Variable frequency control pressure closed loop feedback regulation system and method for a plasma graphitization system

Abstract

The application discloses a variable-frequency control pressure closed-loop feedback regulation system and method for a plasma graphitization system, relates to the technical field of high-temperature plasma material processing equipment, and specifically relates to a variable-frequency control pressure closed-loop feedback regulation system and method for a plasma graphitization system. The system comprises a main reactor, a gas supply unit, a pressure monitoring unit (containing a vacuum gauge P1 and an absolute pressure gauge P2), a variable-frequency water ring pump group, pneumatic valves and burst valves, etc. Through a PLC main controller combined with a PID algorithm, the pump frequency is closed-loop regulated according to the P1 signal, and the valves and the burst valves are linked to control pressure and release. The method comprises the following steps: real-time monitoring of pressure and comparison with a set value, increase of pump frequency and pumping speed when the pressure is higher than the set value, decrease of frequency when the pressure is lower than the set value, and maintenance of the pressure at the set value ± 1% (working pressure 10000-120000 Pa). Safety release control is also provided: gas supply is turned off when the pump fails and the pressure is higher than 1.2 times the set value, V-2 is opened at 0.12 MPa, and the burst valve is started at 0.175 MPa.

Description

Technical Field

[0001] This invention relates to the field of high-temperature plasma material processing equipment technology, specifically to a frequency conversion control pressure closed-loop feedback regulation system and method for plasma graphitization systems. Background Technology

[0002] Graphitization is a crucial process for preparing high-purity, high-performance graphite materials. Its core lies in converting carbonaceous raw materials into graphite with a well-defined crystalline structure under high-temperature conditions. Traditional graphitization methods primarily employ resistance heating or induction heating, which suffers from low heating efficiency, poor temperature uniformity, and high energy consumption. Furthermore, precise control of process parameters is difficult to achieve under ultra-high temperature conditions (typically above 2500℃). In recent years, with the rapid development of plasma technology, magnetic vortex thermal plasma torches have been introduced into the graphitization field due to their advantages such as generating extremely high temperatures (up to tens of thousands of degrees Celsius), rapid heating rates, and concentrated energy density, significantly improving graphitization efficiency and product quality. However, the plasma graphitization process involves complex conditions such as high temperature, high pressure, and strong gas flow. Precise control of system pressure directly affects reaction stability, equipment safety, and product quality, becoming one of the key bottlenecks restricting the industrial application of this technology.

[0003] In plasma graphitization systems, the challenges of pressure control mainly lie in the following aspects: First, a large amount of working gas (such as argon or nitrogen) needs to be introduced during the reaction to maintain stable plasma combustion. Simultaneously, a protective gas in the annular cavity is required to isolate the equipment components from the corrosive effects of the high-temperature environment. Dynamic changes in gas flow rate lead to frequent pressure fluctuations within the system. Second, the interaction between the high-temperature plasma and graphite powder produces gaseous byproducts (such as volatiles and decomposition gases), further exacerbating pressure instability. Furthermore, the system needs to switch pressure modes at multiple stages, including vacuum pretreatment, plasma ignition, stable operation, and shutdown depressurization. The requirements for pressure control accuracy and response speed differ significantly at each stage. Excessive pressure may lead to equipment seal failure, gas leakage, or even explosion risks; conversely, insufficient pressure will disrupt the stable combustion conditions of the plasma torch, affecting the graphitization effect.

[0004] Currently, pressure control in existing graphitization equipment mostly employs a fixed-frequency vacuum pump combined with manual or simple on / off valve regulation. For example, some systems use a constant-power water ring pump for evacuation, combined with mechanical protection that opens a relief valve when the pressure exceeds the limit. However, such methods cannot achieve continuous dynamic pressure regulation, easily leading to "over-evacuation" or "under-evacuation" phenomena when the system experiences pressure fluctuations. Over-evacuation can cause insufficient gas flow and plasma extinction, while under-evacuation may cause safety hazards due to pressure accumulation. In addition, traditional PID control is mostly applied to linear systems with a single parameter, while the pressure changes in the plasma graphitization process have strong nonlinearity, large hysteresis, and multiple disturbance characteristics (such as sudden changes in gas flow and fluctuations in plasma power). Conventional PID algorithms are difficult to achieve high-precision tracking and are prone to problems such as large overshoot and long settling time.

[0005] To address the aforementioned issues, some studies have attempted to introduce variable frequency technology to adjust the vacuum pump speed to change the pumping rate. However, existing solutions still have significant shortcomings: First, the pressure monitoring point is singular, relying solely on the single-point pressure signal at the reactor outlet, which cannot comprehensively reflect the pressure distribution in different areas of the system, leading to a disconnect between the control logic and actual operating conditions. Second, the safety relief mechanism is inadequate, often only a single-stage relief valve is installed, and it is not interlocked with parameters such as the water ring pump's operating status and gas flow rate, making it prone to accidents due to pressure runaway in the event of pump failure. Third, the control strategy does not fully consider the special characteristics of plasma processes, such as the difference between the rapid pressure build-up requirements during the ignition phase and the fine adjustment requirements during the stable operation phase, resulting in poor system adaptability under different operating conditions.

[0006] Furthermore, the gas supply and pressure control in existing plasma graphitization systems are mostly independent modules, lacking a coordinated linkage mechanism. For example, changes in the flow rates of the working gas and protective gas directly affect the system pressure, but in traditional designs, the flow controller and pressure regulator do not interact, requiring manual intervention for adjustment. This not only increases operational complexity but also reduces process repeatability. Simultaneously, the configuration of vacuum units (such as the model, quantity, and operating mode of water ring pumps) is often based on experience-based selection, failing to optimize pumping characteristics for different pressure ranges. This results in both insufficient pumping speed at low pressure and energy waste at high pressure.

[0007] In summary, developing a variable frequency control pressure regulation system that can adapt to the complex working conditions of plasma graphitization, achieve precise closed-loop pressure control, have multi-level safety relief functions, and can coordinate with the gas supply system is of great significance for improving the stability, safety, and automation level of the graphitization process. Summary of the Invention

[0008] The purpose of this invention is to provide a variable frequency control pressure closed-loop feedback regulation system and method for plasma graphitization systems. By dynamically adjusting the pumping speed of the water ring pump through a PID algorithm and linking the valves and the burst valve, precise and stable pressure control is achieved, ensuring safe and efficient operation of the process.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a variable frequency control pressure closed-loop feedback regulation system and method for a plasma graphitization system, comprising: The main reactor adopts a high temperature and pressure resistant structure and has a magnetic vortex thermal plasma torch installation position inside. After the magnetic vortex thermal plasma torch is powered on, it generates a high-speed rotating thermal plasma flow, which uniformly treats the input graphite powder at high temperature, so that the graphite powder completes the graphitization degree improvement within a set time. The gas supply unit includes flow controller 1 and flow controller 2. Flow controller 1 is connected in series to the working gas delivery pipeline and precisely controls the flow rate of the working gas entering the main reactor by adjusting the valve opening. Flow controller 2 is connected in series to the annular cavity protection gas delivery pipeline and is used to control the flow rate of the protection gas surrounding the annular cavity of the main reactor to maintain the annular cavity pressure stability and isolate external impurities. The pressure monitoring unit includes a pressure gauge P1 located in the first section of the pipeline at the outlet of the main reactor and a pressure gauge P2 located in the second section of the pipeline. The first section of the pipeline is close to the outlet of the main reactor, and the second section of the pipeline is located on the connecting pipeline between the outlet of the main reactor and the vacuum unit. Pressure gauges P1 and P2 detect the system pressure at the corresponding positions in real time according to the set sampling period and transmit the pressure signal to the control system. The vacuum unit includes a water ring pump unit with variable frequency control. The motor of the water ring pump unit is electrically connected to the frequency converter. The motor speed is adjusted by the frequency converter to change the pumping rate of the water ring pump unit, thereby controlling the amount of gas extracted from the system. The pneumatic valve unit includes normally open valve V-1, normally open valve V-3, and normally closed relief valve V-2. Normally open valve V-1 is connected in series with the working gas pipeline between the gas supply unit and the main reactor. Normally open valve V-3 is connected in series with the annular protection gas pipeline between the main reactor and the annular cavity. Normally closed relief valve V-2 is connected in series with the main reactor outlet and the relief pipeline. Under normal conditions, V-1 and V-3 are kept connected, and V-2 is kept closed. When relief is required, it is driven to open by the control system. The safety relief unit includes a rupture valve, which is installed at the safety relief port on the top of the main reactor. The rupture valve has a diaphragm with a preset rupture pressure inside. When the system pressure reaches the diaphragm rupture pressure, the diaphragm ruptures to achieve rapid pressure relief. The control system receives the pressure signal output by the pressure monitoring unit and has a built-in PID calculation module. Based on the deviation between the measured pressure value and the set pressure value, it calculates and outputs adjustment commands to the frequency converter through the PID algorithm. The control system then adjusts the motor speed of the water ring pump group in a closed loop to change the pumping rate. At the same time, it sends opening and closing commands to the pneumatic valve unit and status monitoring commands to the safety relief unit according to the pressure change status, thereby realizing the linkage between pressure control and safety relief.

[0010] Furthermore, the pressure gauge P1 is a vacuum gauge, and its detection element adopts a capacitive thin film structure. The detection range is 1–100000 Pa (absolute pressure), and the measurement error does not exceed ±0.5% of the full scale. The output signal of the vacuum gauge is electrically connected to the interlocking adjustment module in the control system. When the detected pressure value is higher or lower than the set pressure range, the interlocking adjustment module is directly triggered to adjust the output frequency of the frequency converter, thereby changing the pumping speed of the water ring pump group. The pressure gauge P2 is an absolute pressure gauge with a Bourdon tube structure for its sensing element. The sensing range is 10,000–200,000 Pa, and the measurement error does not exceed ±0.25% of the full scale. The output signal of the absolute pressure gauge is electrically connected to the relief valve control module in the control system. When the detected pressure value reaches the opening threshold of the relief valve V-2, it directly triggers the control module to drive V-2 to open and release pressure.

[0011] Furthermore, the water ring pump set includes a liquid ring vacuum pump, a gas-liquid separator, and a heat exchanger connected in sequence. The impeller of the liquid ring vacuum pump is eccentrically mounted in the pump body. The pump body is injected with working fluid to form a rotating liquid ring. Gas enters through the inlet and is carried by the liquid ring to the outlet for discharge. The inlet of the gas-liquid separator is connected to the outlet of the liquid ring vacuum pump. A baffle plate is installed inside the separator so that the discharged gas-liquid mixture is separated by collision. The gas is discharged from the upper outlet to the system pipeline, and the liquid settles to the bottom and returns to the liquid ring vacuum pump body through the return pipeline for recycling. The shell side of the heat exchanger is connected to the liquid return pipeline of the gas-liquid separator, and cooling water is introduced into the tube side. The working fluid is cooled by the cooling water when it flows through the heat exchanger, ensuring that the working fluid temperature is maintained at 15–30℃, thus achieving stable gas separation effect and controllable working fluid temperature.

[0012] Furthermore, the adjustment range of the working gas flow controller 1 is 30–100 slm, and the adjustment range of the annular cavity protection gas flow controller 2 is 100–1600 slm. The gas type is selected from argon, nitrogen, helium, and hydrogen, or a mixture of two or more gases. When argon is used as the main working gas, it can provide an inert environment to reduce the oxidation of graphite powder. Nitrogen can help regulate the activity of the reaction atmosphere. Helium can enhance the heat transfer efficiency due to its high thermal conductivity. Hydrogen can participate in the reduction reaction to remove impurities in the graphite powder. The mixed gas is introduced into the main reactor and the annular cavity according to the process requirements.

[0013] Furthermore, the pressure value at the outlet of the main reactor is collected in real time by pressure gauge P1 at a sampling period of once per second. The measured value is transmitted to the PID calculation module of the control system and compared with the pre-set pressure target value in the system to generate a pressure deviation value. When the actual pressure measurement value is greater than the set pressure value, the PID calculation module outputs a frequency increase command to the frequency converter according to the sign and magnitude of the deviation value. The frequency converter increases the output frequency, which increases the speed of the water ring pump group motor and the pumping speed of the water ring pump group increases accordingly. The gas inside the system is accelerated to be extracted until the pressure detected by pressure gauge P1 drops to above the lower limit of the set pressure range. When the actual pressure measurement value is less than the set pressure value, the PID calculation module outputs a frequency reduction command to the frequency converter. The frequency converter reduces the output frequency, which reduces the speed of the water ring pump group motor, reduces the pumping speed of the water ring pump group, and reduces the amount of gas extracted from the system until the pressure detected by pressure gauge P1 rises back to below the upper limit of the set pressure range, maintaining the system pressure within the range of ±1% of the set value for periodic fluctuation.

[0014] Furthermore, during the pressure rise phase, when the pressure deviation is positive and shows an increasing trend, the PID calculation module increases the frequency adjustment increment according to the preset proportional coefficient, so that the frequency of the water ring pump gradually increases in a stepwise manner, and the speed increase of the air pumping rate matches the speed of pressure rise, thus suppressing the pressure rise from being too rapid. When the pressure reaches its peak, and the pressure deviation changes from positive to negative or from large to small and approaches zero, the PID calculation module reduces the frequency adjustment increment according to the preset integral coefficient, so that the frequency of the water ring pump gradually decreases at a slow slope, avoiding a sudden drop in system pressure due to excessively high pumping speed. When the pressure is below the set value, if the pressure deviation is negative for a certain period of time, the PID calculation module will continuously output a frequency reduction command according to the preset differential coefficient, so that the frequency of the water ring pump will gradually decrease to the minimum allowable frequency, reducing the amount of gas extracted, until the pressure detected by the pressure gauge P1 rises back to within the set pressure range. At this time, the PID calculation module will stop reducing the frequency and maintain the current frequency stable.

[0015] Furthermore, the operating status of the water ring pump set is monitored in real time. When the water ring pump motor current is detected to be zero or the frequency converter reports a fault code, it is determined that the water ring pump is faulty. At this time, the control system immediately compares the current pressure measurement value with 1.2 times the set pressure value. If the current pressure has exceeded the threshold, the abnormal shutdown process is triggered: a shutdown command is sent to flow controller 1 and flow controller 2 to cut off the supply of working gas and ring chamber protection gas. After an abnormal shutdown, the pressure value of pressure gauge P2 is continuously monitored. If the pressure continues to rise and reaches 0.12MPa (absolute pressure), the control system sends an opening command to the drive mechanism of normally closed relief valve V-2. The valve core of V-2 moves to open the relief channel, and the high-pressure gas inside the system is discharged to the outdoor safe area through the relief pipeline. If the pressure on pressure gauge P2 rises further to 0.175 MPa (absolute pressure) during the release process, the control system sends a status confirmation command to the rupture valve. The diaphragm with the preset rupture pressure inside the rupture valve ruptures due to overpressure, and the gas inside the system is quickly released through the rupture valve, limiting the pressure to a safe range.

[0016] Furthermore, the operating pressure range during normal system operation is set to absolute pressure of 10,000–120,000 Pa. This range takes into account both the stable combustion of the magnetic vortex thermal plasma torch and the requirement for sufficient graphitization of graphite powder. The pressure control accuracy is achieved through parameter tuning of the PID algorithm, ensuring that the absolute value of the deviation between the actual pressure value detected by pressure gauge P1 and the set pressure value never exceeds 1% of the set value. That is, when the set pressure is 10,000 Pa, the actual pressure fluctuation range is 9,900–10,100 Pa, and when the set pressure is 120,000 Pa, the actual pressure fluctuation range is 118,800–121,200 Pa.

[0017] Furthermore, the water ring pump adopts a fixed frequency operation mode, and its motor power supply is directly connected to the industrial frequency grid, maintaining a constant speed. A proportional valve is installed in series on the inlet pipe of the liquid ring vacuum pump. The valve core opening of the proportional valve is proportional to the input control current signal. The pressure gauge P1 signal of the pressure monitoring unit is converted and amplified by the control system, and outputs a 0-10mA or 4-20mA current signal to the proportional valve. When the pressure is higher than the set value, the current signal increases, causing the proportional valve opening to decrease, the inlet pipe diameter to narrow, the gas suction resistance of the liquid ring vacuum pump to increase, and the pumping speed to decrease (Note: This logic is the opposite of the frequency conversion regulation in claim 1, and is retained according to the original claim). When the pressure is lower than the set value, the current signal decreases, causing the proportional valve opening to increase, the inlet pipe diameter to widen, and the pumping speed to increase. The pumping speed of the system is adjusted in conjunction with the change in the proportional valve opening.

[0018] Furthermore, the pressure closed-loop feedback regulation logic is implemented through a PLC main controller. The PLC main controller uses a multi-channel analog input module. The analog signals output by the pressure gauges P1 and P2 of the pressure monitoring unit are connected to the designated input port of the PLC main controller via shielded cables. The built-in A / D conversion unit of the PLC main controller converts the analog signals into digital signals. The digital signals are sent to the PID function unit of the PLC main controller. The PID function unit performs calculations according to preset proportional gain, integral time, and derivative time parameters, and outputs a digital regulation quantity. This digital regulation quantity is converted into an analog voltage signal by the D / A conversion unit of the PLC main controller and transmitted to the analog input terminal of the frequency converter. The frequency converter adjusts the output frequency according to the analog voltage signal, thereby changing the speed of the water ring pump motor and completing the pressure closed-loop feedback regulation.

[0019] This invention provides a variable frequency control pressure closed-loop feedback regulation system and method for plasma graphitization systems, which has the following beneficial effects: 1. Achieve high-precision, wide-range pressure stability control to ensure consistency in the graphitization process. This system monitors the reactor pressure in real time using a vacuum gauge P1 (1–100000 Pa) and combines this with a PID algorithm to close-loop regulate the frequency of the variable frequency water ring pump. This allows for precise maintenance of the operating pressure within the absolute pressure range of 10000–120000 Pa, with a control accuracy of ±1% of the set value. Traditional fixed-frequency pump sets rely on valve throttling to regulate pumping speed, which is prone to pressure overshoot or lag due to gas flow fluctuations. This system, however, effectively suppresses pressure fluctuations beyond ±1% by dynamically matching the pumping rate with the process gas input, ensuring a stable high-temperature environment for the magnetic vortex thermal plasma torch. Stable pressure conditions improve the heating uniformity of graphite powder, avoiding lattice defects or product performance dispersion caused by localized overheating, and significantly improving the consistency and yield of high-purity graphitized materials in mass production.

[0020] The graded safety relief mechanism significantly reduces the risk of system overpressure and improves operational reliability. The system integrates a three-stage relief logic: "water ring pump failure → relief valve V-2 → rupture valve". When the pressure exceeds the set value by 1.2 times, an abnormal shutdown is triggered, cutting off the gas supply. When the pressure rises to 0.12 MPa absolute pressure, V-2 opens to relieve pressure. When the pressure further rises to 0.175 MPa, the rupture valve activates rapidly. Compared to a single relief device, this staged design avoids gas waste and process interruption caused by small pressure fluctuations triggering violent relief. It also allows for rapid pressure reduction under extreme conditions (such as pump failure or abnormal plasma exothermics), preventing safety accidents caused by reactor deformation due to overpressure or seal failure. Multi-stage interlocking combined with real-time PLC monitoring significantly reduces equipment maintenance costs and downtime, extending the service life of core components.

[0021] Variable frequency water ring pump unit with coordinated heat exchange design optimizes energy consumption and process adaptability The water ring pump set employs variable frequency control combined with a liquid ring vacuum pump, gas-liquid separator, and heat exchanger. The working fluid is deionized water for cooling, achieving simultaneous gas separation and temperature control. Traditional fixed-frequency pump sets require full-power operation to maintain maximum pumping speed, resulting in significant energy waste during low-load periods. Variable frequency control, however, dynamically adjusts the motor speed based on pressure deviations, such as reducing the frequency when the pressure approaches the set value, thus minimizing ineffective power consumption. Simultaneously, the deionized water circulation heat exchange prevents efficiency degradation and component corrosion caused by high temperatures, ensuring that the pumping rate and vacuum stability remain unaffected by temperature drift during long-term continuous graphite powder processing, thus balancing energy efficiency and process continuity requirements.

[0022] Dual pressure gauge zone monitoring and linkage control enhance the precision of pressure management. P1 (vacuum gauge) focuses on interlocking and regulating the frequency of the water ring pump, covering the low-pressure range (1–100,000 Pa); P2 (absolute pressure gauge) controls the relief valve V-2, targeting the medium-high pressure range (10,000–200,000 Pa). This dual-gauge division of labor avoids the accuracy loss associated with single-sensor cross-range monitoring—P1's high sensitivity ensures the capture of subtle fluctuations at low pressures, guaranteeing timely PID control; P2's wide-range detection covers potential abnormal pressure increases, providing reliable triggering information for the relief valve. This zoned monitoring logic enables the system to accurately identify pressure states at different stages of graphitization (such as preheating, high-temperature reaction, and cooling), avoiding control failures due to range mismatch and improving the reliability of pressure management under complex operating conditions.

[0023] Flexible adaptation to multiple gas combinations and flow ranges, expanding process application scenarios The gas supply unit supports independent adjustment of the working gas (30–100 slm) and the annular protective gas (100–1600 slm), with gas types including argon, nitrogen, helium, hydrogen, and combinations thereof. Different gas combinations can regulate the ionization characteristics and thermal conductivity of the plasma; for example, hydrogen can improve the carbon source decomposition efficiency, while argon can enhance arc stability. Traditional systems often limit gas type switching due to pressure control lag, but this system's high-precision closed-loop pressure ensures that pressure fluctuations during multi-gas ratio adjustments are strictly limited to ±1%, guaranteeing the stability of plasma parameters (such as temperature and electron density). This feature allows the equipment to adapt to the personalized process requirements of different products such as lithium battery anode graphite and nuclear-grade graphite, significantly expanding the application boundaries of plasma graphitization technology. Attached Figure Description

[0024] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the variable frequency control pressure closed-loop feedback regulation system of the present invention. Detailed Implementation

[0026] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses consistent with some aspects of this disclosure as detailed in the appended claims.

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] How to use: I. System Preparation and Parameter Setting First, confirm the status of each unit: the main reactor is installed and the magnetic vortex thermal plasma torch is on standby; the flow controller 1 (controlling the working gas) and flow controller 2 (controlling the annular protective gas) of the gas supply unit have been calibrated, and the flow range of the working gas (argon, nitrogen, or a combination thereof) is preset to 30–100 slm, and the flow range of the annular protective gas is preset to 100–1600 slm; the pressure gauge P1 (vacuum gauge, detection range 1–100000 Pa absolute pressure) and pressure gauge P2 (absolute pressure gauge, detection range 10000–200000 Pa) of the pressure monitoring unit are connected to the control system; the variable frequency water ring pump group of the vacuum unit (including liquid ring vacuum pump, gas-liquid separator and heat exchanger, with deionized water as the working fluid) is in a startable state; the normally open valves V-1 and V-3 in the pneumatic valve unit remain open, and the normally closed relief valve V-2 is closed; the explosion valve of the safety relief unit is functioning normally. The system working pressure range is set to absolute pressure 10000–120000 Pa via the PLC main controller, and the pressure control accuracy is ±1% of the set value.

[0029] II. Pressure Closed-Loop Feedback Regulation Operation After the system starts, it enters the pressure closed-loop control stage: Pressure monitoring and comparison: Pressure gauge P1 monitors the main reactor outlet pressure (absolute pressure) in real time and transmits the signal to the PID unit of the PLC main controller, which compares it with the preset set pressure value (such as the intermediate value required by the process) in the control system.

[0030] PID dynamic adjustment of pumping speed: When the actual pressure exceeds the set value, the PID unit gradually increases the frequency of the water ring pump through an algorithm to increase the pumping rate and suppress pressure rise; after the pressure reaches its peak, the frequency is gradually reduced to avoid over-pumping; when the pressure drops to the set range, the current frequency is maintained or finely adjusted to maintain stability. If the actual pressure is lower than the set value, the frequency of the water ring pump is gradually reduced to allow the pressure to rise back to within ±1% of the set range. During this process, the PID algorithm focuses on controlling the rate of pressure rise to ensure smooth regulation.

[0031] III. Safety Discharge Control In case of any abnormal situation, perform the following safety procedures: If the water ring pump malfunctions and causes the pressure to exceed 1.2 times the set value, the PLC will trigger an abnormal shutdown procedure, immediately shutting down flow controller 1 and flow controller 2 to stop the gas supply.

[0032] If the pressure continues to rise to 0.12MPa (absolute pressure), the PLC controls the normally closed relief valve V-2 to open and actively relieve pressure.

[0033] If the pressure rises further to 0.175 MPa (absolute pressure), the burst valve of the safety relief unit will activate to quickly relieve pressure and prevent overpressure risk.

[0034] IV. Operation Monitoring and Termination During operation, pressure gauge P2 (absolute pressure gauge) is used to monitor whether the pressure exceeds the range of 10,000–200,000 Pa, ensuring the effective interlocking control of the relief valve V-2 and the rupture valve. After the process is completed, first shut down the magnetic vortex thermal plasma torch, gradually reduce the gas flow rate, then shut down the water ring pump group, and finally turn off the power to each control unit to complete the operation.

[0035] Example: Example 1: Basic Closed-Loop Pressure Control Scenario This embodiment addresses the stable pressure maintenance requirements of conventional plasma graphitization processes by employing "a frequency conversion control pressure closed-loop feedback regulation system and method for plasma graphitization systems." During system startup, the magnetic vortex thermal plasma torch in the main reactor is in standby mode. Flow controllers 1 and 2 of the gas supply unit respectively introduce working gas and annular protective gas (gas types selected from argon, nitrogen, helium, hydrogen, or combinations thereof) within preset ranges. Pressure gauges P1 (vacuum gauge) and P2 (absolute pressure gauge) are synchronously connected to the PLC main controller to collect the main reactor outlet pressure in real time.

[0036] During operation, the PLC main controller uses the set pressure value as a reference and receives the pressure signal from pressure gauge P1 through a PID algorithm and compares it: when the actual pressure exceeds the set value due to gas expansion caused by the heat release of the plasma torch, the PID unit gradually increases the frequency of the liquid ring vacuum pump in the water ring pump group to increase the pumping speed and suppress the pressure rise rate; after the pressure reaches the peak value, the frequency is gradually reduced to avoid over-pumping; when the pressure falls back to within ±1% of the set range, the current frequency is maintained for stable pumping. If the pressure falls below the set value due to gas supply fluctuations, the frequency of the water ring pump is reduced to allow the pressure to slowly rise back to the set range.

[0037] During this process, the water ring pump unit achieves gas separation through a gas-liquid separator, and the heat exchanger, in conjunction with the deionized water working fluid, controls the temperature. Normally open valves V-1 and V-3 are kept open, while normally closed relief valve V-2 is shut off. Pressure gauge P2 monitors the pressure in real time to ensure it remains within the range of 10,000–200,000 Pa, preventing any abnormal overpressure. After the process is completed, the plasma torch is sequentially shut down, the gas flow rate is reduced, and the water ring pump unit is stopped, completing the closed-loop control cycle.

[0038] Example 2: Suppression of Rapid Pressure Rise Scenario This embodiment simulates a sudden pressure surge during plasma torch start-up / shutdown or a sudden gas overload, using the same system and method. During system operation, a sudden increase in the power of the magnetic vortex thermal plasma torch causes a violent expansion of the gas inside the main reactor, and pressure gauge P1 detects a rapid pressure rise exceeding the set value. At this point, the PID unit of the PLC main controller immediately responds: First, it gradually increases the frequency of the water ring pump to suppress the pressure rise rate and prevent the pressure from instantly exceeding the safety threshold; second, as the pressure approaches its peak, it dynamically adjusts the frequency increase to allow the pressure to reach its peak gradually; third, after the pressure reaches its peak, it gradually reduces the frequency to match the current gas generation rate to prevent a reverse pressure drop due to excessive pumping speed.

[0039] Meanwhile, pressure gauge P2 synchronously monitors the pressure, which does not exceed its detection range (10000–200000 Pa), so relief valve V-2 remains closed. The water ring pump unit maintains gas-liquid separation efficiency through deionized water-cooled working fluid, ensuring stable pumping. Throughout the adjustment process, the PID algorithm prioritizes controlling the pressure rise slope to prevent sudden pressure changes from affecting the uniformity of graphite powder high-temperature processing, ultimately achieving pressure return to within ±1% of the set range.

[0040] Example 3: Safe Discharge Scenario for Water Ring Pump Failure This embodiment verifies the system's safety mechanism in a scenario where a sudden failure of the water ring pump unit (such as motor malfunction) leads to a loss of pumping capacity. During system operation, the water ring pump stops frequency conversion due to the failure, causing a sharp drop in the pumping rate, while the pressure inside the main reactor gradually increases due to continuous gas input. When pressure gauge P1 detects that the pressure exceeds 1.2 times the set value, the PLC main controller immediately triggers the abnormal shutdown procedure: first, it shuts down flow controllers 1 and 2, cutting off the supply of working gas and annular protective gas to reduce the gas source; then, it continuously monitors pressure changes. If the pressure continues to rise to 0.12 MPa (absolute pressure), the PLC controls the normally closed relief valve V-2 to open, actively releasing some gas through the pneumatic valve unit to slow down the pressure rise; if the pressure further rises to 0.175 MPa (absolute pressure), the burst valve of the safety relief unit is activated, using the preset rupture pressure to quickly release pressure and prevent overpressure damage to the main reactor.

[0041] During this process, pressure gauge P2 provides real-time feedback on the pressure status, ensuring that relief valve V-2 and rupture valve operate in sequence; although the gas-liquid separator of the water ring pump unit is temporarily not working due to the pump body stopping, the heat exchanger still maintains basic temperature control through deionized water, creating conditions for troubleshooting.

[0042] Example 4: Low Pressure Recovery Control Scenario This embodiment demonstrates the system's low-pressure compensation capability in cases where insufficient gas supply or excessive pumping causes pressure to fall below the set value. During system operation, due to a temporary decrease in the output flow rate of flow controller 1, the total gas volume in the main reactor decreases, and pressure gauge P1 detects a pressure below the set value. At this time, the PID unit of the PLC main controller initiates low-pressure regulation logic: gradually reducing the frequency of the water ring pump to decrease the pumping rate, allowing the remaining gas in the system to accumulate; as the pumping speed decreases, the balance between gas input and output is disrupted, and the pressure slowly rises; when the pressure rises back to within ±1% of the set range, the PID unit locks the current frequency to maintain the dynamic balance between pumping and input.

[0043] During the adjustment period, the pressure monitored by pressure gauge P2 remained within the range of 10,000–200,000 Pa, eliminating the need to trigger the relief valve V-2. The water ring pump unit reduced energy consumption through the variable frequency reduction of the liquid ring vacuum pump, the gas-liquid separator continued to separate residual gas, and the heat exchanger, in conjunction with deionized water, maintained a stable working fluid temperature. This process avoided problems such as unstable plasma torch combustion or insufficient graphite powder treatment due to excessively low pressure, ensuring process continuity.

[0044] Example 5: Verification Scenario of Alternative Air Extraction Control Scheme This embodiment verifies the feasibility of the alternative solution described in claim 9—adjusting the pumping rate via a proportional valve when the water ring pump operates at a fixed frequency—and is still based on "a variable frequency control pressure closed-loop feedback regulation system and method for a plasma graphitization system." System configuration adjustments: The water ring pump group is switched to fixed frequency operation, and a proportional valve is added to its inlet pipeline; the pressure signal from pressure gauge P1 is still connected to the PLC main controller, and after processing by the PID unit, it is no longer output to the frequency converter, but instead output to the proportional valve control unit.

[0045] During operation, when pressure gauge P1 detects that the pressure exceeds the set value, the PID unit outputs a signal to increase the proportional valve opening, reduce inlet throttling, and increase the pumping rate. When the pressure is below the set value, the proportional valve opening decreases, reducing the pumping rate. During this process, the water ring pump unit maintains its basic pumping capacity at a fixed frequency, and the proportional valve fine-tunes the pumping speed by changing its opening, thus achieving pressure fluctuations within ±1% of the set range. Pressure gauge P2 monitors the pressure status, pneumatic valves V-1 and V-3 remain normally open, and V-2 and the rupture valve are on standby according to safety logic. This solution provides an alternative pumping rate control path while retaining the core pressure closed-loop logic of the original system, adapting to different equipment configuration requirements.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A variable frequency control pressure closed-loop feedback regulation system and method for a plasma graphitization system, characterized in that, include: The main reactor is used for high-temperature treatment of graphite powder by a magnetic vortex thermal plasma torch. The gas supply unit includes flow controller 1 and flow controller 2, which are used to control the flow rates of the working gas and the annular cavity protection gas, respectively. The pressure monitoring unit includes pressure gauges P1 and P2 located at the outlet of the main reactor for real-time monitoring of system pressure. Vacuum unit, including frequency-controlled water ring pump unit, used to adjust the system pumping rate; The pneumatic valve unit includes normally open valves V-1 and V-3, and normally closed relief valve V-2; Safety relief unit, including burst valve; The control system, based on the signal from the pressure monitoring unit, uses a PID algorithm to adjust the frequency of the water ring pump in a closed loop, and links the pneumatic valve and the burst valve to achieve pressure control and safe release.

2. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 1, characterized in that: Pressure gauge P1 is a vacuum gauge with a detection range of 1–100000 Pa (absolute pressure), used for interlocking and adjusting the frequency of the water ring pump; pressure gauge P2 is an absolute pressure gauge with a detection range of 10000–200000 Pa, used for interlocking and controlling the relief valve V-2.

3. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 1, characterized in that: The water ring pump set includes a liquid ring vacuum pump, a gas-liquid separator, and a heat exchanger. The working fluid is cooled by deionized water to achieve gas separation and temperature control.

4. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 1, characterized in that: The working gas flow rate ranges from 30 to 100 slm, and the annular protective gas flow rate ranges from 100 to 1600 slm. The gas type is argon, nitrogen, helium, hydrogen, or a combination thereof.

5. A variable frequency control pressure closed-loop feedback regulation method for a plasma graphitization system, implemented based on the system described in any one of claims 1-4, characterized in that, Includes the following steps: The pressure of the main reactor is monitored in real time by pressure gauge P1, and the measured value is compared with the set pressure value. When the actual pressure exceeds the set value, the frequency of the water ring pump is increased by the PID algorithm to increase the pumping speed until the pressure drops to the set range. When the pressure is lower than the set value, reduce the frequency of the water ring pump to maintain the system pressure within ±1% of the set value.

6. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 5, characterized in that, The adjustment process of the PID algorithm includes: As pressure increases, gradually increase the frequency of the water ring pump to suppress the rate of pressure rise; Once the pressure reaches its peak, gradually reduce the frequency to avoid excessive suction. When the pressure is lower than the set value, the frequency continues to decrease until the pressure rises back to the set range.

7. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 5, characterized in that, It also includes safety release control procedures: If a water ring pump malfunction causes the pressure to exceed 1.2 times the set value, an abnormal shutdown procedure will be triggered, shutting down all gas flow controllers. If the pressure continues to rise to 0.12 MPa (absolute pressure), open the relief valve V-2 to release the pressure; If the pressure rises further to 0.175 MPa (absolute pressure), the rupture valve will activate to quickly release the pressure.

8. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 5, characterized in that: The system's operating pressure range is 10,000–120,000 Pa absolute pressure, and the pressure control accuracy is ±1% of the set value.

9. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 1, characterized in that: The water ring pump operates at a fixed frequency. A proportional valve is added to its inlet pipeline. The opening of the proportional valve is adjusted in conjunction with the pressure monitoring signal to achieve air pumping rate control.

10. The frequency conversion control pressure closed-loop feedback regulation system and method for a plasma graphitization system according to claim 1, characterized in that: The pressure closed-loop feedback regulation logic is implemented by a PLC main controller. The pressure signal is processed by the PID unit and then output to the frequency converter to regulate the speed of the water ring pump motor.

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