JP5803839B2 - Blast furnace operation method - Google Patents

Description

  The present invention relates to a blast furnace operating method in which a coke layer and a mixed layer containing a mixture of ore and coke are alternately stacked and operated in a blast furnace.

  In general blast furnace operation, sintered ore or block ore (hereinafter referred to as “ore”) as iron-containing raw material and lump coke are charged into the blast furnace from the top of the furnace, and the ore layer and lump coke are charged. A massive band in which the layers are alternately stacked is formed in the blast furnace.

  The charged ore softens as the reaction proceeds and the temperature rises, and fuses with each other to form a region called a cohesive zone. The cohesive zone includes an ore fusion layer in which ore is fused and a coke layer called a coke slit. The cohesive zone has a very high ventilation resistance as compared to the massive zone. By reducing the ventilation resistance of the cohesive zone, the operation of the blast furnace can be stabilized.

  For the purpose of promoting the reduction of ore in the blast furnace and reducing the airflow resistance in the cohesive zone, it is carried out by mixing small ingot coke with ore and charging (see Non-Patent Document 1 below). ). By mixing coke with ore, the air permeability of the ore fusion layer is improved by the aggregate effect of coke. As an alternative to small-sized coke, high-reactivity coke is mixed with ore and charged to promote the reduction reaction, reduce the reducing material ratio, and improve productivity (the following patent document) 1).

Small coke coke mixed with ore has a smaller particle size and larger surface area per unit volume, that is, specific surface area, compared with coke forming the coke layer, and is mixed with ore and mixed with ore. Small and medium mass coke present in the bed is in the vicinity of the ore. For this reason, it is considered that small and medium-sized coke can preferentially react with the CO ₂ gas generated by the reduction of the ore and suppress deterioration of the coke forming the coke layer. When highly reactive coke is used as an alternative to small coke, it is considered that deterioration of coke forming the coke layer can be further suppressed.

  In the following Patent Document 2, it is said that by mixing coke with ore together with highly reactive coke (ferrocoke), the chain reaction of reduction of unreduced ore and gasification of highly reactive coke can be promoted. Yes.

  In the following Patent Document 3, it is said that air permeability is improved by including highly reactive coke in both the ore layer and the coke layer.

JP 2006-28594 A JP 2011-58091 A JP 2012-12620 A

Shiro Watanabe, 6 others, “Development of high-mix mixing technology of ore and coke into blast furnace”, Iron and Steel, Japan Iron and Steel Institute, Vol. 92 (2006), No. 12, p. 901-910 Yoshinori Matsukura, 4 others, “Evaluation of the effect of raw material properties on blast furnace air permeability”, Iron and Steel, Japan Iron and Steel Institute, Vol. 87 (2001), No. 5, p. 350-356

In the blast furnace, coke pulverization and coke particle size decrease are caused by the solution loss reaction shown in the following formula (1).
C + CO ₂ → 2CO (1)

  The coke consumed by the solution loss reaction is about 3% by mass with respect to the ore. Even if a large amount of highly reactive coke is mixed with ore for the purpose of improving the reactivity of the reduction reaction, this high reactivity is achieved. The coke reaches the cohesive zone without being consumed in the massive zone. Highly reactive coke deteriorated and reduced in particle size due to the solution loss reaction generates a large amount of powder in the process of moving downward. The generated powder has a problem that the air permeability is remarkably deteriorated.

  In addition, assuming that the coke ratio (mass of coke put into the furnace per 1 ton of pig iron (kg)) is constant, when a large amount of coke (including highly reactive coke) is mixed with ore, The amount of coke that forms the coke layer is reduced. For this reason, the coke slit layer thickness in a cohesive zone becomes small, and there exists a possibility that the air permeability in a furnace may fall.

  Furthermore, the air permeability improvement effect of the fused layer by mixing highly reactive coke with ore is not large (see Patent Document 2).

  Therefore, the object of the present invention is to solve such problems of the prior art and improve the air permeability of the blast furnace when operating using coke (including highly reactive coke) and ore. It is to provide a method of operating a blast furnace.

  In order to improve the air permeability of the blast furnace as a whole, it is necessary to improve the air permeability of the ore fusion layer and not to reduce the air permeability of the coke layer.

The present invention relates to the function (role) of coke charged into the furnace,
(A) Gasification by solution loss reaction,
The coke is divided into three parts: (c) a spacer that forms a coke slit, and (c) an improvement in the air permeability of the ore fusion layer due to the aggregate effect, so that the coke behaves appropriately for each function. By selecting, the air permeability of the blast furnace is improved.

  That is, the present inventors have conducted various studies on the blast furnace operation method capable of improving the air permeability in the cohesive zone. As a result, when operating using coke and ore, coke (high reaction) Coke (not coke) is mixed with ore, and high-reactive coke is included in the coke layer (not mixed with the ore layer), not in the mixed layer with ore. I found out that I can do it.

The air permeability of the ore fusion layer is improved by the aggregate effect of coke having low reactivity. Furthermore, the highly reactive coke mixed with the coke layer is preferentially gasified, suppresses the deterioration of coke in the coke layer, and maintains the air permeability of the coke layer. The present invention is as follows.
(1) In a blast furnace operation method in which a coke layer and a mixed layer containing a mixture of ore and coke are alternately stacked and operated in a blast furnace, the mixed layer is 3 to 9% by mass with respect to the ore. The coke contains coke having a coke reactivity index value of 31 or less, and in the coke layer, high-reactivity coke having a coke reactivity index value of 32 or more is 0.5 mass relative to the ore. A method for operating a blast furnace, characterized in that the blast furnace is contained in an amount of% to 3.2 mass%.
(2) The blast furnace operating method according to (1), wherein in the mixed layer, an average particle size ratio of the coke to an average particle size of the ore is set to 2 to 4.
(3) The average particle size of the highly reactive coke is 10 mm to 50 mm, and the coke other than the highly reactive coke has an average particle size of 10 mm to 60 mm. Or the blast furnace operating method as described in (2).

  Hereinafter, unless otherwise indicated, in the present specification, the term “coke” refers to cokes other than highly reactive coke.

  Unless otherwise stated, the definitions of terms in this specification are as follows.

“Coke reactivity index” (CRI): The mass reduction rate (% by mass) when 200 g of coke sized to 20 ± 1 mm is reacted at 1100 ° C. in a CO ₂ gas atmosphere for 2 hours.

  “Average particle diameter”: 50% diameter in the cumulative distribution of particle diameters.

“High-temperature ventilation resistance index”: a variable indicating the degree of gas permeability to the packed bed, and a value of KS calculated by the following equations (2) and (3) (see Non-Patent Document 2 above). Here, ΔP / ΔL is the ventilation resistance of the entire packed bed (pressure loss due to the entire packed bed; Pa / m), ρ _g is the gas density (kg / m ³ ), and μ _g is the gas viscosity. (kg / m / s) and is, u _g is the superficial gas velocity (m / s), T is the sample temperature (° C.).

According to the present invention, since the highly reactive coke is mixed in the coke layer, deterioration of the coke forming the coke layer is suppressed, and air permeability in the massive band and the cohesive band can be improved. Further, the highly reactive coke reacts with a gas having a high CO ₂ concentration released from the mixed layer preferentially over the coke. This eliminates highly reactive coke by the time it reaches the cohesive zone, suppresses the generation of powder, secures voids in the fused layer by the aggregate effect of coke mixed in the mixed layer, The inside air permeability can be improved.

It is the schematic of a load softening test apparatus. It is a graph which shows the relationship between the mixing ratio with respect to the ore of the coke in a mixed layer, and a high temperature ventilation resistance index. It is a graph which shows the relationship between the mixing ratio with respect to the coke of the highly reactive coke in a coke layer, and a relative pressure loss.

As described above, the present invention provides a method for operating a blast furnace in which a coke layer and a mixed layer containing a mixture of ore and coke are alternately stacked and operated in the blast furnace. 3-9% by mass coke having a coke reactivity index value of 31 or less , coke layer having a coke reactivity index value of 32 or more highly reactive coke in the ore On the other hand, this is a method for operating a blast furnace in which 0.5 to 3.2 mass% is contained. In the mixed layer, the average particle size ratio of coke to the average particle size of the ore is preferably 2-4. The average particle diameter of the highly reactive coke is preferably 10 mm to 50 mm. In this case, it is preferable that the cokes other than the highly reactive coke have an average particle diameter of 10 mm to 60 mm . Hereinafter, the above-described configuration requirements of the present invention will be described in detail.

  In order to improve the air permeability of the blast furnace, it is necessary to reduce the air resistance of the ore fusion layer in the cohesive zone and to form a coke slit with low air resistance.

  First, the influence of the mixing ratio of coke to ore and the average particle size ratio of coke to the average particle diameter of ore on the ventilation resistance of the ore fusion layer will be described.

  In addition, as a method for reducing the airflow resistance of the ore fusion layer, a technique is known in which small medium-coke coke is used in combination with ore. It is known that the air permeability of the blast furnace is also improved by mixing with (see Non-Patent Document 1 above). In order to improve the air permeability of the ore fusion layer, it is considered preferable to use a coke having a larger particle size than that of the small-medium coke. However, conventionally, the influence of the coke particle size on the air permeability has not always been clarified.

  The load that can evaluate the air permeability of the blast furnace fusion layer, and the effect of the mixing ratio of coke to ore and the average particle size ratio of coke to the ore average particle size on the air resistance of the ore fusion layer It investigated using the softening test apparatus.

  FIG. 1 is a diagram showing a schematic configuration of a load softening test apparatus. The load softening test apparatus includes a vertical electric furnace 1 having a graphite heating element 5. The vertical electric furnace 1 is formed with a hole penetrating the vertical electric furnace 1 in the vertical direction (vertical direction) and surrounded by the graphite heating element 5. The load softening test apparatus is arranged in the hole of the vertical electric furnace 1 and is placed above the graphite crucible 2 containing the charged sample 3 and the graphite crucible 2, and applies a load to the charged sample 3 in the graphite crucible 2. A load control device 6 that can be applied is further provided. The inner diameter of the graphite crucible 2 is 72 mm. At the bottom of the graphite crucible 2, a rooster (grate) is provided.

  This load softening test apparatus is provided with a temperature measuring device, and by this temperature measuring device, the temperature at the measuring point 7 above the graphite crucible 2 can be measured as the sample temperature. Below the hole of the vertical electric furnace 1, a dropped sample tray 9 is arranged. The dropped sample tray 9 can receive a sample dropped from the graphite crucible 2 through the rooster.

A gas flow rate control device 10 is connected to the load softening test device via an introduction pipe 13. N ₂ gas and CO gas are individually introduced into the gas flow rate control device 10. N ₂ gas and CO gas are mixed by the gas flow rate control device 10 and sent to the hole of the vertical electric furnace 1 through the gas introduction pipe 13 from below the hole. . The gas flow rate control device 10 can individually adjust the flow rates of N ₂ gas and CO gas sent into the hole.

  The gas introduced into the hole flows upward in the hole and enters the graphite crucible 2 through the rooster. The gas that has entered the crucible 2 exits from the upper portion of the graphite crucible 2 (hereinafter, the gas that has exited the graphite crucible 2 is referred to as “exhaust gas 11”), and flows further upward. And is discharged to the outside of the load softening test apparatus through the gas outlet pipe 14.

An exhaust gas analyzer (infrared spectrometer) 12 is connected to the gas outlet pipe 14. The exhaust gas analyzer 12 can analyze the composition (CO, CO ₂ ) of the exhaust gas 11 flowing through the gas outlet pipe 14. A gas pressure measuring device 8 is connected to the gas inlet pipe 13 and the gas outlet pipe 14. The gas pressure measuring device 8 can measure the ventilation resistance (pressure loss) due to the graphite crucible 2 in which the charged sample 3 is contained.

With this load softening test device, a load control device 6 applies a load to the charged sample 3 in the graphite crucible 2 and a reducing gas (mixed gas of N ₂ gas and CO gas) 4 is introduced into the vertical electric furnace 1. The charged sample 3 can be heated with the graphite heating element 5. By the analysis of the exhaust gas 11 by the exhaust gas analyzer 12, the reducing property of the charged sample 3 and the reduction efficiency of the ore in the charged sample 3 can be examined.

Using this load softening test apparatus, a mixture obtained by mixing coke and pre-reduced sintered ore as ore was charged into a graphite crucible 2 to form a packed bed, and charged sample 3 was obtained. The pre-reduced sintered ore is obtained by adding CO gas and CO ₂ gas to a sintered ore with an average particle size of 9.0 mm, which is sized so that the particle size range is 8.0 to 10.0 mm, at 1000 ° C. , Respectively, at a flow rate of 8 Nl (liter) / min and 5 Nl / min for 1.75 hours. The coke is sized so that the particle size ranges from 16.0 mm to 19.0 mm, 25.4 mm to 31.7 mm, or 35.0 mm to 38.0 mm, and the average particle size is 17.5 mm. Three types of 28.5 mm and 36.5 mm were prepared.

  Table 1 shows the filling conditions of the charged sample 3.

  It was assumed that 1.6 tons of pre-reduced sintered ore would be required to produce 1 ton of hot metal. Under the conditions of test numbers 1 to 12, the mixing ratio of coke to the pre-reduced sintered ore (mixed coke ratio) was set to 3.13, 4.69, 6.25 or 9.38% by mass, The average particle size ratio of coke to the average particle size of the ore ((coke / ore) particle size ratio) was set to 1.94, 3.17 or 4.05. The “filled coke amount” in Table 1 is the amount of coke mixed (included in the packed bed) with the pre-reduced sintered ore so as to have the above setting.

  In test number 0, the mixed coke ratio is 0, and the packed bed is an ore single layer. The layer height of the packed bed at the start of the test was 300 mm for all tests.

  A test for examining the air permeability of the packed bed was performed using the packed bed (charge sample 3) according to the conditions of each test number 0-12. More specifically, the main purpose of this test is to measure the packed bed from when the sample temperature reaches 1200 ° C. until the charged sample 3 melts at a higher temperature and the melt drops. It is to measure the ventilation resistance.

First, the temperature of the packed bed is raised in an N ₂ atmosphere, and after the sample temperature reaches 800 ° C., a load of 98 kPa simulating an actual furnace average load is applied from the upper part of the graphite crucible 2 by the load controller 6. Added to packed bed. In order to make the reduction rate at the start of ore fusion equal among the tests, when the sample temperature is 1200 ° C., the ore reduction rate in each test increases to 80% according to the change in the ore reduction rate. The temperature rate and the introduced gas composition (CO gas flow rate / N ₂ gas flow rate ratio) were manipulated.

After the sample temperature reached 1200 ° C., the reducing gas 4 was introduced into the packed bed while the packed bed was heated at a heating rate of 4.6 ° C./min. Reducing gas 4, the gas flow rate control device 10 to control the flow rate of the CO gas to 13.8Nl / min, N ₂ flow rate of 16.2 Nl / min controlled CO / N ₂ mixture obtained in the flow rate of the gas Gas was used. The CO / N ₂ mixed gas is used so that the gasification reaction of coke becomes only CO ₂ gas generated by reduction of ore. This is because in this test, attention is paid to the effect of improving the air permeability by mixing the coke itself.

  The temperature was continuously raised until the sample temperature reached 1600 ° C. to melt the ore. The melt obtained by melting the ore was dropped via a rooster at the bottom of the graphite crucible 2 and collected in the dropping sample tray 9.

During the test, the composition (CO, CO ₂ ) of the exhaust gas 11 by the exhaust gas analyzer 12, the exhaust gas flow rate by an integrating flow meter (not shown), the ventilation resistance of the packed bed by the gas pressure measuring device 8, and a displacement meter (not shown). The height of the packed bed was measured respectively.

  FIG. 2 is a diagram showing the relationship between the mixing ratio of coke to ore (horizontal axis) and the high temperature ventilation resistance index (vertical axis) obtained in the above test using the load softening test apparatus. The smaller the value of the high temperature ventilation resistance index (KS), the better the air permeability. FIG. 2 shows the relationship between the mixing ratio of coke to ore and the high temperature ventilation resistance index for each average particle size ratio of coke to the average particle diameter of ore (described as “particle size ratio” in FIG. 2). Show.

The parameters for obtaining the high temperature ventilation resistance index (see the definition of the high temperature ventilation resistance index in the section of “Means for Solving the Problems”) were as follows. ΔP / ΔL was a value obtained by dividing the value of the ventilation resistance measured by the gas pressure measuring device 8 by the height of the packed bed. ρ _g (gas density) was calculated by dividing the gas density of CO and the gas density of N ₂ according to the supply gas composition, and correcting the temperature and pressure. μ _g (gas viscosity) was calculated in consideration of the supply gas composition, temperature, and pressure. u _g (superficial gas flow rate) was set to that calculated by the temperature correction and pressure compensation of the gas flow. T (sample temperature) is a measured value at the measurement point 7 by the temperature measuring device.

  From FIG. 2, when the average particle size ratio of the coke to the average particle size of the ore is in the range of 2 to 4, the mixing ratio of the coke to the ore (coke mixing ratio) is 0 mass% to 6 mass%. The value of decreases with increasing coke mixing ratio, and it can be seen that air permeability is improved by mixing coke with ore. On the other hand, when the coke mixing ratio is increased to 9% by mass, the decreasing rate of the high temperature ventilation resistance index is reduced. From the above, it is considered that the mixing ratio of coke in the mixed layer of ore and coke needs to be 3% by mass to 9% by mass.

  Further, when the average particle size ratio of the coke to the average particle size of the ore is in the range of 2 to 4, there is no clear difference in the decrease rate of the high temperature ventilation resistance index with respect to the ratio. From this, it can be seen that if the average particle size ratio of the coke to the average particle size of the ore is in the range of 2 to 4, the air permeability improving effect does not depend on the coke particle size.

In order to ensure the air permeability in the ore fusion layer, it is necessary to avoid the deterioration of coke due to the solution loss reaction. For this purpose, the coke needs to be coarse to some extent and have low reactivity. Specifically, coke is mixed with the ore, it is necessary to have a 31 following CRI values, it is preferable to have an average particle size of 10Mm～60mm.

On the other hand, in order to maintain the air permeability of the coke slit, it is necessary to suppress a decrease in the particle size of the coke forming the coke slit. The decrease in the coke particle size is mainly caused by the contact of the high concentration CO ₂ gas released from the mixed layer with the coke forming the coke slit, and the solution loss reaction shown in the above formula (1) occurs. . Therefore, it is considered that the reduction in the particle size of the coke can be suppressed by reducing the concentration of the CO ₂ gas in contact with the coke forming the coke slit.

In order to reduce the concentration of CO ₂ gas in contact with the coke in the coke layer, the coke layer contains the highly reactive coke, and the CO ₂ gas released from the mixed layer is preferential to the highly reactive coke in the coke layer. Reaction to generate CO gas. In order to generate such a reaction efficiently, it is considered that the highly reactive coke is preferably disposed below the coke layer.

By preferentially reacting highly reactive coke with CO ₂ gas, it not only suppresses the reduction in the particle size of the coke, but also extinguishes the highly reactive coke and suppresses the generation of powder in the lower part of the furnace. The air permeability can be improved.

Therefore, assuming a blast furnace with an internal volume of 3500 m ³ , using a blast furnace total simulator, the amount of highly reactive coke mixed in the coke layer and coke reactivity, which is an index indicating the reactivity of the highly reactive coke. Calculations (simulations) were performed with various values of the index (CRI) changed, and the air permeability improvement effect in the blast furnace was examined.

  FIG. 3 shows the relationship (simulation result) between the mixing ratio of highly reactive coke in the coke layer to ore and the relative pressure loss. The relative pressure loss is a relative value of the pressure loss based on the pressure loss in the furnace during the base operation in which the coke is not mixed into the ore layer and the highly reactive coke is not mixed into the coke layer. The results shown in FIG. 3 indicate that the coke reactivity index of the highly reactive coke is 32 and 40, and the mixing ratio of coke in the mixed layer of ore and coke is 3.13% by mass with respect to the ore. It is a thing when I did it.

  FIG. 3 shows that with the increase in the mixing ratio of the highly reactive coke in the coke layer, the deterioration of the coke is suppressed and the air permeability of the ore fusion layer is improved. When the mixing ratio of highly reactive coke in the coke layer is increased to around 3.2% by mass, the effect of improving air permeability tends to decrease. This is considered to be due to the fact that by increasing the high-reactivity coke, in addition to the air permeability improvement effect, the effect of the high-reactivity coke reaching the fusion layer without reacting appears.

  In order to avoid the unreacted coke from reaching the fused layer, it is necessary that the mixing ratio of the highly reactive coke in the coke layer and the particle size of the highly reactive coke be below a certain level. There is. Specifically, the mixing ratio of the highly reactive coke in the coke layer to the ore needs to be 3.2% by mass or less from the result of FIG. 3, and in this case, the particle size of the highly reactive coke is It is preferable that it is 10 mm-50 mm.

  Further, if the mixing ratio of the highly reactive coke in the coke layer is smaller than 0.5% by mass, the effect of improving the air permeability is small, so it is necessary to set it to 0.5% by mass or more. Further, if the coke reactivity index value of the highly reactive coke is 32 or more, any coke reactivity index has an effect of improving the air permeability. The value of the coke reactivity index of coke needs to be 32 or more.

In order to confirm the effect of the present invention, verification calculation was performed using a blast furnace total simulator. As calculation conditions, a blast furnace with an internal volume of 3500 m ³ is assumed. As calculation preconditions, the blast volume, oxygen enrichment rate, blast temperature, blast moisture, and pulverized coal blowing amount are common, and the hot metal temperature is all The mass ratio of coke (including highly reactive coke) and ore was manipulated and calculated so that the calculation results were equal. The ore particle size was 13 mm, the highly reactive coke particle size was 20 mm, and the coke particle size was 40 mm.

  As comparative examples, an operation in which coke is not mixed into the ore layer (Comparative Example 1), an operation in which 3.13% by mass of coke is mixed in the mixed layer with respect to the ore (Comparative Example 2), and a mixed layer A numerical simulation was performed on an operation (Comparative Example 3) in which 1.88% by mass of highly reactive coke was mixed with the ore.

  As an example of the present invention, 3.13% by mass of coke was mixed in the mixed layer, 3.13% by mass of highly reactive coke was mixed in the coke layer (Inventive Example 1), and in the mixed layer A numerical simulation was performed on the operation (Example 2 of the present invention) in which 6.25% by mass of coke was mixed and 3.13% by mass of highly reactive coke was mixed in the coke layer.

  Table 2 shows calculation conditions and calculation results. The unit (kg / pt) in Table 2 represents the charging amount per 1 ton of pig iron. From Table 2, although coke is mixed in the mixed layer with the ore, the air permeability is improved (Comparative Example 2), and further, by mixing highly reactive coke in the coke layer (the present invention). Examples 1 and 2) show that the deterioration of coke is suppressed, the ventilation resistance is lowered, and the air permeability of the blast furnace is remarkably improved.

Claims (3)

In the blast furnace operation method in which a coke layer and a mixed layer containing a mixture of ore and coke are alternately stacked and operated in the blast furnace,
The mixed layer contains 3 to 9% by mass of coke based on the ore , and coke having a coke reactivity index value of 31 or less ,
A method for operating a blast furnace, characterized in that the coke layer contains 0.5 mass% to 3.2 mass% of highly reactive coke having a coke reactivity index value of 32 or more based on the ore.   2. The blast furnace operating method according to claim 1, wherein, in the mixed layer, an average particle diameter ratio of the coke to an average particle diameter of the ore is set to 2 to 4. 3. The average particle size of the highly reactive coke is 10 mm to 50 mm,
The blast furnace operating method according to claim 1 or 2, wherein cokes other than the highly reactive coke have an average particle diameter of 10 mm to 60 mm .