JPH0483815A - Melting-reduction iron manufacturing method - Google Patents

Abstract

PURPOSE:To enable use of general coal and to efficiently manufacture molten iron by using such coal subjected to specified treatment in the process of melting-reduction refining of iron oxide source material in a top and bottom blown metallurgical furnace. CONSTITUTION:The molten iron alloy is manufactured by supplying the source material containing iron oxide and the coal material to a top and bottom blown metallugical furnace while introducing oxygen gas thereto to effect melting and reduction of the iron oxide. In this process, there are four steps: before the source material and coal are supplied to the furnace for melting-reduction method, the coal together with the source powder is clasified with a sieve of >=3mm mesh (first step), the powder and coal passed through the sieve is pulverized to <=1mm particle size and compression molded (second step), the residual powder and coal on the sieve is heated at >=600 deg.C (third step), and the coal and treated iron source obtained in the second and third steps are both supplied to the furnace for melting reduction (forth step).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention efficiently uses thermal coal, which is the cheapest available as a carbon material, when producing a molten iron alloy from iron ore or its pre-reduced product by smelting reduction. Concerning methods for use in.

[Prior Art] A blast furnace method is currently used as a mass iron manufacturing method. The blast furnace method is an excellent process in terms of productivity and thermal efficiency, but the problem is that ore requires an agglomeration process such as sintering, and coal requires a coking process. In addition, in order to produce coke with high strength, it is necessary to use a specific type of coal called coking coal.

The smelting reduction method is a new process being developed to solve these problems with the current blast furnace method.

Research and development is currently underway as one of the smelting reduction methods, and some problems have already been solved in a method that utilizes the presence of a large amount of slag using a metallurgical furnace that can blow gas from the top and bottom. However, the issue of coal still remained.

In other words, in order to solve the coal problem of the blast furnace method, it is desired to develop a process that uses inexpensive steam coal and does not require a coking process. For these reasons, it was difficult to solve the problem.

First, sift the coal into chunks (for example, about 10 mm).
(above)), and when it is fed into the melting reduction furnace from above,
Rapid heating causes rapid vaporization of volatile components, leading to thermal cracking and an average particle size of about 3 mm. As a result, the following two problems arise.

■ The scattering rate of carbon material is 10% or more.

■ It becomes difficult to get caught up in carbonaceous material or slag, which delays carburization into the metal bath and makes operation unstable.

On the other hand, the method of adding powdered coal from above has a scattering rate of 30%.
In the method of blowing powdered coal into metal, the agitation of the metal accompanying the blowing becomes strong and the amount of iron-based dust generated increases due to the plow. It has been found that the method of using a chemically modified material has problems such as when it is rapidly heated in a furnace, it becomes a caking material or a gas generating material and breaks into small pieces.

As described above, in the conventional method, coal pulverization remained an unavoidable problem, and as a result, stable melting and reduction operations could not be performed.

Furthermore, if the volatile content is too high relative to the fixed carbon content of the carbon material fed into the smelting-reduction furnace, there is a problem of increasing the oxygen consumption rate in the smelting-reduction process. That is,
The fixed carbon content is necessary for the reduction and carburization of oxides, or if the volatile content, which can only be used for combustion and heat generation in the smelting reduction furnace, exceeds the fixed carbon content, secondary combustion occurs. When the rate is high, there is a surplus of r heat (relative to the amount required for the reduction reaction), and in order to adjust this, the secondary combustion rate is lowered, resulting in less oxygen gas per unit calorific value. The amount increases.

The amount of oxygen gas has a great influence on factors related to economic efficiency, such as refractory wear, dust generation, and productivity. in this way,
When steam coal with a high volatile content is used, a problem arises in that it greatly impairs the economic efficiency of melt reduction in normal operations.

[Problems to be solved by the invention] The present invention solves two problems when steam coal with powder is used as a raw material.
We have solved two problems, namely the problem of powdering when rapidly heated in the smelting reduction furnace, and the problem of adjusting the volatile content and fixed carbon content of the carbon material in the smelting reduction furnace to an appropriate state.
The aim is to solve this problem by optimizing the treatment of coal before feeding it into the smelting reduction furnace.

[Means for solving the problem] A metallurgical furnace capable of top-bottom blowing of cogas is used to supply oxygen gas while adding raw materials containing iron oxide and carbonaceous material, melting and reducing iron oxide to produce molten iron alloy. In the manufacturing process,
A first step of sifting the coal with powder through a sieve of 3 mm or more before being introduced into the metallurgical furnace for melting and reduction;
The second part crushes the bottom of the sieve to 1 mm or less and compression molds it.
A third step is carried out in which the top of the sieve is heated to 600°C or higher together with the ore, and then the carbon material and the treated ore obtained in the second and third steps are both charged into the metallurgical furnace and melted and reduced. A feature of the present invention is that the fourth step is performed.

[For production] FIG. 1 shows the process flow of the method of the invention.

Hereinafter, the present invention will be specifically explained in detail with reference to FIG. 1, together with its operation.

Coal is mixed with powder and contains moisture at 12
Heat to 0° C. or higher and dry until the amount of adhering water is 3% or less. This is necessary for sifting the powder in the first step in FIG. 1, and is also an effective pretreatment for agglomeration in the third step. As a heat source for drying, sensible heat of exhaust gas generated during the melting and reduction process can be used.

The purpose of the sieving in the first step of the present invention is to: (1) remove the particles of at least 3n+m or less in particle size from which there is a risk of scattering when the coal is finally put into the smelting reduction furnace if it is not agglomerated in the subsequent steps; ■ Separating the VM (under the sieve), and
Adjusting the ratio of materials that reduce volatile content (volatile matter) and materials that are put into the smelting-reduction furnace without heat treatment, so that the average VM content of the carbon material at the time of putting it into the smelting-reduction furnace is 20% or less; There are two.

The relationship between the average VM content of the carbon material charged into the smelting reduction furnace and the oxygen consumption rate required to produce indexed iron 1 is expressed as the second
As shown in the figure. From the relationship shown in FIG. 2, it can be seen that it is desirable that the average VM content of the carbon material charged into the melting reduction furnace is 20% or less, as described above.

Therefore, the mesh size of the sieve is selected depending on the situation of the coal to be used so as to satisfy the above two conditions, but usually 3
It is within the range of ~7mm.

Next, in the second step, the screened portion of the coal is agglomerated. There are various agglomeration methods, but in the present invention, it is important not to use a caking agent that generates gas that can cause cracks when rapidly heated in a smelting reduction furnace. For this purpose, in the present invention, compression molding is performed using rolls.

Prior to molding, the coal is re-ground. In order to obtain the necessary strength by roll compression molding, the grain size of the coal must be lIn
It is necessary to keep it below In. Also, add 3 liters of water
It is also necessary to keep it below %.

Incidentally, during this molding, a part of the dust generated in the melting reduction furnace can be mixed with the coal.

Figure 3 shows the relationship between the thickness of the roll-formed product and the generation rate of powder of 1 mm or less during rapid heating. It can be seen that the powder generation rate is minimized when the thickness is 2 to 8 mm.

The roll-formed product is divided into appropriate sizes and charged into a melting reduction furnace.

In the present invention, the reason why this roll-formed product is not heated outside the melting reduction furnace is that no caking agent is added, and the edges of the roll-formed product that are split have relatively low strength. This is because powdering progresses during subsequent handling, which ultimately increases the powder generation rate at the time of feeding into the melting reduction furnace.

On the other hand, in the third step, the portion above the sieve in the first step is heat-treated together with the ore. That is, once the ore has been heated to a reducible state in a furnace, such as a rotary kiln, the sieved portion of the coal is added. The heated coal generates VM volatiles, which react with the heated ore to pre-reduce the ore.

FIG. 4 shows the relationship between the ore heating temperature, the utilization efficiency of VM for ore reduction, and the powder generation rate of lump coal. From this figure, from the viewpoint of effectively utilizing VM for ore reduction, it is desirable that the temperature is 600'C or higher. Further, from the viewpoint of powdering, it is desirable that the temperature is 800°C or less.

In addition, unlike when lump coal on a sieve is directly charged into a smelting reduction furnace, by adding it to moderately heated ore as in this invention, the heating rate is significantly reduced and thermal cracking can be prevented. I can do it.

As mentioned above, in the third step, the ore and the coal on the sieve are input, and the sensible heat and latent heat of the gas discharged from the smelting reduction furnace are used to heat the coal without thermal cracking and turn it into char. At the same time, the ore is pre-restored. These are all desirable conditions for reducing the oxygen consumption rate and carbon material consumption rate in the smelting reduction furnace in the fourth step.

The molded carbonaceous material produced in the second step and the char from the lump coal and the pre-reduced ore produced in the third step are charged into a smelting reduction furnace in the next fourth step.

The appropriate operating conditions for the fourth step are as follows.

The metallurgical furnace used to carry out the present invention is a furnace capable of blowing gas from the top and bottom, as shown in FIG. In such a furnace, stirring is performed by blowing a gas such as nitrogen into the melt from the bottom. This stirring maintains the temperature of the molten material uniformly, promotes heat transfer, and promotes the reduction reaction of iron oxide in the molten slag 3, which is an essential requirement in the implementation of the final method. .

However, if the amount of bottom blowing gas is too large, the amount of metal grains mixed into the slag layer 3 will increase, resulting in undesirable phenomena caused by direct contact between the oxygen jet from the last layer 1 and the metal grains.
That is, a decrease in the secondary combustion rate (defined as the secondary combustion rate) and an increase in the amount of dust generated occur. Therefore, there is a suitable gas injection rate, which is in the range of 5 to 45 N+n'/h per molten metal in the furnace.

Smelting reduction is carried out by adding iron raw materials containing iron oxide (iron ore, preliminary reduction products thereof, etc.) and carbonaceous material without top-blowing oxygen. Gas such as GO generated from the carbonaceous material is combusted by this top-blown oxygen and generates heat, and the iron oxide reduction reaction in the slag progresses due to the carbon dissolved in the carbonaceous material and metal grains. As a result, carbon melts into the formed metal, forming a molten iron alloy, which settles into the metal bath.

Here, if the temperature of the molten material becomes too high, it will have a negative effect on the wear and tear of the refractory, so by appropriately adjusting the relationship between the blowing acid rate and the raw material supply rate, the temperature of the molten material can be raised to 20° above the melting point of the metal. Try to keep the temperature within the range of ~150℃ higher.

The molten slag layer 3 in the furnace is important in the present invention as it blocks direct contact between the oxygen jet and the metal bath 5. The larger the amount of slag, the more advantageous it will be to the operation of this bumsess. In other words, the oxygen gas supply rate can be increased, and at least the metal 1 present in the furnace can be increased.
More than 350 kg of slag is required per ton.

However, the fact that a large amount of slag exists in the furnace during operation does not mean that a large amount of slag is generated when Metal 1 is hit.

This is because when the generated metal is discharged outside the furnace, the required amount of slag remains in the furnace and the next heat operation is performed, so the amount of slag in the furnace can be adjusted arbitrarily without increasing the amount of slag generated. This is because it is adjustable.

A large amount of slag is placed in a reaction container having a predetermined volume,
In order to prevent the slag from flowing out of the furnace, it is necessary to coexist with the carbonaceous material 6 to coalesce the fine bubbles in the slag layer 3 and promote the dissipation of the bubbles 4. The amount of carbon material required for the dump is 5 to 50 wj% of the weight of the slag.

It should be noted that the powdered coal formed in the second step is difficult to powder even if it is put into a melting reduction furnace and subjected to rapid heating. The reason for this is presumed to be that the anisotropy peculiar to coal is reduced by molding the powder, and the voids present in the molded product absorb distortion due to vaporization of VM.

Furthermore, since the char obtained in the third step already has a low VM content, it will not undergo thermal cracking even if it is rapidly heated in a melting reduction furnace.

Furthermore, unless the ore moves to the molten slag layer 3 without scattering in the space, it will not scatter thereafter because it has the property of being wetted by the molten slag.

As described above, by implementing the present invention, the cracking and scattering of coal, which had been a problem in the development of the smelting reduction method up to now, and the various problems caused by these, can be solved by taking advantage of the state of lumps and powder when the coal is received. Can be solved with minimal processing.

Example] Examples of the present invention will be described below.

First, Table 1 shows the status of coal used in the first step of the present invention (
components) and their processing conditions.

In the next second step, the sieve obtained by sieving based on the processing conditions in Table 1 is pulverized to 10] m or less, and after confirming that the particle size is as shown in Table 2, Furthermore, roll molding was carried out under the same compression molding conditions shown in Table 2. On the other hand, in the third step, using a rotary kiln, the sieve obtained in the first step is heated under the processing conditions shown in Table 3 together with iron ore in the situation (components and particle size distribution) shown in Table 3. Then, char was obtained from lump lime and iron ore was pre-reduced.

[Actually, the carbonaceous material (roll molded product) obtained in the second step, the carbonaceous material (char) obtained in the third step, and the pre-reduced ore are combined, charged into a metallurgical furnace, and the 344th step is carried out. carried out. Table 3 shows the situation of the mixed charge at this time, and Table 4 shows the operating conditions and operational results of the melting reduction treatment in the metallurgical furnace after charging was completed, as well as the situation (components) of the obtained product.
Shown below.

Table 4 In addition, FIG. 5 is an example of the melting reduction furnace equipment used to implement the fourth step of the present invention. In a container lined with refractory material 2, a bottom blower lower is provided at the bottom for blowing an inert gas such as nitrogen into the molten metal to stir it.

The top blow lance 1 is for supplying oxygen gas into the furnace. On the other hand, ore is supplied into the furnace from an input port 8 provided in the furnace layer. A large amount of slag exists in the furnace, and it is necessary to shut off the bottom-blown and agitated metal bath 5 from the oxygen shed of the top-blown lance 1. The required amount of slag is 350 kg/l metal or more, and when the metal and slag produced by tilting the furnace are discharged, some slag is left in the furnace to adjust the amount of metal and slag.

Therefore, from the operational results of this example shown in Table 4, the generation rate of carbonaceous material powder (1 mm or less) and the average wear rate of refractories are both at a low level, and the secondary combustion rate is within the appropriate range (generally 4 mm or less).
0 to 50%), it can be seen that the present invention provides a very effective means for suppressing the pulverization of steam coal when it is applied to the smelting reduction method.

[Effects of the Invention] By carrying out the present invention, it is possible to efficiently carry out smelting reduction operations using high VM steam coal accompanied by powder, which can be done manually at low cost. Therefore, economic efficiency can be greatly improved. It has great industrial effects as it can improve the

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the process flow of the present invention, and Fig. 2 shows that the average VM content of the carbon material at the time of charging into the smelting reduction furnace is the oxygen source in the smelting reduction furnace in the fourth step of the present invention. Figure 3 shows the relationship between the thickness of the roll compression molded product and the powder generation rate during rapid heating, and Figure 4 shows the influence on the unit.
FIG. 5 is a diagram showing the relationship between the ore heating temperature in the third step of the present invention, the utilization efficiency of VM generated from coal for ore reduction, and the relationship between the powder generation rate of lump coal.
It is a figure showing an example of the equipment used to carry out a process. 1...Lance 3...Slag layer 5...Metal thin valley 7...Bottom blowing tuyere 2...Refractory 4...Bubble 6...Charcoal material 8...Inlet and others 4 Figure 4: Thickness of roll compression molded product (■) Figure 4: Average VM content of carbon material charged into the fusion furnace

Claims (1)

[Claims] 1. Using a metallurgical furnace capable of blowing gas from the top and bottom, oxygen gas is supplied while adding a raw material containing iron oxide and carbonaceous material,
In the process of melting and reducing iron oxide to produce a molten iron alloy, the carbonaceous material fed into the metallurgical furnace is coal treated by the following steps 1 to 3,
A smelting reduction iron manufacturing method using coal, characterized in that it is processed according to the following fourth step. 1st step: Sift the coal with powder through a sieve of 3 mm or more. 2nd step: Pulverize the bottom of the sieve to 1 mm or less before compression molding. 3rd step: Heat the top of the sieve together with the ore to 600°C or above. Step: Both the carbonaceous material and treated ore obtained in the second and third steps are charged into the metallurgical furnace and melted and reduced.