JPH04280931A - Manufacfture of sintered ore - Google Patents

Abstract

PURPOSE:To sufficiently increase strength of sintered one even if a fine powdery iron ore is used as sintering raw material. CONSTITUTION:In the case of sintering a granular material prepared by forming a stuck powder layer of fine powdery ore obtd. by blending powdery CaO source around the core of a coarse grain raw material as a part or the whole of sintering raw material, the blending ratio (mass%) of the powdery CaO source blended in the stuck powder layer is controlled in the range of the following inequality (1) based on the information of the max. burning temp.(T deg.C). A<=CaO (mass%) <=B... (1) Wherein, A and B in the inequality (1) are values decided as the following condition, i.e., in the case of T>=100 deg.C, A=0, and in the case of T<1300 deg.C, A=0.02T+26, and in any range of T, B=-0.0204T+33.5.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention aims to produce a large amount of fine ore by appropriately controlling the amount of powdered CaO source added during granulation when producing sintered ore as a raw material for blast furnace charging in pig iron production. The present invention relates to a method for producing sintered ore that enables improved productivity of sintered ore by improving the permeability of the sintered ore and the yield of sintered ore even when used in industrial applications.

0002

BACKGROUND OF THE INVENTION In recent years, the use of fine ore as a raw material for iron ore has been increasing, but the use of large amounts of fine ore poses a problem as it deteriorates air permeability and yield during sintering. However, since fine ore generally has a small amount of gangue components such as SiO2, it also has the advantage that by blending a large amount of this, it is possible to improve the quality of sintered ore. Therefore, in order to improve air permeability during sintering, which is a problem when mixing a large amount, conventionally, fine ore and some coarse ore are granulated in advance.
Many raw material processing methods have been proposed in which fine ore is turned into pseudo-particles, mixed with other main sintering raw materials, granulated, and charged into a sintering machine. For example, Japanese Patent Publication No. 60-17811 discloses a method for granulating mini-pellets for sintering, and Japanese Patent Application Laid-open No. 60-248827 describes a method for pre-treatment of sintering raw materials. ing.

0003

[Problem to be solved by the invention] The above-mentioned conventional method efficiently turns fine ore into pseudo-particles, improves air permeability during sintering, and
The aim is to shorten the sintering time or increase the sintering rate, thereby improving the productivity of sintered ore. Regarding the concretion strength, it is difficult to say that this method can provide a satisfactory value. Therefore, in order to further improve productivity, it is necessary to take new measures to improve the strength of sintered ore. The present invention aims to solve this problem, and aims to provide a method that not only improves the decrease in air permeability of the sintering bed due to an increase in the amount of fine ore, but also improves the cold strength. .

0004

[Means for Solving the Problems] The gist of the present invention, which aims to achieve the above object, is to form an adhered powder layer of fine ore containing a powdery CaO source around the core of a coarse raw material. When sintering the granules as part or all of the sintering raw material, information on the blending ratio (mass%) of the powdered CaO source to be blended into the adhering powder layer and the maximum sintering temperature (T°C) during sintering. It is characterized by adjusting to the range of the following formula (1) based on the following. A≦CaO (mass%)≦B (1) However,
A and B in equation (1) are as follows: When T is 1300℃ or higher, A=0, T is 1300℃
When the value is less than 1, the value is determined by B=-0.0204T+33.5, regardless of the range of A=-0.02T+26T. Here, coarse grain raw material refers to return ore or fine ore for sintering in which 60% or more has a particle size of 1 mm or more, and fine ore refers to iron ore in which 90% or more has a particle size of less than 0.25 mm. CaO sources consist of quicklime, slaked lime, or limestone.

[Operation] The present inventors conducted various tests and studies to solve the problem, and found that the yield and cold strength of sintered ore were determined by the granules obtained in the preliminary granulation process (hereinafter referred to as It was found that the strength of the fired pre-granules (hereinafter referred to as pre-granules) is controlled by the strength after firing, and that the strength of the fired pre-granules has a strong correlation with the bonding strength of the fine ore particles in the adhering powder layer.

[0006] Therefore, a basic test was conducted on the bonding strength between fine ore particles by preparing briquettes having a density comparable to the apparent density of the adhering powder layer of the preliminary granulation.

FIG. 1 shows the relationship between the CaO addition ratio to the fine ore and the firing temperature on the strength after firing in the briquettes. The ○ mark in the figure indicates that the desired strength is present, and the x mark indicates that the desired strength is not achieved. The test conditions are as follows. CaO source: CaO standard reagent powder Fine powder Iron ore: Hematite ore with an average particle size of 0.05 mm Briquette shape and compact density: 5 mmφ x 5 m
m, 2500-3000 kg/m3 Evaluation method for desired strength of fired product: Pellet crushing strength test Firing conditions: Temperature increase rate 650°C/min in air,
Holding time over 1000℃ 2 min, cooling rate 20
5℃/min,

[0008] As is clear from the results shown in Fig. 1, CaO and Fe2O3 do not react at a firing temperature of 1200°C, and therefore no melt is produced, so even if the CaO ratio is increased, the desired strength cannot be obtained. There wasn't. At a firing temperature of 1250°C, the CaO addition rate is 1 to 8%, 1
The desired strength was obtained at 0 to 7% at 300°C and 0 to 6% at 1350°C.

FIG. 2 shows the relationship with strength when the same test as above was conducted with the firing temperature kept constant at 1250° C. and the CaO addition ratio varied. From the results shown in FIG. 2, it can be seen that the strength increases as the CaO addition ratio increases, but it has a peak value at a certain CaO ratio and tends to decrease even if the CaO addition ratio is increased beyond that point. The reason for this phenomenon is that as the CaO addition rate increases, Fe2O3 in the fine ore reacts with CaO to produce calcium ferrite (hereinafter referred to as CF).
Fine ore particles become bonded to each other through CF, increasing their strength. However, if the CaO addition ratio increases too much, the amount of pores, which causes a decrease in the strength of the briquettes, increases as the CF increases. Therefore, when the amount of pores exceeds a certain amount, the strength-reducing effect due to the presence of pores exceeds the strength-increasing effect due to CF formation, which is thought to have led to a decrease in sintering strength. From this, C
The lower limit of the aO addition rate is determined by the bonding strength between fine ore particles, and the upper limit is regulated by the amount of pores.

[0010] Based on the above knowledge and facts, we investigated the range of CaO addition ratio in order for the adhering powder layer of the pre-granulated product to have the desired strength, using the firing temperature as a variable, and found that (1)
It was found that satisfactory results could be obtained by adjusting the CaO addition ratio within the range of the formula. That is, CaO
(mass%) For the lower limit, the maximum firing temperature
(T) 0 when ≧1300℃, maximum firing temperature (
T) When <1300℃ [-0.02T+26]
On the other hand, the upper limit of CaO (mass%) is calculated using the formula [-0.0204T+33.5] based on the maximum firing temperature (T).
] It was found that the value calculated using the formula can be used.

[0011] The maximum sintering temperature means the temperature in an actual sintering machine. The firing temperature in the sintering machine varies depending on the coke consumption rate and the permeability of the sintering bed. Therefore, the maximum firing temperature may be adjusted to suit the conditions of the CaO source blending ratio of the pre-granulated product by using these coke consumption units, air permeability of the sintering bed, etc. as controlling factors. Alternatively, the maximum sintering temperature when the adjusted pre-granulated material is actually submitted to a sintering machine may be known in advance as an empirical value. In other words, in actual operation, when attempting to sinter using the pre-granulated material, it is necessary to know in advance what the maximum sintering temperature will be based on conditions such as the coke consumption rate and the permeability of the sintering bed. From this known information on the maximum firing temperature, calculate C in the adhesion layer according to equation (1).
The amount of the aO source may be adjusted appropriately. Firing temperature during actual operation can be measured by various methods, such as inserting a thermometer into the bed from the sidewall of the sintering pallet.

0012

[Example] Table 1 shows the compounding conditions of Examples of the present invention and Comparative Examples. As shown, the pre-granulation raw material consists of return ore, fine ore, and powdered quicklime which is a CaO source. Return ore is a coarse raw material and serves as the nucleus of pseudo particles. Fine ore and quicklime become adhesion powder of pseudo particles. Table 2 shows the particle size composition of the return ore and fine ore, and Table 3 shows their chemical composition.

In the pre-granulation step, fine ore, return ore and quicklime were placed in a drum type granulator and granulated with a pre-granulation moisture content of 7.5%. Thereafter, other sintering raw materials (main raw materials) and pre-granulated material were placed in a drum-type granulator, mixed and granulated at a granulation moisture content of 6.5%. Powder ore from Australia and ore from South America were used as the main sintering raw materials other than the pre-granulation raw materials, and serpentinite, silica powder and limestone powder were used within the usual range as auxiliary raw materials.

[0014] The coke addition ratio in the Examples and Comparative Examples shown in Table 1 was adjusted so that the maximum calcination temperature was about 1250°C. At this maximum firing temperature, the appropriate range of CaO addition ratio according to equation (1) is 1≦CaO (mass%)≦8
becomes. In the example, within this appropriate range, with reference to FIG. 2, the CaO addition ratio was set to about 3.3% based on the fine ore. This is approximately 0.5% based on the total sintered raw material. On the other hand, in Comparative Example 1, when the CaO addition ratio is lower than the lower limit,
Comparative Example 2 is a case where the value is higher than the upper limit.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

These sintered raw materials were subjected to a sintering pot test in accordance with the Pigmaking Committee Law. The quality of the obtained sintered ore was evaluated as follows:
Sintering time, drop strength, JIS reduction rate (RI), and reduction pulverization index (RDI) were measured. Table 4 shows the results of the sintering pot test.

[0019]

[Table 4]

As shown in Table 4, the sintering time was about the same in the examples to which the method of the present invention was applied compared to the comparative examples, but the drop strength (cold strength) was higher, so the production rate was lower. This resulted in a higher price. Furthermore, no significant difference was observed in the reduction properties under any conditions.

[0021]

[Effects of the Invention] As described above, when pre-granulating fine powdered iron ore, the ratio of the powdered CaO source added at the time of pre-granulation can be adjusted based on the calcination temperature information. The strength can be improved, and the production rate of the sintering method using fine iron ore can be increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the firing temperature and the CaO addition ratio for obtaining briquettes with desired strength.

FIG. 2 is a diagram showing the influence of CaO addition ratio on sintering strength at a firing temperature of 1250°C.

Claims (2)

[Claims] [Claim 1] A granulated material formed by forming an adhered powder layer of fine ore mixed with a powdered CaO source around the core of a coarse-grained raw material is used for sintering as part or all of the sintering raw material. The blending ratio (mas
A method for producing sintered ore, characterized in that A≦CaO (mass%)≦B is controlled in the range of the following formula (1) based on information on the maximum calcination temperature (T°C) during calcination. ...(1) However,
A and B in equation (1) are as follows: When T is 1300℃ or higher, A=0, T is 1300℃
When the value is less than 1, the value is determined by B=-0.0204T+33.5, regardless of the range of A=-0.02T+26T. 2. The coarse raw material is return ore or fine ore for sintering in which the particle size of 1 mm or more accounts for 60% or more, and the fine ore is 0.
2. The method for producing sintered ore according to claim 1, wherein the iron ore has a particle size of 90% or more less than 25 mm, and the powdered CaO source is quicklime, slaked lime, or limestone.