Precise monitoring and metering of pH

Abstract

The disclosed pH precise monitoring and metering subsystem adopts a closed-loop control architecture of monitoring-computing-executing-feedback, and is composed of a whole-process pH monitoring network, a metering and dosing device group, an intelligent control unit and a data acquisition and processing unit. Through real-time monitoring of pH at multiple points in the whole process of source, storage and process, in combination with a feedforward-feedback compound PID control strategy, the system drives the metering and dosing device to realize precise quantitative dosing of acid-alkaline reclaimed water. The pH of each process section of desulfurization and denitrification wastewater is stably controlled within a target range, the wastewater treatment effect is improved, the replacement rate of reclaimed water medicament can reach more than 90%, the operation cost is greatly reduced, and meanwhile, the system has perfect data acquisition, analysis and man-machine interaction functions, and is suitable for the acid-alkaline reclaimed water reuse scene of desulfurization and denitrification wastewater in a thermal power plant.

Description

Technical Field

[0001] This invention belongs to the field of desulfurization and denitrification wastewater treatment technology, and in particular relates to a pH precision monitoring and metering dosing subsystem. Background Technology

[0002] In the treatment of desulfurization and denitrification wastewater from thermal power plants, different process stages, such as Fenton oxidation, heavy metal precipitation, ammonia nitrogen stripping, and terminal neutralization, have specific and differentiated requirements for the pH value of the water. Currently, the industry mostly uses purchased acid and alkali reagents combined with manual addition for pH adjustment, which has problems such as high reagent costs, low addition accuracy, strong adjustment lag, and low degree of automation.

[0003] With the promotion of industrial water conservation and greywater reuse technologies, using acidic or alkaline greywater discharged from water treatment plants to replace purchased chemicals has become an important direction for cost reduction and efficiency improvement. However, existing greywater dosing systems generally lack full-process pH monitoring capabilities, have simple control strategies, poor resistance to disturbances, and are prone to problems such as large pH fluctuations, insufficient process stability, and low greywater replacement rates. They are unable to meet the precise pH requirements of each process stage and may even affect the wastewater treatment effect and the stability of effluent compliance. Summary of the Invention

[0004] The purpose of this invention is to provide a pH precision monitoring and metering dosing subsystem to solve the technical problems of existing greywater dosing systems, such as simple adjustment and control strategies, poor anti-disturbance ability, easy occurrence of large pH fluctuations, insufficient process stability, and low greywater replacement rate.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The pH precision monitoring and metering dosing subsystem adopts a closed-loop control architecture of monitoring-calculation-execution-feedback, including a full-process pH monitoring network, metering dosing equipment group, intelligent control unit and data acquisition and processing unit.

[0007] The entire process pH monitoring network is set up with monitoring points at the source of recovery, storage and dosing along the entire process of acidic and alkaline wastewater recovery, storage and dosing. Each monitoring point is equipped with an online pH meter to collect the pH data of the water body at the corresponding location in real time, so as to realize pH monitoring of the entire process of wastewater recovery, storage and dosing.

[0008] The metering and dosing equipment group is set up for each process dosing monitoring point. It includes multiple diaphragm metering pumps and supporting pipelines and valve assemblies, which are used to quantitatively add recycled acidic or alkaline wastewater to the corresponding process tank and execute the flow command of the control unit.

[0009] The intelligent control unit is connected to the full-process pH monitoring network and the metering and dosing equipment group. It is used to dynamically adjust the output flow of the diaphragm metering pump based on the deviation between the real-time pH data and the preset target pH, combined with the control algorithm, so as to achieve closed-loop precise control of the dosing process.

[0010] The data acquisition and processing unit is connected to the signals of all system equipment to collect system operation data, complete data storage, statistical analysis, anomaly early warning and human-machine interaction, and support system operation and maintenance and parameter optimization.

[0011] As a further aspect of the present invention, the end-to-end pH monitoring network comprises 10 monitoring points, covering key nodes throughout the entire process:

[0012] There are two source monitoring points for recycling: the first source monitoring point at the end of the acidic wastewater drainage ditch in the water treatment workshop and the second source monitoring point at the end of the alkaline wastewater drainage ditch in the water treatment workshop. These points are used to determine whether the recycled wastewater meets the pH threshold conditions. The pH threshold for acidic wastewater recycling is ≤2, and the pH threshold for alkaline wastewater recycling is ≥12. Wastewater that does not meet the threshold will not be recycled.

[0013] There are a total of 4 monitoring points for storage status, including 2 monitoring points at the outlet of acidic wastewater storage tanks and 2 monitoring points at the outlet of alkaline wastewater storage tanks, realizing independent monitoring of the two tanks. They are used to monitor the pH stability of the stored wastewater. The target pH range for acidic wastewater storage is 1.5 to 2.5. When pH < 1.5, an over-acid corrosion warning is triggered, and when pH > 2.5, a dilution failure warning is triggered. The target pH range for alkaline wastewater storage is 12 to 13. When pH < 12, a failure warning is triggered, and when pH > 13, an over-alkali corrosion warning is triggered.

[0014] There are a total of 4 monitoring points for process addition, including monitoring points in the Fenton reactor, neutralization tank, stripping tank, and terminal neutralization tank, with corresponding pH target ranges of 3.0–4.0, 8.0–9.0, 10.0–11.0, and 6.0–9.0, respectively, to match the reaction requirements of each process stage.

[0015] As a further aspect of the present invention, the online pH meter has a measurement range of 0–14 pH, a measurement accuracy of ±0.1 pH, a response time ≤30s, a temperature compensation range of 0–80℃, outputs a 4–20mA standard analog signal, and has a protection rating of not less than IP68, making it adaptable to the humid and corrosive environment of wastewater treatment sites. The pH meter in the process tank is installed using an immersion method, while the pH meters in the pipeline between the source and storage tank are installed using a flow-through method. Each online pH meter at each monitoring point is equipped with an automatic cleaning device, with a cleaning cycle set at 3–5 hours / time to prevent electrode scaling or contaminant adhesion from affecting measurement accuracy.

[0016] As a preferred embodiment of the present invention, the metering and dosing equipment group is designed and calculated based on a wastewater treatment capacity of 10-20 m³ / h, and a total of 4 dosing systems are set up, corresponding to the Fenton reaction tank, neutralization tank, stripping tank, and terminal neutralization tank, respectively. Each dosing system is equipped with 2 diaphragm metering pumps, one in operation and one on standby; the flow rate of a single pump is 0-800 L / h and continuously adjustable, with an adjustment accuracy of ±1%, and a maximum output pressure of 0.4-0.8 MPa. The pump head of the acidic water dosing system is made of acid-resistant PTFE material, while the pump head of the alkaline water dosing system can be made of 316L stainless steel. Each dosing system is equipped with a high-precision flow sensor and an electric regulating valve to achieve accurate flow detection and closed-loop regulation.

[0017] As a further aspect of the present invention, the diaphragm metering pump is driven by a variable frequency speed control or a stepper motor, receives a 4-20mA or 0-10V control signal, has a response time ≤3s, and an adjustable stroke frequency range of 10-120 times / minute. It also features a power-off position memory function, allowing it to return to its pre-shutdown operating state after restarting. The diaphragm metering pump is installed near the corresponding process tank, shortening the delivery pipeline length and reducing pipeline resistance and hysteresis. The dosing port uses a diffuser nozzle, installed in the turbulent flow area of ​​the liquid within the tank, increasing the mixing speed of the treated water and wastewater and accelerating the pH response.

[0018] As a preferred embodiment of the present invention, considering the large dosage in the stripping tank and the terminal neutralization tank, a straight-through feed pipe is installed in each of the corresponding dosing systems. The straight-through feed pipe is equipped with an electric regulating valve, which can dynamically adjust the flow rate according to the influent conditions, accounting for 55%–65% of the total dosage, undertaking the coarse adjustment of the basic load. The remaining 35%–45% of the recycled water is added in stages via a diaphragm metering pump, undertaking the fine adjustment of deviations. Together, these two systems achieve precise control of the total dosage. This design can reduce the size of the metering pump while ensuring adjustment accuracy, thereby reducing equipment investment and operating energy consumption.

[0019] As a preferred embodiment of the present invention, the intelligent control unit adopts an adaptive control strategy based on the PID algorithm, and the control model is as follows: In the formula, The added flow rate at time t, Add traffic to the baseline obtained from offline calibration; For pH deviation, in the acidic adjustment loop In the alkaline regulation circuit ; This is a proportionality coefficient used for rapid response to the current deviation; These are integral coefficients used to eliminate steady-state errors in the system; It is a differential coefficient used to predict the trend of deviation changes, suppress pH oscillations, and improve system stability.

[0020] As a further aspect of the present invention, the intelligent control unit also includes a feedforward control module, which adopts a feedforward-feedback composite control mode, and the final flow command is: In the formula, This is the feedforward theory dosage. This is the output quantity of the PID feedback control.

[0021] The feedforward theoretical dosage is derived through the material balance equation and calculated using two types of loops:

[0022] Acidic dosing circuit (Fenton reaction cell, terminal neutralization cell): Dosage calculated based on hydrogen ion concentration gradient. ;

[0023] Alkaline dosing circuit (neutralization tank, stripping tank): Dosage calculated based on hydroxide ion concentration difference. In the formula, The wastewater flow rate entering the process tank, The pH value of the influent to the process tank. To ensure the effective concentration of corresponding ions in the recovered water, feedforward control can respond in advance to disturbances in influent flow rate and pH, shorten adjustment time, reduce pH overshoot, and improve the system's anti-interference capability.

[0024] As a further aspect of the present invention, the parameters of the PID algorithm are determined by combining the Ziegler-Nichols engineering tuning method with field trial operation data. The tuning steps are as follows:

[0025] Set the integral and derivative coefficients to 0, retain only the proportional control, gradually increase the proportional coefficient until the system exhibits constant amplitude oscillation, and record the critical proportional coefficient and oscillation period;

[0026] Calculate the initial PID parameters using empirical formulas;

[0027] Fine-tune the parameters based on the pH response curve obtained from the on-site trial operation until the control performance requirements are met.

[0028] Under rated treatment capacity and stable influent water quality, the system control performance meets the following requirements: overshoot ≤ 5%, settling time ≤ 10 minutes, and steady-state error ≤ ±0.1 pH. Independent PID parameters are tuned for different process sections based on tank volume, hydraulic retention time, and hysteresis characteristics.

[0029] As a preferred embodiment of the present invention, the data acquisition and processing unit includes a signal transmission module, a data storage module, and a human-machine interface.

[0030] The signal transmission module acquires analog and digital signals from field devices through field I / O modules and transmits them to the DCS control cabinet in the central control room via RS485 bus or Profibus-DP fieldbus. The transmission cables are shielded twisted-pair cables laid in metal cable trays with good grounding to reduce electromagnetic interference. Redundant transmission paths are used for key monitoring and control signals to improve system reliability.

[0031] The data storage module supports adjustable storage cycles from 1 second / time to 1 minute / time, with a data retention period of ≥2 years. The database adopts a relational architecture, supporting multi-dimensional data querying and statistical analysis by time, location, and operating condition. The system can periodically collect core data such as pH compliance rate at each dosing point, acidic / alkaline wastewater consumption and replacement ratio, PID control performance indicators, and abnormal operating condition records. Furthermore, it uses data mining and machine learning algorithms to establish pH response prediction models under different operating conditions, optimize control parameters, and achieve self-learning and adaptive control strategies.

[0032] The human-machine interface is located at the DCS operator station and is developed using configuration software. It includes a real-time monitoring module, a parameter setting module, a mode switching module, an alarm query module, and a report generation module.

[0033] Real-time monitoring module: Dynamically displays pH values ​​and trend curves, tank liquid levels, dosing flow rates, valve openings and equipment operating status at each monitoring point in the form of a process flow diagram, and indicates the operating status through color changes.

[0034] Parameter setting module: Operators can set target pH value, PID parameters, upper and lower limits of dosing flow rate and alarm thresholds for each dosing point. All parameter modifications require password verification to prevent accidental operation.

[0035] Mode switching module: Supports one-click switching between automatic mode, manual mode and externally purchased reagent backup mode; automatic mode is used for normal operation, manual mode is used for maintenance and debugging, and the system can be quickly switched to the externally purchased reagent backup mode when the wastewater system is abnormal, so as to ensure the continuous and stable operation of the wastewater treatment system.

[0036] Alarm query module: Displays current alarm information in real time, and supports historical alarm query, statistical analysis and alarm push.

[0037] Report generation module: Automatically generates daily, weekly and monthly reports, including content such as greywater consumption, chemical savings, economic benefits, equipment runtime, etc., and supports export in common formats.

[0038] Before the system was put into operation, baseline parameters were calibrated through offline experiments, and after commissioning, it was gradually optimized through online trial operation.

[0039] Offline experimental phase: Prepare simulated wastewater and conduct calibration experiments in Fenton reaction tank, neutralization tank, stripping tank and terminal neutralization tank respectively. Measure the pH response and treatment effect under different dosages and determine the baseline dosage range and initial control parameters for each process section.

[0040] During the online trial operation phase: the proportion of reclaimed water added will be gradually increased in stages. In the first stage, the proportion of reclaimed water added will be 20% to 40%, in the second stage it will be increased to 50% to 80%, and in the third stage it will be increased to more than 90%. The quality of the effluent and the stability of the system will be monitored throughout the process, and the PID parameters and feedforward model will be gradually optimized.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. A full-process pH monitoring network from source to storage to process has been constructed to realize real-time monitoring and early warning of anomalies in all stages of wastewater recycling, storage and dosing, ensuring the quality of the dosing medium from the source and providing a data foundation for precise control.

[0043] 2. By adopting a feedforward-feedback composite PID control strategy, the control logic of the acid and alkaline adjustment loops is distinguished. Combined with high-precision metering and dosing equipment, it can respond to disturbances in influent flow and pH in advance, and eliminate steady-state errors through closed-loop feedback. This greatly improves the pH control accuracy and response speed, ensures that the pH of each process section is stable within the target range, and improves the wastewater treatment effect.

[0044] 3. For processes with large dosage, a dosing mode of coarse adjustment via a straight feed pipe and fine adjustment via a metering pump is adopted to reduce equipment investment and operating energy consumption while ensuring adjustment accuracy, thus balancing economy and control performance.

[0045] 4. A complete set of supporting data acquisition, analysis and human-computer interaction systems, supporting operation data statistics, control parameter self-optimization and multi-mode switching, can achieve a chemical replacement rate of more than 90% in reclaimed water, significantly reducing the cost of purchased chemicals, while improving the system's automation level and operational stability, and reducing the workload of maintenance personnel. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only examples of embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the architecture of an embodiment of the present invention;

[0048] Figure 2This is a schematic diagram of the architecture of the end-to-end pH monitoring network in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the architecture of the metering and dosing equipment group in an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the architecture of the intelligent control unit in an embodiment of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0052] See Figures 1-4 As shown, this embodiment of the invention is designed for a desulfurization and denitrification wastewater treatment system in a thermal power plant, with a wastewater treatment capacity of 15 m³ / h. It is equipped with the pH precision monitoring and metering dosing subsystem of this invention, which is used to reuse acidic and alkaline wastewater discharged from the water treatment workshop to replace purchased acid and alkali reagents.

[0053] 1. System Overall Architecture:

[0054] The pH precision monitoring and metering dosing subsystem in this embodiment adopts a closed-loop control architecture of monitoring-calculation-execution-feedback, consisting of four parts: a full-process pH monitoring network, a metering dosing device group, an intelligent control unit, and a data acquisition and processing unit. The pH monitoring network collects pH data from each node and transmits it to the intelligent control unit. The control unit, combining parameters such as influent flow rate and target pH, calculates the dosing flow command using a feedforward-feedback composite PID algorithm, driving the metering dosing devices to add acidic / alkaline wastewater to the corresponding process tank. The dosing amount is then corrected based on pH monitoring data from the process section, forming a complete closed-loop control. The data acquisition and processing unit is responsible for the acquisition, storage, analysis, and human-machine interaction of all system data.

[0055] 2. Deployment of a full-process pH monitoring network:

[0056] This embodiment sets up a total of 10 monitoring points, as follows:

[0057] Two monitoring points at the source of recycling:

[0058] Point A1: Located at the end of the acidic wastewater drainage ditch in the water treatment workshop, an online pH meter is installed using a flow-through pool to monitor the pH value of the acidic wastewater to be recycled. The recycling threshold is set to pH≤2. If the pH value exceeds the threshold, a recycling valve closing command is triggered.

[0059] Point A2: Located at the end of the alkaline wastewater drainage ditch in the water treatment workshop, an online pH meter is installed using a flow-through pool to monitor the pH value of the alkaline wastewater to be recycled. The recycling threshold is set to pH ≥ 12. If the pH value exceeds the threshold, a recycling valve closure command is triggered.

[0060] Storage status monitoring points (4):

[0061] Points B1 and B2 are respectively located on the outlet pipes of acidic greywater storage tanks No. 1 and No. 2. Online pH meters are installed using a flow-through pool to monitor the pH stability of the stored acidic greywater. The target control range is 1.5 to 2.5. When pH < 1.5, an over-acid corrosion warning is triggered, prompting an inspection of the equipment for corrosion prevention. When pH > 2.5, a dilution failure warning is triggered, indicating a decline in greywater quality.

[0062] Points B3 and B4 are respectively located on the outlet pipes of alkaline greywater storage tanks No. 1 and No. 2. Online pH meters are installed using a flow-through pool to monitor the pH stability of the stored alkaline greywater. The target control range is 12-13. When pH < 12, a failure warning is triggered, indicating insufficient alkalinity. When pH > 13, an over-alkali corrosion warning is triggered, prompting equipment corrosion inspection.

[0063] Process addition monitoring points (4):

[0064] Point C1: Located in the three-compartment Fenton reaction tank, an online pH meter is installed using an immersion type to monitor the pH value of the water after the addition of acidic diluent. The target control range is 3.0 to 4.0 to ensure the optimal pH environment for the Fenton reaction.

[0065] Point C2: Located in the neutralization tank of the triplet, an online pH meter is installed using an immersion type to monitor the pH value of the water after the addition of alkaline water. The target control range is 8.0 to 9.0 to ensure the optimal pH environment for heavy metal precipitation and flocculation reaction.

[0066] Point C3: Located inside the ammonia nitrogen stripping tank, an online pH meter is installed using an immersion type to monitor the pH value of the water after the addition of alkaline water. The target control range is 10.0 to 11.0 to ensure the conversion of ammonium ions to free ammonia and improve stripping efficiency.

[0067] Point C4: Located in the final neutralization tank after stripping, an online pH meter is installed using an immersion type to monitor the pH value of the effluent after the addition of acidic water. The target control range is 6.0 to 9.0, which meets the requirements of environmental protection emission standards.

[0068] The online pH meters used in this embodiment all employ acid and alkali resistant glass electrodes paired with Ag / AgCl reference electrodes. They have a measurement range of 0–14 pH, a measurement accuracy of ±0.1 pH, a response time ≤30s, built-in automatic temperature compensation from 0–80℃, and output a 4–20mA standard analog signal. The protection rating is IP68. Each pH meter is equipped with an automatic cleaning device with a cleaning cycle set at 4 hours / time to periodically rinse the electrode surface and prevent scaling and contamination.

[0069] 3. Configuration of metering and dosing equipment:

[0070] This embodiment is calculated based on a wastewater treatment capacity of 15 m³ / h, and a total of 4 sets of metering and dosing systems are configured. The dosing amount is derived based on material balance:

[0071] Fenton reactor: Influent pH is about 5.5, target pH is 3.5, and the amount of hydrogen ions required to treat 1 m³ of wastewater is about 0.313 mol; acidic water with pH=2.0 (hydrogen ion concentration 0.01 mol / L) is used, the theoretical addition volume is about 31.3 L / m³, and the designed addition flow rate range is 350~500 L / h.

[0072] Neutralization tank: The influent pH is about 3.5, the target pH is 8.5, and the amount of hydroxide ions required to treat 1 m³ of wastewater is about 0.315 mol; alkaline water with pH=12.0 (hydroxide concentration 0.01 mol / L) is used, the theoretical addition volume is about 31.5 L / m³, and the designed addition flow rate range is 350~500 L / h.

[0073] Stripping tank: The influent pH is about 8.5, and the target pH is 10.5. Because the wastewater contains buffer systems such as bicarbonate, the amount of hydroxide substances required to treat 1m³ of wastewater is about 0.63mol. Alkaline reclaimed water with pH=12.0 is used, with a theoretical addition volume of about 63L / m³ and a designed total addition flow rate range of 750~950L / h.

[0074] Terminal neutralization tank: The influent pH is about 10.5, the target pH is 7.0, and the amount of hydrogen ions required to treat 1 m³ of wastewater is about 0.312 mol; acidic water with pH=2.0 is used, the theoretical addition volume is about 31.2 L / m³, and the designed total addition flow rate range is 350~500 L / h.

[0075] The specific configurations of each group's dosing system are as follows:

[0076] Fenton reactor dosing system: equipped with 2 diaphragm metering pumps, one in use and one on standby, with a single pump flow range of 0~800L / h, adjustment accuracy of ±1%, maximum output pressure of 0.6MPa, and pump head material of PTFE; equipped with flow sensor and electric regulating valve.

[0077] Neutralization tank dosing system: Equipped with 2 diaphragm metering pumps, one in use and one on standby, with a single pump flow range of 0~800L / h, adjustment accuracy of ±1%, maximum output pressure of 0.6MPa, and pump head material of 316L stainless steel; equipped with flow sensor and electric regulating valve.

[0078] Stripping tank dosing system: Equipped with two diaphragm metering pumps, one in operation and one on standby, and a direct feed pipe is also installed. Approximately 60% of the alkaline wastewater is coarsely added via the direct feed pipe, and the remaining 40% is finely added via the metering pump; the direct feed pipe is equipped with an electric regulating valve, which is linked to the metering pump for control.

[0079] Terminal neutralization tank dosing system: Equipped with two diaphragm metering pumps, one in operation and one on standby, and a direct feed pipe is also installed. Approximately 60% of the acidic wastewater is coarsely added via the direct feed pipe, and the remaining 40% is finely added via the metering pump; the direct feed pipe is equipped with an electric regulating valve, which is linked to the metering pump for control.

[0080] All diaphragm metering pumps are driven by variable frequency speed control, receive 4-20mA control signals, have a response time of ≤3s, and an adjustable stroke frequency range of 10-120 strokes / minute. They also have a power-off position memory function. The pump body is installed in the dosing room next to the corresponding process tank, and the dosing port uses a diffuser nozzle installed in the turbulent flow zone of the tank's inlet to improve mixing efficiency.

[0081] 4. Intelligent control unit implementation:

[0082] The intelligent control unit is deployed in the DCS system in the central control room and adopts a feedforward-feedback composite PID control strategy.

[0083] Basic PID feedback control: Distinguish between acidic and alkaline control loops, and set separate deviation calculation logic for each; in the acidic loop, increase the dosage when the measured pH is higher than the target value, and in the alkaline loop, increase the dosage when the measured pH is lower than the target value, ensuring correct control direction. The baseline dosage is determined by offline calibration experiments, corresponding to the baseline dosage under steady-state conditions.

[0084] Feedforward compensation control: Influent flow rate and pH data for each process stage are collected. The theoretical dosage is calculated using acidic and alkaline material balance formulas, and this calculation is used as a feedforward value superimposed on the PID output. When influent flow rate or pH fluctuates, the dosage can be adjusted in advance, significantly reducing pH fluctuation amplitude and adjustment time.

[0085] Parameter tuning: Initial parameter tuning was performed using the Ziegler-Nichols method, followed by fine-tuning based on on-site trial operation data. Under the conditions of a rated treatment capacity of 15 m³ / h and stable influent water quality, the control performance of each process section met the following requirements: overshoot ≤ 5%, settling time ≤ 10 minutes, and steady-state error ≤ ±0.1 pH.

[0086] 5. Data Acquisition and Processing System:

[0087] Signal transmission: Analog and digital signals from field devices such as pH meters, flow meters, level gauges, metering pumps, and valves are acquired by local I / O modules and transmitted to the DCS control cabinet in the central control room via the Profibus-DP fieldbus. Shielded twisted-pair cables are used for transmission, laid in metal cable trays and reliably grounded. Redundant transmission is employed for critical signals.

[0088] Data storage and analysis: The DCS system is equipped with a dedicated historical database, with adjustable storage periods supporting 1-second high-speed sampling and 1-minute conventional storage, and a data retention period of no less than 2 years. The system regularly and automatically generates analytical reports such as pH compliance rate, greywater replacement rate, equipment operating rate, and abnormal alarm statistics; at the same time, it establishes an operating condition prediction model based on historical data, and regularly optimizes PID parameters and feedforward coefficients to achieve adaptive control.

[0089] Human-Machine Interface: A dedicated monitoring screen is developed on the DCS operator station, including function pages such as process overview, parameter settings, alarm query, and report management. Operators can monitor the entire system's operating status in real time, modify control parameters, switch operating modes, and query historical data and reports through the interface. Parameter modification requires an operation password to prevent unauthorized misoperation.

[0090] 6. System integration and optimization:

[0091] Offline calibration phase: A two-week laboratory offline experiment was conducted to prepare simulated desulfurization wastewater. The pH change curves and treatment effects of the Fenton tank, neutralization tank, stripping tank, and terminal neutralization tank were measured under different acidic and alkaline water dosages to determine the baseline dosage range and initial PID parameters for each process section.

[0092] Online trial operation phase: Conduct a one-month on-site trial operation, gradually increasing the proportion of greywater replacement in three phases:

[0093] Week 1: The greywater addition ratio is set at 30%, with the remaining 70% supplemented by purchased chemicals. The system stability and pH control effect are observed, equipment operating parameters are recorded, and PID parameters are initially adjusted.

[0094] Weeks 2-3: Gradually increase the proportion of reclaimed water to 60%-80%, while simultaneously reducing the amount of purchased chemicals. Continuously monitor pH and effluent COD, ammonia nitrogen, heavy metals, suspended solids, and other indicators in each process stage to ensure that the effluent meets the standards and further optimize control parameters.

[0095] Week 4: Increase the proportion of reclaimed water added to over 90%, use externally purchased reagents only as emergency backup, continuously run the system to verify its long-term stability, and complete the final parameter tuning and feedforward model optimization.

[0096] Trial operation results show that the system of this embodiment can stably control the pH of each process section within the target range, with a steady-state error of ≤±0.1pH, and the chemical replacement rate of reclaimed water reaches 92%, which significantly reduces the chemical cost of wastewater treatment and improves the system's automation level.

[0097] The above description illustrates the basic principles of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. The above embodiments and descriptions in the specification are only for illustrating the principles of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and scope of the present invention without departing from the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A pH precision monitoring and metering dosing subsystem, applied to the acid-alkaline wastewater reuse treatment of desulfurization and denitrification wastewater, characterized by: It adopts a closed-loop control architecture of monitoring-calculation-execution-feedback, including a full-process pH monitoring network, metering and dosing equipment group, intelligent control unit and data acquisition and processing unit; The entire process pH monitoring network is set up with monitoring points at the source of recovery, storage and dosing along the entire process of acidic and alkaline wastewater recovery-storage and dosing. Each monitoring point is equipped with an online pH meter to collect the pH data of the water body at the corresponding location in real time. The metering and dosing equipment group is set up for each process dosing monitoring point and includes multiple diaphragm metering pumps and supporting pipelines and valve assemblies, used to quantitatively add recycled acidic or alkaline wastewater to the corresponding process tank. The intelligent control unit is connected to the full-process pH monitoring network and the metering and dosing equipment group respectively, and is used to adjust the output flow of the diaphragm metering pump according to the deviation between the real-time pH data and the preset target pH, so as to realize the closed-loop regulation of the dosing process. The data acquisition and processing unit is connected to the signals of all system equipment and is used to collect and store operating data, and to complete operating status analysis and human-machine interaction.

2. The pH precision monitoring and metering dosing subsystem according to claim 1, characterized in that: The entire process pH monitoring network has a total of 10 monitoring points; The recycling source monitoring points include a first source monitoring point at the end of the acidic wastewater drainage ditch in the water treatment workshop and a second source monitoring point at the end of the alkaline wastewater drainage ditch in the water treatment workshop. These points are used to determine whether the recycled wastewater meets the pH threshold conditions, wherein the pH threshold for acidic wastewater recycling is ≤2 and the pH threshold for alkaline wastewater recycling is ≥12. The storage status monitoring points include two acidic greywater storage tank outlet monitoring points and two alkaline greywater storage tank outlet monitoring points, which are used to monitor the pH stability of the stored greywater. The target pH range for acidic greywater storage is 1.5 to 2.

5. When pH < 1.5, an over-acid corrosion warning is triggered, and when pH > 2.5, a dilution failure warning is triggered. The target pH range for alkaline water storage is 12–13. A failure warning is triggered when pH < 12, and an over-alkaline corrosion warning is triggered when pH > 13. The process addition monitoring points include monitoring points in the Fenton reaction tank, neutralization tank, stripping tank, and terminal neutralization tank, with corresponding pH target ranges of 3.0–4.0, 8.0–9.0, 10.0–11.0, and 6.0–9.0, respectively.

3. The pH precision monitoring and metering dosing subsystem according to claim 1 or 2, characterized in that: The online pH meter has a measurement range of 0–14 pH, a measurement accuracy of ±0.1 pH, a response time of ≤30 s, a temperature compensation range of 0–80 °C, outputs a 4–20 mA standard analog signal, and has a protection rating of not less than IP68. Each online pH meter at each monitoring point is equipped with an automatic cleaning device, with a cleaning cycle set to 3–5 hours / time.

4. The pH precision monitoring and metering dosing subsystem according to claim 1, characterized in that: The metering and dosing equipment group consists of four dosing systems, corresponding to the Fenton reaction tank, neutralization tank, stripping tank, and terminal neutralization tank, respectively. Each dosing system is equipped with two diaphragm metering pumps, with a single pump flow rate range of 0 to 800 L / h that is continuously adjustable, an adjustment accuracy of ±1%, and a maximum output pressure of 0.4 to 0.8 MPa. Each dosing system is equipped with a flow sensor and an electric regulating valve.

5. The pH precision monitoring and metering dosing subsystem according to claim 4, characterized in that: The diaphragm metering pump is driven by a variable frequency speed control or a stepper motor, receives a 4-20mA or 0-10V control signal, has a response time of ≤3s, and an adjustable stroke frequency range of 10-120 times / minute. It also has a power-off position memory function. The diaphragm metering pump is installed near the corresponding process tank, and the dosing port is a diffuser nozzle installed in the turbulent flow area of ​​the liquid in the tank.

6. The pH precision monitoring and metering dosing subsystem according to claim 4 or 5, characterized in that: Both the stripping tank and the terminal neutralization tank are equipped with straight feed pipes. The straight feed pipes are equipped with electric regulating valves, which can dynamically adjust the flow rate according to the influent conditions, accounting for 55% to 65% of the total feed amount, and undertake the basic load coarse adjustment. The remaining 35% to 45% of the recycled water is added in stages through diaphragm metering pumps, which undertake the deviation fine adjustment. The two work together to achieve precise control of the total feed amount.

7. The pH precision monitoring and metering dosing subsystem according to claim 1, characterized in that: The intelligent control unit adopts an adaptive control strategy based on the PID algorithm, and the control model is as follows: In the formula, The added flow rate at time t, Add flow rate based on baseline; For pH deviation, in the acidic adjustment loop In the alkaline regulation circuit ; This is the proportionality coefficient. The integral coefficient is... is the differential coefficient.

8. The pH precision monitoring and metering dosing subsystem according to claim 7, characterized in that, The intelligent control unit also includes a feedforward control module, which adopts a feedforward-feedback composite control mode, and the final flow command is: In the formula, This is the feedforward theory dosage. The output is the PID feedback control quantity; the theoretical feedforward dosage is derived through the material balance equation and calculated using two types of loops: Acidic dosing circuit: ; Alkaline dosing circuit: In the formula, The wastewater flow rate entering the process tank, The pH value of the influent to the process tank. The effective concentration of the corresponding ions in the recovered water.

9. The pH precision monitoring and metering dosing subsystem according to claim 7 or 8, characterized in that: The parameters of the PID algorithm were optimized and determined using the Ziegler-Nichols engineering tuning method combined with field trial operation data. Under the conditions of rated treatment capacity and stable influent water quality, the system control performance meets the following requirements: overshoot ≤ 5%, settling time ≤ 10 minutes, and steady-state error ≤ ±0.1 pH.

10. The pH precision monitoring and metering dosing subsystem according to claim 1, characterized in that: The data acquisition and processing unit includes a signal transmission module, a data storage module, and a human-machine interface. The signal transmission module acquires analog and digital signals from field devices through field I / O modules and transmits them to the DCS control cabinet in the central control room via RS485 bus or Profibus-DP fieldbus. The transmission cable is a shielded twisted pair cable and is laid in a metal cable tray. The storage period of the data storage module is adjustable from 1 second / time to 1 minute / time, the data retention period is ≥2 years, and it supports multi-dimensional data query and statistical analysis. The human-machine interface is located in the DCS operator station and includes a real-time monitoring module, a parameter setting module, a mode switching module, an alarm query module, and a report generation module. The real-time monitoring module is used to dynamically display the pH value, tank liquid level, dosing flow rate and valve status at each monitoring point; The parameter setting module is used to set the target pH value, PID parameters, upper and lower limits of dosing flow rate and alarm threshold for each dosing point. Parameter modification requires permission verification. The mode switching module supports one-click switching between automatic mode, manual mode, and externally purchased medicine backup mode; The alarm query module supports real-time alarm display and historical alarm query statistics. The report generation module can automatically generate running reports and supports exporting in a common format.

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