JP2946619B2 - Bottom electrode of DC arc furnace - Google Patents

Description

The present invention relates to a bottom electrode of a DC arc furnace used for melting and refining.

[Conventional technology]

The bottom electrode of a DC arc furnace is, for example, in the case of a steelmaking furnace,
Exposed to severe temperature conditions and thermal stresses due to contact with the molten metal reaching 1600-1800 ° C. and due to the Joule heat due to the high density current flowing through the electrodes. For this reason, it is necessary to surely cool the furnace bottom electrode so that the electrode rod, which is a main constituent member of the furnace bottom electrode, is worn and excessively melted and the molten metal does not leak. As a method of cooling the furnace bottom electrode with water,
For example, as disclosed in Japanese Patent Publication No. 63-43675, an electrode rod projecting downward from the furnace bottom is surrounded by a copper sleeve with a gap, and a spiral groove is provided on the outer periphery of the copper sleeve. There is a method of cooling the copper sleeve by forcibly flowing cooling water.

However, in this water cooling method, the cooling water flows along the cooling surface, so that the cooling effect is inferior. In order to obtain a predetermined cooling effect, the above-mentioned groove has a small cross-sectional shape and, for example, 6 to 10 kg / cm ² It was necessary to supply cooling water of about high pressure to perform cooling by high-speed water flow. For this reason, a very large amount of cooling water is required.In addition, when cracks due to fatigue failure occur in the copper sleeve due to repeated thermal cycling due to the operation of the furnace, the high-pressure cooling water is ejected to the inside of the furnace. Could cause a serious accident such as a steam explosion. Further, it is difficult to control the degree of cooling by this cooling method even if the amount of flowing water is adjusted.

[Problems to be solved by the invention]

The present invention solves the above-mentioned conventional problems, and is directed to a DC arc furnace in which an electrode rod is efficiently cooled by a small amount of cooling water, and a steam explosion accident can be prevented by suppressing injection of cooling water into the inside of the furnace. It is intended to provide a furnace bottom electrode.

[Means for solving the problem]

Thus, the furnace bottom electrode of the present invention, in a refractory constituting the furnace bottom, in a state where the top surface is exposed in the furnace and the lower part protrudes outside the furnace, the electrode rod is embedded, the lower side of the electrode rod, A spray nozzle, which is surrounded by a hollow ring-shaped water-cooling case whose inner wall faces the lower side surface with a gap therebetween and has a spout facing the inner wall and connected to a cooling water supply source, Disposed in the lower part of the water-cooled case, a drain port is provided, and the drain port is connected to a drain means, and a current-carrying terminal is directly connected to a lower end of the electrode rod. It is a furnace bottom electrode.

It is preferable that at least the inner wall of the water-cooled case according to the present invention is made of a material having excellent thermal conductivity such as copper.

As the spray nozzle in the present invention, any of a water spray nozzle in which only water is ejected from the ejection port and a water-water spray nozzle in which water and air are ejected from the ejection port may be used.

In addition, as the drainage means in the present invention, various drainage means such as a jet pump using a bench lily mechanism using water or steam as a driving fluid, in addition to a drainage means of a natural drainage type such as a drainage pipe having an open end in a drainage groove. Drainage means of a system for forcibly draining water by a pump can be used.

In the present invention, the length of the electrode rod surrounded by the water-cooling case is preferably in a range of 0.5 to 2 times the diameter of the electrode rod.

[Action]

In the furnace bottom electrode according to the present invention, the lower side surface of the electrode rod comes into contact with the inner wall surface of the water-cooled case due to thermal expansion accompanying the energization of the electrode rod. The inner side wall of the water-cooled case is cooled by water or air-water spray from a spray nozzle provided inside, so that the lower side surface of the electrode rod is heat-removed through the inner side wall. In the above-mentioned water or air-water spray cooling, since a small droplet of the cooling water collides with the surface to be cooled to perform heat exchange, the heat transfer coefficient is smaller than that of the through-water cooling for the same cooling water flow rate. Since it shows a high value of 2-3 times,
During operation, the electrode rod is efficiently cooled, and the temperature rise is suppressed. Also, when rapid cooling of the bottom electrode between the operation of the furnace is not desirable, by reducing the amount of spray water or adopting water spray by gas (air-water spray),
The cooling intensity can be controlled. Also, the cooling water after cooling is drained by drainage means from the drain port at the bottom of the water cooling case,
It hardly stays in the water cooling case. For this reason, even if the molten metal or the electrode rod melt enters the water-cooled case, there is no possibility of causing a steam explosion as in the case of water-flow cooling. Also, even if a crack due to thermal fatigue etc. occurs in the water cooling case,
Since the pressure inside the water-cooled case is atmospheric pressure, there is no risk of causing a steam explosion accident due to the ejection of high-pressure water to the inside of the furnace as in the case of water-flow cooling, and the safety is high.

Also, during the furnace operation, the electrode rods are melted from the inside of the furnace to the position of the dimension L from the upper surface of the water-cooled case as shown by a chain line 50 in FIG. If the length B (≒ the height of the water-cooled case) of the electrode rod in the portion surrounded by the case is too small, the dimension L becomes too small, and the melting position approaches the water-cooled case, which is dangerous. However, the L dimension does not exceed a certain value, and the hearth space is undesirably large. FIG. 3 is a diagram in which the test results of the inventor are arranged. When the diameter of the electrode rod is D, the length B of the cooled part of the electrode rod is 0.
5D or more is sufficient, and even if it is 2D or more, the increase in L is small, so that 0.5D ≦ B ≦ 2D is preferable.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

In the figure, reference numeral 1 denotes a furnace bottom of a DC arc furnace, 2 denotes a refractory, and 3 denotes a furnace shell. Reference numeral 4 denotes a furnace bottom electrode, in which the middle or upper part of an electrode rod 5 made of an iron rod is embedded in the refractory 2, the lower side surface 5 a of the electrode rod 5 is surrounded by a water-cooled case 6, and the lower end of the electrode rod 5 An energizing terminal 9 is directly connected to 5b by a bolt 8. The top surface 5c of the electrode rod 5 is exposed in the furnace. The water-cooling case 6 has a hollow annular shape having a substantially square cross section, and has a copper inner annular body 10 having an inner side wall 10a and an upper side wall 10b.
And an outer annular body 11 made of heat-resistant steel comprising an outer wall 11a, a lower wall 11b, and a flange 11c, and integrally connected by bolts 14 via seal rings 12, 13. Flange part 11c
Is supported by the steel shell 3 via the insulator 15. A clearance s corresponding to the amount of thermal expansion of the electrode rod 5 up to a predetermined temperature (for example, 700 to 800 ° C.) is provided between the inner side wall 10a and the lower side surface 5a of the electrode rod 5. Reference numeral 16 denotes a bolt connecting the energizing terminal 9 and the outer annular body 11. Reference numeral 21 denotes a water supply channel provided along the inner periphery of the outer wall 11a, and a spray nozzle 22 having a jet port facing the inner wall 10a,
In addition, a spray nozzle 23 having a jet port facing the upper side wall 10b is provided. Reference numeral 24 denotes a water supply port communicating with the water supply passage 21, and reference numeral 25 denotes a water discharge port provided at a lower portion of the water cooling case 6, which is connected to drainage means (not shown) including a jet pump using water or steam as a driving fluid. .

On the other hand, a water-cooling type water-cooled box 26 is attached to the lower surface of the attachment portion of the energizing terminal 9 to the electrode rod 5 with a bolt 8, a water supply port 27 is connected to a cooling water supply source, and a drain port 28 is provided. The connection pipe 29 is connected to the water supply port 24 of the water supply path 21.

In the furnace bottom electrode 4 having the above-described structure, when the electrode rod 5 is heated to, for example, about 700 to 800 ° C. by the contact with the Joule heat and the molten metal due to the arc current, the lower part of the electrode rod 5 due to the thermal expansion of the electrode rod 5. The side surface 5a is the inner wall 10a of the water-cooled case 6.
The inner wall surface 10a expands and contracts almost integrally with the electrode rod 5 at a temperature higher than that. The cooling water supplied to the water supply channel 21 from the cooling water supply source via the water-cooled box 26 is jetted from the spray nozzles 22 and 23 and
a and the upper side wall 10b, so that the lower side
5a is efficiently cooled by heat removal through the inner wall 10a. In addition, the cooling water flowing through the water-cooled box 26 allows for
And the lower end surface of the electrode rod 5 is cooled. The spray-cooled cooling water spouted from each spray nozzle in the water-cooled case 6 is drained from the water-cooled case 6 through the drain 25 through the drainage means, so that the water hardly stays in the water-cooled case 6. Absent.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the water supply passage 21 is connected to the cooling water supply via the water-cooled box 26, but may be directly connected to the cooling water supply. Further, since the lower end surface of the electrode rod 5 is relatively low in temperature, the water-cooled box 26 may be omitted.

〔The invention's effect〕

As described above, according to the present invention, since the lower side surface of the electrode rod is spray-cooled through the inner wall of the water-cooling case, the electrode rod can be efficiently cooled with a small amount of water as compared with water-flow cooling. . Also, since the cooling water hardly stays in the water-cooled case and the inside of the water-cooled case is at atmospheric pressure, even if the molten metal or electrode melt enters the water-cooled case or cracks occur in the water-cooled case, the water High safety with no risk of explosion.

[Brief description of the drawings]

1 is a longitudinal sectional view of a furnace bottom electrode showing one embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. 3 is a length of a cooling portion of the electrode rod of FIG. FIG. 3 is a diagram showing the relationship between the electrode rod non-dissolution length. DESCRIPTION OF SYMBOLS 1 ... Furnace bottom, 2 ... Refractory, 4 ... Furnace bottom electrode, 5 ... Electrode bar, 5a ... Lower side surface, 6 ... Water-cooled case, 9 ... Current-carrying terminal, 10a ... Inner wall, 21 … Water supply channel, 22… spray nozzle, 24… water supply port, 25… drainage port.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F27B 3 / 08,3 / 24 F27D 11 / 08,11 / 10 H05B 7/12

Claims (2)

(57) [Claims] An electrode rod is buried in a refractory constituting a furnace bottom with a top surface exposed in the furnace and a lower part protruding outside the furnace, and a lower side surface of the electrode rod is inserted inside the lower side surface. A spray nozzle, which is surrounded by a hollow annular water-cooling case whose walls oppose each other with a gap, and has a discharge port facing the inner wall and is connected to a cooling water supply source, is disposed in the water-cooling case. A bottom electrode of a DC arc furnace, wherein a drain port is provided at a lower portion of the water-cooling case, and the drain port is connected to a drain unit, and a current-carrying terminal is directly connected to a lower end of the electrode rod. 2. The bottom electrode of a DC arc furnace according to claim 1, wherein the length of the electrode rod in a portion surrounded by the water-cooling case is within a range of 0.5 to 2 times the diameter of the electrode rod.