Stable control method of desalting water system based on film section running state

Abstract

The present application relates to the technical field of water treatment, and particularly relates to a desalted water system stable control method based on membrane section operation state, comprising: obtaining water quantity and water quality information of each membrane section connected in series along water flow direction; determining salt interception load according to salt load change of water body at each membrane section inlet and outlet, and determining membrane section salt interception load distribution state; establishing salt load transfer benchmark according to salt load corresponding relationship of adjacent membrane sections under stable operation; determining downstream explainable load receiving amount according to salt load change from upstream to downstream and the benchmark; determining actual load migration amount according to difference between current and benchmark distribution state, and determining non-transmissibility load migration feature of part not matching with explainable load receiving amount; determining abnormal operation state, abnormal membrane section position and migration direction according to the above, and adjusting water inlet pressure and concentrated water discharge amount of corresponding membrane section. The present application can accurately identify abnormal membrane section under working condition fluctuation, and realize stable control.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for stable control of a demineralized water system based on the operating status of the membrane segment. Background Technology

[0002] Demineralized water systems typically employ multiple reverse osmosis membrane modules operating in series. Each membrane module sequentially receives concentrate from the previous module along the water flow direction and continues desalination. A relatively stable correspondence exists between the membrane modules in terms of salt load distribution. Current technologies for judging the operating status of membrane modules largely rely on absolute parameters such as the feed water pressure, inter-module pressure difference, permeate flow rate, or desalination rate of a single module, comparing these parameters with fixed thresholds or historical trends. However, when the feed water salt content or the total treated water volume fluctuates overall, the absolute parameters of each membrane module change synchronously, easily leading to misjudgments of membrane module anomalies and a mismatch between control actions and the source of the anomaly.

[0003] Chinese Patent Publication No. CN119075684B discloses a reverse osmosis membrane monitoring system and method for a desalination station, comprising: testing the reverse osmosis module, obtaining the relationship between the current inlet water pressure and the outlet water flow rate, obtaining the reverse osmosis membrane attenuation based on the relationship between the current inlet water pressure and the outlet water flow rate, obtaining the relationship between the current speed of the high-pressure pump and the inlet water pressure, obtaining the high-pressure pump performance attenuation, sending the relationship between the current high-pressure pump speed and the inlet water pressure to a correction module, the correction module obtaining the compensated high-pressure pump speed under the same inlet water pressure, obtaining the corrected relationship between the inlet water pressure and the outlet water flow rate based on the obtained reverse osmosis attenuation, and controlling the reverse osmosis module based on the obtained corrected relationship between the inlet water pressure and the outlet water flow rate. It can be seen that the aforementioned reverse osmosis membrane monitoring system and method for a desalination station has the following problems: it fails to separate upstream transmission influences, resulting in the inability to accurately identify abnormal membrane segments and implement targeted control when operating conditions fluctuate. Summary of the Invention

[0004] To address this issue, the present invention provides a method for stable control of a demineralized water system based on the operating status of the membrane segment, thereby overcoming the problem in the prior art where the upstream transmission influence is not separated, resulting in the inability to accurately identify abnormal membrane segments and implement targeted control when operating conditions fluctuate.

[0005] To achieve the above objectives, the present invention provides a method for stable control of a demineralized water system based on the operating status of the membrane segment, comprising: Obtain the operating water volume and water quality information of each membrane segment connected in series along the water flow direction in the demineralized water system; Based on the relationship between the salt load changes of the inlet and outlet water bodies of each membrane segment, the salt retention load of each membrane segment is determined, and the salt retention load distribution status of each membrane segment is determined based on the relationship between the salt retention loads of each membrane segment. Based on the correspondence between the inlet salt load, outlet salt load, and salt retention load of adjacent membrane sections under stable operating conditions, a salt load transfer benchmark for adjacent membrane sections is established. Based on the salt load variation from the upstream membrane segment to the downstream membrane segment in adjacent membrane segments, and in conjunction with the salt load transfer benchmark, the interpretable load capacity of the downstream membrane segment is determined. The actual load migration of the membrane segment is determined based on the difference between the current salt retention load distribution status of the membrane segment and the baseline salt retention load distribution status of the membrane segment. The non-transmissible load migration characteristics are determined based on the portion of the actual load migration of the membrane segment that does not match the explanatory load capacity. The abnormal operating status of the corresponding membrane segment in the demineralized water system is determined based on the aforementioned non-transferable load migration characteristics. Based on the abnormal operating state, the location of the abnormal membrane segment, and the migration direction corresponding to the non-transferable load migration characteristics, determine the pressure regulation amount and concentrate regulation amount of the corresponding membrane segment, and adjust the inlet water pressure and concentrate discharge amount of the corresponding membrane segment respectively.

[0006] Preferably, the operating water volume and water quality information of each membrane segment connected in series along the water flow direction in the demineralized water system are obtained, including: The flow rate and conductivity of the inlet water of each membrane segment, as well as the flow rate and conductivity of the permeate and concentrate in the outlet water of each membrane segment, were obtained. The operating water volume information includes the flow rate information of the inlet water, product water and concentrate, and the water quality information includes the conductivity information of the inlet water, product water and concentrate.

[0007] Preferably, determining the salt rejection load corresponding to each membrane segment includes: The inlet salt load is determined based on the flow rate and conductivity of the inlet water of each membrane segment, the product water salt load is determined based on the flow rate and conductivity of the product water in the outlet water of each membrane segment, and the concentrate salt load is determined based on the flow rate and conductivity of the concentrate. The salt retention load of the corresponding membrane section is determined based on the difference between the inlet salt load and the product water salt load, whereby the concentrate salt load is the salt load output downstream from the corresponding membrane section.

[0008] Preferably, determining the salt retention load distribution status of the membrane segment includes: Arrange the salt rejection loads corresponding to each membrane segment in the order of water flow direction; Calculate the proportion of salt retention load in each membrane segment to the total salt retention load, arrange the proportions according to the water flow direction, and obtain the salt retention load distribution status of the membrane segments.

[0009] Preferably, establishing the salt load transfer reference between adjacent membrane segments includes: The salt load transfer coefficient of the corresponding adjacent membrane section is determined based on the ratio of the inlet salt load of the downstream membrane section to the concentrate salt load of the upstream membrane section. Based on the ratio of the salt rejection load of the downstream membrane segment to the salt load of the concentrate in the upstream membrane segment, the salt rejection capacity coefficient of the corresponding adjacent membrane segment is determined. Based on the salt load transfer coefficient and salt retention and acceptance coefficient within the acquisition cycle corresponding to several stable operating states, the salt load transfer benchmark for adjacent membrane segments is determined.

[0010] Preferably, determining the explanatory load capacity of the downstream membrane segment includes: Determine the change in the current upstream membrane section concentrate salt load relative to the stable operating state; Based on the change and the salt load transfer coefficient in the salt load transfer reference, the expected change in the downstream membrane section inlet salt load is determined; Based on the change and the salt retention carrying capacity coefficient in the salt load transfer benchmark, the expected change in the salt retention load of the downstream membrane segment is determined. The expected salt rejection load of the downstream membrane segment is determined by the sum of the salt rejection load of the downstream membrane segment under stable operating conditions and the expected change in the salt rejection load of the downstream membrane segment. The explainable percentage change of the downstream membrane segment is determined by subtracting the percentage of salt retention load of the downstream membrane segment under the baseline condition from the ratio between the expected salt retention load of the downstream membrane segment and the current total salt retention load.

[0011] Preferably, determining the actual load migration of the membrane segment includes: Calculate the difference between the current salt rejection load percentage of each membrane segment and the corresponding baseline percentage to obtain the percentage change of each membrane segment; The change in the proportion of each membrane segment is determined as the actual load migration of the membrane segment.

[0012] Preferably, determining the non-transitive load migration characteristics includes: The non-transferable percentage change of the downstream membrane segment is determined based on the explainable percentage change of the downstream membrane segment in the explainable load carrying capacity and the percentage change of the corresponding downstream membrane segment in the actual load migration of the membrane segment. The change in the proportion of nontransmissible load and the corresponding position of the membrane segment are defined as the nontransmissible load migration characteristics.

[0013] Preferably, determining the abnormal operating state of the corresponding membrane segment based on the non-transferable load migration characteristics includes: When the change in the non-transferable proportion of the downstream membrane segment is negative and exceeds the preset migration deviation threshold, if the salt load transfer coefficient of the corresponding adjacent membrane segment is lower than the benchmark range, it is determined that the inter-segment salt load transfer is abnormal; if the salt load transfer coefficient of the corresponding adjacent membrane segment is within the benchmark range, it is determined that the downstream membrane segment load acceptance is abnormal. When the change in the nontransferability of the downstream membrane segment is positive and exceeds the preset migration deviation threshold, it is determined that the salt retention load is abnormally migrating to the downstream membrane segment. When the change in the proportion of the upstream membrane segment exceeds the preset migration deviation threshold in a negative direction, and the change in the non-transferable proportion of the corresponding downstream membrane segment is within the deviation threshold range, it is determined that the salt retention load of the upstream membrane segment is abnormally low.

[0014] Preferably, determining the pressure regulation and concentrate regulation for the corresponding membrane segment includes: In response to abnormal salt load transfer between membrane sections, the concentrate adjustment amount of the adjacent upstream membrane section is determined based on the amplitude of the change in the non-transferable proportion of the corresponding downstream membrane section. In response to abnormal load bearing in the downstream membrane segment, the pressure adjustment amount of the downstream membrane segment is determined based on the amplitude of the change in the non-transmissibility ratio of the downstream membrane segment. In response to the abnormal operating state where the salt rejection load migrates to the downstream membrane segment, the pressure regulation and concentrate regulation of the upstream abnormal membrane segment are determined based on the amplitude of the change in the proportion of the upstream abnormal membrane segment.

[0015] Compared with the prior art, the beneficial effects of the present invention are that by determining the salt retention load of each membrane segment and establishing the salt retention load distribution state of the membrane segment, the salt load transfer relationship between adjacent membrane segments under stable operation is solidified as the salt load transfer benchmark. In the current operation process, the explainable load capacity caused by the normal output change of the upstream membrane segment and the non-transferable load migration characteristics that cannot be explained by the normal transfer relationship are distinguished, the abnormal operation state, abnormal location and migration direction of the corresponding membrane segment are determined, and the feed water pressure and concentrate discharge of the corresponding membrane segment are adjusted in a targeted manner. This invention uses the deviation of the salt retention load distribution relationship between multiple membrane segments from the stable transmission benchmark as the judgment object. It separates the load changes caused by normal transmission from the actual load migration in the downstream. Thus, under the overall operating conditions of fluctuation such as influent salt content and total treated water volume, it accurately identifies abnormal operating states of different natures, such as abnormal salt load transmission between segments, abnormal load acceptance in downstream membrane segments, and abnormal migration of salt retention load to downstream membrane segments. It makes the control actions correspond to the source of the abnormality, and finally brings the salt retention load ratio of each membrane segment back to the distribution state determined by the normal transmission relationship, so as to achieve stable control of the demineralized water system at the membrane segment level. Attached Figure Description

[0016] Figure 1This is a flowchart of a demineralized water system stability control method based on membrane segment operating status according to an embodiment of the present invention; Figure 2 This is a logic diagram of the control method 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 Figures 1-2 As shown, the present invention provides a method for stable control of a demineralized water system based on the operating status of the membrane segment, comprising: Step S1: Obtain the operating water volume and water quality information of each membrane segment connected in series along the water flow direction in the demineralized water system; Step S2: Based on the salt load variation relationship between the inlet and outlet water bodies of each membrane segment, determine the salt retention load of each membrane segment, and determine the salt retention load distribution status of each membrane segment based on the salt retention load relationship between each membrane segment. Step S3: Based on the correspondence between the inlet salt load, outlet salt load, and salt retention load of adjacent membrane sections under stable operating conditions, establish a salt load transfer benchmark for adjacent membrane sections. Step S4: Based on the salt load change from the upstream membrane segment to the downstream membrane segment in adjacent membrane segments, and in conjunction with the salt load transfer reference, determine the interpretable load capacity of the downstream membrane segment. Step S5: Determine the actual load migration of the membrane segment based on the difference between the current membrane segment salt retention load distribution status and the baseline membrane segment salt retention load distribution status. Step S6: Determine the non-transmissible load migration characteristics based on the portion of the actual load migration of the membrane segment that does not match the interpretable load capacity; Step S7: Determine the abnormal operating status of the corresponding membrane segment in the demineralized water system based on the non-transferable load migration characteristics; Step S8: Based on the abnormal operating state, the location of the abnormal membrane segment, and the migration direction corresponding to the non-transferable load migration characteristics, determine the pressure regulation amount and concentrate regulation amount of the corresponding membrane segment, and adjust the inlet water pressure and concentrate discharge amount of the corresponding membrane segment respectively.

[0022] This implementation method is applicable to demineralized water systems comprising two or more membrane segments connected in series. For a demineralized water system comprising two membrane segments, the upstream membrane segment and the downstream membrane segment are defined as a group of adjacent membrane segments; for a demineralized water system comprising three or more membrane segments, the i-th membrane segment and the (i+1)-th membrane segment are sequentially defined as a group of adjacent membrane segments according to the water flow direction, and corresponding salt load transfer references are established for each, where i is the sequence number of the membrane segments arranged along the water flow direction.

[0023] In implementation, flow detection devices are selected separately for each membrane section and pipeline. Electromagnetic flow meters are used for the inlet pipeline and concentrate pipeline of each membrane section, while turbine flow meters are used for the permeate pipeline of each membrane section, in order to avoid unstable measurement by electromagnetic flow meters when the permeate conductivity is low.

[0024] For example, for a total water production of 45m³ 3 A single-stage, two-stage reverse osmosis demineralization system with a rated flow rate of 60 m³ / h inlet pipe. 3 / h, select a measuring range of 0~100m 3 Electromagnetic flowmeter with a flow rate of / h; a section of the product water pipeline has a rated flow rate of 30m³ / h. 3 / h, select a measuring range of 0~50m 3 A turbine flow meter with a rated flow rate of 30 m³ / h; a section of concentrate pipeline has a rated flow rate of 30 m³ / h. 3 / h, select a measuring range of 0~50m 3 Electromagnetic flowmeter with a rated flow rate of 30m³ / h; the second-stage inlet pipeline has a rated flow rate of 30m³ / h. 3 / h, select a measuring range of 0~50m 3 Electromagnetic flowmeter with a rated flow rate of 15m³ / h; the second-stage product water pipeline has a rated flow rate of 15m³ / h. 3 / h, select a measuring range of 0~25m 3 A turbine flow meter with a rated flow rate of 15m³ / h; the second-stage concentrate pipeline has a rated flow rate of 15m³ / h. 3 / h, select a measuring range of 0~25m 3 / h electromagnetic flowmeter.

[0025] Specifically, the flow range of each flow meter is selected to be 1.5 to 2 times the rated flow of the corresponding pipeline, so that the flow rate falls within 30% to 70% of the range when the system is operating normally. The accuracy of the electromagnetic flow meter is selected to be ±0.5% of the reading, and the accuracy of the turbine flow meter is selected to be ±1% of the reading. Each flow meter outputs a 4 to 20mA signal or pulse signal to the data acquisition module.

[0026] Conductivity sensors are installed on the inlet, permeate, and concentrate lines of each membrane segment. These sensors are temperature-compensated to convert the measured conductivity to a 25°C reference. The inlet conductivity sensor has a range of 0–2000 μS / cm, the permeate conductivity sensor has a range of 0–20 μS / cm, and the concentrate conductivity sensor has a range of 0–5000 μS / cm. The accuracy of the inlet and concentrate conductivity sensors is ±1%FS, and the accuracy of the permeate conductivity sensor is ±1%FS. The conductivity sensors are installed in the full-length sections of the corresponding pipelines, with their probes in contact with the water.

[0027] During implementation, the flow rate and conductivity of the inlet water, permeate, and concentrate of each membrane segment are read synchronously within the same acquisition cycle. Generally, the acquisition cycle is set to 5 seconds or 10 seconds, depending on the system flow rate change rate and instrument response time. Synchronous reading ensures that the inlet water, permeate, and concentrate data of the same membrane segment at the same time are corresponding in time.

[0028] In this invention, the inlet and concentrate flow rate measurements are not limited by low conductivity, the product water flow rate uses a turbine flow meter adapted to low conductivity, the conductivity range covers the water quality at various locations, and temperature compensation and synchronous acquisition ensure that the water volume and water quality information of each membrane segment are comparable.

[0029] In practice, the data of inlet water, product water and concentrate obtained within the same collection cycle are used as the same set of calculation data to determine the salt rejection load of each membrane segment, so as to avoid data from different collection times from being mixed into the salt load calculation process of the same membrane segment.

[0030] In this embodiment, the inlet salt load, product water salt load, and concentrate salt load are all conductivity salt load indices, which are obtained by multiplying the flow rate by the conductivity after temperature compensation. They are used to characterize the relative changes in salt load of each pipeline under the same water quality system and the same temperature compensation standard.

[0031] For any membrane segment, the inlet salt load is obtained by multiplying the inlet water flow rate by its conductivity, the product water salt load is obtained by multiplying the product water flow rate by its conductivity, and the concentrate salt load is obtained by multiplying the concentrate flow rate by its conductivity. Conductivity is used in the calculation under the same temperature compensation standard, ensuring that the salt loads obtained from different membrane segments and different pipeline locations have the same comparative caliber.

[0032] For a single membrane segment, the salt load is divided into inlet salt load, product water salt load, and concentrate salt load according to the water flow nodes. The inlet salt load is the total amount of salt entering the membrane segment; the product water salt load is the total amount of salt that permeates through the membrane element and is discharged with the product water; the concentrate salt load is the total amount of salt that does not permeate through the membrane element and flows out of the membrane segment with the concentrate.

[0033] The desalination function of the membrane segment is manifested in the retention of salts in the influent. Therefore, the difference between the influent salt load and the product water salt load is taken as the salt retention load of the membrane segment, which is the actual desalination task undertaken by the membrane segment under the current operating conditions. This parameter is calculated by the flow rate and conductivity of the corresponding node, while also taking into account the impact of water volume fluctuations and water quality fluctuations on the membrane segment load.

[0034] In this embodiment, the salt retention load is used to characterize the salt load capacity of the membrane segment that is not discharged with the permeate. It corresponds to the salt load output on the concentrate side and is used to characterize the load distribution relationship between different membrane segments.

[0035] For adjacent membrane segments connected in series along the water flow direction, the concentrate from the upstream membrane segment directly serves as the feed water for the downstream membrane segment. Therefore, the salt load of the concentrate from the upstream membrane segment is the source of the inlet salt load of the downstream membrane segment, forming the physical basis for the transfer of salt load between segments.

[0036] It should be noted that this embodiment applies to a series membrane segment structure where the concentrate from the upstream membrane segment serves as the primary source of inlet water for the downstream membrane segment. The upstream membrane segment concentrate pipeline can be directly connected to the downstream membrane segment inlet pipeline, or it can be connected through an inter-segment manifold or buffer pipeline, as long as the correspondence between the upstream membrane segment concentrate salt load and the downstream membrane segment inlet salt load can be determined between adjacent membrane segments. For conventional sampling, venting, blowdown, or instrument bypass branches that do not alter this correspondence, the establishment of the salt load transfer benchmark between adjacent membrane segments will not be affected.

[0037] When determining the salt rejection load distribution status of the membrane segments, the salt rejection loads of each membrane segment are arranged sequentially according to their arrangement along the water flow direction. The salt rejection loads of each membrane segment are then added together to obtain the sum of the salt rejection loads of all membrane segments. Next, the proportion of the salt rejection load of each membrane segment to the sum of the salt rejection loads of all membrane segments is calculated. The proportions of each membrane segment, combined according to their arrangement along the water flow direction, determine the membrane segment salt rejection load distribution status. This distribution status represents the relative share of the total salt rejection load borne by different membrane segments under the current operating conditions. The reason for using a proportional form is that when the overall salt content of the system influent or the total treated water volume changes, the absolute salt rejection load of each membrane segment may change synchronously, and the proportional relationship can more directly reflect the load-bearing relationship among multiple membrane segments.

[0038] During operation, the detection data of inlet, permeate, and concentrate of each membrane segment within the same acquisition cycle are retrieved simultaneously, and the inlet salt load, permeate salt load, and concentrate salt load of each membrane segment are calculated sequentially. The salt rejection load of each membrane segment is obtained by the difference between the inlet salt load and the permeate salt load, and the concentrate salt load is recorded as the salt load output downstream of the corresponding membrane segment. The salt rejection load of each membrane segment is sorted according to the water flow direction, and the proportion of the salt rejection load of each membrane segment to the total salt rejection load is calculated to form the membrane segment salt rejection load distribution status.

[0039] When establishing the salt load transfer baseline between adjacent membrane sections, multiple data collection cycles during which the demineralized water system was in a stable operating state were selected as the baseline data source. A stable operating state is defined as an operating state in which the demineralized water system is not in the process of start-up, shutdown, flushing, chemical cleaning, valve switching, or rapid adjustment of permeate flow rate, and the inlet water flow rate, permeate flow rate, concentrate flow rate, and corresponding conductivity of each membrane section do not show any unidirectional sudden changes within the continuous data collection cycle.

[0040] For any given acquisition cycle, the salt load at the inlet of the downstream membrane section is divided by the salt load in the concentrate of the upstream membrane section to obtain the salt load transfer coefficient for that acquisition cycle. Conversely, the salt retention load of the downstream membrane section is divided by the salt load in the concentrate of the upstream membrane section to obtain the salt retention carrying capacity coefficient for that acquisition cycle. The salt load transfer coefficient characterizes the correspondence between the salt load output from the concentrate side of the upstream membrane section and the inlet side of the downstream membrane section, i.e., the hydraulic connectivity and consistency of salt load input between adjacent membrane sections. The salt retention carrying capacity coefficient characterizes the retention and carrying capacity relationship of the downstream membrane section for the salt load output from the upstream section, i.e., the processing and carrying capacity relationship of the downstream membrane section for the received salt load.

[0041] The two coefficients can transform the salt load relationship between adjacent membrane sections into a dimensionless ratio, eliminating the influence of overall fluctuations in influent salt load and total treated water volume on absolute values, and enabling direct comparison of data from different operating periods.

[0042] After obtaining the salt load transfer coefficient and salt retention bearing coefficient corresponding to multiple acquisition cycles, abnormal cycle data caused by valve switching, cleaning operation or instrument instantaneous fluctuations are removed. The remaining data are then averaged, or averaged and a standard deviation range is added. Both are used as the salt load transfer benchmark for adjacent membrane segments in this group.

[0043] For example, the salt load transfer coefficient is selected within the range of 0.98 to 1.02, and the salt retention capacity coefficient is selected within the range of 0.3 to 0.6 based on the system design recovery rate and membrane segment arrangement. The specific values ​​are determined by statistical analysis of actual data from adjacent membrane segments under stable operating conditions. If the stable operating data shows a regular change with the influent conditions, the correspondence between the salt load transfer coefficient and the salt retention capacity coefficient and the corresponding operating conditions can also be established through linear regression or other methods, and this correspondence can be used as the salt load transfer benchmark.

[0044] It is understandable that the salt load transfer benchmark is not a fixed limitation on the salt load of a single membrane segment, but rather a record of the inter-segment correspondence between adjacent membrane segments under stable operating conditions. Since the concentrate salt load of the upstream membrane segment in a series of membrane segments constitutes the main source of the inlet salt load of the downstream membrane segment, and the salt retention load of the downstream membrane segment varies with the salt load it receives, the salt load transfer coefficient and the salt retention capacity coefficient jointly characterize the continuous relationship of "upstream output - downstream reception - downstream retention," enabling the salt load transfer benchmark of adjacent membrane segments to reflect the stable transfer law of the group of membrane segments themselves.

[0045] When determining the interpretable load capacity of the downstream membrane segment, the concentrate salt load of the upstream membrane segment in the current acquisition period is compared with the concentrate salt load of the upstream membrane segment under stable operating conditions to obtain the change in the concentrate salt load of the upstream membrane segment, which indicates the extent to which the salt load output by the upstream membrane segment to the inter-segment has increased or decreased.

[0046] Among them, the upstream membrane section concentrate salt load corresponding to the stable operation state is the average value of multiple acquisition cycles used when establishing the salt load transfer benchmark; when the salt load transfer benchmark is represented by the correspondence of operating conditions, the benchmark concentrate salt load corresponding to the current operating conditions is used.

[0047] After obtaining the change in the concentrate salt load of the upstream membrane section, multiply this change by the salt load transfer coefficient in the salt load transfer benchmark to obtain the expected change in the salt load at the downstream membrane section inlet. This represents the change in salt load that the downstream membrane section inlet should receive according to the normal transfer relationship after the upstream output change. Multiply this change by the salt retention and acceptance coefficient in the salt load transfer benchmark to obtain the expected change in the salt retention load of the downstream membrane section. This represents the change in the salt retention task that the downstream membrane section should undertake according to the normal acceptance relationship.

[0048] The expected change in the inlet salt load of the downstream membrane segment, the expected change in the salt retention load of the downstream membrane segment, the expected salt retention load of the downstream membrane segment, and the change in the explainable proportion of the downstream membrane segment are determined as the explainable load capacity of the downstream membrane segment.

[0049] It should be understood that when the concentrate output of the upstream membrane section changes, the inlet side of the downstream membrane section first absorbs this change; simultaneously, the downstream membrane section's capacity to retain the received salt load will also change accordingly. Therefore, by using the salt load transfer coefficient and the salt retention coefficient, the change in the output of the upstream membrane section can be transformed into an interpretable change in the inlet salt load and salt retention load of the downstream membrane section. This facilitates the accurate identification of the portion of the actual load migration in the downstream membrane section that is not part of the normal transfer.

[0050] When determining the actual load migration of the membrane segment, the salt retention load distribution status of the membrane segment in the current sampling period is used, and the baseline membrane segment salt retention load distribution status formed under stable operation is invoked. The baseline membrane segment salt retention load distribution status is obtained by combining the average value of the salt retention load ratio of each membrane segment in multiple sampling periods under stable operation, while maintaining the arrangement order of each membrane segment along the water flow direction.

[0051] For each membrane segment, the salt retention load distribution state determined under stable operating conditions is used as the baseline salt retention load distribution state. For each membrane segment, the salt retention load percentage of that segment is extracted from the current salt retention load distribution state, and the corresponding salt retention load percentage of that segment is extracted from the baseline salt retention load distribution state. The difference between the two is the change in the percentage of that membrane segment.

[0052] When the change in proportion is positive, it means that the proportion of salt retention load undertaken by the membrane segment in the current state is higher than that in the stable operating state; when the change in proportion is negative, it means that the proportion of salt retention load undertaken by the membrane segment in the current state is lower than that in the stable operating state.

[0053] The above calculations are performed on each membrane segment separately, and the change in the proportion of each membrane segment is collectively determined as the actual load migration of the membrane segment. The principle is that the actual load migration of the membrane segment is not expressed as the absolute salt rejection load change of a single membrane segment, but as the change in the proportion of each membrane segment in the total salt rejection load of all membrane segments, thus reflecting the relative transfer of salt rejection load among multiple membrane segments.

[0054] Understandably, using proportional changes rather than absolute salt load changes to characterize the migration of load between membrane segments avoids the influence of overall fluctuations in influent salt load or total treated water volume on the judgment results. Furthermore, the sum of the salt rejection load proportions of each membrane segment is constant. When the proportion of a certain membrane segment increases, the proportion of other membrane segments must decrease. Therefore, the change in proportion can directly reflect the redistribution of salt rejection tasks among membrane segments.

[0055] During operation, the current salt retention load allocation status of the membrane segment is updated in each acquisition cycle and compared segment by segment with the stored baseline salt retention load allocation status to obtain the percentage change of each membrane segment, i.e., the actual load migration of the membrane segment. This actual load migration of the membrane segment represents the actual occurrence of load migration under the current operating state, providing a data basis for subsequently distinguishing between normal transitive migration and non-transitive migration.

[0056] When determining the characteristics of non-transitive load migration, the change in the proportion of downstream membrane segments is first extracted from the actual load migration of the membrane segment, and the explainable change in the proportion of downstream membrane segments is extracted from the explainable load-bearing capacity. Then, the change in the proportion of downstream membrane segments is subtracted from the explainable change in proportion to obtain the non-transitive change in the proportion of downstream membrane segments. This non-transitive change in proportion represents the portion of the actual load change of the downstream membrane segment that cannot be explained by the stable transmission relationship between adjacent membrane segments.

[0057] Understandably, the actual load migration of the membrane segment reflects the actual percentage change of the downstream membrane segment relative to the baseline state, while the explainable percentage change in the explainable load carrying capacity reflects the percentage change that can be explained by the output change of the upstream membrane segment according to the salt load transfer baseline. The non-transferable percentage change obtained by subtracting the two is the percentage deviation that cannot be explained by the transfer relationship between stable segments. Recording this non-transferable percentage change along with the position of the corresponding downstream membrane segment forms the non-transferable load migration characteristic.

[0058] When determining the abnormal operating state of the corresponding membrane segment, the change in the non-transmissibility ratio of the downstream membrane segment is compared with a preset migration deviation threshold. The preset migration deviation threshold is determined based on the historical fluctuation range of the change in the non-transmissibility ratio under stable operating conditions. For example, it can be three times the standard deviation of the change in the non-transmissibility ratio in stable operating samples, or it can be set to 0.02 to 0.05 based on multiple sets of stable operating data during the commissioning phase.

[0059] When the change in the non-transferability ratio of the downstream membrane segment is negative and its absolute value exceeds the preset migration deviation threshold, the current salt load transfer coefficient of the adjacent membrane segment in the current acquisition cycle is further calculated and compared with the reference range corresponding to the salt load transfer reference.

[0060] The benchmark range can be determined by the average value plus standard deviation of the salt load transfer coefficient under stable operating conditions, for example, by using the average value ± two standard deviations, or by using the allowable fluctuation range of the aforementioned salt load transfer coefficient benchmark.

[0061] If the current salt load transfer coefficient is below the baseline range, it indicates that the upstream concentrate salt load has not entered the downstream membrane section according to the stable transfer relationship, and it is judged as an abnormality in the inter-section salt load transfer; if the current salt load transfer coefficient is within the baseline range, it indicates that the inter-section input relationship is maintained within the baseline range, but the salt retention and acceptance of the downstream membrane section is lower than expected, and it is judged as an abnormality in the load acceptance of the downstream membrane section.

[0062] When the change in the non-transferable proportion of the downstream membrane segment is positive and exceeds the preset migration deviation threshold, it is determined that there is an abnormal migration of salt retention load to the downstream membrane segment, indicating that the actual share borne by the downstream membrane segment is higher than expected. For cases where the change in the proportion of the upstream membrane segment exceeds the preset migration deviation threshold negatively, and the change in the non-transferable proportion of the downstream membrane segment is within the deviation threshold range, the preset migration deviation threshold can be determined based on the fluctuation of the membrane segment proportion under the baseline membrane segment salt retention load distribution state. For example, it can be taken as three times the standard deviation of the stable proportion change of that membrane segment, or set to 0.02–0.05. This situation indicates that the proportion borne by the upstream membrane segment has decreased, while the change in the downstream membrane segment's share can still be explained by the inter-segment transfer relationship; therefore, it is determined that there is an abnormally low salt retention load in the upstream membrane segment.

[0063] It should be understood that the sign and magnitude of the change in the non-transferable proportion reflect the direction and degree of the load deviation, while whether the salt load transfer coefficient is normal is used to distinguish whether the deviation occurs in the transfer link or the receiving link.

[0064] Understandably, different abnormal operating states correspond to different deviation locations. For inter-section transmission anomalies, the inter-section output is adjusted first; for load-bearing anomalies, the pressure of the receiving membrane section is adjusted first; and for downstream migration anomalies, the pressure and concentrate side of the upstream abnormal membrane section are adjusted in a coordinated manner, thus ensuring that the adjustment target corresponds to the source of the anomaly. Through targeted adjustments to pressure and concentrate discharge, the control actions correspond to the anomaly type, avoiding unnecessary adjustments to the normal transmission relationship, and restoring the salt retention load ratio of each membrane section to the distribution state determined by the normal transmission relationship.

[0065] When determining the pressure and concentrate regulation amounts, for abnormal salt load transfer between sections, the regulation target is the concentrate discharge rate of the adjacent upstream membrane section. The concentrate regulation amount is determined based on the amplitude of the change in the proportion of non-transferable components in the downstream membrane section; the larger the amplitude, the larger the corresponding concentrate regulation amount. The specific correspondence can be obtained by calibrating the valve opening changes and concentrate flow rate changes during the equipment commissioning phase, or a piecewise linear relationship can be used for configuration. After determining the concentrate regulation amount according to this amplitude, the concentrate discharge rate of the upstream membrane section is adjusted.

[0066] For abnormal load on the downstream membrane section, the adjustment target is the inlet pressure of the downstream membrane section. The pressure adjustment amount is determined based on the amplitude of the change in the non-transmissible proportion of the downstream membrane section. The larger the amplitude, the more serious the deviation of the downstream membrane section's own retention capacity from the normal load relationship, requiring adjustment of the inlet pressure of the downstream membrane section to change its salt retention load. The pressure adjustment amount is determined based on the operational records of the changes in the inlet pressure and salt retention load of the membrane section. A linear correspondence is established through stable operation and slight disturbance operation data, or the pressure adjustment amount is configured separately for multiple deviation intervals.

[0067] For abnormal operating conditions where salt rejection load migrates downstream of the membrane section, the adjustment targets are the influent pressure and concentrate discharge rate of the upstream abnormal membrane section. The larger the amplitude, the greater the abnormal reduction in salt rejection load in the upstream membrane section. Therefore, it is necessary to simultaneously adjust the influent pressure and concentrate discharge rate of the upstream abnormal membrane section to restore its salt rejection load proportion. The pressure and concentrate adjustment amounts are determined based on the amplitude of the change in the proportion of the upstream abnormal membrane section and applied to the influent pressure and concentrate discharge rate of that upstream abnormal membrane section, respectively.

[0068] When performing pressure regulation and concentrate discharge regulation, both the pressure regulation amount and the concentrate discharge amount are regulation amounts with regulation direction. The regulation direction is determined according to the direction that reduces the current change in the non-transferable proportion and makes the current salt load transfer coefficient or salt retention and acceptance relationship tend to the corresponding reference range. After each regulation, the influent pressure and concentrate discharge amount are limited between the upper and lower limits of the allowable operation of the membrane section; when the calculated regulation amount causes the operating parameters to exceed the upper or lower limits of the operation, the regulation is performed according to the corresponding boundary value.

[0069] It should be noted that determining the specific correspondence between pressure regulation and concentrate regulation based on the deviation amplitude is an existing technology in the field of demineralized water system operation control, such as PID control, piecewise linear control, lookup table control, valve opening and flow calibration relationship, high-pressure pump frequency and inlet pressure calibration relationship, etc., which will not be elaborated on in this embodiment. The improvement of this invention does not lie in the specific control algorithm of pressure regulation or concentrate regulation, but in determining abnormal operating states based on non-transitive load migration characteristics, and selecting the corresponding membrane segment and corresponding operating parameters for adjustment according to the abnormal operating states.

[0070] 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.

[0071] 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 stable control of a demineralized water system based on the operating state of the membrane segment, characterized in that, include: Obtain the operating water volume and water quality information of each membrane segment connected in series along the water flow direction in the demineralized water system; Based on the relationship between the salt load changes of the inlet and outlet water bodies of each membrane segment, the salt retention load of each membrane segment is determined, and the salt retention load distribution status of each membrane segment is determined based on the relationship between the salt retention loads of each membrane segment. Based on the correspondence between the inlet salt load, outlet salt load, and salt retention load of adjacent membrane sections under stable operating conditions, a salt load transfer benchmark for adjacent membrane sections is established. Based on the salt load variation from the upstream membrane segment to the downstream membrane segment in adjacent membrane segments, and in conjunction with the salt load transfer benchmark, the interpretable load capacity of the downstream membrane segment is determined. The actual load migration of the membrane segment is determined based on the difference between the current salt retention load distribution status of the membrane segment and the baseline salt retention load distribution status of the membrane segment. The non-transmissible load migration characteristics are determined based on the portion of the actual load migration of the membrane segment that does not match the explanatory load capacity. The abnormal operating status of the corresponding membrane segment in the demineralized water system is determined based on the aforementioned non-transferable load migration characteristics. Based on the abnormal operating state, the location of the abnormal membrane segment, and the migration direction corresponding to the non-transferable load migration characteristics, determine the pressure regulation amount and concentrate regulation amount of the corresponding membrane segment, and adjust the inlet water pressure and concentrate discharge amount of the corresponding membrane segment respectively.

2. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 1, characterized in that, Obtain the operating water volume and water quality information of each membrane segment connected in series along the water flow direction in the demineralized water system, including: The flow rate and conductivity of the inlet water of each membrane segment, as well as the flow rate and conductivity of the permeate and concentrate in the outlet water of each membrane segment, were obtained. The operating water volume information includes the flow rate information of the inlet water, product water and concentrate, and the water quality information includes the conductivity information of the inlet water, product water and concentrate.

3. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 2, characterized in that, Determining the salt rejection load corresponding to each membrane segment includes: The inlet salt load is determined based on the flow rate and conductivity of the inlet water of each membrane segment, the product water salt load is determined based on the flow rate and conductivity of the product water in the outlet water of each membrane segment, and the concentrate salt load is determined based on the flow rate and conductivity of the concentrate. The salt retention load of the corresponding membrane section is determined based on the difference between the inlet salt load and the product water salt load, whereby the concentrate salt load is the salt load output downstream from the corresponding membrane section.

4. The method for stable control of a demineralized water system based on the operating status of the membrane segment according to claim 3, characterized in that, Determining the salt retention load distribution status of the membrane segment includes: Arrange the salt rejection loads corresponding to each membrane segment in the order of water flow direction; Calculate the proportion of salt retention load in each membrane segment to the total salt retention load, arrange the proportions according to the water flow direction, and obtain the salt retention load distribution status of the membrane segments.

5. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 1, characterized in that, Establishing the salt load transfer baseline between adjacent membrane segments includes: The salt load transfer coefficient of the corresponding adjacent membrane section is determined based on the ratio of the inlet salt load of the downstream membrane section to the concentrate salt load of the upstream membrane section. The salt retention capacity coefficient of the corresponding adjacent membrane sections is determined based on the ratio of the salt retention load of the downstream membrane section to the salt load of the concentrate in the upstream membrane section. Based on the salt load transfer coefficient and salt retention and acceptance coefficient within the acquisition cycle corresponding to several stable operating states, the salt load transfer benchmark for adjacent membrane segments is determined.

6. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 5, characterized in that, Determining the explanatory load capacity of the downstream membrane segment includes: Determine the change in the current upstream membrane section concentrate salt load relative to the stable operating state; Based on the change and the salt load transfer coefficient in the salt load transfer reference, the expected change in the downstream membrane section inlet salt load is determined; Based on the change and the salt retention carrying capacity coefficient in the salt load transfer benchmark, the expected change in the salt retention load of the downstream membrane segment is determined. The expected salt rejection load of the downstream membrane segment is determined by the sum of the salt rejection load of the downstream membrane segment under stable operating conditions and the expected change in the salt rejection load of the downstream membrane segment. The explainable percentage change of the downstream membrane segment is determined by subtracting the percentage of salt retention load of the downstream membrane segment under the baseline condition from the ratio between the expected salt retention load of the downstream membrane segment and the current total salt retention load.

7. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 4, characterized in that, Determining the actual load migration of the membrane segment includes: Calculate the difference between the current salt rejection load percentage of each membrane segment and the corresponding baseline percentage to obtain the percentage change of each membrane segment; The change in the proportion of each membrane segment is determined as the actual load migration of the membrane segment.

8. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 7, characterized in that, Determining the nontransitive load migration characteristics includes: The non-transferable percentage change of the downstream membrane segment is determined based on the explainable percentage change of the downstream membrane segment in the explainable load carrying capacity and the percentage change of the corresponding downstream membrane segment in the actual load migration of the membrane segment. The change in the proportion of nontransmissible load and the corresponding position of the membrane segment are defined as the nontransmissible load migration characteristics.

9. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 8, characterized in that, Determining the abnormal operating state of the corresponding membrane segment based on the aforementioned non-transmissive load migration characteristics includes: When the change in the non-transferable proportion of the downstream membrane segment is negative and exceeds the preset migration deviation threshold, if the salt load transfer coefficient of the corresponding adjacent membrane segment is lower than the benchmark range, it is determined that the inter-segment salt load transfer is abnormal; if the salt load transfer coefficient of the corresponding adjacent membrane segment is within the benchmark range, it is determined that the downstream membrane segment load acceptance is abnormal. When the change in the nontransferability of the downstream membrane segment is positive and exceeds the preset migration deviation threshold, it is determined that the salt retention load is abnormally migrating to the downstream membrane segment. When the change in the proportion of the upstream membrane segment exceeds the preset migration deviation threshold in a negative direction, and the change in the non-transferable proportion of the corresponding downstream membrane segment is within the deviation threshold range, it is determined that the salt retention load of the upstream membrane segment is abnormally low.

10. The method for stable control of a demineralized water system based on the operating state of the membrane segment according to claim 9, characterized in that, Determine the pressure regulation and concentrate regulation for the corresponding membrane segment, including: In response to abnormal salt load transfer between membrane sections, the concentrate adjustment amount of the adjacent upstream membrane section is determined based on the amplitude of the change in the non-transferable proportion of the corresponding downstream membrane section. In response to abnormal load bearing in the downstream membrane segment, the pressure adjustment amount of the downstream membrane segment is determined based on the amplitude of the change in the non-transmissibility ratio of the downstream membrane segment. In response to the abnormal operating state where the salt rejection load migrates to the downstream membrane segment, the pressure regulation and concentrate regulation of the upstream abnormal membrane segment are determined based on the amplitude of the change in the proportion of the upstream abnormal membrane segment.

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