EP0170809B1 - Arc furnace with a charging area on its side - Google Patents

Abstract

An arc furnace having a space for accommodating charging material, said space being disposed on one side of the furnace vessel and communicating with the interior of the furnace vessel and being disposed at least partly in the region of radiation of the arc of at least one arc electrode. The arc electrode is movable towards and away from the charging material accommodating space, and thereby permits better utilization of the radiant heat generated by the arc.

Description

The invention relates to an electric arc furnace with at least one receiving space for charging goods, which is provided on one side of the furnace vessel, according to the preamble of claim 1.

In the arc furnace of this type which has become known from EP-A1-56 773, the arc furnace has a lateral bulge, the sole of which is higher than the sole of the hearth. The input material is charged in this bulged part and stored as a pile on the raised sole. The hot furnace gases are passed through the upper part of this pile, and the pile is also exposed to the radiant heat of the arc furnace and is thereby heated. The preheated feed is fed in batches from the lowest section of the pile into the oven hearth. The sole of the side bulge of the furnace is sloping towards the stove.

From US Pat. No. 3,441,651, an arc furnace with a shaft-shaped charge preheater arranged on one side of the furnace vessel has become known, the interior of which is connected to the interior of the furnace vessel by a connecting zone provided at approximately the middle height of the furnace vessel, which serves on the one hand for this purpose to introduce the hot furnace gases formed during the melting process into a column of feed material formed in the charge material preheater and to pass them in countercurrent to the sinking feed material, to preheat it and on the other hand as a discharge opening for the heated charge material in the bottom area of the charge material preheater. By means of a hydraulically actuated slide, the preheated bottom section of the charge column can be conveyed through the connection zone into the oven hearth, i.e. the insert can be fed to the melting vessel in batches. A charging device attached to the top of the charge material preheater allows the charge material to be fed continuously into the preheater and a gas outlet located in the vicinity thereof allows the furnace gases cooled in the heat exchange with the charge material within the charge material column to be drawn off.

The object of the invention is to increase the possible heat transfer into the charge material in an arc furnace according to the preamble of claim 1 and thus to shorten the heating time of the charge material. It should make better use of the radiant heat and the resulting hot furnace gases when heating the charging material and thereby improve the thermal efficiency. The heat load on the furnace walls should be reduced. In addition, a continuous flow of material from the receiving space for the goods to be charged into the oven hearth and thus more uniform operating conditions are to be made possible. Temperature fluctuations and fluctuations in the chemical composition of the weld pool should be reduced.

The invention is characterized by the features of claim 1. Advantageous embodiments of the invention can be found in the subclaims.

In the solution according to the invention, by changing the position of either the arc electrodes or the furnace vessel together with the receiving space, the electrodes can be brought into the immediate vicinity of the receiving space for the cargo to be provided on one side of the furnace vessel, so that the radiant heat generated by the arcs is intensified Charge material can act and at the same time the radiation exposure of the free wall areas of the arc furnace is reduced. The hot gases that are generated in the area of the arcs, particularly when coal and other feedstocks are added, are introduced directly into the charge material, so that their sensible heat can be optimally utilized. These two effects can significantly improve the thermal efficiency.

Due to the direct action of the arcs on the lower area of the pile or the column of charge material, this can be converted into the doughy and liquid state, so that a continuous inflow from the receiving space for the charge material into the oven hearth is made possible.

If burners and / or nozzles are additionally provided on the lower area of the receiving space for the goods to be charged, this area can be additionally heated or oxygen, coal or other additives can be introduced for temperature control and control of the composition of the melt pool.

Preferably, the bottom of the receiving space for the charge is arranged so deep that when a liquid sump is formed in the furnace, it extends into the receiving space and enables a direct material and conductive heat exchange in the lowest zone of the accumulated charge. In this way, an additional heat flow is made possible for the lowermost zone of the charge column standing in the liquid sump. In this zone there is an intensive exchange of material and heat, which is caused by the bath movement that always occurs in the stove. In this way, the melt overheated in the area of the arcs emits heat in this zone, as a result of which the material which has already been preheated is melted in this zone. The liquefied material flows continuously from the receiving space for the charge material into the liquid melt pool of the furnace, so that the operating conditions can be kept largely constant here. In the zone of the festival Liquid transition also takes place chemical-metallurgical reactions, such as slag formation, carburization, etc., which can be promoted by the targeted addition of oxygen, coal or aggregates. Not only can the thermal conditions in the furnace be kept constant and set to an optimal working point, but also larger fluctuations in the composition of the melt can be prevented or the composition of the melt can be controlled.

If a sufficient sump has formed in the furnace, or at the latest when the melting level has reached the tapping height, a change in position of either the arc electrodes or the furnace vessel together with the receiving space brings the electrodes back to the center of the furnace and in this position the bath to heated to the required tapping temperature. The movability of the electrodes or the arc furnace makes it possible to change the position of the heat source within the furnace in the course of the melting process so that both the melting process and metallurgical processes can run optimally within the furnace.

• Fig. 1 in schematischer Darstellung einen senkrechten Schnitt durch einen Lichtbogenofen mit einem auf einer Seite des Ofengefäßes angeordneten Aufnahmeraum für Chargiergut,
• Fig. 2 eine Draufsicht, teilweise geschnitten, der Ausführungsform nach Fig. 1,
• Fig. 3 in vergrößerter Darstellung den Schnitt 111-111 von Fig. 2,
• Fig. 4 den Schnitt IV-IV von Fig. 2,
• Fig. 5 einen der Fig. 4 entsprechenden Schnitt bei anderer Position der Elektrode,
• Fig. 6 und 7 in den Fig. 1 und 2 entsprechenden Ansichten eine zweite Ausführungsform der Erfindung.

The invention is explained in more detail by means of exemplary embodiments with reference to 7 figures. Show it

• 1 is a schematic representation of a vertical section through an electric arc furnace with a receiving space for charge goods arranged on one side of the furnace vessel,
• 2 is a plan view, partially in section, of the embodiment of FIG. 1,
• 3 is an enlarged view of section 111-111 of FIG. 2,
• 4 shows the section IV-IV of FIG. 2,
• 5 shows a section corresponding to FIG. 4 in a different position of the electrode,
• 6 and 7 in FIGS. 1 and 2 corresponding views of a second embodiment of the invention.

The furnace assembly shown in FIGS. 1 and 2 in a vertical section and in a plan view contains an electric arc furnace 1 consisting of a furnace vessel 2 and a removable cover 3, through which 3 electrodes 4 / 1.4 / 2 and 4/3 are passed. The furnace vessel 2 is formed by a stove 5 made of a refractory lining and preferably by liquid-cooled wall elements 6. On one side of the furnace vessel, which in the present case has a round cross-section as shown in FIG. 2, a shaft-shaped charge preheater 7 with a receiving space (interior) 8 for charge goods is arranged, which in a region adjacent to its base 9 is connected by a connecting zone 10 the interior 11 of the furnace vessel 2 is connected. The Chargiergutvorwärmer 7 has a gas-tight feed device 12, z. B. a double bell closure of known type, and a gas outlet 13 to which a suction device, not shown, is connected.

As shown in FIG. 2, the charge preheater 7 extends approximately over a quarter of the circumference of the furnace vessel 2, the shaft wall 14 of the charge preheater facing the furnace vessel being adapted to the outer contour of the furnace vessel. From Fig. 1 it can be seen that the cross section of the interior 8 of the charge preheater 7 extends downward. This is intended to enable unhindered sinking of the cargo in the cargo preheater. Burners 15 or nozzles for blowing in gases, such as oxygen, or solids, such as coal or aggregates, open into the connecting zone 10.

The feed material 16 charged in the charge material preheater 7 can consist of metal scrap, in particular steel scrap and other iron carriers, such as lumpy pig iron, sponge iron and aggregates. It forms in the charge material preheater 7 a gas-permeable pouring column referred to as the charge goods column 17. The molten metal (sump) formed in the arc furnace 1 is designated 18, the melt level 19.

The bottom 9 of the charge material preheater 7, which is preferably designed to drop towards the oven hearth 5, is arranged so deep that a liquid sump 18 formed in the oven hearth extends into the lowermost zone 20 of the charge goods column 17 over a substantial part of the melting process and here a direct one Allows mass and conductive heat exchange. An eccentric bottom cut 21 is provided in the bottom of the oven hearth 5, which is shown in broken lines in FIG. 2. In the present case, the furnace vessel 2 is designed to be tiltable. The tilt level, i.e. the plane in which the tilting movement takes place is designated by 22. The charge preheater 7 is arranged in a direction transverse to the tilting plane of the furnace vessel.

Each of the electrodes 4/1 to 4/3 contains a liquid-cooled metallic upper part 23 and a lower part 24 which forms the electrode tip and is made of an edible material, such as graphite, which is detachably attached to the upper part 23. Each electrode 4/1, 4/2 or 4/3 is clamped with its upper part 23 into an electrode support arm 25/1, 25/2 or 25/3, which is supported by an electrode lifting mechanism 26/1, 26/2 or 26/3 can be raised and lowered. The electrode hoists 26/1 to 26/3 are located on the receiving space for the cargo, i.e. the shaft-shaped charge material preheater 7 opposite side next to the furnace vessel 2.

In the embodiment shown in FIGS. 1 and 2, each of the electrode support arms 25/1 to 25/3 is one Horizontal guide 27/1, 27/2 or 27/3 connected to the associated hoist 26/1, 26/2 or 26/3 and by a two-way drive, which is not shown in the drawing, along the guide movable back and forth. The guides 27/1 and 27/3 of the two outer electrode support arms 25/1 and 25/3 are each curved outwards, so that when the electrode support arms 25/1 and 25/3 move back and forth, they move by a limited angle in the direction horizontal plane are pivotable. The trajectories of the central axes of the electrodes 4/1 to 4/3 during the forward and backward movement of the electrode support arms along the guides 27/1 to 27/3 are shown in dash-dot lines in FIG. 2 and denoted by 28/1 to 28/3. It can be seen that due to the curved guides 27/1 and 27/3, the movement paths 28/1 and 28/3 are also curved outwards. The ends of the trajectories are marked by cross lines, which thus illustrate the extreme positions of the central axes of the electrodes. In the left extreme position shown in FIG. 2, the electrodes 4 / 1.4 / 2 and 4/3 each have approximately the same distance from the receiving space 8.

The horizontal guides 27/1 to 27/3 for the electrode support arms 25/1 to 25/3 can be designed according to FIG. 3. This FIG. Shows the section 111-111 of FIG. 2 on an enlarged scale. Thereafter, the guide 27/2 contains two mutually opposite, trapezoidal cross-section-shaped slide rails 29/2, each with an upper and a lower slide path 30/2, which pass through a pad made of sliding material. The sliding surfaces of a slide 31/2 rest on the slideways, which thereby fixes its position and is displaceable along the rails 29/2. The slide 31/2 carries the support arm 25/2, which is attached to the slide 31/2 with the interposition of a cover plate 32/2 and an insulating plate 33/2 by means of a screw bolt 34/2. The insulating plate 33/2, which has the same length as the slide 31/2, is also shown in part in FIG. 2. From this illustration it can be seen that the slide 31/2 extends for stability reasons over about a third to half the length of the guide 27/2.

The guides 27/1 and 27/3 for the two outer support arms 25/1 and 25/3 have a similar structure. As can be seen from Fig. 2, however, they are curved, i.e. the rails 29/1 and 29/3 in question also have a corresponding curvature in plan view.

In order to enable the movement paths 28/1 to 28/3 of the electrodes 4/1 to 4/3 when the cover is closed, the cover has a slot-shaped electrode passage for each electrode which is adapted to its movement path. The slot-shaped electrode bushings are covered by cover slats 35/1, 36/1, 37/1 to 35/3, 36/3, 37/3 which can be moved along the horizontal movement path, one of which has a passage opening adapted to the electrode cross section. The cover slats close the slot-shaped electrode feedthrough in the cover in every position of the electrode along its path of movement 28/1, 28/2 and 28/3.

4 and 5, the position of the cover plates 35/1 to 37/1 of the electrode 4/1 is shown schematically in its two end positions. An analogous representation applies to the cover plates of the two other electrodes 4/2 and 4/3.

The slot-shaped electrode leadthrough in the cover 3 visible in the illustration according to FIGS. 4 and 5 is designated 38/1, the passage opening in the cover plate 36/1 adapted to the electrode cross section is designated 39/1.

As can be seen from FIGS. 4 and 5, the ends of the middle cover lamella 36/1 each overlap one end of the outer cover lamellae 35/1 and 37/1. At the overlapping ends of these cover slats, drivers 40/1 are provided which, when the electrode 4/1 is displaced along the movement path 28/1 and the movement of the middle cover slat 36/1 caused thereby, each take the outer slats along with them and thus Ensure that the electrode bushing 38/1 is completely closed in every position of the electrode 4/1.

The melting process with the furnace unit described with reference to FIGS. 1 to 5 is explained below.

The solid, lumpy feed material 16 is charged into the receiving space 8 of the charge material preheater 7 by the charging device 12 until a sufficient column 17 has formed. In the area of the connection zone 10, the solid feed material partly reaches the furnace hearth due to the natural angle of repose 41 of the bed.

The electrodes 4/1 to 4/3 are now moved in the direction of the charge preheater 7 and the melting process is started by lowering the electrodes in the region of the bed. The liquid metal sump that forms collects in the stove and causes an intensive material and heat exchange through the bath movement in the lowest zone of the charge column. In this zone, desired metallurgical conversions can also take place, which are controlled by targeted supply of oxygen, coal or aggregates in the area indicated by the burners 15 or by aggregates admixed with the charge. The burner 15 can also be used to introduce additional heat. Simultaneously with the melting process, the feed material 16 of the pouring column 17 sinks down in order to also be melted in the lowest zone. The cross-section of the Interior 8 of the charge material preheater 7 expanded downwards.

As long as the electrodes 4/1 to 4/3 are in the position adjacent to the shaft furnace 7, that is to say in the representation according to FIG. 2, in the vicinity or at the left end position of the movement paths 28/1 to 28/3, the radiation energy the arcs are introduced to an increased extent in the lower area of the charge column and thus optimally used for the melting process. The same applies to the furnace exhaust gases which, due to the extraction via the gas outlet 13, reach the charging material column directly from the arcing areas.

When a sufficient amount of feed material has melted, the electrodes are moved back into the right end position of the movement paths 28/1 to 28/3 shown in FIG. 2 and the bath is brought to the required tapping temperature. The tapping takes place via the tapping device 21 provided in the bottom of the arc furnace. Part of the metal sump is preferably retained in the furnace vessel for the next melting process.

Because the electrode can be moved horizontally, the arcs can always be brought into the most favorable position with regard to the melting process, the heating of the liquid melting bath and the loading of the furnace walls. Any intermediate positions are possible along the movement paths 28/1 to 28/3 of the electrodes 4/1 to 4/3. In this way it is also possible, during the melting process, to have the arcs burn only on an existing liquid sump immediately adjacent to the still solid material and thus to enable more uniform operating conditions. Since only the relative position of the electrodes within the furnace vessel is important, it is also possible to move the furnace vessel 2 together with the receiving space 8 instead of the electrodes. It is also possible, instead of the slot-shaped electrode bushings 38/1 in the cover 3, to provide a round electrode bushing in the cover 3 at the two extreme points of mutual displacement for each electrode. In this case, before the electrodes or the furnace vessel are moved horizontally, the electrodes must be raised by the electrode lifting mechanism 26/1 to 26/3 to above the upper edge of the lid.

In the second exemplary embodiment shown in FIGS. 6 and 7, each of the electrodes 4/1, 4/2 and 4/3 is clamped in a telescopically extendable electrode support arm 51/1, 51/2 and 51/3. The guides 52/1, 52/2 or 52/3 for these electrode support arms can be raised and lowered by means of electrode hoists 26/1, 26/2 or 26/3 and also by a limited angle about vertical axes 53/1, 53 / 2 or 53/3 rotatable. The guides 52/1 to 52/3 are thus each connected to the associated electrode lifting mechanism 26/1 to 26/3 via a connection which is rotatable within a limited angle and is equipped with a drive.

As in the first embodiment, also in the second embodiment according to FIGS. 6 and 7, the arc electrodes 4/1 to 4/3 are of a triangular arrangement in the plan view in the center of the furnace vessel, as shown in FIG. 7, in one arcuate arrangement adjacent to the receiving space for the cargo and movable back. In addition, a limited possibility of rotation (not shown) of each of the two outer support arms 51/1 and 51/3 about their longitudinal axes 54/1 and 54/3 is provided. As a result, the outer electrodes 4/1 and 4/3 can be inclined by a small angle, so that in addition to the change in the distance between the electrode tips due to the predetermined movement paths of the electrodes, a change in the distance is possible by inclination. Since the electrodes in the furnace units described are no longer endangered by scrap collapses when they are burned into a batch of scrap, so-called permanent electrodes made of a liquid-cooled metallic upper part and a lower part which forms the electrode tip and are made of consumable material which is detachably attached to the upper part are particularly suitable .

In the second embodiment, as shown in FIG. 6, the connection zone 10 extends obliquely upwards from the interior 11 of the furnace vessel 2 to the interior 8 of the charge material preheater 7 and a partition 56 provided with gas passage openings 55 is arranged in the expanded region. As a result, the hot furnace gases can be introduced into this column over a larger cross section of the charge column 17.

Claims (14)

1. An electric arc furnace (1) having a space (8) for accomodating charging material, which is provided on one side of the furnace vessel (2) and which is connected to the interior (11) of the furnace vessel (2) and which is disposed at least partially in the area of radiation of the arc of at least one arc electrode (4/1, 4/2, 4/3) characterised in that the arc electrode (4/1,4/2, 4/3) and the furnace vessel (2) are displaceable relative to each other in such a way that the arc electrode can be put into a central position in the furnace vessel (2) or a position adjacent the charging material accomodating space (8).

2. A furnace according to claim 1 characterised in that there are provided three arc electrodes (4/1,4/2,4/3) which can be put into an arrangement which is triangular in plan view in the centre of the furnace vessel (2) or an arrangement which is linear or arcuate in plan view, adjacent to the charging material accommodating space (8).

3. A furnace according to claim 1 or claim 2 characterised in that the electrode (4/1,4/2, 4/3) is gripped in an electrode carrier arm (25/1, 25/2, 25/3; 51/1,51/2, 51/3) which is connected to an electrode lift mechanism (26/1, 26/2, 26/3) by way of a horizontal guide means (27/1, 27/2, 27/3; 52/1, 52/2, 52/3), and is reciprocable along the guide means by a drive means which is operative in two directions.

4. A furnace according to claim 1, claim 2 or claim 3 characterised in that, when the furnace has at least two electrode carrier arms (25/1, 25/2, 25/3; 51/1, 51/2, 51/3) which are disposed in juxtaposed relationship and which each carry a respective arc electrode (4/1, 4/2, 4/3), at least the outer electrode carrier arms (25/1, 25/3; 51/1, 51/3), are pivotable through a restricted angle in a horizontal plane.

5. A furnace according to claim 3 or claim 4 characterised in that the electrode carrier arm (51/1, 51/2, 51/3) is telescopically extensible.

6. A furnace according to one of claims 1 to 5 characterised in that the furnace vessel (2) can be closed by a cover (3) which has a slot-like means (38/1) for an electrode to pass therethrough, said means being adapted to the relative horizontal path of movement (28/1, 28/2, 28/3) as between the respective electrode (4/1,4/2,4/3) and the cover (3).

7. A furnace according to claim 6 characterised in that the slot-like electrode-passing means (38/1) is covered by cover plates (35/1, 36/1, 37/1; 35/2; 35/3) which are displaceable along the relative horizontal path of movement (28/1, 28/2, 28/3) and of which one (36/1, 36/2, 36/3) has a through opening (39/1) adapted to the electrode cross-section, and which in any position of the electrode (4/1, 4/2, 4/3) along the relative path of movement (28/1,28/2,28/3) close the slot-like electrode-passing means (38/1) in the cover (3).

8. A furnace according to one of claims 1 to 5 characterised in that the furnace vessel (2) can he closed by a cover which, for each arc electrode (4/1, 4/2, 4/3) which is displaceable in the direction of the charging material accomodating space (8), has two means for passing electrodes therethrough, of which one said means is provided in the central region of the cover and the other is provided at a location in the cover which is adjacent to the charging material accomodating space (8).

9. A furnace according to one of claims 1 to 8 characterised in that the floor (9) of the charging material accomodating space (8) is disposed at such a depth that, when a liquid sump pool (18) is formed in the furnace hearth, said liquid sump pool extends into said charging material accomodating space and permits direct material exchange and conducive heat exchange, in the lowermost zone of the column (17) of charging material.

10. A furnace according to one of claims 1 to 9 characterised in that the floor (9) of the charging material accomodating space (8) has a fall towards the furnace hearth (5).

11. A furnace according to one of claims 1 to 10 characterised in that the interior of a shaft-like charging material preheater (7) which is disposed on one side of the furnace vessel (2) is provided as the space (8) for accomodating the charging material (16), that the interior of said charging material preheater (7) communicates in a region adjoining its floor (9) with the interior (11) of the furnace vessel (2) through a connecting zone (10) through which charging material can be fed to the furnace hearth (5) from the lower section of a column (17) of charging material which is present in the charging material preheater (7) and hot furnace gases can be passed into the charging material preheater (7), and that the charging material preheater (7), in its upper region, has a charging means (12) for the charging material and a gas outlet (13) with a suction removal means for the furnace gas which is cooled down by being in heat change relationship with the charging material.

12. A furnace according to claim 11 characterised in that at least one burner (15) or nozzle is disposed in the region of the connecting zone (10).

13. A furnace according to claim 11 or claim 12 characterised in that the connecting zone (10) is of an enlarging configuration inclinedly upwardly from the interior (11) of the furnace vessel (2) to the interior (8) of the charging material preheater (7) and disposed in the enlarged region is a partitioning wall which is provided with gas through-flow openings therein, for maintaining a column (17) of charging material.

14. A furnace according to one of claims 1 to 13 characterised in that the cross-section of the space (8) for accommodating the charging material (16) increases in a downward direction.

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