Advanced control system and method for azeotropic distillation dehydrating tower of purified terephthalic acid device

Abstract

The invention discloses an advanced control system and method for an azeotropic distillation dehydrating tower of a purified terephthalic acid device, which are applied to the overall optimization control of a dehydrating tower system and comprise a dehydrating tower system, a DCS (Distributed Control System), an OPC (Optical Product Control) server, an advanced control system and a display feedback system. The method comprises the following steps: acquiring real-time operation data through a dehydrating tower system, and sending the data to a DCS (Distributed Control System); the DCS control system transmits the real-time data to an OPC server; the OPC server periodically transmits historical data and real-time data to the advanced control system; the advanced control system performs control instruction optimization according to the received data and feeds back an optimization result to the DCS control system; the DCS control system carries out control variable adjustment in the tower according to a feedback result; and operating variables and control variables of the three towers are coordinated through a predictive control model, a pressure correction temperature soft measurement model and a dehydration section controller model. The interaction among a plurality of towers is coordinated, the equipment stability is improved, the energy consumption is reduced, and the material loss is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of multivariable control technology, and in particular to an advanced control system and method for an azeotropic distillation dehydration tower of a purified terephthalic acid device. Background Art

[0002] Conventional PID control has many limitations in multi-tower systems (such as dehydration towers, PX extraction towers, and recovery towers), especially when dealing with complex coupled multivariable systems. Conventional PID control is usually based on one-to-one local control, and when fluctuations occur, operators need to manually adjust multiple PID loops. Due to signal lag, feed changes, and operational complexity, traditional control methods often lead to system instability, increased energy consumption, and reduced production efficiency.

[0003] Therefore, a more intelligent and automated control method is needed to coordinate the relationships among multiple towers, maintain the overall optimization of the system, reduce energy consumption and improve material recovery efficiency. Summary of the invention

[0004] In response to the above technical problems, the present application solves the problems in the prior art, such as traditional PID control signal lag, feed variation and operation complexity, and traditional control methods often lead to system instability, increased energy consumption and affected production efficiency.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted in this application is: on the one hand, an advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid unit is applied to the overall optimization control of the dehydration tower system, and the system comprises:

[0006] A dehydration tower system, which includes a dehydration tower, a PX extraction tower and a recovery tower, each tower having independent operating variables and control variables;

[0007] DCS control system, used to receive and send real-time data and instructions, control the operation of the dehydration tower system, and save the real-time data to the DCS database;

[0008] OPC server, used to exchange data with the DCS database and periodically send the received real-time data to the advanced control system;

[0009] Advanced control system, which is used to compare the historical data received from the OPC server with the real-time data, optimize the control instructions, and adjust the operating variables through the control variables to achieve system optimization;

[0010] Display feedback system, used to display the comparison results of the advanced control system and feed back to the DCS control system;

[0011] The advanced control system includes a data storage module, a prediction model operation processor, an advanced control database, and a weight sorting and operation control optimization module.

[0012] In order to better realize the present invention, further, the three towers of the dehydration tower system: the dehydration tower, the PX extraction tower and the recovery tower are coupled with each other, and the operating variables in the tower are coordinated through multivariable control technology to ensure the overall optimized operating conditions and achieve the lowest steam consumption and the highest material recovery efficiency.

[0013] In order to better implement the present invention, further, the advanced control system includes the following control model:

[0014] The pressure-corrected temperature soft measurement model ensures that the temperature at the measuring point can accurately represent the distribution of components in the tower through the relationship between the corrected temperature and pressure;

[0015] Predictive control model, by modeling the relationship between the operating variables and the control variables, predicting the future trend of the control variables, and adjusting the operating variables in real time through the optimization algorithm to achieve the optimal state of the system;

[0016] The dehydration section controller model uses multivariable control technology to replace traditional PID control to achieve unified and coordinated optimization of the dehydration tower, PX extraction tower and recovery tower.

[0017] In order to better implement the present invention, further, the pressure correction temperature soft measurement model is expressed by the formula:

[0018] Corrected temperature = temperature before correction + pressure coefficient × (pressure - reference pressure);

[0019] The pressure coefficient is set according to the specific characteristics of different temperature measurement points to accurately correct the temperature data in the tower.

[0020] In order to better realize the present invention, further, the predictive control model is used to calculate the future optimal state of the system, and make real-time corrections based on deviations in the actual operation process to ensure that the dehydration tower, PX extraction tower and recovery tower always operate under optimized operating conditions.

[0021] In order to better realize the present invention, further, the dehydration section controller model controls the temperature profile of the dehydration tower and the water concentration at the bottom of the tower through range control technology, and predicts the change of water concentration through a feedforward model, thereby avoiding the influence of the lag signal on the control effect.

[0022] In order to better realize the present invention, further, the DCS control system includes monitoring and adjustment functions of the dehydration tower (D601), the NPA recovery tower (D631) and the PX extraction tower (D651), which can monitor the key control points in the tower in real time, such as temperature, pressure, liquid level, etc., and transmit the data in real time to the DCS database for storage and exchange.

[0023] In order to better implement the present invention, further, the display feedback system displays the operating status of each tower of the dehydration tower system in real time according to the optimization results received from the advanced control system, and feeds back to the DCS control system to ensure that the operator adjusts the control strategy in time.

[0024] In order to better implement the present invention, further, the commissioning mechanism of the advanced control system includes:

[0025] The main controller can be put into use manually by the operator when the communication between DCS and advanced control system is normal, and the advanced control system can be enabled for real-time control;

[0026] Loop commissioning conditions: When the DCS meets the preset operating conditions and the main controller has been commissioned, the DCS can request to commission the loop of the advanced control system;

[0027] Commissioning failure judgment: If the commissioning signal from the advanced control system is not received within the predetermined time (within 30 seconds), the DCS will judge that the commissioning has failed and maintain the current control state.

[0028] In order to better implement the present invention, further, the advanced control system setting value adopts the following rules:

[0029] Set value change control: when the difference between the advanced control system set value of the current cycle and the set value of the previous cycle exceeds the set threshold, the set value of the previous cycle is kept in use to prevent large fluctuations from affecting system stability;

[0030] Direct control mode, when the advanced control system directly controls the operating variable (such as a valve),

[0031] When the system is not in use, the DCS control system will use the control value given by the DCS, and when the advanced control system is in use, it will switch to the control value provided by the advanced control system;

[0032] The optimization module comprehensively considers the operating data and historical data of the dehydration tower, PX extraction tower and recovery tower to perform overall coordinated optimization, ensuring that the three towers are always in optimal operating conditions and achieving efficient use of energy and materials.

[0033] In order to achieve the above-mentioned purpose, the technical solution adopted in the present application is: an advanced control method for the azeotropic distillation dehydration tower of a purified terephthalic acid device, the control method comprising the following steps:

[0034] Step 1. Obtain real-time operation data through the dehydration tower system and send the data to the DCS control system;

[0035] Step 2. The DCS control system transmits real-time data to the OPC server;

[0036] Step 3. The OPC server periodically transmits historical data and real-time data to the advanced control system;

[0037] Step 4. The advanced control system optimizes the control instructions according to the received data and feeds back the optimization results to the DCS control system;

[0038] Step 5. The DCS control system adjusts the control variables in the tower according to the feedback results to achieve overall optimization of the entire dehydration tower system;

[0039] This also includes coordinating the operating variables and control variables of the three towers through predictive control models, pressure correction temperature soft measurement models and dehydration section controller models to achieve optimal operating conditions within the towers; the system automatically adapts to load changes and component changes to ensure that the system is always in the best operating state, avoiding errors and system fluctuations caused by manual adjustments, significantly improving production efficiency and reducing energy consumption.

[0040] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0041] 1. Compared with the traditional PID control technology, the advanced control system based on multivariable control technology of the present invention has significant advantages in processing complex dehydration tower systems (including dehydration towers, PX extraction towers and recovery towers). Specifically, the advanced control system can not only coordinate the interaction between multiple towers and perform system-level optimization, but also effectively improve the stability of the equipment, reduce energy consumption, and reduce material losses.

[0042] 2. The traditional PID control system of the present invention is usually local control, which often fails to fully consider the multivariable relationship of the entire dehydration tower system, resulting in difficulty in coordination between various control loops. Once the system fluctuates, the operator needs to manually adjust the set values ​​of multiple PID loops, which is not only cumbersome but also prone to human errors, resulting in poor system stability and increased energy consumption. The advanced control system can optimize the control as a whole, by acquiring data from multiple towers in real time and conducting comprehensive analysis, so that the three towers (dehydration tower, PX extraction tower, recovery tower) are always maintained in the optimal operating state during the dynamic change process. This overall optimization can effectively avoid the shortcomings of local control, ensure stable operation of the equipment, and reduce unnecessary fluctuations.

[0043] 3. The present invention often leads to excessive steam consumption and low material recovery efficiency in traditional PID control due to its control limitations. In particular, when operating conditions change or load fluctuates, PID control may not respond in time, resulting in lag and misadjustment of the control loop. The advanced control system adopts multivariable control technology, which not only considers the mutual influence of various operating variables in the tower, but also adjusts the control strategy through accurate prediction models to minimize steam consumption and improve material recovery rate. The system can automatically adapt to load changes and composition fluctuations to ensure that the dehydration tower, PX extraction tower and recovery tower are always in optimal operating conditions, thereby reducing energy consumption and minimizing material losses.

[0044] 4. Another key advantage of the present invention is that by establishing a pressure-corrected temperature soft measurement model and a predictive control model, the composition distribution and temperature changes in the tower can be controlled more accurately. The traditional PID control system relies on a fixed set point for temperature control. However, due to the constant changes in the feed flow and composition of the dehydration tower and the recovery tower, this method has inherent defects. The intelligent control system dynamically adjusts the control strategy, combines real-time data with historical data, and ensures that the temperature control is more accurate and dynamically adaptable through the temperature correction model and the temperature feedback after pressure correction. Especially for complex systems with multiple feeds such as dehydration towers, the pressure-corrected temperature soft measurement model can adjust the temperature set value according to the actual pressure changes, thereby effectively avoiding the temperature control error caused by pressure fluctuations.

[0045] 5. The feedforward control function of the advanced control system of the present invention can respond to changes in the system in advance. In traditional PID control, the system can only be adjusted after the deviation occurs, which may cause a delayed response. In the intelligent control system, the feedforward model can predict the changing trend of variables such as water concentration in real time, so as to adjust the operating parameters in advance and avoid delayed feedback response. This advance prediction capability can significantly improve the operational stability of the dehydration tower, PX extraction tower and recovery tower, and reduce the need for human intervention.

[0046] 6. The advanced control system of the present invention can not only conduct in-depth analysis of historical data, but also automatically adjust and optimize according to changes in real-time data. When the system load changes or the components fluctuate, traditional PID control often requires manual re-adjustment of multiple parameters, and it is difficult to ensure stability. The intelligent control system can automatically adapt to such changes and make rapid and accurate adjustments, avoiding the lag and errors of manual intervention. This adaptive adjustment function not only improves the operating efficiency of the equipment, but also effectively avoids energy waste caused by load fluctuations.

[0047] 7. The advanced control system of the present invention uses predictive control, pressure correction and multivariable control technology to make the entire dehydration system have higher operating stability. Different from the locality and hysteresis of PID control, the intelligent control system can reflect the relationship between the various operating variables and the target variables of the system in real time, and correct potential abnormalities or fluctuations in advance, so as to ensure that the variables such as temperature, pressure and liquid level in the tower are always maintained within a safe and effective range. In addition, the flexibility of the system enables it to cope with complex operating scenarios, such as load changes, raw material fluctuations, etc., without the need to frequently adjust the control strategy.

[0048] 8. Under the traditional PID control of the present invention, the operator needs to adjust the parameters of each PID loop in real time according to the fluctuation of the system. This not only increases the workload of the operator, but also easily causes system fluctuations due to human errors. The advanced control system greatly reduces the burden on the operator by automatically adjusting and optimizing the control loop. The operator only needs to intervene when the system status is abnormal, and there is no need to continuously monitor each PID loop, thereby improving operational efficiency and reducing the probability of human operational errors.

[0049] 9. The advanced control system of the present invention enables each part of the system to efficiently share information and data through the close cooperation of the DCS control system, OPC server and feedback display system. The DCS system monitors the status of the dehydration tower, recovery tower and PX extraction tower in real time, and exchanges data and provides feedback with the advanced control system. Through this integration, the operator can obtain more accurate operating data and real-time feedback, which facilitates faster decision-making and reduces control errors caused by information lag.

[0050] 10. The intelligent control system of the present invention also has stronger fault warning and automatic recovery capabilities. During the operation of the system, if any key parameter of any tower is abnormal, the advanced control system can timely detect potential faults through real-time monitoring and data analysis, and issue early warning signals. At this time, the system can adopt appropriate adjustment strategies to avoid the expansion of the fault, and automatically perform recovery operations to ensure the safety and stable operation of the entire system.

[0051] 11. Compared with the traditional PID control system, the advanced control system of the present invention can realize the overall optimization and precise control of the dehydration tower system through multivariable control technology. It can not only effectively coordinate the interaction between the dehydration tower, PX extraction tower and recovery tower, improve the stability of the system, but also reduce energy consumption and material loss, and improve the adaptability and flexibility of the system through predictive control and feedforward control technology. Ultimately, the intelligent control system will bring higher operating efficiency, lower energy consumption, less material loss and longer equipment life. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative labor.

[0053] Figure 1 The present invention is a flowchart of an advanced control system and method for an azeotropic distillation dehydration tower of a purified terephthalic acid device;

[0054] Figure 2 It is a schematic diagram of the bottom temperature of D601 tower in the advanced control system and method of the azeotropic distillation dehydration tower of the purified terephthalic acid device of the present invention;

[0055] Figure 3 It is a schematic diagram of the top temperature of D601 in the advanced control system and method of the azeotropic distillation dehydration tower of the purified terephthalic acid device of the present invention;

[0056] Figure 4 It is a schematic diagram of the COD index of the bottom of D631 in the advanced control system and method of the azeotropic distillation dehydration tower of the purified terephthalic acid device of the present invention;

[0057] Figure 5 It is a schematic diagram of the steam unit consumption (calculated based on reflux) of the D601 tower in the advanced control system and method of the azeotropic distillation dehydration tower of the purified terephthalic acid unit of the present invention. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0059] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0060] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0061] In the description of this application, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the application is usually placed when in use. It is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on this application. In addition, if the terms "first", "second", etc. appear in the description of this application, they are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0062] In addition, if the terms "horizontal" or "vertical" appear in the description of this application, it does not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0063] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0064] Embodiment 1:

[0065] like Figures 1 to 5As shown: The present invention discloses an advanced control system (APC) that utilizes the advantages of multivariable control technology to replace the original conventional PID control, comprehensively considers three towers (dehydration tower, PX (paraxylene) extraction tower and recovery tower), coordinates the relationship between various parameters, optimizes the whole, improves the operation stability of the device, and achieves the purpose of reducing energy consumption. It is preset to collect historical data, and the control model is established using the Aspen DMC P l us advanced process control system through the historical data.

[0066] The advanced control system includes a dehydration tower system, a DCS control system, a DCS database, an OPC server, an advanced control system, and a display feedback system.

[0067] Among them, the dehydration tower system reads real-time data and sends it to the DCS control system, and the DCS control system issues instructions to control and adjust the dehydration tower system; the DCS control system saves and retrieves the received real-time data in the DCS database; the OPC server and the DCS database exchange data with each other; the OPC server reads the data in the DCS database and calculates 60 seconds as a cycle, and then sends it to the advanced control system. At the same time, the advanced control system will compare the historical data retrieved from the DCS database by the OPC server with the real-time data detected by the advanced control system, and optimize the adjustment instructions after comparison; the advanced control system exchanges the comparison results with the display feedback system data; the display feedback system displays the comparison results received from the advanced control system and feeds them back to the DCS control system.

[0068] in,

[0069] Dehydration tower system Dehydration tower, PX (paraxylene) extraction tower and recovery tower. NPA is used as entrainer.

[0070] The separation of water and acetic acid is achieved by using the azeotropic principle;

[0071] The PX extraction tower extracts the PX in the dehydration tower to avoid PX accumulation and affect the efficiency of the dehydration tower;

[0072] The function of the recovery tower is to recover methyl acetate (MA) and entrainer in wastewater and reduce the loss of entrainer.

[0073] The dehydration tower (D601), PX extraction tower (D651) and recovery tower (D631) of the dehydration system are an organic whole, which influence each other and are seriously coupled. For the control of the dehydration system, conventional PID is basically one-to-one local control.

[0074] When fluctuations occur, operators need to adjust the set values ​​of multiple PID loops at the same time. However, in practice, it is difficult for operators to make timely and accurate judgments and coordination, which causes fluctuations in the device and affects energy consumption and material recovery efficiency. The advanced control system optimizes the overall control of the dehydration system, so that the three towers are always in overall optimized operating conditions, which can not only ensure that the acetic acid at the top of the tower does not exceed the standard, but also ensure that the entrainer does not enter the bottom of the tower, so as to minimize the overall steam consumption, minimize the loss of acetic acid and entrainer, and automatically adapt to load changes and composition changes.

[0075] The temperature profile of the dehydration tower is controlled by adjusting the reflux flow rate through the PID automatic control loop of the azeotropic layer. This control design has fatal flaws. We know that the dehydration tower has multiple feeds, and the flow and composition of each feed are constantly changing. Therefore, the azeotropic layer cannot be fixed at a certain position. The conventional PID automatic control fixes the azeotropic position, which will inevitably cause unnecessary reflux flow adjustment and bring artificial control disturbance to the dehydration tower. The lower part of the dehydration tower is a temperature PID control loop. The operator sets the temperature according to the water concentration analysis value at the bottom of the tower, and the loop automatically adjusts the steam volume. Since the pressure of the tower is in a floating state, at a certain water concentration, this temperature should also be dynamic. Therefore, fixing its set value will inevitably cause incorrect adjustment of the steam flow, resulting in control interference, making it difficult for the dehydration tower to stabilize.

[0076] The design of the temperature profile control of the distillation section of the recovery tower is similar to that of the dehydration tower. When the condensation capacity is sufficient, this control scheme has good performance; however, when the condensation capacity is insufficient, simply adjusting the methyl acetate extraction rate will deteriorate the operation of the tower and cause the dehydration tower pressure to increase.

[0077] The dehydration system involves three towers. In addition to the above-mentioned single-loop control defects, the entire system must improve the control level and coordinate the three towers to keep the system in an optimized state for a long time. If only a single loop control is emphasized, it will often lose sight of one thing while focusing on another, resulting in low dehydration efficiency and increased steam consumption. Overall coordination and optimization is the difficulty of dehydration system control.

[0078] in,

[0079] The DCS control system includes a dehydration tower (D601), an NPA recovery tower (D631), and a PX extraction tower (D651).

[0080] The advanced control system includes a data storage module, a prediction model operation processor, a database for advanced control, and weight sorting and operation control

[0081] Optimize module.

[0082] In the dehydration tower (D601), the preset key control point temperature, tower pressure and bottom liquid level of the dehydration tower are detected; in the NPA recovery tower (D631), the preset key control point material ratio, recovery tower temperature, recovery tower pressure and bottom liquid level of the recovery tower are detected; in the PX production tower (D651), the preset key control point temperature, bottom liquid level and tower pressure of the PX production tower are detected.

[0083] The display feedback system is used to display the results and feed back to the DCS control system.

[0084] The prediction model operation processor includes a pressure correction temperature soft measurement model, a prediction control model and a dehydration section controller model.

[0085] 1. Pressure-corrected temperature soft measurement model: In order to accurately control the distribution of components in the tower, the component distribution in the tower is modeled, and a pressure-corrected temperature model is established for key temperature measurement points, so that the temperature after pressure correction can truly represent the composition of the temperature measurement point. The model formula is:

[0086] Corrected temperature = uncorrected temperature + pressure coefficient × (pressure - reference pressure).

[0087] 2. Predictive control model, establish the correlation model of operating variables and control variables, predict the future trend of control variables through the state of the system and the action of the operating variables. Through the optimization algorithm, calculate the future optimal state of the system and the optimal action of the operating variables required to achieve the optimal state, and make real-time corrections based on the deviation between the prediction and measurement results.

[0088] The temperature after pressure correction is used as the control variable of the model. It can better reflect the changes in components in the system than the temperature before correction, making the control more precise.

[0089] 3. Dehydration section controller model. The main tower, PX extraction tower and recovery tower of the dehydration system all have azeotropic characteristics. The temperature profiles all control the azeotropic position. By taking advantage of the multivariable control technology, the PID control of the original design is replaced, and the temperature control is better achieved through range control. For example, a certain temperature in the middle of the dehydration tower is controlled within the range of 96 to 101°C. Although there is online analysis of the water concentration at the bottom of the dehydration tower, the signal is still lagging. Using the feedforward model to predict the change of water concentration in advance can improve the water concentration control.

[0090] Among them, the temperature points for pressure correction include key temperature measurement points such as the pre-tower bottom temperature, the pressure tower sensitive temperature, the atmospheric tower sensitive temperature, the atmospheric tower bottom temperature, the recovery tower top temperature and the recovery tower bottom temperature, so as to realize the control of the component distribution profile in each tower on this basis. The pressure correction coefficient is shown in Table 1.

[0091] Table 1. Pressure correction coefficients for key temperature measurement points

[0092] Serial number Correction temperature Temperature bit number Pressure level Pressure coefficient 1 Dehydration tower middle temperature PCT TI_06110 PI_06203 -160 2 Dehydration tower middle temperature PCT TI_06111 PI_06203 -160 3 Dehydration tower lower temperature PCT TI_06116 PI_06117 -160

[0093] The controller model structure is shown in Table 2, and the control model matrix is ​​shown in Figure 1 .

[0094] Table 2. Controller structure

[0095]

[0096]

[0097] Table 3. Comparison of key indicators

[0098]

[0099] Table 4. Comparison of steam consumption per unit of D601

[0100]

[0101] Compared with the previous baseline, at 95.028% load, the baseline value of FT-06226 is 364.658 tons / hour. Selecting data with similar load (greater than 93%), the improved value of FT-06226 is 348.86 tons / hour. According to the agreed calculation formula, the steam consumption is reduced: (364.658-348.86)÷=3.95 tons / hour. Based on the steam price of 250 yuan / ton, it can bring about 7.9 million yuan of economic benefits per year based on 8,000 hours per year.

[0102] If compared with the latest plant operation conditions, according to Table 4, each ton of PTA can save 0.721-0.673=0.048 tons of steam. Based on an annual output of 1 million tons of PTA, the steam price is the same as above, which can bring economic benefits of 0.048×100×250=12 million yuan per year.

[0103] The specific composition analysis is as follows:

[0104] Control system structure

[0105] The advanced control system consists of the following modules:

[0106] 1.1. The dehydration tower system (D601), PX extraction tower system (D651) and recovery tower system (D631) use sensors to monitor key process parameters such as temperature, pressure, liquid level, etc. in the tower in real time, and send these data to the DCS control system.

[0107] 1.2.DCS control system: The DCS system receives real-time data from the dehydration tower, PX extraction tower and recovery tower, generates control instructions and sends them to each tower. The DCS control system also saves historical data and exchanges information with the OPC server.

[0108] 1.3.OPC server: As a data bridge between the DCS control system and the advanced control system, the OPC server is responsible for reading the historical data in the DCS database and transmitting the data to the advanced control system according to a preset period (for example, 60 seconds).

[0109] 1.4. Advanced control system: After receiving the historical data from the OPC server, the advanced control system uses the preset control model for analysis and optimization, outputs adjustment instructions to the DCS system, and feeds back the optimization results to the display feedback system.

[0110] 1.5. Display feedback system: This system is used to display the optimization results output by the advanced control system and feed the results back to the DCS system for real-time monitoring by the operator.

[0111] Control Model and Optimization

[0112] The control system of the present invention mainly includes the following optimization control models:

[0113] 2.1. Pressure Correction Temperature Soft Measurement Model: This model accurately measures the temperature inside the tower by correcting the pressure of the dehydration tower, recovery tower, etc. The model formula is:

[0114] Corrected temperature = temperature before correction + pressure coefficient × (pressure - reference pressure);

[0115] The pressure coefficient is set according to the specific characteristics of different temperature measurement points to accurately correct the temperature data in the tower.

[0116] The function of this model is to accurately adjust the temperature inside the tower, thereby achieving precise control of the distribution of components in the tower.

[0117] 2.2. Predictive control model: This model establishes the correlation between the operating variables and the control variables and uses real-time data to predict the future trend of the control variables. The system uses an optimization algorithm to calculate the best action of the operating variables required to achieve the optimal state and correct the system deviation in real time.

[0118] 2.3. Dehydration section controller model: This model is mainly responsible for the coordinated optimization of the entire dehydration system. It realizes temperature profile control by controlling the range of key variables such as temperature and liquid level of each tower (dehydration tower, PX extraction tower, recovery tower). For example, in the dehydration tower, the temperature is controlled within the range of 96℃ to 101℃ to ensure the maximum dehydration efficiency.

[0119] Multi-tower collaborative optimization

[0120] Since there is a serious coupling relationship between the dehydration tower, PX extraction tower and recovery tower, the advanced control system of the present invention realizes the overall optimization of the entire dehydration system through multivariable control technology. The control strategy takes into account the mutual influence and correlation between the towers, and optimizes the operating parameters of each tower (such as reflux, steam volume, liquid level, etc.) to ensure the stable operation of the system and reduce energy consumption.

[0121] In the dehydration tower system, due to the constant changes in feed flow and components, conventional PID control cannot accurately adjust the reflux flow. The present invention can adjust various control variables in advance according to the real-time status and future trends of the system through range control and feedforward prediction model, thereby reducing unnecessary reflux flow fluctuations.

[0122] System commissioning and exit mechanism

[0123] 4.1. Commissioning conditions: When the communication between the DCS system and the advanced control system is normal and the current process variable (PV) is within the operating range, the operator can request to commission the advanced control system.

[0124] 4.2. Commissioning process: When the commissioning conditions are met, the DCS system will send a signal to the advanced control system, which will return a control signal based on the current system status. If no control loop is normally commissioned within 10 minutes after commissioning, the system will automatically exit the commissioning state.

[0125] 4.3. Exit conditions: The system will automatically exit the control of the advanced control system according to the following conditions:

[0126] The operator manually exits control;

[0127] The communication between DCS and advanced control system is interrupted;

[0128] The advanced control system determines that the loop does not meet the conditions for commissioning;

[0129] The operator modifies the control mode.

[0130] 4.4. Deviation control of set value: If the set value calculated by the advanced control system deviates too much from the set value of the previous cycle, the system will choose to maintain the set value of the previous cycle to prevent excessive fluctuations from interfering with the system.

[0131] System Advantages

[0132] 5.1. Improve stability and efficiency: Through the overall optimization of the advanced control system, the various process parameters of the dehydration tower, PX extraction tower and recovery tower are effectively coordinated and optimized, so that the entire system can be maintained in the best operating state for a long time, improving stability and reducing energy consumption.

[0133] 5.2. Reduce human intervention: The present invention can automatically adapt to complex factors such as load changes and component changes, reduce the operator's frequent adjustments to the PID loop, and improve the automation level and accuracy of the operation.

[0134] 5.3. Reduce energy consumption: By optimizing and controlling operating parameters such as reflux flow rate and steam flow rate, the present invention can effectively reduce energy consumption, reduce material losses, and improve material recovery rate.

[0135] Embodiment 2

[0136] Optimal Control of Dehydration Tower

[0137] The details are as follows:

[0138] In this embodiment, the dehydration tower (D601), PX extraction tower (D651) and recovery tower (D631) are uniformly optimized and controlled by an advanced control system (ACS). In traditional PID control, the operating loops of each tower are independent and cannot be effectively coordinated, while in the intelligent control system, the interaction and coordinated optimization between the towers are realized by multivariable control technology. The key control points of each tower, such as temperature, pressure, liquid level, etc., can dynamically adjust the operating parameters through real-time data acquisition and historical data comparison. Especially in the dehydration tower control, the temperature profile adjustment in the original PID control no longer depends on the fixed reflux volume, but is accurately adjusted according to the actual position of the azeotropic temperature, avoiding the fluctuation caused by the change of the feed composition in the tower, and minimizing unnecessary disturbances and energy consumption.

[0139] Embodiment 3

[0140] Design of data flow and feedback mechanism

[0141] The details are as follows:

[0142] The DCS system and the advanced control system are linked. The DCS system maintains the basic operation of the system through real-time data acquisition and command issuance. On this basis, the advanced control system exchanges data with the DCS database through the OPC server to analyze and predict historical data. The pressure-corrected temperature soft measurement model can reflect the changes in the distribution of components in the tower in real time, thereby optimizing the temperature control strategy. The predictive control model adjusts the control amount in advance according to the future trend of the operating variables to ensure that the system maintains optimal performance under load fluctuations and composition changes. The feedback system provides real-time display, allowing operators to respond quickly to potential abnormalities.

[0143] Embodiment 4

[0144] Pressure correction and temperature control

[0145] The details are as follows:

[0146] This example emphasizes the role of the pressure-corrected temperature model in optimization control. The model corrects the pressure at key temperature points in the tower (such as the middle of the dehydration tower, the top of the recovery tower, etc.) so that the corrected temperature more accurately reflects the actual distribution of the components in the tower. This method is more capable of coping with feed component fluctuations than traditional fixed set values, greatly improving the accuracy and stability of control. For example, the temperature PID control of the lower part of the dehydration tower would originally be misregulated due to pressure fluctuations. Using the pressure-corrected temperature can reduce fluctuations caused by operating pressure fluctuations, thereby improving system stability.

[0147] Embodiment 5

[0148] Circuit commissioning and regulation strategy

[0149] The details are as follows:

[0150] During the implementation process, the control system needs to handle the process and conditions for the commissioning of the loop. When the DCS system meets specific conditions, the operator can request the commissioning of the advanced control system, and the system will determine whether the commissioning requirements are met based on the current data cycle. If the commissioning is successful, the advanced control system will actively control the loop and send optimization instructions to the DCS system. However, if the commissioning request is not completed within the specified time, the system will automatically roll back to the previous control state to ensure that the process is not affected by unnecessary fluctuations. The automatic exit mechanism of the advanced control system ensures that it can be restored to a safe control mode in a timely manner when communication is interrupted or the control signal does not meet the requirements.

[0151] Embodiment 6

[0152] Loop coordination and control optimization

[0153] The details are as follows:

[0154] This example demonstrates how to achieve collaborative work between towers through multivariable control. In particular, in the temperature control of the dehydration tower, PX extraction tower and recovery tower, traditional PID often has the problem of conflicting adjustments. The advanced control system introduces a feedforward prediction model to dynamically predict and adjust the operating variables of each tower to ensure that each tower operates in the optimal state and avoid energy waste caused by over-adjustment of a single control loop. By setting the range limit of the temperature profile (such as controlling the temperature of the dehydration tower to 96-101°C), the temperature fluctuation can be kept within the minimum range, while ensuring that steam consumption and material loss are minimized.

[0155] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An advanced control system for an azeotropic distillation dehydration tower of a purified terephthalic acid plant, characterized in that: Applied to the overall optimization control of the dehydration tower system, the system comprises: A dehydration tower system, which includes a dehydration tower, a PX extraction tower and a recovery tower, each tower having independent operating variables and control variables; DCS control system, used to receive and send real-time data and instructions, control the operation of the dehydration tower system, and save the real-time data to the DCS database; OPC server, used to exchange data with the DCS database and periodically send the received real-time data to the advanced control system; Advanced control system, which is used to compare the historical data received from the OPC server with the real-time data, optimize the control instructions, and adjust the operating variables through the control variables to achieve system optimization; Display feedback system, used to display the comparison results of the advanced control system and feed back to the DCS control system; The advanced control system includes a data storage module, a prediction model operation processor, an advanced control database, and a weight sorting and operation control optimization module.

2. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid device according to claim 1, characterized in that: The three towers of the dehydration tower system: dehydration tower, PX extraction tower and recovery tower are coupled with each other, and the operating variables in the tower are coordinated through multivariable control technology.

3. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid device according to claim 1, characterized in that: The advanced control system includes the following control models: The pressure-corrected temperature soft measurement model ensures that the temperature at the measuring point can accurately represent the distribution of components in the tower through the relationship between the corrected temperature and pressure; Predictive control model, which predicts the future trend of control variables by modeling the relationship between operating variables and control variables, and adjusts operating variables in real time through optimization algorithms; The dehydration section controller model uses multivariable control technology to replace traditional PID control. The pressure-corrected temperature soft-sensing model is expressed by: Corrected temperature = temperature before correction + pressure coefficient × (pressure - reference pressure); The pressure coefficient is set according to the specific characteristics of different temperature measurement points to accurately correct the temperature data in the tower.

4. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid plant according to claim 1, characterized in that: The predictive control model is used to calculate the optimal state of the system in the future and to make real-time corrections based on deviations during actual operation.

5. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid plant according to claim 1, characterized in that: The dehydration section controller model controls the temperature profile of the dehydration tower and the water concentration at the bottom of the tower through the range control technology, and predicts the change of water concentration through the feedforward model.

6. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid plant according to claim 1, characterized in that: The DCS control system includes the monitoring and adjustment functions of the dehydration tower (D601), NPA recovery tower (D631) and PX extraction tower (D651). It can monitor the key control points in the tower in real time and transmit the data to the DCS database in real time for storage and exchange.

7. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid plant according to claim 1, characterized in that: The display feedback system displays the operating status of each tower of the dehydration tower system in real time according to the optimization results received from the advanced control system, and feeds back to the DCS control system.

8. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid plant according to claim 1, characterized in that: The commissioning mechanism of the advanced control system includes: The main controller can be put into use manually by the operator when the communication between DCS and advanced control system is normal, and the advanced control system can be enabled for real-time control; Loop commissioning conditions: When the DCS meets the preset operating conditions and the main controller has been commissioned, the DCS can request to commission the loop of the advanced control system; Commissioning failure judgment: If the commissioning signal from the advanced control system is not received within the predetermined time (within 30 seconds), the DCS will judge that the commissioning has failed and maintain the current control state.

9. The advanced control system for the azeotropic distillation dehydration tower of a purified terephthalic acid plant according to claim 1, characterized in that: The advanced control system setting value adopting rules are as follows: Set value change control: when the difference between the advanced control system set value of the current cycle and the set value of the previous cycle exceeds the set threshold, the set value of the previous cycle is maintained; Direct control mode, when the advanced control system directly controls the operating variable (such as a valve), When the system is not in use, the DCS control system will use the control value given by the DCS, and when the advanced control system is in use, it will switch to the control value provided by the advanced control system; The optimization module performs overall coordinated optimization by comprehensively considering the operating data and historical data of the dehydration tower, PX extraction tower and recovery tower.

10. An advanced control method for an azeotropic distillation dehydration tower of a purified terephthalic acid device, characterized in that: The control method comprises the following steps: Step 1. Obtain real-time operation data through the dehydration tower system and send the data to the DCS control system; Step 2. The DCS control system transmits real-time data to the OPC server; Step 3. The OPC server periodically transmits historical data and real-time data to the advanced control system; Step 4. The advanced control system optimizes the control instructions according to the received data and feeds back the optimization results to the DCS control system; Step 5. The DCS control system adjusts the control variables in the tower according to the feedback results; This also includes coordinating the operating variables and control variables of the three towers through predictive control models, pressure correction temperature soft measurement models and dehydration section controller models.

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