JPH0873914A - Production of molten steel in vertical scrap melting furnace - Google Patents

Abstract

PURPOSE: To obtain molten steel having low carbon concn. with a small scales apparatus without almost using the electric power by using a cupola type scrap melting furnace, filling a refractory block in the space from a blast tuyere surface to the furnace bottom and forming a carbonaceous material-filled layer having a specific height at the upper part from the tuyere surface. CONSTITUTION: The refractory block 5 having low carbon content is filled in the space from the blast tuyere 4 surface to the furnace bottom of the cupola type scrap melting furnace 1 having a molten steel tapping hole 2 at the lower end, a raw material charging hole 3 at the upper part and the heat tuyere 4 at the lower part. Then, the carbonaceous material-filled layer 6 is formed to the height H (m) from the blasting tuyere 4 to the upper surface of the carbonaceous material filled layer defined by H<=0.8D from the blast tuyere 4 surface upward. Wherein, D is the inner diameter (m) of the melting furnace 1 and the average diameter (m) of the used carbonaceous material of coke, etc., is preferably <=100mm. A layer 7 filled by mixing the ferro-scrap and the carbonaceous material is formed at the upper part of the carbonaceous material-filled layer 6. By this method, the steel having <=2% carbon concn. can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a vertical scrap melting furnace in which an iron source material such as iron scrap is melted with a carbon-containing material such as coke to obtain molten steel. In addition,
In the present invention, "molten steel" is defined as a molten iron alloy containing 2% by weight or less of carbon.

[0002]

2. Description of the Related Art Conventionally, molten steel is obtained by decarburizing and refining molten iron having a carbon concentration of 4.3 to 4.7% produced by a blast furnace in a converter or the like by supplying pure oxygen, or iron scrap. A common method is to obtain the product by heating and melting it in an arc electric furnace. On the other hand, even in the melting method using iron scrap as a raw material, for example, in cupola, this iron scrap is melted by the combustion heat of a carbon-containing material such as coke (hereinafter referred to as carbonaceous material). Is melted in the molten metal to obtain hot metal having a carbon concentration of 3 to 4%, and this hot metal is mainly used for castings.

Similarly, as a melting method using iron scrap as a raw material, there is a method using a crucible type induction furnace, which is also a method for producing molten pig iron or molten steel mainly for casting. Table 1 below summarizes the above methods according to (1) type of iron source and (2) type of molten metal to be produced.

[0004]

[Table 1] ──────────────────────────────────── Melting method Iron source Main raw material Manufactured Molten metal and carbon concentration ──────────────────────────────────── Converter converter Obtained by reducing iron ore Hot metal Molten steel 0.05 to 1.5% Electric furnace Iron scrap Molten steel 0.05 to 1.5% Cupola Iron scrap Molten iron 3 to 4% Induction furnace (for casting) Iron scrap Molten iron 3 to 4% or Molten steel to 1.5 ──────────────────────────────────── That is, various molten pig iron and molten steel production methods from iron source materials Among them, the converter method is excellent in mass production and is a process that is carried out all over the world.However, the main raw material is blast furnace hot metal, and not only converter equipment but also blast furnace, coke furnace, and iron ore pretreatment. Equipment (sintering furnace, Tsu capital equipment), it is necessary to other peripheral equipment,
Large-scale capital investment and vast factory grounds are required.

The electric furnace method is excellent in that molten steel can be obtained with a small-scale facility, but in Japan where the electric power price is high, the molten steel price is high and it is not an economical process. Also, in so-called developing countries where the power supply is unstable, the process of relying on the melting energy for power is disadvantageous in terms of operational stability. In addition, melting in an induction furnace has the same drawbacks as an electric furnace in that it also uses electric energy, and in addition to being small in terms of equipment, the production capacity is, for example, a maximum of several t / hr. Is.

On the other hand, since the cupola uses almost no electric power and the molten metal can be obtained with a small-scale facility, it does not have the drawbacks of the other processes described above. However, the molten metal obtained by a general cupola is a hot metal having a carbon concentration of 3 to 4%, and although there is no problem in casting production, steel products could not be produced. Therefore, for example, as disclosed in Japanese Patent Laid-Open No. 61-84309, a two-stage process (Duplex Pr) for refining molten pig iron produced by cupola by oxygen supply in a converter connected to the cupola to obtain molten steel as a final product
process) was invented. However, the two-step process has a problem that the operation becomes complicated and the capital investment becomes large.

As described above, there has been no means for obtaining molten steel by using a small-scale facility with almost no electric power.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a method for obtaining molten steel having a carbon concentration of 2% or less by using a small-scale facility and using almost no electric power. .

[0009]

As a means for solving the above problems, the present invention proposes a method for melting molten steel using a cupola-type scrap melting furnace that melts an iron source material with a carbon-containing material. . That is, in the operation method of the cupola-type scrap melting furnace, the refractory mass is filled between the blast tuyere surface and the furnace bottom, and the height above the tuyere surface is defined by the following formula H. A method for producing molten steel by means of a vertical scrap melting furnace, characterized in that a carbonaceous material packed layer is formed.

H ≦ 0.8D where H: height from blower tuyere to upper surface of carbon material packed bed (m), D: furnace inner diameter of melting furnace (m), the coefficient used in the above method It is preferable that the average diameter of the carbonaceous material such as coix is 100 mm or less.

[0011]

In order to clarify the gist of the present invention, description will be given with reference to the schematic view of the cupola type scrap melting furnace shown in FIG. 1 used in the present invention. The cupola-type scrap melting furnace 1 is provided with a tap hole 2 at the lower end, a raw material inlet 3 at the upper part, and a blower tuyere 4 at the lower part. Further, the first point of the present invention is that the refractory mass 5 having a low carbon content is pre-filled between the horizontal tuyere 4 and the furnace bottom.

It is necessary to select the refractory mass 5 that is not easily corroded by the flow of molten steel and has a low carbon content.
For example, fired dolomite bricks, high-alumina bricks, etc., such as magcro bricks can be used. A filling layer 6 of carbonaceous material is formed above the tuyere 4 in the furnace. Usually, it is a packed bed called coke bed using coke. Also,
It is also possible to use a molded coke which is not fired, a lump of earth-like graphite, a lump of coal, or a powder of these, which are singly or mixed to form a lump (form). H and D shown in the figure correspond to the height from the tuyere surface to the upper surface of the carbon material filling layer 6 and the furnace inner diameter, respectively. The second point of the present invention is to control the relationship between H and D such that H ≦ 0.8D.

Above the carbonaceous material-filled layer 6, there is formed a layer 7 in which the iron scrap and the carbonaceous material charged are mixed and filled. The iron scrap in this layer 7 is heated while descending in the furnace, and is melted at a position near the upper surface of the carbon material-filled layer 6,
The carbonaceous material-filled layer 6 becomes droplets, passes through the refractory mass 5 at the bottom, and is discharged from the tap hole. On the other hand, the carbonaceous material in the layer 7 portion also descends and reaches the upper surface of the carbonaceous material-filled layer 6.
The carbonaceous material in the carbonaceous material packed bed 6 is constantly oxidized (combusted) by oxygen in the blown air and consumed as CO or CO ₂ . Therefore, the height H of the carbonaceous material packed bed in the figure can be controlled by adjusting the balance between the supplied carbonaceous material supply rate and the air flow rate.

The height H can be measured by a bed coke height measuring device disclosed in Japanese Patent Laid-Open No. 2-235987. In this measurement method, the iron skin near the estimated height of the bed coke is changed from its outside to a plurality of heights and hit by a hitting element, and the impact sound determines whether the bed coke existing in the furnace and the molten material. This is a method of measurement by comparing the relationship between the sound pressure level and time due to the difference in specific gravity. Of course, the height of the bed coke may be measured by using other physical means.

In operation, the refractory lumps filled in the furnace bottom are gradually melted and consumed by the molten steel and molten slag. To compensate for this, a refractory mass is sometimes charged from the raw material charging port 3. The iron source material (mainly iron scrap) that can be used in the present invention is not particularly limited, but since molten steel is manufactured, the total amount of the iron source to be charged cannot be pig iron. This is because a new process is required to decarburize the once dissolved carbon. Assuming that carbon is not absorbed in the furnace, the material balance is taken, and the combination of steel scrap and pig iron scrap as the iron source may be determined so that the desired carbon concentration in the molten steel is obtained. However, even if the total amount is steel scrap, it is possible to obtain a desired molten steel within the scope of the present invention by adjusting the blowing conditions.

In developing the present invention, a test cupola was used, the inner diameter of the furnace was φ0.3, φ0.6, and φ0.9 m, and the average coke diameter as carbonaceous material was 40 m.
m or less, 40 to 80 mm, 80 to 100 mm, 100 to
The melting operation of the iron scrap was performed using five types of 200 mm and 200 mm or more, respectively. As the iron scrap, shredder scraps of steel and mold pigs were used, and the former was 70% and the latter was 30% from the initial operation to the stable operation. Only about 1 hour later, the former formulation was used. This is a countermeasure to deal with the risk of solidification in the furnace if molten steel is directly produced since the temperature of the furnace is low at the beginning of operation.

As a carbonaceous material, a blast furnace coke was used after sieving. Like the iron source material, the bed coke height is set slightly higher until the operation enters the stable period, and after the stable period, the coke composition in the charging raw material is adjusted to adjust the bed coke. I changed the height. Average concentration of discharged carbon, coke average particle size and bed coke during stable operation
The relationship between the height H from the tuyere of the cous and the inner diameter of the furnace is shown in FIGS.

By controlling the height H of the carbonaceous material-filled layer 6 to be 0.8 times or less of the furnace inner diameter D, molten steel having a carbon concentration of 2% or less can be obtained for any cupola of the furnace inner diameter. did it. In particular, when the coke average particle size is 100 mm or less under the condition of H ≦ 0.8 × D, molten steel having a carbon concentration of less than 2% can be reliably obtained. The coke average particle size is 1
Molten steel can be obtained by operating H under a smaller condition even if it exceeds 00 mm.

The curves in FIGS. 2 to 4 show a carbon concentration of 0.5%.
The following iron scraps are used as raw materials, and the coke average particle size is 8
It is a curve that connects points (including some estimations) of slightly higher carbon concentration in the data showing the relationship between the carbon material packed bed height H and the carbon concentration under the condition of 0 to 100 mm, and which furnace inner diameter Also in the case of H = 0.8 × D, it can be seen that the line intersects with a straight line having a carbon concentration of 2%.

The lower limit of the height of the carbonaceous material-filled layer is not particularly limited, but if it is too low, the heat of dissolution is insufficiently generated, so that it is preferably about 0.4D or more. Now, the present invention requires that the space from the tuyere surface of the melting furnace to the furnace bottom is filled with a refractory mass having a low carbon content to prevent the carbonaceous material packed bed from descending. This is because if a carbonaceous material packing layer exists below the tuyere surface, the molten steel absorbs carbon during the dropping, resulting in a carbon concentration of more than 2%, and further a carbon concentration of more than 3%. It is because it is taken out of the bath.

In this case, the fact that the refractory mass having a low carbon content is filled up to the tuyere surface can be confirmed from the peep window provided at the tuyere. As described above, filling the refractory mass from the tuyere surface to the furnace bottom proposed in the present invention, and setting the height H of the carbonaceous material packed layer above the refractory mass to 0.8 times the furnace inner diameter D. Molten steel with a carbon concentration of 2% or less can be obtained by
In particular, by setting the average particle size of the carbonaceous material to 100 mm or less, molten steel having a carbon concentration of 2% or less can be reliably obtained.

The reason why the carbon concentration of the molten metal can be lowered by using the carbonaceous material having a small particle diameter of 100 mm or less is not clear. However, the small-diameter coke has a high burning rate and becomes a smaller diameter faster. Therefore, it was considered that the ratio of carbon used for carburization (carburizing) in the coke bed was reduced, and the carbon concentration in the molten metal was unlikely to rise.

[0023]

EXAMPLES The cupola operation under the conditions proposed by the present invention has already been described above, but an example of the operation for producing molten steel will be described in more detail. First, as the melting furnace, a cold air blowing cupola having a furnace inner diameter of 0.6 m, a height of 0.4 m from the furnace bottom to the tuyere, and a height of 5 m from the tuyere to the raw material charging port was selected. As for the tuyere for blowing, 6 pieces with a diameter of 50 mm are installed.

The raw material is charged from a size of 40 mm to 2
170 kg of high alumina brick scraps of about 00 mm were filled from the furnace bottom to the tuyere surface. I confirmed the height from the viewing window in the tuyere. Subsequently, coke lumps having an average particle size of 80 to 100 mm were piled up from the tuyere to a height of about 1 m, and the coke was ignited by an ignition propane burner charged from one of the tuyere. About 1 in the furnace due to combustion of coke
After heating for an hour, 120 kg of coke was added, and then scrap and coke were alternated at 2700 k each.
g, 250 kg was charged. The scrap at this time is type 3
The composition was 0% and shredder-steel scrap 70%.

This state was maintained for about 1 hour and full blown air was started. The blast flow rate was 2400 Nm ³ / hr. About 1
After 7 minutes, the tap hole on the bottom of the furnace was opened and tapping was started. After starting the tapping, 320 kg of shredder steel scrap, 30 kg of coke and 10 kg of limestone were simultaneously intermittently charged from the charging port 3 at the top of the furnace every 6 to 7 minutes. In addition, 5 kg of high alumina brick scraps was mixed in once every three times the raw material was charged.

FIG. 5 shows trends such as the concentration of discharged carbon during operation, temperature, and blowing conditions. After about 1 hour from the start of air blowing, the carbon concentration changes between 0.8 and 1.0%, indicating that molten steel is continuously obtained. In this case, the height H of the coke packed bed during operation was in the range of about 0.35 to 0.40 m. The measurement of H was performed by visually judging the presence or absence of red-hot coke from a viewing window installed at several points in the height direction of the furnace wall.

[0027]

Industrial Applicability According to the present invention, it becomes possible to produce molten steel by using scrap as a base in a cupola type melting furnace of a small-scale facility.
It has become possible to obtain molten steel economically without passing through a converter or an electric furnace for melting with expensive electric power.

The present invention is not limited to the production of ordinary steel,
As a raw material, ore of alloy iron and alloy components (manganese ore,
Chromium ore, etc.), or scraps containing alloy components and wastes (Ni catalyst scraps, stainless steel scraps) can be added as raw materials, so that alloy steel can be manufactured.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a cupola-type melting furnace.

FIG. 2 is a graph showing the relationship between the height of a carbonaceous material packed bed and the average carbon concentration of discharged carbon.

FIG. 3 is a graph showing the relationship between the height of the carbonaceous material packed bed and the average carbon concentration of discharged carbon.

FIG. 4 is a graph showing the relationship between the carbonaceous material packed bed height and the average discharged carbon concentration.

FIG. 5 is a chart showing a trend of operating conditions.

[Explanation of symbols]

 1 Melting furnace 2 Outlet port 3 Raw material input port 4 Blower tuyere 5 Refractory lump 6 Carbon material filling layer 7 layers

Claims (2)

[Claims] 1. In a method of operating a cupola-type scrap melting furnace, a refractory mass is filled between a tuyere surface for blowing and a furnace bottom, and a height defined by the following formula H is provided above the tuyere surface. A method for producing molten steel using a vertical scrap melting furnace, characterized in that a carbonaceous material packed bed is formed. H ≦ 0.8D where H: height from blower tuyere to carbonaceous material packed bed upper surface (m), D: furnace inner diameter of melting furnace (m), 2. The method for producing molten steel by means of a vertical scrap melting furnace according to claim 1, wherein a carbonaceous material having an average diameter of 100 mm or less is used.