Explore the new treatment scheme of high silicon iron in blast furnace

At present, there are five main methods to produce high-quality ferrosilicon in China, one is to produce high-purity ferrosilicon by selecting furnace charge, the other is to produce high-purity low-carbon ferrosilicon by blowing chlorine outside the furnace, the third is to produce high-purity low-aluminum ferrosilicon by blowing oxygen outside the furnace, the fourth is to produce high-purity low-carbon ferrosilicon by hot slag washing, and the fifth is to produce low-aluminum low-carbon ferrosilicon by selecting furnace charge. High-purity ferrosilicon is produced mainly by smelting quartz stone, petroleum coke, wood blocks, charcoal and silicon steel sheets to reduce the content of impurity elements in the products. Because the quality of raw materials fluctuates greatly, some impurities are inevitably brought in during smelting production, so the reduction rate of impurity content in the product is limited, the product quality is not high, the yield is low, and the production furnace condition is difficult to maintain, the furnace mouth operation is difficult, the production cost and energy consumption of the product are high, and the economic index is poor. The effect of calcium and aluminum removal by furnace method is good, but there are many tail gases, and leakage and fracture of chlorine-blowing graphite pipe often occur in production, which seriously pollutes the environment, harms workers' health and corrodes production equipment. The method of blowing oxygen outside the furnace can also remove impurities such as calcium, aluminum and carbon from the product. However, in the process of use, the temperature of molten iron drops rapidly due to the violent churning and large splash loss, resulting in a large loss of sticking ladle and iron, and the statistical loss of data is 12%-20%. The graphite tube used for oxygen blowing often breaks and stops refining, so the output is low and it is uneconomical. The selection of furnace burden to produce low-aluminum and low-carbon ferrosilicon is mainly through smelting raw materials such as blue carbon and gas coal coke, so as to reduce the impurity elements in the product, mainly aluminum content. Because the composition of raw materials fluctuates greatly, this method inevitably brings some impurities in the smelting process, so the reduction rate of impurity content in the product is limited. Generally, the aluminum content can be reduced to 1.6%, and at most it can only be reduced to 1.2%, and the carbon content is 0.2%, so only some brands of products can be produced.

The purpose of the invention is to overcome the shortcomings of the above methods and provide a production method of high-quality ferrosilicon, which is feasible for producing a series of high-quality ferrosilicon.

The production method of high-quality ferrosilicon of the invention comprises the following steps:

(1) screen raw materials of silicon dioxide, reducing agent, steel wool and/or silicon steel sheets, wherein the silicon dioxide is quartzite or white silica and black silica, and the reducing agent is metallurgical coke and gas coal coke, or carbonized matter and gas coal coke, carbonized matter, petroleum coke and wood blocks, calculate the dosage of each raw material according to the known technology, mix the ingredients, and put them into submerged arc furnace to smelt ferrosilicon in a conventional way.

(2) Before blowing oxygen at the bottom of the furnace for refining and taking ferrosilicon out of the submerged arc furnace, add a calculated amount of premelted synthetic slag or/and silica fume, quartz powder, CaF2 or CaO into the refining ladle to adjust the composition of slag until the weight content of SiO2 is more than 60%, Cao is less than 30% and others are less than 65,438+/-00%, and the ladle is baked to above 200℃. Oxygen plus helium, air plus helium, air plus oxygen are refined outside the furnace, with gas pressure > > 0.5MPa, gas flow > 6 nm3/h, refining time of 30-40 minutes, and charging.

(3) The ferrosilicon containing C < 0.03% is required to remove silicon carbide (SiC) precipitated on the surface and slag adhered to the surface of the ingot after the ingot is cooled, so as to obtain high-quality ferrosilicon products.

Quality of this product The quality of raw materials used in the production method of ferrosilicon is as follows:

(1) silica gel Q/HT

(1) silica gel Q/HT

silicon dioxide

name

silicon dioxide

Bigger than ...

Fe2O3

absent

aluminium oxide

absent

Chief administrative officer

absent

titanium

absent

Particle size (mm)

12500KVA submerged arc furnace

6300KVA submerged arc furnace

quartzite

99.5%

0. 1%

0. 1%

0. 1%

0.002

50- 140

45- 120

White silica

98%

0. 15%

0. 15%

0. 15%

0.005

50- 120

45- 100

Black silica

99%

0. 1%

0.%

0. 1%

0.003

50- 120

45- 100

(2) Reducing agent

reductant

Fixed carbon (c) is greater than

Volatility (v) is less than

Ash (a) is less than

Chemical composition of ash% (less than)

Particle size (mm)

silicon dioxide

aluminium oxide

Chief administrative officer

titanium

12500KVA submerged arc furnace

6300KVA submerged arc furnace

Metallurgical coke

85%

3%

12%

-

-

-

-

5-20

3- 10

Semi-coke

83%

10%

7%

50%

25%

25%

0.5

8-25

5-20

Petroleum coke

90%

10%

0.3%

-

-

-

0.7

1-30

1-20

board

26%

70%

4%

-

-

-

-

20-200

20-200

Gas coal coke

84%

8%

8%

45%

Thirty percent

25%

0.6

8-25

5-20

charcoal

75%

20%

4%

-

-

-

-

10-30

10-20

(3) Steel sheet and silicon steel sheet

name

Iron is greater than

Mn is less than

Ti is less than

Particle size (mm)

steel cuttings

95

0.8

0.025

5- 100

Silicon steel sheet

95

0.3

0.0 15

10- 100

The weight content of pre-melted synthetic slag used is SiO2 > 50%, Cao < 40%, Al2O3 < 5%, and the rest are other components. Synthetic slag is made of washed broken silicon dioxide (SiO _ 2 > 97%), broken fluorite caf _ 2 > 80% and quicklime Cao > 85% which are melted in submerged arc furnace or cupola and quenched with water. The particle size of crushed silica used is18-50mm, and the particle size of fluorite is10-50mm.

Refining ladle and premelted synthetic slag are baked by ladle roaster, which is similar in structure to roaster used for steelmaking or casting. Oxygen blowing at the bottom of the ladle is through the permeable brick at the bottom of the ladle, and the permeable brick is made of steel-making permeable brick. When the temperature of molten iron drops below 1450℃, slag removal casting is carried out.

According to the method of the invention, the impurity weight content of ferrosilicon products produced by strictly controlling the process conditions can be controlled within the following ranges: Si: 75%-80%, Al: 0.004- 1.5%, Ca:0.02- 1.0%, and C: 0.0/kloc-. Sulfur: 0.002-0.005%, thallium: 0.025-0.05%, manganese < 0. 1%, calcium: 0. 1%, chromium: < 0. 1%, and vanadium: < 0./.

The invention mainly has the following advantages:

(1) This method has wide coverage and strong applicability. It can accurately control impurity elements according to the quality requirements of various varieties and brands of ferrosilicon alloys, and a series of high-quality ferrosilicon can be produced by the same method.

(2) Controlling the content of impurity elements in products through scientific and reasonable raw material screening and proportioning is beneficial to the maintenance and operation of submerged arc furnace, reducing consumption and improving technical and economic indicators.

(3) Oxygen blowing at the bottom of the ladle has high refining efficiency, sufficient thermodynamic and kinetic conditions, and can effectively control the content of impurity elements in the product, with less refining loss and less equipment damage.

(4) Oxygen blowing refining has no air pollution, which ensures the health of workers and the safe operation of equipment.

(5) Low temperature casting and surface treatment of ferrosilicon can further reduce the impurity content of the alloy and ensure the product quality.

The following are examples of producing several kinds of high-quality ferrosilicon by the method of the present invention:

Example 1, production of high purity ferrosilicon

According to quartz stone (or silica with silica > 99%) 100 kg, carbonized substance 20-40 kg, petroleum coke 35-20 kg, wood block 35-0 kg, silicon steel sheet or steel sheet 8- 14% kg, its reducing agent (carbonized substance+petroleum coke+wood block). Select the appropriate particle size of 50- 140mm, 8-25mm of blue charcoal, 0/-30mm of petroleum coke, 20-200mm of wood block, 5- 100mm of steel sheet and 0/0-1000 of silicon steel sheet. Before the molten iron is discharged from the submerged arc furnace, the ladle for refining molten iron is baked and insulated by a ladle roaster, 30-60 kg/ton of molten iron and 30-50 kg/ton of silica fume are added into the ladle, the ladle is baked by the ladle roaster to a temperature above 800 DEG C and filled with molten iron, and oxygen and air are blown from the bottom of the ladle through a permeable brick for refining for 30 minutes, with a gas pressure of > > 0.5MPa and a gas flow rate of > 6 nm3/h. When the temperature of molten iron drops below 65438 0450℃, slag stripping and casting can be carried out. Slag removal method is the same as that used in ferroalloy production. The weight content of final slag is analyzed, such as SiO2 > 40%, Cao < 30% and Al2O3 < 30%. After the molten iron is cooled, silicon carbide precipitated on the surface of ferrosilicon can be removed. During casting, the slag adheres to the surface of the iron ingot, and the surface is smooth, and the contents of carbon (C) and sulfur (S) in the product are further reduced, with a carbon reduction rate of about 40% and a sulfur reduction rate of about 30%. The main impurities in the product are: aluminum: < 0. 1%, calcium: < 0.05%, 0.02%, carbon: < 0. 1%, 0.05%, and phosphorus: < 0.02%, 0.0 1%. Select charcoal with a particle size of 8-25mm, petroleum coke with a particle size of 65438 0-30mm and wood blocks with a particle size of 20-200mm, mix the raw materials, put them into a 65438 02500kva submerged arc furnace for smelting according to the general conditions and operations for smelting ferrosilicon alloy, bake and refine the ladle with a ladle roaster for heat preservation before the molten iron leaves the submerged arc furnace, and add 30-200 kva. Quartz powder is 30-50kg/ton of molten iron. When the temperature is over 800℃ with a ladle roaster, molten iron is charged, and oxygen is blown from the bottom of the ladle through a permeable brick for refining for 30 minutes. Subsequent operations and process conditions were the same as those in Example 1, and low-carbon ferrosilicon products were obtained. The content of main impurities can be controlled as follows: Al: < 1.0%, Ca: < 0.00. Sulfur: < 0.005%, thallium: < 0.05%, manganese: < 0. 1%, calcium: 0. 1%, chromium: 0. 1%, vanadium: 0. 1%, nickel.

Example 3, Production of Ultra-low Carbon Ferrosilicon

The varieties and proportions of silicon dioxide, reducing agent, silicon steel sheet and steel sheet used are the same as those in Example 1 for producing high-purity ferrosilicon, except that oxygen is blown into the furnace bottom and nitrogen or compressed air is introduced for refining for 30-40 minutes, the dosage of premelted slag is 30-60 kg/ton of molten iron, and the dosage of silica fume is 30-60 kg/ton of molten iron, thus obtaining ultra-low carbon ferrosilicon products containing impurities.

Aluminum: < 1.0%, calcium: < 0.05%, carbon: < 0.02%, phosphorus: 0.02%, sulfur: 0.005%, thallium: 0.03%, manganese: 0. 1%, calcium: 0.

Example 4, low-aluminum ferrosilicon with aluminum < 2.0%, carbon < 0. 1% or aluminum < 1.5% and carbon < 0. 1% was produced.

According to the proportion of silica 100kg, metallurgical coke 20-40kg, gas coal coke 40-20kg, scrap steel 8- 14kg, and total fixed carbon of reducing agent (metallurgical coke+gas coal coke) greater than 50kg, metallurgical coke with particle size of 5-20mm and gas coal coke with particle size of 8-25mm are selected, The raw materials are mixed and put into a 12500KVA submerged arc furnace to smelt molten iron. Before leaving the submerged arc furnace, the ladle is baked with a ladle roaster for heat preservation, and 30-50 kg/ton of premelted synthetic slag and 30-50 kg/ton of silica fume are added into the ladle. Blow nitrogen from the bottom of the ladle or refine with compressed air for 30 minutes. The subsequent operation and process conditions are the same as 1. Ingots can be obtained without surface treatment. The main impurities are controlled as follows:

Aluminum: 1.0- 1.5% calcium: 0. 10- 1.0% carbon: < 0. 1% phosphorus: < 0.02% sulfur: < 0.005.

Example 5: production of 1.0 grade low-aluminum ferrosilicon with Al < 1.0% and C < 0. 1%.

The raw materials, proportion and operation of the 1.0 grade low-aluminum ferrosilicon alloy production gas are the same as in Example 4. The amount of premelted synthetic slag and silica fume added during refining is 30-50 kg/ton of molten iron, and the refining time is 35 minutes. The impurity content of the obtained product is:

Aluminum: 1.0-0.5% calcium: 0. 1-0.5% carbon: < 0. 1% phosphorus: < 0.02% sulfur: < 0.005%.

Example 6: 0.5 grade low-aluminum ferrosilicon alloy was produced, in which Al < 0.5% and C < 0. 1% 4.

100kg silica (white silica or black silica), 20-40kg carbonized matter, 40-20kg gas coal char and 8- 14kg steel scrap, the total fixed carbon content of the reducing agent (carbonized matter+gas coal char) is more than 50kg, and the silica particle size is 50- 120. After the raw materials are mixed, they are put into a 12500KVA submerged arc furnace and smelted according to the general conditions and operation of smelting ferrosilicon alloy. Before the molten iron leaves the submerged arc furnace, the ladle for refining molten iron is baked by a ladle roaster for heat preservation, 40-70 kg/ton of molten iron and 60 kg/ton of silica fume are added into the ladle, the ladle roaster roasts the molten iron to above 800℃, and then molten iron is poured and oxygen is blown from the bottom of the ladle.

Less than 0.5% aluminum, less than 0.07% calcium, less than 0. 1% carbon, less than 0.02% phosphorus and less than 0.005% sulfur.

Example 7, Preparation of Premelted Synthetic Slag

Using crushed silica (SiO _ 2 > 97%) with particle size of 18-50mm and crushed fluorite (caf _ 2 > 80%) with particle size of 10-50mm, after cleaning, mix silica 100kg and quicklime 100.