Red mud and coal powder synergistic heat release electric furnace composite fuel and its preparation method and application

Abstract

This invention relates to the field of electric arc furnace (EAF) steelmaking fuel technology, specifically to an EAF composite fuel of red mud and pulverized coal that synergistically releases heat, its preparation method, and its application. It consists of 78-82 parts by weight of pretreated Bayer process red mud and 18-22 parts by weight of pulverized coal. The Bayer process red mud is dried at 150-200℃ to a moisture content ≤2% and pulverized, then mixed evenly with the pulverized coal in a specific ratio. At the initial stage of EAF power-on and with a furnace temperature ≤800℃, the composite fuel is added to the EAF at an acceleration rate of 1-2 kg / min, with an addition amount of 10-12 kg / t steel. The heating rate is controlled at 5-8℃ / min, allowing Fe2O3 in the red mud and fixed carbon in the pulverized coal to undergo a reduction reaction in the 800-1400℃ range, releasing heat and providing an auxiliary heat source for the EAF's temperature rise. When the furnace temperature reaches 1400℃, scrap steel is added for melting, and the Al2O3 in the residual red mud enters the slag to synergistically regulate viscosity. This will achieve a power saving of 22-28 kWh per ton of steel, a fluorite consumption reduction of 15%-20%, and the consumption of 8-9.6 kg of Bayer process red mud per ton of steel, realizing the high-value resource utilization of red mud and reducing power consumption and steelmaking production costs during the electric furnace heating stage.

Description

Technical Field

[0001] This invention relates to the field of electric arc furnace steelmaking fuel technology, specifically to an electric arc furnace composite fuel of red mud and pulverized coal that synergistically releases heat, its preparation method, and its application. Background Technology

[0002] Electric arc furnace (EAF) steelmaking is a crucial short-process technology in steel production. The heating stage (from ambient temperature to the 1400–1500°C melting point of scrap steel) is the core energy-consuming stage, typically accounting for 30%–40% of the total electricity consumption, with an energy consumption of approximately 150–200 kWh per ton of steel. Traditional EAF heating primarily relies on electricity, resulting in low energy efficiency and high production costs. To reduce EAF heating energy consumption, the industry has explored various technologies: gas-assisted heating provides some auxiliary heat, but gas costs are high and it exacerbates the oxidizing atmosphere within the furnace; scrap preheating technology preheats the scrap steel entering the furnace, but the temperature increase is limited, typically contributing less than 10 kWh to the reduction in energy consumption per ton of steel. None of these technologies have fundamentally solved the problem of excessive energy consumption during the EAF heating stage.

[0003] Bayer process red mud is a solid waste generated by the alumina industry, with huge annual emissions in my country, resulting in high storage costs and significant environmental risks. Bayer process red mud is rich in Fe2O3 (typically 18%–25%) and valuable components such as Al2O3 and CaO, possessing potential for resource utilization. Currently, the utilization of red mud in the iron and steel metallurgy field mainly focuses on iron component recovery and slag-forming fluxing; there are no reports of its development as an auxiliary heat source for electric furnace heating.

[0004] Regarding the comprehensive utilization of red mud, Chinese patent document CN117486252A discloses "a method for the comprehensive utilization of red mud." This method involves mechanically dehydrating the red mud, adding reducing agents and other ingredients in a specific ratio, mixing and pelletizing the mixture, drying the pellets at 300–400℃, and then feeding them into an electric furnace. The furnace is then reduced at 1550–1650℃ to convert iron oxides into molten iron. The slag is used to prepare light calcium carbonate and mullite, and the flue dust is recovered to extract sodium hydroxide. This process has the following shortcomings: the pellet drying temperature is high, resulting in significant energy consumption, and the drying time and energy recovery method are not clearly defined; the electric furnace reduction temperature range is wide, and precise process control parameters are not provided; the slag preparation process is not described in sufficient detail; and the flue dust and wastewater treatment processes are not fully disclosed.

[0005] Chinese patent document CN113088607A discloses a "method for recovering iron, vanadium, and sodium by melting and smelting red mud." The method involves drying red mud to a moisture content of no more than 10%, mixing it with lime and other materials in a specific ratio, briquetting it, drying it again, and then feeding it into a submerged arc furnace. The furnace is then reduced and smelted at 1400–1800℃ for 0.5–2 hours, separating iron from slag and recovering vanadium-containing pig iron and sodium components. The furnace gas is used as a drying heat source. The core shortcomings of this method are: the material mixing ratio is not clearly defined; the reduction and smelting time span is large, and no dynamic adjustment basis is provided; measures for controlling the vanadium grade of the vanadium-containing pig iron are lacking; and the furnace gas heat exchange and safety control schemes are also not described.

[0006] In summary, existing technologies have explored energy conservation in electric arc furnace steelmaking and the resource utilization of red mud, but none have proposed a technical solution to use red mud and pulverized coal in synergistic application during the heating stage of the electric arc furnace to replace part of the electricity consumption. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides an electric furnace composite fuel of red mud and pulverized coal that synergistically releases heat, as well as its preparation method and application, which realizes the high-value resource utilization of red mud while effectively reducing the power consumption during the heating stage of the electric furnace.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A composite fuel for electric arc furnaces that co-exothermics red mud and pulverized coal, the composite fuel comprising the following components by weight: 78-82 parts of pretreated Bayer process red mud; 18-22 parts of pulverized coal; the particle size of both the pretreated Bayer process red mud and the pulverized coal is 80-120 mesh; the pretreated Bayer process red mud has a CaO content of 28wt%-40wt%, an Fe2O3 content of 18wt%-25wt%, an Al2O3 content of 12wt%-18wt%, a Na2O content ≤5wt%, and a moisture content ≤2wt%.

[0009] Furthermore, the weight ratio of the pretreated Bayer red mud to pulverized coal is 8:2.

[0010] Furthermore, the pulverized coal is bituminous coal or anthracite, with a fixed carbon content ≥85wt%, sulfur content ≤0.5wt%, and ash content ≤10wt%.

[0011] The preparation method of the above-mentioned electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction includes the following steps: 1) Dry the Bayer red mud at 150~200℃ until the moisture content is ≤2%, and crush it to 80~120 mesh to obtain pretreated Bayer red mud.

[0012] 2) Crush the coal powder to 80~120 mesh to obtain crushed coal powder.

[0013] 3) Add 78-82 parts by weight of the pretreated Bayer red mud and 18-22 parts by weight of the pulverized coal to a mixer, control the speed at 200-250 r / min, and mix for 15-20 min to obtain the electric furnace composite fuel.

[0014] The application of the above-mentioned electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction includes the following steps: 1) Under the condition that the electric furnace is initially powered on and the furnace temperature is ≤800℃, the composite fuel for the electric furnace is added to the electric furnace at an acceleration rate of 1~2 kg / min, and the amount added is 10~12 kg / t of steel. The electric furnace described in this invention includes electric arc furnaces, medium frequency induction furnaces, and other electric heating furnace types used for steel smelting.

[0015] 2) Control the heating rate of the electric furnace to 5~8℃ / min so that Fe2O3 in the red mud and fixed carbon in the coal powder can undergo a heat-releasing reduction reaction in the range of 800~1400℃.

[0016] 3) Add scrap steel to melt when the furnace temperature reaches 1400℃.

[0017] Furthermore, after the scrap steel is melted, the Al2O3 in the residual red mud from the composite fuel reaction enters the slag, and together with lime and fluorite, it controls the slag viscosity to 0.15~0.22 Pa·s, and controls the content of Al2O3 in the slag to 5wt%~8wt%.

[0018] Furthermore, after the scrap steel has been melted and conventionally smelted, the tapping process also includes the following steps: 1) Slag treatment: The slag is magnetically separated to recover residual iron particles with a grade of ≥65%, and the remaining slag is used as cement admixture; 2) Exhaust gas treatment: The CO gas produced by the reduction reaction is collected through a flue gas treatment system and used as fuel or chemical raw material.

[0019] Furthermore, the composition of the molten steel is tested before tapping, and the P content in the molten steel is controlled to be ≤0.012wt%, S ≤0.018wt%, and H ≤2.0ppm.

[0020] Compared with existing methods, the beneficial effects of the present invention are: 1. Significant reduction in power consumption during the heating phase of the electric furnace. This invention involves preparing a composite fuel by mixing pretreated Bayer red mud with pulverized coal in a specific ratio. This composite fuel is then fed into the electric arc furnace at a controlled rate during the initial power-on phase, with the heating rate controlled. This allows the Fe₂O₃ in the red mud and the fixed carbon in the pulverized coal to undergo a controlled reduction reaction within a temperature range of 800–1400°C. Combined with a small amount of pulverized coal combustion, this creates a dual exothermic effect, providing an auxiliary heat source for the furnace's heating. Specifically, the timing of feeding the fuel at a furnace temperature ≤800°C avoids rapid combustion of the pulverized coal at high temperatures, allowing for a gradual release of chemical energy. The heating rate of 5–8°C / min matches the exothermic rhythm of the reduction reaction, ensuring effective heat absorption and utilization. The matched particle size of the red mud and pulverized coal (80–120 mesh) guarantees sufficient contact area between the two solid particles, ensuring the kinetic conditions for the solid-solid reduction reaction.

[0021] Verification through examples shows that, by adopting the method of this invention, the power consumption during the heating stage is reduced by 20-30 kWh / t of steel, and the total power consumption per ton of steel is reduced by 4%-6%. Based on an annual steel production of 500,000 tons using an 80t electric arc furnace, this can save 100-150 million kWh of electricity annually.

[0022] 2. Realize the high-value resource utilization of red mud and the disposal of solid waste. This invention uses Bayer process red mud as the main component of composite fuel (accounting for 78% to 82%), and utilizes the exothermic reduction reaction of Fe2O3 in it to complete auxiliary heating in a relatively low temperature range of 800 to 1400°C. At the same time, the Al2O3 remaining in the red mud after the composite fuel reaction enters the slag to participate in slag formation, realizing the cascade utilization of Fe2O3 (energy supply) and Al2O3 (slag conditioning) in the red mud.

[0023] Verification through examples shows that each ton of steel can absorb 8-9.6 kg of Bayer process red mud. Based on an annual steel production scale of 500,000 tons, this translates to an annual red mud absorption of 4,000-4,800 tons. Converting industrial solid waste into auxiliary fuel for steelmaking can reduce red mud storage costs by 150-200 yuan / ton, achieving the dual goals of "energy conservation through waste treatment." 3. Reduce steelmaking auxiliary material consumption and overall costs Existing electric arc furnace slag-making processes typically rely on fluorite to adjust slag viscosity, resulting in high fluorite consumption and costs. This invention utilizes Al2O3 from the residual red mud after the composite fuel reaction, which enters the slag and works synergistically with lime and fluorite to precisely control the slag viscosity to a suitable range of 0.15–0.22 Pa·s, while simultaneously controlling the Al2O3 content in the slag to 5%–8%. As a network former, Al2O3 optimizes the slag's fluidity and reactivity. While ensuring a desulfurization rate ≥85% and a dephosphorization rate ≥80%, it reduces fluorite consumption by 15%–20% compared to conventional processes, lowering auxiliary material costs by 15–25 yuan per ton of steel. Furthermore, the composite fuel preparation cost is approximately 300 yuan / ton, only about one-third the cost of natural gas, and the 20–30 kWh / ton of electricity replaced by the fuel, converted at industrial electricity prices, also represents a considerable saving in electricity costs. Considering all these factors, the overall cost per ton of steel is reduced by 30–50 yuan.

[0024] 4. Highly adaptable to various processes, requiring no large-scale equipment modifications. The preparation of the composite fuel described in this invention involves only conventional drying, crushing, and mixing unit operations, requiring minimal equipment investment. During application, it is added through the existing hopper or side opening of the electric furnace, without requiring modification to the main structure of the furnace. The technical solution is applicable to 30-100t electric arc furnaces and medium-frequency induction furnaces, exhibiting good adaptability to different tonnages and furnace types.

[0025] 5. Realize the resource utilization of exhaust gas and comprehensive utilization of slag. The CO gas produced by the reduction reaction is collected by the flue gas treatment system and can be used as fuel or chemical raw material, realizing the secondary utilization of carbon resources. After the residual iron particles with a grade of ≥65% are recovered by magnetic separation, the remaining slag is used as cement admixture, forming a closed-loop treatment system with near-zero solid waste emissions. Detailed Implementation

[0026] This invention discloses a composite fuel for electric furnaces that combines red mud and pulverized coal for synergistic exothermic reaction, its preparation method, and its application. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0027] This invention utilizes a comprehensive technical route encompassing the preparation of red mud-pulverized coal composite fuel, electric furnace preheating, scrap steel melting and synergistic slag formation, and quality and energy consumption control. This approach achieves synergistic energy saving through the exothermic reaction of red mud and pulverized coal, as well as enhanced slag formation efficiency. The main process steps involved in this invention are described in detail below.

[0028] (a) Technical requirements for raw materials The Bayer red mud used in this invention has the following composition by mass: CaO 28%–40%, Fe2O3 18%–25%, Al2O3 12%–18%, and Na2O ≤5%. This composition range ensures that the red mud has sufficient iron oxides for the exothermic reduction and an appropriate amount of Al2O3 for subsequent slag formation control.

[0029] The pulverized coal used is bituminous or anthracite, requiring a fixed carbon content of ≥85%, a sulfur content of ≤0.5%, and an ash content of ≤10%. A higher fixed carbon content provides a sufficient carbon source for the reduction reaction, while a lower sulfur content helps reduce the risk of excessive sulfur in the molten steel.

[0030] The optimal mass ratio of pretreated Bayer red mud to pulverized coal is 8:2. At this ratio, Fe2O3 and the carbon source are stoichiometrically matched, resulting in a reaction efficiency ≥90%, optimal exothermic stability, and effectively avoiding incomplete reactions due to insufficient carbon source and carbon buildup due to excessive carbon source.

[0031] (II) Preparation of red mud / pulverized coal composite fuel Bayer process red mud is placed in a rotary kiln and dried at 150–200°C until the moisture content is ≤2%. It is then pulverized to 80–120 mesh to obtain pretreated Bayer process red mud. Low-temperature drying (150–200°C) only removes the physical water from the red mud, avoiding excessively high temperatures that could lead to Fe2O3 pre-reduction and loss of chemical energy, thus maintaining its reactivity during the subsequent electric furnace heating stage.

[0032] The coal powder is pulverized to 80–120 mesh to match the particle size of the pretreated Bayer red mud. This particle size matching ensures sufficient contact area between the two solid particles in the solid-solid reduction reaction, guaranteeing the reaction kinetics.

[0033] Pretreated Bayer red mud and pulverized coal are fed into a twin-screw mixer at the above mass ratio, and the speed is controlled at 200-250 r / min. The mixture is mixed for 15-20 min to produce a uniform composite fuel.

[0034] (III) Electric furnace preheating and reaction exothermic First, clean the residue inside the 30-100t electric arc furnace or medium-frequency induction furnace, close the furnace door, and connect the power supply.

[0035] In the initial stage of powering on the electric furnace (furnace temperature ≤800℃), composite fuel is added uniformly into the furnace through the top hopper or side holes at a rate of 10-12 kg / t steel, with an acceleration rate of 1-2 kg / min. Adding fuel at a furnace temperature ≤800℃ avoids rapid combustion of pulverized coal at high temperatures, allowing chemical energy to be released gradually in a controlled manner.

[0036] The heating rate of the electric furnace is controlled at 5–8 °C / min. Fe₂O₃ in the red mud undergoes a reduction reaction with fixed carbon in the pulverized coal within the temperature range of 800–1400 °C (Fe₂O₃ + 3C = 2Fe + 3CO↑), with a reaction heat of approximately 824 kJ / mol. Combined with a small amount of combustion of the pulverized coal, this creates a dual exothermic effect, providing an auxiliary heat source for the furnace heating. The heating rate is matched to the exothermic rhythm of the reduction reaction to ensure that the released heat is effectively absorbed and utilized. This heating phase is stopped when the furnace temperature reaches 1400 °C.

[0037] (iv) Scrap steel melting and co-slag formation When the furnace temperature reaches 1400℃, scrap steel with a specification of 50-200mm is added into the furnace and melted using the residual heat in the furnace and continuous power supply.

[0038] After the composite fuel reaction, the Al2O3 in the residual red mud enters the slag and works synergistically with lime and fluorite to regulate the slag viscosity to 0.15–0.22 Pa·s, while controlling the mass fraction of Al2O3 in the slag to 5%–8%. As a network former, Al2O3 can optimize the slag's fluidity and reactivity, improve the slag-steel reaction efficiency, and reduce the amount of fluorite used by 15%–20%.

[0039] After slag formation, the oxidation and reduction phases are carried out according to the conventional electric arc furnace steelmaking process, with a desulfurization rate of ≥85% and a dephosphorization rate of ≥80%. The incompletely reduced Fe2O3 can assist the dephosphorization reaction during the oxidation phase after entering the slag, thus realizing the secondary utilization of iron components.

[0040] (v) Quality and energy consumption control Before tapping, the composition of the molten steel is tested to control the P content to ≤0.012%, S content to ≤0.018%, and H content to ≤2.0ppm.

[0041] Record the power consumption during the heating stage and the total power consumption per ton of steel. After adopting the method of this invention, the power consumption during the heating stage is reduced by 20-30 kWh / t of steel compared with the conventional process.

[0042] After tapping, the slag undergoes magnetic separation to recover residual iron particles with a grade of ≥65%, and the remaining slag is used as a cementitious material. The CO gas generated by the reduction reaction is collected through a flue gas treatment system and used as fuel or chemical raw material, realizing the resource utilization of the exhaust gas.

[0043] (vi) Core Mechanism 1. Synergistic exothermic mechanism Fe₂O₃ in red mud undergoes a reduction reaction with fixed carbon in pulverized coal within a temperature range of 800–1400℃, releasing a large amount of heat. Each ton of composite fuel can release approximately 1.2 × 10⁻⁶ kilowatt-hours of heat. 6The total auxiliary heat generated by the combustion of pulverized coal, combined with the small amount of heat released during combustion, can replace 20-30 kWh / t of electrical energy for steel production. The 8:2 mass ratio of red mud to pulverized coal ensures sufficient amounts of both Fe2O3 and carbon source, avoiding carbon buildup due to excessive carbon source and incomplete reaction due to insufficient carbon source.

[0044] 2. Temperature control mechanism Adding composite fuel when the furnace temperature is ≤800℃ avoids rapid combustion of pulverized coal in the high-temperature furnace, allowing the exothermic reduction reaction and the heating process to proceed in tandem. A heating rate of 5–8℃ / min matches the exothermic rhythm of the reduction reaction, ensuring that the release of chemical energy is synchronized with the heating requirements of the electric furnace. Adding scrap steel when the furnace temperature reaches 1400℃ utilizes the peak residual heat of the reduction reaction, reducing power consumption during the scrap melting stage and preventing premature feeding from eroding the furnace lining.

[0045] 3. Slag-forming efficiency enhancement mechanism After the composite fuel reaction, the Al2O3 in the residual red mud enters the slag, acting as a network form to adjust the slag viscosity to a suitable range of 0.15–0.22 Pa·s, thereby improving the slag-steel reaction efficiency and reducing fluorite usage by 15%–20%. The incompletely reduced Fe2O3, after entering the slag, can assist in the dephosphorization reaction during the oxidation period, achieving secondary utilization of iron components.

[0046] Example 1: Smelting low-carbon steel Q235 in a 50t electric arc furnace By weight, take 80 parts of pretreated Bayer process red mud and 20 parts of bituminous coal powder, totaling 100 parts by weight.

[0047] (a) Raw material parameters The components of the Bayer process red mud are: CaO 35%, Fe2O3 22%, Al2O3 15%, Na2O 4.2%, and moisture content 1.8%. The pulverized coal is bituminous coal with a fixed carbon content of 88%, sulfur content of 0.4%, and ash content of 8%. The scrap steel is Q235 scrap steel, with dimensions of 50–150 mm and a single weight not exceeding 500 kg.

[0048] (II) Process Steps (1) Preparation of composite fuel: Bayer red mud was placed in a drum drying kiln and dried at 158°C to a moisture content of 1.2%, and then pulverized to 100 mesh to obtain pretreated Bayer red mud. Bituminous coal powder was pulverized to 100 mesh, and the bituminous coal powder and pretreated Bayer red mud were fed into a twin-screw mixer. The speed was set to 220 r / min and mixed for 18 min to obtain a uniform composite fuel.

[0049] (2) Electric arc furnace heating: Clean the residue inside the 50t electric arc furnace (rated power 12000kW), close the furnace door, and connect the power supply. When the furnace temperature reaches 650℃, add composite fuel at a uniform rate through the furnace top hopper at a rate of 11kg / t steel (total 550kg), with an acceleration rate of 1.5kg / min. Control the heating rate at 6℃ / min, and the furnace temperature rises from 650℃ to 1400℃. During this process, Fe2O3 in the red mud and fixed carbon in the pulverized coal undergo a reduction reaction in the 800-1400℃ range, releasing heat. Combined with a small amount of pulverized coal combustion, this assists in heating the electric arc furnace. The power consumption during this heating stage is 135kWh / t steel, which is 25kWh / t steel lower than the traditional process (160kWh / t steel).

[0050] (3) Scrap steel melting and slag formation: When the furnace temperature reaches 1400℃, 50t of scrap steel is added to the furnace and melted using the residual heat and continuous power supply in the furnace. The melting time is about 40min. The standard fluorite addition amount for a 50t electric furnace under the same working conditions is 95kg. In this embodiment, 300kg of lime and 80kg of fluorite are added, and the fluorite usage is reduced by 15.8%. The slag viscosity is adjusted to 0.18Pa·s, and the Al2O3 content in the slag is 6.5%.

[0051] (4) Conventional smelting: The oxidation and reduction phases are carried out according to the conventional electric arc furnace steelmaking process. The oxygen supply intensity during the oxidation phase is 2.8 m³ / s. 3 / (t·min), desulfurization rate 92%, dephosphorization rate 88%. During the reduction period, 200kg of ferrosilicon and 150kg of ferromanganese were added for alloying.

[0052] (III) Effectiveness The tapping temperature is 1650℃. Steel composition: P 0.009%, S 0.014%, H 1.8ppm. Total power consumption per ton of steel is 460kWh, a 5.1% reduction compared to the traditional process (485kWh). 8.8kg of Bayer process red mud is consumed per ton of steel.

[0053] Example 2: Smelting of high carbon steel 45# in a 30t medium-frequency induction furnace Based on parts by weight, take 79 parts of pretreated Bayer red mud and 21 parts of bituminous coal powder, totaling 100 parts by weight.

[0054] (a) Raw material parameters The components of the Bayer process red mud are: CaO 30%, Fe2O3 20%, Al2O3 14%, Na2O 3.8%, and moisture content 1.6%. Anthracite is used as the pulverized coal, with a fixed carbon content of 85%, sulfur content of 0.3%, and ash content of 9%. The scrap steel is 45# scrap steel, with dimensions of 80–200 mm and a single weight not exceeding 300 kg.

[0055] (II) Process Steps (1) Preparation of composite fuel: Bayer red mud was placed in a drum drying kiln and dried at 180°C to a moisture content of 1.1%, and then pulverized to 120 mesh to obtain pretreated Bayer red mud. Anthracite coal powder was pulverized to 120 mesh, and the anthracite coal powder and pretreated Bayer red mud were fed into a twin-screw mixer. The speed was set to 250 r / min and mixed for 15 min to obtain a uniform composite fuel.

[0056] (2) Electric furnace heating: Clean the residue inside the 30t medium-frequency induction furnace (rated power 8000kW), close the furnace door, and connect the power supply. When the furnace temperature reaches 700℃, add composite fuel at a uniform rate of 10kg / t steel (total 300kg), with an acceleration rate of 1.0kg / min. Control the heating rate at 5℃ / min, and the furnace temperature rises from 700℃ to 1400℃. During this process, Fe2O3 in the red mud and fixed carbon in the pulverized coal undergo a reduction reaction and release heat in the 800~1400℃ range, which, combined with a small amount of pulverized coal combustion, assists in heating the electric furnace. The power consumption during this heating stage is 128kWh / t steel, which is 22kWh / t steel lower than the traditional process (150kWh / t steel).

[0057] (3) Scrap steel melting and slag formation: When the furnace temperature reaches 1400℃, 30t of scrap steel is added to the furnace and melted using the residual heat and continuous power supply in the furnace. The melting time is about 35min. The standard fluorite addition amount for a 30t medium-frequency furnace under the same working conditions is 60kg. In this embodiment, 200kg of lime and 50kg of fluorite are added, and the fluorite usage is reduced by 16.7%. The slag viscosity is adjusted to 0.16Pa·s, and the Al2O3 content in the slag is 5.8%.

[0058] (4) Conventional smelting: The oxidation and reduction phases are carried out according to the conventional electric arc furnace steelmaking process. The oxygen supply intensity during the oxidation phase is 2.5 m³ / (t·min), the desulfurization rate is 86%, and the dephosphorization rate is 82%. During the reduction phase, 120 kg of ferrosilicon, 80 kg of ferromanganese, and 50 kg of ferrochrome are added for alloying.

[0059] (III) Effectiveness The tapping temperature is 1620℃. Steel composition: P 0.010%, S 0.016%, C 0.45%. Total electricity consumption per ton of steel is 470 kWh, a 5.1% reduction compared to the traditional process (495 kWh). 8.0 kg of Bayer red mud is consumed per ton of steel.

[0060] Example 3: Smelting of 45CrNiMo alloy structural steel in an 80t electric arc furnace By weight, 81 parts of pretreated Bayer red mud and 19 parts of bituminous coal powder were taken, totaling 100 parts by weight.

[0061] (a) Raw material parameters The components of the Bayer process red mud have the following mass content: CaO 38%, Fe2O3 24%, Al2O3 16%, Na2O 3.9%, and a moisture content of 1.7%. The pulverized coal used is bituminous coal with a fixed carbon content of 90%, a sulfur content of 0.35%, and an ash content of 7%. The scrap steel is 45CrNiMo scrap steel, with dimensions ranging from 80 to 200 mm.

[0062] (II) Process Steps (1) Preparation of composite fuel: Bayer red mud was dried at 170°C in a drum dryer until the moisture content was 1.3 wt%, and then pulverized to 80 mesh to obtain pretreated Bayer red mud. Bituminous coal powder was pulverized to 80 mesh, and the bituminous coal powder and pretreated Bayer red mud were fed into a twin-screw mixer. The speed was set to 200 r / min and mixed for 20 min to obtain a uniform composite fuel.

[0063] (2) Electric arc furnace heating: Clean the residue inside the 80t electric arc furnace (rated power 18000kW), close the furnace door, and connect the power supply. When the furnace temperature reaches 750℃, add composite fuel at a uniform rate of 12kg / t steel (total 960kg), with an acceleration rate of 1.8kg / min, and control the heating rate at 7℃ / min. The furnace temperature rises from 750℃ to 1400℃. During this process, Fe2O3 in the red mud and fixed carbon in the pulverized coal undergo a reduction reaction and release heat in the 800-1400℃ range. Combined with a small amount of pulverized coal combustion, this helps to raise the temperature of the electric arc furnace. The power consumption during this heating stage is 132kWh / t steel, which is 28kWh / t steel lower than the traditional process (160kWh / t steel).

[0064] (3) Scrap steel melting and slag formation: When the furnace temperature reaches 1400℃, 80t of scrap steel is added to the furnace for melting, and the melting time is 42min. The standard fluorite addition for an 80t electric furnace under the same operating conditions is 150kg. In this process, 500kg of lime and 120kg of fluorite are added (20% less than the conventional process), and the slag viscosity is adjusted to 0.17Pa·s. The Al2O3 content in the slag is 7.2%. The desulfurization rate during the oxidation period is 90%, and the dephosphorization rate is 85%.

[0065] (4) Conventional smelting: The reduction period is carried out according to the conventional process of electric furnace steelmaking, and alloys such as ferrochrome, ferronickel, and ferromolybdenum are added for alloying.

[0066] (III) Effectiveness Steel composition: P 0.010%, S 0.015%, Cr 0.95%, Ni 1.0%. Total power consumption per ton of steel is 465 kWh, a 6.1% reduction compared to the traditional process (495 kWh). 9.6 kg of Bayer red mud is consumed per ton of steel.

[0067] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite fuel for electric furnaces that combines red mud and pulverized coal for synergistic exothermic reaction, characterized in that, The composite fuel is composed of the following components in parts by weight: 78-82 parts of pretreated Bayer process red mud; 18-22 parts coal powder; The particle size of the pretreated Bayer red mud and the pulverized coal is 80-120 mesh. The pretreated Bayer red mud has a CaO content of 28wt%~40wt%, Fe2O3 content of 18wt%~25wt%, Al2O3 content of 12wt%~18wt%, Na2O content of ≤5wt%, and moisture content of ≤2wt%.

2. The electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in claim 1, characterized in that, The pretreated Bayer red mud to pulverized coal weight ratio is 8:

2.

3. The electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in claim 1, characterized in that, The pulverized coal is bituminous coal or anthracite, with a fixed carbon content ≥85wt%, sulfur content ≤0.5wt%, and ash content ≤10wt%.

4. The method for preparing the electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Dry the Bayer red mud at 150~200℃ until the moisture content is ≤2%, and pulverize it to 80~120 mesh to obtain pretreated Bayer red mud; 2) Grind the coal powder to 80-120 mesh to obtain pulverized coal powder; 3) Add 78-82 parts by weight of the pretreated Bayer red mud and 18-22 parts by weight of the pulverized coal to a mixer, control the speed at 200-250 r / min, and mix for 15-20 min to obtain the electric furnace composite fuel.

5. The application of the electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Under the condition that the electric furnace is powered on and the furnace temperature is ≤800℃ at the initial stage, the electric furnace composite fuel is added to the electric furnace at an acceleration rate of 1~2kg / min, and the amount added is 10~12kg / t steel; 2) Control the heating rate of the electric furnace to 5~8℃ / min, so that Fe2O3 in the red mud and fixed carbon in the coal powder can undergo a heat-releasing reduction reaction in the range of 800~1400℃; 3) Add scrap steel to melt when the furnace temperature reaches 1400℃.

6. The application of the electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in claim 5, characterized in that, After the scrap steel is melted, the Al2O3 in the residual red mud from the composite fuel reaction enters the slag, and together with lime and fluorite, it controls the slag viscosity to 0.15~0.22 Pa·s, and controls the content of Al2O3 in the slag to 5wt%~8wt%.

7. The application of the electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in claim 5, characterized in that, After the scrap steel is melted and conventionally smelted, the process of tapping the steel also includes the following steps: 1) Slag treatment: The slag is magnetically separated to recover residual iron particles with a grade of ≥65%, and the remaining slag is used as cement admixture; 2) Exhaust gas treatment: The CO gas produced by the reduction reaction is collected through a flue gas treatment system and used as fuel or chemical raw material.

8. The application of the electric furnace composite fuel of red mud and pulverized coal synergistic exothermic reaction as described in claim 5, characterized in that, Before tapping, the composition of the molten steel is tested, and the P content is controlled to be ≤0.012wt%, S ≤0.018wt%, and H ≤2.0ppm.