JP6624140B2 - Operating method of electric furnace with combustion burner - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for operating an electric furnace equipped with an auxiliary burner, and more particularly to a method for operating an electric furnace characterized by a usage pattern of the auxiliary burner.

When melting an iron-based scrap using an electric furnace, the iron-based scrap around the electrode melts quickly, but the iron-based scrap located far from the electrode, that is, at the cold spot, melts slowly, and the iron-based scrap in the furnace is melted slowly. Inhomogeneity in the dissolution rate of For this reason, the operating time of the entire furnace was limited by the melting rate of the iron-based scrap at the cold spot.
Therefore, in order to eliminate the non-uniformity of the melting rate of the iron-based scrap and dissolve the iron-based scrap in the entire furnace in a well-balanced manner, an auxiliary burner is installed at the position of the cold spot. The method of preheating, cutting, and melting the iron-based scrap located in Japan has been adopted.

  As such an auxiliary burner, for example, in Patent Literature 1, an oxygen gas for scattering non-combustible substances and cutting iron-based scrap is jetted from a central portion, and a fuel is discharged from an outer peripheral portion of the oxygen gas, and further, the fuel is discharged. A burner with a triple-tube structure for ejecting oxygen gas for combustion from the outer peripheral portion.In order to increase the speed of the oxygen gas ejected from the central portion, a narrow portion is provided at the tip of the oxygen gas ejecting tube in the central portion. And high-speed electric furnace for electric furnaces, in which swirling vanes are installed in an annular space formed by a fuel ejection pipe and a combustion oxygen gas ejection pipe in order to impart a turning force to the combustion oxygen gas ejected from the outermost periphery. Oxygen-assisted burners have been proposed.

Patent Document 2 proposes a burner facility for an electric furnace in which the nozzle tip of an auxiliary burner is decentered and the burner is rotated to expand the directivity of the burner flame over a wide range.
Patent Document 3 discloses an auxiliary furnace burner for an electric furnace including a fuel ejection pipe at a center portion and an oxygen gas ejection pipe arranged at an outer peripheral portion thereof, the discharge flow rate of which is 40 m / s or more, and An auxiliary burner satisfying the following formula (i) has been proposed.
L / D ≧ −0.033 × V + 3.341 (i)
However, L: allowance for drawing in oxygen gas ejection pipe (mm)
D: Inside diameter of burner tip (mm)
V: Burner discharge flow rate (m / s)

JP-A-10-9524 JP-A-2003-4382 JP 2012-172867 A

  By using the technology described in Patent Documents 1 to 3, scrap can be efficiently preheated and melted using a combustion burner.However, in the operation of an electric furnace equipped with a combustion burner, the following factors are caused. There is a problem in that the tip of the auxiliary burner (hereinafter sometimes referred to as “nozzle tip”) tends to be clogged or melted. That is, the splash scatters during the loading of the scrap and adheres to the nozzle tip of the auxiliary burner, and as a result, the nozzle tip is melted or clogged. Also, depending on the operation, the apparent density decreases due to slag forming, the slag height increases, and may reach the auxiliary burner installation position. As a result, slag (metal) adheres to the nozzle tip and the nozzle tip Melting and blockage will occur. Here, slag forming is a phenomenon in which carbon injection is performed to reduce iron oxide, the injected carbon reacts with excess oxygen, generates CO gas, and slag foams.

In particular, in the case of an auxiliary burner using a solid fuel such as pulverized coal, once the nozzle tip is clogged or melted, it becomes difficult to transport and inject the solid fuel, and the function as the auxiliary burner cannot be achieved. Since the operation of the electric furnace is performed continuously, even if clogging or melting damage occurs at the nozzle tip of the burner during the operation, the burner cannot be removed for maintenance. For this reason, it is important that the auxiliary burner does not cause the above-described melting and clogging of the nozzle tip during the operation of the electric furnace.
In order to prevent the melt in the furnace such as splash from adhering to the nozzle tip, measures to increase the flow rate of the discharged gas can be considered as in the combustion burner of Patent Document 3, but in the case of the combustion burner using solid fuel, However, if the design is such that the discharge gas flow rate is simply increased, for example, a design such as a Laval nozzle structure, the solid fuel is not heated sufficiently due to the high discharge flow rate, and there is a risk of misfiring. By adopting the structure, the transport passage of the solid fuel is narrowed, and there is a possibility that clogging may occur.

  Therefore, an object of the present invention is to solve the problems of the prior art as described above, and to operate an electric furnace equipped with an auxiliary burner that uses a solid fuel as a part of the fuel, without impairing the combustibility of the solid fuel. An object of the present invention is to provide a method of operating an electric furnace which can reduce nozzle blockage of a burner and melting damage of a nozzle tip.

  In order to solve the above-mentioned problems, the present inventors have repeatedly studied the use conditions of an auxiliary burner using a solid fuel as a part of the fuel. As a result, when the use of the auxiliary burner was stopped during operation of the electric furnace (especially when the scrap was used) Injection of purge gas from the auxiliary burner during charging, scrap melting, slag discharge, molten iron tapping, etc., when the melt inside the furnace such as splash tends to adhere to the nozzle tip. By purging the in-furnace melt in the vicinity of the burner tip and preventing the in-furnace melt from adhering to the burner tip, we found that the nozzle blockage of the auxiliary burner and the erosion of the nozzle tip could be appropriately reduced. By optimizing the discharge gas flow rate of the purge gas, it has been found that nozzle blockage and erosion at the nozzle tip can be more effectively reduced. Further, according to this method, it is not necessary to adopt a nozzle design such as a Laval nozzle structure, so that the combustibility of the solid fuel used in the combustion burner can be sufficiently ensured. The electric furnace can be operated efficiently with the fact that the erosion is effectively reduced.

The present invention has been made based on the above findings, and has the following gist.
[1] A method for operating an electric furnace having an auxiliary burner having an injection pipe for injecting a gaseous fuel, a solid fuel, and a supporting gas, respectively, wherein when the use of the auxiliary burner is stopped during operation of the electric furnace, By injecting a purge gas from at least a part of the plurality of injection pipes, a gas in the furnace near the tip of the burner is gas-purged, and the adhesion of the melt in the furnace to the tip of the burner is suppressed. A method for operating an electric furnace equipped with an auxiliary burner, characterized in that:
[2] The method for operating an electric furnace having an auxiliary burner according to the above method [1], wherein a purge gas is injected from at least a solid fuel injection pipe.
[3] The method for operating an electric furnace with an auxiliary burner according to [1], wherein the purge gas is injected from all the injection pipes.

[4] In the operating method according to any one of the above [1] to [3], the purge gas is discharged at a discharge gas flow rate satisfying a discharge gas flow rate ratio Vr defined by the following equation (1) of 0.5 to 2.1. A method for operating an electric furnace equipped with an auxiliary burner characterized by injecting.

[5] The operation of the electric furnace with an auxiliary burner according to the operation method of [4], wherein the purge gas is injected at a discharge gas flow rate satisfying a discharge gas flow rate ratio Vr of 0.8 to 1.2. Method.
[6] In the operation method according to any one of the above [1] to [5], the auxiliary burner includes, in order from the center side, an injection pipe for solid fuel, an injection pipe for gaseous fuel, and an injection pipe for supporting gas. A method for operating an electric furnace having an auxiliary burner characterized by having a structure arranged in a shape.
[7] A method for producing molten iron using an electric furnace, wherein the iron-based scrap is melted in an electric furnace to obtain molten iron while performing the operation method according to any one of [1] to [6].

  ADVANTAGE OF THE INVENTION According to this invention, since the adhesion | attachment of the melt in a furnace to the burner front-end | tip part of an auxiliary combustion burner is suppressed, the nozzle blockage of the auxiliary combustion burner and the erosion of the nozzle front-end | tip can be reduced appropriately. Further, by optimizing the discharge gas flow rate of the purge gas, it is possible to more effectively reduce nozzle blockage and erosion at the nozzle tip. For this reason, according to the present invention, the maintenance property of the auxiliary burner is enhanced, so that the cost for maintenance of the burner can be significantly reduced, and the occurrence of operation trouble due to nozzle blockage or the like can be prevented. Furthermore, in the present invention, since it is not necessary to use a nozzle design such as a Laval nozzle structure for the combustion burner, it is possible to sufficiently secure the flammability of the solid fuel used in the combustion burner, and to use an inexpensive solid fuel such as pulverized coal. , The iron-based scrap can be efficiently heated or melted. For this reason, the electric furnace can be operated efficiently, and the productivity of the electric furnace can be improved, together with the fact that the nozzle blockage of the auxiliary combustion burner and the melting damage of the nozzle tip are reduced.

Longitudinal sectional view schematically showing one embodiment of a combustion support burner used in the method of the present invention. Explanatory drawing which shows typically an example of implementation of the method of this invention (vertical cross section in the radial direction of the electric furnace). Explanatory drawing which shows the outline of the installation position of the auxiliary burner in the electric furnace used in the Example Explanatory drawing which shows typically an example of the situation where the melt in the furnace adhered to the tip of the auxiliary burner, and nozzle clogging and melting of the nozzle tip occurred. Explanatory view schematically showing another example of a situation in which the melt in the furnace adheres to the tip of the combustion burner, causing nozzle blockage and melting of the nozzle tip.

The present invention is a method for operating an electric furnace equipped with an auxiliary burner. In the operation of the electric furnace, molten iron is produced by melting iron-based scrap (hereinafter simply referred to as “scrap” for convenience of explanation). The auxiliary burner used in the present invention uses gaseous fuel and solid fuel as fuel, and has injection pipes (a plurality of injection pipes) for respectively injecting gaseous fuel, solid fuel and supporting gas.
FIG. 1 is a longitudinal sectional view schematically showing one embodiment of an auxiliary burner used in the present invention. This auxiliary burner has concentric shapes for injecting a gaseous fuel, a solid fuel, and a supporting gas, respectively. Has a plurality of injection pipes.

  In the auxiliary burner shown in FIG. 1, the main body for supplying fuel and supporting gas has a triple tube structure in which three tubes are concentrically arranged. That is, this triple pipe structure is constituted by a solid fuel injection pipe 1 in the center, a gas fuel injection pipe 2 disposed outside the fuel injection pipe 1, and a combustion supporting gas injection pipe 3 disposed further outside the solid fuel injection pipe 1. I have. The solid fuel injection pipe 1 has a solid fuel flow path 10 inside, and the gas fuel injection pipe 2 has a gas fuel flow path 20 in the space between the solid fuel injection pipe 1 and the solid fuel injection pipe 1. The space between the gas injection pipe 3 and the gaseous fuel injection pipe 2 constitutes a combustion supporting gas flow path 30. The solid fuel flow path 10, the gaseous fuel flow path 20, and the supporting gas flow path 30 are open at their respective ends, and their open ends are ring-shaped solid fuel discharge ports 11 (injection ports) and gas fuel discharge ports, respectively. 21 (injection port) and a flammable gas discharge port 31 (injection port).

On the rear end side of the burner, the combustion supporting gas injection pipe 3 is provided with a combustion supporting gas supply port 32 for supplying a combustion supporting gas to the combustion supporting gas passage 30. Similarly, the gaseous fuel injection pipe 2 is provided with a gaseous fuel supply port 22 for supplying fuel to the gaseous fuel flow path 20. Similarly, the solid fuel injection pipe 1 is provided with a solid fuel supply port 12 for supplying solid fuel to the solid fuel flow path 10 via a carrier gas.
Although not shown, an inner tube and an outer tube are further arranged concentrically outside the combustible gas injection tube 3, between the outer tube and the inner tube, and between the inner tube and the inner tube. A cooling fluid flow path (outgoing path and returning path of the cooling fluid) communicating with each other is formed between the cooling fluid and the combustion supporting gas injection pipe 3.
Normally, a spacer (not shown) is arranged between the injection pipes of the triple pipe structure, and the interval between the injection pipes is maintained.

  In such an auxiliary burner, when the burner is used, solid fuel (and carrier gas) is supplied from the solid fuel injection pipe 1, gaseous fuel such as LNG is supplied from the gaseous fuel injection pipe 2, and oxygen is supplied from the combustion supporting gas injection pipe 3. The combustion of the gaseous fuel and the combustion support gas creates a combustion field above the ignition temperature of the solid fuel, and the solid fuel is sent into this combustion field to raise the temperature to the ignition temperature. Then, the solid fuel burns (vaporization → ignition).

  Examples of the gaseous fuel used in the auxiliary burner include LPG (liquefied petroleum gas), LNG (liquefied natural gas), hydrogen, by-product gas from steelworks (C gas, B gas, etc.), and a mixture of two or more of these. Gas and the like. Examples of the solid fuel include coal (pulverized coal) and plastics (granular or pulverized ones; including waste plastics). One or more of these can be used. Is particularly preferred. As the supporting gas, any of pure oxygen (industrial oxygen), oxygen-enriched air, and air may be used, but when dissolving scrap, it is preferable to use pure oxygen. As the carrier gas for the solid fuel, for example, one or more of an inert gas such as nitrogen and argon and air can be used, but in general, nitrogen, argon and the like are used to prevent self-ignition of the fuel. Inert gas is used.

  FIG. 2 schematically shows an example of the state of implementation of the method of the present invention (vertical cross section in the radial direction of the electric furnace), wherein 7 is a furnace body, 8 is an electrode, 9 is a combustion burner, and x is scrap. is there. The auxiliary burner 9 is installed with an appropriate inclination. Usually, a plurality of such auxiliary burners 9 are provided so as to heat or melt the scrap at a so-called cold spot in the electric furnace. In the operation of electric furnaces, if the amount of scrap melted is large, it is natural that the burner output must be increased, but in order to supply a stable flame, the gas flow rate and cooling structure must be adjusted accordingly. Therefore, there is naturally a limit in increasing the burner output. For this reason, it is preferable to install a plurality of auxiliary burners according to the required amount of scrap dissolved.

  In the operation of an electric furnace using an auxiliary burner as described above, when the use of the burner is stopped (for example, when charging scrap), the melt in the furnace adheres to the tip of the burner due to splash of splash, etc. Melts. FIG. 4 and FIG. 5 schematically show a situation in which the nozzle clogging and the melting of the nozzle tip are caused by the adhesion of the melt in the furnace. In FIG. 4, in FIG. 4, the solid fuel nozzle tip (the tip of the solid fuel injection pipe 1) is almost completely blocked by the in-furnace melt (slag) attached to the burner tip, so that the supply of the solid fuel becomes impossible. In addition, erosion of the nozzle tip also occurs. On the other hand, in FIG. 5, although there is no trouble in supplying the solid fuel due to the in-furnace melt (slag) attached to the burner tip, the nozzle is clogged and the nozzle tip is melted.

In order to solve such a problem, according to the present invention, when the use of the auxiliary burner is stopped during the operation of the electric furnace, the purge gas is injected from at least a part of the plurality of injection tubes of the auxiliary burner, thereby making the burner tip. The furnace melt near the part (in other words, the furnace melt approaching the burner tip by splashing or slag forming) is gas-purged from the front of the burner to suppress the adhesion of the furnace melt to the burner tip. Things.
The type of the purge gas is not particularly limited, and the type of the gas may be appropriately selected in consideration of the relationship between utilities and measures for preventing oxygen deficiency. Usually, nitrogen or air is used.
Further, the purge gas can be injected from any injection pipe constituting the burner. However, since the solid fuel injection pipe 1 is particularly susceptible to nozzle blockage, and the nozzle blockage tends to cause operational trouble, at least the solid fuel It is preferable to inject the purge gas from the injection pipe 1, and it is more preferable to inject the purge gas from all the injection pipes (the solid fuel injection pipe 1, the gas fuel injection pipe 2, and the supporting gas injection pipe 3).

In addition, in order to more surely purge the melt in the furnace near the tip of the burner by injecting the purge gas and suppress the adhesion of the melt in the furnace to the tip of the burner, it is necessary to optimize the gas discharge flow rate of the purge gas. preferable. Specifically, it is preferable to inject the purge gas at a discharge gas flow rate satisfying the discharge gas flow rate ratio Vr defined by the following equation (1) of 0.5 to 2.1 (high-speed purging).

Here, the appropriate discharge gas flow rate v _th of the purge gas injected from the injection pipes (the solid fuel injection pipe 1, the gaseous fuel injection pipe 2, and the supporting gas injection pipe 3) of the auxiliary burner is calculated by the above equation (2). Is done. The appropriate discharge gas flow rate v _th of the purge gas represents a calculated value of an appropriate purge flow rate for gas purging the furnace melt near the burner tip and suppressing the adhesion of the furnace melt to the burner tip. on the other hand, the discharge gas flow rate v _g of the purge gas represents a purge flow rate for actual operation. Therefore, v g _/ v _th represents the ratio of the actual operation values for calculating values of proper purge flow rate.

If the discharge gas flow rate ratio Vr is less than 0.5, the flow rate of the purge gas is not sufficient, so that the furnace melt near the tip of the burner cannot be properly purged, and the melt in the furnace adheres to the tip of the burner and the nozzle is clogged. May occur. On the other hand, from the viewpoint of purging the melt in the furnace such as splash, the discharge gas flow rate ratio Vr is preferably large. However, when the discharge gas flow rate ratio Vr exceeds 2.1, the flow velocity becomes excessive, and the operating cost increases. Invite. Further, since the flow rate of the purge gas is limited in the normal nozzle structure, there is a concern that the nozzle shape needs to be drastically changed. For the above reasons, the discharge gas flow velocity ratio Vr is preferably 0.5 to 2.1, and more preferably 0.8 to 1.2.
Here, the proper discharge gas flow rate v _th a discharge gas velocity v _g is the velocity at the nozzle tip (discharge port), the cross-sectional area of the discharge gas flow rate v _g is the discharged gas flow rate and nozzle tip purged during actual operation Divided by

The injection of the purge gas is performed when the use of the auxiliary burner is stopped during the operation of the electric furnace. Specifically, when the scrap is charged and recharged, which tends to generate splashes, etc. Later time zone), at the time of slag discharge and at the time of molten steel tapping. By appropriately setting the flow rate of the purge gas, it is possible to suppress a decrease in the molten iron temperature due to the high-speed purge.
In the present invention, while using the auxiliary combustion burner as described above, by injecting the purge gas during the burner use stop time, the iron-based scrap can be efficiently heated or melted using a solid fuel such as pulverized coal. In addition, the nozzle blockage of the auxiliary burner and the erosion at the nozzle tip are reduced, so that the maintenance of the burner is improved and the maintenance efficiency can be improved.

The test was performed in an electric furnace equipped with an auxiliary burner having the structure shown in FIG. FIG. 3 schematically shows a horizontal cross section of the electric furnace subjected to the test. This electric furnace has a furnace diameter of about 6.3 m, a furnace height of about 4.1 m, a Tap capacity of about 120 tons, and is a DC type having one electrode at the center. In the circumferential direction of the furnace, there are a total of four auxiliary burners, two at the molten steel tapping side (burner (1) and burner (2)) and two at the slag discharge side (burner (3) and burner (4)). It was installed in the place.
LNG (gas fuel) and pulverized coal (solid fuel) are used as the fuel for the auxiliary burner, oxygen is used as the combustion supporting gas, and pulverized coal is injected from the central solid fuel injection pipe using nitrogen as a carrier gas. LNG was injected from the outer gaseous fuel injection pipe, and oxygen was injected from the outer (outermost) combustible gas injection pipe. Table 1 shows the output and operating conditions of this burner. The energy ratio between pulverized coal and LNG was pulverized coal: LNG = 90: 10. As the pulverized coal, MDT having the components shown in Table 2, a lower calorific value, and a particle size was used.

During the operation of the electric furnace, when the burner is extinguished and the fire burner is off, specifically during scrap loading and reloading, when the scrap burns off (time after the burn-off), and when the slag is discharged At the time of molten steel tapping, a purge gas (nitrogen) was injected from each injection pipe (solid fuel injection pipe 1, gas fuel injection pipe 2, and oxidizing gas injection pipe 3) of the auxiliary burner.
The slag specific unit in this embodiment is 120 kg / ton molten iron, and the appropriate discharge gas flow rate v _{th under} this condition is calculated to be 85.2 m / s from the equation (2). By changing the discharge gas flow rate v _g for this proper discharge gas flow rate v _th, it was injection of the purge gas (nitrogen) at various discharge gas flow rate ratio Vr. The operation of the electric furnace was performed 9 to 11 ch per day. As soon as the operation was completed on that day, the auxiliary burner was taken out of the furnace of the electric furnace, and the state of the nozzle tip was confirmed. Table 3 shows the results of evaluating the maintainability, operability, and cost of the auxiliary burner in this example, together with the purge gas discharge gas flow rate ratio Vr.

  In Table 3, the maintainability of the auxiliary burner was evaluated based on the nozzle blocking rate, and was evaluated as “Δ” if there was no nozzle blocking. In addition, the nozzle blockage to the extent that it does not hinder the operation, specifically, in one or more of the solid fuel injection pipe 1, the gaseous fuel injection pipe 2, and the flammable gas injection pipe 3, the flow path cross-sectional area at the nozzle tip is reduced. On the other hand, if the nozzle was clogged by 5% or less, "と し た" was given. On the other hand, clogging of nozzles that obviously impede operation and require maintenance / cleaning, specifically, one or more of solid fuel injection pipe 1, gas fuel injection pipe 2, and flammable gas injection pipe 3 In the above, if the nozzle clogging was more than 5% with respect to the cross-sectional area of the flow path at the tip of the nozzle, it was evaluated as “x”. Since four burners were installed, the state of the tip of the nozzle of each burner was checked.

The operability was evaluated as “Δ” when the operation was possible without any trouble, and “×” when an operation trouble occurred such as the nozzle was clogged and the pulverized coal could not be conveyed.
The cost was evaluated by the cost index. The cost index is an index obtained by dividing the cost generated by injecting the purge gas by the economic merit at the time of introducing the auxiliary burner. The lower the index is, the more economic merit can be enjoyed. The method of calculating the cost index is shown below.

In an operation using an auxiliary burner in an electric furnace, an economic advantage can be obtained by replacing a part of an expensive fuel such as LNG with an inexpensive fuel such as pulverized coal for the fuel used in the auxiliary burner. For this reason, first, the economic merit (hereinafter, referred to as “economic merit by pulverized coal + LNG burner”) by operating with the auxiliary burner using pulverized coal + LNG as fuel is calculated by the following formula. did.

Here, the LNG cost is an operation cost when a normal auxiliary burner using only LNG as fuel is used, and 200 Nm ³ / h per burner, LNG blowing time 40 minutes / ch, LNG unit price 70 yen Assuming / Nm ³ , the LNG cost is 9333 yen / ch. The pulverized coal + LNG cost is the operating cost when an auxiliary burner using pulverized coal + LNG as a fuel is used. In the present embodiment, pulverized coal per burner is 240 kg / h, LNG 20 Nm ³ / h, pulverized coal is used. Assuming that + LNG injection time is 40 minutes / ch and pulverized coal unit price is 20 yen / kg (including pulverization cost), the pulverized coal + LNG cost is 4133 yen / ch. As described above, the economical advantage of pulverized coal + LNG burner is 43.3 yen / ton of molten iron per burner when the Tap capacity of the electric furnace is 120 ton molten iron / ch.

On the other hand, in the present invention, nozzle clogging is prevented by performing purge gas injection when the use of the auxiliary combustion burner is stopped during operation of the electric furnace, but when a large amount of purge is performed without appropriately setting the purge flow rate. However, the purging cost is increased accordingly, and the economic merit of the pulverized coal + LNG burner is reduced. The purge cost per burner was calculated by the following formula.

Here, the appropriate purge flow rate is a purge flow rate when the discharge gas flow rate ratio Vr is 1.0, and in this embodiment, all of the solid fuel injection pipe, the gas fuel injection pipe, and the supporting gas injection pipe are used. , And the total flow rate was 700 Nm ³ / h. The unit price of the purge gas was 4.5 yen / Nm ^{3 for} nitrogen, and the purge time was 30 minutes / ch. As described above, when the discharge gas flow rate ratio Vr is set to 1.0, the purge cost is 13.1 yen / ton molten iron, and the purge cost increases or decreases by changing Vr.
From the above, for example, if the purge cost when Vr is 1.0 is divided by the economic merit of pulverized coal + LNG burner, the cost index is 0.30.

  According to Table 3, in Comparative Example 1 (Vr = 0.2), the purge gas flow rate was low, so that the gas purge of the melt in the furnace was insufficient, so that the adhesion of the melt in the furnace to the burner tip was appropriate. In all of the burners (1) to (4), nozzle blockage occurred such that pulverized coal could not be supplied during operation. Also in Comparative Example 2 (Vr = 0.4), in the burners (3) and (4) on the slag discharge side, for the same reason as in Comparative Example 1, a nozzle that could not supply pulverized coal during operation was used. An occlusion has occurred. That is, in Comparative Examples 1 and 2, gas purge of the furnace melt was insufficient due to the low flow rate of the purge gas, and therefore, adhesion of the melt in the furnace to the tip of the burner could not be appropriately suppressed. An operation trouble due to blockage occurred.

On the other hand, in Examples 1 to 9, since the purge gas is injected at a sufficient flow rate of the purge gas, the melt in the furnace near the tip of the burner is gas-purged from the front of the burner, and the melt in the furnace to the tip of the burner. Since nozzle adhesion is effectively suppressed, there is no nozzle blockage (and erosion) that would cause an operational trouble.
In particular, Invention Example 3 in which Vr = 0.8, Invention Example 4 in which Vr = 1.0, and Invention Example 5 in which Vr = 1.2 all have maintenance performance and operability all evaluated as “〇”. Yes, and the cost index is low.

On the other hand, in Inventive Example 6 where Vr = 1.5, Inventive Example 7 where Vr = 2.0, and Inventive Example 8 where Vr = 2.1, there is no nozzle clogging and there is no problem in operability. , The cost index is slightly higher. If the flow rate of the purge gas is increased, it may be necessary to take measures on the facilities, such as a necessity of changing a facility for supplying a large amount of purge gas or a burner structure.
In addition, in Invention Example 9 in which Vr = 3.0, there is no nozzle clogging and there is no problem in operability, but the purge gas flow rate is further increased, and the cost required for injection of the purge gas is further increased. Is smaller than other invention examples.

DESCRIPTION OF SYMBOLS 1 Solid fuel injection pipe 2 Gas fuel injection pipe 3 Burning gas injection pipe 7 Furnace body 8 Electrode 9 Supporting burner x Iron-based scrap 10 Solid fuel flow path 11 Solid fuel discharge port 12 Solid fuel supply port 20 Gas fuel flow path 21 Gas fuel discharge port 22 Gas fuel supply port 30 Combustible gas flow path 31 Combustible gas discharge port 32 Combustible gas supply port

Claims (6)

In a method for operating an electric furnace having an auxiliary burner having an injection pipe for injecting a gaseous fuel, a solid fuel, and a supporting gas, respectively ,
When the use of the auxiliary burner is stopped during operation of the electric furnace, a purge gas is injected from at least a part of the plurality of injection pipes, thereby purging a furnace melt near the tip of the burner, thereby purging the burner tip. A method for operating an electric furnace, wherein the furnace melt is prevented from adhering to the part ,
A method for operating an electric furnace equipped with an auxiliary burner , wherein a purge gas is injected at a discharge gas flow rate satisfying a discharge gas flow rate ratio Vr defined by the following equation (1) of 0.5 to 2.1 .

  The method for operating an electric furnace equipped with an auxiliary burner according to claim 1, wherein the purge gas is injected from at least a solid fuel injection pipe.   The method for operating an electric furnace equipped with a burner according to claim 1, wherein the purge gas is injected from all the injection pipes. The method for operating an electric furnace equipped with an auxiliary burner according to any one of claims 1 to 3 , wherein the purge gas is injected at a discharge gas flow rate satisfying a discharge gas flow rate ratio Vr of 0.8 to 1.2. . Auxiliary fuel burner, in order from the center side, the injection pipe of a solid fuel, injection pipe of the gaseous fuel injection pipes of combustion-supporting gas according to claim 1-4, characterized in that it has a placed structure to concentrically An operation method of an electric furnace equipped with the auxiliary burner according to any one of the above. A method for producing molten iron by an electric furnace, comprising melting an iron-based scrap in an electric furnace to obtain molten iron while performing the operation method according to any one of claims 1 to 5 .

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