A method of re-baking impregnated graphite electrodes

Abstract

The application relates to the field of graphite electrode baking technology, and discloses a method for baking and impregnating graphite electrodes in two steps; through the synergistic effect of the intelligent collaborative temperature control method, the whole-process inert protection system, the waste heat step-by-step utilization path and the clean combustion directional pollution discharge, high-precision temperature stability control of the two-step baking process is realized, the coke powder activation temperature fluctuation is compressed to 10-20 DEG C, the uniformity of coke powder activation and the consistency of blank baking are ensured, the mechanical strength and the electric conductivity of the graphite electrode are greatly improved, through the nitrogen gas curtain and the multi-stage oxygen removal design, the blank oxidation loss rate is reduced to below 0.08%, the pollutants are prevented from degrading the protective medium, meanwhile, the waste heat of the first baking is utilized, the waste heat utilization rate is greatly improved, the fuel gas consumption is reduced, and the reuse times of the coke powder are increased, finally, the product quality stability and the production economy are improved.

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 secondary roasting and impregnating graphite electrodes, the waste heat from the primary roasting is recycled to the secondary roasting process to achieve energy saving and consumption reduction. However, due to the inherent characteristics of the waste heat from the primary roasting 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:

[0006] Raw material preparation: Needle coke and petroleum coke calcined at high temperature in the absence of air are used as initial raw materials;

[0007] Raw material processing: The initial raw materials are subjected to medium crushing, grinding, grading and sieving and drying processes in sequence to obtain aggregates;

[0008] 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.

[0009] Compression molding: pressing the plastic paste into a blank and then cooling it to room temperature;

[0010] 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.

[0011] 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.

[0012] 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.

[0013] Machining, Inspection and Packaging: The secondary-fired blanks are shaped and threaded, and after passing inspection, they are packaged and shipped.

[0014] 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.

[0015] 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]. .

[0016] 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:

[0017] 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;

[0018] Temperature gap At that time, the gas power is maintained at 24%~27%, and the nitrogen flow rate is... ;

[0019] Temperature gap Or, when waste heat recovers, the gas power drops to 20%~23%, and the nitrogen flow rate... .

[0020] 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%.

[0021] 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. .

[0022] 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%.

[0023] Preferably, the segmented temperature control parameters for the impregnated green body during the secondary firing are:

[0024] Low temperature phase: From Rise to heating rate ;

[0025] Medium temperature stage: heating rate ;

[0026] High temperature stage: heating rate , After maintaining a constant temperature for 6 hours, allow it to cool down naturally.

[0027] 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;

[0028] 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%;

[0029] 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: ;

[0030] During compression molding, the molding pressure is 30~50MPa, the holding time is 10~15 minutes, and then it is cooled to room temperature. ;

[0031] 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.

[0032] 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.

[0033] The technical effects and advantages of this invention are as follows:

[0034] 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

[0035] 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:

[0036] Figure 1 This is a process flow diagram of the secondary calcination impregnation graphite electrode of the present invention;

[0037] Figure 2 This is a flowchart of the deep learning-PID dual-algorithm collaborative control logic of the present invention. Detailed Implementation

[0038] 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.

[0039] According to the embodiments of the present invention, Figures 1 to 2 As shown.

[0040] 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:

[0041] A method for impregnating graphite electrodes by secondary calcination includes the following steps:

[0042] Raw material preparation: Needle coke and petroleum coke calcined at high temperature in the absence of air are used as initial raw materials;

[0043] Raw material processing: The initial raw materials are subjected to medium crushing, grinding, grading and sieving and drying processes in sequence to obtain aggregates;

[0044] 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.

[0045] Compression molding: pressing the plastic paste into a blank and then cooling it to room temperature;

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Machining, Inspection and Packaging: The secondary-fired blanks are shaped and threaded, and after passing inspection, they are packaged and shipped.

[0050] In this embodiment, the preparation of raw materials specifically includes:

[0051] 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.

[0052] In this embodiment, the raw material processing specifically includes:

[0053] 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.

[0054] In this embodiment, the mixing of ingredients specifically includes:

[0055] 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.

[0056] In this embodiment, the pressing process specifically includes:

[0057] 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.

[0058] In this embodiment, the first roasting specifically includes:

[0059] 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.

[0060] In this embodiment, high-pressure impregnation specifically includes:

[0061] 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.

[0062] In this embodiment, the secondary roasting specifically includes:

[0063] 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 gas 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 oxygen content is monitored by an oxygen sensor until it reaches ≤0.3%, simultaneously completing the initial preheating of the coke powder, raising its temperature to [temperature value missing]. .

[0064] 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.

[0065] 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.

[0066] 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.

[0067] In this embodiment, machining and inspection packaging specifically include:

[0068] 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.

[0069] Example 1

[0070] 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.

[0071] 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.

[0072] 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 , Nitrogen gas is introduced into the furnace under nitrogen protection, followed by a second purging until the oxygen content is ≤0.2%, utilizing waste heat. Heat up to If the residual heat is insufficient, supplement the heat, and then follow the instructions. Rise to , Rise to After being kept at a constant temperature for 6 hours, the product is cooled to recover coke powder. Finally, it is shaped and threaded on a CNC lathe, and its appearance, size, density and other indicators are tested. Qualified products are packaged and put into storage.

[0073] Example 2

[0074] In the raw material pretreatment stage, needle coke with a purity ≥95% and a particle size ≤60mm is selected and mixed with... Petroleum coke calcined in the absence of air is mixed in a 6:4 mass ratio, crushed to ≤15mm using a jaw crusher, and then ground in a ball mill. After grinding, it undergoes only two stages of screening, with 55% being 2-5mm and 45% being ≤2mm. Dry for 4-5 hours until the aggregate moisture content is ≤1.0%, then add 20-28% of the aggregate by weight, softening point Medium-temperature coal tar pitch binder, The following Mix and knead for 30-50 minutes to obtain a plastic paste, press it under 20-40 MPa pressure for 8-12 minutes to form a mold, and let it cool naturally to room temperature for later use.

[0075] During the first baking, 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 air. The temperature is controlled using a constant heating rate. From room temperature to The whole process is at heating up, holding 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 step, the green body after the first baking is directly immersed in molten asphalt without prior vacuum treatment. The atmospheric pressure impregnation method is used for 8 - 10 hours, and after removing the surface asphalt, it is naturally air-dried.

[0076] During the second baking, a new layer of coke powder is directly laid in the furnace chamber, and fixed gas power heating is used for temperature control and temperature fluctuation . The gas-air ratio of the burner is fixed at a ratio of 1:8. There is no device for discharging non-directional impurities in the exhaust 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 down at to , without nitrogen gas curtain protection. Subsequently, it is heated up according to to and heated up to . After holding at a constant temperature for 4 hours, it is naturally cooled, and the coke powder is discarded without recycling. Finally, it is shaped by a common lathe and thread-processed. After the appearance and key dimensions are inspected and qualified, it is packaged and stored in the warehouse.

[0077] Example 3

[0078] In the raw material pretreatment stage, needle coke with a purity ≥ 96% and a particle size ≤ 55 mm is selected and mixed with petroleum coke calcined in an air-insulated manner in a mass ratio of 7:3. It is crushed to ≤ 12 mm by a jaw crusher, and after being pulverized by a ball mill, it is not subjected to classification and screening. The aggregate particle size is ≤ 3 mm. It is dried for 3 - 4 hours until the aggregate moisture content is ≤ 0.8%. Subsequently, a medium-temperature coal tar pitch binder with a content of 21 - 26% of the aggregate mass and a softening point is added. At it is kneaded for 35 - 55 minutes to obtain a plastic paste, which is formed under a pressure of 25 - 45 MPa for 9 - 14 minutes of pressure holding, and then naturally cooled to for standby.

[0079] During the first baking, the green body is wrapped with coke powder with a particle size of 2 - 6 mm and a thickness of 7 - 11 cm to isolate air. The three-stage temperature control is adopted but without precise parameters. The heating rate from room temperature to 300 °C is 6 - 8 °C / h, and the heating rate from 300 - 600 °C is , heating rate , holding at a constant temperature for 3.5 hours, and cooling 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.

[0080] 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, maintaining the pressure 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 without temperature gap prediction function, and the temperature control is... 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.

[0081] The following is a data table combining the core performance and production economy of the product as presented in Examples 1, 2, and 3:

[0082]

[0083] 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.

[0084] 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 for secondary calcination and impregnation of graphite electrodes, characterized in that, 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. During the activation of the recovered coke powder, a two-way heat exchange channel is opened, and the recovered waste heat is introduced as the core heat source. Feedforward adjustment is performed based on the predicted temperature gap estimate. After the recovered coke powder is activated to the standard, the temperature is reduced, 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 waste heat recovered from the primary roasting is used to complete the low-temperature stage heating. When the waste heat is insufficient, the gas is adjusted to supplement the heat through intelligent collaborative temperature control. After the impregnated green body is subjected to segmented temperature control heating, constant temperature and cooling, 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 packaged and shipped after passing inspection; 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. 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 predicts the furnace temperature trend over the next 5-10 minutes using a rolling forecast. The prediction error is... .

2. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: The target temperature for activating the coke powder 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... .

3. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: The coke powder activation process uses a premixed low-NOx burner, where the fuel gas and combustion air are premixed at a ratio of 1:

10. Combined with closed-loop detection of exhaust gas oxygen content, the exhaust gas oxygen content is controlled at 2%~3%, and the combustion efficiency is ≥99% within the range of 20%~30% of the burner's rated power.

4. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: 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%. Waste heat utilization rate is calculated in real-time during activation. If the waste heat utilization rate is ≥ 85%, the upper limit of 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. .

5. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: 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 When the impregnated blank is placed in the container, the 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%.

6. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: The segmented temperature control parameters for the impregnated green body during the secondary firing are as follows: 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.

7. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: In raw material preparation, the purity of needle coke is ≥98%, the particle size is ≤50mm, and the calcination temperature of petroleum coke is [not specified]. Density after calcination The mass ratio of the two is 7:3; In the raw material processing, the particle size of the raw material after medium crushing is ≤10mm, and after grading and screening, the proportion of raw material with a particle size of 1~3mm is 40%, the proportion of raw material with a particle size of 0.15~1mm is 35%, and the proportion of raw material with a particle size of ≤0.15mm is 25%. The drying temperature... Time: 2-3 hours; Aggregate moisture content: ≤0.5%; In the mixing of the ingredients, the medium-temperature coal tar pitch binder accounts for 22-25% of the aggregate mass and has a softening point of [missing information]. Mixing temperature Time: 40-60 minutes, stirring speed: ; In the molding process, the molding pressure is 30~50MPa, the holding time is 10~15 minutes, and the temperature is cooled to room temperature. ; In the first roasting, the coke powder has a particle size of 2-5mm and a thickness of 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.

8. The method for secondary calcination and impregnation of graphite electrodes according to claim 1, characterized in that: The specific parameters for the 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.

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