JP7067372B2 - Granulation method for compounded raw materials - Google Patents

Description

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

The sintering raw material is mainly powdered iron ore (powdered ore), and an auxiliary raw material whose composition is 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 process, it is generally performed to produce granulated products (pseudo-particles) in which fine powder is adhered around nuclear particles (coarse particles). Granulation treatment is an important operation for maintaining and improving sintering productivity, and various studies have been made so far.
Patent Document 1 defines the mass ratio of the powdery substance to the granular material because the strength of the granulated product decreases when the amount of the powdery substance (fine powder) is too large with respect to the granular material (nuclear particles). Have been described. Further, Patent Document 1 describes that the strength of the granulated product is improved by adding fine particles of calcium carbonate.

Patent Document 2 describes that the sinter productivity is improved by effectively utilizing the return ore. The invention described in Patent Document 2 is intended for a powder ore raw material containing the largest amount of pisolite ore (see Table 1 of Patent Document 2). Patent Document 2 describes Invention Example 1 in which a return ore containing 80% by mass or more of 1 mm or more is added to the granulated product after granulation (manual mixing with a shovel), and a sintered raw material to which a return ore of 1 mm or less is added. 2 is shown in Comparative Example 2 in which a granulated product is obtained by granulating the granulated product, and a return ore of 1 mm or more is added to the granulated product (manual mixing with a shovel).

Patent Document 3 also describes that the sinter productivity is improved by effectively utilizing the returned ore. The invention described in Patent Document 3 is intended for a powder ore raw material containing about 70% of Robe River ore and Hamasley ore (see Table 1 of Patent Document 3). Patent Document 3 shows an example (test numbers T1 to T3) of granulating an ungranulated raw material with a drum mixer, and another sintering of a return ore containing about 30% by mass of particles of 1 mm or less. An example of granulating with a drum mixer together with the raw material and an example of adding (manually mixing with a scoop) to the granulated product granulated by the drum mixer are shown. Further, in test numbers T5 and T6, an example is shown in which granulation is performed using a high-speed stirring mixer and a pan pelletizer, and then high-temperature return ore at 600 ° C. is mixed with a drum mixer.

Japanese Unexamined Patent Publication No. 2008-101263 JP-A-2015-193930 Japanese Unexamined Patent Publication No. 2007-284744

In recent years, ore species containing granules that become nuclear particles have been depleted, and ore species with a large amount of fine powder are the main. Even as a compounding raw material that secures a certain amount of nuclear particles by blending multiple ore types, the proportion of fine powder of 250 μm under (powder ore under a sieve with a sieve mesh of 250 μm) is 20% by mass or more and 1 mm over (1 mm over). The ratio of the core particles of the coarse-grained ore on the sieve having a sieve mesh of 1 mm) has to be 65% by mass or less, and the ratio of the fine powder to the core particles is constantly becoming very high. Therefore, there is an increasing need to granulate a sintered raw material having a small amount of nuclear particles and a large amount of fine particles (hereinafter, may be referred to as "fine powder raw material of less nuclear particles"). However, when pseudo-particles are produced using the raw material for fine particles of less nuclear particles, the fine particles adhering to the nuclear particles become thicker than in the past, and a large amount of ungranulated fine particles are generated.

A drum mixer or a high-speed stirrer (kneader) is generally used as a granulator for the granulation process. The drum mixer is mainly suitable for producing pseudo-particles and is also suitable for processing a large amount of raw materials, but the above-mentioned problem of uncranulated fine particles occurs. On the other hand, compared to the drum mixer, the high-speed stirrer can granulate not only pseudo-particles but also pellet particles mainly composed of fine particles, but like the drum mixer, ungranulated fine particles are generated.

The ungranulated fine powder after the granulation treatment includes the fine powder that was not granulated and the fine powder generated by the collapse of the granulated product after the granulation. , The firing speed at the time of sintering decreases, and the productivity of the sinter decreases.

When the fine powder raw material of the less nuclear particles is granulated using the invention described in Patent Document 1, the increase in the fine powder adhesion thickness (increase in the fine powder ratio in the powder ore) is produced by the addition of fine particles of calcium carbonate. There is a limit to the improvement of graininess, and the increase of ungrained fine powder becomes remarkable.
Further, according to the inventions described in Patent Documents 2 and 3, a certain improvement in sintering productivity can be expected, but the invention is not premised on the blending of ore species having a small amount of nuclear particles and a large amount of fine powder, and is a raw material for fine powder of less nuclear particles. On the other hand, improvement in sintering productivity cannot be expected.

The present invention has been made in view of the above circumstances, and is a method capable of reducing ungranulated fine particles and improving the productivity of sinter in the granulation treatment of a compounded raw material having a small amount of nuclear particles and a large amount of fine powder. The purpose is to provide.

In order to achieve the above object, the present invention is a blending of iron ore of a plurality of brands, in which 250 μm under is 20% by mass or more and 1 mm over is 25% by mass or more and 65% by mass or less, and an auxiliary material. It is a method of adding return ore at 200 ° C or lower when the raw material is granulated using a drum mixer.
The return ore shall be added on both the entry side and the exit side of the drum mixer.
The mass of the iron ore under 250 μm is Wpo, the mass of the return ore of 250 μm under added on the inlet side of the drum mixer is Wpr, and the mass of the return ore of 1 mm over added on the inlet side of the drum mixer is Wrrs. Assuming that the mass of the return ore of 1 mm over added on the outlet side of the drum mixer is Wrre and the total length of the drum mixer is L,
The return ore added on the inlet side of the drum mixer is 0.148 ≧ Wpr / Wpo ≧ 0.006 and Wrs / Wpo ≧ 0.039.
The return ore added on the outlet side of the drum mixer is characterized in that 250 μm under is 10% by mass or less, Wrre / Wpo ≧ 0.062, and is added in the range of 0.5 L to 0.98 L.

In addition, "under" refers to the bottom of the sieve when using a sieve with the dimensions described together, and "over" refers to the top of the sieve.

In the granulation process using a drum mixer, pseudo-particles in which fine particles are adhered around the nuclear particles are produced. The nuclear particles are mainly composed of coarse particles over 1 mm. Most of the fine particles adhering to the nuclear particles (adhered fine powders) are particles under 250 μm, and may not adhere to the fine particles and become ungranulated fine particles.

Granulation treatment of iron ore with a small amount of nuclear particles and a large amount of fine particles, which is the target of the present invention, in which the ratio of fine particles under 250 μm is 20% by mass or more and the ratio of coarse particles over 1 mm is 25% by mass or more and 65% by mass or less. If this is the case, the adhesion thickness of the fine particles will be thicker than that of the conventional pseudo-particles. According to the findings of the present inventors, when iron ore having a proportion of fine powder under 250 μm of 20% by mass or more is granulated, the thickness of the adhered fine powder is 300 μm or more. When the conventional sintered raw material with a large amount of nuclear particles is granulated, the fine powder adhesion thickness is approximately 150 μm. It can be said that it is very thick.

Therefore, in the rolling granulation by the drum mixer, in addition to the problem of ungranulated fine particles, the problem is that the granulated pseudo-particles disintegrate during the granulation process. Even when iron ore with a small amount of nuclear particles and a large amount of fine particles is granulated with a high-speed stirrer, the disintegration of ungranulated fine particles and pseudo-particles becomes a problem.
The above tendency is affected by the auxiliary raw materials to be added, but the point that the disintegration of uncranulated fine particles and pseudo-particles due to the decrease of nuclear particles and the increase of fine particles remains a problem.

Therefore, the present inventors have worked on the development of a method for reducing ungranulated fine particles in the granulation treatment of a compounded raw material having a small amount of nuclear particles and a large amount of fine powder.
The present inventors obtained the following findings by carrying out various experiments.
When observing the pseudo-particles after granulation with a drum mixer, the adhesion thickness of most of the pseudo-particles in which the fine particles adhering to the nuclear particles are mixed with the return ore of 250 μm under (fine powder return ore) increases. Was there. From this, it was found that the amount of ungranulated fine powder was reduced by adding fine powder return ore to the sinter raw material before granulation. Since the return ore is a powder generated when the sinter is crushed, it has a more angular shape than the iron ore particles, and after it adheres to the core particles, the surrounding fine powder is exfoliated (collapse of pseudo particles). ) Is considered to be effective.

However, ungranulated fine powder remains even with the addition of fine powder return ore.
The ungranulated fine powder is reduced by adding a return ore (coarse grain return ore) at 200 ° C. or lower and over 1 mm and rolling and granulating with a drum mixer. This effect is maximized when coarse-grained return ore is added in two steps, one before granulation with a drum mixer and one after granulation with a drum mixer for a certain period of time. This is because when granulating a sintered raw material with few nuclear particles, a certain amount of coarse-grained return ore, which becomes nuclear particles, is required even at the time of initial granulation, and further, as new nuclear particles from the middle to the latter half of granulation. It is considered that this is because the ungranulated fine particles remaining at the time of granulation adhere to the added coarse-grained return ore.

Further, in the method for granulating a compounding raw material according to the present invention, the iron ore is divided into two or more groups according to its particle size, and the iron ore of the group having the smallest average particle size is composed of quicklime and / or slaked lime. Even if the binder 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 of the group, and then charged in a high-speed stirrer, it is charged in the inlet side of the drum mixer. good.

The iron ore of the group having the smallest average particle size (hereinafter, also referred to as "ultra-less nuclear particle fine powder raw material") after the fine powder raw material of the less nuclear particles targeted by the present invention is divided into two or more groups. Furthermore, the particle size has a small number of nuclear particles and a large amount of fine powder. When quick lime and / or slaked lime is added to the ultra-less nuclear particle fine powder raw material and granulation is carried out with a high-speed stirrer, pseudo-particles (hereinafter, also referred to as “P-type particles”) composed of only fine particles are formed. , Acts as nuclei particles to which fine powder adheres in the drum mixer.

In the method for granulating a compounded raw material according to the present invention, fine powder return ore and coarse grain return ore are added to a compounded raw material having a small amount of nuclear particles and a large amount of fine powder to perform drum mixer granulation, and then coarse grain return ore is added again. Drum mixer granulation is performed by. As a result, the amount of ungranulated fine powder can be reduced to the extent that the sintering productivity can be significantly improved.

It is a flow chart of the granulation method of the compounding raw material which concerns on 1st Embodiment of this invention. It is a flow chart of the granulation method of the compounding raw material which concerns on 2nd Embodiment of this invention.

Subsequently, an embodiment embodying the present invention will be described with reference to the attached drawings, and the present invention will be understood.

[Granulation method of compounded raw materials according to the first embodiment]
FIG. 1 shows a flow of a granulation method for a compounded raw material according to the first embodiment of the present invention.
In the present embodiment, a return ore is added when the compounding raw material having a small amount of nuclear particles and a large amount of fine powder is granulated by using the drum mixer 10.
In general, return ore is fine powder generated when sinter after firing is crushed to a size suitable for being put into a blast furnace, and is sintered with a small particle size that is not suitable for being put into a blast furnace. It refers to ore powder and contains a large amount of fine powder of 1 mm under.

The compounding raw material includes a mixture of iron ore 14 of a plurality of brands having a 250 μm under of 20% by mass or more and a coarse grain of 1 mm over of 25% by mass or more and 65% by mass or less, and an auxiliary raw material. Auxiliary raw materials are charcoal and limestone.

As described above, when iron ore having a proportion of fine particles under 250 μm of 20% by mass or more is granulated, the thickness of the adhered fine particles 21 becomes 300 μm or more. The problem is that the granulated pseudo-particles disintegrate during the granulation process. The reason why the coarse grain over 1 mm is 65% by mass or less is due to the recent iron ore situation.
On the other hand, when the amount of coarse particles over 1 mm is less than 25% by mass, a remarkable effect of improving sintering productivity could not be obtained even by the present invention. It is considered that this is because the number of the nuclear particles 20 is too small and the thickness of the adhered fine particles 21 becomes extremely thick, and the pseudo particle structure cannot be maintained even by the present invention.
Although the upper limit of fine powder under 250 μm is not specified, since the coarse particles over 1 mm are 25% by mass or more and 65% by mass or less, if ordinary iron ore (sintered raw material) is used, the particle size distribution is distributed. From the actual situation, it will be about 60% by mass or less.

A low temperature return ore of 200 ° C. or lower is used for the return ore. This is because when the temperature exceeds 200 ° C., for example, the temperature of the return ore is about 400 ° C., irregular evaporation of the granulated water is caused and the granulation property is not stable.

The return ore is added on both the entry side and the exit side of the drum mixer 10.
In the following description, the mass of iron ore 14 under 250 μm is added to Wpo and the mass of the return ore (fine powder return) 16 under 250 μm is added on the inlet side of the drum mixer 10. Let the mass of the 1 mm over return (coarse grain return) 17 be Wrrs, and the mass of the 1 mm over return (coarse grain return) 18 added on the outlet side of the drum mixer 10 be 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 granulated return 18 is newly added as nuclear particles, or fine powder that has been granulated once but is generated by the decay of pseudo-particles is produced. The intermediate ungranulated fine powder 22 may be referred to, and the ungranulated fine powder on the exit side of the drum mixer 10 (after the granulation process) may be referred to as the final ungranulated fine powder 23.

The return ore added on the inlet side of the drum mixer 10 is 0.148 ≧ Wpr / Wpo ≧ 0.006 and Wrs / Wpo ≧ 0.039.
The fine powder return ore 16 becomes the fine powder 21 attached to the nuclear particles 20, but since it has a more angular shape than the iron ore 14, it has an effect of preventing the attached fine powder 21 made of iron ore particles from peeling off (). Reduction of intermediate ungranulated fine particles 22).
In order to maintain the above effect, it is considered that as the amount of iron ore 14 under 250 μm increases, so does the fine powder return ore 16 required to prevent its exfoliation. Therefore, the lower limit (0.006) of the fine powder return ore 16 was determined by the mass ratio (Wpr / Wpo) with the iron ore 14 under 250 μm .
On the other hand, if the fine powder return ore 16 is excessively added to the adhered fine powder 21 made of iron ore particles, the effect of preventing the attached fine powder 21 made of iron ore particles from peeling off is saturated. According to the findings of the present inventors, if the value of Wpr / Wpo is 0.148, the effect is saturated.
When fine calcium carbonate powder was used instead of the fine powder return ore 16, the same effect could not be obtained. This is considered to be due to the shape difference from the return ore.

Further, by supplementing the compounded raw material having a small amount of nuclear particles and a large amount of fine powder with the coarse-grained iron ore 17 having an angular shape from the side of the drum mixer 10, the increase in the thickness of the adhered fine powder per 20 nuclear particles is suppressed. It is also possible to suppress the exfoliation of the adhered fine powder 21 composed of iron ore particles. Since the coarse-grained return ore 17 becomes nuclear particles, the amount of intermediate unground fine powder 22 in the front stage of the drum mixer 10 is reduced.
In order to maintain the above effect, it is considered that as the amount of iron ore 14 under 250 μm increases, the amount of coarse-grained ore 17 required to prevent its exfoliation must also increase. Therefore, the lower limit (0.039) of the coarse grain return ore 17 was determined by the mass ratio (Wrrs / Wpo) with the iron ore 14 under 250 μm .

The return ore added on the outlet side of the drum mixer 10 is such that the fine powder return ore 16 is 10% by mass or less and Wrre / Wpo ≧ 0.062.
In the drum mixer 10, the pseudo-particles increase the adhered thickness, but the fine particles that cannot be completely adhered become the intermediate uncranulated fine particles 22. Therefore, by newly adding coarse-grained return ore 18 having an angular surface to which fine powder has not yet adhered from the exit side of the drum mixer 10, intermediate ungranulated fine powder 22 is captured on the uneven surface thereof. The final unground fine powder 23 is reduced.
It is considered that as the amount of iron ore 14 under 250 μm increases, the amount of intermediate ungranulated fine powder 22 increases and the required amount of coarse-grained return ore 18 increases. Therefore, the lower limit (0.062) of the coarse grain return ore 18 was determined by the mass ratio (Wrre / Wpo) with the iron ore 14 under 250 μm .
Since it is necessary to reduce the amount of fine powder, the amount of fine powder return 16 added on the outlet side of the drum mixer 10 is specified to be 10% by mass or less (0% by mass may be used).

With respect to Wrs / Wpo and Wrre / Wpo, there is no effect of inhibiting the reduction of ungranulated fine powder, and no upper limit is set. However, it is desirable that the total of Wrre and Wrrs does not exceed the amount of returned ore of 1 mm over generated in the sintering step, and the upper limit of both is about 1.5 based on the operating conditions.

Wpr / Wpo, Wrs / Wpo, and Wrre / Wpo are mass ratios, but in order to take the ratio, the mass supplied to the drum mixer 10 per unit time, for example, tons / hour may be used as a unit.

The position where the return ore is added on the outlet side of the drum mixer 10 is 0.5 L to 0.98 L, where L is the total length of the drum mixer 10.
When it exceeds 0.98 L, the period for adhering the intermediate ungranulated fine powder 22 to the added coarse granulated fine powder 18 is short, and the effect of reducing the final ungranulated fine powder 23 is limited.
On the other hand, even if it is less than 0.5 L, the effect of reducing the final ungranulated fine powder 23 is limited. This is because the present invention has the effect of significantly reducing the final ungranulated fine powder 23 by adding the coarse-grained ores 17 and 18 at two locations, the inlet side of the drum mixer 10 and the middle to the latter half of the drum mixer 10. However, if the amount is less than 0.5 L, the reduction of the intermediate ungranulated fine powder 22 is not sufficient, and the effect is that the addition is substantially made at one place on the entry side instead of the addition at two places. ..

[Granulation method of compounded raw materials according to the second embodiment]
FIG. 2 shows the flow of the granulation method of the compounded raw material according to the second embodiment of the present invention.
The composition of the compounded raw material in the present embodiment, and the addition amount and addition position of the return ore 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 iron ore 14a and 15) according to the particle size, and quicklime and / or quicklime and / are divided into the iron ore 15 of the group having the smallest average particle size. Alternatively, a binder made of quicklime is added in an amount of 0.5% by mass or more and 6% by mass or less in terms of the total amount of iron ore of the group in terms of quicklime, and charged into the high-speed stirrer 11 to produce P-type particles 24. .. Then, the P-type particles 24 are charged into the inlet side of the drum mixer 10 together with the other compounding raw materials and the returned ore 16 and 17. Fine particles adhere to the P-type particles 24 in the drum mixer 10 to become P-type particles 24a.

In the experiments of the inventors, the ultra-less nuclear particle fine powder raw material (iron ore of the group having the smallest average particle size after the fine powder raw material of the less nuclear particle targeted by the present invention was divided into two or more groups) was used. After adding 0.5% by mass or more of fresh lime, the final ungranulated fine particles 23 could be further reduced by carrying out the granulation method of the compounding raw material according to the first embodiment. Alternatively, the amount of the binder made of slaked lime is set to 0.5% by mass or more in terms of fresh lime in terms of the total amount of the raw material of the ultra-less nuclear particle fine powder. When the amount of quicklime added is less than 0.5% by mass, the P-type particles 24 become fragile, and the P-type particles 24 and 24a are disintegrated during granulation by the drum mixer 10.
On the other hand, if quicklime is excessively added to the raw material of ultra-less nuclear particle fine particles, the effect of increasing the strength of the P-type particles 24a is saturated. In the findings of the present inventors, it was confirmed that the effect tends to be saturated when the amount of quicklime added is 6% by mass.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configuration 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 variations thereof.

The verification test carried out for verifying 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 processing speed was 25 rpm and the granulation time was 4 minutes. Under the condition that the return ore was added during the granulation, the granulation of the sinter raw material was temporarily stopped, the return ore was added, and then the granulation was restarted. The total granulation time before and after the addition of the return ore is 4 minutes.

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

In Examples 1 to 4 and Comparative Examples 3 to 10, the granulated product treated with the drum mixer is 100% by mass (excluding water), and the return ore is 3% by mass from the entrance side of the drum mixer and 2% by mass from the exit side. Each was added.
In Comparative Example 1, no return ore was added. In Comparative Example 2, calcium carbonate was added in an amount of 3% by mass from the side of the drum mixer without adding the return ore. In Comparative Example 11, 3% by mass of calcium carbonate was added without adding return ore on the inlet side of the drum mixer, and 2% by mass of return ore was added on the exit side.

The return ore added at the predetermined positions on the input side and the exit side of the drum mixer is mechanically screened with a low tap shaker in advance, and the particle size is adjusted to match Wpr / Wpo, Wrs / Wpo, and Wrre / Wpo under each test condition. I made some adjustments.
After the raw materials are dried in advance (after absolute drying), the particle size of the iron ore and the particle size of the returned ore are adjusted as described in JIS Z8801-1 "Test Sieve-Part 1: Metal Net Sieve". For sieves with mesh openings (0.25 mm and 1.0 mm), perform mechanical sieving (classification) with a low tap shaker for 300 seconds, measure the top and bottom of the sieve, and calculate using the formula shown below. The particle size was confirmed or the particle size was adjusted so that the calculated particle size distribution ratio was obtained.
Xmm under: Calculated by "(mass under the sieve) / (mass on the sieve + mass under the sieve) x 100 (mass%)" using a sieve with a sieve mesh of X mm.
Xmm over: Calculated by "(mass on the sieve) / (mass on the sieve + mass under the sieve) x 100 (mass%)" using a sieve with a sieve mesh of X mm.

The position where the return ore is added on the exit side of the drum mixer is the value when α × L is set based on the total length L of the drum mixer, assuming application to a continuous drum mixer in the actual manufacturing process. However, it was calculated by the following formula.
α = Granulation time (minutes) / 4 (minutes) until addition of return ore
For example, when the granulation time until the return ore addition is 3 minutes, the granulation time after the addition is 1 minute, so that the return ore addition position is 0.75 L.
In the continuous drum mixer, by tilting the drum, the sintered raw material supplied from one opening of the drum is granulated and conveyed to the other opening, and the granulated material is discharged from the other opening. It is a device to do.

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

The sintering test was carried out by charging a granulated product that had been granulated with a drum mixer into a sintering pot and performing a pot test (sintering pot test). The firing time was the time from the start of ignition of the upper part of the raw material to the time when the exhaust gas temperature measured directly under the pot reached the highest point (generally called BTP).
Then, the sintering productivity was calculated from the results of the pot test by the formula shown below, and the relative value with respect to Comparative Example 1 was described as the productivity improvement rate.
Sinter productivity (ton / day / m ² ) = Sintered ore production amount (ton / pot) ÷ pot cross-sectional area (m ² ) ÷ firing time (day / pot)
Here, the sinter production amount was calculated by dropping the calcined product obtained in the pot test four times from a height of 2 m and measuring the amount over 6 mm. The 6 mm under powder powdered in the dropping process causes a yield drop in the sintering process.

In the evaluation, when the productivity improvement rate is 7.5% or more ◎ (excellent), less than 7.5% 5% or more ○ (good), less than 5% more than 0% △ (possible), 0 In the case of% or less, it was set as × (impossible).

The findings from the verification test 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 set to 8.5%.
Even when the iron ore was divided into 3 or more groups according to its particle size, the same tendency as in Example 4 was observed, although the value of the productivity improvement rate was different.

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

-By setting Wpr / Wpo to 0.006 or more and 0.148 or less, the productivity improvement rate could be improved (Examples 1 and 2 with respect to Comparative Example 4 and Examples with respect to Comparative Example 10). 3). However, when the fine calcium carbonate powder having Wpr / Wpo equivalent to 0.006 was added, the productivity improvement rate could not be improved (Comparative Examples 2 and 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 addition position of the return ore to be added on the exit side of the drum mixer to 0.5 L to 0.98 L with the total length of the drum mixer as L (in Comparative Examples 7 and 8). On the other hand, 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 could be improved by setting the ratio of the return ore of 250 μm under added on the outlet side of the drum mixer to 10% by mass or less (Example 1 with respect to Comparative Example 6).

In Examples 1 to 4, the granulated product treated with the drum mixer was taken as 100% by mass (excluding water), and 5% by mass of the return ore was added. The effect of the invention was recognized.

10: Drum mixer, 11: High-speed stirrer, 14, 14a, 15: Iron ore, 16: Fine particle return (250 μm under return), 17, 18: Coarse grain return (1 mm over return), 20 : Nuclear particles, 21: Adhering fine powder, 22: Intermediate ungranulated fine powder, 23: Final ungranulated fine powder, 24, 24a: P-type particles

Claims (2)

A drum mixer is used to granulate a compounded raw material containing 20% by mass or more of 250 μm under, 25% by mass or more and 65% by mass or less of 1 mm over, and an auxiliary material by blending multiple brands of iron ore. It is a method of adding return ore at 200 ° C or lower.
The return ore shall be added on both the entry side and the exit side of the drum mixer.
The mass of the iron ore under 250 μm is Wpo, the mass of the return ore of 250 μm under added on the inlet side of the drum mixer is Wpr, and the mass of the return ore of 1 mm over added on the inlet side of the drum mixer is Wrrs. Assuming that the mass of the return ore of 1 mm over added on the outlet side of the drum mixer is Wrre and the total length of the drum mixer is L,
The return ore added on the inlet side of the drum mixer is 0.148 ≧ Wpr / Wpo ≧ 0.006 and Wrs / Wpo ≧ 0.039.
The return ore added on the outlet side of the drum mixer is a compounding raw material characterized in that 250 μm under is 10% by mass or less, Wrre / Wpo ≧ 0.062, and is added in the range of 0.5 L to 0.98 L. Granulation method. In the method for granulating a compounded raw material according to claim 1, the iron ore is divided into two or more groups according to its particle size, and the iron ore of the group having the smallest average particle size is combined with a binder composed of fresh lime and / or slaked lime. Is added in an amount of 0.5% by mass or more and 6% by mass or less in terms of the total amount of iron ore of the group in terms of fresh lime, and is charged into the high-speed stirrer and then charged into the inlet side of the drum mixer. Granulation method of compounded raw materials.

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