JPS597327B2 - Low-Si operation method for blast furnace by mixed injection of pulverized coal and basic substance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a blast furnace operating method for reducing both the Si content and the S content in pig iron to be tapped, in a blast furnace operating method in which pulverized coal is blown into the furnace from a blowing tuyere. It is related to.

In addition to coke, heavy oil and coal are also used as fuel for producing pig iron from pig ore in blast furnaces.

In conventional blast furnace operating methods, in order to reduce the consumption of expensive coke (coke ratio), a method was adopted in which cheap heavy oil or tar was injected through the blast tuyeres.

However, due to the recent rise in oil prices, the prices of coke and heavy oil have reversed, leading to low-heavy-oil ratio operations that use less heavy oil, oil-less operations that do not use heavy oil, and all-coke operations. 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.

Under these circumstances, the method of injecting pulverized coal from the air blower causes the H2% in the furnace gas to rise due to the hydrogen content in the coal, increasing the 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 coal is Si02+C-+SiO+CO (1)
This reaction 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 as there is a growing need to stabilize the

Impurities such as Si, Mn, and S contained in the blast furnace charge undergo various reactions within the furnace, and are eventually distributed into 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 sump via SiO 2 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.

In addition, increasing the heat flow ratio reduces the furnace heat, which can easily cause operational troubles.

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

The present invention is a blast furnace operation method for injecting pulverized coal, in which limestone, dolomite, or their calcined products, or basic substances such as calcium and magnesium hydroxides are blown into the blast furnace through the blast tuyeres. , the gist of which is a method for operating a blast furnace with low Si levels by injecting a mixture of pulverized coal and basic substances, which is characterized by simultaneously reducing the Si content and S content in the pig iron being tapped. be.

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

The drawings relate to the injection equipment for pulverized coal and basic substances attached to a blast furnace in order to carry out the method of the present invention, and show the equipment for introducing pulverized coal and basic substances into the tuyeres. This shows each supply system.

A charge mainly consisting of iron ore and coke 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 to be combusted with 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 content suitable for gas transportation, and feeding it from a raw material pumper 4 to an intermediate tank 5, a pressure tank 6 to a transport pipe 10, and a blower using air or various gases as a carrier gas. The air is blown into the furnace through a blow nozzle 11 provided at the port 3.

Basic substances such as limestone and dolomite are crushed to the same level as pulverized coal and sent to the transport pipe 10 via the hopper 7, intermediate tank 8, and pressure tank 9, where they are mixed with the pulverized coal and sent to the blowing nozzle. 11 into the furnace.

The basic substance should be mixed with pulverized coal in advance and then passed through the homper 4.
, intermediate tank 5, and pressure tank 6, but since the additive substance has a higher density than coal, it is likely to cause classification in the hopper or 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 raw material hoppers 4, 7 and the high pressure pressure feeding tanks 6, 9, respectively.

The pressure tanks 6 and 9 are so-called injection tanks for powder, and have the function of quantitatively feeding powder into the transport pipe 10.

When controlling the Si% of pig iron by changing the amount of added substances 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.

Next, we will discuss the effects of basic substances such as limestone, dolomite, their calcined products, and hydroxides that are blown into the blast furnace.

The fired products include Cab and MgO, and the hydroxides include Ca(OH)2 and Mg(OH)2.

In the case of limestone and dolomite, they are heated and decomposed in the high temperature zone at the tip of the tuyere, resulting in CaC03=CaO+CO2 (2)
002 is released in the form MgC03=MgO+CO2 (3).

In the case of Ca and Mg hydroxides, they are heated and decomposed to form Ca (OH) 2=CaO+H20 (4
)Mg(OK)2=MgO+H20 (5)
H20 is released in the reaction.

? Cab and MgO produced by formulas 2) to (5) or injected as a fired product react with FeO and SiO and melt in the high temperature zone at the tip of the tuyere.

Cab and MgO are basic substances, and as the basicity of slag increases, the activity of SiO2 in the slag decreases and the generation of SiO is suppressed, so the Si% in pig iron decreases.

The CO generated in equations (2) and (3) reacts with coke to cause an endothermic reaction known as the Boudouard reaction, reducing the tuyere tip temperature somewhat, and the CO generated in equations (4) and (5). H20 increases the H2% in the furnace gas in the form C+H2O=CO+H22.

For this reason, the utilization rate of the furnace top gas increases, the coke ratio decreases, and the heat flow ratio increases, which indirectly reduces the Si content in the pig iron.

Furthermore, it is well known that S in hot metal is desulfurized by the following process: Ca++orMg+++S→CaS orMgS.

In the present invention, the hot metal that descends to the hearth is effectively desulfurized by basic substances such as limestone and dolomite that are blown into the tuyere.

That is, the basic substance according to the present invention is Si in pig iron.
It is possible to reduce not only %, but also S%.

Furthermore, since the basic substance is blown in through the blast tuyeres, it is more effective and more controllable than charging from the top of the furnace.

As additive substances, each can be used alone, but depending on the situation, they can also be used as a mixture as appropriate.

Normal pulverized coal injection amount is 30-150k per ton of pig iron.
The injection amount of the additive substance is about 5 to 5 g.
Approximately 0 kg is sufficient.

Since the ratio of additives to pulverized coal is small, there is less wear on the transport pipes than with additives alone.

Therefore, as the blowing equipment, it is only necessary to modify a part of the existing pulverized coal blowing equipment, and thereby the pulverized coal and the additive can be blown together.

When an injection test was conducted using the method of the present invention in an example blast furnace, it was found that the following Si content and Pig iron with S content was produced.

(1) In the case of (pulverized coal and limestone) Pulverized coal (steam coal): 55 kg/t single pig iron limestone: 39 kg/t single pig iron Si% in pig iron: O, 39 S%: 0.033 (2) (fine powder In the case of charcoal + calcined dolomite) Pulverized coal (steam coal): 60kg/t ~ Pig iron calcined dolomite: 34k
Si% in g/t pig iron: 0.37 S%: 0.026 (3) (pulverized coal + slaked lime) pulverized coal (steam coal) 253 kg/t pig iron slaked lime (Ca(OH)2 ): 29 kg/t single pig iron Si% in pig iron: 0.45 S%: 0.038 For the above injection, only pulverized coal is 40 to 80 kg/t
In the case of single pig iron injection, the Si% in the pig iron is 0.5 to 0.
7%, and the same <<S% was 0.04 to 0.08%, so the effect of the present invention is clear.

As described in detail above, according to the method of the present invention,
SiO
By suppressing the occurrence of , the Si% in the pig iron can be reduced, and at the same time, the S% in the pig iron can be reduced by the desulfurization effect.

[Brief explanation of the drawing]

The drawings relate to the blowing equipment for pulverized coal and basic substances attached to a blast furnace for carrying out the method of the present invention. This shows each supply system. 1... Blast furnace, 2... Air blowing annular pipe, 3.
...Air blower, 4...Pulverized coal hopper,
5...Intermediate tank, 6...Pressure tank, 7...Basic hopper, 8...Intermediate tank, 9...Pressure tank , 10...
Transport pipe, 11...Blow nozzle.

Claims (1)

[Claims] 1. In the blast furnace operation method for injecting pulverized coal, limestone, dolomite, or their calcined products, or basic substances such as calcium and magnesium hydroxides are injected into the blast furnace through the blast tuyeres, and this 1. A method for operating a blast furnace with low Si by injecting a mixture of pulverized coal and a basic substance, characterized by simultaneously reducing the Si content and S content in pig iron that is tapped.