A multi-variable interlocking control method for micro-oxygen pulse residual carbon removal

Abstract

The application discloses a micro-oxygen pulse residual carbon removal multivariable interlocking control method, relates to the technical field of process control of regenerated carbon fiber manufacturing, and comprises the following steps: establishing an inert atmosphere in a furnace and collecting process parameters to determine a baseline condition; performing pulse access interlocking determination based on process parameter correlation characteristics; performing a micro-oxygen pulse and triggering interlocking protection based on dynamic characteristics between parameters; performing a hierarchical response operation when the interlocking is triggered; performing recovery determination after the pulse ends, returning to the access step after the parameters fall back to the recovery boundary; repeating the above steps and determining the residual carbon removal process according to dynamic characteristic indexes of multiple pulses, and terminating the pulse after completion. The technical problems of poor process safety, large product cleanliness fluctuation and low production efficiency caused by single oxygen supply strategy and lack of a multi-parameter collaborative interlocking mechanism in the prior art are solved.

Description

Technical Field

[0001] This application relates to the field of process control technology for recycled carbon fiber manufacturing, and in particular to a multivariable interlocking control method for removing residual carbon using micro-oxygen pulses. Background Technology

[0002] The production of recycled carbon fiber typically involves pyrolysis in an inert atmosphere to remove resin, followed by oxidation to remove or regulate residual carbides on the fiber surface to achieve the cleanliness and performance consistency required for downstream applications. The residual carbon removal stage is a critical step in the manufacturing process of recycled carbon fiber, and its control precision directly affects product quality and production safety.

[0003] In existing technologies, for example, CN108624751A discloses a method for efficiently recycling carbon fiber, which involves switching to an aerobic atmosphere after pyrolysis in an inert atmosphere to oxidize residual carbon; CN101654820A discloses a method for recycling carbon fiber, which involves detecting and controlling the oxygen content in the atmosphere and controlling the emission of flue gas. These technologies can achieve the basic goals of removing residual carbon and controlling oxygen, but they still face typical risks and consistency issues in engineered continuous production. On the one hand, when continuous oxygen supply or a simple switch to an aerobic atmosphere is used, fluctuations in incoming materials, changes in loading density, localized heat accumulation, or changes in exhaust resistance can easily trigger localized over-oxidation reactions and a sudden temperature rise, accompanied by a momentary increase in carbon monoxide concentration in the exhaust gas, leading to fiber performance damage and safety hazards. On the other hand, an overly conservative oxygen supply strategy can result in reduced residual carbon removal efficiency, longer processing cycles, and increased batch-to-batch cleanliness fluctuations. Existing technologies generally lack multi-parameter collaborative interlocking mechanisms and safety recovery boundary control, making it difficult to obtain a stable process window between processing efficiency, product cleanliness, and process safety.

[0004] Therefore, there is an urgent need for a multivariable interlocking control method for micro-oxygen pulse decarbonization that can promote residual carbon oxidation under strict interlocking constraints and effectively restore the safety boundary during the pulse interval. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a multi-variable interlocking control method for micro-oxygen pulse carbon removal. This method upgrades the oxygen supply mode of the carbon removal process from "continuous oxygen supply or simple switching" to an executable control chain of "controlled pulse oxygen supply, multi-variable interlocking protection, and inert gas interval recovery." This ensures that the target cleanliness level can be stably achieved even under fluctuating incoming materials and operating conditions, while effectively reducing the risk of sudden temperature rises and over-oxidation, thus improving the safety and product consistency of continuous production.

[0006] To achieve the above objectives, this invention provides a multivariable interlocking control method for micro-oxygen pulse carbon removal, comprising the following steps: Inert gas is introduced into the heat treatment furnace and the exhaust unit is started to heat the residual carbon temperature zone to the target temperature range and operate stably; the carbon monoxide concentration in the exhaust gas and the oxygen content in the furnace are collected to determine the baseline conditions. The baseline conditions are that both the carbon monoxide concentration and the oxygen content are lower than the preset baseline threshold. If the conditions are not met, this step is repeated. Before starting the micro-oxygen pulse, process parameters are collected in real time, and pulse access interlock is determined based on the correlation characteristics of process parameters. If the determination fails, inert gas is introduced and this step is repeated. If the determination passes, step S3 is executed. A micro-oxygen pulse is executed by introducing mixed gas into the heat treatment furnace. The process parameters during the execution of the micro-oxygen pulse are collected, and the interlock protection conditions are triggered based on the dynamic characteristics between the process parameters and the deviation of their reference values. If triggered, the current micro-oxygen pulse oxygen supply is immediately stopped and step S4 is executed. If not triggered, step S5 is executed after the pulse ends. According to the dynamic characteristic type of the interlocking protection condition, perform the corresponding graded response operation until the deviation between the dynamic characteristic and its reference value is within the allowable range, and then proceed to step S6. The heat treatment furnace is purged with inert gas to enter the recovery process. The carbon monoxide concentration in the exhaust gas, the oxygen content in the furnace, and the temperature are collected in real time to determine the recovery. If all three fall back to the recovery boundary, step S6 is executed; otherwise, this step is continued. The carbon removal process is judged based on the dynamic characteristic indicators during the execution of multiple pulses. If the carbon removal process has been completed, the pulse execution is terminated and the inert atmosphere is switched for cooling. Otherwise, the process returns to step S2 to perform the next pulse access interlock judgment.

[0007] The technical solution provided in this invention has at least the following technical effects or advantages: By constructing a multi-level, multi-variable interlocking protection system, comprehensive safety monitoring of the residual carbon removal process is achieved. Before pulse initiation, baseline condition judgment and pulse access interlock judgment are set to ensure that each oxygen supply is carried out under the premise that the furnace is in a stable inert state and all process parameters meet safety requirements. During pulse execution, interlocking protection condition trigger judgment based on dynamic characteristic indicators is set to monitor changes in reaction matching degree, thermal response consistency, and exhaust system coupling degree in real time. When the inherent physical relationship between parameters is disrupted, oxygen supply is immediately stopped and degraded protection measures are implemented. During the recovery process, the recovery boundary judgment confirms that the furnace state has returned to the safe starting point. This hierarchical and progressive interlocking mechanism effectively avoids safety risks caused by local over-oxidation, thermal runaway, and exhaust system anomalies. Closed-loop cyclic control organically links pulse access, pulse execution, recovery judgment, hierarchical protection, and endpoint judgment. Each pulse starts from the same safe starting point and undergoes a complete "access-execution-recovery" process. The endpoint judgment determines whether to terminate the cycle based on the decay law of dynamic characteristic indicators of multiple pulses. This closed-loop control mechanism ensures the repeatability of each pulse and dynamically adjusts the number of pulses based on the actual reaction progress. This ensures effective carbon removal while avoiding over-processing, achieving self-optimization of the process. Furthermore, this invention judges the carbon removal progress based on the peak decay pattern of dynamic characteristics during multiple pulse executions, establishing a quantitative correlation between the peak value of reaction matching, the peak value of thermal response consistency, and the fluctuation amplitude of exhaust system coupling degree with the target cleanliness requirements. When the dynamic characteristic indicators of multiple consecutive pulses are all below the corresponding completion threshold, the pulse sequence is automatically terminated and cooling begins. This intelligent endpoint determination method avoids the "under-processing" or "over-processing" problems caused by a fixed number of pulses, maximizing production efficiency while ensuring product quality. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a flowchart illustrating a multivariable interlocking control method for removing residual carbon via micro-oxygen pulses, provided in an embodiment of this application. Detailed Implementation

[0010] The exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0011] Example 1, as Figure 1 As shown, this application provides a multivariable interlocking control method for micro-oxygen pulse carbon removal, wherein the method includes: S1. Inert gas is introduced into the heat treatment furnace and the exhaust unit is started to heat the residual carbon temperature zone to the target temperature range and run it stably; the carbon monoxide concentration in the exhaust gas and the oxygen content in the furnace are collected to determine the baseline conditions. The baseline conditions are that both the carbon monoxide concentration and the oxygen content are lower than the preset baseline threshold. If the conditions are not met, this step is repeated. Specifically, at the start of the carbon removal stage, the control system first activates the gas supply unit to continuously introduce inert gas (such as nitrogen) into the heat treatment furnace, and simultaneously activates the exhaust unit to create an inert atmosphere inside the furnace. The furnace pressure and exhaust flow rate are monitored in real time by the pressure and flow detection unit. Based on the monitoring data, the control system adjusts the opening of the exhaust valve or the frequency of the exhaust fan to maintain the furnace pressure within a preset negative pressure range (e.g., -50Pa to -20Pa) and controls the exhaust flow rate above a preset lower limit (e.g., not less than 50 m³ / h) to ensure that the combustible gases and residual oxygen generated in the furnace reaction are discharged in a timely manner, preventing local accumulation and avoiding backflow of external air into the furnace. After the inert atmosphere is established, the control system activates the heat treatment furnace to heat the carbon removal temperature zone to the target temperature range. According to the carbon removal process requirements of recycled carbon fiber, the target temperature range is set to 600℃-700℃ in this embodiment. During the heating process, the control system adjusts the heating power using PID control based on the real-time thermocouple feedback temperature of the residual carbon removal zone, ensuring the temperature remains stable within the target range and guaranteeing a uniform and stable thermal field within the furnace. Once the furnace temperature, pressure, and flow rate have reached a stable operating state, the control system continuously collects the carbon monoxide concentration in the exhaust gas through the exhaust gas detection unit and the oxygen content in the furnace through an oxygen analyzer. The control system performs baseline condition determination based on the collected carbon monoxide concentration and oxygen content in the exhaust gas, comparing the real-time collected carbon monoxide concentration and oxygen content values ​​with their preset baseline thresholds to determine if both are below the corresponding thresholds. These baseline thresholds are determined based on the inherent characteristics of the carbon fiber raw material to be treated. Specifically, based on historical micro-oxygen pulse residual carbon removal data of carbon fiber raw materials from the same source and of the same specifications under the same process conditions (target temperature, inert gas flow rate, furnace pressure), the gas concentration characteristics at the point of thermal stability before entering the pulse sequence are extracted, namely, the average carbon monoxide concentration and the average residual oxygen content. If both the carbon monoxide concentration and oxygen content are below the baseline threshold, it indicates that the residual air in the furnace has been fully replaced, the furnace atmosphere is pure, there are no residual combustible gases, and the reaction system is in a safe inert state, meeting the baseline conditions for entering the pulse sequence. The control system then proceeds to the next step, S2. If either the carbon monoxide concentration or oxygen content is not below the corresponding baseline threshold, it indicates that the inert atmosphere in the furnace has not been fully established, and there may be residual air or accumulation of reaction products. At this time, the control system maintains the inert gas supply and exhaust unit operation, continues to purge the furnace, and repeats the above collection and judgment process until both the carbon monoxide concentration and oxygen content are below the baseline threshold.

[0012] S2. Before starting the micro-oxygen pulse, process parameters are collected in real time, and pulse access interlock is determined based on the correlation characteristics of process parameters. If the determination fails, inert gas is introduced and this step is repeated. If the determination passes, step S3 is executed. Furthermore, the pulse access interlock determination includes: Before starting the micro-oxygen pulse, various process parameters are collected in real time and the monitoring value sequence within their preset time period is obtained. The process parameters include the temperature of the residual carbon removal temperature zone, the carbon monoxide concentration in the tail gas, the oxygen content in the furnace, the furnace pressure, and the exhaust flow rate. The correlation coefficient matrix between the monitoring value sequences of each process parameter was calculated using the Pearson correlation coefficient method; The pulse access interlocking determination is based on the difference between the correlation coefficient matrix and the standard correlation coefficient matrix. The standard correlation coefficient matrix is ​​pre-established based on stable operating condition data before historical successful pulse initiation. If the difference is less than the preset similarity threshold, the current working condition is determined to meet the pulse admission condition, and step S3 is executed. If the difference is greater than or equal to the preset similarity threshold, it is determined that the current operating condition does not meet the pulse access condition, and inert gas is continued to be introduced and this step is repeated.

[0013] Specifically, before initiating the micro-oxygen pulse, the control system acquires the monitoring value sequence of each process parameter within a preset time period from each detection unit. This includes: continuously monitoring the carbon monoxide concentration and oxygen content in the exhaust gas using the exhaust gas detection unit; continuously monitoring the furnace pressure and exhaust flow rate using the pressure and flow rate detection unit; and continuously monitoring the temperature in the residual carbon removal zone using a temperature sensor. The sampling frequency of the detection units is set according to process requirements. In this embodiment, the sampling frequency is set to 2Hz, and the preset time period is 15 seconds. That is, the data from the 30 sampling points before the current moment are acquired at each judgment to form the monitoring value sequence. This setting is based on the following considerations: on the one hand, 30 sample points can meet the statistical validity requirements for correlation coefficient calculation; on the other hand, the 15-second time window can promptly reflect the latest changes in the current operating conditions and avoid lag in response to rapid fluctuations due to an excessively long window. The following monitoring value sequences are formed: temperature sequence, carbon monoxide concentration sequence, oxygen content sequence, furnace pressure sequence, and exhaust flow rate sequence. The Pearson correlation coefficient method was used to calculate the pairwise correlation of the acquired monitoring value series, resulting in a correlation coefficient matrix. The following is a table showing the values ​​for T (temperature), CO (carbon monoxide concentration), O2 (oxygen content), P (furnace pressure), and F (exhaust flow rate): ; Based on stable operating condition data prior to successful pulse initiation from historically successful pulses, where raw material batches were consistent with the current batch, process parameters were stable, subsequent pulse processes were successfully completed, and product quality was qualified, a correlation coefficient matrix was calculated. This correlation coefficient matrix serves as the standard correlation coefficient matrix. The correlation coefficient matrix was calculated using the Frobenius norm. Correlation coefficient matrix with standard The degree of difference is used to determine the pulse access interlock: If the difference is less than the preset similarity threshold, it is determined that the current operating condition has consistent correlation characteristics with the historical successful operating conditions. That is, the pairwise correlation between the current process parameters is consistent with the inherent characteristics of the stable inert state, indicating that the furnace is in a state where a safe pulse can be started. At this time, the control system determines that the pulse access interlock determination is passed, and then executes step S3 to perform micro-oxygen pulse oxygen supply. The similarity threshold is determined based on the stability of the standard operating condition data. By using the sliding window resampling method on the standard operating condition data, the continuous monitoring period is divided into multiple sub-windows, the difference between each sub-window matrix and the standard matrix is ​​calculated, and 1.2 times its maximum value is taken as the threshold. This value can tolerate random fluctuations under normal operating conditions and effectively identify abnormal states where the correlation characteristics deviate. If the difference is greater than or equal to the preset similarity threshold, the current operating condition is determined to be abnormal, and the correlation characteristics between the parameters deviate from the normal state. Possible reasons include: a localized weak oxidation reaction in the furnace causing an abnormal negative correlation between carbon monoxide and oxygen content; fluctuations in intake or exhaust causing changes in the coupling relationship between pressure and flow rate; abnormal response of a certain detection unit causing its correlation with other parameters to deviate; and a decrease in the furnace's sealing performance leading to air leakage, affecting multiple correlation indicators. At this time, the control system determines that the pulse access conditions are not met, continues to introduce inert gas to maintain the inert atmosphere in the furnace, and repeats this step for monitoring and judgment.

[0014] S3. Introduce mixed gas into the heat treatment furnace to perform a micro-oxygen pulse, collect the process parameters during the micro-oxygen pulse execution, and determine the interlock protection condition trigger based on the dynamic characteristics between the process parameters and the deviation of their reference values. If triggered, immediately stop the current micro-oxygen pulse oxygen supply and execute step S4. If not triggered, execute step S5 after the pulse ends. Furthermore, the interlocking protection condition triggering judgment includes: A micro-oxygen pulse is executed by introducing a mixed gas into the heat treatment furnace, and the process parameters during the execution of the micro-oxygen pulse are collected in real time at a preset sampling frequency. Using the current sampling time as the endpoint, a time window of a preset length is constructed, and the dynamic features within this time window are calculated. These dynamic features characterize the physical relationships between process parameters, including: The reaction matching degree is the ratio of the rate of change in carbon monoxide concentration to the rate of change in oxygen content. Thermal response consistency, defined as the ratio of the rate of temperature change to the difference between the current temperature and the pre-pulse reference temperature, where the pre-pulse reference temperature is the average temperature of the furnace under stable operating conditions before pulse initiation. The exhaust unit coupling degree is the ratio of the furnace pressure change rate to the exhaust flow rate change rate. The interlocking protection conditions are triggered based on the deviation of each dynamic characteristic from its reference value. The reference value is determined based on stoichiometry, heat capacity calculation, and exhaust fan characteristic curve. If any deviation exceeds the allowable range, the interlock protection condition is triggered, the current micro-oxygen pulse is immediately stopped, and step S4 is executed. If no deviation occurs or all deviations are within the allowable range, it is determined that the interlocking protection condition has not been triggered, and step S5 is executed after the current pulse ends.

[0015] Specifically, a micro-oxygen pulse is executed once, with a pulse duration of 60 seconds, introducing a mixed gas (nitrogen and air, with an oxygen content of 3%-5%) into the heat treatment furnace, where the oxygen content is lower than that of air. During the execution of the micro-oxygen pulse, the control system collects process parameters in real time at a sampling frequency of 2Hz, including the temperature of the residual carbon removal zone, the carbon monoxide concentration in the exhaust gas, the oxygen content in the furnace, the furnace pressure, and the exhaust flow rate. A time window of a preset length of 15 seconds is constructed, ending at the current sampling time, encompassing the current sampling time and the preceding 30 sampling points. Within this constructed time window, the dynamic characteristics representing the physical relationship between the following three process parameters are calculated: (1) Reaction matching degree: Reaction matching degree = rate of change of carbon monoxide concentration within the time window / rate of change of oxygen content within the time window, used to characterize the degree of matching between the carbon monoxide generation rate and the oxygen consumption rate; (2) Thermal response consistency: Thermal response consistency = temperature change rate within the time window / temperature at the current sampling moment - reference temperature before the pulse, which is used to characterize the consistency between temperature response and temperature change rate. Among them, the reference temperature before the pulse is the average temperature when the furnace is in a stable operating state before the pulse is started, that is, the average value after the temperature stabilizes when the baseline condition is met in step S2; (3) Coupling degree of exhaust unit: Coupling degree of exhaust unit = rate of change of furnace pressure within the time window / rate of change of exhaust flow within the time window, used to characterize the coupling relationship between furnace pressure change and exhaust flow change; The deviation values ​​of each dynamic characteristic from their baseline values ​​are calculated to determine the triggering conditions for interlocking protection. The reaction matching degree baseline value is determined based on the stoichiometric relationship of the main reaction path of carbon oxidation, C + O2 → CO2. In this reaction, 1 mole of oxygen consumption corresponds to 1 mole of carbon monoxide production; therefore, the reaction matching degree baseline value is 1. The thermal response consistency baseline value is calculated based on the furnace's heat capacity characteristics: Thermal response consistency baseline value = Heating power / Total furnace heat capacity. The exhaust unit coupling degree baseline value is determined based on the characteristic curve of the exhaust fan: Exhaust unit coupling degree = ,in This is the maximum pressure of the fan when there is zero flow (determined by the inherent characteristics of the fan). The furnace pressure at the normal operating point. This refers to the exhaust flow rate at the normal operating point. If any deviation exceeds the allowable range, the interlock protection condition is triggered, the control system immediately stops the current micro-oxygen pulse (cuts off the mixed gas and switches to pure nitrogen purging) and executes step S4; If no deviation occurs or all deviations are within the allowable range, it is determined that the interlock protection condition has not been triggered. The current pulse continues to execute for the preset duration of 60 seconds. After the pulse ends, step S5 is executed to perform inertial recovery purging. The allowable range is determined based on the measurement uncertainty and normal fluctuation characteristics of each dynamic characteristic index, including the measurement error of the measuring tool and fluctuations in the carbon monoxide generation process, furnace thermal inertia, and exhaust unit adjustment process.

[0016] S4. Perform the corresponding graded response operation according to the dynamic characteristic type of the triggering interlock protection condition until the deviation between the dynamic characteristic and its reference value is within the allowable range, and then proceed to step S6. Furthermore, the hierarchical response operation includes: When the reaction matching deviation exceeds the allowable range, the oxygen-containing gas supply is cut off, and the inert gas purging flow rate is adjusted to the flow rate before pulse execution. The formula for calculating the multiple is: ; in The current reaction matching degree, As the baseline value for response matching, This is the flow rate regulation coefficient; When the thermal response consistency deviation exceeds the allowable range, adjust the heating power to the power before pulse execution. The formula for calculating the multiple is: ; in To ensure current thermal response consistency, As a benchmark value for thermal response consistency, This is the power regulation coefficient; When the exhaust unit coupling deviation exceeds the allowable range, adjust the exhaust valve opening. and exhaust fan frequency The calculation formula is: , ; in The current exhaust unit coupling degree, This is the reference value for the coupling degree of the exhaust unit. , This is the adjustment coefficient.

[0017] Specifically, when the interlock protection condition in step S3 is triggered, the control system immediately stops the current micro-oxygen pulse supply and initiates the corresponding degradation protection procedure based on the dynamic characteristic type that triggered the interlock. The trigger types include the following three situations: reaction matching degree exceeds the allowable range, thermal response consistency exceeds the allowable range, and exhaust unit coupling degree exceeds the allowable range. When the reaction matching deviation exceeds the allowable range, it indicates an imbalance in the ratio of carbon monoxide production to oxygen consumption in the current oxidation reaction, posing a risk of reaction runaway. At this point, immediately shut off the oxygen-containing gas supply valve to prevent further oxygen entry into the furnace; and adjust the inert gas purging flow rate to the flow rate before pulse execution. The formula for calculating the multiple is: ; in The current reaction matching degree, As the baseline value for response matching, The flow rate regulation coefficient is pre-calibrated based on the furnace volume and purging response capability. Specifically, a step purging test is conducted under empty furnace conditions to determine the effect of increased flow rate on the oxygen dilution rate. The flow rate multiple required to reduce the oxygen content to a safe value within 30 seconds is taken as the flow rate regulation coefficient. ; When the deviation in thermal response consistency exceeds the allowable range, it indicates an abnormal relationship between temperature response and temperature rise rate, suggesting a risk of localized overheating or thermal runaway. In this case, the heating power should be adjusted to [a certain percentage] of the power before pulse execution. The formula for calculating the multiple is: ; in To ensure current thermal response consistency, As a benchmark value for thermal response consistency, The power regulation coefficient is pre-calibrated based on heating response characteristics and furnace thermal inertia. The furnace's natural cooling rate is measured, and the effect of heating power on temperature rise is considered to determine the required power reduction to match the temperature drop rate with the abnormal temperature rise rate. ; When the coupling deviation of the exhaust unit exceeds the allowable range, it indicates that the normal negative correlation between furnace pressure and exhaust flow rate has been disrupted, posing a risk of exhaust unit blockage or leakage. In this case, adjust the exhaust valve opening. and exhaust fan frequency The calculation formula is: , ; in The current exhaust unit coupling degree, This is the reference value for the coupling degree of the exhaust unit. , The adjustment coefficient is calibrated based on valve characteristics and fan response characteristics. Specifically, the influence of different valve openings and fan frequencies on the pressure-flow relationship is determined in separate tests of the exhaust unit, and the adjustment amount required to reduce the coupling deviation by 50% is taken as the coefficient benchmark. Once all dynamic characteristics have recovered to within the allowable range, the control system determines that the response is complete, terminates the graded response operation, and executes step S6 to determine the carbon removal process.

[0018] S5. Switch the heat treatment furnace to inert gas for purging and enter the recovery process. Real-time collection of carbon monoxide concentration in the exhaust gas, oxygen content in the furnace and temperature are used to determine the recovery. If all three fall back to the recovery boundary, proceed to step S6; otherwise, continue with this step. Furthermore, the recovery determination includes: The heat treatment furnace is purged with inert gas to begin the recovery process, and the carbon monoxide concentration, oxygen content and temperature in the exhaust gas are collected in real time during the recovery process. Obtain historical recovery phase data of several successful pulses of the current batch of raw materials, and extract the decay curves of carbon monoxide concentration in the tail gas, oxygen content in the furnace, and temperature over time. The nonlinear least squares method was used to fit the exponential decay of each decay curve to obtain the standard decay function and its confidence interval of carbon monoxide concentration in tail gas, oxygen content in furnace and temperature during the recovery process. The value of the standard decay function at the time of recovery completion is used as the recovery boundary value, and the width of the confidence interval is used as the allowable fluctuation range of the recovery boundary value; When the carbon monoxide concentration in the exhaust gas, the oxygen content in the furnace, and the temperature during the current recovery process all fall back to the allowable fluctuation range of their recovery boundary values, and this state remains stable for a preset time, it is determined that the recovery boundary conditions are met, and step S6 is executed; otherwise, this step continues.

[0019] Specifically, after the micro-oxygen pulse ends, the control system immediately switches the gas supply to the heat treatment furnace to inert gas (helium) for purging to initiate the recovery process. Simultaneously, the system collects data in real-time at a preset sampling frequency on the carbon monoxide concentration in the exhaust gas, the oxygen content inside the furnace, and the temperature during the current recovery process. The historical recovery phase data of several successful pulses of the current batch of raw materials is obtained. In this embodiment, data from 3 successful productions are selected. For each successful pulse, the complete recovery phase data from the end of the pulse to the moment when the parameters are completely stable is extracted. The sequences of carbon monoxide concentration in the tail gas, oxygen content in the furnace, and temperature change over time are extracted during each recovery process. The decay curves of each parameter over time are plotted with time as the horizontal axis and parameter values ​​as the vertical axis. For the extracted decay curves of each parameter, an exponential decay fitting was performed using the nonlinear least squares method. Taking carbon monoxide concentration as an example, based on the physical law of concentration decay over time during the recovery process, it was fitted into an exponential decay function. Iterative optimization was used to minimize the sum of squared errors between the fitted curve and the actual data points, thus determining the decay function for this recovery process. The above fitting process was repeated for the recovery data of multiple successful pulses to obtain multiple sets of decay functions. Based on this, the statistical average of the function values ​​of each decay function at the same time was taken to construct the standard decay function for carbon monoxide concentration. Simultaneously, based on the distribution of the function values ​​of each decay function at the same time, its standard deviation was calculated, thus obtaining the confidence interval of the standard decay function. The standard decay functions and their confidence intervals for oxygen content and temperature were established using the same method. Based on the established standard decay function and its confidence interval, the recovery boundary values ​​and allowable fluctuation ranges for carbon monoxide concentration in the exhaust gas, oxygen content in the furnace, and temperature are determined. The recovery boundary value is the function value of the standard decay function at the time of recovery completion, where the recovery completion time is defined as the statistical maximum value of the time required for each parameter to decay to its steady-state value. The allowable fluctuation range is based on the width of the confidence interval, specifically taking half the difference between the upper and lower limits of the confidence interval for the standard decay function at the time of recovery completion as the fluctuation amplitude, extending upwards and downwards towards the recovery boundary value to form the allowable fluctuation range for each parameter. This allowable fluctuation range reflects the normal fluctuation range of the parameters at the time of recovery completion during historical successful recovery processes, serving as a quantitative basis for subsequent real-time judgment. During the current recovery process, the control system compares the real-time carbon monoxide concentration in the exhaust gas, the oxygen content in the furnace, and the temperature with the recovery boundary values ​​and allowable fluctuation ranges determined based on historical recovery phase data on an hourly basis. When the real-time values ​​of the three parameters are simultaneously within their respective allowable fluctuation ranges and approach their recovery boundary values, the control system starts a timer to accumulate the duration for which all three parameters remain within their allowable fluctuation ranges. If this state is maintained continuously for a preset stable duration, the recovery boundary conditions are deemed met, and step S6 is executed; if any parameter deviates from its allowable fluctuation range, this step continues until the aforementioned recovery boundary conditions are met. The preset stable duration is the maximum value of the time required for the carbon monoxide concentration in the exhaust gas, the oxygen content in the furnace, and the temperature to stabilize within their allowable fluctuation ranges from the start of recovery, based on historical recovery phase data.

[0020] S6. Based on the dynamic characteristic indicators during the execution of multiple pulses, determine the carbon removal process. If the carbon removal process has been completed, terminate the pulse execution and switch to an inert atmosphere for cooling. Otherwise, return to step S2 to perform the next pulse access interlock determination.

[0021] Furthermore, the determination of the carbon removal process includes: Repeat steps S2 to S5, and extract the dynamic characteristic indicators during the execution of each pulse after the end of each pulse, including the peak value of the reaction matching degree, the peak value of the thermal response consistency, and the fluctuation range of the exhaust unit coupling degree. When the peak values ​​of the reaction matching degree of multiple consecutive pulses are all lower than the reaction matching degree completion threshold, the peak values ​​of the thermal response consistency are all lower than the thermal response consistency completion threshold, and the fluctuation amplitude of the exhaust unit coupling degree is all less than the stability threshold, the carbon removal process is determined to be completed. Both the reaction matching degree completion threshold and the thermal response consistency completion threshold are predetermined based on the target cleanliness requirements of the carbon fiber raw materials, and the calculation formula is as follows: ; in This represents the threshold for achieving reaction matching and the threshold for achieving thermal response consistency. This serves as the baseline value corresponding to the dynamic characteristics. The residual carbon rate corresponding to the target cleanliness level. The initial residual carbon content, This is the attenuation coefficient corresponding to the dynamic characteristics; The stability threshold is determined using the 3σ principle based on the fluctuation data of exhaust unit coupling degree in the later stage of historical successful pulse recovery.

[0022] Specifically, after each pulse ends, the control system extracts three dynamic characteristic indicators from the execution of that pulse: the peak value of the reaction matching degree, the peak value of the thermal response consistency, and the fluctuation amplitude of the exhaust unit coupling degree. The peak value of the reaction matching degree is the maximum value of the reaction matching degree during the pulse execution, reflecting the maximum intensity of the oxidation reaction in that pulse; the peak value of the thermal response consistency is the maximum value of the thermal response consistency during the pulse execution, reflecting the maximum degree of thermal response in that pulse; and the fluctuation amplitude of the exhaust unit coupling degree is calculated as the standard deviation or range of the coupling degree during the pulse execution, reflecting the stability of the exhaust unit in that pulse. In the actual judgment process, the control system collects the peak value of reaction matching degree, peak value of thermal response consistency, and coupling degree fluctuation amplitude of each pulse, and establishes a sliding window with a length of multiple consecutive pulses. In this embodiment, three consecutive pulses are used as the judgment criteria. After each new pulse is completed, it is checked whether the indicators of the three pulses in the window are simultaneously satisfied: the peak value of reaction matching degree is lower than the reaction matching degree completion threshold, the peak value of thermal response consistency is lower than the thermal response consistency completion threshold, and the coupling degree fluctuation amplitude is less than the stability threshold. If all conditions in the window are satisfied, it is determined that the residual carbon removal process has been completed, the control system terminates the execution of subsequent pulses and switches the heat treatment furnace to an inert atmosphere for cooling; if any condition is not satisfied, the window slides in new pulse data and removes the earliest pulse data, returns to the execution step S2 to perform the next pulse access interlock judgment, and continues to repeat the pulse cycle until the completion conditions are met; The thresholds for reaction matching and thermal response consistency are predetermined based on the target cleanliness requirements of the carbon fiber raw materials. Higher target cleanliness requirements necessitate greater attenuation of the required pulse characteristic peak value; higher initial char content also requires a greater number or intensity of pulses. These are calculated using the following unified formula: ; in These represent the threshold for achieving reaction matching and the threshold for achieving thermal response consistency, respectively. This serves as the baseline value corresponding to the dynamic characteristics. The residual carbon rate corresponding to the target cleanliness level. The initial residual carbon content, The attenuation coefficient, corresponding to the dynamic characteristics, reflects the correlation between the raw material properties and the reaction characteristics. The stability threshold for the exhaust unit coupling degree is determined based on fluctuation data from the later stages of the recovery phase of historical successful pulses, using the 3σ principle. Specifically, recovery phase data from multiple successful pulses of the current batch of raw materials are selected, and continuous monitoring values ​​after the parameters have stabilized in the later stages of each recovery process are extracted. The standard deviation of all sampled values ​​is calculated, and the average value plus three times the standard deviation is taken as the stability threshold. This threshold reflects the inherent fluctuation level of the exhaust unit under normal operating conditions.

[0023] This method for judging the carbon removal process achieves more accurate endpoint judgment than a fixed number of pulses by identifying the endpoint based on the pulse characteristic peak decay law; the completion threshold is dynamically calculated according to the raw material characteristics and target cleanliness, which has good raw material adaptability; the multi-indicator collaborative judgment effectively avoids misjudgment of single indicators; and the seamless connection with the pulse cycle forms a complete automated control process.

[0024] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0025] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-variable interlocking control method for micro-oxygen pulse carbon residue removal, applied to a recycled carbon fiber production line, wherein the recycled carbon fiber production line includes a heat treatment furnace, a gas supply unit, an exhaust unit, a tail gas detection unit, a pressure and flow detection unit, an execution and regulation unit, and a control system, characterized in that, The method includes the following steps: S1. Inert gas is introduced into the heat treatment furnace and the exhaust unit is started to heat the residual carbon temperature zone to the target temperature range and run it stably; the carbon monoxide concentration in the exhaust gas and the oxygen content in the furnace are collected to determine the baseline conditions. The baseline conditions are that both the carbon monoxide concentration and the oxygen content are lower than the preset baseline threshold. If the conditions are not met, this step is repeated. S2. Before starting the micro-oxygen pulse, process parameters are collected in real time, and pulse access interlock is determined based on the correlation characteristics of the process parameters. If the determination fails, inert gas is introduced and this step is repeated. If the determination passes, step S3 is executed. S3. Introduce mixed gas into the heat treatment furnace to perform a micro-oxygen pulse, collect the process parameters during the micro-oxygen pulse execution, and determine the interlock protection condition trigger based on the dynamic characteristics between the process parameters and the deviation of their reference values. If triggered, immediately stop the current micro-oxygen pulse oxygen supply and execute step S4. If not triggered, execute step S5 after the pulse ends. S4. Perform the corresponding graded response operation according to the dynamic characteristic type of the triggering interlock protection condition until the deviation between the dynamic characteristic and its reference value is within the allowable range, and then proceed to step S6. S5. Switch the heat treatment furnace to inert gas for purging and enter the recovery process. Real-time collection of carbon monoxide concentration in the exhaust gas, oxygen content in the furnace and temperature are used to determine the recovery. If all three fall back to the recovery boundary, proceed to step S6; otherwise, continue with this step. S6. Based on the dynamic characteristic indicators during the execution of multiple pulses, determine the carbon removal process. If the carbon removal process has been completed, terminate the pulse execution and switch to an inert atmosphere for cooling. Otherwise, return to step S2 to perform the next pulse access interlock determination.

2. The multivariable interlocking control method as described in claim 1, characterized in that, The pulse access interlock determination includes: Before starting the micro-oxygen pulse, various process parameters are collected in real time and the monitoring value sequence within their preset time period is obtained. The process parameters include the temperature of the residual carbon removal temperature zone, the carbon monoxide concentration in the tail gas, the oxygen content in the furnace, the furnace pressure, and the exhaust flow rate. The correlation coefficient matrix between the monitoring value sequences of each process parameter was calculated using the Pearson correlation coefficient method; The pulse access interlocking determination is based on the difference between the correlation coefficient matrix and the standard correlation coefficient matrix. The standard correlation coefficient matrix is ​​pre-established based on stable operating condition data before historical successful pulse initiation. If the difference is less than the preset similarity threshold, the current working condition is determined to meet the pulse admission condition, and step S3 is executed. If the difference is greater than or equal to the preset similarity threshold, it is determined that the current operating condition does not meet the pulse access condition, and inert gas is continued to be introduced and this step is repeated.

3. The multivariable interlocking control method as described in claim 2, characterized in that, The interlocking protection condition triggering judgment includes: A micro-oxygen pulse is executed by introducing a mixed gas into the heat treatment furnace, and the process parameters during the execution of the micro-oxygen pulse are collected in real time at a preset sampling frequency. Using the current sampling time as the endpoint, a time window of a preset length is constructed, and the dynamic features within this time window are calculated. These dynamic features characterize the physical relationships between process parameters, including: The reaction matching degree is the ratio of the rate of change in carbon monoxide concentration to the rate of change in oxygen content. Thermal response consistency, defined as the ratio of the rate of temperature change to the difference between the current temperature and the pre-pulse reference temperature, where the pre-pulse reference temperature is the average temperature of the furnace under stable operating conditions before pulse initiation. The exhaust unit coupling degree is the ratio of the furnace pressure change rate to the exhaust flow rate change rate. The interlocking protection conditions are triggered based on the deviation of each dynamic characteristic from its reference value. The reference value is determined based on stoichiometry, heat capacity calculation, and exhaust fan characteristic curve. If any deviation exceeds the allowable range, the interlock protection condition is triggered, the current micro-oxygen pulse is immediately stopped, and step S4 is executed. If no deviation occurs or all deviations are within the allowable range, it is determined that the interlocking protection condition has not been triggered, and step S5 is executed after the current pulse ends.

4. The multivariable interlocking control method as described in claim 3, characterized in that, The hierarchical response operation includes: When the reaction matching deviation exceeds the allowable range, the oxygen-containing gas supply is cut off, and the inert gas purging flow rate is adjusted to the flow rate before pulse execution. The formula for calculating the multiple is: ； in The current reaction matching degree, As the baseline value for response matching, This is the flow regulation coefficient; When the thermal response consistency deviation exceeds the allowable range, adjust the heating power to the power before pulse execution. The formula for calculating the multiple is: ； in To ensure current thermal response consistency, As a benchmark value for thermal response consistency, This is the power regulation coefficient; When the exhaust unit coupling deviation exceeds the allowable range, adjust the exhaust valve opening. and exhaust fan frequency The calculation formula is: ， ； in The current exhaust unit coupling degree, This is the reference value for the coupling degree of the exhaust unit. , This is the adjustment coefficient.

5. The multivariable interlocking control method as described in claim 4, characterized in that, The recovery determination includes: The heat treatment furnace is purged with inert gas to begin the recovery process, and the carbon monoxide concentration, oxygen content and temperature in the exhaust gas are collected in real time during the recovery process. Obtain historical recovery phase data of several successful pulses of the current batch of raw materials, and extract the decay curves of carbon monoxide concentration in the tail gas, oxygen content in the furnace, and temperature over time. The nonlinear least squares method was used to fit the exponential decay of each decay curve to obtain the standard decay function and its confidence interval of carbon monoxide concentration in tail gas, oxygen content in furnace and temperature during the recovery process. The value of the standard decay function at the time of recovery completion is used as the recovery boundary value, and the width of the confidence interval is used as the allowable fluctuation range of the recovery boundary value; When the carbon monoxide concentration in the exhaust gas, the oxygen content in the furnace, and the temperature during the current recovery process all fall back to the allowable fluctuation range of their recovery boundary values, and this state remains stable for a preset time, it is determined that the recovery boundary conditions are met, and step S6 is executed; otherwise, this step continues.

6. The multivariable interlocking control method as described in claim 5, characterized in that, The determination of the carbon removal process includes: Repeat steps S2 to S5, and extract the dynamic characteristic indicators during the execution of each pulse after the end of each pulse, including the peak value of the reaction matching degree, the peak value of the thermal response consistency, and the fluctuation range of the exhaust unit coupling degree. When the peak values ​​of the reaction matching degree of multiple consecutive pulses are all lower than the reaction matching degree completion threshold, the peak values ​​of the thermal response consistency are all lower than the thermal response consistency completion threshold, and the fluctuation amplitude of the exhaust unit coupling degree is all less than the stability threshold, the carbon removal process is determined to be completed. Both the reaction matching degree completion threshold and the thermal response consistency completion threshold are predetermined based on the target cleanliness requirements of the carbon fiber raw materials, and the calculation formula is as follows: ； in This represents the threshold for achieving reaction matching and the threshold for achieving thermal response consistency. This serves as the baseline value corresponding to the dynamic characteristics. The residual carbon rate corresponding to the target cleanliness level. The initial residual carbon rate, This is the attenuation coefficient corresponding to the dynamic characteristics; The stability threshold is determined using the 3σ principle based on the fluctuation data of exhaust unit coupling degree in the later stage of historical successful pulse recovery.

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