CN114959171A

CN114959171A - Electric furnace and method for manufacturing molten iron using the same

Info

Publication number: CN114959171A
Application number: CN202210685964.9A
Authority: CN
Inventors: 小泽纯仁; 浅沼稔; 松野英寿
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2015-01-27
Filing date: 2015-12-22
Publication date: 2022-08-30
Also published as: WO2016120943A1; CN107208974A; KR102061953B1; KR20170096188A; JP5988014B1; JPWO2016120943A1

Abstract

In a method for obtaining molten iron by melting iron-based scrap using an electric furnace provided with an auxiliary burner, two or more types of fuel, i.e., solid fuel and gas or liquid fuel having different ignition temperatures or/and combustion speeds, and combustion supporting gas for the fuel are supplied to the auxiliary burner, the fuel is burned in the opening, and as the iron-based scrap is melted during operation, the distance between the auxiliary burner and the iron-based scrap to be heated or melted by the auxiliary burner is increased, and the ratio of the solid fuel to the gas or liquid fuel is changed so as to increase the ratio of the solid fuel.

Description

Electric furnace and method for manufacturing molten iron using the same

This application is a divisional application of an invention patent application entitled "method for manufacturing molten iron using electric furnace" filed international application No. 2015, 12, month 22, and application No. 201580074625.5.

Technical Field

The present invention relates to an electric furnace provided with an auxiliary burner and a method for melting iron-based scrap and manufacturing molten iron using the electric furnace.

Background

When the iron scrap is melted by using the electric furnace, the iron scrap around the electrode is melted rapidly, but the iron scrap at a place distant from the electrode, that is, at a cold spot is melted slowly, so that the melting rate of the iron scrap in the furnace is not uniform. Therefore, the operation time of the entire furnace is limited by the melting rate of the iron scrap at the cold spot.

Therefore, in order to eliminate the unevenness in the melting rate of the iron scrap and melt the iron scrap in the entire furnace in a well-balanced manner, a method is adopted in which an auxiliary burner is provided at a cold spot position, and the iron scrap at the cold spot is preheated, cut and melted by the auxiliary burner.

As such an auxiliary burner, for example, patent document 1 describes a burner having a triple tube structure in which fuel is ejected from an outer peripheral portion of oxygen to eject oxygen for scattering of incombustibles and for cutting of iron scrap from a central portion, and further oxygen for combustion is ejected from an outer peripheral portion of the fuel, and proposes a high-speed pure oxygen auxiliary burner for an electric furnace in which a narrowed portion is provided at a tip end of an oxygen ejection tube in the central portion to increase a speed of oxygen ejected from the central portion, and a rotary blade is provided in an annular space formed by the fuel ejection tube and the oxygen for combustion to impart a rotational force to oxygen for combustion ejected from the outermost periphery.

Even if the burner described in patent document 1 is used as an auxiliary burner, the distance between the auxiliary burner and the ferrous scrap is changed by the charging, additional charging, and melting of the ferrous scrap during the operation of the electric furnace. Generally, the distance between the auxiliary burner and the ferrous scrap is small at the start of operation and at the initial stage of additional charging, and the distance increases as the melting of the ferrous scrap progresses. Therefore, in order to efficiently use the supplementary burner, it is important to adjust the length of the burner flame according to the distance between the supplementary burner and the ferrous scrap.

Therefore, patent document 2 discloses an auxiliary burner capable of adjusting the length of a flame by changing the ratio of the amount of oxygen supplied for cutting to the amount of oxygen supplied for combustion in the center.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 10-9524

Patent document 2: japanese patent laid-open publication No. 2012-172867

Disclosure of Invention

Problems to be solved by the invention

By using the technique described in patent document 2, the iron scrap can be efficiently preheated and melted by using the auxiliary burner. However, not only cutting oxygen is required to be used, but also the burner shape becomes complicated, and the oxygen production apparatus needs to be reinforced with an increase in the amount of oxygen used, which causes a problem of an increase in initial investment. Further, since the amount of oxygen for combustion is stoichiometrically dependent on the amount of fuel used, there is also a problem that the operating conditions are limited.

Accordingly, an object of the present invention is to provide a method for manufacturing molten iron, comprising: in the method of obtaining molten iron by melting iron scrap using an electric furnace provided with an auxiliary burner, the problems of the technique of patent document 2 are not caused, and the iron scrap can be efficiently heated or melted using the auxiliary burner.

Means for solving the problems

The present inventors have focused on the fuel used in the auxiliary burner, and have obtained the idea of adjusting the length of the flame of the burner by separately using different types of fuel, and have conducted extensive studies. As a result, the present inventors have found that the flame length varies depending on the difference in the ignition temperature and the combustion speed of the fuel, and therefore, the flame length can be adjusted arbitrarily by using two or more types of fuel having different ignition temperatures and/or different combustion speeds and changing the ratio of the two or more types of fuel.

The present invention has been completed based on such findings, and the gist thereof is as follows.

[1] A method for producing molten iron by an electric furnace, wherein molten iron is obtained by melting iron scrap in an electric furnace provided with an auxiliary burner having a plurality of injection pipes arranged concentrically and a tip member attached to the tip of the injection pipes and having an opening formed therein,

the opening part is provided with a jet hole for jetting combustion-supporting gas, a jet hole for jetting solid fuel and a jet hole for jetting gas or liquid fuel, the jet hole for jetting solid fuel is arranged along the central shaft of the auxiliary burner, the jet hole for jetting gas or liquid fuel and the jet hole for jetting combustion-supporting gas are arranged concentrically around the jet hole for jetting solid fuel, the axis of the jet hole for jetting combustion-supporting gas and the axis of the jet hole for jetting gas or liquid fuel are crossed in the opening part,

supplying two or more kinds of fuel having different ignition temperatures or/and combustion speeds and combustion-supporting gas of the fuel to the auxiliary burner, and burning the fuel in the opening, wherein the two or more kinds of fuel having different ignition temperatures or/and combustion speeds are solid fuel and gas or liquid fuel,

as the ferrous scrap is melted in operation, the distance between the supplementary burner and the ferrous scrap to be heated or melted by the supplementary burner becomes longer, and the ratio of the solid fuel to the gas or liquid fuel is changed in such a manner that the ratio of the solid fuel becomes higher.

[2] In the production method of the above [1], at least a gaseous fuel and a solid fuel are used.

[3] In the production method of [2], the following auxiliary burner is used: the fuel injection device has a plurality of injection pipes arranged concentrically, and injects a solid fuel from the central injection pipe, a gaseous fuel from the outer injection pipe, and a combustion-supporting gas from the outer injection pipe.

[4] An electric furnace for melting iron-based scrap to obtain molten iron, characterized in that,

comprises an auxiliary burner having a plurality of injection pipes arranged concentrically and a front end member attached to the front ends of the injection pipes and having an opening,

the opening is provided with an injection hole for injecting combustion-supporting gas, an injection hole for injecting solid fuel, and an injection hole for injecting gas or liquid fuel, the injection hole for injecting solid fuel is provided along the central axis of the auxiliary burner, the injection hole for injecting gas or liquid fuel and the injection hole for injecting combustion-supporting gas are concentrically arranged around the injection hole for injecting solid fuel, the axis of the injection hole for injecting combustion-supporting gas and the axis of the injection hole for injecting gas or liquid fuel intersect in the opening, solid fuel is injected from the injection pipe at the center, and gas fuel is injected from the injection pipe at the outer side thereof,

the ratio of the solid fuel to be supplied to the gas or solid fuel to be discharged from the auxiliary burner is changed so that the ratio of the solid fuel is increased as the ferrous scrap melts during the operation, and the distance between the auxiliary burner and the ferrous scrap to be heated or melted by the auxiliary burner is increased.

Effects of the invention

According to the present invention, when the ferrous scrap in the electric furnace is heated or melted by using the auxiliary burner, the flame length of the auxiliary burner can be arbitrarily adjusted by using two or more kinds of fuels, i.e., the solid fuel and the gas or liquid fuel, which have different ignition temperatures or/and combustion speeds, and changing the ratio of the two or more kinds of fuels according to the distance between the auxiliary burner and the ferrous scrap to be heated or melted by the auxiliary burner, thereby efficiently heating or melting the ferrous scrap. Therefore, the amount of power used can be reduced, and the operation time can be shortened.

Drawings

Fig. 1 is a partially sectional side view showing an example of an auxiliary burner used in the present invention.

Fig. 2 is an enlarged sectional view of a portion a of fig. 1.

Fig. 3 is a sectional view taken along line III-III of fig. 1.

Fig. 4 is a sectional view taken along line IV-IV of fig. 1.

FIG. 5 is an explanatory view schematically showing an example of the method of the present invention.

Fig. 6 is a graph showing the results of examining the relationship between the solid fuel ratio in the fuel and the flame temperature in a test in which the flame temperature was measured by changing the ratio between a gaseous fuel (LPG) and a solid fuel (fine carbon powder) as the fuel for the auxiliary burner.

Detailed Description

The present invention is a method for obtaining molten iron by melting iron-based scrap (hereinafter, simply referred to as "scrap" for convenience of explanation) in an electric furnace provided with an auxiliary burner, wherein two or more types of fuel having different ignition temperatures and/or combustion speeds are used as the fuel for the auxiliary burner, and the ratio of the two or more types of fuel is changed according to the distance between the auxiliary burner and the scrap to be heated or melted by the auxiliary burner.

The difference in flame length occurs due to the difference in the ignition temperature and the combustion speed of the fuel used for the auxiliary burner. Therefore, by using two or more types of fuel having different ignition temperatures or/and combustion speeds and changing the ratio of the two or more types of fuel, the flame length of the sub-burner (the flame temperature at a position separated from the burner by a certain distance) can be arbitrarily adjusted.

The elements necessary for combustion include three elements, i.e., combustible substance, oxygen, and temperature (ignition source). Further, the ease of combustion is a sort of gas, liquid, and solid as the state of combustible substances. This is because, if the combustible substance is in a gaseous state, mixing of the combustible substance with oxygen and temperature (ignition source) is easy, and combustion can continue (chain reaction).

When a gas is burned as a combustible substance using an auxiliary burner, the gas is generally burned immediately after being injected from the tip of the burner, although it depends on the oxygen concentration, the flow rate, and the burner nozzle shape. On the other hand, when a solid fuel such as coal is used as a combustible substance, it is difficult to rapidly burn the combustible substance as a gas. This is because the ignition temperature of coal is about 400 to 600 ℃, and a temperature rise time is required to maintain the ignition temperature and raise the temperature to the ignition temperature. The temperature rise time for raising the temperature to the light-off temperature depends on the particle diameter (specific surface area), and if the particles are made finer, the light-off time can be shortened. However, it is difficult to burn solids more rapidly than gases.

The present invention utilizes the difference in the light-off temperature or the difference in the combustion speed of the fuel of the kind described to control the flame length of the supplementary burner.

First, a case where two or more types of fuels having different ignition temperatures are used as the fuel for the auxiliary burner will be described.

As the fuels having greatly different ignition temperatures, combinations of fuels having different phases (gas phase, liquid phase, and solid phase) can be cited. That is, a combination of two or more kinds of fuel selected from gas fuel, liquid fuel, and solid fuel. In addition, the light-off temperatures of these fuels are typically solid > liquid > gaseous.

Hereinafter, a case will be described in which a gas fuel and a solid fuel are used in the auxiliary burner, LNG (liquefied natural gas) is used as the gas fuel, coal (fine carbon powder) is used as the solid fuel, and pure oxygen is used as the combustion-supporting gas.

When LNG and coal are used as the fuel for the auxiliary burner, the LNG and pure oxygen are burned to form coal in a combustion field at or above the ignition temperature of the coal, and the coal is fed into the combustion field to raise the temperature to the ignition temperature, thereby initiating combustion of the coal (gasification → ignition). The flame temperature decreases with the amount of heat required for the temperature rise of the coal, but the temperature rises in the region where the initiation of the ignition of the coal is initiated.

Therefore, the flame generated in the auxiliary burner becomes a high temperature (i.e., a short flame) at a position closer to the burner tip when the proportion of LNG is higher than that of coal, but becomes a high temperature (i.e., a long flame) at a position farther from the burner tip due to heat generation after the heat absorption of coal when the proportion of coal is higher than that of LNG. Thus, by varying the ratio of LNG to coal, the flame length (flame temperature at a location separated from the burner by a certain distance) can be controlled.

The above principle is also appropriate for combinations of other fuels having different ignition temperatures. For example, even in a combination of a gaseous fuel (e.g., LNG) and a liquid fuel (e.g., heavy oil, kerosene, etc.), a shorter flame is obtained when the proportion of the gaseous fuel is increased as compared to the liquid fuel, and a longer flame is obtained when the proportion of the liquid fuel is increased as compared to the gaseous fuel. In the combination of a liquid fuel (for example, heavy oil, kerosene, or the like) and a solid fuel (for example, coal, or the like), the flame becomes shorter when the proportion of the liquid fuel is higher than that of the solid fuel, and becomes longer when the proportion of the solid fuel is higher than that of the liquid fuel.

Next, a case where two or more types of fuel having different combustion speeds are used as the fuel for the auxiliary burner will be described.

The fuel having a greatly different combustion rate is included in a part of the combination of the fuels having different ignition temperatures (for example, a combination of a gaseous fuel and a solid fuel, or a combination of a gaseous fuel and a liquid fuel), but other than this, a combination of LNG and hydrogen, which are both gaseous fuels, may be mentioned. Further, the combustion speed of the fuel in the combustor refers to a speed at which the fuel is combusted reversely to the supply direction of the fuel. In addition, the combustion rates of the different fuels are typically gaseous > liquid > solid.

At this time, when the proportion of the fuel having a high combustion speed (for example, a gas fuel such as LNG) is higher than that of the fuel having a low combustion speed (for example, a solid fuel such as coal), the fuel becomes a high temperature (that is, a short flame) at a position close to the burner tip, but when the proportion of the fuel having a low combustion speed is higher than that of the fuel having a high combustion speed, the fuel also becomes a high temperature (that is, a long flame) at a position far from the burner tip. Therefore, by changing the ratio of the two fuels, the flame length (flame temperature at a position separated from the burner by a certain distance) can be controlled.

In the operation of the electric furnace, the distance between the auxiliary burner and the scrap is changed by the charging, additional charging, and melting of the scrap. Generally, the distance between the pilot burner and the scrap is small at the start of operation or at the initial stage of additional charging, and increases as the melting of the scrap progresses. This is because, initially, scrap is melted in order from a scrap closer to the supplementary burner, and therefore, as the melting of the scrap progresses, the distance between the unmelted scrap and the supplementary burner becomes larger. Therefore, in the present invention, two or more types of fuel having different ignition temperatures and/or different combustion speeds are used as the fuel for the pilot burner, and the flame length of the pilot burner is adjusted (changed) by changing the ratio of the two or more types of fuel according to the distance between the pilot burner and the scrap to be heated or melted by the pilot burner, and the flame of the pilot burner reaches the scrap regardless of the distance between the scrap and the pilot burner. For example, in the case of using a gaseous fuel and a solid fuel or a liquid fuel as the fuel, when the distance between the sub-burner and the waste is small, the flame length is shortened by increasing the proportion of the gaseous fuel, and when the distance between the sub-burner and the waste is large, the flame length is lengthened by increasing the proportion of the solid fuel or the liquid fuel. This enables the scrap to be efficiently heated or melted.

In the present invention, the ratio of two or more types of fuel is changed in accordance with the distance between the pilot burner and the scrap in the operation of one charge, but the present invention includes a case where only one type of fuel is temporarily used (supplied) in the operation. For example, the following cases are included: the gas fuel and the solid fuel are used, and the ratio of the two fuels is in the range of gas fuel: more than 0% and 100% or less (e.g., 10 to 100%), solid fuel: the range of 0% or more and less than 100% (e.g., 0 to 90%). Further, in the present invention, the proportion (%) of fuel is the proportion on the energy basis. For example, when the solid fuel ratio is 90% and the gas fuel ratio is 10%, the solid fuel of 900Mcal/h and the gas fuel of 100Mcal/h are put therein, assuming that the output is 1000 Mcal/h.

In the present invention, as the fuel that can be used for the auxiliary burner, as the gas fuel, LPG (liquefied petroleum gas), LNG (liquefied natural gas), hydrogen, a gas (C gas, B gas, etc.) by-produced in a steel plant, a mixed gas of two or more kinds thereof, and the like can be used. The liquid fuel includes heavy oil, kerosene, and the like, and one or more of these can be used. The solid fuel may be coal (fine carbon powder), plastic (granular or powdery material, including waste plastic), or the like, and one or more of these may be used.

Therefore, in the present invention, examples of combinations of fuels having different ignition temperatures and/or combustion speeds for use in the auxiliary burner include combinations of gaseous fuels (e.g., LNG, LPG, hydrogen, gas produced as a secondary product in a steel plant, or one or more of two or more mixed gases thereof) and solid fuels (e.g., one or more of coal and plastic), combinations of gaseous fuels (e.g., LNG, LPG, hydrogen, gas produced as a secondary product in a steel plant, or one or more of two or more mixed gases thereof) and liquid fuels (e.g., one or more of heavy oil and kerosene), combinations of liquid fuels (e.g., heavy oil, one or more of kerosene) and solid fuels (e.g., one or more of coal and plastic), and combinations of gaseous fuels (e.g., one or more of LNG and LPG) and gaseous fuels (hydrogen).

In the present invention, 3 or more types of fuel having different ignition temperatures or/and combustion speeds may be used in the auxiliary burner.

In the method of the present invention, although it is necessary to grasp the distance between the pilot burner and the scrap, for example, a laser distance meter may be provided in the pilot burner and the distance to the scrap may be measured by the laser distance meter. Further, the state in the furnace can be observed through a window such as a slag discharge port by a monitoring camera, and the distance to the scrap can be grasped by the observation in the furnace under the monitoring camera depending on the structure of the electric furnace. In addition, information useful in grasping the distance may sometimes be obtained from the operation data.

As the combustion-supporting gas of the auxiliary burner, any one of pure oxygen (industrial oxygen), oxygen-enriched air, and air may be used, but when melting the scrap, pure oxygen is preferably used.

Fig. 1 to 4 show an example of an auxiliary burner used in the present invention, fig. 1 is a partial sectional side view, fig. 2 is an enlarged sectional view of a portion a of fig. 1, fig. 3 is a sectional view taken along line III-III of fig. 1, and fig. 4 is a sectional view taken along line IV-IV of fig. 1.

In this pilot burner, the main body for supplying fuel and combustion supporting gas has a three-layer tube structure in which 3 tube bodies are arranged concentrically. That is, the three-layer pipe structure is composed of a first fuel injection pipe 1 in the center, a second fuel injection pipe 2 disposed outside the first fuel injection pipe, and a combustion-supporting gas injection pipe 3 disposed outside the second fuel injection pipe. The first fuel injection pipe 1 has a fuel flow path 10 formed therein, a space between the second fuel injection pipe 2 and the first fuel injection pipe 1 forms a fuel flow path 20, and a space between the combustion-supporting gas injection pipe 3 and the second fuel injection pipe 2 forms a combustion-supporting gas flow path 30.

Further, the

tubular bodies

4 and 5 for forming the cooling water flow paths are concentrically arranged outside the combustion supporting gas injection tubes 3, the cooling water flow path 50 (forward path) is formed in a space portion between the

tubular bodies

4 and 5, the cooling water flow path 40 (return path) is formed in a space portion between the tubular bodies 4 and the combustion supporting gas injection tubes 3, and these cooling

water flow paths

40, 50 communicate 13 on the combustor tip end portion side.

A tip member 6 having a conical (conical surface-like) inner peripheral surface 60 is attached to the tip end of the burner, and the tip end of the first fuel injection pipe 1 opens at the center of the inner peripheral surface 60 to form an injection hole 12. The distal end member 6 has a plurality of injection holes 22 that are open at intervals in the circumferential direction of the inner circumferential surface 60 and communicate with the fuel flow path 20, and has a plurality of injection holes 32 that are open at intervals in the circumferential direction of the inner circumferential surface 60 and communicate with the combustion-supporting gas flow path 30 on the outer side thereof.

The pipe 5 is provided with a supply port 51 for supplying cooling water to the cooling water flow path 50 (outward path) on the burner rear end side. Similarly, the pipe 4 is provided with a drain port 41 for discharging the cooling water from the cooling water flow path 40 (circuit). Similarly, the combustion supporting gas injection pipe 3 is provided with a supply port 31 for supplying combustion supporting gas to the combustion supporting gas flow path 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.

Further, a rotary vane for imparting a swirling flow to the combustion-supporting gas may be provided in the combustion-supporting gas flow path 30. By imparting a swirling flow to the combustion-supporting gas, mixing of the injected combustion-supporting gas and the fuel can be promoted.

In the present embodiment, the plurality of injection holes 22 and 32 are provided in the tip member 6 provided to close the tips of the second fuel injection pipe 2 and the combustion supporting gas injection pipe 3, but the tips of the second fuel injection pipe 2 and the combustion supporting gas injection pipe 3 may be opened, and the opened tips may be the injection holes 22 and 32 (both annular injection holes).

In another embodiment, an oxygen supply pipe may be provided inside the first fuel injection pipe 1, and oxygen gas for cutting may be injected from the oxygen supply pipe in the center.

When the method of the present invention is carried out using the auxiliary burner as described above, for example, solid fuel (fine carbon powder or the like) is supplied from the first fuel injection pipe 1 (the fuel flow path 10) using air or nitrogen as a carrier gas, gas fuel (LPG, LNG or the like) is supplied from the second fuel injection pipe 2 (the fuel flow path 20), and combustion-supporting gas such as pure oxygen is supplied from the combustion-supporting gas injection pipe 3 (the combustion-supporting gas flow path 30). Then, the solid fuel is injected from the injection hole 12, the gas fuel is injected from the injection hole 22, and the combustion-supporting gas is injected from the injection hole 32, and these are mixed to generate combustion. In this case, the flame length can be adjusted by changing the supply ratio of the solid fuel to the gas fuel according to the distance between the burner tip and the scrap. Therefore, the scrap can be melted or heated efficiently and appropriately regardless of the distance between the burner tip and the scrap.

Further, a fuel of a different combination (for example, a combination of a solid fuel and a liquid fuel, a combination of a liquid fuel and a gaseous fuel, or the like as described above) may be supplied to the first fuel injection pipe 1 (the fuel flow path 10) and the second fuel injection pipe 2 (the fuel flow path 20).

FIG. 5 schematically shows an example of the method of the present invention (a longitudinal section in a radial direction of an 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 disposed at an appropriate depression angle. Such auxiliary burners 9 are usually provided in plurality in order to be able to heat or melt the scrap at so-called cold spots within the electric furnace.

Examples

In the auxiliary burner having the structure shown in fig. 1 to 4, the burner flame temperature was measured by using two types of fuels having different ignition temperatures. The output of the burner was 30 Mcal/h.

As the fuel, LPG (gas fuel) and fine carbon powder (solid fuel) are used. As the fine powder carbon, lignite having a calorific value of 6200kcal/kg and a particle size d (90) ═ 100 μm was used, and the flow rate of nitrogen gas for transporting the fine powder carbon was 1.2Nm ³ /h。

In the test, the solid fuel ratio was set to 10% and 50%, and the flame temperature at 0.2m and 0.4m from the burner tip was measured using a fiber optic thermometer and an R-type thermocouple.

The relationship between the solid fuel ratio in the fuel and the flame temperature is shown in fig. 6. Under the condition that the ratio of the gas fuel (LPG) is high, the flame temperature at the 0.2m position near the burner is high, but a sharp temperature drop occurs at the 0.4m position. I.e. the flame length is short. On the other hand, under the condition that the proportion of the solid fuel (fine powder carbon) is high, the flame temperature at the 0.2m position near the burner is lower than 100% of that of the gas fuel (LPG), but the temperature is hardly lowered at the 0.4m position. I.e. the flame length is longer. It is considered that the gaseous fuel (LPG) is preferentially combusted in the vicinity of the burner, and the solid fuel (fine carbon powder) having a high temperature in the flame starts to be combusted at a position of 0.4m, and the temperature is maintained.

In this test, although the solid fuel (fine powder carbon) ratio was set to 50% or less in relation to the burner output, the flame was also increased by setting the output high, and the solid fuel (fine powder carbon) ratio could also be increased, so in an actual electric furnace, it was apparent that the flame length (flame temperature at a position separated from the burner by a certain distance) could be arbitrarily adjusted by changing the ratio of the gas fuel to the solid fuel.

Specifically, the charging of scrap is performed about 2 to 3 times in a general operation (one-time charging operation) of the electric furnace. The operation of the electric furnace is started by starting the energization and starting the use of the auxiliary burner after the initial charging of the scrap. The state at the start of the operation includes a case where a molten metal is present in the lower part of the molten iron remaining (liquid remaining) in the previous operation and a case where the molten iron in the previous operation is completely discharged and the furnace is empty, but there is no great difference in the operation method. At the initial stage of charging the scrap, the bulk density is high and the entire inside of the electric furnace is filled with the scrap. Therefore, the distance between the front end of the auxiliary burner and the scrap is short. The distance between the front end of the pilot burner at the initial stage of charging the scrap and the scrap was about 0.5 m. This is to prevent the spatter generated when the scrap is melted from being welded to the pilot burner when the tip of the pilot burner is too close to the scrap. The height of the tip of the auxiliary burner is generally above the liquid level 1m or more after the scrap is melted and dropped, although it depends on the characteristics of the furnace.

When the operation is progressed, the molten metal is melted from the scrap in the vicinity of the lower portion in contact with the molten iron, the electrode, and the auxiliary burner. The scrap near the auxiliary burner drops the scrap located at the upper portion with melting in the initial charging of the scrap and always has a distance of about 0.5m, but if the upper scrap disappears, the distance from the scrap becomes longer. If the distance from the waste material becomes long, the heat of the auxiliary burner cannot be efficiently supplied to the waste material, and therefore, an operation of stopping the auxiliary burner may be performed in the past. In contrast, in an operation to which the present invention is applied, for example, LNG-fine carbon is used in the supplementary burner shown in fig. 1 to 4, and when the scrap is closer, the proportion of LNG is increased to melt the scrap with a shorter flame, and when the melting progresses and the distance from the scrap is longer, the proportion of fine carbon is increased to melt the scrap with a longer flame. This enables more scrap to be efficiently melted, thereby enabling reduction in operation time and reduction in power consumption rate. Since the distance between the auxiliary burner and the scrap is changed by about 2 to 3 times of charging the scrap, the ratio of LNG to fine carbon powder can be appropriately changed every time, and the scrap can be efficiently melted.

As described above, the distance between the scrap and the auxiliary burner can be measured by a laser distance meter attached to the auxiliary burner, and useful information may be obtained from a window such as a slag discharge port or from operation data.

Even when all the scrap is melted and dropped to a flat path (japanese: フラットバス), the flame length can be maximized by increasing the proportion of fine carbon powder, and the flame of the pilot burner can reach the molten iron.

Description of the reference numerals

1 first fuel injection pipe

2 second fuel injection pipe

3 combustion-supporting gas injection pipe

4. 5 tube body

6 front end component

7 furnace body

8 electrode

9 auxiliary burner

10. 20 fuel flow path

11. 21, 31, 51 supply port

12. 22, 32 jet hole

13 communication part

30 flow path of combustion-supporting gas

40. 50 flow path for cooling water

41 drainage outlet

60 inner peripheral surface

x iron-based waste

Claims

1. A method for producing molten iron by an electric furnace, wherein molten iron is obtained by melting iron scrap in an electric furnace provided with an auxiliary burner having a plurality of injection pipes arranged concentrically and a tip member attached to the tip of the injection pipes and having an opening formed therein,

as the ferrous scrap melts in operation, the distance between the supplementary burner and the ferrous scrap to be heated or melted by the supplementary burner becomes longer, and the ratio of the solid fuel to the gas or liquid fuel is changed in such a manner that the ratio of the solid fuel becomes higher.

2. The method of manufacturing molten iron using an electric furnace according to claim 1,

at least gaseous and solid fuels are used.

3. The method of manufacturing molten iron using an electric furnace according to claim 1 or 2,

the following auxiliary burners were used: the fuel injection device has a plurality of injection pipes arranged concentrically, and injects a solid fuel from the central injection pipe, a gaseous fuel from the outer injection pipe, and a combustion-supporting gas from the outer injection pipe.

4. An electric furnace for melting iron-based scrap to obtain molten iron, characterized in that,

comprises an auxiliary burner having a plurality of injection pipes arranged concentrically and a front end member attached to the front end of the injection pipe and having an opening formed therein,