JP2002249813A - Rotary hearth type reducing furnace operating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotary hearth type reducing furnace operating method for manufacturing reduced metal which is capable of minimizing the increase of the facility cost and the operation cost, preventing firm plate-like fixed matter from being built up on a hearth to facilitate the discharge of the fixed matter, preventing or reducing the wear of a blade tip of a screw of a discharging device, performing the continuous operation for a long time, and achieving high rate of operation. SOLUTION: Fixing suppressing agent is added in advance to agglomerate containing powder metal oxide and powder carbonaceous substance, and charged onto the hearth by a charging unit so that the fixing-suppressing agent is dispersed in the fixed matter formed on the hearth. When reduced iron is scraped outside the furnace by the discharging device, the fixed matter is scraped while applying the compression force at the same time, thus generating cracks in the fixed matter with the fixing suppressing agent as a starting point, and the fixed matter is peeled from the hearth while splitting into small pieces, and scraped out together with reduced iron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing reduced metal from metal oxides using a rotary hearth furnace, and more particularly, to a method for preventing the formation of strong adhered substances on a hearth for a long period of time. It relates to the improvement of the operation method that enables the operation.

[0002]

2. Description of the Related Art In recent years, as the production of steel products using an electric furnace has become popular, the demand for reduced iron has been increasing due to the tight supply and demand of scrap, which is the main raw material, and the demand for the production of high-grade steel in electric furnaces. . Also, from the viewpoint of environmental measures, iron, Ni, Cr etc. contained in dust generated at unused steel mills and electric furnace factories that have been discarded in the past are collected as reducing metals, and blast furnaces, converters, Attempts to reuse it as a raw material for electric furnaces and the like have been actively made.

[0003] As one of the processes for producing reduced iron, powdered iron ore is mixed with carbonaceous material such as powdered coal or coke to form agglomerates, for example, pellets, which are then converted into a rotary hearth furnace ( Attention has been paid to a method of reducing the iron oxide in iron ore to obtain solid metallic iron by charging it into a rotary hearth reduction furnace and heating it to a high temperature (for example, Japanese Patent Publication No. 45-1).
9569, JP-A-11-279611, etc.).

This reduction method can be used not only for the production of metallic iron but also for the production of non-ferrous metals such as Ni and Cr by reducing them from their oxides. Less than,
In "Prior art", "Embodiments of the invention" and the like,
Only the production of metallic iron will be described, but the present invention is not necessarily limited thereto, and the present invention can be similarly applied to the production of other non-ferrous metals.

[0005] An example of a conventional reduced iron production process using a rotary hearth furnace (prior art 1) will be described with reference to a plan view illustrating a schematic equipment configuration of a rotary hearth furnace shown in FIG.

[0006] Powdered iron oxide and powdery carbonaceous material are mixed and granulated to produce raw pellets.

[0007] The raw pellets are heated by a dryer or the like to a temperature range in which flammable volatiles generated from the inside of the pellets do not ignite to remove adhering moisture.
It is referred to as "agglomerate P". ).

The dried pellets (agglomerated material P) are supplied into a rotary hearth furnace 1 by using a suitable charging device,
A pellet layer is formed thereon.

The pellet layer is reduced by radiant heating by combustion of a burner 11 installed in the upper part of the furnace, metallization proceeds, and reduced iron R is obtained.

The reduced iron R is cooled by directly blowing a gas to the reduced iron R by the cooler 12 or indirectly cooled by a water-cooled jacket and then discharged to the outside of the furnace by the discharge device 13.

In the reduced iron production process using a rotary hearth furnace, when the agglomerate P is placed on a rotary hearth, the agglomerate is pulverized due to mechanical impact or the like, and powder is generated. Also,
Even after the loading, the furnace is exposed to a high-temperature atmosphere in the furnace, and devolatilization and reduction reaction of volatile components in the carbonaceous material generates CO, CO ₂ gas, etc., and the internal pressure of the agglomerate increases. May crack or explode, generating powder. The powder thus generated is reduced in the rotary hearth furnace to become metallic iron powder.

Further, the agglomerates (reduced iron R) reduced and metallized in the rotary hearth furnace are usually discharged using a screw-type discharge device. Powder is generated due to mechanical handling.

The powder generated in this manner is difficult to completely remove by the discharge device, and part of the powder remains on the hearth or is rubbed into the hearth surface by the discharge device. When the powder stays in the furnace, the powder sinters at a high temperature and adheres to the hearth, and new powder accumulates and grows on the adhered material. The powder contains not only metallic iron but also mineral components (slag components) derived from gangue in iron oxides and ash in carbonaceous materials, and these mineral components (slag components) melt on the hearth.・ Repeat coagulation. Further, the slag component is compressed and rolled together with the metallic iron by the discharging device, so that a plate-like fixed substance having a high hardness structure in which the metallic iron and the slag component are densely mixed is formed on the hearth.

The discharge device is cooled by an appropriate method in order to ensure its mechanical strength. However, since the plate-like fixed material on the hearth is hard and hot, the cutting edge of the discharge device contacts the plate-like fixed material. The temperature rises due to frictional heat or the like generated during the heating and wear occurs. For this reason, it is often necessary to interrupt the operation and replace the screw of the discharge device, and a decrease in the operating rate and an increase in maintenance cost are serious problems (first problem).

Further, sometimes, after the plate-like substance grows large (wide), it is scratched by the screw of the discharging device and peeled off from the hearth, and a serious operation such as winding or catching on the screw is caused. The above problem may be caused (second problem).

To address the first of these problems, various proposals have been made to reduce the wear of the cutting edge by devising a method (structure) of cooling the blades of the screw of the discharge device.

For example, in the invention disclosed in Japanese Patent Application Laid-Open No. 63-91484 (prior art 2), the blades are cooled by hollowing the blades and flowing cooling water through the hollows, and the blades are worn away by corrosion. Is to be reduced.

In the invention disclosed in US Pat. No. 5,924,861 (prior art 3), a water cooling tube is disposed so as to surround a discharge device, and the blades are cooled by radiation cooling. The purpose is to reduce the wear of the cutting edge.

However, in the invention disclosed in Japanese Patent Application Laid-Open No. 63-91484 (prior art 2), even when the blades are water-cooled, the temperature of the cutting edge in contact with the high-temperature, high-hardness hearth is not increased. It is not so effective in reducing the wear of the cutting edge. Moreover, when the wear of the cutting edge progresses and the cooling water leaks out, the reduced iron product is reoxidized.

In the invention (prior art 3) disclosed in US Pat. No. 5,924,861, an indirect cooling method is used by radiant cooling using a water cooling tube. Although there is no problem of leakage of the cutting edge, the effect of cooling the cutting edge portion is smaller than that of the above invention (prior art 2) due to indirect cooling, and has little effect on the wear of the cutting edge.

As described above, simply devising a method of cooling the blades cannot solve the first problem, that is, the problem of wear of the cutting edge, and the second problem cannot be solved at all.

[0022] Therefore, in order to fundamentally solve the first and second problems, a method in which no solid matter is formed on the hearth or a method in which even if the solid matter is formed, it can be removed without causing a problem in operation. Development is requested, for example,
The following proposals have been made, but they do not provide a sufficient solution.

In the invention disclosed in Japanese Patent Application Laid-Open No. 11-50120 (prior art 4), in order to remove metal iron powder and adhered matter remaining on the hearth, the powder is blown off by a jet gas and collected by a suction hood. It proposes a method, a method of sweeping with a rotating broom, and a method of scraping with a scraper. However, with the method of blowing off with a jet gas flow,
It is difficult to remove the adhered matter firmly adhered to the hearth, and there is a problem that the blown-off metal iron powder adheres to the suction hood. Also, with the method of sweeping with a broom with rotating blades, it is also difficult to remove the solid matter firmly fixed to the hearth. Further, in the method of scraping with a scraper, as described above, there is a problem that there is a high possibility that the metal iron powder is crushed by the scraper, compressed and rolled, and rather promotes the formation of adhered substances.

The invention (prior art 5) disclosed in Japanese Patent Application Laid-Open No. 10-140221 discloses a method in which a powdery reducing agent is first spread on a hearth, and a powdery iron raw material and a powdery solid reducing agent are placed thereon. By placing a plate-like molded product composed of a binder and a binder and heating it at a high temperature, the plate-like molded product can be reduced to produce reduced iron while preventing sticking between the plate-like molded product and the hearth ( The so-called "floor carbon material method"). However, this method has the following problems.

(1) An extra charging device for laying the floor covering carbon material on the hearth is required.

(2) Since it is necessary to lay a floor bedding carbon material before placing the plate-like molded product on the hearth, an extra hearth area is required and the reduction furnace equipment becomes large.

(3) Since it is difficult to spread the floor covering carbon material thinly and uniformly on the hearth, it is necessary to spread the floor covering carbon material thickly in order to avoid sticking of the plate-like molded product and the hearth. is there. And
The powder accompanying the plate-like molded product when the plate-like molded product is charged and the powder generated from the plate-shaped molded product in the furnace accumulate on the floor covering carbon material. If the reduced iron is only discharged when the reduced iron is taken out and the bed carbonaceous material is left in the furnace, the powder also remains in the furnace together and stays in the furnace for a long time, and the same mechanism as described above is used. As a result, a large (wide) plate-like sintered material is formed on the carbon floor material. As a result, even if this plate-like sintered material is prevented from sticking to the hearth due to the presence of the floor covering carbon material, the operation due to the problem of the wear of the cutting edge of the screw of the discharge device and the peeling of the plate-like sintered material. The above problems can occur. Therefore, in order to avoid these problems, it is necessary to discharge and remove the powder as much as possible every time the reduced iron is taken out. It is necessary to discharge with reduced iron and to add new carbon materials instead. In this case, not only does the solid unit of reducing agent per unit mass of reduced iron increase, but also the amount of heat required for heating the floor carbon material becomes useless, and the unit of fuel increases.

As described above, in this proposal, the equipment cost,
The operation cost has risen significantly, so it has not been put into practical use.

[0029]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to minimize the increase in equipment costs and operating costs while preventing the formation of strong plate-like fixed substances on the hearth and discharging the fixed substances. Rotating hearth type which can prevent or reduce the wear of the cutting edge of the screw of the discharging device, prevent peeling of the plate-like fixed material, enable long-term continuous operation, and achieve a high operation rate An object of the present invention is to provide a method for operating a reduction furnace.

[0030]

A first invention (an invention of claim 1) is a rotary furnace for producing a reduced metal by heating and reducing an agglomerate containing a powdered metal oxide and a powdery carbonaceous material. A method for operating a bed-type reduction furnace, wherein the agglomerate is charged into the rotary hearth-type reduction furnace, wherein the agglomerate is preliminarily added with a sticking inhibitor. This is a method of operating a hearth-type reduction furnace.

Here, the term "adhesion inhibitor" refers to a substance scattered around the agglomerate or a substance covering the surface of the agglomerate when the agglomerate is placed on the hearth.
This adhesion suppressing material can prevent the formation of a fixed substance such as a plate.

The second invention (the invention of the second invention) is characterized in that, in the first invention (the invention of the first invention), the sticking suppressing material contains a carbonaceous substance such as coal.

According to the first invention or the second invention (the invention of claim 1 or 2), after the sticking inhibitor is added to the agglomerate in advance and then charged on the hearth, It is placed on the hearth in a state where the accompanying powder and the adhesion inhibitor are mixed. Then, on the hearth, a powder generated from the agglomerate during the reduction and a powder generated during the discharge of the reduced metal are added to the mixed powder. Even if this powder remains on the hearth and stays in the furnace for a long time, the particles of the carbonaceous substance added as a sticking suppressant are present between the reduced metal and the slag component and hinder the bonding between them. It does not grow on (wide) plate-like fixed matter. Moreover, even if it becomes a fixed substance, a crack is generated in the fixed substance due to a particle of the carbonaceous substance as a fixing inhibitor due to a relatively small force, and it can be easily separated from the hearth as small pieces. Further, a charging device for laying the adhesion suppressing material on the hearth is not required, and the hearth area does not need to be increased. Furthermore, the amount of the adhesion inhibitor added may be smaller than that of the "bed carbon material method" (prior art 5), so that it is possible to prevent a large increase in the unit consumption of the solid reducing agent and the unit consumption of the fuel.

The third invention (the invention of claim 3) is the first or second invention (the invention of claim 1 or 2) wherein the surplus C% of the generated powder defined by the following formula (1) is 3.8. It is characterized in that the addition amount of the adhesion inhibitor is adjusted so as to be at least% by mass.

[Excess C% of generated powder] = [% by mass of carbon contained in the agglomerate] − [% by mass of oxygen combined with iron and zinc contained in the agglomerate] × 12/16 + [Ratio of the mass of the adhesion inhibitor added to the mass of the agglomerate charged] x [% by mass of carbon contained in the adhesion inhibitor] Formula (1) In the formula (1), "agglomerated material" and ""Anti-stickingmaterial" means that before reduction.

The compressive strength of the adhered material can be significantly reduced by adjusting the amount of the adhesion inhibitor added to make the surplus C% of the generated powder equal to or more than the predetermined value (see Example 1 described later). The operation and effect of the first or second invention (the invention of claim 1 or 2) can be reliably obtained.

It is to be noted that, instead of the sticking suppressing material made of the powdery carbonaceous material, a sticking suppressing material made of a powdery material containing at least one of CaO, MgO and Al ₂ O ₃ as a main component is used. (4th invention). Alternatively, a mixture of a powdery carbonaceous substance and a powdery substance mainly containing at least one of CaO, MgO, and Al ₂ O ₃ may be used (fifth embodiment).
invention).

According to the fourth or fifth invention, CaO, Mg
O, Al ₂ O ₃ component, reduction temperature (up to about 1400 ° C)
And has a high melting point that does not melt, so that the same effect as the above-mentioned powdery carbonaceous material can be obtained. Note that CaO, MgO, A
The l ₂ O ₃ component partially reacts with the mineral component in the powder to form slag, which has a higher melting point than slag generated from only the mineral component in the powder. Even if this is done, a fine structure is not formed as in the prior art 1, and there is no problem. In addition, CaO, MgO, Al ₂ O ₃
Many substances consisting of components are inexpensive, and even if these components are mixed in the product reduced metal in a small amount, the blast furnace,
It is not harmful when used in converters, electric furnaces, and the like, and is not a problem because it is finally removed as slag.

Further, instead of the sticking suppressing material made of the powdery carbonaceous material, a sticking suppressing material made of a liquid carbonaceous material or a slurry-like carbonaceous material may be used (a sixth invention). Alternatively, a liquid carbonaceous substance or a slurry-like carbonaceous substance,
It is also possible to use a sticking suppressing material composed of a powdery substance containing one or more of CaO, MgO and Al ₂ O ₃ as main components (seventh invention).

According to the sixth or seventh aspect, the surface of the agglomerate is coated with a liquid or slurry-like carbonaceous material, and the liquid or slurry-like carbonaceous material is heated in a furnace and solidified by a dry distillation reaction. To harden the agglomerate surface and reduce powder generation from the agglomerate surface due to mechanical handling. Further, even if powder is generated, the carbonaceous material solidified by the dry distillation reaction is contained in the powder at a high concentration, so that the effect is further enhanced.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. Here, FIG. 1 is a diagram showing an example of a method of adding a sticking suppressing material, which is a characteristic part of the present invention, to agglomerates, and FIG. 2 is a schematic equipment configuration of a rotary hearth furnace common to the prior art. It is a top view explaining. Note that the embodiment of the present invention will be described by taking the production of reduced iron as an example.

First, description will be made with reference to FIG. The agglomerate P composed of the powdered iron oxide and the powdered carbonaceous material is dried by the dryer 5 to a water content of about 1% by mass or less, and a predetermined amount of the sticking suppressing material Q is added thereto, and this is piped. Charging device 3
Is placed on the hearth 1.

Here, as the powdered iron oxide, powdered iron ore, iron-containing dust, sludge, scale, etc. generated in ironworks and electric furnace plants may be used alone or in the same manner as in the conventional method. It can be used in combination of more than one species.

As the powdery carbonaceous substance which is one of the sticking suppressing materials, coal, coke powder, petroleum coke, char, charcoal, pitch, etc. can be used alone or in combination of two or more.

The shape of the agglomerate P is not particularly limited, and may be any of pellets, briquettes, plates, nuggets, and the like.

As the adhesion suppressing material Q, the same material as the above-mentioned powdery carbonaceous material may be used, or a liquid carbonaceous material such as tar or asphalt, or the above-mentioned powdery carbonaceous material may be added to these liquid carbonaceous materials. May be used. Alternatively, instead of the carbonaceous substance (powder, liquid, or slurry), dolomite, limestone, alumina, magnesia, or the like, or brick debris or the like made from these materials, that is, any one of CaO, MgO, and Al ₂ O ₃ A powdery high melting point substance containing the above components as main components may be used.
Further, a mixture of a carbonaceous substance (powder, liquid or slurry) and the powdery high melting point substance may be used.

As a method of adding the powdery adhesion suppressing material Q to the agglomerate P, for example, as shown in FIG. 1, a cut-out hopper (adhesion suppressing material) is provided above the receiving hopper 7 above the charging device 3. An addition device 4) is provided, from which a fixed amount of the anti-sticking material Q is cut out using gravity to receive a hopper 7.
It is sufficient to adopt a commonly used addition method such as a method of charging the mixture into the inside and mixing with the agglomerate P. The addition of the adhesion inhibitor is not limited to the above-mentioned place, and is performed before the dryer 5 or at the outlet of the dryer 5 or on the belt conveyor 6 which receives the agglomerate P after drying and sends it to the hopper 7. Is also good.

As a method of adding the liquid or slurry-like sticking suppressing material Q to the agglomerate P, for example, a place a where the agglomerate P falls onto the belt conveyor 6 from the outlet of the dryer 5 or a belt a If the method of spraying the adhesion-suppressing material pumped from a tank (not shown) is used at the place b where the conveyor 6 is dropped to the receiving hopper 7 or at both the places a and b, the agglomeration is almost uniformly fixed. It is preferable because the suppressor can be coated. In this case, as usual, if the tank or the pressure feed pipe (not shown) is heated by a steam tracer or the like, the viscosity of the liquid or slurry can be reduced and the pressure feed / spray can be easily performed.

The addition amount of the sticking suppressor composed of the powdery carbonaceous substance is preferably at least 7.5 parts by mass, more preferably at least 15 parts by mass, per 100 parts by mass of the generated powder. The generated powder surplus C% is + 3.8% by mass and + 10.4% by mass, respectively. As shown in the examples below, by setting the addition amount of the adhesion inhibitor to 7.5 parts by mass or more (the surplus C% of generated powder is 3.8 mass% or more), the compressive strength of the adhered material is significantly reduced, Separation and discharge from the hearth by the discharger becomes easy. Further, the addition amount of the adhesion inhibitor is 15 parts by mass or more (excess C% of generated powder is 10.4% by mass.
By doing so, the strength of the adhered substance is further reduced, and at room temperature, the strength is such that it can be separated into particles by hand. Therefore, separation and discharge from the hearth by the discharger becomes easier.

If the particle size of the sticking suppressing material made of the powdery carbonaceous material is too coarse, the number of particles of the sticking suppressing material scattered in the adhered substance is reduced, and the effect of fragmentation is reduced. Not only does the cost rise, but also the addition yield deteriorates, such as when it is added to agglomerates or when it is charged onto the hearth, so that the particle size is, for example, about -2 mm used in the examples described below. In some cases, the optimum particle size may be determined by appropriately changing the particle size while observing the state of removal of the adhered matter.

In the case of using a sticking inhibitor made of a powdery high melting point substance, it is preferable that the amount of addition (addition mass) is larger than that in the case where a carbonaceous substance is used as the sticking inhibitor. This is because, in order to prevent the formation of large (wide) adhered substances and to serve as a starting point for generating cracks for dividing the adhered substances into small pieces, the adhesion suppressing material is scattered in the adhered substances and has a certain space volume. When a powdery material having CaO, MgO, or Al ₂ O ₃ as a main component having a higher density than that of the carbonaceous material is used, in order to obtain the same effect as that of the carbonaceous material, a larger mass is required. Is required.

Further, it is preferable that the particle size of the adhesion suppressing material composed of the powdery high melting point material is slightly coarser than that of the carbonaceous material.
This is preferable because the specific surface area of the adhesion-suppressing material particles is reduced to reduce the amount of slag produced, and a large amount of unreacted high-melting-point material that does not turn into slag remains to hinder the growth of adhered substances.

When a liquid or slurry-like adhesion inhibitor is used, the amount of addition (addition mass) may be smaller than that of the powdery carbonaceous substance. This is because, when a liquid or slurry-like sticking suppressor is used, the liquid carbonaceous material coated on the surface of the agglomerate is heated and solidified in a furnace to harden the surface of the agglomerate and generate powder itself. It is because it reduces.

The agglomerate P to which the adhesion suppressing material Q has been added in this manner is placed on the hearth 2 by the charging device 3. At this time, when the agglomerates P are placed on the hearth 2 by the charging device 3, powder generated due to friction between the agglomerates P or between the agglomerates P and the pipe inner wall of the charging device 3 (generated powder A). Is mixed with the agglomerates P and is spread on the hearth 2 in a state of being mixed with the adhesion suppressing material Q (mixture M).

Next, description will be made with reference to FIG. And
While the agglomerate P moves in the furnace from the charging device 3 toward the discharging device 13 with the rotation of the hearth 2, fuel and oxygen are supplied from the plurality of burners 11 installed in the furnace body 14 above the hearth 2. The contained gas is blown into the furnace, and the blown fuel, combustible volatile components generated from the powdered carbonaceous material in the agglomerate P, and the CO gas generated by reducing the powdered iron oxide are burned, and the furnace is burned. The internal atmosphere temperature is set to about 1200 to 1500 ° C., and the agglomerate P placed on the hearth 2 is radiantly heated from above.

The fuel for the burner 11 may be natural gas, coke oven gas, propane gas,
Any gaseous fuel such as butane gas, liquid fuel such as heavy oil, or solid fuel such as coal may be used. As the oxygen-containing gas, air or oxygen-enriched air is preferably used.

While moving in the furnace, the agglomerate P placed on the hearth is heated to about 1200 to 1 by radiant heating from the upper part of the hearth 2.
Heated to 450 ° C., the powdered iron oxide in the agglomerate P is reduced by the powdered carbonaceous substance and metallized.

During this time, the powder (generated powder B) generated when the agglomerate P is heated and the powder (generated powder C) generated when the reduced iron R is discharged are deposited on the mixture M (generated powder A + adhesion inhibitor Q). (This is referred to as a mixture N), and a portion of the mixture N which has not been completely removed by the discharge device 13 stays and accumulates on the hearth 2 for a long time, sintering and reduction proceeds, and eventually the solidification occurs. Form a kimono.

Here, since the generated powders A and B are powders originally generated from agglomerates, the amount of carbonaceous substance in these powders is almost necessary for reducing iron oxide to metallic iron. Since only a sufficient amount (or a slight excess) is contained, little carbonaceous material remains when the reduction of these powders is completed. Further, since the generated powder C is generated from reduced iron, it also hardly contains a carbonaceous substance.
However, the carbonaceous substance or the high melting point substance added as the adhesion suppressing material Q is a mixture N (generated powder A + generated powder B + generated powder C).
+ Because it is present in the adhesion-preventing material Q), the carbonaceous substance or the high-melting-point substance is scattered also in the adhesion, hindering the sintering reaction of the adhesion, and the adhesion is not dense and large (wide). Does not grow to a fixed substance. Also, when a liquid or slurry-like carbonaceous material is used, these carbonaceous materials are heated in a furnace to form solid carbon by a dry distillation reaction, and thus have the same effect as a powdery carbonaceous material. Note that the carbonaceous material added as a fixing suppressor is present in the vicinity of the agglomerate in a furnace, because the covered CO rich gas generated from the agglomerate during the reduction, CO ₂ of the burner in the exhaust gas, H ₂ The gasification reaction by O is prevented, and it exists in a solid state and has the above-mentioned effects.

On the other hand, in the conventional method, the adhered substance is formed only from the generated powders A, B, and C, and therefore, there is almost no carbonaceous substance or high melting point substance in the adhered substance. Since there is no substance that inhibits the adhesion, a dense and large (wide) adhered substance is formed.

The metallized agglomerate (reduced iron R) after the reduction is completed is discharged from the rotary hearth furnace 1 and before the discharge device 13 in order to develop mechanical strength enough to withstand handling after the discharge. Is cooled to about 1000 ° C. by the cooler 12 installed at As a cooling method, a method of directly blowing an inert gas such as N ₂ or a hydrocarbon gas such as a natural gas to the reduced iron, or a method of indirectly cooling with a water-cooling jacket may be employed. At this time, the adhered matter is also cooled at the same time.

The reduced iron R cooled to about 1000 ° C. is discharged out of the furnace by the discharge device 13. As the discharge device 13, not only a screw type but also a scraper type discharge device may be employed. Reduced iron R in the discharge device 13
At the same time as scraping out the outside of the furnace, while simultaneously applying a compressive force to the fixed object, a crack is generated in the fixed object starting from a carbonaceous substance or a high melting point substance scattered in the fixed object, and is divided by this crack. The small pieces of the adhered matter are easily peeled off from the hearth and scraped out together with the reduced iron R. The adhered matter scraped out together with the reduced iron R may be removed by sieving or the like, if necessary. Alternatively, the adhered substance is iron, carbonaceous material,
Since it is composed of slag components and the like, it may be used as a part of the reduced iron raw material without sieving or the like.

[0063]

EXAMPLES The following laboratory experiments were performed to confirm the state of formation of the adhered substance when a carbonaceous substance was added as a sticking inhibitor. Example 1 In order to simulate generated powder, a mixture of 89 parts by mass of converter dust and 11 parts by mass of anthracite whose chemical components are shown in Table 1 was pulverized by a ball mill so that the total amount was -2 mm. . Then, as an anti-adhesion material, only the anthracite described above was crushed to a total amount of −2 mm to produce a mixture, and in order to create a state in which the generated powder and the anti-adhesion material were mixed,
Samples were prepared by adding 0 (no addition), 5, 7.5, and 10 parts by mass of the adhesion suppressing material to 100 parts by mass of the simulated powder, respectively.

[0064]

[Table 1]

Each sample was 30 mm square × about 8 m at a pressure of 5 N.
m thickness, and press-mold this in N ₂ gas atmosphere, 1300
The reaction tube was inserted in a horizontal electric furnace having an inner diameter of 60 mm controlled at a temperature of 60 ° C., kept for 30 minutes, and then cooled to room temperature in a N ₂ gas atmosphere to produce a sintered body.

After measuring the apparent density of the sintered body according to the JIS iron ore pellet-volume measuring method, a compressive load was applied to the center of the surface of the sintered body with a rod of 10 mm to break the sintered body. The maximum load at this time was defined as the compressive strength.
Table 2 shows the apparent density and compressive strength of the sintered body.

[0067]

[Table 2]

From the results shown in Table 2, from 0 (no addition) to 5 parts by mass (excess C% of generated powder: -2.8 to +1.6 mass%), The apparent density of the sintered body was significantly higher than 2.39 g / cm ³ , indicating that a dense sintered body was formed.
The above values are very high. Nevertheless, in Experiment No. without addition of the adhesion inhibitor. Compared to 1-1, the one obtained by adding 5 parts by mass of the adhesion inhibitor has a compressive strength of 2970 N to 1
820 N, indicating the effect of adding the adhesion inhibitor. When the addition amount of the adhesion inhibitor is 7.5 parts by mass or more, the apparent density of the sintered body is greatly reduced to 2.14 g / cm ³ or less. This indicates that a low-density sticking suppressing material (anthracite) is present in the sintered body, and it was found that the compressive strength was also sharply reduced to 420 N or less. (Example 2) For 100 parts by mass of the same simulated powder as in Example 1, the same sticking suppressing material (anthracite) as in Example 1 was added (0, no addition), 5, 10, 15, 20, 25, 25, respectively. 30
A sample in which parts by mass were added and mixed was prepared. Generated powder surplus C%
Is -2.8, +1.6, +6.
0, +10.4, +14.8, +19.2, +23.6
It is.

Each sample (10 g) was sized 30 mm wide × 55 mm.
It was spread on an alumina tray with a length of approximately constant thickness, and this was placed in an N ₂ gas atmosphere at 1300 ° C., and the inside diameter of the reaction tube was controlled at 6 ° C.
After inserting into a 0 mm horizontal electric furnace and holding it for 30 minutes, it was cooled to room temperature in a N ₂ gas atmosphere.

Each of the samples after the above experiment was an integrated lump regardless of the amount of the addition of the anti-sticking material. As a result, it was observed that as the amount of addition of the adhesion inhibitor increased, it became coarser.

Next, in order to determine the degree of sticking, the surface of the lump was rubbed with a finger and the amount to be peeled was measured. Table 3 shows the results.

[0072]

[Table 3]

As shown in Table 3, no adhesion inhibitor was added.
In the case of adding 10 parts by mass, the lump formed a strong sintered body and hardly peeled off with the finger, but in the case of adding 5 parts by mass of the adhesion suppressing material, the surface of the lump even on the finger. Particulate matter starts to peel from
With the addition of parts by mass, about half of the mass could be separated as granules, and with the addition of 25 parts by mass or more of the adhesion inhibitor, most of the mass could be separated as granules.

Therefore, from the results of Example 1 described above, the addition of a sticking inhibitor made of a powdery carbonaceous material lowers the compressive strength of the sticking material. % By mass (7.5 parts by mass based on 100 parts by mass of generated powder)
(Parts by mass or more) has been found to be preferable because the compressive strength of the adhered substance is greatly reduced and separation / discharge from the hearth by the discharger becomes easy. From the results of Example 2, the generated powder surplus C% was 10.4% by mass.
By adjusting so as to be above (15 parts by mass or more with respect to 100 parts by mass of the generated powder), the strength becomes such that it can be easily separated into granules by hand, and separation from the hearth by the discharger
It has been found to be even more preferred because the discharge is easier.

[0075]

According to the first or second invention (the invention of claim 1 or 2), particles of the carbonaceous substance added as a sticking inhibitor are formed between reduced metal and slag components formed from generated powder. Large (wide) because they exist and prevent these bonds
It does not grow into a plate-like fixed matter, and even if it becomes a fixed matter, the particles of the carbonaceous substance start and cracks are generated, so that it is separated into small pieces. In addition, the wear of the cutting edge of the screw can be prevented or reduced, the continuous operation can be performed for a long time, the operation rate of the furnace can be improved, and the maintenance cost can be reduced. Further, since a charging device for laying the adhesion suppressing material on the hearth is not required and the hearth area does not need to be increased, a large increase in equipment cost can be avoided. Furthermore, since the addition amount of the sticking suppressing material may be small, it is possible to prevent a large increase in the unit consumption of the solid reducing agent and the unit consumption of the fuel, and it is possible to suppress an increase in the operating cost to a minimum. Powdery carbonaceous material can be used as an adhesion-preventing material, but it is also possible to charge a lumpy substance and make it into a powdery state in a furnace. It is also possible to use it.

According to the third invention (invention of claim 3), the amount of the carbonaceous substance added as a sticking inhibitor is adjusted so that the generated powder surplus C% is equal to or more than a predetermined value. Since the compressive strength of the kimono can be greatly reduced, the effect of the first or second invention (the invention of claim 1 or 2) can be reliably obtained.

According to the fourth or fifth invention, CaO, Mg
O and Al ₂ O ₃ components partially react with mineral components in the powder to form slag, but the generated slag has a high melting point and does not densify the adhered matter, so that there is no problem. Since it has a high melting point that does not melt at the reduction temperature, the same effect as that of the above-mentioned powdery carbonaceous material can be obtained. In addition, since an inexpensive substance can be used as a sticking suppressing material, the cost can be reduced.

According to the sixth or seventh aspect, the surface of the agglomerate is coated with a liquid or slurry-like carbonaceous material, and the liquid or slurry-like carbonaceous material is heated and carbonized in a furnace to be solidified. The surface of the agglomerate becomes harder, and powder generation from the agglomerate surface due to mechanical handling is reduced.Also, even if powder is generated, the powder contains a high concentration of a carbonaceous substance. The first or second invention (claim 1
Alternatively, the same effect can be obtained even if the addition amount of the adhesion inhibitor is reduced as compared with the invention 2).

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one example of a method of adding a sticking inhibitor to an agglomerate according to the present invention.

FIG. 2 is a plan view showing a schematic equipment configuration of a rotary hearth furnace.

[Description of Signs] 1 ... Rotating hearth furnace, 2 ... Heart floor, 3 ... Charging device, 4 ... Fixation inhibitor addition device (cutting hopper), 5 ... Dryer, 6 ...
Belt conveyor, 7: receiving hopper, 11: burner,
12: cooler, 13: discharge device, 14: furnace body, P: agglomerate (dry pellets), Q: sticking inhibitor, R: reduced iron a ... liquid or slurry sticking inhibitor adding position

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Tsuchiya 4-3-1 Bingo-cho, Chuo-ku, Osaka-shi Kobe Steel, Ltd. Osaka branch office (72) Inventor Hidetoshi Tanaka 4-chome, Bingo-cho, Chuo-ku, Osaka-shi No. 1-3 Co., Ltd. Kobe Steel, Osaka Branch F-term (reference) 4K001 AA10 BA14 CA18 GA07 HA01 4K012 DE03 DE06 4K050 AA00 BA02 CA09 CG22

Claims (3)

[Claims] 1. A method for operating a rotary hearth reduction furnace for heating and reducing an agglomerate containing a powdery metal oxide and a pulverulent carbonaceous substance to produce a reduced metal, wherein the agglomerate is produced. A method for operating a rotary hearth-type reduction furnace, characterized in that a sticking inhibitor is added to the agglomerate in advance when charging the rotary hearth-type reduction furnace. 2. The method for operating a rotary hearth-type reduction furnace according to claim 1, wherein the adhesion suppressing material contains a carbonaceous substance. 3. The generated powder surplus C% defined by the following equation is 3.
The method for operating a rotary hearth-type reduction furnace according to claim 2, wherein the amount of the adhesion inhibitor added is adjusted so as to be 8% by mass or more. Formula [Excess powder C%] = [mass% of carbon contained in the agglomerate] − [mass% of oxygen combined with iron and zinc contained in the agglomerate] × 12/16 + [ Ratio of the added mass of the adhesion inhibitor to the mass of the agglomerate charged] × [% by mass of carbon contained in the adhesion inhibitor].