JPH1161217A - Production of reduced iron and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can efficiently execute the reduction, and a device therefor, in reducing at high temp. by charging powdery iron raw material together with powdery solid reducing agent onto a rotary hearth furnace. SOLUTION: The powdery iron raw material on the furnace hearth is heated from the upper part and also, fuel is burnt by injecting the fuel and oxygen- containing gas into a heating space part 25 arranged below the furnace hearth. The powdery iron raw material on the furnace hearth is heated from the lower surface of the furnace hearth, too, while keeping the temp. of the heating space part at >=1100 deg.C, and the powdery iron raw material is reduced and the obtd. reduced iron is discharged to out of the furnace and gas exhausted from the rotary hearth furnace is recovered. At least a part of the recovered gas is introduced into the heating space part and used to enable raising of thermal efficiency in the whole process. This method can easily perform by using this device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a powdery iron raw material containing iron oxide as a main component, that is, dust, sludge, scale, etc. (hereinafter, referred to as powdery iron ore or iron-containing iron ore produced in steel works). In the present specification, these are collectively referred to as “powder iron raw material”) and are referred to as powdery solid reducing agents such as coal, charcoal,
Petroleum coke, coke, etc. (hereinafter “powder solid reducing agent”
The present invention relates to a method and apparatus for producing reduced iron by charging a furnace in which a hearth rotates horizontally (hereinafter, referred to as a "rotating hearth furnace") and heats the furnace.

[0002]

2. Description of the Related Art In recent years, as the production of steel products by an electric furnace has become popular, attention has been paid to a technique for obtaining an iron source used as a raw material by solid reduction of iron ore. A typical example of such a technique is to mix powdered iron ore with a powdered solid reducing agent to form agglomerates, so-called “pellets”, which are heated to a high temperature to produce iron ore. There is a technique of reducing iron oxide therein to obtain solid metallic iron (U.S. Pat. No. 3,443,931, Japanese Patent Application Laid-Open No. 7-2383).
No. 07 publication).

For example, the reduction process of fine iron ore disclosed in US Pat. No. 3,443,931 includes:
The outline consists of the following steps.

1) A raw pellet is prepared by mixing a powdery solid reducing agent such as coal or coke with a powdery iron ore.

[0005] 2) The raw pellets are heated to a temperature range in which combustible volatile components generated in the pellets do not ignite to remove adhering moisture.

[0006] 3) The obtained dried pellets are reduced by heating to a high temperature, and metallization proceeds.

[0007] 4) The metalized pellets are cooled and then discharged outside the furnace.

In Japanese Patent Application Laid-Open No. 7-238307, the same raw material (pellet) as described above is used, and at any time from when the pellets are charged into the reduction furnace until the reduction rate reaches 30%. Combustion of flammable volatile components generated from the powdered solid reducing agent by supplying air etc. to the pellet surface, CO gas generated by reduction of the powdered iron raw material, and carbon material in the pellet surface layer Promotes heating,
A method for reducing the time required for reduction is shown.

Further, "Steel Times" No.
vember, 1996, p. 399 describes a method of reducing the gangue component and sulfur content in reduced iron by simply forming a plurality of layers in a simple alternating layer without mixing “pulverized iron ore” and “pulverized solid reducing agent”. A method of charging a rotary hearth furnace to form and reducing at high temperature is shown.

However, the above-mentioned US Pat.
The conventional methods for producing reduced iron introduced in US Pat. No. 3,931, JP-A-7-238307 and "Steel Times" basically have the following problems.

That is, since the heat necessary for heating the raw material is supplied by the burner combustion heat in the space above the hearth, if the thickness of the raw material layer is increased in order to increase the productivity, the transfer to the lower part of the layer is performed. Since the heat is delayed, the reduction rate of the lower part of the layer decreases, and the productivity decreases. Therefore, the thickness of the raw material layer must be such that heat can be quickly transferred to the lower part of the layer, and the productivity cannot be significantly improved.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional reduced iron production technology. A specific object of the present invention is
An object of the present invention is to provide a method and an apparatus for producing reduced iron, which can efficiently perform reduction when a powdered iron raw material is charged into a rotary hearth furnace together with a powdered solid reducing agent and reduced at a high temperature.

[0013]

The gist of the present invention resides in the following (1) method for producing reduced iron and (2) an apparatus for producing reduced iron.

(1) A powdered iron raw material is placed on a hearth of a rotary hearth furnace together with a powdered solid reducing agent, and a fuel and an oxygen-containing gas are blown into the furnace. The combustible volatile components generated from the agent and the CO gas generated by reducing the powdered iron raw material are burned by the oxygen-containing gas blown into the furnace, and the furnace temperature is maintained at 1100 ° C. or higher. While heating the powdered iron raw material on the hearth from above, the fuel and oxygen-containing gas are blown into the heating space provided under the hearth to burn the fuel, so that the temperature of the heating space becomes 1100 ° C or more. Maintain and heat the powdered iron material on the hearth from the bottom of the hearth to reduce the powdered iron material, discharge the resulting reduced iron out of the furnace, and discharge the gas discharged from the rotary hearth furnace. A method for producing reduced iron.

(2) A furnace body provided with an inlet for the powdered iron raw material, an outlet for reduced iron obtained by heating and reducing the powdered iron raw material, and an outlet for gas generated in the furnace, and provided in the furnace. The main part is a rotary hearth furnace that has a burner that blows fuel and oxygen-containing gas into the furnace, and burns fuel by blowing the fuel and oxygen-containing gas into the furnace, and further discharges gas discharged from the gas outlet. A reduced iron manufacturing apparatus having a gas recovery facility for recovering, wherein a burner that burns fuel by blowing fuel and an oxygen-containing gas into the hearth lower surface heating space below the hearth is provided below the hearth. An apparatus for producing reduced iron, which is provided.

Here, "pulverized iron raw material" is a powdered iron raw material containing iron oxide as a main component, and specifically includes the above-mentioned powdered iron ore and iron generated in an ironworks. Dust, sludge, scale, etc. In the present invention, these can be used alone or in a mixture of two or more.

The “powder solid reducing agent” is a powder of a solid substance mainly containing carbon, such as coal, charcoal, coke (including petroleum coke). These can also be used alone or in combination of two or more.

As a preferred embodiment of the method for producing reduced iron of the present invention (1), the following method can be adopted.

[Preferred Embodiment 1] At least a part of the collected exhaust gas from the rotary hearth furnace is introduced into a heating space provided under the hearth to heat the powdered iron material on the hearth from the lower surface of the hearth. The method of producing reduced iron to be used.

Further, as a preferred embodiment of the reduced iron production apparatus of the present invention (2), the following apparatus can be adopted.

[Preferred Embodiment 2] Means for introducing at least a part of the gas recovered by the gas recovery equipment into the heating space under the hearth to heat the powdered iron raw material on the hearth from the bottom surface of the hearth is provided. Equipped with reduced iron production equipment.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the above-mentioned method (1) for producing reduced iron of the present invention (the method of the present invention) and the above-mentioned (2) the apparatus for producing reduced iron of the present invention (the apparatus of the present invention) will be described with reference to the drawings. This will be described in detail.

FIG. 1 is a diagram showing an outline of the steps of the method of the present invention and an example of equipment used. FIG. 2 is a longitudinal sectional view of a part of a conventional rotary hearth furnace.
1 is a view showing a part of a rotary hearth furnace for carrying out the method of the present invention, (a) is a longitudinal sectional view including a mounting part of a burner for hearth heating, and (b) is a burner mounted. It is a longitudinal cross-sectional view of a part without.

In the method of the present invention (1), first, a powdered iron raw material is placed on a hearth of a rotary hearth furnace together with a powdered solid reducing agent.

For example, as shown in FIG. 1, fine ore 1 and fine solid reducing agent 2 are mixed by a mixer, and then charged into a rotary hearth furnace 20 in a powdery state, and the fine ore 1 and fine solid reducing agent 2 are charged into a rotary hearth furnace 20 as shown in FIG. As shown in a)
Place on the hearth in a thin layer.

As a method of charging the powdered iron raw material together with the powdered solid reducing agent into the rotary hearth furnace, the following several methods are conceivable, and any of these methods may be employed.

The powdery iron raw material and the powdery solid reducing agent are mixed, pelletized or briquetted, dried, and then charged.

The powdery iron raw material and the powdery solid reducing agent are mixed, formed into a tile shape, and then charged.

The powdery iron raw material and the powdery solid reducing agent are mixed, formed into a continuous plate, and then charged.

A mixture of the powdered iron raw material and the powdered solid reducing agent to form agglomerates (pelleting or briquetting) or molding (forming into a tile or plate shape)
Instead, it is charged in powder form and placed on the hearth in layers. The method shown in FIG. 3A corresponds to this.

-The powdered iron raw material and the powdered solid reducing agent are charged simply and in an alternating layer without mixing.

When agglomerating or forming after mixing the powdery iron raw material and the powdery solid reducing agent, a binder such as water, tar or bentonite may be added as necessary. In the example shown in FIG. 1, the binder 3 is added.

In order to reduce the content of sulfur (S) in the produced reduced iron, a desulfurizing agent may be added to the powdery solid reducing agent.

Further, dust produced from a smelting furnace when reducing iron is reduced and melted in a smelting furnace to produce pig iron can be used as a powdery iron raw material. The dust added simultaneously in the example shown in FIG. 1 is dust generated from this smelting furnace.

After charging the powdered iron raw material into the rotary hearth furnace together with the powdered solid reducing agent, the fuel and oxygen-containing gas are blown into the furnace, and the flammability generated from the injected fuel and the powdered solid reducing agent The CO gas generated by the reduction of the volatile components and the powdered iron raw material is burned by the oxygen-containing gas blown into the furnace, and the furnace temperature is maintained at 1100 ° C. or higher and placed on the hearth. The raw material is heated from above.

As the fuel, a commonly used fuel such as natural gas or heavy oil is used. Alternatively, any other fuel that can be used as a fuel may be used. In the example shown in FIG. 1, flammable gas is discharged as exhaust gas from the smelting furnace when reducing iron is reduced and melted in the smelting furnace to produce pig iron.

As the oxygen-containing gas, it is preferable to use air or a gas whose oxygen concentration is equal to or slightly richer than the air composition.

The furnace temperature for performing high-temperature reduction is 110
0 ° C or higher. The reduction proceeds even in a temperature range lower than 1100 ° C., but in such a temperature range, the reduction rate is slow, which is not preferable for industrial production. During the reduction of the iron oxide, the temperature of the charged bed becomes lower than the temperature in the furnace due to the endothermic reaction.
It is desirable to maintain the temperature at about 200 to 1400 ° C.

However, this temperature is a property to be adjusted according to the progress of the reduction, the properties and the mixing ratio of the powdery iron raw material and the solid reducing agent to be used, and the like. That is, in the short period after the raw materials are charged into the furnace, the temperature of the charged material is low. Therefore, it is more advantageous to promote the reduction by maintaining the furnace temperature at a high temperature and raising the temperature of the charged material. It is.

Further, since the melting points of the gangues in the ore and the ash in the coal are varied depending on the composition of the raw materials, the temperature in the furnace is controlled according to the melting point, and the material is not dissolved and flows out during the reduction. It should be noted that However, the production of a moderate amount of melt in the charge should be used positively because it gives good results in both heat transfer and reaction promotion.

In the step of heating the raw material placed on the hearth, in the method of the present invention, in addition to the above-described heating of the raw material from above, the raw material is also heated from the lower surface of the hearth.

In a conventional rotary hearth furnace, FIG.
As shown in (1), the raw material (mixture of the powdered iron raw material and the powdered solid reducing agent) placed on the hearth is simply heated from above by the heat of combustion by the burner 21. However, in the method of the present invention, as shown in FIG. 3A, a rotary furnace having a hearth in which a heating space 25 is provided below the hearth and a burner 26 is installed so as to open in this space. Using a floor furnace, the fuel and oxygen-containing gas are blown from the burner 26 to burn the fuel, the temperature of the heating space is maintained at 1100 ° C. or higher, and the raw material (mixture) placed on the hearth is It also heats from the bottom of the hearth.

The control of the fuel and oxygen-containing gas blown from the burner 26, the temperature in the heating space 25, and the like are the same as in the case of the above-described heating from above.

As described above, the powdered iron raw material on the hearth is heated from above, and also from the bottom of the hearth to reduce the powdered iron raw material, and the obtained reduced iron is discharged out of the furnace.

Further, the gas discharged from the rotary hearth furnace is recovered. In the example shown in FIG. 1, the recovered gas is burned by a waste gas combustion device, and the heat is used for preheating combustion air blown into a rotary hearth furnace.

According to the method of the present invention, the raw material placed on the hearth can be heated not only from the upper part but also from the lower part. Greatly increased as compared with the heating method of (1). As a result, the reduction rate of the powdered iron raw material increases, and the productivity is greatly improved.

The device of the present invention (2) is a device capable of implementing the above-described method of the present invention.
A reduced iron manufacturing apparatus having the rotary hearth furnace shown in FIG.

As shown in FIG. 3 (a), the rotary hearth furnace has a furnace body 30 forming an outer shell of a furnace, a horizontally rotating hearth provided in the furnace, and a fuel hearth. And a burner 21 for injecting an oxygen-containing gas to burn fuel.
Although not shown, the furnace body 30 has an inlet for the powdered iron raw material, an outlet for reduced iron obtained by heating and reducing the powdered iron raw material, and an outlet for gas generated in the furnace. Have been. And in the apparatus of the present invention, under the hearth,
A hearth lower surface heating space portion 25 placed on the hearth to heat the raw material (mixture);
A burner 26 is provided for blowing the fuel and the oxygen-containing gas to burn the fuel.

Here, the "hearth" is a portion made of a refractory (hearth refractory) on which the raw material is placed, among the refractories for creating (surrounding) the heating space under the hearth. Hearth lower surface "
Is the lower surface of this hearth refractory. In addition, refractories other than the hearth refractories are referred to herein as "lower hearth refractories".
That. In the illustrated example, the rail 22 is attached to the lower side of the refractory 31 under the hearth, and the hearth rotates at a constant speed by driving the fixed wheels 27. The inside of the furnace is sealed with seal water 23. The heating space 25 on the lower surface of the hearth is filled with the sealing water 24.
Sealed by.

A plurality of burners 26 for heating the bottom of the hearth for blowing the fuel and the oxygen-containing gas into the space 25 for heating the bottom of the hearth are provided along the length of the hearth as needed. Further, an exhaust gas duct (not shown) for exhausting the combustion exhaust gas is opened from the lower side of the lower refractory 31 of the hearth to the heating space 25 as required, similarly to the burner 26 for heating the lower surface of the hearth. A plurality of flue gases are provided, and the flue gas is discharged out of the furnace through the flue gas duct. That is, the hearth lower surface heating space 25 is a space for fuel combustion and at the same time, a discharge passage for combustion exhaust gas.

As shown in FIG. 3 (b), in the gap other than the portion where the burner 26 for heating the lower surface of the hearth is installed and the portion where the exhaust gas duct is provided, as shown in FIG. An object wall 28 is provided.

As the material of the hearth refractory in the apparatus of the present invention, a material having a high thermal conductivity is selected so as to increase the speed of heat transfer from the heating space under the hearth. In this case, in order to prevent the refractory from being oxidized by the burner combustion gas, a refractory having high oxidation resistance is used for a portion facing the heating space under the hearth, and the inside is made of a material having high thermal conductivity. desirable.

Next, preferred embodiments of the method of the present invention and preferred embodiments of the apparatus of the present invention will be described.

[Preferred Embodiment 1] In the method of the present invention described above, at least a part of the exhaust gas (recovered gas) collected from the rotary hearth furnace when the powdered iron raw material on the hearth is heated from the lower surface of the hearth. Is introduced into the heating space provided below the hearth, the sensible heat of the exhaust gas can be effectively used, and the thermal efficiency of the entire process can be increased.

At this time, the temperature of the exhaust gas from the rotary hearth furnace is 1
When the temperature of the exhaust gas is high, the temperature of the heating space can be increased to 1100 ° C. or higher by merely introducing the exhaust gas into the heating space under the hearth and passing the exhaust gas. If the temperature is low, part or all of the exhaust gas introduced into the heating space is burned in the hearth lower surface heating space.

[Preferred Embodiment 2] An apparatus for carrying out the above-mentioned [Preferred Embodiment 1], wherein in the apparatus of the present invention, at least a part of the gas recovered by the gas recovery equipment is heated at the lower part of the hearth heating space. And a means for heating the powdered iron raw material on the hearth from the lower surface of the hearth.

As this means, for example, there is an apparatus having the configuration shown in FIG. That is, an exhaust gas introduction duct 32 of a rotary hearth furnace in which a part of the burner 26 for heating the lower surface of the hearth is replaced, and the collected exhaust gas (recovered gas) is passed through the exhaust gas introduction duct 32 and the burner 26.
This is a device (portion surrounded by a broken line) composed of a conduit 35 for communicating with the air conditioner and switching valves 33 and 34. At least a part of the exhaust gas is sent to the conduit 35 by the switching valve 33, and further sent to the exhaust gas introducing duct 32 and / or the burner 26 by the switching valve 34.

As described above, when the exhaust gas temperature is high, all or a part of the exhaust gas is
When the exhaust gas temperature is low, all or part of the exhaust gas is sent to the burner 26 and burned in the heating space. At this time, the fuel supplied from the outside may be burned together with the exhaust gas (recovered gas).

[0059]

EXAMPLE A tar as a binder was added to a powdered iron raw material (iron ore) having a composition shown in Table 1 and a powdery solid reducing agent (coal) shown in Table 2, and mixed at a mixing ratio shown in Table 4. It was formed into pellets, square tiles and plate-like molded products shown in the same table. Table 3 shows the particle size composition of the fine iron ore and the fine coal used.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

[0063]

[Table 4]

Using these forming raw materials, reduced iron was produced in a rotary hearth furnace under the conditions shown in each of Cases 1 to 9 in Table 6 and the time required for reduction at that time was determined to obtain the effect of the present invention. Was evaluated. Table 5 shows the equipment use and operating conditions of the rotary hearth furnace used.

[0065]

[Table 5]

[0066]

[Table 6]

Cases 1 to 3 in Table 6 are obtained by a conventional method. The hearth has the structure shown in FIG. 2 and the temperature in the furnace is maintained at 1300 ° C. and only from the upper part of the hearth. Reduction was performed under heating conditions.

Cases 4 to 9 are based on the method of the present invention. The hearth has the structure shown in FIG. 3 and maintains the temperature in the furnace at 1300 ° C. and the heating space at the lower surface of the hearth. This is a case where the operation was performed while maintaining the temperature at 1200 ° C.
Of these, cases 4 to 6 are cases where fuel is burned in the hearth lower surface heating space, and cases 7 to 9 are cases where exhaust gas from the rotary hearth furnace is introduced into the hearth lower surface heating space (gas passing). ) And burned.

During the operation, the rotation speed of the hearth was adjusted so that the metallization ratio of reduced iron was 92%. That is, when the metallization ratio was lower than the target value, the rotation speed was decreased, the firing time was extended, and the metallization ratio was increased. In this case, productivity decreases. Conversely, if the metallization rate is higher than the target value,
The rotation speed was increased, the firing time was shortened, and the metallization ratio was reduced to the target value. In this case, productivity is improved.

Table 6 also shows the time required for reduction in each case.

Case 1 is a case in which pellets having a diameter of 20 mm are produced from a mixed raw material using a 7.5-mm-diameter dish-type pelletizer, dried, and then charged into a rotary hearth furnace with a flat plate chute. The time required for reduction was 10 minutes.

In case 2, three double-roll compressors having a width of 1.67 m were installed in the width direction of the hearth just above the raw material charging portion of the rotary hearth furnace, and the mixed raw materials were converted into a tile-shaped product. The time required for reduction was 15 minutes when charged in a rotary hearth furnace with a flat plate chute. Case 3 was a case where the mixed raw material was not a tile-shaped molded product but a plate-shaped molded product, and the time required for reduction was 16 minutes. In Cases 2 and 3, the time required for reduction is longer than that in the case of using pellets, because the pellets are used after being dried, whereas the tile-shaped or plate-shaped products are used. In the case of, it is considered that the product was used in a state containing water (see Table 4).

On the other hand, in Cases 4 to 9 corresponding to the method of the present invention, the time required for reduction is reduced as compared with the case where the conventional method is used. It was remarkable in the case of molded products and plate-shaped molded products. This is because, considering the heat transfer from the hearth to the molding material, the pellets are in point contact with the hearth,
In the case of the tile-like molded product and the plate-shaped molded product, since they are in surface contact, it is considered that the amount of heat transfer from the hearth to the forming raw material is larger in the latter.

The case 4 in which the fuel was burned by burner
-Case 6 and the exhaust gas from the rotary hearth furnace were introduced (gas-passed) into the heating space under the hearth, and there was no difference in the reduction time between Cases 7 to 9 where they were burned. It turns out that it can be shortened.

[0075]

According to the method of the present invention, when a powdered iron raw material is charged into a rotary hearth furnace together with a powdered solid reducing agent and reduced at a high temperature, the reduction can be performed efficiently. This method can be easily performed by the apparatus of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of the steps of the method of the present invention and an example of equipment used.

FIG. 2 is a vertical sectional view of a part of a conventionally used rotary hearth furnace.

3A and 3B are diagrams showing a part of a rotary hearth furnace for carrying out the method of the present invention, wherein FIG. 3A is a longitudinal sectional view including a mounting portion of a burner for heating the lower surface of the hearth, and FIG. It is a longitudinal cross-sectional view of the part which is not attached.

FIG. 4 is a diagram showing a configuration of an example of a means for heating a powdered iron raw material from a lower surface of a hearth.

[Explanation of symbols]

 1: fine ore 2: reducing agent 3: binder 20: rotary hearth furnace 21: burner 22: rail 23, 24: sealing water 25: hearth lower surface heating space portion 26: burner 27: wheels 28: refractory wall 29: Drive device 30: Furnace body 31: Refractory under the hearth 32: Duct for exhaust gas introduction 33, 34: Switching valve 35: Conduit

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI F27D 17/00 104 F27D 17/00 104G (72) Inventor Koichi Ohne 4-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Tomo Metal Industry Co., Ltd.

Claims (4)

[Claims] 1. A powdered iron raw material is placed on a hearth of a rotary hearth furnace together with a powdered solid reducing agent, and fuel and an oxygen-containing gas are blown into the furnace. The combustible volatile components generated from the raw material and the CO gas generated by reducing the powdered iron raw material are burned by the oxygen-containing gas blown into the furnace, and the furnace temperature is maintained at 1100 ° C. or higher. While heating the powdered iron raw material on the floor from above, the fuel and oxygen-containing gas are blown into the heating space provided under the furnace floor to burn the fuel and maintain the temperature of the heating space at 1100 ° C or higher. The powdered iron raw material on the hearth is also heated from the bottom of the hearth to reduce the powdered iron raw material,
A method for producing reduced iron, comprising discharging the obtained reduced iron out of the furnace and collecting gas discharged from the rotary hearth furnace. 2. At least a part of the recovered gas discharged from the rotary hearth furnace is introduced into a heating space provided under the hearth, and the powdered iron raw material on the hearth is used for heating the lower surface of the hearth. The method for producing reduced iron according to claim 1, wherein: 3. A furnace body provided with an inlet for a powdered iron raw material, an outlet for reduced iron obtained by heating and reducing the powdered iron raw material, and an outlet for gas generated in the furnace. The main part is a rotary hearth furnace having a horizontally rotating hearth and a burner for blowing fuel and oxygen-containing gas into the furnace to burn the fuel, and further recovering gas discharged from the gas outlet. A reduced iron manufacturing apparatus having a gas recovery facility to perform, provided below the hearth, a hearth lower surface heating space portion, and a burner that burns fuel by blowing fuel and oxygen-containing gas into the hearth lower surface heating space portion. An apparatus for producing reduced iron, which is characterized in that: And means for introducing at least a part of the gas recovered by the gas recovery equipment into a heating space under the hearth to heat the powdered iron raw material on the hearth from the lower surface of the hearth. The apparatus for producing reduced iron according to claim 3, wherein: