In general, use of electric arc furnaces causes the release of noxious gases to the atmosphere which clearly has environmental implications. In use, the positive pressure inside the furnace allows gases to escape.

However, the use of an economiser to create a positive pressure on the outside of the furnace roof (relative to the internal pressure in the furnace) allows some control of the gases released and helps to reduce abrasive wear to the furnace electrodes by inhibiting the acceleration of gases past the electrodes.

Figure 1 shows in plan view a conventional economiser having three units each comprising a single stainless steel annulus 2 having an inlet 4. The annulus comprises an open channel through which compressed air or inert gas, such as Argon or Nitrogen, supplied through the inlet 4, is passed. The units are located on the furnace roof centre and the electrodes 6 are passed through apertures formed in an electrode holder located in the centre of the annulus. The inert gas is continuously supplied to the annulus and dissipates into the interior of the furnace.

The economiser creates a positive pressure to stop the ingress of gases.

Even using a conventional economiser, the carbon electrodes are consumable items subject to wear and

consequent breakages and must be replaced frequently.

Such frequent replacement is costly in terms of electrode costs, installation time and shut down-time of the furnace during replacement. The conventional economiser being made from stainless steel, is costly to produce and has a short life span on the furnace due to the heat load which destroys the economiser in a short time. A conventional economiser although effective in inhibiting pollution generally only has a 1 to 2 week life span.

The present invention has been made from a consideration of the disadvantages with the conventional economiser and in order to provide an improved economiser which overcomes one or more of these disadvantages.

A preferred object of the present invention is to provide an improved economiser having, in use, an extended lifespan. Further preferred objects of the invention are to provide an economiser which effectively reduces wear of electrodes and which allows furnace pollution to be controlled or inhibited.

According to a first aspect of the invention there is provided apparatus for mounting in or on a furnace comprising fluid circulation means defining a fluid circulation path, having first and second path portions adapted, in use, to lie towards the exterior and interior of the furnace respectively.

Preferably the apparatus is adapted to be mounted in or on a furnace roof centre. Preferably the apparatus is in the form of an annulus adapted to receive furnace electrodes probes or lances through the aperture formed in the centre thereof. Preferably the apparatus comprises first and second annuli connected by an intermediate

annulus. Preferably the first and second annuli define the first and second path portions. Preferably the intermediate annulus defines an intermediate path portion allowing fluid circulation between said first and second path portions. One or, preferably, both of the first and second annuli may comprise a housing having an internal spiral wall which defines a spiral pathway for fluid circulation around such annulus. Preferably such spiral pathway extends from an outer edge of such housing towards the inner wall defining the aperture of the annulus.

Alternatively one or both of the first and second annuli may comprise a series of concentric sections, typically of square or rectangular cross-section. The concentric sections may be formed from box, e. g. rectangular or square, cross-section tubing which is bent to form the required curvature. Box section tubing is particularly suitable for use in constructing large diameter annuli.

For medium sized annuli, it may be more appropriate to use two angles to form the effective box section, such angles being welded together. The weld joints or seals may be concealed by the outer surfaces of the sections.

Use of welded angles rather than integral box sections avoids undesirable deformation when the concentric sections are formed. Thus box section is difficult to roll effectively without deformation whereas less deformation is obtained with angle sections since stretching and thinning can be avoided. Typically the angles are rolled steel angles.

Preferably, two or more, typically three, concentric sections are provided which are welded together to form the annulus. Coolant flow apertures may be provided for

fluid communication between adjacent tube lengths. The archimedes spiral pathway annulus is preferably used for smaller diameter annuli.

Typically the annuli, whether constructed as an archimedes spiral or box or angled sections, controls the water flow and hence the heat transfer.

Preferably each of said first and second annuli comprises a fluid inlet and/or outlet. Typically the first annulus comprises a fluid inlet and the second annulus comprises a fluid outlet. Preferably such inlet/outlet is provided adjacent the outer edge of the annulus.

Preferably, the intermediate annulus comprises an annular housing having inner and outer annular walls defining a fluid receiving space therebetween. Preferably each end of the intermediate annulus is respectively connected to the first and second annulus adjacent the inner regions thereof. Preferably the height of the intermediate annulus defines the spatial separation of the first and second annuli. In use, fluid may be pumped through an inlet of the first annulus, up through the intermediate annulus and out through an outlet of the second annulus. Preferably the diameter of the aperture of the second annulus is less than the diameter of the intermediate and/or first annulus so that when an electrode holder having a diameter substantially corresponding to that of the second annulus aperture is located therein a gap is formed between the holder and the intermediate and/or first annulus.

Preferably, the apparatus comprises means for creating a positive pressure in the region of the

apparatus, particularly in the gap. Such means may be as described below.

Preferably, the apparatus is adapted to receive liquid such as water. Thus, preferably the fluid circulation path is substantially closed or sealed along the length thereof so that fluid or liquid input or output is by means of the inlet and outlets only.

The invention further provides a cooling system for a furnace comprising apparatus as described above, pump and cooling fluid such as water or water based fluids.

According to a second aspect of the invention there is provided apparatus for mounting in or on a furnace comprising annular means adapted to receive an electrode holder therein and means for creating a positive pressure in a gap formed in use between an inner surface of said annular means and said electrode holder.

Preferably, the annular means comprises a fluid circulation means as described above. Preferably the annular means comprises a second annulus adapted to lie in use on the exterior side of the furnace and having a second aperture diameter corresponding substantially to the diameter of an electrode holder to be located therein and a first annulus adapted to lie in use on an interior side of the furnace and having a first aperture diameter greater than said second diameter. Such first annulus may comprise an intermediate annulus as described above.

Preferably said means for creating a positive pressure comprises one or more inlets extending through the annular means and communicating with said gap. Preferably such inlets are radial and preferably a plurality of such inlets are provided at spaced locations around the

circumference of the annular means. Preferably one or more inlets are provided at spaced locations along the length of the annular means. Preferably two sets of radial inlets are provided, the sets being spatially separated along the length of the annular means.

Preferably, one end of the inlets communicates with a subsidiary annulus located externally of said annular means. Preferably each set communicates with a corresponding subsidiary annulus. Preferably the inlets are adapted to supply fluid, particularly a gas such as compressed air or an inert gas such as argon or nitrogen or a mixture of these, from such subsidiary annuli to the gap. Preferably one set of inlets, typically located towards the exterior of the furnace in use, supplies compressed air to the gap and another set, typically located towards the interior of the furnace in use, supplies nitrogen to the gap. Preferably means is provided for supplying compressed air and/or inert gas such as nitrogen or argon respectively to the first and second subsidiary annuli associated with the first and second sets of inlets.

One or more of the inlets may be adapted to supply compressed air,. argon, nitrogen or any inert gas or any mixture of these. Generally the choice of gas depends on the installation with which the unit is to be used. Use of compressed air tends to be the cheapest option, however a nitrogen shroud may be used for example if the installation or system requires the elimination of compressed air e. g. due to risk of explosion.

The invention includes the combination of any features described with respect to each aspect of the invention. In the combined system the fluid circulation

means and the means for creating a positive pressure are physically isolated so that there is no communication between the circulating fluid or liquid and the pressure fluid or gas. In particular, the invention includes apparatus for mounting on any installation and having the features of the first and second aspects.

The invention includes an electric arc furnace comprising apparatus according to the first and/or second aspects of the invention.

The apparatus may be provided with a refractory lining or an external refractory housing may surround the apparatus.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which Figure 2 is a vertical, cross-sectional view through an economiser of the invention; and Figure 3 is a part cross-sectional view through an alternative annulus constructed from box section tubing.

The economiser of the invention comprises an upper and lower annulus 10,12. The internal structure of each annulus comprises a spiral pathway. Thus each annulus has a top plate 14, a bottom plate 16, an external side wall 18 and an internal spiral wall 20. An inlet 22 connects with the lower annulus 12 and an outlet 24 connects with the upper annulus 10. The upper and lower annuli are connected by an intermediate annulus 26. In use, a fluid, typically water, is pumped in through the inlet 22 circulates through the spiral pathway of the lower annulus 12, passes up through the intermediate annulus 26,

circulates through the spiral pathway of the upper annulus 10 and exits through the outlet 24.

Referring to Figure 3, the upper and lower annuli 10, 12 may alternatively comprise a series of concentric box sections each having a square or rectangular cross- section. In the example shown, each box section 50 is formed from two angles 52,54 welded together at joints 56,58. It will be seen that the joints 56,58 are hidden and thereby protected by the outer legs of the angles 60, 62 respectively. Successive box sections are welded together at weld joints 64 to form a stable annular unit.

Apertures (not shown) are provided between adjacent box sections to allow fluid flow between the sections and through the annulus. Typically fluid flow will enter the annulus through an inlet 66 located adjacent the peripheral edge thereof, flow around the first concentric 68 and pass through an aperture into the next adjacent concentric section 70 and so on until the fluid exits the inner concentric section via outlets 72 located therein.

The economiser is located on a furnace roof centre and may be supported by the roof via flange 28 extending around the periphery of the top plate of the upper annulus. Electrodes 30 mounted in a suitable holder 32 are located through the aperture 34 formed by the annuli.

The upper annulus 10 has a smaller aperture diameter than the intermediate and lower annuli 26,12 so that an annular gap 36 is formed between the electrode holder 32 and the latter annuli. This gap is supplied at its upper end with compressed air and at its lower end with nitrogen via radial inlets 38 and 40 respectively.

Compressed air is supplied via an appropriate inlet to a first auxiliary annulus 42 which is located around

the exterior of the intermediate annulus 26 and adjacent the upper end thereof. A plurality of radial inlets 38 extend from the first auxiliary annulus, through the intermediate annulus and open into the gap 36.

Nitrogen is supplied via an appropriate inlet to a second auxiliary annulus 44 located around the exterior of the intermediate annulus 26 and adjacent the lower end thereof. A plurality of radial inlets 40 extend from the second auxiliary annulus, through the intermediate annulus and open into the gap 36. In use, the compressed air and nitrogen supplied dissipate to atmosphere. The supply of compressed air and nitrogen using the economiser of the invention creates a positive pressure in the gap 36 which prevents gases from the furnace going up into the annular gap.

Although the specific embodiment describes the use of compressed air and nitrogen, as outlined above, it will be appreciated that compressed air or any inert gas or any mixture of these may be used depending on the installation requirements.

The unit described combines a cooling system using the upper, lower and intermediate annuli to counteract the effects of the heat of the furnace and a corrosion inhibiting system using the auxiliary annuli to create positive pressure to counteract the corrosive effect of accelerated gases from the furnace. Thus, when installed on the roof, the economiser creates a positive pressure on the exterior of the furnace and thereby inhibits the acceleration of gases from the furnace up around the unit.

Such acceleration of gases, and the heat of the furnace, would excessively wear the carbon electrodes if the economiser were not installed. The cooling system

effectively extends the lifespan of the economiser compared to conventional economisers by dissipation of the heat load on the unit.

Suitable refractories 46 may be located below the economiser to further improve heat and corrosion resistance.

The economiser may be made from mild steel or stainless steel, typically of a grade to meet industrial standards.

In use, water and gases are supplied as described above. Typically the volume of water used is dependent on the size of the unit which is dictated by the size of the electrodes. In general, sufficient water will be used to eliminate the possibility of nucleate boiling whereby salts in the water deposit on the unit. The gap between the unit and electrodes prevents arcing. The size of the gap typically depends on the furnace and this may determine the gas flow/volume required. Typically the economiser of the invention is designed to operate with similar amounts of gas flow/volume to that of a conventional unit so that it can replace a conventional unit.

It will be appreciated that the present invention is not intended to be restricted to the details of the above embodiment which is described by way of example only. In particular, it will be appreciated that the invention may be applied to any installation involving an industrial process where there is a need or desire to prevent or inhibit gases going to atmosphere.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.