JP4870247B2 - Method for producing sintered ore - Google Patents

Description

The present invention relates to a method for producing a sintered ore. In particular, the present invention relates to a method for producing sintered ore that can reduce NOx contained in exhaust gas while ensuring or improving productivity.
This application claims priority in 2010/4/14 based on Japanese Patent Application No. 2010-93334 for which it applied to Japan, and uses the content for it here.

When producing sintered ore at a steelworks, nitrogen oxides (NOx) are generated in exhaust gas due to combustion of carbonaceous materials used as fuel. This reduction of NOx is an important issue in improving air pollution. As a means for reducing NOx, there is an exhaust gas denitration technique using ammonia as a reducing agent.
However, in the exhaust gas denitration equipment according to such a technique, the construction cost is high and the operation cost is high because ammonia is expensive. There is also a means of using anthracite with a low nitrogen content, but the mining environment of anthracite with a low nitrogen content has deteriorated due to resource depletion, and its usage is limited.

On the other hand, as the method for producing sintered ore, in Patent Document 1, removal techniques NOx by the catalyst composed mainly of CaO-Fe _x O composite oxide CaO content of 5 to 50% by weight is disclosed ing. In this Patent Document 1, a granulated body (S type) in which the catalyst is coated on the surface of coarse coke granules (S type) or a granulated body (P type) in which fine coke granules and a fine powder of the catalyst are mixed is sintered. Used as a raw material.
Patent Document 2 discloses a method for producing a carbon-containing sintered ore using a non-combustible bulk carbon source in which a granular carbon source and a binder are mixed and granulated, and the surface is coated with a binder.

Japanese Laid-Open Patent Publication No. 8-60257 Japanese Unexamined Patent Publication No. 2001-262241

However, in Patent Document 1, in the case of a NOx removal technique using a granulated material (P-type) in which the fine coke particles and the fine powder catalyst are mixed, the NOx reduction effect in a low temperature region of 1,000 ° C. or less. There is a problem that is small. As will be described later, a large amount of NOx due to the combustion of coke is generated in a low temperature region. Therefore, it is considered that the fine coke granules in the granulated body (P type) burn in a low temperature region and a large amount of NOx is generated, and the effect of removing NOx is reduced. On the other hand, in the case of the NOx removal technique using the granulated body (S type) with the above-mentioned catalyst coated on the surface of the coarse coke particles, if the surface of the coke is sufficiently coated with the catalyst, the combustion speed of the coke becomes slow, and the sintering machine Inhibits productivity.
For this reason, there is a problem in that the coke must be coated with a catalyst so that a part of the surface of the coke is exposed, and the effect of removing NOx is reduced. In addition, these granule, because it is granulated and iron ore using a large granulator, when CaO content is 5-50 wt%, mixing of CaO-Fe x _O composite oxide catalyst There is a concern about the decrease in the degree or coverage area.
Moreover, in patent document 2, since the carbon source in this incombustible bulk carbon source hardly burns at the time of sintering, even if the binder in this incombustible bulk carbon source has a catalytic action, the catalytic action of the binder It is thought that almost does not occur. Further, in Patent Document 2, coke as a sintering raw material (fuel) is required in addition to the non-combustible bulk carbon source, and a large amount of carbon source is required.

  An object of the present invention is to provide a method for producing a sintered ore that can (1) suppress generation of NOx in a low temperature region and (2) sufficiently secure or improve the productivity of a sintering machine. That is.

(1) In the manufacturing method of the sintered ore which concerns on 1 aspect of this invention, the coating containing 36 mass% or more of Ca derived from a lime-type raw material is more than 2 mass% with respect to the said carbonaceous material on the carbonaceous material surface, and The surface-coated carbon material coated at a ratio of less than 50% by mass is included in the blended coal as a sintered fuel.
(2) In the method for manufacturing a sintered ore according to (1), the blended coal may include the surface-coated carbon material of 10% by mass to 100% by mass.
(3) In the manufacturing method of the sintered ore as described in said (1) or (2), the said lime-type raw material is calcium hydroxide, and the said coating | cover may contain 67 mass% or more of calcium hydroxide. .
(4) In the method for producing a sintered ore according to (1) or (2) above, on the surface of a carbon material of 0.25 mm or more among the carbon materials, the layer thickness of the coating is 5 μm or more and It may be 500 μm or less.
(5) In the method for producing a sintered ore according to (1) or (2) above, after blending and granulating a blended raw material containing iron ore, return ore and auxiliary raw materials, the surface coated coal is added to the blended raw material. Materials may be added and mixed.
(6) In the method for producing a sintered ore according to (1) or (2) above, when mixing and granulating a blended raw material containing iron ore, return mineral and auxiliary raw materials, half of the total mixed granulation time After the above has elapsed, the surface-coated carbon material may be added to and mixed with the blended raw material.
(7) In the method for producing a sintered ore according to (1) or (2), particles having a particle size of less than 0.5 mm are 20% by mass or less, and particles having a particle size of 0.5 mm or more and 3 mm or less are used. The carbonaceous material may have a particle size distribution of 40% by mass or more.

  By controlling the combustion of the carbonaceous material, it is possible to suppress the generation of NOx during the production of the sintered ore and sufficiently ensure or improve the productivity of the sintering machine.

It is a figure which shows the relationship between NOx conversion rate and temperature. It is a figure which shows the relationship between a coke particle size and the generation amount of NOx. It is the schematic of a sintering pot test apparatus. It is a figure which shows the relationship between the amount of coating, the Ca density | concentration in a coating layer, and NOx conversion rate ((eta) NO). It is a microscope picture of the surface coating coke which has a coating layer with a layer thickness of 500 micrometers or less used for the sintering pot test. It is a microscope picture of the surface coating coke which has a coating layer with a layer thickness exceeding 500 micrometers used for the sintering pot test. It is a figure which shows the relationship between the layer thickness of a coating, and NOx conversion rate. It is a figure which shows the relationship between the kind of coating | covering, and the adhesion ratio of a coating | covering. It is a figure which shows the relationship between the charging time of surface coating coke, and a NOx conversion rate. It is a figure which shows the relationship between the mixture ratio of the surface coating coke with respect to all the coal blends, and NOx conversion rate. It is a figure which shows the relationship between the kind of coating layer, and the production rate of a sintered ore. It is a schematic diagram which shows the process of granulation addition. It is a schematic diagram which shows the process of addition after granulation. It is a figure which shows the EPMA analysis result at the time of adding normal coke to another compounding raw material in front of a primary mixer. It is a figure which shows the EPMA analysis result of the surface coating coke at the time of adding surface coating coke to another compounding raw material in front of a primary drum mixer. It is a figure which shows the EPMA analysis result of surface coating coke at the time of adding surface coating coke to another compounding raw material in the second half part of a secondary drum mixer. It is a figure which shows the test result of a real machine operation test.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows the relationship between the NOx conversion rate by coke combustion and the temperature.

  The NOx conversion rate is a ratio (molar percentage) at which nitrogen atoms in the burned fuel are converted to NOx. Specifically, this NOx conversion rate is calculated by equation (1) described later.

NOx is generated mainly by oxidation of nitrogen in the carbonaceous material during sintering. In particular, as shown in FIG. 1, it has been confirmed that a large amount of NOx is produced at a low temperature of 1,000 ° C. or less. Therefore, in order to suppress the generation of NOx, it is important to burn the carbonaceous material at a high temperature as much as possible.
Here, a carbon material shows the solid fuel used for coke, anthracite, and other sintered ore manufacture.

  Moreover, the fine powder in the carbonaceous material burns at a low temperature and increases NOx. The relationship between the carbonaceous material particle size (coke particle size) and the amount of NOx generated is shown in FIG. The fine powder in the carbonaceous material is considered to increase NOx because the combustion speed is high and combustion is completed at a low temperature. Therefore, it is considered that the amount of NOx generated can be reduced if the fine carbonaceous material having a particle size of 0.5 mm or less can be removed.

Specifically, in order to further reduce the amount of NOx generated in the sintering process, the carbonaceous material (particles) having a particle size of more than 0 mm and less than 0.5 mm is desirably 20% by mass or less, and 11% by mass or less. Is more desirable, and it is especially desirable that it is 5 mass% or less. This is because, as shown in FIG. 2, the amount of NOx generated in the carbonaceous material of less than 0.5 mm is large.
Further, the carbonaceous material (particles) having a particle size of 0.5 mm or more and 3 mm or less is desirably 40% by mass or more, and particularly desirably 70% by mass or more. This is because carbon materials with a particle size of 0.5 mm or more and 3 mm or less have a sufficient combustion rate (combustion efficiency), so that the combustion time in the low temperature region can be reduced, and the NOx reduction effect is secured while being sintered. This is because the productivity can be sufficiently secured or improved. Therefore, it is desirable to use a carbon material having the above particle size distribution. Note that if the particle size of the carbon material becomes too large, the combustion rate decreases, the combustion time in the low temperature region tends to be long, and the NOx reduction effect is saturated. The upper limit or lower limit of each class in the particle size distribution is not particularly limited, but the upper limit is 100% by mass, and the lower limit is 0% by mass.

Even if fine powder (for example, less than 0.5 mm) is removed from the carbonaceous material, it is necessary to burn the carbonaceous material as high as possible in order to suppress the generation of NOx. Therefore, if the surface of the carbon material is covered with a coating layer (coating material) that melts in a high temperature region and oxygen in the surrounding atmosphere can be blocked in the low temperature region, NOx generation can be suppressed.
Patent Document 1, by using the carbonaceous material of CaO content was coated with CaO-Fe _x O composite oxide of 5-50 wt% on the surface, carbon by the catalytic action of CaO-Fe _x O composite oxide It is disclosed that NOx produced during combustion of a material is reduced or decomposed to be removed. The extent CaO-Fe x _O composite oxides restrict the CaO content of 50 wt% or less has a low melting point, to melt at a high temperature range of not lower than 1200 ° C., is to coat it on the surface of the carbonaceous material NOx reduction effect is expected. However, CaO-Fe x _O type composite oxide, because they are produced by melting a lime-based material and iron ore, is more expensive than the lime material used as a secondary raw material in a conventional sintering .
In the present embodiment, a lime-based material used as an auxiliary material in normal sintering is used as a coating on the surface of a carbon material without using an expensive oxide as described above. In particular, in the present embodiment, a surface-coated carbon material in which a coating having a Ca content of 36% by mass or more is used for at least a part of the blended coal charged into the sintering machine as a fuel. As a result, NOx during combustion of the carbonaceous material can be reduced. Here, the blended charcoal is a carbon material used as a solid fuel (sintered fuel) by being mixed with a sintering raw material (blended raw material) other than the blended coal before being charged into the sintering machine.
In the present embodiment, the coating layer on the surface of the carbon material desirably includes at least one selected from the group consisting of calcium hydroxide, calcium carbonate, calcium oxide, and calcium fluoride. In this case, for example, lime-based raw materials such as calcium hydroxide (slaked lime), calcium carbonate (limestone), lime milk, fluorite, and mixtures thereof can be used. The lime-based raw material functions as a solvent because it easily reacts with iron ore powder present at a high temperature to produce calcium ferrite having a low melting point. When this calcium ferrite melts at a high temperature, oxygen is supplied to the surface of the carbon material, so that the combustion of the carbon material is promoted and the carbon material can be burned at a high temperature. Further, in this calcium ferrite (melt), solid ash remaining on the surface during combustion of the carbonaceous material is dissolved, and combustion of the carbonaceous material at a high temperature can be further promoted. The lime-based raw material contained in the coating layer is particularly preferably calcium hydroxide. Calcium hydroxide acts as a binder and forms a coating layer that is strongly adhered to the surface of the carbonaceous material, so that the surface of the carbonaceous material in the conveying process until mixing with other blended raw materials and charging the raw material into the sintering machine. Desorption of the coating can be suppressed.
It is desirable that the coating on the surface of the carbon material contains 36 mass% or more of Ca derived from the lime-based raw material. When the Ca content in the coating is less than 36% by mass, the reaction rate between the surrounding iron ore and the coating (the lime-based raw material in the coating) is not sufficient, so the melting reaction on the carbonaceous material surface is slow. Therefore, the effect of promoting the combustion of the carbonaceous material at a high temperature becomes small.
When calcium hydroxide is used for the lime-based raw material, the coating more preferably contains 67% by mass or more of calcium hydroxide, and particularly preferably 100% by mass. Furthermore, when calcium carbonate, lime milk, fluorite, or the like is used as the lime-based raw material, it is desirable that the coating contains 90% by mass or more of these lime-based raw materials and mixtures, particularly 100% by mass. desirable.

NOx is generated by burning the carbonaceous material at a low temperature of 1,000 ° C. or lower. Therefore, in order to suppress NOx generation during sintering, the carbonaceous material is controlled while suppressing combustion of the carbonaceous material at low temperature. It is necessary to burn at as high a temperature as possible.
In the low temperature region of 1,000 ° C. or lower, since the carbonaceous material surface is covered with the coating layer, combustion of the carbonaceous material can be suppressed and generation of NOx can be suppressed. However, in a high temperature region of 1,200 ° C. or higher, CaO derived from the lime-based raw material in the coating layer reacts with surrounding ore to generate a melt of low-melting calcium ferrite and melt down. At this time, solid phase ash present on the surface of the carbonaceous material can be taken into the melt. Thus, when the coating layer on the surface of the carbon material generates a calcium ferrite melt, the combustion temperature of the carbon material has already reached a high temperature region of 1,200 ° C. or higher, so NOx generation occurs. Less, the charcoal can be actively burned and productivity can be improved. That is, in the present embodiment, the apparent combustion start temperature of the carbon material can be increased to realize rapid combustion of the carbon material in a high temperature region, and the maximum temperature at the time of combustion of the carbon material can be efficiently increased. it can.

The mixing and granulating method of the compounding raw material in this embodiment are demonstrated. Here, a compounding raw material is a raw material mixed and used before charging into a sintering machine.
In addition, in the following description, although the example which used the fine iron ore other than the lime-type raw material as a coating in a surface covering carbon material was shown, it is not limited only to this example. That is, if the Ca content derived from the lime-based material in the coating is 36% by mass or more, fine iron ore and other auxiliary materials can be used as the coating material other than the lime-based material. Here, the other auxiliary materials mean auxiliary materials (silica stone, serpentine, peridotite, etc.) other than lime-based materials.
First, a blended raw material (hereinafter referred to as a first blended raw material) excluding raw materials used for the production of the surface-coated carbon material is granulated by a mixing granulator such as a drum mixer. The first blended raw material includes at least iron ore, return mineral, and auxiliary raw materials. Here, the first blended raw material does not include floor covering ore. The first blended raw material may contain blended coal.

Next, the surface-coated carbon material is a raw material (hereinafter referred to as a second blended raw material) used for the production of the surface-coated carbon material, that is, a carbon material, a lime-based raw material, and a powder using coarse carbon material as core particles. Manufactured by mixing and granulating iron ore. The fine iron ore may contain generated dust in the ironworks. A mixing granulator such as a drum mixer or a centrifugal granulator can be used for mixing and granulating the carbonaceous material with the iron powder ore and the lime-based raw material. Thereby, the surface covering carbonaceous material by which the coarse-grained carbonaceous material (nuclear particle) was coat | covered with the lime-type raw material and fine iron ore is formed. When calcium carbonate, lime milk, fluorite or the like having almost no binder function is used as the lime-based raw material, it is desirable to add a binder to these. As this binder, organic binders such as CMC (carboxymethylcellulose) and gum arabic and inorganic binders such as water glass can be used. Since a coating layer that adheres tightly to the carbonaceous material surface is formed by the addition of the binder, the carbonaceous material surface is coated during the conveyance process until mixing with the first raw material and charging the raw material into the sintering machine. It is possible to suppress detachment of objects and more stably reduce NOx generated during sintering.
The surface-coated carbon material may be produced by mixing and granulating a carbon material and a lime-based material as the second blending material. In this case, the coating layer of the surface-coated carbon material is composed of only a lime-based raw material.

  The amount of the surface-covered carbon material in the carbon material (mixed coal) used by being blended (mixed) in the production of sintered ore is not particularly limited, but it is necessary to include the surface-coated carbon material in the blended coal. That is, it is necessary that a part of the blended coal is a surface-coated carbon material. In particular, in order to more stably reduce NOx generated during sintering, it is desirable that the blended coal includes a surface-coated carbon material of 10% by mass or more and 100% by mass or less. In order to reduce the difference in combustion time for each carbon material type as much as possible and perform combustion in the sintering machine constantly in a high temperature range, the amount of the surface coating carbon material relative to the total amount of the blended coal is 50% by mass or more. More desirably, it is more desirably 70% by mass or more, and particularly desirably 80% by mass or more. In addition, if a large amount of blended coal is used as a solid fuel for sintering, a large amount of melt generated by the sintering reaction of the sintering raw material is generated on the sintering pallet, which deteriorates the air permeability of the sintering raw material packed layer. As a result, the productivity of sintered ore may be reduced. Therefore, in order to supply an appropriate amount of heat for the blended coal as a solid fuel to favorably advance the sintering reaction of the sintered raw material, for example, iron ore and auxiliary materials (excluding lime-based raw materials used for surface-coated carbon materials) The amount of blended coal is preferably 14% by mass or less with respect to the auxiliary material). In this case, the air permeability of the sintered raw material packed layer can be sufficiently ensured. In addition, for example, the amount of blended coal with respect to iron ore and auxiliary materials (auxiliary materials excluding lime-based raw materials used for surface-coated carbon materials) is not particularly limited, but the amount of heat required for the sintering reaction of the sintered raw materials May be 1% by mass or more.

The timing for adding and mixing the surface-coated carbon material to the first blended raw material is not particularly limited. However, after mixing and granulating the first blended raw material, it is desirable to add and mix the surface-coated carbonaceous material into the first blended raw material (addition after granulation). By adding and mixing the surface-coated carbonaceous material to the first blended raw material at such timing, it is possible to suppress the coating on the carbonaceous material surface from collapsing or peeling off. In this case, the first blended raw material may be composed of blended coal other than iron ore, return ore, auxiliary material, and surface-coated carbon material, or may be composed of iron ore, return ore, and auxiliary material.
However, before mixing and granulating the first blended raw material, the surface-coated carbonaceous material is added to the first blended raw material (added before granulation), so that the coating of the surface-coated carbonaceous material does not peel off. The first compounding raw material and the surface-coated carbon material may be mixed and granulated. In this case, the first blended raw material may be composed of iron ore, return mineral, auxiliary raw material, and blended coal.

Usually, when carbonaceous material such as coke is added after granulation, the diffusion of oxygen in the carbonaceous material is good, so the combustion of the carbonaceous material starts at a low temperature. Covers the surface of the carbonaceous material, so that the combustion of the carbonaceous material is hindered. Therefore, in this case, the amount of NOx is greatly increased.
On the other hand, when the surface-coated carbon material is used, the amount of NOx can be suppressed regardless of whether the addition before granulation or the addition after granulation is performed. In particular, the addition of the surface-coated carbon material after granulation can suppress the disintegration and peeling of the coating, so the oxygen blocking action in the air in the low temperature region and the ash melting effect in the high temperature region And the amount of NOx can be greatly suppressed. In this case, the carbon material mixing time with respect to the total mixing granulation time of the sintering raw material (the total of the mixing granulation time of only the first compounding material and the addition and mixing time of the surface coating carbon material to the first compounding material) The input time defined by the ratio of (addition and mixing time of the surface-coated carbonaceous material to the first blended raw material) is preferably 0.5 (half) or more, and particularly preferably 0.8 or more. . For example, when mixing and granulating a sintering raw material with one apparatus, a surface covering carbon material can be added and mixed in the apparatus. For example, when mixing and granulating a sintering raw material with a plurality of apparatuses, the surface-coated carbonaceous material may be added and mixed in an apparatus whose input time has reached a predetermined value (for example, 0.5 or more). it can.

In the surface-coated carbon material of the present embodiment, it is necessary to cover the carbon material surface with a coating material in a ratio of more than 2% by mass and less than 50% by mass with respect to the carbon material (amount of the coating material with respect to the carbon material). . When the mass% of the coating with respect to the carbon material is 2 mass% or less, it becomes difficult to form a sufficient coating layer surrounding the entire surface of the carbon material, and a part of the carbon material surface is exposed, The effect of reducing NOx by blocking oxygen in the atmosphere cannot be obtained. Moreover, when the mass% of the coating with respect to the carbon material is 50 mass% or more, the rate at which calcium ferrite is generated from the lime-based raw material in the high temperature range is decreased, and the combustion efficiency of the carbon material is decreased and the sintering machine. Productivity is reduced. Here, in order to obtain a higher NOx reduction effect, the mass% of the coating with respect to the carbonaceous material is preferably 3 mass% or more, more preferably 5 mass% or more, and 10 mass% or more. It is particularly desirable to be. In order to further increase the combustion efficiency of the carbonaceous material, it is desirable that the mass% of the coating with respect to the carbonaceous material is 40 mass% or less.
Moreover, it is desirable that the layer thickness of the covering layer is 5 μm or more and 500 μm or less on the surface of the carbon material of 0.25 mm or more among the carbon materials forming the surface covering carbon material. Here, the layer thickness of the coating layer means an average layer thickness of the coating layer on the carbonaceous material surface of 0.25 mm or more. Moreover, it is especially desirable that the layer thickness of the coating layer is 5 μm or more and 500 μm or less for each surface-coated carbon material. In addition, by observing 20 or more surface-coated carbon materials with a microscope, the thickness of five or more locations in the coating layer of each surface-coated carbon material is measured, and by calculating the average of these layer thicknesses, The layer thickness can be determined.
When the layer thickness of the coating layer is 5 μm or more, it is possible to suppress the peeling of the coating layer in the mixing step with the above-mentioned first compounding raw material (iron ore, returning mineral, etc.) or the subsequent handling step. It is possible to sufficiently ensure the NOx suppression effect of the coating layer on the carbonaceous material surface. Further, if the layer thickness of the coating layer is 500 μm or less, calcium ferrite can be quickly generated from the lime-based raw material in the high temperature range, and the carbonaceous material can be burned efficiently in the high temperature range, and the sintering machine It is possible to sufficiently secure or improve the productivity.

As described above, in the present embodiment, the coating containing 36% by mass or more of Ca derived from the lime-based raw material so that the mass% of the coating with respect to the carbon material is more than 2% by mass and less than 50% by mass. The surface of the carbon material is coated to prepare a surface-coated carbon material; this surface-coated carbon material is burned in a sintering machine as a sintered fuel. Moreover, in this embodiment, the surface covering carbon material is included in the blended coal. That is, a surface-coated carbon material is used as the blended coal. Further, the blended coal is mixed with a blended raw material including iron ore, return mineral, and auxiliary raw materials before being charged into the sintering machine.
In this way, by burning the surface-coated carbon material in the sintering machine as a sintering fuel, the combustion of the carbon material can be controlled, the generation of NOx is suppressed, and the productivity of the sintering machine is sufficiently secured. Or can be improved.

Next, although the Example of this invention is described, this invention is not limited to this.
Example 1
An experiment was conducted to investigate the influence of the coating amount of the surface-coated coke and the Ca concentration in the coating layer on the amount of NOx produced. A schematic diagram of the sintering pot test apparatus used in this experiment is shown in FIG.
The sintering pot test apparatus includes an ignition furnace 1, a sintering pot 2, an air box 3, a blower 4, and an analyzer 5.
In this sintering pot test apparatus, the sintering raw material containing the surface-coated carbon material is charged into the sintering pot 2 and ignited in the ignition furnace 1 to heat the sintering raw material. At the same time, the blower 4 is started to exhaust the exhaust gas generated in the sintering pan 2 through the wind box 3, and the exhaust gas is analyzed by the analyzer 5. The sintering pan 2 had a diameter of 300 mm and a height of 600 mm, and analyzed CO, CO ₂ , O ₂ , NOx, and SOx in the exhaust gas.
Water 7.5% by mass was externally added to the powdered iron ore (iron ore), the auxiliary material, and the carbonaceous material, and these materials were mixed and granulated for 5 minutes using a drum mixer having a diameter of 1,000 mm. In addition, 9.0 mass% of water was externally added to the coke and the coating, and a surface-coated coke (surface-coated carbon material) was produced using a universal kneader. These sintered raw materials mixed and granulated were filled in a sintering pot test apparatus and fired under a constant condition of an ignition time of 90 seconds and a suction negative pressure of 15 kPa. Table 1 shows the ratio of each raw material used in the test, and Table 2 shows the particle size distribution of the coke.

  FIG. 4 shows the relationship between the amount of coating and the Ca concentration in the coating layer and the NOx conversion rate (ηNO). When the Ca concentration in the coating layer was 36% by mass or more, a sufficient NOx reduction effect could be obtained. Further, when the calcium concentration in the coating layer was adjusted to about 54% by mass using only calcium hydroxide as the coating, the NOx reduction effect was further enhanced. Moreover, the NOx reduction effect was able to be confirmed that the mass% of the coating material with respect to coke (coke for surface coating carbon materials) is more than 2 mass% and less than 50 mass%. In particular, when the mass% of the coating with respect to the coke was 10 to 40 mass%, a higher NOx reduction effect could be obtained.

ηNO = 100 × NOx / ((CO + CO ₂ ) · N _CAKE / (C _LPG + C _CAKE + C _LS )) / 10000 (1)
However, ηNO: NOx conversion (mol%), NOx: NOx in the exhaust gas (ppm) CO: CO in the exhaust gas _{(mol%), CO 2:} CO in the exhaust gas _{(mol%), N COKE:} in coke N (mol), C _LPG : C (mol) in ignition gas, C _CAKE : C (mol) in coke, C _LS : C (mol) in limestone.

(Example 2)
In order to investigate the effect of the layer thickness of the surface-coated carbon material on the NOx reduction effect, the same sintering pot test as in Example 1 was performed. Only calcium hydroxide was used for the coating of the surface-coated coke. FIG. 5A and FIG. 5B show micrographs of surface-coated coke having different coating layer thicknesses used in the sintering pot test. FIG. 6 shows the relationship between the layer thickness of the coating layer (covering layer thickness) and the NOx conversion rate. As shown in FIG. 6, when a surface-coated coke having a coating layer having a layer thickness of 500 μm or less as shown in FIG. 5A is used, the surface having a coating layer having a layer thickness of more than 500 μm as shown in FIG. 5B Compared to the case of using coated coke, the NOx reduction effect (NOx conversion rate) was improved. Therefore, it turns out that it is desirable to adjust the layer thickness of a coating to 500 micrometers or less.

(Example 3)
In order to investigate the effect of the type of lime-based raw material on the coatability (adhesion) of the coating layer to coke, surface coating coke using only calcium carbonate as the coating and using only calcium hydroxide as the coating The production test of the surface-coated coke was performed. The mass% of the coating with respect to the coke before mixing a carbon material and each coating was adjusted to 15 mass%. In FIG. 7, the adhesion ratio after drying of the raw material of a coating to the coke surface at the time of using each coating is shown. The adhesion ratio of calcium carbonate to the coke surface was about 20% by mass. On the other hand, the adhesion ratio of calcium hydroxide to the coke surface was more than 80% by mass. Thus, when manufacturing surface-coated coke, it is thought that the binder function of calcium hydroxide can be utilized effectively and a large NOx suppression effect can be obtained.

Example 4
In order to investigate the influence of the charging time (charging position) of the surface-coated coke on the amount of NOx produced, a sintering pot test was conducted. As described above, the charging time is the ratio of the carbonaceous material mixing time to the total mixed granulation time of the sintered raw material. In addition, the sintering pot test apparatus and the test method are the same as that of the said Example 1.
FIG. 8 shows the relationship between the surface coating coke charging time and the NOx conversion rate. The amount of NOx produced (NOx conversion rate) could be significantly reduced under conditions where the surface coating coke charging time was 0.5 or more, particularly 0.8 or more. In this case, it is considered that the sintered raw material charged into the sintering pan could be prepared while suppressing the coating from collapsing or the coating from peeling off from the coke surface.

(Example 5)
In order to investigate the influence of the amount of surface-coated coke in the blended coal and the time of surface-coated coke on the amount of NOx produced, a sintering pot test was conducted. The sintering pot test apparatus and test method are the same as those in Example 1, except that only calcium hydroxide is used for the coating, the Ca concentration in the coating layer is about 54% by mass, and the coating for coke. The mass% of was adjusted to 15 mass%.
FIG. 9 shows the relationship between the amount of surface-coated coke in the blended coal, the time for charging the surface-coated coke, and the NOx conversion rate. The amount of NOx produced could be suppressed by increasing the blending ratio of the surface-coated coke to the entire coke and increasing the charging time. As shown in FIG. 9, it can be seen that the NOx suppression effect is further increased by blending 50 mass% or more of the surface coating coke in the blended coal and controlling the charging time to 0.5 or more.

In order to investigate the influence of the surface coating layer on the production rate of sintered ore, a sintering pot test was conducted. The sintering pot test apparatus and test method are the same as in Example 1 above, but when only calcium hydroxide was used in the coating, the mass% of the coating relative to coke was adjusted to 15 mass%, When calcium hydroxide and pyrbara blended powdered iron ore were used for the coating, the mass% of the coating relative to coke was adjusted to 30% by mass. When only calcium hydroxide was used for the coating, the Ca concentration in the coating layer was about 54% by mass. In addition, when calcium hydroxide and pyrbara blended iron ore were used for the coating, the Ca concentration in the coating layer was about 36% by mass. Surface-coated coke was used for the total amount of coke (formulated raw material), and the charging time was controlled to 0.85.
The result of the production rate of the obtained sintered ore is shown in FIG. The production rate of sintered ore was improved when the surface-coated coke having a coating layer containing calcium hydroxide was used, as compared with the case where coke without a coating layer was used. Thus, it is considered that when a surface-coated coke having a coating layer containing calcium hydroxide is used, a sintering operation with a low NOx conversion rate can be performed at a high production rate.

(Example 6)
In order to confirm the NOx reduction effect of the surface-coated coke, an actual machine operation test for 5 days was performed twice in a large 660 m ² sintering machine. Table 3 shows the particle size distribution of the coke (coke a to c and coke A to C) used for conducting the actual machine operation test. About coke AC, the surface of coke was manufactured by coating the coke surface with calcium hydroxide in an amount of about 14% by mass of the amount of coke (coke for surface-coated coke). The cokes a to c are normal coke having no surface coating.
Here, the coke a (base) was adjusted so that the proportion of particles of less than 0.5 mm in the particle size distribution was more than 20% by mass and the proportion of particles of 0.5 mm or more and 3 mm or less was less than 40%. Coke. The coke A (surface-coated coke A) is coke in which the surface of the coke a is coated with calcium hydroxide. The coke b is coke adjusted so that the ratio of particles having a particle size distribution of less than 0.5 mm exceeds 20% by mass and the ratio of particles having a particle size of 0.5 mm to 3 mm is 40% by mass or more. The coke B (surface-coated coke B) is coke in which the surface of the coke b is coated with calcium hydroxide. The coke c is coke adjusted so that the proportion of particles having a particle size distribution of less than 0.5 mm is 11% by mass or less. The coke C (surface-coated coke C) is coke in which the surface of the coke c is coated with calcium hydroxide.

Based on normal actual machine operation (using coke a) (1) When granulating the surface-coated coke at the same time as other sintering raw materials (addition before granulation), (2) Firing other than the surface-coated coke After the granulation material was once granulated, the test was conducted for the case of adding surface-coated coke (added after granulation). FIG. 11 shows a schematic diagram of the process of (1) addition before granulation. FIG. 12 shows a schematic diagram of the process of (2) post-granulation addition.
11 and 12, coke and calcium hydroxide are cut out from a coke tank 11 and a calcium hydroxide tank (lime-based raw material tank) 12, and put into a granulator 13 to produce surface-coated coke.
In FIG. 11, the granulated surface-coated coke is taken out from the surface-coated coke tank 19, and together with the raw materials (ores, auxiliary raw materials, return minerals, etc.) cut out from the raw material tank 14, the primary mixer 15 and the secondary mixer 16. Mix and granulate sequentially. In this case, the surface-coated coke is added before mixing and granulating simultaneously with other raw materials.
On the other hand, in FIG. 12, the surface-coated coke taken out from the granulator 13 is further granulated by the pan pelletizer 18 and then mixed by the primary mixer 15 and the secondary mixer 16 in the latter half of the secondary mixer 16. The surface-coated coke is added to and mixed with other granulated raw materials. In this case, the surface-coated coke is mixed after other raw materials and added after granulation.
The EPMA analysis results of the surface-coated coke obtained by coating the surface of coke (coke a) with calcium hydroxide are shown in FIGS. FIG. 13 shows an EPMA analysis result when normal coke is added to the blended raw material before the primary mixer (primary drum mixer).
FIG. 14 shows an EPMA analysis result when the surface-coated coke is added to the blended raw material before the primary drum mixer. It was observed that the surface coating layer (calcium hydroxide layer) of the surface coating coke was broken and peeled. If the surface-coated coke and the blended raw material are simultaneously mixed and granulated with a primary mixer and a secondary mixer (secondary drum mixer), it is considered that the surface-coated coke coating is likely to be destroyed.
FIG. 15 is an EPMA analysis result when surface-coated coke is added to other sintering raw materials in the second half of the secondary drum mixer. In this case, it was observed that a layer of coating (calcium hydroxide) having a layer thickness of 5 to 500 μm was secured on the coke surface.

  The test results of the actual machine operation test are shown in FIG. In the implementation period of actual machine operation using surface-coated coke A (but added after granulation), NOx in the exhaust gas is 25 ppm compared to the base period of actual machine operation using coke a (but added before granulation). Declined. Moreover, in the implementation period of actual machine operation using the surface-coated coke B (but added after granulation), NOx in the exhaust gas decreased by 30 ppm as compared with the base period. The coke b used for the surface-coated coke B has a larger mass% of particles (class) of 0.5 mm or more and 3 mm or less than the coke a used for the surface-coated coke A. Therefore, it is considered that when the surface-coated coke B is used, the amount of NOx produced is lower than when the surface-coated coke A is used. Furthermore, in the implementation period of the actual machine operation using the surface-coated coke C (but added after granulation), NOx in the exhaust gas decreased by 42 ppm as compared with the base period. The coke c used for the surface-coated coke C has a smaller mass% of particles (class) of less than 0.5 mm than the coke a used for the surface-coated coke A. Therefore, it is considered that when the surface-coated coke C is used, the amount of NOx produced is lower than when the surface-coated coke A is used.

  Provided is a method for producing a sintered ore that can suppress the generation of NOx and sufficiently secure or improve the productivity of the sintering machine by controlling the combustion of the carbonaceous material.

DESCRIPTION OF SYMBOLS 1 Ignition furnace 2 Sintering pot 3 Wind box 4 Blower 5 Analyzer 11 Coke tank 12 Slaked lime tank (lime-based raw material tank)
13 Granulator 14 Raw Material Tank 15 Primary Mixer 16 Secondary Mixer 18 Pamperetizer 19 Surface Covered Coke Tank

Claims (7)

  A surface-covered carbon material in which a coating containing 36% by mass or more of Ca derived from a lime-based raw material is coated on the surface of the carbon material at a ratio of more than 2% by mass and less than 50% by mass with respect to the carbon material. A method for producing a sintered ore characterized in that it is included in a blended coal.   2. The method for producing a sintered ore according to claim 1, wherein the blended charcoal includes 10% by mass or more and 100% by mass or less of the surface-coated carbonaceous material.   3. The method for producing a sintered ore according to claim 1, wherein the lime-based raw material is calcium hydroxide, and the coating contains 67 mass% or more of calcium hydroxide.   3. The sintered ore production according to claim 1, wherein a layer thickness of the covering is not less than 5 μm and not more than 500 μm on a surface of a carbon material of 0.25 mm or more among the carbon materials. Method.   3. The sintered ore according to claim 1, wherein the surface-coating carbonaceous material is added to and mixed with the blended raw material after mixing and granulating the blended raw material containing iron ore, return mineral, and auxiliary materials. Manufacturing method.   When mixing and granulating a blended raw material containing iron ore, return ore, and auxiliary materials, the surface-coated carbon material is added to and mixed with the blended raw material after more than half of the total mixed granulation time has elapsed. A method for producing a sintered ore according to claim 1 or 2.   The carbonaceous material has a particle size distribution in which particles having a particle size of less than 0.5 mm are 20% by mass or less, and particles having a particle size of 0.5 mm or more and 3 mm or less are 40% by mass or more. The manufacturing method of the sintered ore as described in 1 or 2.