JP6834719B2 - Blast furnace operation method - Google Patents

Description

The present invention relates to a method for operating a blast furnace.

The coke used for the operation of the blast furnace includes coke via the yard, which is transported to the blast furnace via the yard, and direct coke, which is transported from the coke manufacturing process to the blast furnace using a belt conveyor or the like.

Of these, coke via the yard is used as coke for steelmaking after being temporarily stored in the yard.
One of the reasons why the coke produced in the coke manufacturing process is routed through the yard is that the coke production capacity of the steelworks is smaller than the amount of coke required for the blast furnace, and coke may be purchased from the outside. In this case, the coke unloaded from the transport ship is temporarily stored in the yard, so that it goes through the yard.
Another reason is that coke may be stored in the yard when the blast furnace is closed for maintenance.

Since the yard is an open-air storage place, rainwater penetrates into the coke when it rains, and the average moisture value of the coke rises.

Therefore, coke via the yard has a higher water content than direct coke, and when it is charged into a blast furnace, the temperature may drop.

Since the water content of the coke via the yard depends on the weather around the yard, the coke via the yard is more likely to have a variation in the water content than the direct coke.

In coke via a yard with a large amount of water, the powder raw material adheres to the particles of the raw material due to the water content, so that the powder raw material may not be removed even if classification is performed by a sieve or the like. Since the powder raw material containing water easily adheres to the mesh of the sieve, it causes clogging of the sieve, and there is also a problem that it becomes difficult to sieve the raw material.

As described above, coke via the yard has a problem in terms of moisture as compared with direct coke.

Therefore, the water content is removed by drying the coke via the yard before transporting it to the blast furnace (Patent Document 1).

Japanese Unexamined Patent Publication No. 2010-096491

However, when the coke via the yard is dried as in Patent Document 1, there is a problem that equipment necessary for drying is required and the equipment cost is high.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for operating a blast furnace in which the equipment cost does not increase even when coke via a yard is used.

The blast furnace operating method according to the present invention is a blast furnace operating method using coke via a yard, in which coke via a yard is indispensable, and a central coke that selectively includes direct coke is charged into the center of the blast. It consists of a mass coke charging process in which the charging process and the mass coke consisting of coke via the yard are charged between the central coke and the furnace wall in the furnace radial direction, and coke via the yard, and the grain size is higher than that of the mass coke. An ore layer in which a small coke mixed with small coke, which is also a small coke, is charged is carried out on the central coke and the coke, and the central coke charging step is usually performed on the central coke. It is characterized in that it is a step of charging coke via a yard on a sieve classified with a sieve larger than 8 mm and 12 mm or less with respect to the lower limit classification point of the direct-delivered coke used as.
Here, the coke via the yard means coke that is transported to the blast furnace via the yard, and the direct coke refers to coke that is transported from the coke manufacturing process to the blast furnace using a belt conveyor without passing through the yard. ..

According to the present invention, the porosity of the central coke is increased by increasing the sieving lower limit classification point of the central coke, which greatly affects the air permeability of the blast furnace. As a result, even when a large amount of coke via the yard is used, ventilation can be ensured without installing a new drying facility. By using only the central coke as the coke that increases the porosity, it is possible to minimize the deterioration of the yield due to the increase in the porosity.

In the present invention, in the central coke charging step, it is preferable that the coke via the yard to be charged is on a sieve having a lower sieving classification point of 53 mm or more and 57 mm or less.

According to the present invention, the porosity of the central coke is increased by increasing the sieving lower limit classification point of the central coke. As a result, even when 100% of coke via the yard is used, ventilation can be ensured without installing a new drying facility.

In the present invention, in the mass coke charging step, it is preferable that the mass coke to be charged is on a sieve having a lower sieving classification point of 43 mm or more and 47 mm or less.

According to the present invention, since the porosity of the coke breeze is set to the same level as when the direct coke is used, the deterioration of the yield due to the increase in the porosity of the central coke can be minimized.

In the present invention, in the ore layer charging step, the small coke to be charged has a lower sieving classification point under a sieve having a sieving lower limit of 43 mm or more and 47 mm or less. It is preferably on a sieve classified by a sieve of 13 mm or more and 17 mm or less.

According to the present invention, by using a lump coke classification sieve as a raw material for the small lump coke, deterioration of the yield due to the classification can be suppressed.

The figure for demonstrating the outline of the blast furnace operation method which concerns on this embodiment. The flow chart for demonstrating the blast furnace operation method which concerns on this embodiment. It is a figure which shows the particle size distribution after classification of the central coke, the coke mass coke, and the small coke coke used in an Example and a comparative example. The figure which shows the result of having calculated the relationship between the coke ratio through a yard of the central coke of an Example and a comparative example, and a porosity, using a Suzuki-Ichida model. The figure which shows the result of having calculated the relationship between the coke ratio through a yard of the central coke of an Example and a comparative example, and a pressure loss using the Elgan formula. The figure which shows the result of having calculated the gas flow index when the sieving lower limit classification point of a central coke and the composition are changed.

Hereinafter, embodiments suitable for the present invention will be described in detail with reference to the drawings.
First, before the description of the embodiment, the method of charging the raw material into the blast furnace will be briefly described.
As a method of charging raw materials into a blast furnace, generally, ore (O) and coke (C) are alternately charged in layers to make one charge (C, O1). Coke or ore is divided into two or more batches and charged as one charge (C1, C2, O1), (C1, O1, C2, O2), (C1, C2, O1, O2).

In the present embodiment, the description will be made on the premise of charging three batches of (C1, C2, O1), but the present invention can be applied to other batch charging as long as the method is to charge the central coke (C1). it can.

Next, the outline of the blast furnace operation method according to the present embodiment will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, in the blast furnace operation, the ore layer 13 and the coke layer 9 are alternately charged and laminated.

Specifically, first, the central coke 11 (C1) is charged near the center of the blast furnace (S1 in FIG. 2, the central coke charging process). The central coke 11 (C1) is charged in order to secure the central flow of the blast furnace.
Next, the massive coke 15 (C2) is charged between the central coke 11 and the furnace wall in the furnace radial direction (S2 in FIG. 2, the massive coke charging step).
Next, the ore layer 13 (O1) mixed with the small coke 17 is charged onto the central coke 11 and the coke 15 (S3 in FIG. 2, the ore layer charging step).

After that, the central coke 11 (C1) is charged, the coke 15 (C2) is charged, and the ore layer 13 (O1) is charged repeatedly.

As shown in FIG. 1, in the blast furnace operating method according to the present embodiment, the small coke 17 is mixed with the ore layer 13 (O1). The small coke 17 is mixed with the ore layer 13 (O1) in order to improve the air permeability of the ore layer 13 (O1) and the reducibility of the ore.

In the present embodiment, as the central coke 11, coke via the yard is indispensable, and coke that selectively includes direct coke is used. Coke via the yard is used as coke 15 and coke 17.

Coke via the yard means coke that is transported to the blast furnace via the yard.
Direct coke refers to coke that is transported from the coke manufacturing process to the blast furnace using a belt conveyor without going through the yard.

Further, in the present embodiment, in the central coke 11, the coke via the yard has a larger sieving lower limit classification point than the direct coke.
The reason why the central coke 11, the coke 15 and the small coke 17 have such a configuration is as follows.

In this embodiment, it is intended to operate a blast furnace in which the ratio of coke via the yard is increased to the utmost limit. Ideally, the operation is intended to have a 100% ratio of coke via the yard.
However, since the moisture content of coke via the yard varies more than that of direct-delivered coke, coke with a small particle size may adhere to the coke with a large particle size as so-called "blurring powder" and deteriorate the air permeability. is there.

Therefore, in blast furnace operation in which the ratio of coke via the yard is increased, it is necessary to secure the porosity of coke and stabilize the gas flow of the blast furnace.
For that purpose, it is conceivable to eliminate the coke having a small particle size of the central coke 11 (C1) and the massive coke 15 (C2) and increase the sieving lower limit classification point.

On the other hand, when the sieving classification point is increased, the amount of coke supplied to the central coke 11 (C1) and the coke 15 (C2) decreases. Since the amount of sieving is increased, the yield is also deteriorated.

Therefore, in order to secure the amount of coke supplied to the blast furnace and suppress the deterioration of yield while increasing the ratio of coke via the yard, coke 15 (C2) and coke 17 via the yard are used as coke via the yard and sieved. It was decided not to change the lower limit classification point. The central coke 11 (C1) has a large sieving lower limit classification point and is configured to include coke via the yard.
The above is the outline of the blast furnace operation method according to the present embodiment.

Next, preferable conditions of the central coke 11, the coke 15 and the coke 17 in the blast furnace operating method according to the present embodiment will be described.

<Central coke 11>
The central coke 11 is coke charged in the vicinity of the center of the blast furnace, requires coke via a yard, and selectively includes direct coke. Preferably only coke via the yard is used.
It is desirable that the central coke 11 is on a sieve in which the coke via the yard to be charged is 8 mm or more and 12 mm or less larger than the sifting lower limit classification point of the direct coke normally used as the central coke 11. The reason is to stabilize the gas flow in the blast furnace.
For example, when the sieving lower limit classification point of the direct-delivered coke is 45 mm, the sieving lower limit classification point of the coke via the yard is 53 mm or more and 57 mm or less.

<Mass coke 15>
The mass coke 15 is coke charged in the furnace radial direction between the ore layer 13 and the ore layer 13, and is composed of coke via a yard.
In the mass coke 15, the sieving lower limit classification point of the coke via the yard may be the same as the sieving lower limit classification point of the direct coke that is usually used as the mass coke 15. For example, it is 43 mm or more and 47 mm or less. By setting such a lower limit classification point, the porosity of the mass coke 15 becomes about the same as when the direct coke is used, so that the deterioration of the yield due to the increase in the porosity of the central coke 11 can be minimized.

<Small coke 17>
The small coke 17 is coke to be mixed with the ore layer 13, and is composed of coke via a yard. The small coke 17 is a coke having an average particle size smaller than that of the coke 15, and it is preferable to use the coke under the sieve when classifying the coke 15 as a raw material. As a result, deterioration of yield due to classification can be suppressed.
For example, when the sieving lower limit classification point of the coke 15 is 43 mm or more and 47 mm or less, the lower limit classification point is 43 mm or more and 47 mm or less under the sieve, and the sieving lower limit classification point is 13 mm or more and 17 mm or less. Use a sieve classified by a sieve.
In the small coke 17 the lower limit of sieving of coke via the yard is usually the same as the lower limit of sieving of direct coke used as the small coke 17.

The above are the preferable conditions for the central coke 11, the coke 15 and the coke 17 in the blast furnace operating method according to the present embodiment.

As described above, in the present embodiment, the central coke 11 includes the coke via the yard, and the lower limit classification point for sieving the coke via the yard in the central coke 11 is 8 mm or more with respect to the lower limit classification point for the direct coke. 12 mm or less larger.
Therefore, even when a large amount of coke via the yard is used, ventilation can be ensured without installing a new drying facility.
Further, in the present embodiment, by limiting the coke that increases the porosity to only the central coke 11, it is possible to minimize the deterioration of the yield due to the increase in the porosity.

Hereinafter, the present invention will be specifically described based on Examples. However, the present invention is not limited to Examples and Embodiments. Those skilled in the art will naturally come up with various modifications and improvements within the scope of the present invention, which are also included in the present invention.

First, the porosity and pressure loss when it was assumed that the central coke 11, the coke 15, and the coke 17 according to the present embodiment were charged into the blast furnace were calculated. The specific procedure is as follows.

<Porosity and pressure drop calculation>
As a method for calculating the porosity εc of the ore layer 13 in which fine-grained and coarse-grained sintered ore are mixed, there are Suzuki-Ichida models of the following formulas (1) to (4). The Suzuki-Ichida model is described in detail in Ichida et al., "Estimation of layer porosity and shape coefficient of sinter and coke", Iron and Steel, 1977 (1991), No. 10, p1561. .. The outline is as follows.

The porosity εj of a particle is a partial porosity ε (j, 1), ε (j, 2), ε (j, 3), ... ε (j, m) with a composite mixed fraction Sk. It is assumed that it is the sum of the multiplied items. The porosity εc of the entire layer is calculated by multiplying the individual porosity εj by the volume-based mixed fraction Svj. Here, 0.4 is used as the coefficient γ of the equation for obtaining the composite mixed fraction Sk. This is because, in the case of this Ichida model, γ = 0.4 gives the most accurate result.

In this example, the porosity was calculated by the following procedure using the formulas (1) to (4). First, the coke via the yard and the direct coke with the particle size distribution shown in Table 1 were prepared.

Next, the lower limit classification points for sieving the central coke 11 were set to 45 mm (before change) and 55 mm (after change), coke via the yard was sieved, and the top of the sieve was set as the central coke 11.
Only coke via the yard was used as the coke 15, and the lower limit classification point for sieving was set to 45 mm.
As the small coke 17, only coke via the yard was used, and the coke under the coke was further classified on the sieve having a lower sieve classification point of 15 mm.

The particle size distributions of the central coke 11, the coke 15 and the coke 17 after classification are shown in FIG. In the following description, before the change of the lower sieving classification point is described as "comparative example", and after the change of the lower sieving lower classification point is described as "example".
As shown in Table 2, the amounts (mass%) of the central coke 11, the coke 15 and the coke 17 after the classification were made equal before and after the change of the lower limit classification point for sieving.

Next, the ratio (mass%) of coke via the yard in the central coke 11 was changed, and the porosity of the central coke was calculated using the Suzuki-Ichida model. The results are shown in FIG. In the present invention, the central coke 11 requires coke via the yard. Therefore, the coke ratio via the yard in the example of FIG. 4 is not strictly the product of the present invention, but is included in the example for convenience (the same applies to FIG. 5).

As shown in FIG. 4, in both the examples and the comparative examples, the porosity decreased as the ratio of coke via the yard increased. The examples had a higher porosity than the comparative examples. The porosity when the coke ratio via the yard was set to 100% in the examples was about the same as the porosity when the coke ratio via the yard was set to 0% in the comparative example.

From this result, it was found that if the lower limit classification point for sieving of the central coke 11 is increased by about 10 mm, even if the coke ratio via the yard is 100%, the porosity is about the same as when the coke ratio via the yard is 0%. ..

Next, the porosity was substituted into the following Elgan equation (5) to calculate the pressure loss (ventilation resistance) of the central coke of Examples and Comparative Examples. The results are shown in FIG. The unit of the coke ratio via the yard in FIG. 5 is mass%.

As shown in FIG. 5, in both the examples and the comparative examples, the ventilation resistance increased as the ratio (mass%) of coke via the yard increased. The example had a smaller ventilation resistance than the comparative example. The ventilation resistance when the coke ratio via the yard was set to 100% in the examples was about the same as the ventilation resistance when the coke ratio via the yard was set to 0% in the comparative example.

From this result, it was found that if the sieving lower limit classification point of the central coke 11 is increased by about 10 mm, even if the coke ratio via the yard is 100%, the ventilation resistance becomes the same as when the coke ratio via the yard is 0%. ..

<Change in gas flow index>
Next, the relationship between the coke type and the lower limit classification point for sieving of the central coke 11 and the gas flow index was calculated. The gas flow index referred to here is a value indicating the ratio of the gas flow velocity at the furnace top when the blast furnace is divided into three regions.
First, as the central coke 11, three types shown in Table 3 were prepared. The coke 15 and coke 17 were set to 100% coke via the yard at the same lower limit classification point as in <Porosity and pressure loss calculation>.

Next, the blast furnace was divided into three regions in the radial direction, a central region, an intermediate region, and a peripheral region so as to be equidistant in the radial direction. For each region, the gas flow index was calculated based on the description of Okuno et al., "Development of a container distribution estimation model in the bellless charging method", Iron and Steel, 1973, (1987), No. 1, p91-98. I asked. The outline is as follows.

First, the following assumptions were made regarding the distribution of containers.
1. 1. The accumulation of the charge proceeds by sequentially accumulating the virtual unit amount obtained by subdividing the total input amount.
2. 2. The particle size segregation indicated by the sedimentary layer does not occur in the height direction.
3. 3. Gas flows by plug flow (extrusion flow).

Next, the particle size distribution when a virtual unit amount of the container was deposited was obtained from the following equations (6) to (9).
ln (X _n / (1-X _n )) =-α l _m + β… (6)
α _c L = 8.70 × 10 ^-3 (V _s ² / Lg) ^-0.50 (d _p / L) ^-0.59 (H / L) ^0.17 tan ^{φ 0.46} (1-u / u _mf ) ^0.46 … (7)
α _w L = 4.59 × 10 ^-3 (V _s ² / Lg) ^-0.57 (d _p / L) ^-0.58 (H / L) ^0.19 tan ^{φ 0.69} (1-u / u _mf ) ^0.55 … (8)
V _s = W / (2πRL)… (9)
here,
X _n : Weight ratio of container below the particle size of interest
l _m : Distance in the direction of container flow (m)
α: Proportional constant (1 / m)
β: Constant (1 / m)
α _c : Gradient toward the core side (1 / m)
α _w : Gradient toward the furnace wall side (1 / m)
L: Deposit layer thickness (m) indicated by the amount of charge when the chute makes one turn
d _p : Arithmetic mean particle size (m)
H: Depth from charging line (m)
φ: The angle of repose of the container (°)
u: Gas superficial velocity (m / s)
u _mf : Gas fluidization start speed (m / s)
W: Charge supply speed (m ³ / s)
R: Horizontal distance from the furnace shaft to the drop point of the container (m)
g: Gravitational acceleration (m / s ² )

Based on the obtained particle size distribution, the gas flow velocity distribution was obtained. The surface shape of the sedimentary layer was modified based on the gas flow velocity distribution.
Such a calculation was performed for the total input amount, and the gas flow velocity distribution was obtained.
Finally, from the gas flow velocity distribution, the gas flow velocity in each region was converted into a percentage and used as the gas flow index. Specifically, the gas flow index was obtained from the following equations (10) to (13).
Total gas flow velocity = central region average flow velocity + intermediate region average flow velocity + peripheral region average flow velocity ... (10)
Central gas flow index = (average flow velocity in the central region) / (total gas flow velocity) × 100 ... (11)
Intermediate gas flow index = (intermediate region average flow velocity) / (total gas flow velocity) × 100 ... (12)
Peripheral gas flow index = (average flow velocity in the peripheral region) / (total gas flow velocity) × 100 ... (13)
The results are shown in FIG.

As shown in FIG. 6, the central gas flow index was lower when the central coke B was used than when the central coke A was used. The intermediate gas flow index and the peripheral gas flow index were rising.
From this result, it was suggested that the use of coke via the yard deteriorated the air permeability in the central coke 11 and the gas was flowing from the central region to the intermediate region and the peripheral region.

When the central coke C was used, the central gas flow index was higher than when the central coke A and B were used. The intermediate gas flow index and the peripheral gas flow index were decreasing.
From this result, it was suggested that the porosity of the central coke 11 increased and the gas was flowing to the central region by increasing the sieving lower limit classification point of the coke via the yard. Further, it was found that even when 100% of coke via the yard is used, sufficient air permeability can be ensured by raising the sieving lower limit classification point of the central coke 11.

<Measurement of pressure loss by actual furnace>
Next, in Examples and Comparative Examples, the coke type of the central coke was 100% coke via the yard, and the coke and ore were charged into the blast furnace for operation, and the pressure loss was compared.
First, as a blast furnace, and the volume was using a large blast furnaces ^tertiary 4800 m.
The same ore and coke as used in the calculation in <Porosity and pressure loss calculation> were charged into this blast furnace at the same mass ratio, the blast temperature was 1200 ° C, the blast humidity was 25 g / Nm ³ , and the blast volume was 6000 ^{Nm 3} / min. The operation was carried out with an oxygen consumption of 10000 Nm ³ / h and a pulverized coal injection amount of 160 kg / t, and the pressure loss was actually measured.
The results are shown in Table 4.

表４に示すように、実炉においても実施例の方が、圧力損失が小さくなっていた。

As shown in Table 4, the pressure loss was smaller in the example in the actual furnace as well.

11 ... Central coke, 13 ... Ore layer, 15 ... Mass coke, 17 ... Small coke.

Claims (3)

It is a blast furnace operation method that uses coke via the yard.
The central coke charging process, which requires coke via the yard and selectively includes direct coke, is charged into the center of the blast furnace.
A mass coke charging process in which a mass coke composed of coke via a yard is charged between the central coke and the furnace wall in the furnace radial direction,
An ore layer charging step in which an ore layer composed of coke via a yard and mixed with small coke, which is a coke having a particle size smaller than that of the coke, is charged onto the central coke and the coke.
And carry out
The blast furnace operating method is characterized in that the central coke charging step is a step of charging coke via a yard on a sieve classified by a sieve having a lower sieve classification point of 53 mm or more and 57 mm or less.
Here, the coke via the yard means coke that is transported to the blast furnace via the yard, and the direct coke refers to coke that is transported from the coke manufacturing process to the blast furnace using a belt conveyor without passing through the yard. .. The blast furnace operating method according to claim 1.
The blast furnace operating method is characterized in that the lump coke charging step is on a sieve in which the lump coke to be charged is classified by a sieve having a lower sieving lower limit classification point of 43 mm or more and 47 mm or less. The blast furnace operating method according to claim 1 or 2.
In the ore layer charging step, the small coke to be charged is under a sieve classified by a sieve having a lower sieving lower limit classification point of 43 mm or more and 47 mm or less, and further a sieving lower limit classification point is 13 mm or more and 17 mm. A blast furnace operating method characterized by being on a sieve classified by the following sieve.

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