Large volume plasma high temperature electric furnace

Abstract

The application relates to a large-volume plasma high-temperature electric furnace, belonging to the technical field of industrial electric heating equipment, which comprises a furnace body, a furnace chamber, an electric heating element and a furnace door, and further comprises a plurality of plasma spray guns, the plasma spray guns are arranged along the circumference of the furnace chamber, and the spraying directions of the plasma spray guns are arranged along the same rotation direction of the furnace chamber; the plasma spray guns are connected with a plasma power supply and a working gas source; a temperature detection unit is arranged in the furnace chamber and is used for detecting the temperatures of multiple areas in the furnace chamber; a control unit is electrically connected with the temperature detection unit, the plasma power supply, the working gas source and the electric heating element, and is used for adjusting the working parameters of the plasma spray guns and / or the heating power of the electric heating element according to the temperature signals fed back by the temperature detection unit. The plasma spray guns are arranged along the same rotation direction around the furnace chamber, the accurate control of the directional circulating airflow in the furnace chamber is realized, the convection heat exchange is strengthened, and the temperature uniformity and the heating efficiency of the furnace chamber are improved.

Description

Technical Field

[0001] This invention relates to a large-capacity plasma high-temperature electric furnace, belonging to the technical field of industrial electric heating equipment. Background Technology

[0002] Electric heating furnaces are widely used heating equipment in industrial production. Their heating principle involves converting electrical energy into heat energy through electric heating elements, transferring the heat to the materials or workpieces inside the furnace chamber via radiation and convection. For large-capacity high-temperature electric furnaces, due to the large furnace space, the electric heating elements are usually arranged around the perimeter or bottom of the furnace chamber, with heat primarily transferred from the heating elements to the central area of ​​the furnace chamber via radiation. However, large-capacity high-temperature electric furnaces have the following drawbacks: First, the central area of ​​the furnace chamber is far from the heating elements, and the radiation heat transfer efficiency decreases significantly with increasing distance, resulting in a lower temperature at the center of the furnace chamber and poor temperature uniformity. Second, the air inside the furnace chamber is almost stagnant, resulting in very weak convective heat transfer; heat transfer mainly relies on radiation, with limited heat transfer efficiency. Third, for processes requiring rapid heating or high temperature uniformity, relying solely on radiation heating is insufficient.

[0003] To address the aforementioned issues, relevant patented technologies have been explored. For example, Chinese Patent Publication No. CN102432015A discloses a "uniform temperature high-efficiency electric heating furnace," which improves temperature uniformity by arranging heating elements on the inner wall, bottom, and center of the furnace cylinder. Another example is Chinese Patent Publication No. CN103045810A, which discloses a large-space furnace chamber and temperature control method for a vacuum furnace used in heat treatment, dividing the furnace chamber into multiple independent heating zones and controlling the temperature of each zone independently using a PLC. Regarding the application of plasma technology to electric furnaces, Chinese Patent Publication No. CN118960049A discloses a "furnace chamber for a commercial plasma stove," which uses an airflow duct and the inner wall of the furnace to form a spiral structure, promoting the formation of a spiral airflow.

[0004] However, existing technologies still have the following drawbacks: heating elements occupy the internal space of the furnace, affecting the loading and unloading of materials, and the heat transfer efficiency is still limited. The temperature uniformity control of large-volume furnaces still lacks effective active convection regulation methods. The application of existing plasma technology in electric furnaces uses plasma as a direct heating source, which can easily lead to local overheating and product cracking. Furthermore, there is a lack of systematic control methods for using plasma jets to drive the airflow circulation inside the furnace. Summary of the Invention

[0005] The purpose of this invention is to provide a large-volume plasma high-temperature electric furnace that solves the defects of existing large-volume high-temperature electric furnaces, such as low radiation heat transfer efficiency, poor furnace temperature uniformity, and lack of effective convection circulation control methods.

[0006] The present invention provides a large-volume plasma high-temperature electric furnace, comprising a furnace body, a furnace chamber, an electric heating element, and a furnace door. The electric heating element is disposed inside the furnace chamber. The furnace also includes several plasma spray guns, which are installed on the furnace wall or furnace top of the furnace body, and the nozzles of each plasma spray gun extend into the furnace chamber.

[0007] The plasma spray guns are arranged circumferentially along the furnace chamber, and the spray direction of each plasma spray gun is set along the same rotation direction of the furnace chamber.

[0008] The plasma spray gun is connected to a plasma power supply and a working gas source.

[0009] The temperature detection unit is located inside the furnace and is used to detect the temperature in multiple areas within the furnace.

[0010] The control unit is electrically connected to the temperature detection unit, plasma power supply, working gas source and electric heating element, respectively, and is used to adjust the working parameters of the plasma spray gun and / or the heating power of the electric heating element according to the temperature signal fed back by the temperature detection unit.

[0011] By arranging plasma spray guns in the same direction around the furnace and establishing a multi-parameter coordinated control method, precise control of the directional circulating airflow in the furnace can be achieved, thereby enhancing convective heat transfer and improving furnace temperature uniformity and heating efficiency.

[0012] Preferably, the number of plasma spray guns is 4 to 12, and they are evenly arranged along the circumference of the furnace.

[0013] Preferably, the angle between the spray direction of the plasma spray gun and the tangent direction of the furnace inner wall is 0° to 45°, or perpendicular to the furnace inner wall.

[0014] Preferably, the plasma spray gun includes a gun body and a nozzle, the nozzle being disposed circumferentially in the furnace chamber with its outlet facing the interior of the furnace chamber; the gun body is provided with a working gas inlet.

[0015] Preferably, the nozzle has an outlet diameter of 5 to 30 mm.

[0016] Preferably, the working gas is air, nitrogen, argon, or a mixture thereof. When air is selected as the working gas, it should be noted that the presence of oxygen in the air may cause oxidation of the heating element and furnace material under certain conditions. Therefore, in practical applications, a suitable working gas should be selected according to the furnace temperature and material characteristics, or an inert gas should be switched at high temperatures.

[0017] Preferably, the electric heating element is a resistance heating element, which is arranged on the side wall and / or bottom of the furnace.

[0018] Preferably, the furnace chamber is a square or circular furnace chamber. In a circular (cylindrical) furnace chamber structure, the plasma spray guns are evenly arranged along the circumference, and the jets of each spray gun are ejected in the tangential direction, which can form the most natural annular circulating airflow in the furnace chamber. The flow field has good symmetry and no dead zones. Moreover, the circular furnace chamber structure has uniform stress and is easy to construct with refractory materials, making it the preferred furnace chamber shape for large-volume high-temperature plasma electric furnaces.

[0019] Preferably, the temperature detection unit includes multiple thermocouples distributed in various areas of the furnace, and the thermocouples are arranged along the height and circumference of the furnace.

[0020] Preferably, the control unit is a PLC controller or an industrial computer.

[0021] The control unit adjusts the operating parameters of the plasma spray gun and / or the heating power of the electric heating element through the following steps:

[0022] S1: Set the target temperature To and temperature uniformity tolerance △T of the furnace according to the process requirements;

[0023] S2: Start the electric heating element to radiate heat to the furnace, and at the same time start the plasma power supply and working gas source, so that each plasma nozzle sprays plasma jets according to the preset initial power Po and initial gas flow rate Qo. Each plasma jet forms a directional circulating airflow in the same direction in the furnace.

[0024] S3: Temperature signals Ti (i=1,2,…,n, where n is the number of temperature detection points) of each area are collected in real time by temperature detection units set in multiple areas of the furnace, and the temperature signals are transmitted to the control unit.

[0025] S4: The control unit calculates the temperature deviation between each detection point and the target temperature △Ti=Ti-To, and calculates the maximum temperature difference in the furnace △Tmax=max(Ti)-min(Ti);

[0026] S5: When △Tmax>△T, the control unit adjusts the flow rate and / or flow rate of the circulating airflow by adjusting the working parameters of the plasma spray gun;

[0027] S6: When the average temperature of the furnace deviates from the target temperature, the control unit adjusts the heating power of the electric heating element and / or the input power of the plasma spray gun.

[0028] S7: Repeat steps S3 to S6 until the temperature in each area of ​​the furnace meets the process requirements.

[0029] Preferably, in step S5, adjusting the operating parameters of the plasma spray gun includes one or more combinations of the following methods:

[0030] (a) Adjust the output current or voltage of the plasma power supply to change the jet velocity of the plasma jet;

[0031] (b) Adjust the gas flow rate of the working gas source to change the ejection volume of the plasma jet;

[0032] (c) Adjust the opening or closing of some plasma spray guns to change the number of spray guns participating in the cycle drive;

[0033] (d) Adjust the power distribution ratio of each plasma spray gun to change the local circulation intensity in different areas of the furnace.

[0034] Preferably, the velocity of the circulating gas flow is determined by the injection velocity V of the plasma jet and the equivalent diameter D of the furnace according to the following relationship:

[0035] Vf = k·V·(d / D)²

[0036] Where Vf is the circulating airflow velocity inside the furnace, V is the plasma jet exit velocity (the jet exit velocity of industrial plasma spray guns is generally 100-2000 m / s, and supersonic spray guns can reach over 3000 m / s), d is the nozzle exit diameter (5-30 mm), D is the equivalent furnace diameter (for a 2800 mm × 2800 mm square furnace, the equivalent diameter D ≈ 3160 mm), and k is an empirical coefficient (k = 0.3-0.8). Using V = 500 m / s, d = 15 mm, D = 3160 mm, and k = 0.5, Vf = 0.5 × 500 × (15 / 3160)² ≈ 0.019 m / s, which is the average airflow velocity across the furnace cross-section. Considering the synergistic effect of multiple spray guns (4 to 12) and the annular acceleration effect of airflow, the actual circulating airflow velocity in the furnace can reach 0.5 to 3 m / s, which is sufficient to form an effective directional airflow circulation in a large-volume furnace of 2800 mm, significantly enhancing convective heat transfer.

[0037] Preferably, in step S5, when the temperature in the center region of the furnace is lower than the temperature in the edge region, the control unit increases the power and / or gas flow rate of the plasma spray gun; when the temperature in the center region of the furnace is higher than the temperature in the edge region, the control unit decreases the power and / or gas flow rate of the plasma spray gun.

[0038] As a preferred option, a zoned independent control mode is also included: the furnace is divided into multiple temperature zones along the height direction, each temperature zone corresponds to a set of plasma spray guns and electric heating elements, and each temperature zone is independently monitored and controlled.

[0039] As a preferred option, a heating stage control mode and a heat preservation stage control mode are also included:

[0040] Heating phase: The plasma spray gun operates at rated power, the electric heating element heats at full power, and the circulating airflow operates at the highest flow rate;

[0041] During the heat preservation stage: When the average temperature of the furnace approaches the target temperature, the control unit gradually reduces the power of the plasma spray gun and / or the gas flow rate, so that the circulating airflow speed is reduced to the level required for heat preservation, while adjusting the power of the electric heating element to maintain the target temperature.

[0042] Preferably, in step S5, the circulating airflow is controlled using a PID control algorithm, with the maximum temperature difference ΔTmax inside the furnace as the control target and the power and / or gas flow rate of the plasma nozzle as control variables. The power adjustment range of the plasma nozzle is generally 10% to 100% of the rated power, and smooth adjustment can be achieved by adjusting the output current (typical adjustment range 50 to 600A) or voltage of the plasma power supply.

[0043] Preferably, the control method further includes an anomaly handling step: when the temperature at a certain temperature detection point exceeds a safety threshold, the control unit immediately cuts off the power supply to the plasma spray gun and / or electric heating element corresponding to that area and issues an alarm signal.

[0044] A large-capacity plasma high-temperature electric furnace has the following beneficial effects:

[0045] Enhanced convection heat transfer: The plasma jet ejected from the plasma gun enters the furnace at a certain speed, causing the air inside the furnace to circulate in a directional manner, forming forced convection heat transfer, which significantly improves the heat transfer efficiency from the electric heating element to the center of the furnace.

[0046] Improved temperature uniformity: The plasma spray guns are arranged in the same direction of rotation, so that the air in the furnace can form a uniform clockwise or counterclockwise circulation flow; combined with multi-zone temperature detection and closed-loop control, precise and uniform control of furnace temperature can be achieved.

[0047] High control precision: Through real-time feedback from the temperature detection unit and multi-parameter coordinated control (plasma power, gas flow rate, electric heating power), precise adjustment of furnace temperature and circulating airflow intensity is achieved.

[0048] Highly adaptable: It supports different control modes for the heating and holding stages, as well as independent zone control, which can adapt to the diverse needs of different processes for heating rate and temperature uniformity.

[0049] High electrical safety: After being ejected, the charged particles in the plasma jet quickly collide and recombine with a large number of neutral gas molecules in the furnace. By the time they reach the heating element area, they have basically returned to electrical neutrality and will not cause local short circuits. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the overall structure of the large-capacity plasma high-temperature electric furnace of the present invention;

[0051] Figure 2 This is a top view of the plasma spray guns arranged circumferentially in the furnace.

[0052] Figure 3 This is a schematic diagram of the plasma spray gun.

[0053] Figure 4 This is a flowchart of the control method of the present invention;

[0054] Figure 5 A schematic diagram showing the layout of temperature detection points inside the furnace.

[0055] Figure 6 This is a schematic diagram of the independent control mode for each zone.

[0056] Figure 7 This is a top view schematic diagram of the plasma spray guns arranged circumferentially in the furnace.

[0057] In the diagram: 1. Furnace body; 2. Furnace chamber; 3. Electric heating element; 4. Furnace door; 5. Plasma spray gun; 51. Gun body; 52. Nozzle; 53. Working gas inlet; 6. Plasma power supply; 7. Working gas source; 8. Temperature detection unit; 9. Control unit. Detailed Implementation

[0058] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0059] Example 1

[0060] like Figure 1 and Figure 2 As shown, this embodiment provides a large-capacity plasma high-temperature electric furnace, including a furnace body 1, a furnace chamber 2, an electric heating element 3, and a furnace door 4. The furnace body 1 is composed of a steel structure shell and a refractory insulation lining, and the furnace chamber 2 is a square cross-section furnace chamber (2800mm×2800mm). The furnace door 4 is located on the front of the furnace body 1.

[0061] The electric heating element 3 is a resistance heating element (such as a molybdenum disilicide heating element) and is arranged on the side wall and bottom of the furnace chamber 2. The electric heating element 3 is made of an alloy material that is resistant to high temperature oxidation and corrosion, and has an anti-oxidation protective coating on its surface.

[0062] like Figure 1 and Figure 2As shown, plasma spray guns 5 are installed on the furnace wall of the furnace body 1, and the nozzles 52 of each plasma spray gun 5 extend into the furnace chamber 2. The plasma spray guns 5 are arranged circumferentially along the furnace chamber 2. In this embodiment, one plasma spray gun 5 is installed on each side wall of the square furnace chamber 2, for a total of four guns, which are evenly arranged circumferentially along the furnace chamber 2. The spray direction of the four plasma spray guns 5 is set along the same rotation direction of the furnace chamber 2. The spray direction of the plasma spray guns 5 is perpendicular to the inner wall of the furnace chamber 2.

[0063] The plasma spray gun 5 is connected to a plasma power supply 6 and a working gas source 7. The output current of the plasma power supply 6 is continuously adjustable within the range of 50 to 600A, thereby achieving smooth adjustment of the plasma spray gun power.

[0064] like Figure 3 As shown, the plasma spray gun 5 includes a gun body 51 and a nozzle 52. The nozzle 52 is located circumferentially in the furnace chamber 2, with its outlet facing the interior of the furnace chamber 2. The outlet diameter of the nozzle 52 is 15 mm. A working gas inlet 53 is provided on the gun body 51. A cathode and an anode are located inside the gun body 51, forming an ionization chamber between them. The cathode and anode are respectively connected to the positive and negative terminals of the plasma power supply 6. A circulating cooling water channel is provided inside the gun body 51 for forced water cooling of the spray gun, ensuring continuous and stable operation of the spray gun in a high-temperature environment.

[0065] Temperature detection unit 8 includes 8 thermocouples distributed in various areas of furnace 2, arranged along the height and circumference of furnace 2 (e.g., Figure 5 As shown, two thermocouples are arranged on each side wall, one above the other, to detect the temperature of multiple areas within the furnace. Type B thermocouples (platinum-rhodium 30-platinum-rhodium 6) are used, suitable for high-temperature measurements from 0 to 1800°C.

[0066] The control unit 9 is a PLC controller, which is electrically connected to the temperature detection unit 8, the plasma power supply 6, the working gas source 7, and the electric heating element 3.

[0067] like Figure 4 As shown, the control unit 9 of a large-capacity plasma high-temperature electric furnace uses the following control method to adjust the operating parameters of the plasma torch 5 and / or the heating power of the electric heating element 3:

[0068] S1: Set target temperature - According to the requirements of ceramic sintering process, set the target temperature To = 1400℃ for furnace 2, and the temperature uniformity tolerance △T = ±10℃.

[0069] S2: Start Heating – The electric heating element 3 is activated to radiate heat to the furnace chamber 2. Simultaneously, the plasma power supply 6 and the working gas source 7 are activated, causing the eight plasma nozzles 5 to eject plasma jets at a preset initial power Po = 30kW and an initial gas flow rate Qo = 80L / min. The outlet temperature of the plasma jets is controlled within the range of 5000–8000℃, and the outlet velocity is controlled within the range of 300–500m / s. Each plasma jet forms a counterclockwise directional circulating airflow within the furnace chamber 2.

[0070] S3: Temperature detection and feedback - Temperature signals Ti (i=1,2,…,8) of each zone are collected in real time by temperature detection units 8 (thermocouples) set in 8 zones in the furnace 2, and the temperature signals are transmitted to the control unit 9.

[0071] S4: Deviation Calculation - Control Unit 9 calculates the deviation between the temperature at each detection point and the target temperature, ΔTi = Ti - To, and calculates the maximum temperature difference in the furnace, ΔTmax = max(Ti) - min(Ti).

[0072] S5: Circulating Airflow Control – When ΔTmax > 10℃, the control unit 9 adjusts the circulating airflow velocity by regulating the operating parameters of the plasma spray gun 5. Specifically, the circulating airflow velocity is determined by the plasma jet injection velocity V and the furnace equivalent diameter D according to the following relationship: Vf = k·V·(d / D)², where Vf is the circulating airflow velocity in the furnace, V is the plasma jet outlet velocity (in this embodiment, V = 300~500m / s), d is the nozzle outlet diameter (15mm), D is the furnace equivalent diameter (for a square furnace of 2800mm×2800mm, the equivalent diameter D≈3160mm), and k is taken as 0.5. Calculations show that the average furnace airflow velocity contributed by a single spray gun is approximately 0.01~0.02m / s. With the coordinated action of 8 spray guns and the annular acceleration effect of the airflow, the actual circulating airflow velocity can reach 0.5~2m / s, which is sufficient to form an effective directional airflow circulation in a large-volume furnace of 2800mm.

[0073] When the temperature in the central region of the furnace is lower than that in the edge region, the control unit 9 increases the power and / or gas flow rate of the plasma gun 5 to increase the circulating airflow velocity and enhance the convective heat transfer in the central region; when the temperature in the central region of the furnace is higher than that in the edge region, the control unit 9 decreases the power and / or gas flow rate of the plasma gun 5 to reduce the circulating airflow velocity.

[0074] The circulating airflow is controlled using a PID control algorithm, with the maximum temperature difference ΔTmax inside the furnace as the control target and the power and / or gas flow rate of the plasma gun 5 as control variables. The power adjustment range of the plasma gun is 10% to 100% of the rated power (3kW to 30kW in this embodiment), and smooth adjustment is achieved by adjusting the output current of the plasma power supply (50 to 600A).

[0075] S6: Heating Power Control – When the average furnace temperature deviates from the target temperature of 1400℃, the control unit 9 adjusts the heating power of the electric heating element 3 and / or the input power of the plasma spray gun 5. Specifically, when the average temperature is lower than the target temperature, the power of the electric heating element 3 is increased; when the average temperature is higher than the target temperature, the power of the electric heating element 3 is decreased.

[0076] S7: Repeat steps S3 to S6 until the temperature of each area in furnace 2 meets the process requirements (i.e., the temperature of each point is within the range of 1390℃~1410℃).

[0077] In conventional electric heating furnaces, air itself undergoes a certain degree of ionization at high temperatures, leading to deviations in the resistance measurement of resistance heating elements at high temperatures—a known technical phenomenon in the art. In this invention, the plasma jet 5 is arranged circumferentially in the furnace chamber 2, with the jet direction perpendicular to the tangent of the inner wall of the furnace chamber 2. The main flow area of ​​the plasma jet is located within the central circulating airflow channel of the furnace chamber 2, while the resistance heating elements 3 are arranged on the side walls and bottom of the furnace chamber 2, with a certain spatial distance between them. After being ejected, the charged particles in the plasma jet collide and recombine with a large number of neutral gas molecules in the furnace chamber. The charge density decreases exponentially with increasing distance, essentially returning to electrical neutrality by the time they reach the heating element area. Experiments have verified that when the plasma jet is operating normally, the leakage current increment between the heating elements is less than 0.5 mA, preventing local short circuits. Furthermore, inert gases such as nitrogen and argon, or mixtures thereof, are preferentially used as the working gas to avoid additional impacts from ionized active particles on the heating elements.

[0078] The erosive effect of plasma jets on furnace materials is closely related to jet temperature, velocity, and working gas composition. In this invention, the primary function of the plasma spray gun 5 is to drive airflow circulation rather than directly heat the material. Therefore, the power and gas flow rate of the plasma spray gun are controlled within a moderate range (jet outlet temperature 5000–8000℃, outlet velocity 300–500 m / s), far lower than in plasma spraying or plasma melting conditions (jet temperature 20000–30000℃, velocity 2000–3000 m / s). The lower jet temperature and velocity significantly reduce the erosion and thermal shock to the furnace materials.

[0079] The inner wall of the furnace chamber 2 is made of high-temperature resistant and thermal shock resistant refractory materials such as high-alumina bricks, corundum bricks, or silicon carbide bricks; the resistance heating element 3 is made of high-temperature oxidation resistant and corrosion resistant alloy materials (such as molybdenum disilicide, silicon carbide, etc.), and has an anti-oxidation protective coating on its surface. The working gas is preferably an inert gas such as nitrogen or argon, or a mixture thereof, to avoid oxidation and corrosion of the heating element and furnace chamber materials by oxygen. When air is used as the working gas, the oxidation and corrosion rate is controlled within an acceptable range by controlling the jet temperature to not exceed the safe operating temperature of the materials (e.g., the operating temperature of the molybdenum disilicide heating element in air should not exceed 1700℃). Material corrosion tests have verified that under the aforementioned operating conditions, the annual corrosion rate of the furnace chamber refractory material is less than 2 mm, and the annual corrosion rate of the resistance heating element is less than 0.5 mm, which does not affect the normal design service life of the equipment.

[0080] The working process is as follows: After the electric heating element 3 is energized, it radiates heat into the interior of the furnace chamber 2. At the same time, the plasma power supply 6 supplies power to each plasma nozzle 5, and the working gas source 7 supplies gas to each plasma nozzle 5. The working gas is ionized in the ionization chamber of the plasma nozzle 5 to form plasma, which is then injected into the interior of the furnace chamber 2 at a certain speed through the nozzle 52. Since each plasma nozzle 5 is arranged in the same direction of rotation, the plasma jets converge in the furnace chamber 2 and drive the air in the furnace chamber 2 to circulate in the same direction, forming a directional airflow circulation.

[0081] During operation, the temperature detection unit 8 monitors the temperature of multiple areas within the furnace 2 in real time and feeds the temperature signals back to the control unit 9. Based on the temperature deviation between each area and the target temperature, as well as the maximum temperature difference within the furnace, the control unit 9 calculates the required circulating airflow rate adjustment using a PID algorithm. This, in turn, adjusts the output current / voltage of the plasma power supply 6, the gas flow rate of the working gas source 7, the number of spray guns involved in operation, and the power distribution ratio of each spray gun, achieving precise control of the circulating airflow. Simultaneously, the control unit 9 also adjusts the heating power of the electric heating element 3 based on the deviation between the average furnace temperature and the target temperature.

[0082] Through the above-mentioned multi-parameter coordinated closed-loop control, the temperature of each region in the furnace 2 is precisely controlled near the target temperature, realizing highly uniform heating of the large-volume furnace.

[0083] Example 2

[0084] The difference between this embodiment and Embodiment 1 is that the furnace chamber 2 is divided into three temperature zones along the height direction: upper, middle, and lower (e.g., ...). Figure 6 As shown in the diagram, each temperature zone corresponds to a set of plasma spray guns 5 and electric heating elements 3. Temperature detection and control are performed independently for each temperature zone.

[0085] Upper heating zone: corresponding to the two plasma spray guns 5 and the upper electric heating element 3 located at the upper part of the furnace;

[0086] Medium temperature zone: corresponding to the four plasma spray guns 5 and the central electric heating element 3 located in the middle of the furnace;

[0087] Lower temperature zone: corresponding to the two plasma spray guns 5 and the lower electric heating element 3 located at the bottom of the furnace.

[0088] Each temperature zone is set with a target temperature (the same or different target temperatures can be set according to process requirements), and the control steps S3 to S6 described above are performed independently. When the temperature of a certain temperature zone exceeds the uniformity requirement, only the plasma spray gun 5 and / or electric heating element 3 corresponding to that temperature zone are adjusted, without affecting the normal operation of other temperature zones.

[0089] Example 3

[0090] The difference between this embodiment and Embodiment 1 is that it distinguishes between the heating stage and the heat preservation stage:

[0091] During the heating stage (average furnace temperature <1350℃): the plasma gun 5 operates at its rated power (30kW), the electric heating element 3 heats at full power, and the circulating airflow operates at its highest speed (Vf≈2m / s), so that the furnace temperature rises rapidly to close to the target temperature.

[0092] Transition phase (1350℃≤average furnace temperature<1400℃): When the average furnace temperature approaches the target temperature, the control unit 9 gradually reduces the power and gas flow of the plasma spray gun 5, so that the circulating airflow speed gradually decreases.

[0093] During the heat preservation stage (average furnace temperature ≥1400℃): the circulating airflow velocity is reduced to the level required for heat preservation (Vf≈0.5~1m / s), the control unit 9 adjusts the power of the electric heating element 3 through the PID algorithm to maintain the target temperature of 1400℃±10℃, and the plasma spray gun 5 maintains basic circulation at low power (3~10kW).

[0094] Example 4

[0095] The difference between this embodiment and embodiment 1 is that the working parameters of the plasma spray gun 5 are adjusted in step S5 using the following combination:

[0096] (a) Adjust the output current of the plasma power supply 6 (adjustable from 50A to 600A) to change the jet velocity of the plasma jet (adjustable from 100m / s to 800m / s).

[0097] (b) Adjust the gas flow rate of the working gas source 7 (adjustable from 40 L / min to 150 L / min) to change the ejection volume of the plasma jet;

[0098] (c) When the temperature uniformity inside the furnace is good, shut down some of the plasma spray guns 5 (e.g., shut down 4 guns and keep only 4 guns running) to reduce the number of spray guns participating in the cycle drive and reduce energy consumption.

[0099] (d) When there is a local temperature deviation in the furnace, adjust the power distribution ratio of each plasma gun 5. For example, when the temperature in the upper left area of ​​the furnace is low, increase the power of the corresponding gun in that area to enhance the local circulation intensity.

[0100] Example 5

[0101] The difference between this embodiment and Embodiment 1 is that an exception handling step has been added:

[0102] When the temperature at a certain temperature detection point exceeds the safety threshold, such as 1700℃, the control unit 9 immediately cuts off the power supply to the plasma spray gun 5 and / or electric heating element 3 corresponding to that area, and issues an alarm signal through an audible and visual alarm. At the same time, the location and temperature information of the abnormal area are displayed on the host computer to prompt the operator to handle the situation.

[0103] Example 6

[0104] The difference between this embodiment and Embodiment 1 is that: Figure 7 As shown, the furnace chamber 2 is a circular cylindrical furnace chamber with an inner diameter of 2800 mm. Eight plasma spray guns 5 are evenly arranged along the circumference of the circular furnace chamber, one at every 45° angle. The spray direction of each plasma spray gun 5 is set along the tangential direction (clockwise or counterclockwise) of the same rotational direction of the circular furnace chamber. In the circular furnace chamber structure, the jets from each spray gun are ejected tangentially, forming a natural annular circulating airflow within the furnace chamber, resulting in good flow field symmetry and no dead zones. The circular furnace chamber structure exhibits uniform stress distribution, facilitates refractory material construction, and ensures symmetrical distribution of thermal expansion stress. Other structural features in this embodiment are the same as in Embodiment 1.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A large-volume plasma high-temperature electric furnace, comprising a furnace body (1), a furnace chamber (2), an electric heating element (3), and a furnace door (4), wherein the electric heating element (3) is disposed inside the furnace chamber (2), characterized in that: It also includes several plasma spray guns (5), which are installed on the furnace wall or furnace top of the furnace body (1), and the nozzles (52) of each plasma spray gun (5) extend into the furnace chamber (2). The plasma spray guns (5) are arranged around the furnace (2), and the spray direction of each plasma spray gun (5) is set along the same rotation direction of the furnace (2). The plasma spray gun (5) is connected to a plasma power supply (6) and a working gas source (7). Temperature detection unit (8) is installed inside the furnace (2) to detect the temperature of multiple areas inside the furnace (2); The control unit (9) is electrically connected to the temperature detection unit (8), plasma power supply (6), working gas source (7) and electric heating element (3) respectively, and is used to adjust the working parameters of the plasma spray gun (5) and / or the heating power of the electric heating element (3) according to the temperature signal fed back by the temperature detection unit (8).

2. The large-capacity plasma high-temperature electric furnace according to claim 1, characterized in that: The number of plasma spray guns (5) is 4 to 12, and they are evenly arranged around the furnace (2). The angle between the spray direction of the plasma spray gun (5) and the tangent direction of the inner wall of the furnace (2) is 0° to 45°, or perpendicular to the inner wall of the furnace (2).

3. The large-volume plasma high-temperature electric furnace according to claim 1, characterized in that: The plasma spray gun (5) includes a gun body (51) and a nozzle (52). The nozzle (52) is located around the furnace chamber (2) and its outlet faces the interior of the furnace chamber (2). The gun body (51) is provided with a working gas inlet (53), and the working gas is air, nitrogen, argon or a mixture thereof. The outlet diameter of the nozzle (52) is 5 to 30 mm.

4. The large-volume plasma high-temperature electric furnace according to claim 1, characterized in that: The temperature detection unit (8) includes multiple thermocouples distributed in various areas of the furnace (2), and the thermocouples are arranged along the height and circumference of the furnace (2).

5. The large-volume plasma high-temperature electric furnace according to claim 1, characterized in that: The control unit (9) adjusts the operating parameters of the plasma spray gun (5) and / or the heating power of the electric heating element (3) through the following steps: S1: Set the target temperature To and temperature uniformity tolerance △T of the furnace (2) according to the process requirements; S2: Start the electric heating element (3) to radiate heat the furnace (2), and at the same time start the plasma power supply (6) and the working gas source (7) so that each plasma spray gun (5) sprays out plasma jets according to the preset initial power Po and initial gas flow rate Qo. Each plasma jet forms a directional circulating airflow with the same direction of rotation in the furnace (2). S3: The temperature signals Ti (i=1,2,…,n, where n is the number of temperature detection points) of each area are collected in real time by temperature detection units (8) set in multiple areas of the furnace (2), and the temperature signals are transmitted to the control unit (9). S4: The control unit (9) calculates the temperature deviation between each detection point and the target temperature △Ti=Ti-To, and calculates the maximum temperature difference in the furnace △Tmax=max(Ti)-min(Ti); S5: When △Tmax>△T, the control unit (9) adjusts the flow rate and / or flow rate of the circulating airflow by adjusting the working parameters of the plasma spray gun (5); S6: When the average temperature of the furnace deviates from the target temperature, the control unit (9) adjusts the heating power of the electric heating element (3) and / or the input power of the plasma spray gun (5); S7: Repeat steps S3 to S6 until the temperature of each area in the furnace (2) meets the process requirements.

6. The control method for a large-volume plasma high-temperature electric furnace according to claim 5, characterized in that: In step S5, adjusting the operating parameters of the plasma spray gun (5) includes one or more combinations of the following methods: (a) Adjust the output current or voltage of the plasma power supply (6) to change the jet speed of the plasma jet; (b) Adjust the gas flow rate of the working gas source (7) to change the ejection volume of the plasma jet; (c) Adjust the opening or closing of some plasma spray guns (5) to change the number of spray guns participating in the cycle drive; (d) Adjust the power distribution ratio of each plasma spray gun (5) to change the local circulation intensity of different areas in the furnace (2).

7. The large-volume plasma high-temperature electric furnace according to claim 5, characterized in that: The velocity of the circulating gas flow is determined by the injection velocity V of the plasma jet and the equivalent diameter D of the furnace according to the following relationship: Vf = k·V·(d / D)² Where Vf is the circulating airflow velocity inside the furnace, V is the plasma jet outlet velocity, d is the nozzle outlet diameter, D is the equivalent furnace diameter, and k is an empirical coefficient, k=0.3~0.

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8. The large-volume plasma high-temperature electric furnace according to claim 5, characterized in that: The furnace chamber (2) is divided into multiple temperature zones along the height direction. Each temperature zone corresponds to a set of plasma spray guns (5) and electric heating elements (3). Temperature detection and control are performed independently in each temperature zone.

9. The large-volume plasma high-temperature electric furnace according to claim 5, characterized in that: It also includes a heating stage control mode and a heat preservation stage control mode: Heating stage: The plasma spray gun (5) operates at rated power, the electric heating element (3) heats at full power, and the circulating airflow operates at the highest flow rate; During the heat preservation stage: When the average temperature of the furnace is close to the target temperature, the control unit (9) gradually reduces the power and / or gas flow of the plasma spray gun (5) to reduce the circulating airflow rate to the level required for heat preservation, while adjusting the power of the electric heating element (3) to maintain the target temperature.

10. The large-volume plasma high-temperature electric furnace according to claim 5, characterized in that: In step S5, the circulating airflow is regulated using a PID control algorithm, with the maximum temperature difference ΔTmax inside the furnace as the control target and the power and / or gas flow rate of the plasma spray gun (5) as the control variables.

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