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The basic parameters of the above various furnaces are listed in Table 1. 
+10 64.9% -2.5+1.6 2.5%
-10+7 14.0% -1.6+1.0 1.2%
-7+5 8.2% -1.0+0.4 0.6%
-3+2.5 0.7%
Nickel iron smelting-electric arc furnace and its operation practice
Nickel-iron smelting electric arc steelmaking furnace charge. The thermal arc between the electrode and the melt is the primary source of energy for the steelmaking furnace. The necessary condition for arc generation and maintenance is the electrons emitted from the cathode, and therefore, the emission of hot electrons plays a major role in the electric arc furnace. An electric arc column is a strongly ionized mixture of gas and vapor of a cathode and anode material. The length of the electric arc furnace is proportional to the voltage drop between the electrode and the melt (about 40 volts).
The total Soviet standard ΓOCT7206-73 stipulates that the capacity of the electric arc furnace is 0.5-200 tons. The structure of the furnace depends on the charging method of the charge. Furnaces of various sizes have a special mechanical loading mechanism. In the non-ferrous metallurgy in reproduction, when smelting nickel-iron, to be considered with invertible removable roof or furnace, such as ДCП-6H2, ДCП-12 ДCП-25 and the like of the type most suitable furnace (FIG. 1).
Table 1 Basic parameters of ДCП type electric arc furnace
parameter
ДCП-6H2
ДCП-12
ДCП-25
Furnace capacity (tons)
Transformer power (kVA)
Transformer secondary voltage (volts)
Electrode maximum current (A)
Graphite electrode diameter (mm)
Electrode decomposition diameter (mm)
Diameter (mm) when the pool is tilted
Furnace depth (from the furnace door) (mm)
Flame space height (mm)
6
4000±20%
270-116
9850
300
1000
2230
425
110
12
8000±20%
320～120
17300
350
1000
2740
555
1365
25
12500±20%
390～132
22300
400
1250
3540
775
1500
Figure 1 Electric arc steel furnace
1-inclined transmission device; 2- molten pool rotating mechanism; 3-lifting mechanism for working window;
4- coal gas output tube; 5- roof; 6- electrode; 7- beam; 8- roof lifting and rotating mechanism;
9-electrode holder; 10-base beam; 11-spindle; 12-shell; 13-casting nozzle; 14-working window
This furnace is connected to a transformer secondary tap by a copper busbar having a cross-sectional area of ​​300 x 12 mm (for the CП-25 type) to form a short network (Fig. 102). A flexible cable insulator string can be used to transfer current from the stationary cable to the movable cable that rotates with the electrode holder and to ensure that the furnace is tilted to facilitate the pouring of metal and slag.
Figure 2 Short network of electric furnace
1-transformer room busbar; 2-bendable cable insulator string;
3-electrode holder current conduit; 4-electrode holder line end box; 5-electrode
The busbar in the electrode holder hose can be used to transfer current from the movable cable to the top of the electrode holder. A common water-cooled copper tube.
In the electric arc furnace, a carbon electrode (all Su standard ΓOCT4425-72) and a graphite electrode (all Su standard ΓOCT4426-71) were used.
The carbon electrode is made of anthracite or hot anthracite, coke , petroleum coke, coal tar pitch and tar. The prepared mixture is pre-calcined, crushed, and calcined. Listed below are some technical data for carbon electrodes:
Diameter (mm) 300 350 400 500
Working current density (A/cm 2 , not greater than) 10 10 9 9
Maximum current (kilometers) 7.06 9.6 11.3 17.7
The graphite electrode is produced by artificially graphing a carbon electrode at a temperature of 2000 to 2400 ° C in an electric furnace. Its concise features are as follows:
Diameter (mm) 300 350 400 450 500
Working current density (A/cm 2 , not greater than) 19 18 16 16 15
Standard length of the block (mm) 1500 1500 1500 1700 1700
Maximum current (kilometers) 12.7 16.4 20.1 24.4 28.5
In regenerative metallurgy, self-baking electrodes are not used when smelting ferronickel. [next]
The electric arc furnace is protected by a metal casing lined with refractory bricks. The melting temperature of ferronickel is 1700 °C. In addition, the furnace wall and the furnace roof are subjected to thermal radiation up to 4700 ° C of the arc. This extremely high temperature condition requires the correct selection of insulating refractories. Bottom heat-insulating layer made of asbestos plates, one or two rows of the working layer (Layer) clay bricks made of brick with magnesium. There is a 50 mm gap between the refractory masonry and the outer casing, which is filled with magnesium powder. The furnace wall is made of magnesia chrome brick. This brick can also be used as a top. The ratio of the height of the furnace arch to the chord is 1:10.
The drastically changing thermal load causes the refractory to wear quickly. A furnace roof can smelt 40 furnaces, and the furnace wall can be melted from 100 to 120 furnaces, while the furnace bottom is in the best condition. The furnace bottom often forms a furnace tumor due to crystallization of the insoluble slag.
The furnace can be tilted 40 ° C toward the furnace mouth using a hydraulic transmission. Nickel iron is injected into the water tank near the furnace through the furnace mouth, and nickel particles are the main product. The slag is discharged into a dedicated metal box through the slag outlet. The furnace is tilted 10° to the slag tap. With the hydraulic drive system, the top of the furnace is raised by 300 mm and can be moved to the side with the electrode.
The process is cyclical, the main processes are: preparation before smelting, charging and melting, metal refining, slagging, pouring metal. The whole process of refining a furnace takes 4.5 to 6 hours.
The prepared charge is placed in an electric furnace.
The waste batteries to be processed are first hand sorted according to their specifications. The positive and negative seat plates are separated on a special crusher as shown in FIG. The crusher is composed of a machine base, a mechanical device capable of cutting a battery casing in a long and wide size, a steel knife, a fastening device of a hydraulic system, and an operating system. The capacity of a crusher is 14 tons / day. The size of the crusher is 2.5 x 2.3 x 2.5 meters. The hydraulic system consists of a HШ-46 pump and an 80 mm diameter hydraulic cylinder with a working pressure of 11.2 MPa.
Metal scrap (cutting, trimming, belt, etc.) having a thickness of 6 mm or less and a battery block are made into a charge at a predetermined ratio and fed into a hopper having a CPA-4002B type pressure of 400 kN. The size of the block is 600×600×1000 mm, and the shavings are placed in a press of the Б-1334 type with a pressing force of 2,450 kN and a volume of 360×360×500 mA; the battery casing and the non-metal part are separated. The device and the packing are placed in a press of ПГ-150 and Б-133A, and the obtained compact is sent to the recycling ferrous metal recycling bureau.
Bulk materials such as debris, powder, cathode hooks, etc. can be directly fed into the furnace.
Metal scraps up to 80 mm thick were cut with a crocodile shear. The preparation process for electric furnace smelting is shown in Figure 104, and the metal charge is provided in the most difficult to break mixture. The ratio between metal scrap and non-metal scrap is 1:3 or 1:5.
The material basket for the charge is suspended from the bridge to the front of the furnace and layered according to the volume of the furnace. Quartz is sent to the furnace as a solvent, accounting for 5 to 6% of the total amount of nickel-containing material. After the furnace is full, the top of the furnace is in working condition. Extend the electrode, place it in place, and then the furnace is under load.
Depending on the smelting situation, the charge will gradually sink and the furnace will be emptied and the material will need to be regenerated. When processing unpackaged recycled materials, add five to six times of charge, and sometimes add ten times of charge. The charge should be added to the smelting charge instead of being added to the bath to avoid metal explosion and splashing. The total amount of charge is 10 to 12 tons. After the last addition, complete smelting is carried out, and the molten metal is between 1,700 and 1,730 °C.
Impurities of chromium, tungsten and molybdenum oxide are transferred into the slag. A certain amount of iron oxide-like substances are also transferred to the slag. Silica is a component of slagging; part of the metal oxide enters the gas phase as a lift.
After obtaining the standard ferronickel, the slag is removed from the metal surface. [next]
When smelting, impurities may be selectively removed. To this end, the slagging process is divided into two phases. Chromium is the most easily oxidized impurity. The first batch of slag contains a high amount of chromium (1 to 2% nickel and 15 to 20% Cr 2 O 3 ). The chromium is removed from the metal by about 1.5 to 2.5%. If this condition is maintained, only a small amount of tungsten and molybdenum are transferred to the slag. At this time, the slag should be acidic. After the first slag is discharged, the furnace should be supplemented with an oxidant--------------------------- The secondary slag contains: 3 to 8% of tungsten oxide, 2 to 4% of molybdenum oxide, and 3 to 7% of chromium oxide. The second batch of slag can be used to extract tungsten and molybdenum therefrom, and tungsten and molybdenum in the slag are present in the form of CaWO 4 and CaMoO 4 .
Figure 3 Flow chart of the preparation process of electric furnace charge
The smelting time is extended by about 4 hours due to the selective impurity removal. Therefore, the process should be carried out simultaneously with the slag of one component. The content of nickel in the slag is high, and it is to be put into furnace treatment together with nickel oxide ore. At this time, tungsten, molybdenum and chromium are irreparably lost together with the slag, which is the raw material for the production of the cement plant.
The metal obtained by the smelting is sampled and analyzed, and then granulated by water quenching. The overflow tank is first filled with refractory material, and the ferritic is diverted by the inclined flow of the furnace. Before water quenching, place the metal basket on the bottom of the tank. The following conditions should be maintained before pouring the metal: the water temperature in the water quenching tank is not lower than 15 °C, the temperature of the metal is not higher than 1700 °C, and the size of the particles is less than 1 mm. 6%. The actual particle size composition of the particles is (mm):
-5+3 7.7% -0.4 0.2%
The content of non-metallic slag inclusions should not exceed 10% of the weight of ferronickel. The physical properties are: density 7.1 g/dm 3 , bulk specific gravity 3.64 ton/m 3 , melting point 1326 ° C.
In the case where the recovery of nickel is 97%, the recovery of ferronickel accounts for about 60% of the weight of the solid charge. The technical conditions of the resulting alloy have been approved and are listed in Table 2.
Table 2 Technical conditions of ferronickel
Brand
Ni+Co
Co
Si
C
Cr
Cu
S
P
Al
Mn
Mo
φH-1
25.0
0.25
0.1
0.1
0.1
0.25
0.15
0.02
0.05
0.05
0.30
φH-2
20.0
0.30
0.1
0.1
0.1
0.30
0.20
0.02
0.05
0.05
0.30
φH-3
15.0
0.35
0.1
0.1
0.1
0.30
0.20
0.02
0.05
0.05
0.30
The actual average composition of ferronickel produced by the Rezhis nickel plant is: Ni+Co26.2%, Co0.2%, Si0.5%, Co0.06%, Cr0.07%, Cu0.25%, S0.09%, P0 .015%, Al 0.03%, Mn 0.03%, Mo 0.15%. Only by properly equipping the furnace and strictly following the smelting process rules can such high quality ferronickel be obtained.
With the consent of the user, the change of certain elements in the ferronickel is beneficial to the production of certain grades of steel and iron.
The slag obtained by the smelting contains Ni1 to 3%, Co 0.2% or less, W1% or less, Mo1% or less, Cu 0.03% or less, Cr 2 O 3 10 to 35%, FeO 10 to 20%, and CaO 6 to 15%. , MgO 8 ~ 10%, SiO 2 10 ~ 20%, the yield is 18 ~ 20%.
The gas coming out of the furnace contains dust. The dust content during refining was 0.7 g/ m3 . The chemical composition of the dust-weighted average sample is: Ni4.5%, Fe29.5%, w4.5%, Mo1.1%. Dust particle size: -5 microns accounted for 75%.
Due to the reducing nature of the smelting, the discharged gas contains a high amount of CO, so it should first be put into the combustion chamber to burn it out. The temperature at which the gas exits the furnace is between 1,250 and 1,350 °C. Burn out to add air. The composition before the gas burnout is: CO 2 7.5%, O 2 0.3%, CO 13 %.
The CO content after burnout should not exceed 0.2%.