JPS6254012A - Electric furnace and its operating procedure - Google Patents

Abstract

PURPOSE:To prevent the damage of the water-cooled wall of an electric furnace as well as the loss of arc heat by fixing plural spouting nozzles for obliquely spouting gas toward the surface of molten metal under the nozzles to scatter molten slag in all directions in the water-cooled wall. CONSTITUTION:An electric furnace is composed of the body 1, a lid 4 and plural electrodes 5 placed through the lid 4. The body 1 has a water-cooled wall 3 on the periphery of a molten metal reservoir 2 having a tap hole 2a. Plural spouting nozzles 6 are fixed in the wall 3 and molten slag 7 is scattered by obliquely spouting gas from the nozzles 6 toward the surface of molten metal under the nozzles 6 to form a slag film on the whole surface of the wall 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an electric furnace equipped with a water-cooled furnace wall, which forcibly scatters molten slag when refining raw material scrap, particularly stainless steel scrap. The present invention relates to an electric furnace in which a water-cooled furnace wall is provided with a gas injection nozzle for coating the entire surface of the furnace wall, and a method of operating the same.

(Prior art) Electric furnaces have various advantages in refining scrap as the main raw material, namely, it is easy to adjust the temperature to a high temperature, there is no contamination of harmful impurities due to no use of fuel or hot air, and thermal efficiency. It is widely used in both special steel and ordinary steel fields due to its advantages such as good melting properties and fewer restrictions on the raw materials used.In recent years, transpower has been rapidly increased to increase melting capacity. As a result, the furnace walls were exposed to intense arc heat, and even the fireproof walls were severely damaged. is used.

This water-cooled furnace wall is configured with a water-cooled jacket or water-cooled tube unit made of copper or steel. When refining is performed using an electric furnace equipped with such a water-cooled furnace wall, molten slag scattered during refining adheres to the water-cooled furnace wall, is cooled and solidified, and forms a slag film. This prevents heat dissipation from inside the furnace and protects the water-cooled furnace walls from intense arc heat.

[Problem that the invention seeks to solve]

However, when using the conventional electric furnace as described above, the slag film is not necessarily formed on the entire wall of the water-cooled furnace, so it is not sufficient to prevent heat loss in the furnace, and the furnace wall is not protected against intense arc heat. It was insufficient and there was considerable damage to the furnace wall. In particular, when the main raw material is stainless steel scrap, it is melted in a reducing atmosphere to avoid oxidation loss of the chromium it contains. The strength of the slag film is weak, so once it is formed, the slag film may be exposed to some kind of shock (for example, due to the charging of raw material scrap or the tilting of the furnace body).
It easily peels off and falls off, leaving more of the exposed furnace wall surface.
Heat dissipation from inside the furnace increased, and the furnace walls were often damaged due to exposure to intense arc heat, resulting in an increase in electricity consumption and a shortened lifespan of the furnace body.

In order to solve this problem, attempts have been made to increase the adhesion strength of the solidified slag by attaching many stud bolts or fins to the wall of the water-cooled furnace. When the fins are operated more than 200 to 300 times, the tips of the fins gradually wear out, and after 500 times, the reinforcing function to attach and hold slag is almost completely lost. It didn't happen.

[Means for solving problems]

The present invention was developed as a result of studies aimed at providing means for solving the problems of the prior art described above.

That is, one aspect of the present invention includes a furnace body in which a water-cooled furnace wall is provided above a sump portion having a tap opening, a furnace lid, and a plurality of electrodes installed through the furnace lid. In the electric furnace, a plurality of injection nozzles are provided on the wall of the water-cooled furnace and are capable of injecting gas toward the molten metal surface diagonally downward and scattering the molten slag around the circumference. The present invention relates to an electric furnace characterized by:

Another aspect of the present invention relates to a method for operating the electric furnace of the present invention, in which the water-cooled The furnace is operated by at least injecting gas from an injection nozzle installed on the furnace wall toward the molten metal surface diagonally downward to scatter the molten slag above the molten metal surface and solidify it on the entire surface of the water-cooled furnace wall. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is an explanatory plan view showing one embodiment of the electric furnace of the present invention as seen through the furnace cover, and FIGS. 2 and 3 are explanatory side cross-sectional views showing the state during operation, respectively.

In the drawings, reference numeral 1 denotes a furnace body, which consists of a sump 2 into which raw materials are charged, melted, and stored, and a water-cooled furnace wall 3 provided around and above the sump 2. The sump 2 is equipped with a tap port 2a for discharging the molten steel 8, and an operating port 2b is normally provided on the opposite side of the tap port 2a.
b is normally closed by a furnace front door 2c. Although the water-cooled furnace wall 3 is made of water-cooled tubes in FIGS. 2 and 3, it may be a water-cooled jacket. In addition, in FIGS. 2 and 3, in order to make the drawings easier to read, the positional relationships of various parts in the electric furnace are not necessarily the same as in FIG. 1, but are shown. Reference numeral 4 denotes a furnace lid, and as shown in FIGS. 2 and 3, a through hole 4a is formed through which the electrode passes.

The furnace cover 4 has a through hole 4 extending from the periphery as shown in FIGS. 2 and 3, for example.
The peripheral edge 4b up to nearly 8 may be a water-cooled furnace lid having a water-cooled structure. 5 is a plurality of electrodes, including an electrode support (not shown)
It is supported by and installed at a position where it is inserted into the furnace body 1 through the through hole 4a of the furnace lid 4. The above structure is the same as that of a conventional electric furnace. Reference numeral 6 indicates an injection nozzle such as a Laval type, which is installed on the water-cooled furnace wall 3, and has the function of injecting gas diagonally downward toward the molten metal surface and scattering the molten slag around the molten metal surface. The angle (hereinafter sometimes referred to as the injection direction angle with respect to the molten metal surface) formed with the injection direction of the injection nozzle 6 (that is, the direction of the center line of expansion) is 5. ~45 degrees is suitable, so that the injection nozzle 6
The mounting direction on the water-cooled furnace wall 3 is also set at an angle within the above range. Furthermore, it is more preferable that the injection nozzle 6 can be freely moved up and down, left and right, or in any direction while injecting the gas. Since it is necessary to scatter the particles over the entire surface, it is necessary to install at least two pieces, but preferably three or more pieces.

As shown in FIG. 1, the installation location of the injection nozzle 6 on the plan view is the farthest position from the electrode 5 when arc heat is generated, that is, the cold zone, in order to minimize the influence of arc heat on the injection nozzle 6. A is desirable; conversely, hot zone B, which is the position closest to the electrode 5, should be avoided. When the three electrodes 5 are installed at the vertices of an equilateral triangle in the center of the furnace body 1 as shown in the figure, the desired position of the injection nozzle 6 in the plan view is the equilateral triangle. This is the position of the water-cooled furnace wall 3 approximately on the perpendicular bisector of each side. Once the HUM position is determined on the plan view, the height from the installed molten metal level is determined by the width of the vertical spread angle when the molten slag is dispersed by the gas injected from the injection nozzle 6, and the variability of the injection direction of the injection nozzle 6. It is determined by taking into account the above-mentioned appropriate jet direction angle with respect to the molten metal surface of 5 to 45 degrees.

Each of the injection nozzles 6 installed as described above is connected to a gas supply source. The gas types used are inert gases such as argon, active gases such as nitrogen gas, and oxidizing gases such as oxygen gas and dry air, and some or all of these gases are supplied individually or in a mixture by a switching valve. It has become so. Therefore, it is preferable to include a single supply device and a mixing ratio control supply device for stably mixing the mixed gas at a constant ratio.

Next, a method of operating the electric furnace of the present invention described above will be explained.

First, according to the usual method, main raw materials such as stainless steel and steel scraps, auxiliary raw materials such as a reducing sludge forming agent, and if necessary, a deoxidizer etc. are charged into the furnace body 1, and then the furnace lid 4 and electrodes are charged. 5 is set in a predetermined position, and then, with water flowing through the water-cooled furnace wall 3 and also through the furnace lid 4 if the lid 4 is a water-cooled furnace lid, electricity is applied to the electrode 5 to melt the raw material. In this way, as shown in FIG. 2, after forming a pool consisting of the molten slag 7 in the upper layer and the molten steel 8 in the lower layer, inert gas such as argon gas, nitrogen gas, etc. .

Depending on the case, dry air or a mixed gas thereof is injected from the injection nozzle 6 toward the hot water surface diagonally downward at an injection speed higher than the speed of sound. How much gas should be injected at this time depends on the properties of the molten slag at that time, but in general, the gas pressure guided to the injection nozzle 6 is 5 to 15 kg/
dG, the gas flow rate is preferably 300 to 50 ONrn'/hour/nozzle, and the injection time is preferably 1 to 5 minutes. In this way, the gas injected from each injection nozzle 6 scatters the molten slag 7 on the upper layer around the molten metal surface around the molten metal, causing it to adhere to the water-cooled furnace wall 3 and solidify. In this case, if gas injection is started and finished all at once from a plurality of injection nozzles 6, the injection can be completed in a short time and the injection nozzles 6 will not be blocked without any special operation. It is preferable to carry out the above gas injection by first lifting the electrode 5 upward, but if the predetermined position for generating arc heat does not interfere with the gas injection and scattering the molten slag 7 all around, it may be left as it is. Gas injection may also be performed.

In this way, the molten slag 7 is scattered and the water-cooled furnace wall 3
After forming a slag film on the entire surface of the steel, the molten steel can be basically refined according to a conventional method so that the molten steel has the desired composition. That is, the electrode 5 is set at a predetermined position, arc heat is generated to perform main melting at a predetermined temperature, and if necessary, oxidizing gas such as oxygen gas, dry air, or a mixture thereof is supplied to perform refining. Let's do it. After refining, the steel is tapped and moved to the next process, and the electric furnace is repaired and used for the next refining. It is preferable that gas injection for forming a slag film be performed during each scouring. When the electric furnace of the present invention is used in the steps after the main melting described above, it can be operated while supplying gas into the furnace through the injection nozzle 6 according to the purpose of refining. In particular, by injecting oxygen gas or dry air, the molten slag 7 and molten steel 8 can be stirred and oxidation reactions such as decarburization and desiliconization can be carried out quickly.

〔effect〕

In the present invention, an electric furnace has a structure in which an injection nozzle is provided on the water-cooled furnace wall 3, and prior to main melting in the electric furnace, gas is injected into the molten slag 7 above the melt surface to forcibly By operating so as to scatter the molten slag 7 and form a slag film on the entire surface of the water-cooled furnace wall 3, heat loss due to arc heat during refining is prevented and damage to the furnace wall due to intense arc heat is extremely reduced. . Furthermore, by supplying the gas necessary for refining using the injection nozzle 6 so as to stir the molten slag 7 and molten steel 8, the reaction during refining can be carried out effectively.

[Example, comparative example]

As an example, an electric furnace of the present invention having a capacity of 50 tons and having the configuration illustrated in FIG. 1 was prepared. The comparative example is a conventionally used one having the same configuration as above except that the injection nozzle 6 is not provided. These electric furnaces were repeatedly operated in the same manner as electric furnace refining using stainless steel scrap as raw material.

Comparative Example In the case of the electric furnace of Comparative Example, the formation of a slag film on the water-cooled furnace wall was insufficient, and a large amount of heat was lost from inside the furnace through the water-cooled furnace wall, causing the temperature of the cooling water to rise. As a result of conventional use, it has become unusable after 1,500 to 2,000 refinings.

Example In the case of the electric furnace of the present invention, after forming the molten metal sump, N2 with a pressure of 13 ICg/dG was used as the injection gas, and it was injected all at once from each injection nozzle for 3 minutes at a flow rate of 50 ONrrI3/hour per injection nozzle. . When such gas injection was carried out for each refining, a slag film was well formed on the entire surface of the water-cooled furnace wall each time.

The cooling water temperature was lowered by 3° C. and the electric power consumption was reduced by 20 KWll/T-EF compared to the comparative example. Socite 25
It was able to withstand more than 00 refining cycles.

[Brief explanation of the drawing]

FIG. 1 is an explanatory plan view showing one embodiment of the electric furnace of the present invention as seen through the furnace cover, and FIGS. 2 and 3 are explanatory side cross-sectional views showing the state during operation, respectively. 1... Furnace body 2... Water reservoir 2a... Tap port 2b... Operation port 2c... Furnace front door 3... Water-cooled furnace wall 4... Furnace lid 4a...Through hole 4b...Peripheral portion 5...Electrode 6...Injection nozzle 7...Molten slag 8...Molten steel A...Cold zone B ...Hot zone Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A furnace body in which a water-cooled furnace wall is provided above a sump portion having a tap opening, a furnace lid, and a plurality of electrodes installed through the furnace lid. In an electric furnace equipped with a water-cooled furnace, a plurality of injection nozzles are provided on the wall of the water-cooled furnace and are capable of injecting gas toward the molten metal surface diagonally downward and scattering molten slag around the circumference. Characteristic electric furnace. 2. The electric furnace according to claim 1, wherein the injection nozzle is provided on the wall of the water-cooled furnace in the cold zone in the electric furnace. 3. The electric furnace according to claim 1 or 2, wherein the injection nozzle is provided at an angle between the molten metal surface and the injection direction in a range of 5 to 45 degrees. 4. When refining raw materials using an electric furnace equipped with a water-cooled furnace wall above the periphery of a sump, gas is injected from an injection nozzle installed on the water-cooled furnace wall diagonally downward toward the hot water surface to form a layer above the hot water surface. 1. A method of operating an electric furnace, characterized in that the electric furnace is operated by at least scattering molten slag and causing it to adhere and solidify on the entire surface of a water-cooled furnace wall. 5. The method of operating an electric furnace according to claim 4, wherein the gas injected to scatter the molten slag is an inert gas. 6. The method of operating an electric furnace according to claim 4, wherein the gas injected to scatter the molten slag is nitrogen gas. 7. Scope of claims that operates while injecting gas to scatter the molten slag in the upper layer of the hot water surface and solidifying it on the entire surface of the wall of the water-cooled furnace, and then supplying gas into the furnace from the injection nozzle according to the purpose of refining. The method for operating an electric furnace according to any one of Items 4 to 6. 8. The method of operating an electric furnace according to claim 7, wherein the gas supplied depending on the purpose of refining is oxygen gas. 9. The method of operating an electric furnace according to claim 7, wherein the gas supplied depending on the purpose of refining is dry air. 10. The method of operating an electric furnace according to claim 7, wherein the gas supplied depending on the purpose of refining is a mixed gas of oxygen gas and dry air.