Process for smelting high-carbon ferro-chrome by carbonaceous lining submerged arc furnace

Abstract

The invention discloses a process for smelting high-carbon ferro-chrome by a carbonaceous lining submerged arc furnace, which comprises the following steps: by taking chromium ore, coke and silica as raw materials, proportioning the chromium ore, the coke and the silica in a proportioning station according to the ratio of the chromium ore to the coke to the silica of 100: 25: 7, adding the mixture into the carbonaceous lining electric furnace through a furnace top bin, and smelting, the high-carbon ferrochrome with the Cr content of 46%-56% is produced through smelting, meanwhile, slag is produced, and the slag comprises the following components: 3.5%-6.5% of Cr2O3, 24.0%-28.0% of SiO2, 25.0%-29.0% of MgO, 28.0%-32.0% of Al2O3 and 1.5%-4.0% of FeO. The invention has the advantages that: the carbonaceous furnace lining is beneficial to heat dissipation, slag is in contact with the furnace lining to easily form a false furnace wall, an isolation effect is achieved, corrosion to the furnace lining is reduced, a magnesite material is not needed, and the slag is reduced; meanwhile, more heat in the furnace cannot be taken away, and power consumption is reduced. Slag is reduced, alloy output is increased, 'chromium running 'is reduced, and product quality is improved.

Description

Technical Field

[0001] This invention relates to the field of ferroalloy production technology, specifically to a process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace. Background Technology

[0002] There are various methods for smelting high-carbon ferrochrome, including the blast furnace method and the electric furnace method. Among them, the electric furnace flux method is widely used due to its high chromium content. The electric furnace flux method involves batching raw materials in the order of coke, silica, and chromite. The mixed raw materials are continuously added manually from the furnace opening into the furnace and around the electrodes, or directly into the furnace and around the electrodes using a feed pipe, maintaining a certain material level. The added material should form a flat-topped, large cone shape. Self-baking electrodes are used, with all three phase electrodes deeply embedded in the charge. The charge is heated by the arc heat and the resistance heat generated by the current passing through it, causing the charge to melt and reduce. Slag and iron are periodically discharged through the taphole, and new material is added as the charge sinks to maintain a relatively stable material level. Electrode shells are extended, electrode paste is added, and electrodes are pressed out as needed based on electrode consumption. The entire production process is continuous and cyclical.

[0003] In electric arc furnace flux smelting, a furnace lining is typically constructed inside the furnace to protect it from erosion by high-temperature molten metal and maintain stable internal temperature. Magnesia or carbonaceous linings are commonly used. Chinese Patent Publication No. CN213747885U discloses a high-quality carbonaceous lining structure for a large and medium-sized submerged arc furnace. Magnesia linings primarily use magnesia bricks. Magnesia bricks have advantages such as high refractoriness, stability in oxidizing atmospheres, good resistance to alkaline slags, and good resistance to liquid iron-chromium (FeCr) metallicity. Disadvantages include a low softening point under load at high temperatures, poor resistance to rapid heating and cooling, instability in reducing atmospheres above 1500℃, poor resistance to acidic slags, especially those with high SiO2 content, and a large linear expansion rate after heating.

[0004] In the early stages of my country's ferroalloy industry, submerged arc furnaces with magnesia linings were widely used for ferrochrome alloy smelting. Currently, the magnesia lining of submerged arc furnaces typically involves compacting magnesia-containing slag and other powdered materials to a height of at least 1.2m at the furnace bottom, and lining the furnace walls with magnesia bricks to a thickness of about 1.4m for high-carbon ferrochrome smelting. The raw materials include chromite, coke, silica, and magnesia. The high temperatures during smelting and the generated acidic substances corrode the magnesia lining. Over long periods of production, this corrosion becomes severe, leading to significant lining detachment. The thinning of the lining greatly increases the risk of furnace burn-through. Therefore, magnesia is added to increase the magnesium content of the molten metal, producing slag with a higher magnesium oxide content. This slag remains inside the furnace to increase the lining thickness and prevent burn-through. However, this method is not a long-term solution and has already caused the following problems: 1. During the production process, a large amount of magnesite materials such as serpentine and magnesite are added to increase the magnesium oxide content in the slag, thereby protecting the furnace lining and preventing furnace leakage. However, this results in the addition of extra slag-forming materials, leading to a significant increase in slag and costs. At the same time, the slag carries away heat from the furnace, increasing the electricity consumption per ton of high-carbon ferrochrome, which fails to meet the national requirements for reducing product energy consumption.

[0005] 2. In chromium ore, chromium reacts with oxygen to form slag composed of chromium trioxide, which becomes part of the slag. The increase in magnesia material leads to an increase in slag, and more chromium enters the slag during the smelting process, which is usually called "chromium run-out". A high "chromium run-out" means that the slag contains a lot of chromium trioxide, which will affect the chromium content in the alloy and affect the product quality. Summary of the Invention

[0006] The purpose of this invention is to provide a process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace.

[0007] This invention is implemented by the following technical solution: A process for smelting high-carbon ferrochrome in a carbon-lined electric arc furnace uses chromite, coke, and silica as raw materials. By mass, the chromite contains 36%–42% Cr₂O₃, the coke contains 82%–88% fixed carbon, and the silica contains 96%–98% SiO₂. The raw materials are batched from the batching station according to a chromite:coke:silica ratio of 100:25:7 and then added to the carbon-lined electric furnace via the top hopper for smelting. The smelting produces high-carbon ferrochrome with a chromium (Cr) content of 46%–56%, and simultaneously produces slag. The slag composition is: Cr₂O₃ = 3.5%–6.5%, SiO₂ = 24.0%–28.0%, MgO = 25.0%–29.0%, Al₂O₃ = 28.0%–32.0%, FeO = 1.5%–4.0%. Among them, the carbon furnace lining uses high thermal conductivity carbon brick material, and the thermal conductivity of high thermal conductivity carbon brick reaches more than 25W / mk at 300℃.

[0008] Preferably, the carbonaceous furnace lining includes a furnace substrate laid at the bottom of the electric furnace and a furnace lining wall built into the inner wall of the electric furnace. The furnace substrate and the furnace lining wall are made of carbonaceous material, which is at least a high thermal conductivity carbon brick. The height of the furnace substrate is at least 1.2m and the thickness of the furnace lining wall is at least 0.86m.

[0009] Preferably, the temperature of the contact surface between the slag and the carbon brick is reduced to below 1200°C.

[0010] Preferably, when smelting is carried out in the electric furnace, the working end of the electrode is inserted into the molten metal to a depth of 3.1m-3.2m.

[0011] Preferably, during smelting in the electric furnace, iron is tapped and refueled every 4 hours.

[0012] Advantages of this invention: 1. Replacing the electric furnace with a carbon lining for high-carbon ferrochrome production allows for easier heat dissipation from the furnace. The lower temperature at the slag-carbon brick contact surface allows the slag to solidify more easily at the lining wall, forming a "false furnace wall." This "false furnace wall" acts as an insulator, preventing the carbon bricks from reacting with the high-temperature slag and reducing erosion of the lining. Therefore, there is no need to add magnesite materials such as serpentine or magnesite to the raw materials, thus reducing slag production and lowering costs associated with purchasing magnesite. Simultaneously, the reduced slag content prevents the removal of more heat from the furnace, resulting in lower electricity consumption per ton of high-carbon ferrochrome and meeting the requirements for reduced product energy consumption.

[0013] 2. Comparing the slag from the production of high-carbon ferrochrome with that from the production of high-carbon ferrochrome with the slag ...

[0014] 3. When smelting with carbon-based furnace linings, the amount of slag is reduced, the Al2O3 content in the molten metal is high, the resistivity is high, the conductivity is poor, the electrode insertion depth is increased, and the heating surface is wide and uniform, which can achieve good material processing effect and save power consumption. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] Example A process for smelting high-carbon ferrochrome in a carbon-lined electric arc furnace, using chromite, coke, and silica as raw materials. By mass, the chromite contains 36%–42% Cr₂O₃, the coke contains 82%–88% fixed carbon, and the silica contains 96%–98% SiO₂. The raw materials are batched from the batching station according to a chromite:coke:silica ratio of 100:25:7 and then added to the carbon-lined electric arc furnace via a top hopper. The preferred method for the structure, construction, and laying of the carbon-lined furnace is consistent with the method described in the announcement. This is the same technology as the carbonaceous condensing furnace lining patent CN213747885U for a large and medium-sized submerged arc furnace. The carbonaceous furnace lining includes a furnace base laid at the bottom of the electric furnace and a furnace lining wall built into the inner wall of the electric furnace. The furnace base and the furnace lining wall are made of carbonaceous material, which is at least highly thermally conductive carbon bricks. The height of the furnace base is at least 1.2m and the thickness of the furnace lining wall is at least 0.86m. Compared with the magnesia furnace lining, where the furnace wall is built with magnesia bricks that are about 1.4m thick, the furnace lining wall of the carbonaceous furnace lining is thinner. The carbon furnace lining uses high thermal conductivity carbon bricks, which have a thermal conductivity of over 25 W / mk at 300℃, facilitating the efficient removal of heat from the furnace during production. High-carbon ferrochrome smelting temperatures are generally between 1550 and 1750℃, reducing the temperature at the slag-carbon brick contact surface to below 1200℃. The relatively thinner wall allows the slag to solidify more easily at the furnace lining wall contact surface, forming a hard shell. This shell is called a "false furnace wall," which acts as an isolation barrier, preventing the carbon bricks from reacting with the high-temperature slag and reducing erosion of the furnace lining.

[0017] Electric furnaces producing high-carbon ferrochrome with carbon linings offer several advantages. The change in lining material and the isolation provided by the "false furnace wall" prevent the carbon bricks from reacting with the high-temperature slag, reducing erosion of the lining. Therefore, there's no need to add magnesite materials like serpentine or magnesite to the raw materials, thus reducing slag production and the cost of magnesite. Furthermore, the reduced slag prevents the loss of heat from the furnace, lowering the electricity consumption per ton of high-carbon ferrochrome and meeting the requirement to reduce product energy consumption.

[0018] When smelting is carried out in the electric furnace, the working end of the electrode is inserted into the molten metal to a depth of 3.1m-3.2m.

[0019] The working end of the electrode is the distance from the conductive ring to the electrode tip. The working end of the electrode is inserted into the surface of the molten metal (also known as the material surface), with a minimum distance of 0.5m maintained between the material surface and the conductive ring to avoid damage to the conductive ring due to high temperature. In the original magnesia furnace lining smelting, the electrode insertion depth was approximately 2.7m-2.8m. The electrode insertion depth is affected by the resistivity. High resistivity results in poor conductivity, and a deeper electrode insertion provides a wider and more uniform heating surface, leading to better material processing and lower power consumption. Conversely, low resistivity results in good conductivity, but a shallower electrode insertion leads to a narrower heating surface, uneven heating, poorer material processing, and increased power consumption. Resistivity is mainly affected by the Al2O3 content in the molten metal and slag. In carbonaceous furnace lining smelting, the amount of slag is reduced, and the molten metal contains more carbon and chromium (Al2O3), resulting in high resistivity and poor conductivity. The electrode insertion depth is controlled at approximately 3.1m-3.2m, which is 0.4m deeper than before, achieving better material processing and lower power consumption. This will reduce power consumption by approximately 200 kWh / t to 3300 kWh / t.

[0020] When smelting in the electric furnace, iron is tapped and materials are added every 4 hours.

[0021] Iron is tapped every 4 hours during smelting, releasing molten ferroalloy metal and slag for heat dissipation. During this process, the temperature inside the furnace decreases, the "false furnace wall" is reduced, and material is added continuously to raise the temperature for smelting. After the temperature decreases, the furnace is reheated, and the slag reforms into a new "false furnace wall," achieving a continuous process of reduction and re-increase.

[0022] The smelting process produces high-carbon ferrochrome with a chromium (Cr) content of 46%-56%, and also produces slag. The slag composition is as follows: Cr2O3=3.5%-6.5%, SiO2=24.0%-28.0%, MgO=25.0%-29.0%, Al2O3=28.0%-32.0%, FeO=1.5%-4.0%.

[0023] Comparative Example The production of high-carbon ferrochrome using a magnesia furnace lining involves using chromite, coke, silica, and magnesia as raw materials. By mass, the chromite contains 36%–42% Cr₂O₃, the coke contains 82%–88% fixed carbon, the silica contains 96%–98% SiO₂, and the magnesia contains 38%–42% MgO. The raw materials are batched at a ratio of chromite:coke:silica:magnesia = 100:25:10:18 and then added to the electric furnace via the top hopper for smelting. The smelting produces high-carbon ferrochrome with a chromium (Cr) content of 46%–56%, and simultaneously produces slag with the following composition: Cr₂O₃ = 3.5%–8.0%, SiO₂ = 26.0%–32.0%, MgO = 28.0%–33.5%, Al₂O₃ = 21.0%–28.0%, and FeO = 1.5%–5.0%.

[0024] A comparison of producing high-carbon ferrochrome using carbon furnace lining versus using magnesia furnace lining, under the requirement of producing high-carbon ferrochrome with a Cr content of 46%-56% of the same specifications: 1. Changes in raw materials: First, magnesium stone is no longer used; second, the silica content is reduced in the formula, resulting in fewer reflected components and thus less slag.

[0025] 2. Comparison of slag composition between the two after actual production:

[0026] Note: Recovery rate = Alloy content * Grade / (Pellet * Grade / 152 * 104 + Raw ore * Grade / 152 * 104) * 100.

[0027] Taking the actual production process shown in the table above as an example, the chromium ore is fed in the form of pellets and raw ore. For both types of furnace linings, the feed rate is 1300 tons of pellets and 200 tons of raw ore. The coke feed rate is 370 tons for both types. For the magnesia furnace lining, the silica feed rate is 150 tons and the magnesia material (magnesite) feed rate is 250 tons. For the carbonaceous furnace lining, the silica feed rate is reduced to 80 tons, and no magnesia material feed rate is required. The resulting alloys are: 654.150 tons for the magnesia furnace lining and 883.103 tons of slag; and 667.500 tons for the carbonaceous furnace lining and 754.275 tons of slag. (Pellet particle size: 8-18mm; raw ore particle size: 10-300mm; coke particle size: 10-35mm; silica particle size: 30-80mm; magnesite particle size: 20-80mm).

[0028]

[0029] Note: The slag-to-iron ratio is the ratio of slag output to alloy output, and is a data point for assessing the amount of slag produced.

[0030] The slag produced by carbon furnace lining for high-carbon ferrochrome is an improved slag type, while the slag produced by magnesia furnace lining is the original slag type. It can be clearly seen that the improved slag type has a reduction in all components except Al2O3, which fully reflects the reduction of slag. In addition, the alloy output is increased, the slag-to-iron ratio is high, "chromium runoff" is reduced, and the high-carbon ferrochrome recovery rate is increased from the original 90% to 92%, thus improving product quality.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace, characterised in that, The electric furnace is charged with raw materials of chrome ore, coke and silica, wherein the chrome ore contains 36-42% of Cr2O3 by mass, the coke contains 82-88% of fixed carbon by mass, and the silica contains 96-98% of SiO2 by mass, and the raw materials are charged into the electric furnace in a ratio of 100:25:7 by mass of the chrome ore, coke and silica, respectively. The high thermal conductivity carbon brick has a thermal conductivity of 25 W / mk or more at 300°C.

2. A process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace according to claim 1, characterised in that: The carbon lining includes a lining bottom laid on the bottom of the electric furnace and a lining wall built on the inner wall of the electric furnace, and the lining bottom and the lining wall are made of carbon materials, at least high thermal conductivity carbon bricks, and the height of the lining bottom is at least 1.2 m and the thickness of the lining wall is at least 0.86 m.

3. A process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace according to claim 1, characterised in that: The temperature of the contact surface between the slag and the carbon brick is reduced to 1200°C or less.

4. A process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace according to claim 1, characterised in that: When the electric furnace is used for smelting, the working end of the electrode inserted into the metal solution has a depth of 3.1-3.2 m.

5. A process for smelting high-carbon ferrochrome in a carbon-lined submerged arc furnace according to claim 1, characterised in that: When the electric furnace is used for smelting, tapping and charging are performed once every 4 hours.

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