JP2641913B2 - Operation method of DC arc furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of operating a DC arc furnace for controlling the position of a movable electrode (also called an arc electrode) of a DC arc furnace, and in particular, to increasing the temperature of a molten metal. The present invention relates to a method of operating a DC arc furnace for improving efficiency.

[Conventional technology]

Generally, when melting a solid metal such as iron scrap as a raw material for melting (hereinafter, referred to as scrap), the movable electrode 3 is moved up and down after charging the scrap 2 into the arc furnace 1 as shown in FIG. While controlling, a predetermined DC voltage is applied between the movable electrode 3 and the furnace bottom electrode 4 to generate an arc from the tip of the movable electrode, thereby melting the scrap 2. Then, when the scrap 2 charged for the first time is sufficiently melted as shown in FIG. 4 (b), a reloading step of charging the scrap 2 into the arc furnace 1 again is performed, and a predetermined amount of molten metal (hereinafter referred to as molten steel). 5)
The scrap loading step (initial loading step) and the scrap reloading step are repeated until a predetermined amount of molten steel is obtained. When the last loaded scrap 2 for obtaining a predetermined amount of molten steel is completely melted, the scrap is melted as shown in FIG. 4 (c). It falls. Thereafter, as shown in FIG. 4 (b), a refining process for controlling the temperature rise of the molten steel 5 is performed to adjust the components of the molten steel 5. When this refining process is completed, tapping of the molten steel 5 is performed and the operation is completed.

Reference numerals 6 and 7 denote a furnace lid, 7 a furnace wall water cooling panel, and 8 a slag.

Conventionally, when raising the temperature of molten steel 5 in the burn-through step and the refining step, etc., in an AC arc furnace, the voltage and current are set in advance, and the generated voltage and arc current between both currents 3 and 4 are set to the set voltage. A short arc is generated from the movable electrode 3 while raising and lowering the movable electrode 3 so as to reach the set current, the thickness of the slag 8 on the molten steel is increased, and the arc from the tip of the movable electrode 3 is inserted into the slag 8. So-called submerge operation to foam slag 8 is performed. Therefore, in this AC arc furnace, the above voltage and current are set from the relationship between the slag thickness and the arc length of the movable electrode 3, and this is a method for exclusively controlling the arc voltage constant.

By the way, as a result of examining the relationship between the position of the movable electrode and the voltage in the DC arc furnace, it was found that the characteristic pattern shown in FIG. In the figure, the horizontal axis represents the electrode position lg, and the vertical axis represents the voltage v generated between both electrodes. Therefore, as a result of repeated experimental studies on the above characteristic patterns, the electrode position
It was found that lg, the molten steel surface 5a, and the clag surface 8a had a positional relationship as shown in FIG. 5 and 6.
Are in correspondence. Among them, between −, the molten steel surface 5a is rapidly dented by the arc jet of the movable electrode 3, and the time order is about 1 second. The electrode lift distance at this time is about 50 mm.

On the other hand, between-, when the movable electrode 3 is pulled up due to the dent of the molten steel 5 by the arc jet, the rise of the electrode and the decrease in the dent of the molten steel surface 5a are offset, and the arc length is increased even if the movable electrode 3 is pulled up. Since the indentation does not increase and the dent of the molten steel becomes small, the generated voltage does not increase, and only the voltage fluctuation is caused by the fluctuation of the dent of the molten steel. In consideration of the relationship between the molten steel 5, the movable electrode position lg, the arc, and the like, the heat-up heat efficiency and the slag metal reaction, etc. are examined during this period. In particular, it has been found that the electrode position control in the vicinity is better. It should be noted that between-is the molten steel surface
5a hardly changes, and a voltage corresponding to the arc length is generated.

[Problems to be solved by the invention]

Therefore, in a DC arc furnace using a large current arc, voltage and current are set from the slag thickness and the arc length as in a conventional AC arc furnace, regardless of having the above characteristic patterns, and these are set. When the constant arc voltage control is performed based on the set value, as described above,
There is a problem that the voltage is not changed even if the position of the movable electrode is changed at the dent portion of the molten steel 5 due to the arc jet between them, so that the state becomes completely uncontrollable, and the temperature rise of the molten steel 5 cannot be efficiently controlled in an optimum state. In addition, in the state, the radiant heat from the arc is directed to the furnace wall and the like, so that there is a problem that the temperature rising efficiency of the molten steel is lower than in the state.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and aims to reduce the refining power and shorten the refining time by improving the efficiency of raising the sound of molten steel in the heating and refining process of a molten steel in a DC arc furnace. Accordingly, it is an object of the present invention to provide a method of operating a DC arc furnace in which heat loss to a furnace wall is reduced, and molten steel having a required temperature and composition is obtained by improving stirring of molten steel and slag.

[Means and actions for solving the problem]

The operation method of the DC arc furnace according to the present invention, in order to achieve the above object, with a point where the movable electrode is in contact with the molten steel surface as a reference point, determine in advance the relationship between the position of the movable electrode and the potential of the movable electrode, Point A is a point at which the potential of the movable electrode suddenly rises with respect to the rise and then the change is temporarily small.
Thereafter, when the point at which the potential of the movable electrode starts to rise again with the rise of the movable electrode is point B, the potential of the movable electrode becomes a set potential equal to or higher than the potential of the movable electrode corresponding to the point B in the process of melting the scrap. Control the position of the movable electrode
On the other hand, in the process of raising the temperature of the molten steel, in the refining process, and the like, by controlling the position of the movable electrode so that the position of the movable electrode is at the intermediate position between the points A and B, the temperature rise of the molten steel is increased, and , To control the slag metal reaction to an optimal state.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of an electrode lifting and lowering control system of a DC arc furnace to which the method of the present invention is applied. In the DC arc furnace, in particular, the same parts as those in FIG. Description is omitted. First, means for applying voltage to the DC arc furnace includes a furnace transformer 11 for transforming an AC voltage into a predetermined voltage, and a thyristor AC / DC converter 12 for transforming the AC voltage transformed by the furnace transformer 11 into a DC voltage.
The negative side of the DC voltage converted by the thyristor AC / DC converter 12 is connected to the movable electrode 3 via the smoothing reactor 13, while the positive side is connected to the furnace bottom electrode 4. Then, a voltage is applied so that a predetermined arc current (for example, 40 KA) flows between the movable electrode 3 and the furnace bottom electrode 4, and the position of the desired movable electrode 3 is always controlled.

The position control of the movable electrode 3, particularly the electrode position control means when the scrap 2 is melted, includes a generated voltage detector 21 for detecting a voltage between the electrodes 3 and 4, and a voltage setter 22 for setting a predetermined voltage in advance. And a subtractor 23 for calculating a deviation between the set voltage of the voltage setting device 22 and the generated voltage from the generated voltage detector 21. A solid line shown in the drawing when the scrap 2 is melted, that is, when the scrapping process is performed from the initial load. It is closed as follows,
A switch 24 that is closed to the position shown by the dotted line during the refining process,
A speed set value controller 25 for performing a proportional / integral operation to obtain a speed set value (absolute value) such that a voltage deviation input from the subtractor 23 via the switch 24 becomes zero, and the like; Further, an up / down switching circuit 26, a speed controller 27, an electrode lifting / lowering control motor 28 driven and controlled by an output of the speed controller 27, and the like are provided.

The up / down switching circuit 26 receives the speed set value from the speed setting controller 25, and adds a positive or negative polarity to the speed set value according to the positive / negative polarity of the voltage deviation to raise or lower the moving speed. It has a function to output command values.

The electric motor 28 rotates the winch 31 while rotating forward or backward according to the output of the speed controller 27 to wind or rewind the other end of the wire 32 having one end as a fixed end.
The mast 34 is moved up and down via a pulley 33 and the movable electrode 3 is controlled to move up and down via a horizontal arm 34.

Next, the electrode position control means of the movable electrode 3 in the molten steel temperature raising and refining process includes an electrode position sensor 41 for detecting the movable electrode position.
And the movable electrode 3 sent from the electrode position sensor 41
A molten steel contact position detection circuit 42 which takes in and stores the molten steel contact position detected value of the above, and a relationship between the movable electrode position and the potential of the movable electrode 3 is previously obtained based on the arc current, and based on the molten steel contact position detected value. Electrode raising position calculating means 43 for determining the optimum electrode raising position by using a subtractor 44 for calculating a deviation between the optimum electrode raising position obtained by the calculating means 43 and the current electrode position from the electrode position sensor 21. The deviation signal obtained by the subtractor 44 is supplied to the speed setting controller 26 via the switch 24.

Next, the operation of the electrode lifting / lowering control system configured as described above will be described. After the scrap is charged into the arc furnace 1 and the furnace lid 6 is closed, the movable electrode 3 is inserted through the furnace lid 6, a predetermined voltage is applied between the movable electrode 3 and the furnace bottom electrode 4, and the movable electrode 3 is moved from the tip of the movable electrode. Scraps are sequentially melted while generating an arc. The melting of the scrap is performed during the operation process of the DC arc furnace, in particular, a start-up process, a boring process, a stabilization process, a shelf drop process, a reloading process for reloading the scrap, etc. immediately after charging the scrap.

When the scrap is melted, the switch 24 is automatically or manually closed to the solid line side in the drawing, and the characteristic between B and D in the characteristic pattern (similar pattern in FIG. 5) shown in FIG. The movable electrode 3 is controlled to move up and down while assuming the following.

Specifically, after a generated voltage between the two electrodes 3 and 4 that changes according to the arc length of the movable electrode 3 is detected by the generated voltage detector 21, a deviation signal between the generated voltage and the set voltage of the voltage setting unit 22 is detected. When the speed is supplied to the speed setting controller 25 through the switch 24, the speed setting controller 25 performs a proportional / integral operation so that the deviation signal becomes zero to obtain a speed set value. Supply. Here, the up / down switching circuit 26 adds the polarity of the deviation signal sent from the subtractor 23 and outputs a speed set value as a moving speed command value.
Upon receiving the moving speed command value, the speed controller 27 drives the electrode up / down control motor 28 to rotate in a required direction, and the movable electrode 3 is controlled to move up and down in the required direction according to the rotation direction of the motor 28. . When the scrap is melted, the movable electrode 3 is moved a predetermined distance from the molten steel surface, that is, between B and D in FIG. 2, so that the voltage changes according to the arc length. 3 is controlled to move up and down.

Next, in the molten steel temperature raising and refining process, the switch 24 is automatically or manually closed to the dotted line side in the drawing to control the raising and lowering of the movable electrode 3. In this control, the electrode position sensor 41
After the molten steel contact position detection value l ₀ of the movable electrode 3 sent from the controller is received and stored in the molten steel contact position detection circuit 42, the molten steel contact position detection value l ₀ is supplied to the electrode ascending position calculating means 43. The electrode elevation position calculating means 43 determines the optimum electrode elevation value △ l based on a desired arc current f (I) based on a characteristic pattern as shown in FIG. 2, that is, the relationship between the position of the movable electrode 3 and the potential of the movable electrode 3. because are determined, receives molten steel contacting position detection value l ₀ from the molten steel contacting position detecting circuit 42 when outputting a value obtained by adding the optimal electrode rising value △ l in the detected value l ₀ as the optimum electrode setting position l ₁ This is supplied to the subtractor 44. A deviation signal between the current position of the movable electrode 3 from the subtracter At 44 electrode set position l ₁ and the electrode position sensor 41, and supplies the speed setting controller 25. Therefore, based on the output of the speed setting device 25, an operation output is supplied from the speed setting device 27 to the electric motor 28, and the movable electrode 3 is moved to the electrode setting position l ₁ shown in FIG. Set near. As shown in FIG. 3, the positions of the electrodes are such that the jet arc from the movable electrode 3 passes through the slag 8 to form a dent in the molten steel 2, and heat flows from the side of the arc to the slag 8, and the slag metal Of the reaction is good.

Therefore, according to the configuration of the embodiment described above, the movable electrode is raised to a desired position on the basis of the molten steel contact position of the movable electrode 3 and the electrode rising position determined by the arc current during the heating and refining steps of the molten steel. Therefore, the temperature raising efficiency of the molten steel can be reliably increased, whereby the power consumption in the refining process can be improved and the refining time can be shortened.
In addition, it is possible to reduce the amount of oxygen and coal powder for slag forming, and it is possible to perform an appropriate stirring action by the arc jet of the movable electrode 3 as shown in FIG. The temperature and components can be made uniform, and a molten steel of uniform product can be obtained.

〔The invention's effect〕

As described above in detail, according to the present invention, the heating efficiency of molten steel is greatly improved by eliminating the constant voltage control during the heating and refining of molten steel and setting the position of the movable electrode to a desired optimum position. As a result, the refining power and the refining time can be reduced, and the required temperature and composition of the molten steel can be obtained by improving the stirring of the molten steel and the slag.

[Brief description of the drawings]

FIGS. 1 to 3 show one embodiment of a method of operating a DC arc furnace according to the present invention.
FIG. 2 is a diagram showing the configuration of an electrode raising / lowering control system to which the method of the present invention is applied. FIG. 2 is a diagram for explaining an optimum electrode setting position at the time of raising and refining molten steel. FIG. 4 to 6 are views for explaining a conventional method, FIG. 4 is a view for explaining a general operation process of a DC arc furnace, and FIG. 5 is an arc. Characteristic pattern diagram of electrode position and generated voltage at the time of current,
FIG. 6 is a diagram showing the relationship between each electrode position in FIG. 5, the molten steel position and the slag position. 1 ... arc furnace, 3 ... movable electrode, 4 ... furnace bottom electrode, 5
…… Molten steel, 8 …… Slag, 21 …… Generated voltage detector, 22…
... Voltage setting unit, 24 ... Switch, 25 ... Speed setting controller, 26 ... Up / down switching circuit, 27 ... Speed controller, 28
…… Electric lift control motor, 41 …… Electrode position sensor, 42
... Molten steel contact position detection circuit, 43... Electrode rising position calculation means, 44.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Shoichi Takahashi 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Toshimichi Maki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (72) Inventor Kinzo Okazaki 1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (56) References JP-A-49-121238 (JP, A) JP-A-52- 150311 (JP, A) JP-A-62-8496 (JP, A)

Claims (1)

(57) [Claims] 1. A DC arc furnace for melting a solid metal while controlling the elevation of a movable electrode, wherein a point at which the movable electrode is in contact with a molten metal surface is defined as a reference point.
Find the relationship between the position of the movable electrode and the potential of the movable electrode in advance,
The point at which the potential of the movable electrode suddenly rises slightly with respect to the rise of the movable electrode and temporarily changes slightly is set as point A, and then the potential of the movable electrode starts rising again with the rise of the movable electrode. When the point is point B, in the process of dissolving the solid metal, the position of the movable electrode is operated so that the potential of the movable electrode is equal to or higher than the potential of the movable electrode corresponding to the point B. The method of operating a DC arc furnace, wherein in the refining process, the position of the movable electrode is controlled such that the position of the movable electrode is at a position intermediate between the points A and B.