Power plant waste heat coupling seawater desalination system and energy efficiency optimization method

Abstract

The invention discloses a power plant waste heat coupling seawater desalination system and an energy efficiency optimization method, and belongs to the technical field of water treatment. The system comprises a waste heat cascade recovery unit, a hot film collaborative desalination unit, a strong brine treatment unit and an intelligent regulation and control unit, the waste heat cascade recovery unit realizes graded utilization of waste heat at different temperatures, the hot film collaborative desalination unit adopts a multi-stage dynamic film group and hot film coupling process, and the strong brine treatment unit realizes zero emission and resource recovery of strong brine. And the intelligent regulation and control unit realizes full-process dynamic optimization based on a fuzzy PID algorithm. According to the optimization method, through parameter collection, waste heat distribution optimization, membrane module adaptation optimization, strong brine collaborative optimization and real-time iterative optimization, the waste heat utilization rate is larger than or equal to 90%, and the unit water production energy consumption is smaller than or equal to 0.6 kWh / m. The system solves the problems of low waste heat utilization rate, extensive regulation and control and strong brine pollution in the prior art, remarkably improves the system energy efficiency and operation stability, is suitable for various power plant waste heat coupling seawater desalination scenes, and has important economic and social values.

Description

Technical Field

[0001] This invention belongs to the field of seawater desalination and comprehensive energy utilization technology, specifically involving a power plant waste heat coupled seawater desalination system and energy efficiency optimization method, applicable to the coordinated operation of waste heat recovery and utilization and seawater desalination in various power plants such as thermal power and nuclear power. Background Technology

[0002] The global freshwater shortage is becoming increasingly severe, and seawater desalination has become a key approach to solving the water crisis in coastal areas. Current mainstream seawater desalination technologies include reverse osmosis (RO) and multi-effect distillation (MED), but both suffer from high energy consumption, with energy costs accounting for over 60% of the total water production cost. Meanwhile, power plants (especially thermal and nuclear power plants) generate a large amount of waste heat during power generation, with a particularly high proportion being low-temperature waste heat (40-120℃). This waste heat is often directly discharged, not only wasting energy but also potentially causing thermal pollution. To achieve efficient energy utilization, existing technologies are beginning to explore the coupled application of power plant waste heat and seawater desalination technologies. For example, Shanghai Electric's thermal membrane coupled seawater desalination technology (F-MED-RO) integrates thermal and membrane processes to achieve the cascade utilization of heat and seawater. However, this technology still has the following core shortcomings: First, the waste heat utilization efficiency is low, and the dynamic fluctuation characteristics of the waste heat from the power plant are not accurately matched, resulting in some waste heat not being effectively recovered. Second, the system control is extensive and relies on fixed process parameters, making it difficult to cope with fluctuations in operating conditions such as changes in seawater salinity and membrane fouling, often resulting in problems such as a decrease in desalination rate and a surge in energy consumption. Third, the synergy between concentrated brine treatment and waste heat utilization is poor. Direct discharge of concentrated brine generated by membrane technology can easily cause marine ecological pollution, while separate treatment requires additional energy consumption. Furthermore, while existing multi-stage membrane desalination systems achieve dynamic combination of membrane modules, they are not deeply integrated with the cascade utilization of waste heat from power plants, failing to fully leverage the temperature gradient advantage of waste heat. Simultaneously, energy efficiency optimization is often limited to single process stages, lacking a synergistic optimization strategy for the entire process of waste heat recovery, seawater desalination, and concentrated brine treatment, resulting in low overall system energy efficiency. Therefore, developing a coupled system and method that can achieve precise recovery of waste heat from power plants, efficient operation of seawater desalination, and optimization of energy efficiency throughout the entire process is of great significance for promoting the low-carbon development of the seawater desalination industry and improving the comprehensive energy utilization rate of power plants. It is in line with the national development direction of energy conservation and environmental protection industries and has the technical value and social demand for priority review. Summary of the Invention

[0003] In response to the problems of low utilization rate of waste heat from power plants, extensive regulation and control of seawater desalination systems, poor overall energy efficiency, and concentrated brine treatment in existing technologies, this invention provides a power plant waste heat coupled seawater desalination system and energy efficiency optimization method, which realizes precise utilization of waste heat in stages, dynamic adaptation of seawater desalination, optimal energy efficiency throughout the process, and synergistic treatment of concentrated brine, thereby reducing water production costs and minimizing environmental impact. To achieve the above objectives, the present invention provides the following technical solution: The waste heat coupled seawater desalination system of the power plant includes a waste heat cascade recovery unit, a thermal membrane co-desalination unit, a concentrated brine treatment unit, and an intelligent control unit. Each unit is interconnected with the control system through pipelines. The waste heat cascade recovery unit includes a high-temperature waste heat exchanger, a medium-temperature waste heat exchanger, and a low-temperature waste heat exchanger connected in sequence, which are respectively connected to different process modules of the thermal film co-desalination unit, and are equipped with waste heat flow and temperature monitoring modules. The thermal membrane co-desalination unit includes a pretreatment module, a multi-effect distillation module (MED module), a reverse osmosis membrane module (RO membrane module), and a permeate conditioning module. The pretreatment module uses an ultrafiltration membrane, and the pretreated seawater is divided into two streams and enters the MED module and the RO membrane module respectively. The RO membrane module uses multi-stage membrane components with different desalination rates. The membrane components are prepared by interfacial polymerization reaction controlled by a buffer solution, and the pH value of the aqueous solution of different membrane components is 6-11.5. The permeate conditioning module mixes the permeate from the MED module and the RO membrane module in a certain proportion. The concentrated brine treatment unit includes a concentrated brine collection tank, a reduced pressure evaporation module, and a salt recovery module. The concentrated brine generated by the RO membrane module enters the reduced pressure evaporation module and is concentrated by evaporation using the low-temperature waste heat at the end of the waste heat recovery unit. The concentrated brine enters the salt recovery module, and the steam generated by evaporation is returned to the pretreatment module. The intelligent control unit includes a data acquisition module, an algorithm optimization module, and an actuator; the data acquisition module collects waste heat parameters, seawater parameters, membrane module parameters, and product water parameters in real time; the algorithm optimization module constructs an energy efficiency optimization model based on the fuzzy PID algorithm; and the actuator responds to optimization commands to achieve dynamic control of system parameters. Furthermore, the high-temperature waste heat exchanger is adapted to waste heat of 100-120℃, the medium-temperature waste heat exchanger is adapted to waste heat of 60-100℃, and the low-temperature waste heat exchanger is adapted to waste heat of 40-60℃. Furthermore, the pretreatment module uses an ultrafiltration membrane with a molecular weight cutoff of 20,000-100,000 Da, and the ultrafiltration membrane material is one or more combinations of polysulfone, polyethersulfone, and sulfonated polyethersulfone. Furthermore, in the multi-stage membrane module of the RO membrane module, the pH value of the aqueous phase solution of the first stage membrane module is 10-11.5, that of the second stage is 8-9.5, and that of the third stage is 6-7.5. Furthermore, the evaporation temperature of the reduced pressure evaporation module is controlled at 45-55℃, and the concentration ratio of concentrated brine is ≥10 times. Furthermore, the data acquisition frequency of the intelligent control unit is ≥5Hz, the algorithm optimization module adopts fuzzy PID algorithm, and the actuator includes a solenoid valve, a variable frequency pump, and a membrane module switching device. The energy efficiency optimization method for power plant waste heat coupled with seawater desalination includes the following steps: Step 1: Parameter initialization and real-time acquisition. After the intelligent control unit is started, the system operating parameters are initialized. The data acquisition module collects key parameters in real time, such as waste heat temperature, flow rate, seawater salinity, membrane module transmembrane pressure difference, and product water conductivity. Step 2: Waste heat distribution optimization. The algorithm optimization module dynamically allocates the proportion of waste heat to the MED module and RO preheating module according to the waste heat temperature classification results. High-temperature waste heat is given priority to the MED module, medium-temperature waste heat is used to supplement the heat demand of the MED module, and low-temperature waste heat is used entirely for preheating the RO feed seawater. Step 3: Dynamic adaptation and optimization of membrane modules. Based on the seawater salinity detection results, the optimal multi-level membrane module combination is matched from the membrane module configuration rule library. At the same time, the membrane module operating pressure is adjusted in real time according to the changes in transmembrane pressure difference. Step 4: Co-optimization of concentrated brine treatment. Based on the output and concentration of RO concentrated brine, dynamically adjust the waste heat supply of the vacuum evaporation module, control the evaporation temperature, ensure the concentration ratio of concentrated brine, and recover the evaporated steam to the pretreatment module. Step 5: Real-time feedback and iterative optimization. The data acquisition module continuously monitors the system's energy efficiency indicators. If the energy efficiency indicators deviate from the optimal threshold, the algorithm optimization module re-calculates the optimization parameters and adjusts the system's operating status. Furthermore, the waste heat utilization rate in step 2 is ≥90%. Furthermore, in step 3, high-salinity seawater adopts a combination of high-salinity desalination rate membrane module in front and low-salinity desalination rate membrane module in the back. High-salinity seawater refers to salinity ≥ 35‰, and low-salinity seawater adopts a simplified membrane module stage method. Low-salinity seawater refers to salinity < 35‰. Furthermore, the system energy efficiency indicators in step 5 include unit water production energy consumption and waste heat utilization rate, with unit water production energy consumption ≤ 0.6 kWh / m³. Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved waste heat utilization efficiency: Through the cascade recovery and precise distribution of waste heat, targeted utilization of waste heat at different temperature levels is achieved, increasing the waste heat utilization rate to over 90%, which is more than 30% higher than the traditional coupled system, greatly reducing fossil energy consumption and meeting energy conservation and environmental protection requirements; 2. Improved system energy efficiency and operational stability: By adopting multi-stage membrane module dynamic adaptation and fuzzy PID intelligent control, the operating parameters can be optimized in real time according to changes in operating conditions such as seawater salinity and waste heat fluctuations. The unit water production energy consumption is reduced to below 0.6kWh / m³, which is 25%-30% lower than the traditional thermal membrane coupling system, the membrane fouling rate is reduced by 60%, and the membrane life is extended by more than 30%. 3. Achieve zero discharge and resource recovery of concentrated brine: Concentrated brine is concentrated by evaporation using waste heat at the end of the process, recovering solid salt and steam, avoiding marine pollution while achieving resource recycling and reducing environmental treatment costs; 4. Wide applicability and excellent economy: It is compatible with the waste heat characteristics of various power plants, and the heat film coupling ratio can be flexibly adjusted. It is suitable for high, medium and low salinity seawater desalination scenarios, reducing water production costs by 20%-25%. It has the prospect of large-scale engineering applications and is of great significance to promoting water resource security and low-carbon energy transformation in coastal areas. It is in line with the national interest orientation of priority review. Attached Figure Description Figure 1 This is a structural block diagram of the power plant waste heat coupled seawater desalination system of the present invention; Figure 2 This is a flowchart of the energy efficiency optimization method for power plant waste heat coupled with seawater desalination according to the present invention. Detailed Implementation To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. This invention proposes a waste heat coupled seawater desalination system for power plants, including a waste heat cascade recovery unit, a thermal membrane co-desalination unit, a concentrated brine treatment unit, and an intelligent control unit. Each unit is interconnected with the control system through pipelines. The waste heat recovery unit comprises a high-temperature waste heat exchanger, a medium-temperature waste heat exchanger, and a low-temperature waste heat exchanger connected in sequence. The high-temperature waste heat exchanger is suitable for waste heat of 100-120℃, the medium-temperature waste heat exchanger for 60-100℃, and the low-temperature waste heat exchanger for 40-60℃. Each heat exchanger is made of 316L stainless steel, possessing excellent corrosion resistance and heat exchange efficiency. Its heat exchange area is precisely matched to the waste heat flow rate and heat exchange requirements within the corresponding temperature range to ensure sufficient heat transfer. Each heat exchanger is connected to a different temperature-controlled valve and a thermal film co-processing desalination unit. The process modules are connected accordingly to achieve precise, tiered utilization of waste heat. The waste heat recovery unit is also equipped with a waste heat flow and temperature monitoring module, which uses a platinum resistance temperature sensor with an accuracy of ±0.5℃ and an electromagnetic flow meter with an accuracy of ±1% to collect waste heat parameters in real time. The collected data is transmitted to the intelligent control unit via shielded cables to avoid signal interference that could cause parameter distortion. In addition, the waste heat cascade recovery unit is also equipped with a bypass regulating pipeline. When the waste heat temperature or flow exceeds a preset threshold, a portion of the waste heat can be diverted to the cooling tower through the bypass to prevent subsequent process modules from being damaged by overheating or overflow, thus ensuring the safe operation of the system. The thermal membrane co-desalination unit includes a pretreatment module, a multi-effect distillation module, a reverse osmosis membrane module, and a product water conditioning module. The pretreatment module uses an ultrafiltration membrane to remove suspended solids and colloids from the seawater. The ultrafiltration membrane is made of polyethersulfone with a molecular weight cutoff of 50,000 Da, which has the advantages of strong anti-fouling ability and long service life. At the same time, the pretreatment module is equipped with an automatic backwashing system, which combines timed backwashing with chemical cleaning to avoid membrane pore blockage and ensure stable pretreatment effect. The pretreated seawater is divided into two paths through a three-way valve. One path enters the multi-effect distillation module, which uses high-temperature and medium-temperature waste heat to heat and evaporate the seawater to achieve desalination. The multi-effect distillation module adopts a 5-stage evaporator series design, with the temperature of each stage decreasing by 5-8°C, realizing the cascade reuse of heat and improving heat utilization efficiency. The other path enters the reverse osmosis membrane module, which uses low-temperature waste heat to preheat the feed seawater to 35-40°C. This temperature range is the optimal operating temperature of the reverse osmosis membrane, which can increase the membrane permeate flux by 15%-20% and significantly reduce the energy consumption of membrane operation. The reverse osmosis membrane module adopts a multi-stage series design of membrane modules with different desalination rates. The membrane modules are prepared by controlling the interfacial polymerization reaction through a buffer solution. The pH value of the aqueous solution for different membrane modules is 6-11.5, with high desalination rate membrane modules corresponding to high pH value systems. The desalination performance of the membrane is improved by controlling the degree of crosslinking of the interfacial polymerization reaction, achieving dynamic adaptation of the desalination rate. The permeate conditioning module has built-in water quality monitoring sensors and variable frequency mixing pumps to monitor the conductivity, hardness and other indicators of MED permeate and RO permeate in real time. It automatically adjusts the mixing ratio of the two permeates according to the preset water quality standards to ensure that the water supply quality is stable and meets the standards. The concentrated brine treatment unit includes a concentrated brine collection tank, a reduced pressure evaporation module, and a salt recovery module. The concentrated brine generated by the RO membrane module enters the reduced pressure evaporation module and is concentrated by evaporation using the low-temperature waste heat at the end of the waste heat recovery unit. The concentrated brine enters the salt recovery module to recover solid salt. The steam generated by evaporation is returned to the pretreatment module for seawater preheating, achieving zero discharge of concentrated brine and deep utilization of waste heat. The intelligent control unit includes a data acquisition module, an algorithm optimization module, and an actuator. The data acquisition module collects waste heat parameters (temperature, flow rate), seawater parameters (salinity, temperature), membrane module parameters (transmembrane pressure difference, desalination rate), and permeate parameters (conductivity, yield) in real time. The algorithm optimization module constructs an energy efficiency optimization model based on a fuzzy PID algorithm and outputs optimization commands such as waste heat distribution ratio, membrane module combination mode, and concentrated brine treatment load. The actuator includes a solenoid valve, a variable frequency pump, and a membrane module switching device, which respond to optimization commands to achieve dynamic control of system parameters. This invention also proposes a method for optimizing the energy efficiency of power plant waste heat coupled with seawater desalination, which is implemented based on the above system and includes the following steps: Step 1: Parameter initialization and real-time acquisition. After the intelligent control unit is started, the system operating parameters are initialized. The data acquisition module collects key parameters in real time, such as waste heat temperature, flow rate, seawater salinity, membrane module transmembrane pressure difference, and product water conductivity. Step 2: Waste heat tiered allocation optimization. The algorithm optimization module first determines the temperature gradation based on waste heat temperature monitoring data, and then dynamically allocates the proportion of waste heat to the multi-effect distillation module and the reverse osmosis preheating module based on the real-time load demand of the thermal membrane co-desalination unit. High-temperature waste heat is prioritized for the multi-effect distillation module to drive seawater evaporation, with an allocation ratio of no less than 80%, ensuring stable evaporation temperature in the multi-effect distillation module. Medium-temperature waste heat is flexibly supplemented according to the heat gap in the multi-effect distillation module, with the allocation ratio dynamically adjusted between 50% and 70%. Low-temperature waste heat is entirely used for preheating the reverse osmosis feed seawater. Simultaneously, through temperature feedback closed-loop control, when the preheated seawater temperature is below 35℃, the heat exchange power of the low-temperature waste heat is automatically increased; when the temperature is above 40℃, the heat exchange power is reduced through bypass adjustment, ensuring the preheating temperature remains stable within the optimal range, ultimately achieving a waste heat utilization rate of ≥90%. Step 3: Dynamic adaptation and optimization of membrane modules. Based on the seawater salinity detection results, the optimal multi-stage membrane module combination is matched from the membrane module configuration rule library. For high-salinity seawater (salinity ≥ 35‰), a combination of high-salinity desalination membrane modules (99.5%-99.8%) is used in front and low-salinity desalination membrane modules (98%-99%) are used in the back. For low-salinity seawater (salinity < 35‰), the number of membrane module stages is simplified. At the same time, the membrane module operating pressure is adjusted in real time according to the changes in transmembrane pressure difference to alleviate membrane fouling. Step 4: Co-optimization of concentrated brine treatment. Based on the output and concentration of RO concentrated brine, dynamically adjust the waste heat supply of the vacuum evaporation module, control the evaporation temperature to 45-55℃, ensure that the concentrated brine concentration ratio is ≥10 times, and recover all the evaporated steam to the pretreatment module to achieve closed-loop utilization of waste heat and water resources. Step 5: Real-time feedback and iterative optimization. The data acquisition module continuously monitors the system's energy efficiency indicators (energy consumption per unit of water production, waste heat utilization rate). If the energy efficiency indicators deviate from the optimal threshold, the algorithm optimization module re-calculates the optimization parameters and adjusts the system's operating status through the actuator to ensure optimal energy efficiency throughout the entire process. The present invention will be further described in detail below with reference to specific embodiments: This embodiment selects a 300MW coastal thermal power plant as the application scenario. During normal operation, the waste heat emitted from the turbine exhaust and circulating water processes of this power plant is stable in the temperature range of 40-120℃, with an average flow rate of 500m³ / h, providing a stable waste heat supply capacity. The seawater to be treated is taken from a nearby sea area, with a measured salinity fluctuation range of 35‰-38‰. The suspended solids concentration is approximately 15-25mg / L, and the colloid content is 3-5mg / L. The target water production capacity set for the project is 10,000m³ / d, and the water quality must meet the "Standards for Drinking Water Quality" (GB 5749-2022), with conductivity ≤50μS / cm, total hardness ≤450mg / L (calculated as CaCO3), and total bacterial count ≤100CFU / mL. To ensure stable system operation, key operating thresholds were also set: the maximum transmembrane pressure difference of the RO membrane module is 1.2 MPa, the evaporation temperature fluctuation range of the MED module does not exceed ±5℃, and the concentration ratio of concentrated brine is at least 10 times. This embodiment takes a waste heat coupled with seawater desalination project of a thermal power plant as an example. The temperature range of the waste heat emitted by the power plant is 40-120℃, the flow rate is 500m³ / h, the seawater salinity is 35‰-38‰, the target water production scale is 10000m³ / d, and the water conductivity is ≤50μS / cm. 1. System Construction: The waste heat recovery unit is equipped with a high-temperature heat exchanger (heat exchange area 1000㎡), a medium-temperature heat exchanger (heat exchange area 800㎡), and a low-temperature heat exchanger (heat exchange area 1200㎡), and is equipped with a platinum resistance temperature sensor and an electromagnetic flow meter to monitor waste heat parameters in real time. The pretreatment module of the thermal membrane synergistic desalination unit uses a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 50,000 Da. The MED module is equipped with a 5-stage evaporation effect. The RO membrane module includes a 3-stage membrane module. The first stage membrane module has an aqueous solution pH of 10.5 (desalination rate of 99.8%), the second stage has a pH of 8.5 (desalination rate of 99%), and the third stage has a pH of 7.0 (desalination rate of 98.5%). The product water conditioning module is equipped with a variable frequency mixing pump. The concentrated brine treatment unit has a concentrated brine collection tank with a volume of 500 m³, the reduced pressure evaporation module uses a falling film evaporator (evaporation area of ​​500 m²), and the salt recovery module uses a centrifugal dehydrator. The intelligent control unit uses a PLC controller (model S7-1500) with a data acquisition frequency of 10Hz. The fuzzy PID algorithm is implemented through MATLAB programming, and the actuators are electric regulating valves and variable frequency centrifugal pumps. 2. Optimization process: Step 1: After the system starts up, the data acquisition module collects the waste heat temperature of 85℃, flow rate of 500m³ / h, seawater salinity of 36‰, transmembrane pressure difference of RO membrane module of 0.8MPa, and product water conductivity of 45μS / cm in real time. Step 2: The algorithm optimization module determines that the waste heat is in the medium temperature range, and allocates 60% of the waste heat to the MED module and 40% to the RO preheating module. After preheating, the temperature of the RO feed seawater is increased to 35°C. Step 3: Based on the seawater salinity of 36‰, match the first-stage + second-stage membrane module combination, and control the operating pressure at 5.5MPa; Step 4: The RO concentrated brine production is 4000 m³ / d with a concentration of 70‰. The reduced pressure evaporation module uses low-temperature waste heat to heat the concentrated brine to 50°C. After evaporation and concentration, the brine concentration is 300 g / L. The solid salt is recovered by centrifugation and dehydration. The evaporated steam is returned to the pretreatment module to preheat the seawater. Step 5: During operation, the PLC controller of the intelligent control unit summarizes and analyzes the collected parameters every 10 seconds. The real-time monitoring shows that the unit water production energy consumption is 0.58 kWh / m³ and the waste heat utilization rate is 92%, both within the preset optimal threshold. To verify the stability and anti-interference ability of the system, this embodiment also carried out a 72-hour continuous operation test. During the test, the waste heat temperature fluctuation (from 85℃ to 60℃, and then gradually rising to 100℃) and the seawater salinity change (from 36‰ to 38‰) were artificially simulated. When the seawater salinity rises to 38‰, the algorithm optimization module completes parameter iteration within 2 seconds, automatically activates the three-stage membrane module combination, adjusts the operating pressure to 6.0MPa, and simultaneously fine-tunes the heating power of the MED module to ensure that the permeate conductivity remains stable between 42-48μS / cm. When the waste heat temperature drops sharply to 60℃, the system automatically reduces the waste heat allocation ratio of the MED module to 40%, increases the waste heat allocation ratio of the RO preheating module to 60%, and activates the low-temperature operation compensation program of the RO membrane module to maintain the unit water production energy consumption not exceeding 0.6kWh / m³. After the test, the surface of the RO membrane module was inspected, and it was found that the membrane fouling degree was slight, with the transmembrane pressure difference increasing by only 0.05MPa, which could be restored to the initial state after simple backwashing. The concentrated brine treatment unit continued to operate stably, with a salt recovery efficiency of over 95%, an evaporation steam recovery rate of 100%, and no pollutant emissions. The results of this embodiment show that the system's unit water production energy consumption is reduced by 28% compared to the traditional thermal film coupling system, the waste heat utilization rate reaches 92%, the concentrated brine is discharged zero, and the produced water quality meets the standards, demonstrating good economic and environmental benefits. The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A power plant waste heat coupled seawater desalination system, characterized in that: It includes a waste heat recovery unit, a thermal film co-desalination unit, a concentrated brine treatment unit, and an intelligent control unit. Each unit is interconnected with the control system through pipelines. The waste heat cascade recovery unit includes a high-temperature waste heat exchanger, a medium-temperature waste heat exchanger, and a low-temperature waste heat exchanger connected in sequence, which are respectively connected to different process modules of the thermal film co-desalination unit, and are equipped with waste heat flow and temperature monitoring modules. The thermal membrane co-desalination unit includes a pretreatment module, a multi-effect distillation module (MED module), a reverse osmosis membrane module (RO membrane module), and a product water conditioning module. The pretreatment module uses an ultrafiltration membrane. The pretreated seawater is divided into two streams and enters the multi-effect distillation module and the reverse osmosis membrane module, respectively. The reverse osmosis membrane module uses multi-stage membrane modules with different desalination rates. The membrane modules are prepared by controlling the interfacial polymerization reaction through a buffer solution. The pH value of the aqueous solution of different membrane modules is 6-11.

5. The permeate conditioning module mixes the permeate from the multi-effect distillation module with the permeate from the reverse osmosis membrane module in a specific ratio. The concentrated brine treatment unit includes a concentrated brine collection tank, a reduced pressure evaporation module, and a salt recovery module. The concentrated brine generated by the RO membrane module enters the reduced pressure evaporation module and is concentrated by evaporation using the low-temperature waste heat at the end of the waste heat recovery unit. The concentrated brine enters the salt recovery module, and the steam generated by evaporation is returned to the pretreatment module. The intelligent control unit includes a data acquisition module, an algorithm optimization module, and an actuator; the data acquisition module collects waste heat parameters, seawater parameters, membrane module parameters, and product water parameters in real time; the algorithm optimization module constructs an energy efficiency optimization model based on the fuzzy PID algorithm; and the actuator responds to optimization commands to achieve dynamic control of system parameters.

2. The power plant waste heat coupled seawater desalination system according to claim 1, characterized in that: The high-temperature waste heat exchanger is suitable for waste heat of 100-120℃, the medium-temperature waste heat exchanger is suitable for waste heat of 60-100℃, and the low-temperature waste heat exchanger is suitable for waste heat of 40-60℃.

3. The power plant waste heat coupled seawater desalination system according to claim 1, characterized in that: The pretreatment module uses an ultrafiltration membrane with a molecular weight cutoff of 20,000-100,000 Da, and the ultrafiltration membrane material is one or more combinations of polysulfone, polyethersulfone, and sulfonated polyethersulfone.

4. The power plant waste heat coupled seawater desalination system according to claim 1, characterized in that: In the multi-stage membrane module of the RO membrane module, the pH value of the aqueous solution of the first stage membrane module is 10-11.5, that of the second stage is 8-9.5, and that of the third stage is 6-7.

5.

5. The power plant waste heat coupled seawater desalination system according to claim 1, characterized in that: The evaporation temperature of the reduced pressure evaporation module is controlled at 45-55℃, and the concentration ratio of concentrated brine is ≥10 times.

6. The power plant waste heat coupled seawater desalination system according to claim 1, characterized in that: The data acquisition frequency of the intelligent control unit is ≥5Hz, the algorithm optimization module adopts fuzzy PID algorithm, and the actuator includes solenoid valve, variable frequency pump, and membrane module switching device.

7. A method for optimizing the energy efficiency of power plant waste heat coupled with seawater desalination based on the system described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Parameter initialization and real-time acquisition. After the intelligent control unit is started, the system operating parameters are initialized. The data acquisition module collects key parameters in real time, such as waste heat temperature, flow rate, seawater salinity, membrane module transmembrane pressure difference, and product water conductivity. Step 2: Waste heat distribution optimization. The algorithm optimization module dynamically allocates the proportion of waste heat to the MED module and RO preheating module according to the waste heat temperature classification results. High-temperature waste heat is given priority to the MED module, medium-temperature waste heat is used to supplement the heat demand of the MED module, and low-temperature waste heat is used entirely for preheating the RO feed seawater. Step 3: Dynamic adaptation and optimization of membrane modules. Based on the seawater salinity detection results, the optimal multi-level membrane module combination is matched from the membrane module configuration rule library. At the same time, the membrane module operating pressure is adjusted in real time according to the changes in transmembrane pressure difference. Step 4: Co-optimization of concentrated brine treatment. Based on the output and concentration of RO concentrated brine, dynamically adjust the waste heat supply of the vacuum evaporation module, control the evaporation temperature, ensure the concentration ratio of concentrated brine, and recover the evaporated steam to the pretreatment module. Step 5: Real-time feedback and iterative optimization. The data acquisition module continuously monitors the system's energy efficiency indicators. If the energy efficiency indicators deviate from the optimal threshold, the algorithm optimization module re-calculates the optimization parameters and adjusts the system's operating status.

8. The method for optimizing the energy efficiency of power plant waste heat coupled with seawater desalination according to claim 7, characterized in that: In step 2, the waste heat utilization rate is ≥90%.

9. The method for optimizing the energy efficiency of power plant waste heat coupled with seawater desalination according to claim 7, characterized in that: In step 3, high-salinity seawater uses a combination of a high-salinity desalination rate membrane module placed before and a low-salinity desalination rate membrane module placed after. High-salinity seawater refers to seawater with a salinity ≥ 35‰. Low-salinity seawater uses a simplified membrane module stage approach, where low-salinity seawater refers to seawater with a salinity < 35‰.

10. The method for optimizing the energy efficiency of power plant waste heat coupled with seawater desalination according to claim 7, characterized in that: The system energy efficiency indicators in step 5 include unit water production energy consumption and waste heat utilization rate, with unit water production energy consumption ≤ 0.6 kWh / m³.

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