Method for producing sintered ore

Abstract

Provided is a method for producing sintered ore capable of suppressing the production of sintered ore containing unburned carbon in the upper layer of the raw material layer by suppressing insufficient heat in the upper layer of the raw material layer. A method for producing sintered ore having a raw material blending step (step S1) of blending an iron raw material, a first carbon material, and a second carbon material having a lower combustion start temperature than the first carbon material to produce a sintering raw material, a raw material layer forming step (step S2) of supplying the sintering raw material 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 material. In the raw material layer forming step (step S2), the blending ratio of the second carbon material in the upper layer above the central portion in the thickness direction of the raw material layer 7 is made higher than the blending ratio of the second carbon material in the lower layer below the central portion in the thickness direction.

Description

Technical Field

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

Background Art

[0002] In the iron ore sintering process, iron ore, flux, and a carbon material as solid fuel are mixed to produce a sintering raw material, and the sintering raw material is supplied onto a pallet of a sintering machine to form a raw material layer. Ignition is applied to the upper surface of the raw material layer to burn the carbon material, and the sintering raw material is sintered by the combustion heat, while air is sucked from the lower surface side of the raw material layer. Therefore, generally, due to the influence of the air sucked into the raw material layer from the upper surface of the raw material layer, the upper layer of the raw material layer has insufficient heat compared to the lower layer of the raw material layer. As a result, the carbon material in the upper layer is not completely burned, unburned carbon is generated, and there is a possibility of producing sintered ore with a high content of unburned carbon. When producing sintered ore, the temperature of sintered ore with a high content of unburned carbon is lower than that of sintered ore with a low content of unburned carbon.

[0003] The sintered ore produced by the sintering machine is crushed when discharged from the sintering machine and charged into a cooler for cooling. However, in the cooler, when sintered ore with a high content of unburned carbon comes into contact with uncooled sintered ore, the unburned carbon burns, and there is a possibility that the cooling efficiency of the sintered ore in the cooler decreases.

[0004] Also, in the iron ore sintering process, carbon dioxide gas is generated along with the combustion of the carbon material. Therefore, in recent years, with the increasing awareness of environmental protection, the use of carbon materials derived from biomass as carbon materials has been studied for the purpose of reducing the environmental load. This is because biomass absorbs carbon dioxide gas until the plants that are its raw materials grow, so the fuel using biomass can be counted as having no carbon dioxide emissions from the perspective of carbon neutrality.

[0005] An example of a method for manufacturing sintered ore using a solid carbon material derived from biomass is described in Patent Document 1. In this manufacturing method, babassu coconut shell charcoal is mixed as a solid carbon material derived from biomass into the sintering raw materials. Also, when forming the raw material layer, a solid carbon material other than babassu coconut shell charcoal is segregated in the upper layer of the raw material layer, and a large amount of babassu coconut shell charcoal is distributed in the lower layer of the raw material layer. By this, it is said that the combustibility in the lower layer of the raw material layer can be improved and the productivity of the sintered ore can be enhanced. Further, since babassu coconut shell charcoal is a carbon material derived from biomass, it is said that the amount of carbon dioxide emissions can be suppressed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the manufacturing method of Patent Document 1, by using babassu coconut shell charcoal, the productivity of the sintered ore can be improved and the amount of carbon dioxide emissions can be suppressed. However, there has been no consideration whatsoever regarding the possibility that sintered ore containing unburned carbon may be produced due to heat shortage in the upper layer of the raw material layer, and there is room for improvement in this regard.

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide a method for manufacturing sintered ore capable of suppressing the production of sintered ore containing unburned carbon in the upper layer of the raw material layer by suppressing heat shortage in the upper layer of the raw material layer.

Means for Solving the Problems

[0009] The means for solving the above problems are as follows. [1] A raw material blending step of manufacturing a sintering raw material by blending an iron raw material, a first carbonaceous material, and a second carbonaceous material having a lower combustion start temperature than the first carbonaceous material; a raw material layer forming step of supplying the sintering 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 sintering raw material. In the raw material layer forming step, a method for manufacturing sintered ore is provided in which the blending ratio of the second carbonaceous material in the upper layer above the central portion in the thickness direction of the raw material layer is higher than the blending ratio of the second carbonaceous material in the lower layer below the central portion in the thickness direction. [2] The particle size of the second carbonaceous material is smaller than that of the first carbonaceous material. In the raw material layer forming step, the method for manufacturing sintered ore according to [1], wherein the sintering raw material stored in a surge hopper is cut out by a drum feeder and supplied onto a pallet. [3] The first carbonaceous material blended in the sintering raw material in the raw material blending step is a carbon material derived from fossil fuel, and the second carbonaceous material is a carbon material other than fossil fuel. The method for manufacturing sintered ore according to [1] or [2]. [Effect of the Invention]

[0010] According to the present invention, heat shortage in the upper layer of the raw material layer can be suppressed, and thereby, it is possible to suppress the production of sintered ore containing unburned carbon in the upper layer of the raw material layer. [Brief Description of the Drawings]

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described with reference to the drawings. FIG. 1 is a diagram for explaining a method for manufacturing sintered ore according to the present embodiment. In the example shown in FIG. 1, first, a plurality of raw materials are mixed at a predetermined ratio to granulate a sintering raw material (step S1, raw material blending step). FIG. 2 is a diagram showing an example of a sintered ore manufacturing facility to which the method for manufacturing sintered ore according to the present embodiment can be applied. As shown in FIG. 2, a plurality of hoppers 1 are provided in the sintered ore manufacturing facility, and each raw material is stored in these hoppers 1 respectively.

[0013] Examples of the raw materials for the sintering raw material include an iron raw material, a subsidiary raw material, and a carbon material. Examples of the iron raw material include iron ore powder derived from iron ore and recovered powder within a steelworks. Examples of the subsidiary raw material include limestone, dolomite, quicklime, and the like. Examples of the carbon material include coke powder derived from fossil fuel, anthracite, and biomass carbon derived from biomass. In the present embodiment, the particle size of the biomass carbon is smaller than that of the granulation raw material described later. These raw materials are stored in the hoppers 1 respectively. Then, each raw material is supplied from each hopper 1 onto a conveyor (not shown) at a predetermined ratio and conveyed to a drum mixer 2 by the conveyor. Among the carbon materials described above, coke powder and anthracite correspond to the first carbon material in the present embodiment, and biomass carbon corresponds to the second carbon material in the present embodiment. Biomass carbon will be described later.

[0014] In the drum mixer 2, each raw material is mixed, water is added to the mixture for humidity adjustment, and it is stirred for a predetermined period (hereinafter referred to as the granulation time). Thus, a sintering raw material containing the raw material granulated to a predetermined average particle size (hereinafter referred to as the granulated raw material) is produced. That is, the sintering raw material produced by the drum mixer 2 contains, in addition to the granulated raw material, various raw materials that have not yet been granulated (hereinafter referred to as ungranulated raw materials). The ratio of the ungranulated raw materials contained in the sintering raw material varies depending on the amount of moisture added to the mixture and the granulation time. For example, when the amount of moisture added to the mixture is reduced or the granulation time is shortened, the ratio of the granulated raw material in the sintering raw material decreases and the ratio of the ungranulated raw material increases. The amount of moisture and the granulation time that make the ratios of the granulated raw material and the ungranulated raw material in the sintering raw material the desired ratios can be determined in advance by experiments. The sintering raw material containing the granulated raw material and the ungranulated raw material is conveyed to the surge hopper 3 by a conveyor and stored. The process of producing the sintering raw material as described above corresponds to the raw material blending process of the present embodiment.

[0015] Returning to the description of FIG. 1. Following the raw material blending process in step S1, the process proceeds to the raw material layer forming process in step S2, and the above-described sintering raw material is charged onto the pallet of the sintering machine, and a raw material layer is formed on the pallet. That is, the sintering raw material stored in the surge hopper 3 shown in FIG. 2 is cut out by the drum feeder 4 and charged onto the floor ore layer 6 described below through the chute 5 to form the raw material layer 7. In the example shown in FIG. 2, a floor ore hopper 8 is provided upstream of the surge hopper 3 in the conveying direction of the sintering raw material in the sintering machine, and the floor ore is stored in the floor ore hopper 8. The floor ore is cut out from the drum feeder of the floor ore hopper 8 and charged onto the pallet 10 of the sintering machine 9 through the chute to form the above-described floor ore layer 6.

[0016] A cutoff 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 substantially uniform. As a result, a raw material layer 7 with a predetermined thickness is formed. Thus, the step of loading onto the pallet 10 to form the raw material layer 7 with a predetermined thickness corresponds to the raw material layer forming step of the present embodiment.

[0017] Returning to the description of FIG. 1. Following the raw material layer forming step of step S2, the process proceeds to the sintering step of step S3, and the raw material layer 7 formed on the pallet 10 of the sintering machine 9 is ignited, and the sintering raw material is sintered. Specifically, as shown in FIG. 2, an ignition furnace 12 is provided downstream of the cutoff gate 11 in the conveying direction. The carbon material present on the surface of the raw material layer 7 is ignited by the ignition furnace 12. Further, a plurality of wind boxes 13 are 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 pipe 14. By sucking air into the wind box 13 through the raw material layer 7 by the sintering fan 15, air is circulated from the upper side to the lower side in the thickness direction of the raw material layer 7. As a result, the combustion of the carbon material in the sintering raw material proceeds from the upper side to the lower side of the raw material layer 7. The sintering raw material is heated by the combustion heat of the carbon material, at least a part of the iron raw material is melted and bonded, and the sintering of the sintering raw material proceeds from the upper side to the lower side of the raw material layer 7. Thus, a sintered layer (sometimes referred to as a sintered cake) is formed on the pallet 10 of the sintering machine 9. The step of sintering the sintering raw material as described above corresponds to the sintering step described above.

[0018] Also, in the example shown in FIG. 1, a dust collector 16 for collecting dust in the air and fine particles in the sintering raw material 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 by the sintering fan 15 is discharged to the outside through the chimney 17.

[0019] The sintered layer formed on the pallet 10 of the sintering machine 9 is discharged from the discharge ore section on the downstream side of the sintering machine 9 in the conveying direction to the outside of the sintering machine 9. Thereafter, the sintered layer is crushed by the crusher 18, classified, and sintered ore with a predetermined particle size is recovered as finished sintered ore.

[0020] Here, the above-mentioned biomass charcoal will be described. Biomass charcoal is a carbon material derived from organic resources other than fossil fuels, and the organic resources mean biomass. Biomass means resources that are organic substances derived from animals and plants excluding fossil fuels. Specifically, examples of biomass include coconut shells and bamboo. Examples of biomass charcoal include coconut shell charcoal and bamboo charcoal produced from coconut shells and bamboo as raw materials. In addition, the above-mentioned biomass absorbs carbon dioxide until the plant that is its raw material grows. Therefore, when a fuel using biomass, that is, biomass charcoal, is burned, the amount of carbon dioxide emissions into the environment can be considered to be zero from the perspective of carbon neutrality. That is, from the perspective of carbon neutrality, when biomass charcoal is blended into the sintering raw material, the emission of carbon dioxide can be suppressed accordingly. The characteristics of biomass charcoal include that its combustion start temperature is lower compared to coke. The combustion start temperature of biomass charcoal is generally 550°C or lower, and the combustion start temperature of coke is 650 - 750°C. In addition, the characteristics of biomass charcoal include that the combustion rate of biomass charcoal is higher than that of coke. These are considered to be due to the catalytic effect of alkali metals contained in biomass charcoal and the fact that biomass charcoal is porous. Therefore, biomass charcoal starts combustion more quickly than coke and generates combustion heat. In addition, the volatile content of biomass charcoal is higher compared to coke.

[0021] A method for segregating biomass charcoal on the upper layer side of the raw material layer 7 rather than the lower layer side will be described. In the present embodiment, as described above, in the drum mixer 2, the proportion of ungranulated biomass charcoal contained in the sintering raw material is increased by reducing the amount of moisture added to the mixture or shortening the granulation time. The amount of moisture and the granulation time for setting the proportion of biomass charcoal in the sintering raw material to a desired proportion can be determined in advance by experiments. Also, the particle size of the biomass charcoal is smaller than the particle sizes of the coke powder and anthracite added to the sintering raw material as carbon materials. Therefore, when raw materials with different particle sizes are cut out from the surge hopper 3 by the drum feeder 4, the raw materials with larger particle sizes fall almost directly below the drum feeder 4, and the raw materials with smaller particle sizes fall at positions away from the drum feeder 4. Note that the drum feeder 4 is configured to discharge the cut-out raw materials from the upstream side to the downstream side in the conveying direction.

[0022] Therefore, when the sintering raw material is cut out by the drum feeder 4, the raw materials with larger particle sizes including the granulated raw materials fall along the outer peripheral surface of the drum feeder 4 and are loaded onto the floor ore layer 6 almost directly below the drum feeder 4. On the other hand, the biomass charcoal falls to the side of the chute 5 located at a position away from the drum feeder 4, that is, downstream of the drum feeder 4 in the conveying direction. Thus, biomass charcoal segregates in the upper layer of the raw material layer 7 rather than the lower layer. Note that the upper layer of the raw material layer 7 means the upper side of the approximate center in the thickness direction of the raw material layer 7, and the lower layer of the raw material layer 7 means the lower side of the approximate center in the thickness direction of the raw material layer 7.

[0023] (Function and Effect) In this embodiment, as described above, biomass charcoal is segregated in the upper layer of the raw material layer 7. In the upper layer of the raw material layer 7, the biomass charcoal rapidly starts combustion and generates combustion heat. The combustion heat can raise the temperature of the upper layer of the raw material layer 7. Therefore, it is possible to suppress the heat shortage in the raw material layer 7 that is cooled by the suction of air. Also, in the upper layer, it is possible to suppress the generation of unburned carbon due to heat shortage. As a result, it is possible to obtain a sintered ore with a lower content of unburned carbon than in the past. Also, the yield of the sintered ore can be improved compared to the past.

[0024] Note that the present invention is not limited to the above-described embodiment. For example, when producing the sintering raw material in the drum mixer 2, instead of reducing the amount of moisture added to the mixture or shortening the granulation time, the biomass charcoal may be configured to be supplied from the hopper storing the biomass charcoal to the surge hopper 3. Even with such a configuration, it is possible to obtain substantially the same operations and effects as those of the above-described embodiment. Also, for example, instead of making the particle size of the biomass charcoal smaller than the particle sizes of the coke powder and anthracite, at least two types of sintering raw materials with different blending ratios of the biomass charcoal are prepared, and the upper layer of the raw material layer 7 may be formed with the sintering raw material having a high blending ratio of the biomass charcoal. Specifically, at least two surge hoppers are installed in the sintering machine 9 side by side in the conveying direction. Among the two surge hoppers, the sintering raw material with a low blending ratio of the biomass charcoal is stored in the surge hopper located upstream in the conveying direction. On the other hand, the sintering raw material with a high blending ratio of the biomass charcoal is stored in the surge hopper located downstream in the conveying direction. Then, the sintering raw material is charged from each surge hopper onto the pallet 10 of the sintering machine 9 to form the raw material layer. Thereby, in the lower layer of the raw material layer, the blending ratio of the biomass charcoal becomes low, and in the upper layer, the blending ratio of the biomass charcoal becomes high. That is, the biomass charcoal is segregated in the upper layer of the raw material layer 7. Therefore, even with such a configuration, it is possible to obtain substantially the same operations and effects as those of the above-described embodiment.

Example

[0025] An example of verifying the effect by segregating biomass charcoal in the upper layer of the raw material layer will be described. In this example, a sintering pot test apparatus with a height of 400 mm and a diameter of 300 mm was prepared, and a batch test was conducted using this apparatus. Also, two types of sintering raw materials with different blending ratios of biomass charcoal (mass %, hereinafter simply referred to as %) were prepared. Among these sintering raw materials, the upper layer of the raw material layer was formed in the above-described apparatus using the sintering raw material with a high blending ratio (%) of biomass charcoal. Note that the blending ratio of coke that generates the same amount of heat as the biomass charcoal blended in the sintering raw material is regarded as the blending ratio of biomass charcoal.

[0026] Table 1 shows the blending ratios (%) of biomass charcoal and the blending ratios (%) of coke that form the upper layer and the lower layer of the raw material layer in each of Examples 1-1 to 2-3, Comparative Examples 1 and 2, and Reference Example. Also, Table 1 shows the average blending ratio (%) of biomass charcoal in the entire raw material layer and the blending ratio (%) of biomass charcoal in the upper layer in terms of the average blending ratio (%) of biomass charcoal in the entire raw material layer in each of Examples 1-1 to 2-3, Comparative Examples 1 and 2, and Reference Example.

[0027]

Table 1

[0028] Note that coke and biomass charcoal were blended so that the heat equivalent to 5% in terms of the heat of average pulverized coke was obtained. The reference example was based on the condition of using only coke. In Comparative Example 1 and Examples 1-1 to 1-3, 20% of the entire carbon material was replaced with biomass charcoal, and in Comparative Example 2 and Examples 2-1 to 2-3, 40% of the entire carbon material was replaced with biomass charcoal.

[0029] Ignition was carried out on the surface layer of the raw material layer formed within the above-described apparatus, and air was sucked from the lower side of the raw material layer to sinter the raw material layer to produce a sintered cake. Then, the unburned carbon ratio was measured using a sample sampled from the sintered cake after yield measurement. Specifically, samples were sampled from the upper layer 1 / 2 of the sintered cakes of Comparative Examples 1 and 2 and Examples 1-1 to 2-3, and the carbon content of Comparative Examples 1 and 2 and Examples 1-1 to 2-3 was measured using the samples. The method for measuring the carbon content may be a conventionally known chemical analysis method. Similarly, samples were sampled from the upper layer 1 / 2 of the sintered cake of the reference example, and the carbon content of the reference example was measured using the samples. Then, the carbon content of Comparative Examples 1 and 2 and Examples 1-1 to 2-3 was divided by the carbon content of the reference example to calculate the unburned carbon ratio of the sintered cakes of Comparative Examples 1 and 2 and Examples 1-1 to 2-3. Note that the upper layer 1 / 2 means the approximate center of the upper layer in the thickness direction of the sintered cake.

[0030] Figure 3 is a diagram showing the relationship between the unburned carbon ratio of Comparative Examples 1 and 2 and Examples 1-1 to 2-3 and the blending ratio (%) of biomass carbon in the upper layer to the average blending ratio (%) of biomass carbon in the entire raw material layer. As shown in Figure 3, it was found that as the blending ratio (%) of biomass carbon in the upper layer to the average blending ratio (%) of biomass carbon in the entire raw material layer increases, the unburned carbon ratio decreases accordingly. Also, it was found that as the average blending ratio (%) of biomass carbon in the entire raw material layer increases, the unburned carbon ratio decreases accordingly.

[0031] Figure 4 is a diagram showing the relationship between the unburned carbon ratio of Comparative Examples 1 and 2 and Examples 1-1 to 2-3 and the ratio of biomass carbon in the entire carbon material in the upper layer, that is, the substitution rate (%) of biomass carbon. As shown in Figure 4, it was found that as the substitution rate (%) of biomass carbon increases, the unburned carbon ratio decreases accordingly. From these results, it was found that if the combustion heat of the carbon material in the upper layer of the raw material layer is substantially constant, the unburned carbon ratio of the sintered ore formed in the upper layer of the raw material layer can be reduced by segregating biomass carbon in the upper layer.

[0032] In addition, in the above-described embodiment, biomass charcoal was unevenly distributed in the upper layer of the raw material layer. However, compared with the conventional method for producing sintered ore that does not use biomass charcoal, no decrease in the yield of sintered ore was observed. This is because although the combustion heat of biomass charcoal is lower than that of coke, biomass charcoal starts combustion promptly compared with coke to generate combustion heat, and the combustion heat compensates for the heat quantity in the upper layer of the raw material layer. As a result, it is considered that heat shortage in the upper layer of the raw material layer was suppressed, and generation of unburned carbon was suppressed.

Explanation of Signs

[0033] 1 Hopper 2 Drum mixer 3 Surge hopper 4 Drum feeder 5 Shoot 6 Floor ore layer 7 Raw material layer 8 Floor ore hopper 9 Sintering machine 10 Pallet 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 raw material blending step of producing a sintering raw material by blending an iron raw material, a first carbonaceous material, and a second carbonaceous material having a lower combustion start temperature than the first carbonaceous material; a raw material layer forming step of supplying the sintering 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 sintering raw material. A method for producing sintered ore, wherein: In the raw material layer forming step, the blending ratio of the second carbonaceous material in the upper layer above the central portion in the thickness direction of the raw material layer is higher than the blending ratio of the second carbonaceous material in the lower layer below the central portion in the thickness direction. A method for producing sintered ore.

2. The particle size of the second carbonaceous material is smaller than the particle size of the first carbonaceous material. In the raw material layer forming step, the sintering raw material stored in the surge hopper is cut out by a drum feeder and supplied onto the pallet. The method for producing sintered ore according to claim 1.

3. The first carbonaceous material blended with the sintering raw material in the raw material blending step is a carbon material derived from fossil fuel, and the second carbonaceous material is a carbon material other than fossil fuel. The method for producing sintered ore according to claim 1 or 2.

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