JP5731274B2 - Pellet molding method - Google Patents

Description

The present invention relates to a method for forming pellets for a rotary hearth type reduction furnace in which at least a reducing agent, moisture, and a binder are added to a powdered metal oxide, and the mixture is placed in a discontinuous molding machine, mixed, kneaded and molded. . For example, in non-continuous molding machines where various types of steelmaking dust generated from the ironmaking process are molded and reduced in a rotary hearth type reduction furnace, the strength is high regardless of the properties of the raw material dust, and stable molding is easily performed. The present invention relates to a method for forming pellets.

Rotary hearth type reducing furnace as equipment for kneading raw materials containing powdered metal oxide, reducing agent, moisture and binder to form spherical pellets and reducing them at high temperature to produce economical reduced iron It has been known. The reduction furnace is a type of firing furnace (hereinafter referred to as a rotary furnace) in which a disk-shaped refractory hearth lacking a central portion rotates on a rail at a constant speed under a fixed refractory ceiling and side walls. It is called). The hearth diameter of the rotary furnace is 10-50 meters and the hearth width is 2-6 meters. While the hearth is rotating, the raw material supply unit, heating zone, reduction zone, and product discharge unit are moved. The raw material pellets are put into a high temperature raw material supply section of about 1000 ° C. Then, after heating to about 1200 ° C. or higher in the heating zone, carbon and metal oxide react in the reduction zone to produce reduced metal. In the rotary hearth method, since the heating is rapid, the reaction is completed in 7 to 20 minutes. The reduced pellets are discharged from the furnace and cooled, and then used as a raw material for an electric furnace or a blast furnace.

In the production of reduced iron by the rotary furnace, when the pellet has insufficient strength, there is a problem that the collapsed pellet is built up to the hearth refractory and is rocked and wears the blade of the discharge screw. Thus, in the process of reducing pellets, it is important that the strength of the pellets is high in order to realize stable operation. In particular, pellets that use a reducing agent as a raw material have a problem that it is difficult to mold mainly when the proportions of the reducing agent and moisture are not appropriate, and it is difficult to increase the strength, and it is desired to increase the strength.

In the actual pellet manufacturing process, the strength of the pellets varies in raw material properties, for example, the water content, particle size, blending ratio, powdered metal oxide and reducing agent possessed by the powdered metal oxide and reducing agent. Moisture to be added, amount of binder added, blending ratio of each powdered metal oxide by-product mainly from converters, blast furnaces, sintering, rolling equipment constituting the powdered metal oxide, etc. Depending on the parameters, the ease of molding and the strength of the pellets to be molded vary. Therefore, in reality, a skilled operator always carries out visual observation and inspection on the machine side during operation, and various molding conditions are changed and operated as appropriate according to empirical rules, and the stable strength of the particle size. It is difficult to form a stable high-strength pellet easily.

On the other hand, various proposals have been made regarding the molding method of the high-strength pellets. For example, Japanese Patent No. 3635253 (Patent Document 1 below) discloses a bread-type molding machine which is a discontinuous molding machine. As a method for producing pellets, a method is described in which the raw material is prepared in advance so as to contain 20 to 80% of particles having a particle size of 10 μm or less.

However, since the method of Patent Document 1 needs to pulverize the raw material in advance and select the raw material so as to meet a predetermined particle size, it requires a lot of time for the preliminary process before pellet molding, and is practical. It cannot be applied as a new technology. In addition, as a molding control method, it is described that the moisture of the raw material is measured in advance and the moisture is controlled within a range of 8 to 13%, but a specific control method is not disclosed, and as described above, powder metal oxidation Since the amount of water held by the product and the reducing agent is different, it is difficult to stably form high-strength pellets, which is also not a practical technique.

Japanese Patent No. 3635253

The present invention solves the problems of the prior art as described above. A high-strength pellet can be stably and short-cut regardless of the skill of the driver, even if the properties of the raw material fluctuate. It is an object of the present invention to provide a pellet molding method that can be easily molded in time.

This invention is made | formed in view of the said problem, and the place made into the summary is the following content as described in the claim.
(1) Molding of pellets for rotary hearth-type reduction furnaces that add at least a reducing agent, moisture, and a binder to the powdered metal oxide generated from the iron making process, put them into a discontinuous molding machine, knead and mold In the method, the growth rate A of the pellets during kneading is determined by the following formula (a) every predetermined time, and when the determined growth rate A exceeds 0.3 (% / s), it is determined that the state is enlarged. Then, dry powder is added and mixed and kneaded again. When the growth rate A is less than 0.2 (% / s), it is judged as a non-growth state and water is added and kneaded again. A method for forming pellets, characterized in that in the case of 0.2 to 0.3 (% / s), it is determined that the state is a stable growth state, and the process immediately proceeds to a molding step and is molded.
Pellet growth rate A = ( be−bs ) / t (a) Formula t: kneading time (s)
bs: the kneading time and the ratio of the initial particle diameter of 6 mm or more (%)
be: the kneading time and the ratio of the particle diameter of the last 6 mm or more (%)
(2) The method for molding pellets according to (1), wherein the reducing agent comprises at least one selected from coke powder, coal powder, and CDQ powder.
(3) The powdered metal oxide is composed of a powdered metal oxide by-produced from at least one facility selected from a converter, a blast furnace, sintering, and a rolling facility, which are facilities in the iron making process. The method for molding a pellet according to (1) or (2), characterized in that it is characterized.

According to the present invention, it is possible to stably form a high-strength pellet regardless of the skill of the driver even if the raw material properties fluctuate. In addition, it is not necessary to select the raw material to match the pulverization and particle size of the raw material to be molded, that is, there is no prior process before pellet molding, and the molding time can be greatly shortened, which is practically suitable. It became technology. Furthermore, since the molding state can be continuously grasped, there is a remarkable industrially useful effect, such as providing a pellet molding method that can quickly cope with a molding failure.

It is a figure which illustrates the rotary hearth type reduction process to which this invention is applied. It is a figure explaining the pellet shaping | molding state of the preliminary test 1 in the shaping | molding method of the pellet of this invention. It is a figure explaining the pellet growth state of the preliminary test 2 in the shaping | molding method of the pellet of this invention. (A) (b) It is a figure explaining the measuring method of the pellet growth rate during kneading | mixing in the molding method of the pellet of this invention. It is a figure which illustrates preferable embodiment in the shaping | molding method of the pellet of this invention. It is a figure which shows the Example in the shaping | molding method of the pellet of this invention.

First, a rotary hearth type reduction process to which the present invention is applied is shown in FIG. As shown in FIG. 1, there is a raw material storage facility including a powder metal oxide storage tank 1, a reducing agent storage tank 2, and a binder storage tank 3. Furthermore, there is a raw material processing facility comprising a mixed raw material tank 4, a molding device 5 and a pellet drying device 6, and a rotary hearth type reduction furnace 7 which is a calcining reduction device, which includes a reduced iron cooling device 8 And the exhaust gas treatment device 9 are attached, and the method for molding pellets of the present invention is applied to the molding device 5. The molding device 5 includes an imaging unit 10 that captures and analyzes the kneaded state, a water hopper 12 that supplies water to the molding unit 5 based on a signal from the control unit 11 based on an analysis result of the imaging unit, A dry powder hopper 13 for supplying the dry powder is attached. 14 is a flow control valve.

In completing the pellet molding method of the present invention, the inventors completed the present invention by the following steps. First, the following knowledge was obtained from the various test results as the most important factor in determining the strength of a high-strength pellet when the pellet had a proper particle size as a core during molding. This will be described below.

<Preliminary test 1>
FIG. 2 shows powder metal oxides generated from the iron making process, powder metal oxides by-produced from the blast furnace, converter, sintering, and rolling equipment, respectively, and then by-products from the four equipments. Preliminary test 5 using 10% by weight of water and 1% by weight of bentonite as a binder, and Pelegaia which is one of discontinuous molding machines. Seed was carried out. The result is shown in FIG. As is clear from FIG. 2, in the five types of tests, the growth of grains progressed with time, and in any case, it was found that the growth of grains became stable when the average grain size was around 6 mm. Thus, it was found that the average particle size as a core for molding a high-strength pellet was about 6 mm.

<Preliminary test 2>
Subsequently, the following test was performed. FIG. 3 shows a mixture of powdered metal oxides of blast furnace and converter with 1% by weight of bentonite as a binder, and the amount of water added was changed by 5, 10, and 15% by weight. Two types of preliminary tests were performed using Pelegaia, which is one of discontinuous molding machines. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the ratio of the average particle size of 6 mm or more. As is clear from FIG. 3, in each of the powder metal oxides of the blast furnace and the converter, in both cases, when the amount of water to be added is around 10 wt. It has been found. The ratio of the average particle diameter of 6 mm or more was determined by imaging the pellets during kneading and determining the ratio of the particle diameter of 6 mm or more in the observation area by image processing.

Based on the results of the previous preliminary tests 1 and 2, a method for forming a stable pellet with high strength and easily in a short time even if the properties of the raw material fluctuate was completed as follows. That is, in order to mold the pellets, the increase rate of the average particle size of the core of 6 mm or more is observed and determined as follows, and as a result of the determination, dry powder of water or powdered metal oxide is appropriately used. It was made possible to achieve an appropriate kneading state by adding it, and then to shift to a molding process, thereby completing the present invention.

According to the present invention, by measuring the pellet growth rate (% / s), it is possible to easily grasp the molding condition of the molded product, and when the growth rate increases rapidly, the molded product grows abnormally and becomes muddy. When molding is impossible and no change is observed in the growth rate, the molded product does not become large and remains in powder form. On the other hand, if the growth rate increases slowly within a certain range, it becomes possible to produce a molded product with a strong desired particle size, so by measuring the growth rate (% / s) of the pellet during kneading, In addition to producing stable pellets that do not fluctuate, it is possible to grasp molding defects in advance and to respond quickly.

4 (a) and 4 (b) are diagrams illustrating a method for measuring the pellet growth rate during kneading in the pellet molding method of the present invention. As shown in the figure, the pellets at the kneading time t1 are imaged and processed in the image processing FIG. 4 (a). Similarly, the pellets at t2 are imaged and processed in the image processing FIG. 4 (b). Pellet growth rate (% / s) by calculating the area ratio (%) of giant grains with a diameter of 6 mm or more and calculating the ratio (%) of giant grains with a grain size of 6 mm or more increased between t1 and t2 (s) Can be calculated. The calculation of pellet growth rate (% / s) by this image processing is suitable for online processing, but as a simpler method, it can also be obtained by calculating the weight ratio between the upper and lower sieves using a 6 mm sieve. it can. The frequency (time) for measuring the pellet growth rate is preferably 30 to 60 seconds, although it depends on the degree of pellet growth.

FIG. 5 is a diagram illustrating a preferred embodiment of the pellet molding method of the present invention, in which FIG. 5 (a) is a basic operation, FIG. 5 (b) is a response at the time of enlarging, and FIG. Show the response during growth.

In the basic operation of the discontinuous molding machine in Fig. 5 (a), after mixing (pulverization) to mix a plurality of raw materials, water is added to knead to make pellet nuclei. Mold to grow. During the kneading step, when the pellet molding state is in a huge state, it is possible to prevent abnormal growth due to pelletization by adding dry powder, changing the rotation speed and mixing and kneading again. it can.

Moreover, when the said molding state is a non-growth state, a grain growth can be promoted by adding water after a kneading | mixing process, changing a rotation speed, and kneading again.
As described above, according to the present invention, since the pellet molding state can be continuously grasped, a quick response (recovery) is possible when the above-described molding is impossible. The pellet molding apparatus used in the present invention is not limited, but by using a non-continuous molding apparatus that performs batch processing, it is easy to cope with the case where molding is impossible.

FIG. 6 shows an embodiment of the present invention using iron-making dust generated from an iron-making process as a typical pellet raw material. As described above, iron dust was used as a powdered metal oxide, 10% by weight of water was mixed with 1% by weight of bentonite as a binder, and molding was performed using Peregia, which is one of discontinuous molding machines.
FIG. 6 shows the pellet growth rate (% / s) in the above example.
If the pellet growth rate exceeds 0.3 (% / s) as shown by the broken line, and huge particles with a particle size of 6 mm or more increase rapidly, it becomes mud or less than 0.2 (% / s) as shown by the alternate long and short dash line. When huge particles of 6mm or more did not reach 0.2 (%) and stabilized downward, it was impossible to mold (powdered). As indicated by the solid line, when the pellet growth rate was 0.2 to 0.3 (% / s), molding was easily possible in a short time.

As described above, the pellet molding method of the present invention is not affected by fluctuations in raw material properties, enables stable molding regardless of the skill of the driver, and continuously grasps the molding status. Therefore, when a molding defect occurs, it is possible to quickly cope with it, and the effect of the present invention can be confirmed.

DESCRIPTION OF SYMBOLS 1 Granular metal oxide storage tank 2 Reductant storage tank 3 Binder storage tank 4 Mixed raw material tank 5 Molding device 6 Pellet drying device 7 Rotary hearth type reduction furnace 8 Reduced iron cooling device 9 Exhaust gas treatment device
10 Imaging means
11 Control means
12 water hopper
13 Dry powder hopper
14 Flow control valve

Claims (3)

A method for forming pellets for a rotary hearth-type reduction furnace in which at least a reducing agent, moisture, and a binder are added to a powdered metal oxide generated from an iron making process, and the mixture is put into a discontinuous molding machine, mixed, kneaded and molded. In
The growth rate A of the pellets during kneading is determined by the following formula (a) every predetermined time, and when the determined growth rate A exceeds 0.3 (% / s), it is determined that the state is enlarged and dry powder is obtained. When the growth rate A is less than 0.2 (% / s), it is judged as a non-growth state and water is added and kneaded again, so that the growth rate A is 0.2 to 0.3 (% / s), a method for forming pellets, characterized in that it is determined to be in a stable growth state and immediately proceeds to a molding process and is molded.
Pellet growth rate A = ( be−bs ) / t (a) Formula t: kneading time (s)
bs: the kneading time and the ratio of the initial particle diameter of 6 mm or more (%)
be: the kneading time and the ratio of the particle diameter of the last 6 mm or more (%)   The pellet forming method according to claim 1, wherein the reducing agent is at least one selected from coke powder, coal powder, and CDQ powder.   The powdered metal oxide is composed of a powdered metal oxide by-produced from at least one facility selected from a converter, a blast furnace, sintering, and a rolling facility that are facilities in the iron making process. The molding method of the pellet of Claim 1 or Claim 2.

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