JPH1047860A - Dual type arc melting furnace and melting method of cold iron source employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive the improvement of productivity by recovering the sensitive heat as well as the latent heat of exhaust gas from a furnace more efficiently. SOLUTION: A dual type arc melting furnace, consisting of one set of power supply 2 and two sets of melting furnaces 1, 1', is provided with two sets of combustion chambers 5, 5', burning the exhaust gas of the furnace to obtain the exhaust gas having a higher temperature and provided between two sets of melting furnaces 1, 1', while the combustion chambers 5, 5' are connected through ducts 4, 6, 4', 6', and the furnace bodies are provided with a space in the furnace which is capable of receiving the whole amount of scrap 15' of one melting batch at one time of charging chance. Further, the ratio of a height L from the level of molten metal in the melting furnace to the upper end 17 of side wall in the furnace to the inner diameter D of the furnace or LID is designed so as to be 0.6-1.4. Cold iron source is molten by the dual type arc melting furnaces employing 40Nm<3> /t or more of oxygen for burning auxiliary fuel such as coke and the like. According to this method, an electric power consumption is reduced and productivity is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double arc melting furnace in which two melting furnaces are operated alternately and a method for melting a cold iron source using the same. In particular, the present invention aims at recovering exhaust gas generated from the melting furnace and effectively utilizing energy.

[0002]

2. Description of the Related Art Electric arc furnaces for steelmaking have been switched from AC arc melting furnaces to DC arc melting furnaces, and when newly installed, DC arc melting furnaces are often employed, contributing to environmental improvement and reduction of power consumption. doing. Recently, in order to improve productivity and reduce production costs, multiple melting furnaces are provided for one power supply, and high-temperature exhaust gas generated from the melting furnace during operation is introduced into the standby melting furnace. A so-called double melting furnace capable of performing an operation for preheating the scrap loaded in the melting furnace during standby and reducing the waiting time has been proposed.

[0003] As an example of the above-mentioned double arc melting furnace, for example, Japanese Patent Application Laid-Open No. 62-29889 discloses a method of recovering heat from high-temperature exhaust gas generated from a melting furnace in operation by a plurality of alternately operated melting furnaces. In a double melting furnace equipped with a furnace, the scrap is charged into the melting furnace on standby, while the scrap is preheated by leading a part of the exhaust gas generated from the melting furnace in operation to the melting furnace on standby. In addition to heat recovery, a method of thermally decomposing odor components in scrap to be preheated by combining exhaust gas used for preheating with the remaining portion of exhaust gas generated from the melting furnace in operation (hereinafter, referred to as “ Prior art 1 ").

Japanese Patent Application Laid-Open No. 62-136514 also discloses a method for recovering heat from a high-temperature exhaust gas generated from a melting furnace during operation, in order to further improve the heat recovery rate. A combustion chamber is provided between the melting furnace in the middle and the melting furnace on standby-the combustible gas in the high-temperature exhaust gas generated from the melting furnace in operation is burned in the combustion chamber to produce a higher-temperature exhaust gas, which is known in the prior art. In the same manner as in 1, the waste gas is guided into the standby melting furnace to preheat the scrap, and an exhaust gas inlet for the standby melting furnace is provided at the lower part of the melting furnace, and a discharge port is provided at the upper part of the melting furnace, so that the gas in the melting furnace can be obtained. A method of preventing a short path of exhaust gas and further improving a heat recovery rate (hereinafter, referred to as “prior art 2”) is disclosed.

[0005]

According to the prior arts 1 and 2 described above, the non-energization time can be shortened, and the productivity can be improved.
The heat recovery effect of the exhaust gas can be improved. However, the amount of scrap that can be charged into the melting furnace during standby is limited by the internal volume of the melting furnace, so that it is not possible to preheat the entire amount of scrap for one melting at a time. However, in the case of Prior Art 1, since a separate preheating chamber is provided, the amount heated in the preheating chamber can be added to the amount that can be preheated in the melting furnace in standby. However, even in this case, the internal volume of the melting furnace is limited, and it is not possible to charge the entire amount of scrap for one melting at the first chance of charging the operating furnace. Therefore, there is a problem that it is not possible to avoid dissipating the furnace heat at the time of additional charging of the scrap, and it is not possible to avoid a decrease in productivity due to generation of dust and interruption of power supply at the time of additional charging.

Accordingly, an object of the present invention is to solve the above-mentioned problems and improve the productivity in a double melting furnace, and introduce high-temperature exhaust gas generated from an operating melting furnace into a standby melting furnace. It is an object of the present invention to provide a double arc melting furnace capable of preheating the scrap and improving the heat recovery rate from the high-temperature exhaust gas as compared with the related art, and a method of melting a cold iron source such as scrap using the same.

[0007]

SUMMARY OF THE INVENTION From the above-mentioned viewpoints, the inventors of the present invention have made intensive studies to develop an arc melting furnace capable of reducing power consumption by increasing the heat recovery rate from high-temperature exhaust gas. Was piled up. As a result, the following findings were obtained.

[0008] The melting furnace is a furnace body having an inner volume capable of charging the entire amount of scrap for one melting, and the furnace body is installed in a double type with a single power supply system. The exhaust gas during refining is used for preheating the entire preheated scrap in the other furnace. By doing so, first, since the entire amount of scrap for one melt is charged in the furnace, scrap preheating is efficiently performed. Accordingly, the scrap heating efficiency in the melting period in one furnace body is increased, and
The sensible heat of the exhaust gas generated in the one furnace body is effectively used for the preheating of the scrap to be preheated (the total amount of scrap for one melt) in the other furnace body during standby. Thus, the efficiency of scrap heating and preheating in each furnace body is improved.

[0009] In the operation using the above facilities, when an auxiliary fuel such as coke is further burned, the heat source added by the combustion heat is also applied according to the same principle as the scrap heating and preheating in each of the furnace bodies. Efficiency is improved.

[0010] Further, in the above-mentioned double arc melting furnace equipment, when the shape of the furnace body is set to a predetermined value L / D, which is a ratio of the height L from the molten steel surface to the upper end of the side wall in the furnace and the inner diameter D of the furnace, the scrap is scrapped. Heating and preheating efficiency are further improved. And
In dissolving scrap using such equipment, if the amount of the auxiliary fuel is increased and the amount of oxygen used to burn the auxiliary fuel is increased to 40 Nm ³ / t or more, the effect of the increased auxiliary fuel is obtained. Efficiency is improved. In this way, the sensible heat and latent heat of the exhaust gas generated from the melting furnace during operation are more effectively used for heating and preheating of the scrap.

On the other hand, the maximum input power can be made smaller than before by the operation mode in which melting / refining and scrap preheating are alternately repeated. It has been found that the above-described equipment and the method of using the same enable high-efficiency melting that could not be achieved by a conventional arc furnace, and reduce power consumption per unit weight of melting.

The present invention has been made based on the above-mentioned findings, and the double arc melting furnace according to the first aspect of the present invention has two melting furnaces for alternately performing preheating and melting and refining of raw materials such as scrap. A power supply device that can be switched to operate any one of the two melting furnaces, and a preheated raw material is fed to one of the two melting furnaces. In a double-arc melting furnace equipped with a duct facility for introducing high-temperature exhaust gas generated in one melting furnace during melting and refining to the other melting furnace and for preheating the raw material in the other melting furnace, Each of the furnaces is characterized in that it has a capacity to accommodate the entire amount of scrap used for melting and refining at one chance of initial charging.

A double arc melting furnace according to a second aspect of the present invention is the double arc melting furnace according to the first aspect, in which a high-temperature exhaust gas generated in one of the melting furnaces is burned to generate a higher-temperature combustion gas. It is characterized in that a chamber is additionally provided in a duct facility.

A double arc melting furnace according to a third aspect of the present invention is the double arc melting furnace according to the first or second aspect, wherein the height L and the inner diameter D of the melting furnace from the surface in the furnace to the upper end of the side wall in the furnace.
Is characterized by satisfying the formula: L / D = 0.6 to 1.4.

According to a fourth aspect of the present invention, there is provided a method for melting a cold iron source using a double arc melting furnace, wherein the double arc melting furnace according to any one of claims 1 to 3 is used. It is characterized in that auxiliary fuel such as coke is burned in a melting furnace.

According to a fifth aspect of the present invention, there is provided a method for melting a cold iron source using a double arc melting furnace, comprising the steps of: It is characterized by using oxygen of 40 Nm ³ / t or more for combustion.

[0017]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory view of a multiple direct current arc melting furnace showing one embodiment of the present invention. In the figure, 1 and 1 'are melting furnaces, 1a and 1a' are electrodes, 2 is a DC power supply, and 5 and 5 'are combustion chambers.
The two melting furnaces 1 and 1 ′ have a common DC power supply 2
And the secondary side conductors 3 are selectively connected to operate alternately, and while one melting furnace is in operation, the other melting furnace is designed to be on standby. Furnace exhaust gas ducts 4 and 4 'are provided in these melting furnaces 1 and 1'.
Are connected to each other, and two combustion chambers 5 and 5 ′ are provided between the furnace exhaust gas ducts 4 and 4 ′. The upper and lower portions of the combustion chambers 5 and 5 'are connected by an upper preheating duct 6 and a lower preheating duct 6', respectively. A bypass duct 7 is provided branching from an intermediate portion of the lower preheating duct 6 '. Are connected to one end of two discharge ducts 8 and 8 '. Discharge ducts 8 and 8 '
On the way, the side walls 9 and 9 'of each melting furnace 1 and 1'
Exhaust gas ducts 10 and 10 'each having an outlet at the bottom are connected, and the other ends of the discharge ducts 8 and 8' are joined downstream and connected to a dust collector (not shown) via an exhaust fan (not shown). I have.

On the other hand, the duct is provided with a predetermined damper. That is, dampers 11 and 11 'are provided in the furnace exhaust gas ducts 4 and 4', and dampers 12 and 12 'and 1 are provided in the upper preheating duct 6 and the lower preheating duct 6'.
2 ", the discharge ducts 8 and 8 'are provided with dampers 13 and 13', and the exhaust gas ducts 10 and 10 'are provided with dampers 14 and 14'.

Next, the operation mode of the above-mentioned compound DC arc melting furnace will be described with reference to FIG. The secondary-side conductor 3 is connected from the DC power supply 2 to one of the melting furnaces 1 which has been preheated and contains the entire amount of the scrap 15 for one melting. In the other melting furnace 2, the electrode 1 a ′ is raised and the entire amount of the scrap 15 ′ for one melting is charged therein, and then the furnace opening is sealed with a furnace lid 1 b ′ having an electrode hole covered. Next, predetermined damper operations are performed, that is, the dampers 11 and 11 'of the furnace exhaust gas ducts 4 and 4', the damper 12 of the upper preheating duct 6, the damper 13 'of the discharge duct 8' and the damper 14 'of the exhaust gas duct 10' are opened. West,
With all the other dampers closed, energization of the melting furnace 1 is started, and the scrap 15 in one melting furnace 1 is heated,
Dissolve and perform the specified refining. The high-temperature exhaust gas generated from the melting furnace 1 during this heating, melting and refining is discharged into a discharge duct 8.
And 8 'are introduced into one combustion chamber 5 via a furnace exhaust gas duct 4 by a suction action of a blower (not shown) downstream of the exhaust gas, and then introduced into the other combustion chamber 5' to remove The combustibles are burned to generate a combustion gas whose temperature is further increased, and the combustion gas is introduced into the other melting furnace 1 'through the furnace exhaust gas duct 4', and the scrap 15 'in the furnace is heated and heated. The passage paths of the exhaust gas and the combustion gas described above are shown by solid-line arrows in FIG.

When predetermined refining is completed in one of the melting furnaces 1, the energization is stopped, the furnace exhaust gas duct 4 and the exhaust gas duct 14 are separated from the melting furnace 1, and the melting furnace 1 is tilted to produce steel. Next, the secondary-side conductor 3 is immediately connected to the other melting furnace 1 ', and the operation of the melting furnace 1' is started. At this time, the damper 12 ″ of the lower preheating duct 6 ′ is opened and the dampers 12, 12 ′, 13, and 14 are opened until the furnace repair of the melting furnace 1 and the operation of charging the scrap into the melting furnace 1 are completed. The exhaust gas generated from the melting furnace 1 'is closed by passing the exhaust gas through the combustion chamber 5' to burn combustibles, and then discharged via the discharge duct 8 '. In FIG. 1, it is indicated by a dashed arrow.

When the preparation of the melting furnace 1 is completed, the duct 1
2 "and 13 'are closed, ducts 12 and 13 are opened, and the furnace exhaust gas duct 4 and the exhaust gas duct 14 are connected to the melting furnace 1 so that the exhaust gas generated from the melting furnace 1' is passed through the combustion chambers 5 and 5 '. After the combustible components are burned, the scrap is guided to the melting furnace 1 and the scrap in the furnace is preheated, so that the exhaust gas generated from the melting furnace 1 ′ is used in the melting furnace 1, contrary to the operation of the melting furnace 1. Heat and preheat scrap for one dissolution.

By repeating the above procedure and alternately operating the two melting furnaces 1 and 1 ', the non-energizing time is shortened to shorten the steelmaking cycle time (the time required from tapping to tapping). In addition, the entire amount of scrap for one melting can be preheated to a high temperature in the melting furnace in a standby state, so that heat can be recovered with higher efficiency than before.

Next, regarding the furnace body shape and dimensions of the melting furnace,
Assuming that the entire amount of scrap for one dissolution is charged,
The ratio L / D of the height L from the furnace inner surface to the upper end of the side wall in the furnace and the inner diameter D of the furnace is a factor that affects the relationship between the efficient shape and generation direction of the arc and the scrap distribution in the furnace. This greatly affects the heat transfer efficiency from arc to scrap. Therefore, focusing on this heat transfer efficiency, the condition that L × D ² is constant, that is, using various practical L / D small arc furnaces in which the furnace volume above the surface of the molten metal is constant. The heat loss carried out of the arc furnace by the exhaust gas of the generated gas was tested. Test dissolution was performed in any charge.
The scrap furnace having a constant bulk density was used, all the scraps were initially charged, and an arc furnace test operation was performed by a conventional method.

FIG. 2 is a graph showing the relationship between the ratio L / D of the height L from the molten metal surface to the upper end of the side wall in the furnace and the inner diameter D of the furnace, and the heat loss ratio of the exhaust gas. However, the heat loss ratio of the exhaust gas is
It is expressed as a ratio of the sum of the sensible heat and the latent heat of the exhaust gas in the test charge to the sum of the sensible heat and the latent heat of the exhaust gas in the test charge when L / D = 0.55.

As is clear from FIG. 2, as the L / D increases, the heat loss ratio of the exhaust gas decreases. L / D is 0.
The heat loss ratio of the exhaust gas in 6 decreased to about 0.90,
The effect is also useful in operating costs. Furthermore, L /
As D increases, the heat loss ratio of exhaust gas decreases.
However, even when L / D exceeds 1.4, the amount of decrease in the heat loss ratio of the exhaust gas is small and almost saturated. On the other hand, as the L / D increases, there is a disadvantage that the specifications of the electrode lifting device, the building, the crane equipment, the furnace cooling equipment, and the like must be increased, and the L / D exceeds 1.4. And the disadvantages described above become a problem. In consideration of the heat loss ratio of the exhaust gas, and the investment and operation costs of the above facilities, it is desirable that L / D is in the range of 0.7 to 1.2.

Therefore, in order to improve the melting efficiency of scrap and reduce the total cost, the L / D should be in the range of 0.6 to 1.4, more preferably 0.7 to 1.2. There should be.

Further, each of the furnace bodies of the multiple direct current arc melting furnace of the present invention is capable of charging the entire amount of scrap necessary for tapping one charge in one charging chance. It is necessary to have a product. Thus, a desired furnace size can be obtained by determining the scrap charging amount and L / D of one charge and calculating L and D determined in accordance with the determined amount. In a normal arc furnace, the following equation (2) is provided between L, D and the charged amount W of scrap: L / D = (4 / π) ｛(ρ ₁ −ρ _S ′) / Ρ _l ρ _S '｝ (W / D ³ ) ---------------- (2) where ρ _l : density of molten steel ρ _S ': bulk density of scrap W: There is a relationship between the amount of scrap charged. In the arc furnace, various forms of scrap for steelmaking are used, and the bulk density of these scraps ranges from 0.3 to 1.0 t / m ³ , but the weighted average value is 0. It is about 0.7 t / m ³ . Therefore, the scrap charging amount W for one charge and L /
If D is given, the height L from the molten metal surface to the upper end of the side wall in the furnace,
And the furnace inner diameter D is required. For example, W = 120t
Then, L / D, which is a desirable condition in the present invention, is satisfied.
In order to satisfy ≧ 0.6, the furnace inner diameter D ≦ 6.9 is required.
(M), and the height L from the molten metal surface to the upper end of the furnace inner wall may be L ≧ 0.6 × D (m) in accordance with the value of D.

As described above, L / D is set to 0.6 to 1.
4 or within the range of 0.7 to 1.2, the heat recovery of the exhaust gas is improved according to the respective limits, and the total amount of scrap for one dissolution is increased at the initial charging chance. The size and shape of the furnace that can be charged can be determined.

In the present invention, since the entire amount of scrap for one dissolution is charged at the initial charging chance, it is not necessary to open and close the furnace lid during operation, and the furnace heat loss accompanying the opening and closing of the furnace lid is eliminated. . Further, in the melting period, the arc from the electrode is generated by being surrounded by the scrap, and the heat transfer efficiency to the scrap increases. Further, since the scrap can be charged into the central portion of the furnace, for example, it is likely to occur when scrap is continuously charged into the furnace wall of the furnace body.
Problems such as the fusion of scrap to the furnace inner wall due to insufficient supply of arc heat to the furnace inner wall are solved.

Further, in the arc melting furnace, auxiliary fuel such as coke, oil, and natural gas is used as an auxiliary heat source to reduce the unit power of melting electric power. FIG. 3 shows that in a 140 ton double direct current arc melting furnace having an L / D of 0.85,
The test result of the relationship between the amount of oxygen used for combustion of the auxiliary fuel and the unit power of dissolved electric power is shown. As is clear from the figure, the power consumption unit tends to decrease with an increase in the oxygen amount, and in particular, sharply decreases at 40 Nm ³ / t or more. This is because the effect of heating the scrap in one of the melting furnaces and the effect of preheating the scrap in the other furnace by the exhaust gas generated in the melting furnace are due to the fact that the combustion oxygen of the auxiliary fuel is 40N.
Significant values are shown above m ³ / t. However, when the type of auxiliary fuel is constant, the amount of combustion oxygen is increased in proportion to the supply amount. Therefore, the amount of oxygen used for combustion of the auxiliary fuel should desirably be 40 Nm ³ / t or more.

[0031]

Next, the present invention will be described in more detail with reference to examples. In the embodiment of the present invention shown in FIG.
The preheated scrap 15 of soluble components by dissolving and refining in a melting furnace 1, the combustible components in the high-temperature exhaust gas generated during the two combustion furnace 5 and 5 ', is burned with O ₂ gas supplied thereto, further The heated combustion gas was led to the melting furnace 1 'to preheat the scrap 15', and the used combustion exhaust gas was discharged through a dust collector (not shown). The passage paths of the exhaust gas and the combustion gas are as shown by solid arrows in FIG.

FIG. 4 is a schematic vertical sectional view of a DC arc melting furnace as the melting furnace 1 (1 '). FIG. L to the upper end 17 of the side wall (free board), and D the furnace inner diameter. A furnace lid 19 is fixed to an upper portion of the furnace body 18, an upper electrode rod is inserted into the furnace lid 19 as an electrode 1a, a furnace exhaust gas duct 4 (4 ') is connected, and another furnace bottom 20 is connected to the furnace bottom 20. A furnace bottom electrode 21 and a gate 22 are provided as two electrodes.

Table 1 shows Examples 1 and 2 which are melting methods using a single charging double direct current arc melting furnace within the scope of the present invention, and conventional double charging outside the scope of the present invention. In the comparative example, which is a melting method using a double direct current arc melting furnace, the specifications of the melting furnace and the main operating conditions are shown.

[0034]

[Table 1]

The main difference between Examples 1 and 2 and the comparative example is the value of the ratio L / D between the free board L and the furnace inner diameter D. Since both are double-arc melting furnaces, the operation uses preheated scrap. In the comparative example, only the scrap of the first charging chance is preheated, whereas in Examples 1 and 2, The difference between the two is that the entire amount of scrap for one dissolution is preheated.

Table 2 shows the results of the overall heat balance in a test operation performed using each of the double direct current arc melting furnace of the present invention and the comparative direct current arc melting furnace.

[0037]

[Table 2]

The following items can be understood from the test results in Table 2. The sensible heat of the exhaust gas and the heat output of the latent heat are larger in the comparative example than in Examples 1 and 2. In contrast, Examples 1 and 2
, The heat output of the exhaust gas sensible heat and the latent heat is small. For this reason, comparing the input power in both cases,
In this example, the power consumption is reduced by 50 kWh as compared with the comparative example, and in Example 1, the power consumption is reduced by 125 kWh than in the comparative example. Example 1 is superior to Example 2 because the amount of oxygen used for combustion of the auxiliary fuel in the melting furnace was increased.

The present invention is not limited to a DC arc melting furnace, but can be applied to an AC arc melting furnace.

[0040]

As described above, according to the present invention,
The productivity can be improved by avoiding a decrease in productivity due to interruption of power supply, and at the same time, the heat recovery effect of the exhaust gas can be increased more than before, so that the production cost can be reduced. It is possible to provide a double arc melting furnace capable of preventing dust generation at the time of additional charging and a method for melting a cold iron source using the same, and an industrially useful effect is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view showing one embodiment of a multiple direct current arc melting furnace of the present invention.

FIG. 2 is a graph showing a relationship between a ratio L / D of a height L from a molten metal surface to an upper end of a side wall in the furnace and an inner diameter D of the furnace in a DC arc furnace, and a heat loss ratio of exhaust gas.

FIG. 3 is a graph showing the relationship between the amount of oxygen used and the unit power of dissolved electric power.

FIG. 4 is a schematic vertical sectional view of a main part of the melting furnace of FIG.

[Explanation of symbols]

1, 1 'melting furnace 1a 1a' electrode 1b 1b 'furnace lid 2 DC power supply equipment 3 secondary side conductor 4, 4' furnace exhaust gas duct 4a electrode charging hole 4b exhaust gas port 5, 5 'combustion chamber 6 upper preheating duct 6 'Lower preheating duct 7 Bypass duct 8, 8' Discharge duct 9, 9 'Side wall 10, 10' Discharge duct 11, 11 'Damper 12, 12', 12 "Damper 13, 13 'Damper 14, 14' Damper 15, 15 'Scrap 16 Hot surface 17 Upper side wall 18, 18' Furnace body 19 Furnace bottom 20 Furnace bottom electrode 21 Gate 22 Molten steel 23 Molten steel in the middle of melting period 24 Electric furnace exhaust gas 25 Burned exhaust gas L From furnace surface to upper end of side wall Height (free board) D Furnace inner diameter

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location F27D 17/00 101 F27D 17/00 101G (72) Inventor Keiji Wakahara 1-1-1 Marunouchi, Chiyoda-ku, Tokyo No. 2 Nihon Kokan Co., Ltd.

Claims (5)

[Claims] 1. Two melting furnaces for alternately performing preheating and melting and refining of a raw material, and one melting furnace that can be switched to operate any one of the two melting furnaces. A power supply facility, and a high-temperature exhaust gas generated in one of the two melting furnaces during melting and refining of the preheated raw material in one of the two melting furnaces is introduced into the other melting furnace. In a double arc melting furnace equipped with a duct facility for preheating the raw material in the melting furnace, the melting furnace has a capacity to accommodate the entire amount of scrap used for the melting and refining at one chance of initial charging. A double arc melting furnace. 2. A combustion chamber for burning the high-temperature exhaust gas generated in the one melting furnace to generate a higher-temperature combustion gas is additionally provided in the duct facility. Item 2. The double arc melting furnace according to Item 1. 3. The relation between the height L from the surface of the furnace inside the melting furnace to the upper end of the side wall in the furnace and the inside diameter D of the furnace is expressed by the formula: L / D.
The double arc melting furnace according to claim 1 or 2, wherein a value of 0.6 to 1.4 is satisfied. 4. An auxiliary fuel such as coke is burned in the melting furnace during melting and refining using the double arc melting furnace according to any one of claims 1 to 3. , A method of melting a cold iron source using a double arc melting furnace. 5. The cold iron source according to claim 4, wherein oxygen of 40 Nm ³ / t or more is used to burn the auxiliary fuel such as coke. Dissolution method.