JP3037062B2 - Operating method of scrap melting 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 method for operating a scrap melting furnace, and more particularly to a method for producing a molten metal characterized by controlling the quality of a molten metal and increasing the heat efficiency at a low coke ratio to melt the scrap. .

[0002]

2. Description of the Related Art As a shaft type scrap melting process, there is a cupola method. In the cupola method, scrap and coke are charged in layers or mixed from the upper part of the furnace.
Hot-air cupola with one-stage tuyere at a blowing temperature of around 500 ° C There are two-stage tuyere cold-air cupola with normal-temperature air blowing. Both cupolas have coke quality of C92%, ash content of about 8%, and particle size of 15%.
There is a need for a high-cost casting coke of 0 mm or more.

[0003] When a casting ratio of 30% to 60% (scrap 70% to 40%) is used and a coke for casting is used, the fuel ratio is about 120 to 140 kg / t.
The secondary combustion rate η _CO (= CO ₂ / (CO + CO ₂ )) is operated at around 40% with a hot air cupola and around 50% with a two-stage tuyere / cold air cupola. This secondary combustion rate is affected by the degree of progress in equation (2) following the C combustion reaction in equation (1).

C + O ₂ → CO ₂ +97,000 kcal / (kmol · C) (1) C + CO ₂ → 2CO−38,200 kcal / (kmol · C) (2) When using blast furnace coke having a particle size of 60 mm or less, an endothermic reaction occurs. Since the reaction progress of a certain formula (2) is fast, the secondary combustion rate η _CO is definitely reduced, and the solubility of the scrap is deteriorated. Therefore, in the prior art, in order to reduce the reaction rate of the formula (2), a high-cost casting coke having a particle size of 150 mm or more was required.

In the case of a cupola having a two-stage tuyere,
The CO gas generated at the primary tuyere is burned into CO ₂ by the exothermic reaction (3), and the reaction heat is used for heating and melting scrap, coke, and the like.

CO + 1 / 2O ₂ → CO ₂ +67590 kcal / (kmolt.CO) (3) However, even in this method, when the scrap and the coke are mixed or charged in a layered form, if the coke temperature is 900 ° C. or higher, the secondary The CO ₂ gas generated by the combustion reacts with the coke and starts producing CO by the so-called carbon solution loss reaction shown in the above formula (2). Here, the generated C
Since the O gas is exhausted to the outside of the furnace without being burned, coke is consumed unnecessarily. Further, since the equation (2) is an endothermic reaction, heating and melting of the coke as well as the scrap are hindered. In addition, oxygen enrichment rate of 3%
The temperature before the tuyere at the primary tuyere is low for the following operations.
60% (scrap usage ratio 60 to 40%) must be used.

As described above, in the current cupola operation, the operation is performed with the exhaust gas composition η _CO ^(TOP) ≦ 55%, even if expensive casting coke having a large particle size is used. Operations are in a difficult situation.

In order to use blast furnace coke of 60 mm or less, Japanese Patent Laid-Open No. 3-111505 discloses that scrap and coke are mixed or charged in layers.
In a cupola-type melting furnace having a secondary tuyere, a method for improving the blowing method of the secondary blowing tuyere has been proposed.
This is because an inert carrier gas, such as N 2, is used in place of the combustion supporting gas in order to suppress the carbon solution loss reaction accompanying the overheating of the coke for the next melting, which is charged above the level of the secondary tuyere. _The method is characterized in that powdered limestone and / or iron ore are respectively blown by using ( ₂₎ . Judging from the example, the fluctuation of the secondary combustion rate is reduced, which contributes to the reduction of the solution loss reaction. However, since the value is about 45%, the solution loss reaction of the formula (2) still exists. Suggests that Operationally, there is the complexity of adjusting the secondary air flow according to time or scrap layer descent.

As described above, it is difficult to suppress the solution loss reaction of the formula (2) when the scrap and coke are charged in layers or mixed from the furnace top.

Japanese Unexamined Patent Publication (Kokai) No. 1-501401 discloses a hot metal manufacturing apparatus comprising a blast furnace having tuyere and a hearth having a diameter larger than the diameter of the blast furnace and having a tuyere. In this furnace, only the ore is charged without adding fuel from the furnace top, and the fuel is directly added onto the fuel bed at the joint between the blast furnace and the hearth. When this furnace is used for melting scrap, the solution loss reaction does not proceed in the blast furnace because the fuel layer does not exist in the blast furnace, and efficient operation with high exhaust gas η _CO ^(TOP) can be expected. However, for efficiency,
It was necessary to set a large hearth for the blast furnace.

However, the coke charging portion is a region that comes into contact with the high-temperature gas, and has problems in terms of facilities such as securing heat resistance and sealing against gas leakage. In addition, there is a concern about damage to the side wall bricks and hanging of shelves due to the formation of deposits in the blast furnace. Due to such a furnace structure, it is considered difficult to increase the size of the equipment, and it is difficult to apply the method to melting a large amount of scrap. Also, since the coke charging site is fixed, the coke charging area is defined, and when the coke ratio changes,
As a result of different coke consumption rate and scrap melting rate,
The complexity of charging, such as different charging cycles for coke charging and scrap charging, is also conceivable. According to an operation example that is considered to be applied to scrap melting, the use ratio of casting waste containing carbon is about 60%, and there is no record as to whether or not operation is possible when a large amount of scrap is used.

The present inventors have avoided the above-mentioned drawbacks of the prior art and have proposed a method of melting blast furnace coke having a size of 60 mm or less and a large amount of scrap by using coke in the periphery of the furnace. The Japanese Patent Application No. 05-239272 and Japanese Patent Application No. 05-239
248515. This is a shaft-type scrap melting method that suppresses the carbon solution loss reaction of equation (2) in the furnace to increase thermal efficiency and reduce fuel consumption, while taking into account a simple furnace structure that allows for large-scale equipment. It relates to a furnace. In this case, the coke layer and the scrap layer are separated in the radial direction, and it is not considered to mix and use fine-grained scrap in the coke layer.

On the other hand, regarding the central charging method of coke,
Improvements in the blast furnace operation method are disclosed in Japanese Patent Application Laid-Open No. 64-65209 and Japanese Patent Application No. 4-185495. In the blast furnace operation method, it is considered important to ensure ventilation and liquid permeability of the furnace core, and the central charging coke contributes to renewal of the furnace core and is a means to secure and improve gas permeability. It is considered. Therefore, it is desirable that the central charging coke is as large as possible.

Regarding the supply of carburizing material into the molten metal,
In the normal cupola operation method, in addition to the combustion reaction at the tuyere and the amount of solution loss reaction with the rising gas in equation (2), the amount of coke including the amount of carburizing into the molten metal was charged from the upper part of the furnace. .

The prior art of mixing and charging coke with scrap is commonly found in the cupola process, but most of the scrap particle size is 50 mm or more. There is no idea of limiting the scrap to 12 mm or less and using it for controlling the air permeability in the furnace.

[0016]

In the peripheral coke charging method in the scrap melting method proposed by the present inventors, operation with higher reaction efficiency can be achieved as compared with the prior art, but with an increase in the amount of scrap used. Therefore, it was necessary to supply C material necessary for carburizing the molten metal. Usually, coke had to be charged at appropriate intervals as a carburizing material from the center of the furnace into which the scrap was charged to the middle. However, some of the coke for the purpose of this carburization, for consumption by causing a combustion reaction with the CO ₂ in the lower part of the furnace, when the carburized stock feeding to melt, adding minute amount of coke to be burned in the furnace bottom The additional coke and the coke ratio increased, and the reaction efficiency decreased.

An object of the present invention is to provide an operation method for efficiently supplying a carburizing material to a molten metal and suppressing an increase in a coke ratio.

[0018]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is an operation of a shaft type scrap melting furnace in which coke is charged from the furnace top to the periphery of the furnace and scrap is charged from the center to the middle. In the method, as a method of replenishing the carburizing material to the molten metal, coke is charged separately from peripheral coke so that coke supplied as a carburizing material is not consumed by the solution loss reaction of the formula (2). In that case,
It is desirable to reduce the central charging coke amount as much as possible,
Center charged coke weight / charged scrap weight = 3/10
It is characterized in that charging is performed at a weight ratio of 0 to 1/25, and the amount of coke charged in the vicinity is reduced by the amount of coke.
Further, the present invention is characterized in that the coke particle size is reduced or fine-grained scrap is mixed and used in the coke layer so that gas does not flow in the peripheral portion and the central charging coke.

Assuming that the boundary radius position between the central charging scrap and the peripheral charging coke is R _S and the furnace opening radius is R _O , the furnace peripheral portion referred to here is a dimensionless radius R _S / R _O. ~
It is defined as an area between 1.0. The center is defined as the weight of coke charged at the center / the weight of scrap charged at the center = 3 / 100-1 /
25 is defined as the coke existence area to be charged. The middle part is defined as an area between the central part and the peripheral part.

R _S / R _O is defined by equation (4).

R _S / R _O = {1 / (A + 1)} ^1/2 (4) where A = (W _CR / ρ _CR ) / (W _S / ρ _s ) where W _CR : coke ratio (Kg / t) W _S : Scrap (kg / t) ρ _CR Bulk density of coke (kg / m ³ ) ρ _cr : Bulk density of scrap (kg / m ³ )

[0022]

Hereinafter, the present invention will be described in detail.

FIG. 1 is a schematic view showing a moving bed type scrap melting furnace according to the method of the present invention.

Coke 2 is charged into the peripheral part and the central part of the furnace, and scrap 1 is charged from the central part to the intermediate part. If scrap is mixed in the coke layer, 12
mm or less is used.

A plurality of tuyeres are installed in the vertical direction. In the case of a moving bed having a multi-stage tuyere, the upper tuyere is movable inside the furnace, and the projecting position of the tuyere is usually set at a boundary position between the peripheral charging coke and the scrap layer. In the figure, 1a is fine-grain scrap, 3 is primary tuyere (lower tuyere) (installation site),
Reference numeral 4 denotes a secondary tuyere (upper tuyere) (installation site), and reference numeral 5 denotes a tap hole.

First, the reason why the solution loss reaction amount of the equation (2) can be reduced by employing coke peripheral charging will be described.

The use of coke peripheral charging is performed by charging coke having a small particle size to the peripheral portion with respect to the scrap particle size so that the main flow of gas is introduced into the scrap layer charged from the furnace center to the intermediate portion. Aim to shed. The mainstream gas flows through the scrap layer where no coke is present, but since there is no coke in the scrap layer, the solution loss reaction of the formula (2) does not occur. In the coke layer, the solution loss reaction of the formula (2) partially occurs,
Since the amount of gas is small, it is extremely reduced as compared with the conventional method. Thus, according to the charging method of the present invention, the solution loss reaction amount of the equation (2) can be reduced, and the furnace top exhaust gas secondary combustion rate η _CO ^(TOP) = CO ₂ ^(TOP) / (CO
^(TOP) + CO ₂ ^(TOP) ), which enables operation with high thermal efficiency. This also contributes to reducing the coke ratio.

Regarding the coke peripheral charging method, a conventional charging device, for example, Bell + MA (movable armor)
Control is possible with a mold or bellless charging device.

Next, the scrap particle size and mixing ratio used in the coke layer will be described.

If the space ratio in the coke layer can be reduced by 20%, the gas flow resistance sharply increases. In the peripheral coke charging type scrap melting furnace, if the gas flow flowing in the coke layer can be extremely reduced, the amount of the solution loss reaction of the formula (2) in the coke layer generated in the process of increasing the gas can be reduced.

As a method of reducing the porosity of the coke layer, it is effective to reduce the grain size of the coke charged peripherally, to enlarge the grain size configuration, and to mix and use fine grain scrap.
Japanese Patent Application No. 05-239272 and Japanese Patent Application No. 05-24 disclose the reduction of the particle size of coke charged in the periphery and the expansion of the particle size configuration.
8515.

The use of mixed fine-grained scrap contributes to lowering the porosity of the coke layer and increasing the airflow resistance. If the use ratio of fine-grained scrap is set to 20% or less in volume fraction, the porosity of the coke layer is reduced by 20%, and in order to control the gas flow, the particle size ratio D _SCRAP / D
_COKE (= fine-grain scrap particle size / coke particle size) ≦ 0.2
Is desirable. In other words, the upper limit of the blast furnace coke particle size is 6
When it is 0 mm, the particle size of the fine scrap is preferably 12 mm or less.

Although the mixing ratio of the scrap varies depending on the scrap particle size, in order to reduce the porosity of the coke / scrap mixed layer by 20% with respect to the porosity of the coke single layer, according to FIG. Must be set as follows. When the particle size ratio D _SCRAP / D _COKE = 0.2, the volume fraction of fine-grained scrap is 16%. When the particle size ratio D _SCRAP / D _COKE = 0.1, the volume fraction of fine-grained scrap is 14%. When the particle size ratio D _SCRAP / D _COKE = 0.05, the volume fraction of fine-grained scrap is 13%. When the particle size ratio D _SCRAP / D _COKE = 0.02, the volume fraction of fine-grained scrap is 12%. Since the apparent density of scrap / the apparent density of coke is about 5 to 7, when the mixing ratio of scrap is converted into the weight ratio, the above range becomes about 0.7 to 1.3 of fine-grain scrap weight / coke weight. .

Next, a method for using fine coke having an average particle size of 30 to 60 mm will be described.

With regard to the use of fine-grained coke, which is accompanied by fine-graining or coagulation of the peripherally charged coke,
There is a tendency to increase the flammability at the tuyere, and the action at the tuyere is to increase the solution loss reaction amount of the equation (2). Therefore, a method for increasing the exhaust gas secondary combustion rate η _CO ^(TOP) and reducing the coke ratio by using fine coke having an average particle size of 60 mm or less, such as blast furnace coke, will be described.

As this method, a multi-stage tuyere having a plurality of tuyeres in the furnace height direction was employed. The adoption of multi-stage tuyere means that the combustion rate of the gas burned in the lower tuyere is η _CO ⁽¹⁾ (= CO ₂ ⁽¹⁾
/ (CO ⁽¹⁾ + CO ₂ ⁽¹⁾ )) is arranged to further enhance the reaction of the formula (3) by blowing air from the upper tuyere, and the secondary combustion rate of the exhaust gas from the furnace top It is possible to increase η _CO ^(TOP) . Under charging around coke, by projecting the tuyere projecting position into the boundary between scrap and coke or into the scrap layer, it is possible to suppress the direct reaction between the blown air from the upper tuyere, blown oxygen and coke, It is possible to cause the reaction of the formula (3) efficiently. In the case where the operation with the highest thermal efficiency is intended, the amount of CO gas after primary tuyere combustion is blown with air or oxygen capable of complete combustion according to the formula (3) in a state where the tuyeres are projected into the scrap layer. good. According to this method, when using fine-grain coke, the gas combustion rate η _CO ⁽¹⁾ at the lower tuyere becomes low,
Exhaust gas η _CO ^(TOP) can be improved. Where η _CO ^(TOP) ≧
To achieve a burn rate of 65%, the coke particle size should be 3
Desirably, it is 0 mm or more.

Next, a technique for using a large amount of scrap will be described.

According to the experiments and investigations so far, for the solubility of scrap containing a particle size of about 1500 mm, a high-temperature gas is required, and the temperature between the theoretical combustion gas temperature Tf before the primary tuyere and the scrap usage ratio is high. Has the relationship of FIG. This is because the lower the amount of C in the metal, the higher the melting point of the metal.

In order to achieve the full use of scrap,
Tf needs to be 2650 ° C. or higher. As shown in FIG. 4, the combustion rate η _CO ⁽¹⁾ at the primary tuyere changes depending on the coke particle size. Therefore, in operation, it is necessary to change the blowing conditions according to the coke particle size. When using coke with a large particle size, η _CO ⁽¹⁾ is high and Tf ≧ 2 even without oxygen enrichment.
650 ° C. can be achieved, and the entire amount of scrap can be used. On the other hand, when using blast furnace coke with a particle size of 60 mm or less, η _CO ⁽¹⁾ ≧ 40% is possible with the peripheral coke charging method, which is more efficient than η _CO ⁽¹⁾ ≦ 30% in the conventional cupola operation. However, in order to achieve Tf ≧ 2650 ° C. under normal temperature ventilation, an oxygen enrichment rate of about 5% is required. As described above, when a large amount of scrap is used, it is necessary to change the blowing conditions depending on the coke particle size.
By achieving 2650 ° C., the whole amount of scrap can be used.

Next, the fact that the central coke charging method is effective as a method of replenishing the carburizing material into the molten metal will be described below.

In the peripheral coke charging method, there is no C material from the central portion to the intermediate portion, so that the melting property of the scrap becomes a problem. Carburization is also required after the start of melting in order to ensure the fluidity of the molten metal accompanying the temperature drop in the dropping process after the start of melting. Until the adoption of this method, a method of periodically replenishing the carburizing material into the scrap charging section was used.
Efficiency was reduced due to consumption due to a combustion reaction with O ₂ . On the other hand, in the central coke charging method, the central charging coke contributes to carburization of the molten metal in the hearth even if coke does not exist in the middle part of the furnace. The coke is not present in the furnace middle portion, after generating feathers preoral, CO ₂ through the scrap layer, which reacts a portion coke present in the central portion, compared to the conventional method, the reaction amount Few.

Further, by adopting the peripheral coke charging, the reaction efficiency is improved and the coke ratio is lowered. As a result, the inside of the furnace has a temperature distribution with a low coke ratio operation, that is, a high heat flow ratio. The fact that the temperature range in which the reaction of the formula (2) occurs is smaller than before, which is also the reason why the reaction amount between the central charging coke and CO ₂ flowing through the scrap layer is small.

In charging the central coke in the blast furnace operation, in addition to ensuring ventilation and liquid permeability of the furnace core, improving the permeability of the furnace center is also an important factor. However, in the present method, it is desirable that the central charging coke does not react with the gas, and it is important to keep the gas from flowing as much as possible.

In order to reduce the amount of reaction between the central charging coke and the CO ₂ flowing through the scrap layer, it is effective to mix fine scrap in the central coke layer. This is to prevent the gas from flowing to the center by increasing the porosity of the central charging coke layer and increasing the gas permeation resistance. As a result, central charging coke and CO ₂
The reaction coke can be reduced, and the charged coke functions effectively as a carburizing material in the lower part of the furnace.

Regarding the amount of coke charged in the center of the furnace, the weight of coke charged centrally / the weight of scrap charged = 3 /
Charge at a weight ratio of 100 to 1/25. This corresponds to a carburizing amount in the molten metal of 30 to 40 kg / t per ton of hot metal. When the coke weight is more than 1/25, the coke weight increases the area of the central coke layer and increases the chance of reaction with CO ₂ gas, which can reduce the reaction efficiency. There is. In addition, the center charging coke weight / the charging scrap weight = 3/10
If the coke charge is less than 0, the carburizing material is insufficient and the operation is possible in the short term, but the operation is severe in the long term.

As described above, the coke charging method according to the present invention shares its functions, and the peripherally charged coke is consumed for combustion in front of the tuyere, while the centrally charged coke is discharged into the molten metal. As a carburizing material, which enables stable operation.

As a central coke charging method, the bellless type charging method is easy, but in the case of a bell type charging device,
A dedicated coke charging device is required for central coke charging.

[0048]

EXAMPLES The characteristics of the present invention will be specifically described below with reference to examples.

Furnace diameter 2 m, number of primary tuyeres: 8, number of secondary tuyeres: 4, effective height: 4.6 m, 20 t / h scale normal temperature blast,
A two-stage tuyere type moving bed melting furnace was used. The furnace top exhaust gas composition is η _CO ^(TOP) = (CO ₂ ^(TOP) / (CO ^(TOP) + CO ₂
^(TOP) )). Among the operating specifications, the blast moisture is 1
5g / Nm ³ , the basic unit of limestone charged from the furnace top is 40k
g / t. The charging of coke into the periphery and the center was controlled using a bell-less charging device in this operation.

In Comparative Example 0, in a normal-temperature blasting operation in which two layers of tuyeres were used in a normal-temperature blast in which scraps and coke were layered or mixed from the furnace top and in a two-stage tuyere, the coke was used in a normal operation in which the ratio of the type of iron or the iron castings was 60%. This is an example using a coke for casting having a particle size of 150 mm and a coke for a blast furnace having a particle size of 60 mm.

Comparative Example 1 shows an operation example of a scrap melting method using a peripheral coke charging method in the operation of a scrap melting furnace using normal-temperature air blowing and two-stage tuyere. The protruding position of the secondary tuyere is set at a position 20 cm from the furnace wall so as to be as close as possible to the boundary between scrap and peripheral charging coke. As a method of reinforcing the carburizing material, coke is regularly supplied from the furnace center to the furnace middle part of the scrap charging part. With the conventional cupola method, it is possible to operate with the ratio of the pig iron or the cast iron scrap which is difficult in the peripheral coke melting furnace, and the η _CO can be controlled in the range of 65 to 90%. .

Example 1 is an example in which coke periphery and center charging were carried out using coke for casting having a coke particle size of 150 mm and coke for a blast furnace having an average particle size of 50 mm or 60 mm. The projecting position of the secondary tuyere is the same as in Comparative Example 1. The exhaust gas η _CO could be controlled by the amount of air blown from the upper tuyere, and η _CO could be operated within the range of 68 to 95%. In each operation, the center charged coke weight / scrap weight = 0.
Within the range of 030 to 0.040, stable operation is continued, suggesting that the central charge coke is largely consumed for carburization. Under the same operation conditions, Example 1 was compared with each operation example (a) to (c) of Comparative Example 1.
In the operations (a) to (c), η _CO is high, efficient operation is possible, and the combustion ratio is low. In addition, even under the use of fine coke, compared with Comparative Example 0 of the normal operation, the reduction of the pig iron ratio,
A reduction in fuel ratio has been achieved.

In the operation of Example 2 in which fine coke was charged in the periphery and the center in Example 1 (b), the center charged coke was 35.9 kg / t in order to increase the ventilation resistance in the coke layer. Per kg of 25 kg / t of fine grain scrap of 12 mm or less and 81 kg / t of coke charged peripherally.
This is an example in which 60 kg / t of fine scrap of 2 mm or less is mixed and used. Exhaust gas η _CO ^(TOP) has increased by 2% compared to before fine-grained scrap mixing, and efficient operation can be continued.

[0054]

[Table 1]

[0055]

As described above, according to the present invention, by improving the method of charging raw materials such as scrap and coke into the moving-bed-type scrap melting furnace, the use of fine-grain coke, which has heretofore been difficult to use, is improved. In addition, scrap melting with improved productivity and economic efficiency became possible, for example, with high thermal efficiency, a low fuel ratio, and a reduced pig iron ratio (cast iron scrap ratio).

[Brief description of the drawings]

1 (a) and 1 (b) are conceptual diagrams of a moving bed type scrap melting furnace according to the method of the present invention.

FIG. 2 is a diagram showing a relationship between a porosity and a mixing ratio of a crushed particle mixed layer having two particle sizes.

FIG. 3 is a diagram showing a relationship between a theoretical combustion gas temperature Tf before a primary tuyere and a scrap usage ratio.

FIG. 4 is a diagram showing a relationship between coke particle size and a theoretical combustion gas temperature Tf before a primary tuyere.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Scrap 1a ... Fine-grain scrap 2 ... Coke 3 ... Primary tuyere (lower tuyere) (installation site) 4 ... Secondary tuyere (lower tuyere) (installation site) 5 ... Taphole

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21B 11/02 C21B 13/02

Claims (3)

(57) [Claims] 1. A method for operating a shaft-type scrap melting furnace in which coke is charged from the furnace top to the periphery of the furnace, and scrap is charged from the center to the middle, wherein coke is charged centrally to the center of the furnace. Scrap weight = 3/100
A method for operating a scrap melting furnace, characterized in that charging is performed at a weight ratio of about 1/25. 2. The method for operating a scrap melting furnace according to claim 1, wherein fine-grained scrap having a grain size of 12 mm or less is disposed in the central charging coke layer and the coke layer at the periphery of the furnace. = 0.7-
1.3 and a peripherally charged fine-grained scrap weight / peripherally charged coke weight = 0.7 to 1.3. 3. The method for operating a scrap melting furnace according to claim 1, wherein coke having an average particle diameter of 30 to 60 mm is charged.