JP2002121612A - Method for melting cold iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of dioxin, white fume and malodor in exhaust gas while preventing the abnormal combustion such as explosion, caused by the combustible component in the exhaust gas exhausted from a preheating chamber when cold iron is melted by using an arc melting apparatus having the shaft type preheating chamber. SOLUTION: The arc melting apparatus 1, which is provided with a melting chamber 2 and the shaft type preheating chamber 3 directly connected to the upper part thereof and preheats the cold iron 16 with the exhaust gas produced in the melting chamber, is used, and the cold iron is melted by supplying the arc, carbonaceous material and oxygen into the melting chamber while supplying the cold iron into the preheating chamber so that the cold iron exists in the preheating chamber and the melting chamber. When the molten iron is tapped off in the existing state of the cold iron in the melting chamber and the preheating chamber at the time when a prescribed quantity of molten iron 17 is stored, the exhaust gas flow rate in the exhaust gas flowing path 21 is increased by supplying oxygen-containing gas into the exhaust gas exhausted from the preheating chamber, and also the exhaust gas temperature is heated to a prescribed temperature and above by burning the combustible component in the exhaust gas, and thereafter, the exhaust gas is quenched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melting method for melting a cold iron source such as iron scrap or direct reduced iron by arc heat.

[0002]

2. Description of the Related Art In recent years, due to resource and environmental issues, processes for melting a large amount of iron scrap using an arc melting facility have increased. Such an arc melting equipment consumes a lot of electric power for melting iron scrap,
Many methods have been proposed to reduce the required electric power by melting iron scrap while preheating it using high-temperature exhaust gas generated from a melting chamber of an arc melting facility.

[0003] On the other hand, when iron scrap is melted by an arc melting facility, dioxin is typified in exhaust gas due to oil adhering to the raw material iron scrap and plastic mixed in the iron scrap. Harmful substances such as aromatic chlorine compounds may be contained, and at the same time, white smoke and foul odors are generated, which is an environmental problem and prevents the generation of such harmful substances. Many technologies have been proposed.

In such a situation, the present inventors have previously disclosed in Japanese Patent Application Laid-Open No. H11-183045 that the required power can be greatly reduced,
A method for dissolving a cold iron source that suppresses the generation of harmful substances such as foul odors and dioxins was proposed. This melting method uses an arc melting equipment having a shaft-type preheating chamber directly connected to the upper part of the melting chamber, and uses a cold iron source so that a cold iron source is continuously present in the melting chamber and the preheating chamber. While continuously or intermittently supplying the preheating chamber, arc heating and an auxiliary heat source such as coke and oxygen are supplied into the melting chamber to melt the cold iron source in the melting chamber, and a predetermined amount of molten steel is supplied to the melting chamber. When tapping molten steel in a state where a cold iron source is present in the melting chamber and the preheating chamber at the time of accumulation, after the exhaust gas generated in the melting chamber passes through the preheating chamber, an oxygen-containing gas is supplied to the exhaust gas and the Is a melting method in which the combustible components are burned, the exhaust gas temperature is raised to a predetermined temperature or higher, and then the exhaust gas is rapidly cooled.

[0005] According to this melting method, a cold iron source is always present in the preheating chamber and the melting chamber, and all the cold iron sources to be used are preheated after the next heat, so that a large reduction in electric power consumption is achieved. At the same time, since the exhaust gas is burned to a high temperature equal to or higher than a predetermined temperature, and then the exhaust gas is rapidly cooled, it is possible to prevent the generation of harmful substances such as dioxin and the generation of white smoke and odor.

[0006]

However, in the melting method disclosed in Japanese Patent Application Laid-Open No. 11-183045, a combustible component such as CO gas remains in exhaust gas discharged from a preheating chamber, and the exhaust gas is subjected to oxygen in a combustion chamber. The contained gas is supplied and burned, and the temperature is raised to a predetermined temperature. As described above, since it is necessary to allow flammable components such as CO gas to remain in the exhaust gas discharged from the preheating chamber, the melting operation is performed while minimizing intrusion of air into the melting chamber and the preheating chamber. This is because if the amount of intruded air is large, the unburned portion of the combustible component is reduced and the amount of exhaust gas is also large. Therefore, in the dissolving method according to the same publication,
The gas flow rate in the exhaust gas flow path from the preheating chamber to the combustion chamber is not so fast.

For this reason, the gas flow rate in the exhaust gas passage is controlled so as not to flash back from the combustion chamber toward the preheating chamber during normal operation. When the amount of generation decreases, a flashback occurs from the combustion chamber to the upstream side, and furthermore, for example, iron scrap having a high carbon concentration is rapidly melted, or ground having a high carbon concentration adhered to the side wall of the melting chamber. When the flammable components (in this case, CO gas) in the exhaust gas rapidly increase due to the fall of gold into the molten metal, there is a possibility of explosion in the preheating chamber or the melting chamber.

[0008] The present invention has been made in view of the above circumstances,
The purpose is to prevent abnormal combustion such as explosion due to flammable components in the exhaust gas discharged from the preheating chamber when melting the cold iron source using the arc melting equipment having a shaft type preheating chamber. It is another object of the present invention to provide a method for dissolving a cold iron source that can prevent generation of dioxin, white smoke, and odor in exhaust gas.

[0009]

A method for melting a cold iron source according to the present invention comprises a melting chamber and a shaft-type preheating chamber directly connected to an upper part thereof, and introduces exhaust gas generated in the melting chamber into the preheating chamber. In the method of melting a cold iron source using an arc melting apparatus that preheats the cold iron source in the preheating chamber, the cold iron source is maintained so that the cold iron source continuously exists in the preheating chamber and the melting chamber. While supplying to the preheating chamber, the cold iron source in the melting chamber is melted by arc heating and supplying the carbon material and oxygen to the melting chamber, and when a predetermined amount of molten metal is accumulated in the melting chamber, the melting chamber and the preheating chamber. When the molten metal is discharged in the state where the cold iron source is continuously present, the oxygen-containing gas is supplied to the exhaust gas discharged from the preheating chamber to increase the flow rate of the exhaust gas in the exhaust gas passage and the flammability in the exhaust gas. Combustion of the components to make the exhaust gas temperature higher than the specified temperature Thereafter, those characterized by rapidly cooling the exhaust gas.

According to the present invention, the oxygen-containing gas is supplied to the exhaust gas discharged from the preheating chamber to increase the gas flow rate in the exhaust gas flow path to a sufficiently high flow rate that does not cause flashback. Even if the amount decreases, there is no backfire on the preheating chamber side. At that time, if the gas flow rate in the exhaust gas flow path is 5 m / sec or more, there is no backfire on the preheating chamber side.
It is preferable to maintain m / sec or more. Also, in the present invention, since the exhaust gas flow rate is increased by adding the oxygen-containing gas, the combustible components in the exhaust gas are burned by the oxygen-containing gas, and the temperature is raised to a predetermined temperature without excessively increasing the exhaust gas amount. can do.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic longitudinal sectional view of an arc melting equipment embodying the present invention.

As shown in FIG. 1, a shaft type preheating chamber 3 and a side wall 4 of a water cooling structure are arranged above a melting chamber 2 having a refractory inside and a bottom electrode 6 at the bottom. ,
The upper portion of the side wall 4 not covered by the preheating chamber 3 is covered by a lid 5 having a water cooling structure that can be freely opened and closed. Through this lid 5,
An upper electrode 7 made of graphite that can move up and down into the melting chamber 2 is provided. The lower electrode 6 and the upper electrode 7 are connected to a DC power supply (not shown), and the lower electrode 6 and the upper electrode 7 are connected to each other. An arc 19 is generated between them.

Above the preheating chamber 3, there is provided a bottom-open type supply bucket 15 suspended from a traveling carriage 24,
From this supply bucket 15, a cold iron source 16 such as iron scrap or direct reduced iron is charged into the preheating chamber 3 through an openable / closable supply port 20 provided in the upper part of the preheating chamber 3.

At the upper end of the preheating chamber 3, a duct 21 serving as an exhaust gas discharge channel is provided connected to the other end of the preheating chamber 3, and the high-temperature exhaust gas generated in the melting chamber 2 is preheated. The exhaust gas is discharged to the exhaust gas treatment facility 31 via the chamber 3 and the duct 21. At this time, the cold iron source 16 charged in the preheating chamber 3 is preheated by the exhaust gas passing through the preheating chamber 3, and the preheated cold iron source 16 is melted in the melting chamber 2. And falls freely into the melting chamber 2 according to the amount of
It is charged into the melting chamber 2.

The side wall of the preheating chamber 3 has a taper that spreads downward. By providing a taper,
The preheated cold iron source 16 can be stably supplied to the melting chamber 2. If the taper is not formed, the cold iron source 16 is less likely to fall, causing a rack to be suspended in the preheating chamber 3.

An oxygen blowing lance 8 and a carbon material blowing lance 9 which penetrate through the lid 5 and can move up and down in the melting chamber 2 are provided.
A carbon material such as coke, char, coal, charcoal, graphite or the like is blown into the melting chamber 2 from the carbon material blowing lance 9 using air, nitrogen or the like as a carrier gas.
Further, an air blowing lance 12 is provided through the lid 5, and air for secondary combustion is blown into the melting chamber 2 from the air blowing lance 12.

The projecting portion 2a provided on the opposite side of the melting chamber 2 from the side to which the preheating chamber 3 is directly connected has an outlet side pressed down by a door 22 on the bottom thereof, and sand or mud is filled inside. A tap hole 13 filled with the agent and a tap hole 14 whose inner wall is pressed by a door 23 and filled with sand or a mud agent are provided on the side wall thereof. Further, a burner 1 is provided on the lid 5 at a position corresponding to a position vertically above the tap hole 13.
0 is attached. The burner 10 uses fossil fuels such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas,
It is burned in the melting chamber 2 by air or oxygen or oxygen-enriched air.

An exhaust gas treatment facility 31 downstream of the duct 21
A combustion chamber 36 is provided in connection with the duct 21. The combustion chamber 36 has a blower 37 and a blower 37.
Is provided, and air is supplied into the combustion chamber 36 through the blower 37 and the combustion air supply pipe 38. This air is supplied into the combustion chamber 36 as an oxygen-containing gas for burning combustible components in the exhaust gas generated in the melting chamber 2. In the combustion chamber 36, an auxiliary burner 39 using fuel such as heavy oil, kerosene, or LPG is installed, and the auxiliary burner 39 can promote the combustion of exhaust gas.

An air supply pipe 33 is provided in the duct 21 between the preheating chamber 3 and the combustion chamber 36. The blower 32 connected to the air supply pipe 33 allows the air to be introduced into the duct 21 as oxygen-containing gas. Is supplied. Not surprisingly,
The combustible components in the exhaust gas generated in the melting chamber 2 are also combusted by the air introduced from the air supply pipe 33.

The duct 21 is provided with a gas flow meter 34 between the preheating chamber 3 and the air supply pipe 33. The gas flow meter 34 measures the flow rate of the exhaust gas discharged from the preheating chamber 3, and the measurement result is input to the control device (not shown) of the blower 32 described above. The blower 32 controls the amount of air supplied into the duct 21 based on the measurement result of the gas flow meter 34, and controls the amount of gas introduced into the combustion chamber 36 (the exhaust gas from the preheating chamber 3 and the air supply pipe 33. The amount of gas mixed with air from the air) is always maintained at an arbitrary set value. That is, by maintaining the flow rate of the mixed gas (hereinafter also referred to as “exhaust gas”) of the exhaust gas from the preheating chamber 3 and the air from the air supply pipe 33 at an arbitrary set value,
The flow rate of the exhaust gas within 1 is controlled to a value that does not cause flashback.

On the other hand, between the air supply pipe 33 of the duct 21 and the combustion chamber 36, a gas analyzer 35 for analyzing the composition of the exhaust gas introduced into the combustion chamber 36 is provided.
The measurement result of the gas analyzer 35 is input to the control device (not shown) of the blower 37 described above. Blower 37
Controls the amount of air supplied to the combustion chamber 36 based on the measurement result of the gas analyzer 35, and controls the amount of air supplied to the combustion chamber 36 so that the combustible components in the exhaust gas do not remain unburned. Controlling the amount. Therefore, when the combustible components in the exhaust gas are sufficiently burned by the air from the air supply pipe 33, the blower 37 is stopped, and the combustion air supply pipe 38
Does not supply air. The blower 32, the air supply pipe 33, the gas flow meter 34, and the gas analyzer 35 are one of the facilities constituting the exhaust gas treatment facility 31.

A cooling chamber 40 is provided downstream of the combustion chamber 36. The cooling chamber 40 is provided with a water spray nozzle 41, which sprays cooling water to rapidly cool the exhaust gas, thereby preventing generation of harmful substances such as dioxin.

An exhaust gas duct 44 is connected to the cooling chamber 40, and the exhaust gas quenched in the cooling chamber 40 is discharged through the exhaust gas duct 44. A dilution air supply pipe 43 is connected to the exhaust gas duct 44, and the junction air between the dilution air supply pipe 43 and the exhaust gas duct 44 allows the dilution air and the exhaust gas to join. The air for dilution may be air sucked for collecting dust in the building, or air exclusively supplied as dilution air.

The adsorbent supply section 4 is located downstream of the joining section 42.
5 and a blower 46 connected to the adsorbent supply unit 45 are provided. By supplying the adsorbent into the exhaust gas from the adsorbent supply unit 45 through the blower 46, the harmful substances are further reduced to a low level. be able to. In this case, slaked lime, activated carbon, coal ash and the like can be used as the adsorbent. A bag filter 47 is provided downstream of the adsorbent supply section 45.
Is installed, and the exhaust gas that has passed through the bag filter 47 is
The air is discharged to the atmosphere from a chimney 49 provided downstream of the blower 48 via a blower 48 provided downstream of the bag filter 47. Thus, the DC arc melting equipment 1 is configured.

When melting the cold iron source 16 in the DC arc melting equipment 1 configured as described above, first,
The cold iron source 16 is charged into the preheating chamber 3 using the supply bucket 15. The cold iron source 16 charged in the preheating chamber 3 is also charged in the melting chamber 2 and eventually fills the preheating chamber 3.
In order to uniformly charge the cold iron source 16 into the melting chamber 2,
The lid 5 can be opened and the cold iron source 16 can be inserted into the melting chamber 2 on the opposite side of the preheating chamber 3.

Then, the upper electrode 7 is moved up and down while supplying a direct current between the bottom electrode 6 and the upper electrode 7, and the space between the bottom electrode 6 and the upper electrode 7 or the inserted cold iron source 16. An arc 19 is generated between the electrode and the upper electrode 7. And
The cold iron source 16 is melted by the generated arc heat to melt the molten metal 17.
Is generated. With the generation of the molten metal 17, a flux such as quicklime or fluorite is charged into the melting chamber 2 to form a molten slag 18 on the molten metal 17, thereby preventing oxidation of the molten metal 17 and maintaining the temperature of the molten metal 17. If the amount of the molten slag 18 is too large, it can be discharged from the slag port 14 even during the melting operation.

From the time the molten metal 17 is formed, oxygen is blown from the oxygen blowing lance 8 and carbon material is blown from the carbon material blowing lance 9 into the molten metal 17 or the molten slag 18 in the melting chamber 2. The carbon material blown and dissolved in the molten metal 17 or the carbon material suspended in the molten slag 18 reacts with the blown oxygen to generate combustion heat, and acts as an auxiliary heat source to save power consumption. At the same time, the CO gas bubbles 11 of the reaction product form the molten slag 18 and the arc 19
Is a so-called slag forming operation in which the slag is wrapped in the molten slag 18, so that the efficiency of heating the arc 19 increases.

Also, a large amount of high-temperature CO gas and a part of this CO gas are generated by combustion of air entering the melting chamber 2 and air from the air blowing lance 12.
O ₂ gas passes through the preheating chamber 3 and is discharged through the duct 21 to efficiently preheat the cold iron source 16 in the preheating chamber 3.

The oxygen blown from the oxygen blowing lance 8 reacts with the molten metal 17 to form FeO, which is reduced by the blown carbon material. In this case, the amount of oxygen blown from the oxygen blowing lance 8 is 25 Nm ³ or more, preferably 40 Nm ³ per ton of the melt 17 to be melted.
It is preferably at least Nm ³ . Thereby, the cold iron source 16 can be more efficiently melted. The amount of carbon material blown is determined according to the amount of oxygen blown. That is,
A carbon material having a degree equivalent to the chemical equivalent of the oxygen to be blown is blown. If the amount of the injected carbon material is smaller than the amount of the injected oxygen, the molten metal 17 is excessively oxidized, which is not preferable.

With the formation of the molten metal 17, the cold iron source 16 in the preheating chamber 3 is melted in the melting chamber 2 according to the amount melted in the melting chamber 2.
The free iron source 16 is charged from the supply bucket 15 into the preheating chamber 3 in order to compensate for the decrease. The charging of the cold iron source 16 into the preheating chamber 3 is performed continuously or intermittently so as to keep the state where the cold iron source 16 is continuously present in the preheating chamber 3 and the melting chamber 2. At this time, the charging of the cold iron source 16 may be performed based on a recipe set in advance based on operation results, or the cold iron source 16 in the preheating chamber 3 may be charged.
May be provided, and the supply of the cold iron source 16 by the supply bucket 15 may be controlled based on a signal from the sensor. At that time, the preheating chamber 3
The amount of the cold iron source 16 continuously present in the
It is preferable that the amount is 50% or more of the cold iron source 16 for the heat.

After the cold iron source 16 is melted in this way and a predetermined amount of the molten metal 17, for example, the molten metal 17 for one heat is accumulated in the melting chamber 2, the components of the molten metal 17 are adjusted as necessary. While tilting the melting chamber 2 toward the tap 13, while keeping the state where the cold iron source 16 is continuously present in the melting chamber 2 and the preheating chamber 3, the door 22 that closes the tap 13 is opened,
The molten metal 17 for one heat is discharged from the tap hole 13 into a molten metal holding container (not shown). When the molten metal is poured, the molten metal 17 may be heated by the burner 10 in order to prevent the molten metal 17 from being blocked by the solidification of the molten metal 17. The predetermined amount of molten metal in the present invention is, for example, the amount of molten metal for one heat,
When leaving the molten metal 17 in the melting chamber 2 after tapping,
This is the sum of the amount of molten metal for one heat and the amount of residual molten metal in the melting chamber 2, and is an amount of molten metal that is appropriately determined according to the operating conditions.

In this case, since the cold iron source 16 is buried in the molten metal 17 and coexists, the temperature of the molten metal is close to the solidification temperature, and it is difficult to obtain a sufficient degree of superheat. for that reason,
When raising the temperature of the molten metal at the time of tapping, when a predetermined amount of the molten metal 17, for example, one heat, accumulates in the melting chamber 2, the melting chamber 2 is tilted toward the tapping port 13 side to cool the immersion in the molten metal 17. The iron source 16 is reduced, the contact area between the molten metal 17 and the cold iron source 16 is reduced, the molten metal 17 is heated by arc heating or the combined use of the arc heating and the burner 10, and the temperature is raised. You may take a bath. In this case, the molten metal 17 having a large degree of superheat can be obtained.

After tapping, if necessary, the molten metal 17 is heated and refined in a ladle refining furnace or the like, and then cast by a continuous casting machine or the like. After the molten metal 17 is discharged and the molten slag 18 is discharged as required, the melting chamber 2 is returned to a horizontal position, and the molten metal outlet 1 is discharged.
After filling the filling sand or the mud agent into 3 and the slag port 14, melting of the next heat is started. The method of melting the next heat is also carried out according to the above.

At the time of tapping, the molten metal 17 may be left in the melting chamber 2 to resume the melting of the next heat. In this case, since the molten metal 17 exists in the melting chamber 2, oxygen and carbon material can be blown in from the beginning of the melting, and the initial melting is promoted, and the melting efficiency is further improved. In this case, the residual amount of the molten metal 17 is set to 30 times in one heat so that oxygen and carbon material can be blown immediately after the restart of the next heat.
% Is preferable.

On the other hand, the exhaust gas containing unburned CO gas as a combustible component passes through the preheating chamber 3 and then reaches the combustion chamber 36 through the duct 21. At this time, the blower 32 is operated based on the measurement value of the gas flow meter 34, and the air supply pipe 33
Control the flow rate of the exhaust gas in the duct 21 to a sufficient flow rate that does not cause backfire, for example, 5 m / sec or more,
Maintain that flow rate.

The combustible components in the exhaust gas are supplied to the air supply pipe 33.
Combustion while mixing with air supplied from the
In the combustion chamber 36, the unburned CO gas in the exhaust gas is almost completely burned by air supplied through a combustion air supply pipe 38 as necessary, and the exhaust gas temperature is raised to a high temperature equal to or higher than a predetermined temperature. And From the viewpoint of effectively preventing the generation of harmful substances such as aromatic chlorine compounds typified by dioxin, and the generation of white smoke and offensive odor, the temperature of the exhaust gas after combustion in the combustion chamber 36 is promoted to decompose these. 850
C. or higher, preferably 900 ° C. or higher. An auxiliary burner 39 may be used to ensure that the temperature of the exhaust gas after combustion is equal to or higher than a predetermined temperature.

The exhaust gas heated to a predetermined temperature or higher in the combustion chamber 36 is rapidly cooled to about 200 ° C. in the cooling chamber 40, thereby preventing re-synthesis of harmful substances such as dioxin. Further, the exhaust gas is mixed with the dilution air at the joint 42 and cooled to about 100 ° C. Further, if necessary, the adsorbent supply unit 4
5 to supply an adsorbent to adsorb and remove harmful substances such as dioxin remaining in the exhaust gas. After the exhaust gas is dust-removed by the bag filter 47, the exhaust gas is emitted from the chimney 49 to the atmosphere.

By melting in this manner, the next heat can be started to be melted by the preheated cold iron source 16, and the power consumption can be greatly reduced.
In addition, the CO gas remaining unburned in the combustion chamber 36 is almost completely burned, and the temperature of the exhaust gas discharged therefrom is raised to a predetermined temperature or higher.
Since the exhaust gas is cooled by zero and the dilution air, it is possible to prevent the generation of harmful substances such as aromatic chlorine compounds typified by dioxin, and the generation of white smoke and malodor without a large-scale facility. Further, since the flow rate of the exhaust gas when air is supplied into the duct 21 and introduced into the combustion chamber 36 is increased to a flow rate that does not cause flashback, even if the amount of exhaust gas generated in the melting chamber 2 is reduced. Thus, abnormal combustion such as explosion due to combustible components in the exhaust gas in the preheating chamber 3 and the melting chamber 2 can be prevented without backfire in the duct 21.

In the above description, the case of DC arc melting equipment has been described. However, the present invention can be applied to AC arc melting equipment without any trouble. Further, the positional relationship between the preheating chamber 3 and the tap hole 13 in the melting chamber 2 is not limited to a position facing 180 degrees with respect to the center of the melting chamber 2 but may be a position at 90 degrees. Furthermore, although the blower 32 is operated based on the measurement result of the gas flow meter 34, it goes without saying that other control methods may be used.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention (example of the present invention) in the arc melting equipment shown in FIG. 1 will be described below. The arc melting equipment has a melting chamber with a diameter of 7.2 m, a height of 4 m, and a preheating chamber with a width of 3
m, length 5m, height 7m, melting chamber capacity is 18 in terms of molten steel
0 tons.

First, about 130 tons of normal temperature iron scrap was charged into the preheating chamber and the melting chamber as a cold iron source, and a graphite upper electrode having a diameter of 30 inches was used.
An arc was formed with a power supply capacity of, and melting was started. Immediately after energization, quicklime and fluorite were added, and oxygen was blown from an oxygen blowing lance at about 6000 Nm ³ / hr.
When molten steel had accumulated in the melting chamber, coke was blown into the slag at a rate of about 80 kg / min from a carbon material blowing lance, and the slag forming operation was started, and the tip of the upper electrode was buried in the formed slag. The voltage at this time was set to about 500V. When the iron scrap in the preheating chamber descends due to melting in the melting chamber, the iron scrap is charged into the preheating chamber by the supply bucket, and the height of the iron scrap in the preheating chamber is maintained at a constant height. Dissolution continued.

As described above, the melting is advanced in a state where the iron scrap is continuously present in the melting chamber and the preheating chamber, and when about 180 tons of molten steel is generated in the melting chamber, the molten steel continues into the melting chamber and the preheating chamber. About 60 tons of molten steel was left in the melting chamber while keeping the state in which iron scrap was present, and 120 tons of molten steel for one heat was poured into the ladle. The carbon concentration of molten steel at the time of tapping is 0.1% by mass, and the temperature of molten steel is 1565.
° C.

After the tapping, the electricity was supplied again and the blowing of oxygen and coke was resumed. The voltage at this time was 500 V again. After resuming, melting is continued while maintaining the height of the iron scrap in the preheating chamber at a constant level, and when the molten steel in the melting chamber reaches 180 tons again, about 60 tons of molten steel is left.
The tapping of 0 tons of molten steel was repeatedly performed.

As a result, the oxygen injection amount was 33 Nm ³ per ton of molten steel, and the coke injection amount was 2 N / ton of molten steel.
Under the condition of 6 kg, the average time from hot water to hot water is about 40
The power consumption per minute could be melted at 220 kWh per ton of molten steel. Furthermore, in the present invention example, since a sufficient amount of molten steel remains in the melting chamber and the next heat is restarted, slag forming operation by blowing oxygen and coke from the beginning of the next heat becomes possible, and voltage fluctuation is small,
The amount of flicker was small, the arc heating efficiency was high, and a sufficient melting rate could be ensured even if the power supply equipment was small. Furthermore, the noise at the initial stage of melting could be reduced.

The flow rate of exhaust gas when discharged from the preheating chamber is about 550 Nm ³ / min. Air is supplied from an air supply pipe into a duct connected to the combustion chamber, and unburned CO gas is burned in the combustion chamber. I let it. Exhaust gas temperature after combustion is 95
At 0 ° C., the flow rate was about 900 Nm ³ / min.
Next, the temperature of the exhaust gas was reduced to about 110 ° C. by cooling to 200 ° C. in the cooling chamber and then supplying air of about 1000 Nm ³ / min from the dilution air supply pipe. Further, about 1 kg of activated carbon per ton of molten steel was supplied to the exhaust gas as an adsorbent, and dust was removed by a bag filter.
By treating in this way, the dioxin concentration in the exhaust gas when discharged from the chimney is 0.01 ng TEQ /
An extremely low value of Nm ³ or less could be obtained. Further, the exhaust gas did not explode, and the operation could be continued stably.

For comparison, the same arc melting equipment as described above was used, and 120 tons of iron scrap were charged into the melting chamber and the preheating chamber for each heat, and all the charged iron scraps were melted. The operation by the melting method (conventional example) of tapping was also implemented.

Table 1 shows the results of a survey on the basic unit of power, the power supply equipment, the arc noise during operation, and the like, in comparison between the present invention and the conventional example. As shown in Table 1, under the same conditions of the oxygen consumption unit and the coke consumption unit, the present invention example was able to reduce the power consumption unit by about 30% as compared with the conventional example. or,
The power supply capacity and arc noise were also reduced by about 30%.

[0048]

[Table 1]

[0049]

As described above, according to the present invention,
High-efficiency melting is possible, power consumption can be greatly reduced, and harmful substances such as dioxin, white smoke,
Prevents the generation of offensive odors, and also stably continues operations that prevent abnormal combustion such as explosion of exhaust gas.
An industrially beneficial effect is provided.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an arc melting equipment embodying the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 DC arc melting equipment 2 Melting chamber 3 Preheating chamber 6 Bottom electrode 7 Upper electrode 13 Tap hole 15 Supply bucket 16 Cold iron source 17 Molten metal 18 Melt slag 19 Arc 31 Exhaust gas treatment equipment 33 Air supply pipe 36 Combustion chamber 40 Cooling chamber 47 Bag filter 49 Chimney

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F27D 17/00 104 F27D 17/00 104D (72) Inventor Takeshi Nakayama 1-1-2 Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. (72) Inventor Toshimichi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Nippon Kokan Co., Ltd. (72) Keiji Wakahara 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Shinhei Yamamoto 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4K014 CB01 CB02 CB07 CC00 CD16 4K045 AA04 BA02 DA01 DA04 RB02 RB16 4K056 AA05 BA01 BB08 CA02 DA02 DA33 DB03 DB05 DB08 4K063 AA04 AA12 BA02 CA01 CA02 GA02 GA09 GA37

Claims (2)

[Claims] 1. An arc melting apparatus comprising: a melting chamber; and a shaft-type preheating chamber directly connected to an upper portion of the melting chamber, wherein an exhaust gas generated in the melting chamber is introduced into the preheating chamber to preheat a cold iron source in the preheating chamber. In the method of melting the cold iron source used, while heating the cold iron source to the preheating chamber so as to keep the cold iron source continuously present in the preheating chamber and the melting chamber, the arc heating and the carbon material and oxygen and Is supplied to the melting chamber to melt the cold iron source in the melting chamber, and when a predetermined amount of molten metal has accumulated in the melting chamber, the molten metal is discharged in a state where the cold iron source is continuously present in the melting chamber and the preheating chamber. In doing so, an oxygen-containing gas is supplied to the exhaust gas discharged from the preheating chamber to increase the flow rate of the exhaust gas in the exhaust gas channel and burn the combustible components in the exhaust gas to make the exhaust gas temperature equal to or higher than a predetermined temperature. Cold iron source characterized by rapid cooling of exhaust gas Dissolution method. 2. An exhaust gas flow rate in said exhaust gas flow path of 5 m /
The method for dissolving a cold iron source according to claim 1, wherein the time is not less than seconds.