JP2000248309A - Production of calcium-ferrite for refining molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a calcium-ferrite for molten iron refining agent with high productivity, in high yield and at a low cost. SOLUTION: Lime stone of which >=80 wt.% has <=2 mm grain diameter, and iron oxide raw material having <=1.5 mm average grain diameter, of fine powdery iron ore etc., are used and blended in CaO/Fe mol. ratio of 0.3-1.5, and mixed and the moisture is adjusted, and the mixture is granulated with a disk pelletizer 3 to make green pellet 8, and the surface is coated with powdery coke 4, and the green pellet of which >=70 wt.% has 5-10 mm grain diameter and of which <=20 wt.% has <5 mm grain diameter is calcined with an endless shifting grate type firing furnace 6 to make the calcium-ferrite 11. CaO in the calcined product is regulated to 25-50 wt.% and outer-coated powdery coke of which >=50 wt.% has <=1 mm grain diameter is used and the moisture in the green pellet before the firing furnace is regulated to 9-11 wt.%. Suitably, the following conditions are added, i.e. the lime stone is formed as slurry, a burnt lime is substituted for a part of the lime stone, the surface coated powdery coke amount is >=5 wt.% per dry wt. of the green pellet and the charging layer thickness in the firing furnace 6 is <=400 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a smelting material for molten iron,
More particularly, the present invention relates to a method for producing calcium ferrite at a high production rate, a high yield, and inexpensively, in a method for producing a dephosphorizing material for molten iron.

[0002]

2. Description of the Related Art Conventionally, in the process of refining steel in a converter, oxygen gas is blown onto hot metal in the furnace to reduce carbon dioxide in the hot metal.
And Si with oxygen to react with CO and SiO, respectively.
_{Assume 2} . Simultaneously, quick lime (CaO) is added into the furnace and combined with S and P in the hot metal to remove S and P. Thus, C, Si, S and P in the hot metal
Is reduced to a predetermined value.

[0003] However, the above-mentioned action of removing P and S of CaO is carried out when CaO added into the converter contacts and reacts with hot metal in the furnace. Therefore, this CaO
In order to improve the contact / reaction contribution ratio of
The particle size of O is adjusted to about 10 to 30 mm and added. In order to efficiently perform the de-P and de-S reactions, it is necessary to further form a molten slag in which this CaO and FeO generated by oxygen blowing of the hot metal in the furnace are melted. It is. This molten slag is formed by S
Reacts with iO ₂ to form a CaO—SiO ₂ —FeO-based melt. Usually, this CaO—SiO ₂ —FeO
Weight ratio of CaO to SiO _{2 in} slag
The amount of CaO added is adjusted so that (wt.%) / SiO ₂ (wt.%) Is 3.0 or more.

[0004] However, the above CaO-SiO ₂ -F
In the process of melting the eO-based slag, CaO
SiO ₂ and which has already been generated upon addition, and the reaction SiO ₂ is obtained by subsequently generating the CaO, and forms 2CaO · SiO ₂ or 3CaO · SiO ₂ is produced, which covers the particle surface of the CaO, surrounds Become. However, the above 2
The melting points of CaO.SiO ₂ and 3CaO.SiO ₂ are as high as 2130 ° C. and 2070 ° C., respectively. For this reason, at normal operating temperatures of the converter, the 2CaO.SiO
₂ and 3CaO.SiO ₂ are in a solid state and significantly inhibit the melting of CaO. Thus, CaO (wt.%) / Si, which is important for improving the efficiency of the action of removing P and S from the hot metal,
CaO—SiO ₂ — satisfying O ₂ (wt.%) ≧ 3.0
The generation of FeO-based slag is delayed. Therefore, conventionally, a method of appropriately adding fluorite (CaF ₂ ) to the converter slag to promote melting has been adopted.

As a result, the converter slag used for refining contains a small amount of CaF ₂ . However, recently,
The presence of CaF ₂ in the converter slag contributes to the limitation of the converter slag because the elution of F ions from the converter slag is environmentally undesirable.

[0006] Under the above circumstances, without using fluorite,
Refining material for removing P and S from molten iron in a furnace
Calcium ferrite is extremely effective
System refining materials are attracting attention, and numerous production methods are disclosed.
You. Here, calcium ferrite is 2CaO.Fe
_TwoO_Three, CaO.Fe_TwoO_ThreeAnd CaO.2Fe_TwoO _Three
Is a generic term for For example, JP-A-51-133200
According to the report, in calcium oxide powder such as limestone, converter ash and iron
Granular raw material consisting of ferric oxide such as ore powder
Baking while rolling at 1200 to 1250 ° C to produce
(Hereinafter referred to as Prior Art 1).
However, according to prior art methods,
Temperature control in a rotary furnace when manufacturing
And it is difficult to obtain a homogeneous product. Furthermore, calciu
Since the ferrite refining material has a low melting point,
A large amount of cohesive layer is formed, which often interrupts the operation
Must be removed, which is a major operational problem.
Become.

Japanese Unexamined Patent Publication No. Sho 61-177314 discloses a method using an endless moving grate type firing furnace (Dwyroid type sintering machine) as a firing furnace for calcium ferrite (hereinafter referred to as prior art 2). ) Is a method in which fluorite is added to the flux of the sintering raw material, and a large amount of low melting point calcium ferrite is generated in the firing process, so that the permeability of the sintering bed is significantly deteriorated, and It is believed that the rate drops significantly. Further, since fluorite is added, emission of fluorine and hydrogen fluoride in the exhaust gas poses a problem in the environment and in the corrosion of equipment.

[0008] As described above, at present, a technique for industrially producing calcium ferrite at low cost has not yet been established.

[0009]

As described above, according to the prior art, in converters and other refining furnaces, P and S of impurities in hot metal and molten iron for removing P and S from the molten metal are removed. As an effective refining material mainly for P and S removal, it exhibits an excellent P removal action, especially at a low temperature of about 1250-1400 ° C. As a refining material, calcium ferrite is known. However, in the prior art, when the above-mentioned calcium ferrite is to be manufactured on an industrial scale, the following problems have not been solved, so that there is a practical problem.

(1) CaO particles derived from a lime source material, which is one of the main raw materials for producing calcium ferrite, are mixed with Fe ₂ O ₃ derived from an iron oxide source material, which is another main raw material, to produce calcium ferrite. However, CaO components remain unreacted partially in the calcium ferrite product. Therefore, when used as a refining material, unreacted CaO components that did not contribute to the refining reaction remain in the slag after use. That is, there is a problem that the refining reaction efficiency is reduced. This unreacted residual CaO is also a problem in terms of slag utilization.

(2) Calcium ferrite has a melting point of 11
Since the temperature is as low as 00 to 1200 ° C., the melt generated when the sintering raw material is heated to 1100 ° C. or higher when the endless moving great firing furnace disclosed in Prior Art 2 is used is the raw material. The voids between the raw pellet particles are filled, the air permeability is significantly reduced, and the combustion of coke as a heat source is inhibited. In the worst case, the combustion cannot be continued and the fuel remains unburned. Thus, product yield and production rate are significantly reduced. Thus, a technique for increasing the production rate and stabilizing calcium ferrite has not been established.

Therefore, the present inventors have found that calcium ferrite is not melted inside the manufacturing apparatus and causes troubles, and the CaO particles are not added without adding a flux containing F such as fluorite. To develop a technique that calcium ferrite is generated throughout the entire area of the steel so that unreacted CaO particles do not remain, and a method that can stably produce calcium ferrite for molten iron refining at a high yield and a high production rate. did. Therefore, an object of the present invention is to produce calcium ferrite as a smelting material for molten iron, without lowering the productivity and yield, to maintain a stable product quality and its chemical composition, and to further reduce the cost. Another object of the present invention is to provide a method for industrially producing calcium ferrite as a refining material for molten iron, which can be produced at a low cost.

[0013]

In view of the above, the present inventors have conducted intensive studies.

(1) Desirable particle size distribution of raw pellets to be charged into a firing machine will be described.

In the process of sintering the raw pellets in the baking machine, the melt generated from the raw pellets blocks the particles of the raw pellets, resulting in poor ventilation. In order to ensure this ventilation, it is advantageous that the particle size of the raw pellets is large. However, as the particle size of the raw pellets increases, it takes a longer time for heat conduction of the combustion heat to the center of the raw pellet particles. Therefore, when the particle size of the raw pellets is moderately large, the ventilation between the particles is improved, and the combustion efficiency of the coke powder is improved, and the temperature distribution inside the raw material layer on the sintering bed and its temperature history are improved. Thus, it is possible to obtain conditions suitable for improving the product yield and the production rate.

On the other hand, in an industrial production process of calcium ferrite, raw pellets form a particle size distribution determined by their raw material conditions and granulation conditions. Then, the relatively small particles fill the gaps between the relatively large particles and deteriorate the ventilation.

Accordingly, the particle size range of the appropriately large raw pellet particles (hereinafter referred to as “appropriate particle size range”) d1 to d2
(However, d1 <d2) and the lower limit of the allowable ratio of the composition ratio of the raw pellet particles belonging to the appropriate particle size range (hereinafter, referred to as “appropriate particle size”) to the whole raw pellet particles, ie, Determination of the lower limit α that is acceptable from the viewpoint of improving the product yield and the production rate of calcium ferrite, and the composition of the raw pellet particles (hereinafter, referred to as “small diameter particles”) smaller than the minimum particle diameter d1 in the appropriate particle diameter range. By determining the upper limit value β that is acceptable from the viewpoint of improving the product yield and productivity of calcium ferrite,
The present inventors have focused on solving the main problem of the present invention.

The present inventors have conducted detailed tests to clarify the actual condition of the particle size and its distribution after granulation by a disk pelletizer, and have further repeated firing tests of calcium ferrite in an endless moving grate type firing furnace. It has been found that it is desirable to select 5 to 10 mm as the appropriate particle size range d1 to d2.

Therefore, the present inventors have further conducted research and studies, and found that the lower limit value α of the composition ratio of the proper-size particles such that both the yield and the production rate of calcium ferrite are at a high level.
And the upper limit value β of the composition ratio of the small-diameter particles were found as follows.

FIGS. 1 and 2 show test results on the relationship between the particle size distribution of the raw pellets and the yield of calcium ferrite, and the relationship with the production rate. The test method is based on an appropriate particle size range (d
(1 to d2 = 5 to 10 mm), the composition ratio (x) of those having a particle size within the appropriate particle size range (y), and the composition ratio (z) of the component having a particle size larger than the appropriate particle size range are various combinations. (However, x + y + z = 100
(Wt.%)).

From the above results, the particle size distribution of the raw pellet
The composition ratio (y) of the particles within the appropriate particle size range (d1 to d2 = 5 to 10 mm) occupies 70 wt.% Or more, and the composition ratio (x) of the particles having a particle size of less than 5 mm becomes 20 wt.% Or less. It was found that calcium ferrite can be produced at a high yield and a high production rate when prepared. Such a result was obtained for the following reason.

1. When fired under the above conditions, the air permeability inside the pellet material layer on the sintering bed does not deteriorate,
In addition, stable heat source combustion was performed.

2. Raw pellets with a particle size of less than 5mm are 20w
When the content is at least t.%, the filling properties of the raw pellets having a particle size of 5 to 10 mm due to the raw pellets having a particle size of less than 5 mm are increased, and the average void size between the particles is reduced. Therefore, when a melt of calcium ferrite is generated, the voids are easily filled with the melt, resulting in a marked decrease in air permeability.

3. On the other hand, particles larger than 5 to 10 mm in diameter have insufficient heat transfer to the center of the pellet particles even if the coke breeze can be efficiently burned.
The inside of the pellet is easily left unreacted. As a result, the yield of calcium ferrite decreases.

As described above, the particle size of the raw pellets to be charged into the firing furnace is desirably in the range of 5 to 10 mm, and by adjusting the composition ratio to be 70 wt. improves. Particles having a particle diameter of more than 10 mm form large voids between the particles when raw pellets are formed on a sintering bed in the form of a packed bed during charging of raw materials at the time of firing. Contribute to improvement.
From this viewpoint, the composition ratio of particles exceeding 10 mm is 10 w
It was also found that there was no particular problem if it was about t.% or less.

(2) Next, an appropriate amount of water contained in the raw pellets granulated by the disk pelletizer will be described.

The factors determining the appropriate amount of the water content include the effect of the operating conditions of the disk pelletizer on the economics, the effect of the water content on the particle size distribution of the raw pellets, and the process of transporting the raw pellets. It is important to comprehensively consider the effects on the particle strength during firing and on the yield and production rate of calcium ferrite.

First, it is necessary to economically produce raw pellets having the above-mentioned appropriate particle size distribution. When granulating raw pellets with a disc pelletizer, the particle size distribution after granulation changes depending on the moisture content in the raw material to be granulated and the average residence time in the disc pelletizer. But,
Industrially, the average residence time in a disc pelletizer is 2
It is not economical to make the time longer than about 5 minutes. Increasing the water content in the raw material during granulation increases the granulation speed and can reduce the average residence time. However, it requires calcination of excessive coke breeze (fuel) for evaporating water during the firing of calcium ferrite, which is uneconomical. Furthermore, the raw pellets granulated under such conditions have a large particle size in a short time, and even if a desired particle size distribution is obtained, the filling property in the raw pellet particles is reduced, and the strength is reduced. descend. Therefore, the particles collapse during transportation of the raw pellets or during sintering on the sintering bed, and the yield decreases.

On the other hand, when the moisture content in the raw material during granulation is insufficient, the raw pellets in the above-mentioned appropriate particle size range are used.
It cannot be obtained under the operating conditions of the above-mentioned economical disc pelletizer.

In order to solve the above-mentioned problems, the present inventors adjusted the moisture content of the raw material during granulation with a disk pelletizer, so that the moisture content of the raw pellets after the completion of granulation was adjusted. Was changed to various levels, and each relationship between the moisture content in the raw pellets after granulation, the particle size distribution and drop strength of the raw pellets, and the yield of calcium ferrite after firing was tested. In the test, the operating conditions of the disc pelletizer were set at a constant average residence time of the raw material of about 3.5 minutes, and the raw material conditions such as limestone, quicklime and fine iron ore, and other operating conditions were performed within an appropriate range. .
However, the water content in the raw pellets was considered excluding water of crystallization. This is because the crystallization water has no substantial effect on the granulation action.

3 to 5 show the test results. As is clear from these results, when the moisture content excluding water of crystallization in the raw pellets after granulation is in the range of 9 to 11 wt.%, The particle size distribution of the raw pellets is 5 to 10 mm. The composition ratio is mainly occupied, and those having a particle size of less than 5 mm are few, the drop strength of raw pellets is excellent and excellent, and the yield of calcium ferrite after firing is high and excellent.

(3) As described above, in order to produce calcium ferrite at a high yield and a high production rate in an endless moving grate-type sintering furnace, the temperature of the raw material packed layer on the sintering bed must be uniform to the inside. It is important to keep the required temperature history. Therefore, it is effective to adjust the combustion characteristics of the coke breeze provided on the raw pellet surface.

The present inventors have conducted a test investigation on the particle size of the coke breeze added to the raw pellets and the temperature change in the raw material packed bed during agglomeration in the firing furnace.

FIG. 6 shows the effect of the particle size of the coke flour on the raw pellets on the change over time in the temperature at a fixed point in the sintering material packed bed during agglomeration. Thereby, the particle size 1
When the fine coke powder mainly composed of fine particles having a particle diameter of less than 0.1 mm is used, the surface area of the coke fine powder increases, the combustion speed increases, the holding time at a high temperature is shortened, and the ultimate temperature is temporarily reduced to 145 mm.
0 ° C or higher. On the other hand, when fine particles having a particle size of less than 1 mm are reduced and the particle size of the coke breeze is increased, the burning speed of the coke breeze is reduced, the holding time at 1000 ° C. or more is prolonged, and the temperature reached is 1200 ° C.

Based on the above results, the present inventors have noticed that it is possible to control the agglomeration temperature pattern of calcium ferrite by adjusting the particle size of the coke breeze to coat the raw pellets. Then, the intensive examination was repeated. As a result, with respect to the particle size of the coke breeze, by reducing the composition ratio of less than 1 mm, that is, substantially 1 mm or less, to 50 wt.% Or less, the yield and production rate in the production process of calcium ferrite are reduced. Significant improvement was achieved.

However, the coke breeze used here was collected by a coke fire extinguishing system collected powder (CDQ
Powder). Therefore, the maximum particle size is at most about 5 mm. As the coke breeze in the above test, a non-standard product of about 5 mm under which is produced at a blast furnace coke manufacturing plant and under 1 mm is 50 watts.
Those classified to t.% or less may be used. In this way, by controlling the coke breeze having a particle diameter of less than 1 mm to 50 wt.% Or less, the combustion speed of the coke breeze is suppressed from becoming excessively high, and the portion where the coke breeze is burning inside the raw material packed bed ( Temperature (called the combustion zone). The necessary temperature in the present invention refers to a temperature range of 1000 to 1200 ° C. By baking in this temperature range, a large amount of a melt having a calcium ferrite composition is locally generated, and the melt which has become highly fluid at a high temperature closes the gap between the pellets, and aeration of the raw material packed layer is performed. Can be prevented from deteriorating.

By reducing the composition ratio of powder coke of 1 mm or less in the pellet exterior coke within the range of the above particle size distribution conditions, the temperature attained inside the raw material packed bed also decreases, but the composition of particles having a large particle size is reduced. As the ratio increases, the time for which the temperature is maintained at about 1100 ° C. or more is extended. As a result, it effectively acts on the evaporation of the moisture contained in the raw pellets, and also thermally decomposes the carbon dioxide in the limestone, and furthermore, the thermal energy required for the formation of the calcium ferrite phase reaches the center of the raw pellets. Until it reaches, it acts in a direction to maintain the raw material packed bed at a required temperature. Thus, the reaction rate of the coarse raw pellets was increased, so that the yield of calcium ferrite was improved and the production rate was also improved.

As described above, it is possible to produce calcium ferrite with excellent productivity and stable quality while reducing the deterioration of the gas permeability of the raw material packed layer on the sintered bed due to the generation of the calcium ferrite melt.

The present invention has been mainly made based on the above-mentioned many new findings, and the gist is as follows.

The method for producing calcium ferrite for refining molten iron according to the first aspect is characterized by comprising the following steps.

A CaO source material and an iron oxide source material are used as raw materials, and a CaO source material having a particle size of 2 mm or less is 80 wt. % Of limestone, and an iron oxide raw material comprising at least one of fine iron ore, dust, mill scale and iron sand as an iron oxide source material and having an average particle size of 1.5 mm or less.

The mixture of the limestone and the iron oxide raw material is blended so that the molar ratio of Ca and Fe is in the range of 0.3 to 1.5, and the blended raw material thus obtained is mixed with a mixer. Humidified and mixed, the obtained mixed raw material was humidified and granulated with a disk pelletizer to prepare raw pellets, and the surface of the raw pellets thus prepared was coated with coke breeze,
Then, raw pellets coated with coke breeze are produced.

The humidity control and granulation in the above disk pelletizer are performed so that the granulated raw pellets are covered with coke breeze on the surface, and the particle size distribution is as follows. That is, 70% by weight or more of particles having a particle diameter in the range of 5 to 10 mm and 2% of particles having a particle diameter of less than 5 mm
0 wt.% Or less.

The raw pellets thus prepared are charged into an endless moving grate type firing furnace and fired, so that the CaO content in the fired product thus obtained is in the range of 25 to 50 wt.%. Prepare.

The method for producing calcium ferrite for refining molten iron according to claim 2 is characterized in that it has the following steps. That is, similarly to the first aspect, first, as described above and in the first aspect, the raw pellets coated with the coke breeze are produced. However, in the above section, the coke breeze used to coat the surface of the raw pellets has a particle size distribution of 50 wt.

According to a third aspect of the present invention, there is provided the method for producing calcium ferrite for molten iron refining according to the first or second aspect of the present invention, wherein the granules are granulated by the disk pelletizer, and then the surface is covered with coke breeze. The water content of the raw pellets is 9 to
It is characterized in that the water content is adjusted in the process up to the completion of the previous granulation process so as to fall within the range of 11 wt.%.

The method for producing calcium ferrite for refining molten iron according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, slurry limestone is used as limestone. is there.

According to a fifth aspect of the present invention, there is provided a method for producing calcium ferrite for molten iron refining according to any one of the first to fourth aspects, wherein quicklime is added as a raw material in addition to limestone and / or slurry limestone. It is characterized in that it is used as a partial substitute for the limestone and / or slurry limestone.

A method for producing calcium ferrite for molten iron refining according to a sixth aspect of the present invention is the method according to any one of the first to fifth aspects, wherein the coke powder coated on the surface of the particles granulated by the disk pelletizer is used. Of 5 wt. Per dry weight of raw pellets. % Or more, and
It is characterized in that the thickness of the layer charged into the endless moving great-type firing furnace of the raw pellets is 400 mm or less.

[0050]

Next, an embodiment of the present invention will be described.

FIG. 7 is a schematic flow chart of a production process suitable for producing calcium ferrite for refining molten iron by the method of the present invention.

1 is a raw material hopper, 2 is a drum mixer as a mixer, 3 is a disc pelletizer, 4 is powder coke as a powdered fuel, 5 is a coating mixer, and 6 is an endless moving grate type sintering machine. Note that 12
Is a rod mill as a coke crusher. According to the flow of the manufacturing process shown in FIG.
１1 g is blended in an appropriate ratio, moisture 7 is added to adjust the humidity, and the raw material is uniformly mixed by the drum mixer 2. Next, the humidified and mixed powder material is charged into the disc pelletizer 3. Also in the disc pelletizer 3, moisture 7 ′ is appropriately added to adjust the humidity, and granulated to form raw pellets 8. Next, the coke flour 4 is added to the raw pellets 8,
The raw pellets 8 are charged into the coating mixer 5 and the surface of the raw pellets 8 is coated with an appropriate amount of coke breeze 4. When the coke breeze 4 is not available, the coke 13 is pulverized by a rod mill 12 or the like and used. A raw pellet 9 on which the surface coke 4 is coated is prepared. The raw coke powder raw pellets 9 prepared as described above are charged into an endless moving grate type firing furnace (sintering machine) 6 and fired under predetermined conditions. In this way, a refined material of molten iron containing calcium ferrite as a main component and particularly suitable for dephosphorization is produced.

The production conditions to be satisfied in the above-mentioned refined material production process and the reasons for limiting the conditions will be described along the production flow with reference to FIG.

(1) Raw materials are cut out from the raw material hopper 1 and mixed. The types of raw materials are limestone 1a and quick lime 1b as a CaO-containing substance, fine iron ore 1c as an iron oxide-containing substance, mill scale 1d and dust 1e,
This is 1 g and 4 of coke breeze as a carbon-containing substance used as a fuel for firing the raw pellets 9, and returned ore, which is a return product of calcium ferrite generated in a classifying step of the refined material product. However, in the above section, quicklime (main component:
CaO) is produced by calcining limestone (main component: CaCO ₃ ). This is used not only as a CaO-containing substance but also as a function of a granulation accelerator. Further, the dust in the above item is dust generated in a smelting furnace of an ironworks, etc., and is ferrous trioxide (Fe
It refers to those containing ₂ O ₃₎ as a main component. This is advantageous because it is inexpensive and contains Fe ₂ O ₃ which is a main component of calcium ferrite. As the iron oxide-containing substance of the item, similarly, other than the above, for example, iron sand, pellet feed and other things,
Any material that is inexpensive and contains diiron trioxide (Fe ₂ O ₃ ) as a main component may be used.

(A) In the raw material blending, limestone and one or more of fine iron ore, mill scale and dust are appropriately blended. Here, in mixing the raw materials, the particle size of each raw material needs to be equal to or less than a predetermined value. That is, limestone having a particle size of 2 mm or less accounts for 80 wt.% Or more, and fine iron ore, mill scale and dust have an average particle size of 1.5 mm or less. Limited to. The reasons for limiting the particle size of each raw material as described above are as follows.

The first reason is that if the particle size of the raw material is too coarse, the dispersion becomes uneven in the mixing and granulating steps, and as a result, a homogeneous mixed powder raw material and uniform raw pellets cannot be obtained. For this reason, agglomeration in the sintering process becomes insufficient, and the production rate and yield of the product decrease. According to tests by the present inventors, it has been clarified that by limiting the particle size of limestone and various iron oxides to the above-mentioned ranges, the production rate and yield of products can be improved.

The second reason is that the raw pellets 9 as the raw material charged into the firing furnace 6 are dried by the combustion of 1 g and 4 of coke breeze, and the limestone is decarbonated to CaO particles and iron oxide. Reacts with to form calcium ferrite. At this time, limestone having a particle size of 2 mm or less is 8
If the content is less than 0%, calcium ferrite does not reach the inside of the CaO particles and CaO remains unreacted at the center thereof. To solve this problem,
The present inventors have found that the above conditions must be satisfied.

On the other hand, as described above, when the particle size of the limestone 1a and the various iron oxide raw materials 1c to 1d is mainly a fine powder as described above, when controlling and mixing the humidity, Erich and Erich are used.
The use of a mixing granulator capable of performing so-called vigorous stirring mixing (sticking treatment) of the Loedige type allows the mixing to be homogenized. Even in this case, for homogeneous mixing, the limestone 1a having a particle size of 2 mm or less should be 80 watts.
%, and the raw materials of the various iron oxides 1c to 1d are desirably fine powder having an average particle size of 1.5 mm or less. When a normal drum mixer is used as the raw material mixer, the above conditions must be satisfied for the raw material particle size to be homogeneously mixed.

In the above-mentioned limestone having a particle size of 2 mm or less,
Limestone powder is included with it. Therefore, dust is generated and scattered during handling such as storage and transportation. Therefore, it is effective to handle the limestone with slurry. In the method of the present invention, the moisture is adjusted after mixing the raw materials, so that limestone may be supplied as a raw material in the form of a slurry containing water as appropriate.

Quick lime is produced by calcining limestone. Therefore, when quicklime is used as a partial substitute for limestone as a CaO-containing substance, the raw material cost generally increases. However, quick lime reacts with moisture in the process of adjusting and mixing the blended raw materials to produce calcium hydroxide, and the particle size is several tens of μm.
The following fine particles are obtained. And it has the effect of covering the surface of the granulated particles in the granulation process to promote granulation and improving the particle strength of the raw pellets after granulation. Since quicklime also has such a binder action, it is effective for improving the production rate and the yield of calcium ferrite. Quick lime is generally pulverized in the process of calcining and manufacturing limestone, but the limiting condition of the particle size distribution of quick lime is also in accordance with the above-described reason for the particle size distribution condition of limestone 1a,
It is necessary to use one in which quicklime particles of 2 mm or less account for 80 wt.% Or more.

As described above, when the particle size distribution of each raw material satisfies the above-mentioned conditions, homogeneous mixing and homogenous granulation of the blended raw material are performed, and the production rate and the yield as a refining material of calcium ferrite are improved. In addition, there is a condition that calcium ferrite can be formed not only on the surface of the CaO particles but also inside the CaO particles.

(B) The mixing ratio of the raw material 1 is such that the content of Ca and Fe in the mixed raw material (mixed raw material) is expressed by the ratio of the respective moles of the content expressed by nCa / nFe.
The following formula (1): nCa / nFe = 0.3 to 1.5 (1) where nCa is the number of moles of Ca contained in the blended raw material, and nFe is Fe contained in the blended raw material. It is necessary to adjust so as to satisfy the number of moles. The reason is as follows.

The chemical component of calcium ferrite to be produced by the method of the present invention is 2CaO.Fe
₂ O ₃ , CaO.Fe ₂ O ₃ and CaO.2Fe ₂ O ₃
Of at least one of the above. Therefore, among the component compositions of the calcium ferrite, 2CaO.Fe
_{When 2} O ₃ occupies 100%, the molar ratio of both Ca and Fe in the calcium ferrite (nCa / n)
Fe) takes the maximum value, and its value is 1: 1, that is, 1.0.
It is. On the other hand, CaO.2Fe ₂ O ₃ is one of them.
When occupying 00%, the molar ratio (nCa / nFe) of both Ca and Fe in the calcium ferrite takes the minimum value, and the value is 1: 4, that is, 0.25.

From the stoichiometry of the above reaction, nCa / nF
e needs to be in the range of 0.25 to 1.
In addition to the examination results, the fine iron ore, dust, mill scale, and iron sand used as the iron oxide source material further include the composition ratio of Fe ₂ O ₃ , Fe ₃ O _4, and FeO, and the content of various gangues. Despite the different percentages,
Considering that these iron oxide source materials can be used without any particular limitation, in order to produce calcium ferrite according to the method of the present invention, nCa / nFe should be 0.3 to 1.5. The raw material composition should be adjusted so as to fall within the range.

"On the other hand, according to the experimental results of the present inventors,
For example, if the content of CaO is less than 25 wt.
If it is full, do not raise the firing temperature to about 1400 ° C or higher.
And the formation reaction rate of calcium ferrite is slow,
If the firing temperature is higher than this, the reaction product sintering machine
Fusion begins to occur, causing operational problems. On the contrary,
CaO content exceeds 50wt.% In the ingredients of the compounding raw material
Then, various iron oxide source materials, fine iron ore,
When using small scale, dust, iron sand or other materials
In each case, the freedom of the mixing ratio is ensured for
It becomes difficult to mix the ingredients. The reason is the above oxidation
Each oxide form in the iron source material, that is, Fe_TwoO _Three, Fe_Three
O_FourThe composition ratio and ash content of Fe and FeO fluctuate?
It is. Absorbing the fluctuation of the constituent ratio, the iron oxide
In order to ensure the freedom of the mixing ratio of the raw materials,
It is necessary to limit the CaO content of the feed to 50 wt.
You. ""

(2) As described above, an appropriate powder compounding raw material obtained by mixing predetermined raw materials under predetermined conditions is humidified by a mixer such as a drum mixer 2 and uniformly mixed. Next, this is charged into a granulator such as a disc pelletizer 3 and granulated under appropriate humidity control conditions to prepare a raw pellet 8. Here, it is necessary to prepare raw pellets 8 having a predetermined strength and an appropriate particle size.

Here, regarding the particle size of the raw pellets 9 to be prepared, in the present invention, regarding the particle size distribution of the raw pellets, an appropriate particle size It is necessary that the composition ratio (y) of the particles having a particle size of 5 to 10 mm occupies 70 wt.% Or more and the composition ratio (x) of the particles having a particle size of less than 5 mm be 20 wt.% Or less. The reason is as described in the section of “Means for Solving the Problems”. By securing air permeability between the raw material particles in the firing step and supplying a stable heat source, the calcium ferrite 11 is formed. This is an essential condition for manufacturing at a high yield and a high production rate. In order for the particle size distribution of the raw pellets 9 to satisfy the above conditions, the water content excluding water of crystallization in the raw pellets granulated by the disk pelletizer 3 is 9 to 11 wt.%. Thus, it is desirable to adjust the water content in the granulation step. Meanwhile, raw pellets 8
By adjusting the water content in these components to 9 to 11 wt.%, The strength is improved and the product yield of calcium ferrite is further improved.

Further, in order to increase the particle strength of the raw pellets 8 and 9 and to grow the raw pellets having a particle diameter of 5 mm or more under economical operating conditions of the granulator, the disk pelletizer 3 is used as a granulator. Must be used. In the rotary drum type pelletizer, the strength of the raw pellets is low, and the upper limit of the particle diameter is usually about 3 mm. Therefore, this cannot be adopted in the present invention.

(3) Next, coke powder 4 is added to the raw pellets 8 and the surface of the raw pellets 8 is coated with the coke powder by the coating mixer 5. Here, the type of the coating mixer may be either a drum type or a disk type. The reason why the surface of the raw pellets 8 is exteriorly covered with coke breeze is to appropriately maintain the combustibility of coke during the next baking step. At this time, if the particles of the coke breeze are coarse, the adhesion to the raw pellets is reduced, which leads to deterioration of the product yield and uneven firing. In the next baking step, the coke combustibility is properly maintained during that period, so that the temperature history inside the raw material packed layer on the sintering bed becomes a uniform and desirable pattern. As described above, the particle size distribution of the powder coke for pellet exterior,
By setting the composition ratio of those of 1 mm or less to 50 wt.% Or less, the yield and production rate in the process of manufacturing calcium ferrite can be significantly improved. However,
For coke breeze with a particle size of 1 mm or more, the maximum particle size is 3
It is desirable to limit it to about 4 mm.

As the coke flour used here, it is advantageous in terms of cost to use fine-grain coke classified out of the standard by sieving or the like in a usual coke production process. In addition, the objects classified in this way do not include those larger than about 3 to 4 mm. In addition, the amount of coke breeze required to properly maintain the above-described flammability should be added in an appropriate amount according to the proportion of limestone in the blended raw material. 5w
t. % Or more is desirable. If the amount of coke breeze is too small, the decomposition and decarboxylation of limestone in the raw pellets will not proceed, and the formation reaction of calcium ferrite will also be insufficient, resulting in deterioration of the product yield. It is desirable that the weight of the coke powder is more than 50 wt.% Of the total weight of the coke powder added to the raw pellets 9 for firing. Coating the powdered coke with the exterior is effective in maintaining the combustibility of the coke.

(4) As a device for firing the raw pellets 9 coated with coke breeze, a great firing furnace is used.
The reason is as follows. The calcium ferrite of the refining material produced by the method of the present invention has a low melting point, so that in a conventionally used rotary furnace, a large amount of a fused layer is formed on the inner wall thereof, and actual production was impossible. When using the great-type firing furnace, even if a melt of calcium ferrite is generated, the raw powder coke on the raw pellet surface is burned and sucked downward through the grate, so that the permeability of the raw material packed layer on the sintering bed is improved. Does not deteriorate in operation. Therefore, the product is excellent in productivity, the product quality is stable, and the standard is good. Thus, in the present invention, it is important to use a firing furnace having a downward suction type great. Furthermore, if the endless moving grate type sintering furnace is used, the desired calcium ferrite can be continuously produced, so that the productivity is further improved.

However, it is desirable to set an upper limit on the thickness of the sintering bed packed layer even when using a great firing furnace. The layer thickness of the raw material charged into the firing furnace is desired to be thicker from the viewpoint of improving the yield, but the production rate and the yield are improved at 400 mm or less from the balance between the permeability in the layer and the melting reactivity in the firing process. Become more remarkable, and it is even more desirable.

(5) The calcium ferrite which is a calcined product produced by the method described above has a CaO content of 25 to 50 wt. %. The reason is as follows. When the CaO content in the fired product is lower than 25 wt.%, The effect as a P-free material is reduced. Therefore, it must be added in large quantities,
Costs are also high.

On the other hand, when the molar ratio of Ca and Fe in the mixed raw material of limestone and iron oxide raw material is about 1.5, the crystal form of the formed calcium ferrite is mainly 2CaO ·
Fe ₂ O ₃ , and the CaO content in the fired product at this time was about 50 wt. %Met. However, the CaO content in the calcined calcium ferrite product is 50 wt. %, The melting point of the calcined product rapidly increases, and when used as a refining material for molten iron, the effect is not immediately exhibited. In addition, the proportion of unreacted limestone increases,
Yield decreases. Therefore, in order to improve the production rate of calcium ferrite and sufficiently exhibit its effect as a refining material of molten iron, the CaO content in the product must be 25 to
50 wt. It must be constrained to fall within the range of%.

[0075]

Next, the present invention will be described in more detail with reference to examples.

According to the flow of the process of manufacturing calcium ferrite shown in FIG. 7, a manufacturing test of calcium ferrite (Examples 1 to 1) was carried out under conditions within the scope of the present invention.
8) In addition, according to the conventional manufacturing process of calcium ferrite shown in FIG. 11, a rotating drum-type pelletizer 10 was used as a granulator, and granulation conditions were performed under conditions outside the scope of the present invention. Production tests (conventional examples 1 to 4) and granulation using a disk pelletizer as shown in FIG. 7 and preparation of raw pellets by coating with coke breeze were performed, but the granulation conditions were outside the scope of the present invention. Production tests (Comparative Examples 1 to 4) of calcium ferrite performed under the same conditions were performed. The production test of calcium ferrite is described in [Test 1: Examples 1 to 12, Conventional Examples 1 to 1].
2, Comparative Examples 1-2] and [Test 2: Examples 13-18, Conventional Examples 3-4, Comparative Examples 3-4].

Tables 1 to 3 show the production conditions of calcium ferrite in [Test 1], and Tables 4 and 5 show the production conditions of calcium ferrite in [Test 2].
Table 6 shows the chemical composition of each raw material used in the test, and Table 7 shows the particle size distribution of each raw material.

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

[Table 4]

[0082]

[Table 5]

[0083]

[Table 6]

[0084]

[Table 7]

As can be seen from the above table, the test conditions were changed as follows. (1) Raw material used: Type of raw material: Limestone was used as a CaO-containing raw material, and quick lime was used as a partial substitute thereof. In addition, as a raw material (iron oxide raw material) containing diiron trioxide (Fe ₂ O ₃ ), a case where only fine iron ore is used, and a case where mill scale and / or dust is used as fine iron ore and a partial substitute thereof And were tested. The limestone was in the form of solid particles in a basic state, and was also tested in the case of a water slurry.

Raw material particle size: As for limestone, those having a particle size of 5 mm or less (referred to as “limestone-1”) or those having a particle size of 2 mm or less (referred to as “limestone-2”) shown in Table 7 are used. Was.

(2) Powdered fuel: Powdered coke was added to the above raw material to obtain a fuel for firing. There are two forms of coke breeze mixing: mixing the raw materials together and granulating them together (interior coke), and adding the inner coke powder without granulation and coating the particle surface with coke fines after granulation (exterior coke). Was tested by appropriately changing the amount of addition.

(3) Raw material blending: Under the respective test conditions in which the above items (1) and (2) were appropriately combined, the target component composition of the fired product was changed to monocalcium ferrite (C
aO.Fe ₂ O ₃ ) and dicalcium ferrite (2CaO.Fe ₂ O ₃ ). When the production of CaO.Fe ₂ O ₃ is aimed at (referred to as “raw material blending type“ A ”), the molar ratio of Ca / Fe in the raw material is blended so that 1/2 = 0.5. When the production of 2CaO.Fe ₂ O ₃ is aimed at (referred to as the raw material blending type “B”),
The test was carried out by blending such that the molar ratio of / Fe was 1/1 = 1.0.

(4) Humidity Control, Mixing, Granulation of Powdered Raw Materials, and Coating of Coke Powder: A rotary drum mixer was used for all mixers. There are two types of granulators, one using a rotary drum type granulator and the other using a disk pelletizer. The moisture content in the powder raw material in the granulator is the moisture content excluding water of crystallization in the state of the raw pellets after granulation (when the particle surface is coated with coke breeze, after coating), Almost 8 to 13 wt. Adjusted to vary between%. The raw pellets were granulated with a target particle size in the range of 5 to 10 mm, classified appropriately, and subjected to a firing test. Coke powder was added to the raw pellets as fuel in the baking machine. As the method of addition, a test was conducted for a case where the raw pellets were mixed and added during mixing (interior) and a case where the raw pellet surface after granulation was coated (exterior).

(5) Firing: All firing furnaces used endless moving grate type sintering machines, and the thickness of the bed packed with sintered pellets of green pellets was set to a constant value of 400.

Under the various test conditions described above, a production test of calcium ferrite was performed. As operation results during each test period, the yield and production rate of calcium ferrite products were investigated. The test results are as follows. In addition, all the test results are the results about the thing whose product particle size is 5 mm or more.

Results of Test 1: As can be seen from Table 3 and FIG. 8, in Conventional Examples 1 and 2, the granulating action was insufficient because a dry mixer was used as the granulator.
Since coke breeze was mixed with other raw materials and granulated, coke breeze was embedded inside the pellets, and as the sintering progressed, a large amount of calcium ferrite melt was generated, and the air permeability in the sintering bed was increased. Is significantly impaired and, at the same time, the combustibility of the coke breeze deteriorates, so that both the production rate and the yield are reduced. On the other hand, in Comparative Examples 1 and 2,
After adjusting the humidity and mixing of the raw material and coke breeze, granulating it with a disk pelletizer, and then coating the coke breeze, so that the flammability of the coke breeze is improved and the production rate and yield are improved compared to the conventional example. ing. However, the moisture content during granulation was low, and therefore the moisture in the raw pellets was also low, so that the ratio of particles having a particle size of less than 5 mm was high. For this reason, the packing of the raw materials on the sintering bed becomes dense, and the permeability is easily hindered by the calcium ferrite melt, and the improvement of the production rate is not sufficient.

In contrast, Examples 1 to 12 of the method of the present invention
As can be seen from Tables 1 and 2 and FIG. 9, the production rate and yield are excellent as follows.

In Examples 1, 2, 7 and 8, raw pellets granulated by a disk pelletizer were sieved to adjust the particle size distribution to a desirable range. As a result, the production rate has been improved. On the other hand, in Examples 3 to 6 and 9 to 12, the water content during granulation was adjusted.
After the granulation, the water content of the raw pellets excluding water of crystallization was adjusted to fall within the range of 9 to 11 wt.% Satisfying the conditions of the present invention. The raw pellets thus granulated were baked without classification, without any classification. In this case, mill scale and dust were also used in the raw material, but it was possible to produce calcium ferrite at a high yield and a high production rate.

Results of Test 2: As can be seen from Table 5 and FIG. 10, in Conventional Examples 4 and 5, the use of a dry mixer as a granulator resulted in insufficient granulating action, and The raw material was mixed with the raw materials and granulated, so that coke breeze was embedded inside the pellets, and a large amount of calcium ferrite melt was generated with the progress of sintering.
The air permeability in the sintering bed is significantly impaired, and at the same time, the combustibility of the coke breeze deteriorates, so that both the production rate and the yield are reduced.

On the other hand, in Comparative Examples 3 and 4, after the raw material and the coke breeze were conditioned and mixed, the mixture was granulated with a disk pelletizer, and then the coke breeze was packaged. The production rate and the yield are improved as compared with the example. However, the outer coke breeze has a small particle size and the particle size distribution is less than 1 mm 70 wt.
Was occupied. Therefore, the burning rate of coke breeze during sintering is high, the temperature reached is high, and the permeability is deteriorated by the melt of calcium ferrite in the raw material filling on the sintering bed, and the productivity and yield are not sufficiently improved. .

In contrast, Examples 13 to 1 of the method of the present invention
8, as can be seen from Table 4 and FIG. 10, both the production rate and the yield are excellent as follows.

In Examples 13 to 18, the surface of the raw pellets granulated by the disk pelletizer was coated with coke breeze in which fine particles having a particle size of less than 1 mm accounted for 50 wt.% Or less. Then, the water content during granulation was adjusted so that the water content excluding water of crystallization in the raw pellets after granulation had a constant value of 9 wt.%. The raw pellets thus granulated were baked without classification, without any classification.
In any of the examples, in view of the production conditions, the particle size distribution of the raw pellets is appropriate, and the strength is also desirable, and the particle size distribution and the amount of the outer powder coke are appropriate. Since the combustion state of the coke breeze during firing was appropriate and the temperature history inside the raw material packed bed was appropriate,
Ventilation has been improved. As a result, it was possible to produce calcium ferrite at a high yield and a high production rate.

Further, as a result of identifying the product-forming compound of the product of the present invention in Tests 1 and 2 by X-ray diffraction, in the example in which the type of the raw material mixture was “A”, CaO.Fe ₂ O ₃ was mostly contained. In the examples in which the type of raw material mixture is “B”, 2CaO · Fe ₂ O ₃ is mostly contained, and
The composition of aO.FeO.Fe ₂ O ₃ was also detected. Thus, it was confirmed that in each of the products of the present invention, almost predetermined uniform calcium ferrite was obtained. Table 8 shows the component compositions of the product of the present invention.
As can be seen, the CaO content in the product is 25%.
５０50 wt. % Is within the range.

[0100]

[Table 8]

Monocalcium ferrite (CaO.Fe)
Than ₂ O ₃₎ shall produce a formulation type "A" of the raw materials aimed for, the molar ratio of CaO / Fe ₂ O ₃ is 1.17 to 1.
Is within 34 the range of, while those generating a formulation type "B" of the material aimed die calcium ferrite _{(2CaO · Fe 2 O 3)} , the molar ratio of CaO / Fe ₂ O ₃ is 1.92 ２５2.25, which tends to be larger than the theoretical target value, and a part of Fe is FeO.

[0102]

As described above, according to the present invention,
A refined material of molten iron, particularly a refined material mainly composed of calcium ferrite which is effective for dephosphorization, can be produced under the following conditions.

1. Since the endless moving grate type sintering furnace is used, the production reaction of calcium ferrite is performed stably, and industrial mass production with a high production rate and a high yield is possible.

2. As raw fuel, inexpensive raw materials such as fine limestone, fine iron ore, mill scale, dust and iron sand, and coke breeze, as well as products generated at ironworks and substances to be treated can be used. ,Also,
Therefore, raw material costs are low.

3. Since existing equipment can be used as production equipment, equipment costs are low and space is saved.

A method for producing such calcium ferrite for refining molten iron can be provided, and an industrially advantageous effect is brought about.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the particle size of raw pellets and the production yield of calcium ferrite.

FIG. 2 is a graph showing the relationship between the particle size of raw pellets and the production rate of calcium ferrite production.

FIG. 3 is a graph showing the relationship between the moisture content of the raw pellets after granulation, excluding water of crystallization, and the particle size distribution of the granulated raw pellets.

FIG. 4 is a graph showing the relationship between the moisture content of the raw pellets after granulation, excluding water of crystallization, and the strength of the granulated raw pellets.

FIG. 5 is a graph showing the relationship between the moisture content of the raw pellets after granulation excluding water of crystallization and the product yield of calcium ferrite.

FIG. 6 is a graph illustrating the influence of the particle size of the coke powder on the temperature on the temperature history at a fixed point inside the raw material packed layer of the sintering bed.

FIG. 7 is a schematic flow chart for producing calcium ferrite for refining molten iron suitable for carrying out the present invention.

FIG. 8 is a graph showing operation results and quality levels in Test 1 according to a conventional example and a comparative example.

FIG. 9 is a graph showing operation results and quality levels according to an example in Test 1.

FIG. 10 is a graph showing operation results and quality levels of a conventional example, a comparative example, and an example in Test 2.

FIG. 11 is a schematic flow chart for producing a conventional calcium ferrite for molten iron refining.

[Explanation of symbols]

 Reference Signs List 1 raw material 1a limestone 1b quicklime 1c fine iron ore 1d mill scale 1e dust 1f returned ore 1g coke 2 drum mixer 3 disk pelletizer 4 coke breeze 5 coating mixer 6 endless moving grate furnace (sintering machine) 7, 7 'moisture 8 Raw pellet 9 Coke exterior raw pellet 10 Rotary drum pelletizer 11 Calcium ferrite 12 Rod mill 13 Coke (lump)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C21C 7/064 C21C 7/064 A // C22B 1/16 C22B 1/16 L (72) Inventor Rokukawa Shoichi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nippon Kokan Co., Ltd. (72) Inventor Minoru Kitagawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan, Nippon Kokan Co., Ltd. (72) Hiroshi Shimizu, inventor 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Hidetoshi Matsuno 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. F-term (reference) 4G002 AA08 AB01 4K001 AA42 BA05 BA14 BA15 CA02 CA18 CA20 CA22 CA33 CA35 CA41 GA10 4K002 AB04 AB06 AB07 4K013 EA02 EA03 EA32 EA36 EA39 4K014 AB03 AB04 AB21 AB28

Claims (6)

[Claims] 1. A method for producing calcium ferrite for refining molten iron using a CaO source material and an iron oxide source material as raw materials, wherein the CaO source material having a particle size of 2 mm or less is 80 watts.
t. % Or more, and an iron oxide raw material comprising at least one of fine iron ore, dust, mill scale and iron sand as the iron oxide source material and having an average particle size of 1.5 mm or less. The limestone and the iron oxide raw material are mixed so that the molar ratio of Ca and Fe in the mixed raw material is in the range of 0.3 to 1.5, and the obtained mixed raw material is humidified by a mixer. After mixing, the obtained mixed raw material is humidified and granulated with a disk pelletizer to prepare raw pellets, the surface of the prepared raw pellets is coated with coke breeze, and Raw pellets having a particle size distribution in which 5 to 10 mm is 70 wt.% Or more and less than 5 mm in diameter is less than 20 wt.% Are charged into an endless moving grate type firing furnace and fired. CaO in fired products
A method for producing calcium ferrite for molten iron refining, wherein the content is adjusted to be in the range of 25 to 50 wt.%. 2. A method for producing calcium ferrite for refining molten iron using a CaO source material and an iron oxide source material as raw materials, wherein the CaO source material having a particle size of 2 mm or less is 80 watts.
t. % Or more, and an iron oxide raw material comprising at least one of fine iron ore, dust, mill scale and iron sand as the iron oxide source material and having an average particle size of 1.5 mm or less. The limestone and the iron oxide raw material are mixed so that the molar ratio of Ca and Fe in the mixed raw material is in the range of 0.3 to 1.5, and the obtained mixed raw material is humidified by a mixer. The raw materials thus obtained are mixed and granulated by adjusting the humidity of the resulting mixed raw materials with a disk pelletizer, and the surface of the prepared raw pellets is coated with coke breeze having a particle size of 1 mm or less and 50 wt.% Or less. The raw pellets coated and thus coated with coke breeze were charged into an endless moving great-type firing furnace and fired, and the CaO content in the fired product thus obtained was 25%.
A method for producing calcium ferrite for molten iron refining, characterized in that the content is adjusted to be within the range of 50 wt. 3. The raw pellets granulated by the disk pelletizer have a water content excluding crystallization water of 9-1.
The method for producing calcium ferrite for molten iron refining according to claim 1 or 2, wherein the water content in the granulation step is adjusted so as to be 1 wt.%. 4. The method for producing calcium ferrite for molten iron refining according to claim 1, wherein a limestone in a slurry state is used as the limestone. 5. As the raw material, in addition to the limestone and / or limestone in the form of slurry, quicklime is added to the limestone and / or limestone.
The method for producing calcium ferrite for molten iron refining according to any one of claims 1 to 4, wherein the method is used as a partial substitute for slurry-like limestone. 6. The weight of coke breeze covering the surface of the particles granulated by the disk pelletizer is 5 wt. % Or more, and the thickness of the layer charged into the endless moving great-type firing furnace of the raw pellets is 400 mm or less, wherein the calcium ferrite for refining molten iron according to any one of claims 1 to 5. Production method.