Method for manufacturing sintered ore

Abstract

The present invention provides a method for producing sintered ore that suppresses a decrease in the yield of the finished product in the lower layer of the sintered layer. [Solution] A method for producing sintered ore in a Dwight-Loyd type sintering machine, wherein in a sintered strand subjected to downward suction by a wind box, the length in the strand direction from a first position at the downstream end of the ignition furnace to a second position at the end of the wind box closest to the ore discharge section is L, and when the first position is set to 0 and the second position to L, the suction negative pressure in the range from 0.75L to L is made smaller than the suction negative pressure in the range from 0.25L to 0.75L.

Description

Technical Field

[0001] The present application relates to a method for producing sintered ore.

Background Art

[0002] In a Dwight-Lloyd (DL) type sintering machine, sintering is sequentially performed by downward suction from the upper layer to the lower layer of a raw material bed. It is known that the lower the air volume of downward suction, the longer the sintering reaction time becomes, which improves the product yield and the strength of the sintered ore. However, the lower the suction air volume, the lower the sintering rate and the lower the productivity. Therefore, conventionally, instead of reducing the overall air volume, the air volume is reduced in the first half of sintering when the sintering of the upper layer progresses. This is because this was effective for improving the product yield of the upper layer, which is known as a fragile layer. On the other hand, the lower layer is considered to tend to have excessive heat due to the supply of heat from the upper layer. Therefore, it has been considered desirable to increase the suction air volume in the second half of sintering, when the sintering of the lower layer progresses. For example, Non-Patent Document 1 and Non-Patent Document 2 describe a method for producing sintered ore in which the suction air volume in the first half of sintering is reduced and the suction air volume in the second half of sintering is increased.

[0003] In addition, different from these, Patent Document 1 also describes an air volume control method for a sintering machine, in which the firing reaction in the sintering machine is divided into an initial stage, a middle stage, and a final stage, and the suction negative pressure is reduced compared to that in normal operation in the initial stage and the final stage, and increased in the middle stage.

Prior Art Literature

Patent Literature

[0004]

Patent Literature 1

Non-Patent Literature

[0005]

Non-Patent Literature 1

Non-Patent Literature 2

[0006] As sintering progresses, the airflow resistance tends to decrease, and when firing is performed with a constant suction negative pressure, the airflow may increase during the firing of the lower layers. If cooling becomes excessive due to the increased airflow, the yield of the lower layers may decrease. Furthermore, as described in Non-Patent Documents 1 and 2, increasing the suction airflow during the firing of the lower layers, i.e., in the latter half of the sintering machine, can reduce the yield of the lower layers and thus the overall yield. Also, as described in Patent Document 1, reducing the suction airflow in the section immediately before the completion of firing (final stage) did not sufficiently improve the yield of the lower layers. Moreover, in recent years, segregation charging and other methods have caused uneven distribution of carbon material in the raw material layer, which can lead to a decrease in the yield of the lower layers, but airflow distribution control that takes this into account has not been considered in any of these cases.

[0007] The present invention aims to provide a method for producing sintered ore that suppresses a decrease in the yield of the finished product in the lower layer of the sintered layer. [Means for solving the problem]

[0008] This application was made to solve the above-mentioned problems, and its gist is as follows.

[0009] (1) A method for producing sintered ore in a Dwight-Royd type sintering machine, wherein in a sintered strand subjected to downward suction by a wind box, the length in the strand direction from a first position at the downstream end of the ignition furnace to a second position at the end of the wind box closest to the ore discharge section is L, and when the first position is set to 0 and the second position to L, the suction negative pressure in the range from 0.75L to L is made smaller than the suction negative pressure in the range from 0.25L to 0.75L.

[0010] (2) The method for producing sintered ore according to (1), characterized in that when the sintering raw material layer in the Dwight-Loyd type sintering machine is divided into an upper layer, a middle layer, and a lower layer in the thickness direction, the mass fraction of carbon material in the lower layer of sintering raw material is less than the mass fraction of carbon material in the entire sintering raw material layer.

[0011] (3) The method for producing sintered ore according to (1), characterized in that the sintering raw material charged into the Dwight-Loyd sintering machine contains 35% by mass or more of highly crystalline water ore containing 5% by mass or more of crystalline water.

[0012] (4) The method for producing sintered ore according to (1), characterized in that the suction negative pressure in the range from 0 to 0.25 L, which is the first position, is made smaller than the suction negative pressure in the range from 0.25 L to 0.75 L.

[0013] (5) The method for producing sintered ore as described in (1) above, characterized in that the suction negative pressure in the range from 0.75 L to L is set to 70% or more and 95% or less, when the suction negative pressure in the range from 0.25 L to 0.75 L is set to 100%.

[0014] (6) A method for producing sintered ore, characterized in that, in a Dwight-Loyd type sintering machine, in a sintered strand subjected to downward suction by a wind box, the length in the strand direction from a first position at the downstream end of the ignition furnace to a second position at the end of the wind box closest to the ore discharge section is L, and when the first position is set to 0 and the second position to L, the suction wind velocity in the range from 0.75L to L is made smaller than the suction wind velocity in the range from 0.25L to 0.75L. [Effects of the Invention]

[0015] According to this application, it is possible to provide a method for producing sintered ore that suppresses a decrease in the yield of the finished product in the lower layer of the sintered layer. [Brief explanation of the drawing]

[0016] [Figure 1]It is a diagram illustrating the configuration of a sintering machine that produces sintered ore by the method for producing sintered ore according to the present embodiment. MODE FOR CARRYING OUT THE INVENTION

[0017] (First Embodiment) The method for producing sintered ore according to the present embodiment will be described with reference to the drawings. Fig. 1 is a diagram showing an example configuration of a sintering machine 1 that produces sintered ore using the method for producing sintered ore according to the present embodiment. The sintering machine 1 is a Dwight-Lloyd (DL) type sintering machine. The sintering machine 1 includes a charging device 2, an ignition furnace 4, a pallet (strand) 6, wind boxes 8, exhaust branch pipes 10, dampers 12, a main exhaust pipe 14, a main exhaust fan 16, and the like. A plurality of the wind boxes 8, the exhaust branch pipes 10, and the dampers 12 are arranged below the pallet 6 in the strand direction A indicated by the arrow. In the sintering machine 1, a sintering raw material is continuously charged from the charging device 2 onto the pallet 6 to form a sintering raw material layer B. The pallet 6 is driven by sprocket wheels on both sides to move in the strand direction A (the traveling direction of the pallet). The surface of the sintering raw material layer B is ignited in the ignition furnace 4, and air is sucked below the pallet 6 by the wind boxes 8. A sintering reaction proceeds from the upper layer to the lower layer of the raw material layer by the air flow generated by this downward suction and passing downward through the sintering raw material layer B. The sintering reaction is completed before reaching the ore discharge section 20 to form a sintered layer, which is discharged from the ore discharge section 20 as sintered ore. Note that in the following description, the sintering raw material layer B may be referred to as the sintered layer B.

[0018] The sintering raw material charged into the sintering machine 1 includes a new raw material, return fines, and a coagulant. The new raw material is a raw material newly input into the sintering process, and includes iron ore, miscellaneous raw materials, auxiliary raw materials, and a granulating agent. The miscellaneous raw materials are recycled raw materials generated in an ironworks, such as sintering dust and scale. The auxiliary raw materials are raw materials for adjusting the CaO and MgO contents of the sintered ore, such as limestone, peridotite, and dolomite. The return fines are sintered ore that is not used for a blast furnace, and are undersize powder obtained when sieving sintered ore. The coagulant is a carbonaceous material. The carbonaceous material includes coke breeze, biomass charcoal, coal char, and the like.

[0019] Next, the flow of the method for producing sintered ore according to the present embodiment will be described. In the method for producing sintered ore of the present embodiment, among the sinter strands subjected to downward suction by a wind box 8 in a DL-type sintering machine 1, in the strand direction A, from a first position at the downstream end of an ignition furnace 4 to a second position which is the position of the end of the wind box 8 closest to the ore discharge portion 20 side, when the length of the sinter strand between the two positions is defined as L, the first position is set to 0 and the second position is set to L, sintered ore is produced by setting the suction negative pressure in the range from 0.75L to L to be lower than the suction negative pressure in the range from 0.25L to 0.75L. A detailed description will be given below.

[0020] First, the "sinter strand" refers to the portion of pallets 6 charged with raw material that is subjected to downward suction by the wind box 8. For example, in the case of Fig. 1, it is the range from near the lower part of the charging device 2 where the wind box 8 is arranged to the front side of the ore discharge portion 20.

[0021] In the present embodiment, a predetermined range of the sinter strand is divided into three sections. As described above, the predetermined range is the range in the strand direction A of the pallets 6 from the position of the downstream end of the ignition furnace 4 (the first position) to the position of the end of the wind box 8 closest to the ore discharge portion 20 side (the downstream side) (the second position). When the length of this predetermined range is defined as L, the first position is set as the 0 position, and the second position is set as the L position, the predetermined range is divided into three ranges as follows. That is, 1) A first range from 0 to 0.25L 2) A second range from 0.25L to 0.75L 3) A third range from 0.75L to L These are the three divisions. These three ranges can be expressed as follows when the sintered raw material layer B is divided into three equal parts in the thickness direction (upper layer, middle layer, and lower layer): The range that mainly corresponds to the firing of the upper layer of the sintered strand can be expressed as the range from 0 to 0.25L (first range), the range that mainly corresponds to the firing of the middle layer of the sintered strand can be expressed as the range from 0.25L to 0.75L (second range), and the range that mainly corresponds to the firing of the lower layer of the sintered strand can be expressed as the range from 0.75L to L (third range). In other words, the sintering (firing) of the upper layer mainly proceeds in the first range. The sintering (firing) of the middle layer mainly proceeds in the second range. The sintering (firing) of the lower layer mainly proceeds in the third range.

[0022] More specifically, the first range is the stage where the firing of the upper layer begins after ignition. In the first range, there is no burnt (burning) portion above it, so there is no heat supply from above, resulting in insufficient heat and a tendency for the yield of finished products to decrease. The third range is the stage where a part of the combustion zone reaches the bottom surface of the sintered layer, causing a rapid decrease in airflow resistance and a rapid increase in airflow. This part of the combustion zone is the part of the sintered raw material layer B where firing progresses rapidly, such as the area around the sidewall of pallet 6. The second range is the stage where the firing of the middle layer mainly progresses, and it is unaffected by the phenomena occurring in the first range (upper layer firing) and the third range (lower layer firing) as described above, and sintering proceeds steadily. Based on the inventors' studies using sintering tests and other methods, it was found that the positions in the sintered strand corresponding to each of the above firing stages (ranges in the total firing time) are in the ranges of 0 to 0.25L, 0.25L to 0.75L, and 0.75L to L.

[0023] In this embodiment, the suction negative pressure from the windbox 8 in the third range from 0.75L to L is made smaller than the suction negative pressure in the second range from 0.25L to 0.75L. The suction negative pressure can be adjusted by changing the opening of the damper 12. Reducing the opening of the damper 12 reduces the suction negative pressure, while increasing the opening increases it. The damper 12 is located in the middle of each exhaust branch pipe 10 connecting the windbox 8 and the main exhaust pipe 14, and its opening can be adjusted independently. Reducing the damper opening causes pressure loss. As a result, the absolute value of the pressure inside the windbox 8 becomes smaller than the absolute value of the pressure inside the main exhaust pipe 14, and the suction negative pressure decreases. Therefore, by reducing the opening of the damper 12 in the third range from 0.75L to L compared to the opening of the damper 12 in the second range from 0.25L to 0.75L, the suction negative pressure in the third range can be reduced compared to the second range. The suction negative pressure in the third range can be kept constant at the set suction negative pressure, but if the suction negative pressure in the third range is lower than the suction negative pressure in the second range, the suction negative pressure may be changed in stages rather than kept constant.

[0024] Furthermore, the suction negative pressure in the first range is not particularly limited, but it can be the same as the suction negative pressure in the second range, or lower than the suction negative pressure in the second range (as described in the third embodiment below). The suction negative pressures in the first and second ranges can also be kept constant at the set suction negative pressure.

[0025] The suction negative pressure in the third range can be set to 70% to 95% of the suction negative pressure in the second range, with the suction negative pressure in the second range being set to 100%. By reducing it by this ratio, it is possible to improve the yield of the lower layer product while suppressing the decrease in sintering speed and production rate. Furthermore, the suction negative pressure in the third range can be set to 90% to 95% of the suction negative pressure in the second range. In this case, it is possible to further suppress the decrease in sintering speed and production rate while improving the yield of the lower layer product. The suction negative pressure in the second range is usually constant, and in that case, it can be determined by measuring the suction negative pressure of a representative window box within the second range. The suction negative pressure in the second range can be the suction negative pressure under normal operating conditions in the sintering machine 1. Also, when the suction negative pressure is changed within the second range, the average value of the suction negative pressures of multiple window boxes within the second range may be used.

[0026] Furthermore, since there is a correspondence between suction negative pressure and suction airflow rate, the method of this embodiment can also be expressed by replacing suction negative pressure with suction airflow rate. Specifically, the relationship between suction negative pressure and suction airflow rate is shown in equation (1) below. In equation (1), JPU is an index representing the airflow resistance of the sintered raw material layer, and is a value determined by the raw material conditions and granulation conditions. JPU = F / A × (h / s) 0.6 (1) Here, F: flow rate (suction airflow) [Nm³] 3 / min], A: Suction area [m 2 ], h: charging layer thickness [m], s: suction negative pressure [m H2O] (3rd edition Iron and Steel Handbook, Vol. II, Ironmaking and Steelmaking, 2. Sintering, p. 86). If suction negative pressure is replaced with suction airflow, the method of this embodiment can be a method for producing sintered ore by making the suction airflow in the third range smaller than the suction airflow in the second range.

[0027] The suction airflow rate in the sintering material layer B can be determined from the flow rate measured by flow meters placed in the windbox 8 or exhaust pipe 10, respectively. Specifically, the flow rate in the windbox 8 (or exhaust pipe 10) includes the suction airflow rate at the surface of the sintering material layer plus water vapor, carbon dioxide, and leak air generated during the firing process. Therefore, by knowing this increment in advance, the suction airflow rate drawn into the sintering material layer B can be determined by subtracting this increment from the flow rate measured in the windbox 8, etc. This suction airflow rate can be changed by changing the opening of the damper 12, making the suction airflow rate in the third range smaller than the suction airflow rate in the second range.

[0028] The suction airflow in the third range can be set to 81% to 97% of the suction airflow in the third range during normal operation, with the suction airflow in the third range during normal operation being set to 100%. The suction airflow in the third range during normal operation can be determined in advance by measurement. The reduction ratio (81% to 97%) relative to the above standard airflow can be determined by converting (raising to the power of 0.6) the reduction ratio (70% to 95%) relative to the suction negative pressure in the second range, which was used as an example of the suction negative pressure in the third range, using the above formula (1). Alternatively, the airflow ratio during normal operation (= suction airflow in the third range / suction airflow in the second range) can be determined in advance, and the suction airflow in the third range can be calculated by multiplying the suction airflow in the second range by the airflow ratio and then by the reduction ratio (81-97%).

[0029] Furthermore, since F / A in equation (1) above is the suction wind velocity, the suction negative pressure can also be replaced with the suction wind velocity, which is the wind velocity of the air drawn into the sintering raw material layer B. That is, a method can be used to produce sintered ore by making the suction wind velocity in the third range smaller than the suction wind velocity in the second range. The wind velocity can be measured on the surface of the sintering raw material layer B using a known wind velocity measuring device (for example, as described in Japanese Utility Model Publication No. 58-030198 or in Yoshinaga Mayumi: "Trends in Sintered Ore Manufacturing Technology," 116th Nishiyama Memorial Technical Lecture of the Iron and Steel Institute, February 19, 1987, p. 109, etc.). Alternatively, the wind velocity may be determined from the suction air volume mentioned above.

[0030] By controlling the suction negative pressure as described above, the suction negative pressure in the third range can be made smaller than in the second range, thereby slowing down the combustion reaction of the carbon material at the corresponding height (lower layer) of the sintering raw material layer B and reducing the sintering rate. A decrease in the sintering rate extends the time the lower layer is exposed to high temperatures. This improves the yield of the finished product in the lower layer. It also improves the cold strength. As mentioned above, the lower layer has the largest airflow and is prone to excessive cooling. Therefore, reducing the suction negative pressure in the corresponding range of sintered strands is considered effective in improving yield.

[0031] Furthermore, the sintering ore manufacturing method of this embodiment can be implemented when i) the mass fraction (%) of carbon material in the lower layer of sintering raw material is less than the mass fraction of carbon material in the entire sintering raw material layer, or when non-uniform firing occurs. Under these conditions, the yield of the finished product in the lower layer tends to decrease. Therefore, by applying the sintering ore manufacturing method of this embodiment, the decrease in the yield of the finished product in the lower layer can be suppressed more effectively.

[0032] First, i) In cases where the mass fraction of carbon material in the lower layer is less than the total mass fraction of carbon material, examples include segregation charging and multi-stage charging. Segregation charging is a method of charging by segregating the particle size and amount of carbon material in the thickness direction of the sintering raw material layer. Due to segregation charging, carbon material tends to segregate to the upper layer, so the concentration distribution of carbon material in the lower layer becomes smaller than the overall distribution. Segregation charging can be performed using a segregation charging device. Examples of segregation charging devices include slit bar type charging devices (Ohne et al., Materials and Process 10 (1997), p. 191, Iron and Steel Institute of Japan), slit wire type charging devices (Takai et al., Materials and Process 6 (1993), p. 916), rectifying and dispersing type ISF (Intensified Sifting Feeder) type charging devices (Nagai et al., Materials and Process 29 (2016), p. 563), hybrid magnetic segregation charging devices (Oyama et al., Materials and Process 11 (1998), p. 225), and wind segregation devices (Shibata et al., Materials and Process 14 (2001), p. 193). When sintering raw materials are charged into the sintering machine 1 using these segregation charging devices, if the carbon material segregates to the upper layer and the concentration of carbon material in the lower layer is lower than the overall concentration, the yield of the finished product in the lower layer may decrease. Therefore, when using segregation charging, the method of this embodiment can effectively suppress the decrease in the yield of the lower layer.

[0033] The mass fraction of carbon material in the lower layer can be determined by extracting a portion of the charged sintered raw material layer B and measuring the mass of all raw materials and the mass of carbon material alone in the lower layer. The mass fraction of carbon material in the entire raw material (all layers) can be determined from the blending ratio of the sintered raw materials to be charged.

[0034] Multi-stage charging is a charging method in which multiple charging devices are arranged, and raw materials are charged from each charging device to form a sintered raw material layer B. In multi-stage charging, if the mass fraction (concentration) of carbon material in the lower layer is made lower than the mass fraction of carbon material in the total raw materials, the yield of the finished product in the lower layer may decrease. Even in such cases, the decrease in the yield of the finished product in the lower layer can be effectively suppressed by producing sintered ore using the method of this embodiment.

[0035] Next, ii) non-uniform firing occurs when the raw materials contain a large amount of ore with a high amount of crystalline water, such as pisolite (high-crystallinity ore). Hereafter, this case will also be referred to as "high-crystallinity ore content". This non-uniform firing occurs when there are regions where there is an excess of molten metal (over-melting) and the airflow resistance increases, or regions where the airflow resistance decreases, such as near the side walls of the sintering machine 1. The presence of such regions increases the amount of heat removed from the combustion zone of the sintering raw material layer B, which tends to reduce the yield of the finished product in the lower layer. In particular, when there is a high proportion of high-crystallinity ore such as pisolite, the dissociation reaction of crystalline water causes numerous cracks to occur, making melting easier, which leads to non-uniform firing due to localized over-melting and reduces the yield of the finished product. Specifically, high-crystallinity ore content refers to a case where the sintering raw material (blended raw material) charged into the sintering machine 1 contains 35% or more by mass of iron ore powder containing 5% or more by mass of crystalline water (i.e., high-crystallinity ore). In this case, uneven firing may occur, potentially reducing the yield of the lower layer, making the method of this embodiment preferable. Furthermore, the high-crystallinity water ore content may also be such that the sintering raw material charged into the sintering machine 1 contains 35% by mass or more of iron ore powder containing 8% by mass or more of crystalline water. Alternatively, the high-crystallinity water ore content may also be such that the sintering raw material charged into the sintering machine 1 contains 40% by mass or more of iron ore powder containing 5% by mass or more of crystalline water. In these cases, uneven firing is even more likely to occur, and the method of this embodiment is even more preferable because it further improves the yield of the lower layer.

[0036] As described above, the method of this embodiment can more effectively suppress the decrease in the yield of the lower layer by being implemented under conditions where the mass fraction of carbon material in the lower layer is less than the mass fraction of carbon material in the entire sintering raw material layer, or under conditions where uneven firing occurs.

[0037] (Second embodiment) In the first embodiment, the suction negative pressure was adjusted by changing the opening degree of the damper 12 corresponding to each window box 8. In contrast, the method of this embodiment has multiple blowers in the sintering machine 1, each separately suctioning from the first to third ranges. The suction negative pressure is adjusted in the same way as in the first embodiment by changing the suction negative pressure of the blower corresponding to each range. That is, the suction negative pressure from the blower suctioning from the third range (from 0.75L to L) can be made lower than the suction negative pressure from the blower suctioning from the second range (from 0.25L to 0.75L) to produce sintered ore.

[0038] Multiple blowers can be arranged in any way that allows for adjustment of the suction negative pressure in each of the first to third ranges. For example, a blower can be provided for each wind box 8 (exhaust pipe 10), and the suction negative pressure can be adjusted independently for each. Alternatively, at least one blower can be provided for each of the first to third range divisions, and the suction negative pressure can be adjusted on a divisional basis. The method of this embodiment described above can similarly suppress the decrease in the yield of the finished product in the lower layer of the sintered layer.

[0039] (Third embodiment) In the first embodiment, the suction negative pressure in the third range (from 0.75 L to L) was reduced compared to the suction negative pressure in the second range (from 0.25 L to 0.75 L). In contrast, the method of this embodiment is a method for producing sintered ore by reducing not only the suction negative pressure in the third range, but also the suction negative pressure in the first range (from 0 to 0.25 L) compared to the suction negative pressure in the second range.

[0040] As mentioned above, the upper layer of sintered raw material layer B tends to suffer from insufficient heat. Reducing the suction negative pressure in the first range corresponding to the firing of the upper layer is effective in improving the yield of the finished product in the upper layer. Therefore, by reducing the suction negative pressure in the first range corresponding to the firing of the upper layer, in addition to the third range corresponding to the firing of the lower layer of sintered raw material layer B, it is possible to improve the yield of the finished product in the upper layer while suppressing the decrease in the yield of the finished product in the lower layer. Furthermore, although the sintering speed decreases in this embodiment compared to when the suction negative pressure is normal across the entire range, the decrease is smaller than when the suction negative pressure is reduced across the entire range of the sintered strand. And, a similar level of improvement in the finished product yield can be obtained as when the suction negative pressure is reduced across the entire range.

[0041] The suction negative pressure in the first range can be the same as the suction negative pressure in the third range. Alternatively, the suction negative pressure in the first range can be higher or lower than the suction negative pressure in the third range. The suction negative pressure in the first range can also be set to 70% to 95% of the suction negative pressure in the second range. Furthermore, as in the first embodiment, the suction negative pressure can be replaced with suction airflow rate or suction air velocity. [Examples]

[0042] This embodiment will be further explained by the following examples. In the sintering test (pot test), the change in the yield of the finished product was confirmed by controlling the suction negative pressure during sintering.

[0043] (Experimental method) The sintering test was performed using a sintering pot with a diameter of 300 mm and a height of 500 mm. The sintering raw materials used and their mixing ratios are shown in Table 1. When the new raw materials (iron ore and auxiliary materials) are set to 100% by mass, the mixing ratios of powdered coke (-5 mm sieved) and return ore were set to 4.5% by mass and 15.0% by mass, respectively. Iron ore a to e are iron ore from different sources. Iron ore a and b are highly crystalline hydro ore containing 5% or more by mass of crystal water. From the mixing ratios in Table 1, in mixture A, a total of 28.8% highly crystalline hydro ore is mixed into the raw materials including powdered coke and return ore, and in mixture B, a total of 43.2% highly crystalline hydro ore is mixed into the raw materials.

[0044] [Table 1]

[0045] These sintering raw materials (iron ore, auxiliary materials, powdered coke, and return ore) were mixed in the above proportions to form a blended raw material, which was then mixed in a drum mixer for 4 minutes. After that, 6.5% by mass of water was added to the blended raw material (assuming 100% by mass), and the mixture was mixed for another 4 minutes. Using the obtained raw material, sintering tests were conducted by changing the raw material used (type of blend), charging method, and suction negative pressure conditions, as shown in Table 2. The charging method for the raw material was either uniform charging or segregation charging. In uniform charging, the raw material was charged in a way that prevented segregation. In segregation charging, the raw material packed bed charged using an ISF (Intensified Sifting Feeder) type charging device, which is a rectifying dispersion type, was sampled to confirm the distribution of the raw material, and this distribution was simulated and charged into the sintering pot. In segregation charging, the mass fraction of carbon material in the lower layer was charged so that it was less than the mass fraction of carbon material in the whole. In all test examples, the sintering raw material layer had a thickness of 500 mm.

[0046] The firing process began by using a blower to draw air from the bottom of the sintering pot while simultaneously covering the pot with an ignition burner to ignite the surface of the sintering material layer. Under normal suction negative pressure conditions, the suction negative pressure was kept constant at 11.8 kPa. Under reduced suction negative pressure conditions, the suction negative pressure was kept constant at 10.9 kPa. Reducing the suction negative pressure in the lower or upper layer was achieved by changing the negative pressure at the moment the temperature of the sintering material at the corresponding height position began to rise. Specifically, the temperature rise was measured by placing a thermocouple at the center of the sintering pot at the corresponding height position of the sintering material layer. The thermocouples were placed at 120 mm from the surface of the material (corresponding to 0.25 L) and at 330 mm from the surface (corresponding to 0.75 L). In the "reduced lower layer suction negative pressure" scenario, when the thermocouple at 330 mm began to detect a temperature rise, it was determined that firing of the lower layer had begun, and the suction negative pressure was changed from 11.8 kPa (normal) to 10.9 kPa (reduced). In the "Upper Layer Suction Negative Pressure Reduction" method, the raw material surface was ignited with a suction negative pressure of 10.9 kPa (reduced). When a temperature rise began to be detected by a thermocouple at a position of 120 mm, it was determined that the firing of the upper layer was complete, and the suction negative pressure was changed from 10.9 kPa (reduced) to 11.8 kPa (normal). In the "(All Layers) Suction Negative Pressure Reduction" method, the suction negative pressure was kept at 10.9 kPa (reduced from the normal 11.8 kPa) from ignition to completion of sintering.

[0047] The height positions of 330 mm corresponding to 0.75 L and 120 mm corresponding to 0.25 L in this sintering pot test were determined in advance by the following sintering pot test. A sintering test was conducted using a sintering pot with multiple thermocouples placed at 30 mm intervals in the direction of the raw material layer thickness, using a standard raw material mixture and suction at a normal suction negative pressure (11.8 kPa). The measurement positions of the multiple thermocouples were the same as in the above test, at the center of the sintering pot. Sintering time and temperature measurements using thermocouples were then performed. Sintering time was defined as the time from the start of ignition to the peak time of the exhaust gas temperature. Furthermore, the timing when the temperature exceeded 100°C, as measured by thermocouple temperature measurements, was defined as the start of the sintering reaction at that measurement position. The height positions where a temperature rise was detected (i.e., the sintering reaction started) at 1 / 4 of the firing time (corresponding to 0.25 L) and the height positions where a temperature rise was detected at 3 / 4 of the firing time (corresponding to 0.75 L) were identified. As a result, the position corresponding to 0.25L was determined to be 120mm from the surface, and the position corresponding to 0.75L was determined to be 330mm from the surface. In the sintering pot test, the sintering reaction tends to progress faster around the side walls of the pot and slower in the center. Therefore, the center position of the sintering pot where temperature measurements were taken using multiple thermocouples in the sintering pot test is the part where the sintering reaction progresses more slowly at the same height in the layer thickness direction. Consequently, the determined height positions corresponding to 0.25L and 0.75L do not necessarily coincide with the height positions of 1 / 4 and 3 / 4 of the total layer thickness (500mm) of the sintering material.

[0048] [Table 2]

[0049] (Evaluation criteria) After firing, the resulting sintered cake was divided into five equal parts in the thickness direction, forming layers 1 through 5 from the top. Each layer was then dropped four times from a height of 2 meters. The sintered product was collected using particles with a particle size of +5 mm (on a 5 mm mesh sieve), excluding the bedrock, and its mass was determined to be the yield of each layer. Layer 1 contained the top layer, layer 2 contained the top and middle layers, layer 3 contained the middle layer, layer 4 contained the middle and bottom layers, and layer 5 contained the bottom layer. The sintering rate, product yield (for each layer, weighted average), and production rate were then determined as defined below.

[0050] Sintering rate (mm / min) = Raw material layer thickness / Sintering time Yield of finished product (mass %) for each layer = Amount of finished product in each layer / (Mass of sintered cake excluding the base ore in each layer) Average yield (mass%) = (Yield of 1 layer × Mass of sintered cake excluding 1 layer of base ore + Yield of 2 layers × Mass of sintered cake excluding 2 layers of base ore + ... + Yield of 5 layers × Mass of sintered cake excluding 5 layers of base ore) / (Mass of sintered cake excluding 1 layer of base ore + Mass of sintered cake excluding 2 layers of base ore + ... + Mass of sintered cake excluding 5 layers of base ore) Production rate (t / Dm 2 ) = formed mass [t] / (sintering time (D) x pot bottom area [m 2 ]) The sintering time was defined as the time from the start of ignition until the exhaust gas temperature reached its peak. Table 3 shows the sintering rate, product yield (average, per layer), and production rate for each test example.

[0051] [Table 3]

[0052] Comparing Experimental Example 1 with Comparative Example 1, in Example 1, reducing the lower layer suction negative pressure improved the yield of the 4th and 5th layers, and the average yield improved. In Comparative Example 2, segregation charging resulted in a decrease in the yield of the 4th and 5th layers compared to Comparative Example 1. In contrast, in Example 2 with segregation charging, reducing the lower layer suction negative pressure restored the yield of the 4th and 5th layers to the same level as uniform charging and normal negative pressure (Comparative Example 1). In Comparative Example 3, the high proportion of high-crystallinity water ore resulted in a decrease in the yield of the 3rd to 5th layers compared to Comparative Example 1, which had the same conditions except for the composition. However, in Example 3, which also had a high proportion of high-crystallinity water ore, reducing the lower layer suction negative pressure resulted in a higher and recovered yield of the 4th and 5th layers compared to Comparative Example 3. For the 4th, 5th layer, and average yield, the improvement in Example 2 compared to Comparative Example 2, and the improvement in Example 3 compared to Comparative Example 3, were greater than the improvement in Example 1 compared to Comparative Example 1. Therefore, it was confirmed that reducing the negative pressure from the lower layer suction is particularly effective in cases of non-uniform firing due to segregation charging or high proportion of highly crystalline water ore.

[0053] In Example 1, the sintering rate was lower than in Comparative Example 1, but it was not lower than in Comparative Example 4, where the suction negative pressure was reduced throughout all layers. Furthermore, the decrease in production rate in Example 1 compared to Comparative Example 1 was minor. This was also true when segregation charging was used (Example 2, Comparative Examples 2 and 5) and when a high concentration of high-crystallinity water ore was used (Example 3, Comparative Examples 3 and 6). From Examples 4 and 5, it was confirmed that combining the reduction of lower-layer suction negative pressure with the reduction of upper-layer suction negative pressure improved the yield of one and two layers compared to Examples 2 and 3, and also improved the average yield, thus demonstrating that further improvements in yield can be obtained. [Explanation of Symbols]

[0054] 1. Sintering machine 2 Charging device 4 Ignition furnace 6 pallets 8 Window Box 10 Exhaust branch pipe 12 dampers 14 Main exhaust pipe 16 Main exhaust fan

Claims

1. A method for producing sintered ore, characterized in that, in a Dwight-Royd type sintering machine, a sintered strand subjected to downward suction by a wind box is produced by reducing the suction negative pressure in the range from 0.75L to L, where L is the length in the strand direction from a first position at the downstream end of the ignition furnace to a second position at the end of the wind box closest to the ore discharge section, with the first position being 0 and the second position being L, to a lower suction negative pressure in the range from 0.75L to L than to a suction negative pressure in the range from 0.25L to 0.75L.

2. The method for producing sintered ore according to claim 1, characterized in that when the sintered raw material layer in the Dwight-Loyd type sintering machine is divided into an upper layer, a middle layer, and a lower layer in the thickness direction, the mass fraction of carbon material in the lower layer of sintered raw material is less than the mass fraction of carbon material in the entire sintered raw material layer.

3. The method for producing sintered ore according to claim 1, characterized in that the sintering raw material charged into the Dwight-Loyd sintering machine contains 35% by mass or more of highly crystalline water ore containing 5% by mass or more of crystalline water.

4. The method for producing sintered ore according to claim 1, characterized in that the suction negative pressure in the range of 0 to 0.25 L, which is the first position, is made smaller than the suction negative pressure in the range of 0.25 L to 0.75 L.

5. The method for producing sintered ore according to claim 1, characterized in that the suction negative pressure in the range from 0.75 L to L is set to 70% or more and 95% or less, when the suction negative pressure in the range from 0.25 L to 0.75 L is set to 100%.

6. A method for producing sintered ore in a Dwight-Royd type sintering machine, characterized in that, in a sintered strand subjected to downward suction by a wind box, the length in the strand direction from a first position at the downstream end of the ignition furnace to a second position at the end of the wind box closest to the ore discharge section is L, and when the first position is set to 0 and the second position to L, the suction wind velocity in the range from 0.75L to L is made smaller than the suction wind velocity in the range from 0.25L to 0.75L.

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