Multi-stage circulating concentration reverse osmosis membrane system and control method thereof

Abstract

The invention provides a multi-stage circulating concentration reverse osmosis membrane system and a control method thereof, and belongs to the technical field of ferric phosphate wastewater treatment.The multi-stage circulating concentration reverse osmosis membrane system comprises a multi-stage reverse osmosis membrane system, a water inlet unit, a concentrated water output unit and a control unit; the multi-section reverse osmosis membrane system comprises at least two sections of reverse osmosis membrane units which are sequentially connected, each section of reverse osmosis membrane unit comprises a reverse osmosis membrane and a pumping mechanism, and a first control valve is arranged between every two adjacent sections of reverse osmosis membrane units; the water inlet unit comprises a first conductivity meter; the concentrated water output unit comprises a second conductivity meter and a second control valve; the control unit is used for adjusting the pumping mechanism, the first control valve and the second control valve according to online monitoring numerical values of the first conductivity meter and the second conductivity meter. Through the mode, the multi-section circulating concentration reverse osmosis membrane system provided by the invention can stably operate, effectively shortens the concentration process, and ensures that the finally obtained concentrated water meets the requirement.

Description

Technical Field

[0001] The present application relates to the technical field of iron phosphate wastewater treatment, and in particular to a multi-stage circulating concentration reverse osmosis membrane system and a control method thereof. Background Art

[0002] In recent years, the rapid development of new energy vehicles and related energy storage technologies has greatly increased the demand for lithium-ion batteries. As a precursor for the production of lithium iron phosphate cathode materials for lithium-ion batteries, the demand for iron phosphate has also continued to rise. However, the production process of iron phosphate produces a large amount of wastewater, which is highly acidic and high in salt, making it difficult to treat. This is not only detrimental to environmental protection, but also restricts the development of iron phosphate production companies and the new energy industry. Therefore, it is necessary to treat the wastewater generated in the production process of iron phosphate.

[0003] At present, the treatment process of iron phosphate wastewater mainly includes pretreatment, membrane concentration, evaporation crystallization and other processes. By using membrane concentration to concentrate the pretreated iron phosphate wastewater to a certain concentration range, and then evaporation crystallization, the impurity ions in the wastewater can be effectively removed and used as by-products. Among them, membrane concentration is mainly based on the reverse osmosis membrane concentration system, which uses the salt water separation characteristics of the reverse osmosis membrane to achieve material concentration, so that the subsequent evaporation crystallization process can proceed smoothly.

[0004] The existing reverse osmosis membrane concentration system generally includes a wash water reverse osmosis membrane system, a mother liquor reverse osmosis membrane system, a concentration reverse osmosis membrane system, etc. Among them, the wash water reverse osmosis membrane system is generally designed in three stages, with a recovery rate of 75-85%. After being concentrated by the wash water reverse osmosis membrane system, it is necessary to use the mother liquor reverse osmosis membrane system and the concentration reverse osmosis membrane system for further concentration. There are three main problems with this reverse osmosis membrane concentration system: First, due to the large difference in the concentration of the concentrated water output by the wash water reverse osmosis membrane system and the inlet water of the mother liquor reverse osmosis membrane system, the mother liquor reverse osmosis membrane system is often unstable, which in turn leads to the unstable operation of the concentration reverse osmosis membrane system. The unstable operation of the system requires the operator to frequently adjust the operating parameters, which not only increases the additional labor intensity, but also causes frequent maintenance of the equipment. Secondly, under normal circumstances, the design index of the final concentrated water concentration of the reverse osmosis membrane system is 150,000-180,000 μS / cm, but the actual average operating index of the above reverse osmosis membrane concentration system can generally only reach 130,000 μS / cm, which is significantly lower than the design index, resulting in a high amount of water in the concentrated water, which in turn leads to increased energy consumption in the subsequent evaporation process. Thirdly, since different reverse osmosis membrane systems need to be set up for treatment of wash water and mother liquor, the overall process is long and the energy consumption is high. Summary of the invention

[0005] In view of the technical problems existing in the background technology, the present application provides a multi-stage circulating concentration reverse osmosis membrane system and a control method thereof. The system operates stably, can effectively shorten the concentration process, and ensure that the final concentrated water meets the requirements.

[0006] In a first aspect, an embodiment of the present application provides a multi-stage circulating concentrated reverse osmosis membrane system, including a multi-stage reverse osmosis membrane system, a water inlet unit, a concentrated water output unit and a control unit;

[0007] The multi-stage reverse osmosis membrane system comprises at least two reverse osmosis membrane units connected in sequence, each of the reverse osmosis membrane units comprising a reverse osmosis membrane and a pumping mechanism connected to the inlet of the reverse osmosis membrane; the concentrated water outlet of the reverse osmosis membrane in each reverse osmosis membrane unit is connected to the inlet of the pumping mechanism in the next reverse osmosis membrane unit through a connecting pipe; a first control valve is provided in the connecting pipe;

[0008] The water inlet unit is connected to the inlet of the pumping mechanism in the first stage of the reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system; the water inlet unit includes a first conductivity meter;

[0009] The concentrated water output unit is connected to the concentrated water outlet of the reverse osmosis membrane in the last section of the reverse osmosis membrane unit of the multi-section reverse osmosis membrane system, and the concentrated water output unit includes a second conductivity meter and a second control valve;

[0010] The control unit is used to adjust the pumping mechanism, the first control valve and the second control valve according to the online monitoring values ​​of the first conductivity meter and the second conductivity meter.

[0011] In the technical solution of the embodiment of the present application, by setting a multi-stage reverse osmosis membrane system, the concentration of the raw water input by the water inlet unit is gradually increased by using the reverse osmosis membrane units connected in sequence, so that the raw water can be concentrated, and the concentrated water finally obtained can be output through the concentrated water output unit. The overall structure of the system is simple and the concentration process is short. At the same time, the embodiment of the present application also sets a pumping mechanism and a first control valve in the multi-stage reverse osmosis membrane system, sets a first conductivity meter in the water inlet unit, and sets a second conductivity meter and a second control valve in the concentrated water output unit, so that the control unit can intelligently adjust the pumping mechanism, the first control valve and the second control valve according to the online monitoring values ​​of the first conductivity meter and the second conductivity meter, which provides an accurate basis for the adjustment process, is conducive to the effective control of the recovery rate of each reverse osmosis membrane unit and the total recovery rate of the multi-stage reverse osmosis membrane system, so as to ensure that the concentrated water finally obtained meets the requirements. Moreover, based on the effective control of the concentrated water concentration by the embodiment of the present application, both wash water and mother liquor can be concentrated using the system provided by the embodiment of the present application. Compared with the combination of the traditional wash water concentration membrane system and the mother liquor concentration membrane system, the concentration process is effectively shortened and the stability of the system is improved.

[0012] In some embodiments, the multi-stage circulating concentrated reverse osmosis membrane system further comprises a fresh water output unit; the fresh water output unit comprises a fresh water tank and a fresh water pipeline for connecting the fresh water outlet of the reverse osmosis membrane with the fresh water tank; a flow meter is provided in the fresh water pipeline.

[0013] In this embodiment, by providing a fresh water tank and a flow meter, not only can the fresh water separated in the concentration process be effectively recovered, but also the flow data of the fresh water can be collected so as to calculate the recovery rate of the multi-stage reverse osmosis membrane system.

[0014] In some embodiments, the multi-stage circulating concentration reverse osmosis membrane system also includes a circulating unit; the circulating unit includes a circulating pipe connecting the water inlet unit and the concentrated water output unit, the input end of the circulating pipe is arranged downstream of the second conductivity meter in the concentrated water output unit, and the output end of the circulating pipe is arranged upstream of the first conductivity meter; a third control valve is arranged in the circulating pipe.

[0015] In this embodiment, by setting a circulation pipeline between the downstream of the second conductivity meter and the upstream of the first conductivity meter, and setting a third control valve in the circulation pipeline, concentrated water with concentration not meeting the requirements can be returned to the water inlet unit through the circulation pipeline during the adjustment stage before the system is stably operated or when the system is abnormal, so that it enters the multi-stage reverse osmosis membrane system along the output direction of the water inlet unit for treatment, and the multi-stage reverse osmosis membrane system and the third control valve are regulated according to the online monitoring values ​​of the first conductivity meter and the second conductivity meter to ensure that the concentrated water finally obtained meets the requirements.

[0016] In some embodiments, the water inlet unit includes a raw water tank, a boost pump, a heat exchanger, and a filter that are connected in sequence.

[0017] In this embodiment, by connecting the raw water tank, the boost pump, the heat exchanger and the filter in sequence, the raw water in the raw water tank can be pressurized by the boost pump. The pressurized raw water is first cooled by the heat exchanger, and then the small particles in the raw water are intercepted by the filter to prevent these small particles from affecting the multi-stage reverse osmosis membrane system.

[0018] In some embodiments, the first conductivity meter is disposed between the heat exchanger and the filter.

[0019] In this embodiment, by arranging the first conductivity meter between the heat exchanger and the filter, the conductivity data of raw water can be obtained as quickly as possible while the conductivity error caused by temperature change can be avoided.

[0020] In some embodiments, the concentrated water output unit further includes a concentrated water tank; the concentrated water outlet of the reverse osmosis membrane in the last reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system is connected to the concentrated water tank via the second conductivity meter and the second control valve in sequence.

[0021] In this embodiment, by connecting the concentrated water outlet to the concentrated water tank through the second conductivity meter and the second control valve in sequence, not only can the concentrated water be collected, but the conductivity of the concentrated water can also be tested before collection, and the opening and closing of the second control valve can be controlled according to the test results to ensure that the concentrated water collected in the concentrated water tank meets the requirements.

[0022] In some embodiments, a flow meter is provided between the second control valve and the concentrated water tank.

[0023] In this embodiment, by arranging a flow meter between the second control valve and the concentrated water tank, the flow data of the output concentrated water can be collected so as to calculate the total recovery rate of the multi-stage reverse osmosis membrane system.

[0024] In a second aspect, an embodiment of the present application provides a control method for a multi-stage circulating concentrated reverse osmosis membrane system, comprising the following steps:

[0025] The raw water is transported to the multi-stage reverse osmosis membrane system through the water inlet unit, and the concentration of the raw water is calculated according to the online monitoring value of the first conductivity meter;

[0026] Determining the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system according to the preset concentrated water concentration and the raw water concentration;

[0027] The frequency of the pumping mechanism and the opening of the first control valve are adjusted so that the actual recovery rate of each section of the reverse osmosis membrane unit is consistent with the theoretical recovery rate of the reverse osmosis membrane unit of the section;

[0028] The actual concentration of concentrated water is calculated according to the online monitoring value of the second conductivity meter, and the actual concentration is compared with the preset concentrated water concentration to determine whether the actual concentration meets the requirements; if it meets the requirements, the second control valve is opened to output the concentrated water; otherwise, the second control valve is closed to return the concentrated water to the water inlet unit for circulation treatment.

[0029] In the technical solution of the embodiment of the present application, the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system can be determined by calculating the concentration of the raw water and combining it with the preset concentrate concentration. On this basis, the frequency of the pumping mechanism and the opening of the first control valve are adjusted according to the theoretical recovery rate so that the actual recovery rate of each reverse osmosis membrane unit is consistent with the theoretical recovery rate of the reverse osmosis membrane unit, so that the concentration of the final concentrate meets the preset requirements.

[0030] In some embodiments, the step of determining the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system comprises:

[0031] Calculating the concentration multiple according to the preset concentrated water concentration and the raw water concentration;

[0032] Calculating the total recovery rate of the multi-stage reverse osmosis membrane system according to the concentration multiple;

[0033] The total recovery rate is allocated to each section so that the sum of the theoretical recovery rates of the reverse osmosis membrane units of each section is equal to the total recovery rate.

[0034] In this embodiment, the total recovery rate of the multi-stage reverse osmosis system is determined by first calculating the concentration multiple, so as to effectively control the concentration of the concentrated water finally obtained; at the same time, this embodiment distributes the determined total recovery rate to each stage, thereby facilitating precise control of each reverse osmosis membrane unit, thereby improving the accuracy of control.

[0035] In some embodiments, the step of determining whether the measured concentration meets the requirements includes:

[0036] The ratio of the measured concentration to the preset concentrated water concentration is calculated. If the ratio is between 0.95 and 1.05, it is determined to meet the requirements; otherwise, it is determined to not meet the requirements.

[0037] In this embodiment, by comparing the difference between the measured concentration and the preset concentrated water concentration, it is possible to simply and efficiently determine whether the measured concentration meets the requirements, so as to control the opening and closing of the second control valve according to the result to ensure that concentrated water that meets the requirements is obtained.

[0038] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 It is a schematic diagram of the structure of a multi-stage circulating concentration reverse osmosis membrane system in an embodiment of the present application.

[0041] Explanation of the reference numerals: 11. raw water tank; 12. lifting pump; 13. heat exchanger; 14. first conductivity meter; 15. filter; 21. first pumping mechanism; 22. first reverse osmosis membrane; 23. first control valve a; 24. second pumping mechanism; 25. second reverse osmosis membrane; 26. first control valve b; 27. third pumping mechanism; 28. third reverse osmosis membrane; 31. first flow meter; 32. second flow meter; 33. third flow meter; 34. fresh water tank; 41. second conductivity meter; 42. second control valve; 43. fourth flow meter; 44. concentrated water tank; 51. third control valve. DETAILED DESCRIPTION

[0042] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0044] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0045] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0047] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0048] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0049] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0050] In the prior art, the reverse osmosis membrane concentration system used to treat iron phosphate wastewater needs to set up a wash water reverse osmosis membrane system and a mother liquid reverse osmosis membrane system separately. The combination of the two systems not only has a long process, but also high system energy consumption; and there is a large difference between the concentrated water output by the wash water reverse osmosis membrane system and the inlet water concentration of the mother liquid reverse osmosis membrane system, resulting in unstable system operation and the final concentrated water does not meet the standards. Therefore, it is particularly important to obtain concentrated water that meets the requirements in a short process, stably and efficiently.

[0051] In order to solve the technical problem that it is difficult for existing systems to stably and efficiently obtain concentrated water that meets the requirements, the present application provides a multi-stage circulating concentration reverse osmosis membrane system and a control method thereof, by respectively arranging corresponding conductivity meters in the water inlet unit and the concentrated water output unit, and regulating the operation status of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system according to the online monitoring value of the conductivity meter, thereby effectively controlling the recovery rate of each reverse osmosis membrane unit and the total recovery rate of the multi-stage reverse osmosis membrane system, and stably and efficiently obtaining concentrated water that meets the requirements.

[0052] The multi-stage circulating concentration reverse osmosis membrane system disclosed in the embodiment of the present application can be used, but not limited to, in the treatment process of iron phosphate wastewater, and can achieve good results in other water treatment fields that require the use of reverse osmosis membranes for concentration. When the multi-stage circulating concentration reverse osmosis membrane system provided in the embodiment of the present application is used to treat iron phosphate wastewater, it can replace the wash water reverse osmosis membrane system and the mother liquor reverse osmosis membrane system in the traditional iron phosphate wastewater treatment reverse osmosis membrane concentration system, effectively shorten the concentration process and system energy consumption, and improve the stability of the system.

[0053] Please refer to Figure 1 An embodiment of the present application provides a multi-stage circulating concentration reverse osmosis membrane system, including a multi-stage reverse osmosis membrane system, a water inlet unit, a concentrated water output unit and a control unit.

[0054] The multi-stage reverse osmosis membrane system includes at least two reverse osmosis membrane units connected in sequence, each reverse osmosis membrane unit includes a reverse osmosis membrane and a pumping mechanism connected to the inlet of the reverse osmosis membrane; the concentrated water outlet of the reverse osmosis membrane in each reverse osmosis membrane unit is connected to the inlet of the pumping mechanism in the next reverse osmosis membrane unit through a connecting pipe; a first control valve is arranged in the connecting pipe. With such an arrangement, the raw water entering the multi-stage reverse osmosis membrane system can be concentrated step by step to steadily increase its concentration, and each reverse osmosis membrane unit can be controlled separately through the pumping mechanism and the first control valve to improve the control accuracy.

[0055] The water inlet unit is connected to the inlet of the pumping mechanism in the first reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system, so as to transport the raw water to be concentrated to the multi-stage reverse osmosis membrane system for stage-by-stage concentration treatment. The water inlet unit includes a first conductivity meter 14, which is used to detect the conductivity of the raw water so as to calculate the concentration value of the raw water.

[0056] The concentrated water output unit is connected to the concentrated water outlet of the reverse osmosis membrane in the last reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system, so as to obtain the concentrated water output by the multi-stage reverse osmosis membrane system. The concentrated water output unit includes a second conductivity meter 41 and a second control valve 42. The conductivity of the concentrated water can be detected by the second conductivity meter 41 to determine whether the concentrated water meets the preset requirements. The second control valve 42 can be adjusted according to the determination result to ensure that the concentrated water output by the second control valve 42 meets the requirements.

[0057] The control unit is used to adjust the pumping mechanism, the first control valve and the second control valve 42 according to the online monitoring values ​​of the first conductivity meter 14 and the second conductivity meter 41, so as to obtain concentrated water that meets the requirements. The control mode of the control unit can be manual control or automatic control. Manual control means manual adjustment by the operator, and automatic control means automatic adjustment by the control unit, which can realize unattended automatic operation and effectively reduce the labor intensity of the personnel. When automatic control is adopted, the control unit and the first conductivity meter 14, the second conductivity meter 41, the pumping mechanism, the first control valve and the second control valve 42 can be electrically connected or signal connected, and the control unit can be a single chip microcomputer or other devices containing processors such as a central processing unit, a graphics processing unit, a field programmable gate array, etc. The specific control process of the control unit includes: collecting the online monitoring value of the first conductivity meter 14, determining the theoretical recovery rate of each section of the reverse osmosis membrane unit according to the online monitoring value, and then adjusting the frequency of the pumping mechanism and the opening of the first control valve to make the actual recovery rate of each section of the reverse osmosis membrane unit consistent with the theoretical recovery rate; collecting the online monitoring value of the second conductivity meter 41, judging whether the concentrated water meets the requirements according to the online monitoring value, if it meets the requirements, opening the second control valve 42 to output the concentrated water, if it does not meet the requirements, closing the second control valve 42 to prevent the concentrated water that does not meet the requirements from being output. Among them, the concentrated water that does not meet the requirements can be returned to the water inlet unit so that it can be circulated through the multi-stage reverse osmosis membrane system again to ensure that the concentrated water that meets the requirements is finally obtained.

[0058] Further, in the embodiments of the present application, Figure 1As shown, the multi-stage reverse osmosis membrane system is a three-stage reverse osmosis membrane system, which includes a first reverse osmosis membrane unit, a second reverse osmosis membrane unit and a third reverse osmosis membrane unit connected in sequence along the flow direction. Among them, the first reverse osmosis membrane unit includes a first pumping mechanism 21 and a first reverse osmosis membrane 22, and the outlet of the first pumping mechanism 21 is connected to the inlet of the first reverse osmosis membrane 22; the second reverse osmosis membrane unit includes a second pumping mechanism 24 and a second reverse osmosis membrane 25, the inlet of the second pumping mechanism 24 is connected to the concentrated water outlet of the first reverse osmosis membrane 22, and the outlet of the second pumping mechanism 24 is connected to the inlet of the second reverse osmosis membrane 25; the third reverse osmosis membrane unit includes a third pumping mechanism 27 and a third reverse osmosis membrane 28, the inlet of the third pumping mechanism 27 is connected to the concentrated water outlet of the second reverse osmosis membrane 25, and the outlet of the third pumping mechanism 27 is connected to the inlet of the third reverse osmosis membrane 28. In addition, a first control valve a 23 can be provided in the connecting pipe between the concentrated water outlet of the first reverse osmosis membrane 22 and the second pumping mechanism 24, and a first control valve b 26 can be provided in the connecting pipe between the concentrated water outlet of the second reverse osmosis membrane 25 and the third pumping mechanism 27. With such a configuration, the three-stage reverse osmosis membrane system formed can gradually concentrate the raw water input by the water inlet unit, and is convenient for controlling each reverse osmosis membrane unit through the pumping mechanism of each section and / or the first control valve. In other embodiments of the present application, the number of reverse osmosis membrane units in the multi-stage reverse osmosis membrane system can also be adjusted according to actual needs, for example, adjusted to a two-stage reverse osmosis membrane system, a four-stage reverse osmosis membrane system, etc., and the following is a specific description taking the three-stage reverse osmosis membrane system as an example.

[0059] Specifically, in the embodiment of the present application, the first reverse osmosis membrane 22, the second reverse osmosis membrane 25, and the third reverse osmosis membrane 28 are all pressure-driven reverse osmosis membranes. By applying a pressure greater than the osmotic pressure to the liquid on one side of such reverse osmosis membranes, the solvent is reversely osmotic in the direction of natural osmosis, thereby collecting fresh water on the low-pressure side of the reverse osmosis membrane and collecting concentrated water on the high-pressure side. The first pumping mechanism 21 is a high-pressure pump, which is used to pump the liquid output by the water inlet unit to the first reverse osmosis membrane 22 and provide the first reverse osmosis membrane 22 with a driving pressure greater than the osmotic pressure. At the same time, the first pumping mechanism 21 can also provide a certain driving pressure for the downstream second reverse osmosis membrane 25 and the third reverse osmosis membrane 28, but the pressure will decrease step by step. On this basis, the second pumping mechanism 24 can further enhance the driving pressure on the second reverse osmosis membrane 25, and the third pumping mechanism 27 can further enhance the driving pressure on the third reverse osmosis membrane 28. Among them, the first pumping mechanism 21, the second pumping mechanism 24 and the third pumping mechanism 27 are preferably pumping mechanisms that can be frequency-controlled, so that the driving pressure of the pumping mechanism on the reverse osmosis membrane can be changed by changing the frequency, thereby regulating the reverse osmosis effect of the reverse osmosis membrane.

[0060] Further, in the embodiments of the present application, Figure 1 As shown, the water inlet unit includes a raw water tank 11, a lifting pump 12, a heat exchanger 13 and a filter 15 which are connected in sequence. The raw water stored in the raw water tank 11 is wash water and / or mother liquor, and the lifting pump 12 can lift and pressurize the raw water, which not only provides driving force for the filtration of the filter 15, but also ensures that the raw water input to the first reverse osmosis membrane unit meets the water inlet pressure requirement of the first pumping mechanism 21, so as to ensure the smooth progress of the subsequent process. The raw water pressurized by the lifting pump 12 is first cooled to 25-30°C by the heat exchanger 13, and then the small particles in the raw water are intercepted by the filter 15 to protect the pumping mechanism and the reverse osmosis membrane in the reverse osmosis membrane unit from being damaged by small particles.

[0061] Furthermore, in an embodiment of the present application, the first conductivity meter 14 is arranged between the heat exchanger 13 and the filter 15. This can avoid the conductivity error caused by temperature changes and there is no need to wait for filtration. The conductivity data of the raw water can be obtained as soon as possible, so as to quickly form a control plan for the multi-stage reverse osmosis membrane system based on the conductivity data, thereby improving the processing efficiency.

[0062] Furthermore, in an embodiment of the present application, the multi-stage circulating concentration reverse osmosis membrane system also includes a fresh water output unit. The fresh water output unit includes a fresh water tank 34 and a fresh water pipe for connecting the fresh water outlet of the reverse osmosis membrane and the fresh water tank 34; a flow meter is provided in the fresh water pipe. With such a configuration, the fresh water separated during the concentration process can be effectively recovered using the fresh water tank 34, and the recovery rate of the multi-stage reverse osmosis membrane system can be calculated using the flow meter. Among them, the fresh water pipe can be a pipe connected to the total fresh water outlet of the multi-stage reverse osmosis membrane system, which is used to calculate the total recovery rate of the multi-stage reverse osmosis membrane system; the fresh water pipe is more preferably a plurality of pipes connected to each section of the reverse osmosis membrane unit, respectively, for calculating the recovery rate of each section of the reverse osmosis membrane unit, so as to accurately control each section of the reverse osmosis membrane unit. Taking the three-stage reverse osmosis membrane system as an example, the flowmeter in the fresh water output unit includes a first flowmeter 31, a second flowmeter 32 and a third flowmeter 33. The first flowmeter 31 is arranged in the first fresh water pipeline connecting the fresh water outlet of the first reverse osmosis membrane 22 and the fresh water tank 34, and is used to detect the fresh water flow of the first reverse osmosis membrane unit; the second flowmeter 32 is arranged in the second fresh water pipeline connecting the fresh water outlet of the second reverse osmosis membrane 25 and the fresh water tank 34, and is used to detect the fresh water flow of the second reverse osmosis membrane unit; the third flowmeter 33 is arranged in the third fresh water pipeline connecting the fresh water outlet of the third reverse osmosis membrane 28 and the fresh water tank 34, and is used to detect the fresh water flow of the third reverse osmosis membrane unit.

[0063] Furthermore, in the embodiment of the present application, the concentrated water output unit further includes a concentrated water tank 44 for collecting the obtained concentrated water. The concentrated water outlet of the reverse osmosis membrane in the last reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system is connected to the concentrated water tank 44 through the second conductivity meter 41 and the second control valve 42 in sequence, so as to detect the conductivity of the concentrated water before collecting the concentrated water, and control the opening and closing of the second control valve 42 according to the detection result, so as to ensure that the concentrated water collected in the concentrated water tank 44 meets the requirements.

[0064] Further, in the embodiment of the present application, a fourth flow meter 43 is provided between the second control valve 42 and the concentrated water tank 44, for collecting the flow data of the output concentrated water, so as to calculate the total recovery rate of the multi-stage reverse osmosis membrane system. Taking the three-stage reverse osmosis membrane system as an example, when the fresh water pipeline is a plurality of pipelines connected to each section of the reverse osmosis membrane unit, F1, F2, F3, and F4 respectively represent the flow data collected by the first flow meter 31, the second flow meter 32, the third flow meter 33, and the fourth flow meter 43, then the recovery rate of each section of the reverse osmosis membrane unit and the total recovery rate of the three-stage reverse osmosis membrane system are calculated as follows:

[0065] The recovery rate of the first reverse osmosis membrane unit = F1 / (F1+F2+F3+F4);

[0066] The recovery rate of the second reverse osmosis membrane unit = F2 / (F1+F2+F3+F4);

[0067] The recovery rate of the third reverse osmosis membrane unit = F3 / (F1+F2+F3+F4);

[0068] The total recovery rate of the three-stage reverse osmosis membrane system = 1-F4 / (F1+F2+F3+F4).

[0069] In order to read the total water intake more quickly, preferably, a flow meter can be added before the first pumping mechanism 21, and the reading is recorded as F0. The recovery rate of the first reverse osmosis membrane unit is F1 / F0, the recovery rate of the second reverse osmosis membrane unit is F2 / F0, and the recovery rate of the third reverse osmosis membrane unit is F3 / F0. The total recovery rate is 1-F4 / F0.

[0070] Further, in the embodiments of the present application, Figure 1As shown, the multi-stage circulating concentrated reverse osmosis membrane system also includes a circulation unit. The circulation unit includes a circulation pipeline connecting the water inlet unit and the concentrated water output unit, the input end of the circulation pipeline is arranged downstream of the second conductivity meter 41 in the concentrated water output unit, and the output end of the circulation pipeline is arranged upstream of the first conductivity meter 14; a third control valve 51 is arranged in the circulation pipeline. In this way, in the adjustment stage before the system is stably operated or when the system is abnormal, the concentrated water that does not meet the requirements determined according to the online monitoring value of the second conductivity meter 41 can be returned to the water inlet unit through the circulation pipeline, so that it can first pass through the first conductivity meter 14 along the output direction of the water inlet unit to measure the new raw water concentration, and form a control scheme for the multi-stage reverse osmosis membrane system based on the result, so that the circulating concentrated water enters the multi-stage reverse osmosis membrane system again for treatment, and judges whether the obtained concentrated water concentration meets the requirements according to the online monitoring value of the second conductivity meter 41. If it still does not meet the requirements, it continues to be circulated through the circulation pipeline until the concentrated water concentration meets the requirements, then the third control valve 51 is closed, and the concentrated water that meets the requirements is output through the concentrated water output unit.

[0071] According to one or more embodiments of the present application, the multi-stage circulating concentrated reverse osmosis membrane system provided by the present application can regulate the operation of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system according to the conductivity of the raw water, thereby effectively controlling the total recovery rate of the multi-stage reverse osmosis membrane system to ensure that the concentrated water obtained finally meets the requirements. In addition, the multi-stage circulating concentrated reverse osmosis membrane system adopted by the present application has a high level of integration and automation, and the system stability is good, which not only reduces the labor intensity of operators, but also reduces the maintenance frequency of equipment.

[0072] For the multi-stage circulating concentrated reverse osmosis membrane system provided in the embodiment of the present application, the embodiment of the present application also provides a corresponding control method so as to stably and efficiently obtain concentrated water that meets the requirements. It should be noted that in the present application, concentrated water that meets the requirements can refer to concentrated water whose concentration meets the design requirements, or concentrated water whose conductivity meets the design requirements, which can be set according to actual needs and all belong to the protection scope of the present application. The following is a specific description of the control method of the multi-stage circulating concentrated reverse osmosis membrane system using the concentration meeting the design requirements as an example. The control method includes the following steps:

[0073] S1. The raw water is delivered to the multi-stage reverse osmosis membrane system through the water inlet unit, and the concentration of the raw water is calculated according to the online monitoring value of the first conductivity meter 14;

[0074] S2. Determine the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system according to the preset concentrate concentration and the raw water concentration;

[0075] S3. The frequency of the pumping mechanism and the opening of the first control valve are adjusted so that the actual recovery rate of each section of the reverse osmosis membrane unit is consistent with the theoretical recovery rate of the reverse osmosis membrane unit of the section;

[0076] S4. Calculate the actual concentration of the concentrated water according to the online monitoring value of the second conductivity meter 41, and compare the actual concentration with the preset concentrated water concentration to determine whether the actual concentration meets the requirements; if it meets the requirements, open the second control valve 42 to output the concentrated water; otherwise, close the second control valve 42 to return the concentrated water to the water inlet unit for circulation treatment. In this way, the multi-stage circulating concentration reverse osmosis membrane system can be automatically controlled simply and efficiently, and it is ensured that the concentration of the concentrated water finally obtained meets the preset requirements.

[0077] Furthermore, in an embodiment of the present application, the step of calculating the concentration of raw water according to the online monitoring value of the first conductivity meter 14 in step S1 includes: predetermining a corresponding curve between conductivity and concentration, and the control unit obtains the online monitoring value of the first conductivity meter 14 and then determines the concentration value of the raw water through the corresponding curve.

[0078] Further, in the embodiment of the present application, the step of determining the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system in step S2 includes:

[0079] S21. Calculate the concentration multiple according to the preset concentrate concentration and the raw water concentration: the raw water concentration is recorded as C1, the preset concentrate concentration is recorded as C0, and the concentration multiple n = C0 / C1;

[0080] S22. According to the concentration multiple n, the total recovery rate of the multi-stage reverse osmosis membrane system is calculated to be 1-1 / n;

[0081] S23. Allocate the total recovery rate to each section so that the sum of the theoretical recovery rates of each reverse osmosis membrane unit is equal to the total recovery rate.

[0082] Among them, the way of allocating the total recovery rate to each section can be selected according to actual needs. For example, the ratio of the theoretical recovery rate of each section of the reverse osmosis membrane unit can be pre-set, and then the total recovery rate can be allocated to each section according to the ratio of the set theoretical recovery rate; the theoretical recovery rate range of each section of the reverse osmosis membrane unit can also be pre-set, and the theoretical recovery rate of each section of the reverse osmosis membrane unit can be taken within the corresponding range, and the theoretical recovery rate of each section can be fine-tuned according to the total recovery rate to ensure that the total recovery rate is equal to the theoretical recovery rate of each section of the reverse osmosis unit. In some embodiments of the present application, the theoretical recovery rate of each section of the reverse osmosis membrane unit decreases step by step. Taking the three-stage reverse osmosis membrane system as an example, the theoretical recovery rate of the first section can be set to 40-50%, the theoretical recovery rate of the second section can be set to 20-25%, and the theoretical recovery rate of the third section can be set to 10-25%. In other embodiments of the present application, the corresponding theoretical recovery rate can be adjusted according to actual needs, and the present application is not limited to this.

[0083] In addition, if the preset concentrate standard is concentrate conductivity, the theoretical concentration of concentrate can be calculated based on the preset concentrate conductivity, and then the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system can be determined based on the theoretical concentration and the concentration of raw water.

[0084] Further, in the embodiment of the present application, in step S3, a step-by-step adjustment method is adopted, firstly, the pumping mechanism of the first section of the reverse osmosis membrane unit is opened, and the opening of the pumping mechanism and the corresponding first control valve are adjusted, so that the actual recovery rate of the first section of the reverse osmosis membrane unit is consistent with the theoretical recovery rate, and then the next section of the reverse osmosis membrane unit is adjusted, and so on, until the adjustment of all the reverse osmosis membrane units is completed. Among them, when adjusting the last section of the reverse osmosis membrane unit, in order to prevent the concentrated water that does not meet the standards from entering the concentrated water tank 44 during the adjustment process, the second control valve 42 can be closed, and the third control valve 51 can be opened, and the actual recovery rate of the last section of the reverse osmosis membrane unit is consistent with the theoretical recovery rate by adjusting the pumping mechanism of the last section of the reverse osmosis membrane unit and the opening of the third control valve 51.

[0085] The actual recovery rate of each reverse osmosis membrane unit can be calculated through the test data of the corresponding flow meter. Taking the three-stage reverse osmosis membrane system as an example, the specific adjustment method includes: opening the first control valve a23, the first control valve b26, and the third control valve 51, and continuously adjusting the opening of the first control valve a23 and the frequency of the first pumping mechanism 21 until the calculated recovery rate F1 / (F1+F2+F3+F4) of the first-stage reverse osmosis membrane unit is consistent with the theoretical recovery rate of the first-stage reverse osmosis membrane unit; then adjusting the opening of the first control valve b26 and the frequency of the second pumping mechanism 24 until the calculated recovery rate F2 / (F1+F2+F3+F4) of the second-stage reverse osmosis membrane unit is consistent with the theoretical recovery rate of the second-stage reverse osmosis membrane unit; finally adjusting the opening of the third control valve 51 and the frequency of the third pumping mechanism 27 until the calculated recovery rate F3 / (F1+F2+F3+F4) of the third-stage reverse osmosis membrane unit is consistent with the theoretical recovery rate of the third-stage reverse osmosis membrane unit, that is, completing the adjustment of the three-stage reverse osmosis membrane system.

[0086] Further, in the embodiment of the present application, the step of determining whether the measured concentration meets the requirements in step S4 includes:

[0087] The ratio of the measured concentration to the preset concentrated water concentration is calculated. If the ratio is between 0.95 and 1.05, it is determined to meet the requirements; otherwise, it is determined to not meet the requirements.

[0088] Through the above method, it is possible to simply and efficiently determine whether the measured concentration meets the requirements, so as to control the opening and closing of the second control valve 42 according to the result, and ensure that the concentrated water that meets the requirements is obtained. Specifically, if it is finally determined to meet the requirements, the third control valve 51 is closed, the second control valve 42 is opened, and the concentrated water enters the concentrated water tank 44 for collection; if it is finally determined to not meet the requirements, the second control valve 42 is not opened, and the concentrated water that does not meet the requirements enters the circulation pipeline through the opened third control valve 51, and is then transported to the multi-stage reverse osmosis membrane system for re-concentration treatment.

[0089] In addition, if the pre-set concentrated water standard is concentrated water conductivity, it is not necessary to calculate the measured concentration of concentrated water according to the online monitoring value of the second conductivity meter 41, but directly compare the online monitoring value of the second conductivity meter 41 with the preset concentrated water conductivity, and calculate the ratio between the online monitoring value of the second conductivity meter 41 and the preset concentrated water conductivity. If the ratio is between 0.95 and 1.05, it is determined to meet the requirements; otherwise, it is determined to not meet the requirements. It should be noted that in different embodiments of the present application, whether the concentrated water concentration or the concentrated water conductivity is used as the standard, the set ratio range is not limited to 0.95 to 1.05, and can also be adjusted according to actual needs, and the present application is not limited to this.

[0090] In order to verify the actual effect of the multi-stage circulating concentration reverse osmosis membrane system and its control method provided by the present application, in some embodiments of the present application, wash water is used as raw water for concentration treatment, and the conductivity of 100000μS / cm is used as the standard for judging whether the final concentrated water meets the requirements. In these embodiments, a three-stage reverse osmosis membrane system is adopted, in which the specification of the first reverse osmosis membrane 22 is 8 inches and 7 cores, with a total of 32 pieces; the specification of the second reverse osmosis membrane 25 is 8 inches and 7 cores, with a total of 18 pieces; the specification of the third reverse osmosis membrane 28 is 8 inches and 7 cores, with a total of 18 pieces; the membrane elements in the first reverse osmosis membrane 22, the second reverse osmosis membrane 25 and the third reverse osmosis membrane 28 are all DuPont XC70. In the initial state, the flow rate of the lifting pump 12 in each embodiment is 350m 3 / h, the head is 5 bar; the flow rate of the first pumping mechanism 21 is 350m 3 / h, the head is 25bar; the flow rate of the second pumping mechanism 24 is 200m 3 / h, the head is 15bar; the flow rate of the third pumping mechanism 27 is 150m 3 / h, the head is 10 bar. After washing water with different conductivity is concentrated according to the multi-stage circulating concentration reverse osmosis membrane system and control method provided by the present application, the conductivity of the concentrated water and the flow data of each flow meter under the stable state are shown in Table 1.

[0091] Table 1 Concentration results of wash water with different concentrations

[0092]

[0093] As can be seen from Table 1, for wash water with different initial conductivities, when the multi-stage circulating concentration reverse osmosis membrane system and control method thereof provided by the present application are used for concentration, the recovery rate of each embodiment changes, but the conductivity of the concentrated water finally obtained is basically consistent with the set value. This indicates that the multi-stage circulating concentration reverse osmosis membrane system and control method thereof provided by the present application can adaptively adjust the recovery rate of each stage according to the conductivity of the wash water to ensure that the concentrated water finally obtained meets the preset requirements.

[0094] In summary, the multi-stage circulating concentration reverse osmosis membrane system and its control method provided by the present application, by respectively setting corresponding conductivity meters in the water inlet unit and the concentrated water output unit, and regulating the operation status of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system according to the online monitoring value of the conductivity meter, can effectively control the recovery rate of each reverse osmosis membrane unit and the total recovery rate of the multi-stage reverse osmosis membrane system, thereby stably and efficiently obtaining concentrated water that meets the requirements.

[0095] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A multi-stage circulating concentrated reverse osmosis membrane system, characterized in that: It includes a multi-stage reverse osmosis membrane system, a water inlet unit, a concentrated water output unit and a control unit; The multi-stage reverse osmosis membrane system comprises at least two reverse osmosis membrane units connected in sequence, each of the reverse osmosis membrane units comprising a reverse osmosis membrane and a pumping mechanism connected to the inlet of the reverse osmosis membrane; the concentrated water outlet of the reverse osmosis membrane in each reverse osmosis membrane unit is connected to the inlet of the pumping mechanism in the next reverse osmosis membrane unit through a connecting pipe; a first control valve is provided in the connecting pipe; The water inlet unit is connected to the inlet of the pumping mechanism in the first stage of the reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system; the water inlet unit includes a first conductivity meter; The concentrated water output unit is connected to the concentrated water outlet of the reverse osmosis membrane in the last section of the reverse osmosis membrane unit of the multi-section reverse osmosis membrane system, and the concentrated water output unit includes a second conductivity meter and a second control valve; The control unit is used to adjust the pumping mechanism, the first control valve and the second control valve according to the online monitoring values ​​of the first conductivity meter and the second conductivity meter.

2. The multi-stage circulating concentrated reverse osmosis membrane system according to claim 1, characterized in that: The multi-stage circulating concentrated reverse osmosis membrane system also includes a fresh water output unit; the fresh water output unit includes a fresh water tank and a fresh water pipeline for connecting the fresh water outlet of the reverse osmosis membrane and the fresh water tank; a flow meter is arranged in the fresh water pipeline.

3. The multi-stage circulating concentrated reverse osmosis membrane system according to claim 1, characterized in that: The multi-stage circulating concentrated reverse osmosis membrane system also includes a circulating unit; the circulating unit includes a circulating pipeline connecting the water inlet unit and the concentrated water output unit, the input end of the circulating pipeline is arranged downstream of the second conductivity meter in the concentrated water output unit, and the output end of the circulating pipeline is arranged upstream of the first conductivity meter; a third control valve is arranged in the circulating pipeline.

4. The multi-stage circulating concentrated reverse osmosis membrane system according to claim 1, characterized in that: The water inlet unit comprises a raw water tank, a booster pump, a heat exchanger and a filter which are connected in sequence.

5. The multi-stage circulating concentrated reverse osmosis membrane system according to claim 4, characterized in that: The first conductivity meter is arranged between the heat exchanger and the filter.

6. The multi-stage circulating concentrated reverse osmosis membrane system according to claim 1, characterized in that: The concentrated water output unit also includes a concentrated water tank; the concentrated water outlet of the reverse osmosis membrane in the last reverse osmosis membrane unit of the multi-stage reverse osmosis membrane system is connected to the concentrated water tank through the second conductivity meter and the second control valve in sequence.

7. The multi-stage circulating concentrated reverse osmosis membrane system according to claim 6, characterized in that: A flow meter is provided between the second control valve and the concentrated water tank.

8. A control method for a multi-stage circulating concentrated reverse osmosis membrane system according to any one of claims 1 to 7, characterized in that: The steps include: The raw water is transported to the multi-stage reverse osmosis membrane system through the water inlet unit, and the concentration of the raw water is calculated according to the online monitoring value of the first conductivity meter; Determining the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system according to the preset concentrated water concentration and the raw water concentration; The frequency of the pumping mechanism and the opening of the first control valve are adjusted so that the actual recovery rate of each section of the reverse osmosis membrane unit is consistent with the theoretical recovery rate of the reverse osmosis membrane unit of the section; The actual concentration of concentrated water is calculated according to the online monitoring value of the second conductivity meter, and the actual concentration is compared with the preset concentrated water concentration to determine whether the actual concentration meets the requirements; if it meets the requirements, the second control valve is opened to output the concentrated water; otherwise, the second control valve is closed to return the concentrated water to the water inlet unit for circulation treatment.

9. The control method of the multi-stage circulating concentrated reverse osmosis membrane system according to claim 8, characterized in that: The steps for determining the theoretical recovery rate of each reverse osmosis membrane unit in the multi-stage reverse osmosis membrane system include: Calculating the concentration multiple according to the preset concentrated water concentration and the raw water concentration; Calculating the total recovery rate of the multi-stage reverse osmosis membrane system according to the concentration multiple; The total recovery rate is allocated to each section so that the sum of the theoretical recovery rates of the reverse osmosis membrane units of each section is equal to the total recovery rate.

10. The control method of the multi-stage circulating concentrated reverse osmosis membrane system according to claim 8, characterized in that: The step of judging whether the measured concentration meets the requirements comprises: The ratio of the measured concentration to the preset concentrated water concentration is calculated. If the ratio is between 0.95 and 1.05, it is determined to meet the requirements; otherwise, it is determined to not meet the requirements.

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