JPH07146072A - Cupola type scrap melting furnace - Google Patents

Abstract

PURPOSE:To reduce a cost by using low-cost coke for a blast furnace as compared with coke for casting and to use an entire amount of scraps irrespective of a shape and a size by forming a main section of a cupola type scrap melting furnace of a cupola and a forehearth. CONSTITUTION:A cupola type scrap melting furnace comprises a cupola 1 and a forehearth 2 as main sections. The cupola 1 has a primary tuyere 3 disposed at a lower stage to suck hot air and pulverized coal, a secondary tuyere 4 disposed at an upper stage to feed the hot air, and a scrap charging inlet 6 arranged at an upper part. The hearth 2 has a scrap charging inlet 5 and carbon agent and flap blowing nozzle 8 disposed at an upper part, and a bottom diffusing agitating plug 9 disposed at a lower part. Further, a burner 7 is disposed near the inlet 5. Scraps of arbitrary shape and size are charged from the inlets 5, 6, and low-cost coke for a blast furnace as compared with coke for casting is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cupola-type scrap melting furnace, which is capable of melting regardless of the scrap shape and size, controls the quality of the molten metal, and enhances the thermal efficiency with a low coke ratio to reduce scrap. The present invention relates to a scrap melting furnace for producing a melt that can be melted.

[0002]

2. Description of the Related Art As a scrap melting process in a vertical furnace, 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, and there are hot-air cupola with one-stage tuyere with a blast temperature of around 500 ° C and cold-air cupola with two-stage tuyere by normal temperature blasting. At the same time, a high-cost foundry coke having a coke quality of C92%, an ash content of about 8%, and a grain size of 150 mm or more is required.

When a casting scrap / mold pig charging 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 around 40% in the hot air cupola and around 50% in the case of the two-stage tuyere / cold air cupola. This secondary combustion rate is affected by the degree of progress of equation (2) following the C combustion reaction of equation (1).

C + O ₂ → CO ₂ +97,000 kcal / (kmol · C) (1) C + CO ₂ → 2CO-38200 kcal / (kmol · C) (2) When a coke for a blast furnace having a particle size of 60 mm or less is used, an endothermic reaction occurs. Since the reaction progress of a certain equation (2) is fast, the secondary combustion rate η _CO surely decreases, and the meltability of scrap deteriorates. Therefore, in the prior art, for the purpose of slowing down the reaction rate of the equation (2), a high-cost foundry coke having a particle size of 150 mm or more was required.

In the case of a two-stage tuyere / normal temperature blow cupola aimed at improving the secondary combustion rate, the secondary blow is intended to promote the reaction of the formula (3). The pre-tuyere temperature at the primary tuyere is low due to the operation with an enrichment rate of 3% or less, and in the normal operation, 40 to 60% of C-containing low melting point casting scraps and mold pigs (scrap use ratio 60 to 40%) I have no choice but to use it.

CO + 1 / 2O ₂ → CO ₂ +67590 kcal / (kmol · CO) (3) As described above, in the case of the present cupola, the use of blast furnace coke and the operation of using the entire amount of scrap are severe.

For the purpose of using coke for a blast furnace, Japanese Patent Laid-Open No. 3-111505 proposes a method for improving the blowing method of the secondary blowing tuyere in a cupola type melting furnace having a secondary tuyere. Has been done. This is an inert carrier gas instead of the combustion-supporting gas in order to suppress the carbon solution reaction due to the overheating of the coke for the next melting, which is charged above the secondary tuyere level surface,
For example, N ₂ is used to blow powdery limestone and / or iron ore, respectively. Judging from the examples, the fluctuation of the secondary combustion rate is small and contributes to the reduction of the solution loss reaction, but the value is about 45%, which is almost within the operating range of the current cupola when the coke for casting is used. equal. Operationally, there is the complexity of adjusting the secondary air flow rate according to time or scrap layer fall.

In order to reduce the coke ratio, a scrap melting method using pulverized coal is disclosed in JP-A-1-19522.
5 and JP-A-2-157590.

In both cases, since raceway is not generated in the furnace, in order to secure the pulverized coal combustion space,
Combustion towers or combustion chambers are specially installed, and heat loss generated during combustion and life of refractories are problems.

In the EOF method using a vertical furnace having a water cooling wall member as a refining furnace, oxygen is supplied from a nozzle arranged on the lower side of the bath surface to the upper side of the bath surface in the vertical furnace. Oil / pulverized coal is blown together with oxygen through the burner, and the exhaust gas completely burned by the hot air enriched by the blowing nozzle placed above preheats the scrap iron placed on the furnace . The preheating temperature is about 800 ° C at the maximum, and the structure is such that the preheating furnace is discontinuously charged.

The problem is that the waste gas temperature fluctuates due to the complicated structure of the scrap iron preheating device and the discontinuous charging method.

Regarding the scrap grain size used in the cupola operation, it is considered appropriate that the limit scrap grain size for stabilizing the operation such as gas flow stabilization is about 1/3 or less of the cupola furnace diameter.

Toru Ishino (casting and forging and heat treatment, 7 (19
According to the explanation of the cupola in 91), p3), a gas cupola with a structure combining a shaft furnace and a former furnace was developed in the former Soviet Union, but this furnace has a structure that does not use coke, and also has a scrap charging port. Is the cupola furnace top 1
There is no place in the front furnace.

[0014]

In the prior art, it is difficult to use the blast furnace coke and use the entire amount of scrap, and the shape of the scrap is not more than 1/3 of the cupola furnace diameter. As judged, there was a limit to the shape and size of scrap that could be used.

Further, in the scrap melting method using pulverized coal, a dedicated combustion tower or a combustion chamber for ensuring a combustion space is installed instead of directly sucking the pulverized coal into the scrap or the coke packed bed. In this case, heat loss and life of refractory materials are problems.

Regarding the quality of the molten metal, it is also a problem that S in the molten metal is at a high level.

In the cupola-type scrap melting furnace, the present invention aims to reduce the cost by using blast furnace coke and steam coal, and also improves the secondary combustion rate to improve scrap preheating / melting property and high heat. It is an object of the present invention to provide a cupola-type melting furnace that not only maintains high productivity under efficiency, but can be used regardless of scrap shape and size, and that can carry out a scrap melting method capable of controlling molten metal quality.

[0018]

The present invention is to solve the above-mentioned problems, and the gist thereof is (1) a cupola-type scrap melting furnace characterized by comprising a cupola and a pre-furnace.

(2) The cupola has upper and lower tuyeres,
The cupola-type scrap melting furnace according to (1) above, wherein the lower stage is a primary tuyere for blowing hot air and pulverized coal, and the upper stage is a secondary tuyere for blowing hot air.

(3) A scrap charging port, a combustion burner, and a carbonizing agent / flux blowing nozzle are provided in the upper part of the front furnace,
The cupola-type scrap melting furnace according to the above (1) or (2), characterized in that it has a bottom-blown stirring plug in the lower part of the front furnace.

That is, in the present invention, in order to enable the use of scraps of arbitrary shape and size, scrap inlets are provided in both the cupola and the forehearth, and for scraps larger than 1/3 of the cupola furnace diameter, the forehearth is used. It is configured to be thrown in. Also, to enable the use of blast furnace coke,
The cupola operation is oriented toward low coke ratio operation, and a large amount of pulverized coal injected from the primary tuyere is considered. For the purpose of using the entire amount of scrap, a two-stage tuyere is adopted to increase the secondary combustion rate, and hot air blowing is used to secure scrap meltability.

In order to control the quality of the molten metal, an injection nozzle for spraying pulverized coal directly into the molten metal as a carburizing accelerator is installed, and in consideration of the flux blowing, the nozzle is also used to stir the molten metal and slag by injecting the bottom gas. By adding it, the quality of the molten metal can be controlled by, for example, decreasing S.

The present invention makes it possible to use scrap of any shape by integrating the cupola and the forehearth so that the quality of the molten metal can be controlled and the cost of raw materials can be reduced. This is a cupola-type scrap melting furnace that enables

[0024]

The present invention will be described in detail below.

FIG. 1 is a conceptual diagram of a cupola type scrap melting furnace according to an embodiment of the present invention.

In order to be able to use scraps of arbitrary shape and size, scrap charging ports 5 and 6 are provided in both the cupola 1 and the forehearth 2.

In the cupola operation, the limit scrap grain size for stabilizing the operation such as gas flow stabilization is about 1/3 or less of the cupola furnace diameter, and the scrap of this grain size is charged into the cupola as usual. As a result, large scraps are directly charged into the molten metal / slag bath produced by the cupola in the front furnace.

As a method for ensuring the meltability of large-scale scrap, the sensible heat of molten metal produced by the continuously-generated cupola molten metal is used. The tap hole is arranged as shown in FIG. 1 so that the molten metal discharged from the cupola comes out after being mixed by scrap melting in the previous furnace. In order to improve the meltability, it is desirable that the cupola molten metal / slag temperature is as high as possible, and if possible, the target is about 1530 ° C. As a method for promoting the meltability of large-scale scrap, the oxygen injection from the lower part of the front furnace and the combustion heat associated with the improvement of the secondary combustion rate by the upper part of the front furnace and combustion burner are used. In that case, in order to replenish the decrease in C in the molten metal due to the combustion of C in the molten metal, a method of using pulverized coal as a carburizing material and blowing it into the molten metal from the front furnace upper injection nozzle is adopted.

Next, a method for using the blast furnace coke will be described.

Since the blast furnace coke has a grain size of 60 mm or less, which is smaller than about 150 mm of casting coke, it tends to have high reactivity and lowers the secondary combustion rate, but in order to avoid this, the two-stage tuyeres are used. Adopt and reduce coke ratio. Consider more than one tuyere.

The secondary combustion rate improved in the two-stage tuyere decreases due to the solution loss reaction that occurs thereafter,
If the coke ratio can be reduced, the decrease range of the secondary combustion rate can be suppressed.

As a means for achieving a reduction in the coke ratio, consider injecting a large amount of pulverized coal. Pulverized coal is injected from the primary tuyere directly into the furnace. This aims at suppressing the heat loss during pulverized coal combustion outside the furnace, which has been taken conventionally, and effectively utilizing the reaction heat.

Hot air is blown to accelerate the combustion of pulverized coal. Further, as a means for forming a combustion space, that is, a raceway in the cupola furnace, the coke charged in the upper part of the cupola is charged according to the particle size and the coke charged in the peripheral part is charged.

The present inventor has shown the relationship between the tuyere number, the tuyere diameter, the coke particle size and the raceway depth in Japanese Patent Application No. 052392972. For example, in a cupola with a tapping ability of 41 t / h, the raceway depth is The effect of the coke particle size on the results is shown in Table 1. For example, in order to secure a raceway depth of 0.4 m, the coke grain size charged in the peripheral portion may be 0.030 m or less.

[0035]

[Table 1]

Regarding the method of charging scrap and coke, fine grain coke of 30 mm or less is 30 mm on the wall side.
The above coke was charged by mixing with scrap and then charged from the center to the periphery. The charge distribution control can also be controlled by the conventional charging device, and the fine grain coke charging in the peripheral part can be controlled by the bell + MA (movable armor) type charging device or the bellless charging device. .

Next, the reason why the lowering of the secondary combustion rate can be suppressed as compared with the cupola operation under the conventional use of casting coke even when using blast furnace coke and under hot air blowing will be described. In order to achieve this purpose, a two-stage tuyere structure is used.
When using blast furnace coke, it is inevitable that the burning rate at the primary tuyere will be lower than when using casting coke. Therefore, the reaction of formula (4) is promoted by the secondary blowing.

2CO + O ₂ = 2CO ₂ (4) However, in the case of hot air blowing, C + CO ₂ = 2CO (5) Secondary combustion rate (= CO ₂ / (CO + CO ₂ )) is likely to decrease, the present invention aims at a low coke ratio operation by blowing pulverized coal, thereby reducing the chance of contact between gas and coke and suppressing the solution loss reaction. As a result, it has become possible to achieve or improve the secondary combustion rate during cupola operation using conventional coke for foundry.

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

The relationship between the theoretical combustion gas temperature Tf before the primary tuyere and the scrap usage ratio was arranged by arranging the present cupola operation examples to obtain the relationship shown in FIG. According to FIG. 2, in order to achieve full scrap use, the Tf is 2700.
It is judged that a temperature above ℃ is required. Although the operating conditions differ depending on the blast temperature level, for example, considering an operation at a blast temperature of 500 ° C. and a pulverized coal blowing rate of 90 kg / t, the operating conditions that satisfy the above conditions are an oxygen enrichment rate of 10% and a secondary Blower ratio (2
The next tuyere air flow rate / total air flow rate) was about 0.32, and under this condition, it was possible to use all of the scrap. As a goal, if the condition of Tf ≧ 2700 ° C. is satisfied, the entire scrap can be used.

Next, the molten metal quality control method will be described.

In the present invention, since the total amount of the cupola molten metal flows through the forehearth, the molten metal quality is controlled in the forehearth. The relationship of FIG. 3 is obtained between S in molten metal and basicity of slag, and in order to reduce S, lime powder is blown from the injection nozzle in the upper part of the forehearth to a predetermined basicity, The quality is controlled more effectively by mixing and stirring by injecting an inert gas from the nozzle at the bottom of the front furnace.

[0043]

EXAMPLES The features of the present invention will be specifically described below with reference to the example furnace shown in FIG.

Furnace diameter of 2 m, primary number of tuyeres of 8, secondary number of tuyeres of 4, effective height of 4.6 m, moving bed type melting furnace of 20 t / h scale with a furnace bed diameter of 3 m and height of 2 m A scrap melting furnace having In the figure, 1 is a cupola, 2 is a front furnace, and 3 is 1.
Next tuyere, 4 is a secondary tuyere, 5 is a scrap charging port, 6 is a heavy scrap charging port, 7 is a combustion burner, 8 is a carbon material flux blowing nozzle, and 9 is a bottom blowing stirring plug.

Next, as an operation example 1 using the furnace of this embodiment, 3
An example in which the entire scrap of 0 cm or less is melted will be described. In this example, scrap was charged from the top of the cupola furnace.
Blower temperature is 500 ° C, pulverized coal injection rate is 90kg / t,
This is an operation example of 48.5 kg / t of coke for blast furnace, and is an operation example in which oxygen is enriched by 10.7% (Tf2800 ° C) so that the theoretical combustion gas temperature Tf ≧ 2700 ° C in the primary tuyere portion. . The secondary air flow ratio (secondary air flow rate / total air flow rate) is 0.
At 325, the secondary combustion rate was 44.2%.

Comparative operation example 1 shows an operation example in which the secondary blowing is not performed and a first stage tuyere is used in comparison with the operation example 1, but Tf = 2597 ° C. at the primary tuyere (2 hour burning rate 20 %), Combustion ratio = 173.5 kg / t (coke ratio 83.5 kg / t)
Therefore, the operation was not stable and the all scrap operation was difficult.

The operation example 2 is 6 under the conditions of the operation example 1.
In this example, 0 cm or less scrap and 70 cm or more scrap are charged. Scraps of 60 cm or less were charged from the top of the cupola furnace, and scraps of 70 cm or more were improperly charged into the cupola, so they were directly charged into the molten metal from the previous furnace. The front furnace charging scrap ratio was about 100 kg / t, oxygen was 4.5 Nm ³ / t from the lower part of the front furnace, and
Pulverized coal 10 kg / t, secondary combustion air 22.2 Nm ³ /
By blowing t, large-scale scrap can be melted. At this time, the slag basicity is 0.8 and the S in the molten metal is 0.1.
%, The slag basicity was increased to about 1.3 and S in the molten metal was reduced to 0.06% by injecting 14 kg / t of limestone powder from the upper part of the previous furnace aiming at the reduction of S in the molten metal. I was able to.

In the operation example 3, scraps of 60 cm or less were charged from the top of the cupola furnace, and scraps of 70 cm or more were directly charged into the molten metal from the previous furnace. The amount of pulverized coal injected from the primary tuyere of the cupola was 60 kg / t, and the blowing temperature was 400 ° C. Oxygen enrichment was carried out at 7.6% so that 100% of scrap could be used and the primary tuyere Tf was 27
The temperature was set to 00 ° C or higher. Front furnace charging scrap ratio is 150 kg
/ T, about 5.0 Nm ³ / t of oxygen from the lower part of the front furnace,
Pulverized coal 10 kg / t, secondary combustion air 2
By blowing 5.0 Nm ³ / t, large-scale scrap can be melted. At this time, since the slag basicity was 0.8 and the S in the molten metal was 0.9%, the slag basicity was changed by blowing 15 kg / t of limestone powder from the upper part of the front furnace in order to reduce the S in the molten metal. It was possible to raise it to about 1.3 and reduce S in the molten metal to 0.05%.

[0049]

[Table 2]

[0050]

As described above, in the present invention, the blast furnace coke, which is cheaper than the casting coke, can be used, and the total amount of scrap can be used regardless of the shape of the scrap, and the quality of the molten metal can be controlled. The present invention provides a scrap melting furnace that can be used, and the effect of the invention is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic view of an example cupola-type melting furnace of the present invention.

FIG. 2 is a diagram showing the relationship between the theoretical combustion temperature before tuyere and the scrap ratio (scrap usage ratio).

FIG. 3 is a diagram showing the relationship between slag basicity and S in molten metal.

[Explanation of symbols]

1 ... Cupola 2 ... Forehearth 3 ... Primary tuyere 4 ... Secondary tuyere 5 ... Scrap charging port 6 ... Scrap charging port 7 ... Combustion burner 8 ... Charging agent / flux blowing nozzle 9 ... Porous plug for bottom blowing stirring

Claims (3)

[Claims] 1. A cupola-type scrap melting furnace comprising a cupola and a front furnace. 2. The cupola has upper and lower two tuyeres, the lower one is a primary tuyere for blowing hot air and pulverized coal, and the upper one is a secondary tuyere for blowing hot air. The cupola-type scrap melting furnace according to claim 1. 3. A scrap charging port, a combustion burner, and a carbonaceous material / flux blowing nozzle are provided in an upper portion of the forehearth, and a bottom blowing stirring plug is provided in a lower portion of the forehearth. 2. The cupola-type scrap melting furnace according to 2.