This invention relates to the treatment of gases discharged from metallurgical furnaces (conventionally termed "off-gases") and in particular to the treatment of fume and/or dust laden gases discharged from electric arc furnaces used in the production of steel .

Conventionally, gases discharged from electric arc steelmaking furnaces are cooled by dilution with cold air or by water sprays and are then passed through filters or electrostatic precipitators to remove dust present in the gases before being discharged to atmosphere.

Filtered off-gas fume and/or dust typically represents approximately 1.5% by weight of the steel

^~y ≠ product of the furnace, and contains a mixture of metallic oxides. These are principally oxides of iron. The off- gases may also contain valuable metal oxides such as nickel, chromium and molybdenum, and oxides of volatile

metals such as zinc, lead, tin, cadmium and mercury.

The majority of these oxide wastes are currently dumped in land-fill sites, but this is becoming environmentally unacceptable. Expensive processes are being developed for reducing the dusts in reactor vessels remote from the furnace site, but such processes entail the transport and handling of dust which are notoriously difficult.

Furnace off-gases may also contain traces of polychlorinated dioxines and dibenzofurans, hereinafter referred to collectively as dioxines, which result from the decomposition of organic contaminants, e.g. oil and certain plastics, in the furnace feedstock.

It is an object of this invention to provide a treatment for dust and noxious gases as they leave a metallurgical furnace to enable iron and other metals to be recovered and to reform noxious gases into non-toxic substances for release to the atmosphere. Recovered metals may be returned directly to the steelmaking process.

In one aspect the present invention provides a method of treating gases discharged from a metallurgical furnace which contain fume and/or dust including metallic oxides and organic contaminants, the method including the step of reacting the gases with a chemical matrix.

The metallurgical furnace may be an el.ectric arc steelmaking furnace, and the chemical matrix may be heated by passing an electric current directly through an

electrically conducting bed. Alternatively, the heat contained in the off-gases from the furnace may be sufficient in whole or in part to increase the temperature of the chemical matrix to the reaction temperature. The chemical matrix may include coke and the coke may reduce the metallic oxides to metals. Non-volatile metals may be absorbed by the coke and reduced to the metallic state to form a metal impregnated coke mixture.

The matrix, when heated, may promote decomposition of organic components of the off-gases and the matrix may include lime which may absorb chlorine liberated during the decomposition of organic contaminants. Such coke and lime chemical matrices may be recharged to the steelmaking process. The organic contaminants may include dioxines.

In another aspect, there is provided apparatus for treating gases discharged from a metallurgical furnace comprising a reaction vessel including an electrically heated bed of a matrix of coke and lime, means for admitting gases to be treated to the vessel for reaction with the coke and lime matrix, means for removing the treated gases from the vessel , and means for removing the coke and lime matrix from the vessel.

In order that the invention may be fully understood, one embodiment thereof will now be described by way of example only with reference to the accompanying drawing in which the sole Figure is a cross-sectional view of apparatus in accordance with the invention.

The Figure shows the general arrangement of plant for processing gases discharged from a metallurgical furnace.

Dust laden gases from an arc furnace 1 are ducted to a reaction vessel 2 where they are passed through a heated coke and lime matrix 3 before being discharged via a duct 4 to processing plant (not shown) in which volatile metals present in the off-gas are condensed and the residue recovered.

The reaction vessel 2 is a refractory lined tower having a hopper 5 through which fresh coke and lime can be charged and pi otably mounted doors 6 through which metal impregnated coke and lime can be discharged into a furnace charging bucket 7.

The coke and lime matrix 3 is supported on a grate which may be constructed from refractory covered steel bars 8, which can be withdrawn to allow the reacted coke and lime of the matrix to fall when the doors 6 are opened.

Electrical connections are made to the coke via expendable graphite blocks 9 or the like set in the sides of the reaction vessel 2, and a high electric current is passed through the coke sufficient to maintain the coke temperature at an optimum value, irrespective of the temperature of the furnace gases under treatment.

The process cycle is linked to the melting cycle of the furnace 1 in that fresh coke and lime are charged to the reactor vessel 2 prior to the commencement of melting a steel charge within the furnace, and the metal

impregnated coke and reacted lime are discharged to the furnace charging bucket 7 while the furnace is being tapped.

The coke and lime bed may be heated with fossil fuel burners instead of or in addition to the electric current passed via the graphite blocks , and the coke and lime may be placed on a chain grate which may continuously be refreshed at one end and discharged into the melting furnace 1 at the other end.

The lime (caO) may initially be charged as limestone (CaC0 ₃ ) which becomes calcined at the high temperature prevalent in the reaction vessel.

The reaction vessel 2 may be installed downstream of an arc furnace scrap pre-heating plant which utilises the furnace off-gas as a source of heat.

It is to be understood that the foregoing is merely exemplary of the treatment of gases discharged from metallurgical furnaces and that modifications can readily be made thereto without departing from the true scope of the invention.