JP5703913B2 - Method for producing sintered ore - Google Patents

Description

The present invention relates to a method for producing sintered ore that can reduce NOx in exhaust gas generated by a sintering machine.

Conventionally, in a steel mill, a sintering raw material is sintered using a sintering machine.
Since the exhaust gas generated during sintering of the sintering raw material contains nitrogen oxides (NOx), the generated exhaust gas is released to the atmosphere after removing the nitrogen oxides. As a method for removing nitrogen oxides, for example, in Patent Document 1, using the CaO-Fe t O pseudo particles consisting a fine powder catalyst and the fuel coke containing _(iron oxide) based composite oxide (solid fuel) A method of performing sintering is disclosed.
In addition, steelmaking slag is generated from the steelmaking process of steelworks, and this is used for roadbed materials and landfill materials.

JP-A-8-60257

However, the method disclosed in the above Patent Document 1, it is necessary to prepare a CaO-Fe t _O composite oxide that is not used as a raw material to be sintered is not economical to cause additional costs.
In addition, there are limits to the fields in which steelmaking slag generated from steelworks can be used, and further expansion of usage is desired.
For this reason, it is conceivable to cover the surface of the fuel coke with steelmaking slag and to reduce NOx in the exhaust gas generated by the sintering machine. However, this steelmaking slag is difficult to adhere to the surface of the fuel coke. When the thickness became thin or the adhesion was not sufficient, it was easy to peel off from the surface of the fuel coke during transportation.

The present invention has been made in view of such circumstances, and enables steelmaking slag to adhere to the surface of the solid fuel to a predetermined layer thickness, and makes it difficult to peel the steelmaking slag even during the transfer, thereby sintering the sintered raw material. It is an object of the present invention to provide a method for producing a sintered ore that can economically reduce NOx in exhaust gas generated at the time of sintering and that can also effectively use steelmaking slag.

The gist of the present invention made to solve the above problems is as follows.
(1) iron ore, a pseudo Nizo grains prepared by pseudo granulated solid fuel, and a sintering raw material containing limestone-based raw materials granulator, the surface is covered with a coating comprising a steelmaking slag and hydrated lime In the method for producing sintered ore, which is mixed with a solid fuel for coating , charged on a sintering pallet and sintered.
Said coating solid fuel, adding the steelmaking slag and the slaked lime containing a particle size less than 0.5 mm 60% by weight or more, further by granulating kneaded with addition of water, of the coating for a solid fuel upon covering the surface with the coating material, as Ca (OH) ₂ content of the coating in is more than 60% by weight of the coating amount, method for producing sintered ore, which comprises adding the hydrated lime .

(2) The method for producing a sintered ore according to (1), wherein water is added during kneading so that the water content in the coating is 9% by mass or more and 16% by mass or less.

(3) The method for producing a sintered ore according to (1) or (2), wherein the coating layer thickness of the coating is 5 μm or more and 500 μm or less.

(4) the supply granulator coating solid fuel covered with the coating material from the downstream side of the, match mixed and said the coating solid fuel covered with the coating pseudo granulate Rukoto The method for producing a sintered ore according to any one of (1) to (3).

In the method for producing sintered ore according to the present invention, the coating covering the surface of the solid fuel for coating contains steelmaking slag fine powder containing 60% by mass or more of particle size less than 0.5 mm. The surface area can be increased to improve the generation efficiency of calcium ferrite, and the steelmaking slag fine powder can easily adhere to the surface of the solid fuel for coating.
Furthermore, since Ca _{(OH) 2} content in the coating is the addition of slaked lime so that the above 60 mass% of the coating amount, the steelmaking slag from the Ca _{(OH) 2,} the added hydrated lime Ca _{(OH) 2} The binder function can be exhibited, and the coating can be reliably and firmly formed on the surface of the coating solid fuel with a predetermined layer thickness.
Thereby, low temperature combustion of the solid fuel can be suppressed, and in a high temperature region of 1200 ° C. or higher, CaO in the coating reacts with surrounding iron ore to become low melting point calcium ferrite and melts and melts down. Therefore, NOx in the exhaust gas generated during sintering can be reduced economically, and effective use of the steelmaking slag can be achieved.

In addition, when the solid fuel for coating covered with the coating is supplied to the pseudo-granulated material from the downstream side of the granulator, it is possible to prevent the coating from peeling off from the surface of the solid fuel for coating. In addition, since it is possible to prevent the covering solid fuel covered with the covering from being buried in the pseudo-granulated material, it is possible to efficiently suppress the generation of NOx.

It is explanatory drawing of the manufacturing method of the sintered ore which concerns on one embodiment of this invention. It is explanatory drawing of a pan testing apparatus.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIG. 1, the manufacturing method of the sintered ore which concerns on one embodiment of this invention is a method of charging and sintering a sintering raw material on the sintering pallet of the sintering machine 10, and steelmaking. In this method, slag fine powder is used to economically reduce NOx in the exhaust gas generated during sintering of the sintering raw material and to make effective use of the steelmaking slag. This will be described in detail below.

First, iron ore (for example, iron ore raw material or return ore), coke (an example of solid fuel), limestone-based raw material (for example, CaO or CaCO ₃ ), and other auxiliary materials (for example, MgO source or SiO ₂ source) ) Are respectively cut out from the storage tank 11 at a preset blending ratio.
And the sintering raw material containing this iron ore, coke, a limestone raw material, and other auxiliary materials is thrown into the primary drum mixer (an example of a granulator) 12, and water is added to this to perform granulation. . Further, these are put into a secondary drum mixer (an example of a granulator) 13 disposed on the downstream side of the primary drum mixer 12 for further granulation.

When performing this granulation, the two drum mixers 12 and 13 are arranged in series, but three or more (a plurality of) drum mixers may be arranged in series. It is also possible to use only a drum mixer.
Thereby, powder can be made to adhere to the periphery of the particle | grains used as a nucleus, and the pseudo granulated material whose average particle diameter is about 2-4 mm can be manufactured. For example, if the core particle is coarse iron ore, fine iron ore and fine coke are likely to adhere to it, and if the core particle is coarse coke, fine iron ore is around it. Easy to adhere.

On the downstream side in the secondary drum mixer 13, coke (an example of a solid fuel for coating, that is, a solid fuel to be coated) 15 cut out from the storage tank 14 at a preset ratio is a coating 16. And is supplied as a coated granulated product.
The covering 16 is composed of fine steelmaking slag powder and slaked lime (calcium hydroxide: Ca (OH) ₂ ) and covers the surface of the coke 15.
Here, steelmaking slag such as converter slag, desulfurization slag, dephosphorization slag, electric furnace slag, etc. generated from steelworks can be used as the steelmaking slag fines. This steelmaking slag contains 20 mass% or more (preferably 25 mass% or more) of CaO component system (for example, CaO or Ca (OH) ₂ ), and the upper limit of the CaO component system is, for example, about 50 mass%. It is. The steelmaking slag also contains an Fe component (about 5% by mass or more and 40% by mass or less in terms of T.Fe (total iron)).

This steelmaking slag fine powder may be a fine powder obtained by pulverizing steelmaking slag generated from a steel mill with a pulverizer, but it is originally fine powder, such as desulfurization slag and dephosphorization slag generated in the hot metal pretreatment process. In any case, one containing 60% by mass or more of fine powder having a particle size of less than 0.5 mm is used.
Here, the reason why the fine powder having a particle size of less than 0.5 mm is set to 60% by mass or more is to increase the surface area of the steelmaking slag fine powder and improve the formation efficiency of calcium ferrite. Is less than 5 mm and less than 20% by mass, and a particle size of 0.5 mm or more and 5.0 mm or less is 40% by mass or more, preferably 70% by mass or more. For this reason, the upper limit value of the fine powder amount is not particularly defined, but when steelmaking slag is pulverized, it is about 90% by mass and further about 85% by mass in consideration of the efficiency of the work.

The steelmaking slag described above contains CaO and Ca (OH) ₂ as described above.
This CaO becomes Ca (OH) ₂ due to moisture added when the surface of the coke 15 is covered with the coating 16, and this, together with the Ca (OH) ₂ originally contained, forms the coating 16 on the surface of the coke 15. It functions as a binder to be deposited, but this alone may not be sufficient. For this reason, the slaked lime is added to this steelmaking slag to make up for the lack of binder function.
In addition, as slaked lime to add, a commercially available thing may be sufficient, However, What digested by adding water to raw apatite may be used as it is. In any case, it is preferable that the slaked lime has a particle size of 0.15 mm or less and 70% by mass or more.

Here, when the amount of Ca (OH) _{2 in} the coating is less than 60% by mass of the amount of the coating, the amount of Ca (OH) _{2 in the} coating is too small and the binder function is insufficient. The coke surface is easily exposed and the coke burns in a low temperature region, and the effect of reducing the amount of NOx in the exhaust gas is reduced.
Therefore, the amount of Ca (OH) ₂ in the coating is set to 60% by mass or more of the coating amount.
On the other hand, the upper limit value of the amount of Ca (OH) ₂ in the coating is not particularly defined, but is preferably 95% by mass and more preferably 90% by mass from the viewpoint of effective use of the steelmaking slag.

Note that the amount of coke 15 coated with the coating 16 is 30 mass, which is a part of the total amount of coke supplied to the sintered pallet in consideration of suppressing the burying of coke in the pseudo-granulated product. % Or more (preferably 40% by mass or more), more preferably all (100% by mass).
For this reason, the amount of coke supplied from the storage tank 11 to the primary drum mixer 12 is an amount obtained by subtracting the amount of coke 15 covered with the coating 16 from the total amount of coke supplied to the sintering pallet (70% by mass or less). It becomes.

Moreover, it is preferable that the coating layer thickness of the coating 16 covering the coke 15 is 5 μm or more and 500 μm or less.
Here, when the coating layer thickness of the coating covering the coke is less than 5 μm, the coating layer thickness of the coating is too thin, so that the coating is peeled off from the coke surface and the coke surface is easily exposed, and the coke is in a low temperature region. And the effect of reducing the amount of NOx in the exhaust gas is reduced. On the other hand, when the coating layer thickness exceeds 500 μm, the coating layer thickness of the coating is too thick, so it takes time to melt the coating after being supplied to the sintering pallet, and the coated coke remains unburned. Become.
From the above, the coating layer thickness of the coating covering the coke is 5 μm or more and 500 μm or less, but the lower limit is preferably 50 μm, more preferably 100 μm, and the upper limit is preferably 300 μm, more preferably 200 μm.

Then, when covering the coke 15 with the coating 16, the steelmaking slag fine powder and slaked lime constituting the coating 16, the coke 15, and moisture are supplied to a dow mixer (an example of a kneader) 17 and kneaded. The kneaded product is granulated with a pan pelletizer 18, the coating 16 is adhered around the coke 15, and the coke 15 is covered with the coating 16.
Note that the amount of water added during kneading in the Dow mixer 17 (and also during granulation) increases the amount of water in the coating 16 (moisture in slaked lime) in order to enhance the adhesion effect of the coating 16 on the coke 15 surface. Is preferably adjusted so that it is 9% by mass or more and 16% by mass or less (preferably, the lower limit is 11% by mass and the upper limit is 14% by mass), but is not limited thereto.

However, by adjusting the water content (content of water content) in the coating 16 to the above range, the yield of the coating layer with a coating layer thickness of 5 μm or more and 500 μm or less is, for example, 80% by mass or more, and further 90%. It can be made more than mass%.
In addition, the above-mentioned moisture content is the moisture content in the coating of the final product (the coated granulated product before being charged into the sintering machine), and the steelmaking slag fine powder and slaked lime It is expressed as the total amount of the water content and the amount of water added during mixing (and also during granulation). This moisture content is a ratio (mass%: outer coating) to the dried coating (steel slag fine powder and slaked lime) 100.

Here, the coke 15 and the steelmaking slag fine powder and slaked lime are kneaded using a Dow mixer, but other kneaders such as a Redige mixer can also be used.
By the above-described method, the entire surface of the coke 15 can be covered with the covering 16.
The coke 15 covered with the coating 16 obtained by the above method, that is, the coated granulated product, is downstream in the secondary drum mixer 13 arranged at the most downstream position (from the discharge port toward the supply port). 5m (preferably within 20% of the total length of the secondary drum mixer), this coated granulated product is a pseudo-granulated product in which powder is adhered around the core particles described above, Can be mixed. The addition position of the coated granule is not limited to the above-described position. For example, a belt of a conveyor (not shown) that conveys the pseudo granule disposed on the downstream side of the secondary drum mixer 13. It can also be set to the top (see dotted arrow in FIG. 1).

Then, the coated granulated product is charged onto the sintered pallet via a supply device (for example, a drum feeder) in a state of being mixed with the pseudo granulated product.
At this time, since the surface of the coke is covered with the coating layer composed of the coating, the coated granulated product suppresses the combustion of the coke in the coating layer in the low temperature region at the early stage of the combustion of the coke, thereby reducing the NOx content. Generation can be suppressed. On the other hand, it reaches a high temperature range above 1200 ℃, Ca (OH) ₂ in the coating layer is reacted with the above-mentioned Fe component contained in the steel slag around the ore and coatings in a low melting point calcium It melts as a ferrite and melts down.
As a result, the coating layer disappears on the surface of the coke, but the coke is burned in a high temperature region of 1200 ° C. or higher even in the bare state, so that the generation of NOx is small.
Therefore, by using the method for producing a sintered ore according to the present invention, NOx in the exhaust gas generated during sintering of the sintered raw material can be reduced economically, and the steelmaking slag can be effectively used.

Next, examples carried out for confirming the effects of the present invention will be described.
The prepared raw materials for sintered ore are iron raw materials, limestone raw materials, MgO-based and other auxiliary raw materials, return minerals, and coke. The iron raw material was 67.5% by mass, the limestone-based raw material was 10.7% by mass, the MgO-based and other auxiliary raw materials were 2.3% by mass, the return was 16.1% by mass, and the coke was 3.4% by mass. %.
Here, when manufacturing the coated granulated product, 3% by mass of coke (solid fuel for coating) out of 3.4% by mass of the above-described blended raw material is used, and steelmaking slag and slaked lime are newly added. Prepared for.

First, the production conditions of the coated granulated product are shown below.
The coated granulated product is prepared by supplying the above-mentioned coke, steelmaking slag, slaked lime, and water to a dow mixer (kneading machine) and kneading, and then supplying the kneaded product to a pan pelletizer to granulate, It was manufactured by attaching steelmaking slag and slaked lime. The pan pelletizer had a diameter of 5 m, a rotation speed of 8 rpm, and an inclination angle of 57 degrees (no addition of water).
Here, the particle size distribution and water content of the coke used are shown in Table 1, and the main component composition, water content and particle size distribution of the steelmaking slag are shown in Table 2 and Table 3, respectively.

On the other hand, the blended raw material of sintered ore excluding the raw material of the above-mentioned coated granulated material is mixed using a primary drum mixer, and after adding water to the granulated material, the secondary drum is further mixed. The mixture was put into a mixer and further granulated to give a pseudo granulated product. The primary drum mixer has an inner diameter of 4.8 m and a length of 17.1 m, and the rotational speed is 6 rpm. The secondary drum mixer has an inner diameter of 5.4 m and a length of 26 m, and the rotational speed. Was 6 rpm.
Here, the above-mentioned coated granulated product was supplied into a secondary drum mixer, and the coated granulated product was mixed together with the pseudo-granulated product. The addition position of the coated granulated product was 0.3 minutes (18 seconds) before the mixing granulation by the secondary drum mixer was completed.
And the pot test was done using the mixture of a covering granulated material and a pseudo-granulated material.

Next, the pan test apparatus used for the pan test will be described.
As shown in FIG. 2, the pan test apparatus has a pan body, a dust collector, a cooler, a blower, and a NOx meter. The gas generated in the pan body is sucked from below by the blower and processed by the dust collector and the cooler. Then, it is a device that measures the NOx concentration in the gas with a NOx meter (measuring device of atmospheric pressure chemiluminescence method of Shimadzu Corporation) installed in the flue of the sintered exhaust gas.
The pan body has a cylindrical portion where the above-described mixture is charged, and has a grate bar (grate) on the bottom. The cylindrical portion has a diameter d of 300 mm and a depth h of 500 mm.

In this pan test, the above-mentioned mixture was charged into the pan body, the pseudo-granulated material in the pan body was ignited and sintered, and the generated NOx was measured using a NOx meter.
Table 4 shows the test conditions and test results described above. In addition, A, B, and C described in the type of steelmaking slag in Table 4 correspond to the slag A, slag B, and slag C described in Table 2 and Table 3, respectively.

Examples 1 to 8 shown in Table 4 use steelmaking slags A and B containing 60% by mass or more of particles having a particle size of less than 0.5 mm, and the amount of Ca (OH) ₂ in the coating is 60% by mass of the coating amount. It is the result of adding slaked lime so that it may become the above. As a result, the production efficiency of calcium ferrite was increased, and the coating could be reliably and firmly formed on the surface of the coke. Therefore, the yield of the coated granulated product having a coating layer thickness of 5 to 500 μm was increased to 70% by mass. As a result, the amount of generated NOx could be reduced to 145 ppm or less.
In particular, as shown in Examples 1 to 4, as the amount of Ca (OH) _{2 in the} coating is increased, the yield of the coating with a coating layer thickness of 5 to 500 μm is also 80% by mass or more, and further 90% by mass. % And the NOx concentration could be reduced from 138 ppm to 130 ppm.

On the other hand, Comparative Examples 1 and 2 are the results of reducing the amount of slaked lime added and setting the amount of Ca (OH) ₂ in the coating to less than 60% by mass of the coating. Thus, since the binder function of the coating was reduced by reducing the amount of Ca (OH) ₂ in the coating, the yield of the coating with a coating layer thickness of 5 to 500 μm was 40 regardless of the type of steelmaking slag. As a result, the amount of generated NOx increased to 155 ppm or more.
Moreover, the comparative example 3 is the result of using the steelmaking slag C which contains less than 60 mass% of particle sizes less than 0.5 mm. Thus, by using the steelmaking slag in which the amount of fine powder was reduced, the surface area of the steelmaking slag fine powder was reduced, the production efficiency of calcium ferrite was lowered, and the steelmaking slag became difficult to adhere to the coke surface. For this reason, the yield of the coating layer having a coating layer thickness of 5 to 500 μm was reduced to 20% by mass, and as a result, the amount of NOx generated was increased to 150 ppm.

Examples 5 and 6 are the results of adjusting the moisture content in the coating to the outside of the optimal range (9% by mass to 16% by mass), and adjusting the moisture content in the coating to be within the optimal range. The NOx concentration increased as compared with Examples 1 to 4, but the NOx reduction effect was exhibited as compared with Comparative Examples 1 to 3 (NOx concentration: 145 ppm or less).
Moreover, although Example 7, 8 is a result of using steel-making slag B from which a main component structure and a moisture content and a particle size distribution differ from Examples 1-4, this steel-making slag B is also Examples 1-4. In the same manner as in steelmaking slag A shown in FIG. 4, since it contains 60% by mass or more of particles having a particle size of less than 0.5 mm, the NOx concentration was comparable to those in Examples 1 to 4.

From the above, by using the method for producing sintered ore of the present invention, it is possible to attach steelmaking slag to the surface of the solid fuel with a predetermined layer thickness, and it is difficult to peel the steelmaking slag even during the transportation. Thus, it has been confirmed that NOx in the exhaust gas generated during sintering of the sintered raw material can be economically reduced and that the steelmaking slag can be effectively used.

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included. For example, the case where the sintered ore production method of the present invention is configured by combining a part or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.
Moreover, in the said embodiment, although the coating which covers the surface of a coke was demonstrated about the case where it comprised only with steel-making slag fine powder and slaked lime, it is not limited to this, For example, iron ore in a coating Stone fine powder, solid fuel fine powder, etc. may be included. The solid fuel fine powder is preferably not included in the coating from the viewpoint of NOx reduction, but cannot be completely removed in production.

10: Sintering machine, 11: Storage tank, 12, 13: Drum mixer (granulating machine), 14: Storage tank, 15: Coke (solid fuel for coating), 16: Coating, 17: Dow mixer, 18: Pampereizer

Claims (4)

Iron ore, solid fuel, and a pseudo Nizo grains prepared by pseudo granulated sintering raw material containing limestone-based material in a granulator, coating the solid surface is covered with a coating comprising a steelmaking slag and hydrated lime In the method for producing sintered ore, which is mixed with fuel , charged onto a sintering pallet and sintered.
Said coating solid fuel, adding the steelmaking slag and the slaked lime containing a particle size less than 0.5 mm 60% by weight or more, further by granulating kneaded with addition of water, of the coating for a solid fuel upon covering the surface with the coating material, as Ca (OH) ₂ content of the coating in is more than 60% by weight of the coating amount, method for producing sintered ore, which comprises adding the hydrated lime . The method for producing a sintered ore according to claim 1, wherein water is added during kneading so that the water content in the coating is 9% by mass or more and 16% by mass or less. Production method. 3. The method for producing a sintered ore according to claim 1, wherein the coating layer has a coating layer thickness of 5 μm or more and 500 μm or less. 4. In the manufacturing method of the sintered ore of any one of Claims 1-3, the solid fuel for coating | covering covered with the said coating | coated is supplied from the downstream of the said granulator, and it is covered with this coating | coated thing. method for producing sintered ore in which the coating solid fuel and said pseudo granulated product characterized Rukoto to adjust mixing was.

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