JP3175079B2 - Iron-based scrap melting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for melting iron scrap by using an electric furnace.

[0002]

2. Description of the Related Art In a conventional method of melting iron-based scrap using an electric furnace, since the carbon material is not excessively contained in the molten slag, the piles of iron-based scrap piled up in the electric furnace collapse. Until a flat bath is formed, the oxidation of iron by the air proceeds and the amount of FeO in the molten slag reaches 40%. Thereafter, after the flat bath is formed, electrode heating is performed to adjust to the tapping temperature. Since a carbon material is added to form Fe to reduce FeO and generate CO gas, the molten slag forms, but absorbs heat by the reduction reaction, so that there is a problem that the temperature of the molten iron does not easily rise.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of melting iron-based scrap using an electric furnace, which aims to improve the heating efficiency when the molten iron is heated by the electrodes and to reduce equipment costs.

[0004]

According to the present invention, in order to solve the above-mentioned problems, an electric furnace provided with a bottom blowing port capable of supplying oxygen gas, nitrogen gas and carbonaceous material is provided. From the time that at least about 60% of the scrap is melted due to the melting of the piled iron scrap, until the time when all the scraps are buried under the surface of the molten metal and turned into a flat bath, the carbon material is purged with inert gas. Supply to the molten slag layer as a carrier gas to suppress the generation of FeO due to oxidation of iron,
After the flat bath was adopted, the basic idea was to blow only oxygen-containing gas into the molten iron from the bottom blowing tuyere, decarburize it, and raise the temperature at high speed. After stacking iron-based scraps, in an iron-based scrap melting method in which molten iron is melted in the presence of molten slag to obtain molten iron, at least approximately 60% of the scrap becomes molten metal due to melting of the iron-based scraps. Until the molten metal surface gradually rises and the mountain of the scrap falls below the molten metal surface, the inert gas and carbon After injecting from the tuyere and adding the same carbon material to the molten slag layer, and all the scrap was buried under the surface of the generated molten metal, the blowing amount of the gas blow-through limit determined by the depth of the molten metal was not reached. There only the oxygen-containing gas the melt blown from the furnace bottom tuyeres in ferrous scrap melting method characterized by de TanNoboru temperature.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the reason why the blowing amount of the inert gas as a carrier gas is set to be equal to or more than the blowing amount of the gas blow-through limit determined from the molten iron depth is that the carbon material is melted without contacting the molten iron layer. This is because it is added directly to the slag layer. In other words, if the gas is less than the gas blow-through limit, the carbon material comes into contact with the molten iron, increasing the carbon content of the molten iron, increasing the amount of decarburization after flat bathing, and increasing the refining time. Is generated. As the inert gas, nitrogen, Ar, or CO can be used. However, nitrogen is advantageous in terms of cost, and Ar is used in the case of producing a steel type that needs to reduce the nitrogen concentration in the molten iron. It is desirable.

According to the present invention, since the carbon material can be directly added to the molten slag layer from the tuyere of the furnace bottom, it is necessary to provide a top blowing or side blowing lance for supplying the carbon material to the molten slag layer. However, there is an advantage that equipment costs can be reduced. In the present invention, the gas amount at the gas blow-through limit (Q: Nm ³ / Hr) is calculated by the following equation.

Q = 5.5 × 10 ⁴ × d × H ^1.5 where d is the diameter of the bottom blow nozzle (m) and H is the depth of molten iron (m). The above equation is obtained experimentally based on the relative relationship between the kinetic energy of the injected gas and the static pressure of the molten iron. The upper limit value (Q ': Nm ³ / Hr) of the gas flow amount which is equal to or more than the gas flow limit of the gas blow-through limit is
When the specific gravity of the molten slag is 2 (g / cm ³ ) based on the geometrical shape of the refining vessel and the slag thickness is L (m) from the condition that the blown gas does not blow through the molten slag layer. , Is represented by the following equation.

Q ′ = 5.5 × 10 ⁴ × d × (H + L / 3.5) ^{1.5 The} amount of carbon material added to the molten slag is 25 to 100 kg / molten slag ton. The reason is that when the amount of the carbon material added to the molten slag is less than 25 kg / molten slagton, the FeO in the molten slag is not sufficiently reduced, and therefore the production of FeO cannot be suppressed. This is because, when the temperature exceeds the limit, the amount of carbon material in the molten slag is too large, so that the carbon material comes into contact with the molten iron and the carbon concentration in the molten iron increases.

Further, in the present invention, after all of the iron-based scrap is buried under the surface of the generated molten metal, that is, after being flat-bathed, only oxygen gas having a gas blow-through limit determined by the depth of the molten iron that is less than the blow-in limit is used. Is blown from the furnace bottom tuyere because oxygen sufficiently comes into contact with the molten iron to increase the decarbonation efficiency. In other words, when oxygen gas is blown in at a rate equal to or greater than the amount of gas blown, the amount of gas that floats to the slag layer without reacting with the molten iron increases, so that it is not consumed for decarburization of the molten iron, and oxygen is simply left in the upper space. The problem is that it takes only a long time to decarburize.

FIG. 1 schematically shows an apparatus for implementing the present invention. In the figure, 1 is an electric furnace main body, 2 is an electrode, 3 is a furnace bottom electrode,
Reference numeral 4 denotes a carbon material provided on a furnace wall portion where molten iron is present, a furnace bottom double tube tuyere for injecting a carrier gas and a stirring gas, 5 denotes molten iron, and 6 denotes a molten slag layer. The present invention will be described based on examples.

[0011]

【Example】

Example-1 In a 100 ton electric furnace, after stacking 100 tons of iron-based scrap (hereinafter simply referred to as scrap), a DC electrode was inserted from above, and melting of the scrap was started. The top of the top of the scrap melted and dropped, and the molten metal accumulated at the bottom of the electric furnace. As the amount of scrap dissolved increased, the height of the scrap peak decreased, and the electrode was lowered accordingly. The molten slag was charged with a slag-forming agent (silica sand, quicklime, magnesia, etc.) before energization, and was formed at about 50 to 150 kg / scrap ton. A typical slag composition is as follows. A double tube tuyere (hereinafter simply referred to as tuyere) is installed at the bottom of the furnace. From the inner tube, oxygen or nitrogen is used as a carrier, the particle size is 2 mm or less, volatile matter in carbon material is about 7%, fixed carbon is 75-80% anthracite powder was supplied, and LPG for tuyere cooling was supplied from the outer tube. The nozzle diameter (d) was 5 mm, and the depth (H) after burn-through was about 1 m.

CaO: 25 to 40% Al ₂ O ₃ : 2 to 5% SiO ₂ : 5 to 15% MgO: 5 to 10% Of the scrap, about 60% becomes molten metal, and the molten metal surface gradually rises. Until the pile of scrap is below the surface of the molten metal, the nitrogen gas and the anthracite powder
g / scrap ton. The nitrogen flow rate per tuyere was 50-100 Nm ³ / Hr, and the pulverized coal feed rate was 40-60 kg / min. Nitrogen supply rate (Q; Nm ³
/ Hr) was calculated by the formula of Q = 5.5 × 10 ⁴ × d × H ^1.5 , but the bath depth before the landslide was calculated by calculating the amount of melting from the heat balance calculation based on the bath depth after the burn-through. did.

After 60% or more of the scrap has become molten metal and the mountain of scrap has become below the surface of the molten metal, 200-300 Nm of oxygen gas per tuyere is introduced from the tuyere provided at the furnace bottom.
³ / Hr. As a result, in the slag (T • Fe)
Was reduced to 2 to 5%, and the thermal efficiency calculated from the input power, the latent heat of melting of scrap and the sensible heat reached 81%. Example 2 In the method described in Example 1, two types of tuyeres were provided at the furnace bottom, and tuyere A was a double-tube tuyere having an inner diameter of 5 mm, and 5 kg of anthracite powder / scrap. Tongue, LPG for tuyere cooling is supplied from the outer tube, and tuyere B is a double tube tuyere with an inner diameter of 10 mm. LPG or nitrogen was supplied.

Until about 60% of the scrap becomes molten metal and the peak of the scrap is below the surface of the molten metal, nitrogen gas and pulverized coal are supplied from tuyere A, and the nitrogen flow rate per tuyere is 50 to 1
00Nm ³ / Hr, pulverized coal feed rate is 40-60 kg /
And 80 to 100 Nm ³ / Hr to prevent molten metal from entering the nozzle from the tuyere B.
Supplied with

After the pile of the scrap falls below the surface of the molten metal, from the tuyere B, the oxygen gas per tuyere is
Nm ³ / supplied by Hr, nitrogen 40 to 60 nm ³ / H so as to prevent penetration of molten metal into the nozzle from the tuyere A
r. As a result, the slag (T.Fe)
It decreased to 5%, and the thermal efficiency calculated from the input power, the latent heat of melting of scrap and sensible heat reached 85%.

[0016]

According to the present invention, the thermal efficiency of melting an iron-based scrap by an electric furnace can be remarkably increased, and the equipment cost can be reduced since the top blowing or side blowing lance equipment is not required. .

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an embodiment of the present invention.

[Explanation of symbols]

 1: Electric furnace body 2: Electrode 3: Furnace bottom electrode 4: Furnace bottom double tube tuyere 5: Molten iron 6: Molten slag layer

Claims (1)

(57) [Claims] An iron-based scrap melting method for stacking iron-based scraps in an electric furnace in advance and then melting the scraps in the presence of molten slag to obtain molten iron. From at least 60% of the molten metal, until the molten metal surface gradually rises and the mountain of the scrap falls below the molten metal surface, the gas blow-through limit determined by the depth of the molten metal is equal to or greater than the blowing amount. After the inert gas is blown from the furnace bottom tuyere together with the carbon material, the carbon material is added to the molten slag layer, and all the scrap is buried under the surface of the generated molten metal. An iron-based scrap melting method characterized by blowing only oxygen-containing gas having a blowing amount less than a blow-through limit from a furnace bottom tuyere to decarburize and raise the temperature of a molten metal.