JP2021188107A - Operation method of electric furnace - Google Patents

Abstract

To provide an operation method of an electric furnace in which an arc can be efficiently coated.SOLUTION: An operation method of an electric furnace according to one embodiment of the present invention is an operation method of an arc-type electric furnace for smelting molten steel while forming slag on a bath surface. The operation method includes: a slag formation step (step S1) of forming a slag containing CaO, SiO2, MgO, and FeO; and a step (step S2) of charging an additive containing CaO, SiO2, and FeO and a charcoal material near an electrode after the slag formation step (step S1). The basicity of the additive is smaller than that of the slag formed in the slag formation step (step S1).SELECTED DRAWING: Figure 2

Description

The present invention relates to an operating method of an electric furnace.

In the operation of the arc-type electric furnace, the slag is formed and the arc radiated from the tip of the electrode to the molten steel bath surface is covered with the forming slag, so that the radiant heat generated from the arc is taken into the slag to improve the thermal efficiency.

Japanese Unexamined Patent Publication No. 2003-293024 describes an operation method of an electric furnace in which a carbonaceous material is blown into a slag layer at the same time as oxygen gas to cause forming of slag. In the same gazette, in order to suppress the discharge of iron oxide-containing slag to the outside of the furnace, the height of the forming slag is minimized from the start to a few minutes before the end of the reduction period. It is described that the amount of carbonaceous material blown and / or the tilt angle of the electric furnace is adjusted so as to be covered.

Japanese Unexamined Patent Publication No. 2-107712 describes a blowing melting method in which iron powder and a carbonizing material are blown into the vicinity of an electrode in an arc furnace by a blowing means to dissolve the iron content in the iron powder. .. The publication describes that the charcoal-added material blown at the same time as the iron powder reduces the iron powder or FeO, so that the slag foams and envelops the arc to improve the temperature rise efficiency.

Japanese Unexamined Patent Publication No. 58-73714 describes a dephosphorization method using an arc furnace. In the same gazette, a slag-forming agent that gives highly basic slag is used, and carbon powder is blown into the inside of the solution in the furnace on a flow of inert gas, and oxygen gas is blown into the inside, thereby causing slag. It is described that a foam layer is formed and fluidized therein to facilitate slag removal.

Japanese Unexamined Patent Publication No. 2017-166022 describes a metal melting method using an arc-type electric furnace. In the same publication, the basicity of the slag is 0.5 or more and 1.5 or less, and the Al ₂ O ₃ concentration of the slag is 5% by mass or more for the purpose of solving the bias of the foaming portion and the insufficient amount of foaming. It is stated that it is 15% by mass or less.

Japanese Unexamined Patent Publication No. 2003-293024 Japanese Unexamined Patent Publication No. 2-107712 Japanese Unexamined Patent Publication No. 58-73714 Japanese Unexamined Patent Publication No. 2017-166022

Since the arc is covered with forming slag, it is common practice to increase the amount of slag and the amount of carbonaceous material and oxygen blown into the slag. However, this method requires a large amount of auxiliary raw materials (CaO, etc.), carbonaceous material, and oxygen in order to promote the forming of the entire slag, which greatly increases the cost of producing molten steel.

Therefore, Japanese Patent Application Laid-Open No. 2-107712 described above proposes blowing iron powder and a carbonizing material into the vicinity of the electrodes in an arc furnace. However, the publication does not mention the effect of slag properties on forming behavior. Therefore, as described below, forming in the vicinity of the arc may not be sufficiently promoted, and the covering of the arc may be insufficient.

That is, when the fluidity of the slag is high, the forming slag generated in the vicinity of the arc immediately flows from the vicinity of the arc to the surroundings, so that it becomes difficult to form the slag in the vicinity of the arc to a sufficient height. Further, when slag having high fluidity is used, there is a problem that the amount of melting damage of the refractory material of the furnace body increases.

On the other hand, when the fluidity of the slag is low, even if a large amount of iron powder and carbonaceous material are blown into the vicinity of the arc to generate CO gas, the CO gas escapes from the slag at a stage where the slag does not form so much and reaches a sufficient height. Unable to form slag. Therefore, it becomes difficult to sufficiently cover the arc with the forming slag.

An object of the present invention is to provide a method of operating an electric furnace capable of efficiently covering an arc.

The method for operating an electric furnace according to an embodiment of the present invention is a method for operating an arc-type electric furnace that smelts molten steel while forming slag on the bath surface _{, and includes CaO, SiO 2} , MgO, and FeO. A slag forming step of forming a slag, and after the slag forming step, _{an additive containing CaO, SiO 2} , and FeO in the vicinity of the electrode, and a step of adding a carbonaceous material are provided, and the basicity of the additive is determined. It is smaller than the basicity of the slag formed in the slag forming step.

According to the present invention, the arc can be efficiently covered.

FIG. 1 is a schematic diagram showing an example of the configuration of an electric furnace. FIG. 2 is a flow chart of an operating method of an electric furnace according to an embodiment of the present invention.

The present inventors investigated the forming behavior due to the addition of carbonaceous material to slag. As a result, it was found that the higher the fluidity of the slag (in the case of solid-liquid coexisting slag, the same as the high liquid phase ratio of the slag), the higher the forming height.

Moreover, in the experiment in which the carbonaceous material was put into the vicinity of the center of the slag bath, when the fluidity of the slag was low, the forming generated in the center of the bath was not so high, and the forming slag slowly spread from the center to the surroundings. On the other hand, when the fluidity of the slag was high, the forming slag generated in the center of the bath was considerably high, but the forming slag spread rapidly to the surroundings, and the height of the forming in the center decreased immediately.

From the above results, the present inventors have improved the forming height of the slag near the electrode by increasing the fluidity of the slag near the electrode while reducing the fluidity of the slag other than the vicinity of the electrode. I came up with the idea of being able to cover the arc efficiently.

The present invention has been completed based on the above findings. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated. The dimensional ratio between the constituent members shown in each figure does not necessarily indicate the actual dimensional ratio.

FIG. 1 is a schematic diagram of an electric furnace 1 which is an example of an electric furnace. The configuration of the electric furnace 1 is merely an example for explanation, and does not limit the configuration of the electric furnace used in the operation method of the electric furnace according to the present embodiment.

The electric furnace 1 includes a furnace body 10, electrodes 20, and nozzles 30 and 35. The furnace body 10 includes a furnace bottom portion 11, a side wall portion 12, and a furnace lid 13. Regular and non-standard refractories (not shown) are arranged in at least a part of the bottom 11 and the side wall 12. A part of the furnace bottom portion 11 and the side wall portion 12 may be water-cooled.

The electrode 20 generates an arc between the scrap and the molten steel held in the furnace bottom 11. FIG. 1 shows a case where the number of electrodes 20 is three, but the number of electrodes 20 is arbitrary. The electric furnace 1 may be an AC type or a DC type.

The nozzle 30 blows oxygen into the furnace body 10, and the nozzle 35 blows charcoal material into the furnace body 10. For example, the carbonaceous material is blown with an inert gas such as _{Ar or CO 2 as a carrier gas.} Each of the nozzles 30 and 35 may be in contact with the molten steel M or slag S during melting, or may not be in contact with the molten steel M or slag S. In FIG. 1, the nozzles 30 and 35 are shown to be one each, but a plurality of nozzles 30 and 35 may be arranged respectively.

FIG. 2 is a flow chart of an operating method of an electric furnace according to an embodiment of the present invention. This operation method includes a step of forming a slag (step S1) and a step of adding an additive and a carbonaceous material in the vicinity of the electrode (step S2).

First, the slag S is formed in the furnace body 10 (step S1). Specifically, this step can be performed as follows, for example.

Iron raw materials such as scrap and pig iron, and auxiliary materials such as CaO are charged into the furnace body 10. A voltage is applied to the electrode 20 to generate an arc between the electrode 20 and the iron raw material, and the heat of the arc melts the iron raw material. At this time, it is preferable to blow oxygen and carbonaceous material from the nozzles 30 and 35, respectively, to promote the dissolution of the iron raw material.

When the iron raw material is dissolved, the component separated from the iron raw material and the auxiliary material are mixed to form slag S. Hereinafter, the slag formed in this step is referred to as "bulk slag".

Bulk slag contains CaO, SiO ₂ , MgO, and FeO. The bulk slag may contain _{components other than CaO, SiO 2} , MgO, and FeO (eg, Al ₂ O _3).

The basicity of the bulk slag is preferably 2.0 to 4.0. Here, the basicity of bulk slag _{is the ratio (CaO / SiO 2} ) of the CaO content (unit: mass%) to _{the SiO 2 content (unit: mass%) of the bulk slag.}

If the basicity of the bulk slag is too low, the fluidity of the bulk slag becomes too high, and the bulk slag may overflow from the waste port provided on the furnace wall. Further, if the basicity of the bulk slag is too low, the amount of erosion of the refractory of the furnace body may increase. On the other hand, if the basicity of the bulk slag is too high, the fluidity may be too low and it may be difficult to cover the arc. The lower limit of the basicity of bulk slag is more preferably 2.4, still more preferably 2.8. The upper limit of the basicity of bulk slag is more preferably 3.6, still more preferably 3.2.

The MgO content of the bulk slag is preferably 8 to 14% by mass. If the MgO content of the bulk slag is too low, the amount of melt damage of the refractory of the furnace body may increase. On the other hand, if the MgO content of the bulk slag is too high, free MgO remains in the slag, and when the slag is used as a roadbed material or the like, it may expand due to a reaction with rainwater. The lower limit of the MgO content of the bulk slag is more preferably 10% by mass. The upper limit of the MgO content of the bulk slag is more preferably 13% by mass.

The FeO content of the bulk slag is preferably 20 to 40% by mass. If the FeO content of the bulk slag is too low, the fluidity of the slag may be too low to form. On the other hand, if the FeO content of the bulk slag is too high, the iron yield will decrease. The lower limit of the FeO content of the bulk slag is more preferably 25% by mass. The upper limit of the FeO content of the bulk slag is more preferably 35% by mass.

The total content of the components other than CaO, SiO ₂ , MgO, and FeO in the bulk slag is preferably 20% by mass or less. The total content of the components other than CaO, SiO ₂ , MgO, and FeO is more preferably 10% by mass or less, still more preferably 5% by mass or less.

The basicity and composition of the bulk slag can be adjusted, for example, by the components of the iron raw material and the auxiliary material to be charged into the furnace body 10 and the amount thereof. As will be described later, in order to improve the solubility of the iron raw material and the auxiliary material, the iron raw material and the auxiliary material may be charged while a part of the slag and the molten steel of the previous heat remains in the furnace body 10. In this case, if the components of the iron raw material and auxiliary materials and their amounts are determined so that the basicity of the bulk slag is within the above-mentioned range, taking into consideration the components of the slag and molten steel (seed hot water) remaining in the furnace. good.

When oxygen is blown, the amount of oxygen supplied is not limited to this, but can be, for example, 5 to 50 Nm ³ / (molten steel ton / hour). The lower limit of the amount of oxygen supplied is preferably 10 Nm ³ / (molten steel ton / hour). The upper limit of the amount of oxygen supplied is preferably 40 Nm ³ / (molten steel ton / hour).

The charcoal material is, for example, carbon powder. When the charcoal material is blown, the supply amount of the charcoal material is not limited to this, but is, for example, 10 to 120 kg / min. The lower limit of the supply amount of the carbonaceous material is preferably 30 kg / min. The upper limit of the supply amount of the carbonaceous material is preferably 90 kg / min.

After forming the bulk slag, the additive and the carbonaceous material are added in the vicinity of the electrode 20 (step S2). It should be noted that oxygen and the carbonaceous material may or may not be blown into the bulk slag while the additive and the carbonaceous material are charged in the vicinity of the electrode 20.

Additives include CaO, SiO ₂ , and FeO. Additives, CaO, SiO _2, and to the FeO may be a composition comprising in a predetermined ratio, CaO, SiO _2, and FeO may also be a mixture obtained by mixing at a predetermined ratio. Additives, CaO, SiO _2, and may contain components (e.g. MgO or _Al 2 _{O 3)} other than the FeO. As the additive, for example, slag produced in the electric furnace 1 or another furnace may be used.

In this embodiment, the basicity of the additive is made smaller than the basicity of the bulk slag. Here, the basicity of the additive is _{the ratio (CaO / SiO 2} ) of the _{CaO content (unit: mass%) to the SiO 2} content (unit: mass%) of the additive.

That is, in the present embodiment, an additive having a basicity lower than that of the bulk slag is charged in the vicinity of the electrode together with the carbonaceous material. This lowers the basicity of the slag near the electrode and increases the fluidity of the slag near the electrode. As a result, the forming slag in the vicinity of the electrode 20 can be increased, and the arc generated from the electrode 20 can be covered with the forming slag.

The basicity of the additive is preferably 0.7 or more and less than 2.0. If the basicity of the additive is too high, the basicity of the slag in the vicinity of the electrode cannot be lowered, and the above effects may not be sufficiently obtained. On the other hand, if the basicity of the additive is too low, the basicity of the bulk slag may be too low. The lower limit of the basicity of the additive is more preferably 0.8, still more preferably 0.9. The upper limit of the basicity of the additive is more preferably 1.9, more preferably 1.5, and even more preferably 1.2.

The FeO content of the additive is preferably 10 to 40% by mass. If the FeO content of the additive is too low, the amount of CO gas generated may be small and it may be difficult to form. On the other hand, if the FeO content of the additive is too high, the slag in the vicinity of the electrode may be excessively cooled, making it difficult to form. The lower limit of the FeO content is more preferably 20% by mass. The upper limit of the FeO content is more preferably 35% by mass.

The total content of the additives other than CaO, SiO ₂ , and FeO is preferably 20% by mass or less. The total content of the components other than CaO, SiO ₂ , and FeO is more preferably 10% by mass or less, still more preferably 5% by mass or less.

The additive and the carbonaceous material can be added, for example, by blowing the additive and the carbonaceous material into the vicinity of the electrode 20 by a nozzle (not shown). In this case, the additive and the carbonaceous material may be blown by the same nozzle or may be blown by different nozzles. Alternatively, the additive and the carbonaceous material may be added by pelletizing the additive and the carbonaceous material and dropping them in the vicinity of the electrode 20.

The supply amount of the additive is not limited to this, but can be, for example, 5 to 20% of the mass of the bulk slag. The lower limit of the additive supply is preferably 8% by mass of the bulk slag. The upper limit of the additive supply is preferably 15% of the mass of the bulk slag.

The amount of the carbonaceous material to be charged in the vicinity of the electrode is not limited to this, but may be, for example, 0.2 to 1.0 kg / molten steel ton. The lower limit of the supply amount of the carbonaceous material to be charged in the vicinity of the electrode is preferably 0.3 kg / molten steel ton. The upper limit of the supply amount of the carbonaceous material to be charged in the vicinity of the electrode is preferably 0.8 kg / molten steel ton.

After smelting for a predetermined time, the slag S (including the slag formed by the bulk slag and the subsequent addition of the additive) in the furnace body 10 is discharged. After further reduction work is performed as necessary, the smelted molten steel M is taken out. The molten steel M can be taken out, for example, by tilting the furnace body 10 with a tilting device and discharging the molten steel from an EBT (Eccentric Bottom Tapping) outlet provided at an eccentric position of the furnace bottom portion 11. At this time, as described above, in order to improve the solubility of the iron raw material and the auxiliary material in the next heat, in the step of discharging the slag S and the step of taking out the molten steel M, a part of the slag S and the molten steel M is used as the furnace body 10. You may leave it inside.

The method of operating the electric furnace according to the embodiment of the present invention has been described above. According to this embodiment, the arc can be efficiently covered by increasing the forming slag in the vicinity of the electrodes.

Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to these examples.

[Comparative Example 1]
Approximately 100 tons of scrap, CaO, SiO ₂ , and MgO were charged into an electric furnace, and while oxygen and carbon powder were blown from the furnace wall, an arc was irradiated from an electrode installed above the center of the furnace to melt the scrap. The produced slag was about 7.0 ton, the basicity was 3.0, the MgO content was 12% by mass, and the FeO content was 30% by mass. After that, oxygen (3000 Nm ³ / hour) and carbon powder (60 kg / min) were blown into the slag from the furnace wall to continue arc irradiation while forming, and the molten steel temperature was set to about 1650 ° C.

When the operator observed the inside of the furnace after the undissolved scrap disappeared on the molten steel bath surface, the forming height of the slag near the electrodes was unstable, and sometimes the arc was greatly exposed. It is considered that this is because the basicity of slag (bulk slag) was too high and the fluidity of slag was low.

[Comparative Example 2]
Approximately 100 tons of scrap, CaO, SiO ₂ , and MgO were charged into an electric furnace, and while oxygen and carbon powder were blown from the furnace wall, an arc was irradiated from an electrode installed above the center of the furnace to melt the scrap. The produced slag was about 7.0 ton, the basicity was 1.0, the MgO content was 12% by mass, and the FeO content was 30% by mass. After that, oxygen (3000 Nm ³ / hour) and carbon powder (60 kg / min) were blown into the slag from the furnace wall to continue arc irradiation while forming, and the molten steel temperature was set to about 1650 ° C.

After the undissolved scrap was removed from the molten steel bath surface, the operator observed the inside of the furnace and found that the slag was violently formed and the arc was well covered. Therefore, the power intensity was improved by 5% as compared with Comparative Example 1. On the other hand, the amount of refractory erosion increased by 20%.

[Example]
Approximately 100 tons of scrap, CaO, SiO ₂ , and MgO were charged into an electric furnace, and while oxygen and carbon powder were blown from the furnace wall, an arc was irradiated from an electrode installed above the center of the furnace to melt the scrap. The produced slag was about 6.3 tons, the basicity was 3.0, the MgO content was 12% by mass, and the FeO content was 30% by mass. After that, oxygen (3000 Nm ³ / hour) and carbon powder (60 kg / min) were blown into the slag from the furnace wall to form the slag, and the arc irradiation was continued. In parallel with this, _{additives containing CaO, SiO 2} , and FeO (total amount of about 700 kg, basicity of 1.0, FeO content: 30% by mass) and carbon particles (total amount of about 50 kg, grains) are placed near the electrodes. The mixture (with a diameter of 5 mm or less) was continuously added for 10 minutes until the molten steel reached 1650 ° C.

After the undissolved scrap disappeared on the molten steel bath surface, the operator observed the inside of the furnace. Continued to cover enough. As a result, the power intensity was improved by 5% as compared with Comparative Example 1. The amount of refractory erosion was the same as that of Comparative Example 1.

The embodiment of the present invention has been described above. The embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented without departing from the spirit of the present invention.

1 Electric furnace 10 Furnace 11 Furnace bottom 12 Side wall 13 Furnace lid 20 Electrodes 30, 35 Nozzles M Molten steel S slag

Claims (4)

It is an operation method of an arc-type electric furnace that smelts molten steel while forming slag on the bath surface.
A slag forming step of forming a slag containing CaO, SiO _{2, MgO, and FeO,}
After the slag forming step, _{an additive containing CaO, SiO 2} , and FeO, and a step of adding a carbonaceous material are provided in the vicinity of the electrode.
A method for operating an electric furnace in which the basicity of the additive is smaller than the basicity of the slag formed in the slag forming step. The method for operating an electric furnace according to claim 1.
The basicity of the slag formed in the slag forming step is 2.0 to 4.0, and the slag is 2.0 to 4.0.
A method for operating an electric furnace in which the basicity of the additive is 0.7 or more and less than 2.0. The method for operating an electric furnace according to claim 1 or 2.
The slag formed in the slag forming step contains MgO: 8 to 14% by mass and FeO: 20 to 40% by mass.
The method for operating an electric furnace, wherein the additive contains FeO: 10 to 40% by mass. The method for operating an electric furnace according to any one of claims 1 to 3.
A method for operating an electric furnace in which the forming slag in the vicinity of the electrode is increased by adding the additive and the carbonaceous material, and the arc is covered with the forming slag.

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