GB2166855A

GB2166855A - Heating of scrap

Info

Publication number: GB2166855A
Application number: GB8527509A
Authority: GB
Inventors: Frank Donald Winter
Original assignee: BRYMBO STEEL WORKS
Current assignee: BRYMBO STEEL WORKS
Priority date: 1984-11-09
Filing date: 1985-11-07
Publication date: 1986-05-14
Also published as: GB8527509D0; GB8428409D0

Abstract

A scrap metal charge is heated in an electric arc furnace (10) by hot waste gas emanating from the interior of the furnace during the meltdown cycle. A conduit (20) leads from the combustion chamber (16) of the offtake system for entraining hot gases into the furnace and directing the gases at the scrap charge. The gases are entrained by venturi action of a high pressure oxygen injector (24) and/or fan (26). <IMAGE>

Description

SPECIFICATION Method and apparatus for the heating of scrap This invention relates to the heating of metal scrap used as a charge in an electric arc melting furnace.

It is conventional practice in electric arc steelmaking to introduce a charge of scrap metal to a hot heel in the furnace and then to melt the scrap down by arc discharge. It is also conventional practice to preheat the scrap charge before it is introduced into the furnace and such preheating may be carried out by utilising burners or, when available, utilising hot waste gases from an external source, eg from a furnace other than the furnace to which the scrap is to be charged.

Furthermore, it is known practice to introduce oxygen by way of a lance directed through a door in the side of the furnace at the scrap charge in the furnace during meltdown. After melt-down is completed the oxygen lance may be re-oriented to discharge oxygen below the surface of the melt to speed up the refining process in a known manner.

During the melt-down and refining stages the waste gases are continuously withdrawn by an extractor fan, usually through a port in the furnace roof, and are then led to a combustion chamber and subsequently to a fume cleaning station. Due to the construction of an electric arc furnace it is found that large volumes of air at ambient temperature are sucked into the furnace interior during waste gas extraction and electrical energy is thus wasted in heating the unwanted incoming cool air.

It is a general object of the present invention to provide a method and apparatus for the efficient utilisation of waste gases in an electric arc furnace which will reduce the electrical energy consumption during melt-down of the scrap charge.

In accordance with one aspect of the invention there is provided apparatus for heating a scapr metal charge in an electric arc furnace having a waste gas offtake system comprising a conduit leading from the offtake system to the interior of the furnace and means for entraining hot waste gases through said conduit to heat the scrap charge during melt-down thereof in the furnace.

Also in accordance with the invention there is provided a method of heating a scrap metal charge in an electric arc furnace during meltdown of the scrap in the furnace, the furnace being provided with a waste gas offtake system comprising entraining hot waste gases from the offtake system to the interior of the furnace to heat the scrap charge therein.

The means for entraining the hot waste gases preferably comprises a venturi having a high pressure oxygen outlet directed at the scrap charge; the hot waste gases being sucked through said conduit by the venturi action when high pressure osygen is discharged through the venturi.

Alternatively, or additionally, the means for entraining the hot waste gases through the conduit may comprise a high temperature fan in said conduit.

Other features of the invention will become apparent from the following description given herein solely by way of example with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic top plan view of one embodiment of apparatus in accordance with the invention, Figure 2 is an enlarged diagrammatic side view of a venturi for high pressure oxygen situated in the conduit from the offiake system, and Figure 3 is a diagrammatic top plan view similar to that shown in Fig. 1 but illustrating, additionally, an extractor fan in the conduit from the offtake system.

Referring to Fig. 1 of the drawings there is shown an electric arc furnace 10 which may be of entirely conventional form utilised for the melt-down of a scrap metal charge. Such a type of furnace is provided with a pouring spout 12 and a waste gas offtake system for extracting hot gases from inside the furnace during melt-down; the hot gases being extracted via a water-cooled offtake elbow 14 in the furnace roof.

In a conventional system the waste gases are led to a combustion chamber 16 and subsequently to a fume cleaning station (not shown); an extractor fan (also not shown) being provided downstream of the combustion chamber 16 for extracting the hot gases the interior of the furnace. The furnace conventionally also includes a door at position 18 into the side wall thereof whereby an oxygen lance may be directed at the scrap charge in the furnace during melt-down and subsequently re-oriented to discharge oxygen below the surface of the melt.

In accordance with the present invention, an additional insulated, refractory-lined conduit 20 is provided to lead from the offtake system, preferably downstream of the combustion chamber 16, back to the door 18 in the side wall of the furnace 10. In the embodiment illustrated in Figs. 1 and 2, the offtake gases from the interior of the furnace are entrained through the said conduit 20 back into the furnace interior through the door by means of a venturi 22 provided at the discharge end of the conduit. A high pressure oxygen conduit 24 is co-axially aligned with the venturi 22 through the said wall of the conduit 20 to create the necessary suction to entrain the offlake gases.

Thus, during the melt-down cycle when oxygen is required to be directed at the scrap metal charge in the furnace interior, the oxygen also entrains hot waste gases to heat the scrap metal. When the melt-down cycle is completed, the oxygen conduit may be advanced axially and the offiake gas conduit and oxygen conduit both re-aligned to direct oxygen below the level of the melt. Alternatively, a separate oxygen lance may be utilised for oxygen injection after the melt-down part of the cycle has been completed.

In the embodiment illustrated in Fig. 3 of the drawings, entrainment of the hot waste gases through the conduit 20 is enhanced by the addition of a high temperature extractor fan 26 in the conduit 20. Such an arrangement can offer considerable advantages in that hot waste gases can be directed at the scrap charge in the furnace even when oxygen injectiion is not taking place.

In an alternative embodiment, not illustrated in the drawings, the offiake gases are entrained through the conduit solely by means of a high temperature fan instead of by the venturi system illustrated in Figs. 1 to 3. When a high temperature extractor fan is utilised on its own, it is of course necessary to use a separate oxygen lance for oxygen injection into the melt after the melt-down part of the cycle has been completed.

Claims

1. Apparatus for heating a scrap metal charge in an electric arc furnace having a waste gas offtake system comprising a conduit leading from the offtake system to the interior of the furnace and means for entraining hot waste gases through said conduit to heat the scrap charge during melt-down thereof in the furnace.

2. Apparatus as claimed in claim 1 wherein the means for entraining the hot waste gases comprises a venturi having a high pressure oxygen outlet directed at the scrap charge; the hot waste gases being sucked through said conduit by the venturi action when high pressure oxygen is discharged through the venturi.

3. Apparatus as claimed in claim 2 wherein the venturi is located adjacent a furnace door in the side of the furnace and is selectively movable between operative and inoperative positions relative to the door.

4. Apparatus as claimed in any one of claims 1 to 3 wherein the means for entraining the hot waste gases through said conduit comprises a high temperature fan in said conduit.

5. A method of heating a scrap metal charge in an electric arc furnace during meltdown of the scrap in the furnace, the furnace being provided with a waste gas offtake system comprising entraining hot waste gases from the offiake system to the interior of the furnace to heat the scrap charge therein.

6. A method according to claim 5 wherein high pressure oxygen is discharged through the furnace wall towards the scrap charge and the oxygen is discharged through a venturi to suck the hot waste gases through a conduit leading from the offiake system to the venturi.

7. A method according to either one of claims 5 or 6 wherein the hot waste gases are entrained by means of a high temperature fan located in a conduit leading from the offtake system to the interior of the furnace.

8. Apparatus for heating a scrap metal charge in an electric arc furnace constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

9. A method of heating a scrap metal charge in an electric arc furnace substantially as hereinbefore described with reference to the accompanying drawings.