JPS61231109A - Method for operating blast furnace - Google Patents

Abstract

PURPOSE:To prevent a drop in the temp. of molten pig iron and a rise in the concn. CONSTITUTION:When a blast furnace is operated, pulverized coal and iron oxides are blown into the furnace from separate blast.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention reduces the Si concentration in hot metal by blowing iron oxides such as sintered ore powder and pellet feed into a blast furnace together with pulverized coal through a blast tuyere. In particular, the present invention provides a blast furnace operating method that can reduce the Si concentration without increasing the S11 degree in hot metal.

(Prior art) In the steel manufacturing process using the blast furnace/converter method, the hot metal produced in the blast furnace contains Si and S in order to reduce the basic unit of auxiliary raw materials in the converter process or improve the iron yield. Low concentrations and high temperatures are desirable.

In blast furnaces, in order to reduce the amount of expensive lump coke used as fuel, heavy oil, tar, etc. were injected through the blast tuyeres, but due to the rise in oil prices in recent years, heavy oil and lump coke The price difference has reversed, and all-coke operation, which does not use any auxiliary fuel such as heavy oil, has become commonplace.

However, in all-coke operation, the combustion temperature at the tip of the tuyere increases compared to when heavy oil is injected, and the heat flow ratio increases, which reduces the amount of hydrogen input, which tends to cause operational instability such as an increase in the number of slips. Recently, the method of blowing pulverized coal through the blasting surface (hereinafter referred to as pulverized coal blowing operation method) has become popular.Pulverized coal has a higher volatile content than lump coke and has a higher hydrogen content. In this way, the instability of operation that tends to occur in all-coke operations can be avoided.

However, according to this method, since the coal is directly supplied to the high-temperature combustion zone, the 8102 in the ash in the coal is reduced to SiO gas), and the SiO gas is further reduced to Si in the lower part of the furnace. However, it is absorbed into the hot metal.

Therefore, the 81 concentration in hot metal increases in pulverized coal injection operation compared to heavy oil injection operation.

To solve this problem, iron oxide (ironite, sintered ore, blast furnace dust, sinter dust, converter dust, etc.) is blown into the blast furnace through the blast tuyere along with pulverized coal to reduce the Si concentration in the hot metal. A method (hereinafter referred to as pulverized coal/iron oxide mixed blowing operation method) has been proposed in Japanese Patent Publication No. 58-56721.According to this proposed method, the SiI2 degree in the hot metal decreases, but the temperature of the hot metal decreases. As a result, the S concentration in the hot metal increased, making it impossible to obtain the desired hot metal for reducing the unit consumption of auxiliary raw materials in the converter process or improving yield.

For example, the applicant et al. carried out a test using pulverized coal blowing,
The results of the iron oxide mixed injection operation are as follows.

In a blast furnace having 27 blast tuyere, when an operation was carried out in which sitar was blown into all the blast tuyere (comparative example 1), the temperature of the hot metal was 1512°C, and the Si and S concentrations in the hot metal were each 0.42. %, 0.026%.

This blast furnace was equipped with pulverized coal blowing equipment, and when pulverized coal was blown into all tuyeres at 9/l-p (Comparative Example 2, hot metal temperature was 1513°C, Si was 0.45%, S was 0,
It became 0.025%. Furthermore, when 17 kg/t-p of sintered ore powder is injected into all the tuyeres together with pulverized coal (conventional example), the hot metal temperature is 1507°C and 81 decreases to 0.2296, but S increases to 0.081'%. did. Table 1 summarizes the above results.

Table 1 (Problems to be Solved by the Invention) The object of the present invention is to improve the method of blowing pulverized coal and iron oxides into a blast furnace, thereby lowering the temperature of hot metal and melting it.

(Means for Solving the Problems) The gist of the present invention resides in a blast furnace operating method characterized in that pulverized coal and iron oxides are blown into a blast furnace through independent blowing tuyeres.

Here, iron oxides include iron ore powder such as pellet feed, mill scale, manganese ore powder, a complex compound of iron oxide and basic substances such as self-soluble sintered ore powder, or iron ore powder,
It is a mixture of mill scale and basic substances such as limestone, or dust generated in blast furnaces, sintering machines, and converters.

When blowing pulverized coal and iron oxides into the blast furnace through independent blowing tuyeres, the tuyeres (hereinafter referred to as pulverized coal blowing tuyeres) blow the pulverized coal into the blast furnace, and the tuyeres (hereinafter referred to as pulverized coal blowing tuyeres) blow the iron oxides into the blast furnace. The arrangement of the iron oxide blowing tuyeres (hereinafter referred to as iron oxide blowing tuyeres) is free; for example, even if every other tuyere is arranged evenly around the entire circumference,
Alternatively, the iron oxide blowing tuyeres may be arranged so as to be concentrated near the tap hole.

The present invention will be explained in detail below.

The present inventors investigated the reason why the hot metal temperature decreases and the S concentration increases when iron oxide is blown into the blast furnace from the blast tuyeres together with the pulverized coal. Based on a test operation to reduce the Si concentration in hot metal by blowing into the hot metal, and basic experiments conducted before and after this test operation, we believe that the following is true.

That is, as a basic experiment, a coke packed bed with a length of 400 mm was provided in a graphite crucible with an inner diameter of 90 mm and a length of 1.5 m, and after being heated to 1550° C. by external heating, the temperature was 0.030%.

An experiment was conducted in which hot metal and slag were simultaneously dropped from the top while flowing 70% N2 gas from below.

As a result, as shown in Table 2, when the concentrations of FeO and MnO in the slag are low, an increase in the Si concentration in the hot metal that has passed through the coke packed bed is observed, whereas
Alternatively, when the concentration of MnO increases, the SiI1 degree in the hot metal that has passed through the coke packed bed decreases, and at the same time, the generation of CO gas is observed, and the Fed in the slag.

The Si removal effect of MnO was confirmed.

Table 2 By the way, the main reactions involved in Si transfer in the blast furnace are as follows.

5i02(S)+O=SiO(g)+OO(g)
Listen/Song (1) SiO2(t) 10 = SiO(g
)+OO(g) Song/Song (2) SiO(g)+0
= Ship + Co (g) ・・・・・・・・・ (
3) Si +2 (MO) = Si02 (t) + M
...River... (4)8i0(g)+MO=5i
Oz(t) 10M In the song... (5) (M:
Fe, Mn) 5io2 in the coke ash or 5iOz(t) in the molten dripping slag is the +11. (21
Reacts as shown in the formula, generates SiO(g), and this Si
O(g) reacts with 9 in the molten dropped metal as shown in equation (3), and Si enters the metal. Fed in slag,
When the MnO concentration is high, if the molten metal and molten slag come into contact, not only will the metal in the metal be oxidized by the reaction of equation (4), but also the SiO(g) in the gas will be oxidized by the reaction of equation (5). As a result, the amount of distortion caused by equation (3) is reduced.

Based on the results of the investigation inside the blast furnace after the blow-off and the investigation results of the metal and slag components collected from the inside of the blast furnace during operation, it was found that Si enters the metal in the blast furnace mainly in the area above the tuyere level. It has been found that below the reed and tuyere level, the Si oxidation (desiliconization) reaction according to Equation (4) is more common than the siliconization reaction according to Equation (3).

The effect of injecting iron oxide from the tuyere part is +41 in the furnace, (increasing the desiliconization reaction according to formula 51,
The purpose is to reduce the Si content in hot metal.

According to the experimental results, a part of the injected iron oxide causes a direct reduction reaction of the +61st and +71 formulas with solid C or C in the metal, resulting in a +41. +51 formula and (61, (71
The Si removal efficiency of the injected iron oxide is controlled by the rate at which the reaction with the formula occurs.

MO 10 (S) = Co (g) 1 M ・・・・・・
・・・・・・ (6) MO+ O=OO(g)+M
・・・・・・・・・・・・ (7) (M: Fe
, Mn) No. +41. (While the reaction of formula 51 is an exothermic reaction, the direct reduction reactions of formulas (6) and +7j involve a large endotherm.

According to the raceway coke samples near the tuyere during wind cessation during the iron oxide injection operation period by the present inventors, the more finely sized coke powder there is, the more the blown iron oxide is deSied.
The result was that the efficiency was poor. This is because the finer the particle size of the carbonaceous material, the larger the specific surface area, and the blown iron oxide is
This is thought to be because the proportion consumed by the direct reduction reaction of formula 6) increases. Also, according to similar coke samples, an increase in carbonaceous fine powder near the raceway was observed due to pulverized coal injection.

Therefore, if pulverized coal is injected from the blast tuyere at the same time as iron oxide, the amount of carbonaceous fine powder in and around the raceway will increase, and the proportion of the injected iron oxide to undergo the reaction of equation (6) will increase. Not only does the S1 removal efficiency of
The temperature of the molten iron decreases, which causes an increase in the concentration of metal in the hot metal.

In the experiment in which hot metal and slag were dropped into the heated coke-packed bed described above, we conducted an experiment in which the same hot metal and slag composition was filled with coke containing fine powder, and as shown in Table 3, it did not contain fine powder. For the case, the 81 concentration of hot metal decreases while c.

It was confirmed that the amount of gas generated increased and the Si removal efficiency decreased.

Table 3 Therefore, the present inventors came up with a method of blowing iron oxide and pulverized coal through independent tuyeres.

When this method was implemented in an actual furnace, the temperature of the hot metal was lowered, the S concentration in the hot metal increased, and the Si concentration could be reduced.

Based on basic experimental results, the mechanism by which this effect occurs is as follows.
It can be thought of as follows. By blowing iron oxide and pulverized coal into the blast furnace through independent blast tuyeres, the blown iron oxide does not coexist with fine-grained carbonaceous solids in or near the raceway, so that iron oxide is mixed with solid carbonaceous solids. The proportion consumed by the direct reduction reaction of formula (6) is reduced, the efficiency of removing Si from iron oxide is improved, and a decrease in hot metal temperature and an increase in S concentration can be prevented.

(Example〕 Next, examples of the present invention will be described.

In a blast furnace with 27 blast tuyeres, 85 pulverized coal is poured into every other 14 tuyere out of the 27 blast tuyeres.
h/l-p blowing, and 171 w/l-p of sintered ore powder was blown through the remaining 13 blowing tuyeres (Example 1).

The hot metal temperature at this time was 1510℃, and the Si concentration was 0.18.
%, the S concentration was 0.025%. In addition, 171w/l-p of Brazilian pellet feed was used as a replacement for sintered ore powder.
When blowing (Example 2), the hot metal temperature was 1509°C,
St concentration 0.20%, S concentration 0.027%, and a mixture of pellet feed and limestone powder (pellet feed 1
7kf/l-p, limestone 7kg8-p) was blown into (
Example 3) However, the hot metal temperature was 1509°C and the Si concentration was 0.
．． 18%, and the S concentration was 0.024%. These results are shown in Table 4 together with the comparative example and conventional example described above.

Table 4 (Effects of the Invention) As described above, according to the present invention, compared to a method in which pulverized coal and iron oxides are mixed and blown into the same blowing tuyeres, the same amount of iron oxides can be blown into the same amount of iron oxides. It is possible to obtain hot metal with a low Si concentration and a high temperature, and a low S concentration, which greatly contributes to reducing steel manufacturing costs.

Claims (1)

[Claims] A blast furnace operating method characterized by blowing pulverized coal and iron oxides into the blast furnace through independent blast tuyeres.