Method for impregnating graphite electrode through secondary roasting

Abstract

The invention relates to the technical field of graphite electrode roasting, and discloses a method for impregnating a graphite electrode through secondary roasting. Through the synergistic effect of an intelligent cooperative temperature control method, a whole-process inert protection system, a waste heat gradient utilization path and clean combustion directional pollution discharge, high-precision stable temperature control of the secondary roasting procedure is achieved, the activation temperature fluctuation of the coke powder is compressed to be within, the activation uniformity of the coke powder and the roasting consistency of the green body are guaranteed, and the quality of the green body is improved. The mechanical strength and the conductivity of the graphite electrode are greatly improved, the oxidation loss rate of a green body is reduced to below 0.08% through a nitrogen gas curtain and a multi-stage oxygen removal design, pollutant degradation is avoided, a protective medium is protected, meanwhile, the waste heat utilization rate is greatly improved, the fuel gas consumption is reduced, and the reuse frequency of coke powder is increased by utilizing the waste heat of one-time roasting; and finally, double improvement of product quality stability and production economy is realized.

Description

Technical Field

[0001] This invention relates to the field of graphite electrode calcination technology, and in particular to a method for secondary calcination and impregnation of graphite electrodes. Background Technology

[0002] As the core conductive material in electric arc furnace steelmaking, the performance of graphite electrodes directly affects steelmaking efficiency and molten steel quality. Secondary roasting is a key process in the preparation of graphite electrodes, used to remove the curing binder in the impregnated billet and improve the density, mechanical strength and conductivity of the electrode.

[0003] Regarding the above and existing related technologies, the inventors believe that the following defects often exist: In the existing methods for impregnating graphite electrodes by secondary calcination, the waste heat from the primary calcination is recycled to the secondary calcination process to achieve energy saving and consumption reduction. However, due to the inherent characteristics of the waste heat from the primary calcination being time-varying and fluctuating irregularly, the temperature control accuracy is poor and the temperature is easy to get out of control during the waste heat utilization process, which ultimately leads to uneven activation of coke powder and poor consistency of green body performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the existing technology has the disadvantages of poor temperature control accuracy and easy temperature runaway during the waste heat utilization process. To this end, we propose a method for secondary calcination and impregnation of graphite electrodes.

[0005] To achieve the above objectives, this application adopts the following technical solution: a method for secondary calcination and impregnation of graphite electrodes, comprising the following steps: Raw material preparation: Needle coke and petroleum coke calcined at high temperature in the absence of air are used as initial raw materials; Raw material processing: The initial raw materials are subjected to medium crushing, grinding, grading and sieving and drying processes in sequence to obtain aggregates; Ingredient mixing: The aggregates are weighed according to the formula, medium-temperature coal tar pitch binder is added, and the mixture is heated and kneaded to obtain a plastic paste. Compression molding: pressing the plastic paste into a blank and then cooling it to room temperature; Primary roasting: The billet is placed in a gas-fired annular roasting furnace containing coke powder. The billet is protected from air by the coke powder. After staged temperature control during heating, temperature maintenance, and cooling, it is removed from the furnace to obtain a primary roasted billet. When the temperature inside the gas-fired annular roasting furnace drops to... At that time, the waste heat was recovered using the bidirectional heat exchange channel of the gas-fired ring roasting furnace, and coke powder was also recovered. High-pressure impregnation: The once-fired green body is placed in an impregnation tank, first vacuumed, then molten medium-temperature coal tar pitch is injected, and after pressure is applied and maintained, excess pitch on the surface of the green body is removed to obtain the impregnated green body. Secondary roasting: The recovered coke powder is placed in a gas-fired ring roasting furnace. After pre-deoxygenation in the furnace, the coke powder is activated by intelligent collaborative temperature control. After the recovered coke powder is activated to the standard, it is cooled down, and the nitrogen curtain in the gas-fired ring roasting furnace is opened. Under the protection of the nitrogen curtain, the impregnated green body is placed in. After secondary deoxygenation and preheating, the residual heat recovered from the primary roasting is used to complete the low-temperature stage heating. If the residual heat is insufficient, the gas is adjusted to supplement the heat through intelligent collaborative temperature control. After the impregnated green body is heated, kept at a constant temperature and cooled down in stages, it is taken out of the furnace to obtain the secondary roasted green body. Machining, Inspection and Packaging: The secondary-fired blanks are shaped and threaded, and after passing inspection, they are packaged and shipped.

[0006] Preferably, the intelligent collaborative temperature control method is a deep learning-PID dual-algorithm collaborative control logic, including two linked links: feedforward adjustment and feedback fine-tuning. Feedforward adjustment is performed based on the temperature gap prediction, and PID feedback fine-tuning is performed based on the deviation between the real-time furnace temperature and the target temperature, so as to achieve precise matching between gas supplementary heating power and nitrogen flow rate.

[0007] Preferably, the feedforward regulation is trained based on 10 core data types, including primary roasting waste heat temperature, cooling rate, billet batch size, coke powder thickness, ambient temperature, current furnace temperature, nitrogen flow rate, gas power, furnace air leakage rate, and initial coke powder permeability. It then continuously predicts the furnace temperature trend for the next 5-10 minutes, with a prediction error of [missing information]. .

[0008] Preferably, the target temperature for coke powder activation is: The gas-fired heating power is limited to 20%~30% of the rated power, and the matching relationship between the temperature gap and the gas power and nitrogen flow rate is as follows: Temperature gap At that time, the gas power is adjusted to 28%~30%, and the nitrogen flow rate is... Maintain a slight positive pressure of 0.008~0.01MPa in the furnace; Temperature gap At that time, the gas power is maintained at 24%~27%, and the nitrogen flow rate is... ; Temperature gap Or, when waste heat recovers, the gas power drops to 20%~23%, and the nitrogen flow rate... .

[0009] Preferably, a premixed low-NOx burner is used in the coke powder activation process, where the fuel gas and combustion air are premixed at a ratio of 1:10, and the oxygen content of the exhaust gas is controlled at 2%~3% with closed-loop detection. Within the range of 20%~30% of the burner's rated power, the combustion efficiency is ≥99%.

[0010] Preferably, the criteria for determining whether coke powder activation meets the standards are: CO content in the furnace ≤ 0.02% for 30 minutes, and coke powder permeability ≥ 45%. During activation, the waste heat utilization rate is calculated in real time. If the waste heat utilization rate is ≥ 85%, the upper limit of the gas power is reduced to 28%. If activation meets the standards but the waste heat utilization rate is < 75%, the activation temperature is fine-tuned. .

[0011] Preferably, the flow rate of the nitrogen gas curtain is After the coke powder activation meets the standard, the cooling rate is controlled at... , down to The green body is placed in the impregnation chamber at the time, and secondary deoxygenation is carried out using... High-purity nitrogen was used for purging, pressurized to 0.02 MPa, held for 5 minutes, and then released to 0.01 MPa to ensure that the oxygen content in the furnace was ≤0.2%.

[0012] Preferably, the segmented temperature control parameters for the impregnated green body during the secondary firing are: Low temperature phase: From Rise to heating rate ; Medium temperature stage: heating rate ; High temperature stage: heating rate , After maintaining a constant temperature for 6 hours, allow it to cool down naturally.

[0013] Preferably, in the raw material preparation, the needle coke has a purity of ≥98% and a particle size of ≤50mm, and the petroleum coke calcination temperature is [not specified]. Density after calcination The mass ratio of the two is 7:3; In the raw material processing, after medium crushing, the raw material particle size is ≤10mm. After grading and screening, the raw material particle size is 1~3mm, accounting for 40%, 0.15~1mm, accounting for 35%, and ≤0.15mm, accounting for 25%. The drying temperature... Time: 2-3 hours; Aggregate moisture content: ≤0.5%; In the batching and mixing process, the medium-temperature coal tar pitch binder accounts for 22-25% of the aggregate mass, and its softening point is... Mixing temperature Time: 40-60 minutes, stirring speed: ; During compression molding, the molding pressure is 30~50MPa, the holding time is 10~15 minutes, and then it is cooled to room temperature. ; In a single roasting process, the coke powder particle size is 2-5mm, the layer thickness is 8-10cm, and the temperature is controlled in stages from room temperature to... heating rate , heating rate , heating rate , Maintain constant temperature for 4 hours.

[0014] Preferably, the specific parameters for high-pressure impregnation are: vacuum pressure -0.09~-0.095MPa, pressure holding time 1.5~2 hours, and medium-temperature coal tar pitch temperature. Pressurize to 10-15 MPa and hold for 4-6 hours. After removing excess asphalt from the surface of the billet, Dry for 1 hour.

[0015] The technical effects and advantages of this invention are as follows: In this invention, through the synergistic effect of intelligent collaborative temperature control, a full-process inertial protection system, a waste heat cascade utilization path, and clean combustion directional wastewater discharge, high-precision temperature stability control of the secondary roasting process is achieved, compressing the coke powder activation temperature fluctuation to a minimum. Within this range, the uniformity of coke powder activation and the consistency of green body roasting are ensured, significantly improving the mechanical strength and conductivity of graphite electrodes. Through nitrogen gas curtain and multi-stage deoxygenation design, the oxidation loss rate of the green body is reduced to below 0.08%, preventing contaminants from degrading the protective medium. At the same time, the waste heat from the first roasting is utilized, greatly improving the waste heat utilization rate, reducing gas consumption, and increasing the number of times coke powder can be reused. Ultimately, this achieves a dual improvement in product quality stability and production economy. Attached Figure Description

[0016] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a process flow diagram of the secondary calcination impregnation graphite electrode of the present invention. Figure 2 This is a flowchart of the deep learning-PID dual-algorithm collaborative control logic of the present invention. Detailed Implementation

[0017] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0018] According to the embodiments of the present invention, Figures 1 to 2 As shown.

[0019] Existing methods for impregnating graphite electrodes through secondary calcination utilize waste heat from the primary calcination process to achieve energy conservation and consumption reduction. However, due to the inherent characteristics of time-varying decay and irregular fluctuations in the waste heat from the primary calcination, temperature control accuracy is poor and temperature is prone to runaway during waste heat utilization. Specifically, the temperature fluctuation during the coke powder activation stage exceeds [a certain range]. During the low-temperature baking stage of the green body, the heating rate frequently exhibits unstable phenomena of sudden rises and falls. This temperature runaway not only causes uneven activation of coke powder, resulting in localized high-temperature sintering or low-temperature impurity residues, and fails to effectively restore the heat preservation, oxygen isolation, and air permeability protection properties of coke powder, but also leads to uneven heating of the impregnated green body during baking, generating significant internal thermal stress, which in turn causes microstructural defects in the green body. Ultimately, this results in poor consistency in key indicators such as mechanical strength and conductivity of the graphite electrode products, making it difficult to fully realize the energy-saving benefits of waste heat recovery and increasing the cost of subsequent product testing and rework. To solve this problem, the present invention incorporates the following design in the method of secondary baking and impregnating graphite electrodes: A method for impregnating graphite electrodes by secondary calcination includes the following steps: Raw material preparation: Needle coke and petroleum coke calcined at high temperature in the absence of air are used as initial raw materials; Raw material processing: The initial raw materials are subjected to medium crushing, grinding, grading and sieving and drying processes in sequence to obtain aggregates; Ingredient mixing: The aggregates are weighed according to the formula, medium-temperature coal tar pitch binder is added, and the mixture is heated and kneaded to obtain a plastic paste. Compression molding: pressing the plastic paste into a blank and then cooling it to room temperature; Primary roasting: The billet is placed in a gas-fired annular roasting furnace containing coke powder. The billet is protected from air by the coke powder. After staged temperature control during heating, temperature maintenance, and cooling, it is removed from the furnace to obtain a primary roasted billet. When the temperature inside the gas-fired annular roasting furnace drops to... At that time, the waste heat was recovered using the bidirectional heat exchange channel of the gas-fired ring roasting furnace, and coke powder was also recovered. High-pressure impregnation: The once-fired green body is placed in an impregnation tank, a vacuum is first drawn, then molten medium-temperature coal tar pitch is injected, and after pressure is applied and maintained, excess pitch on the surface of the green body is removed to obtain an impregnated green body. Secondary roasting: The recovered coke powder is placed in a gas-fired ring roasting furnace. After pre-deoxygenation in the furnace, the coke powder is activated by intelligent collaborative temperature control. After the recovered coke powder is activated to the standard, it is cooled down, and the nitrogen curtain in the gas-fired ring roasting furnace is opened. Under the protection of the nitrogen curtain, the impregnated green body is placed in. After secondary deoxygenation and preheating, the residual heat recovered from the primary roasting is used to complete the low-temperature stage heating. If the residual heat is insufficient, the gas is adjusted to supplement the heat through intelligent collaborative temperature control. After the impregnated green body is heated, kept at a constant temperature and cooled down in stages, it is taken out of the furnace to obtain the secondary roasted green body. Machining, Inspection and Packaging: The secondary-fired blanks are shaped and threaded, and after passing inspection, they are packaged and shipped.

[0020] In this embodiment, the preparation of raw materials specifically includes: Select needle coke with a purity ≥98% and a particle size ≤50mm, and mix it with... Petroleum coke calcined at high temperature in the absence of air was used as the initial raw material and mixed evenly at a mass ratio of 7:3 to obtain a mixed raw material.

[0021] In this embodiment, the raw material processing specifically includes: The mixed raw materials are sequentially crushed to a particle size of ≤10mm using a jaw crusher, then ground in a ball mill, and classified using a multi-layer vibrating screen: 40% for 1~3mm, 35% for 0.15~1mm, and 25% for ≤0.15mm. The powder is then fed into a drum dryer. Dry for 2-3 hours, controlling the aggregate moisture content to ≤0.5%, to obtain aggregate with uniform particle size.

[0022] In this embodiment, the mixing of ingredients specifically includes: Weigh the aggregate according to the preset formula, and add 22-25% of medium-temperature coal tar pitch binder by weight of the aggregate. The softening point of the medium-temperature coal tar pitch binder is [missing information]. The mixture is fed into a continuous kneader, where... Heating and kneading for 40-60 minutes at a constant stirring speed. This process yields a lumpy, uniformly fluid plastic paste.

[0023] In this embodiment, the pressing process specifically includes: The plastic paste is fed into the mold of a hydraulic molding machine and pressed under a pressure of 30-50 MPa for 10-15 minutes to obtain a blank. After molding, the blank is removed and allowed to cool naturally to room temperature. Avoid collisions and deformation during the cooling process.

[0024] In this embodiment, the first roasting specifically includes: The cooled green bodies are evenly placed in a gas-fired ring-type calcining furnace. The gaps between the green bodies are filled with a protective medium of coke powder with a particle size of 2-5mm, with a thickness of 8-10cm. The coke powder completely encapsulates the green bodies, isolating them from air. The furnace is then calcined in stages according to a preset temperature curve, from room temperature to... heating rate , heating rate , heating rate , After maintaining a constant temperature for 4 hours, the furnace will naturally cool down. At that time, the bidirectional heat exchange channel of the furnace body is activated, and the waste heat is recovered and stored through the honeycomb ceramic heat storage body. Key parameters such as waste heat temperature, flow rate and cooling rate are recorded simultaneously. After the firing is completed, the blank is taken out of the furnace to obtain a single-fired blank.

[0025] In this embodiment, high-pressure impregnation specifically includes: The pre-fired green body is placed in a high-pressure impregnation tank. After closing the tank door, a vacuum is drawn, and the pressure is maintained for 1.5 to 2 hours to remove air from the pores of the green body. Then, it is injected with... The green body is submerged in molten medium-temperature coal tar pitch and pressurized to 10-15 MPa for 4-6 hours to allow the pitch to fully penetrate. After depressurization, the green body is removed, and excess pitch is scraped off the surface with a scraper. Dry for 1 hour to obtain the impregnated blank.

[0026] In this embodiment, the secondary roasting specifically includes: Furnace pre-deoxygenation: The recovered coke powder is sieved through a 2-5mm grading sieve to remove lumps and impurities, and then evenly spread in the secondary roasting furnace. The furnace door is closed, and the gaps are sealed with refractory sealing material. The air leakage rate is checked and found to be ≤0.3%. The waste heat chamber is started, and high-purity nitrogen with a purity ≥99.9% is preheated to... The coke powder is introduced into the furnace for two pressurization and venting cycles. Each pressurization cycle is initiated at 0.02 MPa, held for 3 minutes, and then released to 0.005 MPa. The pressure is monitored by an oxygen content sensor until the oxygen content inside the furnace is ≤0.3%. Simultaneously, the coke powder undergoes initial preheating, and its temperature rises to [temperature value missing]. .

[0027] Coke powder activation: A smart collaborative temperature control method is used to collect real-time multi-dimensional parameters such as primary roasting waste heat temperature, cooling rate, billet batch size, coke powder thickness, and ambient temperature. This provides a rolling output of the furnace temperature trend and temperature gap prediction for the next 5-10 minutes. A bidirectional heat exchange channel is activated, and recovered waste heat is introduced as the core heat source. Feedforward adjustment is performed based on the predicted temperature gap. If the predicted temperature gap is ≥25℃, the power of the premixed low-NOx burner is adjusted to 28%-30% in advance, and the nitrogen flow rate is simultaneously increased. Maintain a slight positive pressure in the furnace of 0.008~0.01MPa, with a gap. At that time, the power was maintained at 24%~27%, and the nitrogen flow rate was... ,gap Or, when waste heat recovers, the power drops to 20%~23%, and the nitrogen flow rate... To reduce heat absorption, and based on the real-time deviation between the actual furnace temperature and the target temperature, a PID algorithm is used to continuously fine-tune the gas power, ensuring the temperature is above the target temperature. Increase nitrogen flow rate to Auxiliary cooling, below Slightly increase power to ensure temperature fluctuations To achieve matching between gas supplementation and waste heat fluctuations, the premixed burner premixes gas and combustion air at a 1:10 ratio. Within the range of 20%~30% of the burner's rated power, the combustion efficiency is ≥99%. A tail gas oxygen content detector monitors in real time, controlling the tail gas oxygen content to 2%~3%, dynamically fine-tuning the combustion air volume to avoid CO pollution or oxidation. Symmetrical air outlets on the furnace sidewalls are opened, using nitrogen micro-positive pressure to directionally discharge impurities. An external condensation device recovers impurities. Activation is deemed successful when the CO content in the furnace is ≤0.02% for 30 minutes and the coke powder permeability is ≥45%. The energy efficiency calculation logic calculates waste heat utilization and gas consumption in real time. When the waste heat utilization rate is ≥85%, the upper limit of gas power is lowered to 28%. When activation is successful and the waste heat utilization rate is <75%, the activation temperature is fine-tuned. To achieve optimal energy efficiency.

[0028] Place the impregnated preform: After activation is complete, close the heat exchange channel and burner, switch to the ambient temperature nitrogen branch, and adjust the flow rate to [value missing]. Forced convection cooling, controlling the cooling rate , down to The billet is kept at the appropriate temperature, and a slight positive pressure is maintained throughout the process. When the furnace door is opened, the inner annular nitrogen nozzle is activated, and the flow rate is [not specified]. An air curtain is formed, and the impregnated billet is fed into the furnace within 10 minutes. The furnace door is then closed and locked, and the process is switched back to the preheating nitrogen branch. Nitrogen gas is used for secondary replacement, pressurized to 0.02 MPa, held for 5 minutes and then released to 0.01 MPa to reduce the oxygen content to ≤0.2%, while simultaneously preheating the billet.

[0029] Segmented firing of impregnated green bodies: Opening a two-way heat exchange channel, utilizing residual heat to fire the green bodies from... Rise to heating rate When waste heat is insufficient, the gas power is adjusted according to the deep learning-PID dual algorithm control logic, supplementing heat in the 20%~30% range, followed by segmented temperature control. The second stage is... heating rate Phase 3 heating rate , After being kept at a constant temperature for 6 hours, the material is allowed to cool naturally to room temperature. The resulting material is then removed from the furnace to obtain a second-fired blank, and the coke powder is recovered.

[0030] In this embodiment, machining and inspection packaging specifically include: The second-fired blank is fed into a CNC lathe for shaping, and the outer diameter tolerance is adjusted. The threads at both ends are then processed using a thread processing machine. After processing, the appearance, dimensions, density, resistivity, mechanical strength and other indicators are inspected. Qualified products are packaged with waterproof and moisture-proof materials and then put into storage or shipped.

[0031] Example 1 In the raw material pretreatment stage, needle coke with a purity ≥98% and a particle size ≤50mm is selected and mixed with... Petroleum coke calcined in the absence of air was mixed in a 7:3 mass ratio, crushed to ≤10mm using a jaw crusher, ground into powder using a ball mill, and then classified and screened, with 40% being 1~3mm, 35% being 0.15~1mm, and 25% being ≤0.15mm. Dry for 2-3 hours until the aggregate moisture content is ≤0.5%, then add 22-25% of the aggregate mass by weight, softening point Medium-temperature coal tar pitch binder, The following Mix and knead for 40-60 minutes to obtain a plastic paste, then press and hold at 30-50 MPa for 10-15 minutes to form a mold, and allow to cool naturally. spare.

[0032] During the first firing, the green body is wrapped in coke powder with a particle size of 2-5 mm and a thickness of 8-10 cm to isolate it from the air, and the temperature is controlled according to a segmented curve, from room temperature to... The heating rate is , The heating rate is , The heating rate is , Maintain temperature for 4 hours, then cool down to Waste heat is recovered through a bidirectional heat exchange channel and a honeycomb ceramic regenerator, and coke powder is recovered simultaneously. In the high-pressure impregnation process, the once-fired green body is vacuum-pressurized for 1.5 to 2 hours before being injected. Melt the asphalt, hold at 10-15 MPa for 4-6 hours, then remove the surface asphalt. Dry for 1 hour.

[0033] In the secondary roasting process, the recovered coke powder is first sieved to remove impurities and then laid in the furnace. After sealing, the air leakage rate is tested to be ≤0.3%. The nitrogen gas with a purity ≥99.9% is pressurized twice and then vented. The pressure is maintained at 0.02 MPa for 3 minutes until the oxygen content is ≤0.3%, and the coke powder is preheated to... The system employs an intelligent collaborative temperature control method, collecting multi-dimensional parameters to predict the temperature gap over 5-10 minutes. Based on this gap, it adjusts the gas power and nitrogen flow rate, and then fine-tunes the process using a PID algorithm to control the temperature. ,fluctuation The premixed burner mixes air and fuel at a 1:10 air-fuel ratio, controls the oxygen content in the exhaust gas to 2%~3%, and directs the discharge of impurities. The furnace CO ≤ 0.02% and coke powder permeability ≥ 45% are considered satisfactory. Energy efficiency is simultaneously and dynamically optimized. After activation... Cool down to , The furnace is protected by a nitrogen gas curtain and is replaced twice until the oxygen content is ≤ 0.2%. The waste heat is utilized. Heat up to . When the waste heat is insufficient, supplementary heat is provided. Subsequently, according to Rise to , Rise to . After maintaining a constant temperature for 6 hours, it is cooled, the coke powder is recovered, and finally it is shaped by a CNC lathe and thread processed. The appearance, dimensions, density and other indicators are detected, and the qualified products are packaged and stored in the warehouse.

[0034] Example 2 In the raw material pretreatment stage, needle coke with a purity ≥ 95% and a particle size ≤ 60 mm is selected and mixed with Petroleum coke calcined in an air-free environment is mixed in a mass ratio of 6:4, crushed to ≤ 15 mm by a jaw crusher, and only two-stage screening is carried out after grinding by a ball mill. Among them, 2 - 5 mm accounts for 55% and ≤ 2 mm accounts for 45%. It is dried for 4 - 5 hours until the moisture content of the aggregate is ≤ 1.0%. Subsequently, a medium-temperature coal tar pitch binder with a content of 20 - 28% of the aggregate mass and a softening point of is added. At It is kneaded for 30 - 50 minutes to obtain a plastic paste, formed under a pressure of 20 - 40 MPa and held for 8 - 12 minutes, and naturally cooled to room temperature for standby.

[0035] During the first roasting, the green body is loosely covered with coke powder with a particle size of 1 - 8 mm and a thickness of 5 - 12 cm to isolate the air. The temperature is controlled by a constant heating rate. From room temperature to The whole process is heated at . It is kept at a constant temperature for 3 hours. There is no waste heat recovery device during the cooling process, and the coke powder is directly discarded after cooling. In the high-pressure impregnation process, the first-roasted green body is directly immersed in molten asphalt without vacuum treatment. The atmospheric pressure impregnation method is adopted, and the impregnation time is 8 - 10 hours. After removing the surface asphalt, it is naturally dried.

[0036] During the second roasting, new coke powder is directly used to lay the furnace hearth, and it is heated with a fixed gas power. The temperature is controlled at and the temperature fluctuation is . The gas-air ratio of the burner is fixed at a ratio of 1:8, and there is no device for discharging non-directional impurities in the tail gas. When the CO in the furnace is ≤ 0.05% and the air permeability of the coke powder is ≥ 35%, it is considered qualified. After activation, it is cooled to at . There is no nitrogen gas curtain protection. Subsequently, according to Rise to , Rise to After being kept at a constant temperature for 4 hours, the coke is naturally cooled and discarded without being recycled. Finally, it is shaped and threaded on a conventional lathe. After the appearance and key dimensions are inspected and found to be qualified, it is packaged and stored.

[0037] Example 3 In the raw material pretreatment stage, needle coke with a purity ≥96% and a particle size ≤55mm is selected and mixed with... Petroleum coke calcined in the absence of air is mixed in a 7:3 mass ratio, then crushed to ≤12mm using a jaw crusher. After grinding in a ball mill, it is not graded or screened, and the aggregate particle size is ≤3mm. Dry for 3-4 hours until the aggregate moisture content is ≤0.8%, then add 21-26% of the aggregate by weight, softening point Medium-temperature coal tar pitch binder, The following Mix and knead for 35-55 minutes to obtain a plastic paste, then press and hold at 25-45 MPa for 9-14 minutes to form a mold, and allow it to cool naturally. spare.

[0038] During the first firing, the green body is wrapped in coke powder with a particle size of 2-6 mm and a thickness of 7-11 cm to isolate it from the air. A three-stage temperature control is used, but no precise parameters are available. The heating rate from room temperature to 300℃ is 6-8℃ / h, and the heating rate from 300℃ to 600℃ is... , heating rate , Maintain temperature for 3.5 hours, then cool down to Partial waste heat is recovered through a single heat exchange pipe. The coke powder is simply sieved and reused once before being discarded. In the high-pressure impregnation stage, the once-fired green body is vacuum-pressurized for 1.0-1.5 hours and then injected... Melt the asphalt, hold at 5-10 MPa for 3-5 hours, then remove the surface asphalt. Dry for 1.5 hours.

[0039] During secondary roasting, the recovered coke powder is sieved to remove impurities and then laid in the furnace. After sealing, the air leakage rate is tested to be ≤0.5%. First, pressurize and exhaust the gas with nitrogen gas of ≥99% purity at 0.01~0.02MPa for 2 minutes until the oxygen content is ≤0.5%, and then preheat the coke powder to... It adopts conventional PID temperature control and lacks temperature gap prediction function for temperature control. Temperature fluctuations The premixed burner mixes air and fuel at a 1:9 ratio, controls the oxygen content in the exhaust gas to 1%~4%, and features a non-directional impurity removal design. In-furnace CO ≤ 0.03% and coke powder permeability ≥ 40% are sufficient to meet standards. After activation... Cool down to , A nitrogen gas curtain is used to protect the furnace during initial purging until the oxygen content is ≤0.3%, utilizing recovered waste heat to... Heat up to If the residual heat is insufficient, supplement the heat directly, and then follow the instructions. h rises to , Rise to After being kept at a constant temperature for 5 hours, the coke powder is cooled, recycled, reused twice, and then discarded. Finally, it is shaped and threaded on a CNC lathe, and after the appearance, size, density and other indicators are tested and found to be qualified, it is packaged and stored.

[0040] The following is a data table combining the core performance and production economy of the product as presented in Examples 1, 2, and 3:

[0041] A comparison of the three sets of embodiments shows that Embodiment 1, through the synergistic effect of intelligent collaborative temperature control, a full-process inertial protection system, a waste heat cascade utilization path, and clean combustion directional wastewater discharge, achieved high-precision temperature stability control in the secondary roasting process, compressing the coke powder activation temperature fluctuation to a minimum. Within this range, the uniformity of coke powder activation and the consistency of green body roasting are ensured, significantly improving the mechanical strength and conductivity of graphite electrodes. Through nitrogen gas curtain and multi-stage deoxygenation design, the oxidation loss rate of the green body is reduced to below 0.08%, preventing contaminants from degrading the protective medium. At the same time, the waste heat from the first roasting is utilized, greatly improving the waste heat utilization rate, reducing gas consumption, and increasing the number of times coke powder can be reused. Ultimately, this achieves a dual improvement in product quality stability and production economy.

[0042] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method of baking impregnated graphite electrodes, characterized in that, The method comprises the following steps: Raw material preparation: taking needle coke and petroleum coke calcined at high temperature in isolated air as initial raw materials; Raw material treatment: the initial raw materials are sequentially subjected to medium crushing, powdering, grading screening and drying treatment to obtain aggregates; Batching and kneading: the aggregates are weighed according to a formula, a medium-temperature coal pitch binder is added, and a plastic paste is obtained through heating and kneading; Molding: the plastic paste is pressed into a blank and cooled to room temperature; Primary baking: the blank is placed in a gas ring baking furnace containing coke powder, the blank is protected from air by the coke powder, and after temperature rising, constant temperature and temperature falling in stages, the primary baked blank is taken out of the furnace, when the temperature in the gas ring baking furnace falls to , the waste heat is recovered using the two-way heat exchange channel of the gas ring baking furnace, and coke powder is recovered. High-pressure impregnation: the primary baked blank is placed in an impregnation tank, vacuum is first extracted, then molten medium-temperature coal pitch is injected, pressure is maintained after pressure increase, and the blank surface is cleaned to obtain an impregnated blank; Secondary baking: the recycled coke powder is placed in a gas ring baking furnace, oxygen is first removed in the hearth, then the coke powder is activated through an intelligent collaborative temperature control method, the activated coke powder is cooled to standard, the nitrogen gas curtain in the gas ring baking furnace is opened, the impregnated blank is placed in the nitrogen gas curtain, preheating is performed after secondary oxygen removal, the low-temperature stage is completed through the residual heat of the primary baking, the gas is adjusted for heat supplement through the intelligent collaborative temperature control method when the residual heat is insufficient, the impregnated blank is subjected to segmented temperature control, constant temperature and cooling to obtain a secondary baked blank; Machining, inspection and packaging: the secondary baked blank is shaped and threaded, and is packaged and shipped after passing the detection.

2. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized by: The intelligent collaborative temperature control method is a deep learning-PID double algorithm collaborative control logic, which comprises two linkage links of feedforward regulation and feedback fine tuning, performs feedforward regulation based on temperature gap estimation, performs PID feedback fine tuning based on the deviation between the real-time temperature of the hearth and the target temperature, and realizes accurate matching of the gas heat supplement power and the nitrogen flow.

3. The method of baking a secondary impregnated graphite electrode according to claim 2, characterized in that: The feedforward regulation is based on ten types of core data training, including once-fired waste heat temperature, cooling rate, green body batch, coke powder laying thickness, environment temperature, current furnace temperature, nitrogen flow, gas power, furnace air leakage rate, and coke powder initial permeability. The rolling prediction is for the furnace temperature trend in the next 5-10 minutes, and the prediction error is .

4. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized by: The target temperature for activation of the coke powder is The gas reheat power is limited to 20% to 30% of the rated power, and the matching relationship of the temperature gap with the gas power and the nitrogen flow is: Temperature gap Gas power is adjusted to 28%~30%, nitrogen flow , and the furnace is maintained at a slight positive pressure of 0.008~0.01 MPa. Temperature gap Gas power was maintained at 24-27% while nitrogen flow ; Temperature gap Or the heat back to the power of gas to 20% ~ 23%, nitrogen flow .

5. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized by: The premixing low-nitrogen burner is used in the coke powder activation process, the gas and the combustion air are premixed at a ratio of 1:10, the tail gas oxygen content is closed-loop detected, the tail gas oxygen content is controlled to be 2% to 3%, the combustion efficiency is greater than or equal to 99% in the range of 20% to 30% of the rated power of the burner.

6. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized in that: The coke powder activation standard is that the CO content in the furnace is less than or equal to 0.02% and lasts for 30 minutes, and the coke powder permeability is greater than or equal to 45%. The waste heat utilization rate is calculated in real time during the activation process. When the waste heat utilization rate is greater than or equal to 85%, the upper limit of the fuel gas power is lowered to 28%. When the activation standard is met and the waste heat utilization rate is less than 75%, the activation temperature is fine-tuned to .

7. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized in that: The flow rate of the nitrogen gas curtain is , the cooling rate is controlled at , and the temperature is lowered to , the impregnated blank is put in, the secondary deoxygenation is replaced by high-purity nitrogen, the pressure is charged to 0.02 MPa, the pressure is maintained for 5 minutes, and then released to 0.01 MPa, so that the oxygen content in the hearth is ≤0.2%.

8. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized by: The segmented temperature control parameters of the impregnated blank in the secondary baking are as follows: Low temperature phase: from to , heating rate ; Medium temperature stage: , heating rate ; High temperature stage: , heating rate , After 6 hours at constant temperature, natural cooling.

9. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized in that: In the raw material preparation, the purity of needle coke is ≥98%, the particle size is ≤50 mm, the petroleum coke calcination temperature is 800-850°C , the density after calcination is 1.8-2.0 g / cm3 , and the mass ratio of the two is 7:

3. In the raw material processing, the particle size of the raw material after being crushed is less than or equal to 10 mm, the particle size of the raw material after being classified and screened is 1-3 mm, accounting for 40%, the particle size of the raw material is 0.15-1 mm, accounting for 35%, and the particle size of the raw material is less than or equal to 0.15 mm, accounting for 25%, the drying temperature is 80-100 DEG C, the drying time is 2-3 hours, and the water content of the aggregate is less than or equal to 0.5% . In the mixing and kneading of the ingredients, the medium temperature coal pitch binder accounts for 22-25% of the mass of the aggregate, and the softening point of the medium temperature coal pitch binder is 80-90℃ , the mixing and kneading temperature is 80-90℃, the mixing and kneading time is 40-60 minutes, and the stirring speed is 40-60 r / min . In the press forming, the forming pressure is 30 to 50 MPa, the pressure maintaining time is 10 to 15 minutes, and cooling is performed to room temperature ; In the first baking, the coke powder particle size is 2-5 mm, the laying thickness is 8-10 cm, and the segmented temperature control is room temperature to The heating rate , The heating rate , The heating rate , Constant temperature for 4 hours.

10. The method of baking a secondary impregnated graphite electrode according to claim 1, characterized in that: The specific parameters of the high-pressure impregnation are: vacuumizing pressure -0.09~ -0.095 MPa, pressure maintaining for 1.5~2 hours, medium-temperature coal pitch temperature pressurizing to 10~15 MPa, pressure maintaining for 4~6 hours, after removing the excess pitch on the surface of the green body, drying for 1 hour. ​

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