JP3483054B2 - DC electric melting furnace for the production of reduced molten slag. - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct current electric melting furnace for producing reduced molten slag, and more specifically to melting incinerated ash of domestic waste or industrial waste or sewage sludge dried powder and the like to produce incinerated ash. The present invention relates to an electric melting furnace which melt-reduces contained easily-reducible metal oxides and produces molten slag mainly composed of a mineral substance such as SiO ₂ . This is applied to a technique for producing artificial aggregate for concrete that is extremely close to natural sand, river gravel, etc. from molten slag.

[0002]

2. Description of the Related Art Domestic waste and industrial waste are incinerated, and sewage sludge, etc., is reduced to dry powder,
Discarded in landfills. However, there is a limit to the amount of dumped land, and it is becoming possible to further reduce the volume and reuse it as a resource. Recently, research has been advanced from the viewpoint of recycling resources, and composting and recovery of valuable materials have also been carried out. Although detoxification treatment is important for such recycling, the same applies to the case of recycling building materials and the like from the molten slag of incinerated ash, which has been receiving particular attention.

When incinerator ash is melted at a temperature of 1,500 ° C. or higher, harmful substances such as combustible substances and dioxins in the garbage are completely gasified and burned, and heavy metals are trapped in glassy slag. The advantage is that the volume of incinerated ash can be reduced to 1/3. This melts even the inorganic components in the incinerated ash to form a melt, which is disclosed in JP-A-3-27513.
This is because the solidified slag can be obtained by cooling it as described in Japanese Patent Laid-Open No.

By the way, the slag can be used as a roadbed material or an aggregate for building civil engineering, or can be processed into tiles and ornaments by molding. In any case, it goes without saying that detoxification and chemical stability are required, but various devices for producing such molten slag have been proposed. Typical examples include those using various furnaces such as a swirling melting furnace, a coke bed, a surface melting furnace, an arc furnace, and a plasma furnace.

[0005]

When an electric furnace is used to generate molten slag, the incineration ash has a large resistance at room temperature and is difficult to energize. However, when the incineration ash becomes high in temperature, The resistance decreases, and when melted, it becomes relatively conductive. When an electric current is applied to the melt, Joule heat is generated due to the electric resistance of the molten ash, which can be utilized. As an electric furnace used for such a melting process, there is a submerged arc electric furnace described later.

By the way, in the case of arc melting in an electric furnace, when an appropriate voltage is applied to an artificial graphite electrode thrust into the furnace, the electric arc flies from the tip of the electrode rod toward incinerated ash or slag, and other electrodes An electrical circuit is formed that leads to the rod and the preformed base metal. In this way, the device that generates the molten slag by arc heating with an electric furnace,
It is described in JP-A-4-354578. In this type of electric furnace, arc discharge is generally 3,000
The temperature is very high at 0 ° C to 5,000 ° C and high speed, and the heat transfer efficiency is high because it collides with the incineration ash and slag while drawing in the surrounding gas, and the incombustibles and metals in the incineration ash are short It can be melted. This has the advantage that it does not require auxiliary materials for adjusting the basicity or lowering the melting point, regardless of the composition of the incinerated ash, and exhibits a high volume reduction effect.

However, in such a conventional electric furnace, the slag outlet is always in an open state, and the slag outlet part is extremely worn out, and after a few months of operation, a repair suspension period of about one month is required. . Further, since the molten slag is continuously discharged, the iron oxide in the slag is set to 4% to 30%, or the molten slag is exposed to the atmosphere (oxidizing atmosphere). It does not come out. On the other hand, the above-described submerged arc electric furnace is intended to melt the slag by electric arc or electric resistance Joule heat in a state where the slag in the furnace is entirely covered with incinerated ash.

In most of the various melting methods using the swirling melting furnace and the like listed above, since the incineration ash is melted in the combustion gas, a large amount of gas is contained in the outflow slag. However, the submerged arc electromelting method has a great advantage that gas is hardly mixed in the molten slag and defoaming treatment is not required. When the slag discharged from the submerged arc furnace is gradually cooled to produce a sand-grained artificial aggregate, steps such as water cooling or slow cooling of the molten slag are performed. However, since the cooling progresses rapidly,
It becomes an amorphous material far from natural stone, and its use is limited. That is, it is difficult to obtain a high-quality artificial aggregate for concrete as a building material, and it is only possible to use it as a roadbed material or a material for green farmland that can be used even in an amorphous state.

By the way, in order to make the molten slag close to natural stone, the slag must be crystallized to strengthen the structure. For example, Japanese Patent Application Laid-Open No. 4-132642 describes a method of controlling the cooling rate of the molten slag so as to be changed for every several temperature ranges. further,
Japanese Patent Laid-Open No. 3-275539 discloses that crystallized slag is produced by adjusting the components of the molten slag and controlling the cooling rate. However, these have mineralogical questions, and because they are intended to contain harmful substances and metal components in the slag, it is necessary to abandon the collection of substances that can be reused if they can be separated in advance. There are drawbacks such as becoming slag and slag being far from natural stone.

By the way, garbage and sewage sludge are treated by each municipality. In other words, the principle is that collection, incineration, etc. are processed within the area and consumed within the area. Needless to say, the high-temperature treatment method is preferable to the low-temperature treatment method in which elution of heavy metals is inevitable for recycling the ash after incinerating such wastes, and the above-mentioned several melting treatment forms are adopted. On the other hand, it is inevitable that the amount of incinerated ash will vary greatly depending on the local government, but the amount of waste and sewage sludge to be treated should be balanced with the capacity of the incinerator and the amount of consumption within the area when reusing the recovered resources. There is a need. as a result,
In order to meet the processing capacity and consumption, it is often the case that the equipment for melting and slagging the incineration ash and the like generated from the incineration equipment in the area is small in capacity.

Electric furnaces include single-phase / three-phase AC electric furnaces and DC electric furnaces. In such an electric furnace, a furnace ceiling is indispensable for shutting off harmful gas generated from the charged raw material during operation from the outside air. Further, in order to realize the submerged arc electric melting method by additionally charging raw materials such as incineration ash sequentially during operation, a charging hole is provided in the furnace ceiling to enable charging of airtight powdery granular materials. At the same time, it is necessary to rotate the furnace roof or the furnace body to uniformly disperse the charged powder and granules.

However, in the three-phase AC electric furnace, the three fixed electrodes are present and the furnace ceiling cannot be rotated, and therefore the furnace body side is rotated.
However, the three-phase AC electric furnace tends to have a large furnace volume in consideration of the arrangement of electrodes, and as described above, it becomes an excessively large furnace body for melting incineration ash or the like having a small treatment amount. . Further, the melting zone formed under the electrode tends to be different for each electrode, and it is not easy to balance the melting. In particular, it is difficult to achieve the gentle reduction melting that is required when using a powdery material with low specific gravity and low electrical conductivity as a raw material, and as a result, the overall melting balance is disturbed and the generated molten slag becomes uniform. There is a difficulty that is difficult to achieve.

On the other hand, in the single-phase AC electric furnace, the AC power is always reciprocated, so that the heating of the raw material is localized. therefore,
There are drawbacks that it is not possible to gently reduce and melt a powder or granular material having a small specific gravity and a low electric conductivity, and it takes a long time for melting and it is difficult to obtain a uniform melting of raw materials. In addition,
The DC electric furnace has the advantages that it is easy to make the furnace small and the operation control is simpler than that of the AC electric furnace. However, since an arc is generated in the conductor fixed to the furnace body, local heating is likely to occur as in the case of the single-phase AC electric furnace. Therefore, it is possible to rotate the furnace ceiling or the furnace body during operation to charge the granular material while having the advantage of easily reducing the capacity of the furnace body and simplifying control. It is desired to introduce a DC electric furnace having a structure capable of achieving a quiet and uniform melting process by supplying a large electric power to the furnace floor to form a large melting zone.

The present invention has been made in view of the above-mentioned background, and an object thereof is to facilitate miniaturization suitable for melting a relatively small amount of incinerated ash or the like suitable for treatment / consumption within the own area. An electric melting furnace can be used, submerged arc electric melting can be realized that enables the charging of powdery and granular materials even during operation, and forming slag is constantly generated. It is an object of the present invention to provide a direct current electric melting furnace for producing reduced molten slag, which can keep the same potential level widely as much as possible.

[0015]

[Means for Solving the Problems] The present invention melts and reduces easily-reducible metal oxides such as Fe, Cr, and P from raw materials in which coke breeze is mixed with incinerated ash of garbage, dried powder of sewage sludge, and the like. The present invention is applied to a submerged arc electric melting furnace capable of producing molten pig iron and producing molten slag having a low gas content and containing SiO ₂ or the like as a main component.
The feature is that, with reference to FIG. 1, one movable electrode 21 is vertically inserted through the center of the furnace ceiling 20, while a fireproof wall and a fireproof bottom lined with an iron skin are provided. The L-shaped electrode 12 for supplying DC power along the horizontal portion 12
Plural y are arranged so as to be radial with respect to the center of the furnace body 10. The L-shaped electrode 12 is formed of a pure iron bar, and cooling water passages 12r and 12s through which cooling water flows are formed inside the vertical portion 12v. On the bottom of the furnace, a carbon stamp 1 made by arranging and crushing carbon powder so as to cover the horizontal portion 12y where the cooling water passage is not formed
3 is applied, and the graphite block 11 is installed on the carbon stamp 13 and inside the insulating fire wall covering the vertical portion 12v. The furnace ceiling 20 is provided with a plurality of raw material charging holes 23 opened at different radial positions from the movable electrode 21, and the raw material 4 is charged with the raw material 4 from the raw material charging holes 23.
A raw material charging device 22 for supplying the inside is installed. And
That is, there is provided a ceiling rotation device 24 for continuously rotating or swinging the furnace ceiling 20 horizontally on the furnace body 10.

Instead of the ceiling rotating device 24 described above, FIG.
It is also possible to provide a furnace body rotating device 51 for continuously rotating or swinging the furnace body 10 horizontally as shown in FIG.

As the raw material charging device 22, a screw feeder 22A (see FIG. 1) may be adopted.

Further, as shown in FIG. 6, the raw material charging device 22 may be a flexible closed type chute 28.

A guide member 29 (which extends downward into the raw material charging hole 23 to guide the raw material distribution charging in the circumferential direction of the furnace body 10 and which disperses the powdered and granular raw material accumulated in the furnace body 10 ( (See FIG. 8).

A raw material level detector 28A (see FIG. 6) is provided in the middle of the vertical extension of the flexible closed type chute 28.
When the detector 28A detects the stagnation of the raw material in the chute 28, a raw material quantitative cutting device 28B for stopping the feeding of the raw material to the closed type chute 28 is provided in the raw material storage bottle 26 connected to the chute 28. Keep it.

The movable electrode 21 is preferably a self-burning Zedaberg electrode.

As shown in FIG. 1, at the upper portion of the furnace body 10, an air introduction pipe 17 for supplying outside air to above the raw material 4 deposited under the furnace ceiling 20 is inserted.

An auxiliary burner 18 is installed at the upper portion of the furnace body 10 to preheat the raw material 4 and to burn offensive odors and unburned gas generated in the furnace by using the outside air introduced from the air introducing pipe 17. Is arranged in the tangential direction of the furnace body 10, and a smoke exhaust hood 27 surrounding the portion of the movable electrode 21 protruding from the furnace ceiling 20 is preferably attached.

[0024]

[Function] With a slight amount of molten pig iron remaining in the hearth, the raw material 4 in which coke breeze is mixed with incinerated ash of waste or dried powder of sewage sludge is charged into the furnace body 10 so as to cover the movable electrode 21. Deposit. The carbon stamp 13 covering the horizontal portion 12y of the L-shaped electrode 12, the graphite block 11 forming the refractory hearth thereon, and the molten pig iron 2 retained in the hearth make the furnace bottom highly conductive. When DC power is supplied to the L-shaped electrode 12, an electric circuit extending from substantially the entire hearth to the movable electrode 21 is formed, and the arc generated from the tip of the movable electrode 21 becomes extremely stable toward the entire hearth. . Fe, Cr, P, which is easy to reduce, because the raw material 4 with improved conductivity is gently melted by the addition of coke breeze.
The metal oxides such as are melt-reduced to generate the molten pig iron 2, and the molten slag 3 containing SiO ₂ or the like as a main component is generated on the molten pig iron 2. CO gas is generated by the reaction between the carbon component contained in the coke breeze and the metal oxide, which promotes the formation of slag. A carbon floating layer 6 is generated on the upper surface of the forming slag 5, an arc is blown from the movable electrode 21 having a tip protruding into the forming slag 5 to the carbon floating layer 6, and the raw material 4 is melted by heating by the arc. At the same time, due to the resistance Joule heat generated by energizing the molten pig iron 2, the molten slag 3, and the forming slag 5, the reduction melting of the forming slag 5 is promoted. When the raw material decreases due to the progress of melting, the furnace roof 2 rotating from the raw material charging device 22
It is additionally charged after passing 0. The movable electrode 21 is always covered with the raw material supplied from a plurality of raw material charging holes 23 opened at different radial positions, and submerged arc melting is realized. Even if the horizontal portion 12y of the L-shaped electrode 12 is heated to a high temperature by the molten pig iron 2 and the like staying in the hearth, the reducing atmosphere is maintained in the carbonaceous hearth and the L-shaped electrode 21 is not likely to be oxidized. On the other hand, although the vertical portion 12v is exposed to the oxidizing atmosphere, the cooling water circulates and wear is reduced. The molten slag 3 generated as described above is used for manufacturing an artificial aggregate for concrete.

Even when the furnace rotating device 51 is used instead of the ceiling rotating device (see FIG. 11), if the raw material decreases due to the progress of melting, the raw material charging device 22 moves to different radial positions of the furnace ceiling 20. The movable electrode 21 is always covered with the raw material supplied through the plurality of opened raw material charging holes 23, and the submerged arc melting is realized.

From the raw material charging device 22 composed of the screw feeder 22A, the raw material is charged into the furnace body 10 being melted through the raw material charging hole 23 of the furnace ceiling 20. Furnace ceiling 20
Is continuously rotated or oscillated horizontally by the ceiling rotator 24, or the furnace body 10 is rotated or oscillated by the furnace rotator 51, so that the raw material is distributed in the furnace as much as possible.

The same applies when the raw material is charged from the flexible closed chute 28 into the furnace body 10 being melted, instead of the screw feeder 22A.

When the flexible closed chute 28 is employed, if the raw material charging hole 23 is provided with the guide member 29, the raw material charging hole is formed by the horizontal continuous rotation or swing of the furnace ceiling 20 or the furnace body 10. Due to the displacement of 23 and the dispersing action of the guide member 29, the raw material 4 is charged so as to be distributed in the circumferential direction of the furnace body 20.

If the raw material level detector 28A is provided in the middle of the flexible closed type chute 28 extending vertically, when the detector 28A detects the raw material stagnation in the chute 28, the raw material which has received the detection signal is received. The fixed amount cutting device 28B stops supplying the raw material from the raw material storage bin 26 to the chute 28.

Generally, the incinerated ash as a raw material has a small content of oxides, and the consumption of electrodes is small. Therefore, it is possible to use the Zedaberg electrode, which is cheaper than the artificial graphite electrode and is easy to electrically control and operate.

When the air introduction pipe 17 for supplying the outside air is inserted above the raw material 4 deposited under the furnace ceiling 20, the malodor and unburned gas generated when the raw material 4 is melted are incinerated by spontaneous combustion. To be done.

If the auxiliary burner 18 is provided such that the flame is directed in the tangential direction of the furnace body 10 at the same time as the air introduction pipe 17 is provided, it becomes easy to burn the malodor and unburned gas generated in the furnace body, and moreover, The raw material 4 is preheated by the combustion heat. The exhaust gas is exhausted through the periphery of the movable electrode 21, and is sent from a smoke exhaust hood 27 provided on the furnace ceiling 20 so as to surround the movable electrode 21 to a dust collector or the like.

[0033]

According to the present invention, the hearth can be widely kept at substantially the same potential level, and the raw materials such as incineration ash having a small specific gravity and a low electric conductivity can be efficiently and quietly reduced and melted. it can. Metal oxides can be recovered as molten pig iron and recovered, and can be used as an iron source material for steelmaking and casting.
The molten slag is efficiently heated by the electric resistance Joule heat due to the formation of the forming slag, and the molten slag having an extremely small gas content is obtained. Impurities and easily reducible metal components have been removed from the molten slag, and it is possible to obtain a slag suitable for producing a chemically stable and harmless dense artificial aggregate for concrete by crystallization. . The melting furnace is a DC electric furnace, and a wide range of electric conductors are formed on the hearth to realize a wide range of heating and stable arc generation, and the operation control of the electric furnace is easy. The formation of forming slag promotes the improvement of power transfer efficiency and also reduces the electric power consumption of the electric furnace. The raw material is charged into the furnace as dispersed as possible by the horizontal rotation and swing of the furnace ceiling during operation, and the submerged arc melting can be maintained by the raw material deposited around the movable electrode.

Even when a furnace body rotating device is adopted in place of the ceiling rotating device, the raw material is charged in the furnace as dispersed as possible during operation, and the submerged arc is generated by the raw material deposited around the movable electrode. The melting can be maintained and the same effect as described above is exhibited.

According to the screw feeder, the granular material can be charged in an airtight manner even during operation, and the movable electrode is always covered with the raw material together with the horizontal continuous rotation or swing of the furnace ceiling or the furnace body. The state of submerged arc melting can be maintained.

Even when a flexible closed type chute is used, the raw material can be charged in an airtight manner and the submerged arc melting can be maintained. By adopting this chute, the raw material can be hot-charged, the dispersion of the raw material in the furnace is further facilitated, and the electric power consumption rate can be greatly improved.

If a guide member is provided below the raw material charging hole, the raw material can be dispersed and charged in the circumferential direction of the furnace body, and the raw material can easily cover the movable electrode.

When the material level detector is installed on the flexible closed chute, the feeding of the raw material to the closed chute can be stopped. By avoiding excessive accumulation of the raw material in the chute, the load on the flexible chute is reduced, and the wear of the flexible chute is eliminated in a short period of time.

The Zedaberg electrode can be sufficiently used for melting incinerated ash containing a small amount of oxide, is cheaper than the artificial graphite electrode, and can reduce the electrode unit consumption.

If an air introduction pipe is inserted in the upper part of the furnace body, the outside air is introduced into the furnace, unburned gas and bad odors are burned, and harmlessization of furnace exhaust gas is promoted.

When the auxiliary burner faces the air introduction pipe, the combustion of unburned gas and the like is promoted and the preheating of the raw material is realized, so that the power consumption rate can be reduced. The exhaust gas is exhausted from the smoke exhaust hood and prevented from leaking out of the furnace.

[0042]

EXAMPLES A DC electric melting furnace for producing reduced molten slag according to the present invention will be described below in detail with reference to the drawings showing examples thereof. FIG. 5 shows an example in which an electric melting furnace is applied to an apparatus for producing a sand-like artificial aggregate for concrete from slag obtained by melting incinerated ash of garbage, dried powder of sewage sludge and the like.
This is a sand-like slag forming device 30 in addition to the electric melting furnace 1.
And a rotary heat treatment furnace 40. The electric melting furnace used in such an aggregate manufacturing facility is made from a raw material in which coke breeze is mixed with incinerated ash of garbage, dried powder of sewage sludge, etc.
The metal oxides such as Fe, Cr, P, which are easily reduced, are melt-reduced to generate molten pig iron 2, and the gas content is low and Si
The molten slag 3 containing O ₂ or the like as a main component can be generated.

This electric melting furnace 1 is a direct current electric furnace having a reducing and melting function by the submerged arc electric melting method, and its main constitution is, as shown in FIG. 1, a fire wall and a fire resistant wall formed by a graphite block 11. A furnace body 10 in which a plurality of L-shaped electrodes 12 are provided inside the floor, and a raw material charging device 22 which can continuously rotate or oscillate and can charge the granular material in an airtight manner even during the operation of the furnace. It comprises a furnace ceiling 20 provided.

A refractory brick 10a is laminated on the inner surface of the iron shell of the furnace body 10, and a carbon stamp 13 obtained by arranging and crushing carbon powder is applied on the bottom of the furnace, and the carbon stamp 13 and the inner surface side of the insulating fireproof wall 14 are provided. The graphite block 11 described above is arranged in the. On the other hand, the furnace ceiling 20 has a hole at the center where the movable electrode 21 moves up and down, and a plurality of raw material charging holes 23 opened at different positions in the radial direction from the movable electrode 21.
And a raw material charging device 22 for supplying the raw material into the furnace through the raw material charging hole 23. A ceiling rotation device 24 is provided for continuously rotating or swinging the substantially disc-shaped furnace ceiling 20 horizontally on the furnace body.

The vertical portion 12v of the L-shaped electrode 12 is covered with the insulating fireproof wall 14, and the horizontal portion 12y is inside the carbon stamp 13, and as shown in FIG. In the illustrated example, four are arranged at equal intervals so as to be radial. The L-shaped electrode 12 is, for example, 0.
The vertical portion 12v is formed of a pure iron bar of 02% C and has a substantially square cross section as shown by a virtual line in FIG. 2 (a). The return path 12s provided on one side is formed. The horizontal portion 12y is a rectangle having a narrow cross section as shown by an imaginary line, and is covered with the carbon powder 13 as shown in FIG.
The carbon powder is stamped in order to provide a surface for arranging a large number of small rectangular graphite blocks 11 that form the hearth and to improve the electrical conductivity.

Although the graphite block 11 and the carbon stamp 13 are present on the bottom of the furnace, the horizontal portion 12y of the L-shaped electrode 12 is located below where the hot molten pig iron 2 stays, so that the temperature is about 1,100 ° C., for example. Exposed to high temperatures. However, the presence of these carbons creates a reducing atmosphere, and there is no risk of oxidation of the horizontal portion 12y.
On the other hand, the vertical portion 12v is water-cooled as described above because there is a possibility that the vertical portion 12v may come into contact with air and be oxidized when the temperature inside the furnace rises. By the way, the L-shaped electrode 12 is connected to the corbel copper plate 16 arranged around the furnace via the flexible conductive wire 15, and an electric circuit can be formed without being affected even if the furnace body is thermally expanded.

In this way, the carbon stamp 13, the graphite block 11 and the molten pig iron 2 staying in the hearth form a wide conductive part on the bottom of the hearth, and a plurality of L-shaped electrodes 12 feed electricity. The voltage applied between the movable electrode 21 and the movable electrode 21 is likely to be uniformly applied to the entire hearth. When substantially the same potential level is formed on the hearth surface in this way, the raw material 4 can be rapidly and uniformly melted due to the conductive effect of the coke breeze mixed in the incineration ash or the like. Of course, the power transmission efficiency is also dramatically improved by forming the forming slug 5 described later.

A movable electrode 21 is inserted into the furnace ceiling 20, but the incineration ash or the like to be charged generally has a small oxide content, and the consumption of the electrode is small. Therefore, it is possible to employ a self-baking Soderberg electrode that is easier and cheaper to operate than the artificial graphite electrode. As a result, the cost associated with electrode consumption can be significantly reduced. The Zedaberg electrode is used for the production of ferroalloys, etc., but it is a thin iron cylindrical body with carbon sinters inside, though details are omitted, and it self-fires and solidifies due to the resistance heat generated by itself when energized. To do. Such Zedaberg electrodes are known, but not used in DC electric furnaces for submerged arc melting.

The ceiling rotating device 24 described above is a drive device capable of continuous rotation in the example of FIG. 1, and a screw feeder 22A installed on the furnace ceiling 20 is adopted as the raw material charging device 22. The drive for rotating the furnace ceiling 20 is realized by the gear mechanism 24A shown in FIGS. The furnace ceiling 20 may be supported by wheels 20w (see FIG. 1) rolling on rails provided on the deck. Thus, if the furnace ceiling 20 can be rotated, the raw materials can be charged and evenly distributed in the furnace body during the operation of the furnace. In addition, automated operation of the electric furnace can be facilitated.

If a screw feeder 22A is connected to the raw material charging hole 23 of the furnace ceiling 20, powdery particles such as incinerated ash mixed with coke breeze can be easily transported and airtight so that dust is not scattered to the outside. Can be charged as needed. As shown in FIG. 3, normally two screw feeders 22
A and 22A may be provided, but the two raw material charging holes 23 and 23 connected to them are at different radial distances from the movable electrode 21 as shown by the broken line in FIG. By rotating, the incineration ash and the like can be uniformly charged into the furnace body. Thereby, the movable electrode 21
It is possible to surely cover the surroundings with the raw material.
In addition, incineration ash or the like is supplied to the screw feeder 22A from an upper raw material storage bin 26 (see FIG. 3). By the way, the two screw feeders 2 shown in phantom in FIG.
When arranging the three screw feeders at intervals of 120 degrees including 2B and 22B, if the radial distances are different from each other, the raw material can be introduced more widely and uniformly.

Returning to FIG. 1, at the upper portion of the furnace body 10, an air introduction pipe 17 for supplying the outside air to above the raw material 4 deposited under the furnace ceiling 20 is inserted. In the case where the raw material 4 contains sewage sludge dry powder, a bad odor may occur when heated in the furnace due to the presence of the proteinaceous substance in the dry powder. Even in the case of incinerated ash, CO gas generated in the melting process of the raw material exists in the space above the deposited raw material. In order to incinerate the unpleasant odor and unburned gas, a proper number of air introduction pipes 17 are radially installed. When a pressure draft is generated as the temperature inside the furnace rises, the outside air is sucked in, the odor is removed by spontaneous combustion, and CO is burned. In addition,
The exhaust gas in which the harmful gas is reduced is sent from around the movable electrode 21 to the dust collector through the smoke exhaust hood 27 to prevent the exhaust gas from leaking out of the furnace.

In addition to the air introducing pipe 17 described above, it is advisable to provide an auxiliary burner 18 shown by phantom lines that can generate a flame using the outside air introduced thereby. The auxiliary burner 18 is oriented toward the outlet of the air introduction pipe 17 and is arranged so as to be tangential to the circular furnace body. As a result, not only the foul odor and unburned gas are burned, but also swirling flow is promoted to increase the combustion efficiency, and it is possible to greatly contribute to the preheating of the charged raw material. Although the amount of energy supplied is increased by the auxiliary burner 18, it is an amount that can be ignored as a whole because it burns unburned gas. On the contrary, since the raw material can be preheated, power consumption is reduced and the power consumption rate is also reduced.

Here, an example of a manufacturing facility of artificial aggregate for concrete to which the submerged arc melting DC electric furnace 1 of the present invention is applied will be described below. When this electric melting furnace 1 is applied to, for example, a refuse incinerator that produces about 50 tons of incinerated ash per day, the furnace volume is set to accommodate about 4 tons of incinerated ash. This is because if it takes about 2 hours to melt the incinerated ash or the like, it will be commensurate with the daily waste treatment amount of 24 hours / 2 hours × 4 tons = 48 tons.
Therefore, it is small with a diameter of about 3 m.

First, a raw material 4 prepared by previously mixing coke breeze with incinerated ash is shown in FIG.
A and 22A are used to supply from the raw material charging hole 23 of the furnace ceiling 20 of the electric melting furnace 1. The incinerated ash 4 and the like are melted and reduced by the submerged arc electric melting method in 2 to 3 hours. The heat of 1,500 ° C. or more at this time causes the combustibles and dioxins to be gasified and burned. Although powders such as incinerated ash have low specific gravity and low electric conductivity, since coke breeze is mixed in the raw material 4, the carbon improves the electric conductivity of the raw material 4 and melts the incinerated ash and the like. Is promoted. In addition, substantially the same potential level is widely generated due to the power supply from the plurality of L-shaped electrodes 12 buried in the furnace bottom and the formation of the hearth bed to which conductivity is given in a wide range, and in melting the powder or granular material, An indispensable gentle melting form is obtained and a uniform melting process in the furnace is realized. As a result, the metal oxide such as Fe, Cr, P, etc., which can be easily reduced, is melt-reduced and, as shown in FIG.
Is generated. The CO gas generated by the reaction at that time promotes the forming of the slag. The molten pig iron 2 produced by reduction stays in the hearth, and the molten slag 3 floats on it. The forming slag 5 is formed on the molten slag 3, and the carbon floating layer 6 is formed at the boundary between the forming slag 5 and the raw material layer.

The lower part of the movable electrode 21 lowered into the furnace body is covered with the carbon floating layer 12 and the forming slag 5 is formed.
And the arc is always in a submerged state in which it is covered with the raw material 4 and the forming slag 5. Not only heating of the raw material by the arc generated at the carbon floating layer 6 but also efficient melting by electric resistance Joule heat from the forming slag 5 to the molten pig iron 2 is realized. Since the formation of the forming slug 5 dramatically improves the power transmission efficiency as already known, the power consumption rate can be reduced.

When the incineration ash etc. 4 is successively reduced and melted, in order to maintain the submerged arc state, the raw materials are sequentially added from the screw feeder 22A so as to be distributed around the movable electrode 21 through the rotating furnace ceiling 20. Supplied.
While the furnace ceiling 20 is rotating, the screw feeder 22A is disconnected from the raw material storage bin 26 (see FIG. 3).
The furnace roof 20 is stopped at the time of rotation of 120 degrees or 120 degrees, and is again connected to the raw material storage bin 26. Then, the hopper 25 connected to the screw feeder 22A is charged with the amount of raw material to be supplied to the furnace body 10 during the next rotation.

With reference to FIG. 5, the molten pig iron 2 accumulated in the hearth is intentionally left in a small amount for 1 day to 2 days from the tap hole 1a.
It is received by the hot metal ladle 1M every day and used separately as an iron source material for steelmaking and casting. On the other hand, molten slag 3
Does not contain molten metal components, and the main component is SiO ₂ , A
It is a mineral substance such as l ₂ O ₃ , CaO, and MgO, and is in a state containing almost no gas by the submerged arc melting method. Therefore, it is not necessary to perform defoaming treatment after that. The molten slag 3 is discharged from the outlet 1b, but is discharged in a short time of, for example, 20 minutes every 2 hours after pulling out the outlet plug 1d. Therefore, as compared with the case where the generated molten slag is continuously discharged little by little, the amount of heat energy emitted from the molten slag 3 at the time of slag is also suppressed as much as possible.
If an air supply hole is provided in the slag plug 1d and air for stirring the molten slag 3 in the vicinity of the slag opening is sent during melting, it is possible to prevent clogging of the slag at the time of slag. .

Compressed air is jetted from the compressed air ejector 7B toward the molten slag 3 flowing down from the slag trough 7A while retaining high heat energy, and the molten slag 3 is blown off and the water-cooled rotary drum is blown away. It collides with the inner surface of the upper part of 30A. The air is jetted and the impact force at the time of collision with the inner surface of the drum is received to be atomized. Drum cooler 30
The fine particles are cooled by the iron crust that is water-cooled by the water spray from B, and the surface is solidified to suppress mutual adhesion. Then, the sand-like slag 8 having a round outer shell is formed while repeating the rising of the inner peripheral wall and the fall and fall in the drum which is supported by the roller 30a and rotated by a driving device (not shown).

The rotary drum 30A rotates at, for example, about 30 rpm, and the cooling water sprinkled between the rotary drums 30A partially evaporates while flowing around the drum and the water that flows down is stored in the water pool 30.
dropped to b. Further, the cooling water does not reach the sandy slag 8 of about 900 ° C. which successively moves on the transfer chute 9 by the draining fins 30c standing on the outer surface of the drum. The slag extracted from the electric melting furnace 1 in about 20 minutes passes from the sandy slag molding device 30 to the transfer chute 9 and immediately enters the rotary furnace body 40A of the rotary heat treatment furnace 40.
It is charged while the temperature does not drop below 0 ° C.

The rotary furnace body 40A is in a state of being preheated by the heating burner 40B with an air supply pipe (not shown), and when the sandy slag 8 is charged in a predetermined amount, the transfer chute 9 is retracted to about 1 rpm. Slowly rotated at speed. A flame is generated from the heating burner 40B, and the fireproof wall 40
The deposition surface layer of a and slag is heated. Heating refractory wall 4 that wraps around the bottom of the accumulated slag by rotating the furnace body 40A
The sandy slag 8 that touches 0a or directly touches the flame is 80
It is placed in a uniform temperature atmosphere of 0 ° C to 900 ° C. The solidified amorphous outer shell of the sandy slag 8 reaches a temperature required for remelting and crystallization due to the temperature inside the furnace and the heat recovery from the high temperature molten portion inside the slag. After being retained for 3 to 4 hours, the individual sand-like slag 8 becomes a hard sand-like aggregate 8A in which a dense crystallization of the structure is achieved as a whole.

When a predetermined time has passed, the heating burner 40B
Then, the product discharge port lid 40b is removed. When the drum is rotated again, the crystallized sand-like aggregate 8A is discharged every time the discharge port goes down. Since the axis of the furnace body 40A is inclined so as to descend from the charging port, the furnace body 40A moves to the discharging port in the furnace body and all is put into the product receiver 40C. As described above, the sand-like aggregate 8A thus obtained has the metal component that is easily reduced in the electric melting furnace 1 removed, and the gas content is extremely small. Therefore, uniform crystallization is promoted, and it becomes a chemically stable artificial aggregate for a concrete having a dense structure extremely close to natural stone or river sand. The heat energy applied to the molten slag 3 in the electric melting furnace 1 is quickly lost to the heat treatment step with less loss in the middle, and the heat energy consumption for crystallization is also significantly reduced.

As can be seen from the above description, the incineration ash of the granular material having a small specific gravity and a low electric conductivity is gently melted by supplying power from a wide range of the hearth to generate molten pig iron and molten slag. It is possible to manufacture a high-quality artificial aggregate for concrete from molten slag with as little harmful substances as possible. Since the molten pig iron generated at that time can be used separately, metal resources can be recovered. Coke breeze is added to the incineration ash, etc., and the electric conductivity of the raw material is increased to promote melting, and reduction by carbon is realized. Not only that, it also promotes the formation of forming slag and greatly contributes to the reduction of the power consumption rate by improving the power transmission efficiency. Further, the molten slag is prevented from dissipating the retained heat energy during the short time slag for each predetermined time and the rapid transfer form, and the heating energy for the crystallization operation is also reduced. Further, it is possible to provide a facility that realizes processing of waste and sewage sludge generated in the area and reduction in capacity commensurate with consumption of the product in the area.

The submerged arc melting furnace 1 is a DC electric furnace, and the furnace structure is simple and easy to control, and the electric energy supply is stable. AC electric furnaces are generally suitable for large-capacity, in addition, the direction of arcing between electrodes is uneven or unstable, and there is a tendency to heat only the deposition surface layer of the furnace interior contents, It is difficult to obtain a perfect heating state. However, in the present electric furnace using the L-shaped electrode, uniform melting in the furnace is achieved due to the good controllability in the normal DC electric furnace and the improvement in the power feeding property covering a wide area from the hearth. Processing can be realized. Furthermore, the electric furnace operation by the submerged arc melting method is maintained by the screw feeder that can constantly charge the powdery and granular material and the rotation of the furnace ceiling that enables the distributed charging of the material even during operation. . This rotation of the furnace ceiling becomes easier to realize because a large-capacity furnace body is not required as the artificial aggregate manufacturing device for concrete.

FIG. 6 shows an example in which a flexible closed chute 28 is used instead of the screw feeder. The two chutes 28, 28 shown also have respective raw material charging holes 2 at different radial distances from the movable electrode 21.
3, 23, and can be charged in an airtight manner through the furnace ceiling 20. Therefore, if the furnace ceiling 20 is swung in the circumferential direction within a range in which each chute 28 can be deformed while maintaining the connection between the raw material storage bin 26 and the raw material charging hole 23, the incineration ash or the like is dispersed and loaded in the furnace body. You can enter. For this reason, the ceiling rotation device 24 employs a swingable drive device such as a link mechanism or the hydraulic cylinder mechanism 24B shown in FIG. If the raw material such as incinerated ash is normal temperature or up to about 80 ° C., a cloth cylinder can be used as the chute.

When using such a chute 28,
The raw material charging holes 23 are provided in the furnace ceiling 20 at about six places.
The reason why the illustrated raw material charging hole has a rectangular outer shape will be described later, but when the furnace ceiling 20 is swung back and forth in the circumferential direction,
The hole shown by the solid line can be moved to the position of the one-dot chain line or the position of the two-dot chain line. By the way, at the start of the operation of the furnace, pig iron and iron scraps for forming a molten pig iron layer on the hearth,
If necessary, coke or the like is charged, and it is necessary to initially load the raw material such as incineration ash to the extent that the movable electrode 21 is lowered and the periphery thereof is covered. The furnace ceiling 20 is composed of, for example, divided canopies 20A and 20B for every 60 degrees, and every other divided canopy 20A is further divided into an inner peripheral lid 20a and an outer peripheral lid 20 at radial intermediate positions.
b and each of them has a structure in which they are integrally fixed using a clamp device or the like. By doing so, even if the split canopy 20B and the inner peripheral lid 20a cannot be removed because the closed type chute 28 is connected, if the outer peripheral lid 20b is removed, a part of the furnace ceiling 20 is removed. A large opening can be made and raw materials and the like can be charged all at once at the start of furnace operation.

With such arrangement of the raw material charging hole 23, the raw material charged through the hole of the inner peripheral lid 20a is less likely to be dispersed in the inner peripheral portion of the split canopy 20B, and the raw material is not loaded through the hole of the split canopy 20B. The entered raw material is less likely to be dispersed immediately below the outer peripheral lid 20b. Therefore, as shown in FIG. 6, the raw material charging holes 23 extend downward to guide the raw material distribution and charging in the circumferential direction of the furnace body, and the raw material deposited in the furnace body 20 in the furnace ceiling 20. A guide member 29 that disperses in the rotation direction by rocking is provided.

The guide member 29 has a substantially triangular cross section formed in the lower portion of the vertical charging cylinder 29A attached to the raw material charging hole 23. The raw material is dispersed rightward and leftward along the straight or arcuate inclined surface 29a shown in FIG. 8, and the raw material that slides down can be oriented. Further, since the guide member 29 is adapted to be able to push out the deposited raw material in the circumferential direction of the furnace ceiling 20, the inclined surface 29 facing at right angles to the rotation direction.
a must be provided. Therefore, if the charging cylinder 29A made of heat-resistant steel has a rectangular cross section, the guide member 29 can be integrally formed in the lower part thereof, and the discharge port 29b is opened in the front and rear wall surfaces of the inclined surface 29a. It will also be easy.

The uniform charging of the raw material by the guide member 29 will be described below. As shown in FIG. 9A, when the fine raw material 4 is supplied through the closed type chute 28 and the charging cylinder 29A, the height of the deposited layer of the surrounding raw material 4 becomes H _L1 and H _R1 . 4 forms a mountain. When the slope of the mountain reaches the angle of repose, no more raw material is supplied. Therefore, the charging cylinder 29A is swung in the direction of the arrow in (b) by swinging the furnace ceiling. That is, the raw material charging hole 23 shown in FIG. 7 is moved from the position indicated by the solid line to the position indicated by the alternate long and short dash line.

The raw material on the left side of FIG. 9B is the guide member 29.
The slope L ₁ is changed to L ₂ by the raw material that has been pushed by the guide member 29 from the charging cylinder 29A and slid to the left side, and the deposition layer on the left side is raised to the height H _L2 . On the other hand, on the right side, a blank portion is generated due to the movement of the guide member 29. However, if the raw material is not supplied, the slope becomes as indicated by the chain double-dashed line R ₁₁ , but since the hatched amount of the raw material is actually supplied, the slope of the mountain will cause the avalanche of raw material to fall into the right side. The height of the deposited layer is H _R2
Be raised to. As a result, the slope on the right side becomes R ₂ . FIG. 9C shows the raw material charging hole 2 shown by the alternate long and short dash line in FIG.
3 is a state when 3 is returned to the position of the solid line, and the behavior is opposite to the left and right from (b). At this time, the right slope R ₂ is R ₃
And the deposition layer has a height H _R3 . The slope on the left changes from L ₂₁ to L ₃ , and the deposited layer is raised to a height H _L3 . Figure 10
(A) is when the raw material charging hole 23 in FIG. 7 is moved from the position indicated by the solid line to the position indicated by the alternate long and two short dashes line. Thereafter, the process returns to loading cylinder 29A is central to as in (b), however, the process proceeds to the left as it is (c), the height of the left and right of the deposited layer is as such H _L6, H _R6, charged The raw material 4 is filled up to near the opening 29b of the cylindrical body 29A.

As the melting of the raw material 4 progresses, the deposited layer is lowered in volume, but if the furnace ceiling 20 is swung during the operation of the furnace, the periphery of the movable electrode 21 can be always covered with the raw material. If the furnace ceiling 20 does not oscillate, a large number of raw material charging holes will be required, but as shown in FIG. 7, even if the number of raw material charging holes 23 is small, the charging cylinder 29A has a small number. The raw material is uniformly loaded into the furnace body by the rocking and the guide member 29 guiding and pushing the raw material in the sliding direction. Therefore, it is possible to provide the above-mentioned outer peripheral lid 20b for opening the furnace ceiling 20.

By the way, when the closed type chute 28 is adopted, it is not necessary to separate it from the raw material storage bin 26. Therefore, if the chute is made of a material with high heat resistance,
It becomes possible to circulate the high temperature granules. Since the electric melting furnace is provided in a part of the refuse incinerator, incineration ash in a red heat state emitted from the garbage incinerator can be charged into the electric melting furnace. Needless to say, when the hot charging of the raw material is realized in this way, the electric power consumption in the electric melting furnace is dramatically reduced. Not only that, the high-temperature powder and granules have extremely high fluidity, the dispersibility of the raw material through the charging cylinder 29A is good, and the swing range of the furnace ceiling can be kept small.

It is preferable to provide the following automatic supply control device not only for the above-mentioned raw materials at room temperature but also for hot charging. In FIG. 6, a raw material level detector 28A is provided in a lower part of the closed chute 28 which extends vertically, and a raw material fixed quantity cutting device 28B is installed in the raw material storage bin 26. In this way, even if the furnace ceiling 10 is rocking, a large amount of raw material is deposited as shown in FIG. 10C and the charging cylinder 29A does not flow into the furnace body. The raw material level detector 28A detects the stagnation of raw material at that portion.
When the detection signal is input to the controller of the raw material quantitative cutting device 29B, the raw material cutting is stopped, and the closed chute 2
Feeding of the raw material to No. 8 is eliminated, and excessive accumulation of the raw material in the chute is prevented. This makes a long shoot 28
Unnecessary wobbling behavior and wear are suppressed. As the raw material level detector, a short horizontal vibration plate may be arranged in the space where the powder or granular material falls, and the raw material stagnation or the raw material falling can be detected by the presence or absence of vibration. On the contrary to the above, when the raw material level detector 28A detects that the raw material is not stagnant in the chute, the raw material quantitative cutting device 2
9B is operated, and the raw material is charged into the furnace body. Such automatic control can be performed from the refuse incinerator to the rotary heat treatment furnace 40 (see FIG. 5).
It is possible to promote the overall unmanned operation of the equipment up to the reference).

FIG. 11 shows an example in which a furnace body rotating device 51 for horizontally rotating the furnace body 10 is adopted instead of the ceiling rotating device. In this case, the raw material charging device 22 and the like are still provided on the furnace ceiling 20, but the wheels for enabling the rotation of the furnace ceiling 20 are not provided. It goes without saying that the rotation of the furnace body 10 is for facilitating the dispersion of the charging raw material, as in the case of rotating the furnace ceiling 20. The drive for rotation of the furnace body 10 is realized by a device similar to the gear mechanism 24A (see FIG. 4) and the cylinder mechanism 24B (see FIG. 7) described above, and wheels are driven on an annular rail laid on the furnace body foundation. It should be able to move by 10w. On the other hand, in order to feed power to the L-shaped electrode 12, conductive rods 52, 52 corresponding to each L-shaped electrode 12 are arranged outside the furnace, and the tips thereof are fixed to the center of the lower part of the furnace body via an insulating material. Collected in 53. The electric power supplied from the transformer (not shown) via the power supply line 54 is supplied to the power supply ring 53 via the conductive shoe 55 biased by the spring.

Even when the furnace body 10 is rotated in this way, a screw feeder 22A or a closed chute (not shown) can be attached to the furnace ceiling as a raw material charging device. The rotation of the furnace body 10 is generally continuous rotation at a speed of, for example, one rotation per hour, but it goes without saying that it may be rocked. The guide member 29 described above can be arranged in the raw material charging hole not only when the closed chute is used but also when the screw feeder is used, but also when the furnace body 10 is rotated at a low speed. It becomes possible to exert the dispersion effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a submerged arc DC electric melting furnace and auxiliary equipment according to the present invention.

2A is an enlarged cross-sectional view of an L-shaped electrode, and FIG. 2B is a view taken along the line II-II in FIG.

FIG. 3 is an overall schematic configuration diagram of a DC electric melting furnace.

FIG. 4 is a plan view of a furnace ceiling as seen from the direction of an arrow.

FIG. 5 is an overall view of an artificial aggregate production facility for concrete, which produces sandy slag from incinerated ash and produces crystallized sandy aggregate.

FIG. 6 is an overall view of an electric melting furnace when a closed chute is adopted.

FIG. 7 is a plan view of the furnace ceiling in FIG.

FIG. 8 is a perspective view of a charging cylinder body including a guide member.

FIG. 9 is an explanatory view of material distribution and charging by a guide member.

FIG. 10 is an explanatory diagram of raw material charging subsequent to FIG. 9;

FIG. 11 is a schematic configuration diagram of a DC electric furnace provided with a furnace body rotating device.

[Explanation of symbols]

1 ... Submerged arc electric melting furnace, 2 ... Molten pig iron, 3
... Molten slag, 4 ... Raw material, 10 ... Furnace body, 11 ... Graphite block, 12 ... L-shaped electrode, 12r ... Forward path, 12s ... Return path,
12v ... Vertical part, 12y ... Horizontal part, 13 ... Carbon stamp, 17 ... Air introduction pipe, 18 ... Auxiliary burner, 20
... furnace ceiling, 21 ... movable electrode, 22 ... raw material charging device, 22
A, 22B ... screw feeder, 23 ... raw material charging hole,
24 ... Ceiling rotating device, 26 ... Raw material storage bottle, 27 ... Smoke exhaust hood, 28 ... Closed chute, 28A ... Raw material level detector, 28B ... Raw material quantitative cutting device, 29 ... Guide member,
51 ... Furnace body rotating device.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F23G 5/00 115 F23J 1/00 F27B 3/08 F27D 11/08

Claims (9)

(57) [Claims] 1. Fe, which is easily reduced from a raw material in which coke breeze is mixed with incinerated ash of garbage, dried powder of sewage sludge, etc.
A submerged arc electric melting furnace capable of producing a molten pig iron by melting and reducing a metal oxide such as Cr / P and producing a molten slag mainly composed of SiO ₂ having a low gas content. While a single movable electrode is inserted vertically through the center of the furnace ceiling, an L-shaped electrode that supplies DC power along a fire wall and a fire bottom lined with an iron skin A plurality of L-shaped electrodes are arranged in a radial pattern with respect to the center of the furnace body, and the L-shaped electrode is formed of a pure iron bar, and a cooling water passage through which cooling water flows is formed inside the vertical part of A carbon stamp made by arranging and crushing carbon powder so as to cover the horizontal portion where the cooling water passage is not formed is provided on the bottom, and a graphite block is provided inside the insulating fire wall covering the carbon stamp and the vertical portion. Installed The furnace ceiling is provided with a plurality of raw material charging holes opened at different radial positions from the movable electrode, and a raw material charging device for supplying the raw material into the furnace body from the raw material charging holes is installed. A DC electric melting furnace for producing reduced molten slag is provided with a ceiling rotating device for continuously rotating or rocking the furnace ceiling horizontally on the furnace body. 2. A reduced-melt slag generation device, characterized in that a furnace body rotating device for continuously rotating or swinging the furnace body horizontally is provided in place of the ceiling rotating device described in claim 1. DC electric melting furnace for use. 3. The DC electric melting furnace for producing reduced molten slag according to claim 1, wherein the raw material charging device is a screw feeder. 4. The DC electric melting furnace for producing reduced molten slag according to claim 1, wherein the raw material charging device is a flexible closed chute. 5. The raw material charging hole extends downward to guide the raw material distribution charging in the circumferential direction of the furnace body,
A direct current electric melting furnace for producing reduced molten slag according to claim 4, further comprising: a guide member for dispersing the powdery and granular raw material accumulated in the furnace body. 6. A raw material level detector is provided midway in the vertical extension of the flexible closed chute, and when the detector detects stagnation of the raw material in the chute, the raw material level detector A direct current electric melting furnace for reducing molten slag production according to claim 4 or 5, wherein a raw material quantitative cutting device for stopping the feeding is provided in a raw material storage bin connected to the chute. . 7. The DC electric melting furnace for producing reduced molten slag according to claim 1 or 2, wherein the movable electrode is a self-baking electrode. 8. An air introduction pipe for supplying outside air to above the raw material deposited under the furnace ceiling is inserted in an upper portion of the furnace body. A DC electric melting furnace for producing reduced molten slag according to any one of 1. 9. An auxiliary burner is provided at the upper portion of the furnace body for preheating the raw materials and burning offensive odors or unburned gas generated in the furnace body by using the outside air introduced by the air introduction pipe, The smoke exhaust hood that is arranged so that its tip is in the tangential direction of the furnace body and that surrounds the portion of the movable electrode projecting from the furnace ceiling is attached to the furnace ceiling. DC electric melting furnace for producing reduced molten slag.