Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – By means introducing treating material
Reexamination Certificate
1999-10-07
2001-08-14
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
By means introducing treating material
C266S900000, C266S901000, C373S079000
Reexamination Certificate
active
06274081
ABSTRACT:
TECHNICAL FIELD
The invention concerns a smelting unit having an arc furnace.
STATE OF THE ART
A smelting unit of that kind is known from WO 90/10086. In the known smelting unit, an outer segment of the vessel cover is replaced by a shaft which is fixed to a holding structure and which, in its upper region, has a closable charging opening for the feed material, and a gas passage opening. The hot furnace gases are discharged through the shaft and, in heat-exchange relationship, heat charging material which is disposed in the shaft. That makes it possible to save a substantial amount of energy.
In order to be able to perform the smelting process without subsequent charging, it is advantageous if the entire amount of charging material for the weight of liquid metal, which is to be tapped off, fits into the total volume consisting of the furnace and the shaft. For that reason, and having regard to the further requirement of limiting the shaft height, the cross-section of the shaft is preferably rectangular and the furnace vessel in plan view is in the form of an oval which is defined on one side by a straight line. That makes it necessary to adopt a new shape of vessel, including the shape of the underneath vessel, in comparison with the wide-spread round shapes of vessel.
In the known smelting unit, the entire vessel cover is movable relative to the vessel either jointly or independently of the holding structure which carries the shaft. Releasable fixing of the vessel cover to the holding structure has proven to be advantageous so that the vessel cover, including the shaft, is pivotable or linearly displaceable relative to the furnace vessel. In the last-mentioned construction, it is possible to provide for specific targeted charging of feed material into different regions of the furnace vessel, through the shaft.
In the case of the known smelting unit, there is also the possibility of charging material being retained in the space in the shaft by means of retaining members which are provided in the lower region of the shaft so that, after smelting of a charge, during the refining phase, the hot waste gases can be utilised for preheating feed material.
Retaining members of that kind are described in detail in WO 95/04910. Reference is expressly directed thereto in the present application.
The present invention aims at using the tried-and-tested technology in already existing installations. Existing arc furnaces are to be converted at a minimum level of cost in such a way that as many components as possible of the existing installation can still be used and also the building in which the smelting unit is disposed does not have to be substantially altered. In this respect there is the particular problem that, in the case of the conventional arc furnaces with a round or also oval furnace vessel, in which the electrodes are arranged at the centre of the vessel cover, the space requirements for a shaft which is used as a charging material preheater and which is to be arranged beside the electrodes as an outer segment of the vessel cover, in particular having regard to the height of the building, are so restricted that it is not possible to provide sufficient volume in the shaft for the charging material which is to be heated. The furnace vessel may consist of one part or it may be divided above the slag line into an underneath vessel (lower vessel portion) and a top vessel (upper vessel portion). The furnace cover is generally of an arched configuration and has in a concentric arrangement three passage means (three-phase furnace) or centrally one passage means (dc furnace) for the electrode(s), which are referred to as the electrode opening or openings.
STATEMENT OF THE INVENTION
The object of the present invention is to design a smelting unit that as many components as possible of existing arc furnaces can be used, that is to say the minimum number of components have to be replaced or modified.
In the case of an arc furnace with a round or oval lower vessel portion, in which the electrodes are disposed concentrically in the region of the centre, the invention seeks to provide that, with the conditions in respect of space being limited by the electrode arrangement and the height of the building, there is a volume in the shaft for the charging material which is to be heated, that is sufficient to be able to perform the smelting process as far as possible without a post-charging operation.
Retaining members provided in the shaft, for retaining the charging material, are to be adapted to the particular factors involved.
The invention further seeks to ensure that the solution according to the invention can prevent furnace gases from issuing in the region of the cover.
In order to provide an adequate volume for the charging material which is to be preheated, in the shaft which is arranged laterally beside the electrodes on the vessel cover, the shaft cross-section selected is so great that in plan view the internal contour of the shaft wall which is the rear shaft wall as viewed from the electrode openings, of at least the upper shaft portion, lies outside the internal contour of the upper edge of the lower vessel portion. Preferably the cross-sectional profile of the shaft in that portion is of a rectangular configuration or is of a configuration that follows a trapezoidal line. The configuration according to the invention of the sector of the upper vessel portion in the region below the shaft, namely the design configuration of the upper vessel portion with a wall sector which converges from its upper edge to its lower edge, makes a transition from the shaft walls which lie outside the internal contour of the lower vessel portion to the internal contour of the upper edge of the lower vessel portion, that is to say the furnace hearth, which guides the charging material from the outer regions of the shaft unimpededly into the lower vessel portion. The transition from a shaft shape which is of rectangular profile into a round or oval furnace vessel can occur in various ways, for example by way of rectangular-oval-round or rectangular-polygonal-round cross-sections. The converging wall sector, like also the other sectors of the upper vessel portion, is usually formed by water-cooled wallpanels which, when feed material is charged through the shaft, feed it to the lower vessel portion (furnace hearth) which is of round or oval cross-section.
The transition from the internal contour of the shaft walls, which in plan view lies outside the internal contour of the upper edge of the lower vessel portion, to -the upper edge of the round or oval lower vessel portion, can already be started above the upper edge of the upper vessel portion, that is to say above the edge of the vessel, insofar as here the shaft walls which are remote from the electrode openings are guided inclinedly inwardly towards the vessel centre (centre line of the vessel) or the upper edge of the upper vessel portion. Such a configuration can be afforded in the lower shaft portion either by means of a converging oval-shaped wall portion or by means of flat elements which make the transition for the shaft wall that is remote from the electrodes, from a profile that is linear in a horizontal section into a polygonal profile, preferably a profile which follows a trapezoidal line. Preferably the lower edge of the shaft walls which are remote from the electrodes is of approximately the same internal contour as the internal contour of the upper edge of the vessel. That contour then also corresponds to the contour of the second cover portion on which the shaft is arranged.
In the smelting unit according to the invention, the entire furnace substructure including the lower vessel portion and the electrode lifting and pivoting arrangement, can continue to be used, in a conversion situation.
If the converging transition from a rectangular cross-section to the round vessel cross-section already begins in an upper shaft portion, for example just beneath the upper shaft opening, then, as viewed from the electrodes, the front shaft wall must b
ARCMET Technologie GmbH
Foley Hoag & Eliot LLP
Kastler Scott
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