JP2010084221A - Method for operating blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method with which the mixing state of bulky ore, such as high crystallized water-containing bulky ore, and bulky coke are made up, in a blast furnace operational method for alternately charging the ore and the coke through a bell-armor type furnace top device. <P>SOLUTION: When the ore is loaded on a charging belt-conveyor for conveying charging materials to the furnace top part of the blast furnace for charging the ore into the blast furnace, the bulky ores corresponding to ≤5 vol.% of the whole loaded ores are disposed at the top part of the charging belt-conveyor. It is desirable that the bulky ore disposed at the top part is the bulky ore containing ≥4 mass% crystallized water. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, in a blast furnace having a bell armor type top furnace (hereinafter also referred to as “bell armor blast furnace”), a mixed layer of coke and lump ore is formed. The present invention relates to a blast furnace operation method that realizes high productivity and low reducing material ratio operation while maintaining high reaction efficiency and good air permeability.

  In blast furnace operation, coke as a reducing material and sintered ore, pellets, lump ore, etc. as iron sources (hereinafter, these iron sources are collectively referred to as “ores”) are alternately charged from the top of the furnace. Hot air is blown from the tuyeres at the bottom of the furnace, and an auxiliary reducing material such as pulverized coal is usually blown. Coke and ore charged from the top of the furnace (hereinafter, “coke” and “ore” are collectively referred to as “raw material”) forms a coke layer and an ore layer that are alternately stacked, and loads in the blast furnace. As the temperature falls, the temperature is raised by the gas rising from the lower part of the blast furnace while gradually descending toward the lower part of the blast furnace. The ore softens and shrinks due to temperature rise and reduction, passes through a region called a cohesive zone, melts, drops inside the furnace, and reaches the lower part of the furnace.

  Hot air blown from the tuyere (heated air or oxygen-enriched air) reacts with a reducing material such as coke to produce a reducing gas, which is charged into the blast furnace by the coke that disappeared at this time. The processed ingredients are unloaded.

  In order to operate the blast furnace stably and efficiently, heat exchange and reaction between the gas rising in the furnace and the coke and ore descending in the furnace must be performed efficiently to maintain good air permeability and liquid permeability. is important. In particular, in order to increase productivity, the reducing material ratio (the amount of reducing material required to produce 1 ton of pig iron is expressed in kg, and coke and pulverized coal are usually used as the reducing material). When the operation is directed to do so, the ore layer thickness increases compared to the coke layer thickness in the blast furnace, so the reducing gas concentration decreases in the upper part of the ore layer and the reaction efficiency in the furnace decreases. .

In order to realize a reduction in the blast furnace reducing material ratio which is strongly demanded from the viewpoint of suppressing CO ₂ emission as well as high productivity in recent years, the following problem of a decrease in air permeability must be solved.

  When the particle size of the charge is compared, the particle size of the ore is smaller than that of the coke, so when the ratio of ore to the coke charged to reduce the reducing material ratio increases, the packed bed formed of the charge Porosity decreases. In addition, the lower part of the blast furnace has a cohesive zone (a zone where the ore layer is softened and contracted), which has a high ventilation resistance that governs the air permeability of the entire blast furnace, and the ratio of ore to charged coke increases. This cohesive zone is enlarged. Thus, when the reducing material ratio is decreased, the air permeability tends to decrease.

On the other hand, there is a demand for effective use of low-cost inferior raw materials in response to recent changes in the global demand for raw materials. In the case of an ore, the inferior raw material includes a raw material having a particularly high Al ₂ O ₃ concentration and a high crystal water block ore among natural block ores.

  Here, the “high crystal water block ore” means a natural block ore having a relatively large amount of crystal water (usually 4% by mass or more). When the massive ore with a large amount of crystallization water is heated in the furnace, the crystallization water in the massive ore is volatilized, and pores generated by this dehydration deteriorate the strength of the massive ore at a high temperature. That is, the high-crystal water block ore has low resistance to load softening shrinkage at high temperatures, and the high-temperature aeration resistance is significantly higher than that of sintered ore. This tendency becomes prominent when the amount of water of crystallization becomes 4 to 6% by mass or more, and the strength deterioration after heating at a high temperature (973K or more) and the deterioration of load softening properties become remarkable. For this reason, generally, a high crystal water block ore is not used alone but is charged into a blast furnace together with a sintered ore.

  On the other hand, since the specific surface area of the high crystal water block ore increases due to the occurrence of the pores described above, the reducibility is high compared to a block ore or sintered ore with a small amount of crystal water. Therefore, it is preferable to increase the amount of high crystal water block ore as much as possible from the viewpoint of reducing the reducing material ratio and responding to the recent supply and demand situation of raw materials.

  As described above, high-crystal water block ore is generally mixed with sintered ore and charged into the blast furnace, but high-crystal water block ore with different properties from sintered ore must be used properly according to its characteristics. Thus, a technique aimed at improving the reaction efficiency of the entire blast furnace can be seen.

  As a method for using the high crystal water block ore, in Patent Document 1, after removing the fine powder part (specifically, under 3 mm mesh) of the high crystal water block ore in advance, it is inserted into the blast furnace to allow air permeability in the furnace. A method of maintaining good is disclosed. This method can alleviate the deterioration of air permeability due to clogging of powdered ore, but the high-crystal water block ore is preliminarily removed from the fine powder part, even if it is bulky at the time of charging, However, since the strength deteriorates, it is difficult to avoid the basic problem that the inside of the furnace is finely granulated to increase the air flow resistance and hinder the operation.

  In Patent Document 2, a highly reducible highly crystalline water block ore and a highly reactive coke are placed close together by mixing and charging the highly crystalline water block ore and fine-grained highly reactive coke, Techniques have been disclosed for increasing ore reduction and carbonization gasification to improve reaction efficiency in the same region. However, high-crystal water block ore has extremely low strength in the furnace, and fine-grained high-reactivity coke is generally low-strength. Because it is a necessary condition, the deterioration (strength reduction) of the mixed high crystal water block ore and highly reactive coke is in the block zone (region where both the ore and coke above the cohesive zone are mixed in block) At the same time, there is a possibility that a region that significantly impairs air permeability is generated. In addition, when coke located in the vicinity of the cohesive zone disappears or reaction deteriorates, the softening shrinkage of the high crystal mass ore cannot be suppressed and the pressure loss of the cohesive zone increases. There is also a risk of hindering operations.

  Moreover, in patent document 3, the method of mixing ore with a lump coke in advance and charging is disclosed. If high crystal water block ore is selected as the ore to be mixed, block coke as a spacer will be placed around the high crystal water block ore, reducing the load on the high crystal water block ore with low strength, so-called Due to the aggregate effect, softening shrinkage and deterioration of high-crystal water block ore from around 700 ° C are suppressed, and air permeability can be secured.

In Patent Document 4, in order to form a coke-mixed ore layer in which an appropriate amount of coke is dispersed and mixed in the ore, the coke is cut out and disposed on the ore cut out on the charging belt conveyor from the ore hopper. Thus, an invention intended to charge ore and coke into the furnace at the same time is disclosed. The raw material of the blast furnace is conveyed to a furnace top charging device such as a bell armor type furnace top charging device by a charging belt conveyor, and this invention is an invention that defines a loading method on the charging belt conveyor. is there.
Japanese Patent Laid-Open No. 04-263003 Japanese Patent Laid-Open No. 06-145728 JP 2006-299382 A Japanese Patent Laid-Open No. Sho 62-127411

  However, even with the techniques disclosed in Patent Documents 3 and 4, it was not sufficient to form a uniform mixed layer composed of lump coke and ore having a smaller particle diameter in the blast furnace. .

  Therefore, the present invention flexibly responds to changes in the quality of raw materials used in blast furnaces due to demands for high productivity and raw material supply and demand fluctuations in blast furnace operations based on the recent blast furnace operation with low reducing material ratio or low coke ratio with pulverized coal injection. Correspondingly, while using a high crystal water block ore, a uniform mixing state of the ore containing the high crystal water block ore and the block coke is created in the blast furnace, and both the reaction efficiency and air permeability in the blast furnace are improved. It aims at providing the operation method of the blast furnace which can be maintained.

The present invention provided to achieve the above object is as follows.
(1) In the blast furnace operation method in which ore and coke are alternately charged into the blast furnace using a bell armor type top apparatus, the charge to the blast furnace top is charged to charge the ore into the blast furnace. When ore is loaded on the charging belt conveyor that transports the ore, a lump ore corresponding to a volume of 5% by volume or less of the entire loaded ore is disposed at the top of the charging belt conveyor. Blast furnace operation method.

  (2) The blast furnace operating method according to (1) above, wherein the lump ore disposed at the top of the charging belt conveyor is lump ore containing 4% by mass or more of crystal water.

  (3) The coke is a lump coke having an average particle size of 30 mm or more, and the lump ore disposed at the top of the charging belt conveyor can penetrate a coke layer in a blast furnace made of the lump coke. As described above, the method for operating a blast furnace according to (1) or (2), wherein the average particle size is smaller than that of the lump coke.

  According to the present invention, the ore loaded on the charging belt conveyor has a lump ore corresponding to a volume of 5% by volume or less of the total ore to be charged, preferably containing 4% by mass or more of crystal water content. By arranging the lump ore to be formed, a mixed layer of lump coke and lump ore excellent in reactivity and air permeability can be formed in the vicinity of the falling point of the lump ore in the blast furnace. For this reason, it is possible to improve both the ultimate reduction rate in the blast furnace and the high temperature ventilation resistance index. Therefore, even if it is a low reducing material ratio, the blast furnace operation which is excellent in productivity and economy is realized.

The best mode of the blast furnace operating method according to the present invention will be described below.
1. Segregation phenomenon during deposition of a mixture of lump ore and lump coke The inventors of the present invention have found that in order to find a charging method that can create a uniform mixed layer of lump ore and lump coke near the falling point of the lump ore. A detailed experiment was conducted using a full-scale apparatus simulating a bell armor type furnace top charging apparatus. In addition, by changing the position of the armor (movable armor) by a conventional method of the bell armor type charging device, the falling point of the lump ore can be set at an arbitrary position in the radial direction in the furnace. Therefore, it is possible to accurately grasp the phenomenon at any falling point in the radial direction of the furnace, and appropriately control charging based on the result to form a uniform mixed layer of lump ore and lump coke. If possible, it is possible to arrange a uniform mixed layer of lump ore and lump coke over the entire surface in the radial direction of the furnace. Therefore, the behavior of raw materials in the entire charging process was examined in detail.

  First, as disclosed in Patent Document 3, when lump coke and lump ore are mixed in advance and charged into the large bell hopper from the charging belt conveyor, the mixed state on the belt conveyor is maintained immediately after charging. Although a mixture of lump coke and lump ore is deposited, as the material builds up in the large bell hopper, it is in the radial middle of the large bell hopper that is near the drop point from the charging belt conveyor. In this case, a lump ore having a density larger than that of the lump coke and having a small particle size segregates, and lump coke concentrates and accumulates on the outer periphery of the large bell hopper away from the dropping point and in the vicinity of the large bell (near the center). In other words, no matter how uniform the mixture is before it is charged into the large bell hopper, the uniformity is lost in the large bell hopper after charging. A dense region is formed.

This is due to the fact that massive coke and massive ore differ greatly in shape and density. Bulk coke used in a blast furnace generally has a particle specific gravity of about 1.0 g / cm ³ and a particle size of about 30 to 80 mm. On the other hand, a block ore generally has a particle specific gravity of about 3 g / cm ³ and a particle size of about 10 mm to 40 mm. For this reason, a mixture of lump coke with a small density and a large particle size and a lump ore with a large density and a small particle size lose uniformity when subjected to vibration during transportation, falling, and depositing processes, and lump ore takes precedence. Will sink downward. Therefore, even though it is a uniform mixture on the charging belt conveyor, large ores with a small density and small particle size are screened in the lower part of the sedimentary layer while flowing down the slope inside the large bell hopper. It tends to accumulate while being dropped.

  Because of this tendency, when comparing the moving directions of the lump ore and lump coke on the slope, the lump ore moves in a direction closer to vertical (the principle of preferential flow of lump ore). For this reason, the lump coke that has fallen into the large bell hopper is more likely to deposit on the outside in the furnace radial direction than the lump ore than the lump ore. Therefore, more coke is deposited on the outer peripheral side, and a region in which more ore is deposited near the falling point, which is an inner peripheral region than an outer peripheral region where more coke exists. It becomes like this.

  Once accumulated in this order from the outer periphery to the lump coke and lump ore, the lump coke that falls to the inner periphery side than the lump ore has a lighter density than the lump ore and therefore has a lot of lump ore. It is difficult to flow down to the outer peripheral side beyond the point. For this reason, on the inner circumference side of the area near the drop point where there is much lump ore, the area with more lump ore on the outer circumference side and lump coke on the inner circumference side in accordance with the principle of preferential flow of lump ore above. A region having a large amount of is formed.

  The region having a relatively large lump ore on the outer peripheral side in the region on the inner periphery side than the region near the drop point having a large lump ore is integrated with a region near the drop point where a large amount of the lump ore is accumulated. Accordingly, massive ore is preferentially deposited in the vicinity of the falling point, and the massive coke is concentrated in other regions, that is, the outer periphery of the large bell hopper away from the falling point and in the vicinity of the large bell.

  In this way, since the segregation phenomenon in the deposition process in the bell hopper exists in the mixture of lump ore and lump coke, the mixture of lump coke and lump ore is discharged into the blast furnace by opening the large bell. At the top of discharge, the lump coke existing on the outer periphery of the large bell hopper preferentially falls into the blast furnace. After the lump coke discharged at the top falls into the blast furnace, it flows to the vicinity of the center of the furnace, and the distribution density of the lump coke at the center increases. In addition, even when lump coke and lump ore are discharged in the mixed state after the middle discharge, lump ore with a large density and a small particle size is produced when the mixture flows down the raw material slope after falling into the furnace. As a result of depositing while preferentially moving the voids of the mixed coke in the lower layer direction, the ore is selectively unevenly distributed in the vicinity of the drop point.

  As explained above, even if the lump coke and ore charged in the large bell hopper are uniformly mixed on the charging belt conveyor, they are deposited in the furnace due to the difference in density and particle size between the two. Sometimes segregation is inevitable.

2. Based on the above study, the inventors dropped the ore on the slopes of the coke. We focused on the phenomenon in which some ore that fell to the beginning entered the inside of the vicinity of the drop point in the coke layer (the layer in which only coke is deposited) in the blast furnace.

  As described above, the coke in the coke layer that forms the slope is lighter and rougher than the lump ore to be dropped, so when heavy and fine lump ore particles fall, some of the coke layer that falls inside the coke layer near the drop point The lump ore falls through the voids of the lump coke and falls downward (hereinafter, this phenomenon is also referred to as “penetration”).

  As a result of further observation of the charging process of the lump ore by the present inventors, it was found that the infiltration phenomenon into the coke layer leads to the formation of a uniform mixed layer as follows. First, the ore falling to the top penetrates into the coke layer near the drop point, and the voids between the coke particles existing in the region are filled with the intruded mass ore. For this reason, in the coke layer, a region having a high packing density is generated in the vicinity of the lump dropping point. Since this region is formed with a drop impact of ore, the packing density at this stage is larger than the degree of porosity reduction due to normal mixing of different particles, that is, the degree of packing density increase. For this reason, the slope of the coke layer becomes locally unstable. When the lump ore further falls in this area, the impact of the lump ore particles causes the surface layer portion in the high density area to start collapsing, and part of the lump ore that has entered the lump coke is adjacent to it. It flows into the lower part of the slope (that is, the center side of the blast furnace) together with the lump coke.

  As a result, excessive lump ore in the mixed layer formed by intrusion of lump ore into the space between coke particles immediately after dropping is eliminated, and a uniform mixed layer centering on lump ore falling to the top is formed.

3. Formation condition of uniform mixed layer When the formation condition of this uniform mixed layer was investigated, the amount of massive ore contained in this region was the impact energy of the ore when falling, that is, the fall distance, the charge amount, and Depending on the particle size and density of the massive ore particles and the gas flow rate from the bottom, in the normal blast furnace operating range, these factors mainly affect the particle size and the total amount of ore charged. It was found that the influence of other factors was small.

  Explaining the effect of these on the formation of the mixed layer. When the particle size of the lump ore is sufficiently smaller than the coke particle size near the drop point, penetration of the lump ore between the coke particles is promoted, and uniform mixing is achieved. The area where the layer is formed is enlarged. Further, when the total amount of ore charged increases, the effect of the ore intruding into the coke layer in the vicinity of the drop point is pushed by the load, and the region where the uniform mixed layer is formed is also enlarged.

  Further detailed experiments on this point revealed that the ore forming a mixed layer with coke near the drop point was 5% by volume of the total ore charged. Specifically, 5% by volume of the total ore in the large bell hopper permeates the coke layer at the falling point and is involved in forming a uniform mixed layer in the vicinity of the same region. .

  On the other hand, the ores other than the 5% by volume of the lowest end of all ores in the large bell hopper have already formed a uniform mixed layer of lump coke and lump ore near the falling point of the slope of the coke layer. Above that, it hardly penetrates into the coke layer and forms a normal ore layer.

  Here, the raw material of 5 volume% at the bottom of the large bell corresponds to 5 volume% of the top of the ore on the charging belt conveyor conveyed to the top of the furnace. In the very initial stage of charging, the segregation phenomenon in the charging process from the charging belt conveyor to the large bell hopper does not occur as described above, and the state of the raw material in the charging belt conveyor is maintained as it is. . Therefore, when loading ore into the blast furnace, when loading the ore on the charging belt conveyor that conveys the charge to the top of the blast furnace, the volume of the loaded ore is 5% by volume or less. By adopting a method in which the corresponding lump ore is arranged at the head of the charging belt conveyor, it is possible to efficiently form a mixed layer in the blast furnace. Moreover, in order to fully exhibit this effect, it is desirable that the lump ore arranged at the head part of the charging belt conveyor is 3% by volume or more of the entire loaded ore.

  In this way, if a uniform mixed layer of lump coke and lump ore can be formed, lump coke functions as an aggregate in this mixed layer, so even if the amount of crystal water of the lump ore is large, the entire mixed layer The load softening shrinkage resistance is not significantly reduced. Therefore, even if an inferior raw material with a large amount of crystal water of the lump ore is used, the risk that the in-furnace air permeability is reduced is suppressed. Further, as shown in FIG. 1 showing the relationship between the amount of crystal water of natural block ore (CW, unit: mass%) and the reducibility (RI, unit:%), the reducibility of natural block ore is generally shown. Increases as the amount of water of crystallization contained in the ore increases. For this reason, when the amount of crystal water is large, the reactivity and the air permeability improvement effect by the proximity arrangement effect of the lump ore and lump coke in the mixed layer are more likely to be obtained. Here, according to FIG. 1, the amount of crystallization water corresponding to the reducibility 60 to 70% of ordinary sintered ore is 4% by mass. Therefore, because it is an inferior raw material, it is possible to stably realize productivity equivalent to or higher than that of sintered ore by using high-crystal water block ore with a crystal water amount of 4% by mass or more that can be procured at low cost. It is.

  In summary, in the Belle Armor-type blast furnace, when ore is charged after the coke is charged, a massive ore containing crystal water, preferably a crystal water mass ore with a crystal water amount of 4% by mass or more is charged immediately after the coke. By placing it at the top of the ore on the charging belt conveyor that conveys 5% by volume or less of the amount of ore to be introduced to the top of the blast furnace furnace, high reaction efficiency and good air permeability can be achieved even when a large amount of inferior raw material is used Maintained high productivity and low-reducing material ratio operation can be realized stably.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
1. Charging apparatus A charging experiment was conducted with a full-scale charging apparatus simulating a bell-armor type furnace top charging system of an actual blast furnace (internal volume 2150 m ³ ).

  FIG. 2 is a perspective view conceptually showing the charging device used in this embodiment. This charging device has a rectangular shape with the radial direction from the furnace center to the furnace wall at the top of the blast furnace furnace, and its cross section is transparent so that the falling and deposition behavior of raw materials can be observed directly. It is made of an acrylic board. Further, as shown in FIG. 2, as in the bell-armor type top charging system of the actual blast furnace, a large bell hopper a, a large bell b included therein, and an armor plate c are provided at the upper part of the apparatus. Has been placed. The armor plate c is variable in angle from the vertical axis (movable armor) and has a function of adjusting the charging position in the furnace by changing the angle at which the falling material repels.

  From the charging belt conveyor (not shown), the raw material deposited in the large bell hopper a of the charging device falls into the furnace by lowering the large bell b, and then repels the armor plate c in the furnace. Deposit on the slope. At this time, the height of the large bell b can be set together with the large bell hopper a so as to keep the fall distance d constant.

  In the normal bell blast furnace, when the angle from the vertical axis of the armor plate c is 0, the fall distance d is such that the fall trajectory of the raw material flow discharged from the large bell hopper a reaches the furnace periphery sufficiently. In this experiment, d = 3.65 m as a standard value.

  In addition, as shown by f in the figure, independent gas flow rate adjustment is possible for each of the four branch pipes arranged at the lower part of the apparatus. In the actual blast furnace, the gas flow velocity distribution in the furnace top radius direction estimated from the gas composition and temperature measured at several locations in the radial direction was simulated, and the gas flow velocity at the furnace center was set to be larger than the peripheral portion. Specifically, the gas flow velocity at a position where the distance from the center is 12.5% of the radius is 5.3 m / s, and the position where the gas flow velocity is 37.5% by the same calculation is 2.1 m / s. , 62.5% was 0.74 m / s, and 87.5% was 0.34 m / s.

Note that the above experimental conditions are typical examples of normal blast furnace operation, and do not affect the experimental results within the normal blast furnace operation range.
If the actual blast furnace is used as the raw material and the gas flow velocity distribution equivalent to the actual blast furnace is given from the lower part of the equipment by the high-pressure blower, the raw material charged into the furnace falls with the same charging energy as the actual furnace. Since the deposition is performed while receiving a pressure loss due to the rising gas equivalent to the actual blast furnace, it is possible to observe the deposition behavior of the blast furnace raw material, which precisely reproduces the situation in the actual blast furnace with this experimental apparatus.

  Further, after the charging, it is possible to measure the formation state of the mixed layer, for example, the mixing ratio, by collecting the raw material after deposition over the entire radial direction. This “mixing ratio” indicates the ratio of the ore mixed near the drop point to the coke layer (unit:%), (the amount of block ore mixed in the coke layer near the drop point) / (Amount of ore at the top of the charging belt conveyor) × 100. In addition, “the lump ore mixed in the coke layer” refers to a lump ore that exists below the surface level of the coke layer before the lump ore is charged, that is, penetrates the coke layer.

2. Insertion Experiment The following experiment was performed using the above-described charging apparatus.
First, lump coke was charged into the furnace from the charging belt conveyor via a large bell hopper under the actual blast furnace conditions, and a coke layer having a slope was formed at the furnace port of the charging test apparatus. Next, ore is placed on the charging belt conveyor. At this time, the ore is placed at a predetermined volume ratio with respect to the total ore at the top of the charging belt conveyor, and the remaining ore is composed of the remaining lump ore. The sintered ore was mixed and placed on the charging belt conveyor. This mixing ratio changed for each charging experiment, but the mixing ratio was set constant on the charging belt conveyor of each experiment. In addition, for the ore placed at the top of this charging belt conveyor, in order to compare the effect of reducibility according to the level of crystallization water, the ore with a crystallization water content (crystallization water amount) of 3 mass% and 5 mass % Ore. In addition, the same ore brand was used for these lump ores also in the load softening experiment mentioned later.

  Assuming the normal blast furnace operating range, 80% by mass of sintered ore and 20% by mass of lump ore out of all ores, and high crystal water mass ore with crystal water of 5% by mass or more of lump ore. 40% by mass, that is, 8% by mass of the total ore was blended.

  In addition, since the amount of ore that permeates the coke layer varies depending on the experimental conditions, the weight ratio of each raw material changed with each charging experiment. When the example of the weight ratio of the raw material which concerns on an experiment was given, they were 332 kg of coke, 1040 kg of sintered ores, and 260 kg of block ores with a crystal water content of 3% by mass or 5% by mass.

  In consideration of the particle size at which permeation into the coke layer sufficiently occurred, the average particle size of the lump ore was 20 mm, and the average particle size of the lump coke was 35 mm. Here, the average particle size of the lump coke is set on the small diameter side of the particle size range (30 to 80 mm) of the lump coke usually used in a blast furnace. This is due to the following reason. That is, the lump coke charged into the large bell hopper from the charging belt conveyor is such that the smaller particle size is in the downward direction and the larger particle size is in the upper direction in the process of being deposited in the large bell hopper. Segregate. Therefore, at the initial stage of charging the raw material from the large bell hopper into the blast furnace, the particle size of the lump coke supplied to the blast furnace after the lump ore is relatively small. Therefore, in this experiment for reproducing the infiltration of the lump ore into the coke layer at the initial stage of charging the raw material into the blast furnace, the average particle diameter of the lump coke is set to 35 mm in order to reproduce a more realistic charging state.

3. Next, in the above charging experiment, in the above charging experiment, a laminated structure composed of lump coke and lump ore formed in the vicinity of the drop point, i.e., a structure composed of coke layer, ore layer and mixed layer, The particle size was reduced to about 1/3 scale, and a packed bed having a height of 300 mm and a diameter of 70 mm was reproduced in a graphite crucible, and a high temperature load softening dripping experiment was conducted. As shown in FIG. 3, which is a cross-sectional view conceptually showing the lamination state of each layer in the graphite crucible, a coke layer in which a coke layer is deposited at the lowermost portion in the graphite crucible and a lump ore is mixed thereon, That is, a mixed layer was deposited, and an ore layer composed of massive ore and sintered ore was disposed thereon. In this structure, the lump ore in the mixed layer corresponds to “the ore mixed in the coke packed bed”.

  In addition, in order to compare the influence of the arrangement of the packed bed structure consisting of coke, lump ore and sintered ore, coke, lump ore and sintered ore existing in the crucible were also tested when the thickness of each layer was changed. The total volume in each was constant.

  The high temperature load softening dripping experiment is a test that gives a load pattern from the temperature, gas composition and upper part of the packed bed according to the assumed blast furnace conditions, and is an experimental method known as a test for evaluating the high temperature properties of ores. .

In the experiment in this example, the temperature was raised from room temperature to 1923K over about 6 hours as shown in FIG. In addition, the composition of the introduced gas is obtained by changing the supply flow rate of each gas of CO, CO ₂ and N ₂ in the above temperature rising time as shown in FIG. , CO ₂ : 0 to 22% by volume, N ₂ : 54% by volume, and these conditions were constant in all experiments. As shown in FIG. 4C, the load applied to the sample was varied in the range of 30 to 98 kPa, and this condition was also constant in any experiment. These patterns of temperature, gas composition and load are set based on actual blast furnace conditions.

The mixed layer softens and shrinks during the above temperature rising period, and the reduction rate when the gas reduction reaction is completed is determined based on the input / output gas flow rate and the gas composition analysis value, and oxygen based on each sample weight loss measurement value after the experiment, It was calculated from the balance of carbon and used as the “attained reduction rate” (unit:%). Further, during the experiment, the displacement due to the shrinkage of the packed bed and the pressure loss were continuously measured, and the high temperature ventilation resistance per packed bed height was integrated from 1273K to 1873K with the following equation. The “high temperature ventilation resistance index: KS” (unit: K / m ^1.3 ) represented by (1) was determined. This high temperature ventilation resistance index is an index corresponding to the ventilation resistance of the cohesive zone in the blast furnace, and is about 300 to 400 × 10 ⁵ K / m ^1.3 for a normal blast furnace raw material. Gets worse.

ここで、ΔP:圧力損失(N/m²)
μ_g:ガス粘度(kg/m/sec)
ΔL:層厚(m)
ρ_g:ガス密度(kg/m³)
u_g:ガス速度(m/s)
T :温度(K) である。

Where ΔP: Pressure loss (N / m ² )
mu _g: gas viscosity (kg / m / sec)
ΔL: Layer thickness (m)
ρ _g : Gas density (kg / m ³ )
u _g : Gas velocity (m / s)
T: Temperature (K).

4). Results Table 1 shows the conditions of the above charging experiment and the high temperature load softening dripping experiment, and the results thereof.

Here, the determination on the stability of the mixed layer and the determination and evaluation criteria in Evaluation 1 are as follows.
Stable (O): In the charging experiment, the number of experiments under the same conditions was 4 times or more, and the variation ((maximum value−minimum value) / average value) in that case was less than 10% unstable (× ): The number of experiments under the same conditions in the charging experiment is 4 times or more, and the variation in the mixing ratio in that case is 10% or more Undecidable (-): The number of experiments under the same conditions in the charging experiment is 4 times In some cases, a mixed layer cannot be formed.

The evaluation criteria in the evaluation 2 for the ultimate reduction rate are as follows.
○ (good): 80% or more in all experiments under the same conditions Δ (possible): the ultimate reduction rate may be 60% or more and less than 80% × (not possible): the same ultimate reduction rate <60% in all experiments with conditions

The evaluation criteria in Evaluation 3 for the high temperature ventilation resistance index are as follows.
○ (Good): High temperature ventilation resistance index is less than 400 × 10 ⁵ K / m ^1.3 in all experiments under the same conditions. Δ (Yes): High temperature ventilation resistance index is 400 × 10 ⁵ K / m ^1.3 or more. Less than 500 × 10 ⁵ K / m ^1.3 × (impossible): 500 × 10 ⁵ K / m ^1.3 or more in all experiments under the same conditions for high-temperature ventilation resistance

The evaluation criteria for comprehensive evaluation are as follows.
○ (good): Evaluations 1, 2, and 3 are all ○ (good). △ (possible): Both evaluations 1, 2, and 3 are ○ (good) or △ (possible). ): Any of Evaluations 1, 2, and 3 is x (impossible) or-(impossible to judge)

  Since Conventional Example 1 does not define the position of the lump ore on the charging belt conveyor, the lump ore is mixed on the charging belt conveyor for the lump ore mixed in the coke layer near the drop point. It depends on the position where it is done. For this reason, both the ultimate reduction rate and the high temperature ventilation resistance index fluctuated greatly, and it was not possible to improve them.

  Moreover, in the conventional example 2, since the coke and lump ore mixed in advance are easily separated from lump coke and lump ore on the large bell in the large bell hopper, the formation of the mixed layer after dropping in the furnace is stable. However, according to the high temperature load softening dripping experiment that reproduced the best mixing, the ultimate reduction rate was high and the high temperature ventilation resistance index was sometimes low and good. . Although the effect of the mixed layer of massive coke and massive ore is recognized, it can be seen that the method of building a stable mixed layer is important.

  In both the comparative example and the example, a predetermined amount of lump ore was placed at the top of the charging belt conveyor. When the arrangement amount of the lump ore arranged at the top (head lump ore) is 5% by mass or less of the total ore charged (Examples 1 to 4), almost the entire amount is mixed in the coke layer at the dropping point. However, when the arrangement amount of the head ore is increased to 7% by mass (Comparative Examples 1 and 2), about 60% of the ore placed at the beginning is mixed in the coke layer. The rate was about 55 to 60%, and the remaining 40% was present between the coke layer and the ore layer.

  According to a reaction experiment in which the deposition situation near the drop point was reproduced in a graphite crucible, when the leading ore was a lump ore with a crystal water content of 3% by mass, the ultimate reduction rate was all normal blast furnace fusion. Although the required 85% could not be exceeded at the belt level, when the leading ore was a massive ore with a crystal water amount of 5% by mass, it exceeded 90% at any mixing rate. As shown in Fig. 1, it is considered that the ultimate reduction rate of 85% or more required in a normal blast furnace could be maintained by containing 4% by mass or more of crystal water having reducibility equivalent to that of sintered ore. It is done.

As shown in Examples 3 and 4, the high temperature aeration resistance index is as low as 205 to 210 × 10 ⁵ K / m ^1.3 when coke is almost mixed with massive ore, but it is a comparative example. As shown in Fig. 4, when there is a simple layer of ore ore in addition to mixing with coke, it is very high at 980 x 10 ⁵ K / m ^1.3 , which clearly affects air permeability. Became. This is probably because the lump ore simple packed layer portion softens and shrinks from a relatively low temperature of about 773 K or more, and thus the airflow resistance increases from a low temperature and the pressure loss significantly increases after fusion. Therefore, as in Examples 1 and 2, when the ore is mixed in the coke packed bed, the softening shrinkage resistance increases due to the aggregate effect of the coke even when subjected to a load, and the packed bed It is considered that the air gap was maintained and the effect of reducing the airflow resistance was exhibited.

It is a graph which shows the relationship between the crystal water content in a lump ore, and reducibility. It is a perspective view which shows notionally the structure of a real scale charging experiment apparatus, and the lamination | stacking state of the lump coke and lump ore arrange | positioned inside it. It is sectional drawing which shows notionally the lamination | stacking state of the high temperature load softening dripping experimental apparatus and the lump coke and lump ore arrange | positioned inside it. It is a graph which shows the temperature pattern (a), gas flow rate pattern (b), and load pattern (c) in a high temperature load softening dripping experiment.

Explanation of symbols

a-Large bell hopper
b-large bell
c-Armor plate
d-Stock level
e-raw material
f-blower blower

Claims (3)

  In the blast furnace operation method in which ore and coke are alternately charged into the blast furnace using a bell armor type top apparatus, the charge is transferred to the blast furnace top in order to charge the ore into the blast furnace. A blast furnace operating method characterized in that, when ore is loaded on a charging belt conveyor, a lump ore corresponding to a volume of 5% by volume or less of the entire loaded ore is disposed at a leading portion of the charging belt conveyor. .   The blast furnace operating method according to claim 1, wherein the lump ore disposed at the leading portion of the charging belt conveyor is a lump ore containing 4% by mass or more of crystal water.   The coke is a lump coke having an average particle size of 30 mm or more, and the lump ore disposed at the top of the charging belt conveyor is infiltrated into a coke layer in a blast furnace made of the lump coke. The blast furnace operating method according to claim 1 or 2, wherein the average particle size is smaller than that of the lump coke.

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