JP2020139173A - Method for producing sintered ore - Google Patents

Abstract

To provide a method for producing sintered ores, in the case where fine powder iron ores having a grain size of 150 μm or lower are used as a sintering raw material, capable of promoting sintering reaction in a sintering machine, suppressing the collapse of pseudo grains, and suppressing reduction in the productivity of sintered ores.SOLUTION: A method for producing sintered ores has a process where a sintering raw material containing iron ores and a carbonaceous material is charged onto a pallet circulatively moving at a raw material ore feed part in a sintering machine to form a charge layer, thereafter, ignition is performed to the carbonaceous material at the upper surface of a charge layer by an ignition furnace arranged at the lower part of the pallet, a gas at the upper part of the charge layer is sucked by a wind box arranged at the lower part of the pallet, the gas is introduced into the charge layer, and the carbonaceous material in the charge layer is burnt to produce sintered ores, in which the iron ores contain fine powder ores having a grain size of 150 μm or lower by above 10 mass%, a part of the fine powder iron ores is made into a molded part and is mixed into the sintering raw material, and the oxygen concentration of the gas introduced into the charge layer is made higher than 23 vol.%.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for producing a sinter that is sintered using a downward suction type sinter.

Sintered ore, which is the main raw material of the blast furnace ironmaking method, is generally produced in a manufacturing process having a downward suction type dwightroid sintering machine as shown in FIG. The raw materials for sinter are iron powder (generally called sinter feed of 8 mm or less), sinter sinter powder, recovered powder generated in the iron mill, limestone, dolomite, and other CaO-containing secondary substances. Raw materials, granulation aids such as quicklime, and charcoal materials (coagulants) such as coke powder and smokeless charcoal. These raw materials are cut out from each of the plurality of hoppers 1 on a conveyor at a predetermined ratio. An appropriate amount of water is added to the cut raw material by the drum mixers 2 and 3, and the cut raw material is mixed and granulated to be a sintered raw material which is a pseudo particle having an average diameter of 3 to 6 mm.

The sintered raw material is then charged into a pallet 9 that circulates from the surge hopper 5 arranged in the raw material supply section of the sintering machine via the drum feeder 6 and the cutting chute 7, and is charged by the cut gate 8. A charging layer 10 also called a sintered bed having a thickness of 400 to 800 mm is formed. After that, the carbonaceous material on the upper surface of the charging layer 10 is ignited by the ignition furnace 11 arranged above the charging layer 10, and the carbon material on the upper surface of the charging layer 10 is charged via the windbox 12 arranged below the pallet 9. By sucking the gas above the filling layer 10 downward, the carbonaceous material in the charging layer 10 is sequentially burned, and the sintering raw material is melted by the combustion heat generated at this time to obtain a sintered cake. The sintered cake thus obtained is then crushed, cooled, and sized at the sinter, and agglomerates of about 5 mm or more are recovered as adult sinter and supplied to the blast furnace.

In the above manufacturing process, the carbonaceous material in the charging layer 10 ignited by the ignition furnace 11 continues to be burned by the gas sucked from the upper layer to the lower layer in the charging layer 10, and the pallet 9 is on the downstream side. It gradually shifts from the upper layer to the lower layer of the charging layer 10 as it moves to, and forms a combustion / melting zone (hereinafter, also simply referred to as “combustion zone”) having a width in the thickness direction. In FIG. 2, the carbonaceous material on the surface of the charging layer 10 ignited by the ignition furnace continues to burn by the sucked gas to form a combustion zone, which sequentially moves from the upper layer to the lower layer of the charging layer 10. It is the figure which showed typically the process of forming the sintered layer (sintered cake) which completed the sintering reaction after passing through a combustion zone.

Since the molten portion of the combustion zone obstructs the flow of the sucked gas, the sintering time is extended and the productivity is lowered. In addition, as the combustion zone shifts from the upper layer to the lower layer, the water contained in the sintered raw material is vaporized by the combustion heat of the carbonaceous material and concentrated in the sintered raw material of the lower layer whose temperature has not yet risen. And form a wet zone. When this water concentration exceeds a certain level, the voids between the particles of the sintered raw material, which are the flow paths of the suction gas, are filled with water, which causes an increase in airflow resistance as in the combustion zone. FIG. 3 shows a combustion zone moving in the charging layer 10 having a thickness of 600 mm at a position of about 400 mm on the pallet in the charging layer 10 (200 mm below the surface of the charging layer 10). The distribution of pressure loss (hereinafter referred to as pressure loss) and temperature in the charging layer 10 is shown. The distribution of pressure loss at this time is about 30% in the wet zone and about 30% in the combustion zone. It shows that it is 40%.

The production amount (t / h) of the sintering machine is generally determined by the production rate (t / (h × m ² )) × the area of the sintering machine (m ² ). That is, the production volume of the sinter is the specifications of the sinter (machine width, machine length), the thickness of the charging layer 10, the bulk density of the sinter raw material, the sinter (burning) time, and the steps of the product sintered ore. It is decided by retaining. Therefore, in order to increase the production amount of the sinter, the thickness of the charging layer 10 is increased, the air permeability (pressure loss) of the charging layer 10 is improved, and the sintering time is shortened. It is considered effective to increase the strength and improve the yield.

By the way, the powdered iron ore for sintering has been deteriorated in quality in recent years due to the depletion of high quality iron ore. Lowering the grade of high-quality iron ore leads to an increase in the slag component and further pulverization of the iron ore, and the granulation property tends to decrease due to the increase in the alumina (Al ₂ O ₃ ) content and the increase in the fine powder ratio. ing. On the other hand, in blast furnaces, a low slag ratio is required from the viewpoint of reducing the cost of producing hot metal and reducing the amount of CO ₂ generated, and accordingly, the sinter is required to have high reducibility and high strength. ing.

In such an environment surrounding sintering pulverized iron ore, high quality sintered ore is used by using a pellet feed mainly composed of difficult-to-granular fine iron ore (particle size 150 μm or less) with a small amount of slag. Techniques for manufacturing have been proposed. For example, one of such conventional techniques is the Hybrid Pelletized Sinter method (hereinafter, referred to as “HPS method”). This technology uses a drum mixer and a pelletizer to granulate iron ore containing a large amount of fine powder such as pellet feed, granulation aids, coagulants, etc., resulting in low slag component and high reducibility sintering. Techniques for producing ore are disclosed in Patent Documents 1-5.

Further, Patent Document 6 discloses a method for producing sinter by a multi-stage ignition sintering method, in which oxygen-enriched air is introduced into a charging layer on the downstream side of an ignition furnace. There is.

Tokuhei No. 2-4658 Special Fair 6-21297 Gazette Special Fair 6-21298 Special Fair 6-21299 Gazette Special Fair 6-60358 Gazette Japanese Unexamined Patent Publication No. 2015-157980

However, in the method of granulating the pellet feed using the HPS method as described in Patent Documents 1 to 5, not only fine particles of less than 0.5 mm but also coarse particles of more than 10 mm are produced during granulation. Many are generated. Since the specific surface area becomes larger as the particles become finer, the pellet feed, which is a fine powder, preferentially absorbs water, and the pseudo particles in which the fine powder merely aggregates, or the particles in the form in which the fine powder adheres around the nuclear particles. It becomes coarse pseudo-particles with irregular diameters.

As described above, when the compounding raw material containing a large amount of fine iron ore having a particle size of 150 μm or less, such as pellet feed, is granulated, the particle size becomes uneven and the fine particles are merely aggregated coarse pseudo-particles. Is generated. Since such coarse pseudo-particles have weak bond strength, if they are deposited on the pallet of the sintering machine with a certain layer thickness, they will collapse when a load (compressive force) is applied, and the pseudo-particles will be pulverized. It causes a decrease in the porosity of the charge layer. As a result, the air permeability of the charging layer deteriorates, and the combustion of the sintered raw material is hindered. As a result, the sinter time of the sinter becomes long, and the productivity of the sinter becomes low. Further, when the sintering time is the same, the sintering becomes insufficient and the yield of the sinter is lowered, and the productivity of the sinter is also lowered in this case.

Further, even in the multi-stage ignition sintering method as described in Patent Document 6, when fine iron ore having a particle size of 150 μm or less such as pellet feed is used, the fine powder merely aggregates during granulation. The productivity of sinter is reduced because no coarse pseudo-particles are produced.

The present invention has been made in view of the above problems, and an object of the present invention is to promote a sintering reaction in a sintering machine when fine iron ore having a particle size of 150 μm or less is used as a sintering raw material. It is an object of the present invention to provide a method for producing a sinter which can suppress the collapse of pseudo-particles and suppress a decrease in the productivity of the sinter.

The features of the present invention that solve such a problem are as follows.
(1) After the sintering raw material containing iron ore and carbonaceous material is charged onto a pallet that circulates in the raw material supply section of the sintering machine to form a charging layer, the downstream side of the raw material supply section. The carbonaceous material on the upper surface of the charging layer is ignited by the ignition furnace arranged in the above, the gas above the charging layer is sucked by the wind box arranged below the pallet, and the gas is transferred to the charging layer. It is a method for producing sinter by introducing and burning the carbonaceous material of the charging layer, and the iron ore is 10% by mass of fine iron ore having a particle size of 150 μm or less. A method for producing sinter, which contains a larger amount of the fine iron ore and mixes it with the sinter raw material as a molded product to increase the oxygen concentration of the gas to be introduced into the charging layer to more than 23% by volume. ..
(2) The method for producing a sinter according to (1), wherein 50% by mass or more of the fine iron ore is made into a molded product and mixed with the sinter raw material.
(3) The method for producing a sinter according to (1) or (2), wherein the iron ore contains 15% by mass or more of fine iron ore having a particle size of 150 μm or less.
(4) The method for producing a sinter according to any one of (1) to (3), wherein the oxygen concentration of the gas introduced into the charging layer is 24% by volume or more.

By implementing the method for producing a sinter of the present invention, pseudo-particles having high bonding strength can be produced and the flammability of the carbonaceous material in the charging layer can be improved. By improving the bonding strength of the pseudo-particles and improving the flammability of the carbonaceous material, the surface of the pseudo-particles can be sintered before the pseudo-particles in which fine iron ore is aggregated collapse. As a result, even when iron ore containing more than 10% by mass of fine iron ore having a particle size of 150 μm or less is used as the sintering raw material, deterioration of air permeability due to pulverization of pseudo particles can be suppressed. It is possible to suppress a decrease in the productivity of sinter due to the extension of the sinter time. Further, since the conventional sinter machine can be used in the method for producing the sinter of the present invention, it contains more than 10% by mass of fine iron ore having a particle size of 150 μm or less while using simple equipment. Sintered ore can be produced from a sintered raw material containing iron ore without reducing the productivity of the sinter.

It is a figure explaining the manufacturing method of a sinter. It is a figure which showed typically the process of forming a sintered layer. It is the figure which showed typically the pressure loss and temperature distribution in the raw material charge layer in the middle of sintering. It is a graph which shows the difference of the particle size distribution of pseudo-particles with and without pellet feed. It is a schematic diagram which shows the manufacturing process of the sinter to which the manufacturing method of the sinter which concerns on this Embodiment can be applied. It is a graph which shows the relationship between the fine powder ratio of a particle diameter of 150 μm or less, and the production rate of a sinter. It is a graph which shows the relationship between the fine powder ratio of a particle diameter of 150 μm or less and the effect of improving the production rate of a sinter when the oxygen concentration is increased to 24% by volume. It is a graph which shows the relationship between the oxygen concentration and the sinter production rate.

According to the present invention, by introducing oxygen-enriched air having an increased oxygen concentration into the charging layer 10 of a sintered raw material containing fine iron ore having a particle size of 150 μm or less, the carbonaceous material in the charging layer 10 is charged. By improving flammability and forming 50% by mass or more of the fine iron ore into a molded product, deterioration of the air permeability of the charging layer 10 due to pulverization of pseudo particles is suppressed, and the productivity of the sinter is increased. It suppresses the decrease. First, the characteristics of the sintered raw material containing fine iron ore having a particle size of 150 μm or less will be described.

FIG. 4 is a graph showing the difference in particle size distribution of pseudo particles with and without pellet feed. In FIG. 4, the black plot shows the particle size distribution of iron ore in which pellet feed, which is a fine iron ore having a particle size of 150 μm or less, is not blended. The white plot shows the particle size distribution of iron ore whose particle size distribution is shown in the black plot mixed with 40% by mass of pellet feed, which is fine iron ore having a particle size of 150 μm or less.

When the pellet feed is blended at a ratio of 40% by mass as shown in FIG. 4, the particle size distribution shown in the black plot becomes the particle size distribution shown in the white plot. That is, by mixing the pellet feed at a ratio of 40% by mass, not only fine particles (less than 0.5 mm) but also coarse particles (more than 10 mm) were produced in large numbers. If the wettability of the fine iron ore is the same, the finer the granules, the larger the specific surface area and the more water is absorbed, so that a large amount of water is retained between the powders. Therefore, the fine iron ore preferentially absorbs water with respect to the coarse-grained iron ore that is not the fine iron ore. Then, as it absorbs water, the fine iron ore aggregates with each other, and coarse pseudo-particles in which the fine iron ore simply aggregates are generated. In the present embodiment, the particle size and the ratio are determined by sieving the raw materials using a sieve having a mesh size conforming to JIS Z 8801-1, dividing the raw material into each particle size, measuring the mass of each particle size, and measuring each particle size. The ratio of each particle size is calculated from the mass of the above and the total mass. For example, "blending 40% by mass of pellet feed having a particle size of 150 μm or less" means that the pellet feed that has passed through a sieve having a nominal opening of 150 μm according to JIS Z 8801-1 has a ratio of 40 to the total mass of iron ore. It means to mix so that it becomes%.

Coarse pseudo-particles in which such fine iron ore is aggregated have a weak bond strength, and when they are deposited on the pallet of a sintering machine, they collapse when a load (compressive force) is applied, and the pseudo-particles are pulverized. The porosity of the charging layer 10 is reduced. As a result, the air permeability of the charging layer 10 deteriorates, and the combustion of the sintered raw material is hindered. As a result, the sinter time of the sinter becomes long, and the productivity of the sinter becomes low.

Therefore, in the method for producing sinter of the present embodiment, a part of fine iron ore having a particle size of 150 μm or less is used as a molded product and is loaded for the purpose of suppressing a decrease in the productivity of the sinter. The oxygen concentration of the oxygen-enriched air introduced into the charging layer 10 is made higher than 23% by volume to improve the combustibility of the carbonaceous material of the charging layer 10. As a result, the bonding strength of the pseudo-particles is improved and the temperature reached by the charge layer 10 at the time of sintering is increased, whereby the surface of the pseudo-particles is sintered before the pseudo-particles in which the fine iron ore is aggregated collapse. However, the decay of pseudo particles is suppressed. As a result, deterioration of the air permeability of the charging layer 10 due to pulverization of the pseudo particles can be suppressed, and a decrease in the productivity of the sinter can be suppressed. In this embodiment, the oxygen-enriched air is an example of the gas introduced into the charging layer 10. Further, as the carbonaceous material blended in the sintering raw material, it is preferable to use a carbonaceous material having a particle size of less than 3 mm and 50% by mass or more. By using a carbonaceous material having a particle size of less than 3 mm and 50% by mass or more, the carbonaceous material can be segregated into the upper layer of the charging layer 10 and the combustibility can be enhanced, and the sintering reaction of the charging layer 10 can be promoted. ..

On the other hand, since the use of oxygen causes an increase in the cost of producing sinter, it is preferable to narrow the region where the oxygen concentration of the oxygen-enriched air is increased as much as possible. By increasing the oxygen concentration, the temperature of the charging layer 10 at the time of sintering can be raised. Therefore, as a region for increasing the oxygen concentration, air at room temperature is introduced into the charging layer 10 and the charcoal material is combustible. It is preferable to select a region inferior to. That is, in the region where the oxygen concentration is increased, the igniter 11 side in the direction of the sintering machine length from the downstream side of the igniter 11 where air at room temperature is introduced into the charging layer 10 and the combustibility of the carbonaceous material is inferior It is preferable to increase the oxygen concentration of the oxygen-enriched air introduced into the region to improve the combustibility of the carbonaceous material.

FIG. 5 is a schematic view showing a sinter manufacturing process to which the sinter manufacturing method according to the present embodiment can be applied. In FIG. 5, the same equipment as in FIG. 1 is designated by the same reference numerals, and duplicate description will be omitted. In the method for producing sinter according to the present embodiment, a part of fine iron ore contained in the sinter raw material having a particle size of 150 μm or less is cut out from a plurality of hoppers 1 and molded by the molding facility 4. The molded fine iron ore is mixed with the sintering raw material granulated into pseudo particles by a drum mixer 2, 3 or the like. After that, the sinter raw material is charged into a circulating pallet 9 and sintered to produce a sinter. Various raw materials can be independently cut out from a plurality of hoppers 1 into the drum mixer 2 and the molding facility 4 with arbitrary formulations. Further, when molding fine iron ore in the molding facility 4, one or more of inorganic binders such as cement and bentonite and organic binders such as pitch, PVA and pregelatinized starch are added to improve the strength after molding. You may let me. Further, a mixing facility may be provided in front of either one or both of the drum mixer 2 and the molding facility 4 to carry out stirring and mixing.

As described above, the method for producing sinter according to the present embodiment can be carried out by using the existing sinter as it is by adding the molding equipment 4 for molding fine iron ore and the oxygen increasing device 13. Therefore, the method for producing sinter according to the present embodiment uses a sinter raw material containing iron ore containing more than 10% by mass of fine iron ore having a particle size of 150 μm or less, while using simple equipment. Sinter can be produced while suppressing a decrease in the productivity of sinter.

As described above, when the iron ore of the sintering raw material contains a large amount of fine iron ore, coarse pseudo-particles having a weak bond strength are generated in which the fine iron ores are merely aggregated. When a large amount of fine iron ore having a particle size of 150 μm or less is contained, the effect of suppressing a decrease in the productivity of the sinter by the method for producing the sinter of the present embodiment becomes large. Therefore, in the method for producing sinter of the present embodiment, more than 10% by mass of fine iron ore having a particle size of 150 μm or less is blended in the iron ore as a raw material for sinter. In the present embodiment, the iron ore means an iron ore having a fine iron ore having a particle size of 150 μm or less and a coarse-grained iron ore having a particle size larger than 150 μm. Further, the fine iron ore refers to all of the iron ore particles having a particle size of 150 μm or less, regardless of the brand of the ore.

Further, in the experiment described later, even if air having an oxygen concentration of 21% by volume was used, there was no effect of suppressing a decrease in the productivity of the sintered ore, so the oxygen concentration of the oxygen-enriched air was made higher than 23% by volume. ing. The upper limit of the oxygen concentration of the oxygen-enriched air does not have to be particularly limited, but the oxygen concentration of the oxygen-enriched air is preferably 50% by volume or less from the viewpoint of preventing burning of the oxygen increasing device. ..

Further, the ignition means of the ignition furnace 11 is not particularly limited, but it is preferable to use a burner using a gaseous fuel such as C gas, B gas or M gas which is a by-product gas of the steelworks. A burner using gaseous fuel such as LNG, LPG, or city gas, which is often used in steelworks, may be used. Further, in order to ignite the coagulant such as powder coke on the upper surface layer of the charging layer 10 in a short time, the oxygen concentration in the flammable gas supplied to the burner may be increased to raise the flame temperature of the burner. ..

Further, gaseous fuel may be supplied to the upper layer of the charging layer 10 for the purpose of ensuring a sufficient temperature for sintering in the upper layer of the charging layer 10. In this case, a gas fuel supply device having a hood is provided above the charging layer 10 in a section of about 1/3 of the section from immediately after the ignition furnace 11 to the excretion part, and a gas fuel supply pipe is provided inside the gas fuel supply device. Arrange to supply gaseous fuel. This gas fuel supply device may be used to dispose an oxygen supply pipe inside the gas fuel supply device to supply oxygen gas and increase the oxygen concentration of oxygen-enriched air. As the gaseous fuel, at least one of C gas, B gas, M gas, LNG, LPG and city gas may be used.

A sintering experiment was carried out using a cylindrical sintering experiment device (hereinafter referred to as a sintering pot) having an inner diameter of 300 mmφ and a height of 400 mm. A part of the fine iron ore having a particle size of 150 μm or less was mechanically compacted using a double roll type briquette machine to obtain a 1.5 cc molded product. The drop strength of the molded product was evaluated by a mass ratio of 5 mm or more in a 200 g molded product dropped from a height of 1 m. The mass ratio of the molded product of 5 mm or more is calculated by measuring the mass of the molded product on the sieve with a mesh opening of 5 mm after dropping and dividing the mass by the mass of the total molded product. .. The drop strength of the molded product used in this example was 52% by mass.

In this embodiment, the fine iron ore was molded without using the binder, but the fine iron ore may be molded by adding the binder as described above. For example, by adding 1% by mass of pregelatinized starch for molding, the drop strength of the molded product can be increased by about 1.5 times. As a result, a transport means that generates a strong impact can be used, so that the degree of freedom in designing the transport facility is improved. In addition, even if a total of 25% by mass of auxiliary raw materials such as limestone and raw materials of sinter such as carbonaceous material and iron ore having a particle size larger than 150 μm are mixed with fine iron ore, the drop strength is reduced by about 10%. Even if a raw material of a sintered ore other than the fine iron ore is mixed with the fine iron ore, there is almost no decrease in the drop strength of the molded product.

The strength of the molded product may be evaluated by the crushing strength, but when it contains water, it is difficult to evaluate by the crushing strength whether it collapses due to the impact during transportation. For example, for a molded product having a particle size of about 10 to 15 mm, a molded product having a crushing strength of 5 kgf / p when cement or the like is added and dried, and a molded product having a crushing strength using starch or polyvinyl alcohol as a binder are 1 kgf / p. When comparing certain molded products, the crushing strength is higher in the molded products using cement, but when compared by the ratio of the molded products that were 5 mm or more after being conveyed by a conveyor or the like, starch or polyvinyl alcohol was used as the binder. On the contrary, the molded product used is higher. Molded products using starch or polyvinyl alcohol as a binder are plastic in a wet state, and although they are plastically deformed when subjected to a drop impact, the particles are less likely to collapse. On the other hand, a briquette that has been dried with cement or the like is brittlely broken when it receives a drop impact. In order to use the molded raw material in a sintering machine, it is necessary to withstand the drop impact caused by the transfer of the molded raw material from the drum mixer to the charging part of the sintering machine with a belt conveyor, etc., so crushing is a method for evaluating its strength. Drop strength is preferred over strength.

A sintering raw material other than the molded product was rotated at 8 rpm for 300 seconds using a drum mixer having a diameter of 1 m to obtain pseudo particles, and after mixing the molded products at a predetermined ratio, the pseudo particles were placed in a sintering experimental device having a diameter of 400 mm. It is charged to the thickness to form an charging layer, and the upper surface is heated for 60 seconds using a burner using propane as fuel to ignite, and is sucked from the bottom of the sintering pot with 700 mm Aq to obtain a sintered cake. Was produced. In addition, 5% by mass of coke breeze was added as a coagulant to the sintered raw material in which the pseudo particles and the molded product were mixed. In each experiment, the raw material water content was adjusted to be constant at an average of 7.5% by mass.

In the above sintering experiment, the temperature of the combustion exhaust gas discharged from the lower part of the sintering pot was measured, and the time from ignition to the time when this temperature reached the peak was defined as the sintering time. Further, after the completion of the sintering experiment, the sintered cake was dropped once from a height of 2 m, and the sintered ore remaining on the 10 mm mesh was defined as a product. The yield of the sinter was calculated by dividing the mass of the product sinter of 10 mm or more by the mass of the sinter cake. Further, from the cross-sectional area (m ² ) of the sinter pot, the weight (t) of the product sintered ore, and the sinter time (h), the unit hearth area (m ² ) and the unit time (h). The sinter production rate (t / (h × m ² )), which is the sinter production amount (t), was calculated.

In the sintering experiment, the oxygen concentration of the oxygen-enriched air introduced into the charging layer was changed within the range of 21% by volume (no increase in oxygen) to 50% by volume during the first half of the sintering time from ignition. It was. Since the sintering time is different under each condition, repeated experiments were carried out while adjusting the time to increase the oxygen concentration so that the time to increase the oxygen concentration of the oxygen-enriched air would be half of the first half of the sintering time. Adjusted to.

The iron ore used in the sintering experiment is a coarse-grained iron ore having a particle size larger than 150 μm, and one of the coarse-grained iron ores divided into two equal parts is crushed using a splitter to have a particle size of 150 μm or less and a particle size of 150 μm. Two types of iron ore were prepared that differed only in larger grain size. The chemical composition was 4.9% by mass of SiO _{2 and} 1.8% by mass of Al ₂ O ₃ . The basicity (CaO / SiO ₂ ) of the sintering raw material was set to 2.0 by adjusting the blending amount of limestone. In addition, 20% by mass of sinter (return ore) of 5 mm or less was blended by simulating the sintering raw material used in an actual sinter. In the sintering experiment in which the molded fine iron ore was mixed, 50% by mass of the fine iron ore was used as a molded product, and the remaining 50% by mass was used as the fine iron ore.

FIG. 6 is a graph showing the relationship between the fine powder ratio having a particle size of 150 μm or less and the production rate of sinter. In the graph shown in FIG. 6, the horizontal axis is the pulverization rate (mass%) indicating the ratio of pulverized iron ore having a particle size of 150 μm or less in the iron ore, and the vertical axis is the sinter production rate (t /). (H × m ² )).

From FIG. 6, it can be seen that when the oxygen is not increased, the production rate of the sinter is significantly reduced as the pulverization rate is increased. In particular, under the condition that the fine powder ratio is higher than 10% by mass, the decrease in the production rate of the sinter (the slope of the broken line) becomes large due to the increase in the fine powder ratio. The sintered cake obtained by carrying out the sintering test with the fine powder ratio of 15% by mass was divided into three equal parts in the height direction, and the yield of the sintered ore was evaluated by dividing into the upper layer, the middle layer and the lower layer. Compared with the sinter test in which the ratio was 10% by mass, the yield of the sinter in the upper layer was significantly reduced, which was the cause of the decrease in the sinter production rate.

On the other hand, when the oxygen concentration of oxygen-enriched air is increased to 24% by volume in the first half of the sintering time, the production rate of sinter decreases as the fine powder ratio increases, but the amount of decrease is oxygen. It was smaller than when the concentration was not increased. Similarly, the sintered cake obtained by carrying out the sintering test with the fine powder ratio of 15% by mass was divided into three equal parts in the height direction, and the yields of the sintered ores in the upper layer, middle layer and lower layer were evaluated. The decrease in the yield of sinter in the upper layer was suppressed as compared with the case where the oxygen concentration was not increased.

Further, when 50% by mass of the fine iron ore was used as a molded product, the production rate of the sintered ore was greatly improved as compared with the case where the fine iron ore was used as it was. In particular, when the pulverization rate was 20% by mass, the production rate was almost the same as when the pulverized iron ore was not contained.

Next, the effect of improving the production rate when the fine powder ratio was increased was compared under the condition that the oxygen concentration was constant. FIG. 7 is a graph showing the relationship between the fine powder ratio of a particle size of 150 μm or less and the effect of improving the production rate of sinter when the oxygen concentration is increased to 24% by volume. In the graph shown in FIG. 7, the horizontal axis is the same fine powder ratio (mass%) as the horizontal axis of FIG. 6, and the vertical axis is the effect of improving the production rate of sinter (t / (h × m ² )). is there. The effect of improving the production rate of sinter means the production rate of sinter that is improved by using 50% by mass of fine iron ore as a molded product, and sintering when the ratio of the molded product is 50% by mass. It was calculated by taking the difference between the production rate of the ore and the production rate of the sinter when the molded product ratio was 0% by mass.

As shown in FIG. 7, the slope of the graph when the pulverization rate was higher than 10% by mass was larger than the slope of the graph up to the pulverization rate of 10% by mass or less. From this result, it was confirmed that by increasing the pulverization rate in the iron ore to more than 10% by mass, the effect of improving the production rate by forming 50% by mass of the pulverized iron ore into a molded product can be enhanced. It is more preferable that the pulverization rate in the iron ore is 15% by mass or more because the effect of improving the production rate can be further enhanced by forming 50% by mass of the pulverized iron ore into a molded product.

FIG. 8 is a graph showing the relationship between the oxygen concentration and the sinter production rate. In the graph shown in FIG. 8, the horizontal axis represents the oxygen concentration (% by volume) of the oxygen-enriched air, and the vertical axis represents the production rate of sinter (t / (h × m ² )). As shown in FIG. 8, when the fine powder ratio in the iron ore was 0% by mass, the production rate of the sinter increased as the oxygen concentration of the oxygen-enriched air increased. On the other hand, when the fine powder ratio in iron ore is 15% by mass and 7.5% by mass of fine iron ore is used as a molded product, the fine powder ratio in iron ore is 0, as in the case of 0. The production rate of sinter increases as the oxygen concentration of oxygen-enriched air increases, but by increasing the oxygen concentration to more than 23% by volume, the production rate of sinter increases significantly and contains fine iron ore. The production rate was close to the case without it. It is more preferable that the oxygen concentration is 24% by volume or more because the production rate of the sinter can be further improved.

As described above, when the ratio of fine powder in iron ore is 15% by volume or more and 50% by volume of the fine powder is used as a molded raw material, the oxygen concentration of oxygen-enriched air is more than 23% by volume. It was confirmed that the production rate of sinter can be greatly improved by increasing the temperature. If the ratio of fine powder in iron ore is higher than 50% by mass, the air permeability of the charge layer deteriorates and stable sintering may not be possible. Therefore, the fine powder ratio in the iron ore is preferably 50% by mass or less.

These results show that 50% by mass of fine iron ore is used as a molded product to improve the bond strength of the pseudo-particles, and the increase in oxygen concentration improves the flammability of the carbonaceous material, resulting in an increase on the particle surface. It is considered that this is because the temperature rate became faster, the surface sintering reaction proceeded in a short time, and the decay of the pseudo-particles was suppressed, thereby suppressing the decrease in the production rate of the sintered ore. In this example, 50% by mass of fine iron ore having a particle size of 150 μm or less is used as a molded product, but the present invention is not limited to this. If at least a part of the fine iron ore is made into a molded product, the pulverization of pseudo-particles can be suppressed and the decrease in the production rate of the sintered ore can be suppressed as compared with the case where the fine iron ore is used as it is without molding. Further, as the amount of fine iron ore used as a molded product increases, the pulverization of pseudo particles is suppressed and the decrease in the production rate of sinter is suppressed. Therefore, 50% by mass or more of the fine iron ore should be used as a molded product. Is more preferable.

As described above, when iron ore containing more than 10% by mass of fine iron ore having a particle size of 150 μm or less is used as a sinter raw material, the method for producing sinter of the present embodiment can be used. Deterioration of air permeability due to pulverization of pseudo-particles in which fine iron ore is agglomerated can be suppressed, and deterioration of sinter productivity can be suppressed. Further, in the method for producing a sinter of the present embodiment, while suppressing a decrease in productivity from a sinter raw material containing a large amount of pellet feed which is a difficult-to-granulate fine powder (particle size 150 μm or less) having a small slag component. Sintered ore can be produced, and by using the sintered ore as a raw material for blast furnace, it is possible to contribute to the reduction of the slag ratio in blast furnace operation.

1 Hopper 2 Drum Mixer 3 Drum Mixer 4 Molding Equipment 5 Surge Hopper 6 Drum Feeder 7 Cutout Chute 8 Cut Gate 9 Pallet 10 Charge Layer 11 Ignition Furnace 12 Wind Box (Wind Box)
13 Oxygen increasing device

Claims (4)

A sintering raw material containing iron ore and carbonaceous material is charged onto a pallet that circulates in the raw material supply section of the sintering machine to form a charging layer, and then arranged on the downstream side of the raw material supply section. The carbon material on the upper surface of the charging layer is ignited by the firing furnace, the gas above the charging layer is sucked by the wind box arranged below the pallet, and the gas is introduced into the charging layer. It is a method for producing sinter by burning the carbonaceous material of the charging layer.
The iron ore contains more than 10% by mass of fine iron ore having a particle size of 150 μm or less.
A part of the fine iron ore is made into a molded product and mixed with the sintered raw material.
A method for producing a sinter in which the oxygen concentration of the gas introduced into the charging layer is made higher than 23% by volume. The method for producing a sinter according to claim 1, wherein 50% by mass or more of the fine iron ore is made into a molded product and mixed with the sinter raw material. The method for producing a sintered ore according to claim 1 or 2, wherein the iron ore contains 15% by mass or more of fine iron ore having a particle size of 150 μm or less. The method for producing a sinter according to any one of claims 1 to 3, wherein the oxygen concentration of the gas introduced into the charging layer is 24% by volume or more.