JP7187971B2 - Method for producing sintered ore - Google Patents

Description

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

The method for producing sintered ore is outlined below. First, sintering raw materials, which are raw materials for sintered ore, are blended at a predetermined ratio to form a blended raw material, which is then granulated with water. Here, the raw material for sintering is composed of an iron-containing raw material as a main raw material, auxiliary raw materials necessary for sintering reaction and component adjustment, carbonaceous material (solid fuel) as a heat source, return ore, and the like. Iron-containing raw materials are, for example, iron ore such as fine ore and fine ore, ironmaking dust (ironmaking dust, steelmaking dust, scale, etc.), and the like. The auxiliary materials include limestone, quicklime, slaked lime, MgO-containing auxiliary materials (serpentinite, peridotite, dolomite, etc.), converter slag, silica stone, and the like. Since quicklime and slaked lime have a function of promoting granulation, they are hereinafter referred to as granulating agents. Carbonaceous materials are, for example, coke dust and anthracite.

Next, the granules of the blended raw material are charged in layers on a sintering pallet of a sintering machine. Next, the solid fuel in the raw material packed bed is ignited from the surface of the raw material packed bed, and the raw material packed bed is sucked and ventilated from the top to the bottom in the thickness direction. As a result, the combustion zone of the raw material packed bed is sequentially shifted to the lower layer side, and the sintering reaction proceeds. The sintered cake in the sintering pallet after sintering is pulverized and sized so as to have a predetermined particle size suitable for blast furnace sintered ore. A sintered ore is produced by the above process.

By the way, a sintering machine for producing sintered ore generates carbonaceous-derived nitrogen oxides (NO _x ) that are used as a fuel, and the reduction thereof is an important issue. Patent Documents 1 and 2 disclose techniques aimed at reducing nitrogen oxides. Specifically, in Patent Documents 1 and 2, a carbonaceous material is coated with a coating material containing a Ca-based substance. Patent Documents 1 and 2 mention calcium hydroxide as a preferable example of the Ca-based substance.

Patent No. 4870247 JP 2015-86419 A JP 2016-125125 A

However, when the carbonaceous material is coated with a coating material containing a Ca-based substance, a relatively large amount of the coating material is required in order to sufficiently reduce nitrogen oxides. For example, Patent Document 1 describes that the generation of nitrogen oxides can be further suppressed by setting the mass % of the covering material to the carbon material to 10 to 40 mass %.

Here, the coating materials described in Patent Documents 1 and 2 correspond to the granulating material described above. In Patent Documents 1 and 2, since the carbonaceous material is covered with a large amount of the coating material, the amount of the granulating material used increases. That is, when part or all of the carbon material in the raw material for sintering is simply replaced with the coated carbon material (carbon material coated with the coating material) described in Patent Documents 1 and 2, the coated carbon material The amount of granulating material in the entire blended raw material increases. That is, since the amount of granulating material used increases, costs (running costs, facility costs) increase.

One way to solve this problem is to use a constant amount of granulating material. In other words, the amount of granulated material in the original raw material for sintering is reduced by the amount of the coating material. However, in this method, most of the granulating material is used for the coating material, so the ratio of the granulating material when granulating the remaining raw materials is reduced, and the granulation properties of the entire blended raw material are reduced. do. That is, the particle size of the granules becomes smaller. For this reason, there is a possibility that the permeability of the raw material packed bed is lowered, and that the productivity of the sintered ore is lowered.

On the other hand, Patent Document 3 discloses a technique of coating a carbonaceous material with a coating material containing MgO-containing powder and iron ore powder. However, with this technique, the proportion of MgO-containing powder in the coating material is very low (1 to 3% by mass), and nitrogen oxides could not be sufficiently reduced.

Thus, no technology has been proposed yet that can reduce nitrogen oxides while maintaining the productivity of sintered ore.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to reduce nitrogen oxides while maintaining the productivity of sintered ore. To provide an improved method for producing sintered ore.

In order to solve the above problems, according to one aspect of the present invention, a carbon material treatment step of granulating the coating material and the carbon material in order to coat at least part of the surface of the carbon material with the coating material. , a granule preparation step of preparing granules of the blended raw materials by blending the coated carbon material having at least a portion of the surface coated with the coating material and other raw materials for sintering and then granulating them; A sintered ore preparation step of preparing sintered ore by firing granules of the raw material , and the coating material contains 90% by mass or more of the MgO-containing auxiliary raw material with respect to the total mass of the coating material. There is provided a method for producing sintered ore, wherein the mass of the MgO-containing auxiliary raw material contained in the coating material is 5% by mass or more and less than 10% by mass with respect to the carbonaceous material .

Here, in the carbon material treatment step, the coating material and the carbon material, which are composed only of the MgO-containing auxiliary raw material, may be granulated.

Furthermore, the MgO-containing auxiliary material may be one or more of peridotite and serpentinite.

Also, the particle size of the MgO-containing auxiliary material may be 250 μm or less .

As described above, according to the present invention, the carbonaceous material is coated with the MgO-containing auxiliary material that is difficult to decompose in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material. Therefore, the carbonaceous material can be stably isolated from the iron ore in the temperature range from the start of combustion of the carbonaceous material to the middle period of combustion, and as a result, nitrogen oxides can be reduced. Furthermore, since the MgO-containing auxiliary material is more difficult to decompose than the Ca-based material in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material, it is possible to separate the carbonaceous material from the iron ore even if the amount is small. In other words, nitrogen oxides can be reduced even if the amount is small. Therefore, the productivity of sintered ore can be maintained.

It is a graph which shows the result of the basic experiment which this inventor performed.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<1. Examination by the present inventor>
The present inventor conducted a basic experiment using a differential thermal balance-mass spectrometer (TG/DTA-MS) in order to clarify the cause of the generation of nitrogen oxides. The outline of the basic experiment is as follows. First, as test sample 1, a mixture of 13.5 mg of coke breeze and as test sample 2, a mixture of 13.5 mg of coke breeze and 7.4 mg of Fe ₂ O ₃ reagent was prepared. The grain size of each sample was 250 μm or less. Then, each test sample is set in TG/DTA-MS (manufactured by Bruker AXS / TG-DTA2000SA + MS-9610), and the test sample is heated to 1400 ° C. at a heating rate of 50 ° C./min under air flow of 50 ml / min. was heated. A part of the gas generated during the temperature rise was sampled with a quadrupole mass spectrometer, and the gas with a mass number of 30 (mainly NO) generated during combustion was monitored. That is, the amount of nitrogen oxides generated was monitored. The results are shown in FIG.

The horizontal axis of FIG. 1 indicates the temperature of the test sample, and the vertical axis indicates the amount of mass reduction (TG mass reduction) (mg) of the test sample or the detection intensity (Intensity) (A) of the gas with a mass number of 30. A stronger detection intensity indicates a larger amount of gas with a mass number of 30 generated. A graph L1 shows the correlation between the temperature of the test sample 1 and the amount of mass reduction, and the graph L2 shows the correlation between the temperature of the test sample 2 and the amount of mass reduction. A graph L3 shows the correlation between the temperature of the test sample 1 and the detected intensity of the gas with a mass number of 30, and the graph L4 shows the correlation between the temperature of the test sample 2 and the detected intensity of the gas with a mass number of 30.

As shown in Figure 1, the test sample begins to lose mass (ie, burn) at about 550°C. At the same time, a gas with a mass number of 30 began to be generated. In the latter stage of combustion of the carbonaceous material (above the melting start temperature of the raw material for sintering, here above 950 ° C.), the amount of nitrogen oxides generated from test sample 2 (with Fe ₂ O ₃ added) is less than that from test sample 1. It is less than the amount of oxides generated. This indicates that the presence of iron oxide reduces nitrogen oxides, as has often been said.

On the other hand, in the temperature range from the start of combustion of the carbon material (after mass reduction = about 550 ° C.) to the middle period of combustion (about 950 ° C.) (generally below the melting start temperature of the raw material for sintering), nitrogen oxidation from test sample 2 The amount of nitrogen oxides generated from test sample 1 is greatly increased. As a result, it was newly found that the coexistence of Fe ₂ O ₃ in coke breeze significantly increases nitrogen oxides in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material.

In the raw material packed bed, the carbonaceous material is always in contact with iron ore containing Fe ₂ O ₃ as a main component, and Fe ₂ O ₃ is usually present in the combustion field of the carbonaceous material. The above findings show that nitrogen oxides can be further reduced by avoiding contact between the carbonaceous material and the iron ore as much as possible in the temperature range from the start of combustion of the carbonaceous material to the middle period of combustion.

Therefore, the present inventors diligently studied a technology capable of isolating the carbonaceous material from the iron ore in the temperature range from the start of combustion of the carbonaceous material to the middle period of combustion thereof, specifically, a coating material for the carbonaceous material. Various substances can be considered as coating materials, but sintering should be done so as not to affect the normal production of sintered ore as much as possible and not to interfere with the operation of the blast furnace where the sintered ore is used. It is desirable to use auxiliary raw materials that are commonly used as raw materials for use (raw materials for blending).

Patent Documents 1 and 2 disclose the use of a Ca-based substance as a coating material. Patent Documents 1 and 2 state that it is particularly desirable to use calcium hydroxide among Ca-based substances. However, as described above, in order to sufficiently reduce nitrogen oxides, it is necessary to coat the carbonaceous material with a relatively large amount of Ca-based material. One of the reasons for this is as follows. That is, calcium hydroxide, which is cited as a preferable Ca-based substance in Patent Documents 1 and 2, decomposes at a relatively low temperature (400 to 600° C.) to release H ₂ O. The temperature range in which calcium hydroxide decomposes overlaps with the temperature range from the start of combustion to the middle period of combustion of carbonaceous material.

Therefore, when the carbonaceous material is coated with calcium hydroxide, the initially dense coating layer around the carbonaceous material becomes porous in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material, and part of the coating layer decomposes. It peels off with the impact of Therefore, it is presumed that the effect of preventing contact between the carbonaceous material and the iron ore existing around it (in other words, isolating them) in the temperature range from the start of combustion of the carbonaceous material to the middle period of combustion is not so great. Therefore, in order to sufficiently reduce nitrogen oxides, it is necessary to coat the carbonaceous material with a relatively large amount of Ca-based material, resulting in an increase in the amount of auxiliary materials used. As a method for solving this problem, there is a method in which the amount of the auxiliary raw material used is kept constant. However, this method reduces the amount of auxiliary raw materials that can be used as a granulating material, so there is a possibility that the productivity of sintered ore will decrease. Patent Documents 1 and 2 do not disclose coating materials other than Ca-based substances.

Therefore, the present inventors came up with the idea of using a new Mg-based auxiliary raw material (MgO-containing auxiliary raw material) as a coating material. Then, a sintering experiment (described in Examples) was actually conducted to confirm the effect, and the method for producing sintered ore according to the present embodiment was completed. It is also possible to cover the carbonaceous material with substances other than the MgO-containing auxiliary material, such as Al ₂ O ₃ -based and SiO ₂ -based substances. However, these methods are not preferable because they newly introduce an extra slag component into the sintered ore, leading to an increase in blast furnace slag. The present embodiment will be described in detail below.

<2. MgO-containing auxiliary raw material>
In the method for producing sintered ore according to the present embodiment, the surface of the carbonaceous material is coated with the coating material containing the MgO-containing auxiliary raw material. Therefore, the MgO-containing auxiliary material will be explained. The MgO-containing auxiliary raw material means one containing an MgO component among the auxiliary raw materials used as raw materials for sintering.

As described above, in the carbon material combustion field, a large amount of nitrogen oxides are generated in the temperature range from the start of carbon material combustion to the middle period of combustion. When the present inventor compared the MgO-containing auxiliary raw material with a Ca-based material conventionally used as a coating material, it was found that the MgO-containing auxiliary raw material is difficult to decompose in the temperature range from the start of carbon material combustion to the middle period of combustion. . Therefore, when the carbonaceous material is coated with the MgO-containing auxiliary raw material, the carbonaceous material can be stably isolated from the iron ore in the temperature range from the start of combustion of the carbonaceous material to the middle period of combustion of the carbonaceous material, thereby further reducing nitrogen oxides. be able to. Furthermore, since the MgO-containing auxiliary material is more difficult to decompose than the Ca-based material in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material, it is possible to separate the carbonaceous material from the iron ore even if the amount is small. In other words, nitrogen oxides can be reduced even if the amount is small. Therefore, even if the carbonaceous material is coated with the coating material, it is possible to suppress an increase in the amount of auxiliary raw material used, so that the carbonaceous material can be sufficiently burned during firing. Therefore, the productivity of sintered ore can be maintained.

The MgO-containing auxiliary material that can be used in this embodiment is not particularly limited as long as it can be used as a raw material for sintering. Examples of MgO-containing auxiliary materials include dolomite, magnesite, brucite, peridotite, and serpentinite. These may be used alone or in combination.

Among the above MgO-containing auxiliary materials, it is preferable to use an MgO-containing auxiliary material having a loss on ignition (LOI) at 900° C. of 15% by mass or less. Here, LOI was measured by a method conforming to JIS-A-6206 (heating temperature 700±25° C.). Examples of the MgO-containing auxiliary material having an LOI of 15% by mass or less include peridotite and serpentinite. That is, in this embodiment, it is preferable to use at least one of peridotite and serpentinite. Peridotite and serpentinite are particularly difficult to decompose in the temperature range from the start of burning of carbonaceous materials to the middle stage of burning. Therefore, by coating the carbonaceous material with one or more of peridotite and serpentinite, nitrogen oxides can be further reduced. Table 1 below shows analytical values for some MgO-containing auxiliary materials.

As shown in Table 1, the LOI of peridotite and serpentinite is 15% by mass or less, while the LOI of dolomite exceeds 15% by mass.

<3. Method for producing sintered ore>
Next, a method for producing sintered ore according to the present embodiment will be described. The method for producing sintered ore includes a carbon material treatment step, a granule preparation step, and a sintered ore preparation step.

(3-1. Carbon material treatment process)
The carbon material treatment step is a step of granulating the coating material and the carbon material in order to cover at least a part of the surface of the coating material carbon material containing 90% by mass or more of the MgO-containing auxiliary raw material. As a result, the carbonaceous material can be stably isolated from the iron ore during the firing of the raw material for sintering, particularly from the start of combustion of the carbonaceous material to the middle period of combustion of the carbonaceous material, thereby reducing nitrogen oxides. The coating with the coating material includes coating the entire surface of the carbon material with the coating material, as well as attaching the coating material only to a part of the surface of the carbon material. That is, covering at least part of the surface of the carbonaceous material with the covering material is also included.

The type of carbonaceous material is not particularly limited, and any carbonaceous material used as a raw material for sintering can be used without particular limitation. Carbonaceous materials are, for example, coke dust and anthracite. These may be used singly or in combination. The particle size of the carbonaceous material is also not particularly limited, and may be a general particle size (for example, 10 mm or less) of carbonaceous material used as a raw material for sintering. It should be noted that the particle size in the present embodiment is classified by the opening of the sieve. For example, the particle size of a substance dropped from a sieve with an opening of 10 mm is 10 mm or less, and the particle size of a substance remaining on the sieve is greater than 10 mm.

The MgO-containing auxiliary material must be contained in the coating material in an amount of 90% by mass or more (% by mass with respect to the total mass of the coating material). This allows the carbonaceous material to be sufficiently isolated from the iron ore. It is preferable that the coating material is composed only of the MgO-containing auxiliary raw material. In this case, the carbonaceous material can be more stably isolated from the iron ore.

If the coating material contains substances other than MgO-containing auxiliary raw materials, it should not affect the production of ordinary sintered ore as much as possible, and should not interfere with the operation of the blast furnace where the sintered ore is used. Preferably, the substance constitutes a raw material for sintering. More preferably, the substance is a raw material other than iron ore. This is because when the covering material contains iron ore, the iron ore tends to come into contact with the carbonaceous material.

As described above, since the MgO-containing auxiliary material is difficult to decompose, even a small amount can sufficiently separate the carbon material from the iron ore. For this reason, it is possible to suppress an increase in the amount of the auxiliary raw material used, thereby maintaining the productivity of the sintered ore. Specifically, the mass of the MgO-containing auxiliary material contained in the coating material is preferably less than 10% by mass with respect to the carbonaceous material. In this case, it is possible not only to reduce nitrogen oxides, but also to more reliably maintain the productivity of sintered ore. Nitrogen oxides are particularly reduced when a MgO-containing auxiliary material with an LOI of 15% by mass or less is used.

Although the particle size of the MgO-containing auxiliary material is not particularly limited, it is preferably smaller than the particle size of the carbonaceous material. This is because the surface of the carbonaceous material can be efficiently coated with the MgO-containing auxiliary material. For example, the particle size of the MgO-containing auxiliary material may be 250 μm or less. In this case, the surface of the carbonaceous material can be coated with the MgO-containing auxiliary material so as to minimize voids.

Pelletization of the carbonaceous material and the MgO-containing auxiliary raw material may be performed by using a granulator such as a drum mixer or a pan pelletizer alone or in series. For example, after the carbonaceous material and the MgO-containing auxiliary raw material are kneaded together with a binder such as water in a kneader, the kneaded material may be fed into these granulators for granulation.

(3-2. Granule preparation step)
In the granule production step, a granule of the blended raw material is produced by blending the coated carbonaceous material having at least a portion of the surface coated with the coating material and another raw material for sintering and then granulating the mixture. Other raw materials for sintering are composed of iron-containing raw materials, auxiliary raw materials, return ores, and the like. Iron-containing raw materials are, for example, iron ore such as fine ore and fine ore, ironmaking dust (ironmaking dust, steelmaking dust, scale, etc.), and the like. The auxiliary materials are limestone, the above-mentioned MgO-containing auxiliary materials, converter slag, silica stone, and the like.

All of the carbonaceous materials granulated together with other raw materials for sintering are preferably coated carbonaceous materials according to the present embodiment. In this case, the effect of reducing nitrogen oxides is maximized. A part of the coated carbon material may be a normal carbon material (that is, a carbon material not coated with a coating material), but if the amount of the coated carbon material used is too small, a sufficient effect of reducing nitrogen oxides cannot be obtained. may not. Therefore, the amount of the coated carbonaceous material used is preferably 10% by mass or more of the total carbonaceous material.

In addition, since the mass of the MgO-containing auxiliary raw material contained in the coating material is small, even if the carbon material to be granulated with other sintering raw materials is simply replaced with the coated carbon material according to the present embodiment, The mass of secondary raw materials in Therefore, it hardly affects the productivity of sintered ore.

In addition, the amount of auxiliary materials in other raw materials for sintering may be reduced by the amount of MgO-containing auxiliary materials in the coating material. Even in this case, the productivity of the sintered ore is maintained because many auxiliary raw materials can be used as the granulating material.

A specific granulation method is not particularly limited, and may be the same as a conventional granulation method. For example, after blending the coated carbonaceous material and other raw materials for sintering in a predetermined ratio (this ratio is adjusted according to the characteristics required for the sintered ore) to form a mixed raw material, granulate it with water. do. Granulators such as drum mixers and pan pelletizers can be used without particular limitations. Granulation may be performed by using these granulators alone or in series. However, when the coated carbon material and other raw materials for sintering are blended from the beginning, the possibility that the coating of the coated carbon material will peel off in the subsequent granulation process cannot be denied. A so-called post-addition, which is added after the middle stage of the process, may be employed. When using a mixture of coated carbonaceous materials and normal carbonaceous materials (uncoated carbonaceous materials), even if only the coated carbonaceous materials are post-added, all the carbonaceous materials including the coated carbonaceous materials are post-added. Either way is fine.

(3-3. Sintered ore preparation process)
In the sintered ore preparation step, the sintered ore is prepared by firing the granules of the mixed raw material. This step may be performed in a conventional manner.

As described above, according to the present embodiment, the carbonaceous material is coated with the MgO-containing auxiliary material that is difficult to decompose in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material. Therefore, the carbonaceous material can be stably isolated from the iron ore in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material, and as a result, nitrogen oxides can be further reduced. Furthermore, since the MgO-containing auxiliary material is more difficult to decompose than the Ca-based material in the temperature range from the start of combustion to the middle period of combustion of the carbonaceous material, it is possible to separate the carbonaceous material from the iron ore even if the amount is small. In other words, nitrogen oxides can be reduced even if the amount is small. Therefore, even if the other sintering raw material and the carbonaceous material to be granulated are simply replaced with the coated carbonaceous material according to the present embodiment, the mass of the auxiliary material in the granules does not increase so much. Further, even when the amount of auxiliary materials in other raw materials for sintering is reduced by the amount of the MgO-containing auxiliary materials in the coating material, many auxiliary materials can be used as the granulating material. Therefore, the productivity of sintered ore can be maintained.

<1. Example 1>
Next, an example of this embodiment will be described. In Example 1, the following sintering experiment was conducted to confirm the effects of the present embodiment. First, raw materials for sintering shown in Table 2 were prepared. In Example 1, peridotite (LOI=1.3% by mass) was used as the MgO-containing auxiliary material. Also, the coke breeze has the particle size distribution shown in Table 3. In Table 3, "AB" of the particle size indicates more than B and less than or equal to A.

(1-1. Carbon material treatment process)
In the carbon material treatment step, of the raw materials for sintering shown in Table 2, all of the coke fines and part of the peridotite were granulated. Specifically, the total amount of coke breeze and 5% by mass (outside number) of peridotite with respect to the total mass of coke breeze were put into a universal kneader. Next, coke fine and peridotite were kneaded for 3 minutes while adding water such that the target water content was 15% by mass (external number). Then, the kneaded product was put into a pan pelletizer and granulated for 5 minutes. Thus, a coated carbonaceous material was produced.

(1-2. Granule preparation step)
Next, raw materials for sintering other than the coke fines and peridotite used in the carbon material treatment step (peridotite remains) were put into a drum mixer (diameter 1 m, 23 rpm) and mixed for 1 minute. Then, the mixture in the drum mixer was granulated for 3.5 minutes while adding water to the drum mixer so that the target moisture content was 7.5% by mass (external number). Then, the coated carbon material prepared above was added to the drum mixer, and the mixture in the drum mixer was further mixed (granulated) for 0.5 minutes. Through the above steps, granules of the blended raw material were produced.

(1-3. Sintered ore preparation process)
By filling a test pot with a diameter of 300 mm with granules of blended raw materials, a raw material packed layer was formed in the test pot. The layer thickness of the raw material packed layer was 600 mm. The bottom surface of the test pot is mesh-shaped, and a blower is connected to it. Then, after igniting the surface of the raw material packed bed for 90 seconds, the air in the test pot was sucked under a negative suction pressure of 1530 kPa. Then, the temperature of the sucked gas was monitored, and the time when the temperature of the sucked gas reached its maximum was defined as the end of sintering (burn-through). Subsequently, the sintered ore was produced by crushing the produced sintered cake. Here, the sintered ore having a particle size of more than 5 mm was used as the product.

Here, the exhaust gas was monitored from the start of ignition to the end of sintering (sintering time), and the amount of NO _x (NO+NO ₂ ) contained in the exhaust gas was measured. NO _x was measured using a continuous gas analyzer (CLM-108) manufactured by Shimadzu Corporation. Then, a value obtained by converting the _NOx amount into nitrogen mass (a value that does not contain oxygen) was taken as the _NOx emission amount. Furthermore, the production rate (productivity) (t/24h/m ² ) of the sintered ore was calculated based on the mass of the product, the sintering time, and the like. The results are summarized in Table 4.

<2. Comparative example>
The same treatment as in Example 1 was performed except that the granule preparation step was performed as follows without performing the carbon material treatment step. The results are summarized in Table 4.

(2-1. Granule preparation step)
All the raw materials for sintering shown in Table 2 were put into a drum mixer (1 m diameter, 23 rpm) and granulated for 1 minute. Then, the mixture in the drum mixer was granulated for 4 minutes while adding water to the drum mixer so that the target moisture content was 7.5% by mass (external number). Through the above steps, granules of the blended raw material were produced.

<3. Reference example 1>
In Reference Example 1, the same treatment as in Example 1 was performed, except that the carbon material treatment step and the granule production step were performed as follows. Schematically, in Reference Example 1, the carbonaceous material was coated with 20% by mass of slaked lime. The MgO-containing auxiliary material was the same as in Example 1. The results are summarized in Table 4.

(3-1. Carbon material treatment process)
In the carbon material treatment step, of the raw materials for sintering shown in Table 2, all of the coke fines and part of the hydrated lime were granulated. Specifically, the total amount of coke breeze and 20% by mass (outside number) of slaked lime with respect to the total mass of coke breeze were put into a universal kneader. Next, coke dust and hydrated lime were kneaded for 3 minutes while adding water such that the target water content was 15% by mass (external number). Then, the kneaded product was put into a pan pelletizer and granulated for 5 minutes. Thus, a coated carbonaceous material was produced.

(3-2. Granule preparation step)
Next, raw materials for sintering other than the coke fine and slaked lime used in the carbon material treatment step (with remaining slaked lime) were put into a drum mixer (diameter 1 m, 23 rpm) and mixed for 1 minute. Then, the mixture in the drum mixer was granulated for 3.5 minutes while adding water to the drum mixer so that the target moisture content was 7.5% by mass. Then, the coated carbon material prepared above was added to the drum mixer, and the mixture in the drum mixer was further mixed (granulated) for 0.5 minutes. Through the above steps, granules of the blended raw material were produced.

<4. Reference example 2>
In Reference Example 2, the same treatment as in Reference Example 1 was performed, except that the mass% of slaked lime coating the carbonaceous material was 5% by mass with respect to the total mass of coke breeze. The results are summarized in Table 4.

<5. Example 2>
The same treatment as in Example 1 was performed except that serpentinite (LOI = 13.9% by mass) was used as the MgO-containing auxiliary material. The results are summarized in Table 4.

<6. Example 3>
The same treatment as in Example 1 was performed except that dolomite (LOI = 46.9% by mass) was used as the MgO-containing auxiliary material. The results are summarized in Table 4.

<7. Example 4>
Same as Example 1 except that the MgO-containing auxiliary raw material was a mixture of peridotite of Example 1 and serpentinite of Example 2 (mixture of 30% by mass of peridotite + 70% by mass of serpentinite, LOI = 10% by mass). A similar treatment was performed. The results are summarized in Table 4.

<8. Example 5>
The same procedure as in Example 1 was performed except that the MgO-containing auxiliary raw material was a mixture of the serpentinite of Example 2 and the dolomite of Example 3 (mixture of 90% by mass of serpentinite + 10% by mass of dolomite, LOI = 17% by mass). processed. The results are summarized in Table 4.

In Reference Example 1, since the carbonaceous material was covered with a large amount of slaked lime, nitrogen oxides were greatly reduced. However, since the amount of slaked lime used in the granulating agent decreased, the granulation properties of the blended raw material deteriorated, and the productivity of the sintered ore decreased. In Reference Example 2, the amount of slaked lime covering the carbonaceous material was reduced, so the reduction amount of nitrogen oxides was not as high as in Reference Example 1. However, since the amount of slaked lime used as a granulating agent increased, the productivity of sintered ore recovered to the same level as in the comparative example. As a result, it was confirmed that both the reduction of nitrogen oxides and the productivity of sintered ore cannot be achieved when the carbonaceous material is coated with slaked lime.

On the other hand, in all the examples, the amount of reduction of nitrogen oxides was larger than that of Reference Example 2, and the productivity of sintered ore was at a level not much different from that of Comparative Examples. In particular, in Examples 1, 2, and 4 in which the LOI was 15% by mass or less, the reduction in nitrogen oxides was remarkable. Thus, when the carbonaceous material was coated with the MgO-containing auxiliary raw material, nitrogen oxides could be sufficiently reduced even with a small amount of coating. A possible reason for this is that the MgO-containing auxiliary material is more difficult to decompose than slaked lime in the temperature range from the start of combustion of the carbonaceous material to the middle period of combustion. Since the amount of the MgO-containing auxiliary material used as the coating material was small, the productivity was also maintained.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

Claims (4)

a carbon material treatment step of granulating the coating material and the carbon material in order to coat at least part of the surface of the carbon material with the coating material;
a granule producing step of producing granules of the blended raw materials by blending the coated carbonaceous material having at least a portion of the surface coated with the coating material and other sintering raw materials and then granulating them;
A sintered ore producing step of producing sintered ore by firing the granules of the blended raw materials ,
The coating material contains 90% by mass or more of the MgO-containing auxiliary raw material with respect to the total mass of the coating material,
A method for producing sintered ore , wherein the mass of the MgO-containing auxiliary raw material contained in the coating material is 5% by mass or more and less than 10% by mass with respect to the carbonaceous material . 2. The method for producing sintered ore according to claim 1, wherein in the carbon material treatment step, the coating material and the carbon material composed only of the MgO-containing auxiliary raw material are granulated. The method for producing sintered ore according to claim 1 or 2, wherein the MgO-containing auxiliary raw material is at least one of peridotite and serpentinite . The method for producing sintered ore according to any one of claims 1 to 3, wherein the particle size of the MgO-containing auxiliary material is 250 µm or less .

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