JPH10226813A - Method for melting cold iron source in arc melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a melting method of cold iron source, by which heat conductivity is improved to scrap from arc and generated gas in a melting period. SOLUTION: An arc melting furnace having the vol. in the furnace which can charge the whole quantity of scrap as one melting quantity in the initial charging chance, and oxygen for primary combustion is blown to execute oxidize-combustion of auxiliary fuel and scrap during melting and refining. Further, as the shape of the furnace body, the one having the relation of L/D=0.6-1.4 between the height L from molten steel surface in the furnace to the upper end of side wall in the furnace and the inner diameter D of the furnace, is used. The oxygen for primary combustion is made to >=40Nm<3> /t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc furnace used for melting a metal raw material and refining a molten metal, and in particular, can charge a large amount of scrap in one charging chance. The present invention relates to a method for melting a cold iron source such as scrap using an arc melting furnace.

[0002]

2. Description of the Related Art Generally, scrap charging into an arc melting furnace used for melting a metal raw material and refining a molten metal is performed by using a scrap bucket, so-called batch charging. However, since the bulk density of the scrap is small, it is difficult to load the required amount of scrap for the tapping of the arc furnace 1 charge by the charging operation of one charging chance. The second charging operation (additional charging operation) is performed after the scrap charged in the charging operation at the first charging chance is melted to some extent and a volume for charging the scrap is formed in the furnace. ) Is needed. For this reason, there is a problem that the furnace lid needs to be opened and closed at the time of the additional charging operation, productivity is reduced, and heat in the furnace is radiated outside the furnace when the furnace lid is opened and closed. Therefore, in order to eliminate the need to open and close the furnace lid after the start of melting, the entire amount of scrap necessary for tapping one charge should be prepared in the furnace before the start of melting. Various proposals have been made as a method of charging the battery.

For example, Japanese Utility Model Laid-Open No. 1-167594
In the furnace when additional metal scrap is charged during melting
In order to reduce thermal energy loss,
To obtain a furnace shape capable of charging the entire amount of
From the sill level (indicating the top surface of the slag discharge port)
The height H to the upper end of the main body should be 0.75 times or more the inner diameter D of the furnace shell.
Above, that is, an arc melting furnace with H ≧ 0.75D
Disclosed, and as a secondary combustion technology,
O on the inner wall of the furnace 0.33D or more from the level _TwoAlso
Is provided with an opening for air injection and responds to CO concentration in exhaust gas.
Just CO of CO_TwoInjecting the amount of air required for oxidation
(Hereinafter referred to as “prior art 1”).

Japanese Patent Publication No. Hei 7-92337 discloses that the ratio of the furnace shell height H to the furnace shell inner diameter D at the furnace bottom is 0.9 or more, that is, H / D ≧ 0.9
(Hereinafter referred to as "prior art 2").

[0005]

In the above-mentioned prior arts 1 and 2, there is proposed a furnace-shaped arc melting furnace capable of accommodating the entire amount of scrap for one melting at only one chance of initial charging. In this case, it is not necessary to open and close the furnace lid at the time of additional charging, so that the heat loss can be reduced, and the entire amount of scrap is stored in the furnace from the start of melting. Therefore, scrap from the exhaust gas generated during operation, for example, CO gas generated by supplementary fuel such as coke and oxygen injection, or CO ₂ gas secondary-combusted with this CO gas and air entering the furnace, etc. The heat effect on the surface can be exhibited. However, the prior arts 1 and 2 do not disclose any specific operation method for exhibiting the above-described heat effect.

Accordingly, an object of the present invention is to find an appropriate operation method in melting and refining using an arc melting furnace capable of accommodating the entire amount of scrap, and thereby to improve the heat transfer efficiency of the gas generated in the arc melting furnace to scrap in the furnace. It is an object of the present invention to provide a method for melting a cold iron source using an arc melting furnace, which can improve the melting point.

[0007]

SUMMARY OF THE INVENTION The present inventor has made intensive studies from the above viewpoints in order to develop a method for melting a cold iron source for improving the efficiency of heating the scrap from the exhaust gas of an arc melting furnace to scrap. As a result, by appropriately increasing the volume inside the furnace of the arc melting furnace and appropriately oxidizing and burning the auxiliary fuel and the scrap supplied into the furnace, the heating effect on the scrap by the high-temperature exhaust gas is higher than before. I knew that it would grow.

The present invention has been made based on such knowledge, and the method for melting a cold iron source by an arc melting furnace according to the first aspect of the present invention uses the entire amount of scrap for one melting as one melting furnace and one chance for initial charging. Using an arc melting furnace (one-time charging arc melting furnace) having a furnace capacity that can be accommodated by charging
Further, the present invention is characterized in that oxygen for primary combustion for oxidizing and burning auxiliary fuel and scrap is blown during melting in an arc melting furnace.

According to a second aspect of the present invention, there is provided a method for melting a cold iron source using an arc melting furnace, wherein the shape of the furnace body is the height L from the furnace inner surface to the upper end of the furnace inner wall, and It is characterized by using a material having a relationship of L / D = 0.6 to 1.4 with respect to the inner diameter D.

The method for melting a cold iron source by an arc melting furnace according to claim 3 is characterized in that, in claim 1 or 2, oxygen for primary combustion is blown into the arc melting furnace at a flow rate of 40 Nm ³ / t or more. It is.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic longitudinal section of an arc melting furnace suitable for carrying out the melting method of the present invention. In the figure, L indicates the height from the furnace inner surface 11a to the furnace inner wall upper end 1a when the entire amount of scrap for one melt is melted, and D indicates the furnace inner diameter.

The reason why the amount of oxygen used for primary combustion is limited to 40 Nm ³ / t or more in the present invention is as follows. In an operation using a single-load DC arc melting furnace with a melting amount of 150 tons, the furnace body shape was set to L / D = 0.85, and a charge was discharged in which the amount of oxygen injected for primary combustion from the water-cooled lance was varied. Made of steel. Then, the relationship between the oxygen intensity and the power intensity per unit weight of molten steel was investigated.

FIG. 1 shows the results of the above investigation. As is evident from the figure, when the oxygen consumption rate is 40 Nm ³ / t or more, the tendency of the reduction effect of the power consumption rate increases.
That is, when the oxygen intensity is 40 Nm ³ / t or more, CO 2
A large amount of high-temperature exhaust gas is generated mainly, and the efficiency of heat transfer to scrap in the furnace is improved from CO ₂ -based gas generated by the secondary combustion reaction between oxygen and CO in the air entering the furnace. Indicates that you have done so. Therefore, in the present invention, the amount of oxygen used is limited to 40 Nm ³ / t or more.

Next, according to the present invention, a height from the furnace surface of the arc melting furnace to the upper end of the furnace inner wall: L;
The reason for limiting the relationship with D to the above equation (1) is as follows.

In a scrap charging type arc melting furnace,
As the first factors affecting the melting efficiency of the scrap, the distribution of the charged scrap with respect to the distribution of the arc and the positional relationship between the distribution of the arc and the inner wall of the furnace are important. That is, it is advantageous for the scrap to be as close as possible to the arc, and for the furnace inner wall to be at least a certain distance from the arc.

As the second of the above factors, it is important to transfer the sensible heat of the generated gas in the furnace and the latent heat to the scrap.
In other words, the surface area of the scrap in contact with the generated gas is large,
In addition, it is advantageous that the contact time is long. On the other hand, since the inner diameter of the furnace of the arc furnace is generally larger than the inner diameter of the furnace exhaust gas duct installed as a device for preheating the scrap, the gas flow rate in the furnace is slower. Therefore, it is also advantageous from the viewpoint of heat transfer of the exhaust gas to the scrap.

Therefore, in the present invention, the ratio of the height from the molten metal surface to the upper end of the furnace inner wall: L and the inner diameter of the furnace: D: L / D
Is suitable as an index that quantitatively represents a factor affecting the dissolving efficiency of scrap.

On the other hand, as described above, the melting efficiency of scrap in the operation of an arc furnace largely depends on the heat transfer efficiency of the scrap from the arc and the generated gas to the scrap.
Focusing on this heat transfer efficiency, the condition that L × D ² is constant, that is, using a small L / D small test arc furnace with a constant furnace volume above the surface of the molten metal, is used. The heat loss carried out of the arc furnace by the exhaust gas was tested. In each of the tests, a scrap having a constant bulk density was used, and all scraps were initially charged, and an arc furnace test operation was performed by a conventional method.

FIG. 2 is a graph showing the relationship between the ratio L / D of the height L from the surface of the molten metal to the upper end of the inner wall of the furnace and the inner diameter D of the furnace, and the heat loss ratio of the exhaust gas. However, the heat loss ratio of the exhaust gas is calculated based on the sum of the sensible heat and the latent heat of the exhaust gas in the test charger when L / D = 0.55.
It is expressed as the sum of the sensible heat and the latent heat of the exhaust gas in the nozzle.

As is apparent from FIG. 2, as the L / D increases, the heat loss ratio of the exhaust gas decreases. L / D is 0.
The heat loss ratio of the exhaust gas in 6 decreased to about 0.90,
The effect is also useful in operating costs. Furthermore, L /
As D increases, the heat loss ratio of exhaust gas decreases.

However, even when L / D exceeds 1.4, the amount of decrease in the heat loss ratio of exhaust gas is small and almost saturated. On the other hand, as the L / D increases, there is a disadvantage that the specifications of the electrode lifting device, the building, the crane equipment, the furnace cooling equipment, and the like must be increased, and the L / D exceeds 1.4. And the disadvantages described above become a problem.

Therefore, in order to improve the melting efficiency of the scrap, at least the ratio L / D of the height: L from the molten metal surface to the upper end of the inner wall of the furnace to the inner diameter of the furnace: D is 0.6 to 1 .4
Should be within the range.

On the other hand, the arc furnace of the present invention needs to have a furnace internal volume capable of charging the entire amount of scrap required for tapping one charge in one charging chance. It is. Thus, a desired furnace size can be obtained by determining the scrap charging amount and L / D of one charge and calculating L and D determined in accordance with the determined amount. In a normal arc furnace, the following formula (2) is used between the height from the molten metal surface to the upper end of the furnace inner wall: L, the furnace inner diameter D, and the amount of scrap charged: W. However, there is a relationship of ρ _l : density of molten steel ρ _S ': bulk density of scrap W: amount of charged scrap.

Various forms of steelmaking scrap are used in an arc furnace. Accordingly, although the bulk density of these scraps also ranges from 0.3 to 1.0 t / m ³ , the weighted average value is 0.7
It is about t / m ³ . Therefore, given the scrap charging amount of one charge: W and L / D, the height from the molten metal surface to the upper end of the furnace inner wall: L and the furnace inner diameter: D can be obtained. For example, if W = 50t, in order to satisfy L / D ≧ 0.6 which is a feature of the present invention, the furnace inner diameter: D
Is D ≦ 5.1 (m), and the height from the molten metal surface to the upper end of the furnace inner wall: L is L ≧ 0.6 in accordance with the value of D.
XD (m).

Therefore, by limiting the ratio L / D of the height L from the molten metal surface to the upper end of the inner wall of the furnace to the inner diameter D of the furnace within the range of 0.6 to 1.4, melting of the scrap can be achieved. The size and shape of the arc furnace are such that it is effective to improve the efficiency and that the entire amount of scrap used for tapping one charge can be charged before the start of melting. You can decide.

In the present invention, since the entire amount of scrap can be charged into the arc furnace before melting starts, it is not necessary to open and close the furnace lid during operation. Accordingly, heat loss from inside the furnace due to such opening and closing of the furnace lid is eliminated. Further, in the melting period, the arc from the electrode is generated by being surrounded by the scrap, and the heat transfer efficiency to the scrap increases. Furthermore, since scrap can be charged into the central part of the furnace, for example, when scrap is continuously charged into the furnace wall of the furnace body as disclosed in Prior Art 1, the furnace inner wall Since the arc heat is not sufficiently supplied to the furnace part, the fusion of the scrap on the inner wall of the furnace tends to occur, but such a problem is solved.

[0027]

Next, the present invention will be described in more detail with reference to examples. Method for melting a cold iron source within the scope of the present invention using an arc melting furnace having a schematic vertical cross-sectional shape shown in FIG. 3 (Example)
Was performed. The furnace body shown in FIG. 3 has a raised freeboard provided with a raised portion forming a furnace inner wall portion in contact with the upper surface of the furnace body of a conventional DC arc furnace. Things. Reference numeral 1 denotes a furnace body of an arc melting furnace, which includes a furnace main body 2 and a furnace body raising section 3. A furnace lid 4 is fixed to an upper portion of the furnace body raising portion 3, and the furnace lid 4 is provided with an electrode insertion hole 4 a into which an upper electrode rod 5 is inserted, and an exhaust gas port 4 b connected to an exhaust gas duct 6. ing. The exhaust gas generated from the arc furnace passes through an exhaust gas duct 6 and is discharged through a dust collector (not shown) and a blower (not shown). On the other hand, the lower electrode 8 and the molten metal 1
A gate 9 for discharging 1 is provided.

FIG. 4 is a schematic longitudinal sectional view showing an example of a conventional DC arc furnace, except that there is no furnace raising portion 3 provided in contact with the upper surface of the furnace main body 2 in FIG. There is no difference from the arc furnace shown in FIG. Using the arc melting furnace shown in FIG. 4, a method of melting a cold iron source outside the scope of the present invention (Comparative Example) was performed.

Table 1 shows that the relationship between the height L of the free board and the inner diameter D of the furnace is L / D = 0.85, and that the entire amount of scrap is charged at the initial charging chance. In the case where melting and refining were performed by blowing a predetermined value of oxygen for primary combustion for oxidizing and burning auxiliary fuel and scrap in the furnace into the furnace (Examples 1 and 2), and L / D = 0.55 Then, when the scrap is charged at the first charging chance, the remaining 1/2 is added after the burn-down, and the oxygen for the primary combustion is blown at a predetermined value to perform melting and refining (comparison) The test operation of Example) was performed.

[0030]

[Table 1] The operating methods in the examples and comparative examples are the same except for the method of charging the scrap. That is, the furnace lid 4 of the arc melting furnace is opened, and the furnace body 1 is opened by a scrap charging bucket.
A predetermined amount of scrap is charged therein, the furnace lid 4 is closed, and the upper electrode 5 is lowered through the furnace lid 4 to a predetermined position in the furnace.
Next, energization is started, an arc is generated between the electrode 5 and the scrap 7, and melting of the scrap 7 is started. The lowering of the upper electrode 5 is performed while boring the scrap 7 with the upper electrode 5. Part of the scrap 7 is melted to form a pool in the vicinity of the lower end of the upper electrode 5, and the pool gradually expands. In the operation of the comparative arc furnace, when a predetermined amount of pool is formed, the power supply is temporarily stopped, the upper electrode 5 is raised, the furnace lid 4 is opened, and the remaining amount of scrap is removed. And then start melting operation again. During this time, the scrap is heated and melted by the arc heat and the sensible heat of the generated gas. Next, after the temperature is raised and predetermined refining is performed, the chemical composition of the molten steel is adjusted to a predetermined value, and then the furnace body 1 is tilted by a tilting mechanism (not shown) to discharge molten steel from the gate 9.

The arc melting furnace according to the present invention is not limited to a DC arc melting furnace, but can be applied to a three-phase AC arc melting furnace and the like. Table 2 shows the results of the overall heat balance in Examples 1 and 2 and Comparative Example.

[0032]

[Table 2] From Table 2 and the results of this test, the following matters become clear. In the operation using the arc furnace of the present invention, in particular,
It was found that the sensible heat and latent heat of the generated gas were used effectively. That is, the efficiency of heat generation from generated gas to scrap is 2
70-70% compared to 50-60% in the case of multiple scrap loading
Up to 80%. For this reason, the power consumption in the arc furnace operation is reduced. High thermal efficiency from arc to scrap. Since no additional scrap is charged between the start of energization and the tapping, no heat is dissipated from the inside of the furnace to the outside due to the opening and closing of the furnace lid, and the heat loss from the furnace body is 5 kWh.
/ T about less. Since no additional scrap is charged during the period from the start of energization to the tapping, the required time for one heat is reduced, and the productivity is improved accordingly. Since no additional charging of scrap is performed during the period from the start of energization to tapping of the hot water, the furnace lid is not opened and closed, and problems associated with dust generation and the like are eliminated. Since the height of the scrap to be charged can be made uniform, the melting becomes uniform, so that there is no residual melting of the scrap. There is no need to install a burner to perform the operation. Due to the above effects, the operation cost can be reduced.

[0033]

As described above, according to the present invention, a special device for preheating scrap and a special device for charging scrap into an arc furnace can be provided without using any special equipment. For the arc melting furnace, the equipment must be remodeled with a simple structure in which a predetermined raised portion having the same diameter as the furnace body of the arc furnace is provided. For the new arc furnace, the furnace inner diameter is changed. The ratio of the height from the molten metal surface to the upper end of the inner wall of the furnace to an appropriate value, and the operation of blowing oxygen for primary combustion is performed appropriately to increase the heat transfer efficiency from the arc to the scrap during the melting period In addition, the efficiency of heating the scrap from the gas generated in the furnace to the scrap can be improved. Thus, it is possible to provide a method for melting a cold iron source using an arc melting furnace, which is excellent in operability and can greatly reduce the operation cost, and has an extremely industrially useful effect.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a basic unit of blown oxygen for primary combustion and a basic unit of power consumption per unit weight of molten steel in a DC arc melting furnace.

FIG. 2 shows the height L from the molten metal surface to the upper end of the inner wall of the furnace and the inner diameter D of the furnace.
4 is a graph showing the relationship between the ratio L / D of the exhaust gas and the heat loss ratio of exhaust gas.

FIG. 3 is a schematic vertical sectional view showing a DC arc melting furnace used to carry out the method of the present invention.

FIG. 4 is a schematic longitudinal section showing an example of a conventional DC arc furnace.

[Explanation of symbols]

 L Height from furnace inner surface to upper end of furnace inner wall D Furnace inner diameter 1 Furnace body of arc furnace 1a Furnace inner wall upper end 2 Furnace main body 3 Furnace body raising section 4 Furnace lid 4a Electrode charging hole 4b Exhaust gas outlet 5 Upper part Electrode 6 Exhaust gas duct 7 Scrap 8 Lower electrode 9 Gate 10 Furnace bottom 11 Molten metal 11a Metal surface

Claims (3)

[Claims] 1. The total amount of scrap for one dissolution is set to 1
An arc melting furnace having a furnace internal volume to accommodate the chance, and blowing oxygen for primary combustion for oxidizing and burning auxiliary fuel and scrap during melting and refining in the arc melting furnace. A method of melting a cold iron source using a melting furnace. 2. The arc melting furnace further has a relationship between a height: L from the furnace surface to the upper end of the furnace inner wall and a furnace inner diameter: D, the following equation (1): L / D = 0. An arc melting furnace that satisfies 0.6 to 1.4 (1) is used. A method for melting a cold iron source by the arc melting furnace according to 1. 3. The method for melting a cold iron source using an arc melting furnace according to claim 1, wherein the oxygen for primary combustion is blown into the arc melting furnace at a rate of 40 Nm ³ / t or more.