper end of the shaft, as indicated in Figures 4a and 4b. The attachment plate is formed by flattening a tube that projects outwardly from an end of the shaft (2). The flattened outwardly projecting tube may be tube may be a double tube in order to provide additional rigidity. The discharge electrode assembly (1) is securable by means of

the attachment plate (4) to a supporting frame (not shown) that can be located in a flow path of a gaseous emission from which particulate matter is to be removed.

A plurality of discharge electrode assemblies (1) may be suspended from a supporting frame (not shown) by means of their respective attachment plates (4), to form a discharge electrode curtain (not shown). One or more discharge electrode curtains may be arranged, together with corresponding collector electrodes, to form an electrostatic precipitator (not shown).

It will be appreciated by those skilled in the art that the manufacture of the discharge electrodes (3) as single piece metal pressings enables a discharge electrode assembly (1) to be easily and quickly constructed. The applicant has found that the use of discharge electrodes (3) having tines (9) as described above produces higher corona discharge levels than those produced by prior art equivalent discharge electrodes. The corona effect occurs at the sharp pointed end of each one of the tines (9). The oblong apertures (11) on each radially extending arm are designed to minimise flow resistance in the flow path of the gaseous emission.

Numerous modifications are possible to this embodiment without departing from the scope of the invention. In particular, the curvature of each one of the tines (9) can be adjusted according to a type of collecting electrode that is used in conjunction with the discharge electrode (1). Further, a threaded aperture (7) may be centrally located on each half loop of the ring formation (6), enabling, in use, a number of discharge electrodes (3) to be secured to the shaft (2) by means of a threaded bolt through each one of the threaded apertures (7) on each half loop of the ring formation (6). Still further, the configuration of the discharge electrode (3) on the shaft (2) can be optimized on tube-type electrostatic precipitators to provide a uniform corona over an entire circumference of the tube surface. Still further, the elongate shaft (2) may be composed of multiple interlocking sections as illustrated in Figure 4c.

The invention therefore provides a discharge electrode which is more efficient, and a discharge electrode assembly which is easier to assemble and is more cost- effective, than prior art equivalents, and which can be easily incorporated in discharge electrode curtains for use in the electrostatic precipitators.