JPS6311613A - Construction of bottom blowing tuyere for electric furnace - Google Patents

Abstract

PURPOSE:To prevent the flow of induction current to gas discharge capillaries in tuyeres in the bottom of an electric furnace and to prevent the damage of the tuyeres by forming part of said discharge capillaries of nonconductive ceramics. CONSTITUTION:The tuyere 2 having plural gas discharge passages 4 is provided to the bottom of the electric furnace and various kinds of gases such as O2, CO, CO2, Ar and N2 are blown into a molten steel during refining of the molten steel to stir the molten steel and to accelerate the refining reaction. The tuyere 2 is constituted of MgO-C refractories and the plural gas flow passages 4 are provided therein zigzag at the tuyere section. The gas flow passages run through the furnace bottom wall into the electric furnace from a lower gas distribution chamber 1. The upper parts 5' and lower parts 5 thereof are made of metallic pipes made of a stainless steel, etc., in order to maintain the strength thereof. The insulating pipes 7 made of MgO, Al2O3, ZrO2 and other nonconductive ceramics are interposed at the intermediate thereof. The generation of an accident such as the erosion of the gas flow pipes 4 of the tuyere 2 by the flow of the in-furnace current to said pipes is thus prevented.

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention provides a method for installing electric furnaces that are installed at the bottom of an electric furnace for steelmaking. 81
! Concerning the structure of the tuyere for blowing various gases into a.
In particular, the present invention relates to a structure of a tuyere in which at least a portion of a gas discharge capillary buried in the tuyere is non-conductive.

(Prior art) When bottom blowing refining, which has been conventionally carried out in converters, is used in electric steelmaking furnaces, ? Because the depth of 8 steel is shallow, it tends to cause the level of the hot water to rise, increasing the risk of excessive hot water overflowing, resulting in a lack of safety, and it was not adopted because of poor slag conditions. However, in recent years, gas injection refractories (tuyeres) made of refractories have been installed at the bottom of electric furnaces for the purpose of shortening steelmaking time, reducing slag, and lowering the consumption unit of auxiliary materials such as lime and ferroalloy. Bottom-blowing refining in an electric furnace is now performed, in which refining is promoted by blowing various gases such as oxygen, carbon oxide, carbon dioxide, argon, and nitrogen into the molten steel and stirring the molten steel.

Various structures have been used as the gas blowing tuyeres, such as porous plugs, pore-through tuyeres, thin tube porous tuyeres, tuyeres made of plate-shaped bodies with slits pasted together, and double-pipe nozzles. ing.

(Problems with conventional technology) However, in electric furnace steelmaking, the metal in the furnace body is heated with an induction coil or melted using an arc.
During the melting, an induced current flows through the molten steel. In addition, the tuyere used in bottom-blown refining is equipped with a gas discharge tube such as a metal pipe on the inner periphery to ensure a passage for various gases to be blown in, increasing the strength of the tuyere, and Deterioration of refractories (MgO-C, etc.) due to (C+0□-CO,
> is often prevented. At that time, if the gas discharge capillary is a metal pipe, conduction will occur between the molten steel and the outside of the furnace body, so the current flowing through the molten steel will be short-circuited as an induced current through the gas discharge capillary, interfering with the operation of the electric furnace. There is a risk of this happening.

(Means for Solving the Problems) The present invention has a gas discharge capillary fitted in a required number of gas discharge passages, and is fitted into an opening in the bottom of an electric furnace to form a gas separation chamber and an inside of the furnace. A bottom-blowing tuyere for an electric furnace comprising a refractory layer that communicates with each other, wherein at least a portion of the gas discharge thin tube is formed of a non-conductive material. The main feature is that the gas discharge tubes are integrated without being separated in the length direction, and that no induced current flows through the gas discharge tubes.

The gas discharge capillary of the present invention, at least a part of which is formed of a non-conductive material, is inserted into a bottom blowing tuyere made of a refractory material such as Mg0-C, which is fitted into an opening at the bottom of an electric furnace. Preferably, the upper and lower ends (tip and base ends) are fitted into the plurality of gas discharge passages arranged in such a way that the upper and lower ends (tip and base ends) are aligned with both upper and lower surfaces of the tuyere and communicate with the furnace body and the gas distribution chamber at the lower end of the tuyere. . The gas discharge capillary may be formed by forming the entire length thereof with an insulating tube made of a non-conductive material, or by forming only a portion of the length thereof with the insulating tube and the remaining portion may be formed of stainless steel. The conductive tube may be made of a conductive material such as metal or the like.

Further, the insulating tube may be entirely formed of a non-conductive material, or the surface of the conductive material may be coated with a non-conductive material to prevent current from flowing.

The non-conductive material used in the present invention is selected from ceramics such as magnesia, alumina, zirconia, silicon carbide, silicon nitride, and sialon. The non-conductive material may constitute an insulating tube by itself, or it may constitute an insulating tube by coating the surface of an existing metal pipe. In the latter case, even if the insulating coating layer inside the furnace is worn out by molten steel, it is necessary to configure the furnace so that no current leaks inside the furnace body.

When the gas discharge thin tube is formed from the insulating tube and the conductive tube, it is preferable that the conductive tube is formed into a relatively small-diameter pipe shape whose inner diameter is equal to the inner diameter of the insulating tube. The insulating tube is connected, for example, between the pair of conductive tubes that are separated in the vertical direction, such that the inner diameters of the two heating tubes coincide with each other, and a gas discharge passage is formed inside. For example, the method for fitting the gas discharge thin tube made of a conductive tube with an insulating tube connected in the middle in the length direction into the tuyere is as follows.

The required number of conductive pipes is lengthwise sectioned, and the proximal end of each lower conductive pipe is fixed to the gas distribution chamber by conventional means such as welding, screwing, or caulking. Then, the tips of the upper conductive tubes are aligned so as to match the outline of the operating surface of the tuyeres, and, for example, there are grooves at both the upper and lower ends to engage with the lower and upper ends of the heating tubes. A recess is formed,
An insulating tube having an outer diameter slightly larger than that of the conductive tube is connected to the insulating tube by engaging the concave portions of the insulating tube with the lower and upper ends of both hot tubes. Then, the outer periphery is lined with a refractory material such as magnesia-carbon, magnesia, magnesia-chromium, or high alumina to form a tuyere shape.

When only an insulating tube is used as the gas discharge capillary, the non-conductive material of the insulating tube must be a material that hardly deteriorates even if it comes into contact with molten steel.

To fit the insulating tube into the tuyere, for example, the lower end of the insulating tube, which has a length approximately equal to the vertical width of the tuyere, is fixed to the gas distribution chamber, and the upper end is aligned with the outline of the working surface of the tuyere. The outer periphery is lined with refractory material to form a tuyere shape.

Increasing the number of gas discharge thin tubes including the insulated tubes narrows the gas discharge interval and widens the discharge range, so it is preferable to increase the required number, but from the viewpoint of manufacturing and construction, it is difficult to increase the number. There is a limit to what you can do too much. In addition, if too many gas discharge tubes are provided, the gas discharge tubes will be too close to each other and it will not be possible to sufficiently fill the space between the gas discharge tubes with refractory material during tuyere manufacturing, resulting in a low packing density and a decrease in the corrosion resistance of the tuyere. Become. On the other hand, if the number is small, the distance between the discharge ports for discharging gas into the molten steel becomes wide, and stirring becomes insufficient, making it impossible to perform effective bubbling.

Therefore, the spacing between the discharge ports is such that it is possible to sufficiently fill the refractory material including coarse particles during tuyere manufacture, and at the same time that stirring is not insufficient, and the spacing is preferably a few square meters.

When the gas discharge tube is composed of a conductive tube and an insulating tube, its vertical position may be anywhere as long as the non-conductive material of the insulating tube is a material that hardly deteriorates even if it comes into contact with molten steel. If the non-conductive material is a material that deteriorates when it comes into contact with molten steel, the location is such that even if the tuyere is damaged by the molten steel and the operating surface side becomes concave, the non-conductive material will not come into contact with the molten steel. It is necessary to set the position so that even if the tuyere is damaged in a concave manner, the concave surface of the tuyere does not reach the end of the insulating tube on the furnace body side. The rate of damage to the tuyeres varies depending on the shape of the tuyere, the material and quality of the refractory lining the outer periphery, the amount of gas blown, etc., so the vertical position of the insulating tube cannot be specified in part. According to actual results, if the tuyere part becomes concave by about 150 to 200 mm or more from the general hearth bottom, it will have an adverse effect on the surroundings and shorten the life of the hearth bottom stamp. Therefore, since the damage to the hearth stamp material is almost zero due to the adhesion of slag, base metal, etc., it is necessary to replace and repair the tuyere before the damage to the tuyere itself reaches about 150 to 200 IIla from the operating surface. Therefore, it is desirable that the insulating tube be installed at a location 150 to 200 mm or more away from the operating surface and as close to the gas distribution chamber as possible.

(Function) In the present invention, a gas discharge thin tube, at least a portion of which is made of a non-conductive material, is fitted into the gas discharge passage of the tuyere. When steelmaking is carried out while supplying gas into the electric furnace from the gas discharge capillary of the tuyere, even if an arc current or the like flows through the molten metal in the electric furnace, the current cannot flow through the gas discharge capillary, There is no problem with refining, and the gas flowing through the gas discharge tube does not come into contact with the refractories that make up the tuyere, so even if the gas is corrosive, the tuyere will not be damaged by the gas. Never.

(Example) The present invention will be described in more detail below based on an example shown in FIGS. 1 to 3, but the present invention is not limited to this example.

1 to 3 show an embodiment of a bottom-blowing tuyere for an electric furnace according to the present invention, and FIG. 1 is a vertical cross-sectional view thereof, and FIG. FIG. 3 is an enlarged vertical sectional view of the connecting portion between the insulating tube and the conductive tube in FIG. 1.

At the opening between the gas distribution chamber l for distributing gas and the space inside the furnace body on the lower surface of the furnace body, there is a tuyere 2 made of a refractory material shaped like a truncated cone and having a gently tapered surface. are fitted. The tuyere 2 is formed with a required number of gas discharge passages 3 passing through the tuyere 2 in the longitudinal direction, thereby forming the gas distribution chamber 1.
It communicates with the inside of the furnace body. A portion of each gas discharge passage 3 close to the gas distribution chamber 1 is made of an electrically sensitive material such as stainless steel so that the lower end is aligned with the upper surface of the gas distribution chamber 1, and a gas flow passage 4 is formed inside. A relatively short lower conductive tube 5 is fitted inside. Note that it is desirable that the diameter of the electric shock tube 5 is as small as possible; for example, the outer diameter is 2.5 fins,
Let the inner diameter be l x m. As shown in FIG. 3, at the upper end of the conductive tube 5, there is a non-conductive material such as ceramic sock, which has an inner diameter equal to that of the gas flow passage 4 and a slightly larger outer diameter, and has four portions 6° and 6 formed at both upper and lower ends. An insulating tube 7 made of a flexible material is connected by engaging the recess 6 with the upper end of the conductive tube 5. Further, in the recessed portion 6'' at the upper end of the insulating tube 7, there is a long piece having the same cross-sectional shape as the lower conductive tube 5 and whose upper end is aligned with the surface of the working surface of the tuyere to form a discharge port 8. By engaging the lower ends of the upper 4 conductive tubes 5'', the conductive tubes 5
A gas discharge thin tube is formed by the insulating tube 7 and the upper and lower pair of conductive tubes 5.5''.

The planar arrangement of the gas discharge passages and gas discharge tubes is preferably as evenly distributed as possible, and as shown in FIG. It is possible to arrange them in any desired arrangement, such as placing them on a concentric circle or randomly placing them on concentric circles.

In this embodiment, the insulating tubes 7 are connected to the same height of each gas discharge thin tube, but the vertical positions of the plurality of insulating tubes may be different from each other.

In addition, the shape and material of the tuyere, the diameter and number of holes in the gas discharge tube, the position of the insulating tube, etc. vary depending on the capacity of the electric furnace, the type of steel to be refined, the amount of gas blown, etc., and these values may vary depending on the operating conditions. can be selected as appropriate.

(Effects of the Invention) In the present invention, a gas discharge capillary, at least a portion of which is formed of a non-conductive material, is embedded in the tuyere.

Therefore, even if leakage current generated by electricity used to melt steel leaks toward the gas discharge capillary, it will not flow as an induced current because the gas discharge capillary is insulated by the non-conductive material. There is no problem in the operation of the furnace. Furthermore, since the gas flow path formed in the gas discharge capillary is completely blocked off from the large tuyere material by the gas discharge capillary, damage to the large tuyere material due to the corrosive nature of the gas can be prevented.

[Brief explanation of drawings]

1 to 3 show an embodiment of a bottom-blowing tuyere for an electric furnace according to the present invention, and FIG. 1 is a vertical cross-sectional view thereof, and FIG. FIG. 3 is an enlarged vertical sectional view of the connecting portion between the insulating tube and the conductive tube in FIG. 1.

Claims (4)

[Claims] (1) Consisting of a refractory layer that has gas discharge capillaries fitted into the required number of gas discharge passages and is fitted into the opening in the bottom of the electric furnace to communicate the gas separation chamber with the inside of the furnace. A bottom-blowing tuyere structure for an electric furnace, wherein at least a portion of the gas discharge thin tube is formed of a non-conductive material. (2) The gas discharge thin tube consists of a conductive tube and an insulating tube, and the conductive tube is formed between a pair of conductive tubes fitted in each gas discharge passage using a non-conductive material whose inner diameter is approximately the same as that of the conductive tube. A tuyere structure according to claim (1), which is provided with an insulating tube. (3) The tuyere structure according to claim (1), wherein the gas discharge capillary is an insulating tube made entirely of a non-conductive material. (4) The tuyere structure according to any one of claims (1) to (3), wherein the non-conductive material has deterioration resistance against molten steel.