JP2015086419A - Method of producing sintered ore - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of NOx in the low-temperature region and reduce sinter NOx by combustion control of fine coal without impairing productivity of a sintering machine.SOLUTION: A method of producing a sintered ore comprises adding a granulating agent and water to a raw material consisting of iron ore, sinter dust, return ore and auxiliary material and mixing and granulating to prepare a raw material and sintering by using surface-coated carbonaceous material surface-coated with a coating, and the composition of the coating of the surface-coated carbonaceous material includes 0.1-0.6 of CaO/(CaO+FeO), where the content of FeO is based on FeO converted from the content of metal Fe.

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.

In the production of sintered ore at an ironworks, 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 means for reducing the NOx, there is an exhaust gas denitration technique using ammonia as a reducing agent.
However, the exhaust gas denitration equipment according to the technology has a high construction cost, and the operation cost is high because ammonia is expensive. There is also a means to use anthracite with a low nitrogen content, but anthracite with a low nitrogen content has deteriorated in the mining environment due to resource depletion, and its use is limited.

On the other hand, a technique is disclosed in which the surface of a solid fuel used in the production of sintered ore is coated with a coating material containing CaO or the like to reduce NOx in exhaust gas.
A technique has been disclosed in which the coating material functions as a catalyst and the catalyst removes NOx. A catalyst CaO content is composed mainly of CaO-Fe _x O composite oxide is 5 to 50 wt%, is a technique for nitrogen oxide reduction or decomposition to remove nitrogen oxides (JP 1).
Moreover, the surface covering carbon material which coat | covered the coating material containing 36 mass% or more of Ca derived from lime-type raw material on the carbon material surface in the ratio of more than 2 mass% and less than 50 mass% with respect to the said carbon material is baked. A technique to be included in blended coal as a fuel is disclosed (Patent Document 2).
In the method for producing sintered ore, the solid fuel is covered with a steelmaking slag fine powder containing at least 30% by mass of a CaO component system, and the solid fuel is covered with a sintered pallet with a thickness of 50 μm to 250 μm. A technique for suppressing generation of NOx when the solid fuel is burned on the sintering pallet during sintering by being charged on top is disclosed (Patent Document 3).

JP-A-8-60257 Japanese Patent No. 4870247 JP 2012-36464 A

However, in Patent Document 1, in the case of a NOx removal technique using a granulated body (P-type) in which the fine coke granules and the fine powder catalyst are mixed, NOx in a low temperature region of 1,000 ° C. or less.
There is a problem that the reduction effect 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 catalyst coated on the surface of the coarse coke particles, if the surface of the coke is sufficiently covered with the catalyst, the combustion rate of the coke becomes slow, Impairs the productivity of the sintering machine. For this reason, there is a problem 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.
The invention described in Patent Document 2, the surface dressing of the coarse coke granules is characterized in that it contains Ca 36 wt% or more, is not described composition of Fe _x O of the surface covering material.
In the invention described in Patent Document 3, the effect of coating the surface of the solid fuel with the steelmaking slag fine powder is as follows. That is, when the sintering raw material is sintered, calcium ferrite (CaO—Fe ₃ O ₄ ) can be generated in the vicinity of the solid fuel, and this calcium ferrite has a reducing action of NOx generated during combustion of the solid fuel. Since a part of NOx can be decomposed into N _2, it is assumed that the amount of NOx in the exhaust gas generated during sintering of the sintering raw material can be reduced. However, no mention of the composition of the steelmaking slag in order to produce calcium ferrite (CaO and Fe _x O), there is a problem that the composition of a suitable steel slag is unknown. An appropriate steelmaking slag composition needs to be examined from the viewpoint of the melting temperature of the surface coating material of coarse coke granules, and is not described here.

  An object of the present invention is to provide a method for producing sintered ore which (1) suppresses the generation of NOx in a low temperature region and (2) does not hinder the productivity of the sintering machine.

(1) A surface-coated carbon material obtained by adding a granulating agent and water to a raw material consisting of iron ore, sintered dust, return ore and auxiliary raw materials, mixing and granulating the raw material, and coating the granulated raw material with a coating. A method for producing a sintered ore that is fired using,
The composition of the coating of the surface-coated carbonaceous material is CaO / (CaO + FeO) being 0.1 or more and 0.6 or less, the method for producing a sintered ore.
However, the FeO content includes the metal Fe content converted to FeO.
(2) The method for producing a sintered ore according to (1), wherein the coating of the surface-coated carbon material includes steelmaking slag having a CaO / (CaO + FeO) of 0.6 or less.
(3) The method for producing a sintered ore according to (2), wherein the steelmaking slag is desulfurization slag.

  The generation of NOx in the low temperature region can be suppressed, and the reduction of sintered NOx by the carbonaceous material combustion control without impeding the productivity of the sintering machine can be achieved.

The figure which shows the relationship between NOx conversion rate and temperature. The figure which shows the relationship between a coke particle size and NOx generation amount. The figure explaining the NOx reduction mechanism of surface coating coke. CaO-FeO system phase diagram. The figure which shows the flow of this invention. The figure which shows the manufacturing process of the surface coating coke in an Example. Schematic diagram of sintering pot test equipment.

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 and temperature due to coke combustion. Here, the NOx conversion rate is a ratio (molar percentage) at which nitrogen atoms in the burned fuel are converted to NOx.

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, since the fine powder in the carbonaceous material has a small particle size, it 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 step, it is desirable that the carbonaceous material (particles) having a particle size of more than 0 mm and less than 0.5 mm is 20% by mass or less. On the other hand, 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.

  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.

  In Patent Document 1, using a carbonaceous material having a CaO-FexO-based composite oxide having a CaO content of 5 to 50% by weight coated on the surface, the catalytic action of the CaO-FexO-based composite oxide causes the combustion of the carbonaceous material. It is disclosed that the produced NOx is removed by reduction or decomposition. However, the CaO-FexO-based composite oxide is manufactured by melting and molding a lime-based raw material and iron ore, and thus is more expensive than a lime-based raw material used as an auxiliary material in normal sintering.

  In the present embodiment, a lime-based raw material and steelmaking slag generated in the refining process in the steelworks are used without using the expensive oxide as described above. CaO-FeO is contained in the steelmaking slag and can be obtained at a low cost as a coating material for carbonaceous materials.

  Steelmaking slag is a steelmaking process in a steelworks, and hot metal, scrap iron, and auxiliary materials (quick lime, dolomite, iron oxide, firefly stone, etc.) are charged into a converter, etc., and oxygen is blown from the pig iron to C, Si, Mn , Slag, P, S, etc. are removed to produce molten steel. Since a refining furnace such as a converter has a short refining time, a part of quick lime remains in the slag without hatching.

  In order to reduce the load on a refining furnace such as a converter and improve productivity, pretreatment such as desiliconization, desulfurization, and dephosphorization may be performed before refining the hot metal in the converter. Steelmaking slag includes desiliconized slag, desulfurized slag, dephosphorized slag and the like generated in the hot metal pretreatment. Moreover, if the hot metal preliminary treatment is sufficiently performed, the converter or the like mainly performs decarburization, and in this case, decarburization slag is generated. Further, in a refining process such as a converter, slag may be discharged after desulfurization / dephosphorization. In this case, the slag becomes desulfurization and dephosphorization slag.

Desiliconization slag is generated in the desiliconization process, in which dust collection dust, fine iron ore, etc. are blown into the hot metal discharged from the blast furnace at the ironworks, and the silicon in the pig iron is oxidized and removed by oxygen contained in the fine iron ore. To do. CaO is small and SiO ₂ , Fe ₂ O _{3 and the} like are contained in a large amount.
The desulfurization slag is slag generated in a desulfurization process in which soda ash (Na ₂ Co ₃ ), carbide (CaC ₂ ), quicklime (CaO) or the like is blown into the molten iron to remove sulfur (S) in the pig iron.
CaO is abundant and metallic iron (M.Fe) is also contained a lot. When dephosphorization (P) is performed together with sulfur (S), dust collection dust, iron ore and the like are simultaneously blown in addition to quick lime (CaO) and the like.
Decarburization slag is slag generated in a refining process in which hot metal that has been pretreated is put into a refining furnace such as a converter and oxygen is blown to mainly remove carbon in pig iron. Contains a lot of unhatched CaO.
As described above, various slags having various compositions are generated in steelmaking slag by a refining process, and it is important to use these slags well.
Table 1 shows a comparison of components between typical steelmaking slag components and other CaO and FeO sources.

For FeO, FeO conversion from FeO and metallic iron measured by chemical analysis was considered. That is, since metallic iron is oxidized to FeO in the liquid phase generation stage of the sintering process, the amount of FeO derived from metallic iron is calculated by the following formula (1), and this metal-derived FeO and FeO from the beginning are present. The amount that was being added was added.
(Formula 1)
Conversion FeO (%) = M-Fe (%) × (55.8 + 16) /55.8+FeO (%) (1)

In the present invention, inexpensive steelmaking slag is used as the surface covering material of the carbonaceous material, but a surface covering material having a low melting point is used. The objectives are (1) in the low temperature region (below 1200 ° C), to prevent coke combustion by the coke surface coating layer and to suppress the generation of NOx, (2) in the high temperature region (1200 ° C or higher) The lower surface coating layer is dissolved, and NOx is reduced by the CO gas generated by the solution loss reaction of the exposed coke, thereby suppressing the generation of NOx.
The NOx reduction mechanism of the surface-coated coke will be described with reference to FIG.
The effect of the surface coating coke is roughly divided into a coating effect and a peeling effect shown in FIG. NOx generated in the sintering process is Fuel / NOx, and contrary to thermal NOx, NOx generation is suppressed in a high temperature range. This basic mechanism is considered as follows.
In FIG. 3, in the low temperature region (below 1200 ° C.), if the coke is coated with a coating layer composed of a CaO-based raw material and FeO, the surface coating material prevents the contact between the coke and oxygen and suppresses the coke combustion itself. Therefore, the generation of NOx is also suppressed. This is the covering effect.
On the other hand, in the high temperature region (approximately 1200 ° C. or higher), the coating material approaches the melting point and starts generating a liquid phase. Due to the liquid phase generation, the coating layer is fluidized and separated, and full-scale coke combustion starts. However, since the solution loss reaction is activated because it is already in the high temperature region, NOx generation is suppressed. That is, in the high temperature range, the solution loss reaction (C + CO2⇒2CO) becomes active in the coke surface layer, and a large amount of generated CO gas reduces the nitrogen compounds produced by coke combustion near the coke particles. Thus, NOx generation is suppressed. Here, the solution loss reaction becomes active at about 1000 ° C. or more.
In the present invention, a part of CaO is replaced with FeO, and the temperature of liquid formation is lowered from about 1200 ° C. to about 1100 ° C. (FIG. 4). Even when the coating peeling start temperature is lowered to 1100 ° C., the solution loss reaction has already been activated, and the NOx reduction effect is not lowered. On the contrary, when the coating layer is made of FeO—CaO, the liquid phase ratio and fluidity of the coating layer are increased, and the peeling rate of the coating layer is increased. It is considered that the rapid combustion of coke is promoted to further increase the CO / CO ₂ ratio in the vicinity of the coke grains and further reduce NOx. This is a peeling effect and is the gist of the present invention.

FIG. 4 shows a CaO—FeO system phase diagram. The surface coating material preferably has a low melting temperature. In FIG. 4, the eutectic point P is CaO / (CaO + FeO) of 0.26, the eutectic point has the lowest melting temperature, and is most preferable as the composition of the surface coating material. When CaO / (CaO + FeO) is smaller than 10% by mass of the Q point, the solidus A rapidly rises and the solid phase increases. Therefore, CaO / (CaO + FeO) of the surface covering material is preferably 0.1 or more.
Also, the upper limit of CaO / (CaO + FeO) is difficult to judge because the coexistence range of the solid phase and the liquid phase is wide. Then, the sintering pot test mentioned later was implemented and it turned out that 0.6 is preferable.

The composition of the coating of the surface-coated carbon material according to the present invention is such that CaO / (CaO + FeO) is 0.1 or more and 0.6 or less, and most preferably 0.26. However, the steelmaking slag is produced by various different processes. As a result, CaO / (CaO + FeO) varies with each slag. When CaO / (CaO + FeO) is less than 0.1, it can be made 0.1 or more by adding a lime-based raw material to steelmaking slag. Moreover, also in the case of 0.26 or less, the optimal surface covering carbon | charcoal material of CaO / (CaO + FeO) 0.26 can be obtained by adding a lime-type raw material. On the other hand, when CaO / (CaO + FeO) exceeds 0.6, the CaO content is too large and cannot be used as a surface-coated carbon material.
The steelmaking slag is preferably pulverized to 0.1 mm or less. It is for making it act efficiently as a surface covering material.

  As the lime-based raw material added to the steelmaking slag, calcium hydroxide is more preferable in addition to quick lime. Calcium hydroxide acts as a binder to form a coating layer that adheres closely to the surface of the carbonaceous material, so that the coating on the surface of the carbonaceous material is detached during mixing with the blended raw materials and during the conveyance process until the raw material is charged into the sintering machine. It is because it can suppress.

The flow of the present invention is shown in FIG.
The blended raw material is cut out from the raw material tank 14, and sequentially mixed and granulated by the primary mixer 15 and the secondary mixer 16. Here, the blended raw material is a raw material excluding the raw material used for the production of the surface-coated carbonaceous material, and excludes the bedding ore.
Next, the surface-coated coke uses coarse coke having a particle diameter of 0.5 mm or more cut out from the coke tank 11 as core particles, and granulates the slaked lime and steel slag cut out from the slaked lime tank 12 and the steelmaking slag tank 20. And granulated with a pan pelletizer 18 to produce a surface-coated coke 19. The surface-coated coke 19 is added to and mixed with the raw material mixed and granulated by the primary mixer 15 and the secondary mixer 16 in the latter half of the secondary mixer 16. In this case, the surface coating coke 19 is added after the other raw materials are mixed and granulated. In order to prevent the coating layer on the surface of the carbonaceous material from collapsing and peeling when the surface-coated carbonaceous material is added when mixing and granulating the blended raw materials, the surface-coated coke is preferably added afterwards.

In the above description, the lime-based raw material has been described as slaked lime. However, in the case of quicklime, it is preferable to use slaked lime after hydration reaction by adding water by a digester. This is to accelerate the hydration reaction of quicklime and prevent dust generation. Since the lime-based raw quicklime or slaked lime has a binder function, a coating layer that is in close contact with the surface of the carbonaceous material is formed, and the mixing process with the compounding raw material and the conveyance process until the raw material is charged into the sintering machine Thus, desorption of the coating on the surface of the carbon material can be suppressed, and NOx generated during sintering can be more stably reduced.
The method for mixing and granulating coarse coke with steelmaking slag and lime-based raw material may be any drum mixer, centrifugal granulator and other mixing and granulating machines.

Next, examples of the present invention will be described, but the present invention is not limited thereto.
(Preparation of coated carbon material)
A desulfurization slag, decarburization slag, desiliconization slag and quicklime were used to form a coating layer of 10% by mass with respect to the powdered coke. Any slag is finely pulverized to 0.1 mm or less. And the CaO / (CaO + FeO) of the coating layer was changed, and the NOx reduction effect by the composition of the coating layer was investigated.
A production flow of the surface-coated coke used in the experiment is shown in FIG. Powdered coke and quicklime were kneaded for 3 minutes with the universal kneader 21 and then granulated for 3 minutes with the small drum mixer 22 to produce surface-coated coke with a moisture content of 13.5%.
(Sintering pot test)
A schematic view of the sintering pot test apparatus used for the implementation 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 surface covering carbon material used as a test body is inserted into the sintering pot 2 and ignited in the ignition furnace 1 to heat the surface covering carbon material. At the same time, the blower 4 is started, exhaust gas generated in the sintering pot 2 is exhausted through the wind box 3, and the exhaust gas is analyzed by the analyzer 5.
The diameter of the sintering pot 2 was 300 mm and the bed height was 600 mm, and the exhaust gas was analyzed for CO, CO ₂ , O ₂ , NOx, and SOx. Water of 7.5% by mass was externally added to ore and coke, and mixed and granulated for 4 minutes using a drum mixer having a diameter of 1,000 mm.
The blended raw materials mixed and granulated were filled in a sintering pot test apparatus and fired under conditions of ignition for 90 seconds and suction negative pressure of 15 kPa. During firing, the temperature in the sintered layer and the concentration of NOx in the exhaust gas were measured at three locations with different layer heights. The raw material composition used in the test is shown in Table 2, and the particle size distribution of coke is shown in Table 3.

Table 4 shows the results of the pan test.
The base is a case where the powder coke is not surface-coated.
In Example 1, Comparative Example 1, and Comparative Example 2, the coating layer thickness was constant (10% by mass) with respect to the powder coke, and the composition of the coating layer was changed. The composition of the coating layer was such that CaO derived from quick lime and CaO derived from steelmaking slag were fixed at 50:50, and FeO mass was adjusted to change CaO / (CaO + FeO). CaO / (CaO + FeO) of the coating layer is 0.566 (Example 1), 0.889 (Comparative Example 1), and 0.701 (Comparative Example 2).
As a result of the pan test, in the example in which CaO / (CaO + FeO) was 0.566, the NOx concentration in the exhaust gas was 109.3 ppm, which was low and achieved the target value (110 ppm). Comparative Example 1 and Comparative Example 2 Could not clear the target value.

  The generation of NOx in the low temperature region can be suppressed, and the reduction of sintered NOx by the carbonaceous material combustion control without impeding the productivity of the sintering machine can be achieved.

DESCRIPTION OF SYMBOLS 1 ... Ignition furnace, 2 ... Sintering pan, 3 ... Wind box, 4 ... Blower, 5 ... Analyzer, 11 ... Coke tank, 12 ... Slaked lime tank, 13 ... Granulator, 14 ... Raw material tank, 15 ... Primary mixer , 16 ... secondary mixer, 18 ... pan pelletizer, 19 ... surface-coated coke tank, 20 ... steelmaking slag tank, 21 ... universal kneader, 22 ... small drum mixer.

Claims (3)

A granulated material and water are added to a raw material consisting of iron ore, sintered dust, return mineral, and auxiliary materials, mixed and granulated, and the granulated raw material is calcined using a surface-coated carbon material that is coated with a coating. A method for producing a sintered ore comprising:
The composition of the coating of the surface-coated carbonaceous material is CaO / (CaO + FeO) being 0.1 or more and 0.6 or less, the method for producing a sintered ore.
However, the FeO content includes the metal Fe content converted to FeO.   2. The method for producing a sintered ore according to claim 1, wherein the coating of the surface-coated carbon material includes steelmaking slag having a CaO / (CaO + FeO) of 0.6 or less.   The method for producing a sintered ore according to claim 2, wherein the steelmaking slag is desulfurization slag.

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