JPH07331341A - Method for adjusting grain size of limestone for sintered ore - Google Patents

Abstract

PURPOSE:To adjust grain size of limestone for a sintered ore within a suitable range regardless of kind of limestone by heating limestone placed on Fe2O3 calcined tablet and adjusting grain size of the limestone according to a sectional area of unmelted part of the heated limestone. CONSTITUTION:Limestone is placed on the Fe2O3 tablet and both are heated at 1250-1300 deg.C. When area percentage of unmelted part in cross section of the limestone after heating with respect to cross section of the one before heating is below 30%, grain size of the limestone is adjusted to 1 to below 3mm. When the area percentage is 30 to 70%, grain size of the limestone is adjusted to 3 to below 5mm. When the area percentage is above 70%, grain size of the limestone is adjusted to 5 to below 7mm. Either one kind of the limestones having adjusted grain size is used as an anxiliary material for the sintered ore. For adjusting the grain size, cross section of the limestone is polished and then the grain size is adjusted corresponding to crystaline grain size in cross section structure. Thus, the sintered ore having high productivity and high quality is manufactured by adjusting grain size of the limestone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the particle size of limestone for sinter used in the production of sinter, which is a raw material for the blast furnace ironmaking process.

[0002]

The particle size range of limestone used for the production of sinter is less than 5 mm, and particles of 5 mm or more are crushed to 5 m.
It is used as less than m. However, since the particle size distribution of less than 5 mm is often not constant, the yield, production rate,
There were variations in strength and resistance to reduction dusting (RDI). Moreover, even if they had the same particle size distribution, the same variation occurred when limestone different in assimilation rate with iron ore was used or when limestone different in crystal grain size was used.
As an example of the former countermeasure, Japanese Patent Laid-Open No. 58-84931 discloses that particles of 0.25 mm or less in limestone used have a particle size of 19 or less.
There is described a technique for improving the yield, strength and RDI by adjusting the grain size so as to be not more than%. Also,
Japanese Unexamined Patent Publication No. 61-34119 discloses a limestone of 3-5 m.
A technique for improving the production rate and RDI by setting the particle size of m to 35 wt% or more in limestone is described. However, since the particle size composition of limestone is determined by the particle size, they cannot be used as a countermeasure when using limestone having a different assimilation rate with iron ore or limestone having a different crystal particle size.

[0003]

The limestone in the sintering raw material reacts with Fe ₂ O ₃ in the ore at around 1205 ° C., and CaO
To produce -fe ₂ O ₃ KeiTorueki. The amount of this melt produced greatly differs depending on the assimilation reactivity of limestone with Fe ₂ O ₃ . If the assimilation rate is high, the melt becomes excessive, which deteriorates the air permeability in the sintered layer and lowers the productivity. Further, when the assimilation rate is low, the amount of melt is small, so that the effect as a binder is reduced and the strength is reduced.

Further, limestone in the sintering raw material is decomposed into CaO and CO ₂ at around 830 ° C. At this time, if limestone having a different crystal particle size is used, a difference occurs in strength as CaO,
This has been a cause of producing a raw burned portion during the production of sinter ore and causing a decrease in strength, or by causing excessive melting to deteriorate air permeability, resulting in a decrease in productivity and a deterioration in RDI.

As described above, it has been desired to develop a proper treatment method for limestone in order to avoid the production of low-quality sinter. Therefore, the present invention provides a method for adjusting limestone to an appropriate particle size range regardless of the type of limestone used for producing sinter.

[0006]

According to the present invention, in a method for adjusting the particle size of limestone for sinter, 1250 of Fe ₂ O ₃ and limestone are placed by placing limestone on a Fe ₂ O ₃ fired tablet.
After heating to ˜1300 ° C., of the limestone, limestone having an area ratio of the unmelted portion of the cross section of the limestone after heating with respect to the cross-sectional area of the limestone before heating of less than 30% is adjusted to a particle size of less than 1 mm. , The area ratio is 30 ~ 70% limestone is 3 ~
A limestone for sinter that is adjusted to a particle size of less than 5 mm, and the limestone having an area ratio of more than 70% is adjusted to a particle size of 5 to less than 7 mm, and any one of them is used as a sintering auxiliary material. In the particle size adjusting method and the particle size adjusting method of limestone for sinter, the cross section of limestone is polished, and the average crystal particle diameter of the cross sectional structure is 1 to 3 mm for limestone.
Adjusted to a particle size of less than 10 and an average crystal particle size of 10 to 100.
Limestone of less than μm is adjusted to a particle size of 3 to less than 5 mm, limestone having an average crystal grain size of 100 to less than 2000 μm is adjusted to a particle size of 5 to less than 10 mm, and one of them is used as a sintering auxiliary material. It is a characteristic method for adjusting the particle size of limestone for sinter.

[0007]

[Function] As mentioned above, the production rate, yield, and
Deterioration of strength and RDI is caused by a phenomenon of over-melting or uneven burning in the sintered layer, and this is due to the assimilation reactivity of limestone with Fe ₂ O _{3 in} iron ore. Limestone, which has a large influence and has a high assimilation rate, needs to have a large use grain size, and conversely, limestone having a low assimilation rate needs to have a small use grain size. As described above, the assimilation reactivity between limestone and Fe ₂ O ₃ is a great index for determining the particle size of limestone for sintering.

A usual sintering raw material is T. Fe = 55%, C
4.5% coke was mixed with aO = 10%, SiO ₂ = 5%, and MgO = 2%, 6% water was added, and the mixture was granulated with a drum mixer for 5 minutes and filled in the sintered layer. To do.
The packing density at this time is 1.8 t / m ³ , and the raw material layer thickness is 500 mm. Ignite the surface of the raw material with an ignition burner,
Suction with a blower from below to produce sinter. In this process, limestone first reacts with Fe ₂ O ₃ in the ore at 1200 ° C. to form a CaO—Fe ₂ O ₃ system melt. Ca
O is consumed 80% reaction, remaining clay mineral or silica of CaO and in the ore to produce in response CaO-SiO _2.

Therefore, it is understood that the assimilation rate of limestone which is the source of CaO can be judged from the reaction amount with iron ore. But,
Originally, iron ore contains 5 gangue components such as clay minerals and quartz.
Since the content is ˜7%, and the gangue content and distribution vary depending on the ore, the assimilation property of limestone may change depending on the gangue form and gangue content in the ore. Therefore, in the present invention, as a substitute for iron ore, a first-grade or special-grade reagent Fe ₂ O is used.
_Decided to use ₃ .

The assimilation property of limestone is determined as the assimilation rate which is the area ratio of the unmelted portion of the cross section of limestone after heating to the cross-sectional area of limestone before heating. As shown in FIG. 1, the reagent Fe ₂ O
₃ Limestone b to be measured is cut out and placed on a baking tablet a in an arbitrary size. After that, it is heated to 1250 to 1300 ° C., and after cooling, the cross section of the limestone b is polished, and the sectional area A1 of the unmelted portion c of the limestone after heating shown in FIG. 1 and the area A0 of the limestone b before heating are assimilated by Equation 1. Find the rate. The higher the assimilation rate, the greater the assimilation rate.

[0011]

## EQU1 ## Assimilation rate (%) = 1- (A1 / A0) × 100

Reagent Fe ₂ O ₃ baking tablet is 8 to 15
It was molded to 10 to 20 mmH with a mmφ die. If the tablet diameter is less than 8 mm, the generated melt will spill out, and if it exceeds 15 mm, the density of the central portion of the ore will be low, and the amount of pores after firing will not be constant. Height is 10m
If it is less than m, the melt will penetrate to the bottom surface, and if it exceeds 20 mm, the stability when placing limestone will be significantly reduced. This F
e ₂ O ₃ baking tablets are baked at 1300 ° C. for 3 hours,
The porosity of 100 μm or less was set to be 0.05 cm ³ / g. This porosity is an average value for iron ore.

The limestone used was cut into a 3 to 5 mm square. This is because if it is less than 3 mm, there is a possibility that everything will melt, and if it exceeds 5 mm, it will exceed the practical range.

The firing temperature was set to 1300 ° C. by approximating the highest temperature reached to the actual sintering.

The assimilability was investigated in two samples of limestones A, B and C having different origins. The results are shown in FIG. 2. The assimilation rates were 12% and 23% for limestone A, 33% and 67% for limestone B, and 75% and 90% for limestone C. In this way, limestones having different assimilation rates are classified into 1 mm or less, 1 to 3 mm, 3 to 5 mm, 5 to 7 mm and 7 mm or more, and 1 kg for each particle size.
A sintering pot experiment was conducted to investigate the relationship between the assimilation rate of limestone and the particle size of limestone used. The experimental conditions are similar to the current sintering operation,
SiO ₂ in the blended raw material is 5.5%, basicity (CaO / S
iO ₂ ) is constant at 2.0, and the coke content is 4.5%
And The results are shown in Tables 1, 2 and 3. Depending on the assimilation rate of limestone, the particle size used in limestone A is less than 1 to 3 mm, limestone B is less than 3 to 5 mm, and limestone C is less than 5 to 7 mm in production rate, yield, TI strength and RDI.
The value of was the best. Therefore, as for the relationship with the optimum grain size, limestone with an assimilation rate of less than 30% is less than 1 to 3 mm, limestone with an assimilation rate of 30 to 70% is less than 3 to 5 mm, and assimilation rate is 70.
% Of limestone will be adjusted to a particle size of less than 5-7 mm.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

Further, limestone having different crystal particle diameters becomes CaO having different strength due to thermal decomposition. Usually, the strength of limestone increases as the crystal grain size increases, and limestone with low strength is easily pulverized. Therefore, it is necessary to increase the particle size of limestone as much as possible. If the strength does not decrease, the particle size of limestone can be reduced. Limestone A, limestone B, and limestone C are individually embedded in a resin or an adhesive, the cross section is mirror-polished, and the average diameter of crystal grains is measured from the cross-sectional structure. A generally used image analysis device is used. First, the cross-sectional structure of each sample is photographed. The image capturing device may be any device capable of clearly displaying crystal particles, but a metallographic microscope or a scanning electron microscope is particularly preferable. Shooting magnification is 3
It is set to 00 to 500 times. This is because if the thickness is less than that, the resolution for separating crystals of 5 μm or less in image processing is lowered, and if the magnification is larger than that, crystal particles of 100 μm or more do not enter the photographing screen. There were 5 imaging locations in the sample, and the imaging location was arbitrary. This is because there are large variations in the results when the number is less than 5, and the reliability is low.

Table 4 shows the particle size distribution and average crystal particle size of each limestone obtained by image analysis. Limestone A was 5 μm, limestone B was 65 μm, and limestone C was 130 μm. Since the range of the particle size distribution was 1 to 9 μm, 10 to less than 100 μm and 100 μm to 1000 μm, the crystal particle size was less than 10 μm, less than 10 to 100 μm and 1
It was classified to be less than 00 to less than 1000 μm. These limestones having different average crystal particle sizes are 1 mm or less, less than 1 to 3 mm, and 3
The particle size was adjusted to less than 5 mm, less than 5 to 10 mm, and 10 mm or more, and an experiment was performed for each particle size to examine the relationship between the average crystal particle size of limestone and the limestone particle size used.

[0021]

[Table 4]

The test results are shown in Tables 5, 6 and 7. This is the result of measuring the crystal grain size of the purchased limestone in advance, adjusting the grain size according to the crystal grain size, and conducting a sintering pot experiment. T. Fe = 55%, CaO = 10%, SiO ₂
= 5% and MgO = 2%, the iron ore and the auxiliary raw materials were adjusted, and 4.5% of coke was added to this, and
% Moisture was added and granulated for 5 minutes with a drum mixer.

[0023]

[Table 5]

[0024]

[Table 6]

[0025]

[Table 7]

The results show that there is an optimum particle size to be used which has a good production rate, product yield, TI strength and RDI depending on the crystal particle size of limestone. Limestone A having an average crystal particle size of less than 10 μm has a particle size of less than 1 to 3 mm, and limestone B having an average crystal particle size of less than 10 to 100 μm has 3
~ Less than 5 mm, average crystal particle size is 100 ~ 2000μ
Limestone C of less than m is adjusted to a particle size of less than 5 to 10 mm.

[0027]

Example 1 FIG. 3 shows an example in which limestone whose grain size was adjusted by the method of the present invention was used as an auxiliary sintering material in an actual sintering machine.
This is a result of performing a sintering operation after adjusting the particle size of limestone to less than 3 to 5 mm, since the assimilation rate of the purchased limestone was 45% as a result of preliminary investigation. In the conventional particle size adjustment of limestone, a particle size of less than 5 mm was used, and a particle size of 5 mm or more was crushed to less than 5 mm before use.

The production rate is 33 to 34 t / D / m ² , and the product yield is 8 although there are some differences depending on the sintering machine or the raw materials used.
An average value of 0%, TI strength of 70%, and RDI value of 32 to 35% is set. Before adopting the present invention, the production rate was 30.0 t / D / m ² , the product yield was 77.4%, the TI strength was 68.4%, and the RDI was 33.9%. The production rate was 4.6%, the product yield was 4.1%, the TI strength was improved by 3.8%, the RDI was decreased by 3.6%, and high-quality sinter was manufactured. Since the present invention was adopted, variations in product yield, TI strength, and RDI were reduced, and high-quality and high-quality sinter was produced.

[0029]

[Example 2] The cross-section of the purchased limestone was polished, and the average crystal particle size was measured to be 6 µm. Therefore, the particle size was adjusted to 1 to 3 mm by the method of the present invention, and the result of the actual machine sintering operation is shown in Fig. 4. Show. Conventionally, the particle size of limestone is 5 m
It used less than m.

Before adopting the present invention, the production rate is 31.4t.
/ D / m ² , product yield 79.2%, TI strength 70.
8% and RDI was 32.5%, but after adoption, the production rate was 4.6%, the product yield was 3.4%, and the TI strength was 3.3.
%, The RDI was reduced by 3.2%, and high quality sinter was produced.

[0031]

EFFECTS OF THE INVENTION By adjusting the limestone used for producing sinter according to the method of the present invention within an appropriate particle size range, it becomes possible to produce high-quality sinter with high production.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a sample used in an assimilation rate measurement experiment.

FIG. 2 is a diagram showing the assimilation rate of limestone at 1300 ° C.

FIG. 3 is a diagram showing a result of an actual machine sintering experiment when the present invention is carried out.

FIG. 4 is a diagram showing a result of an actual sintering test when the present invention is carried out.

[Explanation of symbols]

a Reagent Fe ₂ O ₃ tablet b Limestone c Unmelted part

Claims (2)

[Claims] 1. A method for adjusting the particle size of limestone for sinter, wherein limestone is placed on a Fe ₂ O ₃ fired tablet and F is added.
After heating e ₂ O ₃ and limestone to 1250 to 1300 ° C., among the limestones, 1 is the limestone in which the area ratio of the unmelted portion of the cross section of the limestone after heating to the cross-sectional area of the limestone before heating is less than 30%. Adjusted to a particle size of less than 3 mm, the limestone having an area ratio of 30 to 70% is adjusted to a particle size of less than 3 to 5 mm, and the limestone having an area ratio of more than 70% is adjusted to a particle size of less than 5 to 7 mm, A method for adjusting the particle size of limestone for sinter, comprising using one of them as a sintering auxiliary material. 2. A method for adjusting the particle size of limestone for sinter, wherein a cross section of limestone is polished, and limestone having an average crystal particle size of the cross-sectional structure of less than 10 μm is adjusted to a particle size of less than 1 to 3 mm. Limestone having an average particle size of 10 to less than 100 μm is adjusted to a particle size of 3 to less than 5 mm, and limestone having an average crystal particle size of 100 to less than 2000 μm is 5 to 10 mm.
A method for adjusting the particle size of limestone for sinter, comprising adjusting the particle size to less than 1 and using one of them as a sintering auxiliary material.