JP3781153B2 - Production method of cheap reduced iron from steelmaking dust - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a processing method for recycling various kinds of dust generated in iron ore or steelworks, and in particular, when reducing iron is produced using ironmaking dust as a raw material, the drying process can be shortened. In addition, the present invention relates to a method for producing reduced iron that is easy to handle reduced iron products.
[0002]
Conventionally, various dusts are generated in processing and refining processes such as sintering, blast furnaces, converters, electric furnaces, etc. at steelworks. In these steps, the dust is extremely fine because it is mainly collected by the dust collector accompanying the process gas. When reducing iron is produced using this as a raw material for dust, a carbonaceous material is blended as a reducing agent to form spherical pellets, which are then reduced in a reduction firing furnace. Hereinafter, the spherical pellet is referred to as a pellet.
This pellet uses the surface tension of water to adhere the dust particles, makes the aggregate of particles spherical for rolling operation, and at the same time improves the surface tension of the water by increasing the surface tension of the particles and increasing the crushing strength of the pellet Is.
[0003]
As a manufacturing method of this pellet, there are a drum type and a disk type. Both have a difference in rolling method. In the drum type, the drum is placed sideways and rotated to roll the particles. The disc mold tilts the disc to about 45 degrees, rotates, and rolls the particles in the disc. In any method, rolling causes the air inside the pellet to be pushed out of the pellet, reducing the pores and increasing the crushing strength.
In general, the adhered moisture of the pellets thus produced is 8 to 25%. The smaller the particles, the greater the surface area of the particles and the greater the moisture attached.
[0004]
[Problems to be solved by the invention]
When iron-making dust is made into pellets by the above method, there are many fine particles and the adhering moisture is 20 to 25%. When reducing pellets with a moisture content of 20 to 25% in a firing furnace, the temperature of the firing furnace is as high as 1100 to 1300 ° C. Therefore, if pellets with a moisture content of 20 to 25% are directly charged, the moisture content inside the pellet is reduced. It rapidly gasifies and explodes. In order to avoid this explosion, the pellets are dried in advance to eliminate the moisture causing the explosion. For this reason, in an actual reduced iron production facility, it is necessary to install a dryer and remove moisture in the charging process into the firing furnace. This has the problem that a large amount of energy for drying is required and the equipment cost is high. As a result, recycling of steelmaking dust has a great economic burden and is an obstacle to realization.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have made extensive developments. As a result, the present invention proposes a method in which the material to be reduced does not explode even when the material to be reduced is directly placed in the firing furnace at 1100-1300 ° C. To do. The gist of the invention is that
(1) When producing reduced iron from iron ore or iron-making dust, a cylindrical granule having a diameter of 8 to 20 mm and a length of 10 to 50 mm is obtained from a mixture composed of iron ore or a plurality of types of dust and charcoal. After manufacturing and drying to a moisture content of 15% or less with a dryer, reduction treatment is performed at a temperature of 1100 to 1300 ° C. in a rotary hearth-type firing furnace. Method.
(2) The method for producing reduced reduced iron from iron-making dust or the like according to the above (1), which comprises a columnar granulated product having a diameter of 10 mm to 15 mm and a length of 20 mm to 40 mm.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
It is necessary not to cause explosion even if the material to be reduced is directly put into the temperature of the firing furnace of 1100 to 1300 ° C. For this purpose, a gas passage, that is, a pore for releasing the gas to the outside even if the adhering moisture is rapidly gasified may be formed.
However, the conventional pellets for rolling operation are dense and spherical when dried, so the shrinkage is constant in any direction, cracking is difficult to occur in the drying process, and as a result, the gas path, that is, the pores are increased. It is difficult to let
[0007]
Therefore, as a method of increasing the pores and obtaining the same crushing strength as the pellet, if the conventional spherical shape is stopped and the cylindrical shape is used, the shrinkage amount varies between the diameter direction and the longitudinal direction during drying. Arise. It has been found that the generation of cracks is effective in preventing gas explosion during gasification of the adhering moisture and preventing explosion.
Based on such knowledge, iron ore as a raw material, or in particular, the dust generated in the steel mill is used, the main components of the dust consists of Fe, Zn, Cr, C and slag, And the particle diameter is almost 1 mm or less.
[0008]
When a raw material having such a component and particle size is used, reducing carbon and a binder are added to the raw material and kneaded. Moreover, in the present invention, this kneaded product needs to be granulated into a columnar shape. For that purpose, proper adhesion moisture is required. Therefore, if the adhering moisture exceeds an appropriate value, the raw material must be dried, and if it is insufficient, water must be added. Moreover, the granulation is made into a cylindrical shape using an extrusion granulator. The dimensions of the granulated product at that time are 8-20 mm in diameter and 10-50 mm in length. The diameter is related to the reduction time. On the premise of industrial productivity, the diameter is preferably 8 to 20, and if the diameter exceeds 20 mm, the reduction time is extended and the reduction rate is lowered. More preferably, the diameter is 10 mm to 15 mm and the length is 20 mm to 40 mm.
[0009]
As described above, when a typical iron-making dust is used, the proper adhesion moisture at the time of granulation is 20 to 25%. This granulated product is dried to a moisture content of 15% or less with a dryer. The granulated material is put into the rotary hearth with cracks. The extrusion pressure is increased to increase the drop strength of the granulated material so that it does not break when thrown. Even if the amount of binder added is increased, the drop strength increases. And the granulated product supplied to the rotary hearth is gasified in the furnace atmosphere at 1100 to 1300 ° C., and the attached moisture is rapidly gasified and discharged out of the granulated product. Then, C which is an interior thing reduces Fe etc. as a reducing agent. The reduced granulated product is discharged out of the system, cooled, and the powder is removed with a screen to obtain a product.
[0010]
Since the finished product is cylindrical, it can be transported efficiently on the belt conveyor without any rolling phenomenon, even when it is tilted large. Moreover, even if it directly granulates into a high temperature atmosphere by granulating it into a cylindrical shape using an extrusion granulator and drying the adhering moisture to 15% or less, the explosion phenomenon of the granulated material can be avoided. This has the great effect that the installation capacity of the dryer may be small and the drying cost is reduced.
[0011]
【Example】
Hereinafter, the present invention will be specifically described with reference to the drawings.
FIG. 1 is a diagram showing an equipment flow for producing reduced iron of the present invention. Carbonaceous material for reduction is added to dust generated by iron making, and a binder such as bentonite is added. These blended raw materials are kneaded with a kneader. Further, if necessary, water is added and granulated into a cylindrical shape by an extrusion granulator. When there are many fine particles such as neutralized sludge in the dust, the appropriate moisture during granulation is 20 to 25%. In order to increase the drop strength of the granulated product, it is possible to increase the extrusion pressure. The -5mm powder in the granulated product is removed with a screen and dried with a dryer to 4% of 3%, 8%, 15% and 22%, and inserted in a rotary hearth type firing furnace. Reduction treatment was performed at 1300 ° C. for 5 to 10 minutes. The reduced granulated product is discharged out of the system, cooled, the powder is removed with a screen, and the rest is made into a product.
[0012]
FIG. 2 is a diagram showing the explosion characteristics of a spherical granulated product. As shown in FIG. 2, explosions or cracks occur when the moisture content of the granulated material is in the range of 3% to 22%. That is, it can be seen that when the moisture content is 15% or more, explosion occurs when the firing temperature is already 1100 ° C., and explosion occurs when the firing temperature is 1200% and 8% or more. It was also found that cracks occurred even at less than 8% and a firing temperature of 1100 ° C., and cracks occurred at 1200 ° C. even with 3% attached moisture. Here, the explosion means a state where the granulated product is shattered.
[0013]
FIG. 3 is a diagram showing the explosion characteristics of a columnar granulated product. As shown in FIG. 3, in the case of a columnar granule according to the present invention, cracks and explosions do not occur unless the adhering moisture exceeds 22%. That is, it was found that if the temperature is 15% or less, the test furnace does not explode in any temperature range from 1100 to 1300 ° C.
[0014]
FIG. 4 is a diagram showing the measurement results of the porosity of columnar and spherical granules. As shown in FIG. 4, the measured objects were all those that had no adhered moisture after drying. The porosity is about twice as high as that of a cylindrical column. It is considered that the high porosity does not cause explosion even when the gas is rapidly generated from the inside.
FIG. 5 is a diagram showing the measurement results of the drop strength after columnar and spherical granulation. As shown in FIG. 5, in the case of a cylindrical shape, by increasing the extrusion pressure, the spherical granulated product improves the drop strength along with rolling, but the rolling pressure is only the weight of the granulated product and the drop strength is increased. There are also limitations. When the drop strength is high, powdering during handling is less and it is possible to produce reduced iron that is effective.
[0015]
【The invention's effect】
As described above, according to the present invention, in particular, when reducing iron is produced using dust generated at a steel mill as a raw material, if it is formed into a columnar granulated product, if the adhering moisture is dried to 15% or less, it can be used in a firing furnace. Explosion due to moisture evaporation is avoided. Further, if the adhering moisture is dried to 15% or less, the capacity of the dryer is small and the energy for drying may be small. As a result, reduced iron can be produced at a lower cost, and the product has a cylindrical shape, so that various excellent effects can be obtained such that there is little spillage during transportation on a belt conveyor.
[Brief description of the drawings]
FIG. 1 is a diagram showing an equipment flow for producing reduced iron of the present invention.
FIG. 2 is a diagram showing explosion characteristics of a spherical granulated product.
FIG. 3 is a diagram showing explosion characteristics of a cylindrical granulated product.
FIG. 4 is a diagram showing the measurement results of the porosity of cylindrical and spherical granules.
FIG. 5 is a diagram showing measurement results of drop strength after columnar and spherical granulation.

Claims (2)

When producing reduced iron from iron ore or iron-making dust, a cylindrical granule having a diameter of 8 to 20 mm and a length of 10 to 50 mm is produced from a mixture composed of iron ore or a plurality of types of dust and charcoal, A method for producing cheap reduced iron from iron-making dust or the like, characterized in that after drying to a moisture content of 15% or less with a dryer, reduction treatment is performed at a temperature of 1100 to 1300 ° C. in a rotary hearth-type firing furnace. The manufacturing method of cheap reduced iron from the iron-making dust etc. of Claim 1 which consists of a column-shaped granule of diameter 10mm to 15mm and length 20mm to 40mm.

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