WO2016008018A1

WO2016008018A1 - A device for injecting gas into an electric arc oven and a method for mounting a gas-injection device

Info

Publication number: WO2016008018A1
Application number: PCT/BR2015/050046
Authority: WO
Inventors: Rodrigo NAZARETH BORGES; Romulo BATISTA BAITZ; Edmilson DIAS GONZAGA
Original assignee: Magnesita Refratários S/A
Priority date: 2014-07-16
Filing date: 2015-04-17
Publication date: 2016-01-21
Also published as: BR102014017541A2; AR100097A1

Abstract

One describes a device (2) for injecting gas into an electric arc oven (1), the device (2) being positioned in an opening in the bottom part of the electric arc oven (1). The device (2) of the present invention solves prior-art problems, enabling greater safety against leakage of molten metal and is composed by a seat (3) and a plug (4) inserted concentrically into the seat (3). The plug (4) is provided, in its bottom part opposite the side of the oven, with a connection block (7). The connection block (7) contains a copper nucleus (8). The device (2) further has a sub-plug (16) positioned below the connection block (7), a base plate (15) and a cover (17). The present invention further relates to a method for mounting a gas-injection device (2).

Description

Specification of the Patent of Invention for: "A DEVICE FOR INJECTING GAS INTO AN ELECTRIC ARC OVEN AND A METHOD FOR MOUNTING A GAS-INJECTION DEVICE"

The present invention relates to a device for injecting gas into an electric arc oven. The device is positioned in an opening at the upper part of an electric arc oven and composed by a seat and a plug inserted concentrically into the seat. The plug is provided, in its inside, with a plurality of longitudinal parallel and through-passing injection tubes connected to a source of an inert gas and a longitudinal reference tube that is shorter than the plug length, connected to an additional source of inert gas. The invention further relates to a method for mounting a gas-injection device.

Description of the prior art

Since the beginning of the Eighties various systems for injection of oxygen and inert gas have been introduced in the market in order to improve the efficiency of electric arc ovens. However, the usual technology of electric arc oven exhibit few solutions to mover and homogenize the bath, that is to say, to mix the molten steel and the slag. For instance, injectors of oxygen into electric arc oven on alternating current have effect only on the surface of the steel volume, with restricted efficiency when a viscous slag layer covers the steel. It is known that the most efficient way to move molten steel is by applying injection gas, wherein bubble columns rise from the oven bottom to the surface of the molten steel.

Systems for injecting gas through a single tube or through a plug with a number of bores have been developed, which are either inserted into a layer of refractory material of the electric arc oven (indirect injection) or in direct contact with the molten steel (direct injection). At present, most systems for injecting gas into electric arc ovens is of direct injection with multiple bores. The reason for this is the greater efficiency in transferring mass and energy, which takes place on electric arc ovens that operate with direct injection systems.

The injection-gas plugs are installed on the electric arc oven through a channel surrounded by blocks of refractory material, thus facilitating the replacement thereof. In order to guarantee safety and prevent metal leakages in the space between the plug and the refractory material of the oven, a suitable battering refractory mass is introduced.

The plug per se is manufactured from an IVfgO-C mixture with density in the same range as the refractory material surrounding it. The inert gas is blown into the metaliic bath through a plurality of small-diameter bores, and it is usual to employ bores with a diameter of 1 to 2 mm. With the use of multiple bores of small diameter, the penetration of liquid steel into the bores, in the case of low flows of inert gas, is limited to a few millimeters. The movement itself of the metallic bath caused by non-blocked bores unblocks the other bores. When plugs with a single tube are used, in the case of infiltration by liquid metal the blocking, when it takes place, may be permanent.

If is also usual to employ a reference tube for verifying the wear of the plug. The length of the reference tube is shorter than that of the plug and is pressurized by an independent inert gas line. When the wear of the tube reaches the reference tube, thus releasing the passage of gas into the metallic bath, the pressure inside it drops, generating an indication of the need to replace the plug.

Usually in the prior art one employs, as inert gas, nitrogen, but argon may also be employed. The jet of inert gas, upon getting into the molten metal bath, changes into bubbles that rise to the surface. A large number of tubes with smaller diameter reduce the risk of blockage by the steel and increase the number of bubbles, even in low gas flows. Finally, it should be observed that the low flow of inert gas is recommendab!e for the sake of handling and also to prevent the formation of an opening in the surface of the liquid metal.

As it is dear, the technology of direct injection by means of a plug with multiple bores in direct contact with the molten steel has a number of advantages, this being the reason for its rapid spread in the steel industry at present. This technological solution, however, should guarantee total safety in its operation, preventing leakage of liquid steel between the seat and the plug and through the plug tubes, besides enabling easy replacement of the plug when it is worn out,

Brief description of the invention

The present invention solves the prior-art problem by guaranteeing tightness of the plug during its operation inside the electric arc oven, keeping its ease of replacement in the case of wear.

According to the present invention, a device for injecting gas into an electric arc oven is positioned in an opening at the lower part of the oven and is composed by a seat and a plug inserted concentrically into the seat. The plug is provided, in its inside, with a plurality of parallel and through- passing longitudinal injection tubes, connected to a source of inert gas, and a longitudinal reference tube with a length shorter than the length of the plug, connected to an additional source of gas. The plug of the present invention is provided, on its lower part opposite the inside of the oven, with a connection block. The connection block exhibits, on its lower part, a tube for connection of a source of inert gas for the injection tubes and a tube for connection of an additional source of gas for the reference tube. The connection block, as a result of the passage of injection gas through it, has a temperature that is lower than that of the materials of the circulating parts. Besides, it contains a body made of copper and composed of a number of bores. In this way, if the liquid steel comes in contact with this connection block, the copper body will be capable of absorbing the heat from the liquid steel, leading to solidification of the liquid steel that may penetrate from inside the plug and its injection tubes. The device of the present invention further has a sub-plug positioned below the connection block. The sub-plug acts as a sealing element, preventing passage of liquid steel between the plug and the seat. A base plate welded to the oven body is positioned concentrically and out of the sub- plug, guaranteeing support of the whole system. Locking elements are inserted into this plate, which secure the cover to the sub-plug, preventing any movement of the assembly in a direction opposite the oven. The conjunction of the connection block with the sub-plug guarantees good operational safety for the gas-injection device of the present invention, which is superior to that of the prior-art object.

Additionally, the present invention, as a result of its characteristic constructive shape, guarantees ease of installation on existing ovens and subsequent replacement of the plug in case of wear.

The method for mounting a gas-injection device according to the present invention comprises the steps of:

welding the base plate to the outer wail around the opening of the electric arc oven;

positioning a first annular heat segment on the inner wall, on the inner side of the opening of the arc oven;

positioning the other annular seat segments;

filling with mortar the space between the seat and the inner coating of the electric arc oven;

positioning, on the outer side of the oven, the sub-plug on the cover;

inserting the sub-plug into the opening of the electric arc oven and fitting the cover onto the pins of the base plate;

- locking the cover by inserting the wedge-shaped locking elements into the tears of the pins and securing the safety dams;

inserting, from the inner side of the electric arc oven, the plug into the annular seat bore;

inserting the battering mass between the plug and the seat, and - connecting feed hoses to the tubes of connection of inert gas and connection of additional inert gas.

Brief description of the drawings

The present invention will now be described in greater detail with reference to an example of embodiment represented in the drawings. The figures show.

Figure 1 is a cross-sectional view of the device of the present invention; Figure 2 is a perspective view of the plug and of the connection block of the present invention;

Figure 3 is a perspective view of the seat-and-plug assembly of the device of the present invention, and

Figure 4 is an exploded view showing the components of the device of the present invention.

Detailed description of the figures

As can be seen in figure 1 , the device 2 of the present invention is installed in an opening in the electric arc oven 1 . The device 2 is surrounded by refractory material of the oven 1 floor, its upper part virtually facing the inner surface of the refractory material of the oven 1 .

The device 2 has a seat 3 and a plug 4 inserted concentrically into the seat 3, the plug 4 being provided, in its inside, with a plurality of parallel and through-passing longitudinal injection tubes 5, connected to a source of inert gas, and a longitudinal reference tube of shorter length that that of the plug 4, connected to an additional source of gas.

The plug 4 is provided, on its lower part opposite the inside of the oven 1 , with a connection block 7. The connection block 7 has, at its lower part, a tube for connecting a source of inert gas 13 to the injection tubes 5 and a tube for connecting an additional source of inert gas 14 to the reference tube 6. The device 2 further has a sub-plug 16 positioned below the connection block 7, a base plate 15 positioned concentrically and externally with respect to the sub-plug 16, a cover 17 detachabiy joined to the base plate 15 by locking elements 18, 19.

The seat 3, in turn, is composed by annular segments made of molten MgO and carbon, the segments having annular surfaces with protrusions 3a for engagement of a segment with another.

The plug 4 is cylindrical and complementary to the inner shape of the seat 3, being manufactured of isostaticaily pressed MgO and carbon.

The connection block 7 is cylindrical, has a nucleus 8 made of electrolytic copper, provided with a plurality of through-bores 9. The nucleus

8 has recesses that form, respectively, a chamber 1 1 downstream and an chamber 10 upstream of the gas flow coming from the tube for connection of a source of inert gas 13. Nucleus 8 further has a through-bore to the reference tube 8. Since the nucleus 8 is manufactured from electrolytic copper, it has good thermal conductivity and, by virtue of the plurality of through-bores 9 and the consequent larger area of contact with the flow of inert gas, exhibits a relatively low temperature as compared with the material of the other surrounding parts. In this way, the connection block 7 assembly acts as a safety element causing any leakage of molten steel from the plug 4 penetrating the chamber 10 to solidify immediately in contact with the nucleus 8. Alternatively, the connection block 7 may further have at least three centering handles 12 welded onto its outer surface. The centering handles 12 enable correct positioning of the plug 4 within the seat 3, leaving enough clearance for subsequent introduction of battering mass.

The sub-plug 16 is manufactured from AI203 and has a cylindrical shape with a flat bottom face 16a, a flat top face 16d, central bore 16b and an annular protrusion 16c on its top face 16d facing the inside of the oven 1 . The protrusion 16c is positioned between the outer circumference of the connection block 7 and the inner surface of the seat 3, The annular protrusion 16c performs the function of mechanical barrier to prevent any flow of liquid sfeel that may penetrate between the plug 4 and the seat 3 from leaving the device 2.

The flat annular base plate 15 has at least three pins 19 provided with tears for insertion of locking elements 18.

The fiat annular cover 17 has a central bore and a flat face 17a for contact with the flat bottom face 16a of the sub-plug 16,

The injection tubes 5 preferably have a diameter of about 1 - 2mm. The diameter of the injection tube may vary depending on the flow and on the inert gas necessary to the process.

The locking elements 18 a wedge-shaped and include safety clams 20. Any other shape of mechanical locking element may be applied in this case, as long as the easy fixation and removal thereof is guaranteed. Figure 2 shows a perspective view of the inside of the plug 4 in an transparent manner, where one can see the plurality of injection tubes 5 and the reference tube 6, the length of which is shorter than that of the plug 4, The tubes 5 and 8 get into the connection block 7, the sub-plug 18 rests below the connection block 7 and its annular protrusion 18c constitutes a wail-shaped barrier to retain any flow of liquid steel that may drain along the plug 4 or leak through the connection block 7.

The base plate 15 is welded outside the oven 1 wail, thus guaranteeing the support of the whole system and that now flow of liquid steel will leave the device of the present invention.

Figure 3 shows the plug 4 inserted into the seat 3, and figure 4 shows an exploded view of the device 2. These figures also facilitate the understanding of the method of mounting the device 2 on the oven 1 .

Initially one makes a cut in the oven 1 carcass to make an opening in the oven. Then, the base plate 15 is welded onto the outer wail around the opening of the electric arc oven 1 .

After this, a first annular seat segment 3 is centrally position in the inner wail of the opening of the arc oven 1 ,

Then, the other two annular segments of the seat 3 are placed onto the first one and fixed with mortar. Between the seat 3 and the refractory material of the oven floor a specific mortar is battered and then the work mass of the oven floor is places with protection of the seat 3 bore.

Thereafter, the sub-plug 16 is positioned on the cover 17 from the outside. The side surfaces of the sub-plug 16 should be treated with mortar.

The sub-plug 16 is inserted into the opening of the electric arc oven 1 , and the cover 17 is fitted onto the pins 19 of the base plate 15.

Now the cover 17 is locked by inserting the wedge-shaped locking elements 18 into the tears of the pins 19 and the safety dams 20 are secured, !n this way the tightness of the device 2 is guaranteed. From the inside of the electric arc oven 1 , the plug 4 is inserted into the annular bore of the seat 3, as shown in figure 3. The surface of the sub-plug is covered with a specific mortar before the plug 4 is inserted.

Then the battering mass is inserted between the plug 4 and the seat 3 and finally the feed hoses are connected to the inert-gas connection tube 13 and the additional inert-gas connection tube 14. Thus, the device 2 of the present invention is ready to operate.

If there is wear of the plug 4 indicated by the reference 6, the replacement thereof is made by following these steps:

- initially, the feed hoses are disconnected from the inert-gas connectio9n tube 13 and the additional inert-gas connection tube 14;

then the cover 17 is removed by removing the clamps 20 and the wedge-shaped locking elements 18;

after this, one applies mechanical force within the oven 1 onto the plug 4 to remove it together with the sub-plug 16 through the bottom of the oven 1 ;

thereafter one removes the mortar that may have remained adhered to the inner surface of the seat 3 segments; the seat 3 segments that exhibit wear should be replaced;

- the sub-plug 18 treated with mortar is placed together with the cover 17 through the bottom of the oven 1 ;

the cover 17 is secured with the wedge-shaped locking element 18, and the safety dams 20 are inserted;

a new plug 4 is placed from the inside of the oven 1 ; the plug 4 should be centered with respect to the seat 3;

finally the feed hoses are connected to the inert-gas connection tube 13 and the additional inert-gas connection tube 14.

A preferred example of embodiment having been described, one should understand that the scope of the present invention embraces other possible variations, being limited only by the contents of the accompanying claims, which include the possible equivalents.

Claims

1 , A device for injecting gas into an electric arc oven, the device (2) being positioned in an opening in the lower part of an electric arc oven (1 ) and composed by a seat (3) and a plug (4) inserted concentrically into the seat (3), the plug (4) being provided, in its inside, with a plurality of parallel and through-passing longitudinal injection tubes (5), connected to a source of inert gas and a longitudinal reference tube (6) with a length shorter than that of the plug (4), connected to an additional source of gas, the plug (4) being provided, on its lower part opposite the inner side of the oven (1 ), with a connection block (7), exhibiting at its lower part a tube for connection of a source of inert gas (13) to the injection tube (5) and a tube for connection of an additional source of gas (14) to the reference tube (8), characterized in that the connection block (7) has a copper nucleus (8), the device (2) further exhibiting a sub-plug (16) positioned below the connection block (7).

2. The gas injection device according to claim 1 , characterized in that the seat (3) is composed by annular segments made of !VlgO and C, the segments having annular surfaces (3a) with protrusions for engaging a segment with another.

3. The gas-injection device according to claim 1 , characterized in that the plug (4) is cylindrical and complementary to the inner shape of the seat (3), being made of isostatically pressed MgO-C.

4. The gas-injection device according to claim 1 , characterized in that the connection block (7) is cylindrical, and the nucleus (8) of electrolytic copper is provided with a plurality of through-bores (9), the nucleus (8) having recesses forming, respectively, a chamber (1 1 ) downstream and a chamber (10) upstream of the gas flow from the tubing for connection of a source of inert gas (13), the nucleus (8) further having a through-bore to the reference tube (6).

5. The gas-injection device according to claim 1 , characterized in that the sub-plug (16) is made of AI203 and has annular shape with a fiat bottom face (16a), a flat top face (16d), a central bore (16b) and an annular protrusion (16c) on its top face (16d) facing the inside of the oven (1 ), the protrusion (16c) being positioned between the outer circumference of the connection block (7) and the inner surface of the seat (3).

6. The gas-injection device according to claim 1 , characterized by having a fiat annular base plate (15) with at least three pins (19) provided with tears for insertion of locking elements (18), the base plate (15) being positioned concentrically and out of the sub-plug (16).

7. The gas-injection device according to claim 1 , characterized by having a flat annular cover (17) with a central bore and a flat face (17a) for contact with the flat bottom face (16a) of the sub-plug (16), the cover (17) being detachably joined to the base plate (15) by locking elements (18, 19).

8. The gas-injection device according to claim 1 , characterized in that the injection tubes (5) have a diameter of about 1 to 2 mm.

9. The gas-injection device according to claim 7, characterized in that the locking elements (18) are wedge-shaped and include safety clams (20).

10. A method for mounting a gas-injection device as defined in any one of claims 1 to 9, the method being characterized by comprising the combination of the following steps:

welding the base plafe (15) to the outer wall around the opening of the electric arc oven (1 );

positioning a first annular segment of seat (3) on the inner wail on the inner side of the opening of the arc oven (1 );

filling with mortar the clearance between the seat (3) and the inner coating of the electric arc oven (1 );

- positioning, from the inside of the oven (1 ), the sub-plug (16) on the cover (17);

inserting the sub-plug (16) into the opening of the electric arc oven (1 ) and fitting the cover (17) onto the pins (19) of the base plate (15;

locking the cover (17) by inserting the wedge-shaped locking elements (18) into the tears of the pins (19) and securing the safety dams (20); inserting, from the inside of the electric arc oven (1 ), the plug (4) into the annular bore of the seat (3); and

connecting feed hoses to the inert-gas connection tube (13) and the additional inert-gas connection tube (14).

1 1 . The Method for mounting a gas-injection device according to claim 10, characterized in that the replacement of the plug (4) further includes the combination of the following steps:

disconnecting the feed hoses from the inert-gas connection tube (13) and additional inert-gas connection tube (14);

- removing the cover (17) by removing the claims (12) and locking elements (18);

pressing, from the inside of the oven (1 ), the plug (4) to remove it together with the sub-plug (16) through the bottom of the oven (1 );

replacing seat (3) segments in the case of wear;

- placing the sub-plug (18) together with the cover (17) through the bottom of the oven (1 );

securing the cover (17) with the wedge-shaped locking elements (18) and placing the safety clams (20);

inserting the plug (4) into the oven (1 ) centered with respect to the seat (3); and

reconnecting the feed hoses to the inert-gas connection tube (13) and the additional inert-gas connection tube (14).