JPH0798969B2 - Smelting reduction method for iron ore - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for improving the yield of coal charged as a fuel in the smelting reduction of iron ore.

[Prior Art] In iron smelting reduction using a converter-type smelting reduction furnace, as a method of charging raw materials such as iron ore and coal into the furnace, a so-called top-down method of dropping the raw materials by gravity from the upper part of the furnace There is an injection method in which raw materials are blown into a molten metal through a nozzle.

Of these, the injection method has the advantage of reacting with good yield because the raw materials are blown directly into the molten metal.
It has the following drawbacks.

 The raw material needs to be crushed and the manufacturing cost is high.

Especially for carbonaceous materials, there is a danger of coal dust explosion, and explosion-proof measures are necessary. Therefore, the equipment cost is high.

The raw material supply equipment is easily worn and the equipment cost increases.

On the other hand, the superposition method does not require the pretreatment of the raw material and there is no problem in terms of equipment such as the injection method.

[Problems to be Solved by the Invention]

However, in this superposition method, raw materials, particularly fine particles of coal, which is a fuel, are scattered outside the furnace together with the gas discharged from the inside of the furnace, so that the yield of the carbonaceous material is very poor.

[Means for Solving the Problems]

In view of such problems, the inventors of the present invention have made repeated studies for the purpose of improving the yield of coal, and as a result, have found the following facts.

The poor yield of coal in the top-up method is due to thermal cracking of coal due to rapid heat rise. Coal is steam coal and has a volatile content of about 30%, but since the temperature inside the smelting reduction furnace is extremely high (1400 ° C or higher), the top-loaded coal rapidly heats up, Along with this, volatile components are rapidly gasified and thermal cracking occurs. Then, some of the fine particles generated by the thermal cracking are discharged outside the furnace together with the exhaust gas.

The particle size distribution after thermal cracking of coal is almost constant regardless of the particle size distribution before thermal cracking. Therefore, since the limit particle size of coal scattering is determined by the gas rising speed in the furnace, it is possible to effectively suppress the scattering of fine coal particles by suppressing the gas flow velocity in the furnace to a certain value or less.

It is most effective to control the gas flow velocity in the furnace by providing a damper in the exhaust gas duct of the furnace and adjusting the pressure in the furnace by the opening degree of the damper.

The present invention has been made on the basis of such findings, using a converter-type smelting reduction furnace, iron ore carried out by placing a part or all of the coal, which is carbonaceous material, through a chute at the top of the furnace. The basic characteristic of the smelting reduction method is that the operation is performed while controlling the gas flow rate in the furnace by adjusting the opening degree of a damper provided in the exhaust gas duct of the furnace.

Hereinafter, the details of the present invention will be described.

As described above, the yield of coal deteriorates in the top-up method because the coal causes thermal cracking due to rapid gasification of its volatile matter (VM). Figure 1 shows coal (steam coal)
The following shows an example of the particle size distribution before heat cracking and the particle size distribution after heat cracking. The particle size distribution after heat cracking is almost constant regardless of the particle size distribution after heat cracking if the volatile content is the same. .

On the other hand, the factor that regulates the amount of coal scattered is the flow velocity of the throat gas. FIG. 2 shows the relationship between the gas velocity at the furnace port and the particle size of the scattering limit. As can be seen from the figure, since iron ore has a larger true specific gravity than coal, it does not pose a big problem in terms of scattering.

From the viewpoint of manufacturing cost, it is preferable to keep the amount of coal scattered to 10% or less. In the case of Fig. 1, the amount of scattered coal is 10%.
In order to suppress this, it is necessary to set the dispersed particle size to 0.75 mm or less, and to secure this, it is necessary to set the gas flow velocity to 3 m / sec or less from FIG. Here, the volatile content of normally used coal is about 30% as shown in Fig. 1 and the upper limit is almost the same. Therefore, by setting the gas flow velocity to 3 m / sec or less, the amount of scattering is 10% or less regardless of the type of coal. Can be suppressed to

In the present invention, the control of the in-furnace gas flow velocity is performed by adjusting the in-reactor pressure by adjusting the opening degree of the damper provided in the exhaust gas duct of the furnace.

The furnace port gas flow rate U is expressed by the following equation (1).

However, V: Exhaust gas amount (Nm ³ / sec) A: Furnace cross-sectional area (m ² ) Tg: Gas temperature (° C) P: Furnace pressure (kg / cm ² · g) According to the formula (1), Factors V, A, Tg, and P are involved in the decrease in U.

However, of these, a decrease in V causes a decrease in productivity, resulting in an increase in equipment load such as an increase in the size of equipment and a plurality of equipment. Further, an increase in A also leads to an increase in the size of equipment. Tg is a value that changes depending on operating conditions, and it is extremely difficult to maintain that value at a low level.

On the other hand, P can be arbitrarily changed by installing a damper on the exhaust gas outlet side and adjusting the opening thereof, and the gas flow velocity can be easily controlled by the adjustment.

FIGS. 3 (a) and 3 (b) show an example of equipment provided with the above-mentioned damper. 1 is a furnace body, 2 and 2'are charging chutes,
3 is a top blowing lance, 4 is a cyclone, 5 is an exhaust duct, 6
Is a preliminary reduction furnace, and a damper 7 is provided in the middle of the exhaust duct 5.

The gas flow velocity control by adjusting the opening degree of the damper 7 is as follows.
For example, it can be executed based on the measured value of the gas flow velocity in the furnace or the measured value of the dust collected by the cyclone. 4 and 5 are control flowcharts thereof. Of these, FIG. 4 is an example of control based on measurement of the gas flow velocity in the furnace. In this case, the amount of scattering is determined from the particle size distribution (corresponding to FIG. 1) of the coal used after thermal cracking. The upper limit gas flow rate Um for making it 10% or less is calculated in advance, the operating exhaust gas amount V, the gas temperature Tg, and the furnace pressure P are measured, and the furnace port gas flow rate U is calculated based on the above equation (1). To do. Then, comparing this with the upper limit gas flow velocity Um, U is Um
If it exceeds, a command for operating the damper 7 in the closing direction by a predetermined amount is issued. By adjusting the opening of this damper, the above (1)
In-furnace pressure P increases and the furnace port gas flow velocity decreases.

Further, FIG. 5 is an example of control based on the measured value of dust collected by the cyclone. In this case, the weight increase amount of the cyclone (= the amount of captured dust) is measured and calculated by a load cell or the like, and this value is calculated. The scattering rate S of coal is calculated from Then, the scattering rate S is compared with the set value S _0, and when S exceeds S ₀ , a command for operating the damper 7 in the closing direction by a predetermined amount is issued.

〔Example〕

In the equipment shown in FIG. 3 (a), the present invention was carried out by controlling the furnace port gas flow velocity as shown in FIG. As a comparative example, operation was performed under the same manufacturing conditions as in the present invention using equipment without a damper. Table 1 shows the coal scattering rate in each of these cases.

As is clear from the table, in the comparative example in which the gas flow rate control is not performed, the coal scattering rate reaches 30%,
In the example of the present invention in which the gas flow rate was controlled to 3.0 m / sec by adjusting the damper opening, the coal scattering rate was suppressed to 8%, and the carbon material consumption rate was greatly improved.

[Brief description of drawings]

FIG. 1 shows an example of a particle size distribution of coal charged into a smelting reduction furnace before thermal cracking and a particle size distribution after thermal cracking. FIG. 2 shows the relationship between the rising rate of gas in the furnace and the limit particle size of coal and iron ore scattering. 3 (a) and (b) are
It is explanatory drawing which shows the example of equipment which should be each used for implementation of this invention. FIG. 4 and FIG. 5 are flowcharts of control examples of gas flow velocity in the present invention.

Claims (2)

[Claims] 1. A smelting reduction method for iron ore, which is carried out by using a converter-type smelting reduction furnace and placing a part or all of coal, which is a carbonaceous material, through a chute at the top of the furnace. A smelting reduction method for iron ore, which is characterized in that the operation is performed while controlling the gas flow rate in the furnace by adjusting the opening degree of a damper provided. 2. The method for smelting reduction of iron ore according to claim 1, wherein the opening degree of the damper is adjusted so that the gas velocity at the furnace opening is 3 m / sec or less.