Low-sulfur carbonaceous heat supplementing agent for electric furnace steelmaking and preparation method of low-sulfur carbonaceous heat supplementing agent

Abstract

The invention relates to the technical field of metallurgical materials, and discloses a low-sulfur carbonaceous heat supplementing agent for electric furnace steelmaking and a preparation method of the low-sulfur carbonaceous heat supplementing agent for electric furnace steelmaking. The preparation method comprises the following steps: melting coal pitch, phenolic resin, nano aluminum oxide powder and sodium carboxymethyl cellulose at 150-180 DEG C to prepare a composite binder; kneading the main material and a binder according to a ratio of 100: (20-30) under the protection of nitrogen, and adding a zinc borate flame retardant; extruding and molding into a cylindrical green body of 30-40mm by using a twin-screw extruder; carbonizing in an argon atmosphere at the temperature of 600-800 DEG C; and finally, carrying out ultrasonic impregnation and curing by using a coating solution prepared from silica sol, aluminum dihydrogen phosphate and silicon carbide micro powder. The cleanliness grade of high-end special steel and the safety and stability of the smelting process are improved, meanwhile, the desulfurization cost per ton of steel is reduced, and the problems of heat value loss of a high-ash-content heat compensation agent and environmental pollution are solved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical materials technology, specifically to a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking and its preparation. Background Technology

[0002] Metallurgy refers to the process and technology of extracting metals and metal compounds from minerals and processing them into metallic materials with certain properties using various processing methods. Metallurgy has a long history of development, from the Stone Age to the subsequent Bronze Age, and then to the large-scale development of iron and steel smelting in modern times. The history of human development is intertwined with the history of metallurgical development. Metallurgical technologies mainly include pyrometallurgy, hydrometallurgy, and electrometallurgy.

[0003] Currently, existing carbonaceous heat-replenishing agents generally suffer from sulfur contamination, which restricts the cleanliness of steel. Conventional petroleum coke and coal tar pitch-based heat-replenishing agents have high sulfur content, making it difficult to smelt high-end steel grades. Sulfides released in the high-temperature molten pool will cause the sulfur content of molten steel to exceed the standard. Metallurgical data shows that the increased sulfur content of heat-replenishing agents increases the desulfurization cost per ton of steel and easily causes surface cracks in the billet. Especially when smelting high-grade bearing steel, pipeline steel and other high-end steel grades, existing heat-replenishing agents are unable to meet the requirements for low sulfur content.

[0004] Therefore, a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking and its preparation method are proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking and its preparation method. The low-sulfur carbonaceous heat-replenishing agent and its preparation method provided by this invention solve the problems mentioned in the background art, such as sulfur pollution restricting the cleanliness of steel and easily causing surface cracks in cast billets.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-sulfur carbonaceous heat replenishing agent for electric arc furnace steelmaking and its preparation method, comprising:

[0007] (a) Raw material pretreatment: Mix 50-70% pitch coke with 30-50% petroleum coke, with fixed carbon greater than 83.00% and sulfur less than 0.050%, crush to 0.5-3mm particles, pickle with 0-18% hydrochloric acid at 50-70℃ for 1-2 hours, wash with water and dry until the moisture content is less than 0.8%;

[0008] (II) Preparation of composite binder: By weight, 40-60 parts of coal tar pitch, 15-25 parts of phenolic resin, 3-8 parts of nano alumina powder, and 2-5 parts of sodium carboxymethyl cellulose are melted and stirred at 150-180℃ for 30-50 minutes.

[0009] (III) Mixing and kneading: Mix the pretreated main material and composite binder at a ratio of 100:(20-30), add 0.5-2% zinc borate, and knead at 80-100℃ for 20-40 minutes under nitrogen protection;

[0010] (iv) Extrusion molding: Twin-screw extruder, zone 1 100-120℃, zone 2 130-150℃, die pressure 8-15MPa, extruding preforms with a diameter of 30-40mm;

[0011] (V) Carbonization activation: Place the green body in an inert atmosphere furnace and calcine it at 600-800℃ for 2-4 hours with a heating rate of 5-10℃ / min. Then, activate it by introducing a mixture of steam and CO2 in a ratio of 1:(1-3).

[0012] (vi) Surface coating: Paraffin melt impregnation and treatment with 2-6% silicon carbide micro powder coating liquid, curing at 200-250℃ for 30-60 min;

[0013] The resulting heat-replenishing agent has a sulfur content of less than 0.050%, a fixed carbon content of more than 83.00%, an ash content of less than 12.00%, a resistivity of less than 500 μΩ·m, and a volatile content of less than 6.00%.

[0014] Furthermore, in step (a), the crushing and screening process uses a combination of a jaw crusher and a vibrating screen. After crushing, the particles are classified into three grades according to their particle size: 0.5-1mm, 1-2mm, and 2-3mm, and the mass ratio of the three grades of particles is controlled to be 3:5:2.

[0015] Furthermore, in step (a), the pickling tank is equipped with a variable frequency stirrer with a stirring rate of 60-120 r / min, and the amount of dilute hydrochloric acid solution added is 2-3 times the total weight of the material.

[0016] Furthermore, in step (ii), the nano-alumina powder has a particle size of 30-80 nm and a specific surface area greater than 150 m² / g; the sodium carboxymethyl cellulose has a degree of substitution greater than 0.7 and a viscosity of 800-1200 mPa·s.

[0017] Furthermore, in step (iii), the inner wall of the high-speed mixer is coated with polytetrafluoroethylene, and nitrogen gas with a flow rate of 0.5-1.5 m³ / h is continuously introduced during the mixing process.

[0018] Furthermore, the kneading process in step (iii) is carried out in two stages. In the first stage, the mixture is stirred at 300-350 r / min at 80-90℃ for 10-15 min. In the second stage, the temperature is raised to 95-100℃ and the kneading is intensified at 450-500 r / min for 30-40 min.

[0019] Furthermore, in step (iv), the screw of the twin-screw extruder has a length-to-diameter ratio of (25-40):1, and the die head adopts a honeycomb porous structure design with an opening rate of 60-75%.

[0020] Furthermore, in step (v), the flow rate of argon gas introduced into the inert atmosphere furnace is 5-10 L / min, and the partial pressure of water vapor during the activation treatment stage is controlled at 0.1-0.3 MPa.

[0021] Furthermore, in step (vi), when preparing the coating solution, first prepare paraffin melt impregnation, stir at 60-80℃ for 20-40 min, then add silicon carbide micro powder and ultrasonically disperse for 10-15 min; the D50 particle size of the silicon carbide micro powder is 2-5 μm.

[0022] Furthermore, its bulk density is 0.8-1.2 g / cm³, compressive strength is 30-40 N, dissolution time in molten steel at 1550℃ is less than 180 s, sulfur fixation rate is greater than 92%, and heat replenishment efficiency is greater than 320 kcal / kg.

[0023] Compared with the prior art, the present invention provides a low-sulfur carbonaceous heat replenishing agent for electric arc furnace steelmaking and its preparation method, which has the following beneficial effects:

[0024] 1. In this invention, a micron-level directional desulfurization channel is constructed in a composite matrix of pitch coke and petroleum coke by employing a deep pickling synergistic steam-carbon dioxide dual-phase activation process. This technology is based on the chemical mechanism of hydrochloric acid selectively dissolving metal sulfides, and simultaneously combines the cracking effect of high-temperature steam and carbon dioxide on organic sulfur, achieving efficient removal of sulfur at the molecular level and in-situ fixation at the atomic level. This reduces the sulfur content of the heat-replenishing agent, solves the problem of sulfur increase in molten steel caused by high sulfur impurities, stabilizes the sulfur content of high-end bearing steel, reduces the desulfurization cost per ton of steel refining, and reduces surface crack defects on the billet, providing core material assurance for special steel smelting.

[0025] 2. In this invention, by introducing a nano-alumina-reinforced composite binder system, a three-dimensional network reinforcement skeleton is formed inside the carbon matrix. The nano-alumina particles, with their ultra-high specific surface area, construct a rigid support network in the coal tar pitch-phenolic resin system, improving the density of the carbon skeleton structure. Combined with a gradient temperature-controlled carbonization process, the ash content of the heat-replenishing agent is reduced, and the utilization rate of fixed carbon exceeds the critical value. The ceramic coating layer, through the synergistic effect of silicon carbide micropowder and silica sol, forms a micron-level dense protective film on the surface of the heat-replenishing agent, resisting the shear force of the high-pressure jet airflow and reducing the dust escape rate at the production site. While ensuring the heat-replenishing efficiency, it solves the problems of calorific value loss and environmental pollution caused by high-ash heat-replenishing agents.

[0026] 3. In this invention, a gradient pore structure is formed inside the heat-replenishing agent through multi-stage particle size ratio optimization and high-precision extrusion molding technology. A combined jaw crushing and vibrating screening process is used to control the mass ratio of the three-stage particles, so that particles of different sizes can achieve the densest packing during extrusion. The twin-screw extruder constructs directional channels with decreasing pore size from the core to the surface through zoned temperature control and honeycomb die design. After surface curing treatment of aluminum dihydrogen phosphate, this structure forms a closed microporous network. In the high-temperature molten steel environment, the gradient pores guide the uniform release of carbon elements, control the dissolution time, and compress the fluctuation rate of carbon element release, reducing the molten pool splashing accident caused by the explosion and pulverization of traditional heat-replenishing agents, thus improving the safety of the smelting process.

[0027] 4. In this invention, by incorporating zinc borate flame retardant into a nitrogen-protected kneading system, a boron-carbon composite heat-resistant layer is generated during the high-temperature activation stage. Boron element diffuses into the carbon lattice during carbonization, forming a diamond-like structure with extremely high thermal stability, which reduces the high-temperature volatilization rate of sulfur element. Simultaneously, through coating the surface of silicon carbide micropowder, a micro-area conductive network is constructed on the outer edge of the heat-replenishing agent. Due to its intrinsic semiconductor properties, silicon carbide crystal forms electron transition channels in the molten steel environment, which reduces resistivity and improves charge conduction efficiency, thereby improving the electrical energy to heat energy conversion efficiency in the electric arc furnace smelting process and reducing the power consumption per ton of steel. This provides key technical support for the low-carbon transformation of short-process steelmaking. Detailed Implementation

[0028] 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.

[0029] Example 1: A low-sulfur carbonaceous heat replenishing agent for electric arc furnace steelmaking and its preparation method, comprising:

[0030] (a) Raw material pretreatment: Mix 50% pitch coke and 30% petroleum coke, with fixed carbon greater than 83.00% and sulfur less than 0.050%, crush to 0.5mm particles, pickle with 1% hydrochloric acid at 50℃ for 1 hour, wash with water and dry until the moisture content is less than 0.8%;

[0031] (II) Preparation of composite binder: By weight, 40 parts of coal tar pitch, 15 parts of phenolic resin, 3 parts of nano alumina powder and 2 parts of sodium carboxymethyl cellulose are melted and stirred at 150℃ for 30 min.

[0032] (III) Mixing and kneading: Mix the pretreated main material and composite binder at a ratio of 100:20, add 0.5% zinc borate, and knead at 80°C for 20 minutes under nitrogen protection;

[0033] (iv) Extrusion molding: The twin-screw extruder is set at 100°C in zone one and 130°C in zone two, with a die pressure of 8MPa, to extrude a preform with a diameter of 30mm;

[0034] (v) Carbonization activation: The green body is placed in an inert atmosphere furnace and calcined at 600℃ for 2 hours with a temperature increase of 5℃ / min. A mixture of water vapor and CO2 = 1:1 is introduced for activation.

[0035] (vi) Surface coating: Paraffin melt impregnation and treatment with 2% silicon carbide micro powder coating liquid, cured at 200℃ for 30 min;

[0036] The resulting heat-replenishing agent has a sulfur content of less than 0.050%, a fixed carbon content of more than 83.00%, an ash content of less than 12.00%, a resistivity of less than 500 μΩ·m, and a volatile content of less than 6.00%.

[0037] In step (1), the crushing and screening process uses a combination of a jaw crusher and a vibrating screen. After crushing, the particles are classified into three grades according to their particle size: 0.5mm, 1mm, and 2mm, and the mass ratio of the three grades of particles is controlled to be 3:5:2.

[0038] Step (1): The pickling tank is equipped with a variable frequency stirrer, the stirring speed is set to 60 r / min, and the amount of dilute hydrochloric acid solution added is twice the total weight of the material.

[0039] In step (ii), the nano-alumina powder has a particle size of 30 nm and a specific surface area greater than 150 m² / g; the sodium carboxymethyl cellulose has a degree of substitution greater than 0.7 and a viscosity of 800 mPa·s.

[0040] Step (3) The inner wall of the high-speed mixer is coated with polytetrafluoroethylene, and nitrogen gas with a flow rate of 0.5 m³ / h is continuously introduced during the mixing process.

[0041] Step (3) The kneading process is carried out in two stages. In the first stage, the mixture is stirred at 300 r / min for 10 min at 80℃. In the second stage, the temperature is raised to 95℃ and the kneading is intensified at 450 r / min for 30 min.

[0042] Step (4) The screw of the twin-screw extruder has a length-to-diameter ratio of 25:1 and the die head adopts a honeycomb porous structure design with an opening rate of 60%.

[0043] Step (5): Argon gas is introduced into the inert atmosphere furnace at a flow rate of 5 L / min, and the water vapor partial pressure is controlled at 0.1 MPa during the activation treatment stage.

[0044] In step (six), when preparing the coating solution, first prepare paraffin melt impregnation, stir at 60℃ for 20 min, then add silicon carbide micro powder and ultrasonically disperse for 10 min; the D50 particle size of silicon carbide micro powder is 2 μm.

[0045] Its bulk density is 0.8 g / cm³, compressive strength is 30 N, dissolution time in molten steel at 1550℃ is less than 180 s, sulfur fixation rate is greater than 92%, and heat replenishment efficiency is greater than 320 kcal / kg.

[0046] Example 2: A low-sulfur carbonaceous heat replenishing agent for electric arc furnace steelmaking and its preparation method, comprising:

[0047] (a) Raw material pretreatment: Take 60% pitch coke and 40% petroleum coke, mix them together, with fixed carbon greater than 83.00% and sulfur less than 0.050%, crush them into 1.75mm particles, pickle them with 9% hydrochloric acid at 60℃ for 1.5h, wash them with water and dry them until the moisture content is less than 0.8%;

[0048] (II) Preparation of composite binder: By weight, 50 parts of coal tar pitch, 20 parts of phenolic resin, 5.5 parts of nano alumina powder and 3.5 parts of sodium carboxymethyl cellulose are melted and stirred at 165℃ for 40 min;

[0049] (III) Mixing and kneading: Mix the pretreated main material and composite binder at a ratio of 100:25, add 1.25% zinc borate, and knead at 90°C for 30 minutes under nitrogen protection;

[0050] (iv) Extrusion molding: The twin-screw extruder is set at 110℃ in zone one, 140℃ in zone two, and a die pressure of 11.5MPa to extrude a preform with a diameter of 35mm;

[0051] (v) Carbonization activation: The green body is placed in an inert atmosphere furnace and heated to 700℃ at 7.5℃ / min for 3 hours, and activated by a mixture of steam and CO2 in a ratio of 1:2.

[0052] (vi) Surface coating: Paraffin melt impregnation and treatment with 4% silicon carbide micro powder coating liquid, cured at 225℃ for 45min;

[0053] The resulting heat-replenishing agent has a sulfur content of less than 0.050%, a fixed carbon content of more than 83.00%, an ash content of less than 12.00%, a resistivity of less than 500 μΩ·m, and a volatile content of less than 6.00%.

[0054] In step (1), the crushing and screening process uses a combination of a jaw crusher and a vibrating screen. After crushing, the particles are classified into three grades according to their particle size: 0.75mm, 1.5mm, and 2.5mm, and the mass ratio of the three grades of particles is controlled to be 3:5:2.

[0055] Step (1): The pickling tank is equipped with a variable frequency agitator with a stirring rate of 90 r / min. The amount of dilute hydrochloric acid solution added is 2.5 times the total weight of the material.

[0056] In step (ii), the nano-alumina powder has a particle size of 55 nm and a specific surface area greater than 150 m² / g; the sodium carboxymethyl cellulose has a degree of substitution greater than 0.7 and a viscosity of 1000 mPa·s.

[0057] Step (3) The inner wall of the high-speed mixer is coated with polytetrafluoroethylene, and nitrogen gas with a flow rate of 1.0 m³ / h is continuously introduced during the mixing process.

[0058] Step (3) The kneading process is carried out in two stages. In the first stage, the mixture is stirred at 325 r / min at 85℃ for 12.5 min. In the second stage, the temperature is raised to 97.5℃ and the kneading is intensified at 475 r / min for 35 min.

[0059] Step (4) The screw of the twin-screw extruder has a length-to-diameter ratio of 65:2 and the die head adopts a honeycomb porous structure design with an opening rate of 67.5%.

[0060] Step (5): Argon gas is introduced into the inert atmosphere furnace at a flow rate of 7.5 L / min, and the water vapor partial pressure is controlled at 0.2 MPa during the activation treatment stage.

[0061] In step (six), when preparing the coating solution, first prepare paraffin melt impregnation, stir at 70℃ for 30 min, then add silicon carbide micro powder and ultrasonically disperse for 12.5 min; the D50 particle size of silicon carbide micro powder is 3.5 μm.

[0062] Its bulk density is 1.0 g / cm³, compressive strength is 35 N, dissolution time in molten steel at 1550℃ is less than 180 s, sulfur fixation rate is greater than 92%, and heat replenishment efficiency is greater than 320 kcal / kg.

[0063] Example 3: A low-sulfur carbonaceous heat replenishing agent for electric arc furnace steelmaking and its preparation method, comprising:

[0064] (a) Raw material pretreatment: Mix 60% pitch coke with 50% petroleum coke, with fixed carbon greater than 83.00% and sulfur less than 0.050%, crush to 3mm particles, pickle with 17% hydrochloric acid at 70℃ for 2 hours, wash with water and dry until the moisture content is less than 0.8%;

[0065] (II) Preparation of composite binder: By weight, 60 parts of coal tar pitch, 25 parts of phenolic resin, 8 parts of nano alumina powder and 5 parts of sodium carboxymethyl cellulose are melted and stirred at 180℃ for 50 min.

[0066] (III) Mixing and kneading: Mix the pretreated main material and composite binder at a ratio of 100:30, add 2% zinc borate, and knead at 100℃ for 40 minutes under nitrogen protection;

[0067] (iv) Extrusion molding: The twin-screw extruder is set at 120°C in zone one and 150°C in zone two, with a die pressure of 15MPa, to extrude a preform with a diameter of 40mm;

[0068] (v) Carbonization activation: The green body is placed in an inert atmosphere furnace and heated to 800℃ at 10℃ / min for 4 hours, and activated by a mixture of steam and CO2 in a ratio of 1:3.

[0069] (vi) Surface coating: Paraffin melt impregnation and treatment with 6% silicon carbide micro powder coating liquid, cured at 250℃ for 60min;

[0070] The resulting heat-replenishing agent has a sulfur content of less than 0.050%, a fixed carbon content of more than 83.00%, an ash content of less than 12.00%, a resistivity of less than 500 μΩ·m, and a volatile content of less than 6.00%.

[0071] In step (1), the crushing and screening process uses a combination of a jaw crusher and a vibrating screen. After crushing, the particles are classified into three grades: 1mm, 2mm, and 3mm according to their particle size, and the mass ratio of the three grades of particles is controlled to be 3:5:2.

[0072] Step (1): The pickling tank is equipped with a variable frequency agitator, the agitation rate is set to 120 r / min, and the amount of dilute hydrochloric acid solution added is 3 times the total weight of the material.

[0073] In step (ii), the nano-alumina powder has a particle size of 80 nm and a specific surface area greater than 150 m² / g; the sodium carboxymethyl cellulose has a degree of substitution greater than 0.7 and a viscosity of 1200 mPa·s.

[0074] Step (3) The inner wall of the high-speed mixer is coated with polytetrafluoroethylene, and nitrogen gas with a flow rate of 1.5 m³ / h is continuously introduced during the mixing process.

[0075] Step (3) The kneading process is carried out in two stages. In the first stage, the mixture is stirred at 350 r / min at 90℃ for 15 min. In the second stage, the temperature is raised to 100℃ and the kneading is intensified at 500 r / min for 40 min.

[0076] Step (4) The screw of the twin-screw extruder has a length-to-diameter ratio of 40:1 and the die head adopts a honeycomb porous structure design with an opening rate of 75%.

[0077] Step (5): Argon gas is introduced into the inert atmosphere furnace at a flow rate of 10 L / min, and the water vapor partial pressure is controlled at 0.3 MPa during the activation treatment stage.

[0078] In step (six), when preparing the coating solution, first prepare paraffin melt impregnation, stir at 80℃ for 40 min, then add silicon carbide micro powder and ultrasonically disperse for 15 min; the D50 particle size of silicon carbide micro powder is 5 μm.

[0079] Its bulk density is 1.2 g / cm³, compressive strength is 40 N, dissolution time in molten steel at 1550℃ is less than 180 s, sulfur fixation rate is greater than 92%, and heat replenishment efficiency is greater than 320 kcal / kg.

[0080] Comparative Example 1: The difference between this comparative example and Example 1 is that the hydrochloric acid pickling treatment in step (I) was not performed, and the original pitch coke / petroleum coke mixture was used directly.

[0081] Comparative Example 2: The difference between this comparative example and Example 2 is that nano-alumina powder was not added in step (II) of the preparation of the composite adhesive.

[0082] Comparative Example 3: The difference between this comparative example and Example 3 is that only pure water vapor is introduced in step (5) activation treatment stage.

[0083] Comparative Example 4: The difference between this comparative example and Example 3 is that only paraffin wax impregnation is used in step (6) surface coating.

[0084] The performance of the low-sulfur carbonaceous heat replenishing agents used in electric arc furnace steelmaking in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and methods are as follows:

[0085] Sulfur content test: High-temperature combustion iodometric titration;

[0086] Dust emission rate test: Simulate the blowing process and collect the mass percentage of dust particles with a diameter of less than 10μm;

[0087] Dissolution kinetics test: Real-time monitoring of the mass loss rate of the heat-replenishing agent in molten steel at 1550℃;

[0088] Resistivity testing: Four-probe method;

[0089] Thermal efficiency test: The combustion heat value is determined by an oxygen bomb calorimeter.

[0090] The test data of a low-sulfur carbonaceous heat supplement agent for electric arc furnace steelmaking and its preparation method in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0091] Testing items Sulfur content (wt%) Ash content (wt%) Compressive strength (MPa) Resistivity (μΩ·m) Dissolution time at 1550℃ (s) Dust emission rate (%) Heat replenishment efficiency (kcal / kg) Volatile matter (%) Example 1 0.048 3.5 18.3 475 152 2.8 335 5.2 Example 2 0.041 3.8 19.1 360 146 2.5 346 5.0 Example 3 0.037 3.2 20.5 285 138 2.1 358 4.8 Comparative Example 1 0.42 4.1 6.2 510 300 18.7 285 7.5 Comparative Example 2 0.050 8.7 9.8 690 215 12.3 295 6.8 Comparative Example 3 0.040 3.9 15.7 620 192 3.9 312 6.2 Comparative Example 4 0.038 3.6 12.4 580 240 15.6 301 7.0

[0092] By comparing and analyzing the data in the table, it can be seen that the low-sulfur carbonaceous heat-replenishing agent and its preparation method used in Examples 1-3 for electric arc furnace steelmaking have significantly superior performance compared to the low-sulfur carbonaceous heat-replenishing agent and its preparation method used in Comparative Examples 1-4. This indicates that by employing a deep pickling synergistic steam-carbon dioxide dual-phase activation process, micron-level directional desulfurization channels are constructed in the asphalt coke and petroleum coke composite matrix. This technology is based on the chemical mechanism of hydrochloric acid selectively dissolving metal sulfides, and simultaneously combines the cracking effect of high-temperature steam and carbon dioxide on organic sulfur, achieving efficient removal of sulfur at the molecular level and in-situ fixation at the atomic level. This reduces the sulfur content of the heat-replenishing agent and solves the problem of increased sulfur content in molten steel caused by high-sulfur impurities. The challenge lies in stabilizing the sulfur content of high-end bearing steel, reducing desulfurization costs per ton of steel refining, and minimizing surface cracks in cast billets. This provides core material support for special steel smelting. By introducing a nano-alumina-reinforced composite binder system, a three-dimensional network is formed within the carbon matrix to strengthen the skeleton. The nano-alumina particles, with their ultra-high specific surface area, construct a rigid support network within the coal tar pitch-phenol resin system, enhancing the density of the carbon skeleton structure. Combined with a gradient temperature-controlled carbonization process, the ash content of the heat-replenishing agent is reduced, and the utilization rate of fixed carbon exceeds the critical value. The ceramic coating layer, through the synergistic effect of silicon carbide micropowder and silica sol, forms a micron-level dense protective film on the surface of the heat-replenishing agent, resisting the shear force of the high-pressure jet airflow and reducing dust in the production area. The reduced escape rate, while ensuring heating efficiency, solves the problems of calorific value loss and environmental pollution associated with high-ash heating agents. Through multi-stage particle size ratio optimization and high-precision extrusion molding technology, a gradient pore structure is formed within the heating agent. A combined jaw crushing and vibrating screening process controls the mass ratio of the three-stage particles, ensuring the densest packing of particles of different sizes during extrusion. The twin-screw extruder, through zoned temperature control and a honeycomb die design, constructs directional channels with decreasing pore size from the core to the surface. After surface curing treatment with aluminum dihydrogen phosphate, this structure forms a closed microporous network. In a high-temperature molten steel environment, the gradient pores guide the uniform release of carbon elements, controlling the dissolution time and compressing the fluctuation rate of carbon element release, reducing transmission... The safety of the smelting process has been improved by addressing the molten pool splashing accident caused by the explosion and pulverization of the superheater. This is achieved by incorporating zinc borate flame retardant into a nitrogen-protected kneading system, generating a boron-carbon composite heat-resistant layer during the high-temperature activation stage. Boron permeates into the carbon lattice during carbonization, forming a highly thermally stable diamond-like structure, which reduces the high-temperature volatilization rate of sulfur. Simultaneously, a micro-conductive network is constructed on the outer edge of the superheater through surface coating with silicon carbide micropowder. The silicon carbide crystals, with their intrinsic semiconductor properties, form electron transition channels in the molten steel environment, reducing resistivity and improving charge conduction efficiency. This enhances the electrical-to-thermal energy conversion efficiency in the electric arc furnace smelting process, reducing electricity consumption per ton of steel and providing key technological support for the low-carbon transformation of short-process steelmaking.

[0093] By comparing and analyzing the relevant data in the table, it can be seen that the low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking and its preparation method of this invention not only reduce the sulfur content to the industry limit, but also simultaneously solve the pollution control and energy efficiency bottlenecks in the steelmaking process through four-dimensional technological innovation. This indicates that the low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking and its preparation method provided by this invention provide core material support for high-end special steel smelting and the short-process low-carbon transformation of electric arc furnaces, and have industrial promotion value and market competition barriers compared to traditional heat-replenishing agent technologies.

[0094] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0095] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking, characterized in that: include: (a) Raw material pretreatment: Mix 50-70% pitch coke with 30-50% petroleum coke, with fixed carbon greater than 83.00% and sulfur less than 0.050%, crush to 0.5-3mm particles, pickle with 0-18% hydrochloric acid at 50-70℃ for 1-2 hours, wash with water and dry until the moisture content is less than 0.8%; (II) Preparation of composite binder: By weight, 40-60 parts of coal tar pitch, 15-25 parts of phenolic resin, 3-8 parts of nano alumina powder, and 2-5 parts of sodium carboxymethyl cellulose are melted and stirred at 150-180℃ for 30-50 minutes. (III) Mixing and kneading: Mix the pretreated main material and composite binder at a ratio of 100:(20-30), add 0.5-2% zinc borate, and knead at 80-100℃ for 20-40 minutes under nitrogen protection; (iv) Extrusion molding: Twin-screw extruder, zone 1 100-120℃, zone 2 130-150℃, die pressure 8-15MPa, extruding preforms with a diameter of 30-40mm; (V) Carbonization activation: Place the green body in an inert atmosphere furnace and calcine it at 600-800℃ for 2-4 hours with a heating rate of 5-10℃ / min. Then, activate it by introducing a mixture of steam and CO2 in a ratio of 1:(1-3). (vi) Surface coating: Paraffin melt impregnation and treatment with 2-6% silicon carbide micro powder coating liquid, curing at 200-250℃ for 30-60 min; The resulting heat-replenishing agent has a sulfur content of less than 0.050%, a fixed carbon content of more than 83.00%, an ash content of less than 12.00%, a resistivity of less than 500 μΩ·m, and a volatile content of less than 6.00%.

2. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (a), the crushing and screening process uses a combination of a jaw crusher and a vibrating screen. After crushing, the particles are classified into three grades according to their particle size: 0.5-1mm, 1-2mm, and 2-3mm, and the mass ratio of the three grades of particles is controlled to be 3:5:

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3. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (a), the pickling tank is equipped with a variable frequency stirrer with a stirring rate of 60-120 r / min, and the amount of dilute hydrochloric acid solution added is 2-3 times the total weight of the material.

4. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (ii), the nano-alumina powder has a particle size of 30-80 nm and a specific surface area greater than 150 m² / g; the sodium carboxymethyl cellulose has a degree of substitution greater than 0.7 and a viscosity of 800-1200 mPa·s.

5. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (iii), the inner wall of the high-speed mixer is coated with polytetrafluoroethylene, and nitrogen gas with a flow rate of 0.5-1.5 m³ / h is continuously introduced during the mixing process.

6. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: The kneading process in step (iii) is carried out in two stages. In the first stage, the mixture is stirred at 300-350 r / min at 80-90℃ for 10-15 min. In the second stage, the temperature is raised to 95-100℃ and the kneading is intensified at 450-500 r / min for 30-40 min.

7. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (iv), the screw length-to-diameter ratio of the twin-screw extruder is (25-40):1, and the die head adopts a honeycomb porous structure design with an opening rate of 60-75%.

8. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (v), the flow rate of argon gas introduced into the inert atmosphere furnace is 5-10 L / min, and the partial pressure of water vapor during the activation treatment stage is controlled at 0.1-0.3 MPa.

9. The method for preparing a low-sulfur carbonaceous heat-replenishing agent for electric arc furnace steelmaking according to claim 1, characterized in that: In step (vi), when preparing the coating solution, first prepare paraffin melt impregnation, stir at 60-80℃ for 20-40 minutes, then add silicon carbide micro powder and ultrasonically disperse for 10-15 minutes; the D50 particle size of the silicon carbide micro powder is 2-5 μm.

10. A low-sulfur carbonaceous heat-replenishing agent prepared by the method according to any one of claims 1-9, characterized in that: Its bulk density is 0.8-1.2 g / cm³, compressive strength is 30-40 N, dissolution time in molten steel at 1550℃ is less than 180 s, sulfur fixation rate is greater than 92%, and heat replenishment efficiency is greater than 320 kcal / kg.