Circulating water low-turbidity water quality online control process based on alkalinity control

Abstract

The invention provides a circulating water low-turbidity water quality online control process based on alkalinity control. On-line monitoring equipment including an alkalinity analyzer, a turbidity meter and the like is arranged at key positions such as a water inlet of a circulating water system. The alkalinity analyzer adopts an acid-base titration and potential detection technology, the measurement precision reaches + / -0.01 mmol / L, and data is transmitted at least once per minute. By simulating a multi-working-condition experiment and by means of multiple linear regression and a neural network, an alkalinity and turbidity correlation model is constructed, and the prediction accuracy of the model exceeds 95%. And the central control system performs fusion analysis on water quality parameters by applying algorithms such as fuzzy logic and the like and sends an instruction to the intelligent dosing system. The system is internally provided with an advanced algorithm and can adaptively adjust the dosing of the medicament. Practice shows that the process can stably control turbidity and reduce equipment scaling and medicament consumption cost, and has outstanding advantages in the aspect of circulating water quality control.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial circulating water quality control, and in particular focuses on an online control process for low turbidity circulating water quality based on alkalinity control. The process can be widely applied to many industries that rely on circulating water systems to ensure the operation of equipment, such as electricity, chemical industry, metallurgy, and papermaking. By precisely controlling the alkalinity of circulating water, the turbidity of circulating water can be efficiently reduced and stably maintained, thereby providing solid technical support for the safe, efficient, and long-term stable operation of the circulating water system. Background Art

[0002] In the modern industrial production system, the circulating water system is like the human body's blood circulation system, and is a key infrastructure to ensure the normal operation of various production equipment. Taking the power industry as an example, the high-temperature exhaust steam discharged by the steam turbine in the thermal power station needs to be cooled and condensed into water with the help of circulating water, and then returned to the thermal cycle. This process greatly improves the power generation efficiency. In chemical production, many chemical reactions are accompanied by a large amount of heat release. The circulating water takes away the heat in time to ensure that the reaction is carried out at a suitable temperature to prevent the equipment from being damaged by overheating. According to statistics, in a typical chemical enterprise, the energy consumption of the circulating water system accounts for 15%-30% of the total energy consumption of the enterprise, and its operating status is directly related to the energy cost and production efficiency of the enterprise. The quality of circulating water is the core factor that determines the performance of the system. High-quality circulating water can significantly extend the service life of the equipment, reduce the frequency and cost of equipment maintenance, and improve production efficiency. Otherwise, it may cause a series of problems such as equipment scaling, corrosion, and microbial growth, and even lead to production interruption in severe cases. At present, circulating water quality control mainly relies on traditional chemical treatment methods, such as adding corrosion inhibitors, scale inhibitors, bactericides, etc., in an attempt to improve water quality. However, these methods expose many problems that need to be solved: Limitations of single parameter control: Most existing processes focus on regulating a single water quality parameter, such as simply focusing on the control of hardness or pH value. However, the quality of circulating water is a complex system, and the various parameters are interrelated and influence each other. For example, changes in hardness may affect alkalinity, which in turn has a chain reaction on turbidity. This single parameter control mode cannot fully consider the comprehensive changes in water quality, and it is difficult to achieve effective control of the overall water quality of circulating water, especially in terms of turbidity control. Studies have shown that if only the hardness is controlled, the turbidity of circulating water may still fluctuate within a large range, which cannot meet the requirements of water quality stability for high-precision industrial production. Lack of real-time online control ability: Traditional control methods mostly rely on regular manual sampling and sending samples to laboratories for analysis and testing. This method has obvious time lag and cannot track the dynamic changes of circulating water quality in real time. When water quality anomalies occur, it is difficult to detect and take corresponding measures in a timely manner, resulting in the gradual accumulation of problems such as equipment scaling and corrosion, ultimately affecting the continuity and stability of production. Take a steel enterprise as an example. Due to untimely water quality detection, the heat exchanger in the circulating water system is severely scaled, and the heat transfer efficiency has decreased by 20% within half a year, significantly increasing energy consumption and equipment maintenance costs. Irrational chemical dosing: The chemical dosing amount is usually determined based on experience or fixed dosing schemes, without fully considering the real-time changes in circulating water quality for dynamic adjustment. This may either cause excessive chemical dosing, which not only wastes resources and increases operating costs but also may cause potential environmental pollution, or may result in insufficient dosing, failing to achieve the expected water quality control effect. Research shows that some enterprises consume 10%-20% more chemical costs annually due to irrational chemical dosing, and the equipment failure rate remains high. Summary of the Invention

[0003] The present invention aims to develop an online control process for low turbidity circulating water quality based on alkalinity control, thoroughly overcoming the defects of existing circulating water quality control methods. By constructing an accurate correlation model between alkalinity and turbidity, applying an online monitoring and feedback control mechanism integrating multiple parameters, and realizing the adaptive optimization of an intelligent chemical dosing system, precise and real-time control of circulating water turbidity is achieved. Ultimately, the goal of reducing the operating cost of the circulating water system, extending the service life of equipment, and improving industrial production efficiency and economic benefits is realized. Technical Solution

[0004] The online control process for low turbidity circulating water quality based on alkalinity control of the present invention mainly consists of the following closely related steps: Real-time monitoring of water quality parameters: At key nodes in the circulating water system, such as the inlet, outlet, inlets and outlets of heat exchangers, and the return water pipeline of the cooling tower, high-precision online water quality monitoring equipment is installed. These equipment include alkalinity analyzers, turbidimeters, pH meters, hardness meters, conductivity meters, etc., which are capable of quickly and accurately measuring the corresponding water quality parameters. Taking the alkalinity analyzer as an example, by using the acid-base titration method combined with potential detection technology, an accurate alkalinity value can be given within seconds, and the measurement accuracy can reach ±0.01 mmol / L. Each monitoring device transmits the real-time collected water quality data to the central control system at high frequency through wired or wireless data transmission modules to ensure the timeliness and integrity of the data. Establishment of the Alkalinity-Turbidity Correlation Model: To deeply reveal the internal relationship between the alkalinity and turbidity of circulating water, a large number of systematic experimental studies were carried out. During the experiment, various actual working conditions were simulated. By changing key factors such as the water quality components of circulating water (such as adjusting the concentrations of calcium, magnesium, carbonate, bicarbonate ions, etc.), temperature (setting different temperature gradients in the range of 20°C - 60°C), and flow rate (adjusting the frequency of the circulating water pump to change the water flow rate), the corresponding alkalinity and turbidity data were recorded synchronously. Data analysis methods such as multiple linear regression and neural network were used to deeply mine and model the massive experimental data. After repeated verification and optimization, a highly accurate correlation model was established as follows: Among them, T represents turbidity, with the unit of NTU; A represents alkalinity, with the unit of mmol / L; etc. are the concentrations of calcium, magnesium, carbonate, bicarbonate ions, etc. in the water quality, with the unit of mg / L; T is the water temperature, with the unit of °C; Q is the water flow rate, with the unit of m³ / h. This model fully considers the comprehensive influence of various factors on the relationship between alkalinity and turbidity, and can accurately predict the change trend of turbidity based on the real-time monitored alkalinity and other relevant parameters, with a prediction accuracy of over 95%.

[0005] Multi-parameter Fusion Analysis and Feedback Control: The central control system uses advanced data fusion algorithms to comprehensively analyze multi-dimensional water quality parameters such as alkalinity, turbidity, pH value, hardness, conductivity, etc. collected in real time. When an abnormal fluctuation occurs in a certain parameter, the system quickly starts the correlation analysis mechanism to evaluate the potential impact of this change on other parameters and the overall water quality balance. For example, when the alkalinity increases and the pH value rises synchronously, the system analyzes the historical data and the correlation model to judge that it may be due to the increase in the concentration of carbonate ions in the water. At this time, if the turbidity also shows an upward trend, the system issues precise instructions to the intelligent dosing system according to the preset control strategy to adjust the dosing amount and dosing frequency of corrosion inhibitors, scale inhibitors and other chemicals to maintain water quality stability and control the turbidity within the target range. Adaptive Optimization of Intelligent Chemical Dosing System: The intelligent chemical dosing system consists of core components such as chemical dosing pumps, chemical storage tanks, and intelligent controllers. The intelligent controller is built with control programs based on advanced algorithms such as fuzzy control and model predictive control. It can automatically and accurately adjust the chemical dosing amount and dosing frequency according to the instructions from the central control system, combined with real-time water quality data and system operating conditions. In the initial stage of the circulating water system startup, the water quality is unstable and microorganisms are prone to grow. The dosing system automatically increases the dosing amount of bactericide to quickly inhibit the reproduction of microorganisms and establish a good water quality environment. During the normal operation stage of the system, the dosing system dynamically adjusts the dosing amount of scale inhibitor with an accuracy of 0.1 L / h based on real-time turbidity data to ensure the minimum chemical consumption while meeting the water quality control requirements. At the same time, the dosing system has the ability of self-learning. It can continuously optimize control parameters based on the data accumulated during long-term operation to improve the accuracy and efficiency of chemical dosing.

[0006] Precise Turbidity Control By establishing the correlation model between alkalinity and turbidity, it can predict turbidity changes in advance and accurately, providing a scientific basis for timely adjusting the chemical dosing strategy. The actual application data shows that after adopting this process, the turbidity of circulating water can be stably controlled below 5 NTU. Compared with the traditional process, the turbidity fluctuation range is reduced by more than 80%, effectively reducing equipment scaling and blockage problems and extending the equipment cleaning cycle. Taking the circulating water system of a chemical industrial park as an example, after implementing this process, the cleaning cycle of the heat exchanger is extended from the original 3 months to 12 months, significantly reducing the equipment maintenance cost. Real-time Online Control: Through online water quality monitoring equipment and multi-parameter fusion analysis technology, 24-hour uninterrupted real-time monitoring and dynamic adjustment of circulating water quality are realized. Once the water quality is abnormal, the system can respond within 1 minute and take timely measures to correct it, greatly improving the timeliness and reliability of water quality control. Compared with the traditional regular sampling and analysis method, it effectively avoids the equipment failure risk caused by lagging water quality monitoring, ensures the stable operation of the circulating water system, and reduces the number of production interruptions. According to statistics, the number of production interruptions of the circulating water system due to water quality problems in enterprises adopting this process is reduced by more than 90%. Reduction of Operating Costs: The adaptive optimization function of the intelligent chemical dosing system realizes the precise matching of the chemical dosing amount and the real-time water quality requirements, avoiding excessive waste of chemicals. At the same time, due to the effective control of turbidity, equipment scaling and corrosion are reduced, the service life of the equipment is extended, and the maintenance cost is reduced. Through comprehensive calculation, after adopting this process, the operating cost of the enterprise's circulating water system can be reduced by 15% - 30%, including a 20% - 40% reduction in chemical costs and a 10% - 20% reduction in equipment maintenance costs, with significant economic benefits. Specific Implementation Modes

[0007] Online water quality monitoring equipment: High-precision monitoring instruments of internationally renowned brands are selected. For the alkalinity analyzer, an automatic potentiometric titrator from Metrohm Switzerland is used, which has high-precision titration and potentiometric detection functions and can accurately measure different types of alkalinity; for the turbidity meter, a 2100P turbidity meter from Hach is selected, which adopts the 90° scattered light detection principle, with a measurement range of 0 - 1000 NTU and an accuracy of up to ±0.01 NTU; for the pH meter, the SevenExcellence series from Mettler Toledo is used, with a measurement accuracy of ±0.001 pH; for the hardness meter, a Multi 3430 type from WTW Germany is used, which can measure calcium hardness and total hardness simultaneously, with an accuracy of up to ±0.1 mg / L; for the conductivity meter, a DDSJ-308F type from Leici is selected, with a wide measurement range and an accuracy of up to ±0.01 μS / cm. Intelligent chemical dosing system: Independently developed and designed. The chemical dosing pump uses an electromagnetic-driven metering pump from Prominent Germany, with a flow regulation range of 0 - 100 L / h and an adjustment accuracy of ±0.1 L / h; the chemical storage tanks are made of corrosion-resistant polyethylene, with capacities of 500 L (corrosion inhibitor), 300 L (scale inhibitor), and 200 L (biocide) respectively; the intelligent controller is developed based on the STM32 microcontroller and integrates functional modules such as data processing, communication, and control algorithms. Circulating water experimental device: Built by simulating an actual industrial circulating water system, including a circulating water pump (with a power of 15 kW and a flow rate adjustable in the range of 50 - 200 m³ / h), a cooling tower (with a cooling capacity of 500 kW), a heat exchanger (a shell-and-tube heat exchanger with a heat transfer area of 50 m²), etc. These devices are connected by pipelines to form a complete circulating loop. Experimental chemicals: Corrosion inhibitor: An organophosphonate corrosion inhibitor with excellent performance is selected, such as hydroxyethylidene diphosphonic acid (HEDP), with an active ingredient content of ≥50%. It has good corrosion inhibition performance and chemical stability, can form a dense protective film on the metal surface, and inhibit corrosion. Scale inhibitor: A polycarboxylate scale inhibitor is used, such as sodium polyacrylate (PAAS), with a molecular weight between 3000 - 5000. Through chelation and dispersion effects, it prevents the formation of scale by calcium, magnesium and other ions in water and reduces the scale layer adhesion rate. Biocide: A compounding scheme combining an oxidizing biocide (such as sodium hypochlorite, with an available chlorine content of ≥10%) and a non-oxidizing biocide (such as isothiazolinone, with an active ingredient content of ≥14%) is adopted. Utilizing the synergistic effect of the two, it can broadly kill various microorganisms in the circulating water and inhibit the growth and slime formation of microorganisms. Experimental process: Real-time monitoring of water quality parameters: The on-line water quality monitoring equipment was accurately installed at key positions such as the inlet, outlet, inlet and outlet of the heat exchanger, and the return water pipeline of the cooling tower of the circulating water experimental device according to the design scheme. After each monitoring device was debugged and calibrated, it began to collect water quality data in real time. The data was transmitted to the industrial computer of the central control system through the RS485 communication interface. The industrial computer ran the self-developed data acquisition and monitoring software to display, store and preliminarily analyze the data in real time. Establishment of the alkalinity-turbidity correlation model: During the operation of the circulating water experimental device, the working conditions such as the water quality composition, temperature, and flow rate of the circulating water were systematically changed. The concentrations of calcium, magnesium, carbonate, bicarbonate and other ions were adjusted by adding chemical reagents to the circulating water; the water temperature was adjusted by using an electric heating device and a cooling tower; the water flow rate was changed by adjusting the frequency of the circulating water pump. After stabilizing for 30 minutes under each working condition, the data of alkalinity, turbidity and other related water quality parameters were synchronously recorded. A total of 500 groups of data under different working conditions were collected, and the MATLAB data analysis software was used to establish a model by combining multiple linear regression and neural network. After multiple model trainings and optimizations, the root mean square error (RMSE) of the finally established alkalinity-turbidity correlation model on the test set was less than 0.5 NTU, with extremely high prediction accuracy. Multi-parameter fusion analysis and feedback control: The industrial computer of the central control system ran the multi-parameter fusion analysis software. Based on fuzzy logic and expert system algorithms, this software comprehensively analyzed the water quality parameters such as alkalinity, turbidity, pH value, hardness, and conductivity collected in real time. When a certain parameter changed, the software automatically called the correlation model and historical data to analyze the impact of this change on other parameters and the overall water quality. For example, when the alkalinity increased by 0.5 mmol / L and the pH value increased by 0.2, the software analyzed and judged that it might be due to the change in the makeup water quality, resulting in an increase in the carbonate ion concentration. If the turbidity also began to rise at this time, according to the preset control strategy, the software calculated that the dosage of the scale inhibitor needed to be increased by 2 L / h, and at the same time, the dosage of the corrosion inhibitor was slightly adjusted by 0.5 L / h, and the control instruction was sent to the intelligent dosing system. Adaptive Optimization of Intelligent Chemical Dosing System: After receiving the control instructions sent by the central control system, the intelligent controller of the intelligent chemical dosing system accurately controls the operating frequency and stroke of the chemical dosing pump according to the built-in control algorithm, realizing precise adjustment of the chemical dosing amount and dosing frequency. At the initial stage of starting the circulating water experimental device, due to the risk of microbial growth in the system, the intelligent chemical dosing system automatically increases the bactericide dosing amount to 10 L / h and runs continuously for 24 hours, effectively inhibiting microbial reproduction. During the normal operation stage of the system, the intelligent chemical dosing system dynamically adjusts the scale inhibitor dosing amount with an accuracy of 0.1 L / h according to the real-time turbidity data. For example, when the turbidity rises from 3 NTU to 4 NTU, the intelligent chemical dosing system automatically increases the scale inhibitor dosing amount from 5 L / h to 6 L / h to ensure that the turbidity is stable within the target range. At the same time, the intelligent chemical dosing system records and analyzes the operation data every 1 hour, optimizes the control parameters according to the long-term operation data, and continuously improves the accuracy and efficiency of chemical dosing. By continuously operating the circulating water experimental device for 30 days, a comprehensive comparative analysis of the circulating water quality before and after adopting this process was carried out. The experimental results are shown in the following table:

[0008] It can be clearly seen from the experimental data that after adopting this process, the turbidity of the circulating water has been significantly improved, the average turbidity has dropped from 18 NTU to 4 NTU, the turbidity fluctuation range has been greatly reduced, the equipment scaling rate has been reduced by 80%, and the chemical consumption cost has been reduced by 37.5%. This fully verifies the excellent effect of this process in controlling the low-turbidity water quality of circulating water, can effectively solve the problems existing in the existing process, and realize the efficient and economical operation of the circulating water system.

Claims

1. An on-line control process for low turbidity circulating water quality based on alkalinity control, characterized in that, It includes the following steps: Real-time monitoring of water quality parameters: Install online water quality monitoring equipment with fast and accurate measurement capabilities at key nodes such as the inlet, outlet, inlet and outlet of heat exchangers, and the return water pipeline of the cooling tower in the circulating water system; the equipment includes an alkalinity analyzer, a turbidity meter, a pH meter, a hardness meter, and a conductivity meter; The alkalinity analyzer combines acid-base titration with potentiometric detection technology, and the measurement accuracy can reach ±0.01 mmol / L. Each device uses a wired or wireless data transmission module to transmit the collected water quality data to the central control system at a frequency of no less than once per minute; Establishment of the alkalinity-turbidity correlation model: Conduct multi-condition simulation experiments by changing the water quality components of the circulating water, adjusting the concentrations of ions such as calcium, magnesium, carbonate, and bicarbonate; control the temperature in the range of 20°C - 60°C; adjust the water flow by changing the frequency of the circulating water pump; simultaneously record the alkalinity, turbidity, and related water quality parameter data under each condition; use a data analysis method combining multiple linear regression and neural network to construct the alkalinity-turbidity correlation model, and the model expression is: Among them, T represents turbidity with the unit of NTU; A represents alkalinity with the unit of mmol / L; etc. are respectively the concentrations of calcium, magnesium, carbonate, bicarbonate and other ions in water quality, with the unit of mg / L; T is the water temperature with the unit of °C; Q is the water flow rate with the unit of m³ / h. This model fully considers the comprehensive influence of various factors on the relationship between alkalinity and turbidity, and can accurately predict the change trend of turbidity based on the real-time monitored alkalinity and other relevant parameters, with a prediction accuracy rate of over 95%; Multi-parameter fusion analysis and feedback control: The central control system uses fuzzy logic and expert system algorithms to perform fusion analysis on multi-dimensional water quality parameters such as alkalinity, turbidity, pH value, hardness, and conductivity collected in real time; when the fluctuation range of a certain parameter exceeds the preset threshold, the system automatically calls the correlation model and historical data to evaluate the impact of this change on other parameters and the overall water quality balance; according to the evaluation results, send precise chemical dosing adjustment instructions to the intelligent chemical dosing system according to the preset control strategy; Adaptive optimization of the intelligent chemical dosing system: The intelligent chemical dosing system consists of a chemical dosing pump, a chemical storage tank, and an intelligent controller; the intelligent controller is built-in with fuzzy control and model predictive control algorithms; at the initial stage of starting the circulating water system, automatically increase the bactericide dosing amount to 10 L / h and continue for 24 hours; during the normal operation stage of the system, dynamically adjust the scale inhibitor dosing amount with an accuracy of 0.1 L / h according to the real-time turbidity data; at the same time, the system records and analyzes the operation data every 1 hour, and optimizes the control parameters according to the long-term operation data.

2. The online control process for low turbidity circulating water quality based on alkalinity control according to claim 1, characterized in that, The alkalinity analyzer is a Metrohm automatic potentiometric titrator, the turbidity meter is a Hach 2100P turbidity meter, the pH meter is a Mettler-Toledo SevenExcellence series, the hardness meter is a WTW Multi 3430 type from Germany, and the conductivity meter is a Leici DDSJ-308F type.

3. The online control process for low turbidity circulating water quality based on alkalinity control according to claim 1, wherein The chemical dosing pump is a Prominent electromagnetic drive metering pump from Germany, with a flow regulation range of 0 - 100 L / h and an adjustment accuracy of ±0.1 L / h; the chemical storage tank is made of corrosion-resistant polyethylene, the capacity of the corrosion inhibitor storage tank is 500 L, the capacity of the scale inhibitor storage tank is 300 L, and the capacity of the bactericide storage tank is 200 L.

4. The online control process for low turbidity circulating water quality based on alkalinity control according to claim 1, characterized in that, The corrosion inhibitor is hydroxyethylidene diphosphonic acid (HEDP), and the content of the active ingredient is ≥ 50%; the scale inhibitor is sodium polyacrylate (PAAS), and the molecular weight is between 3000 and 5000; the bactericide adopts the compounding scheme of sodium hypochlorite (effective chlorine content ≥ 10%) and isothiazolinone (active ingredient content ≥ 14%).

5. The online control process for low-turbidity circulating water quality based on alkalinity control according to claim 1, characterized in that The central control system operates based on an industrial computer, integrates functions such as data acquisition, multi-parameter fusion analysis, and instruction sending, can display and store water quality data in real time, and the storage period is not less than one year.

6. The online control process for low turbidity circulating water quality based on alkalinity control according to claim 1, characterized in that, The intelligent controller is developed based on the STM32 microcontroller, integrates data processing, communication, and control algorithm function modules, and the communication interface adopts the RS485 standard interface.

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