JP6638680B2 - Blast furnace operation method - Google Patents

Description

  The present invention relates to a method for operating a blast furnace using ferro-coke, which is made by molding and carbonizing a mixture of coal and iron ore and containing metal iron in coke, as a blast furnace raw material.

  In a blast furnace, usually, iron ore as a raw material (also simply referred to as “ore”) and coke as a reducing agent are charged from the furnace top so as to be alternately layered, and the ore layer is introduced into the blast furnace. And a coke layer. In order to reduce the reducing agent ratio in the blast furnace, it is effective to use ferro-coke as a raw material for the blast furnace and use the effect of lowering the temperature of the heat preservation zone of the blast furnace by using ferro-coke. Here, the “reducing material ratio” is the total mass of the reducing material (coke, pulverized coal, etc.) necessary to produce one ton of hot metal, regardless of the type of the reducing material, and “kg / hot metal−t Is displayed. Further, as the coke forming the coke layer, coke produced in a coke oven is usually used.Hereinafter, in order to distinguish it from ferro coke, coke produced in a coke oven is also referred to as `` room furnace coke ''. Call.

  Ferro-coke produced by dry-distilling a molded product obtained by mixing and molding coal and iron ore contains iron (Fe) as a catalyst. Reduce the temperature of the preservative. The reduction of the temperature of the heat preservation body shifts the reduction equilibrium point in the direction in which the reduction reaction proceeds, so that the reduction of the sintered ore is promoted and the ratio of the reducing material decreases.

  As a method of operating a blast furnace using ferro-coke, as disclosed in Patent Document 1, coke is independently charged into a blast furnace to form a coke layer, and iron ore and ferro-coke are mixed with iron ore and ferro-coke. There is a method of forming an ore layer in which coke is mixed and charged into a blast furnace to mix ferro-coke.

Ferro coke is characterized by having higher reactivity with CO ₂ gas represented by the following formula (1) than conventional coke for metallurgy produced by carbonizing coal in a coke oven or the like. The reaction represented by the following formula (1) can be said to be a reaction for regenerating CO ₂ gas generated by the reduction reaction of iron ore represented by the following formula (2) into CO gas having a reducing power.

CO ₂ + C → 2CO (1)
FeO + CO → Fe + CO ₂ (2)
Therefore, in the region where the CO ₂ gas concentration is increased by the reaction of the above formula (2), if the reaction of the above formula (1) occurs promptly, the CO ₂ gas is regenerated to a CO gas having a reducing power. The reduction of iron ore is promoted.

  By using ferro-coke, a reduction in the reducing agent ratio can be expected. On the other hand, when ferro-coke is mixed with iron ore and used in a large amount, the amount of coke used decreases because coke is replaced with ferro-coke.

  When the amount of coke charged into the blast furnace decreases, the coke layer (coke slit), which is a gas flow site, becomes thinner in the cohesive zone in the blast furnace, and the ventilation resistance increases. An increase in the ventilation resistance may hinder stable operation of the blast furnace. In recent years, the operation at a high pulverized coal ratio and a low coke ratio has been advanced, and the problem of thinning the coke slit has become more and more prominent. Here, the “coke ratio” is the mass of coke required to produce one ton of hot metal, and is expressed as “kg / hot metal-t”. Coke in ferro coke is also counted in the coke ratio.

  Conventionally, as a technique for reducing the airflow resistance of the cohesive zone, as disclosed in Patent Document 2, a technique of mixing small coke with iron ore and charging it into a blast furnace, that is, mixed with small coke A technique for forming an ore layer and a coke layer in layers is known and is practiced in many blast furnaces.

  Further, when using ferro coke, as disclosed in Patent Document 3, a method for improving the particle size and strength of co-used coke to ensure air permeability, and as disclosed in Patent Document 4, A method has been proposed in which ferrocoke is not charged into the center of the furnace to ensure the air permeability of the furnace core.

JP 2006-28594 A JP-A-3-211210 JP 2008-106320 A JP 2008-56985 A

  However, the above prior art has the following problems.

  That is, Patent Literature 1 does not show a measure for improving air permeability when using ferro-coke, so that the thinning of the coke slit increases the airflow resistance of the cohesive zone, and makes blow-through and unloading unstable. May occur and the reactor condition may become unstable.

  As described in Patent Document 2, the method of mixing small coke with the ore layer is effective when the mixed small coke is consumed by the gasification reaction before reaching the furnace lower part. When used together, ferro coke having higher reactivity than small coke is preferentially consumed, so that small coke having a reduced diameter remains at the lower part of the furnace, which may deteriorate air permeability.

  In addition, the permeability of the cohesive zone is influenced by both the permeability of the coke slit and the permeability of the fused ore layer. It is a technology to improve the permeability of the layer, and as the coke slit becomes thinner, the deterioration of the permeability of the coke slit exceeds the effect of improving the permeability of the ore layer by mixing small coke into the ore layer, There is a problem that a sufficient effect cannot be obtained.

  Patent Document 3 proposes to use coke having a harmonic average particle size of 40 mm or more as coke for forming a coke layer. Usually, particle size adjustment of coke used in a blast furnace is performed by sieving with a sieve. Increasing the particle size of the coke to be used means increasing the size of the sieve, and as a result, the coke under the unused sieve increases, and the yield of usable coke deteriorates. . Further, in order to increase the coke strength, it is necessary to mix a high-grade coal brand, which causes a large increase in coke production cost, which is not practical.

  Patent Document 4 can prevent deterioration of ventilation of the furnace core, but cannot prevent deterioration of ventilation of the cohesive zone due to thinning of the coke slit. Therefore, when the permeability of the cohesive zone becomes a bottleneck, it cannot be a drastic measure.

  The present invention has been made in view of the above circumstances, and an object thereof is to reduce coke ratio by securing good air permeability of a cohesive zone in a blast furnace operating method using ferro-coke as a blast furnace raw material. And a method of operating a blast furnace.

The gist of the present invention for solving the above problems is as follows.
[1] A method of operating a blast furnace in which an ore layer and a coke layer in which small coke and ferro-coke are mixed are alternately formed in a blast furnace,
When using the ferro coke, the amount of the furnace coke forming the coke layer is reduced in the range of less than twice the same amount or more and the same amount as the coke component contained in the ferro coke,
Blast furnace operation, characterized by replenishing and charging small coke of the same amount in the range of ± 20 mass% as the reduced coke in the reduced furnace coke as coke forming a coke layer. Method.
[2] The blast furnace according to [1], wherein the small lump coke replenished as coke for forming a coke layer is charged separately from the lump coke on the furnace wall side of the coke layer. Operation method.
[3] forming a layer thickness distribution such that an ore layer thickness ratio (= ore layer thickness / (ore layer thickness + coke layer thickness)) at the blast furnace wall becomes 0.5 or less; The method for operating a blast furnace according to the above [1] or [2].

  According to the present invention, when ferro-coke is used in a blast furnace, the amount of the coke in the chamber furnace forming the coke layer is reduced within a range of the same amount or more and less than twice the same amount as that of the coke contained in the ferrokes. The small coke having the same amount as that of the reduced coke in the furnace coke in the range of ± 20% by mass is replenished as coke for forming a coke layer. It is possible to prevent the deterioration of the permeability of the cohesive zone due to the thinning of the coke slit. Also, when charging the small coke into the coke layer, by separating the small coke from the coke and charging the small coke to the furnace wall side, it is possible to prevent a decrease in the porosity and to suppress the deterioration of the air permeability of the massive band. . Furthermore, by lowering the ore layer thickness ratio of the furnace wall, the partial pressure of CO gas in the peripheral portion increases, and it is possible to prevent powdering in the lower part of the furnace due to the reaction deterioration of small coke. As a result, not only the cohesive zone, but also the air permeability of the lump zone and the drip zone can be improved, and the air permeability of the entire blast furnace can be greatly improved. It can be used.

It is a conceptual diagram of the blast furnace charge distribution at the time of applying this invention. Comparison of reduction rate at 1200 ° C when load softening test was performed under simulated conditions in a blast furnace when the small coke and ferro-coke were mixed into the ore layer and when the ferro-coke alone was mixed into the ore layer FIG. The maximum differential pressure during softening and melting during load softening test under simulated conditions in a blast furnace was compared between the case where small coke and ferro-coke were mixed in the ore layer and the case where ferro-coke alone was mixed in the ore layer. FIG. It is a figure which shows the relationship between a slit coke ratio and the pressure loss of a blast furnace.

  Hereinafter, the present invention will be described specifically.

  Conventionally, the coke layer plays an important role as a coke slit layer for ensuring the air permeability of the blast furnace cohesive zone. It is common to use coke having a large particle size (referred to as “lump coke”) sieved with a sieve having meshes (for example, a mesh size of 35 mm). However, the furnace coke produced in the coke oven has a wide particle size distribution, and a small amount of small coke, which is under the mass of coke, is always generated. As a method of effectively utilizing the small coke as a reducing agent in a blast furnace, a technique of mixing small coke with an ore layer proposed in Patent Document 2 (also referred to as "small coke mixing charging technique"). Has been implemented.

  However, when ferro-coke is used, ferro-coke is basically used in a mixed state with the ore layer, and the coke component in the ferro-coke is used in place of the room-furnace coke. Depending on the amount, the amount of coke used in the furnace decreases, and the coke slit layer becomes thinner. When the coke slit layer is made thinner, the ventilation resistance of the cohesive zone increases, causing blow-through and slippage. As a result, continuation of stable operation becomes difficult, and it is necessary to take measures such as reducing production and increasing the coke ratio.

  In the present invention, when ferro-coke is used, the amount of the chamber furnace coke forming the coke layer is reduced in the range of the same amount or more and less than twice the same amount as the coke contained in the ferrokes, and the reduced chamber is used. In order to supplement the reduced amount of the lump coke in the furnace coke, a small lump coke having the same amount as the reduced amount of the lump coke in the room furnace coke in the range of ± 20% by mass is coke-formed to form a coke layer. And charged to the coke layer.

  This prevents the coke slit layer from becoming thinner due to the use of ferro-coke, and secures the coke slit layer thickness. In addition, it is preferable to sort the small coke mixed in the ore layer with the small coke to be added to the coke layer.

  In the present invention, the reason for reducing the amount of the coke in the furnace furnace forming the coke layer by at least the same amount as the coke in the ferro coke is because the total use amount of coke is not increased (precondition of the present invention). The reason that the upper limit of the reduction amount of the furnace coke forming the layer is less than twice is that if the furnace coke is reduced by at least twice the same amount as the coke contained in the ferrokes, the air permeability deteriorates. This is because the operation becomes difficult.

  In the present invention, the reason for replenishing small coke in the same amount in the range of ± 20% by mass as the coke in the reduced coke in the furnace coke as the coke forming the coke layer is as follows. When the lump coke is less than the same amount -20% by mass, the amount of coke forming the coke layer is small, the effect of the present invention cannot be sufficiently exhibited, and the small lump coke to be replenished exceeds the same amount + 20% by mass. This is because the amount of coke forming the coke layer becomes sufficient, the effect of the present invention is saturated, and rather, there is a concern that the average particle size of the coke layer is reduced and the air permeability is deteriorated.

  When the small coke is mixed with the coke layer, the small coke and the lump coke are separated, and the small coke and the lump coke are charged so that the small coke is charged on the furnace wall side of the blast furnace. It is preferred to control the method.

  FIG. 1 shows a conceptual diagram of a blast furnace charge distribution when the present invention is applied. In FIG. 1, reference numeral 1 is a blast furnace center line, 2 is a blast furnace wall, 3 is a coke layer formed of lump coke, 4 is a coke layer formed of small lump coke, 5 is an ore layer, 6 is iron ore in the ore layer, 7 is ferro coke in the ore layer, and 8 is small coke in the ore layer.

  The present inventors have found that in a blast furnace, ferro-coke expresses an effect of improving the permeability of a cohesive layer similar to the small-coke coke mixed charging technique, and moreover, expresses an effect preferentially over the small-coke coke. And reached the present invention.

  FIGS. 2 and 3 show blast furnaces in a case where ferro-coke is additionally mixed in an ore layer in which small coke of 60 kg / hot metal-t is mixed and a case where ferro-coke alone is mixed in an ore layer. The results of a load softening test performed under simulated conditions are shown.

  FIG. 2 shows the reduction ratio when the temperature reached 1200 ° C., and FIG. 3 shows the maximum differential pressure during softening and melting. From FIGS. 2 and 3, as the usage of ferro-coke increases, specifically, when the usage of ferro-coke is 30 kg / hot metal-t or more, the effect of reducing small coke and the improvement of air permeability are improved. The effect was reduced, and was found to be equivalent to the case of ferrocoke alone. This is because ferro coke reacts preferentially over small coke to improve the reduction of iron ore.

  That is, the present invention focuses on the point that, when ferro-coke is mixed into an ore layer, the advantage of mixing small-lume coke into an ore layer is reduced, and has found a new method of utilizing small-lume coke.

  The present inventors have noticed that the basic unit of coke charged as a coke layer (hereinafter referred to as “slit coke ratio”) strongly affects the blast furnace air permeability. FIG. 4 shows the relationship between the slit coke ratio and the pressure loss of the blast furnace.

  As shown in FIG. 4, it is found that the pressure loss increases as the slit coke ratio decreases, and the tendency becomes remarkable when the slit coke ratio becomes 250 kg / hot metal-t or less, particularly 230 kg / hot metal-t or less. Was. In other words, it has been found that an increase in pressure loss can be suppressed by securing the slit coke ratio to 230 kg / hot metal-t or more, desirably 250 kg / hot metal-t or more.

  In the present invention, by reducing the amount of lump coke replaced with ferro coke with small lump coke, it is possible to prevent a decrease in the slit coke ratio without increasing the amount of lump coke used. When the lump coke ratio is less than 250 kg / hot metal-t, particularly when the lump coke ratio is less than 230 kg / hot metal-t, the present invention is applied to make the slit coke ratio 230 kg / hot metal-t or more, preferably 250 kg / hot metal-t. By setting the hot metal to -t or more, an effect of improving the permeability of the blast furnace can be obtained.

  When the small coke is mixed with the coke layer, it is preferable that the coke is charged at the center side in the furnace radial direction and the small coke is charged at the furnace wall side in the furnace radial direction. Specifically, the small coke is charged in a range from the 1/2 position in the furnace radial direction to the outside, preferably in a range from the 2/3 position in the furnace radial direction to the outside. Charge inside the furnace in the radial direction. Thereby, it is possible to prevent small coke from flowing into the furnace core, and it is possible to prevent a decrease in porosity due to an increase in the particle size range of the chamber coke forming the coke layer. As a result, it is possible to further suppress an increase in pressure loss in the furnace.

  In addition, when ferro-coke is used, the amount of small coke remaining in the lower part of the furnace, which has not been completely consumed in the furnace reaction and has been reduced in diameter, generally increases, and there is a concern that the permeability of the furnace lower part may deteriorate. However, in the present invention, by transferring a part of the small coke from the ore layer to the coke layer, the proximity arrangement effect (= reaction promoting effect) between the small coke and the ore is reduced, and the reaction speed of the small coke is reduced. Is reduced, and a reduction in diameter and a decrease in strength due to a reaction can be prevented. Thereby, the effect that the deterioration of the air permeability in the lower part of the furnace can be suppressed is also exerted.

Further, by controlling the ore layer thickness ratio (= ore layer thickness / (ore layer thickness + coke layer thickness)) of the blast furnace wall to 0.5 or less, the partial pressure of CO ₂ gas at the furnace wall can be reduced. The reaction of the small coke can be further suppressed. However, if the ore layer thickness ratio of the furnace wall is excessively reduced, gas flowing near the furnace wall increases, which leads to an increase in heat loss and a decrease in gas utilization rate. It is desirable to set it to about 2.

  In the present invention, the small coke and the lump coke are controlled so that the ratio between the use amount of the small coke and the use amount of the lump coke is maintained at a certain value without being affected by the use amount of the ferro coke. It is preferable to set the usage amount.

  Small lump coke, which is below the lump coke, is generated at a substantially constant ratio to the mass of the lump coke obtained by sieving. By setting the ratio of the amount of small coke used to the blast furnace and the amount of lump coke used to the same ratio as the rate of generation under the sieve, the small coke under the sieve is effectively used as a reducing agent without waste. Can be used.

In order to confirm the effect of the present invention, an operation test was performed in a blast furnace having a furnace volume of 5000 m ³ . The ferro-coke used was formed by blending and molding coal and iron ore such that the coke content in the ferro-coke after dry distillation was 70% by mass and the metallic iron content was approximately 30% by mass. It was manufactured by carbonization. The test was performed by changing the usage amount of ferro-coke in the range of 0 to 60 kg / hot metal-t, and the air permeability, tapping ratio, coke ratio, and the like were evaluated. Table 1 shows the operating conditions and test results.

Periods 1 to 7 are comparative examples, and periods 8 to 13 are inventive examples. Here, the coke ratio is shown as the sum of the basic unit of coke in ferro coke (the coke in ferro coke) and the room furnace coke. The ratio of small coke in the coke in the furnace was set to a constant value of about 23.1% by mass. The ventilation resistance _index, using the K value obtained by ^{_{K = (P B 2 -P T}} 2) / V B 1.7 × 10 6. Here, P _B is the blowing pressure (atm), _PT is the furnace top pressure (atm), and V _B is the blowing amount (Nm ³ / min). When the small coke was mixed into the coke layer, the small coke and the mass coke were separated, and the small coke was charged in a range outside from a half position in the furnace radial direction.

  Period 1 is an operation result when ferro coke was not used, the entire amount of small lump coke was mixed with the ore layer, and the coke layer was formed only with lump coke. The slit coke ratio in period 1 was 240 kg / hot metal-t. Hereinafter, other periods will be compared based on the operation conditions and operation results in the period 1.

  The period 2 is an operation result in a case where the coke ratio is lower than that in the period 1 without using the ferro coke, and the reduced coke ratio is refilled by transferring the small coke to the coke layer.

  In period 2, as compared with period 1, air permeability deteriorated, and stable operation could not be continued unless the tapping ratio was reduced. This is because the transferability of the small coke from the ore layer to the coke layer deteriorated the reducibility of the ore and increased the size of the cohesive zone. Unreduced ore fell to the lower part of the furnace, and the ratio of reducing material also increased.

  Periods 3 and 4 are operation results when 30 kg / hot metal-t or 60 kg / hot metal-t of ferro-coke was mixed into the ore layer, and the entire amount of small coke was mixed with the ore layer and used. In period 3 and period 4, the small coke was not transferred from the ore layer to the coke layer. Therefore, the slit coke ratio was 219 kg / hot metal-t in period 3, 203 kg / hot metal-t in period 4, and the slit coke ratio was in period 1. On the other hand, it dropped significantly.

  As a result, in period 3 and period 4, the reducing agent ratio decreased due to the use of ferro-coke, but the slit coke ratio decreased significantly. Was forced to rise. In particular, in period 4, the coke ratio did not decrease compared to period 3, and it can be said that the effect of using ferro-coke was not sufficiently obtained.

  Period 5 is an operation result when 30 kg / hot metal-t of ferro-coke is mixed into the ore layer, and the amount of the coke in the room furnace which is at least twice the coke content of ferro-coke (21 kg / hot metal-t) is reduced. is there. In the period 5, since the amount of the room furnace coke was excessively reduced with respect to the amount of the ferro coke used, the air permeability deteriorated and the production was forced to be reduced.

  In period 6, the ferro coke of 30 kg / hot metal-t was mixed into the ore layer, and the lump coke was reduced in the range of the same amount or more and less than twice the same amount as the coke contained in the ferrokes. This is an operation result when the amount of small coke replenished in the coke layer is less than the reduced amount of coke by less than -20% by mass with respect to the reduced amount of coke. In period 6, the slit coke ratio could not be maintained, the air permeability deteriorated, and the production had to be reduced.

  In period 7, 30 kg / hot metal-t of ferro-coke was mixed into the ore layer, and the lump coke was reduced in the range of the same amount or more and less than twice the same amount as the coke contained in the ferrokes. This is an operation result when the small coke replenished in the coke layer exceeds the coke reduction amount by more than the coke reduction amount of + 20% by mass. In the period 7, the deterioration of the air permeability due to the decrease in the average particle diameter of the coke layer exceeded the effect of improving the air permeability by the ferro-coke, and forced to reduce the production.

  Period 8 uses 30 kg / hot metal-t of ferro-coke, and period 9 uses 60 kg / hot metal-t of ferro-coke so that the slit coke ratio becomes 240 kg / hot metal-t which is the same as in period 1. In addition, it is an operation result when small coke is transferred to a coke layer according to the usage amount of ferro coke.

  In periods 8 and 9, the coke ratio and the reducing agent ratio were significantly reduced as compared to periods 3 and 4 in which the amount of ferrocoke used was the same, while maintaining the same air permeability and tapping ratio as period 1. As a result, high and low coke rate operation and low coke rate operation were able to continue stably.

  Period 10 uses ferro coke of 60 kg / hot metal-t, and transfers small coke to a coke layer so that the slit coke ratio becomes 240 kg / hot metal-t, which is the same as period 1, and further, ore on the furnace wall portion It is an operation result when the layer thickness ratio is adjusted to 0.3. In the period 10, the coke ratio could be further reduced by 3 kg / hot metal-t as compared with the period 9 in which the amount of ferrocoke used was the same.

  In the period 11, 30 kg / hot metal-t of ferro-coke is mixed into the ore layer, the lump coke is reduced by the same amount as the coke contained in the ferrokes, and the same amount of small lump is reduced by the lump coke. It is an operation result when coke is transferred from an ore layer to a coke layer. In the period 11, since the coke ratio was the same as that in the period 1, the improvement of the air permeability was remarkable, and the tapping ratio could be greatly increased.

  In the period 12 and the period 13, the ferro coke of 30 kg / hot metal-t is used, and the coke ratio and the lump coke ratio of the coke layer are set to be the same as those in the period 8, but the amount of the reduced lump coke is transferred to the coke layer. It is an operation result when the amount of the small coke was changed within a specified range. In the period 12 and the period 13, both the air permeability and the tapping ratio were equal to those in the period 8, and the operation could be performed without any problem.

  From the above results, the effectiveness of the present invention was confirmed.

Reference Signs List 1 blast furnace center line 2 blast furnace wall 3 coke layer formed of lump coke 4 coke layer formed of small lump coke 5 ore layer 6 iron ore in ore layer 7 ferro coke in ore layer 8 small in ore layer Lump coke

Claims (3)

A method of operating a blast furnace by forming an ore layer and a coke layer in which small coke and ferro-coke are mixed alternately in a blast furnace,
When using the ferro coke, the amount of the furnace coke forming the coke layer is reduced in the range of less than twice the same amount or more and the same amount as the coke component contained in the ferro coke,
Small lump coke in the amount of volume and the same amount ± 20 wt% range of lump coke was reduced chamber furnace coke, charged supplemented as coke that forms a coke layer,
A method for operating a blast furnace, wherein a basic unit (slit coke ratio) of coke charged as a coke layer is 230 kg / hot metal-t or more .   The blast furnace operating method according to claim 1, wherein the small lump coke replenished as coke forming the coke layer is charged separately from the lump coke on the furnace wall side of the coke layer.   2. A layer thickness distribution such that an ore layer thickness ratio (= ore layer thickness / (ore layer thickness + coke layer thickness)) at the blast furnace wall is 0.5 or less. Or the method for operating a blast furnace according to claim 2.

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