DESCRIPTION
METHOD OF TREATMENT OF GRANULATED MATERIAL FOR SINTERING USE
Technical Field
The present invention relates to a method of treatment of a granulated material for sintering use which is used for feedstock of a blast furnace.
Background Art
Sintered ore, a feedstock for a blast furnace, is obtained by mixing iron ore, fuel, fluxes, etc. while adding water for granulation using a granulating machine, then firing the mixture in a sintering machine. To maintain and further improve the productivity of the sintered ore, it is important to secure gas permeability of the sintering material during firing in the sintering machine. Granulation is becoming an essential operation.
However, the moisture which is used for granulation evaporates in the process of firing and condenses at the unfired granulated material at the bottom, forming a so-called "wet zone" causing the problems of the granulated material exposed to excessive moisture crumbling and inhibiting the gas permeation at the sintering machine. Note that, in such an existing granulation line, a granulated material comprised of coarse particles forming core particles on which fine powder is deposited, that is, a pseudo-granulated material, is produced.
On the other hand, in recent years, to deal with the fine powder in the sintering material which increases along with the degradation of the sintering material, the "semipellet method" extracting the fine powder material from this sintering material, granulating this at a separate granulation line provided in parallel with the above-mentioned existing granulation line, and firing this granulated material (below, also referred to as the
"fine powder granulated material") together with the pseudo-granulated material which was granulated at the existing granulation line is studied.
For example, PLT 1 describes to further dry the fine powder granulated material produced by the above-mentioned method so as to try to increase the effect of improving the strength and securing gas permeability at the sintering machine.
However, if mixing the dried fine powder granulated material and the wet state pseudo-granulated material, the problem arises that the moisture in the pseudo-granulated material is absorbed by the dried fine powder granulated material and therefore the dried granulated material falls in strength.
Due to the above, art which can secure the strength of the pseudo-granulated material and the fine powder granulated material even if the pseudo-granulated material is exposed to excessive moisture in the wet zone during firing or if dried fine powder granulated material is mixed with the wet pseudo-granulated material and the fine powder granulated material reabsorbs moisture has been sought.
As the means for improving the strength of the granulated material, including improvement of the strength of the granulated material in the wet state, there is, for example, the method of using a tacky binder, clay-based binder, dispersive binder, carbonation, or hydraulic binder. This will be explained in detail below.
A "tacky binder" is a binder which exhibits an action of binding granules through a tacky substance. As typical examples, there are cellulose, starch, etc.
For example, PLT 2 discloses to use a rosin-based compound ingredient with excellent tackiness as a tacky binder at the time of granulation and thereby obtain a granulated material for feedstock use which is excellent in wet strength and dry strength.
Further, a "clay-based binder" is a binder which contains a large amount of fine particles of a particle size of 10 µm or less which exhibit the action of entering between granules and binding them. As typical examples, there are bentonite etc.
PLT 3 describes this clay-based binder bentonite as a flocculant and suggests that the clay content also has a flocculating function. Further, PLT 3 discloses use of bentonite or another inorganic flocculant in addition to an organic binder so as to obtain iron oxide pellets with a high dry strength. Further, PLT 3 describes adding bentonite to the feedstock, then adding water for granulation and use of this as an aggregate and suggests that there is some flocculating action of fine particles.
A "dispersive binder" is a binder which exhibits an action promoting binding by dispersing the clay content contained in ore in the water for rearrangement between the grains. As typical examples, there are sodium polyacrylate etc.
PLT 4 discloses to use a granulation additive including a high molecular weight compound superior in dispersibility as a dispersive binder to obtain a granular material for feedstock use which is excellent in wet strength and dry strength.
Further, "carbonation" is a method of using a chemical reaction to improve the strength of the granulated material.
PLT 5 discloses the method of adding quick lime for granulation during which bringing the material into contact with exhaust gas or other gas containing C02 so as to carbonize the quick lime and form strong chemical bonds. According to this method, even when the granulated material is exposed to excessive moisture or when it reabsorbs water, it is possible to maintain the material at a certain extent of strength.
Furthermore, PLT 6 describes using a hydraulic mineral binder including iron as a hydraulic binder for
granulation and curing it over a long time so as to obtain a high strength granulated material. Due to this, even when the granulated material is exposed to excessive moisture or when it reabsorbs water, the granulated material can be provided with a strength to sufficiently withstand this.
PLT 7 discloses a method of production of sintered ore comprising mixing parts of the powdered iron ore and carbonaceous material, granulating this to form a preliminary granulated material, coating the outside of this preliminary granulated material with a flux containing CaO to form a coated preliminary granulated material, mixing this coated preliminary granulated material with the remaining mixing materials to form three-layer structure pseudo-granules, and feeding these to a sintering machine. Due to this, it is considered possible to produce sintered ore which is high in dropping strength and can prevent deterioration of the reducibility even with small contents of slag forming ingredients such as SiO2 and CaO.
PLT 8 discloses a method of pretreatment of a sintering material comprising premixing and granulating pellet feed or other fine powder ore and quick lime powder or slaked lime powder forming a CaO source with returned ore, limonite, or other coarse grain ore using a pellet feed or other fine powder ore with a low reactivity as a binder layer and mixing this with other sintering materials. Due to this, it is considered possible to improve the gas permeability and reducibility.
Citation List Patent Literature
PLT 1: Japanese Patent Publication (A) No. 2006-336064
PLT 2: Japanese Patent Publication (A) No. 2005-89861
PLT 3: Japanese Patent Publication (A) No. 11-193423
PLT 4: Japanese Patent Publication (A) No. 2005-15919
PLT 5: Japanese Patent Publication (A) No. 2001-279335
PLT 6: Japanese Patent Publication (A) No. 2006-508251
PLT 7: Japanese Patent Publication (A) No. 2007-211289
PLT 8: Japanese Patent Publication (A) No. 60-248827
Summary of Invention Technical Problem
However, the above conventional methods still had the following problems to be solved:
In PLT 2, the tacky binder is water soluble, so there is the problem that when the granulated material is exposed to excessive moisture or when it reabsorbs water, the tacky binder dissolves and it becomes difficult for the strength of the granulated material to be sufficiently maintained.
Further, in PLT 3, bentonite with the flocculating action is mixed into the sintering material from the start of granulation, so a drop in the strength of the granulated material is invited. To produce a strong granulated material, a good dispersion of the binder and the particulate (clay) is necessary, but with the above-mentioned method, due to the flocculating action of the bentonite, dispersion is inhibited. This becomes a defect.
Note that, the flocculating action of bentonite is small. Even if a good dispersion is obtained, the clay-based binder easily redisperses in the water, so when the granulated material is exposed to excessive moisture or when it reabsorbs water, its strength cannot be sufficiently secured.
Further, the dispersive action of the binder
described in PLT 4 is not lost upon granulation of the sintering material. Even after granulating and drying the sintering material once, this function is exhibited. For this reason, when the granulated material is exposed to excessive moisture or when it reabsorbs water, redispersion of the clay content occurs and the strength of the granulated material can no longer be sufficiently maintained.
Further, in PLT 5, a long time is required for causing a sufficient reaction for carbonation of the quick lime, so introduction of this method into the current continuous treatment process, for example, the process of granulation of several hundred tons per hour, is difficult. Further, a long time is required for the above-mentioned reaction, so when the granulated material is exposed to excessive moisture or when it reabsorbs water before this reaction sufficiently proceeds, redispersion of the quick lime occurs and the strength of the granulated material cannot be sufficiently maintained.
Furthermore, the method of PLT 6 is predicated on curing the granulated material for a long time, so this method is hard to apply to the current continuous treatment process. Further, if the granulated material is exposed to excessive moisture before curing of the granulated material, there are problems similar to those of the above-mentioned PLT 5.
In the method of PLT 7, the CaO layer is present at the center layer of the three-layer structure granulated material (pseudo-particles), so the flocculated region has little effect of hydrophobicity or water repellency with respect to the moisture which penetrates from the surface layer of the pseudo-particles. For this reason, it is not possible to sufficiently maintain the strength of the surface layer part of the granulated material (pseudo-particles) .
Further, in PLT 8, the layer deposited on the
surface of the coarse ore is present as a mixture of the fine powder ore and the lime powder serving as the CaO source. It raises the CaO/Si02 ratio and delays the reaction between the CaO and Si02. Such CaO, as explained above, has a small flocculating effect and hydrophobic/water repellent effect and cannot suppress the drop in the strength of the granulated material.
The present invention was made in consideration of this situation and has as its object the provision of a method of treatment of a granulated material for sintering use which enables the strength of the granulated material to be maintained and further which enables continuous granulation in a continuous treatment line even when the granulated material is exposed to excessive moisture in the wet zone or when dry granulated material is mixed with the wet granulated material and the dry granulated material reabsorbs moisture.
Solution to Problem
The method of treatment of a granulated material for sintering use according to the present invention which achieves this object is a method of treatment of a granulated material for sintering use comprising depositing on a surface layer of a granulated material, which is obtained by wet granulation of a mixed material containing an iron-source material including a powdered iron ore, a carbonaceous material, and a flux including lime using a binder, a strength-drop suppressant comprised of one or more of any of a flocculant, hydrophobic agent, and water repellant agent to obtain a coated granulated material for feeding to a sintering machine. Note that, in the present invention, the "coated granulated material" means a granulated material produced by wet granulation which is coated on at least part of its surface with a strength-drop suppressant.
In the method of treatment of a granulated material for sintering use according to the present invention, it
is preferable to dry the granulated material before depositing the strength-drop suppressant on the granulated material.
In the method of treatment of a granulated material for sintering use according to the present invention, the binder may be one or more of a tacky binder, clay-based binder, and dispersive binder.
Advantageous Effects of Invention
The method of treatment of a granulated material for sintering use according to the present invention deposits a strength-drop suppressant on the surface layer of the granulated material which is wet granulated using a binder to form a coated granulated material, so a drop in the strength of the granulated material can be suppressed.
Here, when using a flocculant as the strength-drop suppressant, it is possible to maintain the flocculated state of the grains forming the surface layer of the granulated material, so even when the granulated material is exposed to excessive moisture or when it reabsorbs moisture, the granulated material can be kept from redispersing.
Further, when using a hydrophobic agent or water repellant agent for the strength-drop suppressant, moisture can be kept from excessively penetrating the inside of the granulated material, so even if the granulated material is exposed to excessive moisture, the granulated material can be kept from redispersion.
Furthermore, the strength-drop suppressant need only be deposited on the surface layer of the granulated material, so treatment for deposition can be completed in a short time.
Therefore, even when the granulated material is exposed to excessive moisture in the wet zone or when dry granulated material is mixed with the wet granulated material so that the dry granulated material absorbs
moisture again, the strength of the granulated material can be maintained. Further, continuous granulation can be performed in a continuous treatment line.
Further, if drying the granulated material before depositing a strength-drop suppressant on the granulated material, the effect of maintenance of the strength of the granulated material is manifested more remarkably.
When drying the granulated material, the strength of the granulated material rises compared with before drying, but when this granulated material is exposed to excessive moisture or when it reabsorbs moisture, the strength of the granulated material falls to the same extent as before drying. That is, by depositing the strength-drop suppressant on the surface layer of the dry granulated material, the strength after drying can be maintained.
Further, when the binder is one or more of a tacky binder, clay-based binder, and dispersive binder, the effect of maintenance of the strength of the granulated material is more remarkably manifested. This is due to the fact that a tacky binder, clay-based binder, and dispersive binder are binders which lose their binding force due to moisture.
Note that, a binder which uses chemical bonding such as quick lime, cement, and a hydraulic binder differs from the above-mentioned tacky binder, clay-based binder, and dispersive binder in that the effect of moisture on the binding force is small. However, before the chemical bonds are formed, the problem identified by the present invention, that is, a drop in the strength of the granulated material due to moisture, occurs, so the effect of maintenance of the strength of the granulated material due to the deposition of the strength-drop suppressant is remarkably manifested. Further, even after the chemical bonds are formed, there is little room for improvement, but the effect due to the strength-drop suppressant is not small.
Brief Description of Drawings
FIG. 1 is a view explaining the relationship between the clay ratio of the granulated material and compressive ultimate strength.
FIG. 2 is a view explaining the relationship between the type and solid content ratio of the binder used for granulation of the granulated material and the compressive ultimate strength of the granulated material produced.
FIG.3 is a view explaining the relationship between the amount of deposition of the flocculant on the granulated material and the compressive ultimate strength of the granulated material.
FIG. 4 is a view explaining the relationship between the amount of deposition of the water repellant agent on the granulated material and the compressive ultimate strength of the granulated material.
FIG. 5 is a view explaining the change in the compressive ultimate strength of the dry granulated material due to the presence/absence of a strength-drop suppressant.
FIG. 6 is a view explaining the change in the compressive ultimate strength of the non-dry granulated material due to the presence/absence of a strength-drop suppressant.
FIG. 7(A) is a view explaining the relationship between the amount of deposition of the flocculant solution on the granulated material and the gas permeation index.
FIG. 7(B) is a view explaining the relationship between the amount of deposition of the flocculant powder on the granulated material and the gas permeation index.
FIG. 7(C) is a view explaining the relationship between the amount of deposition of the water repellant agent on the granulated material and the gas permeation index.
Description of Embodiments
Referring to the attached drawings, embodiments of the present invention will be explained for facilitating understanding of the present invention.
First, the background leading to the conception of the method of treatment of a granulated material for sintering use according to an embodiment of the present invention will be explained, then the method of treatment of a granulated material for sintering use will be explained.
First, the inventors studied the reason why the strength of the granulated material falls when the granulated material is exposed to excessive moisture or reabsorbs moisture.
The strength of the granulated material is maintained not only by deposition due to liquid cross-linking of water, but also, as shown in FIG. 1, by the fine particles (clay) entering between the granules to give rise to a bonding action. Note that, this granulated material is a fine powder granulated material produced by granulating fine powder using a dispersive binder (polymer dispersant).
Here, the "clay ratio" of the abscissa of FIG. 1 means the ratio of the clay in the total sintering material forming the granulated material. Further, in FIG. 1, the compressive ultimate strength of the ordinate (hereinafter sometimes simply referred to as the "strength") is the value obtained by taking samples of a granulated material with a diameter of 7 to 8 mm, placing each of these granulated materials on a load cell, pressing down from above by a metal plate descending by 5 mm/min, determining the maximum compressive force (N) at the time when the value of the compressive force shown by the load cell rises, then rapidly falls, dividing this by the cross-sectional area (cm2) of the granulated material, and averaging the thus measured values for five samples
of granulated material (same below).
However, as shown in FIG. 2, when drying the fine powder granulated material produced using the dispersive binder (O) , then mixing it together with a wet granulated material (•) , the dried granulated material absorbs the moisture of the wet granulated material, so the phenomenon of a drop in the compressive ultimate strength occurs (O→l) . This is believed because the dispersive action of the binder functions even after the sintering material is granulated and dried, so the clay content flocculated between the granules redisperse once due to the absorbed moisture and lose their binding force.
Further, the tacky binder (cellulose) is also water soluble, so a similar trend (A→▲) is exhibited. It is learned that excessive moisture causes the tacky binder as well to lose its binding force.
Note that, in FIG. 2, the abscissa shows the ratio of the solid contents (effective ingredients) of the binders.
Based on these phenomena, the inventors studied measures enabling continuous granulation in a continuous treatment line (in-line) and as a result came up with the idea of the method of treatment of a granulated material for sintering use according to an embodiment of the present invention. That is, the method of treatment of a granulated material for sintering use according to an embodiment of the present invention is a method of depositing a strength-drop suppressant comprised of one or more of a flocculant, hydrophobic agent, and water repellant agent on the surface layer of a granulated material produced by wet granulation using a binder. This will be explained in detail below.
First, the effect of deposition of a flocculant on the surface layer of the granulated material will be explained.
The inventors granulated and dried fine powder using
a dispersive binder (polymer dispersant), mixed this dried state granulated material once with a wet material, took out the result, and compared its compressive ultimate strength. The results are shown in FIG. 3. Note that, the amount of deposition of the flocculant of the abscissa of FIG. 3 is the weight ratio (mass%) of the solid content of the flocculant to the sum of the dry weight (g) of the granulated material and the solid content weight (g) of the flocculant deposited on the surface layer of the granulated material. Therefore, on the abscissa of FIG. 3, the amount of deposition of the flocculant of "0" means the result of the case where no flocculant is deposited on the surface layer of the granulated material.
As shown in FIG. 3, after drying, the granulated material exhibited an approximately 1 MPa (10 kgf/cm2) compressive ultimate strength, but when mixed with a wet material without deposition of the flocculant on the surface layer of the granulated material, the compressive ultimate strength fell to about 0.2 MPa (2 kgf/cm2).
As opposed to this, when using a high molecular weight compound, one example of a flocculant, and depositing an aqueous solution of this flocculant () on the surface layer of the granulated material in advance, with an amount of deposition of about 0.06 mass%, the compressive ultimate strength becomes maximum (0.8 MPa). Above this, the effect becomes saturated. This is believed to be that while the strength of the surface layer of the granulated material is secured by the flocculant, moisture permeates to the inside resulting in a drop in the strength inside the granulated material whereby its effect is cancelled out. There are believed to be "suitable amounts" of the amount of deposition and surface layer thickness of the flocculant.
Further, for the purpose of easing the effect of the water in the aqueous solution of the flocculant, when depositing the flocculant as is as a powder, the
compressive ultimate strength tends to gradually rise in accordance with the amount of powder.
Therefore, it is considered necessary to suitably select and suitably apply the method of deposition of the flocculant based on the targeted strength, granularity, and distribution of the granulated material.
Next, the effect of deposition of the water repellant agent (hydrophobic agent) on the surface layer of the granulated material will be explained.
The result of using, instead of the above-mentioned flocculant, liquid paraffin (liquid), one example of a water repellant agent, is shown in FIG. 4. Note that, the amount of deposition of the water repellant agent of the abscissa of FIG. 4 is the weight ratio (mass%) of the solid content of the water repellant agent to the sum of the dry weight (g) of the granulated material and the weight (g) of the water repellant agent deposited on the surface layer of the granulated material. Therefore, on the abscissa of FIG. 4, the amount of deposition of the water repellant agent of "0" means the result of the case where no water repellant agent is deposited on the surface layer of the granulated material.
As shown in FIG. 4, along with the increase in the amount of deposition of the water repellant agent, the compressive ultimate strength is improved, but the effect tends to gradually become saturated.
Therefore, it is guessed that there is a "suitable amount" of deposition or deposited thickness of the water repellant agent. It is believed necessary to suitably determine the method of deposition in accordance with the targeted strength or granularity of the granulated material.
As the method for depositing a strength-drop suppressant comprised of one or more of a flocculant, water repellant agent, and hydrophobic agent on a granulated material in a continuous treatment line (in-line) to obtain a coated granulated material, for
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example, there is the method of performing this in either the state of either a powder, liquid, aqueous solution, or slurry or the method of performing this in a combination of two or more states. Note that, the strength-drop suppressant is preferably deposited in a state covering the entire surface layer of the granulated material, but the effect is obtained even if deposited in a state partially covering one part of the surface layer (for example, at least 50% of the surface area). Specifically, the following method is used.
To spray on the strength-drop suppressant in the powder state, for example, there is the method of pneumatically conveying the powder in a dry state as it is to spray it on the granulated material or the method of conveying it by a belt conveyor to add it over the granulated material.
Further, for spraying it on in the liquid state, if the strength-drop suppressant itself is a liquid, for example, there is the method of using a nozzle to spray the granulated material or the method of mixing in a foam agent, forming a foam, and mixing this in with the granulated material. Note that, if the strength-drop suppressant itself is a liquid, there is the method of spraying it on by the above-mentioned methods in the form of an aqueous solution or slurry.
As the positions for depositing this strength-drop suppressant, there are the following positions.
For example, when using an existing granulation line to produce a pseudo-granulated material comprised of coarse granules of core granules made by a granulating machine on which fine powder is deposited, the strength-drop suppressant is added and deposited to form the coated granulated material at the conveyor apparatus from the latter half of the granulating machine to loading in the sintering machine. Note that, the "latter half of the granulating machine" means the middle of granulation of the granulating machine, for example, the stage where the
granulation is 70 to 90% finished. Here, the stage where the granulation is, for example, 90% finished means the timing of 0.9xT (min) with respect to the granulation completion time (total granulation time) T minutes of a granulated material. Therefore, the strength-drop suppressant is deposited on the granulated material at the end of 90% of the granulation completion time.
Further, when using a separate granulation line provided parallel to the above-mentioned existing granulation line so as to granulate, by the granulating machine, a fine powder material extracted from the sintering material so as to produce a fine powder granulated material, this fine powder granulated material is discharged from a dryer drying it, then is mixed with the above-mentioned pseudo-granulated material (wet material). In the conveyance route, the strength-drop suppressant is added and deposited to obtain the coated granulated material.
When granulating such a granulated material by the above-mentioned existing granulation line or separate granulation line, the sintering material, binder, water, etc. are fed to the granulating machine (for example, drum mixer, Eirich mixer, etc.) for wet granulation.
For this binder, for example, one or more of a tacky binder, clay-based binder, dispersive binder, and hydraulic binder can be used.
Here, as the tacky binder, there is, for example, cellulose, starch, etc., as the clay-based binder, there is, for example, bentonite, quick lime, etc., as the dispersive binder, there is, for example, sodium polyacrylate, and as the hydraulic binder, there is, for example, a hydraulic mineral binder containing iron, but the invention is not limited to these.
Note that, the above-mentioned dispersive binder need only be one which has the action of promoting dispersion, in moisture, of ultra fine particles of 10 µm or less contained in the sintering material by addition
together with water at the time of granulation of the sintering material. It is not limited to an inorganic compound, organic compound, low molecular weight compound, or high molecular weight compound. It is not particularly limited, but a high molecular weight compound which has an acid group and/or its salt is preferable. Among these, sodium polyacrylate or ammonium polyacrylate having a weight average molecular weight of 1000 to 100,000 has a high ability to disperse fine particles and is also inexpensive in price, so can be most optimally used.
Further, when using, among the above-mentioned binders, a tacky binder, clay-based binder, or dispersive binder which is susceptible to the effects of moisture after granulation, the effect of the strength-drop suppressant of the present invention is remarkably obtained.
Here, the granulated material on which the strength-drop suppressant is to be deposited includes the above-mentioned pseudo-granulated material and fine powder granulated material, but among these as well, granulated material which includes grains of over 2 mm in sieve mesh size in 50 mass% or more (including 100 mass%) is preferable.
If the size of the granulated material is under 2 mm in sieve mesh size, the surface area of the granulated material becomes excessive and the amount of use of strength-drop suppressant increases, so this is not economical. Further, even if the strength-drop suppressant is deposited on the small granulated material in this way, this effect is not manifested.
Note that, if the granulated material becomes larger, the effect of the strength-drop suppressant appears. While not particularly limited, the upper limit of the granulated material which is produced by granulation at the granulating machine is, by common sense, about 20 mm or so.
Next, the types of the flocculant, water repellant agent, and hydrophobic agent used for the strength-drop suppressant will be explained. The "flocculant" is a substance which has a flocculating effect (suppressing the dispersion function) so that the clay content once in the solidified state will not redisperse even in excessive moisture.
As such substances, there are aluminum sulfate, aluminum polychloride, ferric chloride, ferrous sulfate, and aqueous solutions containing magnesium ions and calcium ions. Further, there are an aniline-formaldehyde polycondensate hydrochloride, polyhexamethylene thiourea acetate, polyvinylbenzyl trimethyl ammonium chloride, or other organic coagulating agents, anionic, nonionic, or cationic polymer flocculants etc.
Note that, the flocculant is not limited to the above. It is sufficient that it be a substance which has the effect of causing flocculation of the clay content. Further, at the time of use, the above-mentioned substances and forms may be combined for use.
The water repellant agent or hydrophobic agent is a substance which suppresses the penetration of moisture into the granulated material and has a water repellent effect or a hydrophobic effect which prevents excessive penetration into the granulated material.
As such a substance, there are liquid paraffin or paraffin chloride, natural wax or synthetic wax or other paraffinic water repellant agents, trimethyl silicon or modified alkyl silicone or other silicone-based water repellant agents, trichloromethylsilane or other silane-based polymer, fluorine-based water repellant agent, urethane-based polymer, etc.
Note that, the water repellant agent or hydrophobic agent is not limited to the ones explained above. It may be a substance having a water repellent action or a hydrophobic action. Further, at the time of use, it is also possible to use the above-mentioned substances or
forms in combination- Here, the substances illustrated as water repellant agents or hydrophobic agents are not strictly differentiated when surveying the prior case studies, but mean substances which worsen the wettability between water and iron ore.
Further, the above-mentioned strength-drop suppressant does not include calcium oxide (quick lime) powder. This is because the flocculation effect and the hydrophobic/water repellent effect are small and it is not possible to suppress a drop in the strength of the granulated material. Further, calcium oxide (quick lime) is important for improving the strength of sintered ore after sintering. A change in the amount of calcium oxide which is included in the sintered ore has an effect on operations, so use as a strength-drop suppressant is not preferred.
The effect of the treatment for depositing a strength-drop suppressant on the surface layer of the granulated material shown above becomes more pronounced by performing it on granulated material which has been dried in advance. The results are shown in FIG. 5 and FIG. 6.
Here, FIG. 5 shows the results of dry treated granulated material, while FIG. 6 shows the results of non-dry treated granulated material. Note that the granulated materials used in FIG. 5 and FIG. 6 are both fine powder granulated materials produced by granulating fine powder using a dispersive binder (polymer dispersant). In FIG. 5 and FIG. 6, the "O" marks indicate the results when depositing one example of a flocculant, that is, an aluminum sulfate aqueous solution (solid content weight: 0.06 mass%), on the surface layer of the granulated material (treatment)), while the "A" marks indicate the results when not depositing an aluminum sulfate aqueous solution (no treatment) on it.
As shown in FIG. 5, when drying the granulated material, the drying causes the strength of the
granulated material to rise once, but when rewet as is, the strength falls down to the same degree as before drying (in FIG. 5, ▲) . As opposed to this, when depositing the aluminum sulfate aqueous solution on the surface layer of the granulated material, it is possible to suppress the drop in the strength of the granulated material due to the rewetting and possible to maintain a high strength (in FIG. 5, O) .
Further, as shown in FIG. 6, when not drying the granulated material, while it is possible to maintain the strength even with rewetting by depositing an aluminum sulfate aqueous solution on the surface layer of the granulated material, the strength level becomes low (in FIG. 6, O) .
From the above, it could be confirmed that by drying the granulated material, then depositing the strength-drop suppressant on the surface layer of the granulated material, it is possible to maintain the strength of the granulated material higher.
Examples
Next, examples performed for confirming the operation and effect of the present invention will be explained.
First, the effects obtained by depositing a strength-drop suppressant on the surface layer of the pseudo granulated material using the above existing granulation line will be explained.
Several types of mixed materials of iron ore powder and carbonaceous material, lime, serpentine, and other sintering material mixed together (iron ore powder: 70.5%, lime: 10.0%, serpentine: 1.0%, carbonaceous material: 3.5%, returned ore: 15.0%, total 100%) were used in a drum mixer (granulating machine) while adding water and mixing for 4 minutes for granulation so as to adjust the moisture content of the granulated material to 7 mass%. At the time of this wet granulation, quick lime having an action as a clay-based binder was added. Note that, the amount of moisture of the granulated material is the ratio of the moisture to the total of the dry weight of the granulated material and the moisture.
Each granulated material which was produced in this way was coated with a strength-drop suppressant under the test conditions explained below to obtain a coated granulated material. This was piled in a pot firing device. While sucking out the air from the bottom of the pot at a negative pressure of 1000 mmH20, the top surface layer of the piled up granulated material was ignited to fire the granulated material. The flow rate of suction during the firing (Nm3/hour) was measured. Using the flow rate of suction of Comparative Example 1 as "1", the gas permeation indexes of the examples were calculated. Therefore, the larger the gas permeation index, the better the gas permeability becomes.
These test conditions and results are shown in Table 1. The test results are shown in FIG. 7(A) to FIG. 7(C).
Table 1
(Table Removed)
In Table 1, Comparative Example 1 shows the results in the case of firing a granulated material as is without depositing a strength-drop suppressant.
On the other hand, Examples 1 to 11 show the results in the case of making the granulation time in the drum mixer 4 minutes, sprinkling various types of strength-drop suppressants (flocculants and water repellant agents) at the point of time when 3 minutes elapse in the middle of granulation (point of time when granulation is 75% ended), and depositing them on the surface layer of the granulated material. Note that a test changing the amount of deposition of the strength-drop suppressant was run for 0.01 to 0.1 mass% in range, but as shown in the above FIG. 3 and FIG. 4, along with the increase in the amount of deposition of the strength-drop suppressant, the effect gradually becomes saturated, so only 0.01 to 0.03 mass% in range is described. Here, for the solution of the flocculant (aluminum sulfate) used in Examples 1 to 3, an aqueous solution is made once then this is press fed and sprayed over the granulated material by a nozzle. FIG.7(A) shows the relationship between the amount of deposition of the flocculant solution and the gas permeation index (same in following examples). Note that, the "amount of deposition of the flocculant solution" is the powder weight of the flocculant (effective ingredient).
Further, the powder of the flocculant (aluminum sulfate) used in Examples 4 to 6 was broken up using a sieve and uniformly sprinkled over the granulated material. FIG. 7{B) shows the relationship between the amount of deposition of the flocculant powder and the gas permeation index (same in following examples).
Further, for the water repellant agent (liquid paraffin) used in Examples 7 to 9, the liquid itself is press fed and sprayed on the granulated material by a nozzle. FIG. 7(C) shows the relationship between the amount of deposition of the water repellant agent and the gas permeation index (same in the following examples). Furthermore, Examples 10 and 11 show the results of spraying the same amounts of the above-mentioned solution
of the flocculant and water repellant agent.
As clear from Table 1 and FIG. 7(A) to FIG. 7(C), in Examples 1 to 11, a trend is seen for improvement of the gas permeability compared with Comparative Example 1. Further, along with an increase in the amount of deposition of the strength-drop suppressant, a greater effect is obtained as a result (in FIG. 7(A) to FIG. 7(C), quick lime: ♦) . In particular, as shown in Example 11, the solution of the flocculant and the water repellant agent were sprayed in the same amounts of 0.02 mass% to enable a 5% improvement of gas permeation.
From the above results, it is believed that by depositing a strength-drop suppressant on the surface layer of the granulated material, an effect is exhibited of suppression of decay of the granulated material accompanying condensation of moisture and improvement of the gas permeation.
Note that, the above-mentioned results are the results in the case of depositing a strength-drop suppressant on the surface layer of the granulated material in the latter half of granulation at the drum mixer, but a similar trend to the above results was observed even when depositing a strength-drop suppressant on the surface layer of the granulated material from after granulation at the drum mixer to charging into a pot firing device.
Next, the results of depositing a strength-drop suppressant on he surface layer of a fine powder granulated material produced using a separate granulation line provided in parallel with the existing granulation line will be explained.
From various types of ores, 20 mass% of ore with a large content of fine powder was extracted. This was pulverized by a ball mill, various types of binders explained below were added in 0.1 mass%, the moisture of the granulated material was made 9 mass%, and the result was granulated at a drum mixer, then the granulated
material was dried until the moisture became 2 mass% by a conventionally known hot air band dryer. Note that, in the granulation process, a strength-drop suppressant was added.
Further, this fine powder granulated material was mixed with pseudo-granulated material produced from the remaining 80 mass% of ore, then was piled in a pot firing device. While sucking out the air from the bottom of the pot at a negative pressure of 1000 mmH20, the top surface layer of the piled up granulated material was ignited to fire the granulated material. The above-mentioned method was used to calculate the gas permeation index of the examples. Note that, the pseudo-granulated material obtained by mixing the fine powder granulated material is a granulated material of the above-mentioned Comparative Example 1, that is, a wet state granulated material of a moisture of 7 mass% with no strength-drop suppressant deposited on its surface layer.
The test conditions and results are shown in Table 2, while the test results are shown in FIG. 7(A) to FIG. 7(C) .Here, at the time of wet granulation of the fine powder ore, as the binder, tacky cellulose (one example of a tacky binder), a clay-based bentonite (one example of a clay-based binder), or a dispersive polymer dispersant (one example of a dispersive binder) was used.
Further, Comparative Example 2 in Table 2 shows the results of firing a mixed fine powder granulated material and pseudo-granulated material as is without depositing a strength-drop suppressant on the fine powder granulated material.
On the other hand, Examples 12 to 22 show the results of drying a fine powder granulated material, then mixing it with 80 mass% of a wet pseudo-granulated material, before which depositing various types of strength-drop suppressants (flocculants and water repellant agents) on the surface layer of the fine powder granulated material. Note that, a test changing the amount of deposition of the strength-drop suppressant was run for 0.01 to 0.1 mass% in range. For similar reasons to the above test, here, only 0.02 to 0.06 mass% in range will be described.
Here, the strength-drop suppressant was deposited by inserting the dried fine powder granulated material in a drum mixer, sprinkling the strength-drop suppressant, then turning the drum three times for mixing.
Note that, the strength-drop suppressant constituted by the powder of the flocculant was sprinkled or constituted by the solution of the flocculant or the water repellant agent was sprayed by the same method as the above-mentioned test.
In this way, various types of fine powder granulated material on which strength-drop suppressants were deposited were combined with 80 mass% of wet pseudo-granulated material. These were mixed by rotation five times using a drum mixer. After this, part of each fine powder granulated material was sampled and measured for compressive ultimate strength.
As clear from Table 2 and FIG. 7(A) to FIG. 7(C), in each of Examples 12 to 22, the strength of the granulated material was secured and an effect of improvement of the gas permeation was observed compared with Comparative Example 2. Further, along with an increase in the amount of deposition of the strength-drop suppressant, a greater effect was obtained (in FIG. 7(A) to FIG. 7(C), cellulose: , bentonite: ▲, polymer dispersant: □) .
Note that, when using a powder of a flocculant, compared with a solution of a flocculant or a water repellant agent, a somewhat lower effect was obtained, but it is believed that this is because a powder is harder to disperse uniformly in the surface layer of a granulated material. Further, even if used as a solution, a flocculant gives a somewhat smaller effect with respect to a tacky binder (cellulose).
From the above results, by using the method of treatment of a granulated material for sintering use of the present invention, it could be confirmed that it was possible to maintain the strength of the granulated material and further to enable continuous granulation in a continuous treatment line even when the granulated material is exposed to excessive moisture in a wet zone or when dry granulated material is mixed with the wet granulated material and the dry granulated material reabsorbs moisture.
Above, the present invention was explained with reference to embodiments, but the present invention is not limited in any way to the configurations described in the above-mentioned embodiments. Other embodiments and modifications which may be conceived within the scope of matters described in the claims are also included. For example, combinations of parts or all of the above embodiments to form a method of treatment of a granulated material for sintering use are also included in the scope of rights of the present invention.

CLAIMS Claim 1
A method of treatment of a granulated material for sintering use comprising depositing on a surface layer of a granulated material, which is obtained by wet granulation of a mixed material containing an iron-source material including a powdered iron ore, a carbonaceous material, and a flux including lime using a binder, a strength-drop suppressant comprised of one or more of any of a flocculant, hydrophobic agent, and water repellant agent to obtain a coated granulated material for feeding to a sintering machine. Claim 2
A method of treatment of a granulated material for sintering use as set forth in claim 1, said method of treatment of a granulated material for sintering use characterized by drying said granulated material before depositing said strength-drop suppressant on said granulated material. Claim 3
A method of treatment of a granulated material for sintering use as set forth in either of claims 1 and 2, said method of treatment of a granulated material for sintering use characterized in that said binder is one or more of any of a tacky binder, clay-based binder, and dispersive binder.