JPWO2016120943A1 - Method for producing molten iron with electric furnace - Google Patents

Abstract

In a method of melting iron scrap in an electric furnace equipped with an auxiliary burner to obtain molten iron, the iron scrap is efficiently heated or melted by the auxiliary burner. When heating or melting iron-based scrap in an electric furnace using an auxiliary combustion burner, two or more kinds of fuels having different ignition temperatures or / and combustion speeds are used as auxiliary combustion burner fuel. The auxiliary combustion burner and the auxiliary combustion burner The ratio of the two or more kinds of fuels is changed according to the distance from the iron-based scrap to be heated or melted. The flame length of the auxiliary burner can be arbitrarily adjusted by the ratio of two or more kinds of fuels, and iron-based scrap can be efficiently heated or melted.

Description

  The present invention relates to a method for producing molten iron by melting iron-based scrap in an electric furnace equipped with an auxiliary burner.

When melting iron-based scrap using an electric furnace, the iron-based scrap around the electrode dissolves quickly, but the iron-based scrap away from the electrode, that is, in the cold spot, dissolves slowly. Non-uniformity occurs in the melting rate of the system scrap. For this reason, the operation time of the entire furnace was limited to the melting rate of cold scrap iron-based scrap.
Therefore, in order to eliminate such non-uniformity in the melting rate of iron scrap and to dissolve the iron scrap in the entire furnace in a well-balanced manner, an auxiliary burner is installed at the cold spot, and the cold spot is used with this auxiliary burner. A method of preheating, cutting and melting iron-based scrap located in the area has been adopted.

  As such an auxiliary combustion burner, for example, in Patent Document 1, oxygen gas for scattering of incombustibles and cutting of iron-based scrap is ejected from the center, and fuel is further supplied from the outer periphery of the oxygen gas. A burner having a triple tube structure is described for injecting combustion oxygen gas from the outer periphery, and in order to increase the velocity of oxygen gas ejected from the center, the tip of the oxygen gas ejection tube in the center is described. A high-speed electric furnace for electric furnaces that has a constricted portion and has swirl vanes installed in an annular space formed by a fuel jet pipe and a combustion oxygen gas jet pipe to impart a swirling force to the combustion oxygen gas jetted from the outermost periphery. A pure oxygen-assisted burner has been proposed.

Even if the burner described in Patent Document 1 is used as an auxiliary burner, in the operation of the electric furnace, the distance between the auxiliary burner and the iron scrap changes due to the charging, additional charging and melting of the iron scrap. In general, the distance between the auxiliary burner and the iron-based scrap is small at the start of operation and in the initial stage of addition, and the distance increases as the melting of the iron-based scrap proceeds. Therefore, in order to operate the auxiliary burner efficiently, it is important to adjust the length of the burner flame according to the distance between the auxiliary burner and the iron-based scrap.
Therefore, Patent Document 2 discloses an auxiliary burner in which the length of the flame can be adjusted by changing the ratio of the cutting oxygen gas supply amount and the combustion oxygen gas supply amount at the center.

Japanese Patent Laid-Open No. 10-9524 JP 2012-172867 A

  By using the technique described in Patent Document 2, iron-based scrap can be efficiently preheated and melted using an auxiliary burner. However, there is a problem in that cutting oxygen is essential and not only the shape of the burner is complicated, but also the oxygen production apparatus needs to be enhanced with an increase in the amount of oxygen used, and the initial investment is increased. In addition, since the amount of combustion oxygen gas is stoichiometrically dependent on the amount of fuel used, there is a problem that operating conditions are restricted.

  Therefore, the object of the present invention is to solve the above-described problems of the prior art and to melt iron-based scrap in an electric furnace equipped with an auxiliary combustion burner to obtain molten iron when the technique of Patent Document 2 is used. It is an object of the present invention to provide a method for producing molten iron that can efficiently heat or melt iron-based scrap with an auxiliary burner without causing a problem.

  The present inventors paid attention to the fuel used for the auxiliary combustion burner, and obtained the idea of adjusting the length of the burner flame by properly using different types of fuels, and repeated studies. As a result, the inventors have a difference in the flame length depending on the ignition temperature and combustion speed of the fuel. For this reason, two or more kinds of fuels having different ignition temperatures or / and combustion speeds are used. It has been found that the flame length can be arbitrarily adjusted by changing the fuel ratio.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] A method of melting molten iron scrap in an electric furnace equipped with an auxiliary burner to obtain molten iron, using two or more types of fuels with different ignition temperatures and / or burning rates as auxiliary burner fuel. A method for producing molten iron using an electric furnace, wherein the ratio of the two or more fuels is changed according to the distance between the burner and the iron scrap to be heated or melted by the auxiliary burner.
[2] A method for producing molten iron using an electric furnace, characterized in that, in the production method of [1], two or more kinds of fuels selected from gaseous fuel, liquid fuel and solid fuel are used.
[3] A method for producing molten iron using an electric furnace, wherein at least gaseous fuel and solid fuel are used in the production method of [2].

[4] In the manufacturing method according to any one of [1] to [3] above, a plurality of injection tubes arranged concentrically, a solid fuel is injected from a central injection tube, and an injection tube outside thereof A method for producing molten iron using an electric furnace, comprising using an auxiliary burner for injecting gaseous fuel from a gas and further injecting combustion-supporting gas from an outer injection pipe.
[5] In the manufacturing method according to any one of [1] to [3], a plurality of injection tubes arranged concentrically are provided, cutting oxygen is injected from a central injection tube, and injection is performed outside of the cutting oxygen. A method for producing molten iron by an electric furnace, comprising using an auxiliary burner for injecting solid fuel from a pipe, further injecting gaseous fuel from an outer injection pipe, and further injecting supporting gas from the outer injection pipe .

[6] An electric furnace for melting iron scrap and obtaining molten iron, having a plurality of concentric injection pipes, injecting solid fuel from a central injection pipe, An electric furnace comprising an auxiliary combustion burner for injecting gaseous fuel from an injection pipe and further injecting combustion-supporting gas from an outer injection pipe.
[7] An electric furnace for melting iron-based scrap to obtain molten iron, having a plurality of concentric injection pipes, and injecting cutting oxygen from a central injection pipe An electric furnace comprising an auxiliary combustion burner for injecting solid fuel from an injection tube of the gas, further injecting gaseous fuel from an outer injection tube, and injecting combustion-supporting gas from the outer injection tube.

  According to the present invention, when heating or melting iron-based scrap in an electric furnace using an auxiliary combustion burner, two or more kinds of fuels having different ignition temperatures or / and combustion rates are used, and the auxiliary combustion burner and the auxiliary combustion burner are used. The flame length of the auxiliary burner can be adjusted arbitrarily by changing the ratio of the two or more types of fuel according to the distance from the iron scrap to be heated or melted, and the iron scrap can be efficiently heated or melted. can do. For this reason, it is possible to save power consumption and shorten the operation time.

FIG. 1 is a partial cross-sectional side view showing an example of an auxiliary combustion burner used in the present invention. FIG. 2 is an enlarged cross-sectional view of a part A in FIG. 3 is a cross-sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is an explanatory diagram schematically showing an example of the implementation status of the method of the present invention. FIG. 6 shows the ratio of the solid fuel in the fuel and the flame temperature in the test in which the gas temperature (LPG) and the solid fuel (pulverized coal) were used as the fuel for the auxiliary burner and the flame temperature was measured by changing the ratio between them. It is a graph which shows the result of having investigated the relationship.

The present invention is a method of obtaining molten iron by melting iron-based scrap (hereinafter simply referred to as “scrap” for convenience of explanation) in an electric furnace equipped with an auxiliary combustion burner, and as an auxiliary combustion burner fuel, an ignition temperature or / and Two or more kinds of fuels having different combustion rates are used, and the ratio of the two or more kinds of fuels is changed according to the distance between the auxiliary burner and the scrap to be heated or melted by the auxiliary burner.
The flame length varies depending on the ignition temperature and combustion speed of the fuel used for the auxiliary burner. For this reason, by using two or more kinds of fuels having different ignition temperatures or / and burning speeds and changing the ratio of these two or more kinds of fuels, the flame length of the auxiliary burner (at a position away from the burner by a certain distance). The flame temperature can be adjusted arbitrarily.

As elements necessary for combustion, there are three elements of a combustible substance, oxygen, and temperature (fire source). Moreover, as the state of the combustible substance, the ease of combustion is in the order of gas, liquid, and solid. This is because, in a gaseous state, mixing of the combustible substance with oxygen and temperature (fire source) is easy, and continuation of combustion (chain reaction) is performed.
When gas is burned as a flammable substance using an auxiliary burner, the gas generally burns immediately immediately after being injected from the tip of the burner, depending on the oxygen concentration, flow velocity, and burner tip shape. On the other hand, when a solid fuel typified by coal is used as a combustible substance, it is difficult to burn it quickly like a gas. This is due to the fact that the ignition temperature of coal is about 400 to 600 ° C., and that this ignition temperature is maintained and that the temperature rise time to the ignition temperature is necessary. The temperature raising time to the ignition temperature depends on the particle size (specific surface area), and if the particles are made fine, the ignition time can be shortened. However, it is difficult to make solid combustion faster than gas combustion.

The present invention controls the flame length of the auxiliary burner using the difference in the ignition temperature or the combustion speed of the fuel as described above.
First, a case where two or more kinds of fuels having different ignition temperatures are used as fuel for the auxiliary combustion burner will be described.
Examples of fuels having greatly different ignition temperatures include combinations of fuels having different phases (gas phase, liquid phase, solid phase). That is, it is a combination of two or more kinds of fuels selected from gaseous fuel, liquid fuel, and solid fuel. The ignition temperature of these fuels is generally solid fuel> liquid fuel> gaseous fuel.
Hereinafter, a case will be described in which gaseous fuel and solid fuel are used for the auxiliary burner, LNG (liquefied natural gas) is used as the gaseous fuel, coal (pulverized coal) is used as the solid fuel, and pure oxygen is used as the combustion support gas.

When LNG and coal are used as fuel for the auxiliary combustion burner, a combustion field above the ignition temperature of coal is created by the combustion of LNG and pure oxygen, and the temperature rises to the ignition temperature when coal is sent to this combustion field. Combustion (vaporization → ignition) occurs. The flame temperature decreases with the amount of heat required to increase the coal temperature, but the temperature increases in the region where coal ignition occurs.
Therefore, when the LNG ratio is higher than that of coal, the flame generated by the auxiliary burner has a high temperature near the burner tip (that is, a short flame). However, if the ratio of coal is higher than LNG, the endotherm of coal Due to the subsequent heat generation, a high temperature is obtained even at a position far from the tip of the burner (that is, a long flame is formed). Therefore, by changing the ratio of LNG to coal, the flame length (flame temperature at a position away from the burner by a certain distance) can be controlled.

  The principle as described above is also applicable to combinations of other fuels having different ignition temperatures. For example, even in a combination of gaseous fuel (for example, LNG) and liquid fuel (for example, heavy oil, kerosene, etc.), if the ratio of gaseous fuel is made higher than that of liquid fuel, a short flame is produced, and if the ratio of liquid fuel is made higher than gaseous fuel. It becomes a long flame. Also, in a combination of liquid fuel (eg, heavy oil, kerosene, etc.) and solid fuel (eg, coal, etc.), if the ratio of liquid fuel is made higher than that of solid fuel, a short flame will result, and if the ratio of solid fuel is made higher than that of liquid fuel. It becomes a long flame.

Next, a case where two or more kinds of fuels having different combustion rates are used as the fuel for the auxiliary combustion burner will be described.
Fuels with greatly different combustion rates include some of the above-mentioned combinations of fuels with different ignition temperatures (for example, a combination of gaseous fuel and solid fuel, gaseous fuel and liquid fuel). And a combination of LNG and hydrogen. The fuel burning speed in the burner is a speed at which the fuel burns in the direction opposite to the fuel supply direction. In general, the burning speed of fuels having different phases is gas fuel> liquid fuel> solid fuel.
In this case, when the ratio of the fuel having a high combustion rate (for example, gaseous fuel such as LNG) is higher than the fuel having a low combustion rate (for example, solid fuel such as coal), the position close to the burner tip becomes high (that is, If the ratio of the fuel having a low combustion rate is higher than that of the fuel having a high combustion rate, the temperature becomes high even at a position far from the burner tip (that is, a long flame). Therefore, the flame length (flame temperature at a position away from the burner by a certain distance) can be controlled by changing the ratio of both fuels.

  In the operation of an electric furnace, the distance between the auxiliary burner and the scrap changes due to the charging, additional charging and melting of the scrap. Generally, the distance between the auxiliary burner and the scrap is small at the start of operation or in the initial stage of addition, and increases with the progress of melting of the scrap. This is because the distance from the undissolved scrap to the auxiliary burner increases with the progress of melting of the scrap because the scrap is first melted in order from the scrap closest to the auxiliary burner. Therefore, in the present invention, as the fuel for the auxiliary burner, two or more kinds of fuels having different ignition temperatures or / and combustion rates are used, and depending on the distance between the auxiliary burner and the scrap to be heated or melted by the auxiliary burner, The flame length of the auxiliary burner is adjusted (changed) by changing the ratio of two or more types of fuel so that the flame of the auxiliary burner reaches the scrap regardless of the distance between the scrap and the auxiliary burner. For example, when gaseous fuel and solid fuel or liquid fuel are used as fuel, when the distance between the auxiliary burner and scrap is small, the ratio of the gaseous fuel is increased to shorten the flame length, and the distance between the auxiliary burner and scrap is When it is larger, the flame length is increased by increasing the ratio of solid fuel or liquid fuel. Thereby, a scrap can be heated or melt | dissolved efficiently.

  In the present invention, in the operation of one charge, the ratio of two or more kinds of fuels is changed according to the distance between the auxiliary burner and the scrap, but only one kind of fuel is temporarily used during the operation ( Supply). For example, gaseous fuel and solid fuel are used, and the ratio of both fuels is gaseous fuel: more than 0% and 100% or less (for example, 10 to 100%), solid fuel: 0% or more and less than 100% (for example, 0 to 90%). This includes cases where the range is changed. In the present invention, the fuel ratio (%) is an energy standard ratio. For example, if the solid fuel ratio is 90% and the gaseous fuel ratio is 10%, if the output is 1000 Mcal / h, the solid fuel for 900 Mcal / h and the gaseous fuel for 100 Mcal / h are to be input. It is.

  The fuel that can be used for the auxiliary burner in the present invention includes, as gaseous fuel, LPG (liquefied petroleum gas), LNG (liquefied natural gas), hydrogen, steelworks byproduct gas (C gas, B gas, etc.), and these two types The above mixed gas etc. are mentioned, 1 or more types of these can be used. In addition, examples of the liquid fuel include heavy oil and kerosene, and one or more of these can be used. In addition, examples of the solid fuel include coal (pulverized coal), plastic (particulate or powdery, including waste plastic), and one or more of these can be used.

Accordingly, when a combination of fuels having different ignition temperatures or / and burning rates used in the auxiliary burner in the present invention is exemplified, gaseous fuel (for example, LNG, LPG, hydrogen, steelworks byproduct gas, a mixture of two or more of these) One or more of gas) and a solid fuel (for example, one or more of coal, plastic), gaseous fuel (for example, LNG, LPG, hydrogen, steelworks by-product gas, two or more of these) A combination of one or more of a mixed gas) and a liquid fuel (eg, one or more of heavy oil or kerosene), a liquid fuel (eg, one or more of heavy oil or kerosene) and a solid fuel (eg, coal , A combination of one or more of plastic), a combination of gaseous fuel (one or more of LNG and LPG) and gaseous fuel (hydrogen), and the like.
In the present invention, three or more kinds of fuels having different ignition temperatures and / or combustion rates may be used for the auxiliary burner.

In the method of the present invention, it is necessary to grasp the distance between the auxiliary combustion burner and the scrap. For example, a laser distance meter is installed in the auxiliary combustion burner, and the distance to the scrap can be measured by this laser distance meter. Moreover, the situation in the furnace can be observed with a monitoring camera through a window such as a discharge port. Depending on the structure of the electric furnace, the distance to the scrap can be grasped by observation in the furnace with the monitoring camera. In addition, information useful for grasping the distance may be obtained from the operation data.
Note that pure oxygen (industrial oxygen), oxygen-enriched air, or air may be used as a supporting gas for the auxiliary burner, but it is preferable to use pure oxygen when dissolving scrap.

1 to 4 show an example of an auxiliary combustion burner used in the present invention. FIG. 1 is a partial sectional side view, FIG. 2 is an enlarged sectional view of part A in FIG. 1, and FIG. FIG. 4 is a sectional view taken along line IV-IV in FIG.
In this auxiliary burner, the main part for supplying fuel and supporting gas has a triple pipe structure in which three pipes are arranged concentrically. That is, this triple pipe structure is composed of a first fuel injection pipe 1 at the center, a second fuel injection pipe 2 arranged on the outside thereof, and a combustion support gas injection pipe 3 arranged on the outside thereof. ing. The interior of the first fuel injection pipe 1 constitutes a fuel flow path 10, and the space between the second fuel injection pipe 2 and the first fuel injection pipe 1 constitutes a fuel flow path 20, and supports fuel The space between the gas injection pipe 3 and the second fuel injection pipe 2 constitutes a combustion support gas flow path 30.

Further, a tube 4 and a tube 5 for forming a cooling water flow path are arranged concentrically outside the combustion support gas injection tube 3, and a space between the tube 4 and the tube 5. The cooling water flow path 50 (outward path) is formed in the section, and the cooling water flow path 40 (return path) is formed in the space between the tube body 4 and the combustion supporting gas injection pipe 3, respectively. 40 and 50 communicate 13 on the burner tip side.
A tip member 6 having a cone-shaped (conical surface) inner peripheral surface 60 is attached to the tip of the burner, and the tip of the first fuel injection pipe 1 is opened at the center of the inner peripheral surface 60 to inject the fuel. A hole 12 is formed. The tip member 6 is formed with a plurality of injection holes 22 that open at intervals along the circumferential direction of the inner peripheral surface 60 and communicate with the fuel flow path 20. A plurality of injection holes 32 that open at intervals along the circumferential direction of the 60 and communicate with the combustion support gas flow path 30 are formed.

On the rear end side of the burner, the pipe body 5 is provided with a supply port 51 for supplying cooling water to the cooling water flow path 50 (outward path). Similarly, the pipe body 4 is provided with a drain port 41 for discharging the cooling water from the cooling water flow path 40 (return path). Similarly, the support gas injection pipe 3 is provided with a supply port 31 for supplying support gas to the support gas passage 30. Similarly, the second fuel injection pipe 2 is provided with a supply port 21 for supplying fuel to the fuel flow path 20. Similarly, the first fuel injection pipe 1 is provided with a supply port 11 for supplying fuel to the fuel flow path 10.
In addition, in the combustion support gas flow path 30, you may provide the swirl | wing blade for providing a swirl flow to combustion support gas. By imparting a swirling flow to the support gas, mixing of the injected support gas and fuel can be promoted.
In the present embodiment, the plurality of injection holes 22 and the injection holes 32 are provided in the tip member 6 provided so as to close the tips of the second fuel injection pipe 2 and the combustion support gas injection pipe 3. The front ends of the fuel injection pipe 2 and the combustion support gas injection pipe 3 may be opened, and the open front ends may be used as the injection holes 22 and 32 (both ring-shaped injection holes).
As another embodiment, an oxygen supply pipe may be provided inside the first fuel injection pipe 1 and cutting oxygen gas may be injected from the oxygen supply pipe at the center.

When carrying out the method of the present invention using the auxiliary combustion burner as described above, for example, solid fuel (such as pulverized coal) is supplied from the first fuel injection pipe 1 (fuel passage 10) as air or nitrogen gas as a carrier gas. Gas fuel (LPG or LNG, etc.) is supplied from the second fuel injection pipe 2 (fuel flow path 20), and combustion support gas such as pure oxygen is supplied from the combustion support gas injection pipe 3 (fuel support gas flow path 30). Is done. Then, solid fuel is injected from the injection hole 12, gaseous fuel is injected from the injection hole 22, and combustion-supporting gas is injected from the injection hole 32, and they are mixed to cause combustion. At that time, the flame length can be adjusted by changing the supply ratio of the solid fuel and the gaseous fuel according to the distance between the burner tip and the scrap. For this reason, regardless of the distance between the burner tip and the scrap, the scrap can be efficiently and appropriately melted or heated.
The first fuel injection pipe 1 (fuel flow path 10) and the second fuel injection pipe 2 (fuel flow path 20) have different combinations of fuels (for example, solid fuel and liquid as mentioned above). A combination of fuels, a combination of liquid fuel and gaseous fuel, etc.) may be supplied.

  FIG. 5 schematically shows an example of the implementation status of the method according to the present invention (vertical cross section in the radial direction of the electric furnace), where 7 is a furnace body, 8 is an electrode, 9 is an auxiliary burner, and x is scrap. . The auxiliary burner 9 is installed with an appropriate depression angle. Usually, a plurality of such auxiliary burners 9 are installed so that scrap in a so-called cold spot in the electric furnace can be heated or melted.

In the auxiliary burner having the structure shown in FIGS. 1 to 4, the burner flame temperature was measured using two types of fuels having different ignition temperatures. The burner output is 30 Mcal / h.
As the fuel, LPG (gaseous fuel) and pulverized coal (solid fuel) were used. As the pulverized coal, lignite having a calorific value of 6200 kcal / kg and a particle size of d (90) = 100 μm was used, and the flow rate of nitrogen for conveying the pulverized coal was 1.2 Nm ³ / h.
In the test, the solid fuel ratio was 10% and 50%, and the flame temperature at 0.2 m and 0.4 m from the tip of the burner was measured using an optical fiber thermometer and an R-type thermocouple.

  FIG. 6 shows the relationship between the solid fuel ratio in the fuel and the flame temperature. Under the condition where the ratio of gaseous fuel (LPG) is high, the flame temperature at the 0.2 m position in the vicinity of the burner is high, but a rapid temperature drop occurs at the 0.4 m position. That is, the flame length is short. On the other hand, under the condition where the ratio of the solid fuel (pulverized coal) is high, the flame temperature at the 0.2 m position near the burner is lower than that of the gaseous fuel (LPG) 100%. No temperature drop has occurred. That is, the flame length is long. This is because gas fuel (LPG) burns preferentially in the vicinity of the burner, and solid fuel (pulverized coal) heated to a high temperature within the flame starts to burn at a position of 0.4 m and the temperature is maintained. It is done.

In this test, the solid fuel (pulverized coal) ratio was set to 50% due to the burner output. However, the higher the output, the larger the flame and the higher the solid fuel (pulverized coal) ratio. It is obvious that the flame length (flame temperature at a certain distance from the burner) can be arbitrarily adjusted by changing the ratio of gaseous fuel and solid fuel in the electric furnace.
Specifically, in general operation of an electric furnace (operation of one charge), charging of scraps is performed about 2 to 3 times. The operation of the electric furnace begins with the start of energization and the start of use of the auxiliary burner after the initial scrap is charged. At the start of operation, some molten iron from the previous operation remains (residual hot water), and there is molten metal in the lower part, or the entire molten iron from the previous operation is discharged and the furnace may be empty. There is no big difference in the method. In the initial stage of scrap charging, the bulk density is high, and the entire interior of the electric furnace is filled with scrap. Therefore, the distance between the tip of the auxiliary burner and the scrap is close. The distance between the tip of the auxiliary burner and the scrap at the initial stage of scrap charging is about 0.5 m. This is to prevent the splash generated when the scrap melts from welding to the auxiliary burner if the distance between the tip of the auxiliary burner and the scrap is too short. Moreover, although the position of the auxiliary | assistant combustion burner front-end | tip part height is based also on the characteristic of a furnace, it is common that it is 1 m or more upwards from the hot-water surface height after scrap burn-off.

  As the operation proceeds, melting proceeds from the scrap in contact with the molten iron, near the electrodes, and near the auxiliary burner. The scrap in the vicinity of the auxiliary burner is always at a distance of about 0.5 m as the scrap at the upper part of the scrap is melted and drops at the initial stage of scrap charging, but the distance from the scrap becomes longer when the upper scrap disappears. If the distance from the scrap increases, the heat of the auxiliary burner cannot be efficiently supplied to the scrap. Therefore, conventionally, an operation to stop the auxiliary burner has been performed. On the other hand, in the operation to which the present invention is applied, for example, in the auxiliary burner shown in FIGS. 1 to 4, LNG-pulverized coal is used, and when the scrap is near, the LNG ratio is increased and the scrap is melted with a short flame. When the melting progresses and the distance from the scrap increases, the scrap is melted with a long flame by increasing the ratio of pulverized coal. As a result, more scrap can be efficiently melted, and the operation time can be shortened and the power consumption can be reduced. Since the distance between the auxiliary burner and the scrap changes by inserting the scraps about 2 to 3 times, the scrap can be efficiently dissolved by appropriately changing the ratio of LNG and pulverized coal each time. .

As described above, the distance between scrap and auxiliary burner can be measured with a laser rangefinder attached to the auxiliary burner. Information may be obtained.
In addition, even if the scraps are all melted down and become a flat bath, the flame of the auxiliary burner reaches the molten iron by increasing the ratio of pulverized coal and maximizing the flame length. It is also possible.

DESCRIPTION OF SYMBOLS 1 1st fuel injection pipe 2 2nd fuel injection pipe 3 Supporting gas injection pipe 4,5 Pipe body 6 End member 7 Furnace body 8 Electrode 9 Auxiliary burner 10,20 Fuel flow path 11,21,31,51 Supply port 12 , 22, 32 Injection hole 13 Communication part 30 Combustion gas flow path 40, 50 Cooling water flow path 41 Drain port 60 Inner peripheral surface x Iron-based scrap

Claims (7)

A method of melting iron scrap in an electric furnace equipped with an auxiliary burner to obtain molten iron,
As the fuel for the auxiliary burner, two or more kinds of fuels having different ignition temperatures or / and burning rates are used, and the two kinds are selected according to the distance between the auxiliary burner and the iron-based scrap to be heated or melted by the auxiliary burner. A method for producing molten iron using an electric furnace, wherein the ratio of the fuel is changed.   The method for producing molten iron using an electric furnace according to claim 1, wherein two or more kinds of fuels of gaseous fuel, liquid fuel, and solid fuel are used.   The method for producing molten iron using an electric furnace according to claim 2, wherein at least gaseous fuel and solid fuel are used.   It has a plurality of concentric injection pipes, injects solid fuel from the central injection pipe, injects gaseous fuel from the outer injection pipe, and injects combustion support gas from the outer injection pipe A method for producing molten iron using an electric furnace according to any one of claims 1 to 3, wherein an auxiliary combustion burner is used.   It has a plurality of concentric injection pipes, injecting cutting oxygen from the central injection pipe, injecting solid fuel from the outer injection pipe, and injecting gaseous fuel from the outer injection pipe Furthermore, the auxiliary combustion burner which injects combustion support gas from the injection pipe of the outer side is used, The manufacturing method of the molten iron by the electric furnace in any one of Claims 1-3 characterized by the above-mentioned. An electric furnace for melting iron scrap and obtaining molten iron,
It has a plurality of concentric injection pipes, injects solid fuel from the central injection pipe, injects gaseous fuel from the outer injection pipe, and injects combustion support gas from the outer injection pipe An electric furnace comprising an auxiliary combustion burner. An electric furnace for melting iron scrap and obtaining molten iron,
It has a plurality of concentric injection pipes, injecting cutting oxygen from the central injection pipe, injecting solid fuel from the outer injection pipe, and injecting gaseous fuel from the outer injection pipe And an auxiliary combustion burner for injecting combustion-supporting gas from the outer injection pipe.

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