Method for producing sintered ore

Abstract

To provide a method for producing sintered ore capable of suppressing lowering of a product yield of sintered ore by suppressing heat shortage in an upper layer of a raw material layer, and by blending biomass charcoal in sintering ore.SOLUTION: A method for producing sintered ore, comprising a raw material mixing step (Step S1) of producing sintering raw materials by mixing iron raw materials, biomass charcoal, and char materials other than biomass charcoal, a raw material layer forming step (Step S2) of supplying the sintering raw materials onto a pallet of a sintering machine to form a raw material layer, and a sintering step (Step S3) of igniting the surface of the raw material layer to sinter the sintering raw materials, wherein in the raw material mixing step (Step S1), at least two types of sintering raw materials are produced with different biomass charcoal compositions based on calorific value, and in the raw material layer forming step (Step S2), the upper layer of the raw material layer is formed by the sintering raw material having a lower biomass charcoal composition than the other sintering raw material, and the lower layer of the raw material layer is formed by the other sintering raw material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The iron ore sintering process involves sintering raw materials, consisting of iron ore, flux, and a carbonaceous material as a solid fuel, in a sintering machine using the heat generated by combustion of the carbonaceous material. While breeze coke is typically used as the carbonaceous material, other materials, such as anthracite, are sometimes used to mitigate risk factors, such as price fluctuations in the raw coal used for coke breeze and equipment malfunctions. In the iron ore sintering process, the raw materials are fed onto a pallet in the sintering machine to form a raw material layer. The surface (top) of the raw material layer is ignited to combust the carbonaceous material, sintering the raw material with the resulting combustion heat. Air is also drawn in from the bottom of the raw material layer. Therefore, the upper layer of the raw material layer may generally experience a heat deficit compared to the lower layer due to the air drawn into the raw material layer from the top.

[0003] Meanwhile, with growing awareness of environmental conservation in recent years, carbon materials are becoming more diverse in order to reduce environmental impact. Biomass-derived carbon materials (hereinafter referred to as biomass charcoal) have been attracting attention as a means of diversifying carbon materials to reduce environmental impact. Biomass absorbs carbon dioxide during the growth of the plants that produce it. Therefore, biomass-based fuels can be considered carbon-neutral and therefore can be counted as emitting no carbon dioxide. Therefore, the use of biomass charcoal in iron ore sintering processes, which typically use coke breeze, is being considered. Furthermore, biomass charcoal has a higher proportion of volatile matter (VM) than coke breeze. When biomass charcoal is ignited, the volatile matter ignites first. Therefore, a high proportion of volatile matter contributes to improved combustibility of biomass charcoal, resulting in a high combustion rate even at low temperatures.

[0004] Patent Document 1 discloses a method for producing sintered ore using biomass charcoal. In this production method, oil palm kernel shell coal is mixed as a solid carbonaceous material derived from biomass with the sintering raw material used in a sintering machine. When a raw material layer is formed on the pallet of the sintering machine, solid carbonaceous materials other than oil palm kernel shell coal are segregated in the upper layer of the raw material layer, and oil palm kernel shell coal is segregated in the lower layer of the raw material layer. This is achieved by adjusting the particle size of the oil palm kernel shell coal. It is said that segregating oil palm kernel shell coal in the lower layer of the raw material layer improves combustibility in the lower layer of the raw material layer and reduces carbon dioxide emissions.

[0005] Patent Document 2 discloses a method for producing palm kernel shell charcoal, a type of biomass charcoal, and also discloses the particle size of palm kernel shell charcoal that can segregate the palm kernel shell charcoal in the lower layer of the packed bed of a sintering machine when using the palm kernel shell charcoal as fuel for producing sintered ore, as well as a method for adjusting the particle size of the palm kernel shell charcoal.

[0006] Patent Document 3 discloses a method for producing sintered ore that uses a low-combustibility carbonaceous material made of coke breeze or anthracite as a coagulating agent in combination with a highly combustible carbonaceous material made of biomass charcoal that has a lower combustion start temperature than the low-combustibility carbonaceous material. Patent Document 3 also discloses that the highly combustible carbonaceous material is attached to the surface layer of the sintering raw material granules in the latter half of the granulation process for producing the sintering raw material granules. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5786795 [Patent Document 2] Patent No. 6167851 [Patent Document 3] Japanese Patent Application Publication No. 2022-33594 Summary of the Invention [Problem to be solved by the invention]

[0008] In a sintering machine, after ignition of the upper surface of the raw material bed, air is drawn in from the lower surface of the raw material bed. Therefore, if oil palm kernel shell coal is segregated in the lower layer of the raw material bed, some of the combustion heat of the oil palm kernel shell coal is discharged outside the sintering machine without being used to sinter the sintering raw material, resulting in a decrease in the product yield of sintered ore. Furthermore, as mentioned above, there is a general possibility of heat shortage occurring in the upper layer of the raw material bed. Patent Document 1 does not disclose any appropriate carbon material arrangement or biomass coal segregation conditions that would prevent heat shortage in the upper layer of the raw material bed and prevent a decrease in the product yield of sintered ore due to the mixing of biomass coal with the sintering raw material. These points leave room for improvement.

[0009] As mentioned above, Patent Document 2 discloses segregating palm kernel shell coal in the lower layer of the raw material layer. However, like Patent Document 1, Patent Document 2 does not disclose appropriate raw material arrangement or conditions for segregating palm kernel shell coal when palm kernel shell coal is used in combination with ordinary carbonaceous materials, such as coke fines. Therefore, like Patent Document 1, there is room for improvement in terms of suppressing heat shortage in the upper layer of the raw material layer and suppressing a decrease in the product yield of sintered ore caused by mixing biomass coal with the sintering raw material.

[0010] Patent Document 3 does not consider the influence of volatile matter in highly combustible carbonaceous materials made from biomass charcoal. Furthermore, it does not disclose any appropriate carbon material arrangement when using low combustible carbonaceous materials and highly combustible carbonaceous materials in combination, or the conditions for segregation of biomass charcoal. Therefore, as with Patent Document 1, there is room for improvement in terms of suppressing heat shortage in the upper layer of the raw material layer and suppressing a decrease in the product yield of sintered ore caused by mixing biomass charcoal with the sintering raw material.

[0011] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for producing sintered ore that can suppress heat shortage in the upper layer of the raw material layer and suppress a decrease in the product yield of sintered ore caused by blending biomass charcoal into the sintering raw material. [Means for solving the problem]

[0012] The means for solving the above problems are as follows. [1] A method for producing sintered ore, comprising: a raw material blending step of blending and granulating an iron raw material, biomass charcoal, and a carbonaceous material other than the biomass charcoal to produce a sintered raw material; a raw material layer forming step of supplying the sintered raw material onto a pallet of a sintering machine to form a raw material layer; and a sintering step of igniting the surface of the raw material layer to sinter the sintered raw material, wherein in the raw material blending step, at least two types of sintered raw material are produced, each having a different blending ratio of biomass charcoal in terms of calorific value; and in the raw material layer forming step, an upper layer of the raw material layer is formed using one of the two types of sintered raw material, which has a lower blending ratio of biomass charcoal in terms of calorific value than the other sintered raw material, and the other sintered raw material is used to form a lower layer below the upper layer in the thickness direction of the raw material layer. [2] The method for producing sintered ore described in [1], wherein the total calorific value of the biomass charcoal and the carbonaceous material in the upper layer formed in the raw material layer formation process is greater than the total calorific value of the biomass charcoal and the carbonaceous material in the lower layer. [3] The method for producing sintered ore according to [1] or [2], in the raw material layer forming step, the lower layer is formed below one-third of the thickness of the raw material layer from the surface of the raw material layer. [4] A method for producing sintered ore according to any one of [1] to [3], wherein the carbonaceous material mixed with the sintering raw material in the raw material mixing step is a carbonaceous material derived from a fossil fuel with a volatile content of less than 3%, and the biomass charcoal has a volatile content of 3% or more. [Effects of the Invention]

[0013] According to the present invention, it is possible to suppress a heat shortage in the upper layer of the raw material layer and to suppress a decrease in the product yield of sintered ore caused by blending biomass charcoal into the sintering raw material. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram for explaining a method for producing sintered ore according to an embodiment of the present invention; [Figure 2]1 is a diagram showing an example of a sintered ore manufacturing facility to which the sintered ore manufacturing method according to the present embodiment can be applied. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present inventors investigated the effect of mixing biomass charcoal with coke breeze and anthracite, which are commonly used as sintering raw materials, on the sinter ore product yield and the effect on the temperature of the raw material layer on the sintering machine pallet when producing sintered ore. As a result, as the biomass charcoal usage rate, i.e., the biomass charcoal blending rate in the sintering raw material, increased, the sintered ore product yield decreased and a temperature drop in the upper layer of the raw material layer was observed. On the other hand, no temperature drop was observed in the lower layer of the raw material layer. Therefore, the present inventors attempted to concentrate biomass charcoal in the lower layer of the raw material layer. As a result, they found that the temperature drop in the upper layer of the raw material layer could be suppressed and a decrease in the sintered ore product yield could be suppressed. Hereinafter, an embodiment of the present invention (hereinafter referred to as the present embodiment) will be described with reference to the drawings.

[0016] FIG. 1 is a diagram for explaining the method for producing sintered ore according to this embodiment. In the example shown in FIG. 1, first, a plurality of raw materials are mixed in a predetermined ratio to produce a sintered raw material (step S1, raw material blending step). The production of the sintered raw material will now be explained. FIG. 2 is a diagram showing an example of a sintered ore production facility to which the sintered ore production method according to this embodiment can be applied. As shown in FIG. 2, the sintered ore production facility is provided with a plurality of hoppers 1, and each raw material is stored in each of these hoppers 1.

[0017] Examples of raw materials for the sintering raw material include iron raw materials, auxiliary materials, and carbon materials. Examples of iron raw materials include iron ore powder derived from iron ore and powder recovered in steelworks. Examples of auxiliary materials include limestone, dolomite, and quicklime. Examples of carbon materials include fine coke derived from fossil fuels, anthracite, and biomass charcoal derived from biomass. These raw materials are supplied at a predetermined ratio from a hopper 1 storing the raw materials onto a conveyor (not shown), and then transported to a drum mixer 2. Of the carbon materials described above, fine coke and anthracite correspond to carbon materials other than biomass charcoal in this embodiment. Biomass charcoal will be described later.

[0018] In the drum mixer 2, the raw materials are mixed, and water is added to the mixture to adjust the humidity, producing a sinter raw material containing granulated raw material (sometimes called pseudo-particles) granulated to a predetermined average particle size. The sinter raw material is transported by a conveyor to a surge hopper 3 and stored. The process of producing the sinter raw material as described above corresponds to the raw material blending process of this embodiment. In this embodiment, at least two sinter raw materials are produced, each with a different blending ratio of biomass charcoal in terms of calorific value.

[0019] In the example shown in FIG. 2, two surge hoppers 3a, 3b are installed side by side in the conveying direction of the sintering raw material. Sintering raw material with a high blending ratio of biomass coal is stored in the first surge hopper 3a. Sintering raw material with a low blending ratio of biomass coal is stored in the second surge hopper 3b, which is located downstream of the first surge hopper 3a in the conveying direction. The sintering raw material with a high blending ratio of biomass coal stored in the first surge hopper 3a corresponds to the other sintering raw material in the sintering ore manufacturing method according to this embodiment. The sintering raw material with a low blending ratio of biomass coal stored in the second surge hopper 3b corresponds to one of the sintering raw materials in the sintering ore manufacturing method according to this embodiment.

[0020] Returning to the explanation of FIG. 1, following the raw material blending step of step S1, the process proceeds to the raw material layer formation step of step S2, where the above-mentioned sinter raw materials are loaded onto the pallet of the sinter machine, and a raw material layer is formed on the pallet. That is, the sinter raw materials stored in the first surge hopper 3a shown in FIG. 2 are fed by the drum feeder 4 and charged onto the bedding ore layer 6 described below, thereby forming the lower layer of the raw material layer 7. In addition, the sinter raw materials stored in the second surge hopper 3b are fed by the drum feeder 4 and charged onto the lower layer of the raw material layer 7 via the chute 5, thereby forming the upper layer of the raw material layer 7. It is preferable that the thickness of the lower layer 7b of the raw material layer 7 is one-half to one-third of the thickness of the raw material layer 7.

[0021] In the example shown in Fig. 2, a bedding ore hopper 8 is provided upstream of the first surge hopper 3a in the conveying direction of the sinter raw material in the sinter machine. Bedding ore is stored in the bedding ore hopper 8. The bedding ore is cut out from a drum feeder of the bedding ore hopper 8 and charged onto a pallet 10 of the sinter machine 9 through a chute, thereby forming the bedding ore layer 6.

[0022] A cut-off gate 11 is installed downstream of the surge hopper 3 in the conveying direction of the sintering raw material to level the surface of the raw material layer 7 on the pallet 10 and make the thickness of the raw material layer 7 approximately uniform. This allows the raw material layer 7 to be formed with a predetermined thickness. The process of charging the raw material onto the pallet 10 and forming the raw material layer 7 with a predetermined thickness in this manner corresponds to the raw material layer forming process in this embodiment.

[0023] Returning to the explanation of FIG. 1 , following the raw material layer formation process of step S2, the process proceeds to the sintering process of step S3, in which the raw material layer 7 formed on the pallet 10 of the sintering machine 9 is ignited to sinter the sintering raw material. As shown in FIG. 2 , an ignition furnace 12 is installed downstream of the cutoff gate 11 in the conveying direction. The ignition furnace 12 ignites the carbon material present on the surface (upper surface) of the raw material layer 7. Multiple wind boxes 13 are also arranged below the pallet 10 in the vertical direction of the sintering machine 9. A sintering fan 15 is connected to each wind box 13 via an exhaust duct 14. The sintering fan 15 draws air from the wind box 13 through the raw material layer 7, thereby circulating air from the top to the bottom in the thickness direction of the raw material layer 7. This causes the combustion of the carbon material in the sintering raw material to proceed from the top to the bottom of the raw material layer 7. The sintering raw material is heated by the heat of combustion of the carbon material, at least a portion of the iron raw material melts and bonds, and the sintering of the sintering raw material proceeds from the top to the bottom of the raw material layer 7. In this way, a sintered layer (sometimes referred to as a sintered cake) is formed on the pallet 10 of the sintering machine 9. The process of sintering the raw material in this way corresponds to the sintering process described above.

[0024] In the example shown in Fig. 1, a dust collector 16 that collects dust in the air and fine particles in the sintering raw materials is provided upstream of the sintering fan 15 in the air flow direction. A chimney 17 is provided downstream of the sintering fan 15 in the air flow direction. The air sucked in by the sintering fan 15 is discharged to the outside through the chimney 17.

[0025] The sintered layer formed on the pallet 10 of the sintering machine 9 is discharged from the ore discharge section downstream of the sintering machine 9 in the conveying direction to the outside of the sintering machine 9. The sintered layer is then crushed by a crusher 18 and classified into particles, and sintered ore of a predetermined particle size is collected as product sintered ore.

[0026] Here, we will explain biomass charcoal. Biomass charcoal is a carbon material derived from organic resources other than fossil fuels, and organic resources refer to biomass. Biomass refers to organic resources derived from plants and animals, excluding fossil fuels. Examples of biomass include coconut shells and bamboo. Examples of biomass charcoal include coconut shell charcoal and bamboo charcoal, which are produced from coconut shells and bamboo. Biomass absorbs carbon dioxide while the plants that produce it grow. Therefore, when biomass charcoal, a fuel made from biomass, is burned, it can be considered that no carbon dioxide is emitted into the environment from the carbon-neutral perspective. In other words, from the carbon-neutral perspective, blending biomass charcoal with sintering raw materials can reduce carbon dioxide emissions accordingly. A characteristic of biomass charcoal is that it has a higher proportion of volatile matter compared to coke breeze and anthracite. Therefore, when biomass charcoal is ignited, it ignites from the volatile matter of the biomass charcoal. Furthermore, biomass charcoal is characterized by its inclusion of alkali metals and its porosity. The aforementioned characteristics of biomass charcoal contribute to improved combustibility, enabling a high combustion rate even at low temperatures. The volatile content of biomass charcoal is 3% by mass or more, while the volatile content of coke breeze is less than 3% by mass. The combustion start temperature of biomass charcoal is generally 550°C or less, while the combustion start temperature of coke is 650 to 750°C. The combustion rate of biomass charcoal is higher than that of coke.

[0027] (Actions and Effects) When the surface of the raw material layer 7 is ignited, combustion of the carbon material in the sintering raw material progresses from the top to the bottom of the raw material layer 7. Therefore, the temperature of the lower layer 7b becomes higher than that of the upper layer 7a. In addition, in this embodiment, biomass charcoal is segregated in the lower layer 7b. Because the combustion start temperature of biomass charcoal is lower than that of coke breeze and anthracite, the volatile matter generated in the biomass charcoal rapidly burns in the lower layer 7b and generates combustion heat. This combustion heat increases the temperature of the upper layer 7a of the raw material layer 7. As a result, heat shortage in the upper layer 7a of the raw material layer 7 can be suppressed. In addition, a decrease in the strength of the sintered ore and the product yield due to the incorporation of biomass charcoal into the sintering raw material can be suppressed. Furthermore, in this embodiment, the upper layer 7a and the lower layer 7b of the raw material layer 7 are formed from two types of sintering raw material. Therefore, biomass charcoal can be reliably segregated in the lower layer 7b.

[0028] The present invention is not limited to the above-described embodiment. For example, three or more types of sintered raw materials with different biomass charcoal blending ratios may be produced. In this case, surge hoppers are installed according to the type of sintered raw material, and sintered raw materials with different biomass charcoal blending ratios are charged into the sintering machine from each surge hopper to form a raw material layer. This allows the biomass charcoal blending ratio to be varied in thickness across the raw material layer. Therefore, functions and effects similar to those of the above-described embodiment can be obtained. Furthermore, instead of preparing multiple sintered raw materials with different biomass charcoal blending ratios, the particle size of the biomass charcoal may be adjusted to cause the biomass charcoal to segregate in the lower layer of the raw material layer. For example, the drum mixer 2 produces sintered raw materials containing pseudo-particles, which are granulated by various raw materials adhering to the periphery of a carbon material containing biomass charcoal. Therefore, the particle size of the pseudo-particles can be increased by coarsening the biomass charcoal, which serves as the nucleus of the pseudo-particles. When the sinter raw material containing the granulated coarse pseudo-particles is cut out from the drum feeder and loaded into a sinter machine, the coarse pseudo-particles and large particle size biomass charcoal roll and accumulate at the lower layer of the raw material layer when they are piled up on the pallet. Then, particles smaller than the coarse pseudo-particles and large particle size biomass charcoal, i.e., various raw materials that have not been granulated, are piled up on top of them. Therefore, by adjusting the particle size in this way, it is possible to segregate the biomass charcoal at the lower layer of the raw material layer, and it is possible to obtain actions and effects similar to those of the present embodiment described above. [Example]

[0029] Example 1, which verified the effect of segregating biomass charcoal in the lower layer of the raw material layer, will be described. First, the raw materials forming the raw material layer will be described. Iron ore, limestone, return ore, coke fines, and biomass charcoal were prepared as raw materials. Using these raw materials, multiple types of sintered raw materials were blended, each with a different biomass charcoal blending ratio (mass %; hereinafter simply referred to as %) converted into calorific value. The volatile content of the coke fines was 1.1%, and the volatile content of the biomass carbonaceous material was 4.8%. The calorific value of the coke fines was 28 MJ / kg, and the volatile content of the biomass carbonaceous material was 31 MJ / kg. The volatile content can be measured using the method described in JIS M8812:2006. The calorific value of the carbonaceous material can be measured using the method described in JIS M8814:2003.

[0030] In Example 1, a sintering pot test apparatus with a height of 600 mm and a diameter of 300 mm was prepared, and a batch test was performed using this apparatus. Sintering raw materials were charged to a height of 300 mm from the bottom of the apparatus to form a lower layer of the raw material layer. Then, another sintering raw material was charged on top of the lower layer to a height of 600 mm to form an upper layer of the raw material layer. In Example 1, the thickness of both the upper and lower layers of the raw material layer was 300 mm.

[0031] The above-mentioned equipment is equipped with exhaust gas equipment such as an ignition furnace, a wind box, and a sintering fan. The upper surface of the raw material bed is ignited using the ignition furnace, and air is drawn from the bottom of the raw material bed using the wind box and sintering fan. This allows combustion to proceed from the top to the bottom in the thickness direction of the raw material bed, and the firing is completed when the raw material bed reaches the bottom (bottom) of the bed. The sintered cake is then removed from the above-mentioned equipment and dropped four times from a height of approximately 2 m to recover sintered ore particles 5 mm or larger in size. The proportion of sintered ore particles 5 mm or larger in size in the sintered cake is then calculated and used as the product yield of sintered ore. Table 1 summarizes the biomass charcoal blending ratio (%) in the upper and lower layers of the raw material bed, the biomass charcoal blending ratio (%) in the entire sintered raw material, and the product yield (%) for Examples 1 to 4 and Comparative Examples 1 to 7.

[0032] [Table 1]

[0033] Comparative Example 1 is an example in which 4.0% of coke powder was blended as an outer percentage of the total sintering raw material in both the sintering raw material forming the upper layer and the sintering raw material forming the lower layer of the raw material layer. In other words, Comparative Example 1 is a base condition in which only coke powder was used as the carbon material of the sintering raw material. A sintered cake was produced by firing the raw material layer of Comparative Example 1, and the product yield (%) of the sintered ore was calculated as described above. Note that the calorific value in the upper layer of Comparative Example 1 is equal to the calorific value in the lower layer.

[0034] Comparative Example 2 is an example in which 25% of the coke breeze, calculated as calorific value, was replaced with biomass charcoal in each of the sintering raw materials forming the upper and lower layers of the raw material layer in Comparative Example 1. In Comparative Example 2, biomass charcoal was contained in each of the upper and lower layers, but the total calorific value of each layer in Comparative Example 2 was equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0035] Comparative Example 3 is an example in which, in terms of calorific value, 50% of the coke fines of the sintering raw material forming the upper layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal. In Comparative Example 3, biomass charcoal was included in the upper layer, but the total calorific value of each layer in Comparative Example 3 was equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0036] Comparative Example 4 is an example in which 50% of the coke breeze, in terms of calorific value, was replaced with biomass charcoal in each of the sintering raw materials forming the upper and lower layers of the raw material layer in Comparative Example 1. In Comparative Example 4, biomass charcoal was contained in each of the upper and lower layers, but the total calorific value of each layer in Comparative Example 4 was equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0037] Comparative Example 5 is an example in which, in terms of calorific value, 100% of the coke fines of the sintering raw material forming the upper layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal. In Comparative Example 5, biomass charcoal was included in the upper layer, but the total calorific value of each layer in Comparative Example 5 was equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0038] Comparative Example 6 is an example in which, in terms of calorific value, 50% of the coke fines of the sintering raw material forming the upper layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal, and 25% of the coke fines of the sintering raw material forming the lower layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal. In Comparative Example 6, biomass charcoal is contained in both the upper and lower layers, but the total calorific value of each layer in Comparative Example 6 is equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0039] Comparative Example 7 is an example in which, in terms of calorific value, 100% of the coke fines of the sintering raw material forming the upper layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal, and 25% of the coke fines of the sintering raw material forming the lower layer of the raw material layer was replaced with biomass charcoal. In Comparative Example 7, biomass charcoal is contained in both the upper and lower layers, but the total calorific value of each layer in Comparative Example 7 is equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0040] In Example 1, 50% of the coke fines in the sintering raw material forming the lower layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal in terms of calorific value. In Example 1, biomass charcoal was included in the lower layer, but the total calorific value of each layer in Example 1 was equal to the total calorific value of each layer in Comparative Example 1. A sintered cake was otherwise produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0041] Inventive Example 2, 100% of the coke fines in the sintering raw material forming the lower layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal in terms of calorific value. In Inventive Example 2, biomass charcoal was included in the lower layer, but the total calorific value of each layer in Inventive Example 2 was equal to the total calorific value of each layer in Comparative Example 1. A sintered cake was otherwise produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0042] In Example 3, 25% of the coke fines in the sintering raw material forming the upper layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal, and 50% of the coke fines in the sintering raw material forming the lower layer of the raw material layer was replaced with biomass charcoal, in terms of calorific value. In Example 3, biomass charcoal is contained in both the upper and lower layers, but the total calorific value of each layer in Example 3 is equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0043] In Example 4, 50% of the coke fines in the sintering raw material forming the upper layer of the raw material layer in Comparative Example 1 was replaced with biomass charcoal, and 100% of the coke fines in the sintering raw material forming the lower layer of the raw material layer was replaced with biomass charcoal, in terms of calorific value. In Example 4, biomass charcoal is contained in both the upper and lower layers, but the total calorific value of each layer in Example 4 is equal to the total calorific value of each layer in Comparative Example 1. Otherwise, a sintered cake was produced in the same manner as in Comparative Example 1, and the product yield (%) was calculated.

[0044] (evaluation) As shown in Table 1, when biomass charcoal was blended into the sintering raw material, the product yield (%) of the sintered ore was reduced in each of Comparative Examples 2 to 7 and Invention Examples 1 to 4 compared to Comparative Example 1. However, when looking at Comparative Examples 2 and 3 and Invention Example 1, in which the biomass charcoal blending rate (%) in the entire sintering raw material was 25%, it was confirmed that Invention Example 1, in which biomass charcoal was blended concentratedly in the lower layer, had a higher product yield (%) than Comparative Examples 2 and 3. It was also confirmed that Comparative Example 3, in which biomass charcoal was blended concentratedly in the upper layer, had a lower product yield (%) than Comparative Example 2. These results confirmed that blending biomass charcoal concentrated in the lower layer of the raw material layer can suppress the decrease in product yield (%) caused by blending biomass charcoal.

[0045] Similar results were also confirmed when the blending rate (%) of biomass charcoal in the entire sintering raw material was 50%, 38%, and 75%. That is, it was confirmed that in Example 2, in which biomass charcoal was blended concentratedly in the lower layer, the product yield (%) was improved compared to Comparative Examples 4 and 5. It was also confirmed that in Example 3, in which biomass charcoal was blended concentratedly in the lower layer, the product yield (%) was improved compared to Comparative Example 6. It was also confirmed that in Example 4, in which biomass charcoal was blended concentratedly in the lower layer, the product yield (%) was improved compared to Comparative Example 7.

[0046] This is thought to be due to the high combustibility of biomass charcoal. In other words, if a large amount of biomass charcoal is blended in the upper layer, the biomass charcoal burns out before its combustion spreads to the coke fines in the lower layer. This is thought to worsen the combustion of the coke fines in the lower layer. On the other hand, if a large amount of biomass charcoal is blended in the lower layer, the propagation of combustion to the lower layer, which has a high volatile content and high combustibility, is improved. This is thought to enable the sintering raw materials to be sintered efficiently using the heat associated with the combustion of the coke fines and the heat associated with the combustion of the biomass charcoal, thereby suppressing a decrease in product yield (%). [Example]

[0047] In a conventional sintering machine having one surge hopper, when sintering raw materials are continuously charged onto a pallet from the surge hopper to form a raw material layer, a gradient in the carbon material blending ratio (%) may occur in the thickness direction of the raw material layer. That is, the carbon material blending ratio (%) in the lower layer of the raw material layer may be lower than the carbon material blending ratio (%) in the upper layer of the raw material layer. In such a case, the total calorific value of the biomass coal, coke fines, etc. in the upper layer becomes greater than the total calorific value of the biomass coal, coke fines, etc. in the lower layer. In Example 2, even in such a case, the effect of increasing the biomass coal blending ratio (%) in the lower layer of the raw material layer compared to the biomass coal blending ratio (%) in the upper layer was verified. This section explains why a gradient in the carbon material blending ratio (%) occurs in the thickness direction of the raw material layer when raw materials are continuously charged onto a pallet from the surge hopper to form a raw material layer in a conventional sintering machine having one surge hopper. In a drum mixer, various raw materials adhere to the carbon material core around the carbon material to form pseudo-particles. However, the sintering raw material formed by the drum mixer contains not only pseudo-particles but also various small-diameter raw materials that have not been granulated. These various ungranulated raw materials include carbon materials. Therefore, when such sintering raw material is cut out from the drum feeder and loaded onto the pallet of the sintering machine, the coarse pseudo-particles roll to the lower layer of the raw material layer as they accumulate on the pallet, and the various small-diameter raw materials accumulate on top of them. Due to this principle, a gradient in the carbon material content (%) occurs in the thickness direction of the raw material layer, and the carbon material content (%) in the lower layer may be lower than the carbon material content (%) in the upper layer.

[0048] In Example 5, the raw materials for the lower layer were charged to a height of 300 mm from the bottom of the sintering pot test apparatus, and the raw materials for the upper layer were charged on top of that to a height of 600 mm. The raw materials for the lower layer were blended with coke breeze and biomass charcoal so that the outer percentage was 3.7% of the total sinter material, equivalent to the coke breeze. In terms of calorific value, 50% of the coke breeze was replaced with biomass charcoal. The raw materials for the upper layer were blended with coke breeze so that the outer percentage was 4.2% of the total sinter material. A sintered cake was produced in the same manner as in Comparative Example 1 of Example 1, and the product yield (%) was calculated. The results are shown in Table 2.

[0049] [Table 2]

[0050] (evaluation) In Example 5, the product yield (%) was improved compared to Example 1. This is thought to be because biomass charcoal was blended concentratedly in the lower layer of the raw material layer, and the biomass charcoal blending rate (%) in the entire sintering raw material was lower than in Example 1. In Example 5, the biomass charcoal blending rate (%) in the entire sintering raw material was approximately 23%. [Example]

[0051] In Examples 1 and 2, the boundary between the upper and lower raw material layers was located approximately in the center in the height direction of the pot testing device, and the thickness of each layer was made uniform for the above-mentioned verification. In Example 3, the thickness of each raw material layer was varied to verify the optimal thickness of the upper and lower raw material layers.

[0052] First, sintering raw materials without biomass charcoal and sintering raw materials with biomass charcoal were prepared. In Example 6, a lower layer of the raw material layer was formed from the sintering raw materials with biomass charcoal blended to a height of two-thirds of the height of the pot test apparatus from the bottom. An upper layer of the raw material layer was formed on top of that from the sintering raw materials without biomass charcoal blended.

[0053] In Example 7, a lower layer of the raw material layer was formed from sintering raw material blended with biomass charcoal, extending from the bottom of the pot test apparatus to a height of 5 / 6 of the height of the apparatus. An upper layer of the raw material layer was formed on top of this from sintering raw material not blended with biomass charcoal.

[0054] The biomass charcoal blending rate (%) was kept constant throughout the sintering raw material that made up the raw material layer. The carbon material was blended so that the calorific value per unit mass of the upper layer was approximately equal to the calorific value per unit mass of the lower layer. Table 3 shows the biomass charcoal blending rate (%) in the lower layer of the raw material layer, the thickness of each layer, the biomass charcoal blending rate (%) in the entire sintering raw material, and the product yield.

[0055] [Table 3]

[0056] (evaluation) As shown in Table 3, in Example 7, the product yield (%) was lower than in Examples 2 and 6. Therefore, in order to maximize the product yield (%) when using biomass charcoal, it was found that it is preferable to position the boundary between the upper and lower layers below one-third of the surface of the raw material layer. [Explanation of symbols]

[0057] 1 Hopper 2 Drum Mixer 3 Surge Hopper 3a No. 1 surge hopper 3b Second surge hopper 4 Drum Feeder 5 Shoot 6. Bedding layer 7 Raw material layer 8 Bed Ore Hopper 9. Sintering machine 10 palettes 11 Cut-off Gate 12 Ignition furnace 13 Wind Box 14 Exhaust pipe 15 Sintering Fan 16 Dust collector 17 Chimney 18 Crusher S1 Raw material blending process S2 Raw material layer formation process S3 sintering process

Claims

1. A method for producing sintered ore, comprising: a raw material blending step of blending and granulating an iron raw material, biomass charcoal, and a carbonaceous material other than the biomass charcoal to produce a sintered raw material; a raw material layer forming step of supplying the sintered raw material onto a pallet of a sintering machine to form a raw material layer; and a sintering step of igniting a surface of the raw material layer to sinter the sintered raw material, In the raw material blending step, at least two types of sintered raw materials are produced in which the blending ratio of the biomass charcoal is changed in terms of calorific value, In the raw material layer forming process, an upper layer of the raw material layer is formed using one of the two types of sintering raw materials, which has a lower biomass charcoal blending ratio in terms of calorific value than the other sintering raw material, and a lower layer below the upper layer in the thickness direction of the raw material layer is formed using the other sintering raw material.

2. 2. The method for producing sintered ore according to claim 1, wherein a total calorific value of the calorific value of the biomass charcoal and the calorific value of the carbonaceous material in the upper layer formed in the raw material layer formation process is greater than a total calorific value of the calorific value of the biomass charcoal and the calorific value of the carbonaceous material in the lower layer.

3. 3. The method for producing sintered ore according to claim 1, wherein the raw material layer forming step forms the lower layer below one-third of the thickness of the raw material layer from the surface of the raw material layer.

4. 3. The method for producing sintered ore according to claim 1, wherein the carbonaceous material mixed with the sintering raw material in the raw material mixing step is a carbonaceous material derived from a fossil fuel having a volatile content of less than 3%, and the biomass charcoal has a volatile content of 3% or more.

5. 4. The method for producing sintered ore according to claim 3, wherein the carbonaceous material mixed with the sintering raw material in the raw material mixing step is a carbon material derived from a fossil fuel having a volatile content of less than 3%, and the biomass charcoal has a volatile content of 3% or more.

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