JP7244805B2 - Blast furnace operation method - Google Patents

Description

The present invention relates to a method of operating a blast furnace using a specific MgO source as an auxiliary material.

In blast furnace operation, coke, which is a reducing agent, and ore raw material, which is an iron source, are generally introduced into the furnace sequentially from the top of the furnace so that layers of coke and ore raw material are alternately formed in the furnace. The ore raw material may be mixed with an auxiliary raw material such as a slag forming agent. A predetermined amount of coke or ore raw material for one layer is determined as an amount for one charge and charged into the furnace. At this time, the thickness of the coke layer or ore raw material layer in the radial direction in the furnace By adjusting , the gas flow distribution in the radial direction in the blast furnace is controlled. Further, in order to control the gas flow distribution more appropriately, one charge of coke or ore raw material is divided and charged as a plurality of batches.

In a blast furnace, high-temperature air or oxygen-enriched air is blown into the furnace from the tuyeres at the bottom of the furnace to burn the coke inside the furnace. Hot metal is produced by melting.
Ore raw materials are roughly divided into lump ore obtained by crushing and sieving mined iron ore, and processed ore such as sintered ore and pellets made by agglomerating iron ore smaller than lump ore. be. Lump ore and treated ore are selectively used according to the operating conditions of each blast furnace. It is used as the main ore raw material because it remains constant. In addition to coke, which is charged from the top of the furnace, as a reducing material, low-cost pulverized coal, which is pulverized coal, is also blown from the tuyere at the bottom of the furnace and burned. As the amount of charcoal used increases, the amount of coke used is decreasing.

When hot metal is produced in a blast furnace, the gangue contained in the ore raw material and the ash contained in the reducing material are present as impurities, and these must be discharged from the tap hole together with the hot metal. Therefore, a slag forming agent is added as an auxiliary raw material to produce blast furnace slag adjusted to have appropriate components. In general, the main constituents of blast furnace slag _are four components, _SiO2 , CaO, MgO and _Al2O3 . Of these, the contents of SiO ₂ and CaO are adjusted so that the slag basicity (CaO/SiO ₂ ) becomes a predetermined value from the viewpoint of the slag viscosity and the reduction of the S concentration in the hot metal. On the other hand, Al ₂ O ₃ is mainly contained in ash and ore in coke, so its content fluctuates depending on the supply and demand balance of raw materials and fuels, making it difficult to adjust.

On the other hand, by properly adjusting the MgO concentration of blast furnace slag, it is possible to reduce the viscosity of blast furnace slag and improve the slag discharge property. Addition of an MgO source is necessary due to the need to increase the index of (CaO+MgO+Al ₂ O ₃ )/(SiO ₂ ) to a standard value or higher. In general, _MgO —CaO based dolomite and MgO—SiO ₂ based serpentinite are used as MgO sources. In addition, the increase in the slag ratio leads to an increase in cost, and the increase in slag volume leads to deterioration in air permeability, so the amount used is limited. In some cases, magnesite is used as the MgO source, but since magnesite is a massive zone and easily pulverized, there is a problem that the air permeability in the furnace tends to deteriorate.

On the other hand, Patent Document 1 discloses a method of increasing the MgO concentration in the slag while suppressing the increase in the slag ratio by charging magnesium hydroxide ore as a slag forming agent into the furnace from the top of the furnace. disclosed. According to this method, the MgO concentration of the blast furnace slag can be increased without causing the problems that occur when using dolomite or magnesite.

Japanese Patent Application Laid-Open No. 2008-240109

However, magnesium hydroxide ore, which is generally called brucite, has a high raw material unit price, and when it is used as an MgO source for a blast furnace, there is a problem that the production cost of hot metal increases.
Accordingly, an object of the present invention is to solve the problems of the prior art as described above, and to increase the MgO concentration of blast furnace slag at low cost without causing problems such as deterioration of air permeability in the blast furnace. It is to provide an operation method.

The inventor of the present invention focused on MgO—C-based waste refractories (used refractories) generated in steelworks as an inexpensive source of MgO while conducting studies to solve the above problems. MgO—C refractories are used in reaction vessels and transport vessels used in the refining process in steelworks. This is because the MgO--C refractory has the property of withstanding the high temperature of molten steel and the like, and hardly reacting chemically with molten steel and steelmaking slag. MgO-C waste refractory is a waste material (dismantling waste) generated when these containers are repaired, and since it contains a high content of MgO, it may be used as a source of MgO for blast furnaces. There is

However, given the above properties of the MgO-C refractory, and the melting point of the used MgO-C refractory is particularly high, the MgO-C waste refractory can be used as it is for the blast furnace. When used as an auxiliary raw material, it is unknown whether it will melt together with the above-mentioned gangue and ash in the blast furnace to form blast furnace slag. Since there is no example of using waste refractories in a blast furnace, it was not clear about the impact inside the blast furnace when using massive MgO—C-based waste refractories. Therefore, as a result of further studies by the present inventors, even if a massive MgO-C waste refractory is used as an auxiliary raw material (MgO source), problems such as deterioration of air permeability in the blast furnace occur. However, it has been found that the following advantages can be obtained without hindrance to the generation of blast furnace slag. That is, by using massive MgO-C waste refractories as an auxiliary raw material, (i) the MgO of the MgO-C waste refractories is in an unreduced state in the cohesive zone with the lowest air permeability in the blast furnace. By dissolving in FeO to form a high-melting compound, the air permeability of the cohesive zone is improved. It has been found to have the effect of increasing the air permeability of the cohesive zone, which also improves the breathability of the cohesive zone.

The present invention was made based on such findings, and has the following gist.
[1] A method of operating a blast furnace in which at least a part of an ore raw material is mixed with an auxiliary raw material and charged into a furnace, wherein at least part of the auxiliary raw material mixed with the ore raw material is a massive MgO—C waste refractory A blast furnace operating method, characterized in that it is a material.
[2] In the blast furnace operating method of [1] above, the lumpy MgO-C waste refractories are obtained by crushing and granulating used MgO-C refractories. blast furnace operation method.
[3] The method for operating a blast furnace according to [1] or [2] above, wherein the particle size of the MgO—C-based waste refractories is 10 to 50 mm.
[4] The blast furnace operating method according to any one of [1] to [3] above, wherein the ore raw material comprises treated ore and lump ore.
[5] In the blast furnace operating method of [4] above, the ore raw material for one charge is divided into two batches and charged, and only the batch with the higher mass ratio of lump ore is MgO—C-based waste refractories. A blast furnace operating method characterized by mixing.
[6] In the blast furnace operating method of [4] above, the ore raw material for one charge is divided into two batches and charged, each batch is mixed with MgO-C waste refractories, and the lumps of the two batches are mixed. The mixing ratio of the MgO—C-based waste refractory in the batch with the higher ore mass ratio is the same as or higher than the mixing ratio of the MgO—C-based waste refractory in the batch with the lower lump ore mass ratio. A blast furnace operating method characterized by:

According to the present invention, by using inexpensive MgO—C-based waste refractories as an auxiliary raw material (MgO source), the cost of hot metal production can be suppressed, and at the same time, the permeability in the blast furnace can be deteriorated, and blast furnace slag can be generated. The MgO concentration of the blast furnace slag can be increased without interfering with the Furthermore, by using massive MgO-C waste refractories as an auxiliary raw material, MgO of the MgO-C waste refractories is solid-dissolved in unreduced FeO to form a high melting point compound. Since the MgO—C waste refractories have a high melting point, the void ratio between particles in the cohesive zone is increased, thereby improving the air permeability of the cohesive zone, which has the lowest air permeability in the blast furnace. By improving the air permeability in this way, it is possible to increase the amount of pulverized coal that is cheaper than coke as a reducing agent, so even if the operation is performed with the same tapping ratio and reducing agent ratio, the coke ratio can be reduced, and the hot metal production cost can be further reduced.

Results of a sample test conducted to evaluate the ease of pulverization in the massive zone of the blast furnace for MgO-C waste refractories, brucite, dolomite, and magnesite, which are MgO sources (-2.8 mm of the sample after heating ratio) Results of a high-temperature load softening test conducted to evaluate the effect on air permeability in the cohesive zone of a blast furnace for MgO-C waste refractories, brucite, dolomite, and magnesite, which are MgO sources (estimated temperature inside the furnace Graph showing changes in crucible pressure loss against Explanatory diagram showing the high-temperature load softening test apparatus used in the test of FIG.

In order to evaluate the effect of the MgO source charged into the blast furnace as an auxiliary raw material on the blast furnace, the present inventors used MgO—C-based waste refractories (hereinafter, for convenience of explanation, “MgO -C refractory scrap"), magnesite, brucite, and dolomite were used to conduct laboratory tests, and the respective test results were compared. Table 1 shows the chemical components of the MgO—C refractory scrap, magnesite, brucite, and dolomite used in the test. Since the MgO--C refractory scraps have been used in refining vessels and the like, their chemical composition also includes adhering slag components (CaO, Al ₂ O ₃ , etc.).
In addition, the particle size of the material in the following description means the particle size of the material that is above or below the sieve when sieved through a sieve with the aperture of the numerical value.

First, in order to evaluate the easiness of pulverization of the MgO source in the massive zone of the blast furnace, a 500 g sample with a grain size of 15 to 20 mm was placed on a perforated plate and placed in a reaction tube with an inner diameter of 70 mm. placed. After that, the inside of the reaction tube was replaced with N ₂ gas at 15 NL/min, and the inside of the reaction tube was heated to 700° C. for 60 minutes while introducing N ₂ gas at 15 NL/min. After that, after introducing 15 NL/min of N ₂ gas at 700° C. for 30 minutes, the mixed gas of 15 NL/min of CO:CO ₂ =30:70 was introduced for 30 minutes, and the sample was reacted with the reducing gas. let me Thereafter, the sample was cooled to room temperature by switching to N ₂ gas at 15 NL/min and introducing it again. After measuring the mass of the sample after cooling, the entire amount of the sample was placed in a rotation tester described in JISM8720, rotated at 30 rpm for 30 minutes, a total of 900 times, and then sieved with 15 mm and 2.8 mm meshes. Classified using The mass ratio of particles having a particle size of 2.8 mm or less to the mass charged into the rotary tester was calculated and compared between the raw materials. The results are shown in FIG.

According to FIG. 1, the mass ratio of magnesite with a particle size of 2.8 mm or less is close to 60 mass%, and the mass ratio of other MgO-C refractory scraps, brucite, and dolomite with a particle size of 2.8 mm or less. are all less than 20 mass%, it can be said that powdering is remarkable. This is believed to be due to the fact that magnesite releases _CO2 through thermal decomposition and cracks occur. It is thought that dolomite also releases _CO2 through thermal decomposition and causes cracks, but since the thermal decomposition temperature of magnesite was lower than that of magnesite, it is thought that only magnesite was significantly pulverized in this test. . From the above results, it can be said that the use of magnesite as an MgO source is not preferable because it deteriorates air permeability due to pulverization in the massive zone of the blast furnace. On the other hand, MgO-C refractory scraps are originally high in strength and do not crack due to thermal decomposition, so they are difficult to pulverize, and air permeability is not deteriorated due to pulverization in the lumpy zone of the blast furnace. .

Next, a high-temperature load softening test was conducted to evaluate the effect of the MgO source on air permeability in the cohesive zone of the blast furnace. The outline of the high-temperature load softening experimental apparatus used is shown in FIG. . The inner diameter of the graphite crucible was 100 mm, and the test was conducted by covering the upper and lower sides of the sample with packed layers of zirconia balls having a particle size of 15 mm. It is common to use coke particles for the filling layers above and below the sample. We tried to differentiate from The sample is a uniform mixture of sintered ore with a grain size of 10 to 15 mm and an MgO source, and the mass of the entire sample is 900 g. experiment. As MgO sources, MgO—C refractory scraps, brucite, and dolomite, which had low pulverization in the lumpy zone, were used.

The temperature, gas composition, and load simulating the atmosphere of a blast furnace were applied to the experimental sample charged into the graphite crucible as described above, and the pressure loss in the crucible and the variation in thickness of the sample layer were investigated. The temperature inside the furnace was adjusted so that the rate of temperature increase was 5°C/min from room temperature to 900°C, 2°C/min from 900°C to 1100°C, and 5°C/min from 1100°C to 1650°C. As for the gas composition, only _N2 gas was introduced from room temperature to the furnace temperature of 300°C. adjusted to be The load is applied linearly with respect to the furnace temperature so that it will be 80 kgf/ ^cm2 at 1000°C until the furnace temperature reaches 1000°C, and after 1000°C it will be constant at 80 kgf/ ^cm2 . It was adjusted.

As an example of the test results, FIG. 2 shows the transition of pressure loss in the crucible with respect to the temperature in the furnace when the mixed amount of the MgO source is 24 g. The mixed amount of the MgO source at this time corresponds to the mixed amount of 44 kg/t (t: ton of hot metal; the same shall apply hereinafter) in the actual machine. According to FIG. 2, compared to the case of using dolomite as the MgO source, when MgO—C refractory scraps and brucite are used, the temperature at which the pressure loss peaks is higher, and the maximum pressure loss is lower. became. This is because MgO contained in MgO—C refractory scraps and MgO generated by thermal decomposition of magnesium hydroxide in brucite dissolved in unreduced FeO to form a high melting point compound. It is believed that there is. In addition, the reason why the maximum pressure loss of the MgO--C refractory scraps was lower than that of the brucite is considered to be that the MgO particles remained even in the fused state and the high inter-particle porosity was maintained. Residuals other than zirconia balls in the graphite crucible after the experiment were recovered, but no undissolved MgO source was recovered in any of the samples. From this, it is considered that the MgO-C refractory scrap remaining in the fused state melted in the slag at the burn-through stage where the temperature was further increased, and did not remain in the furnace as unmelted matter. be done. The used MgO—C refractory has a particularly high melting point, and there was a concern that it would remain unmelted when used in bulk. From these results, it was found that MgO--C refractory scraps had the highest effect of improving air permeability in the cohesive zone.

If the MgO—C refractory scraps do not completely react and dissolve in the cohesive zone and the unmelted material remains in the lower part of the furnace, the dissolution rate of MgO into the blast furnace slag with a low FeO concentration is low, and the unmelted MgO in the lower part of the furnace is low. Because the melted material stays, it causes deterioration of air permeability. Therefore, the MgO—C refractory scraps are preferably mixed in an appropriate amount according to the MgO concentration required in the blast furnace. The possibility of undissolved MgO--C refractory scrap was investigated using a sample sized to 20-25 mm, which is the representative particle size of MgO--C refractory scrap used in actual equipment. As a result, when the test was conducted with the mixed amount of MgO-C refractory scraps set to 24 g (equivalent to the mixed amount of 44 kg/t in the actual machine), the same as when the particle size was 10-15 mm, the maximum pressure loss was 0. 42 kPa, which was slightly lower than when the particle size was 10-15 mm, but no undissolved matter remained in the graphite crucible after the test. Here, 44 kg / t as the mixed amount of MgO-C refractory scraps is a sufficiently large mixed amount with respect to the MgO concentration normally required in the blast furnace. was found to pose no problem in terms of solubility.

Therefore, in the present invention, in a method of operating a blast furnace in which at least a part of an ore raw material is mixed with an auxiliary raw material and charged into a furnace, at least a part of the auxiliary raw material (MgO source) mixed with the ore raw material is massive MgO. -C refractory scraps (MgO-C waste refractories) are used.
Here, the MgO-C refractory (so-called "MgO-C refractory") is mainly composed of MgO (magnesia raw material) and C (carbon raw material), and if necessary, additives such as metal additives are added. It contains a small amount, and the general composition is 1.5 mass% or less (no (including the case of addition).
MgO-C refractories (shaped refractories, monolithic refractories) are used for the lining of reaction vessels and transport vessels used in the refining process in steelworks, etc., and repair of these reaction vessels and transport vessels. Used refractories are generated at times (such as when replacing linings). The MgO—C refractory scrap used in the present invention is mainly lump-like refractory scrap obtained by crushing and sizing such used refractories (usually sieving).

Massive MgO—C refractory scraps may be mixed with all of the ore raw material charged into the blast furnace, or may be part of the ore raw material (for example, multiple batches of ore raw material for one charge) as in the form described later. may be mixed only with a part of the batch of ore raw material). In order to mix the MgO--C refractory scrap with the ore raw material, for example, the MgO--C refractory scrap may be cut out on the ore raw material being conveyed by the charging conveyor.
The ore raw material mixed with the MgO—C refractory scrap may be mixed with other auxiliary raw materials.

If the particle size of the massive MgO-C refractory scrap is too large, it may not react and dissolve completely in the cohesive zone, and unmelted material may remain in the lower part of the furnace, while the particle size is too small. The particle size is preferably about 10 to 50 mm, more preferably 10 to 40 mm, because there is a risk of impairing air permeability in the furnace. Here, the particle size of 10 to 50 mm is the particle size that does not pass through a sieve with an opening of 10 mm and does not pass through a sieve with an opening of 50 mm. It is a particle size that does not pass through a sieve with an opening of 40 mm.
Examples of ore raw materials include lump ore obtained by crushing and classifying mined iron ore, and treated ore such as sintered ore and pellets obtained by agglomerating iron ore smaller than lump ore. Lump ore and treated ore are selectively used depending on the operating conditions of the blast furnace. In general, treated ore is mainly used, and lump ore + treated ore is used, or only treated ore is used.

In addition, since MgO-C refractory scrap reacts most with FeO among the gangue components in the ore raw material, the MgO-C refractory scrap is appropriately reacted and melted in the cohesive zone, and unmelted in the lower part of the furnace. From the viewpoint of preventing the formation of residues, it is desirable that FeO remains in the ore raw material in the cohesive zone. Here, between the treated ore and the lump ore, the reducibility of the lump ore is lower, and FeO tends to remain without being reduced in the cohesive zone, so MgO—C refractory scraps are placed around the lump ore. It can be said that it is advantageous because it is easier to dissolve. Therefore, when the ore raw material consists of treated ore and lump ore, the ore raw material for one charge is divided into two batches and charged, and only the batch with a high mass ratio of lump ore is MgO-C refractory. It is preferred to mix the waste. As a result, the melting of the MgO--C refractory scraps in the cohesive zone can be promoted, and unmelted residue is less likely to occur in the lower part of the furnace. In addition, for the same purpose, one charge of ore raw material is divided into two batches and charged, each batch is mixed with MgO-C refractory scrap, and one of the two batches with a higher mass ratio of lump ore is charged. The mixing ratio of MgO—C refractory scraps in the batch (the ratio of the amount of MgO—C refractory scraps to the total amount of ore raw materials and MgO—C refractory scraps; the same applies hereinafter) is set to the lower mass ratio of lump ore The mixing ratio may be the same as or higher than that of the MgO--C refractory scrap in the batch. Even in this case, although the effect may be slightly lower than when the MgO-C refractory scrap is mixed only in the batch having a high lump ore mass ratio as described above, the MgO-C refractory Dissolution of the scrap in the cohesive zone can be accelerated and undissolved residue is less likely to occur in the lower part of the furnace.

In addition, in order to confirm the substantial upper limit of the mixed amount of MgO—C refractory scrap, the mixed amount of MgO—C refractory scrap was further increased to 30 g, which corresponds to the mixed amount of 54 kg / t in the actual machine. As a result of the test, the maximum pressure loss was 0.37 kPa, and the pressure loss was further reduced. It was confirmed that Based on this result, it is preferable that the upper limit of the mixed amount of MgO—C refractory scraps in an actual machine is about 50 kg/t.

Using an actual bell-less blast furnace (inner volume: 5153 m ³ , furnace caliber: 11.4 m), the following test operation was performed. As raw materials for one charge, one batch of coke and two batches of ore raw materials consisting of lump ore and sintered ore were charged. In charging the ore raw materials, in order to keep the ratio of the central flow and the peripheral flow of the blast furnace gas at an appropriate level and to ensure the ventilation inside the furnace, the ratio of sintered ore to the raw ore (processed ore ratio) is adjusted in the first batch. In the second batch, the ore raw material a-1 having a ratio of sintered ore to the ore raw material (processed ore ratio) of 73 mass% was charged, respectively. Here, the lump ore constituting the ore raw material is T.I. Fe is 63 mass%, and the sintered ore is T.I. Fe was 57 mass%.

The average particle diameter of the coke used (harmonic mean diameter calculated based on the classified opening) was 40 mm, and the average particle diameter of each of the ore raw material a-1 and the ore raw material a-2 (classified opening The harmonic mean diameter calculated based on ) was 12 mm. Here, the harmonic mean diameter was calculated by sieving properly sampled samples with the sieves of coke shown in Table 5 and the ore with meshes shown in Table 6, and using the representative diameters shown in each table.
The charging amounts of ore raw material a-1 and ore raw material a-2 were determined from the tapping ratio and the coke ratio, and ranged from 90 to 100 tons per batch.
As MgO sources, MgO—C refractory scrap, brucite, dolomite, and magnesite were used. These MgO sources use the unsieved material sieved through a sieve with an opening of 50 mm and the sieved material further sieved through a sieve with an opening of 10 mm. was mixed while changing the mixing amount. Tables 3 and 4 show the operation results of this example.
Among the examples in which the MgO source was mixed with both ore raw materials a-1 and a-2, in invention examples 3 and 6 and comparative examples 7 to 12, the ores of ore raw materials a-1 and a-2 were used. The MgO source was mixed so as to have the same mixing ratio with respect to the raw material amount, while in Examples 8 to 11, the mixing ratio of ore raw material a-1 to the ore raw material amount was the ore raw material amount of ore raw material a-2. The MgO source was mixed so as to be higher than the mixing ratio for .

In Examples 1 to 11, the MgO—C refractory scrap was mixed in the ore raw material at a mixing amount of 50 kg/t or less. In these invention examples, in the cohesive zone in the blast furnace, MgO dissolved in unreduced FeO to form a high-melting compound. This is thought to be due to the increased air permeability in the furnace. As a result, the pulverized coal ratio could be increased without lowering the tapping ratio, and the coke ratio could be 350 kg/t or less.
In Invention Examples 1 to 3, 8, and 9, the mixed amount of MgO—C refractory scraps was 10 kg/t, and mixed with ore raw material a-1, ore raw material a-2, ore raw material a-1 and a-2, respectively. bottom. In these invention examples, since the mixed amount of MgO—C refractory scraps is relatively small, there is no difference in the melting behavior of the MgO—C refractory scraps in the cohesive zone, and the coke ratio is 350 kg under any conditions. /t.

On the other hand, in Invention Examples 4 to 6, 10, and 11, the mixed amount of MgO—C refractory scrap was 25 kg/t, and ore raw material a-1, ore raw material a-2, ore raw material a-1 and a-2, respectively. mixed into Among these invention examples, the coke ratio of invention example 4, in which MgO-C refractory scrap was mixed only with ore raw material a-1, was the lowest at 347 kg/t. and a-2, the coke ratio of invention examples 6, 10, and 11, which were mixed so that the mixing ratio of ore raw material a-1 ≧ ore raw material a-2, was the next lowest at 348 kg / t, The coke ratio of Invention Example 5, in which waste was mixed only with ore raw material a-2, was the highest at 349 kg/t. This is because, in Invention Example 4, the MgO—C refractory scrap was mixed only with the ore raw material a-1, which has a relatively high lump ore mass ratio, and the MgO—C refractory scrap melted in the cohesive zone. This is thought to be due to the fact that the unmelted refractory scraps are less likely to hinder ventilation to the lower part of the furnace. In addition, in Invention Examples 6, 10, and 11, the MgO—C refractory scrap was mixed with ore raw materials a-1 and a-2, but the mixing ratio with ore raw materials a-1 and a-2 was made equal or lumps were mixed. Since more of the ore raw material a-1, which has a relatively high mass ratio of ore, was mixed, the melting of MgO—C refractory scrap in the cohesive zone progressed next to Invention Example 4, and undissolved refractory It is believed that this is due to the fact that the obstruction of ventilation to the lower part of the furnace by scraps is less likely to occur. That is, in Invention Examples 4 to 6, 10, and 11, the mixed amount of MgO—C refractory scraps is the same, but in terms of the mixing ratio of MgO—C refractory scraps to ore raw material a-1, Invention Example 4 >Invention Examples 6, 10, 11>Invention Example 5, in which the MgO-C refractory scraps are easily dissolved in this order (undissolved refractory scraps are small), so the above difference in the coke ratio occurred. it is conceivable that.
In Invention Example 7, the MgO—C refractory scrap was mixed only with the ore raw material a-1, but it is thought that the unmelted refractory scrap hindered ventilation to the lower part of the furnace because the mixed amount was as large as 45 kg/t. and the coke ratio increased to 349 kg/t.

On the other hand, in Comparative Examples 1 and 2 in which brucite was mixed only in ore raw material a-1 as an MgO source, and in Comparative Examples 7 and 8 in which brucite was similarly mixed in ore raw materials a-1 and a-2, MgO was Although there is an effect of improving air permeability by forming a high melting point compound by dissolving in unreduced FeO, the MgO source (brucite) does not have a high melting point like MgO—C refractory scrap, so it is difficult to melt. In layering, the effect of increasing the void ratio between particles by the MgO source was not obtained. Therefore, compared with Invention Examples 1 to 11, the effect of improving ventilation was low, and the coke ratio was 351 kg/t or more.
In Comparative Examples 3 and 4, in which dolomite was mixed only with ore raw material a-1 as the MgO source, and in Comparative Examples 9 and 10, in which dolomite was mixed with ore raw materials a-1 and a-2 as well, the increase in slag volume caused deterioration of ventilation. , the coke ratio became 352 kg/t or more.
In Comparative Examples 5 and 6, in which magnesite as the MgO source was mixed only with ore raw material a-1, and in Comparative Examples 11 and 12, where magnesite was mixed with ore raw materials a-1 and a-2 as the MgO source, aeration occurred due to progress of pulverization in the massive zone. deteriorated, the coke ratio became 352 kg/t or more.

Claims (5)

A blast furnace operating method of mixing at least a part of an ore raw material with an auxiliary raw material and charging it into a furnace,
At least part of the auxiliary raw material mixed with the ore raw material is a massive MgO—C-based waste refractory,
A method of operating a blast furnace, wherein the massive MgO—C-based waste refractories are obtained by crushing and granulating used MgO—C-based refractories. 2. The method of operating a blast furnace according to claim 1, wherein the particle size of the MgO—C-based waste refractories is 10 to 50 mm. 3. The method of operating a blast furnace according to claim 1 or 2, wherein the ore raw material comprises treated ore and lump ore. 4. The method according to claim 3 , wherein the ore raw material for one charge is divided into two batches and charged, and only the batch having a higher lump ore mass ratio is mixed with the MgO—C-based waste refractories. blast furnace operation method. One charge of ore raw material is divided into two batches and charged, each batch is mixed with MgO-C-based waste refractories, and the MgO-C of the batch with the higher lump ore mass ratio among the two batches. The blast furnace according to claim 3 , wherein the mixing ratio of the waste refractories is the same as or higher than the mixing ratio of the MgO—C waste refractories of the batch with the lower lump ore mass ratio. Operation method.

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