JPH10318675A - Steel making electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use in common an oxygen feed refining and an arc refining, to recover thermal energy retained in exhaust gas by preheating a solid iron source such as scraps and to melt and refine the solid iron source with high thermal efficiency. SOLUTION: Two furnace casing shells 4 and 5 are arranged in symmetrical positions on a turntable 3. An oxygen feed refining by a large volume of oxygen feeding and water cooling lance 6 from a furnace belly shell 7 with which the furnace casing shell 4 is covered is separated from an arc refining from a graphite electrode 11 disposed on the upper part of a furnace belly shell 8 with which the furnace casing shell 5 is covered. They respectively perform melt and refine half of the solid iron source. The turntable 3 is turned during a refining process to change the position of the lance 6 for the position of the electrode 11, After that, the oxygen feed refining and the arc refining are respectively carried out in the remaining half of the melting and refining process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric furnace for steelmaking provided with a preheater for recovering thermal energy possessed by exhaust gas and preheating a solid iron source such as scrap for melting and refining efficiently. .

[0002]

2. Description of the Related Art In general, an electric furnace for steelmaking has used iron scrap (so-called commercial iron waste) as a main raw material as a solid iron source. In a steelmaking electric furnace, an electric arc is used as a heat source for melting and refining iron scrap (hereinafter, referred to as scrap), so that the ratio of electric power cost to cost is high. For this reason, there are various systems that preheat the scrap charged into the steelmaking electric furnace by using the heat of the exhaust gas discharged from the furnace, thereby reducing the electricity cost of the steelmaking electric furnace and improving the furnace operation efficiency. Proposed.

As an electric furnace for steelmaking provided with a preheater for scrap, for example, Japanese Patent Publication No. 6-51883 discloses an electric furnace mounted on a plurality of trolleys at first, second, third and fourth stations. And an electric furnace of a multiple furnace type which simultaneously operates as a first station for standby, a second station for preheating scrap, a third station for heating, and a fourth station for melting and refining.

Further, Japanese Patent Publication No. 63-1366, Japanese Patent Publication No. 6-31
Japanese Patent Publication No. 686 and Japanese Patent Application Laid-Open No. 62-156218 disclose an electric furnace utilizing a two-furnace body, in which scrap preheating and melting using the heat of exhaust gas discharged from the furnace are alternately repeated in two furnaces. JP-A-8-21691 discloses that exhaust gas from an electric furnace is introduced into a kiln type preheater to preheat scrap,
Subsequently, an electric furnace with a kiln-type / shaft-type preheater is disclosed, in which exhaust gas from a kiln-type preheater is guided to a shaft-type preheater to preheat scrap.

On the other hand, a recent iron source for an electric furnace is to reduce the energy cost of the electric furnace by using both hot metal and scrap, and to increase the variety of steel types produced in the electric furnace and to increase the content of Pb contained in the steel scrap in the market due to the upgrading of steel grades. The use of virgin iron and reduced iron as diluents for trap elements such as Cu, Cu and the like has been diversified, and further enhancement of the melting function of electric furnaces for steelmaking is required. Such enhancement of the melting function is not sufficient simply by improving the conventional melting function mainly based on scrap preheating as disclosed in the above-mentioned publication, and large-capacity acid decarburization is applied to a steelmaking electric furnace. It is required to enhance the dissolution function.

That is, the above-mentioned iron sources such as hot metal, virgin iron, and reduced iron contain 1 to 4% of carbon [C] and have a higher [C] than that of iron scrap. It is necessary to carry out acid decarburization. In order to provide the steelmaking electric furnace with an acid-supplying function, a means for inserting an acid-supplying water-cooling lance through a discharge hole in the back of the furnace to feed the acid into the furnace, or as disclosed in JP-A-60-174813. Means for injecting oxygen and coke powder into a furnace from an auxiliary burner for promoting melting provided in a furnace body and burning the same are conventionally known.

[0007]

As described above, since hot metal, solid virgin iron and reduced iron contain 1-4% of [C], the use ratio of these iron sources is reduced to, for example, 50%. Then, [C] immediately after melting in the steelmaking electric furnace is 1 to 2%. In order to carry out acid decarburization without extending the refining time, an acid supply amount of 100 to 500 Nm ³ / min is required depending on the heat size. However, conventional acid-water cooling lances are tens of tens.
The acid supply rate of Nm ³ / min is the upper limit that can maintain the stable operation of the electric furnace, and the acid supply capacity is insufficient, so it is inevitable to extend the refining time. Regarding the furnace body arrangement, all of those disclosed in each of the above publications focus on scrap preheating, and no consideration is given to shortening of the refining time by high-speed acid supply. We can't expect any reinforcement.

[C] When refining by dissolving a solid iron source having a high content, it is important to minimize the melting time and the unit power consumption as much as possible. In order to meet such demands, in addition to electric energy, heat from an oxidation reaction is used to promote melting of scrap by preheating and raise the temperature of molten steel. The present invention solves the problems of the prior art by utilizing the heat of the oxidation reaction, without increasing the melting time even when a large amount of hot metal having a high carbon content, virgin iron, and reduced iron are used. Another object of the present invention is to provide an electric furnace for steelmaking provided with a preheater capable of reducing electric power costs.

[0009]

According to a first aspect of the present invention, there is provided a turntable rotatable about a rotating shaft, and a turntable arranged on the turntable so as to be axially symmetrical, A pair of furnace shells that constitute a furnace body lower part by opening the furnace body, are arranged stationary on the swirl locus of the furnace body shell, one is provided with an acid lance, and the other is provided with an arc arc electrode, A pair of furnace shells which can constitute a furnace body for melting and refining integrally with the furnace body shell, an exhaust gas duct for leading high-temperature exhaust gas accompanying melting and refining from the furnace body shells, And a preheater disposed on at least one between the furnace belly shells and preheating a solid iron source to be charged into the furnace shell with high-temperature exhaust gas from the exhaust gas duct.

According to a second aspect of the present invention, the preheater includes:
A pair is disposed between the furnace shells on the swirl locus, one of which is for introducing high-temperature exhaust gas from the furnace shell having an acid supply lance, and the other is a furnace shell having an arc electrode. 2. The steelmaking electric furnace according to claim 1, wherein said high-temperature exhaust gas is introduced.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIGS. 1 and 2, the turntable 3 is supported via a thrust bearing 1 provided on a support frame (not shown),
Can be turned horizontally around the center. On the turntable 3, two furnace shells 4, 5, which constitute the lower part of the electric furnace for AC type steelmaking and are open at the top, are arranged symmetrically about the rotation axis 2. The turntable 3 is a rotating shaft 2
The motor can be turned freely by a turning drive device (not shown) connected to the motor. Each of the furnace shells 4 and 5 is lined with a refractory on the inner surface, and has a tapping gutter 12. Each of the furnace shells 4 and 5 is provided with a tilting cylinder 13, and the tilting cylinder 13 on the turntable 3 can be tilted about a bearing 14 provided on the opposite side by extending and contracting the tilting cylinder 13. .

In the drawing, when the two furnace shells 4 and 5 arranged on the turntable 3 are stopped at predetermined melting processing positions II and IV, respectively, one furnace shell is shown in the drawing. 4 is covered with a stationary furnace belly shell 7 having a large capacity acid water cooling lance 6 at the top, and a furnace shell 5 on the other side.
3 shows a case where three graphite electrodes 11 for applying an alternating current are covered by a stationary belly shell 8 having a stationary arrangement provided at the top. Here, the furnace belly shell 7 has a sufficient height for splashing and spitting, which are problems during high-speed acid feeding. Further, a preheater 9 for preheating a small solid iron source is provided above an intermediate position on one side on a swirl locus where the furnace shells 4 and 5 existing below the stationary belly shells 7 and 8 respectively turn. And a preheater 10 for preheating a large solid iron source is disposed above the intermediate position on the other side. Preheater 9,
A plate-shaped cut gate 19 is provided at the lower end of the 10, and the lower end is opened and closed by sliding the cut gate 19 horizontally.

The upper part of the furnace shell 7 on one side is covered with an exhaust gas hood 15 through which the acid-water cooling lance 6 penetrates, and is removed from the exhaust gas duct 16A taken out from the exhaust gas hood 15 and the upper part of the furnace shell 8. The exhaust gas duct 16B is connected by a duct relay section 17. In addition, duct relay section 17
One of the exhaust gas ducts 16C and 16D branched from the exhaust gas duct 16C is connected to the preheater 9 and the other exhaust gas duct 16D is connected to the preheater 10. Further, a switching valve 18 is provided in the duct relay section 17, and by operating the switching valve 18, the flow path of the exhaust gas can be switched.

Next, the operation of the present invention will be described. FIG.
As shown in FIG. 2 and FIG. 2, four processing positions are formed in a state where the furnace shells 4, 5 arranged on the turntable 3 are stopped at predetermined refining positions. That is,
Preheating / injection position I of small solid iron source by preheater 9, Dissolution processing position of small solid iron source by acid supply formed by furnace shell 4 and furnace bottom shell II, Large solid by preheater 10 Preheating and charging position III of iron source, melting position of large solid iron source by arc formed by furnace shell 5 and furnace shell 8
There are four locations IV, and the processing time at each of these four locations can be approximately the same, for example, about 30 minutes. Therefore, it is possible to perform processing synchronously on the turntable 3. Of course, there may be a difference between the processing times at the four locations due to changes in various operating conditions. Therefore, the processing time is adjusted by controlling the longest processing time among the time required at each location. In this case, the treatment time is adjusted with emphasis on melting / refining by acid supply and melting / refining by arc rather than preheating of the solid iron source.

Here, the switching valve 18 installed in the duct relay section 17 is provided with the exhaust gas ducts 16A and 16C and the exhaust gas duct 16A and 16C.
The position is adjusted to allow communication between 16B and 16D. Switching valve
By switching 18 to 90 °, exhaust gas ducts 16A and 16D
In addition, the exhaust gas ducts 16B and 16C can communicate with each other. The turntable 3 is turned so that the furnace shells 4 and 5 are moved directly below the preheaters 9 and 10, respectively. Cut gate of preheater 9 at preheating / input position I
Opening 19, reduced iron with high [C] concentration (for example, 50% by weight of the total iron source is reduced iron) in addition to shredder scrap, Dalai powder, commercially available iron shavings, etc. Is charged into the furnace shell 4 having a hot heel at the bottom of the furnace. At the same time, the cutting gate 19 of the preheater 10 is opened at the preheating / injection position III to open a large solid iron source (having a weight of 2.0 t or more) such as a high-temperature preheated slab or bloom cutting scrap, an ingot bottom mass, or the like. The molten steel 20 formed in the first half of the process by the acid supply in advance in the melting position II is charged into the furnace shell 5 in which the molten steel 20 exists.

After that, the turntable 3 is turned by 90 ° to move the furnace shell 4 to the melting treatment position II of the small solid iron source immediately below the furnace shell 7 and the furnace shell 5 to the furnace shell 8. It is moved to the dissolution processing position IV of the massive solid iron source immediately below. Either the furnace shells 7, 8 or the turntable 3 is moved up and down by a lifting device, and the lifting device is driven to drive the furnace shell 4 and the furnace shell 7, the furnace shell 5 and the furnace shell. It is preferable to eliminate the vertical gap formed by the shell 8.

The small solid raw material charged in the furnace shell 4 is
Oxygen gas is blown into the furnace at a rate of 100 to 500 Nm ³ / min from a large capacity acid water cooling lance 6 penetrating through the exhaust gas hood 15 covering the upper part of the furnace belly shell 7 to reduce the reduced iron. The dissolution is promoted by the heat of the decarburization reaction by the acid supply in the first half step by oxidizing the carbon [C] of the included small solid iron source. At this time, the melting heat source uses coal, coke powder, etc. added on a hot heel (molten steel remaining at the furnace bottom) or uses a solid iron source in advance in the process of preheating / injection position III and melting treatment position IV. It is preferable to prepare a sufficient amount of molten steel by melting and then charge reduced iron after preheating.

On the other hand, the massive solid iron source 21 charged with the molten steel 20 in the furnace shell 5 is provided with three graphite electrodes 11 vertically penetrating through the upper part of the furnace belly shell 8. In addition to promoting the temperature rise and melting by the arc in the latter half of the process, the decarburization of molten steel 20 is promoted. Molten steel in furnace shell 5 by processing for about 30 minutes
After the decarburization refining of 20 and the predetermined molten steel temperature and carbon concentration are obtained, the melting and decarburizing treatment by acid supply in the furnace shell 4 and the melting and decarburizing treatment by arc in the furnace shell 5 End 20 refining at the same time.

Among the exhaust gas generated in the melting and refining process, the high-temperature exhaust gas generated during the dissolving and decarburizing treatment of a small solid iron source including reduced iron due to acid supply in the furnace shell 4 is Heat is recovered by the exhaust gas hood 15 provided at the upper part of the furnace belly shell 7 and guided into the preheater 9 via the exhaust gas ducts 16A and 16C to exchange heat with the small solid iron source charged therein. To preheat it. On the other hand, the high-temperature exhaust gas generated during the melting of the large solid iron source in the furnace shell 5 and the decarburization of the molten steel 20 is supplied to an exhaust gas duct provided at the upper part of the furnace shell 8.
It is led into the preheater 10 via 16B and 16D, and is preheated by heat exchange with the massive solid iron source charged therein. Exhaust gas that has passed through the preheaters 9 and 10 and is used for preheating is sucked by a blower via a discharge duct 22, guided to a dust collector, and collected.

When the tapping from the furnace shell 5 is completed, the furnace belly shells 7 and 8 are lifted up and separated from the furnace shells 4 and 5 by, for example, a lifting device, and then placed on the furnace shell 5 side. By operating the tilting cylinder 13 thus tilted, the furnace shell 5 is tilted with the bearing 14 as a fulcrum, and molten steel 20 in the furnace is tapped through the tapping gutter 12. At this time, molten steel for hot heel is left at the bottom of the furnace shell 5.

After that, the turntable 3 is turned by 90 ° and the furnace shell 4 having completed the first half process is placed immediately below the preheater 10 and the furnace shell 5 having a hot heel at the furnace bottom is placed directly below the preheater 9. Position. The large solid iron source preheated in the preheater 10 is charged into the furnace shell 4, and the small solid iron source preheated in the preheater 9 is charged into the furnace shell 5. After turning the turntable 3 further by 90 °, the furnace shell 4 is replaced immediately below the furnace shell 8 and the furnace shell 5 is replaced immediately below the furnace shell 7, and melting and refining are performed in the same manner as described above. repeat. At this time, the high-temperature exhaust gas generated in the furnace shells 4 and 5 whose positions have been exchanged is guided into the preheaters 9 and 10 by the same route as in the case described above.

In the above-described embodiment, the preheating and charging position I of the small solid iron source, the dissolving treatment position II of the small solid iron source by acid supply, the preheating and charging position III of the large solid iron source, The molten steel at a predetermined temperature and carbon concentration is refined by treating the massive solid iron source in the order of the melting treatment position IV, and finally the furnace shell located immediately below the furnace shell 8 provided with the graphite electrode 11 The case of tapping from 4 or 5 has been described. By changing this order, the preheating and charging position of the large solid iron source
Starting from III, the treatment should be performed in the order of melting position IV of large solid iron source by arc, preheating / injection position I of small solid iron source, and melting treatment position II of small solid iron source by acid supply. Preheating, melting and refining processing to refine molten steel at a predetermined temperature and carbon concentration, and finally tapping from a furnace shell 4 or 5 located immediately below a furnace belly shell 7 provided with an acid water cooling lance 6. It is also possible to do so.

At this time, the high-temperature exhaust gas generated during the melting of the large solid iron source in the furnace shell 5 and the decarburization of the molten steel 20 is first discharged to the exhaust gas duct 16B provided at the upper part of the furnace belly shell 8.
, 16D and is introduced into the preheater 10 to preheat it by heat exchange with the massive solid iron source charged therein. The high-temperature exhaust gas generated during the melting and decarburizing treatment of the small solid iron source in the furnace shell 4 is collected by an exhaust gas hood 15 provided above the furnace shell 7, and the exhaust gas duct 16A,
It is led into the preheater 9 via 16C and exchanges heat with a small solid iron source containing reduced iron charged therein.
Preheating this is basically the same as in the previous case.

In this case, the large solid iron source 21 in the furnace shell 5 at the melting treatment position IV of the large solid iron source by the arc penetrates the upper part of the furnace belly shell 8 and is vertically suspended from three pieces. The melting and refining in the first half of the process is performed by the arc from the graphite electrode 11. On the other hand, the lump solid raw material containing reduced iron charged in the furnace shell 5 is supplied to the furnace from a large-capacity acid-water cooling lance 6 vertically provided on the upper part of the furnace belly shell 7 to reach 100 to 500 Nm ^3. / min oxygen gas is blown, and strong oxygen blowing similar to that of a converter is performed to oxidize the carbon [C] of the small solid iron source including reduced iron and dissolve in the latter half of the process by the heat of decarburization reaction. And decarburizing refining to form molten steel at a predetermined temperature and carbon concentration, and finally a furnace shell 7 provided with an acid-feed water-cooling lance 6
From the furnace shell 4 or 5 located immediately below the steel shell. At this time, the melting heat source uses the coal, coke powder, etc.
Refining is achieved.

When only the small solid iron source is used, the preheater 10 installed at the preheating / charging position III of the large solid iron source is not installed, and the preheating / charging position I or the preheating / charging position I is not used. It is also possible to install a single preheater 9 for preheating the small solid iron source only in III and charge the small solid iron source into the furnace shell 4 or 5. In this case, the exhaust gas generated in the furnace belly shells 7 and 8 during the melting and refining is collected from the exhaust gas ducts 16A and 16B to the duct junction 17, and then guided to the preheater 9 through the exhaust gas duct 16C.

In the above embodiment, the case where the present invention is applied to an AC type electric furnace for steelmaking has been described.
The present invention is a direct current type steelmaking electric machine having a single graphite electrode on an upper part, which has attracted attention due to a small noise and a low flicker and a great improvement in an electrode basic unit, and having a plurality of iron bottom electrodes embedded in a furnace bottom. Needless to say, the same can be applied to a furnace.

[0027]

As described above, according to the present invention, two furnace shells are symmetrically arranged so as to be able to swivel, and alternately between acid refining and arc refining, so that a series of melting operations is performed. The refining process can be performed at a high speed, and in particular, a solid iron source having a high carbon content can be easily dissolved and refined because acid refining by a large-volume acid lance is also used. In addition, high-temperature exhaust gas generated in the furnace due to melting and refining of the solid iron source is continuously guided to the preheater to preheat the solid iron source, and then charged into the furnace shell, so that the solid iron source is melted. Refining can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a plan view showing an arrangement of an electric furnace for steelmaking of the present invention.

FIG. 2 is a cross-sectional view showing the direction of arrow AA in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thrust bearing 2 Rotary shaft 3 Turntable 4 and 5 Furnace shell 6 Acid cooling lance 7, 8 Furnace shell 9 and 10 Preheater 11 Graphite electrode 12 Steel tapping gutter 13 Tilt cylinder 14 Bearing 15 Exhaust gas hood 16 Exhaust gas duct 17 Duct junction 18 Switching valve 19 Cut gate 20 Molten steel 21 Large solid iron source 22 Discharge duct

Claims (2)

[Claims] A turntable rotatable about a rotation axis; a pair of furnace shells arranged on the turntable symmetrically about an axial center and open upward to form a furnace body lower part; A furnace body which is arranged stationary on the turning trajectory of the shell, one of which is provided with an acid supply lance and the other which is provided with an arc arc electrode, and which can be integrated with the furnace body shell to perform melting and refining. A pair of furnace shells, an exhaust gas duct that derives high-temperature exhaust gas accompanying melting and refining from the furnace shell, and a hot exhaust gas from the exhaust gas duct, which is disposed at least between the furnace shells on the swirl locus; And a preheater for preheating a solid iron source to be introduced into the furnace shell. 2. The preheater is disposed as a pair between the furnace shells on the swirl locus, one of which is for introducing high-temperature exhaust gas from the furnace shell having an acid supply lance, and the other is for introducing the high temperature exhaust gas. 2. The electric furnace for steelmaking according to claim 1, wherein high-temperature exhaust gas from a furnace belly shell having an arc electrode is introduced.