Operation method of a vertical furnace

Abstract

To provide a technique, in a screen in a feed process of raw materials to a vertical furnace, which can prevent clogging of the screen upon using raw materials having a high water content and can feed charging massive raw materials having reduced fine particles and having high strength to the vertical furnace at a high yield.SOLUTION: Provided is a vertical furnace operation method in which a powdery water absorbent is added to ore raw materials in a wet state so as to be mixed, the mixture is sieved in a mixed state to separate the wetted ore raw materials into undersieve powders and raw materials for a vertical furnace after fine powder removal, and when the oversieve ore raw materials as the raw materials for a vertical furnace after fine powder removal are charged to a vertical furnace, a particle diameter after swelling of the water absorber is controlled to 1 / 2 or less of an opening of a sieve used for the sieving.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for efficiently operating a shaft furnace by screening raw materials such as iron ore in an iron-making process and pre-removing fine powder.

Background Art

[0002] In an iron-making process using a shaft furnace such as a blast furnace, it is necessary to circulate a reducing gas in the raw material packed bed in the furnace to reduce the raw materials. Therefore, it is necessary to secure voids through which gas can flow in order to perform efficient and low-cost operation. It is desirable to charge raw materials for shaft furnace charging such as iron ore, coke, and sintered ore into the shaft furnace after pre-removing fine powder. For this reason, each iron-making plant has installed screening equipment (vibrating screen) for removing fine powder from these raw materials. However, for raw materials stored in an outdoor yard, when the moisture content increases due to rain or the like during storage of the raw materials, the adhesion force of the fine powder increases, so the removal of powder by the conventional screen is not sufficient. In particular, iron ore has a high affinity for moisture, and it is very difficult to remove fine powder when it is wet. In addition, when the moisture content of the raw materials is high, clay-based raw materials adhere to the screen of the sieve, causing clogging.

[0003] For this reason, in screening equipment for raw materials with high moisture adhesion, for example, sieves with a relatively large normal mesh opening have been used. For example, even for the same blast furnace raw materials, sintered ore directly sent from a sintering plant contains almost no moisture and powder easily falls, so a sieve with a normal mesh opening of about 4 mm is used for removing fine powder. On the other hand, in the case of sintered ore that has been stored in the yard and thus contains moisture and often has powder adhering to it, a sieve with a mesh opening of about 5 mm is used to enhance the powder removal performance and suppress clogging. That is, raw materials within the range of 4 to 5 mm that can be directly used as normal blast furnace raw materials are also screened out, which is a factor in reducing the yield. Also, even when using a sieve with a mesh opening of 5 mm, a part of the powder with a particle size of 1 mm or less still adheres to the raw materials of 5 mm or more and does not fall, and the powder removal efficiency has not been significantly improved.

[0004] A sieving method that can improve the efficiency of removing powder from wet raw materials such as iron ore is known, which includes a special screen having an expandable sieve mesh and a movable mechanism that transports the raw material while deforming the mesh in a linked up-down and left-right motion, such as the Jumping Screen (registered trademark). In the Jumping Screen (registered trademark), the raw material is bounced up by repeatedly applying tension and release to the urethane mesh, and the impact force upon falling is expected to disperse any attached powder. In addition, because the mesh is constantly deforming, clogging is less likely to occur even when using wet raw materials.

[0005] As a method for removing adhering powder from wet raw materials other than sieving, a method is known in which iron ore with fine powder adhering to it is washed with water using a screen-type jet washing machine to remove the adhering powder (see, for example, Patent Document 1). Because the washing water is forcefully sprayed over the screen, the powder adhering to the iron ore is thoroughly washed, and the washing liquid containing the adhering powder is effectively removed by a screen-type dewatering machine and a liquid cyclone. It is considered that it can be processed efficiently.

[0006] Furthermore, Patent Document 2 discloses a method for operating a blast furnace in which a moisture absorbent is added to the blast furnace raw materials in a wet state, mixed, and the sieved mixture is then charged into the blast furnace. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 07-113127 [Patent Document 2] Japanese Patent Publication No. 2009-114516 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, conventional technology had the following problems: Blast furnace raw materials, which contain a large amount of adhering powder when wet, have traditionally been classified using sieves with large mesh sizes. However, although this significantly reduces yield, adhering powder still remains on the sieve, and the effect of removing adhering powder is not very significant.

[0009] Furthermore, while the sieving method using special screens can be expected to separate adhering powder from wet raw materials, the screen material is made of resin such as urethane and is constantly deforming and expanding, so durability is a problem, especially when using hard, high-density materials such as iron ore. If the screen durability is low, not only will the running costs associated with screen replacement be high, but the frequency of stopping the line for replacement will increase, which can be a major factor in the deterioration of productivity. In addition, since the format is significantly different from the vibrating screens conventionally used in steel mills, it is necessary to remove the conventional screens and construct new equipment for the special screens, which is expected to require enormous equipment costs. For these reasons, special screens are not widely used as a sieving method for steelmaking raw materials.

[0010] The method of washing iron ore with water using a screen-type jet washer described in Patent Document 1 requires enormous construction costs to build new equipment such as a screen-type jet washer, a screen-type dewaterer, and a liquid cyclone. Furthermore, especially when treating water containing fine iron ore powder, there is a problem of high maintenance costs due to severe wear on the equipment. In addition, the amount of water carried into the blast furnace by the water adhering to the iron ore after washing may decrease the blast furnace top temperature and potentially destabilize operations.

[0011] The technology described in Patent Document 2 uses a sieve with an opening of about 10 mm and does not specify the particle size of the moisture absorbent. Therefore, if a sieve with an opening of 5 mm is used, for example, there is a risk that some of the moisture absorbent will remain on the sieve.

[0012] The present invention has been made in view of the above circumstances, and aims to propose a method for operating a vertical furnace that prevents screen clogging when using raw materials with high moisture content in the raw material supply process to the vertical furnace, and that can supply solid raw materials with fewer fine particles and high strength to the vertical furnace with good yield. [Means for solving the problem]

[0013] The present invention provides a method for operating a vertical furnace that advantageously solves the above problems, characterized by adding a powdered moisture absorbent to a wet ore raw material and mixing it, sieving the mixed material to separate the wet ore raw material into a sieved powder and a material to be sent to the vertical furnace after the fine powder has been removed, and when charging the sieved ore raw material, which is the material to be sent to the vertical furnace after the fine powder has been removed, the particle size of the moisture absorbent after swelling is set to be 1 / 2 or less of the mesh opening of the sieve used for sieving.

[0014] Furthermore, the operating method of the vertical furnace according to the present invention is as follows: (a) Use a superabsorbent polymer as a moisture absorbent. (b) Adding a moisture absorbent to the ore raw material on a belt conveyor, and mixing the ore raw material and the moisture absorbent by utilizing the impact of the drop in height when transferring between belts on the belt conveyor. These are considered to be more desirable solutions. [Effects of the Invention]

[0015] According to the present invention, in the process of supplying raw materials to a vertical furnace, the screen is prevented from clogging when using raw materials with a high moisture content, thereby improving productivity. Furthermore, since lumpy raw materials with fewer fine particles and high strength can be supplied to the vertical furnace with good yield, the ventilation inside the vertical furnace is ensured, and operational stability is improved. [Brief explanation of the drawing]

[0016] [Figure 1]It is a graph showing the influence of the addition of a moisture absorbent on the relationship between the ratio of particle size of ore less than or equal to 5 mm and the clogging rate of an ore screen.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be specifically described. The technical idea of the present invention can be variously modified within the technical scope described in the claims.

[0018] In the present invention, by adding a moisture absorbent to the raw materials of a shaft furnace, mixing them, and performing sieving, moisture is removed from the blast furnace raw materials in a wet state due to the presence of moisture, and the adhesion of fine powder due to moisture bridging can be reduced. As a result, fine powder can be easily removed while preventing clogging of the ore screen. Then, the oversize, which is the raw material of the shaft furnace from which fine powder has been removed by sieving, is charged into the shaft furnace for operation, for example, to produce pig iron. The present invention is applicable to all raw materials of shaft furnaces in a wet state, but particularly shows remarkable effects when applied to sieving of iron ore, coal, coke, sintered ore, limestone, etc., which have strong moisture adhesion.

[0019] Incidentally, the wet state means a state in which moisture exists on the surface of particles such as iron ore. The effect of the surfactant on the water content of raw materials such as sintered ore varies depending on the pore distribution inside the particles of the raw materials (since the moisture on the particle surface after moisture is absorbed into the pores inside the target particles is the problem), and the effect is significant when the water content of the raw material is 5 mass% or more.

[0020] The moisture absorbent used in this invention is preferably a substance that has a very fast moisture absorption rate and does not exhibit stickiness by trapping moisture within its molecular structure after absorption. Examples of such substances include silica gel and various polymeric water absorbents. Polymeric water absorbents such as polyacrylate (sodium, potassium) resins are particularly suitable. These polymeric water absorbents are more suitable because they can absorb several hundred times their own weight in water and have a remarkably fast moisture absorption rate. Therefore, it is especially preferable to use polymeric water absorbents as the moisture absorbent. It is also particularly preferable to use inorganic silica gel, activated alumina, zeolite, activated carbon, etc. in combination.

[0021] Superabsorbent polymers are chemicals that absorb hundreds of times their own weight in water and swell. For example, superabsorbent polymers (water-absorbing polymers) have the property of swelling to about 400 times their original size in pure water. For example, in suspended spring water where powder and spring water are suspended, it has been confirmed that the practical limit is about 200 times. When the swelling rate of the added superabsorbent polymer is small, the swollen material tends to bounce, and it is expected that it will scatter outside the conveyor belt during transport. Therefore, it is preferable to ensure that the swelling rate is 30 times or more. Furthermore, the particle size of the superabsorbent polymer after swelling should be less than or equal to 1 / 2 of the sieve opening. Preferably, it should be less than or equal to 1 / 3. This ensures that the swollen superabsorbent polymer falls through the sieve and prevents it from contaminating the vertical furnace.

[0022] As a method of adding a moisture absorbent to the raw materials of a vertical furnace, there are methods such as adding it in the yard and mixing with heavy machinery, or adding it onto the blast furnace raw materials on a belt conveyor and mixing by utilizing the dropping impact in the transfer chute of the belt conveyor. If the mixing effect is sufficient, the latter method is more desirable because it is lower in cost. Also, the position where the moisture absorbent is added on the belt conveyor is preferably as far away from the sieve as possible and preferably at a position closer to the raw material yard side. This is because when it passes through a larger transfer drop and is conveyed for a longer time, the moisture absorbent is more likely to spread throughout the object, and it is possible to ensure more time required for water absorption.

[0023] Furthermore, as a method of cutting out the moisture absorbent when adding the moisture absorbent to the raw materials of the vertical furnace, various powder metering cutting methods such as cutting out by a vibrating feeder can be applied. Since the moisture absorbent takes in moisture in the air and may deteriorate or condense, it is preferably in a sealed state that is blocked from the outside air until immediately before being added to the raw materials of the vertical furnace. Therefore, from the above viewpoints, the method of pneumatically transporting it through the pipe by pressure from a storage tank in a sealed state and spraying it onto the raw materials of the vertical furnace using the pressure is the most suitable. After adding and mixing the moisture absorbent, screening is performed using a conventional screening facility. The screening facility can be operated under the same operating conditions as conventional ones and does not require special operations.

Example

[0024] To confirm the effects of the present invention, tests were conducted under the following conditions. Using various types of ore and sintered ore, the difference in the clogging rate of a 5mm mesh ore screen was compared when a superabsorbent polymer (SAP) was added as a moisture absorbent and when it was not. After each type of sintered ore was thoroughly dried, the ratio of particle size minus 5mm was investigated as a percentage of the mass below the 5mm mesh sieve. The clogging rate (%) of the ore screen was expressed as a percentage of the number of clogging sieve openings, as visually determined. Figure 1 shows the effect of the presence or absence of moisture absorbent on the relationship between the clogging rate of the ore screen and the ratio of particle size minus 5mm (mass%) of each ore. At this time, the moisture content of the ore was in the range of 7-9 mass%. The amount of moisture absorbent added was such that the swelling rate was 100 times that of the moisture content of the ore, and the particle size of the moisture absorbent after swelling was at most about 30% of the mesh opening. The clogging rate of the ore screen was investigated after approximately 200 tons of ore had passed through.

[0025] As is clear from Figure 1, the clogging rate of the ore screen increases as the proportion of ore particles with a particle size of -5 mm increases. When comparing ore with the same proportion of -5 mm particles, it can be seen that the clogging rate of the ore screen improves by about 20% with the addition of a moisture absorbent. Normally, when the clogging rate of the ore screen exceeds 20%, the screen needs to be cleaned or replaced. By adding a moisture absorbent, the frequency of this cleaning or replacement is greatly reduced, and productivity is improved. In addition, when no moisture absorbent was added, it was observed that a large amount of fine powder with a particle size of -5 mm adhered to the ore on the sieve of the ore screen. On the other hand, when a moisture absorbent was added, more than 90% of the fine powder with a particle size of -5 mm was recovered below the 5 mm sieve. In other words, it became possible to transport high-strength, lumpy ore, from which the fine powder had been removed, to the vertical furnace.

Claims

1. A powdered moisture absorbent is added to the wet ore raw material and mixed. The mixed material is then sieved to separate the wet ore raw material into the sieved powder and the material for the vertical furnace after the fine powder has been removed. When the sieved ore raw material, which is the material for the vertical furnace from which the fine powder has been removed, is charged into the vertical furnace, The particle size of the moisture absorbent after swelling is set to be 1 / 3 or less of the 5 mm mesh size of the sieve used for sieving. A method for operating a vertical furnace, wherein the swelling rate of the aforementioned moisture absorbent is 30 times or more and 200 times or less.

2. The method for operating a vertical furnace according to claim 1, wherein a superabsorbent polymer is used as the moisture absorbent.

3. A method for operating a vertical furnace according to claim 1 or 2, comprising adding a moisture absorbent to the ore raw material on a belt conveyor and mixing the ore raw material and the moisture absorbent using the impact of the drop in height when the belt conveyor is transferred.

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