CN1298033A - AC plasma melting reduction process and equipment for direct smelting of ferroalloy with very low carbon content - Google Patents

Abstract

A method and device for directly smelting micro-carbon ferroalloys by adopting AC plasma smelting reduction of chromium, tungsten and molybdenum concentrates. The smelting device is a three-phase AC small-hole graphite electrode plasma furnace, injecting Ar gas or coke oven gas as a carrier gas, and one of the electrodes is also used as a feeding electrode, and the chromium concentrate powder, or molybdenum concentrate powder, or tungsten concentrate powder , ferrosilicon powder, lime and fluorite are sprayed into the molten pool through the center hole of the electrode. The reduced metals such as Cr, W and Mo are dissolved into the quantitative scrap steel scrap or iron filings to reach the alloy target value required by the ferroalloy. The whole process of smelting reduction and ferroalloying has high speed, high yield and low cost.

Description

Alternating current plasma smelting reduction method and device for direct smelting micro-carbon ferroalloy

The invention belongs to the plasma smelting reduction technology, in particular to a method and a device for directly smelting micro-carbon ferroalloy by smelting reduction in an AC plasma furnace.

At present, the methods for smelting micro-carbon refractory ferroalloys at home and abroad include electric furnace method (smelting ferro-tungsten), electric furnace or vacuum resistance furnace method (smelting micro-carbon ferrochrome) and metallothermal reduction method outside the furnace (smelting ferromolybdenum). In order to obtain micro-carbon ferroalloys, non-carbon raw materials are used as reducing agents, such as using silicon-chromium alloys to smelt micro-carbon ferrochrome, and using silicon and aluminum as reducing agents to smelt ferromolybdenum and ferrotungsten. The reduction temperature and melting point of this type of iron alloy are relatively high. For example, the melting point of ferro-tungsten is above 2800K. It is in a semi-molten state when smelted in an electric furnace, and cannot flow out of the furnace by itself. The smelting time is very long and the energy consumption is too large. As mentioned above, when smelting such ferroalloys, the cost of such ferroalloys is too high due to the need for special smelting processes, or the need to use expensive non-carbonaceous raw materials as reducing agents, or the need for excessive energy consumption, etc. , Eventually also lead to the high cost of alloy steel using such iron alloys as alloying additives.

The object of the present invention is to provide a fast, efficient, simple and economical method and device for directly smelting micro-carbon ferroalloys through smelting reduction of chromium, tungsten and molybdenum concentrates in a plasma electric furnace.

In order to achieve the above-mentioned purpose, the technical solution adopted in the process of the present invention is: pre-load the required steel scrap or scrap iron scrap in the three-phase AC plasma furnace at one time, and add chrome concentrate, or tungsten concentrate, or Molybdenum concentrate, ferrosilicon, lime and magnesium oxide account for about 2/3 of the total furnace capacity.

When smelting Cr55 micro-carbon ferrochrome, the content percentage and proportion of the ingredients used in the furnace charge are: 100 parts of chrome concentrate with 52.10% Cr ₂ O ₃ ; 25-27 parts of ferrosilicon powder with 75% silicon; scrap steel shavings 8-10 parts; 8-10 parts of lime with CaO≥75%; 4-6 parts of magnesium oxide with MgO≥90%.

When smelting W75 ferro-tungsten, the content percentage and share of the ingredients used in the charge are: 100 parts of tungsten concentrate with WO ₃ being 67.87%; 21-23 parts of ferrosilicon powder with 75% silicon; SiO ₂ ≥ 95% 6-8 parts of silica; 2-3 parts of fluorite with CaF ₂ ≥85%; 4-5 parts of steel scrap.

When smelting Mo60 molybdenum ferromolybdenum, the content percentage and proportion of the ingredients used in the charge are: 100 parts of molybdenum concentrate with MoO ₃ being 69.82%; 30-32 parts of ferrosilicon powder with 75% silicon; lime with CaO≥75% 4-6 parts; 1-2 parts of fluorite with CaF ₂ ≥85%; 15-17 parts of steel scrap.

The carrier gas used in the plasma generator is Ar gas or coke oven gas. Coke oven gas can generate reducing plasma, which is beneficial to the smelting reduction process.

During smelting, after most of the charge has been melted, add dried and mixed powdered raw materials into the plasma furnace to control the particle size to <20 mesh. The method is to use a fluidized powder spraying device to spray evenly into the plasma furnace arc area through a small hole graphite electrode. The reduced metals Cr, W and Mo are dissolved into the melted steel scrap or scrap iron liquid to reach the target value of the ferroalloy of the specified brand.

In order to realize the purpose of the invention, the technical scheme adopted in the device of the present invention is: the plasma furnace used for smelting and reducing chromium, tungsten, and molybdenum concentrates to directly smelt micro-carbon ferroalloys consists of a three-phase AC plasma generator and a furnace body. The generator is composed of three graphite electrodes with small holes, the three electrodes are installed vertically parallel to each other, and the centers of the three electrodes are evenly arranged in an equilateral triangle. Each electrode can move up and down and parallel, and each movement can be self-locking. The furnace body is composed of a furnace cover and a garden-shaped furnace shell. The lining is made of high-temperature refractory materials. The furnace cover and the furnace body are welded with steel plates and cooled by water; the furnace cover has holes for the insertion and lifting of electrodes. There are ferroalloy outlets and slag outlets at the bottom.

Three graphite electrodes drill a small hole of φ4～φ8mm along the axis to inject a stable flow of carrier gas. One of the three graphite electrodes is used as the powder-spraying feeding electrode. The size of the hole is such that the powder can flow smoothly, and the powder is evenly sprayed in with a certain gas-powder ratio, so that the powder will be larger when it flows out of the graphite electrode port. It is advisable to partly be melted and reduced by plasma at high temperature.

Owing to adopting above-mentioned technical scheme, the present invention has following series of characteristics:

The use of smelting reduction will not produce heavy oxidation of the reduced alloy elements, and can reduce the oxygen content in the iron alloy to a very low level;

Using ferrosilicon powder as the reducing agent, the C content in the steel can be reduced to the requirement of C content in the micro-C ferroalloy at one time; all raw materials are evenly sprayed into the high-temperature plasma arc area through the center hole of the electrode by a fluidized powder spraying device, not only melting and reducing The speed is extremely fast, and the feeding process is simplified;

Three-phase AC low-voltage and high-current transformers are used to provide the power required for the plasma generator, and the transformers for ordinary electric arc furnaces with the same capacity can meet this requirement. Therefore, it has wide adaptability.

By adopting the small-hole graphite electrode of the present invention, the plasma arc is easy to start, and the arc body is stable without being affected by the charge. The arc length of the plasma arc can be adjusted by lifting the graphite electrode; the power and arc length of the plasma can also be adjusted by adjusting the secondary voltage of the transformer and the flow rate of the carrier gas to meet the requirements of the smelting process.

Coke oven gas can also be used instead of Ar gas as a carrier gas to generate reducing plasma, which is beneficial to the technological requirements of the smelting reduction process, and is more economical and applicable than Ar gas.

The powder is used to enter the furnace, and there is no need to pelletize the furnace charge, and there is no need to add a binder. The charge has wide adaptability, and there are no special requirements for the grade, particle size and shape of the charge.

Therefore the present invention can reach following technical and economic index:

1. Smelting time <30 minutes;

2. The recovery rate of Cr can reach 90-95%, and the recovery rate of W and Mo can reach 96-98%;

3. The cost of ferroalloy can be reduced by 1/3.

Its indicators are detailed in the attached table.

Now in conjunction with accompanying drawing and embodiment the present invention will be further described:

Fig. 1 is a schematic diagram of the process flow of direct smelting of micro-C ferroalloy by three-phase AC plasma smelting reduction of chromium, tungsten and molybdenum concentrates of the present invention.

Fig. 2 is a schematic diagram of the structure of the device for direct smelting of micro-carbon ferroalloys by three-phase alternating current plasma smelting reduction of chromium, tungsten and molybdenum concentrates of the present invention.

Process flow of the present invention is as shown in Figure 1:

The first step is to dry chromium, tungsten, molybdenum concentrate powder, ferrosilicon powder and flux with a particle size of <20 mesh at 120°C, and then mix them evenly after batching. Smooth fluidization and transportation inside, and also ensure accurate ingredients.

In the second step, the steel scrap or scrap iron scrap is loaded into the furnace at one time according to the batching requirements, and then part of the mixture is added to fill up to about 2/3 of the entire furnace volume. The rest of the powder is put into the powder spray tank and pressurized and fluidized with Ar gas.

The third step is plasma smelting reduction. First, inject Ar gas into the graphite electrode with small holes, start the transformer power supply (the transformer is a three-phase AC low-voltage high-current transformer), and start the plasma arc. After about 5 minutes, when the charge in the plasma furnace is basically melted and filled with plasma, open the ball valve of the powder spray tank to spray the rest of the mixed powder, and control the gas-powder ratio properly so that the powder can be discharged as soon as it leaves the electrode port. Melted and reduced by high temperature plasma arc. Then adjust the electrode height, adopt plasma submerged arc refining, and reduce the plasma power used appropriately.

The fourth step is to lift the electrode, cut off the power, stop the gas, tap the steel, and tap the slag.

Example 1

When smelting Cr55 micro-carbon ferrochrome, the content percentage and share of the ingredients used in the charge are: 100 parts of chrome concentrate with 52.10% Cr ₂ O ₃ ; 25 parts of ferrosilicon powder with 75% silicon; 8 parts of steel scrap , 8 parts of lime with CaO≥75%; 4 parts of magnesium oxide with MgO≥90%. The composition of the obtained ferrochrome is as follows: 55-57% of Cr, 0.1-0.25% of C, Si≤1.0-1.5%, S<0.02%, P<0.02%; the yield of Cr is 90-95%.

Example 2

When smelting W75 micro-carbon ferrotungsten, the content percentage and share of the ingredients used in the furnace charge are: 100 parts of tungsten concentrate with WO ₃ being 67.87%; 21 parts of ferrosilicon powder with 75% silicon; SiO ₂ ≥ 95% 6 parts of silica; 2 parts of fluorite with CaF ₂ ≥ 85%; 4 parts of steel scrap. The obtained tungsten-iron composition is as follows: W is 75-77%, C is 0.1-0.2%, Si≤0.5-1.0%, S<0.02%, P<0.02%; W yield is 96-98%.

Example 3

When smelting Mo60 micro-carbon ferromolybdenum, the content percentage and share of the ingredients used in the charge are: 100 parts of molybdenum concentrate with MoO ₃ being 69.82%; 30 parts of silicon ferrosilicon powder with 75% silicon, and lime with CaO≥75% 4 parts, 1 part of fluorspar with CaF ₂ ≥ 85%, 15 parts of steel scrap. The obtained ferromolybdenum composition is: Mo is 60-62%, C is 0.1-0.2%, S≤0.1-0.2%, P≤0.05-0.1%, Si≤1.0-1.5%; the yield of Mo is 96～ 98%.

The three-phase alternating current plasma smelting reduction chromium, tungsten, and molybdenum concentrate direct smelting micro-carbon ferroalloy device is shown in Figure 2. It includes two parts, a plasma furnace and a plasma generator, and the plasma furnace is composed of a furnace cover "4" and a furnace body "5". The furnace cover "4" is arc-shaped, with electrodes "2", "8" and "9" inserted and lifted holes in the center; The ferroalloy outlet "7", the furnace cover "4" and the furnace shell of the furnace body "5" are welded with steel plates, all cooled by water, and built with high-temperature refractories inside.

The plasma generator is composed of three graphite electrodes "2", "8" and "9" with small holes drilled along the axis, one of which has a larger hole diameter, which is also used for spraying the charge from the powder spray tank "1". The water-cooled copper electrode holder "3" supplies 100-135V three-phase AC input, and is connected and insulated with the electrode lifting device to realize the technical requirements of the electrode's lifting and translation.

The stable flow of plasma carrier gas Ar or coke oven gas is injected through the small hole of the electrode, and the powder spray tank "1" uses a certain pressure of Ar gas as the gas source to provide stable flow of powder into the furnace.

The specific operation of the present invention is: lift the electrodes "2", "8" and "9", open the furnace cover "4", first add scrap steel chips or scrap iron required for batching into the furnace at one time; , Mix and batch the mixture into the furnace, fill it to about 2/3 of the entire furnace capacity, cover the furnace cover "4", insert electrodes "2", "8", and "9", start the water pump to make the furnace The cover "4", the furnace shell "5" and the water-cooled copper electrode holder "3" are fed with cooling water. Put the remaining mixed powder into the powder spray tank "1", and pressurize it to a certain pressure with Ar gas; inject the electrodes "8" and "9" into the plasma carrier gas, start the power supply, start the plasma arc, and adjust the electrodes to make the plasma arc Stablize. After about 5 minutes, when most of the charge has been melted and reduced, the level of the charge has dropped, and the upper space has been filled with plasma gas. At this time, the plasma arc is very stable, and the powder spraying tank is opened to feed the ball and feed the material into the furnace until the material is sprayed. Adjust the lifting of electrodes "2", "8" and "9" for submerged arc refining. After the smelting is completed, the electrodes "2", "8", and "9" are lifted, the power is cut off, the gas is stopped, the ferroalloy is produced with slag, and finally all the slag is produced.

schedule

Claims (10)

1. A method for directly smelting micro-carbon ferroalloys by using plasma smelting reduction, which is characterized by: pre-filling steel scrap or iron filings in a three-phase AC small-hole graphite electrode plasma furnace, and adding chromium concentrate, or molybdenum concentrate, or tungsten Concentrates, ferrosilicon, lime and magnesia. 2. The method for directly smelting micro-carbon ferroalloys by plasma smelting reduction according to claim 1, characterized in that when smelting Cr55 micro-carbon ferrochrome, the content percentage and proportion of the ingredients used in the charge are: Cr ₂ O ₃ is 52.10% chromium 100 parts of concentrate; 25-27 parts of ferrosilicon powder with 75% silicon; 8-10 parts of steel scrap; 8-10 parts of lime with CaO≥75%; 4-6 parts of magnesium oxide with MgO≥90%. 3. The method for directly smelting micro-carbon ferroalloys by plasma smelting reduction according to claim 1, characterized in that when smelting W75 ferro-tungsten, the content percentage and proportion of the components used in the furnace charge are: 100 parts of tungsten concentrate with WO ₃ being 67.87% ; 21-23 parts of ferrosilicon powder with 75% silicon; 6-8 parts of silica with SiO ₂ ≥ 95%; 2-3 parts of fluorite with CaF ₂ ≥ 85%, 4-6 parts of steel scrap. 4. The method for directly smelting micro-carbon ferroalloys by plasma smelting reduction according to claim 1, characterized in that when smelting Mo60 ferromolybdenum, the content percentage and share of the ingredients used in the charge are: MoO ₃ is 100 parts of molybdenum concentrate of 69.82% 30-32 parts of ferrosilicon powder with 75% silicon, 4-6 parts of lime with CaO≥75%, 1-2 parts of fluorite with CaF ₂ ≥85%, 15-17 parts of steel scrap. 5. The method for directly smelting micro-carbon ferroalloys through plasma smelting reduction according to claims 1 to 4, characterized in that the raw material added to the plasma furnace is dried powder with a particle size of <20 mesh. 6. The method for directly smelting micro-carbon ferroalloys by plasma smelting reduction according to claims 1 to 5 is characterized in that the method of adding materials to the plasma furnace is to use a fluidized powder spraying device to pass the powder through a small hole graphite electrode through the gas Spray evenly into the plasma arc area. 7. A device for smelting reduction and directly smelting micro-carbon ferroalloys is characterized in that it consists of a three-phase AC plasma generator and a furnace body. The three-phase AC generator consists of three small-hole graphite electrodes "2", "8", and "9". Use Ar gas or coke oven gas as carrier gas. The furnace body is composed of a furnace cover "4" and a garden-shaped furnace shell "5". The lining is made of high-temperature refractory materials. There is a hole on the cover "4", and the bottom of the furnace is provided with a ferroalloy outflow port "7" and a slag discharge port "6". 8. The device for smelting micro-carbon ferroalloy according to claim 7, characterized in that the three electrodes "2", "8", and "9" are vertically installed parallel to each other, and the three electrodes "2", "8", " 9"The center of the garden is equilateral triangle evenly arranged. 9. The device for smelting micro-carbon ferroalloy according to claim 8, characterized in that three graphite electrodes "2", "8" and "9" drill a small hole of φ4-φ8mm along the axis. 10. The device for smelting micro-carbon ferroalloy according to claim 9, characterized in that one of the three graphite electrodes "2", "8" and "9" is used as a powder-spraying feeding pole.

Images