JPH1047862A - Arc melting furnace and melting method of cold iron source employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of secondary combustion of exhaust gas of a DC arc melting furnace and contrive the improvement of heat transfer efficiency to the total amount of scrap. SOLUTION: Three sets or more of nozzles 3a-3c, blowing oxygen O2 for burning combustible substances in exhaust gas, are disposed at such positions that the ratio of a height (h) from the level of molten metal to the height L from the level of molten metal to the upper end of a side wall becomes h/L=0.15-0.55 in such a direction of a gas port that an angle θ formed by the line of projection Lg in the horizontal plane of the blow line of gas and the line of projection Lc in a horizontal plane of a straight line, connecting the gas port and the center line G of an electrode satisfies a relation θr<θ<40 deg., wherein the angle θr represents an angle formed by the line of projection Lc and the line of projection Lg in the horizontal plane of the blowing line when the electrode is lowered and the blowing line comes in contacted with the circumferential surface of the electrode. Respective three pieces or more of nozzles are provided at tow or more steps The internal volume of the furnace can receive the initial charge of total amount of scrap. L/D=0.6-1.4 (here D is the inner diameter of the furnace). Cold iron source is molten by the melting furnace employing auxiliary fuel and more than 40Nm<3> /t of oxygen for primary combustion for oxidizing and burning the scrap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc melting furnace, in which CO in exhaust gas generated from a melting furnace in operation is burned in a scrap layer in the furnace, and the combustion heat generated at the time is burned. TECHNICAL FIELD The present invention relates to an arc melting furnace that can efficiently heat scrap or molten steel therein.

[0002]

2. Description of the Related Art A so-called in-furnace combustion technique, that is, oxidative combustion of coke and scrap as auxiliary fuel in operation, is a technique for efficient energy recovery in a furnace from gas generated in an arc melting furnace. Generated by primary combustion due to oxygen injection and CO generated by primary combustion
Chakunetsu further techniques to accelerate the reaction in the furnace with the O ₂ blown for so-called two places to burn to CO ₂ post combustion in the furnace, as well as, the secondary combustion heat generated by the secondary combustion scrapped There is technology to make it.

[0003] As an arc melting furnace which is advantageous for heating of the exhaust gas generated in the arc melting furnace in the furnace, for example, Japanese Utility Model Laid-Open No.
Japanese Patent No. 167594 discloses that a furnace body shape capable of charging the entire amount of scrap at the initial charging in order to suppress heat energy loss in the furnace when additional metal scrap is charged during melting is provided. The height H from the sill level (indicating the upper end surface of the slag discharge port) to the upper end of the furnace body is 0.75 times or more the inner diameter D of the furnace shell, that is, H ≧ 0.75D
Further, as a secondary combustion technique, an opening for injecting O ₂ or air is provided on the inner wall of the furnace at a height of 0.35 D or more from the sill level in the furnace, and CO in the exhaust gas is provided. It discloses a method of blowing the amount of air necessary for oxidizing CO to CO ₂ according to the concentration (hereinafter referred to as “prior art 1”).

On the other hand, as a secondary combustion technique for recovering latent heat of exhaust gas in an arc melting furnace, for example, Japanese Patent Laid-Open No.
Japanese Patent No. 98364 discloses that an O ₂ gas jet lance is provided on the inner wall of a furnace at two positions in the height direction and at equal intervals at the same height on the inner circumference of the side wall in a direction substantially perpendicular to the vertical axis of the furnace space; An arc melting furnace having a blowing device in which the O ₂ gas ejection direction of each stage is directed in the same circumferential direction, and the upper and lower stages are directed in opposite directions to each other (hereinafter referred to as “prior art 2”). Is disclosed.

[0005]

The above-mentioned prior arts 1 and 2 both have the advantage of contributing to a reduction in the unit power consumption of the electric furnace by recovering energy from the exhaust gas to scrap in the furnace and to molten steel. However, prior art 1 is excellent in that a scrap preheating effect by the exhaust gas is exerted, but it cannot be said that secondary combustion of the exhaust gas is still sufficient. That is, detailed settings such as the position of the secondary combustion nozzle are not made. It merely describes sending air or the like into the furnace by a blower.

On the other hand, the prior art 2 is advantageous in that the improvement of the secondary combustion technology improves the heat-releasing efficiency. However, since it is not a furnace body that can be charged once, it is not possible to improve the heating efficiency with respect to the entire amount of melting scrap. Also, in order to properly employ the secondary combustion technology disclosed in Prior Art 2 for an arc melting furnace having a furnace body having the shape disclosed in Prior Art 1, and achieve the intended purpose,
It is necessary to optimize the arrangement position of the O ₂ gas jet lance, the number of the lances to be disposed, and the ejection direction of the lances.

[0007] Accordingly, an object of the present invention is to solve the above-mentioned problems, and to recover energy by an effective secondary combustion technique in the furnace from exhaust gas generated from an arc melting furnace, from both sensible heat and latent heat. It is an object of the present invention to provide an arc melting furnace which can be performed by improving the heating efficiency and thus can exhibit a comprehensive energy recovery effect.

[0008]

SUMMARY OF THE INVENTION The present inventors have developed an arc melting furnace capable of reducing the power consumption by further increasing the energy recovery rate from the exhaust gas of the arc melting furnace from the above-mentioned viewpoint. I did my utmost research.

First, the melting heat balance equation in the melting period of the arc melting furnace can be simplified to be expressed by the following equation (3). η _e Q _e + η _c Q _c + η _m Q _m + Q _pr = Q _s (3) where Q _{e is the} input electric energy Q _{c is the} calorific value of carbon combustion in the furnace = (Q _CO + Q _CO2 × PCD) × W _C / 860 Q _m : calorific value due to oxidation of metal (mainly Fe, Mn, Al, Si, etc.) (usually about 80 to 90 kWh / ton) η _e : input Average heat transfer efficiency of electric power (approximately 0.7 to 0.8) η _c : Average heat transfer efficiency of combustion heat of carbon in the furnace η _m : Average heat transfer efficiency of metal oxidation heat, Q _pr : Sensible heat amount by scrap preheating Q _s : The amount of heat required to dissolve the scrap (normally 380kWh / ton
) W _C : Burning C in furnace per unit weight of molten steel in melting period (Kg / to
n) PCD (Post Combination Degre)
e): post combustion ratio i.e. Chakunetsuryo Q _s necessary scrap melting, the input power amount Q _e, the average of the calorific value consisting of the calorific value Q _m by the furnace combustion calorific value Q _c and the metal oxide of the carbon It depends on the heat transfer efficiency and the sensible heat brought in by scrap preheating. Among these the heat of the object of the present invention, in particular lies in utilizing the furnace combustion heat of carbon at high efficiency, therefore, is to increase the average deposition thermal efficiency eta _c. Thus, the exhaust gas energy can be used.

In the above equation (3), η _c is generated by the primary combustion of carbon in the bath according to the following equation (4) and the secondary combustion of carbon in the furnace space according to the following equation (5). This is the average heat transfer efficiency of the combustion heat to the heating target (scrap and molten metal) in the furnace.

C + (1/2) O ₂ → CO + Q _co , Q _co = 2450 Kcal / Kg carbon --- (4) CO + (1/2) O ₂ → CO ₂ + Q _co2 , Q _co2 = 5630 Kcal / Kg carbon ---------------- (5) And η _c can be expressed by the following equation (6).

[0012] _{η c = {Q co η co} + Q co2 PCDη co2} / (Q co + Q co2 × PCD) ------------------ (6) However, CO ₂ : CO ₂ ratio in exhaust gas (vol.%) CO: CO ratio in exhaust gas (vol.%) Where η _co is the heat transfer efficiency of the heat of combustion of carbon in the bath, which is the shape of the melting furnace And high efficiency with little influence from operating conditions. The secondary combustion rate PCD has been increased to about 0.8 by recent technological development. Therefore, increasing the PCD in reducing power consumption rate, raising the Q _c, and, in order to increase the eta _c, C in the furnace space
It is an essential requirement to increase the heat transfer efficiency η _co2 of the combustion heat of O.

[0013] If a furnace capable of accommodating the entire amount of scrap for one melting in the initial charging (referred to as "single charging furnace") is used, the scrap is additionally charged after the initial charging scrap burns down. Compared to the charging furnace or the triple charging furnace, η _co2 can be increased because the entire amount of scrap for one charge is charged into the furnace from the beginning of melting, and therefore η _co2 can be increased.
_{Since c} can be increased, the present invention is based on the premise that one-time charging, that is, the entire amount of scrap for one charge can be charged at the chance of initial charging.

When oxygen-containing gas is blown into the furnace space of the arc melting furnace to burn CO in exhaust gas generated from the melting furnace, one, two or three gas nozzles for blowing are used.
It was found that the average heat transfer efficiency η _{c of the} combustion heat of the carbon in the furnace in the above equation (3) increases as the number of books increases.
According to the equation (6), it is considered that this increase is due to the increase in the COD heat rate η _co2 in the furnace space together with the improvement in the secondary combustion rate PCD of CO.

FIG. 1 is a graph showing the relationship between the number of gas nozzles and the average heat transfer efficiency η _{c of} combustion heat of carbon in a furnace.
Here, the melting furnace is a DC arc melting furnace having a nominal 120 ton, the furnace inner diameter D is 7000 mm, the height (hereinafter, referred to as “free board”) L from the furnace surface to the upper end of the furnace inner wall is 4000 mm, and L / D = 0.57, the mounting height h of the gas nozzle is 1000 mm from the surface of the furnace, h / L =
0.25. According to the figure, the number of gas nozzles should be three or more in order to increase the average heat transfer efficiency η _c of combustion heat of carbon in the furnace.

Note that the in-furnace surface refers to the upper surface of molten steel when the entire amount of scrap for one melting is melted (the same applies hereinafter). FIG. 2 illustrates the definitions of the free board L and the furnace inner diameter D.

On the other hand, if the number of the gas nozzles is too large, the equipment and operation costs are increased, so that there is a restriction from this point. The appropriate number of gas nozzles is affected by the relationship between each gas nozzle interval that affects η _c and the initial speed or pressure of the blown gas. In consideration of the above, it is desirable that the number of gas nozzles installed at the same height be within a range of 3 to 6.

Next, as the height at which the gas nozzle is installed is lower, the average heat transfer efficiency η _c of the combustion heat of carbon in the furnace increases, but the gas nozzle is damaged by the molten metal splash unless a certain height is maintained from the surface of the molten metal. Easy to do. On the other hand, if the position is too high, η _c will decrease significantly.

FIG. 3 shows the arrangement height of the gas nozzle from the molten metal surface.
h to the ratio of h / L to the free board L and the heat of combustion of carbon in the furnace
Average heat transfer efficiency η_c6 is a graph showing a relationship with the graph. here
The melting furnace is a 120 ton DC arc melting furnace, furnace
Inner diameter D is 7000 mm, free board L is 4000 mm
And three gas nozzles are installed at the same height h.
is there. According to the figure, the average heat transfer efficiency of carbon combustion heat in the furnace
η_cHeight where the gas nozzle should be installed to increase the height
Depends on the installation height h from the surface,
The relationship between the height L to the end is from h / L = 0.55.
Η under small conditions _cYou can see that
You. The smaller h / L is η_CRises, but the
H / L> 0.15 is necessary due to the problem of the splash.

The number of levels (number of stages) at which the gas nozzles are installed is increased as the L / D value of the melting furnace increases and the furnace body becomes longer in length, thereby maintaining the turbulence of the gas flow to maintain η _c.
Can be kept high. From this viewpoint, in the case of a furnace body in which the L / D of the melting furnace exceeds 1.0, it is desirable to set the number of gas nozzle installation stages to two or more.

Next, the direction of the outlet of the gas nozzle should not collide with the outlet line of the oxygen-containing gas when the upper arc electrode is lowered. In other words, the direction of the gas outlet of the gas nozzle is such that the projection line of the oxygen-containing gas outlet line into the horizontal plane and the straight line connecting the outlet and the central axis of the upper arc electrode into the horizontal plane (projection line) Lc
The angle θ between the projected line of the oxygen-containing gas and the projected line of the oxygen-containing gas when the upper arc electrode is in contact with the peripheral surface of the arc electrode when the upper arc electrode is in a lowered state. The angle formed by the projection line Lc is θr
(°), the angle θ is made larger than θr. Moreover, the angle θ should be less than 40 °.

The reason for limiting the direction of the outlet of the gas nozzle in this way is to prevent the oxygen-containing gas from causing oxidative damage to the electrode carbon, while the angle θ
Is set to less than 40 ° in order to prevent damage to the refractory due to collision of the oxygen-containing gas with the furnace inner wall (refractory, water-cooled panel, etc.) material. Furthermore, in addition to the above conditions, it is desirable that the direction of the outlet of the gas nozzle is directed obliquely downward from the horizontal direction, and is directed toward the bath surface when the number of gas nozzle installation stages is one.

When pure oxygen gas is used as the oxygen-containing gas, the secondary combustion rate PCD can be further improved.
If pure oxygen gas is used after being heated by exhaust gas, the utilization rate of exhaust gas energy is further improved.

The effect of the oxygen consumption rate for primary combustion on the power consumption rate when applying the present invention was examined by variously changing the oxygen consumption rate. A furnace in which the entire amount of scrap can be charged into the furnace with one chance of initial charging with a melting amount of 150 tons.
Five secondary combustion nozzles were installed around /L=0.25. The amount of oxygen for secondary combustion is 30 times the amount of oxygen for primary combustion.
%.

FIG. 4 shows the test results. As shown in the figure, when the oxygen intensity is 40 Nm ³ / t or more, the power intensity per unit weight is significantly reduced, and the effect of the secondary combustion becomes remarkable. Therefore, in the present invention, the amount of oxygen for primary combustion is set to 40N.
m ³ / t or more.

Ratio L / D between free board L and inner diameter D of furnace
Is a factor that affects the relationship between the shape and direction of efficient arc generation and the distribution of scrap charged in the furnace.
It is thought that this greatly affects the heat transfer efficiency from scrap to scrap. Focusing on this heat transfer efficiency, L × D
² is constant, that is, the heat of the exhaust gas carried out of the arc furnace using a practical small-scale arc furnace of various L / Ds in which the furnace volume above the furnace surface is constant. Tested for loss. In the test dissolution, scraps having a constant bulk density were used in each of the chargers, all the scraps were initially charged, and an arc furnace test operation was performed by a conventional method.

FIG. 5 is a graph showing the relationship between the ratio L / D between the freeboard L and the inner diameter D of the furnace and the heat loss ratio of the exhaust gas. The figure shows the case where the in-furnace secondary combustion with the oxygen-containing gas was not performed, and the heat loss ratio of the exhaust gas was L / D = 0.
It is expressed as a ratio of the sum of the sensible heat and the latent heat of the exhaust gas in the test charge to the sum of the sensible heat and the latent heat of the exhaust gas in the test charge in the case of 55.

As is apparent from FIG. 5, the heat loss ratio of the exhaust gas decreases as L / D increases. L / D is 0.
The heat loss ratio of the exhaust gas in No. 6 is improved to about 0.90, and the effect is also useful in operating costs. Furthermore, as L / D increases, the heat loss ratio of the exhaust gas further decreases. However, even if L / D exceeds 1.4, the improvement in the heat loss ratio of the exhaust gas is small and almost saturated. on the other hand,
As the L / D increases, the electrode lifting device, building,
Disadvantages are that the specifications of the heating equipment and the furnace body cooling equipment must be increased. When the L / D exceeds 1.4, the disadvantage becomes a problem. Considering the heat loss ratio of the exhaust gas, and the investment and operating costs of the above facilities,
L / D is desirably in the range of 0.7 to 1.2.

Therefore, in order to improve the dissolving efficiency of scrap and reduce the total cost, the L / D should be in the range of 0.6 to 1.4, preferably 0.7 to 1.2. Is good.

Here, the requirements for a single charging furnace are determined. By determining the amount of scrap charged per charge and L / D, and calculating L and D determined in accordance therewith, a desired furnace size can be obtained. In a normal arc furnace, the following equation (7) is applied between L, D and the charged amount W of scrap: L / D = (4 / π) ｛(ρ ₁ −ρ _S ′) / (Ρ _l ρ _S ')｝ (W / D ³ ) ------------ (7) where ρ _l : density of molten steel ρ _S ': bulk density of scrap W: density of scrap There is a relationship with the charge. In the arc furnace, various forms of scrap for steelmaking are used, and the bulk density of these scraps ranges from 0.3 to 1.0 t / m ³ , but the weighted average value is 0. It is about 0.7 t / m ³ . Therefore, the scrap charging amount W for one charge and L /
Given D, the free board L and the furnace inner diameter D are obtained. For example, if W = 120t, in order to satisfy L / D ≧ 0.6, which is a desirable condition in the present invention, the furnace inner diameter D ≦ 6.9 (m) and the furnace must be The height L to the upper end of the inner wall depends on the value of D,
L ≧ 0.6 × D (m), that is, L / D ≧ 0.6. On the other hand, if the L / D is too large, the heat loss to the furnace side wall will be large, and it is preferable to set the L / D to 1.4 or less as described above.

Accordingly, the shape of the furnace body of the single charging furnace is as follows.
It is desirable that L / D = 0.6 to 1.4. In addition, 1
When operating in a recharge furnace, there is no furnace heat loss due to opening and closing of the furnace lid during operation, and in the melting period, the arc from the electrode is surrounded by scrap, so the input power scrap The two effects of increasing the heat transfer efficiency to the surface are also added.

The average heat transfer efficiency η _c of the combustion heat in the furnace of carbon is compared between the case where the above-described one-time charging furnace is used and the case where the conventional two- or three-time charging furnace is used. FIG. 6 is a graph showing the influence on the average heat transfer efficiency η _c of the in-furnace combustion heat of carbon during the melting period due to the difference between once, twice and three-time charging furnaces. According to the figure, in the case of the single charging furnace, the average heat transfer efficiency η _{c of the} combustion heat of carbon in the furnace is significantly improved as compared with the double charging furnace and the triple charging furnace.

Based on the findings described above, the present inventors can obtain a higher heat transfer efficiency to the objects to be heated (scrap and molten metal during heating) in the furnace by using the total energy of the exhaust gas from the arc melting furnace. By devising an arc melting furnace, and then charging the entire amount in one chance without adding additional scrap for one melting point, heating and melting in the above-mentioned high heat-charging arc melting furnace, It was confirmed that an effect that could not be obtained was obtained.

The arc melting furnace of the present invention is as follows. The arc melting furnace according to the first aspect has the following features. The inner volume of the melting furnace can accommodate the entire amount of scrap for one melting at the initial charging chance, and the high temperature generated when the raw material is heated, melted and refined in the melting furnace on the inner wall of the furnace. Combustible substances in exhaust gas of
In order to burn the gas, that is, to perform the secondary combustion, a gas nozzle for blowing an oxygen-containing gas into the furnace space is provided. If the gas nozzle is provided with three or more gas nozzles to improve the combustion efficiency of combustible substances in the exhaust gas, the height is set to h from the furnace surface, and the free board is set to L, the following equation (1): h / L = 0.15 to 0.55 (1)

Further, the direction of the gas outlet of the gas nozzle is such that the projected line of the oxygen-containing gas outlet line onto the horizontal plane (hereinafter referred to as "projected line Lg") and the central axis of the outlet and the upper arc electrode. (Hereinafter referred to as “G”) and a projection line onto the horizontal plane (hereinafter referred to as “projection line Lc”).
Is defined as the projection of the oxygen-containing gas blowout line into the horizontal plane when the oxygen-containing gas blowout line contacts the peripheral surface of the arc electrode when the upper arc electrode is in a lowered state. The angle between the line and the projection line Lc is θ
When r (°), the relationship of θr <θ <40 ° is satisfied. The present invention is characterized by satisfying all the above conditions.

The arc melting furnace according to the second aspect is the first aspect of the invention.
In the melting furnace described above, further, the mounting position of the above-mentioned gas nozzle is not limited to a certain level from the surface of the furnace, and the height of the free board is large in order to further increase the effect of the secondary combustion. Has two or more heights. And it is characterized by providing three or more gas nozzles at each level of height.

The arc melting furnace according to the third aspect is the second aspect of the invention.
In order to further increase the internal volume of the melting furnace to a volume capable of charging the entire amount of scrap for one melting at the initial charging chance, the freeboard L and the inner diameter D of the furnace were described.
By satisfying the following equation (2): L / D = 0.6 to 1.4 ---------------- (2) It is characterized in that exhaust gas energy and arc energy can be used more efficiently.

The method for melting a cold iron source using an arc melting furnace according to the present invention is as follows. The method for melting a cold iron source using the arc melting furnace according to claim 4 has the following features. That is, using the arc melting furnace according to any one of claims 1 to 3, utilizing all the functions provided in the melting furnace, further, in the melting furnace during melting and refining,
It is characterized by blowing primary combustion oxygen for oxidizing and burning auxiliary fuel such as coke and scrap.

The method for melting a cold iron source using an arc melting furnace according to the fifth aspect of the present invention is characterized in that the primary combustion oxygen is added to the melting method according to the fourth aspect to make the effect of the present invention more remarkable. It is characterized by using at least 40 Nm ³ / t.

[0040]

Next, the present invention will be further described with reference to the drawings. FIG. 7 is a partially cutaway schematic configuration view showing an embodiment of the arc melting furnace of the present invention.
8 to 9 are horizontal cross-sectional views taken along lines XX and YY of FIG. 7, respectively, and FIGS. 10 and 11 are sectional views taken along line A of FIGS. 8 and 9, respectively. -A
FIG. 3 is a vertical sectional view taken along line BB and line BB.

As shown in FIG. 7, inside the side wall 2 of the DC arc melting furnace 1, three gas nozzles for blowing oxygen-containing gas into the furnace over two stages in the height direction are provided.
A total of six gas nozzles 3a, 3b,..., 3f are attached.
Is connected to the oxygen-containing gas supply device 5 via the. On the other hand, an exhaust gas piping 7 (see FIG. 2) is connected to a furnace cover 6 (see FIG. 2) of the DC arc melting furnace 1 and communicates with a melting furnace exhaust fan (not shown). An exhaust gas analyzer 9 is connected to a part of the exhaust gas piping 7 via an exhaust gas sampling device 8, a transmission cable is connected to the oxygen-containing gas supply control device 10, and further connected to the oxygen-containing gas supply device 5.

The furnace body shape of the melting furnace is such that the height (free board) from the furnace surface 11a to the upper end 13 of the furnace inner wall 2 when the entire amount of scrap for one melting is melted is L, and the inner diameter of the furnace is Assuming that D is in the range of L / D = 0.6 to 1.4, the scrap for one dissolution can be accommodated in the first charging chance, and is a so-called single charging furnace.

As shown in FIGS. 8 and 9, three gas nozzles are attached to each stage at equal intervals on the inner circumference of the furnace inner wall 2, and each gas nozzle is provided with one gas blowing hole. Projection line (straight line Lg)
) And a projection line (straight line Lc) of a straight line connecting the gas outlet and the central axis (G) of the upper arc electrode into a horizontal plane.
(See FIG. 8) are directed at a predetermined angle in the furnace direction. Here, the angle θ is larger than the angle θr when the blowing line of the oxygen-containing gas comes into contact with the peripheral surface of the upper arc electrode when the upper arc electrode is lowered, and 40 °.
Set to less than °. The blowing directions from the lower and upper gas nozzles are clockwise and counterclockwise, respectively.

As shown in FIGS. 10 and 11, the heights of the gas nozzles mounted on the lower and upper stages are respectively at positions h ₁ /L=0.25 and h ₂ /L=0.50 from the surface of the molten metal. Each gas nozzle faces downward at a predetermined angle α with respect to the horizontal direction H (see H and α in FIG. 10).

Next, an embodiment of the method for operating the DC arc melting furnace will be described. The entire preheated or unheated scrap for one melt is charged into the DC arc melting furnace 1, the furnace lid 6 is closed, the furnace is sealed, and the upper arc electrode 12 is heated.
To start the arc melting. A predetermined exhaust fan and a damper are operated, and a sample collected from a high-temperature exhaust gas generated in the furnace by an exhaust gas sampling device 8 is analyzed for CO, H ₂ , and CO ₂ gas contents by an exhaust gas analyzer 9. Oxygen-containing gas supply control device 1 based on
The oxygen-containing gas at a flow rate controlled at 0 is supplied from the oxygen-containing gas supply device 5 and injected from the gas nozzle 3 into the furnace.
After heating and melting the entire amount of the scrap, a predetermined slag-making material is put into a furnace, a predetermined refining is performed, and steel is tapped into a ladle.

[0046]

Next, the present invention will be further described with reference to examples. In the embodiment of the present invention shown in FIGS. 7 and 8 to 11, tests were performed under the electric furnace facilities and operating conditions shown in Table 1. Table 2 shows the details of the installation conditions and the acid supply conditions of the secondary combustion gas nozzle.

[0047]

[Table 1]

[0048]

[Table 2]

The test was carried out as shown in Table 1 with a dissolution capacity of 15
0 ton / charge DC arc melting furnace or 120t
In an on / charge DC arc furnace, four different combinations of differences in L / D values, the presence or absence of a secondary combustion nozzle, and differences in the amount of oxygen used for primary combustion were performed. The first is within the scope of the present invention (Example 1). When the primary combustion oxygen is used at 42 Nm ³ / t and the secondary combustion is performed in a single charge furnace for scrap, the second is the present invention. (Example 2), and when the oxygen for primary combustion in Example 1 is 33 Nm ³ / t, the third is out of the scope of the present invention (Comparative Example 1), and the single charging furnace for scrap is used. And the fourth case is outside the scope of the present invention (Comparative Example 2), in which the secondary combustion was not performed in the double charging furnace for scrap.

Further, in Examples 1 and 2, three gas nozzles for secondary combustion were attached to the lower and upper stages at equal intervals on the inner wall of the furnace wall, and the gas outlets were reversed in upper and lower stages. Directed to blow gas in the direction. Each gas outlet was provided with one gas outlet, and the projection angle θ in the horizontal plane was set to 30 ° and the projection angle α in the vertical plane was set to 15 ° in the blowing direction.

Here, the projection angle α in the vertical direction in the gas blowing direction refers to the angle between the projection line of the gas blowing line in the vertical plane and the horizontal line in the vertical plane. Also, the commercially pure oxygen as a secondary combustion oxygen-containing gas, in Example 1, 9.6 nm ³ / t and Example 2, 13.2 nm ^3,
/ T.

Table 3 shows the test results. Table 3 shows the following.

[0053]

[Table 3]

According to the operation of the melting method using the arc melting furnace of the present invention according to Examples 1 and 2, the thermal efficiency is greatly increased as compared with the operation according to Comparative Examples 1 and 2, which are conventional arc furnaces. . The reason for this is that, in Examples 1 and 2, the increase in the in-furnace secondary combustion rate PCD increased the in-furnace calorific value of carbon due to the improvement in the in-furnace secondary combustion rate, and the efficiency of heat transfer of CO gas combustion heat in exhaust gas to the in-furnace scrap It can be seen that this is due to the rise in In addition, the first embodiment is much better than the second embodiment.

[0055]

As described above, according to the present invention,
Provided is an arc melting furnace capable of efficiently recovering energy from generated gas generated in an electric furnace by improving an in-furnace secondary combustion rate and an efficiency of heat transfer of sensible heat of exhaust gas to scrap in the furnace. Further, a method for melting a cold iron source using the arc melting furnace can be provided, and an industrially useful effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number of gas nozzles and the average heat transfer efficiency η _{c of} combustion heat of carbon in a furnace.

FIG. 2 is a diagram for explaining definitions of a free board L and a furnace inner diameter D.

FIG. 3 shows a relationship between a ratio h / L of an arrangement height h of the gas nozzle from the molten metal surface to a height L from the molten metal surface to the upper end of the side wall, and an average heat transfer efficiency η _{c of} combustion heat in the furnace of carbon. FIG.

FIG. 4 is a graph showing an effect of an oxygen consumption unit for primary combustion on a power consumption unit.

FIG. 5 is a graph showing a relationship between a ratio L / D of a height L from a molten metal surface to an upper end of a side wall in the furnace and an inner diameter D of the furnace, and a heat loss ratio of exhaust gas.

FIG. 6 is a graph showing the influence on the average heat transfer efficiency η _c of the combustion heat of carbon in the furnace due to the difference between the once, twice and three times charging furnaces.

FIG. 7 is a partially cut-away schematic configuration view showing one embodiment of the present invention.

FIG. 8 is a horizontal sectional view taken along line XX of FIG. 7;

FIG. 9 is a horizontal sectional view taken along line YY of FIG. 7;

FIG. 10 is a vertical sectional view taken along line AA of FIG. 8;

FIG. 11 is a vertical sectional view taken along line BB of FIG. 9;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 DC arc melting furnace 2 Side wall 3 Gas nozzle 3a, 3b, ..., 3f Gas nozzle 4 Oxygen-containing gas piping system 5 Oxygen-containing gas supply device 6 Furnace lid 7 Exhaust gas system piping 8 Exhaust gas sampling device 9 Exhaust gas analyzer 10 Oxygen-containing gas the height of the height h ₂ upper gas nozzle supply controller 11 melt 11a molten metal surface 12 central axis h ₁ lower gas nozzle of the upper arc electrode 13 upper 14 bottom electrode 15 hearth L freeboard D furnace inner diameter G upper arc electrode

Continued on the front page (72) Inventor Shuzo Uchino 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (5)

[Claims] 1. The furnace has a volume capable of accommodating the entire amount of scrap for one melting at an initial charging chance, and burns combustible substances in exhaust gas generated when heating, melting and refining raw materials on a furnace inner wall. In an arc melting furnace provided with a gas nozzle for blowing an oxygen-containing gas for secondary combustion into the furnace space, three or more gas nozzles are provided, and the gas nozzle is provided at a position where the entire amount of scrap for one melt is melted. The relationship between the height h from the molten steel surface to the gas nozzle and the height L from the molten steel surface to the upper end of the furnace inner wall is expressed by the following formula (1): h / L = 0.15-0. 55 ---------------- (1) is satisfied, and the direction of the gas outlet of the gas nozzle is a projection line of the oxygen-containing gas blowing line into a horizontal plane. A straight line connecting the outlet and the central axis of the upper arc electrode. Angle θ between the line and a projection line (referred to as projection line Lc) in the horizontal plane
(°) is a projection line of the oxygen-containing gas blowing line into the horizontal plane when the blowing line of the oxygen-containing gas comes into contact with the peripheral surface of the upper arc electrode when the upper arc electrode is lowered. Is the angle between the projection line Lc and θr
An arc melting furnace characterized by satisfying a relationship of θr <θ <40 ° when (°). 2. The arc melting furnace according to claim 1, wherein three or more gas nozzles are respectively provided at a height of two or more levels from a surface of the furnace. 3. In the melting furnace, the relationship between the height L from the furnace surface to the upper end of the furnace inner wall and the furnace inner diameter D is expressed by the following equation (2): L / D = 0.6 to The arc melting furnace according to claim 2, wherein 1.4 ---------------- (2) is satisfied. 4. An arc melting furnace according to any one of claims 1 to 3 for oxidizing and burning auxiliary fuel such as coke and scrap in the melting furnace during melting and refining. A method for melting a cold iron source using an arc melting furnace, characterized by blowing oxygen for primary combustion. 5. The method according to claim 5, wherein the oxygen for the primary combustion is 40 Nm ³ / t.
The method for melting a cold iron source using an arc melting furnace according to claim 4, wherein the method is used as described above.