Chemical wastewater zero discharge energy efficiency dynamic optimization method

Abstract

The present application relates to wastewater zero discharge optimization technical field, especially to a kind of chemical wastewater zero discharge energy efficiency dynamic optimization method, comprising: the pretreated chemical wastewater is separated into monovalent salt concentrated water and divalent salt concentrated water and is stored in tank, with the liquid level difference of double-side storage tank and variation trend as scheduling trigger basis, with carbon emission quota total balance as top rigid constraint, combined with low-grade link waste heat available amount layered matching ion matching, concentration adaptation, energy consumption constraint three kinds of scheduling optimization strategy;Strategy execution whole process synchronous linkage adjusts the feed preheating load of evaporation crystallization link and mechanical steam re-compressor operating frequency, when liquid level tends to be stable, dynamically adjusts evaporation crystallization operating load upper limit and external energy supply ratio.The present application maximizes concentrated water degradation reuse consumption amount under the premise of guaranteeing carbon emission compliance, efficiently consumes low-grade waste heat, reduces evaporation crystallization energy consumption and solid waste disposal cost, realizes system multi-objective dynamic optimal adaptation.

Description

Technical Field

[0001] This invention relates to the field of wastewater zero-discharge optimization technology, and in particular to a dynamic optimization method for energy efficiency of zero-discharge chemical wastewater. Background Technology

[0002] In existing zero-discharge systems for chemical wastewater, concentrated wastewater is treated sequentially through membrane concentration and evaporation crystallization. However, the evaporation crystallization process has high carbon emission intensity and lacks operational flexibility under carbon quota constraints. After salt separation, the production rates of monovalent and divalent salt concentrates are often uneven, resulting in alternating high liquid levels in the two storage tanks, and there is a lack of dynamic response mechanisms to address liquid level imbalances.

[0003] Chinese Patent Publication No. CN118324365B discloses a low-energy-consumption, zero-emission treatment method and system for wastewater deep concentration coupled with evaporation and crystallization. The industrial wastewater treatment method includes: after conventional treatment, the industrial wastewater undergoes at least one stage of low-pressure, high-multiplier reverse osmosis treatment, followed by evaporation and salt crystallization to obtain crystalline salt and residual liquid; the residual liquid is then returned to the permeate side of each stage of low-pressure, high-multiplier reverse osmosis treatment, and the water from the permeate side of each stage is further returned to the conventional treatment steps; or the residual liquid is returned to the permeate side of the last stage of low-pressure, high-multiplier reverse osmosis treatment, and the water from the subsequent permeate side of each stage of low-pressure, high-multiplier reverse osmosis treatment is returned to the adjacent preceding stage. On the product water side, the product water from the first-stage low-pressure high-density reverse osmosis treatment is returned to the conventional treatment steps. Therefore, the low-energy, zero-emission wastewater deep concentration coupled with evaporation and crystallization treatment method and system has the following problems: It fails to dynamically adjust the imbalance of liquid levels in the two storage tanks when storing monovalent and divalent salt concentrates separately after nanofiltration desalination; it also fails to use carbon emission quota surplus and low-grade waste heat availability as constraints for scheduling decisions, making it impossible to achieve a dynamic balance between degradation and evaporation through ion matching and concentration adaptation when carbon quotas are tight. Summary of the Invention

[0004] To address this, the present invention provides a dynamic optimization method for zero-discharge energy efficiency of chemical wastewater, which overcomes the problems in the prior art where the liquid levels of the two storage tanks are not dynamically adjusted when the monovalent salt concentrate and divalent salt concentrate after nanofiltration are stored separately, and where carbon emission quota surplus and low-grade waste heat availability are not used as constraints for scheduling decisions. This makes it impossible to achieve a dynamic balance between degradation and evaporation through ion matching and concentration adaptation when carbon quotas are tight.

[0005] To achieve the above objectives, this invention provides a method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater, comprising: The pretreated chemical wastewater is separated into monovalent salt concentrate and divalent salt concentrate, which are then sent to monovalent salt concentrate storage tank and divalent salt concentrate storage tank, respectively. The liquid level values ​​of the two concentrate storage tanks are obtained to calculate the liquid level difference. Obtain the tolerance thresholds for monovalent and divalent ion concentrations in the influent of each low-quality water use process; Obtain the total remaining carbon emission allowances for all stages and the usable waste heat from low-grade stages; The trend of the liquid level difference is determined, and the scheduling optimization strategy corresponding to the next optimization cycle is determined in combination with the total carbon emission quota surplus and the amount of waste heat available. The scheduling optimization strategy includes ion matching strategy, concentration adaptation strategy and energy consumption constraint strategy. During the execution of any of the aforementioned scheduling optimization strategies, the operating parameters of the evaporation and crystallization stage are simultaneously adjusted based on the available waste heat of the low-grade stage. In response to the trend of the liquid level difference becoming stable, the current scheduling status is maintained, the upper limit of the operating load of the evaporation and crystallization stage is adjusted according to the total carbon emission quota surplus of all stages, and the external energy supply ratio of the low-grade stage is adjusted according to the amount of waste heat available.

[0006] As a preferred technical solution for the dynamic optimization of energy efficiency for zero discharge of chemical wastewater, the pretreated chemical wastewater is separated into monovalent salt concentrate and divalent salt concentrate by nanofiltration membrane. Wherein, the monovalent ion in the concentrated monovalent salt solution is chloride ion, and the divalent ion in the concentrated divalent salt solution is sulfate ion.

[0007] As a preferred technical solution for the dynamic optimization method of zero-discharge energy efficiency of chemical wastewater, the calculation of the liquid level difference by obtaining the liquid level values ​​of two concentrated water storage tanks includes: The liquid level values ​​of the monovalent salt concentrate storage tank and the divalent salt concentrate storage tank for each sampling period are obtained, and the difference between the liquid level values ​​of the monovalent salt concentrate storage tank and the divalent salt concentrate storage tank is taken as the liquid level difference value.

[0008] As a preferred technical solution for the dynamic optimization of energy efficiency for zero discharge of chemical wastewater, the monovalent ion tolerance threshold and divalent ion tolerance threshold corresponding to each of the low-quality water use links are configured independently.

[0009] As a preferred technical solution for the dynamic optimization method of zero-discharge energy efficiency of chemical wastewater, obtaining the total carbon emission quota surplus of all stages and the usable waste heat of the low-grade stages includes: Obtain the total carbon emission quota and actual carbon emission of each stage within the sampling period, and record the difference between the total carbon emission quota of each stage and the actual carbon emission of the corresponding sampling period as the carbon emission quota surplus. The carbon emission quota surplus of each stage is summarized to obtain the total carbon emission quota surplus of all stages within the sampling period. Obtain the medium inlet temperature, medium outlet temperature and medium flow rate of each heat exchange node in the low-grade process, and calculate the waste heat usable heat power of each heat exchange node. The usable heat power of the waste heat at each heat exchange node during the sampling period is summarized to obtain the amount of waste heat available in the low-grade stage.

[0010] As a preferred technical solution for the dynamic optimization method of zero discharge energy efficiency of chemical wastewater, the liquid level difference value is obtained for several consecutive sampling periods, and the changing trend of the liquid level difference value in the current optimization period is determined. The optimization period includes several complete sampling periods.

[0011] As a preferred technical solution for the dynamic optimization method of zero-discharge energy efficiency of chemical wastewater, the scheduling optimization strategy corresponding to the next optimization cycle is determined based on the changing trend of the liquid level difference, the carbon emission quota surplus, and the available waste heat, including: If the total carbon emission allowance does not meet the preset evaporation expansion conditions, the energy consumption constraint strategy will be implemented to limit the operating load of the evaporation and crystallization process, and the amount of concentrated water stored on the side with a high and continuously rising liquid level will be consumed through concentrated water degradation and reuse. If the total carbon emission quota surplus meets the preset evaporation expansion conditions, in response to the concentration of ions in the concentrate on the side to be reused exceeding the tolerance threshold of all low-quality water use links, the concentration adaptation strategy is executed, and it is mixed with the concentrate on the other side in a constrained ratio and then scheduled for reuse. The surplus that cannot be reused is subjected to evaporation and crystallization treatment. If the liquid level difference exceeds a preset threshold and shows a corresponding continuous changing trend, and the concentration of the corresponding concentrate ion is lower than the tolerance threshold of at least one low-quality water use stage, then the ion matching strategy is executed, the corresponding concentrate is dispatched to that stage for downgrading and reuse, and the remaining unbalanced water volume is treated by evaporation and crystallization.

[0012] As a preferred technical solution for the dynamic optimization method of zero-discharge energy efficiency of chemical wastewater, the constraint ratio satisfies that the chloride ion concentration in the mixed water does not exceed the chloride ion tolerance threshold of the corresponding low-quality water use stage, and the sulfate ion concentration does not exceed the sulfate ion tolerance threshold of the corresponding low-quality water use stage.

[0013] As a preferred technical solution for the dynamic optimization of energy efficiency in zero-discharge of chemical wastewater, the operating parameters of the evaporation and crystallization stage are adjusted based on the available waste heat from the low-grade stage, including: Based on the available waste heat in the low-grade stage, adjust the feed preheating load of the preheater utilizing the low-grade waste heat in the evaporation and crystallization stage, and adjust the operating frequency of the mechanical vapor recompressor in the evaporation and crystallization stage. When the amount of available waste heat increases, the feed preheating load of the preheater is increased and the operating frequency of the mechanical steam recompressor is reduced.

[0014] As a preferred technical solution for the dynamic optimization method of zero-discharge energy efficiency of chemical wastewater, if the change range of the liquid level difference is within a preset stable range in several consecutive sampling periods, then the currently executed scheduling optimization strategy remains unchanged. Based on the total carbon emission allowance surplus of all processes within the current optimization cycle, set the upper limit of the operating load for the evaporation and crystallization process; Based on the available waste heat from the low-grade stage, adjust the energy supply ratio of the external energy source for the evaporation and crystallization stage. The lower the total carbon emission allowance, the lower the upper limit of the operating load; when the amount of usable waste heat increases, the proportion of low-grade waste heat in the total energy supply of the evaporation and crystallization process is increased, while the proportion of external energy supply is reduced.

[0015] Compared with existing technologies, the beneficial effects of this invention are as follows: by separating pretreated chemical wastewater into monovalent salt concentrate and divalent salt concentrate and storing them in separate tanks, and using the liquid level difference and its changing trend between the two concentrate tanks as the scheduling trigger, and taking the total carbon emission quota surplus as the top-level rigid constraint, this invention combines three types of scheduling optimization strategies: stratified matching of usable waste heat in low-grade links, ion matching, concentration adaptation, and energy consumption constraints. During the execution of any strategy, the preheating load of the feed and the operating frequency of the mechanical steam recompressor in the evaporation and crystallization link are synchronously and dynamically adjusted. When the liquid level difference changes tend to be stable, the upper limit of the evaporation and crystallization operating load and the external energy supply ratio are dynamically adjusted. This can maximize the amount of concentrate downgraded and reused and reduce the scale of evaporation and crystallization treatment under the premise of carbon emission compliance, and can fully and efficiently consume low-grade waste heat and optimize the system energy supply structure. At the same time, the salt-separated scheduling mode can also improve the recovery purity of by-product crystallized salt and reduce solid waste disposal costs, ultimately achieving a dynamic optimal match between zero-discharge energy efficiency of chemical wastewater and carbon emission compliance. Attached Figure Description

[0016] Figure 1 This is a flowchart of the dynamic optimization method for zero-discharge energy efficiency of chemical wastewater according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the dynamic optimization method for zero-discharge energy efficiency of chemical wastewater according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0019] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0020] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] Please see Figure 1 and Figure 2 As shown, this invention provides a method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater, comprising: Step S1: Separate the pretreated chemical wastewater into monovalent salt concentrate and divalent salt concentrate, which are then fed into a monovalent salt concentrate storage tank and a divalent salt concentrate storage tank, respectively. Obtain the liquid level values ​​of the two concentrate storage tanks and calculate the liquid level difference. Step S2: Obtain the tolerance thresholds for the concentrations of monovalent and divalent ions in the influent of each low-quality water use process. Step S3: Obtain the total remaining carbon emission allowances for all stages and the usable waste heat from low-grade stages; Step S4: Determine the changing trend of the liquid level difference, and determine the scheduling optimization strategy corresponding to the next optimization cycle in combination with the total carbon emission quota surplus and the amount of waste heat available. The scheduling optimization strategy includes ion matching strategy, concentration adaptation strategy and energy consumption constraint strategy. Step S5: During the execution of any of the scheduling optimization strategies, the operating parameters of the evaporation and crystallization stage are simultaneously adjusted according to the available waste heat of the low-grade stage. Step S6: In response to the trend of the liquid level difference becoming stable, the current scheduling state is maintained, the upper limit of the operating load of the evaporation and crystallization stage is adjusted according to the total carbon emission quota surplus of all stages, and the external energy supply ratio of the low-grade stage is adjusted according to the amount of waste heat available.

[0022] Understandably, nanofiltration membranes have selective separation characteristics. The surface of nanofiltration membranes carries charged groups, which have a stronger electrostatic repulsion effect on polyvalent ions than on monovalent ions. Moreover, the membrane pore size can retain polyvalent ions with larger diameters. Divalent sulfate ions, due to their high charge density and large hydrated ion diameter, can be effectively retained by nanofiltration membranes and enriched into divalent salt concentrate. Monovalent chloride ions, due to their low charge density and small hydrated ion diameter, can pass through nanofiltration membranes and be enriched into monovalent salt concentrate through subsequent concentration processes, thus achieving the separation of the two types of concentrate.

[0023] In practice, the chemical wastewater, after being concentrated by ultrafiltration and reverse osmosis at the front end, enters the nanofiltration membrane separation unit. Driven by operating pressure, the sodium chloride in the wastewater mainly forms a stream dominated by monovalent salt concentrate with the permeate, in which chloride ions are the characteristic ion. The concentrate on the intercept side is dominated by sodium sulfate, with sulfate ions as the characteristic ion. The two concentrate streams are temporarily stored in monovalent salt concentrate storage tanks and divalent salt concentrate storage tanks through independent pipelines.

[0024] The operating pressure and recovery rate of the nanofiltration membrane are determined by taking the chloride to sulfate ion concentration ratio of the wastewater as input, and calibrating the relationship between the chloride ion purity on the product water side and the sulfate ion enrichment factor on the concentrate water side under different operating conditions through a limited number of orthogonal experiments. The parameter combination that meets the subsequent scheduling requirements and the membrane flux decay rate is within an acceptable range is selected as the set value. Generally, the operating pressure is taken as 0.8MPa to 1.2MPa, and the sulfate rejection rate control threshold of the nanofiltration unit is not less than 90%, and the chloride ion permeability control threshold is not less than 70%.

[0025] In this invention, the separation of wastewater effectively avoids interference from mixed salts on subsequent scheduling strategies. The two concentrated streams after salt separation are stored separately, so that during subsequent dynamic scheduling, the destination of each concentrated stream can be independently decided according to its respective liquid level change trend and ion concentration characteristics. This reduces the ineffective energy consumption of the evaporation and crystallization process, while improving the recovery purity of by-product salts and reducing solid waste disposal costs.

[0026] The difference between the liquid levels on both sides is calculated. The magnitude and sign of the difference reflect the relationship between the liquid levels on both sides of the tank. The difference under continuous sampling represents the degree of imbalance in the stock of the concentrate tanks on both sides. Compared with the liquid level of a single tank, it can more accurately reflect the scheduling needs and material bias of the system.

[0027] During each sampling period, real-time liquid level values ​​are synchronously collected by liquid level detection elements installed in the monovalent salt concentrate storage tank and the divalent salt concentrate storage tank respectively. At the end of each sampling period, two liquid level values ​​are read, and the difference between the liquid level value of the monovalent salt concentrate storage tank and the liquid level value of the divalent salt concentrate storage tank is used as the liquid level difference value of that sampling period.

[0028] The sampling period is 5s to 30s, which is set according to the total volume of the storage tank and the maximum processing rate of the evaporation and crystallization unit. This ensures that the liquid level in the storage tank will not fluctuate beyond the safe range due to normal water inflow and outflow within a single sampling period. A shorter sampling period is selected for operating conditions with drastic flow fluctuations to ensure data real-time performance, while a longer sampling period is selected for operating conditions with stable flow to reduce the system's computational load.

[0029] Low-quality water use refers to auxiliary water use processes within a chemical plant that have low requirements for the salinity and ion concentration of influent water and do not need to meet the standards for production process water. These processes can accept wastewater with a certain concentration of salinity as supplementary water. Typical examples include slag flushing water use, flue gas desulfurization water use, and wet dust removal water use. The water used in these processes is mainly used for media washing, slag cooling, and other procedures. Reusing moderately saline concentrated water will not have a negative impact on the main production process and product quality. Moreover, the water consumption in these processes accounts for a relatively stable proportion in the overall plant water balance, and the plant has the basic conditions to dispose of concentrated water.

[0030] The process media, equipment materials, and operating conditions of each low-quality water use link are different, and their sensitivity to pitting corrosion caused by chloride ions and scaling caused by sulfate ions are significantly different. Independently configuring thresholds can achieve precise matching of reuse and maximize the adaptability of downgraded reuse.

[0031] For each low-quality water usage stage, the tolerance thresholds for monovalent and divalent ions were determined using an independent calibration method. Through a limited number of coupled-plate corrosion tests and scaling trend simulation tests, test water with different chloride ion concentrations was introduced into the stage, and the changes in key process indicators with chloride ion concentration were monitored. The chloride ion concentration corresponding to the degradation of this key process indicator to the lower limit of the process tolerance was taken as the chloride ion tolerance threshold for that stage. Similarly, test water with different sulfate ion concentrations was introduced into the stage, and the changes in key process indicators with sulfate ion concentration were monitored. The sulfate ion concentration corresponding to the degradation of this key process indicator to the lower limit of the process tolerance was taken as the sulfate ion tolerance threshold for that stage. The aforementioned key process indicators were selected separately according to the different process types of each low-quality water usage stage, and included, but were not limited to, one of the following: equipment corrosion rate, heat exchange surface scaling rate, or material crystallization quality.

[0032] Taking common operating conditions as an example, the chloride ion tolerance threshold for the slag flushing water process can be set to 500 mg / L to 3000 mg / L, and the sulfate ion tolerance threshold for the flue gas desulfurization water process can be set to 5000 mg / L to 10000 mg / L.

[0033] In this invention, by independently configuring tolerance thresholds, differentiated reuse access standards can be formulated for different water use stages, thereby improving the adaptability of concentrated wastewater degradation and reuse and the overall absorption capacity of the system.

[0034] It should be understood that the total carbon emission allowance margin for all stages is a hard constraint on production and operation, which determines the allowable operating intensity of high-energy-consuming stages such as evaporation and crystallization. The usable waste heat of low-grade stages is the recovered energy that can replace external energy, which directly affects the external energy supply demand of the evaporation stage. By adopting the method of separate calculation and unified summary, all relevant stages can be covered, ensuring the completeness of parameter statistics and the accuracy of calculation.

[0035] Low-grade processes refer to process units or equipment groups within a chemical plant that generate waste heat at temperatures of 70–120°C, and where this waste heat has not yet been fully recovered and utilized. Typically, low-grade processes include reactor cooling systems, compressor interstage coolers, the outlet of high-temperature flue gas waste heat recovery devices, and sensible heat discharge outlets for process materials. Because the waste heat generated in these processes is of a low temperature, it is difficult to directly use it for power generation or high-temperature process heating. However, its calorific value closely matches the temperature range required for preheating evaporation crystallization feed in zero-discharge wastewater systems, making it suitable as an alternative heat source for the preheater of the evaporation crystallization unit. The available amount of waste heat from low-grade processes varies with the chemical production load.

[0036] During the operation, the total carbon emission allowance is collected by reading the carbon emission allowance values ​​allocated to each process stage within the current optimization cycle from the plant-wide carbon emission management system or the superior carbon emission control platform. If the plant-wide allowance is uniformly determined, the plant-wide allowance is allocated to each process stage according to the proportion of carbon emissions in the previous statistical cycle to the total carbon emissions of all processes, serving as the allowance calculation base for that stage. The total allowance for each sampling cycle is obtained by dividing the total allowance for that stage's optimization cycle according to the time ratio.

[0037] The actual carbon emissions are collected as follows: For processes where electricity consumption is the primary emission source, smart meters installed in the power supply circuit of that process collect electricity consumption in real time for each sampling period, multiply it by the corresponding grid carbon emission factor, and calculate the actual carbon emissions for that sampling period. For processes where steam or fuel consumption is the primary emission source, steam flow meters or fuel meters installed in that process collect steam or fuel consumption in real time for each sampling period, multiply it by the corresponding emission factor, and calculate the actual carbon emissions for that sampling period. For processes equipped with continuous emission monitoring devices, the direct carbon emissions for that sampling period are calculated based on the accounting methods specified in the "General Rules for Accounting and Reporting of Greenhouse Gas Emissions from Industrial Enterprises" (GB / T 32150-2015), using the real-time data collected by the device on flue gas flow rate, carbon dioxide concentration, flue gas temperature, and pressure parameters. The actual carbon emissions collected above are aligned by process stage and timestamp to ensure consistency with the total quota calculation.

[0038] The carbon emission allowance margin for each stage is obtained by subtracting the actual carbon emissions during the corresponding sampling period from the total allowance for that stage. The total carbon emission allowance margin for all stages is obtained by summing up the margins for each stage.

[0039] The acquisition of usable waste heat in the low-grade stage is performed simultaneously. Temperature and flow sensors are installed on the waste heat output pipes at each heat exchange node in the low-grade stage. The inlet temperature, outlet temperature, and flow rate of the waste heat medium are collected according to the same synchronous sampling period as the carbon emission monitoring unit. Based on the heat calculation model, using the specific heat capacity, inlet and outlet temperature difference, and flow rate of the waste heat medium as inputs, the usable waste heat power of each heat exchange node within the current sampling period is calculated. The usable waste heat power of each node is summarized to obtain the usable waste heat amount in the low-grade stage within the current sampling period. This usable waste heat amount is continuously updated with the sampling period, providing real-time basis for judging waste heat conditions and adjusting evaporation and crystallization operation parameters in the scheduling strategy.

[0040] Among them, the minimum usable temperature threshold for low-grade waste heat is set at 70℃. This threshold is calibrated based on the minimum temperature requirement for preheating the evaporation crystallization feed and the reasonable heat transfer temperature difference of the heat exchange equipment. Waste heat below this temperature is not included in the usable quantity statistics due to insufficient recovery benefits. The sampling cycle is consistent with the liquid level sampling cycle to ensure the time sequence synchronization of each physical quantity.

[0041] Through the above steps, the total carbon emission allowance and the amount of waste heat available are the latest values ​​before each scheduling decision, and both are based on the same time base, ensuring that the judgment of energy consumption constraint strategy is not biased due to data time misalignment.

[0042] The liquid level difference in a single sampling period is easily affected by instantaneous operating conditions and may fluctuate abnormally, failing to reflect the true direction of material inventory imbalance. Based on trend judgment of multiple consecutive sampling periods, the direction of continuous liquid level change can be identified. At the same time, by optimizing the unified scheduling decision rhythm of the cycle, a balance can be achieved between scheduling response speed and system operation stability.

[0043] At the end of each optimization cycle, the controller reads the liquid level difference sequence from all sampling cycles within the current optimization cycle and performs trend analysis on the sequence. The trend analysis uses a sliding linear fitting method to calculate the average slope of the liquid level difference sequence within the optimization cycle. If the average slope is consistently positive and exceeds a preset trend threshold, the liquid level difference is determined to be on a continuous upward trend. If the average slope is consistently negative and its absolute value exceeds the preset trend threshold, the liquid level difference is determined to be on a continuous downward trend. If the absolute value of the average slope is within the preset trend threshold, the liquid level difference trend is determined to be stable.

[0044] Taking a total liquid level height of ten meters in the storage tank and an optimization cycle consisting of ten sampling cycles as an example, the preset trend threshold can be taken as the change in liquid level difference of 0.1 meters to 0.2 meters in each optimization cycle, corresponding to the average rate of change of liquid level difference within a single sampling cycle. This threshold is tested within the fluctuation range of normal concentrate production on both sides to determine the relationship between the recognition delay time and the number of false alarms under different trend thresholds. The threshold with recognition delay not exceeding the allowable response time for the safe liquid level of the storage tank and the number of false alarms within an acceptable range is selected as the set value.

[0045] The number of sampling cycles included in the optimization cycle is determined by using the ratio of the total volume of the storage tank to the maximum processing rate of the evaporation and crystallization unit as the reference time constant, and selecting the number of sampling cycles corresponding to the response delay not exceeding the allowable time of the safe liquid level of the storage tank as the set value. Usually, the number of sampling cycles included in the optimization cycle is 5 to 20. For operating conditions with drastic flow fluctuations, a shorter optimization cycle is selected to improve the response speed, while for operating conditions with stable flow, a longer optimization cycle is selected to reduce the frequency of strategy switching.

[0046] The carbon emission allowance margin corresponds to the available energy consumption space of the entire plant. Evaporation and crystallization are the main sources of energy consumption and carbon emissions in the wastewater treatment system. Its operating load directly consumes carbon emission allowances. If it is not prioritized for control, it will lead to the plant's energy consumption indicators exceeding the limit, triggering the linkage restriction of energy consumption control in the production system and affecting the overall operational stability. On the other hand, waste heat utilization and concentrated water reuse are energy efficiency optimization methods within the energy consumption index. They only affect operating energy consumption and material consumption efficiency and do not involve the continuity boundary of the overall system operation. If only waste heat is used for scheduling, a large amount of evaporation may occur when waste heat is sufficient, but at this time the carbon allowance is almost exhausted. Therefore, carbon emission constraints need to be placed at the highest priority level of the decision-making logic.

[0047] Decision priorities are divided according to the rigidity of different constraints. Among them, carbon emission quotas are a rigid compliance constraint for the entire plant and are placed at the top level of the decision-making logic. Ion concentration adaptability determines the feasibility of concentrated water downgrading and reuse, which is an intermediate constraint. The liquid level difference directly reflects the material imbalance state of the two storage tanks and serves as the trigger condition for scheduling actions. By judging and matching the corresponding scheduling strategies in a hierarchical and progressive manner, the scale of reuse and consumption can be maximized and the energy consumption of evaporation can be minimized under the premise of compliance.

[0048] During the operation, at the end of each optimization cycle, the results of the liquid level difference change trend, the total carbon emission allowance surplus of all stages, and the current ion concentrations of monovalent and divalent salt concentrates are obtained. It is then determined whether the total carbon emission allowance surplus meets the preset evaporation expansion conditions. The lower limit threshold of the carbon emission allowance corresponding to these preset evaporation expansion conditions is calibrated based on the carbon emissions required for the evaporation and crystallization unit to operate at full load for one optimization cycle. When the total carbon emission allowance surplus is lower than this lower limit threshold, it is considered that the evaporation expansion conditions are not met. If not, an energy consumption constraint strategy is implemented to limit the operating load of the evaporation and crystallization stage. Priority is given to using concentrate downgrading and reuse to absorb the concentrate stock on the side with a high and continuously rising liquid level, because the downgrading and reuse path itself does not generate additional carbon emissions and can resolve the liquid level imbalance without consuming carbon allowances.

[0049] When the liquid level is high and the concentration of concentrated water ions on the continuously rising side simultaneously exceeds the tolerance threshold of all low-quality water use processes, the concentrated water on this side cannot be directly downgraded for reuse. In this case, the concentrated water is temporarily stored in the corresponding storage tank, and the evaporation and crystallization unit is maintained at the minimum safe load. Evaporation is carried out only at the minimum processing capacity necessary to suppress the continued rise in liquid level. Meanwhile, the remaining concentrated water that cannot be consumed is reserved for processing after the carbon emission quota is restored in the next optimization cycle, and a quota warning signal is sent to the carbon emission management system. This situation is a scheduling delay caused by a temporary shortage of carbon quota. The combination of storage tank safety margin buffer and minimum safe load evaporation buys time for carbon quota restoration.

[0050] If the total carbon quota surplus meets the preset evaporation expansion conditions, it is further determined whether the ion concentration of the concentrate on the side with the higher liquid level exceeds the corresponding tolerance threshold of all low-quality water processes. If it does, a concentration matching strategy is implemented, mixing it with the concentrate on the opposite side according to the constrained ratio and then scheduling it for reuse. The unusable surplus is sent to the corresponding evaporation and crystallization unit for treatment. In response to the liquid level difference exceeding the preset threshold and showing a corresponding continuous changing trend, and the ion concentration of the concentrate on the corresponding side being lower than the tolerance threshold of at least one low-quality water process, an ion matching strategy is implemented, scheduling the concentrate on the corresponding side to that process for downgrading and reuse, and the remaining unbalanced water volume is handled by the evaporation and crystallization unit.

[0051] The preset positive threshold for the liquid level difference is selected as 10% to 20% of the total liquid level height of the corresponding storage tank, and the preset negative threshold is its opposite. This threshold is calibrated through a limited number of storage tank liquid level scheduling tests and determined in combination with the fluctuation range of the concentrate production rate on both sides. If the liquid level difference exceeds this threshold range, it is determined that the liquid level is unbalanced and scheduling needs to be initiated.

[0052] In this invention, a hierarchical decision-making mechanism can dynamically adapt the system's material state and energy consumption space within the carbon constraint boundary, ensuring carbon emission compliance while fully leveraging the energy efficiency optimization potential of downgraded reuse, thus guaranteeing the system's material balance and operational stability.

[0053] Based on the concentration dilution law of material conservation, and utilizing the complementary characteristics of monovalent and divalent salt concentrates in terms of chloride and sulfate ion concentrations, the mixing ratio that satisfies dual ion constraints is solved through material balance calculations. This allows the concentrations of both types of ions to simultaneously drop to within the tolerance threshold of the target process, eliminating the need to introduce fresh water for dilution and improving the concentrate utilization capacity while ensuring safe reuse.

[0054] During the operation, when implementing the concentration matching strategy, the low-quality water stage for target reuse is first selected. The chloride and sulfate tolerance thresholds for this stage are read. Combined with the real-time ion concentrations of the monovalent and divalent salt concentrates, and using the volume mixing ratio of the concentrate on the side with higher liquid level to the concentrate on the opposite side as a variable, the chloride and sulfate ion concentrations in the mixed water are calculated separately. The mixing ratio range that satisfies the requirement that the concentrations of both types of ions do not exceed their corresponding tolerance thresholds is derived. The ratio with the largest concentrate consumption within the range is selected as the execution ratio. The concentrates from both sides are fed into the mixing device for uniform mixing according to this ratio and then dispatched to the target low-quality water stage for reuse. If no feasible solution exists for any low-quality water stage, the concentration matching strategy is abandoned, and the unusable concentrate is sent to the corresponding evaporation and crystallization unit for treatment.

[0055] By using a dual-containment ratio of ion concentrations, the process safety of the reuse process can be guaranteed. At the same time, the complementary concentration characteristics of the concentrates on both sides can be maximized, expanding the applicable scenarios for concentrate reuse and reducing the processing load of the evaporation treatment stage.

[0056] Low-grade waste heat can be used for preheating the feed for evaporation and crystallization. After the feed temperature is increased, the amount of work required for the mechanical steam recompressor to complete the steam temperature rise and compression is reduced accordingly. There is a negative correlation between the amount of waste heat available and the energy consumption of the compressor. By adjusting the preheating load and the operating frequency of the compressor in a coordinated manner, the utilization of low-grade waste heat can be maximized while ensuring the stability of the evaporation processing capacity, thereby reducing the input of external energy and improving energy efficiency.

[0057] During operation, the available waste heat in the low-grade stage is read in real time throughout the execution of any scheduling optimization strategy. The operating parameters of the feed preheater and mechanical vapor re-compressor of the evaporation crystallization unit are adjusted simultaneously. During adjustment, the operating parameters of the evaporation crystallization unit are always dynamically matched with the available waste heat. When the available waste heat increases, the feed preheating load of the preheater is increased to raise the temperature of the concentrate entering the evaporation system, while the operating frequency of the mechanical vapor re-compressor is reduced to reduce its power consumption. When the available waste heat decreases, the preheater load is reduced accordingly, and the compressor operating frequency is increased to maintain the stability of the evaporation system's processing load and steam production.

[0058] In this invention, by synchronously adjusting the waste heat parameters and evaporation operation parameters, the real-time absorption and efficient utilization of low-grade waste heat can be achieved. Without affecting the progress of concentrated water treatment, the energy supply structure of the evaporation process can be optimized, thereby improving the overall energy efficiency of the system.

[0059] The stable trend of the liquid level difference indicates that the current load distribution between degradation and reuse and evaporation and crystallization is basically matched with the water production rate, and there is no need to frequently switch the scheduling strategy. By adjusting the load limit and energy supply structure of the evaporation and crystallization unit, the total carbon emission quota surplus constitutes the rigid upper limit of energy consumption in the evaporation process. The smaller the surplus, the lower the operating load limit needs to be set to avoid carbon emissions exceeding the quota limit. The amount of waste heat available determines the scale of external energy that can be replaced. The more abundant the waste heat, the lower the proportion of external energy supply can be, thereby further reducing operating energy consumption and carbon emissions within the load limit constraint.

[0060] During operation, when the controller detects that the change in liquid level difference remains within a preset stable range over several consecutive sampling periods, it maintains the currently executing scheduling optimization strategy. The operating load limit for the evaporation and crystallization stage is set based on the total carbon emission allowance surplus for all stages within the current optimization period; the lower the total carbon emission allowance surplus, the lower the operating load limit. The proportion of external energy supply for the evaporation and crystallization stage is adjusted based on the available waste heat from the low-grade stage; when the available waste heat increases, the proportion of low-grade waste heat in the total energy supply is increased, while the proportion of external energy supply is simultaneously decreased.

[0061] During operation, when the liquid level difference changes within a preset stable range over several consecutive sampling periods, the current scheduling optimization strategy remains unchanged. Simultaneously, the operating load limit for the evaporation and crystallization process is set based on the total carbon emission allowance surplus of all processes within the current optimization period. The smaller the total allowance surplus, the lower the corresponding operating load limit, ensuring that the carbon emissions of the evaporation process are always controlled within the remaining allowance range. At the same time, the energy supply ratio of external energy sources for the evaporation and crystallization process is adjusted according to the available waste heat from the low-grade process. When the available waste heat increases, the proportion of low-grade waste heat in the total energy supply of evaporation and crystallization is increased, correspondingly reducing the proportion of external energy supply, thereby maximizing waste heat utilization efficiency within the operating load limit constraint.

[0062] Through two-dimensional dynamic adjustment under steady state, carbon emission constraints and waste heat resources can be finely matched while maintaining the stability of system material balance, ensuring compliance and energy efficiency during long-term continuous operation of the system.

[0063] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater, characterized in that, include: The pretreated chemical wastewater is separated into monovalent salt concentrate and divalent salt concentrate, which are then sent to monovalent salt concentrate storage tank and divalent salt concentrate storage tank, respectively. The liquid level values ​​of the two concentrate storage tanks are obtained to calculate the liquid level difference. Obtain the tolerance thresholds for monovalent and divalent ion concentrations in the influent of each low-quality water use process; Obtain the total remaining carbon emission allowances for all stages and the usable waste heat from low-grade stages; The trend of the liquid level difference is determined, and the scheduling optimization strategy corresponding to the next optimization cycle is determined in combination with the total carbon emission quota surplus and the amount of waste heat available. The scheduling optimization strategy includes ion matching strategy, concentration adaptation strategy and energy consumption constraint strategy. Based on the changing trend of the liquid level difference, the total remaining carbon emission quota, and the available waste heat, the scheduling optimization strategy for the next optimization cycle is determined, including: If the total carbon emission allowance does not meet the preset evaporation expansion conditions, the energy consumption constraint strategy will be implemented to limit the operating load of the evaporation and crystallization process, and the amount of concentrated water stored on the side with a high and continuously rising liquid level will be consumed through concentrated water degradation and reuse. If the total carbon emission quota surplus meets the preset evaporation expansion conditions, in response to the concentration of ions in the concentrate on the side to be reused exceeding the tolerance threshold of all low-quality water use links, the concentration adaptation strategy is executed, and it is mixed with the concentrate on the other side in a constrained ratio and then scheduled for reuse. The surplus that cannot be reused is subjected to evaporation and crystallization treatment. If the total carbon emission allowance balance meets the preset evaporation expansion conditions, in response to the liquid level difference exceeding the preset threshold and showing a corresponding continuous changing trend, and the corresponding side concentrate ion concentration being lower than the tolerance threshold of at least one low-quality water use link, then the ion matching strategy is executed, the corresponding side concentrate is dispatched to that link for downgrading and reuse, and the remaining unbalanced water volume is subjected to evaporation and crystallization treatment. During the execution of any of the aforementioned scheduling optimization strategies, the operating parameters of the evaporation and crystallization process are simultaneously adjusted based on the available waste heat of the low-grade process. Based on the available waste heat in the low-grade stage, adjust the feed preheating load of the preheater utilizing the low-grade waste heat in the evaporation and crystallization stage, and adjust the operating frequency of the mechanical vapor recompressor in the evaporation and crystallization stage. When the amount of available waste heat increases, the feed preheating load of the preheater is increased and the operating frequency of the mechanical steam recompressor is reduced. In response to the trend of the liquid level difference becoming stable, the current scheduling status is maintained, the upper limit of the operating load of the evaporation and crystallization stage is adjusted according to the total carbon emission quota surplus of all stages, and the external energy supply ratio of the low-grade stage is adjusted according to the amount of waste heat available. If the change in the liquid level difference is within a preset stable range over several consecutive sampling periods, the currently executing scheduling optimization strategy will remain unchanged. Based on the total carbon emission allowance surplus of all processes within the current optimization cycle, set the upper limit of the operating load for the evaporation and crystallization process; Based on the available waste heat from the low-grade stage, adjust the energy supply ratio of the external energy source for the evaporation and crystallization stage. The lower the total carbon emission allowance, the lower the upper limit of the operating load; when the amount of usable waste heat increases, the proportion of low-grade waste heat in the total energy supply of the evaporation and crystallization process is increased, while the proportion of external energy supply is reduced.

2. The method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater according to claim 1, characterized in that, The pretreated chemical wastewater is separated into monovalent salt concentrate and divalent salt concentrate using a nanofiltration membrane. Wherein, the monovalent ion in the monovalent salt concentrate is chloride ion, and the divalent ion in the divalent salt concentrate is sulfate ion.

3. The method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater according to claim 2, characterized in that, Calculating the level difference by obtaining the liquid level values ​​of the two concentrate storage tanks includes: The liquid level values ​​of the monovalent salt concentrate storage tank and the divalent salt concentrate storage tank for each sampling period are obtained, and the difference between the liquid level values ​​of the monovalent salt concentrate storage tank and the divalent salt concentrate storage tank is taken as the liquid level difference value.

4. The method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater according to claim 1, characterized in that, The tolerance thresholds for monovalent ions and divalent ions for each of the low-quality water use stages are configured independently.

5. The method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater according to claim 1, characterized in that, Obtaining the total carbon emission allowance surplus for all stages and the usable waste heat from the low-grade stages includes: Obtain the total carbon emission quota and actual carbon emission of each stage within the sampling period, and record the difference between the total carbon emission quota of each stage and the actual carbon emission of the corresponding sampling period as the carbon emission quota surplus. The carbon emission quota surplus of each stage is summarized to obtain the total carbon emission quota surplus of all stages within the sampling period. Obtain the medium inlet temperature, medium outlet temperature and medium flow rate of each heat exchange node in the low-grade process, and calculate the waste heat usable heat power of each heat exchange node. The usable heat power of the waste heat at each heat exchange node during the sampling period is summarized to obtain the amount of waste heat available in the low-grade stage.

6. The method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater according to claim 3, characterized in that, Obtain the liquid level difference value for several consecutive sampling periods, and determine the changing trend of the liquid level difference value in the current optimization period; The optimization period includes several complete sampling periods.

7. The method for dynamic optimization of energy efficiency for zero discharge of chemical wastewater according to claim 1, characterized in that, The constraint ratio satisfies the requirement that the chloride ion concentration in the mixed water does not exceed the chloride ion tolerance threshold of the corresponding low-quality water use stage, and the sulfate ion concentration does not exceed the sulfate ion tolerance threshold of the corresponding low-quality water use stage.

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