JP2003239007A - Method for producing reduced metal from metal content - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In the production of reduced iron in a moving hearth furnace, there is provided a method for improving the heat transfer mechanism in a raw material deposition layer on a moving hearth and improving the productivity of reduced iron. suggest. A mixed raw material containing a metal oxide and a solid reducing agent is deposited on a moving hearth, and the mixed raw material is heated and reduced while the moving hearth moves in the furnace, and is melted at least once. In a method for producing a reduced metal by cooling after being cooled, a material containing a metal produced through a melting process is used as the mixed raw material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a type in which a raw material is charged on a hearth that moves horizontally in a heating furnace and the raw material is heated and reduced while the hearth moves in the furnace. A method for producing reduced metal from a raw material containing metal oxides, etc. charged in the moving hearth furnace of No. 3, especially by improving the heat transfer mechanism inside the raw material deposit layer on the moving hearth. Then, it proposes an advantageous method for improving productivity.

[0002]

2. Description of the Related Art Generally, steel is usually manufactured in a converter or an electric furnace. Of these, the electric furnace method is
This is a method in which scrap and reduced iron are heated and melted by using electric energy, and in some cases, further refined into steel. However, in recent years, there is a tendency to use reduced iron in place of scrap due to the tight supply and demand of scrap and the increasing demand for higher quality steel. Recently, a reduced iron manufacturing technique has been developed as a technique capable of meeting such demands. This technology uses a horizontally moving hearth (hereinafter referred to as the moving hearth)
A metal-containing material, for example, a mixture of a metal oxide such as iron ore and a solid reducing agent is charged and deposited, and the metal-containing material (hereinafter referred to as “metal oxide”) by radiant heat transfer from above.
The method of producing a reduced metal by heating and reducing the reduction product) and further melting the reduction product at least once on the hearth to separate it into slag and metal (Japanese Patent Laid-Open No. 11-172312). (See the official gazette).

In this technique, a moving hearth furnace is used,
This type of furnace is of a type in which the hearth moves horizontally in the furnace and the raw material is heated and reduced and melted in the course of the movement. It should be noted that the horizontally moving hearth is usually of the type that rotationally moves as shown in FIG. 1, and because of this type, the moving hearth is also called a rotary hearth furnace. .

As shown in FIG. 1, the mobile hearth furnace has the following structure.
From the supply side of the raw material toward the discharge side, there is an annular furnace body 10 divided into a pre-tropical zone 10a, a reduction zone 10b, a melting zone 10c and a cooling zone 10d, and in the furnace body, an annular moving hearth 11 is configured to rotate. On the moving hearth 11, a mixed raw material composed of a mixture of a metal oxide such as iron ore and a solid reducing agent is charged. The moving hearth 11 has refractory bricks on its surface, but it may also have a granular refractory material deposited thereon. And, a burner 12 is disposed on the upper part of the furnace body 10 of this furnace,
Using this burner 12 as a heat source, metal oxide such as iron ore deposited on the moving hearth 11 is heated under the presence of a reducing agent to reduce the reduced iron. In FIG. 1, reference numeral 14 is a charging device for charging the raw material onto the moving hearth 11, and reference numeral 15 is a discharging device for discharging a reduction product (reduced metal).

When operating the above-mentioned mobile hearth furnace,
The atmospheric temperature in 10 is usually maintained at about 1300 ° C, but it is preferable to control the temperature in the melting zone 10c to a high temperature of about 1500 ° C. Then, the reduced product after the reduction treatment is cooled in the cooling zone 10d on the moving hearth 11 and discharged to the outside of the furnace to prevent oxidation outside the furnace and facilitate handling. To do.

[0006]

In the operation of the above moving type hearth furnace, the mixed raw materials are powdery metal oxides such as iron ore as a metal-containing material, dust and sludge, and powders such as coal and coke. A mixture of solid solid reducing agents is preferably used, and the mixed raw materials are charged and deposited on the moving hearth in a mixed state. However, the powdery mixed raw material deposited on the moving hearth has a problem that the rate of temperature rise is small because the heat transfer between particles constituting the raw material is rate-determining. Particularly, in the operation of the moving hearth furnace, the surface of the raw material deposition layer 2 is heated by the radiant heat transfer from the heating burner 12 while the moving hearth moves in the heating furnace, and the inside of the raw material deposition layer 2 is heated. Since the mechanism is such that the temperature of the entire raw material deposition layer 2 is increased by sequentially performing heat transfer, heat transfer between particles becomes extremely important.

To solve such a problem, of course, a method of mixing powdery metal oxide and a solid reducing agent and then agglomerating into pellets, and powdery raw material deposition deposited on a moving hearth Measures such as a method of increasing the contact between particles of the powdery raw material by consolidating the layer 2 from above are taken. However, in any of these methods, equipment and special operations for agglomeration and consolidation are required separately. Moreover,
Although these measures improve the heat transfer between particles, the heat transfer characteristics of raw materials such as ore, dust, coal, and coke are determined by their physical properties, so stable productivity improvement is achieved only by these measures. It cannot be done.

Therefore, an object of the present invention is to improve the heat transfer mechanism in the raw material deposit layer deposited on the moving hearth during the production of reduced metal in the moving hearth furnace.
It is to propose a method for improving the productivity of reduced metal by a moving hearth furnace.

[0009]

[Means for Solving the Problems] As a result of earnestly studying the above-mentioned problems of the prior art and studying what kind of means is effective, the inventors have found that in order to achieve the above-mentioned object, The present invention was conceived based on the finding that the adoption of the technology related to the gist configuration of the above is effective. That is, the present invention is to deposit a mixed raw material containing a metal-containing material and a solid reducing agent on a moving hearth in a moving hearth furnace, and to mix the mixed raw material while the moving hearth moves in the furnace. In the method of producing a reduced metal by heating, reducing and melting at least once and then cooling, as the mixed raw material, one containing a metal produced through a melting process is used. It is a manufacturing method.

In the present invention, the metal added to the mixed raw material is reduced iron and / or iron scrap, and the carbon content is preferably 1 mass% or more and 5 mass% or less.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The operation of a moving hearth furnace will be described below. As shown in FIG. 2, on the moving hearth 11,
Prior to charging the mixed raw material, solid reducing agent particles are preliminarily spread so as to be spread to form a solid reducing agent layer 1, and then the solid reducing agent layer 1 contains a metal oxide and a solid reducing agent. Charge and deposit mixed raw materials. After that, the radiant heat is applied from above the raw material deposition layer 2 through the heating burner 12. As a result, the metal oxide in the raw material is reduced by the action of the solid reducing agent mixed in the raw material deposition layer 2 to produce a reduced product containing gangue and ash.

In addition to the above-mentioned mixed raw material, an auxiliary raw material effective as an auxiliary agent for melting the reduced product and the ash may be added. As such an auxiliary material, those containing CaCO ₃ , MgCO _3, etc. are preferable, and limestone, dolomite, serpentine, etc. can be used. Before melting, these auxiliary materials cause evaporation of crystal water and a partial decomposition reaction (for example, CaCO ₃ is thermally decomposed into CaO), but remain in a solid state at high temperature. In addition, slag and the like generated in the refining process such as blast furnace slag and converter slag containing CaO and MgO can also be used.

Thereafter, the reduced product of metal oxide, the ash and the auxiliary raw material start to be melted when heated further, and molten metal (hereinafter, simply referred to as “metal”) and molten slag (hereinafter, simply referred to as “metal”). (Referred to as “slag”) and is retained in a state of staying on the solid reducing agent layer 1.

At this time, the reduction product produced on the solid reducing agent layer 1 varies depending on the mixing method of the raw materials, the type of metal oxide, or the type of the solid reducing agent. Since it is consumed by the reduction reaction, it becomes smaller than the initial volume. Therefore, the metal and slag generated by the melting of the reduction product are aggregated into particles together with the action of the surface tension, and the solid reducing agent layer 1
Will be scattered on the top.

Therefore, the solid reducing agent layer 1 is provided with
By forming a plurality of recesses 1a as shown in Fig. 1, the aggregated particles of the metal and the slag that have been melted (granulated by surface tension) are moved and accommodated in the recesses 1a by the action of gravity, and are dispersed. Therefore, the product (reduced metal) that has been sized to a desired size is generated without crushing, and therefore the product can be smoothly discharged.

The solid reducing agent contains ash in it.
Although it contains about 10 wt%, most of the rest is carbonaceous and maintains this solid state even at temperatures of about 1000 to 1500 ° C. Therefore, even if the raw material melts Even if metal or slag is produced, the solid reducing agent layer 1 itself does not weld to the refractory material of the moving hearth 11 and functions as a protective layer for the refractory material.

The above-described embodiment is an example of charging and depositing powdered ore or the like on the moving hearth 11 and performing heat treatment.
As shown in Fig. 4, even when the pellets or briquettes that have been agglomerated in advance are stacked on the moving hearth 11 and subjected to heating and reduction treatment, reduction in a state in which the metal and slag are granulated and separated as in the above example A metal can be obtained. Note that, although FIG. 4 shows a schematic diagram in which the pellets are arranged in one layer as an example, it is of course possible to stack the pellets in multiple layers.

In the operation of such a moving hearth furnace,
A feature of the present invention is that a metal produced through a melting process (hereinafter referred to as a melt-processed metal), for example, a reduced metal or scrap obtained under the method of the present invention is added to the mixed raw material. is there. That is, the metal produced through such a melting treatment step has a very high thermal conductivity as compared with a raw material mainly containing an oxide such as ore and dust, and therefore these metals are mixed in the mixed raw material. With the addition, the thermal conductivity of the entire raw material deposition layer 2 can be considerably improved, and the productivity is remarkably improved.

As an example of the above-mentioned melt-processed metal, a product metal produced under the moving hearth furnace method to which the present invention is applied may be used as it is, or under a general melting and refining method. You may use the odd-quality products manufactured in.
Of course, in cupolas, electric furnaces, blast furnaces, etc., the metal ingots produced during the respective treatments, the pig iron mixed in the slag produced from these processes, and the like can also be used. In any case, any metal may be used as long as it is solidified at least once.

Further, the scraps mixed and mixed in the mixed raw materials are those generated in an iron manufacturing plant, for example, scraps produced from a factory such as scraps generated in the manufacturing and processing steps, or when dismantling waste. Even the scraps that occur in the can be used without problems. However, since these eventually melt again to become a part of the reduced metal as a product, it is necessary to use those whose components do not affect the product quality.

Next, with respect to the slag and metal solidified in the recess 1a formed on the upper surface of the solid reducing layer 1, the metal component is cooled and solidified to obtain a reduced metal.
At this time, a reduced metal with a small particle size (about 5 mm or less) may be generated, but such a reduced metal with a small particle size is generally difficult to separate from the slag particles and the solid reducing agent. Is discarded with the slag particles. However, these reduced metals are also added to the mixed raw material as described above,
It can be reused and is actively reused.

By the way, in the above-described reduced metal manufacturing process, heating (heating), reduction, and melting process steps proceed in succession. Therefore, if the time required for each of these steps can be reduced, the total operating time can be reduced, and eventually the productivity can be improved. Therefore, the present inventors have examined suitable conditions for the conditions of the above-mentioned melt-treated metal added to the raw material instead of the metal oxide, and further examining the melting process of the metal after reduction. As a result, it was found that the content of carbon contained in the melt-processed metal had an effect, and more preferable conditions for the melt-processed metal were found. Hereinafter, this finding will be described in detail.

FIG. 5 is a Fe-C system phase diagram. As shown in this figure, Fe-C system metals such as reduced metal and scrap,
That is, in the case of steel, if the temperature is 1150 ° C. or higher and the carbon content is 2.1 mass% or higher, it is understood that the liquid phase is generated together with the γ phase.
On the other hand, for example, the Japan Iron and Steel Institute performance summary (CAMP
-ISIJ Vol.14 (2001) -83) reports that when iron ore / carbonaceous material mixed pellets are heated at high temperature, metal carburization / melting does not occur unless the temperature is raised to 1330-1380 ° C or higher. ing.

It was thought that the above-mentioned melting delay of iron ore or the like could be solved by lowering the temperature of the melting reaction of carbon into iron (hereinafter referred to as "carburizing reaction").

That is, before the start of melting, the carburization reaction proceeds due to mass transfer between the solid carbon content and the unmelted iron between the solids. However, it is known that mass transfer between solids is generally slower than mass transfer between solid and liquid because the atomic motion is restricted. Therefore, it is understood that the early generation of liquid iron leads to the promotion of the carburization reaction.

Therefore, the inventors have found that the metal melting start temperature is
A metal having a melt formation temperature of 1350 ° C. or lower, and, for example, in the case of iron-carbon metal, the carbon concentration is 1 mass% or more to 5 mass%
It has been found that the addition of the following melt-processed metal (metallic iron) is effective. Therefore, it has been decided to include not only the metal oxide but also the C-containing metallic iron in the mixed raw material. As a result, the mixed raw materials are
The metallic iron first starts melting at 1350 ° C. or lower, and grows large while absorbing solid iron having a low carbon concentration in the surroundings. Moreover, since the solid metallic iron having a low carbon concentration is sequentially absorbed, the carbon concentration in the molten iron is temporarily reduced, but since it is in the molten state, the carbon can be rapidly absorbed from the lower solid reducing agent layer 1. It can also be absorbed and thus accelerate carburization.

Moreover, when molten metal is produced in the raw material deposition layer 2 early as described above, the heat transfer between the molten metal and the solid raw material is changed, and the heat transfer coefficient is dramatically improved. The heat transfer efficiency of the raw material deposition layer 2 is further accelerated. As described above, by partially mixing the melt-processed metallic iron having a low melting temperature in the mixed raw material, the melting start temperature can be lowered, the carburizing and melting can be promoted, and the heat transfer efficiency in the raw material deposition layer 2 is improved. Therefore, the time required for melting is shortened, which in turn contributes to improvement in productivity.

[0028]

[Example] The following operation test was conducted using the equipment shown in FIG. 1, which is a moving hearth furnace having a furnace diameter of 20 m and a furnace width of 3 m. LNG was used for the burner 12 as a heating source, and the oxygen concentration was adjusted to about 35%. The temperature in the furnace is 1000 ℃,
The temperature was controlled so that the pre-tropics were 1350 ℃, the reduction zone was 1350 ℃, the melting zone was 1500 ℃, and the cooling zone was 100 ℃.

As a raw material to be charged on the hearth, an iron content of about 60 is used.
Mainly iron ore of mass%, and coal of 10vol% volatile matter and 8mass% ash was used as a carbonaceous material as a reducing agent.
The one sieved to 1 mm or less was used. In addition, limestone was used for adjusting the slag component, and coke was used as a solid reducing material layer for protecting the hearth. The coke laid in the lower layer on the moving hearth is almost never consumed and can be used repeatedly. In addition, the carbonaceous material basic unit in this example indicates only the amount blended in iron ore as a reducing agent.

In Example 1, the total amount of reduced iron having a size of 5 mm or less was mixed in the raw ore, and in Example 2, the carbon concentration was 4 mass% and the particle size was 5 mm or less from the blast furnace slag by magnetic separation and sieving. A mixture of small-grain pig iron and ore was used. As a comparative example, a conventional operating method was carried out. A flow chart of each process is shown in FIG. The magnetic separator used was a drum type magnetic separator with a surface magnetic force of 1200 gauss. In addition, an observation camera and a non-contact type in-furnace thermometer were installed in the furnace, and the melting start temperature was measured by observing the camera and the thermometer. In the description of this example, the processing time means the time until the charged raw materials pass through the melting zone.

Table 1 shows the operating conditions in this example, and Table 2 shows the balance of the iron content after the heat treatment. At this time, all basic units are calculated as a ratio to the iron content at the time of charging. As a result, for the comparative example, as described above,
Reduced iron with a small particle size that could not be used as a product had to be discarded together with slag.
On the other hand, in the examples suitable for the present invention, even reduced iron having a small particle size could be used as a product. Therefore, the recovery efficiency of iron in the mobile hearth furnace method was improved, and the unit consumption of ore was also reduced.

[0032]

[Table 1]

[0033]

[Table 2]

Next, when the melting start temperature of the slag was observed, it was found that when blast furnace pig iron having a high carbon concentration was blended, the melting start temperature was lower and the treatment time was shorter. Also, by lowering the melting temperature, it was possible to reduce the fuel consumption for heating, and it was also possible to lower the LNG intensity. From these results, it was found that when the method of the present invention is used, it is possible to improve the productivity by reducing the ore and energy intensity and reducing the processing time.

[0035]

As described above, according to the present invention, in the operation of the mobile hearth furnace, the recovery rate and productivity of iron from the raw material can be improved, and the equipment cost can be reduced by reducing the equipment scale. Can also be reduced. In addition, since the heating fuel can be reduced, the CO
_{2 The} amount can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a moving hearth furnace.

2A and 2B are a partial cross-sectional view and a cross-sectional perspective view showing a loading state of raw materials.

FIG. 3 is a partial cross-sectional view showing a state where raw materials are stacked on a solid reducing agent layer having an uneven top surface.

FIG. 4 is a partial cross-sectional view showing a state in which molding raw materials are stacked.

FIG. 5 is a phase diagram of Fe—C system.

FIG. 6 is a process diagram showing a flow of a comparative example and an example of the present invention.

[Explanation of symbols]

1 Solid reducing agent layer 2,2 'raw material 4 metal 5 slag 10 furnace body 10a Pretropical zone 10b Reduction zone 10c melting zone 10d cooling zone 11 hearth 12 burners 14 Charging device 15 Ejector 17 Cooling system

Claims (2)

[Claims] 1. A mixed raw material containing a metal-containing material and a solid reducing agent is deposited on a moving hearth in a moving hearth furnace, and the mixed raw material is heated while the moving hearth moves in the furnace. In the method for producing a reduced metal by reducing, melting at least once, and then cooling, a method of producing a reduced metal, characterized in that a material containing a metal produced through a melting process is used as the mixed raw material. Method. 2. The metal added to the mixed raw material is reduced iron and / or iron scrap and has a carbon content of 1 m.
The method for producing a reduced metal according to claim 1, wherein the content is ass% or more and 5 mass% or less.