JPS58123837A - Manufacture of sintered iron ore having improved reduction powdering property at low temperature - Google Patents

Abstract

PURPOSE:To improve the reduction powdering properties of sintered iron ore at low temp. by setting a period of time for which a nonoxidizing gas or a weakly oxidizing gas is fed after a combustion zone reaches the lowest layer and before sintered ore is discharged from a grate. CONSTITUTION:Iron ore is charged onto a grate to form a starting material layer for sintering, the surface of the layer is ignited while feeding air downward, and the combustion zone is allowed to reach the lowest layer. The resulting sintered ore is discharged from the grate. After the sintering and before the discharge, a period of time for which a nonoxidizing gas or a weakly oxidizing gas is fed is set. Gaseous N2 is used as the nonoxidizing gas, and a gaseous mixture of >=50vol% N2 with air is used as the weakly oxidizing gas.

Description

Detailed Description of the Invention The present invention provides iron ore sintered ore with improved low-temperature reduction powdering properties, which suppresses the degree of powdering when charged into a reduction furnace (blast furnace) as a raw material for iron making. Concerning the manufacturing method.

When reducing iron ore sinter in a blast furnace, it is desirable to suppress the degree of pulverization during the descent process in the furnace, so-called low-temperature reduction pulverization, as much as possible. This phenomenon of low-temperature reduction and powdering of sintered ore occurs when the hexagonal skeleton-like rhomboid hematite produced during sintering changes into cubic crystals as the reduction progresses, causing a volume change. It is said that not only a large number of fine particles are produced, but also a difference in reduction rate occurs between the hematite crystal and the mixture in the hematite crystal, and the difference in expansion causes reduction cracking and powdering.

Conventionally, as a method for producing sintered ore with the aim of improving the low-temperature reduction and powdering properties of this iron ore sintered ore, there have been several methods for producing sintered ore: (1) avoiding overheating during sintering;
A low-temperature sintering method in which the maximum temperature within the layer is maintained at about 1300 r or less, or (2) a chloride addition method in which chloride, for example about 0.15% calcium chloride, is mixed into the sintering raw material and sintered. Sintering method, etc. have been proposed.

However, the low-temperature sintering method (No. 11) requires a special combustion device for gaseous fuel, and the maximum temperature within the sintering JfII is about 100 to 150c lower, so the ore particles are not sufficiently melted. Therefore, the strength of the sintered ore is inevitably reduced and the yield is reduced.In addition, in the chloride addition method (2), chlorine-based exhaust gas is generated, which reduces the durability of the piping in the exhaust system. There are concerns that the reducibility will deteriorate in inverse proportion to the improvement in the low-temperature reduction powdering properties of sintered ore.
There are problems like this.

The present invention was made with the aim of solving such problems. For example, in a Dotroid type sintering machine, a layer of sintering raw material charged on a grate (pallet) is ventilated downward. In the iron ore sintering method in which sintered crystals are ignited on the top surface and discharged from the grate after the combustion zone reaches the lowest layer, the grate is discharged after the combustion zone reaches the lowest layer. It is characterized by providing a ventilation period with a non-oxidizing or weakly oxidizing gas such as nitrogen gas or a mixed gas of nitrogen gas and air during mining.

According to the method of the present invention, after the combustion zone reaches the lowest level and until the ore is discharged, there is a ventilation zone (
2), as shown in Examples below, the low-temperature reduction powdering property of the obtained sintered mineral product can be greatly improved.

This is presumed to be due to the fact that the formation of skeletal rhombic hematite, which occurs particularly in the lower layer of the sintered layer, is effectively prevented.

In practicing the method of the invention, nitrogen is conveniently used as the non-oxidizing gas. Although it is not necessarily completely non-oxidizing, it may be a mixed gas of nitrogen and air with a lower oxygen partial pressure than normal air. The effect appears even when it is contained to a certain extent. Other inert gases may be used in place of this nitrogen gas.

1 Sound 1 It is important to provide this ventilation section (period) of non-oxidizing or weakly oxidizing gas after (immediately after) the combustion zone reaches the lowest layer L5. If such a gas is ventilated during the combustion period when the combustion zone is descending through the layer, the oxidation reaction will be suppressed and there is a risk that sintered crystals with sufficient strength will not be obtained, and depending on the VC, combustion may become impossible. do. It takes a long time to burn and burn, which significantly reduces productivity. After the combustion zone reaches the lowest layer, that is, when the combustion of the raw material layer has progressed and the blended coke breeze has been almost completely burned, even if non-oxidizing gas or weakly oxidizing gas is ventilated, the above-mentioned problem will not occur. In this case, VC effectively prevents the formation of skeletal rhombic hematite.

The prevention of the formation of this skeletal rhomboid hematite can be better understood by assuming the following sintering mechanism.

Generally, during the sintering of iron ore, hematite 2-1 in the raw ore is thermally dissociated into magnetite in the high temperature region exceeding about 1550 ce of the combustion zone, and reacts with the slag melt to form a multicomponent system. Magnetite ICX Ru.

In conventional sintering methods, aeration is normally performed during the temperature cooling process after combustion, even around 1200 to 1350 °C at the beginning of the temperature drop, but the multicomponent magnetite produced passes through the sintered layer. It is oxidized by oxygen in the air, forming skeletal rhomboid matite. That is, in the normal forced downward suction draft sintering method, a sintering raw material mixed with a solid fuel such as coke powder as a heat source is charged onto a grate to a thickness of 300 to 700 cm, and the raw material is The upper surface of the layer is ignited to form a combustion zone, and the sintering progresses as this is gradually lowered by downward ventilation.In this case, in the sintered layer, high temperature gas IC, U, As the lower part is preheated, the highest combustion zone in the lower layer rises, and the high-temperature region where the generated multi-component magnetite turns into skeletal rhombic hematite due to oxygen VC in the ventilation air also expands. VC
Become. As mentioned above, when this skeleton-like rhombic hematite is generated, the low-temperature reduction and powdering properties of the sintered mineral product deteriorate. This prevents the expansion of the high-temperature region in the lower layer and lowers the oxygen partial pressure, effectively suppressing the formation of skeletal rhombic hematite, and as a result, reducing the low-temperature reduced powder of the sintered ore product. It is thought that this will improve the chemical properties.

In addition, considering the sintering mechanism as described above, i' (to suppress the formation of skeletal rhomboid hematite tt can be achieved by taking measures to reduce the time that the oxidized material exists in the oxidation reaction temperature range, or by , measures to reduce the amount of multicomponent maggiotite, which is an oxidizable substance, are also considered to be an effective solution.

However, in the case of the method of the present invention, fc is a devised post-reaction treatment without substantially changing the existing sintering reaction conditions, so it is possible to change the sintering operating conditions and other necessary physical properties of the sintered product. This is even more advantageous in that it can be carried out without substantially affecting, for example, strength or reducibility.

Example 1 2 kg of bedding ore (sintered ore of size 10 to 20IlII) was charged into a steel sintering pot with an inner diameter of 0.3 m and a height of 0.65 m. A sintering raw material with the composition shown in Table 1111 (H55 kg) was charged, a thermocouple for temperature measurement was embedded in the bottom of the raw material layer, and LPG was burned on the upper surface while a forced downward suction ventilation was carried out by an exhaust blower. The flame ignited it and started sintering.

Then, when the temperature at the bottom of the raw material layer measured by the thermocouple reaches the highest point, the ventilation gas is switched to a mixed gas containing nitrogen in various proportions, and this mixed gas is Both were aerated for 3 minutes.

The obtained sintered ore was taken out from the sintering pot, sized, and then subjected to a low-temperature reduction powdering test. The test results are shown in FIG.

As is clear from the results shown in FIG. 1, as the amount of nitrogen gas in the mixed gas increases, the low-temperature reduction powdering index of the sintered ore decreases, and the low-temperature reduction powdering properties are improved. Nitrogen 100
The effect is greatest when Vol, -, but nitrogen 50 Vo
It can be seen that sufficient effects can be obtained even when the amount is 1.1% or more.

Example 2 Sintering was carried out using a Dwight Lloyd sintering machine with effective machine length som, width 3 m, effective area 150771'', and 20 wind boxes (2.5 m x 3 m), using sintering raw materials with the composition shown in Table 2. did.

Then, the height of the raw material layer was set to f450 m, and the let speed i was set to 1.85 m7 minutes, and the combustion zone reached the bottom of the sintered raw material layer when it reached the position corresponding to the 19th wind box. Then, an operation was carried out in which ore was discharged after passing through the position of the 20th and final wind box. At the 20th and final wind box, nitrogen gas was blown onto the surface of the sintered layer so that the nitrogen gas was sucked and passed into the sintered layer.

The sintered lump discharged from the sintering machine was cooled in a cooler, and the crushed sieve fraction was sized in the process to obtain sintered ore for iron manufacturing. This sintered ore was subjected to a low-temperature reduction powdering test, and the low-temperature reduction powdering index was measured, and the results shown in Table 3 were obtained.

Table 3 also shows the test results when the conventional method of ventilating air at the 20th wind box was followed.

As is clear from the results in Table 3 and Table 5, according to the method of the present invention,
By simply passing non-oxidizing gas after the combustion zone reaches the bottom layer, the low-temperature reduction pulverization properties of sintered ore are significantly improved, and the low-temperature reduction pulverization index drops from 37.22 to 33.50. did.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the ratio of air and nitrogen (volume %) in the gas vented after the combustion zone reaches its lowest level and the low-temperature reduction powdering index of sintered ore. Applicant: Nisshin Steel Co., Ltd. company

Claims (1)

[Scope of Claims] ill The sintered raw material layer charged on the grate is ignited on the upper surface while providing downward ventilation, and after the combustion zone reaches the lowest layer, the sintered convex metal is discharged from the grate. A method of sintering iron ore for mining, which is characterized by providing a period of ventilation with non-oxidizing or weakly oxidizing gas after the combustion zone reaches the lowest level and before the ore is discharged from the grate. A method for producing sintered iron ore with improved low-temperature reduction powdering properties. 1. The manufacturing method according to claim 1, wherein the non-oxidizing gas is nitrogen gas. (The manufacturing method according to claim 1, wherein the arsenic gas is a mixed gas of nitrogen and air containing at least 50 volumes of nitrogen.