JP2020033582A - Granulation method of blending raw material - Google Patents

Abstract

To provide a method capable of enhancing productivity of a sintered ore by reducing non-granulated fine powder in a granulation treatment of a blending raw material less in nuclear particles and large in fine powders.SOLUTION: There is provided a method including addition of a returned ore at 200°C or lower when a granulation treatment is conducted on a blending raw material containing a plurality of brands of iron ores with the under 250 μm of 20 mass% or more and the over 1 mm of 25 mas% to 65 mass% by blending and an auxiliary raw material by using a drum mixer, in which the returned ore is added in both of an inlet side and an outlet side of the drum mixer, the returned ore added in the inlet side of the drum mixer defines a mass ratio of the returned ore under 250 μm to iron ore under 250 mm and a mass ratio of the returned ore over 1 mm to iron ore under 250 mm, and the returned ore added in the outlet side of the drum mixer defines a mass ratio of the returned ore over 1 mm to iron ore under 250 mm and is added in a range of 0.5 L to 0.98 L (L: total length of the drum mixer).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for granulating a blended raw material having a small amount of core particles and a large amount of fine powder.

  As a sintering raw material, powdered iron ore (fine ore) is used as a main raw material, and an auxiliary raw material whose components are adjusted as necessary is blended. Then, by mixing water and a binder with the sintering raw material and performing a granulation treatment, the amount of fine powder charged into the sintering machine is reduced.

In the granulation treatment, it is generally performed to produce a granulated substance (pseudo particle) in which fine powder is attached around core particles (coarse particles). Granulation is an important operation for maintaining and improving sintering productivity, and various studies have been made in the past.
Patent Literature 1 states that if the amount of a powdery substance (fine powder) is too large relative to a granular substance (core particles), the strength of the granulated substance is reduced. Has been described. Patent Document 1 describes that the strength of a granulated product is improved by adding fine particles of calcium carbonate.

  Patent Literature 2 describes that sintering productivity is improved by effectively utilizing ore return. The invention described in Patent Document 2 is directed to a fine ore raw material in which pisolite ore is most mixed (see Table 1 in Patent Document 2). Patent Literature 2 discloses Invention Example 1 in which returned ore containing 1% or more of 80% by mass or more is added to a granulated product after granulation (hand mixing with a scoop), or a sintering raw material to which returned ore of 1 mm or less is added. Comparative Example 2 or the like is shown in which Comparative Example 2 and the like are granulated into granules, and the ore returned to the granules is 1 mm or more (mixed with a scoop).

  Patent Literature 3 also describes that sintering productivity is improved by effectively utilizing returned ore. The invention described in Patent Document 3 is directed to a powder ore raw material in which about 70% of Loeb River ore and Hamasley ore are blended (see Table 1 of Patent Document 3). Patent Literature 3 discloses an example of granulating an ungranulated sintering raw material with a drum mixer (test numbers T1 to T3), and returns ore containing about 30% by mass of particles of 1 mm or less to another sintering process. An example in which the raw material is granulated with a drum mixer and an example in which the raw material is added to a granulated material granulated by a drum mixer (mixing with a scoop) are shown. In Test Nos. T5 and T6, an example is shown in which after high-speed agitation is performed using a high-speed stirring mixer and a pan pelletizer, high-temperature ore return at 600 ° C. is mixed with a drum mixer.

JP 2008-101263 A JP 2015-193930 A JP 2007-284744 A

  In recent years, ore types including particulate matter serving as core particles have been depleted, and ore types with many fine powders have been mainly used. Even as a compounding raw material in which a certain amount of core particles is secured by mixing a plurality of ore types, the ratio of fine powder of 250 μm under (ore under a 250 μm sieve) in fine ore is 20% by mass or more and 1 mm over ( The ratio of the core particles of the coarse ore on the sieve having a sieve of 1 mm must be 65% by mass or less, and the ratio of the fine powder to the core particles is constantly in a very large state. Therefore, the necessity of granulating a sintering raw material having a small amount of core particles and a large amount of fine powder (hereinafter, sometimes referred to as a “fine powder raw material of loess core particles”) is increasing. However, when the pseudo particles are produced using the fine powder raw material of the loess core particles, the fine powder attached to the core particles becomes thicker than before, and more ungranulated fine powder is generated.

  A drum mixer or a high-speed stirrer (kneader) is generally used as a granulator for the granulation process. Drum mixers are primarily suitable for the production of pseudo-particles and are suitable for processing large quantities of raw materials, but suffer from the above-mentioned problem of ungranulated fines. On the other hand, compared with a drum mixer, a high-speed stirrer can granulate not only pseudo particles but also pellet particles mainly composed of only fine powder, but like a drum mixer, ungranulated fine powder is generated.

  The non-granulated fine powder after the granulation treatment includes fine powder that has not been granulated, fine powder generated by the collapse of the granulated material after granulation, and the like. In addition, the sintering rate during sintering decreases, and the productivity of sinter decreases.

When the fine powder raw material of the loess core particles is granulated using the invention described in Patent Document 1, the increase in the fine powder adhesion thickness (the increase in the fine powder ratio in the fine ore) is not achieved by the addition of fine calcium carbonate. There is a limit to the improvement of the graininess, and the increase of ungranulated fine powder becomes remarkable.
According to the inventions described in Patent Documents 2 and 3, a certain improvement in sintering productivity can be expected, but the invention does not presuppose the blending of ore species having a small number of core particles and a large number of fine powders. However, improvement in sintering productivity cannot be expected.

  The present invention has been made in view of such circumstances, and in a granulation process of a compounding raw material having a small number of core particles and a large amount of fine powder, a method capable of reducing ungranulated fine powder and improving the productivity of sintered ore. The purpose is to provide.

In order to achieve the above object, the present invention provides a blend comprising a mixture of iron ores of a plurality of brands, wherein a 250 μm under is 20% by mass or more and a 1 mm over is 25% by mass or more and 65% by mass or less and an auxiliary material. When the raw material is subjected to granulation treatment using a drum mixer, a method of adding a return of 200 ° C. or less,
The return ore is to be added on both the inlet side and the outlet side of the drum mixer,
The mass of the iron ore under 250 mm is Wpo, the mass of the returned ore under 250 μm added at the inlet of the drum mixer is Wpr, and the mass of the returned ore over 1 mm added at the inlet of the drum mixer is Wrrs. Assuming that the mass of the returned ore returned over 1 mm added at the outlet side of the drum mixer is Wrre, and the total length of the drum mixer is L,
The returned ore added at the entrance of the drum mixer is 0.148 ≧ Wpr / Wpo ≧ 0.006 and Wrrs / Wpo ≧ 0.039,
The returned ore added at the outlet side of the drum mixer is characterized in that 250 μm under is 10 mass% or less, Wrre / Wpo ≧ 0.062, and is added in the range of 0.5 L to 0.98 L.

  In addition, "under" indicates the bottom of the sieve when the sieve having the size described is used, and "over" indicates the top of the sieve.

  In the granulation process using a drum mixer, pseudo particles in which fine powder is attached around core particles are produced. The core particles are mainly composed of coarse particles exceeding 1 mm. The fine powder (adhered fine powder) adhering to the core particles has a large particle size of 250 μm or less, and may not be adhered to become ungranulated fine powder.

  Granulation treatment of iron ore with a small amount of core particles and a large amount of fine particles, in which the ratio of fine particles under 250 μm is 20% by mass or more and the ratio of coarse particles exceeding 1 mm is 25% by mass or more and 65% by mass or less, which is the object of the present invention. In this case, the attached thickness of the fine powder becomes larger than that of the conventional pseudo particles. According to the knowledge of the present inventors, when iron ore in which the ratio of fine powder under 250 μm is 20% by mass or more is granulated, the thickness of the attached fine powder is 300 μm or more. When the conventional sintering raw material having a large number of core particles is subjected to granulation treatment, the fine powder adhesion thickness is approximately 150 μm. It can be said that it is very thick.

Therefore, in rolling granulation using a drum mixer, in addition to the problem of ungranulated fine powder, there is a problem that the granulated pseudo-particles collapse during the granulation process. Even when iron ore having a small amount of core particles and a large amount of fine particles is granulated with a high-speed stirrer, disintegration of ungranulated fine particles and pseudo particles becomes a problem.
Although the above tendency is affected by the added auxiliary material, the point that the problem of disintegration of ungranulated fine powder and pseudo particles due to the decrease of core particles and the increase of fine powder remains unchanged.

Therefore, the present inventors worked on the development of a method for reducing ungranulated fine powder in the granulation treatment of a blended raw material having a small number of core particles and a large amount of fine powder.
The present inventors have obtained the following findings by performing various experiments.
Observation of the pseudo-particles after granulation with a drum mixer revealed that many of the pseudo-particles in which fine particles adhering to the core particles were mixed with returned ore under 250 μm (fine particle returned ore) increased in adhesion thickness. I was From this, it has been found that when fine powder refining is added to the sintering raw material before granulation, ungranulated fine powder is reduced. Since returned ore is powder generated when sinter is crushed, it has a more angular shape than iron ore particles, and after being attached to core particles, the surrounding attached fine powder is peeled off (collapse of pseudo particles). ) Is considered to be effective.

However, ungranulated fine powder remains even by the addition of fine powder returned.
The ungranulated fine powder is reduced by rolling and granulating with a drum mixer by adding returned ore (coarse ore return) of 200 ° C. or less and over 1 mm. This effect is greatest when the coarse-grained ore is added twice before granulation of the drum mixer and after granulation for a certain time in the drum mixer. This is because, when granulating a sintering raw material with a small number of core particles, a certain amount of coarse-grained ore returned as core particles is necessary even at the time of initial granulation, and as new core particles in the middle and late stages of granulation. It is considered that ungranulated fine powder remaining during granulation adheres to the added coarse-grained ore.

  Further, in the method for granulating a blended raw material according to the present invention, the iron ore is divided into two or more groups according to its particle diameter, and the iron ore of the group having the smallest average particle diameter is formed of quicklime and / or slaked lime. The binder may be added in an amount of 0.5% by mass or more and 6% by mass or less in terms of quicklime in terms of the total amount of iron ore in the group, and charged into the high-speed stirrer, and then charged into the inlet side of the drum mixer. Good.

  The iron ore of the group having the smallest average particle diameter after dividing the fine powder raw material of the loess core particles targeted by the present invention into two or more groups (hereinafter also referred to as “ultra-less core fine particle raw material”) is as follows. Further, the particle size is such that the core particles are small and the fine powder is large. When quicklime and / or slaked lime are added to the ultraless core particle fine powder raw material and granulation is performed by a high-speed stirrer, pseudo particles composed of only fine powder (hereinafter, also referred to as “P-type particles”) are formed. , Acts as core particles for adhering fine powder in a drum mixer.

  In the method for granulating the blended raw material according to the present invention, the fine powder returned and the coarse ground return are added to the raw material having a small number of core particles and the fine powder is subjected to drum mixer granulation, and then the coarse return is added again. Granulation by drum mixer. As a result, ungranulated fine powder can be reduced to such an extent that sintering productivity can be significantly improved.

It is a flow figure of the granulation method of the compounding material concerning a 1st embodiment of the present invention. It is a flow figure of the granulation method of the compounding material concerning a 2nd embodiment of the present invention.

  Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

[Method of Granulating Compounding Raw Material According to First Embodiment]
FIG. 1 shows a flow of a granulation method of a compounding raw material according to the first embodiment of the present invention.
In the present embodiment, when the compounded raw material having a small amount of core particles and a large amount of fine powder is subjected to granulation using the drum mixer 10, return ore is added.
Generally, returned ore is fine powder that is generated when sinter after firing is pulverized to a size suitable for introduction into a blast furnace, and has a small particle size that is not suitable for introduction into a blast furnace. It refers to mineral powder and contains a lot of fine powder under 1 mm.

  The blending raw material contains a mixture of iron ores 14 of a plurality of brands, and a coarse raw material with a 250 μm under 20% by mass or more and a 1 mm over coarse particle of 25% by mass or more and 65% by mass or less and an auxiliary material. The auxiliary raw materials are carbonaceous materials, limestone, and the like.

As described above, when iron ore in which the ratio of fines under 250 μm is 20% by mass or more is granulated, the thickness of the attached fines 21 becomes 300 μm or more. The problem is that the quasi-particles that have been granulated collapse during the granulation process. The reason why the amount of coarse particles exceeding 1 mm is set to 65% by mass or less is due to the iron ore circumstances in recent years.
On the other hand, when the amount of coarse particles exceeding 1 mm is less than 25% by mass, a remarkable sintering productivity improvement effect cannot be obtained even by the present invention. This is presumably because the core particles 20 were too small, the thickness of the attached fine powder 21 was extremely large, and the pseudo particle structure could not be maintained even by the present invention.
Although the upper limit of the fine powder under 250 μm is not specified, the coarse particles exceeding 1 mm are 25% by mass or more and 65% by mass or less. Is about 60% by mass or less from the actual state.

  For the ore return, use low-temperature return at 200 ° C or lower. This is because, when the temperature exceeds 200 ° C., for example, the temperature of the ore return is about 400 ° C., irregular evaporation of the granulation water is caused, and the granulation property is not stabilized.

The returned ore is added on both the input side and the output side of the drum mixer 10.
In the following description, the mass of iron ore 14 under 250 mm is added at the entry side of drum mixer 10 at Wpo, and the mass of returned ore 16 (under fine powder return) 16 under 250 μm is added at the entry side of drum mixer 10 at Wpr. The mass of the returned ore (coarse-grain return) 17 over 1 mm is Wrrs, and the mass of the returned ore (coarse-grain return) 18 over 1 mm added at the outlet side of the drum mixer 10 is Wrre.
Further, from the middle to the latter half of the drum mixer 10, fine powder that has not been granulated to the position where the coarse-grained ore return 18 is newly added as core particles, or fine powder that has been granulated but has been generated by the collapse of pseudo-particles is removed. The non-granulated fine powder 22 on the exit side of the drum mixer 10 (after the granulation process) may be referred to as the intermediate non-granulated fine powder 22 and the final non-granulated fine powder 23 in some cases.

The returned ore added at the input side of the drum mixer 10 is set to 0.148 ≧ Wpr / Wpo ≧ 0.006 and Wrrs / Wpo ≧ 0.039.
Although the fine powder returned ore 16 becomes the fine powder 21 attached to the core particles 20, the fine ore 16 has a square shape as compared with the iron ore 14, and thus has an effect of preventing the attached fine powder 21 made of iron ore particles from falling off ( Reduction of intermediate non-granulated fine powder 22).
In order to maintain the above effect, it is considered that as the iron ore 14 under 250 mm increases, the fine ore return 16 necessary to prevent the iron ore 14 from falling off must be increased. Therefore, the lower limit value (0.006) of the fine powder returned ore 16 was determined based on the mass ratio (Wpr / Wpo) with the iron ore 14 under 250 mm.
On the other hand, if the fine ore return 16 is excessively added to the attached fine powder 21 made of iron ore particles, the effect of preventing the attached fine powder 21 made of iron ore particles from falling off is saturated. According to the findings of the present inventors, the effect is saturated when the value of Wpr / Wpo is 0.148.
In addition, when fine calcium carbonate powder was used instead of fine powder return 16, the same effect could not be obtained. This is considered to be due to the shape difference from the returned ore.

In addition, for the blended raw material having a small amount of core particles and a large amount of fine powder, the coarse-grained ore return 17 having a square shape is supplemented from the side of the drum mixer 10 to suppress an increase in the thickness of the attached fine powder per core particle 20. Also, the separation of the attached fine powder 21 composed of iron ore particles can be suppressed. Since the coarse-grained ore 17 becomes the core particle, the intermediate ungranulated fine powder 22 in the preceding stage of the drum mixer 10 is reduced.
In order to maintain the above effect, it is considered that as the iron ore 14 under 250 mm increases, the coarse-grained ore 17 necessary to prevent the iron ore 14 from falling off must also be increased. Therefore, the lower limit (0.039) of the coarse-grained ore return 17 was determined based on the mass ratio (Wrrs / Wpo) with the iron ore 14 under 250 mm.

As for the ore return added at the outlet side of the drum mixer 10, the fine ore return 16 is 10% by mass or less and Wrre / Wpo ≧ 0.062.
In the drum mixer 10, the pseudo particles increase the adhesion thickness, but the fine powder that has not adhered becomes the intermediate non-granulated fine powder 22. Therefore, the intermediate ungranulated fine powder 22 is captured on the uneven surface by newly adding the coarse-grain returned ore 18 having a square surface with no fine powder yet attached from the outlet side of the drum mixer 10. To reduce the final ungranulated fine powder 23.
It is considered that as the iron ore 14 under 250 mm increases, the amount of the intermediate ungranulated fine powder 22 increases and the required amount of the coarse-grain returned ore 18 increases. Therefore, the lower limit (0.062) of the coarse-grained ore return 18 was determined based on the mass ratio (Wrre / Wpo) to the iron ore 14 under 250 mm.
Since it is necessary to reduce the fines, the fines returned 16 added at the outlet of the drum mixer 10 are specified to be 10% by mass or less (0% by mass may be used).

  Regarding Wrrs / Wpo and Wrre / Wpo, there is no effect of inhibiting reduction of ungranulated fine powder, and the upper limit is not particularly defined. However, it is desirable to carry out the process in a range where the sum of Wrre and Wrrs does not exceed the amount of returned ore that exceeds 1 mm generated in the sintering process, and both upper limits are generally about 1.5 based on operating conditions.

  In addition, Wpr / Wpo, Wrrs / Wpo, and Wrre / Wpo are mass ratios. However, in order to obtain a ratio, mass supplied to the drum mixer 10 per unit time, for example, ton / hour may be used as a unit.

The position where the return ore is added at the outlet side of the drum mixer 10 is set to 0.5 L to 0.98 L, where L is the total length of the drum mixer 10.
In the case of more than 0.98 L, the period for attaching the intermediate ungranulated fine powder 22 to the added coarse-grained ore return 18 is short, and the effect of reducing the final ungranulated fine powder 23 is limited.
On the other hand, in the case of less than 0.5 L, the effect of reducing the final ungranulated fine powder 23 is limited. This is because the present invention remarkably reduces the final ungranulated fine powder 23 by adding the coarse-grained ore return 17, 18 at two places, the inlet side of the drum mixer 10 and the middle to the latter half of the drum mixer 10. However, if it is less than 0.5 L, the reduction of the intermediate non-granulated fine powder 22 is not sufficient, and the effect of adding one place on the inlet side rather than adding two places substantially is obtained. .

[Granulation method of compounding raw material according to second embodiment]
FIG. 2 shows a flow of a method for granulating compounded raw materials according to the second embodiment of the present invention.
The configuration of the blended raw materials, the amount and position of the returned ore in this embodiment are the same as those in the first embodiment.

  In the present embodiment, the iron ore 14 is divided into two or more groups (here, groups of the iron ores 14a and 15) according to their particle diameters, and the quick-lime and / or Alternatively, a binder composed of slaked lime is added in an amount of 0.5% by mass or more and 6% by mass or less in terms of quicklime in terms of the total amount of iron ore in the group, and charged into the high-speed stirrer 11 to produce P-type particles 24. . Then, the P-type particles 24 are charged into the input side of the drum mixer 10 together with the other compounding raw materials and the ore returns 16 and 17. The fine powder adheres to the P-type particles 24 in the drum mixer 10 to form P-type particles 24a.

In the experiments by the inventors, the ultra-less core particle fine powder raw material (iron ore of the group having the smallest average particle size after dividing the fine powder material of the loess core particle targeted by the present invention into two or more groups) was used. After adding 0.5% by mass or more of quicklime, the method of granulating the blended raw material according to the first embodiment further reduced the final ungranulated fine powder 23. Alternatively, the amount of the binder made of slaked lime is set to 0.5% by mass or more in outer caliper of the total amount of the ultraless core particle fine powder raw material in terms of quicklime. When the amount of quicklime added is less than 0.5% by mass, the P-type particles 24 become brittle, and the P-type particles 24 and 24a collapse during granulation by the drum mixer 10.
On the other hand, if the quick lime is excessively added to the ultra-less core particle fine powder raw material, the effect of increasing the strength of the P-type particles 24a is saturated. According to the findings of the present inventors, it was confirmed that the effect tended to be saturated when the amount of quicklime added was 6% by mass.

  As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the configurations described in the above-described embodiments, and is considered within the scope of the matters described in the claims. It also includes other embodiments and modified examples.

A verification test performed to verify the effect of the present invention will be described.
Table 1 shows a list of test results. In the table, "+" means "over" and "-" means "under".

  As the granulator, a batch type drum mixer tester having an inner diameter (diameter) of 1 m was used. The granulation speed was 25 rpm and the granulation time was 4 minutes. Under the condition of adding the ore return during the granulation, the granulation of the sintering raw material was temporarily stopped, and after adding the return ore, the granulation was restarted. The total granulation time before and after the reversion addition is 4 minutes.

The iron ore used had a fine powder content of less than 250 μm and a ratio of 20% by mass.
As auxiliary materials, 4% by mass of coke breeze, 10% by mass of limestone, and 1% by mass of peridotite were blended.
The moisture before firing after granulation by a drum mixer was kept constant at 8.0% by mass.

In Examples 1 to 4 and Comparative Examples 3 to 10, the granulated material treated by the drum mixer was regarded as 100% by mass (excluding water), and the ore returned was 3% by mass from the inlet side of the drum mixer and 2% by mass from the outlet side. Each was added.
Comparative Example 1 did not include the return ore. In Comparative Example 2, calcium carbonate was added in an amount of 3% by mass from the inlet side of the drum mixer without adding the ore return. In Comparative Example 11, calcium carbonate was added at 3% by mass without adding remineralization on the drum mixer input side, and remineralization was added at 2% by mass on the output side.

The returned ore to be added at predetermined positions on the inlet and outlet sides of the drum mixer is subjected to mechanical sieving using a low tap shaker in advance, and the particle size is adjusted to match Wpr / Wpo, Wrrs / Wpo, and Wrre / Wpo under each test condition. Adjustments were made.
After confirming the particle size of iron ore and adjusting the particle size of returned ore, after drying each raw material in advance (after absolute drying), the nominal size described in JIS Z8801-1 "Test sieve-Part 1: Metal mesh sieve" A sieve with openings (0.25 mm and 1.0 mm) is subjected to mechanical sieving using a low tap shaker for 300 seconds (classified), and the upper and lower sieves are measured and calculated by the following formula. The particle size was confirmed or adjusted so that the calculated particle size distribution ratio was obtained.
Xmm under: Using a sieve with a sieve mesh of Xmm, calculated by "(mass under sieve) / (mass over sieve + mass under sieve) x 100 (mass%)".
Xmm over: Calculated as "(mass on sieve) / (mass on sieve + mass under sieve) x 100 (mass%)" using a sieve with a sieve mesh of Xmm.

The position where the return ore is added at the drum mixer outlet side is described as a value when α × L based on the total length L of the drum mixer assuming application to a continuous drum mixer in an actual manufacturing process. Was calculated by the following equation.
α = Granulation time (min) / 4 (min) until the return ore addition
For example, if the granulation time until the addition of the return is 3 minutes, the granulation time after the addition is 1 minute, and the return addition position is 0.75 L.
In the continuous drum mixer, the sintering raw material supplied from one opening of the drum is conveyed to the other opening while granulating, and the granulated material is discharged from the other opening by inclining the drum. It is a device to do.

  In Example 4, the iron ore was divided into two groups according to its particle size, and a group having a small average particle size (the ratio of fine powder under 250 μm was 30% by mass) was divided into 0.5% Was charged into an Erich mixer (high-speed stirrer) and pre-granulated, and then charged together with iron ore of another group into a drum mixer and granulated.

The sintering test was carried out by charging a granulated material subjected to a granulation treatment with a drum mixer into a sintering pot and performing a pot test (sintering pot test). The firing time was defined as the time from the start of ignition of the upper portion of the raw material to the time when the temperature of the exhaust gas measured immediately below the pan reaches the highest point (generally referred to as BTP).
Then, the sintering productivity was calculated from the results of the pot test by the following formula, and the relative value to Comparative Example 1 was described as the productivity improvement rate.
Sintering productivity (ton / day / m ² ) = sinter production volume (ton / pot) ÷ pot cross-sectional area (m ² ) ÷ firing time (day / pot)
Here, the sinter production amount was calculated by dropping the fired product obtained in the pot test four times from a height of 2 m and measuring the amount of over 6 mm. The 6 mm under which is powdered in the dropping step results in a yield drop in the sintering step.

  In the evaluation, when the productivity improvement rate is 7.5% or more, ◎ (excellent), when less than 7.5%, 5% or more, （(good), when less than 5%, more than 0%, 可 (acceptable), 0 % Or less x (impossible).

The findings from the verification tests are listed below.
-In all the examples, the productivity improvement rate was 5% or more. In particular, in Example 4, the productivity improvement rate could be 8.5%.
When the iron ore was divided into three or more groups according to its particle size, the same tendency as in Example 4 was recognized, though the productivity improvement rate was different.

-The productivity improvement rate was able to be improved by setting the coarse particles over 1 mm in the iron ore containing a plurality of brands to 25% by mass or more (Comparative Example 3 with Example 1).

The productivity improvement rate could be improved by setting Wpr / Wpo to be 0.006 or more and 0.148 or less (Examples 1 and 2 for Comparative Example 4 and Examples for Comparative Example 10). 3). However, when a fine calcium carbonate powder having a Wpr / Wpo equivalent to 0.006 was added, the productivity improvement rate could not be improved (Comparative Examples 2, 11).
-The productivity improvement rate could be improved by setting Wrrs / Wpo to 0.039 or more (Example 1 with respect to Comparative Example 5).

The productivity improvement rate could be improved by setting the position of the returned ore added at the outlet side of the drum mixer to 0.5 L to 0.98 L, where L is the total length of the drum mixer (Comparative Examples 7 and 8). Examples 1 and 3).
-The productivity improvement rate could be improved by setting Wrre / Wpo to 0.062 or more (Example 1 with respect to Comparative Example 9).
-The productivity improvement rate was able to be improved by setting the ratio of the returned ore under 250 μm added at the drum mixer outlet side to 10% by mass or less (Comparative Example 6 with Example 1).

  In Examples 1 to 4, the granulated material treated by the drum mixer was set to 100% by mass (excluding water), and 5% by mass of the returned mineral was added. However, even if it was increased to about 30% by mass, The effect of the invention was recognized.

10: Drum mixer, 11: High-speed stirrer, 14, 14a, 15: Iron ore, 16: Fine return (return 250 μm under), 17, 18: Coarse return (return over 1 mm), 20 : Core particles, 21: attached fine powder, 22: intermediate non-granulated fine powder, 23: final non-granulated fine powder, 24, 24a: P-type particles

Claims (2)

A plurality of brands of iron ore are blended, and a blended raw material containing 250 mass% or less of 250 μm or less and 25 mass% or more and 65 mass% or less of 1 mm over and an auxiliary material is granulated using a drum mixer. A method of adding return minerals at a temperature of 200 ° C. or less,
The return ore is to be added on both the inlet side and the outlet side of the drum mixer,
The mass of the iron ore under 250 mm is Wpo, the mass of the returned ore under 250 μm added at the inlet of the drum mixer is Wpr, and the mass of the returned ore over 1 mm added at the inlet of the drum mixer is Wrrs. Assuming that the mass of the returned ore returned over 1 mm added at the outlet side of the drum mixer is Wrre, and the total length of the drum mixer is L,
The returned ore added at the entrance of the drum mixer is 0.148 ≧ Wpr / Wpo ≧ 0.006 and Wrrs / Wpo ≧ 0.039,
The blended raw material is characterized in that the returned ore added at the outlet side of the drum mixer is added in a range of 0.5 L to 0.98 L, with Wrre / Wpo ≧ 0.062, under 250 μm under 10% by mass. Granulation method.   2. The method according to claim 1, wherein the iron ore is divided into two or more groups according to its particle size, and a binder made of quicklime and / or slaked lime is added to the iron ore of the group having the smallest average particle size. Is added in an amount of 0.5% by mass or more and 6% by mass or less in the total amount of iron ore in the group in terms of quick lime, and charged into a high-speed stirrer and then charged into the inlet side of the drum mixer. Granulation method of compounding raw material to be.

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