JP2001158908A - Method of operating electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of operating an electric furnace, with which the high efficient operation can be executed by using an assist combustion burner having a triple tube structure, and the oxidized losses of iron content and chromium content are reduced. SOLUTION: (1) In the operating method of the electric furnace by using the assist combustion burner having the triple tube structure and arranging a Laval contracting part in a gaseous oxygen apouting tube at the center part and disposed with circular blades at the outer peripheral part, the combustion condition in the assist combustion burner, has the characteristic satisfying the formulas, A/(B×α+C×0.93+D×0.8)<=2.0 and A/(B×α)>=0.7 (wherein, α is the theoretical combustion ratio of oxygen; A is the unit requirement of oxygen; B is the unit requirement of fuel; C is a carbon blending amount in melted raw material; and D is Si blending amount in melted raw material). (2) In the above operating method of the electric furnace, the ratio of (the oxygen flow rate spouted from the center point/the oxygen flow rate spouted from the outer peripheral part) in the assist combustion burner is desirably in the range of 0.05-20.0 and gas containing >=15% oxygen instead of the gaseous oxygen may be used. Further, as the fuel, coke furnace gas or liquid fuel may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric furnace operating method using an auxiliary burner, and more particularly, to melting an ordinary steel, a chromium-containing special steel, and a stainless steel using an auxiliary burner having a triple pipe structure. In addition to reducing melting time and reducing power consumption, high efficiency
e), a method of operating an electric furnace capable of reducing oxidization loss of chromium (Cr).

[0002]

2. Description of the Related Art When an electric furnace is used to dissolve iron scraps, the iron scraps around the electrodes can be melted quickly. The speed is reduced, causing an imbalance in the melting speed of the iron swarf in the furnace. At this time, the melting speed of the electric furnace as a whole is limited to a place where the melting speed is low, so that the melting operation is inevitably performed for a long time, and the power consumption increases.

[0003] Conventionally, in order to eliminate the imbalance in the melting rate in an electric furnace, an auxiliary combustion burner is installed in the furnace, and the auxiliary combustion burner is injected toward a place where the melting rate is low, thereby making the melting rate uniform. A method of operating an electric furnace has been proposed. However, the conventional burner burner is not suitable for use as an electric furnace burner, and it is easy to cause blockage troubles during operation.It is necessary to increase the local melting speed and eliminate the imbalance in the melting speed. Not reached.

FIG. 1 is a view for explaining the cross-sectional structure of a conventionally used auxiliary burner. A conventional auxiliary burner 1 is configured by concentrically arranging a fuel ejection pipe 2 and an oxygen gas ejection pipe 3, ejects fuel from a central portion, and is formed by the fuel ejection pipe 2 and the oxygen gas ejection pipe 3. In this structure, combustion oxygen is ejected from the annular space 4. However, the combustion flame formed by the combustion burner having this structure has a relatively wide and long shape, and the discharge flow velocity is low. For this reason, the tip of the burner is likely to be closed by splash or non-combustible material scattered when the scrap falls into the molten steel, and it is not an auxiliary burner that can be used satisfactorily in an electric furnace for adjusting the scrap melting speed.

Therefore, even when used as an auxiliary burner in an electric furnace for melting ordinary steel, special steel, and stainless steel, no clogging due to splash occurs at the tip of the burner, further shortening the melting time and reducing power consumption. There has been proposed an auxiliary burner capable of reducing the unit (for example, see Japanese Patent Application Laid-Open No. 10-9524).

FIG. 2 is a view for explaining a cross-sectional structure of a combustion assist burner proposed in Japanese Patent Application Laid-Open No. 10-9524. As shown in the figure, the newly proposed auxiliary combustion burner 11 arranges an oxygen gas ejection pipe 12 that ejects oxygen gas from the center,
The outer periphery of the oxygen gas ejection pipe 12 is coaxial with the fuel ejection pipe 13.
In addition, the fuel jet pipe 13 has a triple pipe structure in which an oxygen gas jet pipe 14 is coaxially arranged on the outer peripheral portion. Further, a Laval-shaped throttle portion 12a (hereinafter, simply referred to as a "Laval throttle portion") is provided inside the tip of the oxygen gas ejection tube 12 at the center, and at the same time, the fuel ejection tube 13 and the oxygen gas ejection tube 14 at the outermost periphery are provided. The swirl vanes 16 are installed in the annular space 15 formed by.

[0007] By adopting such a structure for the auxiliary burner, the formed combustion flame becomes a narrow and sharp short flame, and even if heavy debris or incombustible material exists in front, the combustion flame is reflected. The tip of the burner may be melted,
Splashes and incombustibles can avoid the problem of the burner clogging the tip. This makes it possible to eliminate the imbalance in the melting rate in the furnace, thereby shortening the melting time and reducing the power consumption.

[0008]

As described above, FIG.
The auxiliary burner shown in (3) has a triple-tube structure so that oxygen gas is ejected from the center, fuel is ejected from the outer periphery of the oxygen gas, and oxygen gas is ejected from the outer periphery of the fuel. The contact area can be increased.

Further, since the Lavalre throttle is provided at the end of the oxygen gas ejection pipe at the center, it is possible to secure an oxygen gas flow at a supersonic discharge speed. Specifically, as shown in FIG. 2, a throat portion having a shape in which the cross-sectional area is narrowed in the flow direction at the subsonic portion and widened at the portion generating the supersonic speed is provided inside the tip of the pipe. by this,
The oxygen gas spouted from the oxygen gas spouting tube in the center becomes high speed, which promotes splash and removal of incombustibles,
Further, the oxidative exothermic reaction between oxygen and fuel proceeds rapidly, and a high-temperature combustion flame can be secured in addition to the increase in the above-mentioned reaction contact area.

As shown in FIG. 2, in order to further improve the mixing state of the oxygen gas for combustion and the fuel to prevent incomplete combustion, the fuel injection pipe and the outermost oxygen gas injection pipe are used. The swirling vanes are installed in the formed annular space.
As described above, the auxiliary burner shown in FIG. 2 employs various excellent structures for melting the scrap, so that the melting speed in the furnace can be easily made uniform, and the melting time can be shortened and the power consumption can be reduced. Can be reduced.

[0011] However, in a triple-tube combustion burner, since oxygen is easily supplied excessively, the content of Fe in molten steel and
The Cr component is oxidized and burned, so that the oxidation loss increases, and the yield decreases. Furthermore, among them, when slag containing a large amount of chromium oxide is used for landfill, etc., elution of hexavalent chromium is concerned, and there is a concern about a problem unfavorable in the global environment.

The present invention has been made in view of the above-mentioned problems, and shows a case where a triple structure combustion-support burner shown in FIG. 2 is used in an electric furnace for melting ordinary steel, chromium-containing special steel, and stainless steel. Another object of the present invention is to provide a method of operating an electric furnace capable of shortening the melting time and reducing the unit power consumption, achieving high efficiency, and reducing the oxidation loss of Fe and Cr.

[0013]

Means for Solving the Problems The present inventor has conducted intensive studies in order to achieve the above-mentioned object, and as a result, the use of a triple-structure auxiliary burner shown in FIG. In addition to ensuring efficient operation of the electric furnace and preventing flow of the oxygen gas and fuel supplied to the auxiliary burner within a predetermined range, it is possible to prevent the supply of oxygen At the same time as eliminating incomplete combustion of fuel due to lack of fuel,
It has been found that the oxidation loss of Fe and Cr in molten steel due to excessive supply of oxygen can be reduced.

The present invention has been completed based on the above findings, and has as its gist the following electric furnace operating methods (1) and (2).

(1) It has a triple pipe structure in which oxygen gas is ejected from the central portion, fuel is ejected from the outer peripheral portion of the oxygen gas, and oxygen gas is ejected from the outer peripheral portion of the fuel. At the end of the tube, a Laval throttle is provided,
An electric furnace operating method using an auxiliary burner in which swirling vanes are installed in an annular space formed by a fuel injection pipe and an outermost oxygen gas injection pipe, wherein the combustion condition of the auxiliary combustion burner is as follows: An electric furnace operation method characterized by satisfying the following equation.

A / (B × α + C × 0.93 + D × 0.8) ≦ 2.0 A / (B × α) ≧ 0.7 where α: theoretical combustion ratio of oxygen to fuel A: oxygen intensity (Nm ³ / ton of molten steel) B) Fuel consumption rate (Nm ³ / ton of molten steel, kg of liquid fuel / ton of molten steel) C: Carbon content of molten raw material (kg / ton of molten steel) D: Silicon content of molten raw material (kg / ton of molten steel) (2) In the electric furnace operating method described above, it is preferable that the ratio of (flow rate of oxygen spouted from the center / flow rate of oxygen spouted from the outer circumference) in the auxiliary burner be in the range of 0.05 to 20.0. A gas containing 15% or more of oxygen may be used. It is most efficient to use coke oven gas as fuel, but liquid fuel may be used.

In this case, the value of the theoretical combustion ratio α of oxygen with respect to various fuels is, for example, coke oven gas: 1.0, L
PG: 6.5, LNG: 2.3, kerosene: 2.4, heavy oil: 2.4.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electric furnace operating method according to the present invention is characterized in that the amount of oxygen and the fuel supplied to the triple-tube auxiliary burner shown in FIG. I have.

FIG. 3 shows the value of A / (B × α + C × 0.93 + D × 0.8) and the chromium oxide in the slag when stainless steel (SUS 304 steel) was melted using a triple tube structure combustion burner. is a graph showing the relationship between the content of (Cr ₂ O _3). Here, A is an oxygen consumption rate per ton of molten steel, and B × α, C × 0.93, and D × 0.8 are theoretical combustion oxygen amounts (ton of molten steel) with respect to fuel, carbon (C) and silicon (Si), respectively. Per). Therefore, A / (B × α + C × 0.93 + D × 0.8) which is the left side of the above equation
Indicates the ratio of the supplied oxygen amount to the total theoretical combustion oxygen amount of elements (fuel, C, Si) having an affinity for oxygen higher than that of Fe or Cr.

As shown in FIG. 3, when oxygen is excessively supplied to the auxiliary burner and the value on the left side of the equation becomes 2.0 or more, Cr in the molten steel becomes easy to burn, and chromium oxide ( The content of Cr ₂ O ₃ ) increases rapidly. This is because the oxidation reaction between the supplied oxygen and the fuel, C, and Si becomes saturated, and excess oxygen starts to react with Cr in the molten steel, thereby increasing chromium oxide in the slag. Therefore, A / (B × α + C × 0.93 +)
D x 0.8) ≤ 2.0, so that Fe in molten steel and
The oxidation amount of Cr can be minimized.

The carbon content C of the above-mentioned dissolved raw material is
It is necessary to consider the amount of C contained in the ferroalloys and scraps, and also to consider the amount of Si contained in the ferroalloys and scraps as to the Si content D of the melting raw material.

On the other hand, even when the above equation is satisfied, the dissolving speed of the scrap may be reduced, and the dissolving time may not be shortened.

FIG. 4 is a graph showing the relationship between the value of A / (B × α) and the flame temperature of the auxiliary burner when scrap was melted using an auxiliary burner having a triple-tube structure for supplying oxygen gas having a content of 95% or more. It is a figure showing a relation. Here, the value of A / (B × α), which is the left side of the above equation, means the ratio of the supplied oxygen amount to the theoretical oxygen amount of the fuel.

As shown in FIG. 4, the value of A / (B × α) is
If it is less than 0.7, the flame temperature of the auxiliary burner rapidly decreases to 2,000 ° C. or less, which causes a reduction in the melting efficiency of scrap. This is due to the fact that although there was intrusion of oxygen from outside the furnace, the absolute amount of oxygen required for combustion was insufficient, resulting in incomplete combustion. In this case, not only the fuel is wastedly exhausted with the exhaust gas, but also the melting rate cannot be adjusted, and the melting time of the electric furnace becomes long. Therefore, A / (B ×
It is necessary to adjust α) ≧ 0.7 to prevent incomplete combustion of the auxiliary burner.

In the electric furnace melting, if the tip of the burner is clogged with splash or incombustible material scattered when the scrap falls into the molten steel, the function of the auxiliary burner cannot be exhibited. In this case, it is necessary to temporarily stop the operation and remove the obstruction, which significantly deteriorates the workability of dissolving the scrap. In order to prevent burner blockage, it is necessary to secure the flow rate of the oxygen gas ejected from the central portion and not to stop the oxygen ejected from the central portion and the outer peripheral portion. It is desirable to control the ratio of the flow rate of oxygen ejected from the fuel cell.

The flow rate of the oxygen gas ejected from the center is
The characteristics of the Laval throttle section provided in the oxygen gas ejection pipe,
Although determined by the flow rate and pressure of the supplied oxygen gas, the scattering effect such as splash saturates at about Mach 3, and therefore it is desirable to adjust the discharge speed with this as the upper limit.

Next, regarding the ratio of (oxygen flow rate ejected from the center portion / oxygen flow rate ejected from the outer peripheral portion) of the triple-tube combustion burner, when this ratio becomes extremely small, the oxygen ejected from the central portion becomes too small. Vigorous mixing action from gas to fuel cannot be expected. Therefore, the effect of increasing the reaction contact area, which is a feature of the auxiliary burner used in the present invention, cannot be obtained, and the calorific value of the burner decreases.

Conversely, when the above ratio becomes extremely large, the fuel is wrapped from the outer periphery and the supply of the amount of oxygen gas that burns completely becomes insufficient, and the amount of unreacted fuel gas released outside the system increases. The calorific value of the burner decreases. Therefore,
Regardless of whether the above ratio is reduced or increased, the calorific value of the burner is reduced and the burner flame temperature is reduced, so that the scrap dissolution rate is reduced.
To prevent these, it is desirable to control the ratio of (the amount of oxygen ejected from the center / the amount of oxygen ejected from the outer periphery) in the range of 0.05 to 20.0.

Even when an oxygen-containing gas is used as an alternative to the oxygen gas supplied to the auxiliary burner, no decrease in the burner flame temperature is observed as long as a predetermined oxygen content ratio is secured. It was confirmed that there was no problem with the dissolution rate of

FIG. 5 is a diagram showing the relationship between the oxygen content ratio of the gas supplied to the auxiliary burner and the burner flame temperature when A / (B × α) = 1.0. Here, a mixed gas of oxygen and nitrogen is used as the supply gas, and the oxygen content ratio is represented by [oxygen gas flow rate / (oxygen gas flow rate + nitrogen gas flow rate)] (%).

As shown in FIG. 5, when an oxygen-containing gas having an oxygen content ratio of less than 15% is supplied to the auxiliary burner, the burner flame temperature is remarkably reduced due to the cooling effect of the mixed nitrogen gas and the increase in the volume of the flame. are doing. On the other hand, as long as the oxygen content ratio is 15% or more, the burner flame temperature is secured at 2000 ° C or more.
It turns out that it does not affect the dissolution rate of scrap. Therefore, when using an oxygen-containing gas as an alternative to oxygen gas, it is necessary to contain oxygen at 15% or more. In the case where the above-mentioned alternative gas is used, the above formula and the oxygen unit consumption in the formula are converted from the oxygen content contained in the gas.

As the fuel for the auxiliary burner used in the present invention, any of a general gaseous fuel such as LPG and LNG, a coke oven gas, an exhaust gas of a blast furnace and a converter, and a liquid fuel such as heavy oil and kerosene can be used. There is no problem to use. In particular, a coke oven gas having a typical composition shown in Table 1 below is generated in a large amount as a by-product gas in a steelworks that manufactures coke, and furthermore, contains a large amount of hydrogen in the gas. Therefore, it is preferable to use a coke oven gas because the calorific value per unit amount is large.

[0033]

[Table 1]

[0034]

(Example 1) An electric furnace with a melting capacity of 80 tons at a time using an auxiliary burner having a triple tube structure shown in FIG.
18% Cr-8% Ni stainless steel scrap was dissolved. At this time, coke oven gas, LPG, NPG, kerosene and heavy oil are used as fuel types, and the oxygen consumption unit (ANm ³ / ton of molten steel), the fuel consumption unit (BNm ³ / ton of molten steel or kg / ton of molten steel), and C The time required for slag melting and the content of Cr ₂ O ₃ contained in the slag after melting by varying the amount (C kg / ton of molten steel) and the amount of Si (D kg / ton of molten steel) (%)
investigated. Table 2 shows the conditions and results.

[0035]

[Table 2]

In the present invention, the content of Cr ₂ O ₃ contained in the slag after melting is as low as 2.9 to 4.1%, while Comparative Example 1, which does not satisfy the condition of the above formula, 4 is
7.4% and 14.9%, respectively, which are about twice or more as compared with the example of the present invention. Since oxygen is excessively supplied into the furnace, the oxidation loss of Cr is large, and there are problems in terms of cost and global environment. .

On the other hand, regarding the dissolution time, in the present invention,
In contrast, in Comparative Examples 2, 3, and 5, which do not satisfy the conditions of the above formula, the incomplete combustion of the burner is not eliminated, and a long-term operation exceeding 100 minutes is required for melting. .

(Example 2) Using an auxiliary burner shown in FIG. 2, an ordinary furnace (Fe ≧
90%, Cr ≦ 5%, other components ≦ 5%). At this time, as in the case of the first embodiment, the type of fuel, the basic unit of oxygen (ANm ³ / ton of molten steel), the basic unit of fuel (BNm ³ / ton of molten steel or kg / ton of molten steel), and the compounding amount of C (Ckg / ton of molten steel) T) and
The time required for melting the slag and the total Fe concentration (%) contained in the slag after melting were investigated by varying the amount of Si (D kg / ton of molten steel). Table 3 shows the conditions and results.

[0039]

[Table 3]

The total Fe concentration in the slag after melting is
In the examples of the present invention, the low concentrations of 0.9 to 1.2% are maintained, whereas in comparative examples 1 and 4, which do not satisfy the conditions of the above formula, are 3.2% and 4.2%, respectively, which are about three times as large as those of the present invention. It is more than that, because oxygen is supplied excessively in the furnace, Fe
Has a large oxidation loss and generates a large amount of slag.

With respect to the dissolution time, in the present invention, the dissolution time is 74 to
In contrast, in Comparative Examples 2 and 3, which did not satisfy the condition of the above formula, the incomplete combustion of the burner was not eliminated, and the melting was performed for a long time exceeding 100 minutes.

(Embodiment 3) Under the same conditions as in Embodiment 1, FIG.
The 18% Cr-8% Ni stainless steel scrap was melted in an electric furnace having a melting capacity of 80 tons at a time using the burner of the auxiliary combustion shown in FIG.
At this time, only the coke oven gas was used as fuel, and the oxygen intensity (ANm ³ / ton of molten steel), the fuel intensity (BNm ³ / ton of molten steel or kg / ton of molten steel), the C content (Ckg / ton of molten steel) and The Si content (D kg / ton of molten steel) was kept almost constant, and instead of oxygen gas, an oxygen-containing gas whose oxygen concentration fluctuated from 8% to 100% was used. The flame temperature of the burner, the time required for slag melting and The Cr ₂ O ₃ content in the slag after melting was investigated. Table 4 shows the conditions and results.

[0043]

[Table 4]

In the example of the present invention, a high burner flame temperature of 2400 ° C. or more is secured, and accordingly, the melting time, Cr ₂ O
The results equivalent to the results shown in Table 2 above (Example 1) were obtained for all _three contents. However, in a comparative example using an alternative gas having an oxygen concentration of less than 15%, the Cr ₂ O ₃ content was equivalent to the result shown in Table 2 above, but the burner flame temperature was lower due to incomplete combustion. The results were low and required a long time of over 110 minutes for dissolution.

[0045]

According to the electric furnace operating method of the present invention, even when a common steel, a chromium-containing special steel, and a stainless steel are melted by using an auxiliary burner having a triple pipe structure,
Splashes and incombustibles do not block the tip of the burner, shorten melting time and reduce power consumption, and achieve high efficiency.
And the oxidation loss of Cr and Cr can be suppressed, which is useful in terms of production cost and, in turn, global environment caused by hexavalent chromium.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a cross-sectional structure of a conventional auxiliary burner that ejects fuel from an inner tube and oxygen from an outer tube.

FIG. 2 is a diagram illustrating a cross-sectional structure of an auxiliary burner proposed in Japanese Patent Application Laid-Open No. 10-9524.

FIG. 3 shows A / (B × α + C × 0.93 +) in a case where stainless steel is melted using an auxiliary burner having a triple tube structure.
FIG. 2 is a diagram showing the relationship between the value of (D × 0.8) and the content of chromium oxide (Cr ₂ O ₃ ) in slag.

FIG. 4 shows the relationship between the value of A / (B × α) and the flame temperature of an auxiliary burner when scrap melting is performed using an auxiliary burner having a triple tube structure that supplies oxygen gas having a content of 95% or more. FIG.

FIG. 5 is a diagram showing the relationship between the oxygen content ratio of the gas supplied to the auxiliary burner and the burner flame temperature when A / (B × α) = 1.0.

[Explanation of symbols]

 1, 11: combustion burner, 2, 13: fuel jet pipe 3, 12, 14: oxygen gas jet pipe, 4, 15: annular space 12a: Laval throttle section, 16: swirl vane

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // C21B 11/10 C21B 11/10 4K055 13/12 13/12 4K063 C22B 9/20 C22B 9/20 F term (reference 4K001 AA10 BA22 BA23 FA10 FA14 GA16 JA01 4K012 CA09 DE08 4K013 AA01 AA02 BA00 CD00 CD02 4K014 CA03 CA04 CC01 CD18 4K045 AA04 BA02 RB02 RB13 RB21 4K055 AA03 MA01 4K063 AA04 AA12 DA06 CA06

Claims (5)

[Claims] 1. A triple pipe structure for ejecting oxygen gas from a central portion, ejecting fuel from an outer peripheral portion of the oxygen gas, and ejecting oxygen gas from an outer peripheral portion of the fuel, and an oxygen gas ejecting tube in the central portion. A method of operating an electric furnace using an auxiliary burner in which a swirl vane is provided in an annular space formed by a fuel ejection pipe and an outermost oxygen gas ejection pipe, provided with a Laval-shaped throttle portion at the tip of An electric furnace operating method, wherein the combustion conditions of the auxiliary burner satisfy the following formulas and formulas. A / (B × α + C × 0.93 + D × 0.8) ≦ 2.0 A / (B × α) ≧ 0.7 where α is the theoretical combustion ratio of oxygen to fuel A: Oxygen intensity (Nm ³ / ton of molten steel) B: Fuel intensity (Nm ³ / ton of molten steel, kg of liquid fuel / ton of molten steel) C: Carbon content of molten raw material (kg / ton of molten steel) D: Silicon content of molten raw material (kg / ton of molten steel) 2. A ratio of (a flow rate of oxygen spouted from a central portion / a flow rate of oxygen spouted from an outer peripheral portion) in the auxiliary combustion burner is defined as follows.
The method for operating an electric furnace according to claim 1, wherein the range is 0.05 to 20.0. 3. The electric furnace operating method according to claim 1, wherein a gas containing 15% or more of oxygen is supplied in place of the oxygen gas supplied to the auxiliary combustion burner. 4. The electric furnace operating method according to claim 1, wherein a coke oven gas is supplied as fuel for said auxiliary burner. 5. The electric furnace operating method according to claim 1, wherein a liquid fuel is supplied as fuel for said auxiliary burner.