JPS5856721B2 - Low-Si operation method for blast furnace in pulverized coal injection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blast furnace operating method in which pulverized coal is blown into the furnace through a blast tuyere, and is used to reduce the Si content in tapped iron.

In the conventional blast furnace operation method, in which coke is mainly used as a fuel to produce pig iron from iron ore, heavy oil and coal are also used, reducing the consumption of expensive coke (coke ratio) In order to do this, a method was used in which cheap heavy oil or tar was injected through the tuyeres.

However, due to the recent rise in oil prices, the prices of coke and heavy oil have reversed, leading to reduced heavy oil operation, oil-less operation, or all-coke operation that uses less heavy oil. There is.

All-coke operation is prone to operational abnormalities such as slippage due to increased tuyere tip temperature.

In addition, since the hydrogen content in coke is lower than in heavy oil, a decrease in H2% in the furnace gas will reduce the furnace top gas utilization rate, and the coke ratio will increase significantly more than the decrease in heavy oil. A problem has occurred.

In such a situation, the method of injecting pulverized coal from the air blower causes the H2% in the furnace gas to rise due to the hydrogen valve contained in the coal, increasing the furnace top gas utilization rate and decreasing the fuel ratio. In addition, coal, which is the raw material for pulverized coal, is cheaper than heavy oil or coke, so it is considered an effective means of reducing fuel costs for blast furnaces.

However, pulverized coal injection has the following problem of increasing Si in the hot metal.

The pulverized coal blown through the tuyeres reaches a temperature of 2000℃ at the tip of the tuyere.
Since combustion occurs in the combustion zone with the highest temperature in the blast furnace,
SiO2 in the ash in the coal becomes SiO+(, +SiO
The reaction of +CO(1) generates SiO, which is reduced by C while rising through the high-temperature zone at the bottom of the furnace to become Si, which is absorbed into the pig iron and increases the Si content in the pig iron.

Regarding the Si% in pig iron, the Si% in pig iron is
The above-mentioned phenomenon is a major problem, especially since there is an increasing need to keep the % low and stable.

Si and Mn contained in blast furnace charge. Impurities such as S go through various reactions within the furnace and are eventually distributed to the slag and pig iron that are discharged outside the furnace.

It is known that the transfer of Si to pig iron occurs in the region from the melting position of the ore to the surface of the slag bath in the hearth pit, via SiO generated at the tip of the tuyere and in the high-temperature zone at the bottom of the furnace.

Therefore, in order to reduce Si in pig iron, Si
It is necessary to suppress the generation of O or move the ore melting position downward to increase the amount of FeO to the lower part of the furnace.

The conventional low-Si operation method increases the heat flow ratio (ratio of solid heat flow rate to gas heat flow rate) and moves the melting position of iron ore downward to reduce Si. Since it takes a long time to descend to the bottom of the furnace after it is charged from the top, it is not effective immediately.

Increasing the heat flow ratio also means keeping the furnace heat low, which tends to cause operational troubles.

An object of the present invention is to eliminate the above-mentioned problems that occur in the blast furnace operation method using pulverized coal injection, and to reduce the Si content in the pig iron to be tapped.

The present invention is a method of operating a blast furnace in which pulverized coal is injected, in which iron oxide or reduced iron is injected into the blast furnace from the blast tuyeres together with pulverized coal, thereby reducing the Si content in the pig iron being tapped. The gist of this paper is a method for operating a blast furnace with low Si in the injection of pulverized coal, which is characterized by the following.

The operating method of the present invention will be explained with reference to the drawings.

The drawings relate to equipment attached to a blast furnace for carrying out the method of the present invention, for injecting additives such as iron ore into the blast furnace together with pulverized coal through the tuyeres. It shows each supply system to lead each to a separate outlet.

A charge consisting mainly of iron ore and coaster is charged from the top of the blast furnace 1, and pig iron and slag are discharged from the bottom of the furnace.

High-temperature air for burning coke is introduced into the furnace through a large number of blowing tuyeres 3 via an annular pipe 2.

Pulverized coal is produced by drying and pulverizing coal to a moisture level suitable for gas transportation, and feeding it from a raw material hopper 4 through an intermediate tank 5, from a pressure tank 6 to a transport pipe 10, and then using air or various gases as carrier gas to blow the air into a blower. The air is blown into the furnace through a blow nozzle 11 provided at the port 3.

Iron oxide or reduced iron is pulverized to the same level as pulverized coal, usually 50% or more of 100 mesh or less, and then transported to a transport pipe 10 via a raw material pumper 7, an intermediate tank 8, and a pressure tank 9. It is mixed with pulverized coal and blown into the furnace from the blowing nozzle 11.

These additive substances can be mixed with pulverized coal in advance and then fed through the raw material hopper 4, intermediate tank 5, and pressure tank 6, but since the additive substances have a higher density and force than coal, It is easy to cause classification in the tank.

The intermediate tanks 5, 8 have a pressure equalization or exhaust pressure function according to the opening/closing operation of intermediate valves between the normal pressure material pumpers 4, 7 and the high pressure pressure feeding tank 6.9.

The pressure tank 6.9 is a so-called powder injection tank, and has a function of quantitatively feeding powder into the transport pipe 10.

When controlling the Si% of pig iron by changing the amount of additives while keeping the amount of pulverized coal injected constant, it is more convenient to use separate raw material supply systems as described above.

Note that although it is also possible to inject only the additive substance by gas transport, it is more effective to inject a mixture with pulverized coal.

In addition to iron ore and sintered ore, iron oxides include blast furnace dust,
Sintering dust, converter dust, etc. can be used.

Next, we will discuss the effects of iron oxide or reduced iron injected into the blast furnace.

In the case of iron ore, it is heated and melted in the high temperature zone at the tip of the tuyere.
It is partially reduced and reacts as F'e O which drips into the hearth, lowering the Si content in the pig iron.

If the injected iron ore does not complete melting in the high temperature zone at the tuyere tip, it will clog the coke packed layer around the coke circulation zone (raceway) at the tuyere tip, increasing wind pressure and causing operational troubles. Therefore, it is necessary to reduce the particle size.

In the case of sintered ore, the same reaction as in equation (2) occurs, but it is melted during firing and calcium ferrite is generated, so it is easy to melt.

In the case of iron ore, fine powder ore is easily available because PB powder (raw material for pellet production) is imported, but in the case of sintered ore, it is necessary to crush it.

In the case of reduced iron injection, it is oxidized by a reaction in the high temperature zone at the tip of the tuyere, and is heated and melted by the heat generated by its own oxidation reaction.
It has the advantage of being much easier to melt than iron ore or sintered ore.

However, since reduced iron is iron ore reduced to 50% or more, it is more expensive than iron ore or sintered ore.

Each of the additives can be used alone, or they can be mixed as appropriate depending on the situation.

Normal pulverized coal injection amount is 30-150k per ton of pig iron.
In contrast, the amount of iron oxide or reduced iron blown may be about 5 to 50 kg.

As for the blowing equipment, it is only necessary to modify a part of the existing pulverized coal blowing equipment, thereby making it possible to blow pulverized coal and additives together.

Example In a blast furnace, an injection test using the method of the present invention was conducted, and the results were as follows for each injection amount of pulverized coal, iron ore, sintered ore, and reduced iron per tapped pig iron. Pig iron with a Si content of .

(1) In the case of (fine powdered Koji iron ore) Pulverized coal (steam coal): 52kV, - Pig iron ore (PB powder from Brazilian MBR ore): 13kg/l
- Si% in pig iron: 0.31% (2) (pulverized coal + sintered ore) Pulverized coal (sintered coal): 6'#/, - Pig iron sintered pig iron sintered ore fine powder: 15 pig iron Si% in: 0.34% (3) (pulverized coal + reduced iron powder): pulverized coal (steam coal) 263 kg/1 pig iron reduced iron powder (reduction rate 97%): 25 kP/, - pig iron Si% inside: 0.29% For the above injection, only pulverized coal was 40 to 80 kVt-
In the case of pig iron injection, the Si% in the pig iron is 0.4 to 0.6.
%, the effect of the present invention is clear as described above.

The effects of the present invention can be summarized as follows.

1) S of pig iron can be improved without changing other operating conditions of the blast furnace.
i% can be lowered.

2) Pulverized coal can be blown using pulverized coal injection equipment.

3) Since it is blown in through the tuyeres, it is effective immediately.

4) It is easy to adjust the amount of additives charged and to start and stop blowing.

5) Since it is mixed with pulverized coal and blown in, there is less wear on the transport pipe compared to transporting additives alone.

6) Pulverized coal mixed with additives is better in terms of explosion protection than pulverized coal alone.

As described in detail above, according to the present invention, FeO is dropped into the lower part of the blast furnace to reduce the Si content in pig iron and to control the Si level in the pig iron, regardless of the heat flow ratio of the blast furnace. I can do it.

[Brief explanation of the drawing]

The drawings relate to equipment attached to a blast furnace for injecting pulverized coal and additive substances into the blast furnace for carrying out the method of the present invention, and the drawings show equipment for injecting pulverized coal and additive substances into the blast furnace. This shows the system. 1... Blast furnace, 2... Air blowing annular pipe, 3.
...Blow tuyere, 4...Raw material hopper, 5
...Intermediate tank, 6...Pressure tank,
7... Raw material hopper 8... Intermediate tank, 9... Pressure feeding tank, 10... Transport pipe, 11... Blowing nozzle.

Claims (1)

[Claims] 1. A blast furnace operation method for injection of pulverized coal is characterized by injecting iron oxide or reduced iron together with pulverized coal into the blast furnace from the blast tuyeres, thereby reducing the Si content in the pig iron being tapped. , a method for operating a blast furnace with low Si in pulverized coal injection.