JP3032454B2 - Apparatus and method for dissolving iron scrap - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for heating and melting iron scrap (hereinafter simply referred to as "scrap") efficiently using electric energy and combustion energy of carbonaceous material.

[0002]

2. Description of the Related Art Scrap is usually melted in an electric furnace. However, since a large amount of electric power is required and the cost of electric power is large, the combustion energy of the carbon material having a low energy cost can be effectively used to generate electric energy. The issue is how to reduce the usage ratio of

[0003] In a conventional electric furnace, as a method of utilizing the combustion energy of the carbon material as a secondary method, there is a method in which a granular or massive carbon material is charged into the furnace before charging scrap, after burning out, or the like. Examples include a method of blowing a granular carbon material into an iron bath and a method of heating scrap and an iron bath in a furnace by a pulverized coal combustion burner.

However, in the above method, the amount of the carbon material itself is limited because the oxygen source for burning the charged carbon material is limited to the air entering the furnace and the blown oxygen used as an auxiliary. Is done. Furthermore, simply blowing a large amount of oxygen-containing gas into the furnace not only oxidizes and depletes the graphite electrode,
Scrap is oxidized and iron oxide in the slag increases remarkably, which has a large adverse effect such as prolonging the time required for reduction of the slag and melting of the furnace wall refractory. In addition, the cost of equipment for storing and supplying pulverized coal is large, the thermal efficiency is relatively low, and the method is not necessarily economical.

[0005] On the other hand, in order to utilize the thermal energy of the exhaust gas from the melting furnace, a method of preheating the scrap by introducing the exhaust gas into a basket in which the scrap is loaded has been used in part. However, the amount of exhaust gas in the melting furnace is small, and the amount and temperature of exhaust gas generated in one melting cycle fluctuate. Therefore, the temperature of preheated scrap is low and the efficiency of using thermal energy is not sufficient. It is a fact.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to melt scrap in an electric furnace. It is an object of the present invention to greatly increase the usage ratio and the thermal efficiency of the combustion energy of the carbonaceous material, and to dramatically reduce the usage ratio of the electric energy.

For this purpose, the amount of carbon material burned in the furnace is greatly increased, and the object is to prevent the oxidation of the electrode and the increase in the amount of iron oxide in the slag accompanying this. It is a further object of the present invention to provide means for effectively utilizing a large amount of thermal energy of melting furnace exhaust gas for preheating scrap.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its gist is as follows. (1) A melting furnace having an oxygen-containing gas blowing means on a side surface. The furnace comprises a furnace body, an arc heating electrode, a device for supplying a carbon material to the periphery of the arc heating electrode, and a horizontal rotary furnace for introducing exhaust gas from the melting furnace to preheat iron scrap. This is an apparatus for melting iron scrap having means for controlling the amount of iron scrap supplied from the furnace to the melting furnace.

(2) More preferably, a movable weir is provided near the iron scrap discharge port of the horizontal rotary furnace, and the position of the movable weir is adjusted so that the amount of iron scrap supplied from the horizontal rotary furnace to the melting furnace is adjusted. The apparatus for melting scrap iron according to the above (1), characterized in that:

(3) As a method for carrying out the present invention, in the apparatus for melting scrap iron according to the above item (1) or (2), after charging the scrap iron into the melting furnace, the arc melting method is performed.
Melted holes in the deposited layer of iron scrap with
Then, the supply of the carbon material into the narrowed hole, the blowing of the oxygen-containing gas from the side of the furnace body and the arc heating are continuously performed, and simultaneously, the exhaust gas of the melting furnace is introduced into the horizontal rotary furnace to preheat the iron scrap. And supplying the preheated iron scrap from the horizontal rotary furnace to the melting furnace.

In carrying out the melting method of the present invention, the iron scrap is transferred from the horizontal rotary furnace to the melting furnace so that the height of the deposited layer of the iron scrap formed in the melting furnace is maintained within a certain range. It is desirable to control the feed rate.

As means for effectively utilizing carbonaceous materials such as pulverized coal and coke that are easily scattered outside the furnace, (4) a hollow arc heating electrode is used, and (3) The method for dissolving iron scrap according to the above (3), wherein a carbon material is supplied to the narrow hole portion of the iron scrap deposition layer.

[0013]

FIG. 1 shows the configuration of a scrap melting apparatus for carrying out the present invention. The furnace body 1 has an oxygen-containing gas blowing means 2 on the side surface, and an arc heating electrode 3a is inserted from above the furnace body. The arc heating electrode 3a is connected to a power supply device (not shown), and a DC arc discharge occurs between the arc heating electrode 3a and the furnace bottom electrode 3b. FIG.
Shows the case of DC arc heating, but the melting method of the present invention can be similarly carried out in the case of AC arc heating.

The oxygen-containing gas injecting means 2 is connected to an oxygen supply source (not shown), generally has a flow control means, and has a water-cooling lance, a refractory nozzle at a tip portion inserted into the furnace. Are used. A carbon material supply shot 4a is inserted into the furnace through the furnace opening hood 1a or the exhaust gas duct 5, and the carbon material is supplied from the carbon material supply device 4 to the narrowed portion 12 of the scrap accumulation layer. You. The melting furnace is connected to a horizontal rotary furnace 6 for preheating scrap through an exhaust gas duct 5, and the exhaust gas from the melting furnace is discharged through the horizontal rotary furnace 6 by a suction blower (not shown). .

Providing the movable weir 7 on the side of the scrap discharge port 6a of the horizontal rotary furnace 6 is effective in increasing the heat efficiency of the preheating of the scrap in the present invention and in smoothly supplying the scrap into the furnace. It is desirable that the movable weir 7 be provided so as to be in close contact with and sliding on the rotating scrap discharge port 6a. Further, it has a function of moving up and down in the direction of arrow A in FIG. 1 to adjust the amount of retained scrap in the rotary furnace.

The material of the movable weir is only required to have predetermined strength and heat resistance, and refractories or water-cooled metal materials can be used. Further, the movable weir is preferably of a fire tray type or a fence type having an opening for allowing exhaust gas having a size that does not allow scrap to pass.

The working procedure for implementing the present invention using the melting apparatus shown in FIG. 1 and the operation and effect of the present invention are as follows. First, 1/1 of the raw material scrap used in one melting
First charge 4 to 1/2 amount. It is desirable to sort the raw material scrap into large and small ones, use the former for initial charging, and preheat the latter in a horizontal rotary furnace before charging.

After the initial loading of the scrap, the arc heating electrode 3a is lowered to start an arc discharge, and a hole is formed in the scrap deposition layer by melting. When a hole having a predetermined size is formed, a carbon material is supplied to the hole, and an oxygen-containing gas is blown into the furnace from the oxygen-containing gas supply means 2 at the same time. As the oxygen-containing gas, besides pure oxygen gas, crude oxygen gas containing a small amount of nitrogen or oxygen gas containing non-flammable gas such as some air can be used, but the oxygen concentration is 70%. It is desirable that this is the case.

The carbon material reacts with the molten iron oxide in the high temperature part of the arc spot 13 to form an ascending gas flow of reducing CO gas around the electrode. One of the important functions and effects of the present invention is that the CO gas flow is formed so as to include the electrode in the narrowed portion of the scrap deposition layer, so that the oxidation of the electrode by the oxygen-containing gas blown into the furnace can be prevented. is there.

It is also important to adjust the direction of blowing the oxygen-containing gas so that the jet of the oxygen-containing gas does not directly collide with the electrode, in order to ensure the above-mentioned effects.
It is also useful to control the supply rate of the oxygen-containing gas from the analysis result of the composition of the exhaust gas from the melting furnace so that excess oxygen is not generated.

Part of the oxygen-containing gas blown into the furnace is:
The CO gas around the electrodes is burned into CO ₂ gas, and the heat of combustion is effectively used for heating the scrap. The remaining oxygen-containing gas is mainly used for scrap oxidation, and the heat of oxidation of iron is effectively used for heating the scrap.

The iron oxide dissolves into iron oxide in the slag, but reacts with the carbonaceous material at an extremely high temperature arc spot and is rapidly reduced to prevent the iron oxide concentration in the slag from becoming excessive. I do. One of the functions and effects of the present invention is to promptly reduce the iron oxide generated by blowing the oxygen-containing gas at the arc spot. In addition, pouring from the furnace bottom
Blowing an inert gas with a lath plug or the like to stir the molten metal or molten slag is also effective in enhancing the above-mentioned effect.

As one of the functions and effects of the present invention, the carbon material charged into the hole of the scrap deposit layer is heated by a high-temperature arc spot, and the sulfur content in the carbon material is reduced to SO ₂ gas or dust. The effect of so-called vaporization de-flushing, which is discharged outside the furnace as sulfur content therein, can be given. Thus, even if a large amount of a carbon material having a high sulfur content is used, it is possible to make [S] in the molten iron almost equal to that in the conventional electric furnace melting.

The high-temperature exhaust gas mainly composed of CO ₂ generated in the melting furnace is passed through an exhaust gas duct 5 to a horizontal rotary furnace 6.
Will be introduced. During this time, the temperature is maintained at a sufficiently high temperature, though it is diluted somewhat by intruding air or the like, and heat exchange with the scrap is performed in the horizontal rotary furnace so that the scrap can be preheated to a considerably high temperature.

When the melting of the initially charged scrap deposited in the furnace has progressed to some extent, a predetermined amount of scrap 9 preheated by the horizontal rotary furnace is continuously or intermittently fed into the melting furnace. It is desirable to control the feed rate of the preheated scrap so that the height of the pile of scrap formed in the furnace is maintained within a predetermined range.

In order to reduce the deviation of the pile height of the scrap in the furnace, a preheated furnace charged between the scrap discharge port of the horizontal rotary furnace and the furnace port of the melting furnace is used. It is also effective to provide a means for controlling the falling direction or the falling position of the scrap. Until the charging of all the raw material scrap of one batch is completed, heating while maintaining a state where a deposited layer of scrap of a predetermined height is formed in the furnace,
Continue dissolution. When the melting of all the raw material scraps in one batch is completed, the supply of the carbonaceous material and the oxygen-containing gas is stopped. The generated molten iron 10 opens the tap hole 11 and is discharged out of the furnace.

[0027] When the amount of the carbonaceous material charged into the furnace increases, the thermal energy of the exhaust gas increases accordingly, and the preheating temperature of the scrap can be raised correspondingly. Compared to the preheating of scrap by exhaust gas in the conventional electric furnace, the preheating temperature of the scrap is greatly increased, and the use of electric energy in the melting furnace is dramatically improved by using the combustion energy of the carbonaceous material together. It is an effect of the present invention that it can be reduced.

Further, when using pulverized coal, pulverized coke or the like as the carbonaceous material, these are liable to be scattered outside the furnace together with the exhaust gas stream. A method of using a hollow arc heating electrode and supplying a carbonaceous material from the hollow portion of the electrode is effective as means for using these inexpensive carbonaceous materials in the melting method of the present invention. In addition, since the powdery carbon material has a large surface area, it is effective in further increasing the reduction rate of molten iron oxide and the rate of vaporization and deflow.

[0029]

EXAMPLE A furnace of a commercial 80-ton three-phase AC arc furnace was partially remodeled, and a test of the method of melting iron scrap of the present invention was conducted using the furnace and a horizontal rotary furnace for testing. The melting material is ordinary steel scrap, about 1/3 of the total scrap charged.
And the rest were preheated and charged in a horizontal rotary furnace. A small coke of 10 to 30 mm was used as the carbonaceous material. S in the carbonaceous material was about 0.05% by weight. Pure oxygen was used as the oxygen-containing gas, and the oxygen was blown into the furnace with three water-cooled lances arranged at equal intervals on the upper side of the furnace body.

As an example, a representative example of the test operation by the melting method of the present invention was selected, and the amount of carbon material, the amount of oxygen used, the unit of electric power, the average preheating temperature of scrap, the electrode erosion index obtained from the test results. And the value of [S] in the molten iron (average of several heats) are shown in Table 1. The average scrap preheating temperature is a value estimated from the heat balance of the horizontal rotary furnace for the scrap preheated in the horizontal rotary furnace. Also,
The electrode erosion index is a numerical value indicating the ratio of the amount of electrode erosion in the example to the amount of electrode erosion in the comparative example.

The comparative example is a normal electric furnace operation without scrap preheating, and the average operation data is shown in Table 1.

[0032]

[Table 1]

[0033]

According to the present invention, when melting scrap in an electric furnace, the use ratio and heat efficiency of the combustion energy of the carbon material are greatly increased, and the use ratio of the electric energy is drastically reduced. It is now possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a scrap melting device for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Melting furnace furnace body 1a Furnace opening hood 2 Oxygen-containing gas blowing means 3a Arc heating electrode 3b Furnace bottom electrode 4 Carbon material supply device 4a Carbon material charging start 5 Exhaust gas duct 6 Horizontal rotary furnace 6a Scrap discharge Exit 7 Movable weir 8 Scrap deposit layer 9 Preheated scrap 10 Molten 11 Tap hole 12 Scrap deposit layer constriction 13 Arc spot

Continued on the front page (72) Inventor Hiromitsu Morita 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Toshiya Harada 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation (56) References JP-A-5-312475 (JP, A) JP-A-3-20403 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21B 11/00 C22B 9/16 F27D 11/10 F27D 13/00

Claims (4)

(57) [Claims] A melting furnace furnace body having an oxygen-containing gas blowing means on a side surface thereof, an arc heating electrode, a device for supplying a carbon material to a periphery of the arc heating electrode, and an exhaust gas from the melting furnace. And a horizontal rotary furnace for pre-heating the iron scrap by heating, and a means for controlling a supply amount of the iron scrap from the horizontal rotary furnace to the melting furnace. 2. A method for controlling a supply amount of iron scrap from a horizontal rotary furnace to a melting furnace by providing a movable weir near an iron scrap discharge port of a horizontal rotary furnace and adjusting a position of the movable weir. The apparatus for melting scrap iron according to claim 1, wherein: 3. A melting apparatus for an iron scrap according to claim 1 or 2, wherein after the iron scrap is charged into the melting furnace, a hole is formed in the deposited layer of the iron scrap by an arc heating device. The supply of carbonaceous material to the hole and the blowing of oxygen-containing gas from the side of the furnace body and the arc heating are continuously performed. At the same time, the exhaust gas of the melting furnace is introduced into the horizontal rotary furnace to preheat the iron scrap. And melting the preheated iron scrap from the horizontal rotary furnace to the melting furnace. 4. The iron scrap according to claim 3, wherein a hollow arc heating electrode is used, and a carbon material is supplied from a hollow portion of the electrode to a narrowed portion of the iron scrap deposition layer. Dissolution method.