Patent Application
20210087652
The present invention relates to a granulated material including sludge generated in an iron-making process, the granulated material having improved conveyor transportability. The present invention also relates to a method for producing the granulated material and further relates to a method for producing sintered ore by using the granulated material.
Various iron-making processes, such as pig iron making, steel making, and rolling, generate large amounts of dust and sludge. The dust and sludge have high iron and carbon contents, and, therefore, it is preferable that the dust and sludge be recycled as an iron source and a heat source instead of being discarded. Typically, the dust and sludge are used in high-temperature processes in pig iron making and steel making. The dust and sludge are recycled as an iron source by being remelted and dissolved into molten pig iron in high-temperature processes.
The dust is a fine powder that contains iron and has a moisture content of 0 to 20 mass %, or in many cases, a moisture content of 0 to 5 mass %. Since the dust has a low moisture content, when the dust is transported on a belt conveyor, dust emission occurs. The sludge is a fine powder that contains iron and has a moisture content of greater than or equal to 20 mass %. Since the sludge has a high moisture content and therefore has a high adhesion property, when the sludge is transported on a belt conveyor, adhesion to a conveyor junction occurs, which causes clogging. Fine powders have an average particle diameter of less than or equal to 0.5 mm and, therefore, pose particularly significant problems associated with adhesion and dust emission. As described, when the dust and sludge are transported on a belt conveyor, clogging due to adhesion and/or dust emission occurs. In the process of transportation, while dust emission is a problem that can be mitigated by providing dust collection equipment, sludge adhesion is a particularly significant problem.
In connection with such a problem, Patent Literature 1 discloses a method for producing a granulated material. The method uses a granulated material production apparatus that includes a stirring impeller, which revolves within a drum, and a stirring rotor, which revolves with the stirring impeller and rotates. With the apparatus, sludge resulting from iron making and in the form of a cake is crushed, and after a solidifying agent and dust resulting from iron making are added thereto, a granulation process is performed. According to the disclosure, using the method enables proper granulation to be achieved without performing a particular drying process, to form a granulated material suitable for use in a high-temperature process.
Patent Literature 2 discloses a method of granulating a sinter feed material. In the method, coke breeze and coarse grains are mixed with dust and/or sludge, and the mixture is granulated in a vibration kneading granulator, and, in addition, exterior coating granulation is performed to apply coke breeze.
Patent Literature 3 discloses a method for holding sludge in a recessed portion of sintered ore, which is achieved by ensuring that a mixture in which fine-particle sintered ore is mixed with water-containing sludge has a moisture content within a range of 3 to 15%.
However, since the granulated material disclosed in Patent Literature 1 has a high moisture content, transporting the granulated material on a belt conveyor results in a large amount of adhesion of the granulated material to a conveyor junction. In particular, in ironworks, a belt conveyor is installed outdoors, and, therefore, in rainy weather, rain also falls on the belt conveyor. Thus, there was a problem in that, in rainy weather, the granulated material had an increased moisture content, which increased the amount of adhesion of the granulated material to a conveyor junction, and, consequently, the adhesion resulted in clogging due to the granulated material.
In Patent Literature 2, the moisture content of sludge was not considered, and, therefore, there was a problem in that adhesion of the granulated material during transportation could not be overcome by the method. In the method of Patent Literature 3, sludge is adhered to sintered ore, which reduces an impediment to transportation associated with a transportation process. However, the method of Patent Literature 3 does not include a step of granulation and is, therefore, subject to the requirement that the moisture content after mixing be 3 to 15%. Accordingly, there was a problem in that if the amount of mixed sludge was greater than or equal to 30 mass %, favorable results could not be obtained, and, therefore, the method had a narrow range of applications.
Aspects of the present invention have been made in view of the problems with the related art technologies, and an object according to aspects of the present invention is to provide a granulated material that enables a reduction in the amount of adhesion of the granulated material to a conveyor junction.
A summary of aspects of the present invention, which solves the problems described above, is as follows.
(1) A granulated material including: sludge in an amount of greater than 30 mass % and 90 mass % or less; and sintered ore powder in an amount of 10 mass % or greater and less than 70 mass %, the granulated material including granulated particles in which at least a portion of the sludge adheres to at least a portion of the sintered ore powder.
(2) The granulated material according to (1), wherein the granulated particles further include dust.
(3) The granulated material according to (1) or (2), wherein the sludge has a moisture content of 20 mass % or greater and less than 30 mass %.
(4) A method for producing a granulated material, the method including: a dewatering step of dewatering sludge into a dewatered cake; and a granulation step of mixing and granulating the dewatered cake and sintered ore powder together.
(5) The method for producing a granulated material according to (4), wherein, in the granulation step, dust is additionally mixed.
(6) The method for producing a granulated material according to (4) or (5), wherein the dewatered cake has a moisture content of 20 mass % or greater and less than 30 mass %.
(7) A method for producing sintered ore, the method including: a combining step of combining a granulated material produced by using the method for producing a granulated material according to any one of (4) to (6), an iron-containing raw material, a CaO-containing raw material, and solid fuel to form a sinter feed material; a granulation step of adding water to the sinter feed material and granulating the sinter feed material; and a sintering step of sintering a granulated form of the sinter feed material in a sintering machine to form sintered ore.
Using a granulated material in accordance with aspects of the present invention enables a reduction in the amount of adhesion of the granulated material to a conveyor junction. As a result, the occurrence of clogging due to the granulated material during transportation on a belt conveyor is controlled.
Aspects of the present invention will now be described with reference to an embodiment of the invention. According to the present embodiment, a granulated material includes sludge in an amount of greater than 30 mass % and 90 mass % or less and sintered ore powder in an amount of 10 mass % or greater and less than 70 mass %. The sludge is sludge generated in an iron-making process. The granulated material is a material granulated to include granulated particles in which at least a portion of the sludge adheres to at least a portion of the sintered ore powder. The granulated material may include dust generated in an iron-making process.
As shown in
The granulated material 10, which has such a weak portion in a middle, easily breaks when an impact occurs during transportation on a belt conveyor, and as a result, fine powder is generated, and moisture inside is released. The generation of fine powder and the release of moisture from the granulated material 10 increases the amount of adhesion of the granulated material 10 to a conveyor junction.
As shown in
In the granulated material 20 according to the present embodiment, a content of the sintered ore powder 24 needs to be greater than or equal to 10 mass %. When the granulated material 20 includes the sintered ore powder 24 in an amount greater than or equal to 10 mass %, the amount of adhesion of the granulated material 20 to a conveyor junction is reduced. The content of the sintered ore powder 24 is more preferably greater than or equal to 25 mass % and even more preferably greater than or equal to 50 mass %. As the content of the sintered ore powder 24 increases, the amount of adhesion to a conveyor junction decreases, until the content reaches 50 mass %. When the content of the sintered ore powder 24 is 50 mass %, the amount of adhesion to a conveyor junction is substantially 0. Accordingly, further increasing the content of the sintered ore powder 24 produces no further effect of reducing the amount of adhesion to a conveyor junction and results in a reduction in the amount of processing of the sludge 28. Accordingly, the upper limit of the content of the sintered ore powder 24 may be set to be less than 70 mass % from the standpoint of reducing the amount of adhesion to a conveyor junction. However, from the standpoint of increasing the amount of processing of the sludge 28, it is preferable that the content of the sintered ore powder 24 be less than or equal to 50 mass %. In the granulated material according to the present embodiment, the content of the sludge 28 is greater than 30 mass % and 90 mass % or less, which corresponds to the content of the sintered ore powder 24.
A method for producing the granulated material 20, according to the present embodiment, will now be described. First, a dewatering step is carried out in which the sludge 28, which has been generated in an iron-making process, is dewatered into a dewatered cake by using a press-type dewatering apparatus. Next, a granulation step is carried out in which the dewatered cake and the sintered ore powder 24 are mixed and granulated together in a stirring device. In the present embodiment, the masses of the raw materials to be fed to a granulator are all the masses of the raw materials including the moisture content. In the process, dust generated in an iron-making process may be added, and the raw materials may be mixed and granulated together. In this manner, the granulated material according to the present embodiment is produced. Examples of the press-type dewatering apparatus include filter presses and vacuum filters. Any dewatering apparatus, other than a press-type dewatering apparatus, may be used without limitation provided that the sludge can be dewatered to a state suitable for feeding to a stirring device. It is preferable that the dewatered sludge have a moisture content of approximately 20 to 40 mass %. It is more preferable that the degree of dewatering of the sludge be increased so that the moisture content of the sludge (dewatered cake) can be 20 mass % or greater and less than 30 mass %. With such a moisture content, sludge processing efficiency and granulability can be enhanced.
The sludge used in the present embodiment is sludge generated in an iron-making process, such as a pig-iron-making step, a steel-making step, a rolling step, a coating step, or a pickling step. Before being dewatered, sludge has a high moisture content. The moisture content is approximately 40 to 70 mass %.
The granulated material 20 according to the present embodiment may include dust. The dust used in the production of the granulated material 20 is dust generated in an iron-making process, such as a pig-iron-making step, a sinter production step, or a steel-making step. The dust is collected by using a method such as dry dust collection and has a low moisture content. The moisture content is approximately 0 to 20 mass % or, in many cases, approximately 0 to 5 mass %.
The sintered ore powder used in the present embodiment is sintered ore having particle diameters of less than or equal to 5 mm, which is obtained from sieving in a sintered ore production process or transportation process or in a charging process for charging sintered ore into a blast furnace; the sintered ore powder is sintered ore powder that has passed through a sieve having a sieve opening of 5 mm. Sintered ore, which is produced by sintering, has a low moisture content. The moisture content is 0 mass % or greater and 5 mass % or less. For the production of the granulated material 20 in which sludge coats sintered ore powder that serves as a core, it is preferable that the sintered ore powder have particle diameters of greater than or equal to 2 mm. Sintered ore powder having particle diameters of less than or equal to 5 mm, which has passed through a sieve having a sieve opening of 5 mm, contains a large number of particles having a particle diameter of 0.1 to 5 mm, and, therefore, it is not necessary to laboriously remove fine powder having particle diameters of less than or equal to 2 mm. The particle diameters of the sintered ore powder may be controlled such that the sintered ore powder has an average particle diameter of greater than or equal to 2 mm, to ensure that sintered ore powder having a certain degree of sizes is included.
The stirring device 30 includes a cylindrical vessel 32, into which a dewatered cake and/or dust are to be loaded, a stirring impeller 34, and a weir 36. Providing the weir 36 is preferable for the purpose of scraping the granulation feed material; however, the weir 36 may not be provided. The cylindrical vessel 32 includes a cylinder 38 and a bottom plate 40, which has a circular shape. The cylindrical vessel 32 has an opening (not illustrated) provided for the feeding and discharging of a dewatered cake and/or dust. The bottom plate 40 is provided integrally with the cylinder 38. The bottom plate 40 rotates with the cylinder 38 upon receiving a driving force. The cylindrical vessel 32 may include a top plate that seals an upper side of the cylindrical vessel 32.
The stirring impeller 34 includes a rotatable shaft 42 and a plurality of stirring blades 44. The rotatable shaft 42 is provided at a position offset from a center of the cylindrical vessel 32. The stirring impeller 34 rotates upon receiving a driving force from a drive unit (not illustrated) provided above the cylindrical vessel 32. Thus, the cylindrical vessel 32 and the stirring impeller 34 rotate upon receiving driving forces from different respective drive units, that is, rotate independently of each other. The rotatable shaft 42 may be provided at the center of the cylindrical vessel 32.
The stirring blades 44 are provided to project radially outwardly from the rotatable shaft 42. At two locations of the rotatable shaft 42 with respect to a vertical direction thereof, the stirring blades 44 are provided at intervals of 60°, in six directions. The locations with respect to a vertical direction at which the stirring blades 44 are to be provided and the number of the stirring blades 44 may be appropriately varied in accordance with the amounts of the dewatered cake and dust to be filled into the cylindrical vessel 32.
In a state in which a dewatered cake is loaded in the cylindrical vessel 32, the bottom plate 40 rotates clockwise, and the stirring impeller 34 rotates counterclockwise, for example. The clockwise rotation of the bottom plate 40 causes the dewatered cake loaded in the cylindrical vessel 32 to rotate clockwise along the direction of rotation of the bottom plate 40. The dewatered cake rotated clockwise collides with the stirring impeller 34, which rotates counterclockwise, and is crushed accordingly. The directions of rotation of the bottom plate 40 and the stirring impeller 34 may be clockwise or counterclockwise. The directions of rotation of the bottom plate 40 and the stirring impeller 34 may be different from or identical to each other.
In the example illustrated in
With the use of the stirring device 30 illustrated in FIG. 2 and
In the stirring device illustrated in
The granulated material 20 according to the present embodiment can be used in the production of sintered ore. For example, sintered ore is produced as follows. In a combining step in which an iron-containing raw material, a CaO-containing raw material, and solid fuel are combined to form a sinter feed material, the granulated material 20 according to the present embodiment is combined. In a granulation step, water is added to granulate the sinter feed material. In a sintering step, a granulated form of the sinter feed material is sintered in a sintering machine.
Instead of combining the granulated material 20 according to the present embodiment in the combining step, the granulated material 20 according to the present embodiment may be combined at a later time in the granulation step so that an outer layer of the granulated form of the sinter feed material can be formed of the granulated material 20 according to the present embodiment. As described, the granulated material 20 according to the present embodiment can be used in the production of sintered ore and can be recycled as an iron source and a heat source in the production of sintered ore.
Examples will now be described. In the examples, granulated material 20 according to the present embodiment were produced, and transportation properties of the granulated materials were evaluated. To produce the granulated material 20 according to the present embodiment, two different granulation methods were used for the production of the granulated materials. In one of the granulation methods, granulated materials were produced by using an intensive mixer Type R02, manufactured by Eirich, which has the same configuration as the stirring device 30, illustrated in
An adhesion property of the granulated materials produced as described above was evaluated.
As shown in
In the evaluation of the granulated material having a sintered ore powder content of 50 mass %, it was found that the amount of adhesion to the chute 54 was substantially 0. Thus, even when the content of the sintered ore powder was 70 mass %, the result was that the amount of adhesion to the chute 54 was not reduced while the amount of processing of dust and sludge was reduced. These results indicate that the content of the sintered ore powder is preferably greater than or equal to 10 mass %, more preferably greater than or equal to 25 mass %, and even more preferably greater than or equal to 50 mass %. With such a content, the amount of adhesion to the chute 54 during transportation on the belt conveyor can be reduced. A similar experiment was conducted; in the experiment, however, no dust was added, and a dewatered cake and sintered ore powder were used at a ratio of 1:1 (sintered ore powder content=50 mass %). The result was that the amount of adhesion was 1.5 g. Thus, it was confirmed that a reduction in the amount of adhesion to the chute 54 could also be achieved under conditions in which no dust was added. The adhesion property of a granulated material was measured; the granulated material included sludge in an amount of 75 mass % and sintered ore powder in an amount of 25%, and the sludge had been dewatered to have a moisture content of 21 mass %. The amount of adhesion was 2.1 g, and thus it was confirmed that a reduction in the amount of adhesion was also achieved under this condition.
Also, regarding the granulated materials produced by using the drum-type granulator, when the content of the sintered ore powder was 10 mass %, the amount of adhesion to the chute 54 was reduced compared with that of the granulated material containing no sintered ore powder. Furthermore, when the content of the sintered ore powder was 25 mass %, the amount of adhesion to the chute 54 was reduced compared with that of the granulated material having a sintered ore powder content of 10 mass %.
However, drum-type granulators have a lower stirring capability than intensive mixers and, therefore, cannot crush dewatered cakes as much as intensive mixers can. Thus, presumably, in the case where the drum-type granulator was used to produce a granulated material, a greater number of granulated materials having a weak portion in a middle were produced, the weak portion being a portion having a high moisture content, than in the case where the intensive mixer was used to produce a granulated material; consequently, the amount of adhesion to the chute 54 was increased.
Now, the results of a confirmation will be described regarding a relationship between the rotational speed and rotation time of the stirring impeller of the intensive mixer and the amount of adhesion. A dewatered cake obtained by dewatering sludge, which was the same as the sludge shown in Table 1, and having a moisture content of 25 mass %, dust having a moisture content of 5 mass %, and sintered ore powder having a moisture content of 1.5 mass % were loaded into an intensive mixer at a mass ratio of 12:3:5 (sludge: 60 mass %, dust: 15 mass %, and the sintered ore powder: 25 mass %). Then, granulated materials were produced by employing various rotational speeds and various rotation times. The adhesion property of the granulated materials produced as described above was evaluated by using the adhesion property evaluation device 50, illustrated in
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-064037 | Mar 2018 | JP | national |
This is the U.S. National Phase application of PCT/JP2019/011724, filed Mar. 20, 2019, which claims priority to Japanese Patent Application No. 2018-064037, filed Mar. 29, 2018, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/011724 | 3/20/2019 | WO | 00 |
