Formaldehyde absorption tower automatic circulating liquid supplementing and concentration regulating system and method

Abstract

The application discloses a kind of formaldehyde absorption tower automatic circulation liquid supplementing and concentration regulation system and method, belong to formaldehyde absorption tower circulation liquid supplementing and concentration regulation technical field, comprising: liquid storage and double-path supply unit, liquid level and concentration double detection unit, intelligent decoupling control unit and execution unit;The liquid storage and double-path supply unit is used to store and provide process water and concentrated formaldehyde solution respectively, as the supply source of adjusting absorption tower circulating liquid level and concentration;The liquid level and concentration double detection unit is used to detect the liquid level and formaldehyde concentration of absorption tower circulating liquid in real time and continuously, and provides measurement signal to the intelligent decoupling control unit, the present application directly improves the reaction selectivity and yield of downstream trioxymethylene synthesis by the improvement of concentration accuracy, predictive safety interlock and self-diagnosis function greatly reduce the number of unplanned shutdown, fully automated operation significantly reduces post personnel configuration and labor intensity.

Description

Technical Field

[0001] This invention belongs to the technical field of formaldehyde absorption tower circulation replenishment and concentration control methods. Specifically, it relates to an automatic circulation replenishment and concentration control system and method for formaldehyde absorption towers. Background Technology

[0002] In the production of polyoxymethylene (POM), formaldehyde is the core raw material. Typically, formaldehyde gas from upstream processes (such as that obtained from methanol oxidation) needs to be absorbed by water or dilute formaldehyde solution in a formaldehyde absorption tower to prepare a formaldehyde solution with the required polymerization concentration (usually 37%-55%). The operational stability of this absorption tower directly determines the quality of the raw materials supplied to the downstream trioxymethylene synthesis section, thus affecting the molecular weight distribution and properties of the final POM product.

[0003] Currently, in the formaldehyde absorption section of polyoxymethylene (POM) production plants, the following pain points are commonly encountered in controlling the level and concentration of the circulating liquid: Manual control is slow and inaccurate: Replenishment of the circulating liquid (water or concentrated formaldehyde) mainly relies on on-site inspections and manual operation by personnel. Humans cannot perceive the dynamic changes in the column bottom liquid level and concentration in real time, especially when there are fluctuations in feed gas flow or concentration, resulting in a severe lag in response. Too low a liquid level may cause cavitation damage to the circulating pump; concentration deviations from the process range (such as being too high or too low) will directly affect the synthesis efficiency and selectivity of downstream paraformaldehyde, causing fluctuations in product indicators.

[0004] High safety risks and high labor intensity: Formaldehyde is highly irritating and toxic, and its aqueous solution (formalin) is easily volatile during operation. Frequent manual on-site operations, such as opening and closing valves and sampling for concentration analysis, increase the risk of personnel exposure to formaldehyde vapor, resulting in high labor intensity and posing a threat to occupational health.

[0005] The process parameters are highly coupled, making traditional automation methods inadequate: Formaldehyde absorption is a typical process involving both gas-liquid mass transfer and liquid-liquid mixing. The circulating liquid level and formaldehyde concentration are two strongly coupled key parameters. Traditional single-point level control (such as float switches) or simple proportional water replenishment completely ignores the need for concentration control. Commercially available simple water replenishment devices cannot automatically adjust the ratio of water to concentrated formaldehyde based on concentration changes, causing the system to constantly oscillate in concentration and level, preventing steady-state optimized operation.

[0006] Lack of intelligent diagnostics and safety assurance: The existing system cannot effectively identify abnormal operating conditions caused by instrument failure (such as concentration analyzer drift), valve internal leakage or pipeline leakage, and cannot provide early warning before the liquid level or concentration is out of control, which poses a risk of the entire line being shut down due to unqualified raw materials.

[0007] Therefore, an automatic circulating replenishment and concentration control system and method for formaldehyde absorption tower is proposed. Summary of the Invention

[0008] To address the aforementioned problems and technical deficiencies, the present invention adopts the following technical solution: an automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower, comprising: a liquid storage and dual-path supply unit, a liquid level and concentration dual detection unit, an intelligent decoupling control unit, and an execution unit; The liquid storage and dual-supply unit is used to store and supply process water and concentrated formaldehyde solution respectively, as a source of replenishment for adjusting the liquid level and concentration of the absorption tower circulating liquid. The dual detection unit for liquid level and concentration is used to detect the liquid level and formaldehyde concentration of the circulating liquid in the absorption tower in real time and continuously, and to provide measurement signals to the intelligent decoupling control unit. The intelligent decoupling control unit includes: A level controller is used to generate a total replenishment demand signal based on the deviation between the setpoint and the real-time level. A concentration controller is used to generate a mixing ratio coefficient based on the deviation between the concentration setpoint and the real-time concentration. A dynamic decoupling calculator is used to convert the total replenishment demand signal into process water replenishment flow instructions and concentrated formaldehyde replenishment flow instructions based on the ratio coefficient. The intelligent decoupling control unit also includes a self-diagnostic module based on material balance. The self-diagnostic module is used to calculate an index η that characterizes the health of the system, and dynamically adjust the control parameters of the level controller and / or concentration controller according to the index η.

[0009] Preferably, it also includes a dynamic compensation module for evaporation loss; the dynamic compensation module for evaporation loss is used to collect the temperature of the tail gas at the top of the absorption tower, the temperature of the circulating liquid, and the tail gas flow rate, and to calculate the real-time evaporation loss F. evap The real-time evaporation loss F evap The feedforward superimposed onto the total fluid replacement demand signal; the self-diagnostic module is also used to use an adaptive factor The model parameters of the dynamic compensation module for evaporation loss are corrected online to eliminate the impact of liquid level deviation separated by leak diagnosis on evaporation estimation.

[0010] Preferably, it also includes a predictive safety coordination module, which embeds a concentrated digital twin model. The digital twin model is used to simulate the liquid level and concentration trajectory over a future period of time on a faster-than-real-time timescale, using the current replenishment flow rate and air intake conditions as input. When the simulated trajectory will trigger a preset safety interlock threshold, the intelligent decoupling control unit adds a hard constraint to avoid triggering the safety interlock threshold when generating the total replenishment demand signal and the proportioning coefficient.

[0011] Furthermore, the execution unit includes a main circulation pump, the inlet pipe of which is equipped with a pressure transmitter, and the pump body is equipped with a vibration sensor; the intelligent decoupling control unit is also used to calculate the cavitation risk index R based on the signals from the pressure transmitter and the vibration sensor. cav Based on the cavitation risk index R cav The liquid level interlock threshold and the liquid level setpoint in the predictive safety collaboration module are dynamically increased.

[0012] Preferably, it also includes a cross-section collaborative optimizer, which obtains the real-time status parameters of the downstream paraformaldehyde synthesis reactor through the system integration interface unit, and fine-tunes the liquid level setpoint and concentration setpoint online with the liquid level safety of this section as a constraint and the optimization objective of minimizing the impurity content of the downstream reaction or maximizing the conversion rate.

[0013] Preferably, in the execution unit, the process water supply pipeline and the concentrated formaldehyde supply pipeline each include a parallel low-flow high-precision metering pump and a high-flow fast regulating valve; the intelligent decoupling control unit also includes a working condition self-identifier, which is used to control the alternating or coordinated operation of the metering pump and the fast regulating valve according to the change rate of total replenishment demand and the absolute value of concentration deviation.

[0014] Preferably, the operating condition self-identifier is also used to control the frequency converter of the main circulation pump, and to calculate the optimal liquid-gas ratio in real time based on the feed gas load, so as to adjust the main circulation flow rate F. out .

[0015] An automatic circulating replenishment and concentration control method for formaldehyde absorption towers used in polyoxymethylene (POM) production processes includes the following steps: S1. Real-time acquisition of circulating liquid level L and formaldehyde concentration C, as well as upstream air intake parameters and downstream reactor status parameters; S2. In the level controller, the total replenishment requirement F is calculated based on the deviation between the liquid level L and the set liquid level value. total In the concentration controller, the proportioning coefficient K is calculated based on the deviation between the concentration C and the set concentration value. S3, the total fluid replenishment requirement F total The process water supply flow rate command F is output from the input dynamic decoupling calculator along with the ratio coefficient K. water and concentrated formaldehyde supply flow instruction F formalin ; S4. The total fluid replenishment requirement F is generated. total Before or simultaneously with the ratio coefficient K, the real-time evaporation loss F calculated by the dynamic evaporation loss compensation module is received. evapThe system health index η calculated by the self-diagnosis module is fed back to compensate for the total fluid replenishment requirement and to adaptively correct the control parameters of the liquid level controller and concentration controller, respectively. S5. Execute the process water replenishment flow rate command and the concentrated formaldehyde replenishment flow rate command, and use the embedded digital twin model to verify whether the future liquid level and concentration trajectory after execution is safe in a way that is faster than real-time. If the predicted trajectory will trigger the preset safety interlock threshold, then correct the command and execute it again.

[0016] Preferably, between step S2 and step S4, the following step further includes: continuously calculating the cavitation risk index R of the circulating pump. cav When the cavitation risk index R cav When the level rises, the liquid level setpoint is forcibly increased, and the total replenishment requirement F is also increased. total The lower bound for generation.

[0017] Furthermore, the downstream reactor state parameters received in step S1 include impurity content feedback, and step S2 also includes constructing a multi-objective optimization model. ,in The initial concentration setpoint is given, and Imp represents the downstream impurity content. , These are the weighting coefficients; The liquid level setpoint and concentration setpoint are obtained online by the optimization model under the condition of satisfying the liquid level safety constraint.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This automatic circulating liquid replenishment and concentration control system and method for formaldehyde absorption towers used in polyoxymethylene (POM) production replaces manual inspection and operation modes through a collaborative architecture of a level controller, a concentration controller, and a dynamic decoupling calculator. The dual level and concentration detection units continuously collect process parameters at second-level intervals. The dynamic decoupling calculator collaboratively calculates the total replenishment demand output from the level loop and the mixing ratio coefficient output from the concentration loop, automatically and synchronously correcting concentration deviations while replenishing liquid to maintain the level, thus solving the problem of periodic oscillations caused by the strong coupling between level and concentration.

[0019] 2. This automatic circulating liquid replenishment and concentration control system and method for formaldehyde absorption towers used in the polyoxymethylene (POM) production process achieves fully automated, unmanned operation from data acquisition and control decision-making to liquid replenishment execution. Operators only need to remotely monitor from the control room, fundamentally avoiding the risk of exposure to formaldehyde vapor. Simultaneously, the embedded predictive safety collaboration module uses a digital twin model to predict future parameter trajectories faster than real-time, proactively intervening before danger occurs, upgrading traditional "post-event loss mitigation" to "pre-event prevention." Furthermore, by calculating the circulating pump cavitation risk index in real time and dynamically raising the liquid level interlock threshold, the system proactively increases the protection threshold and liquid level setpoint when the pump shows slight signs of cavitation, preventing pump damage and unplanned shutdowns from the source of the control strategy.

[0020] 3. This automatic circulating replenishment and concentration control system and method for formaldehyde absorption towers used in the polyoxymethylene (POM) production process achieves deep synergy at multiple levels: At the control level, when the concentration deviation is too large, the liquid level setpoint is automatically adjusted to allow for rapid concentration recovery; at the sensing and control level, evaporation losses are fed forward and added to the total replenishment demand, ensuring that the liquid level PID controller only handles minute dynamic deviations; at the diagnostic and control level, the system health index directly feeds back to correct controller parameters, automatically reducing gain when instruments drift, preventing system oscillations caused by suspicious signals; at the diagnostic and sensing level, adaptive factors collaboratively correct the evaporation model, calibrating material balance after eliminating leakage interference; at the execution level, the operating condition self-identifier automatically switches between fine-tuning of the metering pump and coarse-tuning of the high-flow valve based on the magnitude of the deviation; at the process level, the circulating pump frequency converter dynamically matches the optimal liquid-to-gas ratio based on the feed load. The organic integration of these synergistic mechanisms elevates the system from single-loop regulation to intelligent collaborative optimization across the entire system.

[0021] 4. This automatic circulating replenishment and concentration control system and method for formaldehyde absorption towers used in the polyoxymethylene (POM) production process quantifies the system's health index online by continuously comparing the cumulative replenishment volume with the theoretical consumption. It can trigger diagnostic alarms in the early stages, even when the leakage is as low as 0.2 m³ / h, allowing operators to promptly identify internal leaks. The predictive safety collaboration module performs safety verification before control commands are executed, providing constrained corrections to hazardous commands. The cross-section collaborative optimizer incorporates the real-time impurity content of the downstream trioxymethylene synthesis reactor into the optimization target, fine-tuning the setpoints online while meeting the liquid level safety constraints of this section. This creates a closed-loop collaboration between the formaldehyde absorption section and downstream quality control, ensuring the quality of the final product from the source. Furthermore, liquid level detection employs redundant configurations of radar level gauges and tuning fork switches, and concentration detection features periodic automatic sampling and laboratory chromatographic comparison and calibration, providing a reliable hardware foundation for intelligent diagnosis and interlocking protection. Attached Figure Description

[0022] In the attached diagram: Figure 1This is a schematic diagram of the method flow according to an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0024] Referring to the system architecture of this invention, an automatic circulating liquid replenishment and concentration control system for formaldehyde absorption towers used in the production process of polyoxymethylene mainly consists of a liquid storage and dual-path supply unit, a liquid level and concentration dual detection unit, an intelligent decoupling control unit, and an execution unit.

[0025] The liquid storage and dual-supply unit includes a 50m³ process water storage tank and a 30m³ concentrated formaldehyde storage tank, used to store demineralized water and a concentrated formaldehyde solution with a concentration of approximately 70%, respectively. The outlets of both tanks are connected to the absorption tower's circulating liquid pool via independent pipelines to provide makeup water and concentrated formaldehyde replenishment.

[0026] The dual detection unit for liquid level and concentration enables real-time sensing of key process parameters. Liquid level detection utilizes a high-frequency radar level gauge, providing a continuous 4-20mA level signal to the control unit. Redundant tuning fork switches are also included for independent high and low level interlock protection. Concentration detection employs an online near-infrared analyzer to measure the mass percentage concentration of formaldehyde in the main circulation pipeline in real time. An automatic sampler is also included, and the results are compared and calibrated with laboratory chromatographic analysis every 8 hours to ensure long-term measurement accuracy.

[0027] The intelligent decoupling control unit is the core of the entire system, and it contains the following functional modules: Liquid level controller: Based on the real-time liquid level L obtained from the dual detection unit and the preset liquid level setpoint L... SP deviation e L =L SP -L, through proportional-integral calculation, generates the total fluid replenishment demand signal F. total This signal represents the total fluid replenishment rate required to maintain the ideal fluid level.

[0028] Concentration controller: Based on the real-time concentration C and the preset concentration setpoint C SP deviation e C =C SP -C is used to generate a proportioning coefficient K between 0 and 1 through proportional-integral-differential operations. This coefficient represents the ideal proportion of concentrated formaldehyde supply required to adjust the concentration in the total replenishment solution.

[0029] Dynamic decoupling calculator: Receives total fluid replenishment requirement signal F total The decoupling operation is performed with the proportioning coefficient K, specifically according to the following formula:

[0030]

[0031] in, Instructions for replenishing concentrated formaldehyde flow. This calculation method, which provides process water replenishment flow instructions, ensures that the replenishment liquid maintains the liquid level while automatically and collaboratively correcting concentration deviations.

[0032] Self-diagnosis module: This is key to achieving intelligent operation and maintenance. This module continuously calculates an index η characterizing the system's health online. The calculation method is as follows: continuously accumulate the actual total replenishment of process water and concentrated formaldehyde over a period of time, and compare it with the theoretical formaldehyde absorption and consumption (converted to liquid volume) estimated based on the inlet air flow rate and concentration during the same period, calculated according to the following formula:

[0033] in, , These are the real-time replenishment flow rates for process water and concentrated formaldehyde, respectively. This is the liquid volume equivalent flow rate estimated based on the feed gas flow rate and concentration for formaldehyde absorption and consumption.

[0034] When η continuously exceeds a set threshold (e.g., 15%) and remains so for a period of time (e.g., 2 calculation cycles), the self-diagnostic module determines that there may be a system leak or instrument drift. At this time, it not only issues a diagnostic alarm but also works in deep coordination with the control process: proactively adjusting the gain of the concentration controller to reduce the response speed to concentration signals that may have deviations; or adjusting the proportional band of the level controller to make its regulation action smoother and avoid system oscillations caused by frequent compensation for suspected leaks.

[0035] The execution unit is responsible for implementing control commands. Both the process water and concentrated formaldehyde supply pipelines employ a unique configuration of parallel low-flow, high-precision metering pumps and high-flow, fast-acting regulating valves, all uniformly controlled by a condition self-identifier within the intelligent decoupled control unit. This identifier adjusts based on the rate of change in total replenishment demand. absolute value of concentration deviation The combinational logic automatically determines the current operating condition: Fine-tuning operating conditions: When and When the preset upper limit threshold is exceeded, the high flow rate regulating valve is quickly opened for rapid coarse adjustment, while the metering pump switches to auxiliary fine adjustment. After the deviation is reduced, the system smoothly switches back to the metering pump-dominated mode. This collaborative working mechanism of "coarse adjustment + fine adjustment" takes into account both the speed and accuracy of adjustment.

[0036] Furthermore, when the operating condition self-identifier determines that the feed gas load has changed significantly, it will also dynamically adjust the frequency converter of the main circulation pump based on the ideal liquid-gas ratio calculated in real time, thereby optimizing the main circulation flow rate F. out This allows for optimal matching between fluid replenishment regulation and absorption mass transfer efficiency.

[0037] To further enhance the overall performance of the system, this embodiment also embeds modules with other collaborative functions: An evaporation loss dynamic compensation module is added, which collects the tail gas temperature T at the top of the absorption tower. top Circulating fluid temperature T liq and exhaust gas flow rate G vent Using a model based on the Antoine equation and mass transfer principle, the evaporation loss F is calculated in real time. evap The estimation model is as follows:

[0038] in, For temperature The partial pressure of saturated water vapor under certain conditions can be obtained using the Antoine equation; The partial pressure of water vapor in the gas phase at the top of the tower can be approximately calculated from the temperature and humidity of the tail gas or the tail gas flow rate and water balance. The mass transfer coefficient is obtained by regression analysis based on historical operating data and can be used to... and Online dynamic correction; This is an adaptive factor, with an initial value of 1.

[0039] Calculated This is directly fed forward and superimposed into the total fluid replacement demand signal; more importantly, the aforementioned self-diagnostic module will use the adaptive factor... The parameters of the evaporation estimation model are corrected online. After the self-diagnostic module eliminates the leak, the residual material imbalance can be used to refine the evaporation model, and vice versa. The two work together to ensure the long-term accuracy of material balance.

[0040] A predictive safety collaboration module has been added: This module embeds a concentrated digital twin model consisting of the material and component dynamic equations of the tower. Its core dynamic equations can be simplified to:

[0041]

[0042] Where A is the cross-sectional area of ​​the tower, and M is the total number of moles of liquid in the tower. and These represent the equivalent flow rate of liquid carried over from the gas phase and the molar flow rate of formaldehyde, respectively. To replenish the concentration of concentrated formaldehyde, This is the outlet flow rate of the circulating pump.

[0043] The model takes current supply flow and intake conditions as inputs and continuously simulates future conditions in the controller backend at a speed several times faster than the actual process. The module measures the liquid level trajectory L(t) and concentration trajectory C(t) within minutes. Once it predicts that the future trajectory will exceed the preset safety interlock threshold, the module immediately treats "avoiding limit triggering" as a hard constraint and passes it "backward" to the dynamic decoupling calculator. At this time, the generation of the total replenishment demand signal and the ratio coefficient will prioritize meeting the safety constraint, realizing a leap from "post-event response" to "pre-event prevention" in safety concepts.

[0044] Furthermore, this embodiment introduces a circulating pump health status sensing and liquid level safety collaborative protection mechanism based on the predictive safety collaborative module. The main circulating pump inlet pipe of the execution unit is equipped with a pressure transmitter, and the pump body is equipped with a vibration sensor. It also monitors the pump motor current. The intelligent decoupling control unit is based on the inlet pressure. Vibration value Current And the calculation of cavitation risk index based on liquid level L Its functional relationship can be expressed as:

[0045] In practice, the degree to which each variable deviates from its normal range can be weighted and summed to obtain the result. Subsequently, the system is based on Dynamically generate liquid level interlock threshold :

[0046] in, The preset fixed low-low liquid level interlock threshold, This is a preset positive proportional coefficient. This means that when the pump shows slight signs of cavitation, the protection threshold will be actively raised even if the liquid level has not yet reached the hard interlock value. Simultaneously, when... When the level rises, the liquid level setpoint The total fluid replacement requirement was also forcibly increased. The lower limit of output is raised, and water replenishment is forcibly increased from the source of the control strategy to quickly escape the danger zone.

[0047] This system also includes a cross-process collaborative optimizer, which obtains the real-time impurity content of the downstream paraformaldehyde synthesis reactor through standard industrial communication protocols. The state parameters are such that the liquid level L in this absorption tower is within the safe limit. and The internal parameters are hard constraints that must be met; the optimizer will make slight adjustments to the system's liquid level setpoint online. and concentration set value The adjusted objective function aims to minimize the downstream impurity content, and its multi-objective optimization model is expressed as:

[0048]

[0049] in, This is the initial default concentration setting. and The preset weighting coefficients, based on process requirements, are used to balance the two objectives of maintaining concentration and suppressing impurities. For example, when the downstream impurity content shows an increasing trend, the optimizer may, within the allowable range, adjust the formaldehyde concentration setpoint towards a more economical fine-tuning value, achieving closed-loop collaborative optimization across different processes.

[0050] The workflow of the automatic circulating fluid replenishment and concentration control method of the present invention is described in detail below: S1. Real-time data acquisition: After the system is powered on and initialized, it continuously and stably acquires the circulating liquid level L and formaldehyde concentration C signals from the dual detection unit. At the same time, it obtains parameters such as upstream air flow rate and concentration, as well as real-time impurity content Imp and other status parameters from the device DCS through the system integration interface.

[0051] S2, Core Decoupling Calculation: This is the core decision-making process of this method. Inside the intelligent decoupling control unit, the level controller calculates the liquid level deviation... Generate the current total fluid replenishment requirement. The concentration controller is based on the concentration deviation. The matching coefficient K is generated. Subsequently, these two values ​​are fed into the dynamic decoupling calculator.

[0052] S3. Cooperative Instruction Generation: The dynamically decoupled calculator generates total fluid replenishment requirements according to fixed logic. Co-decomposition into concentrated formaldehyde supply flow instructions Process water supply flow instructions :

[0053]

[0054] S4. Multi-source information collaborative correction: This step is synchronized with or continues to run before step S2, reflecting multi-dimensional collaboration.

[0055] Evaporation Synergy: The dynamic compensation module for evaporation loss is based on the formula. The evaporation loss is calculated in real time and directly fed forward and added to the total make-up liquid requirement. This allows for more proactive control of the liquid level.

[0056] Diagnostic Collaboration: The self-diagnosis module calculates the system's health index online. It is used to adaptively correct the control parameters of the level controller and concentration controller in real time, for example, automatically reducing the gain of the concentration controller when the indicator instrument is drifting due to a continuously high η.

[0057] Pump safety coordination: Continuously collect inlet pressure of circulating pump and pump body vibration ,according to Calculate the cavitation risk index, once Upon elevation, the system performs two actions: Firstly, according to Dynamically increase the liquid level interlock threshold; Secondly, forcibly increase the liquid level setpoint. And increase total fluid replacement requirements. The lower limit of the output is used to prevent pump cavitation damage from the source of the control strategy.

[0058] Cross-process collaboration: downstream reactor status parameters Included in multi-objective optimization model Under the condition of meeting the liquid level safety constraints Under the given conditions, the liquid level setpoint is obtained through online solution. and concentration set value This is for use in step S2.

[0059] S5. Predictive Security Verification and Execution: Before sending the final supply flow command to the execution unit, the embedded digital twin model follows dynamic equations. and Conduct a "safety rehearsal" to examine the future after executing the current instruction on a hyperreal-time time scale. The parameter trajectory within the time period. If the pre-simulation results indicate safety, the command is directly issued to the execution unit. If the pre-simulation results indicate that a safety interlock threshold will be triggered in the future, the system will modify the calculated command with safety constraints before issuing the modified safety command. Under the scheduling of the operating condition self-identifier, the metering pumps and regulating valves in the execution unit coordinate and accurately complete the material replenishment.

[0060] Through the above system and method, this invention upgrades the control of liquid level and concentration from passive and isolated correction to proactive, collaborative, and predictive intelligent closed-loop management, comprehensively improving the stability, safety, and economy of the polyoxymethylene formaldehyde absorption process.

[0061] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower, characterized in that, include: Liquid storage and dual-supply unit, liquid level and concentration dual detection unit, intelligent decoupling control unit and execution unit; The liquid storage and dual-supply unit is used to store and supply process water and concentrated formaldehyde solution respectively, as a source of replenishment for adjusting the liquid level and concentration of the absorption tower circulating liquid. The dual detection unit for liquid level and concentration is used to detect the liquid level and formaldehyde concentration of the circulating liquid in the absorption tower in real time and continuously, and to provide measurement signals to the intelligent decoupling control unit. The intelligent decoupling control unit includes: A level controller is used to generate a total replenishment demand signal based on the deviation between the setpoint and the real-time level. A concentration controller is used to generate a mixing ratio coefficient based on the deviation between the concentration setpoint and the real-time concentration. A dynamic decoupling calculator is used to convert the total replenishment demand signal into process water replenishment flow instructions and concentrated formaldehyde replenishment flow instructions based on the ratio coefficient. The intelligent decoupling control unit also includes a self-diagnostic module based on material balance. The self-diagnostic module is used to calculate an index η that characterizes the health of the system, and dynamically adjust the control parameters of the level controller and / or concentration controller according to the index η.

2. The automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower according to claim 1, characterized in that, It also includes a dynamic compensation module for evaporation loss; The dynamic compensation module for evaporation loss is used to collect the temperature of the tail gas at the top of the absorption tower, the temperature of the circulating liquid, and the tail gas flow rate, and to calculate the real-time evaporation loss F. evap The real-time evaporation loss F evap It is fed forward and superimposed onto the total fluid replenishment demand signal; The self-diagnostic module is also used to use adaptive factors. The model parameters of the dynamic compensation module for evaporation loss are corrected online to eliminate the impact of liquid level deviation separated by leak diagnosis on evaporation estimation.

3. The automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower according to claim 1, characterized in that, It also includes a predictive safety collaboration module, which embeds a concentrated digital twin model. The digital twin model is used to simulate the liquid level and concentration trajectory over a future period of time on a faster-than-real-time timescale, using the current replenishment flow rate and air intake conditions as input. When the simulated trajectory is about to trigger a preset safety interlock threshold, the intelligent decoupling control unit adds a hard constraint to avoid triggering the safety interlock threshold when generating the total replenishment demand signal and the ratio coefficient.

4. The automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower according to claim 3, characterized in that, The execution unit includes a main circulation pump, the inlet pipe of which is equipped with a pressure transmitter, and the pump body is equipped with a vibration sensor. The intelligent decoupling control unit is also used to calculate the cavitation risk index R based on the signals from the pressure transmitter and vibration sensor. cav Based on the cavitation risk index R cav The liquid level interlock threshold and the liquid level setpoint in the predictive safety collaboration module are dynamically increased.

5. The automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower according to claim 1, characterized in that, It also includes a cross-process collaborative optimizer, which obtains the real-time status parameters of the downstream paraformaldehyde synthesis reactor through the system integration interface unit, and fine-tunes the liquid level setpoint and concentration setpoint online with the liquid level safety of this process as a constraint and the optimization goal of minimizing the impurity content of the downstream reaction or maximizing the conversion rate.

6. The automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower according to claim 1, characterized in that, In the execution unit, the process water supply pipeline and the concentrated formaldehyde supply pipeline each contain a parallel small-flow high-precision metering pump and a large-flow fast regulating valve. The intelligent decoupling control unit also includes a condition self-identifier, which is used to control the alternating or coordinated operation of the metering pump and the fast regulating valve based on the rate of change of total replenishment demand and the absolute value of concentration deviation.

7. The automatic circulating liquid replenishment and concentration control system for a formaldehyde absorption tower according to claim 6, characterized in that, The operating condition self-identifier is also used to control the frequency converter of the main circulation pump, and calculates the optimal liquid-gas ratio in real time based on the feed gas load to adjust the main circulation flow rate F. out .

8. A method for automatic circulating replenishment and concentration control of formaldehyde absorption tower in polyoxymethylene production process, employing the automatic circulating replenishment and concentration control system for formaldehyde absorption tower as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Real-time acquisition of circulating liquid level L and formaldehyde concentration C, as well as upstream air intake parameters and downstream reactor status parameters; S2. In the level controller, the total replenishment requirement F is calculated based on the deviation between the liquid level L and the set liquid level value. total In the concentration controller, the proportioning coefficient K is calculated based on the deviation between the concentration C and the set concentration value. S3, the total fluid replenishment requirement F total The process water supply flow rate command F is output from the input dynamic decoupling calculator along with the ratio coefficient K. water and concentrated formaldehyde supply flow instruction F formalin ; S4. The total fluid replenishment requirement F is generated. total Before or simultaneously with the ratio coefficient K, the real-time evaporation loss F calculated by the dynamic evaporation loss compensation module is received. evap The system health index η calculated by the self-diagnosis module is fed back to compensate for the total fluid replenishment requirement and to adaptively correct the control parameters of the liquid level controller and concentration controller, respectively. S5. Execute the process water replenishment flow rate command and the concentrated formaldehyde replenishment flow rate command, and use the embedded digital twin model to verify whether the future liquid level and concentration trajectory after execution is safe in a way that is faster than real-time. If the predicted trajectory will trigger the preset safety interlock threshold, then correct the command and execute it again.

9. The method for automatic circulating replenishment and concentration control of formaldehyde absorption tower in polyoxymethylene production process according to claim 1, characterized in that, Between steps S2 and S4, the following is also included: continuously calculating the cavitation risk index R of the circulating pump. cav When the cavitation risk index R cav When the level rises, the liquid level setpoint is forcibly increased, and the total replenishment requirement F is also increased. total The lower bound for generation.

10. The method for automatic circulating replenishment and concentration control of formaldehyde absorption tower in polyoxymethylene production process according to claim 8, characterized in that, The downstream reactor state parameters received in step S1 include impurity content feedback, and step S2 also includes constructing a multi-objective optimization model. ,in The initial concentration setpoint is given, and Imp represents the downstream impurity content. , These are the weighting coefficients; The liquid level setpoint and concentration setpoint are obtained online by the optimization model under the condition of satisfying the liquid level safety constraint.

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