JP3403091B2 - Method for reducing wet pellets by rotary bed type reduction furnace and rotary bed type reduction furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary bed type reduction furnace for supplying wet pellets of a raw material onto a rotary hearth in a furnace and heating the wet pellets for reduction, and a reduction method thereof.

[0002]

2. Description of the Related Art Conventionally, as a rotary bed type reduction furnace of this type,
For example, fine powder of iron oxide such as iron ore and fine powder of carbonaceous reducing agent such as coal are mixed, wet pellets are kneaded and granulated by adding water thereto, without drying in advance, Some of them are reduced by heating, which will be described below with reference to the drawings.

FIG. 4 is a schematic perspective view of a conventional rotary bed type reduction furnace, and FIG. 5 illustrates a wet pellet reduction method by expanding the rotary bed type reduction furnace shown in FIG. 4 in the rotating direction of the rotary hearth. FIG. Reference numeral 6 indicates a storage tank of iron oxide fine powder raw material such as iron ore powder, reference numeral 7 indicates a storage tank of carbonaceous reducing agent powder such as coal powder, and reference numeral 8 indicates a storage tank of binder particles such as bentonite. Then, the kneading machine 9 is provided in each of the storage layers 6, 7, 8
The powder cut out from each is kneaded while adding water, and the granulator 10 granulates the kneaded powder into pellets while adding water to produce wet pellets as a raw material. On the other hand, reference numeral 1 indicates a rotary bed type reduction furnace main body, and wet pellets (raw material pellets) which have not been dried are continuously formed on the rotary hearth 20 in the rotary bed type reduction furnace main body 1 by the pellet charging device 2. Charged. Reference numeral 11 is a pellet conveying device such as a conveyor for conveying the wet pellets to the pellet charging device 2, and reference numeral 12 is 1 to 2 on the rotary hearth 20 by the pellet charging device 2. Figure 7 shows wet pellets evenly loaded in layers.

As the rotary hearth 20 rotates (the direction of rotation is indicated by arrow A), the wet pellets 12 (pellet layer) on the rotary hearth 20 are heated and reduced by the burner 13. Reference numeral 3 indicates a reduced iron pellet discharging device (product reduced product discharging device) for discharging the high temperature reduced iron pellets reduced at high temperature to the outside of the furnace body 1, and reference numeral 4 indicates the discharged high temperature reduced iron pellets. A container for temporarily storing is shown, and a reference numeral 5 is an exhaust pipe for combustion gas in the furnace.

The operation of the rotary bed type reduction furnace will be described in detail. A predetermined amount of each powder continuously cut out from the iron oxide fine powder raw material tank 6, the carbonaceous reducing agent powder storage tank 7, and the binder powder storage tank 8 is continuously kneaded while adding water by the kneading machine 9 to be uniform. The composition is a wet mixed powder. Thereafter, the wet mixed powder is continuously supplied to the granulator 10 and granulated in the granulator 10 into wet pellets having a diameter of about 10 mm. After the wet pellets are sieved by a sieve (not shown) to a predetermined upper and lower limit size, only wet pellets having a predetermined size range are subjected to rotary bed reduction by the pellet charging device 2 via the pellet conveying device 11. One or two layers are uniformly loaded on the rotary hearth 20 of the furnace. The wet pellet layer 12 is heated by the burner 13 while the rotary hearth 20 in the furnace makes one rotation, and is sequentially dried,
Preheated and heated to high temperature to obtain reduced iron pellets. Thereafter, the high-temperature reduced iron pellets are discharged to the outside of the furnace by the reduced iron pellet discharging device 3, further stored temporarily in the container 4 and processed in a subsequent step (for example, a melting step).

[0006]

By the way, when the wet pellets are supplied onto the rotary hearth 20 by the pellet charging device 2, if the surface temperature of the rotary hearth 20 is about 700 ° C. or higher, the wet pellets are It is heated rapidly, and when water evaporates from the inside of the pellets, the water vapor pressure inside the pellets rapidly increases and the pellets are destroyed. That is, a burst phenomenon called bursting occurs. When such a phenomenon occurs, naturally, the yield of the product reduced iron decreases.

Therefore, conventionally, in order to prevent such a decrease in yield, as shown in FIG. 6, the hearth surface temperature (T when supplying wet pellets onto the rotary hearth 20).
i), that is, the surface temperature of the rotary hearth 20 at point (a) is set to about 700 ° C. or lower. Therefore, the high-temperature reduced iron pellets are discharged from the reduced iron pellet discharging device 3 (see FIG.
Immediately after being discharged to the outside of the furnace by
The hearth surface temperature (To) at point (c) is about 1100 ° C. In order to lower this temperature to the temperature Ti (about 700 ° C.) or less at the point (a), it is necessary to increase the distance between (c) and (a) of the rotary hearth 20.
There is a problem that the furnace floor area as a whole becomes large and the equipment cost increases. In addition, (b) in FIG. 6 shows the time immediately after the drying step of the wet pellets, and the hearth surface temperature at this time is the lowest.

The present invention has been made in view of the above problems of the prior art, and shortens the distance between the product reduced product discharge part (device) and the wet pellet supply part (device) of the rotary hearth. An object of the present invention is to provide a method for reducing wet pellets by a rotary bed type reduction furnace and a rotary bed type reduction furnace, which reduce the overall hearth floor area and reduce equipment costs.

[0009]

In order to achieve the above object, the present invention provides a rotary furnace type reduction in which raw material wet pellets are supplied onto a rotary hearth in a furnace, and the wet pellets are reduced by heating. In the method for reducing wet pellets in a furnace, on the rotary hearth immediately before supplying the wet pellets onto the rotary bed, in advance, a bedding particle layer is spread by laying insulating particles having a melting point higher than the heating temperature. It is characterized in that it is formed, and then the wet pellets are supplied onto the bedding bed particle layer. Here, the heat insulating particles may be limestone particles, dolomite particles, or basic oxide particles in which these particles are mixed.

Further, the rotary bed type reduction furnace of the present invention is equipped with a wet pellet supply device for supplying the wet pellets of the raw material onto the rotary hearth in the furnace, and the wet pellets supplied are reduced by heating. In the rotary bed type reduction furnace to be, on the rotary hearth immediately before the wet pellet charging device, heat insulating particles for spreading the heat insulating particles having a melting point higher than the heating temperature to form a bedding particle layer It is characterized in that a supply device is provided.

Here, the adiabatic particle supply device receives a first hopper for storing the adiabatic particles, the adiabatic particles discharged from the first hopper, and has an opening at the lower end. And a second hopper provided with this opening so as to face the rotary hearth with a gap therebetween.

The operation of the present invention will be described. Before supplying the wet pellets to the high-temperature rotary hearth, high-melting-point heat insulating particles are spread in advance to form a bed bed particle layer, which acts as a heat insulating layer for the wet pellets of the raw material supplied immediately after this. Let Therefore, after the hot reduced iron pellets are discharged from the rotary hearth to the outside of the furnace, the surface temperature on the rotary hearth is cooled to about 1000 ° C. before the wet pellets of the raw material are charged (supplied) into the furnace. Therefore, the distance (section) for radiating and cooling the product after the reduction product (such as reduced iron pellets) is discharged from the rotary hearth can be shorter than before. Further, as described above, by increasing the hearth temperature at the time of supplying the wet pellets from about 700 ° C. to about 1000 ° C. of the prior art, the heating time after supplying the wet pellets can be shortened and, in addition, the rotary hearth The distance from the wet pellet supply device to the product reduced product discharge device can be made shorter than before. The wet pellet is a component mainly composed of iron ore powder (iron oxide powder), and is usually heated to about 1300 ° C. and reduced, so that the heat insulating particles do not soften or melt at this heating temperature (furnace temperature). Thus, it is required to have a melting point higher than 1300 ° C., and it is particularly preferable to have a melting point of about 1400 ° C. or higher.

By using basic oxide particles such as limestone particles and dolomite particles as the heat insulating particles, the basic oxide particles have a small thermal conductivity and a relatively large specific heat. The bedding bed layer of the particles becomes an extremely effective heat insulating layer for the wet pellets of the raw material supplied immediately after. Further, the basic oxide particles have the advantage that they are stable in a high temperature and reducing atmosphere in the furnace, and after being cut out into a container together with the high temperature reduced iron pellets by a reduced iron pellet discharging device. , It functions as a desulfurizing agent in the subsequent pig iron dissolution process of reduced iron pellets.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described with reference to the drawings. 1 is a configuration diagram of an embodiment of a rotary bed type reduction furnace of the present invention, and FIG. 2 is a graph showing a relationship between a rotational direction position of the rotary hearth and a surface temperature in the rotary bed type reduction furnace shown in FIG. FIG. 3 is a graph showing the relationship between the thickness of the bedding bed layer and the allowable surface temperature of the rotary hearth in the rotary bed type reduction furnace shown in FIG.

First, as shown in FIG.
Reference numerals 12 and 20 are the same as those shown in FIG. 4 and FIG. 5, and therefore description thereof will be omitted. Reference numeral 21
Is a first particle hopper for storing heat insulating particles 23 such as limestone particles for bedding bed layer, and reference numeral 22 is the first particle hopper.
Particles 23 discharged from the particle hopper 21 of
It is a second particle hopper which is provided with an opening at the lower end 22a and is opposed to the rotary hearth 20 with a gap S through which the heat insulating particles 23 can pass. These two particle hoppers 21 and 22
Is used for forming a bedding bed particle layer 24 (heat insulating layer) by spreading a large number of heat insulating particles 23 having a melting point higher than the furnace temperature on the rotary hearth 20 immediately before the wet pellet charging device 2. The heat insulating particle supply device 200 is configured. The heat insulating particles 3 are required to have a melting point higher than the heating temperature (about 1300 ° C.) of the wet pellets so as not to melt in the furnace body 1, and particularly those having a melting point of about 1400 ° C. or more. Is preferred. Further, not only limestone particles but also dolomite particles or a basic oxide obtained by mixing these particles may be used.

In the rotary bed type reduction furnace main body 1, as shown in FIGS. 1 and 2, first, at a point (A) in FIG. Is uniformly supplied onto the rotary hearth 20 by the particle hopper 22 to form the bedding bed particle layer 24. Since the heat insulating particle supply device 200 is configured by the two-stage particle hoppers 21 and 22, even if any one particle hopper becomes empty due to clogging of the heat insulating particles 23 or the like, There is no fear that the supply of the heat insulating particles 23 will be interrupted for a long period of time.

Here, as shown in FIG.
From the viewpoint of heat insulation effect and crushing power cost, 1 to 5 mm is desirable. In addition, the layer thickness of the heat insulating particles 23 is preferably 3 to 5 mm from the viewpoint of heat insulating properties and melting costs associated with the amount of slabs generated during melting in the subsequent step. Immediately after the bedding bed 24 is formed on the rotary hearth 20, wet pellets as a raw material pellet for reduction (the manufacturing method thereof is described above) are supplied onto the bedding bed 24 by the pellet charging device 2. Then, the wet pellet layer 12 is formed. The size of the wet pellets in this case is generally 7 to 20 mmφ from the viewpoint of heat transfer within the pellets and pellet strength, and the wet pellet layer 12 is generally formed of 1 to 2 layers. Is.

The wet pellet layer 12 is heated while passing through the inside of the furnace main body 1 to dry the wet pellets first.
Then, by receiving preheating and being heated to a high temperature, the reduction reaction proceeds and is converted into reduced iron pellets to become a product,
At point (C) in FIG. 2, the reduced iron pellet discharging device 3
Is cut out from the furnace body 1 and stored in the container 4. After that, the reduced iron pellets are sent to a melting step and subjected to melting and smelting to become clean molten iron.

Floor surface temperature (T
o) is about 1100 ° C. as described above. Then, in the conventional method, the rotary hearth 20 is radiatively cooled over a time period so that the hearth temperature becomes about 700 ° C. or lower. However, as in the present embodiment, the rotary hearth 20 is preliminarily cooled to the floor. By forming the bed particle layer 24, bursting (explosion) of the wet pellets does not occur even when the hearth temperature (Ti) when supplying the wet pellets is about 1000 ° C.
The distance between (A) is about 20 compared to the conventional rotary bed reduction furnace.
% Can also be reduced. Further, the temperature of the rotary hearth, which has been conventionally raised from 700 ° C., is raised from 1000 ° C., and the distance between (A) to (C) can be shortened accordingly. The temperature (TiO) at the point (A), which is the supply part of the heat insulating particles 23, is about 1060 ° C., and (B) in FIG. 2 shows the time point after the wet pellets are dried. The floor temperature will be the lowest temperature.

Further, in the present embodiment, the basic oxide particles such as limestone particles and dolomite particles have the function of the heat insulating layer as described above, and the reduced iron pellet discharging device 3 causes the reduced iron pellets at a high temperature. After being cut out into the container 4 together with it, it also functions as a desulfurizing agent in the dissolution process of the reduced iron pellets in the subsequent process, and also has the action of removing the sulfur content in the reduced iron, which is extremely useful in industry is there.

[0021]

Since the present invention is configured as described above, it has the following effects. In the invention according to claim 1, before supplying the wet pellets to a high-temperature rotary hearth, particles of high-melting heat insulating particles are spread in advance to form a bedding bed particle layer, and a raw material supplied immediately after this is formed. It acts as an insulating layer on the wet pellets. Therefore, after the hot reduced iron pellets are discharged from the rotary hearth to the outside of the furnace, the surface temperature on the rotary hearth is cooled to about 1000 ° C. before the wet pellets of the raw material are charged (supplied) into the furnace. Therefore, the distance (section) for radiating and cooling the product after the reduction product (such as reduced iron pellets) is discharged from the rotary hearth can be shorter than before. Further, as described above, by increasing the hearth temperature at the time of supplying the wet pellets from about 700 ° C. to about 1000 ° C. of the prior art, the heating time after supplying the wet pellets can be shortened and, in addition, the rotary hearth The distance from the wet pellet supply device to the product reduced product discharge device can be made shorter than before, resulting in a compact hearth area and reduced equipment costs.

Further, the inventions according to claims 2 and 5 use the basic oxide particles such as limestone particles and dolomite particles as the heat insulating particles, so that the basic oxide particles are thermally conductive. Due to its low rate and relatively high specific heat, the bedding bed layer of this particle is a very effective heat insulating layer for the wet pellets of the raw material supplied immediately after. Further, the basic oxide particles, after being cut out in a container together with the high-temperature reduced iron pellets by the reduced iron pellet discharging device, function as a desulfurizing agent in the subsequent reduced iron pellet dissolution treatment step. Since it also has a function of removing the sulfur content in the reduced iron, it is extremely useful industrially.

The invention according to claim 3 can provide a small rotary bed type reduction furnace having a small hearth area and a reduced equipment cost. In the invention according to claim 4, the heat insulating particle supply device is 2
As it is composed of stepped particle hoppers, by any chance,
Even if any one of the particle hoppers becomes empty due to clogging of the heat insulating particles, the supply of the heat insulating particles does not have to be interrupted for a long period of time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a rotary bed reduction furnace of the present invention.

FIG. 2 is a graph showing the relationship between the rotational direction position of the rotary hearth and the surface temperature in the rotary bed type reduction furnace shown in FIG.

FIG. 3 is a graph showing the relationship between the thickness of the bedding bed layer and the allowable surface temperature of the rotary hearth in the rotary bed type reduction furnace shown in FIG.

FIG. 4 is a schematic perspective view of a conventional rotary bed reduction furnace.

FIG. 5 is a diagram for explaining a wet pellet reduction method by expanding the main part X of the rotary bed type reduction furnace shown in FIG. 4 in the rotation direction of the rotary hearth.

6 is a graph showing the relationship between the rotational direction position of the rotary hearth and the surface temperature in the rotary bed type reduction furnace shown in FIG.

[Explanation of symbols]

1 Rotating bed type reduction furnace body 2 Pellet charging device 3 Reduced iron pellet discharging device 4 containers 5 exhaust pipe 9 kneader 10 granulator 12 Wet pellet layer 20 rotary hearth 21 First particle hopper 22 Second particle hopper 23 Insulation particles 24 Bedding floor particle layer 200 Insulation particle feeder

Front page continuation (72) Inventor Shigeo Itano 1-20-24 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Ryomei Giken Co., Ltd. (56) References JP-A-5-125454 (JP, A) JP-A-10 -204516 (JP, A) JP 10-237519 (JP, A) JP 10-152711 (JP, A) JP 46-16807 (JP, B1) (58) Fields investigated (Int.Cl) . ⁷ , DB name) C21B 13/08 C22B 1/16 101 C22B 1/20 C22B 1/216 F27B 9/16

Claims (5)

(57) [Claims] 1. A method for reducing wet pellets in a rotary furnace-type reduction furnace, comprising supplying the raw material wet pellets onto a rotary hearth in a furnace and heating the wet pellets to reduce the wet pellets. Immediately before being supplied onto the rotary bed, the rotary hearth is preliminarily spread with heat insulating particles having a melting point higher than the heating temperature to form a bed particle layer, and then the wet pellets are formed on the bed particle layer. A method for reducing wet pellets in a rotary bed reduction furnace, comprising: 2. The method for reducing wet pellets in a rotary bed reduction furnace according to claim 1, wherein the heat insulating particles are limestone particles, dolomite particles, or basic oxide particles in which these particles are mixed. 3. A rotary bed reduction furnace comprising a wet pellet supply device for supplying wet pellets of a raw material onto a rotary hearth in a furnace, and reducing the supplied wet pellets by heating the wet pellets. On the rotary hearth just before the pellet charging device,
A rotating bed type reduction furnace comprising an adiabatic particle supply device for spreading adiabatic particles having a melting point higher than the heating temperature to form a bedding particle layer. 4. The heat insulating particle supply device has a first hopper for storing the heat insulating particles, the heat insulating particles discharged from the first hopper, and an opening at a lower end. The rotary bed reduction furnace according to claim 3, further comprising a second hopper provided so that the opening faces the rotary hearth with a gap. 5. The rotary bed reduction furnace according to claim 3, wherein the heat insulating particles are limestone particles, dolomite particles, or basic oxide particles in which these particles are mixed.