JP2021188073A - Producing method of molten iron using electric furnace - Google Patents

Abstract

To produce molten iron with high productivity and energy utilization efficiency, using an electric furnace with a preheating chamber for preheating iron-based scrap with a furnace exhaust gas.SOLUTION: A lime-based slag-forming material is charged into a preheating chamber 2 together with an iron-based scrap, the slag-forming material is preheated together with the iron-based scrap in the preheating chamber 2, and then is supplied into a melting chamber 1. Since slag is formed in a short time, slag-formation is stabilized so that energy utilization efficiency is improved. Furthermore, peroxidation due to excessive preheating of iron-based scrap can be prevented and energy loss for reducing iron-based scrap that has been oxidized is suppressed, and hanging of the iron-based scrap in the preheating chamber 2 is suppressed which enables energy utilization efficiency to be improved, and enables a stable operation with high productivity to be performed.SELECTED DRAWING: Figure 1

Description

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

In an electric furnace, molten iron is produced by melting iron-based scrap (cold iron source) with arc heat, but it consumes a large amount of electric power to generate arc heat. Conventionally, in order to reduce power consumption in an electric furnace, methods such as preheating iron-based scrap with high-temperature exhaust gas generated during melting and blowing carbonaceous material such as coke as an auxiliary heat source have been adopted. ..
In Patent Document 1, as a method of melting iron scrap while preheating iron scrap with high-temperature exhaust gas generated during melting, a preheating chamber for iron scrap is continuously provided in the upper part of the melting chamber, and the melting chamber is used. A melting method is shown in which the generated high-temperature exhaust gas is passed through a preheating chamber filled with iron-based scrap to preheat the iron-based scrap, and the preheated iron-based scrap is supplied to the melting chamber. ing. Further, in the method of Patent Document 1, a charcoal material is blown into a melting chamber and used as an auxiliary heat source. CO gas is generated by the reduction of iron oxide and the combustion of the carbon material by such injection of the carbon material, and this CO gas promotes so-called "slag forming" in which molten slag foams. This reduces the radiant heat of the arc and improves the melting efficiency of iron-based scrap.

Japanese Unexamined Patent Publication No. 2012-180560

In recent years, there has been a strong demand for energy efficiency improvement and power saving in the operation of electric furnaces from the viewpoint of global environmental problems, and in response to such demands, the melting method shown in Patent Document 1 uses energy. Although some effect can be obtained in terms of improving efficiency, it cannot be said that it is a sufficient effect. Further, according to the results of the tests conducted by the present inventors regarding the melting method shown in Patent Document 1, excessive preheating of iron-based scrap in the preheating chamber may cause deterioration of operation and troubles. It turned out. Specifically, it was found that the iron-based scrap is excessively oxidized by preheating, and energy loss for reducing the oxidized iron-based scrap occurs. In addition, when iron-based scrap is excessively oxidized in the preheating chamber, some iron-based scrap is melted by the heat of oxidation and fused to the surrounding iron-based scrap, causing the iron-based scrap to drop in the preheating chamber. It turned out that the trouble of stopping, that is, the suspension of the shelf occurs. When such shelving occurs and the iron scrap cannot be lowered, the iron scrap in the preheating chamber continues to be preheated, iron oxidation is further promoted, further shelving is caused, and normal operation cannot be performed. In addition, since electric power continues to be input even while the shelves are suspended, wasteful energy is consumed. Therefore, it was found that it is necessary to suppress excessive preheating of iron-based scrap in the preheating chamber in order to obtain high productivity and energy utilization efficiency.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to achieve high productivity and energy utilization efficiency in a method for producing molten iron by an electric furnace equipped with a preheating chamber for preheating iron-based scrap with furnace exhaust gas. An object of the present invention is to provide a method for producing molten iron, which can produce molten iron at low cost.

As a result of diligent studies to solve the above problems, the present inventors charged the slag-making material together with the iron-based scrap into the preheating chamber to preheat it, and melted the preheated iron-based scrap and the slag-making material. It turned out that it is effective to supply it indoors. That is, it was found that according to this method, the slag forming material supplied into the melting chamber is slagged in a short time, so that the slag forming is stabilized and the energy utilization efficiency is improved. Furthermore, since the heat of the furnace exhaust gas also adheres to the slag-making material, it is possible to prevent peroxidation due to excessive preheating of iron-based scrap, and energy loss for reducing the oxidized iron-based scrap can be suppressed. At the same time, it was found that the suspension of iron scrap in the preheating chamber was suppressed, the energy utilization efficiency was improved in this respect as well, and stable operation could be performed with high productivity.
Furthermore, by using a lime-based slag material (quick lime or / and limestone) as the slag-making material to be charged into the preheating chamber, an excess of iron-based scrap is caused by the endothermic reaction when the slag-making material is heated (preheated). It was found that peroxidation due to preheating can be prevented more effectively.

The present invention has been made based on such findings, and has the following gist.
[1] In an electric furnace equipped with a melting chamber (1) for melting iron scrap by arc heating and a preheating chamber (2) for preheating the iron scrap supplied to the melting chamber (1), the melting chamber. The iron scrap is preheated by passing the exhaust gas generated in (1) through the preheating chamber (2) filled with iron scrap, and the preheated iron scrap is supplied into the melting chamber (1). , A method of obtaining molten iron by melting in the melting chamber (1).
The slag-making material is charged into the preheating chamber (2) together with the iron-based scrap, the slag-making material is preheated in the preheating chamber (2) together with the iron-based scrap, and then supplied into the melting chamber (1). A characteristic method for producing molten iron using an electric furnace.
[2] The method for producing molten iron by an electric furnace, which comprises charging quicklime and / or limestone as a lime-based slag material into the preheating chamber (2) in the production method of the above [1].

[3] The method for producing molten iron by an electric furnace, which comprises charging quicklime and limestone as a lime-based slag material into the preheating chamber (2) in the production method of the above [2].
[4] In the production method of the above [2] or [3], the R-CO ₂ of the lime-based slag material charged in the preheating chamber (2) is less than 25 mass% by an electric furnace. Method of manufacturing molten iron.
[5] In the production method of the above [2] or [3], the R-CO ₂ of the lime-based slag material charged into the preheating chamber (2) is 5 mass% or more and less than 15 mass%. A method of manufacturing molten iron using an electric furnace.
[6] In any of the above-mentioned manufacturing methods [1] to [5], the electric furnace has a melting chamber (1) and a shaft-type preheating chamber (2) connected to the upper part of the melting chamber (1). ) Is an electric furnace equipped with
By sequentially charging iron-based scrap and slag-making material into the preheating chamber (2), the preheating chamber (2) is filled with iron-based scrap and slag-making material, and it is generated in the melting chamber (1). The iron-based scrap and the slag-making material are preheated by passing the exhausted exhaust gas through the preheating chamber (2) filled with the iron-based scrap and the slag-making material, and the preheated iron-based scrap and the slag-making material are put into the preheating chamber. A method for producing molten iron by an electric furnace, which comprises sequentially lowering the iron in (2) and supplying it into the melting chamber (1).

[7] In the manufacturing method of the above [6], a preheating chamber (2) is provided in the upper part of the melting chamber (1) at a position away from the arc heating portion so as to communicate with the melting chamber (1). It is an electric furnace having a raw material inlet (20) at the upper part of this preheating chamber (2).
The iron-based scrap and the slag-making material charged into the preheating chamber (2) from the raw material charging inlet (20) are filled in the space portion (1a) of the preheating chamber (2) and the melting chamber (1) below it. , A method for producing molten iron by an electric furnace, wherein the iron-based scrap and the slag-making material of this space portion (1a) are sequentially extruded to the arc heating portion side.
[8] In the manufacturing method of the above [7], the iron-based scrap and the slag-making material of the space portion (1a) are sequentially extruded to the arc heating portion side by the extruder (3), and the molten iron by the electric furnace is characterized. Manufacturing method.
[9] In any of the above-mentioned manufacturing methods [1] to [8], the slag-making material is charged into the supply bucket (4) together with the iron-based scrap, and the iron-based scrap is manufactured by the supply bucket (4). It is a method of charging the slag material into the preheating chamber (2) at the same time.
When charging iron-based scrap and slag-making material into the supply bucket (4), molten iron by an electric furnace is characterized in that the iron-based scrap is first charged and then the slag-making material is charged. Manufacturing method.

According to the present invention, (i) the slag forming material supplied into the melting chamber is slagified in a short time, so that slag forming is stabilized and energy utilization efficiency is improved, and (ii) the heat of the reactor exhaust gas is used as the slag forming material. It also heats up, so it is possible to prevent peroxidation due to excessive preheating of iron-based scrap, suppress energy loss for reducing oxidized iron-based scrap, and reduce iron-based scrap in the preheating chamber. Suspension of shelves is suppressed, energy utilization efficiency is improved in this respect as well, and stable operation can be performed with high productivity. These have the effect of reducing the cost of molten iron with high productivity and energy utilization efficiency. Can be manufactured.

In addition, by using a lime-based slag-making material (quick lime or / and limestone) as the slag-making material to be charged into the preheating chamber, the slag-making material is heated in the preheating chamber and undergoes thermal decomposition due to the endothermic reaction. Excessive preheating of the scrap is suppressed, and peroxidation of the iron-based scrap can be prevented more effectively. Furthermore, by using limestone together with quicklime as a limestone slag material (a part of quicklime is replaced with limestone), it is not necessary to calcin the limestone in advance, so that the production cost of molten iron can be further reduced. can.

Explanatory drawing schematically showing an embodiment of the present invention in a state where an electric furnace is cross-sectionally crossed.

The method for producing molten iron based on the present invention is in an electric furnace provided with a melting chamber 1 for melting iron scrap by arc heating and a preheating chamber 2 for preheating the iron scrap supplied to the melting chamber 1. The iron scrap is preheated by passing the exhaust gas generated in the melting chamber 1 through the preheating chamber 2 filled with the iron scrap, and the preheated iron scrap is supplied to the melting chamber 1 to supply the preheated iron scrap to the melting chamber 1. It is a method of obtaining molten iron by melting with. Conventionally, various types of such molten iron manufacturing processes have been known, which differ in the installation form and structure of the preheating chamber, the method of moving iron-based scrap from the preheating chamber to the melting chamber, and the like. According to the method, in such a molten iron manufacturing process, a slag-making material is charged into the preheating chamber 2 together with iron-based scrap, and the slag-making material is preheated in the preheating chamber 2 together with the iron-based scrap, and then in the melting chamber 1. It is to supply to. Further, in the present invention, as the slag-making material to be charged into the preheating chamber 2 together with the iron-based scrap, a lime-based slag-making material made of quicklime and / or limestone is particularly preferable.

In the operation of a conventional electric furnace (arc furnace), it is general that the slag-making material is directly charged into the melting chamber from the auxiliary raw material input chute provided in the upper part of the melting chamber. On the other hand, by charging the slag-making material into the preheating chamber 2 and preheating it together with the iron-based scrap as in the present invention, the following effects can be obtained, and as a result, high productivity and energy can be obtained. Molten iron can be manufactured at low cost with high utilization efficiency.
(I) By preheating the slag-making material with the exhaust gas from the furnace, the time required for slagging is shortened and the efficiency is reduced compared to the conventional method in which the slag-making material is directly charged into the melting chamber from the auxiliary raw material input chute. Melted slag is often made. The molten slag contains iron oxide (FeO) generated by blowing oxygen, and normally, CO gas is generated by the reduction of FeO by blowing the charcoal material into the molten slag and the combustion of the charcoal material, and this CO gas is generated. The gas causes the molten slag to foam, resulting in a so-called "slag forming" state. When this slag forming is appropriately generated, the radiant heat of the arc is reduced and the melting efficiency of iron-based scrap is improved. Therefore, by slagging the slag-making material supplied into the melting chamber 1 in a short time, the time during which the slag forming state can be stably maintained becomes longer, and the energy utilization efficiency is improved accordingly.

(Ii) Oxidation of iron-based scrap in the preheating chamber begins to proceed from about 800 ° C. The temperature of the exhaust gas flowing into the preheating chamber 2 is about 1000 to 1500 ° C., and the temperature in the preheating chamber is 1000 ° C. or higher in the vicinity of the melting chamber, so that the iron-based scrap is excessively oxidized, and this oxidized iron Energy loss occurs for reducing system scrap. Further, when the iron-based scrap is excessively preheated in the preheating chamber, small pieces of iron-based scrap are fused to each other, and the fusion grows to cause shelf suspension in the preheating chamber. On the other hand, in the present invention, since the heat of the reactor exhaust gas also adheres to the slag-making material, it is possible to prevent peroxidation due to excessive preheating of the iron-based scrap, and to reduce the oxidized iron-based scrap. In addition to suppressing energy loss, the shelving of iron-based scrap in the preheating chamber 2 is suppressed, energy utilization efficiency is improved in this respect as well, and stable operation can be performed with high productivity.

(Iii) In particular, when quicklime and / or limestone is charged into the preheating chamber 2 as a lime-based slag-making material, CaCO ₃ contained in the slag-making material is heated in the preheating chamber 2 and thermally decomposed (baked). Due to the endothermic reaction during this process, excessive preheating of the iron-based scrap can be suppressed, and peroxidation of the iron-based scrap can be prevented more effectively. _{The reaction when CaCO 3} in the lime-based slag material is thermally decomposed (calcined) in the preheating chamber 2 is represented by the following equation (1). This reaction is an endothermic reaction and proceeds at a temperature of about 900 ° C. or higher, so that the reaction sufficiently proceeds at the temperature inside the preheating chamber 2.
CaCO ₃ = CaO + CO ₂ + ΔH… (1)
ΔH = -42.5 kcal / mol
Furthermore, by using limestone together with quicklime as a limestone slag material (a part of quicklime is replaced with limestone), it is not necessary to calcin the limestone in advance, so that the production cost of molten iron can be further reduced. can.

The lime-based slag material (quick lime and / and limestone) charged into the preheating chamber 2 _{preferably has R-CO 2} of less than 25 mass%. R-CO ₂ is a value indicating the content ratio (mass%) of _{CO 2} caused by _{CaCO 3} in quicklime or limestone. Quicklime is made by calcining limestone (CaCO ₃ ), and generally has a CaO content of 90 mass% or more, but contains uncalcined CaCO ₃ in part, and CO ₂ remains.
Here, _{R-CO 2} of a lime-based slag material obtained by mixing _{materials having different CaCO 3} contents (for example, quick lime and limestone, or _{two or more types of quick lime having different CaCO 3 contents) is the lime-based slag. It is a ratio of CO 2 to} the amount of lime-based slag material due to the _{total amount of CaCO 3} contained in the material.
Here, R-CO ₂ can be calculated by measuring the C concentration in lime with a solid carbon / sulfur analyzer (CS analyzer) and converting it into the amount of _{CO 2.}

By charging the lime-based slag material into the preheating chamber 2, excessive preheating of the iron-based scrap is suppressed by the endothermic reaction when _{CaCO 3 is thermally decomposed (baked) as described above, and the iron-based scrap is excessive.} Oxidation can be effectively prevented, but if the R-CO ₂ of the lime-based slag material is 25 mass% or more, the _{endothermic reaction due to the thermal decomposition (firing) of CaCO 3} becomes excessive, which may lead to deterioration of the electric power intensity. Further, from the above viewpoints, the more preferable R-CO ₂ of the lime-based slag material is 5 mass% or more and less than 15 mass%.
Therefore, for example, when quicklime and limestone are used as the lime-based slag material, the charging ratio (mixing ratio) of quicklime and limestone is adjusted so _{that the R-CO 2 satisfies the above conditions. Specifically, the R-CO 2} and CaO pure content of the quicklime and limestone to be used are calculated in advance, and the CaO pure content basic unit [kg-CaO / t] required for the operation and the desired R-CO ₂ are combined. Adjust the charging ratio of quicklime and limestone so that it becomes.

The method and timing for charging the slag-making material into the preheating chamber 2 are arbitrary. For example, when iron-based scrap is charged into the preheating chamber 2 with the supply bucket 4, the slag-making material is also supplied to the supply bucket. It is convenient to put it in 4 and charge it in the preheating chamber 2. That is, in normal operation, one charge of iron-based scrap (for example, 130 tons) is divided into a plurality of times (for example, 13 times) and charged into the preheating chamber 2 by the supply bucket 4. Therefore, according to this, one charge of slag slag (for example, slag slag material in which quicklime and limestone are mixed) is divided into multiple batches, and each is placed in a supply bucket 4 containing iron-based scrap, and iron-based. It can be charged into the preheating chamber 2 together with the scrap. When iron-based scrap and slag-making material are put into the supply bucket 4, it is desirable to put the iron-based scrap first and then the slag-making material. This is because the small-diameter slag-making material enters the gaps of the iron-based scrap that has been put in earlier, so that the scrap is uniformly distributed (dispersed state) with respect to the iron-based scrap.

The iron-based scrap (cold iron source) that melts in the present invention usually includes, but is not limited to, own scrap generated from a steel mill, scrap generated from the market, and pig iron obtained by solidifying hot metal. The self-made scraps generated from the steelworks include, for example, unsteady parts (parts generated at the start of casting and parts generated at the end of casting) of slabs cast by continuous casting or ingot formation, and rolling of steel materials such as steel strips. In addition, scraps generated from the market include, but are not limited to, construction steel materials (H-shaped steel, etc.), automobile steel materials, recycled materials such as cans, and the like. Pig iron obtained by solidifying hot metal is pig iron obtained by using iron ore, coke, or the like as raw materials in a blast furnace or other blast furnace.
Further, the iron-based scrap may contain an organic substance (for example, plastic, rubber, biomass, etc.).

In the present invention, as the slag-making material charged into the preheating chamber 2 together with the iron-based scrap, in addition to the lime-based slag-making material (quick lime, limestone), for example, recycled slag generated in light-baked dolomite or steelmaking is used. It may be used, and one or more of them may be used, including a lime-based slag material. However, for the reasons described above, it is particularly preferable to use a lime-based slag material (quick lime and / or limestone).
Further, in the present invention, for example, in order to suppress excessive endothermic heat due to thermal decomposition of the slag-making material in the preheating chamber 2, a part of the slag-making material to be charged into the electric furnace is charged into the preheating furnace 2. The remaining slag-making material may be charged directly into the melting chamber 1 from the auxiliary raw material input chute.

FIG. 1 is an explanatory diagram schematically showing an embodiment of the present invention in a state where an electric furnace is vertically crossed.
The electric furnace includes a melting chamber 1 for melting iron-based scrap by arc heating, and a preheating chamber 2 for preheating the iron-based scrap supplied to the melting chamber 1.
The upper part of the melting chamber 1 is covered with a furnace lid 13 having a water-cooled structure that can be opened and closed. A plurality of electrodes 5 are inserted from above through the furnace lid 13 in the substantially central portion of the melting chamber 1, and an arc heating unit A that melts iron-based scrap by blowing an arc between these electrodes 5 is configured. Will be done. Normally, the electrode 5 is made of graphite or the like and can move up and down.

A shaft-shaped preheating chamber 2 is provided in the upper part of the melting chamber 1 at a position away from the arc heating portion A so as to communicate with the melting chamber 1, and an openable and closable raw material inlet is provided in the upper part of the preheating chamber 2. 20 is provided. Further, an exhaust port 21 is provided on the upper side of the preheating chamber 2, and an exhaust duct 6 is connected to the exhaust port 21. The exhaust duct 6 is connected to a suction blower (not shown), and the high-temperature exhaust gas generated in the melting chamber 1 flows into the preheating chamber 2 by suction by the suction blower, passes through the preheating chamber 2, and then the exhaust duct 6. Exhaust from 6. A dust collector (not shown) is provided in the middle of the exhaust duct 6.

Above the preheating chamber 2, a bottom-opening type supply bucket 4 suspended from the traveling carriage 16 can be moved, and iron-based scrap x (from this supply bucket 4 through the raw material charging inlet 20 into the preheating chamber 2 ( And the slag material y) is charged.
In the melting chamber 1, facing the space portion 1a below the preheating chamber 2, the iron-based scrap x (and the slag-making material y) filled in the space portion 1a is pushed out to the arc heating portion A side by the electrode 5. An extruder 3 (pusher) for this purpose is provided. The extruder 3 is provided so as to be able to advance and retreat in the arc heating portion A (in the present embodiment, toward the center of the furnace) through the side wall of the melting chamber 1, and is driven by a driving device (not shown), and a space is provided at the tip thereof. The iron-based scrap x (and the slag-making material y) in the portion 1a is extruded to the arc heating portion A side.
For example, the iron-based scrap x (and the slag slag) in the space portion 1a due to the weight of the iron-based scrap x (and the slag slag y) filled in the preheating chamber 2 and the space portion 1a without providing the extruder 3. The material y) may be naturally extruded to the arc heating portion A side.

An oxygen blowing lance 7 and a carbonaceous material blowing lance 8 are inserted into the melting chamber 1 from above through the furnace lid 13.
From the coal material blowing lance 8, a charcoal material composed of one or more kinds such as coke, char, coal, charcoal, and graphite is blown into the molten slag s using air, nitrogen, or the like as a transport gas. Further, oxygen is supplied (injected) from the oxygen blowing lance 7, and the molten slag s is pushed away by this oxygen, and oxygen is blown into the molten iron m.
An oxygen-containing gas (for example, a mixed gas of pure oxygen and air) may be blown from the oxygen blowing lance 7 instead of pure oxygen.

In the melting chamber 1, a hot water outlet 11 is provided on the bottom of the furnace on the side opposite to the side where the preheating chamber 2 is provided, and a slag outlet 12 is provided on the side wall above the hot water outlet 11. The hot water outlet 11 and the slag outlet 12 are closed by a filling sand or a mud agent filled inside, a hot water outlet door 14 that presses the mud agent on the outside, and a slag door 15.
A combustion assist burner 9 is provided at a position substantially directly above the hot water outlet 11 so as to penetrate the furnace lid 13 and be inserted into the melting chamber 1 from above. The combustion auxiliary burner 9 burns fossil fuels such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas from a fuel supporting gas (oxygen, air, or oxygen-enriched air) in the melting chamber 1. For example, undissolved iron-based scrap may remain when the molten iron m is discharged, and in such a case, the combustion assist burner 9 can help the iron-based scrap to be melted.
The inner wall of the electric furnace 1 is made of a refractory material, and the furnace wall 10 of the melting chamber 1 has a water-cooled structure.
In the other drawings, reference numeral 17 denotes an auxiliary raw material charging chute, and the auxiliary raw material is charged into the melting chamber 1 from the auxiliary raw material charging chute 17 as needed.

In the operation of the electric furnace (manufacturing of molten iron) of the present embodiment, the arc heating portion A is configured by the plurality of electrodes 5 in the melting chamber 1, and the iron-based scrap x is melted by using this as the main heat source. Further, the charcoal material is blown into the molten slag s from the charcoal material blowing lance 8 and used as an auxiliary heat source. On the other hand, oxygen is blown into the molten iron m from the oxygen blowing lance 7, and the molten iron is decarburized to a predetermined carbon amount by the oxygen. Further, in order to dissolve the undissolved iron-based scrap x, a combustion assist burner 9 is used as needed.
By the melting treatment of iron-based scrap x in the melting chamber 1 as described above, _{high-temperature exhaust gas including CO, CO 2} , unreacted O ₂ and outside air flowing in from an opening or the like is generated.

The iron-based scrap x, which is a raw material for molten iron, and the slag material y (for example, quicklime and limestone) are charged into an electric furnace using the supply bucket 4. Iron-based scrap x is temporarily stored in the scrap storage area by type, and iron-based scrap x of a predetermined type and mass ratio is mixed according to the steel type of molten iron to be manufactured, and put into the supply bucket 4. At the same time, the slag-making material y is also put into the supply bucket 4. At this time, as described above, the iron-based scrap x is first added so that the slag-making material y is uniformly distributed (dispersed state) with respect to the iron-based scrap x, and then the slag is made. It is desirable to put the material y.

The supply bucket 4 containing the iron-based scrap x and the slag-making material y is moved directly above the preheating chamber 2 by the traveling bogie 16, and the iron-based scrap x is moved from the supply bucket 4 through the opened raw material charging inlet 20. And the slag making material y is charged into the preheating chamber 2. As shown in FIG. 1, the iron-based scrap x and the slag-making material y charged from the raw material charging inlet 20 are in a state of being filled in the space portion 1a of the preheating chamber 2 and the melting chamber 1 below the preheating chamber 2.
The high-temperature exhaust gas generated when the iron-based scrap x is melted in the melting chamber 1 flows into the preheating chamber 2 by suction of the exhaust gas as described above, rises in the preheating chamber 2, and then is exhausted from the exhaust port 21. Will be done. In the case of this embodiment, the temperature of the exhaust gas flowing into the preheating chamber 2 is about 1000 to 1500 ° C. In the process of the exhaust gas passing through the preheating chamber 2, the iron-based scrap x and the slag-making material y filled in the preheating chamber 2 are preheated, but the heat of the exhaust gas also adheres to the slag-making material y. By the amount, peroxidation due to excessive preheating of iron scrap x is suppressed. Further, when the slag-making material y is a lime-based slag-making material (quick lime or / and limestone), the endothermic reaction when the slag-making material y thermally decomposes causes more peroxidation of the iron-based scrap x due to excessive preheating. Effectively prevented.

According to the progress of melting of the iron-based scrap x in the arc heating portion A in the melting chamber 1, the iron-based scrap x and the slag-making material y filled in the space portion 1a of the melting chamber 1 are sequentially ejected by the extruder 3. Extrude to the arc heating part A side. Along with this, the iron-based scrap x and the slag-making material y filled in the preheating chamber 2 descend in sequence, and accordingly, as described above, the supply bucket 4 causes new iron-based scrap in the preheating chamber 2. Charge x and the slag material y, and repeat this. When the melting of the iron-based scrap x progresses and a predetermined amount (1 charge) of molten iron is accumulated in the melting chamber 1, the iron-based scrap x and the slag-making material y are placed in the space portion 1a of the preheating chamber 2 and the melting chamber 1. While maintaining the filled state, molten iron m is discharged from the hot water outlet 11, and molten slag s is discharged from the slag opening 12.
At the start of operation of the electric furnace, in order to uniformly charge the iron-based scrap into the melting chamber 1, with the furnace lid 13 open, in the space of the melting chamber 2 on the opposite side of the preheating chamber 2. Iron-based scrap or carbonaceous material may be charged, or hot metal may be charged into the melting chamber 1 at the time of charging the iron-based scrap. This hot metal can be charged into the melting chamber 1 by a supply ladle (not shown) or a hot metal gutter leading to the melting chamber 1 (not shown).

As a method of adding carbonaceous material or oxygen, in addition to the lance blowing method as in the present embodiment, a method of injecting into the bath from above the melting chamber 1, a method of providing a dedicated nozzle at the bottom of the furnace and injecting bottom blowing, etc. May be adopted. Further, the carbonaceous material and the oxygen blowing lance may be immersed in the molten slag or molten iron, but the molten slag or the molten iron may be immersed in the molten iron without being immersed in the molten slag or the molten iron as in the present embodiment, depending on the fluctuation of the molten metal level. It may be a method of following. Alternatively, a method in which an oxygen blowing lance is installed on the furnace wall and oxygen is blown from the furnace wall may be used.

There are two types of electric furnaces, a DC type and an AC type. Since the electric furnace of the present embodiment is an AC type, it has an electrode 5 as described above. On the other hand, when the electric furnace is a direct current type, electrodes are present at each of the bottom and the top, and an arc is blown between the electrodes to melt the iron-based scrap. The present invention can also be applied to the production of molten iron by such a DC type electric furnace.
Further, in the present invention, there is no limitation on the type of the electric furnace to be used as long as it is a method of guiding the exhaust gas generated in the melting chamber 1 to the preheating chamber 2 to preheat the iron-based scrap x and the slag-making material y, for example. It can be applied to a method for producing molten iron using various types of electric furnaces, such as a method for producing molten iron using an electric furnace in which the melting chamber does not have an extruder.

In an electric furnace facility provided with a melting chamber 1 and a preheating chamber 2 as shown in FIG. 1, iron-based scrap was melted to produce molten iron. The equipment specifications of this electric furnace equipment are shown below.
Melting chamber: furnace diameter 7m, furnace height 5m
Preheating room: width 3m, depth 4m, height 5m
Furnace capacity: 210 tons Power: AC 50Hz
Transformer capacity: 75MVA
Number of electrodes: 3

Table 1 shows the operating conditions of the electric furnace in this embodiment. Heavy H2 (specified in the "Iron-based scrap inspection unified standard" of the Japan Iron Source Association) was used as the scrap type. 210 tons of iron-based scrap was charged into the melting chamber 1 and the preheating chamber 2, and an arc was generated by the electrode 5 (upper graphite electrode) to melt the iron-based scrap. In addition, pure oxygen was sent from the oxygen blowing lance 7 at 3000 to 5000 Nm ³ / hr, and coke powder was blown from the carbonaceous material blowing lance 8 at 60 to 70 kg / min. During the operation, the inside of the preheating chamber 2 is monitored by a monitoring camera, and when the iron-based scrap filled in the preheating chamber 2 sequentially drops as the iron-based scrap in the melting chamber 1 melts, the supply bucket 4 The new iron-based scrap transported in 1 was supplied into the preheating chamber 2 from the raw material charging inlet 20 at the upper part of the preheating chamber, and the filling height of the iron-based scrap in the preheating chamber 2 was maintained within a certain range.

As the slag-making material, quick lime or quick lime + limestone was used. In the comparative example, the slag-making material was directly charged into the melting chamber 1 from the auxiliary raw material charging chute 17 at the upper part of the furnace lid 13. On the other hand, in the example of the invention, the slag-making material was charged into the preheating chamber 2 together with the iron-based scrap in the supply bucket 4. That is, when the iron scrap for one charge is divided into 13 times (10 tons x 13 times = 130 tons in total) by the supply bucket 4 and charged into the preheating chamber 2, the slag slag is also divided into 13 times. Each was placed in a supply bucket 4 together with iron scrap, and the iron scrap and the slag-making material were charged together in the preheating chamber 2.
Table 2 shows the CaO pure content and R-CO _{2 of the quicklime and limestone used.} Based on this value, the charge ratio of quicklime and limestone was adjusted so as to have a predetermined R-CO _2.
As the coke powder blown from the charcoal material blowing lance 8, a coke powder having a fixed carbon content of 85 mass% or more, a water content of 1.0 mass% or less, a volatile content of 1.5 mass% or less, and an average particle size of 5 mm or less was used.

When iron-based scrap is continuously present in the melting chamber 1 (space portion 1a) and the preheating chamber 2, melting proceeds, and 200 tons of molten iron is generated in the melting chamber 1, 80 tons. Was left in the furnace, and 120 tons of molten iron for one charge was discharged from the hot water outlet 11 into the ladle. The operation was carried out so that the molten iron temperature at the time of hot water discharge was about 1600 ° C. and the C concentration in the molten iron was 0.060 mass%.
Continue melting iron-based scrap while sending acid and blowing coke even after 120 tons of hot water is discharged, and when the amount of molten iron in the melting chamber 1 reaches 200 tons again, 120 tons of hot water should be discharged under the same conditions for 20 channels. The power intensity unit (20ch average) was repeatedly calculated.
In order to confirm the preheating status of iron scrap in the preheating chamber, the average exhaust gas temperature on the exit side of the preheating chamber was measured. This average exhaust gas temperature is an average value of the measured exhaust gas temperature from the start of the charge operation to the end of the operation by continuously measuring the exhaust gas temperature on the exit side of the preheating chamber every second.

In order to evaluate the energy efficiency of each example, the difference from the power intensity of Comparative Example 1 was determined based on the power intensity of Comparative Example 1. The larger the difference in power intensity, the better the energy efficiency. If the difference in power intensity is 1.0kWh / t or more, it is "○", 0.0kWh / t or more, and less than 1.0kWh / t. If it is "Δ", if it is less than 0.0kWh / t (minus), it is "x".
Further, in order to evaluate the shelving, the case where the iron-based scrap and the slag-making material did not drop in the preheating chamber 2 even when the extruder 3 was operated was counted as the number of shelving. In addition, the time from the start of shelf suspension to the elimination of shelf suspension was counted as the total shelf suspension time. Shelf suspension is caused by melting some iron-based scrap and fusing it to the surrounding iron-based scrap. When such shelving occurs, iron scrap does not descend until the shelving is resolved, so the iron scrap in the preheating chamber continues to be preheated, further promoting iron oxidation and causing further shelving. It will be lost. In addition, since electric power continues to be input even while the shelves are suspended, wasteful energy is consumed and productivity deteriorates. In this embodiment, as an evaluation of the number of times of shelving, if the number of times of shelving is less than 3 times in 20 channels, it is "○", if it is 3 times or more and less than 5 times, it is "△", and it is 5 times or more. If it is, it is set as "x". The evaluation of the total shelf suspension time is "○" if the total shelf suspension time is less than 10 minutes, "△" if the total shelf suspension time is 10 minutes or more, less than 20 minutes, and "×" if the total shelf suspension time is 20 minutes or more. did.

Further, in order to judge the quality of the slag forming, the slag forming port 12 was opened in the middle of the operation and the state of the slag forming in the melting chamber 1 was visually confirmed. At this time, when the electrode 5 is covered with slag forming and the arc sound is a stable energizing sound such as a propeller machine sound, the slag forming is set to “〇”, while the slag forming is calmed down and the arc sound is lightning. If the sound is exploding like, the slag forming is bad and "x".
Furthermore, as a comprehensive evaluation, if there is even one "x" in the evaluation of the power intensity unit difference, the number of shelving times, the total shelf suspension time, and slag forming, if there is even one "x", if there is even one "△", then " △ ”, otherwise“ ○ ”.

The above results are shown in Table 3 together with the charging conditions for the slag-making material.
According to Table 3, all of Comparative Examples 1 to 4 have poor power intensity units. This is because the slag-making material is directly charged into the melting chamber 1 from the auxiliary raw material input chute 17, and as the R-CO _{2 of the} slag-making material becomes higher, the power intensity is reduced by the endothermic reaction in the furnace. It is probable that the deterioration was caused, and further, the iron-based scrap was suspended in the preheating chamber 2 to cause energy loss, and it is also considered that the electric power intensity deteriorated in this respect as well. Since the power intensity deteriorated and the shelf suspension time became 21 minutes or more in this way, the overall evaluation of Comparative Examples 1 to 4 was "x".
On the other hand, all of Invention Examples 1 to 7 have a low power intensity. It is considered that this is because the slag-making material was preheated in the preheating chamber 2 to improve the energy efficiency until slagging and to improve the electric power intensity. In addition, the number of shelf suspensions and the total shelf suspension time were also improved, and as a result, it is considered that the operation was energy efficient. The overall evaluation of Invention Examples 1, 6 and 7 was “Δ”, and the overall evaluation of Invention Examples 2 to 5 was “〇”.

1 Melting chamber 1a Space part 2 Preheating chamber 3 Extruder 4 Supply bucket 5 Electrode 6 Exhaust duct 7 Oxygen blowing lance 8 Charcoal blowing lance 9 Auxiliary burner 10 Furnace wall 11 Hot water outlet 12 Outlet outlet 13 Furnace lid 14 Hot water outlet 15 Door for exit 16 Driving trolley 17 Auxiliary material input chute 20 Material loading inlet 21 Exhaust port
x Iron scrap
y slag material
m molten iron
s Molten slag A arc heating part

Claims (9)

In an electric furnace equipped with a melting chamber (1) for melting iron scrap by arc heating and a preheating chamber (2) for preheating the iron scrap supplied to the melting chamber (1), the melting chamber (1) The iron scrap is preheated by passing the exhaust gas generated in the above through a preheating chamber (2) filled with iron scrap, and the preheated iron scrap is supplied into the melting chamber (1) to be supplied into the melting chamber. It is a method of obtaining molten iron by melting in (1).
The slag-making material is charged into the preheating chamber (2) together with the iron-based scrap, the slag-making material is preheated in the preheating chamber (2) together with the iron-based scrap, and then supplied into the melting chamber (1). A characteristic method for producing molten iron using an electric furnace. The method for producing molten iron by an electric furnace according to claim 1, wherein quick lime and / or limestone is charged into the preheating chamber (2) as a lime-based slag-forming material. The method for producing molten iron by an electric furnace according to claim 2, wherein quicklime and limestone are charged into the preheating chamber (2) as a lime-based slag-forming material. The method for producing molten iron by an electric furnace according to claim 2 or 3, wherein _{the R-CO 2} of the lime-based slag material charged into the preheating chamber (2) is less than 25 mass%. The method for producing molten iron by an electric furnace according to claim 2 or 3, wherein _{the R-CO 2} of the lime-based slag material charged into the preheating chamber (2) is 5 mass% or more and less than 15 mass%. .. The electric furnace is an electric furnace provided with a melting chamber (1) and a shaft-type preheating chamber (2) connected to the upper part of the melting chamber (1).
By sequentially charging iron-based scrap and slag-making material into the preheating chamber (2), the preheating chamber (2) is filled with iron-based scrap and slag-making material, and it is generated in the melting chamber (1). The iron-based scrap and the slag-making material are preheated by passing the exhausted exhaust gas through the preheating chamber (2) filled with the iron-based scrap and the slag-making material, and the preheated iron-based scrap and the slag-making material are put into the preheating chamber. The method for producing molten iron by an electric furnace according to any one of claims 1 to 5, wherein the iron is sequentially lowered in (2) and supplied into the melting chamber (1). A preheating chamber (2) is provided in the upper part of the melting chamber (1) at a position away from the arc heating part so as to communicate with the melting chamber (1), and the raw material is provided in the upper part of the preheating chamber (2). It is an electric furnace having an inlet (20) and has an inlet (20).
The iron-based scrap and the slag-making material charged into the preheating chamber (2) from the raw material charging inlet (20) are filled in the space portion (1a) of the preheating chamber (2) and the melting chamber (1) below it. The method for producing molten iron by an electric furnace according to claim 6, wherein the iron-based scrap and the slag-making material of the space portion (1a) are sequentially extruded to the arc heating portion side. The method for producing molten iron by an electric furnace according to claim 7, wherein the iron-based scrap and the slag-making material of the space portion (1a) are sequentially extruded to the arc heating portion side by the extruder (3). It is a method in which the iron-based scrap and the slag-making material are charged into the supply bucket (4), and the iron-based scrap and the slag-making material are simultaneously charged into the preheating chamber (2) by the supply bucket (4).
When charging iron-based scrap and slag-making material into the supply bucket (4), claims 1 to 1, characterized in that the iron-based scrap is first charged and then the slag-making material is charged. 8. The method for producing molten iron by an electric furnace according to any one of 8.

Images