JP6260751B2 - Raw material charging method to blast furnace - Google Patents

Description

  The present invention relates to a method of charging a raw material into a blast furnace in which the charging of the raw material is performed with a turning chute.

In recent years, CO ₂ emission reduction has been demanded from the viewpoint of preventing global warming. In the steel industry, about 70% of CO ₂ emissions is due to blast furnace, the reduction of CO ₂ emissions in the blast furnace is required.

  In a blast furnace, generally, ore raw materials such as sintered ore, pellets, and massive ore and coke are alternately charged in layers from the top of the furnace, and combustion gas flows from the tuyere to obtain pig iron. The coke and ore raw material, which are the charged raw materials for the blast furnace, descend from the top of the furnace to the blast furnace abdomen, and ore reduction and raw material temperature rise occur. The ore raw material layer (hereinafter also simply referred to as the ore layer) is gradually deformed while filling the gap between the ore raw materials due to the temperature rise and the load from above, and the ventilation resistance is very high in the blast furnace belly. A so-called fusion layer is formed in which a large amount of gas hardly flows.

In general, reduction of CO ₂ emissions in a blast furnace can be realized by reducing reducing materials (coke, pulverized coal, natural gas, etc.) used in the blast furnace.
However, when reducing the reducing material, particularly coke, the thickness of the coke layer is reduced, and the airflow resistance is increased in the fusion zone where the ore is softened and melted. It has been empirically known that the ventilation resistance of the cohesive zone greatly affects the air permeability of the entire blast furnace, and that the stable operation of the blast furnace is hindered when the ventilation resistance of the cohesive zone increases.

Therefore, various measures for improving the ventilation resistance of the cohesive zone have been studied. In order to improve the ventilation resistance of the cohesive zone, it has been known that mixing coke with the ore layer is effective, and many inventions for mixing coke with the ore layer have been reported. ing.
For example, in Patent Document 1, in a bell-less blast furnace, coke is charged into a downstream hopper among ore hoppers, and coke is deposited on the ore on a conveyor, and then these are charged into a furnace top bunker. Thus, a technique for charging ore and coke into a blast furnace through a turning chute is disclosed.

  Further, Patent Document 2 discloses that coke and ore are mixed and charged simultaneously in a bunker at the top of the furnace, and coke and ore are mixed and charged at the same time. A technique for simultaneously charging three charging batches is disclosed.

  Furthermore, in Patent Document 3, as a raw material charging method in a blast furnace, instability of a cohesive zone shape in blast furnace operation and a decrease in gas utilization rate in the vicinity of the center are prevented, and stable operation and improvement of thermal efficiency are aimed at. Discloses a technique in which all ore and all coke are thoroughly mixed and then charged into a blast furnace as a raw material.

  Further, in Patent Document 4, as a means for enjoying the effect of improving the reactivity by mixed coke, high reactive coke and ore having low JIS reducing ability are mixed to react low reactive ore with high efficiency, A technique for improving the reactivity is disclosed.

JP-A-3-211210 JP 2004-107794 A JP-A-53-152800 JP-A-7-76366

  Here, in general, inside the blast furnace, gas tends to flow in both the radial center of the furnace port and its peripheral part, while the middle part on the furnace wall side often has difficulty in flowing gas. There is a gas flow distribution in the radial direction. Therefore, it is necessary to design the arrangement of the coke mixing ratio and mixed coke properties in the radial direction according to the gas flow distribution.

  However, Patent Documents 1 to 3 only describe means for mixing coke into the ore layer, and no suitable coke mixing rate distribution in the blast furnace radial direction is disclosed.

  Further, Patent Document 4 only describes the reactivity of coke and ore and the maximum particle size thereof, and neither the preferred mixing ratio of coke and ore nor the preferred distribution in the furnace caliber direction is disclosed. .

Furthermore, recently, the use of acidic pellets has increased due to an increase in demand for raw materials, but the use of acidic pellets is accompanied by a decrease in air permeability as the ratio of the reducing agent increases.
Therefore, in order to further improve the airflow resistance of the cohesive zone when using acidic pellets, it is necessary to newly construct a suitable mixed coke distribution in the furnace.

  The present invention has been developed to solve the above-described problems. Generally, since the gas flow is large in the central portion and the peripheral portion in the furnace caliber direction, and there are few intermediate portions, the gas flow is focused on. The presence of a large amount of coke having a good reactivity and a relatively small particle size in the middle part in the furnace caliber direction with a small amount makes it possible to improve the in-reactor reactivity and further reduce the reducing material ratio. The purpose is to provide a raw material charging method.

That is, the gist configuration of the present invention is as follows.
1. A raw material charging method into a blast furnace, in which ore raw materials and coke are charged into a blast furnace using a turning chute for each charge,
Of the total amount of coke in one charge, 25 to 80% by mass of coke is charged into a blast furnace to form a coke layer, then the remaining coke in the one charge and 10 ore raw materials in the one charge. When the mixed raw material mixed with the ore raw material containing acid pellets at a mass% or more is divided into two batches and charged onto the coke layer, the coke mixed in the first batch has a particle size in the range of 15 to 40 mm. The first batch is charged in the range of the furnace port dimensionless radius 0-0.8, and the remaining mixed raw material is charged in the range of the furnace port dimensionless radius 0.6-1.0 as the second batch. Raw material charging method to blast furnace.

2. 2. The raw material charging method to the blast furnace according to 1 above, wherein the reactivity index CRI of coke mixed in the first batch is 35% or more.

3. 3. The raw material charging method to the blast furnace according to 1 and 2 above, wherein the amount of coke mixed in the first batch is 70% by mass or more of the amount of coke mixed with the ore raw material.

  According to the present invention, a large amount of coke having good reactivity and low particle size is mixed in a portion where the gas flow is small, so that the in-furnace reactivity is improved and the reduction ratio of the reducing material is further reduced. Realize.

It is a figure which shows gas flow velocity distribution in a blast furnace. It is a figure which shows the raw material deposition condition to a blast furnace.

Hereinafter, the present invention will be specifically described.
In the present invention, as raw materials charged into the blast furnace, ore raw materials and coke are charged into the blast furnace using a turning chute every charge. As the ore material, acidic pellets are used in addition to sintered ore and / or massive ore.
Here, one charge in the present invention refers to a series of flows in which a coke is charged to form a coke layer, and then a mixed raw material mixed with ore raw material and coke is charged to form a mixed layer once. Means to do.

  Here, the raw material charging into the blast furnace can be performed by using a bellless charging device equipped with a publicly known turning chute.

The ore raw material and coke are respectively stored in the furnace top bunker. And the raw material charging order from these furnace top bunkers is as follows.
First, charge coke.
That is, when the raw material charging destination of the swirl chute is moved from the center of the blast furnace toward the inner peripheral portion of the blast furnace wall, only the coke is charged from the furnace top bunker storing only the coke. Form.
At that time, a central coke layer is formed in the central part of the blast furnace, or the central axis part (furnace port dimensionless radius: 0) from the furnace wall part (furnace port dimensionless radius: 1.0) to the inner peripheral part of the furnace wall. ), The peripheral coke layer may be formed with a furnace port dimensionless radius: 0.6 to 1.0.

  The amount of coke charged here is set to 25 to 80% by mass of the total amount of coke in one charge. That is, in order to ensure the air permeability of the coke layer, it is necessary to use coke of at least 25% by mass of the total coke amount in one charge as the coke layer. On the other hand, in order to obtain the effect of improving the air permeability and the reducibility by mixing the coke by setting the amount of coke in one charge mixed with ore raw material to be charged to 20% by mass or more, the coke layer is set to 80%. It is necessary to make the mass% or less.

  Next, the coke and the ore raw material are simultaneously cut out from the furnace bunker, and the mixed raw material of the coke and the ore raw material is charged into the blast furnace through a turning chute. At that time, the swivel chute is moved from the center axis of the blast furnace to the outer periphery of the furnace wall (furnace) from the position close to the center axis of the blast furnace, that is, from the position where the dimensionless radius of the furnace port is 0 to the outside. Mouth dimensionless radius: 1.0) The mixed raw material is charged to the side.

The ore raw material charged into the blast furnace is made into one pellet ore raw material, that is, 10% by mass or more of the total weight of the ore raw material in the one charge (hereinafter referred to as all ore) as acidic pellets.
This is because when the use ratio of acidic pellets is 10% by mass or more of the total ore, an increase in the reducing material ratio and a deterioration in air permeability become remarkable, but the reducing material is applied by applying the raw material charging method of the present invention. This is because the increase in the ratio and the deterioration of the air permeability are suppressed and further improvement can be achieved. In addition, it is preferable that the upper limit of the usage rate of acidic pellets is about 50% by mass of the total ore from the viewpoint of preventing significant deterioration of blast furnace operation. Further, the acidic pellets in the present invention, basicity, expressed by the ratio of the CaO and SiO ₂ contained in the pellets is that the pellets of 0.5 or less iron oxide.

  In the present invention, the ore raw material includes a predetermined amount of acidic pellets as described above, and may include at least one of sintered ore and massive ore.

And it is important that the remaining coke of the coke charged with the above-mentioned coke alone, that is, 20 to 75% by mass of the total amount of coke in one charge is mixed and charged with the ore raw material.
This is because, by setting the amount of coke in one charge to be mixed and charged with the ore raw material to 20% by mass or more, it is possible to obtain an improvement effect of air permeability and reduction by mixing the coke. On the other hand, in order to maintain the air permeability of the blast furnace, the formation of a coke (single) layer is also important. When the mixed coke is 75 mass% or more, that is, the coke layer is less than 25 mass%, it is difficult to maintain the airflow. .

  Here, FIG. 1 shows a gas flow distribution in a general blast furnace. As shown in the figure, the area where the furnace port dimensionless radius is less than 0.4, and the area where 0.8 or more is filled are filled with coke as a spacer, so that gas flows easily. In the region of 0.4 or more and less than 0.8, the coke is low, but a large amount of ore layer is charged and the gas does not flow easily, so it is understood that the reduction reaction may be delayed compared to other regions. .

  Therefore, in the present invention, in order to eliminate the delay of the reduction reaction in the region where the furnace port dimensionless radius is 0.4 or more and less than 0.8, a mixed raw material obtained by mixing coke and ore raw material is 1 Divide into 2 batches per charge and charge into blast furnace. Hereinafter, a procedure for charging the mixed raw material into the blast furnace will be described in detail.

In FIG. 2, the raw material deposition condition to the blast furnace in this invention is shown.
In the present invention, when charging the mixed raw material of the ore raw material and coke in two batches per charge, the first batch is charged in the range of 0.0 to 0.8 of the dimensionless radius of the furnace port, Furthermore, the second batch is charged in the range of 0.6 to 1.0 of the furnace port dimensionless radius.
In the present invention, the most important control factor is to set the coke mixed in the first batch to a particle size in the range of 15 to 40 mm. This is because when the coke having a particle size of 15 to 40 mm is segregated in the first batch, the reactivity in the reaction delay region can be improved. That is, when the particle size of the coke mixed in the first batch is less than 15 mm, the particle size becomes too small and the ventilation of the blast furnace deteriorates. On the other hand, if the particle diameter exceeds 40 mm, the particle diameter becomes too large, the reactivity is lowered, and it is difficult to enjoy the improvement in reducing property.

The first batch of coke does not have to have a total particle size in the range of 15 to 40 mm. Even if coke that does not have a particle size in the range of 15 to 40 mm is mixed, If it is about 5% by mass or less of the total amount of coke, the present invention is not affected.
On the other hand, the particle size of the second batch of coke does not need to be particularly limited, but the same particle size as that of the first batch of coke, for example, in the range of 15 to 50 mm can be used.

Further, as shown in FIG. 2, by charging the mixed raw material according to the present invention, a portion where two mixed layers formed of the mixed raw material exist is formed on the coke layer. Specifically, the first batch is charged into the region of 0.0 to 0.8 in the dimensionless radius of the furnace port to form the first mixed layer, and the second batch is set to a dimension of 0.6 or more in the dimensionless radius of the furnace port. The region is charged as a second mixed layer. As described above, it is important that the second batch is charged in the vicinity of the furnace wall where gas is likely to flow.
As shown in FIG. 1, the portion of the blast furnace with a dimensionless radius of less than 0.4 and more than 0.8 has a large amount of coke and good air permeability. In this gas flow, the charging positions of the mixed raw material in the first batch and the second batch are overlapped as described above because the charging start of the second batch is caused by the deposition angle of the mixed raw material. Since the layer thickness tends to be thin, in order to form the thickened portion in the region near the dimensionless radius 0.8 of the furnace port, it is necessary to repeatedly charge the mixed raw material at a level of 0.6 to 0.8. Because.

  Further, it is preferable to set the reactivity index CRI of the coke mixed in the first batch to 35% or more because the reactivity in the furnace can be further improved and the blast furnace operation can be performed more stably. Although there is no particular limitation on the upper limit of the reactivity index CRI, it is about 40% industrially.

  Furthermore, by reducing the amount of coke mixed in the first batch to 70% by mass or more of the amount of coke mixed with the ore raw material, the reducibility of the first batch charged in the portion where the ore raw material is large is achieved. Can be improved. In addition, the whole amount of coke mixed with the ore raw material can be mixed in the first batch, and in this case, the second batch becomes the entire amount of the ore raw material.

In the example, using a turning chute, the raw material was charged every charge. The amount of coke mixed with the ore raw material in coke during one charge was 10 to 80% by mass of the total amount of coke, and the remaining coke was provided to the coke layer. Moreover, the mixed raw material was changed to two batches per charge, and the charging positions of the mixed raw material in the first and second batches were variously changed. The particle size of the coke mixed in the first batch was also changed variously. The coke reactivity index CRI was set to 30-35%. Specific test conditions are shown in Table 1.
Here, the raw materials used in the examples include those containing 58% by mass of iron as a raw material for ores (sintered ore and / or massive ore), 65% by mass of iron as acidic pellets, and CaO. A SiO ₂ ratio of CaO / SiO ₂ = 0.05 was used, and a coke containing 88% by mass of carbon was used.
The output ratio is a value obtained by dividing the daily output (t / d) of the blast furnace by the furnace volume (m ³ ). The reducing material ratio, the coke ratio, and the pulverized coal ratio are the amount of reducing material, the amount of coke, and the amount of pulverized coal (kg / t) used when producing the hot metal 1t.
The average particle diameter (mm) of the mixed coke mixed with the ore raw material is the arithmetic average diameter, and the CRI (%) of the mixed coke is 1100 ° C. when the coke is reacted for 2 hours in a CO ₂ atmosphere. Each was determined by the weight loss rate.

Furthermore, the gas utilization rate and packed bed pressure loss under the above blast furnace raw material charging conditions were evaluated by the following procedure. The evaluation results are also shown in Table 1.
[Gas utilization rate]
It is defined as CO ₂ / (CO ₂ + CO) × 100. The CO ₂ and CO concentration (% by volume) used in this equation were measured using a device called a horizontal sonde that measures the operational gas distribution from the center to the periphery in the blast furnace.
[Filled bed pressure loss]
The total pressure loss of the blast furnace is divided by the air flow rate, and the pressure loss of the raw material packed bed (packed bed pressure loss) can be obtained by the following equation. Therefore, the packed bed pressure loss can be considered as an index representing the ventilation resistance required for the unit air volume to flow.
Packed bed pressure loss (ΔP / V) = total pressure loss (kPa) / air flow rate (Nm ³ / min)

From Table 1, when comparing the inventive example and the comparative example, all of the inventive examples are excellent in the packed bed pressure loss, and the reducing material ratio, the ventilation resistance index (filled bed pressure loss) and the gas utilization rate are improved. Recognize.
From the above, it is possible to improve the reactivity in the blast furnace by mixing a large amount of coke with an appropriate particle size with good reactivity at an appropriate position in a place where the gas flow in the blast furnace is small. It was confirmed.

Claims (3)

A raw material charging method into a blast furnace, in which ore raw materials and coke are charged into a blast furnace using a turning chute for each charge,
Of the total amount of coke in one charge, 25 to 80% by mass of coke is charged into a blast furnace to form a coke layer, then the remaining coke in the one charge and 10 ore raw materials in the one charge. When the mixed raw material mixed with ore raw material whose mass% or more is an acidic pellet is divided into two batches and charged onto the coke layer, the coke mixed in the first batch has a particle size in the range of 15 to 40 mm. The first batch is charged in the range of the furnace port dimensionless radius 0-0.8, and the remaining mixed raw material is charged in the range of the furnace port dimensionless radius 0.6-1.0 as the second batch. Raw material charging method to blast furnace.   The method for charging raw materials into a blast furnace according to claim 1, wherein the reactivity index CRI of coke mixed in the first batch is 35% or more.   The raw material charging method to the blast furnace according to claim 1 or 2, wherein the amount of coke mixed in the first batch is 70% by mass or more of the amount of coke mixed with the ore raw material.

Images