JP2000234114A - Method for melting scrap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing slopping and efficiently realizing scrap melting in a scrap melting furnace. SOLUTION: In the method for melting the scrap and producing molten steel having <=0.5% C concn. by using the scrap melting furnace having oxygen top-blown lance, while the C concn. in the molten steel is 3% to 0.5%, the molten steel temp. is regulated to be higher by T deg.C shown in the following equation or more than the liquidus temp. of the steel at the C concn. T( deg.C)=2.5×([%C]+1). Wherein, [%C] is C concn. in the molten steel.

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 scrap.

[0002]

2. Description of the Related Art Conventionally, "Iron and Steel" vol.78 (1992), p.520
As reported by the Iron and Steel Institute of Japan, it is hot metal after smelting, so converters are needed in the post-process, so fossil energy such as carbon material is burned with oxygen and the heat of combustion is used to generate scrap. It is difficult to produce molten steel by the method of melting molten iron, and molten iron is produced in all practical applications.

[0003] In the case of a scrap melting method using a normal carbon material, the carbon unit consumption is high, and the S concentration in the produced molten metal is high due to the sulfur content brought from the carbon material. Therefore, when molten steel is produced by decarburization, the oxygen potential becomes high and desulfurization becomes difficult. Therefore, considering the desulfurization cost,
It is more advantageous to produce hot metal in a scrap melting furnace, perform hot metal desulfurization, and then decarburize in the converter process.

[0004] As a means for reducing the total energy and reducing the carbon unit consumption, a rotary furnace and a shaft furnace are connected in series to a melting furnace, and after the exhaust gas and the scrap are heat-exchanged in the rotary furnace, the scrap is removed in the shaft furnace. A method for preheating is disclosed in International Publication WO06 / 30709, Japanese Patent Application Laid-Open No. 8-27116.
No. 4 discloses a method of preheating scrap with high efficiency and melting the preheated scrap using electric power or fossil energy.

[0005] By using such a method, the basic unit of carbon material can be reduced, and it is possible to produce molten steel at low cost. When electric energy is used together, the basic unit of carbon material is further reduced.

[0006] However, when the carbon material is burned with the top-blown oxygen and the scrap is melted, the oxygen potential in the melt and the slag increases as the C concentration in the melt decreases, and the iron oxide of the slag is reduced. There has been a frequent problem that a rapid bubbling phenomenon of slag called slopping caused by a rapid reaction of carbon in the molten metal occurs, and the slag overflows outside the furnace, significantly impairing the operation. In order to prevent slopping and operate stably, it was necessary to slow down the supply rate of the top-blown oxygen, thus reducing productivity and increasing total energy.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preventing scraping and efficiently melting scrap in a scrap melting furnace.

[0008]

Means for Solving the Problems To solve the above problems, the gist of the present invention is as follows. (1) Scrap is melted by using a scrap melting furnace having a lance for blowing over oxygen to obtain a C concentration of 0.5. % In the steel bath, when the C concentration in the steel bath is 3% or less and 0.5% or more, the steel bath temperature is lower than the liquidus temperature of the steel at the C concentration. A method for dissolving scrap, wherein the temperature is set to be higher than T ° C represented by the formula. T (° C.) = 25 × ([% C] +1) (a) where [% C]: C concentration (%) in the molten metal.

(2) The scrap is melted by using a scrap preheating / melting device in which a scrap melting furnace having an oxygen top blowing lance and a rotary furnace type preheating device are connected to form molten steel having a C concentration of 0.5% or less. In the scrap melting method to be manufactured, when the C concentration in the steel bath is 3% or less and 0.5% or more, the steel bath temperature is expressed by the above equation (a) from the liquidus temperature of the steel at the C concentration. A method for melting scrap, comprising adjusting the rotation speed of a rotary furnace type preheating device so as to increase the temperature by at least T ° C.

(3) A scrap melting furnace having an oxygen blowing lance and an arc heating electrode and a shaft furnace for scrap preheating are connected in series via a rotary furnace, and exhaust gas generated from the melting furnace is introduced to rotate the furnace. The scrap melting method according to the above (1) or (2), wherein the scrap is charged into the melting furnace while preheating the scrap inside the furnace and in the shaft furnace. It is in.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been made to solve the above-mentioned problems, and realizes a stable operation that does not cause slopping even when producing molten steel while melting scrap using carbon material and oxygen. It provides a way to increase productivity and reduce energy.

The inventors of the present invention have found that, through a scrap dissolution test of several tens of charges, the conditions with and without the occurrence of slopping are represented as shown in FIG.
In other words, when the predetermined blowing stop temperature, the supply speed of the scrap is faster than the supply speed of the heat and the temperature of the molten metal is close to or below the liquidus line before reaching the C concentration, A semi-solid part is formed around the supplied scrap, where oxygen hits and a large amount of iron oxide is generated,
It was found that when the iron oxide was dissolved, the iron oxide and C in the molten metal rapidly reacted to generate CO gas, and slopping occurred.

According to the results of the scrap melting test, as a stable operating condition with no occurrence of slopping, when the C concentration in the molten metal is 3% or less and 0.5% or more, the molten metal temperature is higher than the liquidus temperature by a certain degree or more. It turned out to be good. As a result of determining the critical conditions based on the results in FIG. 1, it was found that the temperature T (° C.) at which the temperature was raised to the liquidus temperature or higher was roughly expressed by the equation (a). T (° C.) = 25 × ([% C] +1) (a) where [% C]: C concentration (%) in the molten metal.

That is, if the temperature of the molten metal during operation is set higher than the liquidus temperature by T ° C. or more according to the C concentration in the molten metal, no slopping occurs. However, if the temperature of the molten metal becomes unnecessarily high, it leads to an increase in the total energy and promotes the erosion of the refractory in the furnace. Therefore, it is desirable to keep the liquidus temperature + 200 ° C. within a controllable range.

The liquidus temperature is defined as a value obtained by the following equation derived by Mori et al. For a high C concentration. Liquidus temperature (℃) = 1536-54 x [% C]-8.13 x [% C] 2 where [% C]: C concentration in molten metal (%) It can be appropriately measured by the attached probe.

In order to always satisfy the condition, it is important to control the supply rate of the scrap in accordance with the supply rate of oxygen and the preheating temperature of the scrap.

When a rotary furnace is used as a preheating device,
The rotation speed may be adjusted according to the transition of the molten metal temperature and the C concentration.

[0018]

FIG. 2 shows a schematic diagram of the equipment used as an example of the present invention. Top blow lance 2 and upper electrode 3 and furnace bottom electrode 4
A 15 ton-scale scrap melting furnace 1 having a radius of about 2.
Using a scrap preheating / melting device with a rotary furnace 5 having a length of about 7 m and a shaft furnace 6 having a height of about 7 m which are connected in series,
A scrap dissolution test was performed.

A hopper 9 for cutting scraps into the shaft furnace 6 is provided above the shaft furnace 6, and a hopper 10 is provided so that scraps can be cut out at the joint between the shaft furnace 6 and the rotary furnace 5. . The scrap in the shaft furnace is cut out to the lower part of the shaft furnace by opening the finger 11, pushed out into the rotary furnace 5 by the pusher 7, transferred to the downstream side by rotating the rotary furnace, and transferred to the melting furnace 1. It is thrown.

At the entrance of the rotary furnace 5 on the melting furnace side, an auxiliary burner 8 for supplying an auxiliary gas for burning the exhaust gas is installed. If necessary, the latent heat of the exhaust gas is converted into sensible heat. To preheat the scrap. The melting furnace 1 can be supplied with an auxiliary material such as a carbonaceous material serving as a fuel or quicklime or dolomite for adjusting the slag composition from the auxiliary material hopper 12.

The scrap dissolution test was performed as follows. First, 6 tons of unheated scrap, 200 kg of coke, 160 kg of quicklime, and lightly-burned dolomite 80 are placed in the melting furnace 1.
kg and charged by means of direct current using the upper electrode 3 and the lower electrode 4. The input power was 2000 kWh. Meanwhile, the scrap 6t for the next charge cut out from the hopper 9 in the shaft furnace 6 was preheated by sensible heat of the exhaust gas.

Thereafter, the upper electrode 3 is switched to the upper blowing lance 2, and while the coke is added, the upper lance 2
A total of ⁴ tons of scrap continuously fed from the hopper 10 to the melting furnace 1 via the rotary furnace 5 was melted while feeding at a feed rate of 00 Nm ³ / h.

At this time, the supply of the scrap is not started until the temperature of the molten metal becomes higher than the liquidus line by 100 ° C. or more before the acid supply, and the C concentration of the molten metal is 2% or more after the start of the supply of the scrap. Is always 100 ° C or more 1
At a time when the C concentration is 1% or more and less than 2%, the temperature becomes 80 ° C or more and less than 100 ° C so that the C concentration becomes 1% or less and less than 2%. While adjusting the rotation speed of the rotary furnace, the scrap was melted by adjusting the coke amount and the acid supply amount so that the blowing temperature was 1600 ° C. and the C concentration was 0.1%.

The temperature of the molten metal and the C concentration in the molten metal were measured about every 4 minutes by a probe attached to a sub-lance with a thermocouple and a C sensor. In addition, oxygen for burning combustible gas (CO, H ₂ gas) contained in the exhaust gas is blown from the auxiliary burner 8, and the scrap supplied from the hopper 10 is supplied to the rotary furnace 5 by the exhaust gas having increased sensible heat.
The scrap in the shaft furnace 6 was preheated by the remaining exhaust gas sensible heat.

After reaching the above blowing stop conditions, the top blowing acid supply was stopped, and the tapping / scrapping operation was performed while leaving 3 t of seed water for the next charge. After the next charge, top lance 2 again
Was switched to the upper electrode 3, the scrap 6t preheated in the shaft furnace 6 was discharged to the melting furnace 1, and then the above-described electric melting and melting by top blowing acid were repeated.

As Comparative Example 1, a test in which the supply of scrap was started immediately after the start of the top blowing acid transfer and the initial molten metal temperature was lowered to the liquidus temperature, and as Comparative Example 2, the C concentration in the molten metal was 2%. At that point, a test was conducted in which the rotating speed of the rotary furnace was increased and the temperature of the molten metal in the middle was lowered to the liquidus temperature. The other conditions were the same as those of the present invention.

In the example of the present invention, a stable scrap melting operation was performed, the molten steel was produced with a small energy of 60 kg / t in total carbonaceous material unit, the acid supply time was as short as 10 minutes, and the productivity was high.

In Comparative Examples 1 and 2, large slopping occurred during the dissolution by top blowing acid, and the operation had to be interrupted. After the next charge, set the acid transfer rate to 10
Stable operation was achieved by reducing to 00Nm ³ / h, but the acid supply time was about twice that of the example, the heat dissipation increased, and the unit carbon material was about 1.3 times that of the example. .

[0029]

Industrial Applicability According to the present invention, it is possible to stably dissolve scrap without generating slopping, to produce molten steel with a small amount of energy per unit of total carbon material, and to reduce scraping time and productivity with high productivity. It has become possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of the C concentration in the molten metal and the temperature of the molten metal on the occurrence of slopping.

FIG. 2 is a configuration diagram of an apparatus used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Scrap melting furnace 7 Pusher 2 Top blowing lance 8 Burning burner 3 Upper electrode 9 Hopper 4 Furnace bottom electrode 10 Hopper 5 Rotary furnace 11 Finger 6 Shaft furnace 12 Secondary material hopper

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F27D 13/00 F27D 13 / 00D // C22B 9/16 C22B 9/16 (72) Inventor Yoji Demoto 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division of Nippon Steel Corporation (reference) 4K001 AA10 BA22 DA05 EA03 FA10 FA11 GA06 GA07 GA16 GB03 4K002 AB01 AC03 AC04 AC05 AD02 BF00 CA00 4K012 CA08 CA09 CA10 DD01 DD08 DF07 DF08 DF10 4K063 AA04 BA02 CA06 GA02 GA09

Claims (3)

[Claims] 1. A scrap melting method for producing molten steel having a C concentration of 0.5% or less by melting a scrap using a scrap melting furnace having an oxygen blowing lance, wherein the C concentration in the steel bath is 3% or less. A method for melting scrap, wherein the steel bath temperature is higher than the liquidus temperature of steel at the C concentration by at least T ° C represented by the formula (a) during 0.5% or more. T (° C.) = 25 × ([% C] +1) (a) where [% C]: C concentration in molten metal (%) 2. A scrap preheating / melting device in which a scrap melting furnace having an oxygen top blowing lance and a rotary furnace type preheating device are connected to each other to melt the scrap and obtain a C concentration of 0.5.
% In the steel bath, when the C concentration in the steel bath is 3% or less and 0.5% or more, the steel bath temperature is lower than the liquidus temperature of the steel at the C concentration. A method for melting scrap, comprising adjusting a rotation speed of a rotary furnace type preheating device so as to be higher than T ° C represented by the formula. T (° C.) = 25 × ([% C] +1) (a) where [% C]: C concentration in molten metal (%) 3. A scrap melting furnace having an oxygen blowing lance and an arc heating electrode and a shaft furnace for scrap preheating are connected in series via a rotary furnace, and exhaust gas generated from the melting furnace is introduced into the rotary furnace. The method for melting scrap according to claim 1 or 2, wherein the scrap is charged into a melting furnace while preheating the scrap in a shaft furnace.