JPH10306304A - Operation of shifting furnace hearth type furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve radiation heat transfer and heat conduction and to increase the production of reduced iron per unit area of furnace hearth without increasing fuel consumption in reducing iron ore with a shifting furnace hearth type furnace. SOLUTION: At the time of operating the shifting furnace hearth type furnace for the reduction of iron ore by heating a layer composed of the powdery iron ore and powdery solid reducing agent from the upper part, a ruggedness shape is formed on the upper layer surface so that this shape simultaneously satisfies the following (1), (2) and (3) inequalities. (1) A>=A'×1.2, (2) Lmax <=120, (3) L×0.8<= distance between peaks of the ruggedness on the upper layer. Wherein, A is the upper surface area of the ruggedness shape layer (mm<2> ), A' is the upper surface area of the layer in the case the upper surface is flat (mm<2> ), Lmax is the max. thickness of the layer (mm) and L is the average thickness of the layer (mm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for producing reduced iron from iron ore using a moving hearth furnace, and more particularly to a method for operating a moving hearth furnace having excellent fuel efficiency and productivity. It is a suggestion.

[0002]

2. Description of the Related Art The production of crude steel is roughly divided into a blast furnace-converter method and an electric furnace method. Among them, the electric furnace method uses scrap or reduced iron as an iron raw material, heats and melts them with electric energy, and in some cases, refines the steel to produce steel. At present, scrap is used as a main raw material in such an electric furnace method, but in recent years, the demand for reduced iron has been increasing due to the tightening demand for scrap and the trend of upgrading products.

[0003] As one of the processes for producing reduced iron, for example, Japanese Patent Application Laid-Open No. 63-108188 (movable hearth furnace and heat treatment method) discloses that iron ore is added to a horizontally rotating hearth. A technique has been proposed in which a layer made of a solid reducing agent is stacked and heated by radiant heat from above in the furnace to reduce iron ore and produce reduced iron. By this means,
Iron ore is successively reduced by direct reduction in a layer composed of iron ore and a solid reducing agent. Since the direct reduction involves a large endotherm, the reduction rate of the iron ore is limited by the amount of heat supplied to the bed.

Therefore, if the thickness of the layer is too large, heat supply to the lower part of the layer becomes insufficient. Therefore, the thickness of the layer is usually reduced to about several tens of mm. The production volume was small, and it was necessary to increase the hearth area to increase the production volume. As a method of improving the heat supply to the bed, a method of raising the temperature of the furnace can be considered. However, if this method is used, there is a certain effect.
Increasing the furnace temperature increases the heat dissipated from the furnace body, lowering the fuel efficiency, that is, increasing the fuel consumption, and shortening the life of the furnace.

[0005]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and can increase the production amount per hearth unit area without increasing the amount of fuel used. That is, an object of the present invention is to propose a method of operating a movable hearth furnace capable of improving fuel efficiency and reducing equipment.

[0006]

The gist of the present invention is as follows.

[0007] A moving furnace in which fine iron ore and a powdery solid reducing agent are supplied to a horizontally moving hearth, stacked in a layer of a predetermined thickness, and reduced by heating from above the furnace. In the method of operating a floor furnace, an uneven shape is formed on the upper surface of the layer, and the uneven shape has the following formula (1), (2) and (3)
A method for operating a movable hearth furnace characterized by simultaneously satisfying the following. [Note] A ≧ A ′ × 1.2 --- (1) L _max ≤120 --- (2) L × 0.8 ≤Distance between peaks of unevenness on the upper surface of the layer --- (3) where A: Upper surface area of layer (mm ² ) A ′: Upper surface area of layer when upper surface is flat (mm ² ) L _max : Maximum thickness of layer (mm) L: Average thickness of layer (mm)

[0008] Here, a layer in which a mixture of fine iron ore and a powdery solid reducing agent is stacked on the hearth is advantageous from the viewpoint of workability and reduction efficiency. Iron ore and a powdery solid reducing agent may be alternately stacked to form a multilayer.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation and effect of the present invention will be described. As mentioned above, in the operation of the mobile hearth furnace,
To reduce the iron ore by heating the layer of fine iron ore and the solid reductant in powder form stacked on the horizontally moving hearth by radiant heat transfer from above in the furnace, heat supply to the layer It is important how to carry out efficiently.

FIG. 1 is an explanatory view of a heat transfer mode of a movable hearth furnace. In the figure, 1 is a layer made of fine iron ore and a powdery solid reducing agent, 2 is a burner, 3 is a furnace body, and 4
Arrows indicate radiant heat transfer, and arrows 5 indicate heat conduction in the layer 1.

In such a form of heat transfer to the layer 1, the heat transfer efficiency can be improved by reducing the amount of radiant heat transfer from the flame of the burner 1 or the upper wall of the furnace body 3 on the upper surface of the layer 1. It is made possible by simultaneously increasing the amount of heat transfer and the amount of heat transfer from the upper surface of the layer 1 to the bottom of the layer 1.

Therefore, according to the present invention, an irregular shape is formed on the upper surface of the layer 1 and the following formulas (1), (2) and (3)
Is satisfied, it is possible to achieve an increase in the amount of radiation heat absorbed on the surface of the layer 1 and an increase in the amount of heat transfer from the upper surface of the layer 1 to the bottom thereof. A ≧ A ′ × 1.2 --- (1) L _max ≦ 120 --- (2) L × 0.8 ≦ distance between peaks of the irregularities on the upper surface of the layer --- (3) where A: upper part of the irregular-shaped layer Surface area (mm ² ) A ′: Upper surface area of layer when upper surface is flat (mm ² ) L _max : Maximum thickness of layer (mm) L: Average thickness of layer (mm)

The meaning of these equations (1), (2) and (3) will be described below. Meaning of A ≧ A ′ × 1.2 (1) Formula (1) specifically indicates that the upper surface of the layer 1 is not flat.

Here, the upper surface area A of the layer composed of the fine iron ore and the powdery solid reducing agent is defined. FIG. 2 is an explanatory diagram for defining the upper surface area A, 6 shows individual particles of fine iron ore or powdery solid reducing agent, and 7 shows the upper surface of the layer 1 formed by these particles. Show. The upper surface area A of the layer 1 in the present invention does not refer to the area of the fine uneven surface formed by connecting the outer peripheries of the individual particles located in the uppermost layer as shown in FIG.
The area of the surface formed by connecting the uppermost points of the individual grains located in the uppermost layer as shown in (b).

Effect 1 If the layer 1 composed of iron ore and the powdery solid reducing agent is a perfect black body, all the radiant heat transfer from above can be absorbed. Forming into a shape has no effect. However, it is actually a gray body, and a part of the radiant heat transfer from above is reflected. At this time, if the upper surface of the layer 1 is a flat surface, almost all of the radiated heat transfer reaches the upper wall surface of the furnace body, where a part of the heat is absorbed by the furnace wall and dissipated outside the furnace. .

Therefore, when the upper surface of the layer 1 is formed to have an uneven shape so as to satisfy the expression (1), specifically, by forming a wavy shape or a saw blade shape, a part of the radiant heat transfer from above is When reflected from the upper surface of the layer 1, a part of the reflected radiant heat transfer reaches the other upper surface of the layer 1 again, where a part of the heat is absorbed. That is, the amount of heat absorption is substantially larger than when the upper surface of the layer 1 is flat.

Here, FIG. 3 is an explanatory view showing radiation heat transfer behavior when the upper surface of the layer is wavy. In the figure,
The radiant heat transfer 4 reaching the point A on the upper surface 7 of the layer 1 is partially reflected. This reflected radiant heat transfer 8 reaches the point B on the upper surface 7 of the layer 1 where a part of the heat is absorbed.

Effect 2 In the process to which the present invention is applied, the amount of heat required for reduction must be supplied to the entire layer 1. The heat transmitted to the upper surface of the layer 1 by radiant heat transfer is supplied into the layer 1 by heat conduction.

The heat conduction inside the layer 1 due to the difference in the upper surface of the layer 1 will be described with reference to FIG. FIG. 4 is an explanatory view of the heat conduction in the layer. FIG. 4 (a) shows the case where the upper surface of the layer does not satisfy the condition of the equation (1) where the plane is flat, and FIG.
It is assumed that the condition of (1) is satisfied, the average thickness of the layer 1 and the upper surface temperature are the same in (a) and (b), and there is no heat loss from the hearth.

In these figures, the portion 9 on the upper surface of the layer 1 heated by the radiant heat transfer 4, that is, the zone to be heated by the radiant heat transfer can be considered as a heat source for heating the inside of the layer 1. Therefore, the upper surface 7 having a larger surface area, that is, a wider upper surface 7 of the heated zone 9 is more advantageous for heating the inside of the layer 1 than the case where the upper surface 7 is flat. On the other hand, looking at points C, D and E at the bottom of layer 1, point D when the upper surface 7 is wavy has a distance from heated zone 9 smaller than the average thickness of layer 1 and upper surface 7 is flat. Naturally, the temperature rises earlier than point C. When the upper surface 7 has a wavy shape, there always exists a point such as a point E whose distance from the heated zone 9 is larger than the average thickness of the layer 1. This E
At first glance, it seems that the heat transfer distance is longer, so that the temperature rise is slower than point C when the upper surface 7 is flat, but when the upper surface 7 is wavy as described above, the heated zone serving as a heat source 9
In addition, since there is an effect of being heated from directions other than the vertical direction as indicated by the arrow 5, the disadvantage of the length of the heat transfer distance is eliminated, and an extra heating effect can be obtained.

Meaning of L _max ≦ 120 --- (2) If the unevenness of the upper surface 7 of the layer 1 satisfies the above expression (1),
It is not a matter of increasing the average thickness of the layer 1 to any value. For example, as shown in FIG. 5 showing the top surface shape of the layer that deviates from the condition of the expression (2), the shape of the upper surface 7 of the layer 1 satisfies the expression (1), but the bottom surface of the layer 1 is too much. A portion such as point F, where the heat transfer distance to the point is too long, takes too much time for heating. Therefore, the expression (2) is necessary for exhibiting the effect of improving the heat conduction in the layer 1 by the expression (1) (the effect 2 described above).

L × 0.8 ≦ distance between peaks of layer unevenness The unevenness of the upper surface 7 of the layer 1 is obtained by the above-described formulas (1) and (2).
Is satisfied, the upper surface 7 may not have any irregularities such as wavy or saw-tooth shapes at any peak-to-peak distance.

For example, as shown in FIG. 6 showing an upper surface shape of a layer which deviates from the condition of the expression (3), the unevenness of the upper surface 7 is made to have a wavy shape with a very fine period with respect to the average layer thickness. The heat conduction in the layer 1 is substantially only in the vertical direction as in the case where the upper surface 7 is flat, and the effect of improving the heat conduction in the layer 1 according to the equation (1) (the effect 2 described above) ) Will not be exhibited. Therefore, it is necessary to satisfy Expression (3) in order to exert the effect.

Here, the peak-to-peak distance of the irregularities of the upper surface 7 of the layer 1 means, for example, when the irregularities are formed on the upper surface 7 by the saw blade leveling device shown in FIG. It refers to the distance between adjacent peaks in the shape of a blade. In the case where the unevenness is formed in a two-dimensional direction as shown in a bird's-eye view showing an example of the upper surface shape of the layer in which the unevenness is formed in the two-dimensional direction in FIG. It means the average distance between adjacent peaks.

FIG. 7 is an explanatory view of a saw-blade leveling apparatus. The saw-blade leveling apparatus 13 applies a saw-blade to the upper surface 7 of the layer 1 on the rotary hearth 12 rotating in the horizontal direction. The unevenness is formed.

Next, a description will be given of an experimental example on which the specific numerical ranges of the expressions (1), (2) and (3) are limited.
Using the electric furnace shown in FIG. 9, reduction experiments of fine iron ore were respectively performed under the conditions shown in Table 1 and FIG. 10.

[0027]

[Table 1]

FIG. 9 is an explanatory view of an electric furnace used for a reduction test of fine iron ore. Is heated while blowing nitrogen to reduce the fine iron ore. FIG. 10 is an explanatory view showing the unevenness of the upper surface of the layer under the experimental condition 1. The unevenness in this experiment was all saw-toothed.
The average thickness (L) and the maximum thickness (L _max ) of the sample, the distance between peaks of the irregularities on the upper surface 7, and the like were changed.

In an experiment using this electric furnace, a sample of the layer 1 comprising fine iron ore and a powdery solid reducing agent was charged into the furnace together with the container 11 when the furnace reached a specified temperature. After a lapse of a specified time, the sample was taken out of the furnace, cooled, and reduced, and the reduction ratio of the reduced sample was analyzed and analyzed. In addition, during this experiment, the input electric energy was controlled to be constant, and the nitrogen atmosphere in the furnace was controlled so that the gas generated from the layer 1 composed of the iron ore and the powdery solid reducing agent during the reduction was not burned. Was adjusted.

The reduction ratio of each sample thus obtained is also shown in Table 1 above. Table 1 shows the following. Layer 1
The required amount of heat naturally depends on the difference in the average thickness L, ie, the amount of sample charged.

In Experiment Nos. 1 to 12, the average thickness L of the layer 1 was 20 mm.
Is the condition. Among them, Experiment Nos. 1 to 4 correspond to Equations (1) and (2)
(3) are satisfied simultaneously (conform to the present invention), and the reduction ratio of these samples is excellent at 95% or more.

On the other hand, Experiment Nos. 5 and 6 correspond to the formula (1)
In particular, Experiment No. 5 is a case where the upper surface 7 is a flat surface, and these are inferior to the reduction rate of less than 90% even if the input power amount and the reduction time are the same as Experiment Nos. 1 to 4.

Compared with Experiment Nos. 5 and 6, the reduction rates of Experiment Nos. 7 and 8 in which only the reduction time was extended by 14%, and Experiment Nos. 9 and 10 in which only the input power was increased by 14% were 95%. That is all. However, in these, reduction rates equivalent to those of Experiment Nos. 1 to 4 were obtained by extending the reduction time or increasing the amount of input power, indicating that productivity or thermal efficiency was poor.

Experiment Nos. 11 and 12 deviate from the condition of equation (3), and have the same input power amount and reduction time as Experiment Nos. 1 to 4, but the reduction rate is inferior to 91% or less.

On the other hand, in Experiment Nos. 21 to 30, the average thickness of the layer 1 was
The condition is 80 mm. Among them, Experiment Nos. 21 to 24 correspond to Equation (1),
(2) and (3) are satisfied at the same time, and their reduction rates are all 95% or more.

On the other hand, Experiment Nos. 25 and 26 correspond to the formula (1)
In particular, Experiment No. 25 is the case where the upper surface 7 is flat, and these are the input power and the reduction time.
Despite being the same as 21-24, the reduction rate is inferior to less than 90%.

Experiment No. 27 which deviates from the condition of equation (2)
And 28 and Experiment Nos. 29 and 30, which deviate from the conditions of the formula (3), are inferior in the reduction ratio to less than 90% and less than 91% even with the same input power amount and reduction time as Experiment Nos. 21 to 24. .

It should be noted that even if the cross-sectional view of the upper surface shape of the layer in which the small wavy irregularities and the large wavy irregularities in FIG. While satisfying the condition, the condition of the formula (2) can be removed. Even in this case, if the condition of the formula (2) is not satisfied, an excellent reduction rate cannot be obtained.

As is clear from these experimental results, A
≦ A ′ × 1.15, L _max ≧ 125 mm or L × 0.7 ≧ Under the condition of the distance between the peaks of the irregularities on the upper surface of the layer, an excellent reduction rate cannot be obtained. It is limited.

[0040]

EXAMPLE Using the movable hearth furnace shown in FIG. 12, the operation under the following conditions was carried out on a trial basis, and the reduction ratio was examined.

FIG. 12 is an explanatory view of a movable hearth furnace having a rotary hearth, in which a rotary hearth rotating in a direction indicated by an arrow in the furnace body 3 is shown.
A layer 1 made of fine iron ore and a powdery solid reducing agent is formed on 12 and the burner 2 is burned to heat the layer 1 from above by radiant heat transfer.

The upper surface 7 of the layer 1 composed of fine iron ore and the powdery solid reducing agent is formed with an uneven shape by the surface leveling device shown in FIG. And as a suitable example that conforms to the present invention, the layer 1
And the average thickness of A / A 'was No. 1: 1.41,
2: 1.66, peak-to-peak distance between No. 1: 20 mm, N
o. 2: 40 mm. Naturally, these L _max values are 120 mm or less. Further, as a comparative example, a layer 1 was formed using a leveling device shown in FIG.
The thickness of the layer whose upper surface 7 was flat was 20 mm.

Thus, in the reduction operation, iron ore having a sieve of 6 mm or less and coal having a sieve of 6 mm or less are used as a powdery solid reducing agent, and these are mixed and moved at a weight ratio of 3: 1. To the upper hearth of the above-mentioned conforming examples No. 1, No. 2 and comparative example, respectively.
The furnace temperature was controlled to 1420 ° C. by adjusting the combustion of the burner 2. The residence time of the layer 1 in the furnace, that is, the reduction time, was kept constant at 23 minutes depending on the rotation speed of the hearth 12.

As a result, No. 1 of the adaptation example of the present invention and
No. 2 reduced iron had a reduction rate of 95% or more,
The reduction ratio of the comparative example was less than 90%.

[0045]

According to the present invention, in a reduction operation of iron ore in a movable hearth furnace, a specific uneven shape is formed on the upper surface of a layer comprising iron ore and a powdery solid reducing agent in the furnace. According to the present invention, since an excellent reduction rate can be obtained, the production of reduced iron per unit section of the hearth can be increased without increasing the fuel consumption.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a heat transfer mode of a movable hearth furnace.

FIG. 2 is an explanatory diagram for defining an upper surface area A.

FIG. 3 is an explanatory view showing radiation heat transfer behavior when the upper surface of a layer is wavy.

FIG. 4 is an explanatory diagram of heat conduction in a layer.

FIG. 5 is an explanatory diagram showing an upper surface shape of a layer that deviates from the condition of Expression (2).

FIG. 6 is an explanatory diagram showing an upper surface shape of a layer that deviates from the condition of Expression (3).

FIG. 7 is an explanatory diagram of a saw blade leveling device.

FIG. 8 is a bird's-eye view showing an example of a layer upper surface shape in which unevenness is formed in a two-dimensional direction.

FIG. 9 is an explanatory view of an electric furnace used in a reduction experiment of fine iron ore.

FIG. 10 is an explanatory diagram showing an uneven shape of a layer upper surface under an experimental condition 1.

FIG. 11 is a cross-sectional view of an upper surface shape of a layer in which small wavy irregularities and large wavy irregularities overlap each other.

FIG. 12 is an explanatory view of a movable hearth furnace with a rotary hearth.

FIG. 13 is an explanatory diagram of a leveling device for averaging an upper surface.

[Explanation of symbols]

 Reference Signs List 1 layer composed of fine iron ore and powdery solid reducing agent 2 burner 3 furnace body 4 radiant heat transfer 5 heat conduction in layer 6 individual particles of fine iron ore or powdery solid reducing agent 7 upper surface of layer 8 Reflected radiant heat transfer 9 Heated zone by radiant heat transfer 10 Heating element 11 Vessel 12 Rotary hearth 13 Upper surface leveling device

Claims (1)

[Claims] 1. A fine iron ore and a pulverulent solid reducing agent are supplied on a horizontally moving hearth and stacked in a layer having a predetermined thickness.
In a method for operating a movable hearth furnace in which iron ore is reduced by heating from above the furnace, an uneven shape is formed on the upper surface of the layer, and the uneven shape is expressed by the following formulas (1), (2) and (3) A method for operating a movable hearth furnace characterized by simultaneously satisfying (3). [Note] A ≧ A ′ × 1.2 --- (1) L _max ≤120 --- (2) L × 0.8 ≤Distance between peaks of unevenness on the upper surface of the layer --- (3) where A: Upper surface area of layer (mm ² ) A ′: Upper surface area of layer when upper surface is flat (mm ² ) L _max : Maximum thickness of layer (mm) L: Average thickness of layer (mm)