JP3247781B2 - Operation method of electric furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating an electric furnace, and more particularly, to a method for constantly setting the height of slag after forming (slag forming) during the refining period and the heating period. TECHNICAL FIELD The present invention relates to a technique for controlling a refining reaction so as to rapidly progress, thereby improving productivity and reducing various basic units.

[0002]

2. Description of the Related Art Steel refining using an electric furnace is generally performed through various stages such as a melting period, a refining period (oxidation period and reduction period), and a heating period of a charged raw material, and a main component of a reaction occurring there. Is
It is intended for decarburization, dephosphorization, desulfurization, etc. Incidentally, dephosphorization is a slag agent mainly composed of CaO in refining stage was added to the steel bath, blowing an oxygen gas, by oxidizing phosphorus by reaction _{2P + 5O → P 2 O 5} , it was produced The phosphorus pentoxide is absorbed by the slag-making agent. It is better to remove this slag promptly because the reaction in the opposite direction proceeds if left untreated and phosphorus reversion occurs. With respect to this problem,
Japanese Patent Application Publication No. 7-71414 discloses that carbon powder is blown into molten steel using an inert gas as a carrier gas to generate a large amount of fine bubbles in slag, and to form a so-called slag, thereby realizing rapid waste disposal. Is disclosed. At that time, the slag raised on the molten steel not only becomes easier to discharge by slightly tilting the electric furnace, but also wraps around the arc-generating part under the electrode, and the heat generated by the arc hardly radiates to the outside. It also helps to reduce the basic unit.

Further, regarding desulfurization, Japanese Patent Laid-Open No.
No. 022 discloses the effectiveness of blowing CaCO ₃ powder into slag using an inert gas or air, and performing slag forming in the same manner as in the above-described dephosphorization. Further, in Japanese Patent Application Laid-Open No. 2-107712, a method of injecting iron powder and a carburizing agent into the vicinity of an electrode of an arc furnace to promote slag forming to cover an arc portion and reduce electric power consumption of an electric furnace. Is described.

However, in the current operation of the electric furnace, the method of managing the slag forming height during the operation is performed visually by an operator, and the determination of the height is ambiguous and lacks instantaneous information. . Visual observation is an operation in which the operator observes the inside of the furnace at a high temperature, which is not only a safety problem, but also hinders labor saving of operation personnel and automation of operation. Furthermore, due to the ambiguity in the determination of the slag forming height, carbon powder and oxygen for causing slag forming are blown more than necessary to raise their basic unit, thereby increasing operating costs. I have a problem.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and automatically measures and controls the slag forming height on-line when refining steel in an electric furnace. It is an object of the present invention to provide a method for improving the productivity of various types and reducing various basic units.

[0006]

In order to achieve the above object, the inventor repeated many experiments and studies on automatically measuring and controlling the slag forming height. The present invention has been completed based on the results, in the operation of an electric furnace for refining steel while forming slag on the steel bath surface, by measuring the distance from above the electric furnace to the slag surface, The measured forming
The oxygen gas blowing speed and the carbon or aluminum powder blowing speed are automatically adjusted so that the slag height matches the set arc length target value .
An operation method of an electric furnace, wherein the operation is performed by covering an arc . Further, the present invention relates to a method for operating an electric furnace according to claim 1, wherein the distance to the slag surface is measured by a microwave distance meter.

[0007] In this case, any of a direct current and an alternating current arc furnace may be used as the electric furnace.

[0008]

According to the present invention, in the operation of an electric furnace for refining steel while forming slag on the steel bath surface in the electric furnace, the distance from above the electric furnace to the slag surface is measured. Since the oxygen blowing speed and the carbon or aluminum powder blowing speed were automatically adjusted to match the target slag forming height, the slag forming became more accurate than the conventional operator's visual observation, Also, the height can be managed with high accuracy. As a result, the slag completely covers the arc near the electrode, and the control of the arc voltage is improved,
In addition, since the slag is discharged quickly and the stirring is good, the refining reaction time can be shortened. As a measuring device for the slag forming height, various devices using light or sound waves can be applied, but it is preferable to use a microwave distance meter that has a proven track record when receiving hot metal with a torpedo car.

The contents of the present invention will be described below with reference to FIG. FIG. 1 is a longitudinal sectional view of an electric furnace 3 embodying the present invention. First, a distance sensor 1 for measuring a distance l ₁ between the furnace lid and the slag surface is installed on the furnace lid 2 of the electric furnace 3. The distance sensor 1 is preferably a non-contact type on the surface of the slag 14, for example, a microwave range finder or an ultrasonic range finder, but is not affected by the furnace atmosphere (temperature, dust) during operation of the electric furnace 3. When emphasis is placed on the above, a microwave distance meter is preferable. Next, the slag level height l ₂ of the electric furnace 3 during operation, if constantly measuring the l ₁ in refining period, based on the distance to the steel bath 18 surface that has been measured initially operational data operation Processing unit 21
Can be easily calculated by performing the above processing. The present invention
Is intended to utilize the slag foaming height l ₁ being asked constantly during this operation is specifically performed as follows.

First, the case where the formed slag 14 does not cover the arc 19 (ie, the case where the length of the arc 19 is larger than the slag forming height) will be described. Here, the length of the arc 19 substantially corresponds to the arc voltage in a DC electric furnace. For example, arc voltage 400V
At this time, the arc length is about 400 mm. If such a situation occurs during operation, the amount of carbon powder added is increased and the slag is increased so that the measured forming slag height matches the target value of the set arc length (described later). Increase the forming height. As for the target value, it is known that the relationship between the slag forming height and the addition amount of carbon powder or the like is obtained in advance from conventional operation data, and it is slightly better than the actual slag height from the relationship. Further, the addition of carbon powder or the like can be easily performed by automatically adjusting the hopper opening / closing valve 22 for carbon powder or the like based on a signal from the data processing unit 21.

On the other hand, if the formed slag 14 covers the arc 19 excessively, on the contrary, the operation of reducing the carbon powder or the like or adding aluminum ash is performed. All you have to do is keep watching the monitor. In this case, an operation of increasing the arc voltage may be performed instead of reducing the carbon powder and the like.

[0012]

EXAMPLE A DC arc furnace having a furnace capacity of 100 tons / charge (provided with one upper electrode 5 and three furnace bottom electrodes 8, having a furnace inner diameter of 6700 mm and a furnace height of 3100 mm) is usually used. Steel (SD, SS, etc.) was refined. First, as a comparative example, since the scrap charged in the furnace melted and the refining period was started, the arc voltage was reduced to 400V. Until then, only oxygen gas was blown (flow rate 120 Nm ³ / min or less), but carbon powder (particle diameter 5 mm or less) was blown at a speed of about 20 for the purpose of slag forming.
Blowing was performed at 0 kg / min. When the operator started observing the inside of the furnace, slag forming occurred immediately and the electrode 5
The tip is hidden. At that time, the thermal efficiency (the amount of heat applied to the molten steel / input power) was in the best state, but since the present invention was not applied, this state did not continue for a long time, and sometimes the arc 1
9 is greatly exposed. In order to correct this, if the amount of carbon powder is increased and blown in, the slag forming height depends on the visual observation of the operator. Conversely, excessive blowing causes the slag 14 to form too much and overflow the furnace. In some cases, the unit consumption of carbon powder and the unit consumption of electric power increased, and the unit consumption of aluminum ash, which is a heating material, also increased.

Next, the refining of another charge was performed under the same operating conditions as described above, and the operating method according to the present invention was carried out for slag forming. At that time, when the slag forming height became equal to or more than the set target value, aluminum ash was blown in place of carbon powder to take measures in a direction to calm the forming. The results are shown in Table 1. Compared with the comparative example, the unit consumption of carbon powder and aluminum ash can be reduced by about 15%, the power consumption during refining can be reduced by about 10%, and decarburization, dephosphorization and desulfurization are also reduced. The operation was performed as planned, and smooth operation was achieved.

[0014]

[Table 1] (Displayed as an index with the result of the conventional method as 1) ───────────────────────────────── ─── Evaluation index Result of conventional method Result of the present invention Carbon powder basic unit 1 0.85 Al ash basic unit 1 0.85 Electric power basic unit during refining period 1 0.9 ─────────── ───────────────────────── After that, the operation method of the present invention is applied, and operation of several tens of charges is performed, and the slag forming height Set value l _sb
The following formula was confirmed as (mm).

L _sb = E _a -50 where E _a is the arc voltage (V) and corresponds to the arc length (mm) at that time. It should be noted that this formula is: 300 ≦ E _a
≦ 500, the blowing speed of carbon powder is about 200Kg / mi
It was effective when the blowing speed of n and aluminum ash was about 150 kg / min.

[0016]

As described above, when the method for operating an electric furnace according to the present invention is used, the slag forming height based on the visual observation of the operator is automatically controlled, and the refining is performed. In this period, it was possible to optimize the input voltage, improve productivity, and reduce the unit consumption of power and raw materials used. In addition, labor saving of operation personnel can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing equipment of an electric furnace in which an operation method according to the present invention is performed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Microwave distance meter (sensor) 2 Furnace lid 3 Electric furnace main body 4 Slag door 5 Upper electrode 6 Elevating device of 5 7 Hearth refractory 8 Hearth bottom electrode 9 Feeder 10 Transformer 11 Thyristor 12 Slag pot 13 Outflow slag 14 Formed Slag 15 Blowing pipe for carbon powder, etc. 16 Carbon powder, aluminum ash dispenser blowing hopper 17 Blowing hose 18 Molten steel 19 Arc 20 Drain outlet 21 Data processing unit 22 Hopper open / close valve

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21C 5/52

Claims (2)

(57) [Claims] In an operation of an electric furnace for refining steel while forming slag on a steel bath surface, a distance from above the electric furnace to a slag surface is measured,
Arc measured by the measured forming slag height
Operation of an electric furnace characterized by automatically adjusting the oxygen gas injection speed and the carbon or aluminum powder injection speed so as to match the target value of the length, and operating by covering the electrode arc with slag. Method. 2. The method for operating an electric furnace according to claim 1, wherein the distance to the slag surface is measured by a microwave distance meter.