JPH0347906A - Production of low sulfur iron - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention uses a cylindrical furnace with a relatively simple structure similar to a converter for steelmaking, uses both scrap and iron ore as iron sources, and has a low The present invention relates to a method for producing sulfur hot metal.

(Prior Art) In recent years, the production of low-sulfur steel has been increasing as one of the advances in the quality of steel materials. On the other hand, there is a strong demand for lower prices of steel materials, and there is an urgent need to establish an inexpensive manufacturing method for low-sulfur steel.

Normally, low sulfur steel is first produced using limestone as a slag-forming agent in a blast furnace.
By charging serpentine, the sulfur content in the hot metal is 0.03 to 0.0.
S'io, 01 is produced according to the type of molten steel by the KR method, injection method, etc. in a torpedo car or ladle that transports the hot metal to the converter.
Hot metal is desulfurized to ~0.002%.

However, in the above method, the temperature of the hot metal decreases significantly due to various steps, and a heat source is required.
The disadvantage is that the manufacturing cost increases due to a decrease in yield and an increase in the amount of required materials.

Therefore, in the smelting reduction ironmaking method to replace the blast furnace method, a method was proposed in which hot metal is desulfurized in a smelting reduction furnace (Japanese Patent Application Laid-open No. 199010/1983). The method is characterized by injecting desulfurization flux into hot metal in a smelting reduction furnace to desulfurize the hot metal.

According to this method, since desulfurization is carried out in the same furnace, it is thermally advantageous, but since a large amount of energy is required in the melting reduction process, the total thermal efficiency is low. Furthermore, -
The limit is to lower 5- to about 0.02%, and the above K
It is not possible to produce hot metal with extremely low sulfur (S<0.005%) comparable to hot metal desulfurization methods such as the R method and the injection method.

(Problems to be Solved by the Invention) The purpose of the present invention is to provide a new method for producing low-sulfur pig iron that has higher thermal efficiency than conventional blast furnace pig iron making methods and smelting reduction methods and can produce extremely low-sulfur hot metal. That is.

(Means for Solving the Problems) The present applicant previously proposed a method for thermally efficiently producing hot metal using a converter-type cylindrical furnace and using scrap and iron ore as iron sources (Japanese Patent Application No. 63-122292 issue).

In the method for producing hot metal, a converter-type cylindrical furnace 1 as shown in FIG. 1 is used. As shown in the figure, this cylindrical furnace 1 has an opening 2 in the upper part of the furnace for discharging furnace gas and charging raw materials, and a primary tuyere 3 in the lower part of the furnace wall for injecting combustion-supporting gas and fuel as necessary.
, a secondary tuyere 4 for blowing combustion-supporting gas into the upper furnace wall, and a tap hole 5 for discharging hot metal and slag at the bottom of the furnace.

To produce hot metal using the cylindrical furnace 1, first, a coke packed bed 7 is formed in the lower part of the furnace, and a packed bed 8 of scrap and iron ore is formed thereon. Then, a combustion-supporting gas and, if necessary, fuel are blown into the lower coke layer 7 from the primary tuyere 3 to cause a reaction according to the following formula (1), and the coke layer 7 is kept at a high temperature by the reaction heat.

C+1/202→CO+29,400kcal/kmo
l-C=・(1) The CO generated in the above equation (1) reacts with the combustion-supporting gas injected from the secondary tuyere 4 in the packed bed 8 of scrap and iron ore as shown in the following equation (2). secondary combustion). The heat of reaction is used to heat and melt the scrap and iron ore.

CO+1/20z→COz+67.590kcal/k
mol-CO-(2) The iron ore (molten iron oxide) molten in this reaction is dropped into the lower coke layer 7, reacts with the high temperature coke according to the following equation (3), and is quickly reduced.

FetCh +3 C→2 Fe +3 C0108,
090kcal/kIIlol-Fe2O2...(3
) When the reaction of the above formula (3) occurs, the reaction of the formula (3) is not inhibited by CO2 since there is no CO□ nearby.

The CO generated in equations (1) and (2) is effectively used for heating and melting scrap and iron ore for secondary combustion in the packed bed 8, achieving high fuel efficiency. .

As described above, according to the method for producing hot metal previously proposed by the present applicant, hot metal can be produced from scrap and iron ore with thermal efficiency in a converter-type cylindrical furnace.

The present inventors have developed a new method for producing low-sulfur hot metal by further developing the method for producing hot metal using a cylindrical furnace. The gist of the present invention is the following method for producing low sulfur pig iron.

"A cylinder with openings for gas discharge and material charging in the upper part of the furnace, a primary tuyere, a slag outlet, and a taphole in the furnace bottom and/or lower furnace wall, and a secondary tuyere in the upper furnace wall." Using a mold furnace, a packed bed of coke is formed from the bottom of the furnace to a level that includes the primary tuyere, and a packed bed mainly consisting of scrap and iron ore is formed above that up to a level that includes the secondary tuyere. , - Produce hot metal by blowing combustion-supporting gas through the secondary port and secondary tuyere, and blow powder mainly composed of CaO into the hot metal using an inert gas as a carrier gas, and desulfurize the hot metal while stirring. (hereinafter referred to as the method of the present invention) In the method of the present invention, the ore charged through the upper opening of the furnace contains not only ordinary iron ore but also Mn, Ores containing a large amount of Cr, Mo, Ni, etc. or their oxides can be used.Additionally, auxiliary raw materials such as silica, limestone, serpentine, and fluorite can be charged together with these ores and coke. As for scrap, it is possible to use high-alloy scrap such as stainless steel scrap and reuse the useful elements therein.

Iron ore can be blown not only through the upper opening of the furnace, but also pulverulent ore can be blown through the primary and/or secondary tuyeres.

The combustion supporting gas injected from the primary and secondary tuyeres is 0.
□ Contains gas, and gas or liquid fuel such as pulverized coal, heavy oil, or natural gas can be blown into the tuyere along with combustion-supporting gas.

- If the secondary tuyere is located at the bottom of the hearth or the lowest part of the hearth wall,
Although it can also be used for blowing in the desulfurizing agent, which will be described later, as shown at 3' in FIG.

The desulfurizing agent is a powder whose main component is CaO. In addition to CaO, the powder may be a mixture of CaC0a, CaFz, or a metal ^P. It is desirable that the amount of injection is sufficient to make the basicity of the slag 2.0 or more.

The desulfurization agent is blown into the hot metal using an inert gas such as nitrogen or argon as a carrier gas. This carrier gas has the effect of stirring the hot metal and promoting the desulfurization reaction. In addition to the carrier gas, an inert gas is also blown in as a stirring gas, but as will be described later, the amount of inert gas is 0.00 mm per ton of hot metal. It is preferable to set the flow rate to 37 minutes or more of O3Nm.

The desulfurization agent is injected after the melting of the ore and scrap is almost completed, but it is preferable to inject the desulfurizing agent into the remaining hot metal after the slag produced at the same time is discharged from the slag outlet. However, it is also possible to carry out a desulfurization treatment before the slag is discharged, and then discharge the generated slag from the slag discharge port.

After the desulfurization process is completed, the produced low sulfur pig iron is taken out from the taphole.

(Function) A high secondary combustion rate can be obtained in the method for producing hot metal using the cylindrical furnace of the present invention. Additionally, since more scrap is used instead of iron ore, the coke consumption rate is low. That is, since less sulfur is introduced from the charged raw material, hot metal with relatively low sulfur can be obtained.

In addition, the upper part of the furnace around the secondary tuyere serves as a zone for melt reduction and melting of iron ore and scrap, while the lower part of the furnace around the secondary tuyere serves as a zone for reduction (i.e., desulfurization) of the produced hot metal. Because it is separated, the desulfurization reaction progresses easily. In particular, extremely low sulfur pig iron can be easily obtained by adding CaF2 to promote slag formation and adding A2 to create a strongly reducing atmosphere.

As mentioned above, it is desirable to drain the slag before blowing the desulfurization agent. That is, after the generated slag with a high sulfur content is once discharged, low-sulfur pig iron can be produced more efficiently by desulfurizing the remaining hot metal. Therefore, as shown in Fig. 1, the cylindrical furnace to be used has a slag discharge port 10 provided at the bottom of the furnace separately from the tap hole (with the slag discharge port facing upward), and is tiltable. A converter-type structure that can remove slag is desirable.

In the method of the present invention, as mentioned above, Mn, Cr, M
o.

An ore with a high content of Ni or the like can be used.

When producing hot metal for low-alloy steel or high-alloy steel, cheap Mn, Cr, Mo, Ni is used instead of expensive ferroalloy.
By using such ores or oxides, low-sulfur pig iron with a high alloy content can be produced at low cost.In general, ores are produced in large quantities in the form of powders as well as lumps. In particular, oxides such as Ni01003 refined from ores often exist in powder form. Therefore, in addition to charging the lumpy ore through the upper opening, the cost of producing hot metal can be further reduced by blowing in powdered ore and oxides as they are from the slats.

An advantage of the method using the cylindrical furnace of the present invention is that batch-type small loft production is possible. Hot metal can be quickly made to suit a variety of steel types, and since it performs complete slag removal and tapping like a converter, contamination of the next charge by alloying elements from the previous charge is reduced.

Next, preferred conditions for desulfurization treatment will be described.

FIG. 2 is a diagram showing the distribution ratio of sulfur to the slag and hot metal (S distribution ratio) with respect to the weight percent of FeO in the slag. In addition, it is 5■W9 of Ntaniganko, and the large S distribution ratio means that the sulfur in the hot metal (
Σ) is low, which means that the desulfurization rate is high.

As shown in the figure, the S distribution ratio is related to PeO in the slag and the basicity (Cab/5int) of the slag, and the S distribution ratio can be improved by reducing FeO in the slag, that is, by lowering the oxidation boticals of the slag. Furthermore, if the basicity of the slag is increased, the S distribution ratio will be improved.

In normal blast furnace operation, the S distribution ratio is in the shaded area in the diagram.
An S distribution ratio of -20 to 50 can be obtained.

This is because a strong reducing atmosphere can be obtained in the lower part of the blast furnace due to the sufficient coke packed bed.

Also in the method of the present invention, there is a coke packed bed in the lower part of the furnace,
Since the conditions are similar to those in the lower part of a blast furnace, an S distribution ratio comparable to that of a blast furnace can be expected. However, by increasing the basicity of the slag by injecting a desulfurization agent mainly composed of CaO using inert gas as a carrier gas through the slag placed at the immersion position of the hot metal, and by using the strong stirring of the hot metal by gas, it is possible to The S distribution ratio is obtained.

1 The box shown in Figure 2 is an example of the method of the present invention in which the basicity of the slag is 2.0. At this time, metal A! When the Fen content in the slag is injected to 2.0% or less, an S distribution ratio equal to or higher than that of the blast furnace method can be achieved, and hot metal with an extremely low sulfur content can be produced.

FIG. 3 is a diagram showing changes in the S distribution ratio depending on the flow rate of the stirring gas when the slag basicity is 2.0 (no addition of ^l). It can be seen that in order to obtain the same level of S distribution ratio (approximately 40) as in a blast furnace, it is sufficient to ensure a flow rate of 0.03 Nm for 7 minutes or more per ton of hot metal as the stirring gas.

From the above results, Ca
When injecting O-based powder, the slag basicity is 2.
In addition, the flow rate of the stirring gas should be set at 0.00000000000000000000000000000000000000000000000000000000000000000000. O3Nm3/
It can be said that it is desirable to make it more than 1 minute. It is also recommended to add CaFz to the powder to promote slag formation.

(Example) Hereinafter, the method for producing low sulfur hot metal of the present invention will be explained in more detail with reference to Examples.

2 In the second example, a small cylindrical test furnace having a converter-like structure shown in FIG. 1 was used. This furnace has a diameter of 1.5 m, a height of 3.6 m from the furnace bottom to the furnace mouth, and an internal volume of 6.0 m.The furnace wall has a primary tuyere 3 and a secondary tuyere 4, each extending from the hearth bottom to the furnace wall. 0.
Four of them are installed at 90 degree intervals at positions of 8 m and 1.2 m, and a tap hole 5 is provided in the center of the furnace bottom, and a slag discharge port 10 is provided on the furnace wall 0.6 m above the furnace bottom. In addition, a slat 3'' was provided at the bottom of the furnace for injecting desulfurization agent.

The raw material scrap has the composition shown in Table 1, and has a bulk specific gravity of 3.
．． The composition and size of the raw material iron ore, ore containing alloying elements, and oxide containing alloying elements are shown in Table 2. The composition and size are shown in Table 3.

Pure oxygen is used as the combustion-supporting gas, and the combustion rate is 2,50ONm'/
I blew h. Using N2 gas as the siding cooling gas, 1
．． 00 ONm'/min was blown. After the melting of the charged scrap and ore is completed, powder containing CaO as a main component or CaFz is added to the powder from the tuyere 3 installed at the bottom of the furnace.
and/or powder mixed with metal AA at 1.5 kg/
minutes (however, N2 gas as an inert gas carrier is
．． lNm37min=0. It was blown into the hot metal at a rate of OINm'/min.molten pig iron.

The composition of the injected powder is shown in Table 4. The desulfurizing agent il-2 in Table 5 is the il-2 in table 4.

The operation was carried out using the equipment and raw fuel as described above, and the low sulfur hot metal shown in Table 5 was produced. Note that the English symbols in parentheses in the column for ores and oxides in Table 5 indicate the ores and oxides listed in Table 2.

In Table 5, Invention Example 1 is a case in which low-sulfur hot metal for low-carbon, low-Mn steel was produced using scrap and iron ore (A in Table 2). The sulfur concentration of this hot metal is as low as 0.003% by weight. When compared with the sulfur concentration o, oos weight % of hot metal produced by the blast furnace method shown as a conventional example, it can be seen how low the sulfur concentration of hot metal produced by the method of the present invention is.

(The following is a blank space) Inventive Example 2 is a hot metal for high tensile strength steel, Inventive Example 3 is a hot metal for high tensile strength steel, and Inventive Example 4 is a hot metal for molten iron for 3% N+ steel. In both cases, the sulfur concentration in the hot metal is extremely low.

(Effects of the Invention) According to the method of the present invention, not only can hot metal be efficiently produced using scrap and ore as an iron source, but also hot metal with low sulfur content can be produced much more easily than conventional methods. can be manufactured.

If this method is used in combination with conventional steelmaking processes, the manufacturing cost of low-sulfur steel can be significantly reduced, and its practical effects are extremely significant.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a sump apparatus for producing low-sulfur pig iron by the method of the present invention. FIG. 2 is a diagram showing the relationship between slag (Fed) and basicity and S distribution ratio. The figure is a diagram showing the relationship between the flow rate of the stirring gas and the S distribution ratio. 7

Claims (1)

[Claims] Cylindrical type with openings for gas discharge and raw material charging in the upper part of the furnace, primary tuyere, slag outlet, and tap hole in the furnace bottom and/or lower furnace wall, and secondary tuyere in the upper furnace wall. Using a furnace,
A packed bed of coke is formed from the bottom of the furnace to a level that includes the primary tuyere, and a packed bed mainly composed of scrap and iron ore is formed above that up to a level that includes the secondary tuyere. The method is characterized by producing hot metal by blowing a combustion-supporting gas through the secondary tuyere, and blowing powder mainly composed of CaO into the hot metal using an inert gas as a carrier gas, and desulfurizing the hot metal while stirring it. A method for producing low sulfur pig iron.