Sintered ore production method

Abstract

Provided is a sintered ore production method capable of suppressing production of sintered ore containing unburned carbon in an upper layer of a raw material layer by suppressing heat deficiency in the upper layer of the raw material layer.　The present invention provides a sintered ore production method including: a raw material blending step (step S1) for producing a sintering raw material by blending an iron raw material, a first carbonaceous material, and a second carbonaceous material having a combustion start temperature lower than that of the first carbonaceous material; a raw material layer forming step (step S2) for forming a raw material layer by supplying the sintering raw material onto a pallet of a sintering machine; and a sintering step (step S3) for sintering the sintering raw material by igniting the surface of the raw material layer, wherein, in the raw material layer forming step (step S2), the blending ratio of the second carbonaceous material in an upper layer above the central part in the thickness direction of a raw material layer 7 is made higher than the blending ratio of the second carbonaceous material in a lower layer below the central part in the thickness direction.

Description

Sinter manufacturing method

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

[0002] In the iron ore sintering process, iron ore, flux, and a carbonaceous material as a solid fuel are mixed to produce sintering raw materials, which are then fed onto a pallet in a sintering machine to form a raw material bed. The upper surface of the raw material bed is ignited to burn the carbonaceous material, which then solidifies the sintering raw materials with the heat of combustion. Air is then drawn in from the lower surface of the raw material bed. Therefore, the upper layer of the raw material bed generally suffers from a heat deficit compared to the lower layer due to the influence of the air drawn into the raw material bed from the upper surface. This can result in the carbonaceous material in the upper layer not being completely burned, resulting in unburned carbon, potentially resulting in sintered ore with a high unburned carbon content. During sinter production, the temperature of sintered ore with a high unburned carbon content is lower than that of sintered ore with a low unburned carbon content.

[0003] Sintered ore produced in a sintering machine is crushed when it is discharged from the sintering machine and then charged into a cooler where it is cooled. However, if sintered ore with a high unburned carbon content comes into contact with uncooled sintered ore in the cooler, the unburned carbon may burn, potentially reducing the cooling efficiency of the sintered ore in the cooler.

[0004] Furthermore, carbon dioxide is generated during the combustion of carbon materials during the iron ore sintering process. Therefore, in response to growing awareness of environmental conservation in recent years, the use of biomass-derived carbon materials is being considered as a way to reduce the burden on the environment. This is because biomass absorbs carbon dioxide while the plants that serve as its raw material grow, and biomass-based fuels can be counted as having no carbon dioxide emissions under the carbon-neutral concept.

[0005] Patent Document 1 describes an example of a method for producing sintered ore using a biomass-derived solid carbonaceous material. In this production method, oil palm kernel shell charcoal is mixed into the sintering raw material as a biomass-derived solid carbonaceous material. Furthermore, when forming the raw material layer, solid carbonaceous materials other than oil palm kernel shell charcoal are segregated in the upper layer of the raw material layer, and a large amount of oil palm kernel shell charcoal is distributed in the lower layer of the raw material layer. This is said to improve the combustibility of the lower layer of the raw material layer and increase the productivity of sintered ore. Furthermore, because oil palm kernel shell charcoal is a biomass-derived carbonaceous material, it is said to be able to suppress carbon dioxide emissions.

[0006] Patent No. 5786795

[0007] In the manufacturing method of Patent Document 1, the use of oil palm kernel shell charcoal can improve the productivity of sintered ore and also suppress carbon dioxide emissions. However, no consideration is given to the possibility that sintered ore containing unburned carbon may be produced due to insufficient heat in the upper layer of the raw material bed, and there is room for improvement in this regard.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for producing sintered ore that can prevent sintered ore containing unburned carbon from being produced in the upper layer of the raw material layer by suppressing heat shortage in the upper layer of the raw material layer.

[0009] Means for solving the above problems are as follows: [1] A method for producing sintered ore, comprising: a raw material blending step of 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 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 layer forming step, a blending ratio of the second carbonaceous material in an upper layer above a center in the thickness direction of the raw material layer is higher than a blending ratio of the second carbonaceous material in a lower layer below the center in the thickness direction. [2] A method for producing sintered ore according to [1], wherein a particle size of the second carbonaceous material is smaller than that of the first carbonaceous material, and in the raw material layer forming step, the sintered raw material stored in a surge hopper is fed by a drum feeder onto a pallet. [3] The method for producing sintered ore described in [1] or [2], wherein the first carbonaceous material to be mixed with the sintering raw material in the raw material mixing step is a carbonaceous material derived from a fossil fuel, and the second carbonaceous material is a carbonaceous material other than a fossil fuel.

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

[0011] Fig. 1 is a diagram for explaining the sintered ore manufacturing method of the present embodiment. Fig. 2 is a diagram showing an example of a sintered ore manufacturing facility to which the sintered ore manufacturing method of the present embodiment can be applied. Fig. 3 is a diagram showing the relationship between the unburned carbon ratio in a comparative example and an example and the blending ratio of biomass charcoal in the upper layer relative to the average blending ratio of biomass charcoal in the entire raw material layer. Fig. 4 is a diagram showing the relationship between the unburned carbon ratio in a comparative example and an example and the proportion of biomass charcoal in the entire carbon material in the upper layer, i.e., the biomass char replacement rate.

[0012] An embodiment of the present invention (hereinafter referred to as the present embodiment) will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a method for producing sintered ore according to the present embodiment. In the example shown in FIG. 1, first, a plurality of raw materials are mixed in a predetermined ratio to granulate the sintered raw material (step S1, raw material blending step). FIG. 2 is a diagram showing an example of a sintered ore production facility to which the sintered ore production method according to the present 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.

[0013] 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 coke powder derived from fossil fuels, anthracite, and biomass charcoal derived from biomass. In this embodiment, the particle size of the biomass charcoal is smaller than that of the granulated raw material described below. These raw materials are stored in hoppers 1. Then, each raw material is supplied from each hopper 1 to a conveyor (not shown) at a predetermined ratio and transported to the drum mixer 2 by the conveyor. Of the carbon materials described above, coke powder and anthracite correspond to the first carbonaceous material in this embodiment, and biomass charcoal corresponds to the second carbonaceous material in this embodiment. Biomass charcoal will be described later.

[0014] In the drum mixer 2, the raw materials are mixed, water is added to the mixture to adjust the humidity, and the mixture is stirred for a predetermined period of time (hereinafter referred to as the granulation time). In this way, a sinter raw material containing raw materials granulated to a predetermined average particle size (hereinafter referred to as the granulated raw material) is produced. In other words, the sinter raw material produced by the drum mixer 2 contains not only the granulated raw material but also various raw materials that have not yet been granulated (hereinafter referred to as the ungranulated raw material). The proportion of the ungranulated raw material contained in the sinter raw material varies depending on the amount of water added to the mixture and the granulation time. For example, reducing the amount of water added to the mixture or shortening the granulation time decreases the proportion of the granulated raw material in the sinter raw material and increases the proportion of the ungranulated raw material. The water amount and granulation time that achieve the desired proportions of the granulated raw material and the ungranulated raw material in the sinter raw material can be determined in advance through experimentation. The sinter raw material containing the granulated raw material and the ungranulated raw material is transported by a conveyor to the 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.

[0015] Returning to the explanation of Fig. 1, following the raw material blending step of step S1, the process proceeds to the raw material layer forming step of step S2, where the above-mentioned sinter raw materials are charged 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 surge hopper 3 shown in Fig. 2 are fed by the drum feeder 4 and charged onto the bedding ore layer 6 described below via the chute 5, thereby forming the raw material layer 7. In the example shown in Fig. 2, a bedding ore hopper 8 is provided upstream of the surge hopper 3 in the conveying direction of the sinter raw materials in the sinter machine, and bedding ore is stored in the bedding ore hopper 8. The bedding ore is fed from the drum feeder of the bedding ore hopper 8 and charged onto the pallet 10 of the sinter machine 9 via the chute, thereby forming the above-mentioned bedding ore layer 6.

[0016] 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.

[0017] 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. Specifically, as shown in FIG. 2 , an ignition furnace 12 is provided downstream of the cutoff gate 11 in the conveying direction. The ignition furnace 12 ignites the carbon material present on the surface of the raw material layer 7. Furthermore, multiple 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 duct 14. The sintering fan 15 draws air into 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 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 combustion heat of the carbon material, at least a portion of the iron raw material melts and bonds, and 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 sintering raw material as described above corresponds to the sintering process described above.

[0018] 1, a dust collector 16 for collecting dust particles 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.

[0019] 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 recovered as product sintered ore.

[0020] Here, we will explain the aforementioned 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. Specific examples of biomass include coconut shells and bamboo. Examples of biomass charcoal include coconut shell charcoal and bamboo charcoal, which are produced using coconut shells and bamboo as raw materials. Furthermore, the aforementioned biomass absorbs carbon dioxide while the plants that serve as its raw materials grow. Therefore, when biomass-based fuel, i.e., biomass charcoal, is burned, it can be considered that no carbon dioxide is emitted into the environment from the perspective of carbon neutrality. In other words, from the perspective of carbon neutrality, blending biomass charcoal with sintering raw materials can reduce carbon dioxide emissions accordingly. One characteristic of biomass charcoal is its lower combustion initiation temperature compared to coke. The combustion initiation temperature of biomass charcoal is generally below 550°C, while the combustion initiation temperature of coke is 650-750°C. Another feature of biomass charcoal is that it burns faster than coke. This is thought to be due to the catalytic effect of the alkali metals contained in biomass charcoal and the porous nature of biomass charcoal. Therefore, biomass charcoal begins to burn faster than coke and generates combustion heat. Biomass charcoal also has a higher volatile content than coke.

[0021] A method for segregating biomass charcoal in the upper layer of the raw material layer 7 relative to the lower layer will be described. In this embodiment, as described above, the proportion of ungranulated biomass charcoal in the sintering raw material is increased by reducing the amount of water added to the mixture in the drum mixer 2 and shortening the granulation time. The water content and granulation time required to achieve a desired proportion of biomass charcoal in the sintering raw material can be determined in advance through experiments. Furthermore, the particle size of biomass charcoal is smaller than that of coke powder and anthracite, which are added to the sintering raw material as carbonaceous materials. Therefore, when raw materials of different particle sizes are fed from the surge hopper 3 by the drum feeder 4, the larger particle size falls almost directly below the drum feeder 4, while the smaller particle size falls at a position farther away from the drum feeder 4. The drum feeder 4 discharges the fed raw material from the upstream side to the downstream side in the conveying direction.

[0022] Therefore, when the sinter raw material is fed by the drum feeder 4, the larger particle size raw material, including the granulated raw material, falls along the outer peripheral surface of the drum feeder 4 and is charged onto the bedding ore layer 6 almost directly below the drum feeder 4. On the other hand, the biomass charcoal falls to a position away from the drum feeder 4, that is, to the side of the chute 5 located downstream of the drum feeder 4 in the conveying direction. Thus, more biomass charcoal segregates in the upper layer of the raw material layer 7 than in the lower layer. Note that the upper layer of the raw material layer 7 means the side above approximately the center in the thickness direction of the raw material layer 7, and the lower layer of the raw material layer 7 means the side below approximately the center in the thickness direction of the raw material layer 7.

[0023] (Actions and Effects) In this embodiment, biomass charcoal is segregated in the upper layer of the raw material layer 7 as described above. In the upper layer of the raw material layer 7, the biomass charcoal quickly starts to burn and generates combustion heat. This combustion heat can raise the temperature of the upper layer of the raw material layer 7. This can suppress heat shortage in the raw material layer 7, which is cooled by air suction. In addition, it can suppress the generation of unburned carbon in the upper layer due to heat shortage. As a result, it is possible to obtain sintered ore with a lower unburned carbon content than conventional sintered ore. In addition, it is possible to improve the yield of sintered ore compared to conventional sintered ore.

[0024] The present invention is not limited to the above-described embodiment. For example, when producing sinter raw materials using a drum mixer 2, instead of reducing the amount of water added to the mixture or shortening the granulation time, a configuration may be adopted in which biomass charcoal is supplied from a hopper storing biomass charcoal to the surge hopper 3. Even with this configuration, substantially the same functions and effects as those of the above-described embodiment can be obtained. Furthermore, for example, instead of making the particle size of the biomass charcoal smaller than that of the coke powder or anthracite, at least two types of sinter raw materials with different biomass charcoal blending ratios may be prepared, and the upper layer of the raw material layer 7 may be formed from the sinter raw material with a higher biomass charcoal blending ratio. Specifically, at least two surge hoppers are installed in the sintering machine 9, lined up in the conveying direction. Of the two surge hoppers, the surge hopper located upstream in the conveying direction stores sinter raw materials with a lower biomass charcoal blending ratio. On the other hand, the surge hopper located downstream in the conveying direction stores sinter raw materials with a higher biomass charcoal blending ratio. Then, sinter raw materials are charged from each surge hopper onto the pallet 10 of the sintering machine 9 to form a raw material layer. As a result, the blending ratio of biomass charcoal becomes lower in the lower layer of the raw material layer and becomes higher in the upper layer. In other words, biomass charcoal segregates in the upper layer of the raw material layer 7. Therefore, even with this configuration, it is possible to obtain actions and effects that are almost the same as those of the present embodiment described above.

[0025] An example will be described that verified the effect of segregating biomass charcoal in the upper layer of the raw material layer. In this example, a sintering pot test device with a height of 400 mm and a diameter of 300 mm was prepared, and a batch test was performed using this device. Two types of sintering raw materials with different biomass charcoal blending ratios (mass %; hereinafter simply referred to as %) were prepared. Of these sintering raw materials, the sintering raw material with the higher biomass charcoal blending ratio (%) was used to form the upper layer of the raw material layer in the above-mentioned device. Note that the biomass charcoal blending ratio is defined as the blending ratio of coke that generates the same amount of heat as the biomass charcoal blended in the sintering raw material.

[0026] Table 1 shows the blending ratio (%) of biomass coal and the blending ratio (%) of coke forming the upper and lower layers of the raw material layer in each of Examples 1-1 to 2-3, Comparative Examples 1 and 2, and the Reference Example. Table 1 also shows the average blending ratio (%) of biomass coal in the entire raw material layer, and the blending ratio (%) of biomass coal in the upper layer relative to the average blending ratio (%) of biomass coal in the entire raw material layer in each of Examples 1-1 to 2-3, Comparative Examples 1 and 2, and the Reference Example.

[0027]

[0028] The coke and biomass charcoal were blended so that the calorific value was equivalent to 5% of the average calorific value of coke breeze. The reference example was a base condition using only coke. In Comparative Example 1 and Examples 1-1 to 1-3, 20% of the total carbon material was replaced with biomass charcoal, and in Comparative Example 2 and Examples 2-1 to 2-3, 40% of the total carbon material was replaced with biomass charcoal.

[0029] The surface layer of the raw material layer formed in the above-described apparatus was ignited, and air was sucked from below the raw material layer to sinter the raw material layer and produce a sintered cake. Then, the unburned carbon ratio was measured using a sample sampled from the sintered cake after the yield measurement. Specifically, samples were sampled from the upper half of the sintered cakes of Comparative Examples 1 and 2 and Examples 1-1 to 2-3, and the carbon amounts of Comparative Examples 1 and 2 and Examples 1-1 to 2-3 were measured using the samples. The carbon amount measurement method may be a conventional chemical analysis method. Similarly, a sample was sampled from the upper half of the sintered cake of the Reference Example, and the carbon amount of the Reference Example was measured using the sample. The carbon amounts of Comparative Examples 1 and 2 and Examples 1-1 to 2-3 were then divided by the carbon amount 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. The upper half of the sintered cakes refers to the approximate center of the upper layer in the thickness direction of the sintered cake.

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

[0031] 4 is a diagram showing the relationship between the unburned carbon ratio and the proportion of biomass charcoal in the total carbon material in the upper layer, i.e., the biomass charcoal replacement rate (%), for Comparative Examples 1 and 2 and Examples 1-1 to 2-3. As shown in FIG. 4, it was found that as the biomass charcoal replacement rate (%) increases, the unburned carbon ratio decreases accordingly. These results show that, if the heat of combustion of the carbon material in the upper layer of the raw material layer is approximately 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 charcoal in the upper layer.

[0032] Furthermore, in the above-described examples, biomass charcoal was unevenly distributed in the upper layer of the raw material layer, but no decrease in sinter yield was observed compared to conventional sintered ore manufacturing methods that do not use biomass charcoal. This is because, although the combustion heat of biomass charcoal is lower than that of coke, biomass charcoal begins to burn more quickly than coke and generates combustion heat, which compensates for the heat in the upper layer of the raw material layer. As a result, heat shortage in the upper layer of the raw material layer was suppressed, and the generation of unburned carbon was suppressed.

[0033] REFERENCE SIGNS LIST 1 Hopper 2 Drum mixer 3 Surge hopper 4 Drum feeder 5 Chute 6 Bed ore layer 7 Raw material layer 8 Bed ore hopper 9 Sintering machine 10 Pallet 11 Cut-off gate 12 Ignition furnace 13 Wind box 14 Exhaust duct 15 Sintering fan 16 Dust collector 17 Chimney 18 Crusher S1 Raw material blending process S2 Raw material layer forming process S3 Sintering process

Claims

1. A method for producing sintered ore, comprising: a raw material blending step of 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 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 layer forming step, the blending ratio of the second carbonaceous material in an upper layer above the center in the thickness direction of the raw material layer is made higher than the blending ratio of the second carbonaceous material in a lower layer below the center in the thickness direction.

2. A method for producing sintered ore as described in claim 1, wherein the particle size of the second carbonaceous material is smaller than the particle size of the first carbonaceous material, and in the raw material layer forming process, the sintered raw material stored in a surge hopper is cut out by a drum feeder and supplied onto a pallet.

3. A method for producing sintered ore as described in claim 1 or 2, wherein the first carbonaceous material mixed with the sintering raw material in the raw material mixing process is a carbonaceous material derived from fossil fuel, and the second carbonaceous material is a carbonaceous material other than fossil fuel.

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