JP2001303144A - Method for forming and drying powdery iron ore, and the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming and drying method of powdery iron ore, and the like, for producing a high strength dried formed-material, in a process for producing sintered agglomerate or lump reduced iron by beforehand forming and drying powdery iron ore, or the like, and then charging the powdery iron ore, or the like, treated into a sintering furnace or a reducing furnace at high temperature. SOLUTION: In the process for drying the formed material produced by hydrolytic-formation and granulation, the formation and the granulation are peculiarly performed by beforehand blending fine powdery plastics having fractionating component a part or the whole of which becomes liquid or paste in the temperature range of 100-250 deg.C with a raw material, in order to improve the dropping strength after drying the formed material by filling the pasty plastics into the voids in the formed material produced by dehydration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a process for producing fine agglomerate or lump reduced iron by forming and drying fine iron ore in advance and charging the iron ore into a high temperature sintering furnace or reduction furnace. The present invention relates to a method for forming and drying fine iron ores for producing a dry molded product having high strength.

[0002]

2. Description of the Related Art Generally, raw ore powder, iron-making dust, and the like, which are metal powders generated in the iron-making process, contain a large amount of iron. Has been conceived by solidifying with a resin binder into briquettes and putting them into a blast furnace, a converter, an electric furnace or the like.
That is, for example, when preforming iron oxide ores, powdery iron ore, ironmaking dust, and other materials are uniformly stirred and kneaded with a mixing and kneading machine such as a mixer, and mixed with water or a binder having an appropriate concentration. After adding the so-called binding medium, the mixture is molded by a granulator, briquette molding machine, extrusion molding machine or the like to produce a molded product having a required shape, particle size configuration and molding strength. As the binding medium used at this time, inorganic binders such as bentonite and cement, and organic binders such as starch, molasses, and polymer binder are used.

However, the binder used in this method is expensive and impractical for briquetting metal powder from the viewpoint of strength. A method for improving this is disclosed in, for example, JP-A-9-241766. As described above, a mixture containing 91 to 99% by weight of a metal powder and 1 to 9% by weight of a thermoplastic waste plastic is kneaded, and the waste plastic is softened by frictional heat of the metal powder. A method for producing a metal powder briquette to be molded, that is, a plastic plastic is blended in a range of 1 to 9% by weight of a raw material, and the plastic is melted and fluidized using frictional heat during molding, and a binder effect is used. There has been proposed a technique of obtaining a strong crushing strength by consolidation using a molding pressure in a molding process.

[0004]

However, the metal powder briquette described in Japanese Patent Application Laid-Open No. 9-241766 can be manufactured at a low cost because it does not use an expensive binder. According to
In the formed product, water (10-20
%), And in this method, it is difficult to bring the water to a state close to absolutely dry water of about 2% or less. Therefore, when this molded product is put into a baking furnace at a high temperature of about 1000 ° C., there is a problem that the vaporized water rapidly explodes due to a force far exceeding the adhesive force of the binder. For this reason, the strength after drying is insufficient, for example, as a molded product to be put into a blast furnace, a converter, an electric furnace, or the like and reused as a metal resource.

[0005] The cause of the strength decrease due to this drying is as follows.
Due to the decrease in the liquid bridge due to the evaporation of water in the liquid bridge network of the so-called green molded product formed by water in the dehydration process, the decrease in adhesion between particles and the embrittlement of the tissue matrix due to the increase in porosity It is. Therefore, as a method of improving the strength, as in the above patent, simply using waste plastic instead of the binder, and improving the strength after molding, the intended strength after drying cannot be obtained, and It is necessary not only to use a binder but also to reduce the water content during molding and granulation and to improve the drying step involving separation and removal of water.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive developments. As a result, in the present invention, the solid phase is formed at the time of mixing the raw materials, that is, near the atmospheric temperature. In a drying oven temperature range of 100 to 250 ° C., 1 to 10% by weight of a hydrocarbon-based fine plastic, part or almost all of which becomes a liquid or paste-like fractionation component, is added at the time of mixing the raw materials and uniformly mixed. And molding
After granulation, the green molded product is dried. In the drying step, part of the solid fine powder plastic changes into a liquid or fluid state simultaneously with the dehydration of water, penetrates into the voids of the green molded product such as the space created by the dehydration, and the viscous force of the liquid plastic causes A method for forming and drying fine iron ores that increases the adhesion between particles and increases the strength of the molded product after drying, that is, employs a medium-to-low temperature drying process as a prerequisite that the iron ore is put into a high-temperature sintering furnace at about 1000 ° C. In addition, the present invention provides a method for forming and drying iron ore fines, characterized by utilizing for the first time the cohesive force of a plastic in the step of releasing moisture.

The gist of the invention is as follows: (1) In the step of drying a molded product produced by hydroforming / granulating, by filling paste-like plastic into voids of the molded product produced by dehydration. In order to improve the drop strength after drying of the molded product,
A method for forming and drying fine iron ores, which comprises mixing and granulating fine powdered plastics having a fractionation component, part or all of which is liquid or pasty, in a temperature range of 250 ° C. .

(2) A method for forming and drying fine iron ores, which comprises mixing and pulverizing 1 to 10% by weight of the finely divided plastic described in (1) with respect to the raw material. (3) A method for forming and drying fine iron ores, wherein waste plastics targeted for general waste or industrial waste are used as the plastic according to (1) or (2).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, the mechanism of developing the bonding strength of the molded product (green molded product) immediately after the fine iron ore subject to the present invention by the molding and granulating operations will be described. (1) Fine iron ores are usually aggregates of particles containing adhering moisture, and are aggregated by the formation of a liquid bridge due to the moisture between the individual fine iron ores due to the adsorbed moisture and the capillary condensation of water vapor. When forming and aggregating the aggregates, add a suitable amount of water to promote the formation of a liquid bridge between the particles, and apply compression and rolling operations with a molding machine or a granulator to set the distance between the particles. A fine liquid bridge network is generated by mechanically reducing the amount of air and deaeration of air and the like, thereby expressing the strength of the green molded product. Therefore, in the industrial process, the basic properties such as the type, shape, and surface roughness of fine iron ores are investigated, the optimum amount of water to be added is determined, and the bonding force between particles is strengthened by the liquid crosslinking force of water. It is necessary to ensure the strength of the green molded product.

(2) Further, when the strength of the green molded product is insufficient only by the liquid crosslinking power of water, the above-mentioned paste-like plastic or the like is added to improve the strength of the green molded product. In this case, the bonding force between the particles is enhanced by utilizing the adhesive force of the viscous component such as a paste-like plastic under the molding and granulation operation conditions, and the amount of the paste-like waste plastic and the like and the amount of the viscous component are reduced. It is also necessary to select molding and granulation operating conditions such as temperature and molding pressure that maximize the adhesive force.

In order to process the green molded product thus manufactured into an agglomerate, which is the final object, it is fired at a high temperature in an oxidation firing furnace to obtain fired pellets. Alternatively, it is charged into a high-temperature reduction furnace and processed as lump reduced iron, and then supplied as a raw material for a blast furnace or a raw material for a steelmaking furnace such as an electric furnace or a converter as a final agglomerate. In this case, the oxidation sintering furnace and the high-temperature reduction furnace are operated at a high temperature of 1000 to 1300 ° C. When the green molded product is directly charged, explosion occurs due to rapid evaporation of moisture, and the green molding with high strength is performed. Even objects are broken down into powder. Therefore, in an industrial process, as a means for preventing explosion destruction by steam, a drying furnace or a drying step for removing moisture from the green molded product before charging the high temperature furnace is required.

For the above-mentioned reasons, in the present invention, there are several modes such as a case where waste plastic is added and solid or dissolved in water or a suitable solvent, and a case where paste is added. In order to fully demonstrate the function of a binder in the process, it is mixed uniformly with the molding raw material, and the molding temperature and molding are performed in the process of compression molding or rolling granulation by a molding machine or granulator. Under appropriate conditions such as pressure, it is used in such a way that it acts to bind the individual particles of the molding raw material.

For this purpose, it is necessary to previously mix and mold a fine powdered plastic having a fractionation component in which a part or all of the waste plastic becomes liquid or paste in a temperature range of 100 to 250 ° C. There is. Suitably the temperature is from 100 to 250 ° C, preferably from 150 to 190 ° C. This temperature was regulated by
If the temperature is lower than 00 ° C., the resin is decomposed and gasified before the drying temperature (100 to 250 ° C.) and does not function as a binder. If the temperature exceeds 250 ° C., the plastic does not become a liquid or a paste and exhibits a function as a binder. This is because they do not.

In the drying furnace, the green molded product is dried at a temperature of 100 to 250 ° C. to a water content of several percent or less. However, the liquid bridge network of the green molded product is extremely reduced in the dehydration step, so that the strength after drying is reduced. However, in order to exhibit the effect of a binder for supplementing the strength or the function of a binder exhibiting a large strength in a drying temperature range, a part or the entire amount of the waste plastic needs to be in a liquid or paste form in advance. Furthermore, in the present invention, waste plastics
10 to 10% by weight, preferably 2 to 5% by weight, are used. If the amount of waste plastic is regulated in this way, if the amount is less than 1% by weight, the effect as a binder is insufficient, the strength of the briquette is insufficient, and if it exceeds 10% by weight, the production cost is disadvantageous. . Therefore, the range was set to 1 to 10% by weight.

FIG. 1 shows the measurement results of the strength after granulation and the strength after drying of a green molded product granulated by using a binder or a fine powdered plastic. As shown in this figure, a is a strength measurement result of a green pellet manufactured by granulating only with moisture without using a binder, and the strength after granulation is sufficient, but the strength after drying is greatly reduced. It turns out that there is. This is because the molded product becomes brittle due to drying, and the drop impact resistance is reduced. B is a measurement result of a green pellet manufactured using a highly swellable viscous bentonite as a binder, and both the strength after granulation and the strength after drying are improved as compared with the case where the binder of a is not used. It indicates that there is no problem in use. Further, c is a measurement result of a green pellet produced by adding waste plastic after use and granulating only with moisture without using a binder, and the strength after granulation is slightly improved compared to a. However, the strength after drying was significantly improved from a, and further improved from b, confirming the effects of the present invention.

The method for measuring the drop strength shown in FIG.
This is the drop strength method described in the Granulation Handbook (edited by the Japan Powder Industry Association), in which the number of drops from a height of 45 cm onto an iron plate until breakage is obtained. From the results of FIG. 1, it is understood that not only the use of waste plastic but also the use of waste plastic
No limitation is also imposed on the use of an inorganic binder such as viscous bentonite and cement as the binder, and an organic binder such as starch, sugar cane, and a high molecular binder at the same time.

[0017]

The present invention will be specifically described below with reference to examples. FIG. 2 is a process diagram of a facility for producing reduced iron by pelletizing and drying a powdered iron-containing raw material according to the present invention and then reducing the dried iron-containing raw material in a rotary hearth type high-temperature reduction furnace. As shown in this figure, iron ore and various types of coal-containing dusts are mixed in a raw material tank 2, and an iron-containing raw material mixture obtained by adding 3 to 5% by weight of finely divided plastic from a finely divided plastic supply hopper 1 is kneaded by a ball mill 3. Then, the green pellets produced by granulating with a pelletizer 4 are dehydrated and dried to a moisture content of several percent or less by a drier 5 and then charged into a rotary hearth-type reduction furnace 6 maintained at 1000 ° C. or higher, and containing carbonic acid. The reduced pellets are reduced and cooled by the product cooler 7 to produce reduced iron, which is transferred to the product tank 8.

In this case, the pulverized plastic is stored via a pulverizer, mixed with raw materials via a quantitative feeder, homogenized by a ball mill, and uniformly dispersed inside the green pellets. The properties of the finely divided plastic are solid at room temperature, but a part or almost all of it becomes a liquid or paste-like fractionated component in a drying temperature range of 100 to 250 ° C. It is economical to finely pulverize to a predetermined particle size and use it for waste products or industrial plastics.

[0019]

As described above, according to the present invention, the strength after drying of a green molded product can be secured to a level that cannot be obtained with a binder, preventing the final product from being powdered, improving the product yield, and improving the product yield. When a green molded product is processed in a high-temperature firing furnace or reduction furnace, residual hydrocarbons of plastic can be used as firing fuel or carbon material. Further, the present invention has extremely excellent effects, such as an economic advantage as a method of effectively utilizing waste plastic which is an increasing general waste or industrial waste.

[Brief description of the drawings]

FIG. 1 is a diagram showing the measurement results of the strength after granulation and the strength after drying of a green molded product granulated using a binder or a finely divided plastic,

FIG. 2 is a process diagram of a facility for producing reduced iron by pelletizing and drying a powdered iron-containing raw material according to the present invention, and then reducing the dried iron-containing raw material in a rotary hearth type high-temperature reduction furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fine powder supply hopper 2 Raw material tank 3 Ball mill 4 Pelletizer 5 Dryer 6 Reduction furnace 7 Product cooler 8 Product tank

Claims (3)

[Claims] In the step of drying a molded product produced by hydroforming / granulating, the gap of the molded product produced by dehydration is filled with a paste-like plastic to reduce the drop strength of the molded product after drying. In order to improve the powder, a powdered plastic characterized in that it is preliminarily mixed with a fine powdered plastic having a fractionation component in which a part or the whole thereof becomes liquid or paste in a temperature range of 100 to 250 ° C., and is molded and granulated. A method for forming and drying iron ores. 2. A method for forming and drying fine iron ores, comprising mixing and granulating the fine powdered plastic according to claim 1 in an amount of 1 to 10% by weight with respect to a raw material. 3. A method for forming and drying iron ore fines, characterized in that waste plastics targeted for general waste or industrial waste are used as the plastic according to claim 1 or 2.