JPS63219534A - Manufacture of self-fluxing pellet - Google Patents

Abstract

PURPOSE:To attain the prevention of reduction delay, the inhibition of deteriora tion in collapsing strength, and the prevention of the occurrence of structural change on burning in the titled pellet, by regulating the weight ratio of CaO/ SiO2, etc., in a raw material in which CaO, etc., of a specific grain-size region are blended with iron-ore fines to the prescribed values, and by subjecting the above raw material to pelletizing and then to heating and burning. CONSTITUTION:Dolomite as an auxiliary material which contains CaO and MgO and in which grains of 44-1,000mum grain size comprise >=80wt.% is blended with iron-ore fines so as to be formed into a raw material for pellets. After silica and limestone are blended with the above raw material so that weight ratio of CaO to SiO2 and weight ratio of MgO to SiO2 are regulated to >=1.2 and >=0.5, respectively, the resulting raw material is pelletized to be formed into green pellets. Subsequently, the green pellets are heated and burnt at the prescribed temp. so as to be formed into self-fluxing pellets. Moreover, it is desirable that the green pellets are heated and burnt at about 1,220-1,320 deg.C to regulate the volume of the pores with >=about 10mum diameter to >=about 0.01cm<3>/g.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing self-fusing pellets having excellent reducibility as an iron raw material for blast furnaces.

(Prior art) In the manufacturing process of self-fusing pellets, conventional techniques have been used to ensure that the pellet raw materials are uniformly dispersed and that the iron ore and gangue components quickly react and sinter in the sintering process, as well as to improve granulation efficiency. In order to increase the strength, fine powder with a particle size of 44 l or less is
The pellet raw material is finely pulverized until it reaches ~30% by weight, and this is granulated to form raw pellets.

In the firing process in which such raw pellets are heated and fired to produce self-fusing pellets, the pellets create molten slag and exhibit high strength, but on the other hand, the porosity decreases,
In a reducing atmosphere at a high temperature of 1100° C. or higher, the outer shell metallic iron of the pellet becomes densified and the liquid phase of slag is easily generated inside the pellet. As a result, the pores become clogged, causing reduction stagnation in the pellets and reducing reducibility.

Therefore, in the blast furnace, gas diffusion into the self-fusing pellets with reduced reducibility is hindered, and the direct reduction of coke and FeO seeping out onto the pellet surface increases. Therefore, unfavorable situations occur in terms of blast furnace operation, such as an increase in coke consumption.

Therefore, in order to prevent the above-mentioned reduction stagnation and obtain excellent reducibility, various methods for producing self-soluble pellets have been proposed.

That is, as a first prior art example, there is one shown in Japanese Patent Publication No. 11300/1983 filed by the present applicant. In this configuration, Mg is added to the pellet raw material to improve the reducibility of the pellets.
It is blended with O-containing auxiliary raw materials, such as tatsuki rock, which is finely pulverized to a particle size of 44 or less, which increases the melting point of the slag produced in the firing process of raw pellets using this as a raw material, thereby increasing self-soluble properties. This prevents the pores of the pellet from being blocked.

Further, as a second conventional example, there is one shown in Japanese Patent Publication No. 56-11291. According to this configuration, a combustible substance having a particle size of 0.1+ug to 3μ intestine coarse powder, such as coal or coke please, is mixed with the pellet raw material, and a heat source is used to burn the combustible substance in the process of burning the raw pellets. This creates large-diameter pores inside the pellet that are not blocked by molten slag.

(Problems to be Solved by the Invention) However, in the first conventional example, the millimeter rock is finely pulverized to a particle size of 44 mm or less, which makes the pulverization process complicated and the pulverization cost high. There is an inconvenience that this happens.

In the second conventional example, since large-diameter pores are formed, the crushing strength of the self-fusing pellets is greatly reduced, and the structure of the pellets changes due to combustion of the flammable substance.

(Objective of the Invention) This invention was made in view of the above-mentioned circumstances, and is aimed at preventing reduction stagnation of self-soluble pellets and obtaining excellent reducibility by using an auxiliary raw material containing MgO. The purpose of the present invention is to simplify the pulverization process to reduce the pulverization cost, to suppress a decrease in the crushing strength of self-soluble pellets, and to prevent the structure of the pellets from changing.

(Structure of the Invention) A feature of the present invention for achieving the above object is that an auxiliary material containing CaO and MgO having 80% by weight or more of particles in the particle size range of 44p to 1000μ is added to fine iron ore powder. Then, this blended raw material is mixed with Ca.
O/S i02 weight ratio is 1.2 or more, and MgO/5
Adjust the i02 weight ratio to be 0.5 or more, and
The method involves granulating the adjusted raw material to form green pellets, and heating and baking the green pellets at a predetermined temperature.

(Example) The present invention will be described in detail below.

First, dolomite, which is an auxiliary raw material containing CaO and MgO, and which has particles in the particle size range of 44 to 1000 l in an amount of 80% by weight or more, is mixed with iron ore fine powder to obtain a pellet raw material. In this case, the dolomite is a coarse powder whose particle size is larger than the fine powder whose particle size is 44 or less as shown in the first conventional example, so the process of crushing this dolomite is simplified and the crushing cost is reduced. can.

Next, a particle size of 4 was added to the pellet raw material blended as above.
By blending silica stone or limestone containing 70% by weight or more of particles of 4p or less, the Cab/5i02 weight ratio is 1.2 or more and Mg
The O/5i (h weight ratio is adjusted to be 0.5 or more. Then, this adjusted pellet raw material is granulated to form green pellets.

Next, the raw pellets are heated and calcined in a temperature range of 1220° C. to 1320° C., thereby obtaining self-soluble pellets. In this case, the coarse dolomite powder is turned into slag during the firing process. As a result, large-diameter pores are formed inside the pellet, and a high-melting-point slag structure is formed around the pores. As a result, the pores are prevented from being blocked due to melting of the slag during the firing process. Therefore, self-soluble pellets having excellent reducibility without reduction stagnation at high temperatures can be obtained.

Furthermore, since the large-diameter pores are surrounded by a high-melting-point slab, the crushing strength of the pellets is suppressed from decreasing.

Furthermore, since these pores are not formed as in the second conventional example, changes in the structure of the pellet are prevented.

In the above example, dolomite was used as an auxiliary raw material containing MgO, but it may also be a mineral that contains CaO and MgO and reacts with 5i02 to form basic slag. Preferably, minerals with

(Specific Examples) The present inventors conducted the following experiment in order to confirm the effects of the method of the present invention.

Table 1 below shows the chemical composition of the pellet raw material and its auxiliary raw materials used in the experiment.

Table 1 Chemical composition of pellet raw materials (%) After pulverizing the above pellet raw materials and their auxiliary raw materials to a predetermined particle size, the desired CaO/
They are mixed and adjusted so that the SiO2 weight ratio and MgO/5i02 weight ratio are achieved. At this time, the particle size of dolomite was changed to 44J.
L or less (equivalent to conventional dolomite), 44g ~ 10
0 ru, 1001L ~ 500 ru, 500 end ~ 1000
There are five levels of dolomite, from 1000 #L to 1500 pieces, and each level of dolomite contains 80% by weight or more of each particle size range.

Next, the raw pellets obtained by granulating the pellet raw material prepared as described above were heated and calcined at a constant oxygen partial pressure of 1250°C and 1275°C. Table 2 below shows the chemical composition of the fired pellets heated and fired at 1250°C.

(Space below) In addition, the relationships between the dolomite particle size, porosity, and high-temperature reduction rate of the above-mentioned fired pellets are shown in Figures 1 and 2, respectively.The above-mentioned high-temperature reduction rate refers to C (h = 80/90 in a reducing atmosphere of 40
Preliminary reduction to (Fed) at 0°C,
Using this as a sample, the reduction temperature was 1250℃, and the reducing gas GO/
This is the reduction rate when a 2-hour reduction test was conducted at N2 = 30770.

As is clear from FIGS. 1 and 2, compared to conventional pellets, the pellets of the present invention have an increased porosity at any firing temperature of 1250.127σ°C, and the reduction rate changes accordingly. I understand.

In other words, it is assumed that the porosity increases due to the slag formation of dolomite, and the porosity increases due to the dolomite particle size.
It can be seen that there is an optimal particle size range that provides a good reduction rate. The particle size range is 4 when the firing temperature is 1250℃.
4μ～500 bar, 100～10 at 1275℃
00μ. It can be seen that when the dolomite particle size becomes coarser than these particle sizes, the slag formation of dolomite worsens, and the porosity and reduction rate conversely decrease.

Next, FIG. 3 shows an example of the pore size distribution of the fired pellets measured using a mercury intrusion porosimeter.

As is clear from Figure 3, if the volume of pores with a diameter of 10JL or more is adjusted to 0.01c3/g or more, a higher reduction rate can be obtained than the conventional pellets with a dolomite particle size of 44g or less. .

Furthermore, the relationship between dolomite particle size and crushing strength of fired pellets is shown in FIG. 4. According to FIG. 4, it can be seen that the crushing strength of the pellets of the present invention is lower than that of conventional pellets. However, the pellets of this invention are 300Kg/P.
Since it has a certain level of strength, there is no problem in blast furnace operation.

From the above results, it can be seen that when the particle size range is 44 l to 1000 g, the porosity and high temperature reduction rate are improved compared to conventional pellets depending on the firing temperature.

Next, the dolomite particle size was set to 1001L to 500JL at a constant Motochi CaO/5i023i amount ratio of 8Yt1. Mg
A case where the O/5i02 weight ratio is changed will be explained.

The relationship between the high temperature reduction rate of the fired pellets and the CaO/Ji02 weight ratio and MgO/Si02 weight ratio is shown in FIGS. 5 and 6. In this case, CaO/5i02 = 1.
26, MgO/5i02 = 0.58.5i02 =
It is a constant condition of 3.5%.

As is clear from the results in Figures 5 and 6, 125
The reduction rate at high calcination temperatures of 0°C and 1275°C is determined by the CaO/Si02 weight ratio and the MgO/
It increases as the weight ratio of 5402 increases, indicating that the reducibility at high temperatures is improved.

In addition, the reduction rate of conventional pellets at high temperature (calcination temperature 12
(78% at 50℃ and 71% at 1275℃), the CaO/5iO2yiit amount ratio was 1.2.
As described above, pellets with excellent high-temperature properties can be obtained by mixing and adjusting the MgO/5i02 weight ratio to 0.5 or more.

(Effect of the invention) According to this invention, iron ore fine powder contains 44 to 1000
CaO having 80% by weight or more of particles in the uL particle size range
and MgO-containing auxiliary raw materials, and then combine the blended raw materials with a CaO/5i02 weight ratio of 1.2 or more,
The weight ratio of MgO/Si02 is adjusted to be 0.5 or more, and the adjusted raw material is granulated to form raw pellets, and the raw pellets are heated and fired at a predetermined temperature. Therefore, in this firing process, large diameter pores are formed by the above-mentioned auxiliary raw materials, and high melting point slag is formed around the pores. Therefore, the pores are prevented from being blocked due to melting of the slab in the firing process.

Therefore, the self-soluble pellets produced by the method of the present invention do not suffer from reduction stagnation at high temperatures, and as a result,
Excellent reducibility can be obtained.

In the above case, the auxiliary raw material is not a fine powder of 441 L or less as in the first conventional example, but a coarse powder with a large particle size.

Therefore, there is no need to finely pulverize the auxiliary raw material, which simplifies the process of pulverizing the auxiliary raw material, and also reduces the number of pulverizing steps.

In addition, high melting point slag is formed around the pores in the firing process. Therefore, the crushing strength of the self-soluble pellets is prevented from decreasing.

Furthermore, since the formation of the pores is not due to combustion of combustible substances as in the second conventional example, the structure of the pellet is prevented from changing due to combustion.

[Brief explanation of the drawing]

The figures are graphs showing the quality of self-soluble pellets obtained in each experiment. Figure 1 is the relationship between porosity and dolomite particle size, Figure 2 is the relationship between reduction rate and dolomite particle size, and Figure 3 is the relationship between porosity and dolomite particle size. The relationship between volume and pore diameter, Figure 4 shows the relationship between crushing strength and dolomite particle size, and Figure 5 shows the relationship between reduction rate and CaO/S 402
Figure 6 shows the relationship between weight ratio and reduction rate and MgO/5i (h
The relationship with weight ratio is shown respectively. Fig. 1 YY: l Mite company friend 01) Fig. 2 Dolomite ηQ busy (μ→ Fig. 3 low) L (μ) Dolomite (reverse &(lA> Fig. 5 Fig. 6)

Claims (1)

[Scope of Claims] 1. Sub-raw materials containing CaO and MgO having 80% by weight or more of particles in the particle size range of 44μ to 1000μ are blended into iron ore fine powder, and then this blended raw material is mixed with CaO and MgO.
O/SiO_2 weight ratio is 1.2 or more, and MgO/S
Adjust the iO_2 weight ratio to 0.5 or more, and granulate this adjusted raw material to form raw pellets,
A method for producing self-soluble pellets, which comprises heating and baking the raw pellets at a predetermined temperature. 2. The raw pellets are heated and calcined in a temperature range of 1220℃ to 1320℃ so that the volume of pores with a diameter of 10μ or more is 0.01c.
The method for producing self-soluble pellets according to claim 1, characterized in that the content is m^3/g or more.