JP2000017319A - Arc furnace operation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently melt iron scrap and to reduce the consumption of electric power, at the time of melting the iron scrap together with molten iron in an arc furnace providing a preheating chamber directly connected with a melting chamber. SOLUTION: In the operating method in the arc furnace 1 provided with the melting chamber 2 and the shaft furnace type preheating chamber 3 directly connected with the melting chamber and introducing exhaust gas generated in the melting chamber, the molten iron is directly charged and also, while continuously or intermittently charging the iron scrap 15 into the preheating chamber so as to hold the state, in which the iron scrap continuously exists in the preheating chamber and the melting chamber, the iron scrap and the molten iron in the melting chamber are heated with the arc 19 to melt the iron scrap. At the point of time when the molten steel 17 is stored at least by one heat quantity in the melting chamber, the molten steel is tapped off in the state, in which the iron scrap continuously exists in the preheating chamber and the melting chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating an arc furnace for producing molten steel by melting iron scrap and hot metal in combination as iron sources.

[0002]

2. Description of the Related Art In an arc furnace for steelmaking, an iron source such as an iron scrap is heated and melted by arc heat and refined to produce molten steel. However, a large amount of electric power is consumed. Many methods have been proposed for preheating iron scrap using high-temperature exhaust gas generated from the melting chamber and reducing the amount of power consumption by melting the preheated iron scrap.

For example, Japanese Patent Application Laid-Open No. 7-180975 (hereinafter referred to as “prior art 1”) discloses a shaft-type preheating chamber equipped with an openable / closable grate, and an iron scrap introduction path above a melting chamber. There is disclosed a facility in which an iron scrap held by a grate is preheated by exhaust gas, and the preheated iron scrap is charged into a melting chamber by a pusher provided in an iron scrap introduction path. However, in the prior art 1, a device for holding and transporting iron scrap such as a grate and a pusher is necessary. Therefore, when preheating with exhaust gas from the melting chamber, there is a limit to the preheating temperature,
Can not preheat efficiently. This is because preheating with high-temperature exhaust gas improves preheating efficiency, but equipment troubles such as thermal deformation and fusion of the holding / transporting device occur, so that the exhaust gas temperature cannot be increased.

[0004] Also, Japanese Patent Publication No. 6-46145 (hereinafter referred to as Japanese Patent Publication No.
In “Prior art 2”, a shaft-type preheating chamber is provided directly connected to the melting chamber, iron scrap for one heat is charged into the melting chamber and the preheating chamber for each melting, and the charged iron is charged. A facility for melting scrap while preheating scrap with exhaust gas is disclosed. In the prior art 2, since the preheating chamber is directly connected to the melting chamber, the holding / transporting device as in the prior art 1 is not required, and therefore, there is no need to worry about equipment trouble of the holding / transporting device due to heat. In addition, the exhaust gas temperature can be raised to increase the preheating temperature of the iron scrap. However, in prior art 2, every time the amount of molten steel for one heat is melted, all the iron scrap in the preheating chamber is melted, and the molten steel is tapped without leaving the iron scrap in the preheating chamber. It is not possible to preheat the scrap iron that has been used, and it is still not enough in terms of effective use of exhaust gas.

[0005] On the other hand, with the recent production of high-grade steel by arc furnaces, Cu, Sn,
An operation using hot metal as an iron source with iron scrap to dilute impurities such as Cr is disclosed. For example, Japanese Patent Laying-Open No. 57-47815 (hereinafter referred to as "prior art 3") discloses a method of charging hot metal into an arc furnace during or after melting of scrap iron. JP-A-8-109408 (hereinafter referred to as "prior art 4") discloses that when 30 to 40% of iron scrap is melted, the mixing ratio of hot metal is set to 30 to 85% and hot metal is loaded from the furnace top. An entry method is disclosed. Prior art 3
And according to prior art 4, it is possible to melt efficiently by the latent heat and sensible heat of the hot metal, but it does not disclose that the iron scrap is preheated by using the exhaust gas of the melting chamber to melt more efficiently. .

[0006]

As shown in the above prior art 2, in an arc furnace having a preheating chamber directly connected to a melting chamber, the preheating method is not yet sufficient, and there is room for improving the preheating efficiency. In an arc furnace provided with a preheating chamber directly connected to a melting chamber, an efficient operation method using both iron scrap and hot metal has not been disclosed yet.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an arc furnace having a preheating chamber directly connected to a melting chamber, in which an iron scrap and hot metal are melted together. Another object of the present invention is to provide an operation method capable of efficiently dissolving and reducing power consumption.

[0008]

An arc furnace operating method according to a first aspect of the present invention includes a melting chamber, and a shaft-type preheating chamber directly connected to the melting chamber and into which exhaust gas generated in the melting chamber is introduced. An operation method in an arc furnace, in which molten iron is directly charged into a melting chamber and iron scrap is continuously or intermittently maintained so that iron scrap is continuously present in a preheating chamber and a melting chamber. While charging the steel scrap and the hot metal in the melting chamber with an arc while melting into the preheating chamber, the iron scrap is melted, and when at least one heat of molten steel has accumulated in the melting chamber, the iron scrap is connected to the preheating chamber. The present invention is characterized in that molten steel is tapped in a state where the molten steel is continuously present in a melting chamber.

An arc furnace operating method according to a second invention is characterized in that, in the first invention, oxygen is blown into the melting chamber.

[0010] The arc furnace operating method according to a third invention is characterized in that, in the second invention, a carbon material is blown into the melting chamber as an auxiliary heat source.

An arc furnace operating method according to a fourth invention is characterized in that, in the second invention or the third invention, the amount of oxygen blown is 25 Nm ³ or more per ton of molten steel.

According to a fifth aspect of the present invention, there is provided the arc furnace operating method according to any one of the first to fourth aspects, wherein the iron scrap continuously present in the preheating chamber and the melting chamber during melting and tapping. Is 50 wt% or more for one heat.

In the present invention, the hot metal is used by directly charging it into the melting chamber. Therefore, the temperature of the iron scrap is raised by the latent heat and the sensible heat of the hot metal, and the iron scrap can be quickly melted with a small amount of power consumption. In addition, since hot metal contains 3 to 5% by weight of carbon, oxygen is blown into the melting chamber and the carbon in the hot metal is burned with oxygen. CO gas preheats the iron scrap, which further promotes a reduction in power consumption and rapid dissolution. Further, by blowing the carbon material into the melting chamber and burning the carbon material with oxygen, the carbon material exerts the same operation and effect as the carbon in the hot metal, thereby contributing to a reduction in power consumption.

The amount of oxygen blown is 25 tons of molten steel per ton.
It is preferable to be Nm ³ or more. FIG. 3 shows that, in the arc furnace shown in the following example, the mixing ratio of hot metal (the weight ratio of the hot metal in the iron source used) was set to 20%, and the amount of oxygen blown in the melting chamber from the start of melting to tapping. FIG. 3 is a diagram showing a change in power consumption when a test is performed by changing to 15 to 40 Nm ³ per ton of molten steel to be retained, as shown in FIG.
By setting the amount of oxygen blown to 25 Nm ³ or more per ton of molten steel, it is possible to stably reduce the unit power consumption to 200 kWh / t or less.

On the other hand, the iron scrap preheated in the preheating chamber falls naturally and is charged into the melting chamber in accordance with the amount of iron scrap dissolved in the melting chamber. This eliminates the need for a transfer device, and can increase the preheating temperature. Then, the iron scrap in the melting chamber is melted while the loading of the iron scrap into the preheating chamber is continued so that the iron scrap continuously exists in the preheating chamber and the melting chamber. Since molten steel is tapped in a state that exists continuously in the chamber and the melting chamber,
All of the iron scrap used in the next heat is preheated and can be melted with extremely high preheating efficiency. In particular, during melting and tapping, by making the iron scrap continuously present in the preheating chamber and the melting chamber 50 wt% or more for one heat,
The preheating time of the iron scrap is secured, and high preheating efficiency can be obtained.

The molten steel for one heat according to the present invention is the amount of molten steel contained in one of the molten steel holding and transporting containers such as a ladle used for a casting operation such as continuous casting. It is the amount determined by the lifting load of the crane etc. of the building to be implemented. The hot metal used in the present invention is produced in a blast furnace, a smelting reduction furnace, a cupola, or the like.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
1 and 2 are schematic vertical sectional views of an arc furnace facility showing an example of an embodiment of the present invention. FIG. 1 is a view showing a state in the middle of melting, and FIG. It is a figure which shows the time of charging.

In these figures, the upper part of the melting chamber 2 which is constructed of a refractory inside and has a bottom electrode 6 at the bottom,
A shaft-type preheating chamber 3 and a water-cooled furnace wall 4 are arranged, and an upper opening of the furnace wall 4 not covered by the preheating chamber 3 is
It is covered with a furnace lid 5 having a water-cooling structure that can be freely opened and closed. An upper electrode 7 made of graphite is provided which penetrates through the furnace lid 5 and can move up and down into the melting chamber 2, and constitutes a base of the DC arc furnace 1. The furnace bottom electrode 6 and the upper electrode 7 are connected to a DC power supply (not shown) to generate an arc 19 between the furnace bottom electrode 6 and the upper electrode 7.

Above the preheating chamber 3, there is provided a bottom-opening supply bucket 13 suspended from a traveling carriage 24,
From the supply bucket 13, an iron scrap 15 is charged into the preheating chamber 3 via an openable / closable supply port 20 provided in the upper part of the preheating chamber 3. The duct 21 provided at the upper end of the preheating chamber 3 is connected to a dust collector (not shown), and the high-temperature exhaust gas generated in the melting chamber 2 is discharged from the preheating chamber 3 and the duct 21.
And the iron scrap 15 in the preheating chamber 3
Is preheated. And the preheated iron scrap 15
Is dropped into the melting chamber 2 in accordance with the amount of the iron scrap 15 to be melted in the melting chamber 2 and is charged into the melting chamber 2.

An oxygen blowing lance 8 and a carbon material blowing lance 9 which penetrate the furnace lid 5 and can move up and down in the melting chamber 2 are provided, and oxygen is blown into the melting chamber 2 from the oxygen blowing lance 8. A carbon material such as coke, char, coal, charcoal, graphite or the like is blown into the melting chamber 2 from the carbon material blowing lance 9 using air, nitrogen or the like as a carrier gas.
On the other side of the melting chamber 2 opposite to the site where the preheating chamber 3 is installed,
The outlet of the furnace is pressed against the outlet side by a door 22 and filled with sand or mud agent. Alternatively, a slag port 12 filled with a mud agent is provided. Furnace lid 5 at a position corresponding to vertically above tap hole 11
, A burner 10 is attached. Burner 1
0 burns fossil fuels such as heavy oil, kerosene, pulverized coal, propane gas, and natural gas in the melting chamber 2 by air or oxygen or oxygen-enriched air.

A crane (not shown) is provided above the melting chamber 2.
The furnace lid 5 from which the upper electrode 7, the oxygen blowing lance 8, the carbon material blowing lance 9, and the burner 10 are removed in advance is opened, and hot metal is transferred from the supply ladle 14 transported by the crane. 16 is placed in the melting chamber 2.

In the operation of the DC arc furnace 1, first, iron scrap 15 is charged into the preheating chamber 3 from the supply bucket 13. The iron scrap 15 charged in the preheating chamber 3 is also charged in the melting chamber 2 and eventually fills the preheating chamber 3. Next, as shown in FIG. 2, the furnace lid 5 is opened, the supply ladle 14 containing the hot metal 16 is transported by a crane to a position directly above the melting chamber 2, and the molten metal is transferred from the supply ladle 14 into the melting chamber 2. The hot metal 16 is charged. After the charging is completed, the furnace lid 5 is closed, and the upper electrode 7 is lowered into the melting chamber 2. Further, a flux such as quicklime or fluorite is charged into the melting chamber 2 from a supply port (not shown) provided in the furnace wall 4. In order to uniformly charge the iron scrap 15 into the melting chamber 2, the furnace lid 5 was opened,
An iron scrap 15 can be charged into the melting chamber 2 on the opposite side of the preheating chamber 3.

Next, while supplying DC current between the furnace bottom electrode 6 and the upper electrode 7, the upper electrode 7 is raised and lowered,
Between iron and upper electrode 7 or charged iron scrap 1
An arc 19 is generated between the electrode 5 and the upper electrode 7, and the iron scrap 15 is melted by the arc heat. At the same time, the flux is dissolved to produce a molten slag 18. The molten slag 18 prevents the generated molten steel 17 from being oxidized and keeps the molten steel 17 warm. If the amount of the molten slag 18 is too large, it can be discharged from the slag port 12 even during operation.

After the energization, when the oxygen blowing lance 8 and the carbon material blowing lance 9 can be inserted into the melting chamber 2, as shown in FIG. It is preferable to blow the carbon material into the hot metal 16 or the molten slag 18 in the melting chamber 2.

The carbon in the hot metal 16 reacts with oxygen and is decarburized to form molten steel 17, and the reaction product CO gas forms the molten slag 18 so that the arc 19 is wrapped in the molten slag 18. , The efficiency of heating the arc 19 increases. Further, a large amount of high-temperature CO gas and CO ₂ gas generated by burning this CO gas efficiently preheat the iron scrap 15 in the preheating chamber 3. The amount of oxygen blown is 25 Nm ³ per ton of molten steel 17 staying in the melting chamber 2 from the start of melting to tapping (hereinafter, “Nm
³ / t ”) or more.

The carbon material blown into the melting chamber 2 and dissolved in the molten steel 17 or suspended in the molten slag 18 reacts with oxygen to generate combustion heat and acts as an auxiliary heat source. At the same time as saving power consumption, as with the carbon in the hot metal 16, the heating efficiency of the arc 19 is increased and the preheating efficiency of the iron scrap 15 is improved. The blowing amount of the carbon material is determined according to the oxygen blowing amount. That is, the carbon material is blown in such a manner that the total carbon amount of the carbon material contained in the hot metal 16 and the carbon material to be blown is equal to the chemical equivalent of the oxygen to be blown. If the amount of the injected carbon material is small and the total amount of carbon is smaller than the amount of injected oxygen, the molten steel 17 is excessively oxidized, which is not preferable. Note that the carbon concentration of the molten steel 17 can be adjusted by adjusting the oxygen blowing amount such that the carbon concentration of the molten steel 17 at the time of tapping becomes a target value.

Further, as the iron scrap 15 in the melting chamber 2 is melted, the iron scrap 15 in the preheating chamber 3 falls freely into the melting chamber 2 according to the amount melted in the melting chamber 2 and decreases. Therefore, in order to compensate for this decrease, the supply bucket 13
, Iron scrap 15 is charged into the preheating chamber 3. The charging of the iron scrap 15 into the preheating chamber 3 is performed by the iron scrap 1
5 is carried out continuously or intermittently so as to keep the state where it is present continuously in the preheating chamber 3 and the melting chamber 2. At this time, it is preferable that the amount of the iron scrap 15 continuously present in the preheating chamber 3 and the melting chamber 2 be 50 wt% or more of the iron scrap 15 for one heat.

In this way, the iron scrap 15 and the hot metal 16 are heated to melt the iron scrap 15, and the molten steel 17 for at least one heat is stored in the melting chamber 2, and the carbon concentration of the molten steel 17 is measured. The amount of oxygen injected from the oxygen injection lance 8 and the carbon material injection lance 9
The carbon concentration of the molten steel 17 is adjusted by adjusting the amount of carbon material blown from the furnace. Next, the melting chamber 2 is tilted by a tilting device (not shown) to discharge the molten steel 17 from the tapping port 11 to a molten steel holding and transporting container (not shown). In this case, since the iron scrap 15 is buried in the molten steel 17 and coexists, the molten steel temperature is about 1550 ° C., and a large degree of superheat of the molten steel cannot be obtained. Therefore, it is preferable to heat the molten steel 17 with the burner 10 at the time of tapping in order to prevent troubles caused by a drop in the molten steel temperature such as blockage of the tapping port 11.

After tapping, if necessary, the molten steel 17 is heated and refined in a ladle refining furnace or the like, and then cast by a continuous casting machine or the like. After the molten steel 17 is tapped and the molten slag 18 is drained, the melting chamber 2 is returned to a horizontal position by a tilting device, and the tapping port 11 is discharged.
Then, filling sand or mud material is filled in the slag port 12, and then the hot metal 16 is charged into the melting chamber 2 again to continue the operation. The next heat can start melting with the preheated iron scrap 15. At the time of tapping, several to several tens of tons of molten steel 17 may be left in the melting chamber 2 to resume the melting of the next heat. By doing so, the initial dissolution is promoted and the dissolution efficiency is improved.

By heating and melting the iron scrap 15 and the hot metal 16 in this way, the temperature of the iron scrap 15 is increased by the latent heat and sensible heat of the hot metal 16,
The iron scrap 15 melted in the first heat of the operation is not preheated, but the iron scrap 15 melted in the subsequent heat is all preheated and can be operated in an extremely high preheating efficiency, thereby improving productivity. The power consumption can be reduced.

In the above description, the hot metal 16 is charged into the melting chamber 2 before the start of melting in one heat, but the timing of charging the hot metal 16 into the melting chamber 2 is not limited to the above. It may be during the dissolution. However, since it is necessary to decarbonize the carbon in the hot metal, it is preferable to complete the charging by the middle stage of melting. The method of charging the hot metal 16 is not limited to the above, and a gutter penetrating the furnace wall 4 may be provided and charged from the gutter. If the furnace lid 5 is inserted by using a gutter, it is not necessary to open and close the furnace lid 5, thereby further improving productivity and reducing power consumption.
In the above description, the case of the DC arc furnace 1 has been described, but the present invention can be applied to an AC arc furnace without any trouble.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the DC arc furnace shown in FIG. 1 will be described below. In the arc furnace, the melting chamber has a furnace diameter of 7.2 m,
The height is 4m, the preheating chamber is 3m in width, 5m in length, 7m in height, and the furnace capacity is 180 tons. First, 70 tons of normal temperature iron scrap are charged into the preheating chamber, and then, 40 tons of hot metal (carbon concentration: 4.5 wt%) and 50 tons of normal temperature iron scrap are charged into the melting chamber. Using a graphite upper electrode having a diameter of 30 inches, melting was started with a maximum power of 750 V and 130 KA. Immediately after energization, quicklime and fluorite were added, and oxygen was injected from an oxygen blowing lance to 6000.
Nm ³ / hr, 36 coke from carbon material injection lance
It was blown into the melting chamber at kg / min. The quicklime and fluorite were heated to form molten slag, and the molten slag was formed by blowing oxygen and coke, and the tip of the upper electrode was buried in the molten slag. The voltage at this time was set to 550V.

Thereafter, when the iron scrap in the preheating chamber descends as it melts, the iron scrap is charged into the preheating chamber by the supply bucket, and melting is continued while maintaining the height of the iron scrap in the preheating chamber at a constant level. And one in the melting chamber
When 80 tons of molten steel was generated, about 60 tons of molten steel was left in the melting chamber, and 120 tons of molten steel for one heat was discharged to a ladle. During tapping, the molten steel was heated by a heavy oil burner.
The carbon concentration of the molten steel at the time of tapping was 0.1 wt%, and the molten steel temperature was 1560 ° C. After tapping, 40 tons of hot metal was charged again into the melting chamber, and then the injection of oxygen and coke was restarted. When the molten steel amount reached 180 tons, tapping of 120 tons was repeated. The molten steel after tapping was refined in a ladle refining furnace, heated to 1620 ° C., and then cast by a continuous casting machine. The average power consumption in the ladle refining furnace was 60 kWh / t.

As a result, the molten metal mixing ratio: 33%, the oxygen blowing amount: 33 Nm ³ / t, and the coke blowing amount: 1
Under the condition of 2 kg / t, the average time from tapping to tapping is 4
In 0 minutes, it was able to dissolve at a power consumption of 80 kWh / t. The total power consumption of the arc furnace and the ladle refining furnace is 1
It was 40 kWh / t.

For comparison, in the arc furnace shown in FIG. 1, 70 tons of normal-temperature iron scrap was charged into a preheating chamber, and then 40 tons of molten iron (carbon concentration;
5 wt%) and 10 tons of normal-temperature iron scrap were charged to start melting, and even if molten steel was formed, melting was continued without additional iron scrap to obtain 120 tons of molten steel. After raising the temperature of the molten steel to 1600 ° C., a tapping operation (comparative example) was also performed. In addition, the oxygen injection amount and the coke injection amount in the comparative example are the same as those in the above-described example,
The power consumption in the ladle refining furnace was 30 kWh / t. Table 1 shows operating conditions and operating results in the examples and comparative examples.

[0036]

[Table 1]

As shown in Table 1, in the comparative example, the electric power consumption in the arc furnace was 240 kWh / t, and the total electric power consumption in the arc furnace and the ladle refining furnace was 270 kWh / t.
The time from tapping to tapping was 60 minutes on average. Thus, in the example according to the present invention, the total power consumption can be reduced by 130 kWh / t as compared with the comparative example, and the time from tapping to tapping can be reduced by 20 minutes.

FIG. 4 shows that the oxygen blowing rate is 33 Nm ³ / t.
The power consumption in the arc furnace according to the example in which the mixing ratio of the hot metal is changed to 20 to 45% is shown as the constant condition. FIG.
As shown in the figure, when the mixing ratio of hot metal increases, the power consumption decreases, and if the mixing ratio of hot metal is increased to about 50% or more, the arc furnace can be operated using only the combustion heat of the carbon in the hot metal without using electric power. It turns out that it is possible.

[0039]

According to the present invention, the heat and carbon possessed by the hot metal can be effectively utilized, and all of the iron scrap that is melted except for the first heat can be preheated.
It is possible to improve the productivity of the arc furnace and greatly reduce the electric power consumption, and the industrial effect is remarkable.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an arc furnace facility showing an example of an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view of an arc furnace facility showing an example of an embodiment of the present invention.

FIG. 3 is a diagram showing a result of investigating an influence of an oxygen blowing amount on a basic unit of electric power.

FIG. 4 is a diagram showing a result of investigating an influence of a mixing ratio of hot metal on a basic unit of electric power.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc furnace 2 Melting chamber 3 Preheating chamber 4 Furnace wall 5 Furnace lid 6 Furnace bottom electrode 7 Upper electrode 8 Oxygen injection lance 9 Carbon material injection lance 10 Burner 11 Steel tap 12 Sink port 13 Supply bucket 14 Supply ladle 15 Iron scrap 16 Hot metal 17 Molten steel 18 Molten slag 19 Arc

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K001 FA11 GA16 4K014 CB01 CC04 CD02 CD11 CD15 CD18 4K045 AA04 BA02 RA06 RA09 RB02 RB08 RB16 RB22 4K063 AA04 BA02 CA01 CA08 GA02 GA09

Claims (5)

[Claims] 1. A method for operating an arc furnace having a melting chamber and a shaft-type preheating chamber directly connected to the melting chamber and into which exhaust gas generated in the melting chamber is introduced, wherein the hot metal is supplied to the melting chamber. While being directly charged, the iron scrap in the melting chamber and the iron scrap in the melting chamber are continuously or intermittently charged so as to keep the state in which the iron scrap is continuously present in the preheating chamber and the melting chamber. The molten iron is heated by an arc to melt the iron scrap, and when at least one heat of molten steel has accumulated in the melting chamber, the molten steel is discharged while the iron scrap is continuously present in the preheating chamber and the melting chamber. An arc furnace operating method comprising: 2. The arc furnace operating method according to claim 1, wherein oxygen is blown into the melting chamber. 3. The method according to claim 2, wherein a carbon material is blown into the melting chamber as an auxiliary heat source. 4. An oxygen injection amount of 25 tons of molten steel
The method for operating an arc furnace according to claim 2 or ^{3, wherein} Nm ³ or more is set. 5. During melting and tapping, an iron scrap continuously present in the preheating chamber and the melting chamber is heated for 50 watts for one heat.
5. The method according to claim 1, wherein the value is at least t%.
The arc furnace operating method according to any one of the above.