Method for producing sintered ore

Abstract

To improve yield and productivity while maintaining reducibility of a sintered ore.SOLUTION: A method for producing a sintered ore by sintering a raw material packed bed, comprises: charging a sintering raw material granulated by adding moisture and a carbonaceous material to a pallet constituting a Dwight Lloyd (DL) type sintering machine to form the raw material packed bed; igniting the raw material packed bed from above; and sintering the raw material packed bed by sucking air from below. The sintering raw material contains a preliminary granulated product and a main granulated product which are granulated by a divided granulation method in which the preliminary granulated product and the main granulated product are granulated in different systems. The DL type sintering machine performs reignition by an ignition furnace and a reignition furnace, using the ignition furnace and the reignition furnace disposed on a downstream side of the ignition furnace at a predetermined interval. A distance d1 (mm) between the ignition furnace and the re-ignition furnace is set to be 2% to 10% of a length distance of the following L1. L1: machine length (mm)-a length of the ignition furnace in a pallet in a travel direction direction-a length of the reignition furnace in the pallet travel direction (mm)SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing sintered ore. [Background technology]

[0002] Currently, sintered ore is the primary raw material for blast furnace pig iron production. Sintered ore is typically produced as follows: First, iron ore, return ore, steelmaking dust, and other iron-containing raw material powders, carbonaceous materials, and auxiliary materials containing CaO are blended and mixed in predetermined proportions, and the resulting mixture is granulated or agglomerated to produce sintered ore. Next, the granulated or agglomerated sintered ore is placed on the pallet of a downward-suction-type Dwight Lloyd (DL) sintering machine, forming a sintered or agglomerated bed. The sintered or agglomerated ore is then ignited from the upper (surface) layer of the sintered ore bed by an ignition furnace. The pallet is then continuously moved, and oxygen is supplied by sucking air from below the pallet. The combustion of the carbonaceous materials in the sintered ore bed progresses from the upper layer to the lower layer, resulting in sequential sintering due to the heat of combustion. The resulting sintered ore (sinter cake) is then crushed and sieved to a predetermined particle size to produce sintered ore, the raw material for blast furnace pig iron production. In the above manufacturing process, granulation or agglomeration is performed in order to heat and sinter the sintered material by sucking in air during sintering. If the sintered raw material is not granulated, small pieces of sintered raw material will clog the gaps between the sintered raw materials, hindering air permeability and slowing down sintering.

[0003] However, with the recent depletion of high-quality iron ore, there is an increasing demand for a higher blend ratio of raw materials, such as fine powder, which is difficult to granulate and agglomerate, as sintering raw materials. If the amount of fine powder increases relative to the coarse powder during granulation, the fine powder that adheres to the coarse powder in the granules becomes excessive relative to the surface area of ​​the coarse powder and is prone to falling off. The fine powder that falls off from the coarse powder fills the gaps in the granules, inhibiting their breathability.

[0004] To address these issues, a separate granulation technique (pre-granulation technique) is known (see, for example, Patent Document 1 and Non-Patent Document 1). This technique involves granulating only the difficult-to-granulate raw materials, such as fine powder, separately from the easy-to-granulate coarse powder. The resulting granules are then mixed with the fine powder and charged into a sintering machine. This technique is described as pre-granulating the difficult-to-granulate raw materials under separate granulation conditions, which prevents the generation of fine powder due to the breakdown of the granules from the difficult-to-granulate raw materials and prevents the generated fine powder from blocking the gaps between the granules. This ensures permeability, improves the sintered bed permeability, and improves the FFS, thereby increasing productivity. This improved sintered bed permeability facilitates the retention of pores, making the sintered ore more porous (high porosity), and improving reducibility. This technique allows the production of sintered ore with excellent reducibility.

[0005] However, the improved permeability and increased combustion front descending speed achieved by separate granulation technology means that a large amount of air is supplied, causing the fuel to burn out quickly.If the fuel burns out quickly, the time available to heat the sintering raw material is effectively reduced, resulting in insufficient sintering and a decrease in product yield. Therefore, if the product yield can be maintained in the separate granulation method (pre-granulation technology), the productivity will be further improved. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-271949 [Non-patent literature]

[0007] [Non-Patent Document 1] Iron and Steel Vol.76(1990) No.10 P.1642-1649 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to improve the product yield and productivity in separate granulation methods. [Means for solving the problem]

[0009] The gist of the present invention to solve the above problems is as follows. [1] A method for producing sintered ore by sintering a raw material packed bed, which is formed by adding moisture and carbonaceous material and charging sintering raw material into a pallet constituting a Dwight Lloyd (DL) type sintering machine, and igniting the raw material packed bed from above, and sintering by sucking in air from below. The sintering raw material contains pre-granulated material and main granulated material, which are granulated by a separate granulation method in which granulation is performed in separate systems. The DL type sintering machine uses an ignition furnace and a re-ignition furnace located downstream of the ignition furnace at a predetermined distance, and performs re-ignition by the ignition furnace and the re-ignition furnace. The distance d1 (mm) between the ignition furnace and the re-ignition furnace is set to 2% to 10% of the following L1. The method for producing sintered ore is characterized in that the upper surface of the raw material packed bed is heated by the re-ignition furnace. L1: Machine length L2 (mm) - length of ignition furnace pallet in the direction of travel X1 - length of re-ignition furnace pallet in the direction of travel X2 (mm) [2] The method for producing sintered ore according to [1], characterized in that the ratio of the pre-granulated material to the total amount of the sintering raw material and the main granulated material is 5 to 30 mass% in terms of the inner percentage excluding the carbonaceous material and moisture. [3] The method for producing sintered ore according to [1], characterized in that the pre-granulated material is produced by granulating iron ore in which fine powder having a particle size of 0.5 mm or less accounts for 80 mass % or more of the total. [4] The method for producing sintered ore according to [3], wherein the iron ore is a magnetite-based fine iron ore. [5] The method for producing sintered ore according to [4], wherein the pre-granulated material is coated with fine carbonaceous material. [6] The method for producing sintered ore according to any one of [1] to [5], wherein ignition is started by the re-ignition furnace 0.5 to 2.5 minutes after completion of the ignition.

[0010] The details of how the problem was solved are explained below. In a DL-type sintering machine, when sintering is carried out in succession from the top layer to the bottom, the thermal distribution in the height direction of the raw material layer generally results in a sufficient amount of heat in the lower layer, but an insufficient amount of heat in the upper layer. This is because the temperature of the lower layer gradually rises as the firing of the upper layer progresses, and after it is sufficiently preheated, the carbonaceous materials such as coke begin to burn, and even after combustion is complete, it is gradually cooled by the residual heat of the upper layer, whereas the upper layer is rapidly cooled by the low-temperature air drawn in from the upper layer after combustion of the coke in the raw material is complete. If the upper layer does not receive enough heat, sintering will not proceed sufficiently in this area, causing the strength of the sintered ore in the upper layer to be insufficient and reducing the overall yield.

[0011] The inventors investigated the yield, cold strength, and reducibility of sintered ore under various conditions for heating the top surface of the raw material packed bed after ignition in an ignition furnace. As a result, they discovered that by providing an air suction area of ​​a predetermined range after ignition in an ignition furnace (hereinafter also referred to as initial ignition) is completed, and then re-igniting the top surface of the raw material packed bed again in a re-ignition furnace at a predetermined timing, both the yield and cold strength of the sintered ore can be improved while maintaining the reducibility. The re-ignition is performed to ignite the carbonaceous material (coke) that was not sufficiently ignited during the initial ignition and to sufficiently heat the upper layer to replenish heat. This technique of re-igniting at a predetermined interval after the initial ignition is hereinafter referred to as the re-ignition sintering method. According to the re-ignition sintering method, the space above the sintered bed is kept at a high temperature by a re-ignition furnace installed at a predetermined distance from the ignition furnace, and the air in the space above the sintered packed bed, which is kept at a high temperature, is drawn into the sintered bed. Therefore, there is no heat extraction from the top of the sintered bed, and instead, the sensible heat of the gas is used to supply heat to the raw materials in the sintered packed bed. This results in efficient heating by fuel, preventing poor sintering due to insufficient heat or insufficient high-temperature holding time, and is effective in improving the yield strength of the upper part of the sintered packed bed (upper layer). Since the yield of the upper layer, which had been lowering the overall yield, is improved, the overall yield is also improved.

[0012] This re-ignition sintering method, based on the principle of heating the upper layer, which is prone to insufficient sintering, can improve both the yield and cold strength of the sintered ore while maintaining reducibility, regardless of the type of sintering raw material, for normal sintering raw materials. Therefore, the re-ignition sintering method was applied to the separate granulation method, which has yield issues, with the aim of improving yield. As a result, it became clear that a synergistic effect between the separate granulation method and the re-ignition sintering method could be obtained, which exceeded expectations. [Effects of the Invention]

[0013] According to the present invention, in the separate granulation method in which a portion of the raw materials is granulated in a separate system, the permeability of the sintered packed bed is improved, thereby increasing productivity. Furthermore, by re-igniting the sintered packed bed in a re-ignition furnace at a predetermined interval after ignition and heating in the ignition furnace, the combustion zone advances to a lower position due to the increase in superficial air velocity during the air intake from the initial ignition to the re-ignition, and its thickness is expanded before re-ignition, resulting in a significant productivity improvement with an improved yield. As a result, an improvement in sintering yield and productivity can be achieved while maintaining reducibility. [Brief explanation of the drawings]

[0014] [Figure 1] Illustration of the re-ignition sintering method [Figure 2] Conceptual diagram of a sintering machine with a separate granulation process and re-ignition sintering method DETAILED DESCRIPTION OF THE INVENTION

[0015] (Divided granulation method) The characteristics of the separate granulation method will be explained with reference to FIG. In general granulation without separate granulation, powdered metal oxide (iron ore) is granulated in a single batch using a drum mixer 15 suitable for mass processing, along with other sintering raw materials, such as quicklime, silicon oxide, and coke powder, as well as fuel (carbonaceous materials such as coke), fine ore (pellet feed, etc.), and organic binders. Granulation can be strengthened by adding a separate process for granulating some of the sintering raw materials, such as fine ore (pellet feed, etc.), which tend to crumble during granulation. This additional process is called pre-granulation (or selective granulation), and the granules obtained by pre-granulation are referred to as pre-granulated material. Granulation other than pre-granulation is referred to as main granulation. For pre-granulation, it is also effective to use a high-speed agitating mixer 16 and a pan pelletizer 17 instead of a drum mixer. These mixers and other devices are designed to enhance granulation of fine ore (pellet feed, etc.) by independently adopting granulation conditions different from those of the main granulation process. However, because the throughput is lower than that of a drum mixer, when using these devices, the ratio of pre-granulated material to the total amount of sinter raw material is preferably 5% to 30% by mass (excluding carbonaceous materials such as coke and moisture). This is because the use ratio of fine raw material is usually within this range, the effects of the present invention cannot be fully achieved at a ratio less than 5%, and partial granulation of more than 25% requires excessively large equipment, making the investment in equipment unjustifiable. Furthermore, selecting fine raw material as the raw material for pre-granulation, such as PF (pellet feed) or Conc (concentrate: fine ore after ore dressing treatment), in which fine particles with a particle size of 0.5 mm or less account for 80% or more by mass of the total, results in a significant granulation effect. Selecting iron ore within this particle size range fully demonstrates the benefits of separate processing systems compared to granulation processing on a single granulation line. The proportion of particles with a particle size of 0.5 mm or less is measured as follows: The entire iron ore of a given brand is sieved through a 0.5 mm mesh sieve. The mass of the undersize iron ore divided by the total mass of the iron ore of the arbitrary brand is the ratio of particles with a particle size of 0.5 mm or less. The fine iron ore is preferably a magnetite-based fine ore. Since magnetite-based fine ore is more difficult to granulate than hematite-based fine ore, the effect of treating it in a separate system is fully realized. When magnetite-based fine iron ore is used as the fine iron ore, the surface of the pre-granulated granules may be further coated with fine carbonaceous materials with a particle size of 0.5 mm or less. Fine carbonaceous materials tend to become embedded in the granules, resulting in lower combustion efficiency than carbonaceous materials with a particle size exceeding 0.5 mm. However, using them as a coating layer on the pre-granulated granules can prevent embedding and improve combustion efficiency. Examples of fine carbonaceous materials include CDQ powder, collected dust from the cokemaking process, or blast furnace ash, which is dust discharged from the top of a blast furnace. A disk-type granulator is preferably used for the coating process. By feeding the pre-granulated granules and the fine carbonaceous materials into the disk-type granulator and rolling them, the surface of the granules can be coated with fine carbonaceous materials. Raw materials other than those used for pre-granulation can be processed in a conventional drum mixer for main granulation. A conventional drum mixer 15 is sufficient for main granulation. There are two methods for adding the pre-granulated material: before granulation of the main granulation raw material, and after granulation. Figure 2 shows the latter method.

[0016] (Reignition sintering method) Next, the re-ignition sintering method will be described with reference to Fig. 1. Details of the re-ignition sintering method are disclosed in Japanese Patent Application Laid-Open No. 2020-2457.

[0017] The re-ignition sintering method is characterized in that a re-ignition furnace 4 is provided downstream of an ignition furnace 2 in a sintering machine, spaced a predetermined distance from the ignition furnace 2, and an air suction zone 3 is formed between the ignition furnace 2 and the re-ignition furnace 4. The specific distance d1 (mm) must be 2% to 10% of the length L1 below. L1: Machine length L2 (mm) - length of ignition furnace pallet in the direction of travel X1 - length of re-ignition furnace pallet in the direction of travel X2 (mm)

[0018] The "atmospheric suction region 3" refers to the section (region) between the ignition furnace 2 and the re-ignition furnace 4 in the direction of pallet travel, where direct heating by a burner or the like is not performed from above and where atmospheric air is sucked in by downward suction. The machine length L2 refers to the length from the start point of the ignition furnace 2 (the most upstream point of the ignition furnace) to the sintering end point, which is the end of the wind box. In Figures 1 and 2, the combustion zone 5 is illustrated as a relatively very thick and large area. These figures are conceptual diagrams that are exaggerated in thickness to make them easier to understand, and the combustion zone 5 does not actually occupy the illustrated proportion of the raw material packed bed. (Embodiments of the present invention)

[0019] The present invention is a method for simultaneously carrying out the re-ignition sintering method and the separate granulation method described above, in which the timing for starting re-ignition is further limited to the above range, and the distance between the end point of initial ignition (end point of the ignition furnace) and the start point of re-ignition (start point of the re-ignition furnace) is set to 2% to 10% of the distance L1, which is set to 100%. The basis for this numerical limitation is based on the examples described below. By setting this range, the yield and productivity are improved simultaneously due to the synergistic effect of separate granulation.

[0020] In the present invention, as shown in Figure 2, some of the raw materials are granulated in a separate system, thereby increasing the particle size of the resulting granules and improving the permeability of the sintered bed. As a result, productivity is improved. Meanwhile, the increase in superficial air velocity in the air suction zone 3, located between the ignition furnace 2 and the re-ignition furnace 4, further expands the combustion zone 5, especially in the upper layer. This action improves the yield. In other words, both the yield and productivity are improved. [Example]

[0021] The effectiveness of the method of the present invention was confirmed in a pot test. In the pot test, sintering is carried out under conditions simulating those of a DL sintering machine. Although there is no moving conveyor like in a DL sintering machine, the sintering raw materials including fuel are charged into a container of a specified size that can be sucked downward, and the material is ignited from above, and sintering proceeds by sucking downward. 1. Synergistic effect by utilizing the reignition sintering method The reignition effect in separate granulation was confirmed by pot tests. (Preparation of blended raw materials) Table 1 shows the blending conditions of the sinter raw materials used for granulation. Blend 1 was a normal lump-granulation test, while Blend 2 (adding 5% pre-granulated material in the inner blend) and Blend 3 (adding 30% pre-granulated material in the inner blend) were tests in which separate granulation was performed with pre-granulation and main granulation in separate systems. The coke fine blending rate was 4.5 mass% (outer blend) in all cases. Here, the lump granulation of Blend 1 and the main granulation of Blends 2 and 3 were put into a drum mixer and mixed for 4 minutes. Then, a predetermined amount of water was added, and the mixture was mixed for another 4 minutes. On the other hand, for the preliminary granulation, the material was put into a high-speed agitating mixer together with a specified amount of water, mixed for 1 minute, and then granulated for 5 minutes using a pan pelletizer. For Blends 2 and 3, the granules obtained by the main granulation and the granules obtained by the preliminary granulation were mixed for 15 seconds using a drum mixer to prepare the samples. The particle size distributions of hematite A, limonite B, limonite C, hematite D, pellet feed (PF) E, and pellet feed F are shown in Table 2. Among the six types of ore mentioned above, hematite D and pellet feed (PF) E, which have the finest particles, are blended to strengthen granulation and improve permeability, thereby improving the sintering rate. This improves both productivity and reducibility.

[0022] [Table 1]

[0023] [Table 2]

[0024] For each compound, test cases were conducted with and without re-ignition. In the cases where re-ignition was conducted, the re-ignition time was set to 1 minute after the completion of initial ignition. 1 minute after the completion of initial ignition corresponds to the timing of re-ignition being initiated after a distance interval of 4% of L1 from the position where initial ignition was completed. The pot test equipment had dimensions of 300 mm in diameter and 500 mm in height, and sintering was carried out at a constant negative pressure of 1300 mmAq from below. The initial ignition time and re-ignition time were both 1 minute. The heat amount imparted to the sintered material by 1 minute of initial ignition and 1 minute of re-ignition was 25 MJ / ton of raw material, respectively. The ignition conditions for initial ignition and re-ignition are shown in Table 3. The numbers in parentheses for initial ignition, re-ignition, and interval indicate the heating time or rest time. (1) means 1 minute of heating or 1 minute of interval. Initial ignition and re-ignition indicate the start and end times of heating, with the initial ignition time set to 0 minutes. An initial ignition time of 0-1 means that initial ignition started at the initial ignition start time (0 minutes) and ended 1 minute after the initial ignition start time (0 minutes). Similarly, a re-ignition time of 2-3 means that re-ignition started 2 minutes after the re-ignition start time (0 minutes) and ended 3 minutes after the re-ignition start time (0 minutes). Interval 1-2 means that the heating pause time started 1 minute after the initial ignition start time (0 minutes), and the pause time ended 2 minutes later, at which point re-ignition started.

[0025] [Table 3]

[0026] The negative suction pressure during firing was controlled to a constant 1300 mmAq as measured below the pot, and the suction of the blower was stopped three minutes after the exhaust gas temperature reached its peak. The resulting sintered cake was dropped four times from a height of 2 m, and the sintered product was made up of particles with a particle size of +5 mm or more, excluding the bedding ore. The product yield was defined as the weight of the sintered product divided by the weight of the sinter cake excluding the bedding ore. The reducible RI of the resulting sintered product was also measured. The productivity was calculated by dividing the amount of product by the sintering time and the area of ​​the bottom of the pot, using the sintering time as the time required from the start of ignition until the exhaust gas temperature reached its peak.

[0027] Table 3 shows the results of the flame front speed (FFS), product yield, productivity, and reducibility RI. The combustion front descent velocity improved in Blends 2 and 3, in which some raw materials were granulated separately (pre-granulation). It was especially high in Blend 3, in which fine powder ore (PF)E was pre-granulated. This reflects the improvement in permeability of the sintered layer due to the strengthened granulation. The product yield improved with re-ignition for all blends 1, 2, and 3. The effect was particularly significant for blends 2 and 3, in which some of the raw materials were granulated in a separate system (pre-granulation). When comparing Blends 1, 2, and 3 only in the case of no reignition, Blend 1 had the highest product yield and Blend 3 had the lowest. This reflects the general tendency that when the combustion front descent speed is fast, the sintering time becomes shorter, resulting in a lower product yield. As mentioned above, the improvement in product yield due to re-ignition increases the higher the FFS. As a result, when comparing blends 1, 2, and 3 with only re-ignition, the difference in product yield is small. In other words, re-ignition can suppress the decrease in product yield when the FFS is increased by strengthening the granulation of sintering raw materials, etc. As a result, when some raw materials were granulated in a separate system (pre-granulation) and then re-ignited, the productivity improved significantly. It was also confirmed that the reducibility was maintained even after re-ignition. From the above, in a process in which some of the raw materials are granulated in a separate system, the effect of re-ignition on improving product yield is greater than in a process in which all of the raw materials are granulated at once, and productivity is also improved.

[0028] 2. Effect of reignition conditions Next, the effect of changing the re-ignition conditions will be described. We conducted a pot test in which the re-ignition time was changed to 0.5, 2.5, and 3.5 minutes after the completion of ignition. These re-ignition timings correspond to 2%, 10%, and 14% of the distance L1 in the actual machine. The pot test equipment had dimensions of 300 mm in diameter and 500 mm in height, and sintering was carried out at a constant negative pressure of 1300 mmAq from below. The negative suction pressure during firing was adjusted by adjusting the valve opening on the blower suction side so that the measured value below the pot was constant at 1300 mmAq. Temperature measurements were also taken below the pot with a thermocouple, along with the pressure. During sintering, when the combustion zone reached the bottom of the sintered layer, the temperature below the pot began to rise, eventually peaking, and then decreasing as the coke combustion was completed. The blower suction was stopped three minutes after this exhaust gas temperature peak. The sintering time was defined as the time from the start of ignition to the peak of the exhaust gas. The ignition and re-ignition times were both 1 minute (heat amount 25 MJ / ton of raw material).

[0029] The test cases are listed in Table 4. The granules in Table 4 with a preliminary granulation ratio of 0% (lump granulation) and those with preliminary granulation ratios of 5% and 30% were placed in a drum mixer and mixed for 4 minutes. Next, a predetermined amount of water was added, and the mixture was mixed for another 4 minutes. On the other hand, the preliminary granules were placed in a high-speed agitating mixer together with the predetermined amount of water, mixed for 1 minute, and then granulated for 5 minutes in a pan pelletizer. At preliminary granulation ratios of 5% and 30%, the granules obtained by the main granulation and the granules obtained by the preliminary granulation were mixed for 15 seconds in a drum mixer to prepare the samples.

[0030] After firing, the sintered cake was dropped four times from a height of 2 m, and the sintered product was made up of particles with a particle size of 5 mm or more, excluding the bedding ore. The product yield was defined as the weight of the sintered product divided by the weight of the sintered cake excluding the bedding ore. The reducible RI of the resulting sintered product was also measured. The production rate was calculated by dividing the amount of product by the sintering time and the area of ​​the bottom of the pot, taking the time required from the start of ignition until the exhaust gas temperature reached its peak as the sintering time. In Table 4, the production rate is calculated as the production rate per unit area of ​​the sintering machine (t / Dm 2 (tons per square meter per day).

[0031] Table 4 shows the results of the combustion front descent velocity, product yield, productivity, and reducibility RI. The flame front velocity was improved in the pre-granulated case, which reflects the improved permeability of the sintered layer due to the enhanced granulation. The product yield decreased when the interval between initial ignition and re-ignition was 14%. This decrease reflects the general tendency that when the flame front descending speed is fast, the sintering time becomes shorter, resulting in a decrease in product yield. On the other hand, when the interval between initial ignition and re-ignition was 2% and 10%, the product yield was maintained. This was due to the optimization of the interval between initial ignition and re-ignition. As mentioned above, when the interval between initial ignition and re-ignition is less than 2%, the necessary length of air suction region 3 cannot be secured, and the high-temperature holding time of 1100°C or higher, which is sufficient to promote sintering, cannot be secured at the top surface of the raw material packed bed 1, and the high-temperature holding time becomes shorter, resulting in a decrease in yield. As a result, the production rate improved significantly when the interval between the first ignition and the re-ignition was 2% and 10%. It was confirmed that reducibility was maintained in all cases. From the above, by optimizing the interval between the initial ignition and re-ignition, a significant improvement in productivity was achieved through separate granulation.

[0032] [Table 4]

[0033] 3. Effect of using magnetite-based fine ore and coating of granulated material with fine carbonaceous material In addition to Example 7, similar pot tests were conducted in the case where the pre-granulated material was pellet feed F (magnetite fine ore) and in the case where fine carbonaceous materials (CDQ powder) were added during granulation in the pan pelletizer. The results are shown in Table 5 as Example 8 and Example 9, respectively. When magnetite-based fine ore and fine carbonaceous materials were used, the amount of coke powder listed in Table 1 was reduced so that the total heat generated by the combustion of the carbonaceous materials and the oxidation heat of magnetite would be roughly constant.

[0034] [Table 5]

[0035] In Example 8, an even higher product yield was obtained compared to Example 7. It is believed that the magnetite-based fine ore was oxidized during firing and changed to hematite, generating heat, which further promoted the melting and assimilation of the granulated material in the preliminary granulation system, thereby increasing the product yield. In Example 9, a higher product yield was obtained than in Example 8. It is presumed that the ignition of the coated fine carbonaceous materials caused the temperature near the surface of the granules to rise, and the reoxidation of the magnetite-based fine ore proceeded more efficiently.

[0036] In this example, both the initial ignition time and the re-ignition time were 1 minute, but the invention is not limited to these values. The reason is that the ignition time in the example takes into account the heat loss in the pot test. In a practical (commercial) sintering machine, for example, if the initial ignition time is 30 seconds, there is no need to set this initial ignition time to 1 minute; re-ignition can be performed by maintaining the ignition time of the actual operation. Furthermore, the re-ignition time does not need to be 1 minute in a practical machine. [Industrial Applicability]

[0037] In a method for producing sintered ore, after initial ignition in an ignition furnace, an air suction area is provided at a predetermined interval, and re-ignition is performed in a re-ignition furnace, thereby providing a method for producing sintered ore that improves the product yield of the sintered ore without reducing the reducibility of the sintered ore.This method allows for constant product yield operation, thereby reducing the amount of coke fines and the like mixed, and therefore reducing fuel costs. Furthermore, if some of the raw materials are granulated in a separate system (pre-granulation) and then re-ignited, the product yield can be further improved, and the productivity can also be improved. [Explanation of symbols]

[0038] 1...raw material packed bed, 2...ignition furnace, 3...atmospheric suction zone, 4...re-ignition furnace, 5...combustion zone, 6...sintered bed, 7...hopper, 8...hood, 15...drum mixer, 16...high-speed agitating mixer, 17...pan pelletizer

Claims

1. A method for producing sintered ore, comprising: charging granulated sintering raw materials, which have been prepared by adding moisture and carbonaceous material, into a pallet constituting a Dwight Lloyd (DL) type sintering machine, to form a raw material packed bed; igniting the raw material packed bed from above; and sucking in air from below to sinter the raw material packed bed; The sintering raw material contains a pre-granulated material and a main granulated material, each of which is granulated by a separate granulation method in which granulation is performed in a separate system, The DL-type sintering machine uses an ignition furnace and a re-ignition furnace arranged downstream of the ignition furnace at a predetermined interval, and performs re-ignition by the ignition furnace and the re-ignition furnace, A method for producing sintered ore, characterized in that the distance d1 (mm) between the ignition furnace and the re-ignition furnace is set to 2% to 10% of the length L1 described below, and the upper surface of the raw material packed bed is heated by the re-ignition furnace. L1: Machine length L2 (mm) - length X1 of the ignition furnace in the direction of pallet travel - length X2 of the re-ignition furnace in the direction of pallet travel (mm)

2. 2. The method for producing sintered ore according to claim 1, wherein the ratio of the pre-granulated material to the total amount of the sintered raw material and the main granulated material is 5 to 30 mass% in terms of inner percentage excluding carbonaceous material and moisture.

3. 2. The method for producing sintered ore according to claim 1, wherein the pre-granulated material is obtained by granulating iron ore in which fine powder having a particle size of 0.5 mm or less accounts for 80 mass % or more of the total.

4. 4. The method for producing sintered ore according to claim 3, wherein the iron ore is a magnetite-based fine iron ore.

5. 5. The method for producing sintered ore according to claim 4, wherein the pre-granulated material is coated with fine carbonaceous material.

6. The method for producing sintered ore according to any one of claims 1 to 5, wherein ignition is started by the re-ignition furnace 0.5 to 2.5 minutes after completion of the ignition.

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