FR2796138A1 - Method for the melting of a metal material and an installation for putting this method into service with a feed zone that can be regulated to improve control of the melting process - Google Patents

Abstract

Method of melting a metal in a furnace involves progressively introducing the metal at a rate that can be regulated into a feed zone (15) of which the position can be regulated, at least in terms of height, inside the enclosure (10) of the furnace (1). A method for the melting of a first metal material in an installation for the production of metal incorporating a melting furnace (1) made up of a closed enclosure (10), some means for the introduction of a first metal material and some means (12) for heating the enclosure (10) to melt the first metal material and to form, in the lower part (21) of the enclosure (10), a bath (4) of molten metal with a variable height and covered with layer of slag (41) to a higher level (42), is characterized by the fact that the first metal material to be smelted is introduced progressively, at a flow rate that can be regulated, into a feed zone (15) of which the position can be regulated, at least in terms of height, inside the enclosure (10) of the furnace (1). The installation for the production of a molten metal using this method is also claimed.

Description

The invention relates to a process for melting a metal raw material and also covers a facility for producing molten metal by implementing the method.

Processes and facilities for the production of molten metal, in particular steel, have been known for a long time.

The methods used depend essentially on the nature of the raw materials and the desired quality for the molten metal. However, electric arc furnaces are increasingly being used which have the advantage of great flexibility of operation since it is possible to process ferrous materials of any type, for example scrap metal, molten iron, iron carbide or iron ore pre-reduced and introduce into the same oven various additives to obtain the desired quality. In addition, to control the melting process, it can inject all kinds of gases, oxygen, reducing gas or neutral gas.

Usually, the product to be melted, for example scrap metal, is introduced through the upper part of the oven, which generally consists of a vessel closed by a vault forming a removable cover. During a loading phase, after emptying the bath of molten metal made during the previous operation, the electrodes are raised, the vault is opened to introduce into the furnace a quantity of scrap corresponding to the capacity of the tank, the vault is closed and the electrodes are introduced into the furnace for a new melting phase.

To avoid a periodic opening of the vault, it was proposed to equip it with a loading column opening into the furnace and traversed by an updraft of gas that escapes during the melting, against the current scrap coming down into the oven, which is thus preheated. Such an arrangement, which is described, for example, in US-A-2382534 or US-A-5264020 complicates the construction of the vault and the mounting of the electrodes.

Other known arrangements allow to introduce a ferrous material continuously using at least one hopper which flows into a feed device passing through the vault to open into the tank, above the bath. It is then necessary for the ferrous material introduced to be reduced into pieces of sufficiently small dimensions to allow their continuous introduction through a conduit or a conveyor belt. This mode of introduction can be used, for example, with a prereduced ore which is usually in the form of pellets.

When the ferrous material is thus introduced through the vault of the furnace, it falls on the layer of slag which normally covers the liquid bath. However, it has been observed that heterogeneous blocks, commonly referred to as "icebergs", whose melting time is variable and uncontrollable, then occur. This may result in a lack of homogeneity of the liquid metal bath.

The invention overcomes such drawbacks through a new method of introducing raw material into the furnace and an installation for carrying out the process. In addition, thanks to the invention, it is possible to introduce into the furnace solid or gaseous products of any kind and to control the melting process under the best conditions.

The invention therefore relates, in a general manner, to the melting of a metal raw material in a metal production plant comprising a melting furnace consisting of a closed enclosure, means for feeding the furnace in a raw material melting material and means for heating the enclosure for melting the raw material and forming a molten metal bath which collects in the lower portion of the enclosure to a higher level of metal, said bath being covered with an upper layer of slag to a higher level of slag.

According to the invention, the raw material to be melted is introduced gradually and with an adjustable flow rate into a feed zone whose position can be adjusted, at least in height, inside the chamber of the oven.

In particular, the position of the feed zone inside the enclosure is determined so as to ensure a homogeneous introduction of the material, during its fusion, in the existing metal bath.

Particularly advantageously, the progressive feeding zone is placed at an adjustable level depending on the height of the metal bath, so as to be maintained inside the slag layer.

Furthermore, in a preferred embodiment, at least one gas is injected into the feed zone, so as to cause an immediate dynamic stirring of the raw material during its introduction into the existing metal bath. Advantageously, this gas may be an oxidizing gas making it possible to cause a thermal input directly into the feed zone.

According to another preferred feature, the gas is injected in a direction forming a non-zero angle with the direction of introduction of the material.

The invention also covers a facility for producing molten metal characterized in that it comprises a device for gradually introducing the raw material penetrating inside the chamber of the furnace to an outlet orifice and means for adjusting the position, at least in height, of the outlet orifice of the raw material with respect to the metal bath.

Particularly advantageously, the device for introducing the raw material comprises an elongate conduit extending in an axial direction of introduction through an orifice on one side of the furnace enclosure, said conduit being associated with means for gradually pushing the material between an inlet orifice placed outside the oven and an outlet opening opening inside the oven.

Advantageously, the introduction device comprises means for adjusting, respectively, the orientation of the duct and the length thereof penetrating inside the enclosure of the oven, which make it possible to determine, according to the needs , the position of the outlet of the material inside the oven.

In a preferred embodiment, the introduction device is carried by a carriage movable longitudinally on a frame hinged about a horizontal axis and is associated with control means of the orientation of the frame and control means of the longitudinal displacement of the carriage on the frame.

But the invention will be better understood from the following description of a particular embodiment, given by way of example and shown in the accompanying drawings.

Figure 1 is an overall schematic view, in elevation, of a metal production plant according to the invention.

Figure 2 is a side view of the assembly of the introducer.

Figure 3 is a detail view, in axial section, of the insertion device.

Figure 4 is a detail view, in axial section, of another embodiment of the introduction device. FIG. 1 shows the assembly of a metal melting installation mounted on a frame 11 and comprising an electric furnace 1 consisting of a tank 2 closed at its upper part by a removable lid 3 in the form of an arch , so as to limit an enclosure 10.

As usual, the lower part of the tank 2 is covered with refractory material and forms a bowl 21 which rises on the sides at a level sufficient to contain a bath 4 of molten metal covered with a layer of slag 41. The bowl 21 is extended upwards by a lateral wall 22, generally consisting of panels cooled by water, which limits an upper orifice on which the cover 3 is applied. The latter is provided with one or more orifices 31 through which it is possible to introduce in the tank one or more electrodes 12 mounted at the end of a carrying arm 13 and connected to a current source. In the example shown in FIG. 1, the furnace 1 is of the DC type and comprises a bottom electrode 14 placed in the bottom of the tank 2, but the invention also applies to furnaces supplied with alternating current.

In addition, the lid 3 is provided with at least one orifice 32 opening into a pipe 33 for evacuating gases produced in the chamber 10 to a purification device and a chimney.

As indicated above, such an electric furnace is generally fed discontinuously by a load of scrap adapted to the capacity of the tank 2. For this purpose, the lid 3 can be raised and spread laterally to open the tank .

However, such an oven can also be supplied with a ferrous raw material such as a prereduced ore which can constitute either the totality of the filler to be melted or an addition element, the main load then being constituted, for example, of scrap. or liquid iron. In this case, the prereduced ore, which is in the form of fairly small pieces, can be fed continuously from a feed plant 5 placed next to the furnace on a raised frame 51 and comprising less a storage hopper 52 extended by a feed sheath 53.

Usually, the sheath 53 opens into a central orifice of the vault and the pre-reduced ore falls on the bath covered with slag. As indicated above, it can then form agglomerated pieces whose fusion is irregular.

According to the invention, the supply sheath 53 is connected to a device 6 for gradually introducing ore, comprising a receiving chamber 61 having an upper orifice into which the outlet end 54 of the supply sheath 53 opens. and a lateral orifice 71 on which is connected a tubular duct 7 extending in a transverse direction 70 and which passes through an orifice 23 formed in the side wall 22 of the tank 2, above the upper edge of the bowl 21, for to penetrate inside the enclosure 10 of the furnace 1 to an outlet orifice 72. In a particularly advantageous manner, this outlet orifice 72 is placed in the central part of the enclosure 10, close to the axis 20 thereof and substantially at the level of the slag layer 41 covering the metal bath 4.

In a preferred embodiment, shown in more detail in FIG. 2, the duct 7 forms a tubular sheath in which is threaded a helical screw 8 driven by a motor 74 and which extends axially inside the sheath 7 until at the outlet port 72 thereof.

The screw 8 comprises an upstream portion 8 'which passes through the receiving chamber 61, below the outlet orifice 54 of the supply sheath 53 so that the substances discharged by it are entrained in the conduit 7 by the rotation of the screw 8 and out through the orifice 72, inside the enclosure 10 of the furnace.

In addition, the entire device 6 comprising the duct 7, the receiving chamber 61 and the drive motor 74 is mounted on a carriage 62 which can slide, parallel to the axis 70 of the duct 7, on a chassis of support 63, for example, under the action of a cylinder 64.

It is thus possible to entirely remove the device for introducing the chamber 10, in the position shown in dashed lines in FIG. 2, or for introducing the pipe 7 inside the chamber 10, over a length which can be adjusted by means of the jack 64.

Furthermore, the frame 63 is hinged about a horizontal axis on a support frame 65 and can tilt about its axis, under the action of a cylinder 66. By simultaneously adjusting the penetration length of the conduit 7 in the enclosure 10 and the inclination of the frame 62, it is therefore possible to change the position of the outlet orifice 72 inside the chamber 10 of the furnace furnace 1, so that the supply of raw material in the furnace is in a feeding zone 15 placed in the best possible place for the melting.

In Figure 2, for example, which is a schematic partial view of the furnace 1 at the introducer 6, it is seen that it is set so that the outlet port 72 of the conduit 7 is below. the upper level 42 of the slag layer 41 covering the metal bath 4, and preferably slightly above the upper level 40 thereof. In this way, the material 50 conveyed by the screw 8 opens into a feed zone 15 inside the slag. As it is disintegrated by the rotation of the screw, the material 50 is spread in the slag 41 in the form of small pieces that go down separately in the metal bath 4 and gradually melt without risk of agglomeration.

If necessary, it can act on the cylinders 64 and 66 so as to horizontally change the position of the outlet orifice 72 within the slag layer 41 to distribute the ore introduced into the entire bath 4 and maintain the homogeneity of it. Preferably, however, the device 6 will be adjusted so that the outlet orifice 72 is always in the central part of the furnace chamber 10, near the axis 20 of the tank and just above the level 40. In a more advanced embodiment of the invention, shown in Figure 3, the feedstock device also allows the injection of a gas under pressure. In this case, the screw 8 is mounted on a hollow shaft 81 forming a central duct 82 connected to a source of gas under pressure and whose end 83, at the outlet orifice 72 of the duct 7, forms a nozzle injection. Preferably, the injected gas is an oxidizing gas, for example oxygen, which burns while releasing calories.

Such injection of gas into the feed zone 15 causes the feedstock to stir at the best point in the bath. In addition, the use of an oxidizing gas adds a thermal stirring effect in the feed zone 15.

In addition, the combustion of the injected gas causes oxidation of the carbon contained in the raw material and therefore participates in the process of making the steel. The use of such a combined device for supplying raw material and injecting oxidizing gas into the same point of the already molten bath in the furnace is therefore particularly advantageous.

However, it is necessary to provide protection for the screw feeder by cooling the central shaft 81 thereof. For this purpose, as shown schematically in Figure 3, the shaft 81 on which is fixed the thread 80 of the screw is constituted by a hollow envelope limiting an annular space 84 in which is circulated a heat transfer fluid, for example water.

For this purpose, the hollow casing 81 is associated with a double rotary joint 9 on which are connected hoses 91, <B> 91 ', </ B> respectively supply and discharge of the cooling fluid and means not shown such as baffles make it possible to ensure the return flow of the coolant fluid in the annular space 84, up to the level of the nozzle 83, at the end of the hollow shaft 81.

Another rotary joint 92 connected by a hose 92 'to a pressurized gas supply circuit makes it possible to introduce the oxidizing gas into the central space 82 of the shaft 81, to open through the nozzle 83.

As shown in FIG. 4, this nozzle 83 may advantageously be arranged in such a way that the jet of gas 16, symbolized by an arrow in FIG. 4, forms a non-zero angle with the axis of the screw 7, which facilitates the disintegration of the raw material introduced through the orifice 72 into the feed zone 15 and its gradual distribution in the bath 4.

In an even more advantageous embodiment, two different gases are simultaneously injected, at the same time as the raw material, into the enclosure 10 of the furnace 1.

Such a dual injection device is shown schematically in FIG. 4.

The central shaft then consists of two coaxial tubes centered on the axis 70 of the sheath 7 and separated by an annular space 87, respectively an inner tube 81 and an outer tube 88 on which is fixed the thread 80 of the screw 8 rotating in the sheath 7. The outer tube 88 is centered, outwardly, on the end of the inner tube 81, by a bearing 94 and inwards, on a bearing not shown.

Moreover, the outer tube 88 may also consist of a double jacket so as to allow the circulation of a cooling fluid, the inner annular space 84 of the tube 88 being, as previously, connected by a double seal 9 to conduits 91, 91 ', respectively supply and discharge of the heat transfer fluid. Similarly, the inner tube 81 is supplied with gas under pressure by a rotary joint 92 on which is connected a supply hose 92 '. In this case, a second gas can be introduced under pressure into the annular space 87 between the two tubes 81, 88, via a third rotary joint 93 to which is connected a supply hose 93 '.

Thus, it is possible to inject a first gas, for example an oxidizing gas such as oxygen, into the central tube 81 and a second gas into the annular space 87. Advantageously, this second gas can be a fuel gas, for example methane or city gas, thus increasing the supply of fossil energy in the furnace enclosure. In addition, this fuel gas injection increases the thermal brewing effect in the ore feed zone.

The outer tube 88 being cooled, it is possible to introduce the prereduced ore at a relatively high temperature, for example 600 C.

It should be noted that the injection of a reducing gas such as methane around the central jet of oxygen makes it possible to limit the temperature of the end 83 of the inner tube 81 forming a nozzle and, consequently, to increase the duration of life of it.

Of course, the flows and volumes of injected gas can be adjusted according to the needs by means of external valves not shown in the drawings. The rate of introduction of the material can be adjusted simply by acting on the speed of rotation of the screw 8.

Such a device thus makes it possible to adjust the respective flow rates of the material and the injected gas or gases according to the successive phases of the melting process in the furnace.

However, the invention is obviously not limited to the details of the embodiments that have just been described as mere examples, other equivalent devices that can be used for the same purpose without departing from the protection framework defined by the revendications.

In particular, the use of a screw device to achieve a continuous introduction and with an adjustable flow rate of the raw material, also ensures the tightness of the enclosure. Indeed, the material compressed between the screw 8 and the sleeve 7 may constitute a kind of continuous stopper, the lateral orifice 23 of the wall 22 of the vessel can be closed, for example by means of a bellows not impeding the adjusting the position of the device 67. Thus, it is possible to continuously introduce the material inside the chamber 10 of the oven 1 without changing the stoichiometry thereof.

However, other means could be used to push the raw material inside the supply duct 7, for example vibrating devices.

Similarly, the adjustment of the position of the outlet port 72 of the material within the enclosure 10 could be effected by other means.

Moreover, the introduction device according to the invention makes it possible to introduce into the furnace not only prereduced ore, but also addition elements or any other material reduced into pieces so as to allow its continuous transport.

As indicated, the supply duct 7 should normally open into the slag layer 41. However, the outlet orifice 72 could be more or less immersed in the bath 4 if the supply duct 7 is designed to withstand high temperatures, in particular, in the case where the central jet of combustion gas is protected by a jet of reducing fluid.

The reference signs inserted after the technical features mentioned in the claims, are intended only to facilitate the understanding of the latter and in no way limit the scope.

Claims (18)

<U> CLAIMS </ U> Process for melting a metal raw material in a metal production plant comprising a melting furnace (1) consisting of a closed chamber (10), means for introducing into the chamber (10) a metal raw material and means (12) for heating the enclosure (10) for melting the raw material and forming, in the lower part (21) of the enclosure, a bath (4) of molten metal, said metal bath (4) having a variable height and being covered with a layer of slag (41) to a higher level (42), characterized in that the raw material to be melted is introduced gradually and with an adjustable flow rate, into a feed zone (15) whose position can be adjusted, at least in height, inside the chamber (10) of the oven (1). 2. Method according to claim 1, characterized in that the position of the feed zone (15) inside the enclosure (10) is determined so as to ensure a homogeneous introduction of the raw material (50). ), during its fusion, in the existing metal bath. 3. Method according to claim 1, characterized in that the progressive feeding zone (15) is placed at an adjustable level as a function of the height of the metal bath (4), so as to be kept inside. the slag layer (41). 4. Method according to one of the preceding claims, characterized in that at least one gas (16) is injected into the feed zone (15), so as to cause dynamic stirring of the raw material (50). ) during its fusion into the existing metal bath (4). 5. Method according to claim 4, characterized in that at least two different gases are injected into the feed zone (15) by separately adjusting the flow rates and injected volumes. 6. Method according to one of claims 4 to 5, characterized in that a combustion gas is injected into the supply zone (15) so as to cause a thermal input directly into this zone (15) for the fusion of the raw material introduced. 7. Method according to one of claims 4 to 6, characterized in that, the raw material (50) being introduced in a direction (70), at least one gas is injected in a direction (16) at an angle not no one with the direction of introduction of the material. 8. Method according to one of the preceding claims, characterized in that the raw material (50) is reduced in pieces of fairly small dimensions to allow continuous feeding by a tubular conduit (7) penetrating inside the oven enclosure (1). 9. Method according to one of the preceding claims, characterized in that the raw material is a prereduced ore. 10. Method according to one of claims 1 to 8, characterized in that the metal raw material is scrap metal reduced to pieces. 11. A molten metal production plant, comprising a melting furnace (1) forming a closed enclosure (10), means (5) for supplying the furnace (1) with a metal raw material to be melted and means (12) ) for heating the furnace (1) for melting the raw material and forming a molten metal bath (4) which collects in the lower portion (21) of the enclosure (10) to a level metal top (40), said bath being covered with a layer of slag (41) to a higher level of slag (42), characterized in that the supply means (5) comprise a device (6) , 7) of progressive introduction of the raw material, penetrating the furnace and extending to an outlet (72) placed in the central part of the enclosure (10), close to the surface (40). ) of the metal bath (4). 12. Installation according to claim 11, characterized in that the introduction device 6 is associated with means for adjusting the position of the outlet orifice (72) of the raw material (50) relative to the bath of metal (4). 13. Production plant according to claim 11, characterized in that the device (6) for introducing the raw material comprises an elongated conduit (7) extending in an axial direction (70) of introduction through an orifice (23) formed on one side of the enclosure (10) of the furnace, said duct (7) being associated with means (8) of progressive thrust of the material introduced by an inlet orifice (71) placed at the outside of the oven (1), to an outlet (72) opening into the oven. 14. Installation according to claim 13, characterized in that it comprises means (66, 64) for adjusting, respectively, the orientation of the duct (7) and the length of the latter penetrating inside. the enclosure (10) of the oven (1). 15. Installation according to claim 13, characterized in that the insertion device (6) is carried by a carriage (62) movable longitudinally on a frame (63) hinged about a horizontal axis and is associated with means (63) for adjusting the orientation of the frame and means (64) for controlling the longitudinal displacement of the carriage (62) on the frame (63). 16. Installation according to one of claims 13 to 15, characterized in that the conduit 7 for introducing the raw material forms a tubular sheath (7) inside which is threaded at least one screw (8) associated means (74) driving in rotation about its axis for the thrust of the material (50) introduced by an inlet (71) of the sheath (7), to an outlet (72) opening into the furnace chamber (1). 17. Installation according to claim 16, characterized in that, the screw (8) comprising a helical thread surrounding a rotation shaft, said shaft 81 is provided with at least one central duct (82) which is connected to a circuit supplying pressurized gas and opens into the chamber (10) via a gas injection orifice (83). 18. Installation according to claim 17, characterized in that the central shaft consists of two coaxial tubes (81, 88) delimiting respectively a central space (82) and an annular space (87) respectively connected to two circuits. injection of two different gases.