JPS6119909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slag melting furnace and a melting method.

Slag produced in melting furnaces and the like is non-conductive once solidified. This kind of solidified slag can be heated and melted using a gas burner or the like, but this method has problems such as it takes time to melt the slag and the working efficiency is low.

The main object of this invention is to provide a slag melting furnace that can electrically melt solidified slag at high speed and with high efficiency.

In order to electrically melt this type of slag, there are various problems to be solved as listed below.

In other words, since slag has a high specific resistance in a solidified state, it is difficult to start melting it electrically. One possible method is to make a seed bath and add slag to dissolve it.

However, when metal is used as a starting material, there is a problem that the resistance is low, so unless a large current is applied, sufficient power cannot be obtained to obtain the seed water.This requires a large-capacity power source and takes a long time to start. become longer. Furthermore, when metal is used as a starting material, it does not disappear after melting but remains in the molten metal in a layer, so current tends to flow through that metal layer even after starting, making it difficult to obtain large input power. . Moreover, the metal remaining in the molten metal becomes an obstacle when recycling the slag.

On the other hand, when electricity is applied to the slag via an electrode and melting is progressed by the Joule heat generated by the electricity, as the resistance between the electrodes decreases due to an increase in the amount of melted slag, the power that can be supplied to the slag decreases. However, there is a problem that the desired dissolution cannot be achieved.

In addition, this type of slag contains a large amount of calcium oxide (CaO), so the refractory that makes up the crucible that stores the slag needs to be refractory to the melting temperature of 1500Ω and 1700℃, and must be made of a material with high basicity. The crucible must have high melting resistance, and it must also be easy to construct a furnace.

The refractories used in various conventional melting furnaces include (1) high MgO monolithic refractories, (2) zirconia electroformed bricks, and (3) MgO electroformed bricks.

However, high MgO monolithic refractories are subject to extreme erosion. In addition, electroformed bricks are zirconia-based, MgO
It is thought that the system also has high resistance to erosion, but
It is difficult to form it into a crucible shape. Furthermore, when using small molded bricks, it is difficult to build a furnace, and the joints become weak points, causing selective erosion.

This invention has been made in consideration of the various points mentioned above, and aims to provide a relatively inexpensive slag melting furnace and melting method that can melt slag at high speed and has a long life. This is the purpose.

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

In FIG. 1, 1 is a slag melting furnace main body, 2 is a crucible for storing and melting slag, and this crucible 2 is made of carbon bond graphite and has a cylindrical shape, as will be described later, and an opening 3 at the top thereof. Hafuta 4
It is closed so that it can be opened and closed freely. The outer periphery of the body and the outer bottom surface of the crucible 2 are covered with a back lining 5 made of an amorphous refractory material, and a water cooling coil 6 having a passage 6a for cooling water is further wound around the outer periphery. The water cooling coil 6 also serves as an induction heating coil as will be described later. The crucible 2 is supported by an outer frame 7 of the furnace body via a back lining 5.

With the above configuration, by passing water through the water cooling coil 6, the heat of the crucible 2 is transferred to the water cooling coil 6 via the back lining 5, thereby cooling the crucible and removing cracks generated in the crucible 2. When hot water is generated in the crucible 2 due to such reasons, this back lining 5 prevents the molten metal from seeping out.

By constructing the crucible 2 from carbon bond graphite, durability (erosion resistance) is increased,
Even when melting slag at high temperatures, the crucible is hardly damaged by melting. Moreover, it is easy to mold and construct the crucible 2, and the manufacturing cost is also low.

The reason why graphite-based refractories are highly durable against slag is that when slag melts, the atmosphere becomes reducing, making it difficult for the chemical reaction 2C + O ₂ → CO → CO ₂ to occur. This is because graphite-based refractories are resistant to relatively high basicity molten metals.

A pouring port 8 is provided in the upper part of the crucible 2, and by tilting the melting furnace body 1 as appropriate,
The hot water in the crucible 2 is poured out from a pouring port 8.

Reference numerals 10a, 10b, and 10c are three-phase rod-shaped melting electrodes, and each electrode 10a, 10b, and 10c is attached to an electrode holder 11 whose details are shown in FIGS. 2 and 3 so as to hang in parallel. and is suspended into the crucible 2 through a long hole 12 (FIG. 3) opened in the lid 4.

The electrode holder 11 is mounted on a substantially circular substrate 13, with guide plates 14a and 1 bent at 120 degrees, respectively.
4b, 14c are fixed symmetrically with respect to the center with a predetermined distance D between them, and each guide plate 14a, 14b, 1
Y-shaped guide passage 15 formed by 4c
Electrode support plates 16a, 16b, 16c made of an insulator are slidably fitted to a, 15b, 15c.

Adjustment bolts 18a, 18b, 18c are inserted through screw holes into adjustment plates 17a, 17b17c, which are fixed upright at the outer ends of each guide plate 14a, 14b, 14c, and these adjustment bolts 18a,
The tips of 18b and 18c are connected to each electrode support plate 16a,
The electrode support plates 16a, 16b, 16c are rotatably engaged with the rear ends of the electrode support plates 16b, 16c, and can be adjusted by turning the adjusting bolts 18a, 18b, 18c.
are moved along the guide passages 15a, 15b, 15c to change the spacing between the electrodes 10a, 10b, 10c.

On the other hand, the board 13 is inserted through three guide bars 19a, 19b, and 19c set upright on the lid 4, and a shackle 20 fixed to the lid 4 is inserted into the board 13.
By moving the hanger 31 up and down by the rotation of the electric hoist 33, the electrode holder 11 is moved up and down, and each electrode 1
The immersion depth of 0a, 10b, and 10c into the slag can be adjusted.

On the other hand, the guide bars 19a, 19b, 19c
Large diameter locking pieces 21a, 21b, 21c are provided at the upper end of the
is fixed, and when the electrode holder 11 is lifted up to a predetermined height, the substrate 13 of the electrode holder 11
When the upper surface of the electrode holder 11 is engaged with the locking pieces 21a, 21b, and 21c and the electrode holder 11 is further lifted, the lid 4 is also lifted at the same time.

Each electrode 10a, 10b, 10c is connected to a water-cooled cable 40 through appropriate terminals, and this cable is connected to a water-cooled cable 40 through a current limiting reactor 41 and a main contactor 42 as shown in FIG. It is connected to a transformer 43 that outputs alternating current.

In FIG. 4, 44 is a voltmeter that indicates the power supply voltage, 45 is a voltmeter that indicates the voltage of the electrodes 10a, 10b, and 10c, and 46 is an ammeter that is supplied to the electrodes.

Reference numeral 50 denotes a hot water leak detection unit, which detects hot water leakage by detecting the voltage between an electrode 51 provided at the bottom of the crucible 2 and a coil 52 provided around the crucible 2 using a detection circuit (not shown). do.

When melting slag in the melting furnace configured as described above, first, the lid 4 is pulled upward by the overhead crane 30, the upper part of the crucible 2 is appropriately opened, and a small amount of slag is melted through this opening. and graphite are sequentially introduced as starting materials to form a layer of slag and a layer of graphite. The thickness of the layer at the start is, for example, about several tens of millimeters. Alternatively, slag and graphite may be mixed and placed in the crucible 2.

Next, rotate the electric hoist 33 and
At the same time, lower the hanger 31 and move the electrode holder 11 onto the guide bar 1.
The height of the electrodes 10a, 10b, 10c is set so that the lower ends of the electrodes 10a, 10b, 10c are embedded in the graphite layer by lowering the electrodes 9a, 19b, 19c while guiding them.

If crucible 2 is conductive, electrodes 10a, 10b, 10 are used to prevent short circuit currents through the crucible.
The electrodes 10A, 10B, 10C are set to be in contact with or close to the inner surface of the crucible 2 if the crucible is non-conductive. This electrode position can be set by rotating the adjustment bolts 18a, 18b, and 18c to change the protrusion length toward the center of the crucible.
The electrode support plates 16a, 16b, 16c are connected to the guide plate 14.
This is done by moving along lines a, 14b, and 14c. Note that the electrodes 10a, 10b, and 10c are set symmetrically with respect to the center of the crucible 2.

After setting the electrode position and height as above,
The main contactor 42 is turned on, and each electrode 10a, 10
Commercial three-phase AC is supplied between b and 10c. As a result, a short circuit current flows between each electrode through the graphite layer of low resistance, and the graphite evaporates and melts due to the Joule heat, and the slag is also melted by the heat generated. The current then flows through the melted slag and stabilizes at a steady current value.

Once the seed water is produced in the crucible 2 as described above, the main contactor 42 is once cut off, the lid 4 is opened, and an appropriate amount of slag is added. and,
The height of the electrodes 10a, 10b, 10c is adjusted by raising the hanger 31 of the overhead crane 30 so that the tip of each electrode 10a, 10a, 10c is embedded in the slag by about 50 mm to 500 mm.

Then, the main contactor 42 is turned on again, and electricity is applied between each electrode to melt the additionally charged slag. Thereafter, the above-described operation is repeated to dissolve a predetermined amount of slag.

As described above, when a layer of graphite is used as a starting material and a current is passed through it, conductivity can be obtained even at a lower voltage than when a mixture of graphite and slag is used. In addition, the current is lower than when metal is used as the starting material, and the starting current is close to the steady current, so sufficient power can be obtained to make the seed water, so the power supply capacity can be small, and starting control is easy to perform. .

In the above process, the melted graphite combines with oxygen and disappears at high temperatures, so the resistance of the molten metal is not lowered more than necessary during melting. Therefore,
This prevents the problem of a decrease in input power due to a decrease in interelectrode resistance after graphite and slag are melted.

The power input to the melting furnace is
It can be adjusted by changing the distance between b and 10c and the immersion depth into the molten metal.

Note that, as in the above-mentioned embodiments, by using a three-phase electrode as the heating electrode, the molten metal can be stirred. That is, as shown in FIGS. 5 and 6, the stirring force between the magnetic flux _A and the current ibc flowing between the electrodes 10b and 10c is generated by the current flowing between adjacent electrodes, for example, the current iab between the electrodes 10a and 10b. f _c occurs. This force f has a larger value as it is closer to the electrode. Due to this force distribution, the sixth
Stirring forces are generated as shown by f _a , f _b , and f _c in the figure. By applying such stirring force, the slag is stirred, uniformly heated, and melted.

Note that the stirring force can be adjusted by changing the radius of the electrodes 10a, 10b, and 10c.

On the other hand, by passing water through the water cooling coil 6 while the above-mentioned slag is being melted, the heat generated outside the crucible 2 is absorbed by the water cooling coil through the back lining 5, resulting in an unnecessary rise in temperature. to prevent

By cooling the outer periphery of the crucible 2 with water in this manner, the thermal shock from the slag to the crucible 2, that is, the high-temperature refractory, can be alleviated, and the life of the high-temperature refractory can be extended.

Further, even if a crack occurs in the crucible 2 and the crucible 2 is poured, the flowing molten metal is solidified in a short period of time due to the water cooling effect described above, so that the progress of the pouring can be completely prevented. Since the molten metal is inorganic, the solidified portions behave like refractories, which helps improve safety.

In the above-mentioned melting process, each electrode 10a, 10
If the heights of electrodes b and 10c are kept constant regardless of the amount of slag, as the amount of molten metal increases, the height of electrodes 10c will increase.
The immersion depth of a, 10b, and 10c into the molten metal increases and the resistance between each electrode decreases, so the power input to the melting furnace decreases and the melting efficiency decreases. However, according to the present invention, as the amount of slag introduced increases, the electrodes 10a, 10b, 1
By increasing 0c and limiting the immersion depth of each electrode into the molten metal, the inter-electrode resistance is maintained at an optimal value, and the power input to the melting furnace is maintained at an optimal value (maximum value). Slag can be efficiently dissolved.

After a predetermined amount of slag has been melted, the temperature begins to rise, but in order to maintain the power input to the melting furnace at approximately the same value as during melting, the depth of immersion of the electrodes 10a, 10b, and 10c into the melting process must be adjusted. It is sufficient to maintain the same depth as the melting depth. On the other hand, in order to equalize the temperature of the molten metal,
The electrodes 10a, 10b, and 10c may be lowered to near the bottom of the furnace.

After the temperature rise is completed, the hanger 31 of the overhead crane 30 is raised and the electrodes 10a, 10b, 10
c is removed from the melting furnace together with the electrode holder 11.

At that time, the board 13 is
Locking pieces 21a, 21 provided at the upper ends of b, 19c
b, 21c. When the hanger 31 is further raised, the lid 4 is also pulled up. By rotating the cantilever 32 of the overhead crane 30, the electrodes 10a, 10
b, 10c, and lid 4 are both removed.

In the above-described embodiment, the electrode height can be automatically controlled by a configuration as shown in FIG. 7 in order to keep the input power constant.

That is, the current detector 60 detects the electrodes 10a, 10b, 1
0c is detected, and the difference between the detected current and the setting value set by the setting device 61 is calculated by the operational amplifier 6.
2, and according to the deviation, the electrode lifting device 6
3 to control the electrode height and maintain the input current at the set value.

In the embodiments described above, the slag may be, for example,
Blast furnace slag or converter slag whose main component is SiC ₂ , CaO or Al ₂ O ₃ , and the melting temperature is 1500 ~
The electrical specifications of the melting furnace are 1700℃, Furnace capacity 600Kg Furnace power nominal 220KW (maximum 350KW) Furnace voltage 220V Frequency 60Hz Number of phases 3 phases Furnace current 1850A maximum.

Next, a case where the melting furnace shown in FIG. 1 is used as an induction heating furnace will be described.

The water cooling coil 6 is wound around the outer periphery of the crucible 2 in a coil shape.
By passing a current (60 Hz) or high frequency (500 to 3000 Hz), an induction magnetic field is generated in the crucible 2 and a conductor such as metal can be heated.

As detailed above, according to the present invention, slag, which is non-conductive in a solidified state, can be electrically melted using a pair of electrodes, so compared to the case where slag is melted with a gas burner, etc. High efficiency and improved workability.

Further, according to the present invention, a graphite-based material and slag are placed in a crucible as a starting material for slag melting, and an electrode is embedded in the starting material and electricity is applied to melt the graphite-based material and melt the seed liquid. , the melting of the slag can be started at high speed and with relatively low power, and therefore the melting of the slag can be performed with high efficiency.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the slag melting furnace of the present invention, Fig. 2 is a plan view showing the detailed structure of the electrode holder in the embodiment of Fig. 1, and Fig. 3 is a - 4 is an electric circuit diagram of the embodiment shown in FIG. 1, FIGS. 5 and 6 are diagrams illustrating the stirring force generated in the molten slag, and FIG. 7 is a block diagram showing the automatic current adjustment device. It is a diagram. 1... Melting furnace body, 2... Crucible, 3... Opening, 4... Lid, 5... Cross lining, 6...
...Water cooling coil, 7...Outer frame, 8...Pouring spout, 10
a, 10b, 10c... electrode, 11... electrode holder, 12... long hole, 13... substrate, 14a, 14
b, 14c... Information board, 15a, 15b, 15c
...Guidance passage, 16a, 16b, 16c...Electrode support plate, 17a, 17b, 17c...Adjustment plate, 1
8a, 18b, 18c...adjustment bolt, 19a,
19b, 19c...guide bar, 21...locking piece, 30...overhead crane.

Claims (1)

[Claims] 1. A crucible that accommodates slag, a lid that can open and close the upper opening of the crucible, a plurality of electrodes that are inserted into the crucible so that they can be raised and lowered, and a refractory material that surrounds the outer periphery of the crucible. A slag melting furnace comprising: water cooling means surrounding the outer periphery of a refractory material; a lifting device for lifting and lowering the plurality of electrodes; and a power source for supplying electric power to the electrodes. 2. A slag melting furnace according to claim 1, in which the crucible is made of a carbon bond graphite material. 3. A slag melting furnace according to claim 1, in which the plurality of electrodes are movable in the diametrical direction of the crucible and the electrode spacing can be adjusted. 4. The slag melting furnace according to claim 1, which has three electrodes arranged symmetrically to supply three-phase alternating current. 5. The slag melting furnace according to claim 1, wherein the water cooling means is a tubular conductor having a passageway wound into a coil, and also serves as an induction heating coil. 6. A slag melting furnace according to claim 1, in which the electrode and the lid are interlocked so that the lid opens when the electrode is raised from the crucible by a predetermined height. 7. Spread a predetermined amount of slag and graphite-based material as a starting material in a crucible, insert multiple electrodes into the starting material, and heat the starting material by supplying a predetermined amount of power to the starting material through each electrode. A slag melting method characterized in that after melting a system material to create a seed water, a predetermined amount of slag is added and the slag is melted. 8. The slag melting method according to claim 7, wherein the starting material is slag and graphite-based material laid in separate layers. 9. The slag melting method according to claim 7, in which the electrode is raised each time slag is added to control the length of the electrode immersed in the molten metal. 10. The slag melting method according to claim 7, in which the supplied power is kept constant by controlling the length of the electrode immersed in the molten metal. 11. The slag melting method according to claim 7, wherein the supplied power is commercial three-phase alternating current.