A multi-stage closed-circuit desalination system based on reverse osmosis

Abstract

The present invention relates to the technical field of reverse osmosis seawater desalination, and in particular to a multi-stage closed-circuit desalination system based on reverse osmosis. The system comprises a pretreatment module for pretreating seawater; a reverse osmosis module connected to the pretreatment module for performing reverse osmosis on the pretreated seawater; a high-pressure pump module connected to the reverse osmosis module for providing pressure for the seawater to undergo reverse osmosis; a valve module connected to the reverse osmosis module for controlling the flow direction of concentrated water; and a control module respectively connected to the pretreatment module, the reverse osmosis module, the high-pressure pump module, and the valve module for controlling the working process of the seawater desalination system. The control module further comprises a data analysis unit, a control unit, and an adjustment unit. The present invention uses a multi-stage closed-circuit desalination system to desalinate seawater, thereby not only improving the utilization efficiency of seawater but also improving the quality of desalinated product water.

Description

Technical Field

[0001] The present invention relates to the technical field of reverse osmosis seawater desalination, in particular to a multi-stage closed-circuit desalination system based on reverse osmosis. Background Art

[0002] As human demand for fresh water grows, seawater desalination is one of the effective ways to solve the shortage of freshwater resources. Traditional seawater desalination technologies mostly have problems such as single seawater desalination system, low seawater desalination efficiency and poor system flexibility.

[0003] Chinese patent application publication number CN110436655A discloses a reverse osmosis seawater desalination system comprising a pretreatment unit, a reverse osmosis unit, and a freshwater tank. The reverse osmosis unit includes a reverse osmosis membrane assembly, a turbine booster pump connected between the pretreatment unit and the reverse osmosis membrane assembly, an electromagnetic three-way valve connected in series between the freshwater side and the freshwater tank, another branch of the electromagnetic three-way valve communicating with a discharge port, and the freshwater tank connected to a user via a pipeline. A bypass is provided between the high-pressure inlet and the low-pressure outlet, and a regulating valve is provided on the bypass to adjust the bypass flow rate. Furthermore, a lubrication pipeline connected to the thrust bearing and a connecting pipeline between the lubrication pipeline and the low-pressure inlet are constructed on the pump body. This reverse osmosis seawater desalination system can adjust the flow rate in the high-pressure inlet to maintain the optimal flow rate under design conditions, thereby effectively ensuring the operating efficiency of the turbine booster pump and improving the recovery efficiency of residual pressure energy.

[0004] It can be seen that the existing technology has the problem of low control accuracy of the seawater desalination system working process, resulting in low seawater desalination efficiency and low quality of desalinated product water. Summary of the Invention

[0005] To this end, the present invention provides a multi-stage closed-circuit desalination system based on reverse osmosis to overcome the problems in the prior art of low control precision of the working process of the seawater desalination system, resulting in low seawater desalination efficiency and low quality of desalinated product water.

[0006] To achieve the above object, the present invention provides a multi-stage closed-circuit desalination system based on reverse osmosis, comprising:

[0007] a pre-treatment module comprising a filter for filtering seawater and a treatment tank for chemically treating the seawater;

[0008] The reverse osmosis module is connected to the pretreatment module and includes a raw water storage tank for storing pretreated seawater, a primary reverse osmosis tank, a secondary reverse osmosis tank, and a tertiary reverse osmosis tank for desalinating seawater, and a product water storage tank for storing desalinated product water;

[0009] A high-pressure pump module connected to the reverse osmosis module includes a first high-pressure pump, a second high-pressure pump, and a third high-pressure pump for applying pressure to concentrated water;

[0010] a valve module connected to the reverse osmosis module, comprising a first valve for controlling the flow direction of pretreated seawater, a second valve for controlling the flow direction of concentrate in the primary reverse osmosis tank, a third valve for controlling the flow direction of concentrate in the secondary reverse osmosis tank, and a fourth valve for controlling the flow direction of concentrate in the tertiary reverse osmosis tank;

[0011] The control module is connected to the pretreatment module, the reverse osmosis module, the high-pressure pump module and the valve module respectively, and the control module includes:

[0012] A data analysis unit, which is used to determine the eligibility of seawater entering the raw water tank based on the pre-treated seawater state evaluation value;

[0013] a control unit connected to the data analysis unit, for controlling the opening and closing of the valve according to the analysis result of the data analysis unit;

[0014] an adjustment unit connected to the control unit and configured to determine adjustments to the seawater desalination process according to the performance of the desalination system;

[0015] The adjustment unit preliminarily determines the adjustment of the seawater desalination process according to the desalination efficiency of the desalination system, and further analyzes the purity of the desalinated product water to determine the adjustment of the seawater desalination process under the condition that the seawater desalination efficiency is qualified.

[0016] Furthermore, the data analysis unit determines that the seawater entering the raw water tank is unqualified based on a comparison result that a seawater state evaluation value determined by the pH value of the seawater and the free chlorine content in the seawater after pretreatment is less than a preset evaluation value, and the data analysis unit determines that the seawater entering the raw water tank is qualified based on a comparison result that the seawater state evaluation value after pretreatment is greater than or equal to the preset evaluation value.

[0017] Furthermore, when the data analysis unit determines that the seawater entering the raw water tank is unqualified, the control unit determines to control the first control valve to control the unqualified seawater to re-enter the pretreatment module for secondary pretreatment.

[0018] Furthermore, under the condition that the data analysis unit determines that the seawater entering the raw water tank is qualified, the adjustment unit determines to adjust the preset evaluation value with the first adjustment coefficient based on the comparison result that the replacement cycle of the reverse osmosis membrane in the reverse osmosis tank is less than the preset replacement cycle for a consecutive number of times greater than or equal to the preset number of times.

[0019] Furthermore, the adjustment unit determines the adjustment of the seawater desalination process according to the comparison result that the seawater desalination efficiency is less than the first preset desalination efficiency.

[0020] Furthermore, the adjustment unit performs a secondary determination on the adjustment of the seawater desalination process according to the comparison result that the seawater desalination efficiency is greater than or equal to the second preset desalination efficiency.

[0021] Furthermore, the adjustment unit determines to adjust the seawater desalination process according to the comparison result that the purity of the product water is not within a preset purity range.

[0022] Furthermore, the adjustment unit determines the control mode of the third valve and the fourth valve by adjusting the control unit according to the comparison result that the difference between the seawater desalination efficiency and the second preset desalination efficiency is greater than the preset difference.

[0023] Furthermore, the adjustment unit determines to adjust the preset replacement period of the reverse osmosis membrane by the second adjustment coefficient according to a comparison result that the difference between the seawater desalination efficiency and the second preset desalination efficiency is less than or equal to the preset difference.

[0024] Furthermore, the seawater state evaluation value is calculated by the following formula:

[0025]

[0026] Wherein, P represents the seawater state evaluation value, X represents the pH value of the pretreated seawater, Y0 represents the preset free chlorine content of the pretreated seawater, and Y represents the free chlorine content of the pretreated seawater.

[0027] Compared with the prior art, the present invention has the beneficial effect of pretreating seawater by physical and chemical methods to obtain raw water with low turbidity and neutral pH, thereby improving the efficiency of seawater desalination and the service life of the reverse osmosis membrane. At the same time, through the pretreatment of seawater, the impact of residual chlorine on the reverse osmosis membrane can be reduced and the formation of scaling precipitation of insoluble inorganic salts in seawater on the surface of the reverse osmosis membrane can be effectively prevented. The above method improves the accuracy of control of the multi-stage closed-circuit desalination system based on reverse osmosis.

[0028] Furthermore, the present invention improves the accuracy of control of a multi-stage closed-circuit desalination system based on reverse osmosis by performing secondary pretreatment on unqualified seawater to obtain qualified seawater for subsequent desalination treatment. At the same time, it avoids the occurrence of pipeline blockage and osmotic membrane damage caused by large particles of impurities in seawater.

[0029] Furthermore, the present invention determines whether to adjust the pretreatment process by comparing the consecutive number of times the replacement cycle of the reverse osmosis membrane is less than the preset replacement cycle with the preset number of times. If the consecutive number of times is greater than the preset number, it means that the damage frequency of the reverse osmosis membrane is high and thus the pretreatment process of the seawater is unqualified, and the pretreatment process needs to be adjusted. The present invention avoids the contingency of reverse osmosis membrane damage by analyzing the consecutive number of times the replacement cycle of the reverse osmosis membrane is less than the preset replacement cycle and thus accurately judges the eligibility of the pretreatment process. The above method improves the accuracy of control of the multi-stage closed-loop desalination system based on reverse osmosis.

[0030] Furthermore, the present invention determines the adjustment of the seawater desalination process according to the comparison result of the seawater desalination efficiency and the preset desalination efficiency through the adjustment unit. If the desalination efficiency is less than the first preset desalination efficiency, it means that the permeate of the reverse osmosis membrane of the desalination system is low and the permeate of the reverse osmosis membrane needs to be adjusted. If the desalination efficiency is greater than or equal to the first preset desalination efficiency and less than the second preset desalination efficiency, it means that the desalination efficiency of the desalination system is qualified. If the desalination efficiency is greater than or equal to the second preset desalination efficiency, it means that the desalination efficiency of the desalination system is excellent. At this time, the purity of the product water is determined. The above method improves the control accuracy of the multi-stage closed-circuit desalination system based on reverse osmosis, thereby producing high-quality product water.

[0031] Furthermore, the present invention determines adjustments to the seawater desalination process by comparing the purity of product water with qualified desalination efficiency with a preset purity range, thereby improving the accuracy of control of a multi-stage closed-circuit desalination system based on reverse osmosis, thereby efficiently obtaining high-quality product water.

[0032] Furthermore, the present invention determines the adjustment method according to the comparison result of the difference between the seawater desalination efficiency and the second preset desalination efficiency and the preset difference through the adjustment unit. If the difference is greater than the preset difference, it means that the purity of the desalinated product water is unqualified. The third valve and the fourth valve are used to control the concentrated water to flow to the second high-pressure pump and the third high-pressure pump respectively to improve the utilization rate of raw water and thus improve the purity of the product water. The above method improves the accuracy of the control of the multi-stage closed-loop desalination system based on reverse osmosis, thereby efficiently obtaining high-quality product water. In addition, the present invention adopts a multi-stage closed-loop desalination system to increase the system complexity and reduce the system flexibility, thereby overcoming the problem that the first reverse osmosis membrane is prone to pollution and the last reverse osmosis membrane is prone to scaling. The present invention improves the utilization rate of raw water and saves energy consumption by circulating pressurization. The present invention uses the second adjustment coefficient to reduce the preset replacement cycle of the reverse osmosis membrane, increase the number of adjustments to the pretreatment process, and thus reduce the erosion of the reverse osmosis membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1This is a schematic structural diagram of a multi-stage closed-circuit desalination system based on reverse osmosis according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic structural diagram of a control module of a multi-stage closed-circuit desalination system based on reverse osmosis according to an embodiment of the present invention;

[0035] Figure 3 This is a structural diagram of a multi-stage closed-circuit desalination system based on reverse osmosis according to an embodiment of the present invention;

[0036] In the figure, 1-treatment tank, 2-first valve, 3-raw water storage tank, 4-first high-pressure pump, 5-reverse osmosis membrane, 6-first reverse osmosis tank, 7-second high-pressure pump, 8-second reverse osmosis tank, 9-third high-pressure pump, 10-third reverse osmosis tank, 11-second valve, 12-third valve, 13-fourth valve, 14-product water storage tank. DETAILED DESCRIPTION

[0037] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0038] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0039] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating 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 does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0040] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0041] See also Figure 1-Figure 3 As shown, Figure 1 This is a schematic structural diagram of a multi-stage closed-circuit desalination system based on reverse osmosis according to an embodiment of the present invention; Figure 2This is a schematic structural diagram of a control module of a multi-stage closed-circuit desalination system based on reverse osmosis according to an embodiment of the present invention; Figure 3 This is a structural diagram of a multi-stage closed-circuit desalination system based on reverse osmosis according to an embodiment of the present invention.

[0042] The multi-stage closed-circuit desalination system based on reverse osmosis in the embodiment of the present invention includes:

[0043] A pre-treatment module, comprising a filter (not shown) for filtering seawater and a treatment tank 1 for chemically treating the seawater;

[0044] The reverse osmosis module is connected to the pretreatment module and includes a raw water storage tank 3 for storing pretreated seawater, a primary reverse osmosis tank 6, a secondary reverse osmosis tank 8, and a tertiary reverse osmosis tank 10 for desalinating seawater, and a product water storage tank 14 for storing desalinated product water;

[0045] A high-pressure pump module, connected to the reverse osmosis module, includes a first high-pressure pump 4, a second high-pressure pump 7, and a third high-pressure pump 9 for applying pressure to concentrated water;

[0046] a valve module connected to the reverse osmosis module, comprising a first valve 2 for controlling the flow direction of the pretreated seawater, a second valve 11 for controlling the flow direction of the concentrate in the primary reverse osmosis tank, a third valve 12 for controlling the flow direction of the concentrate in the secondary reverse osmosis tank, and a fourth valve 13 for controlling the flow direction of the concentrate in the tertiary reverse osmosis tank;

[0047] The control module is connected to the pretreatment module, the reverse osmosis module, the high-pressure pump module and the valve module respectively, and the control module includes:

[0048] A data analysis unit, which is used to determine the eligibility of seawater entering the raw water tank based on the pre-treated seawater state evaluation value;

[0049] a control unit connected to the data analysis unit, for controlling the opening and closing of the valve according to the analysis result of the data analysis unit;

[0050] The adjustment unit is connected to the control unit and is used to determine the adjustment of the seawater desalination process according to the effect of the desalination system.

[0051] The chemical treatment of seawater described in the embodiments of the present invention includes but is not limited to "adding FeCl3 to the seawater to reduce the pollution index of the seawater, adding sodium bisulfite to the seawater to reduce the free chlorine content in the seawater, and adding sulfuric acid to the seawater to control the pH value of the seawater to be between 7 and 7.5."

[0052] Specifically, the data analysis unit determines the eligibility of the seawater entering the raw water tank by comparing the pre-processed seawater state evaluation value P with the preset evaluation value P0;

[0053] If P<P0, the data analysis unit determines that the seawater entering the raw water tank is unqualified;

[0054] If P≥P0, the data analysis unit determines that the seawater entering the raw water tank is qualified;

[0055] The preset evaluation value P0 is a historical average of the seawater state evaluation values ​​that meet the requirements for reverse osmosis membrane corrosion. The above value is not limited thereto, and those skilled in the art may adjust the value according to actual needs.

[0056] In the embodiment of the present invention, the seawater having a qualified degree of corrosion to the reverse osmosis membrane includes the seawater having a replacement time of the reverse osmosis membrane that is greater than or equal to an average value of the historical replacement time of the reverse osmosis membrane.

[0057] Specifically, the seawater state evaluation value P is calculated by the following formula and is set:

[0058]

[0059] Wherein, X represents the pH value of the pretreated seawater, Y0 represents the preset free chlorine content of the pretreated seawater, which is 0.1, and Y represents the free chlorine content of the pretreated seawater.

[0060] The preset free chlorine content in the embodiment of the present invention is the standard for the seawater desalination pretreatment process.

[0061] Specifically, the present invention pre-treats seawater using physical and chemical methods to obtain raw water with low turbidity and neutral pH, thereby improving the efficiency of seawater desalination and the service life of the reverse osmosis membrane. At the same time, through the pre-treatment of seawater, the impact of residual chlorine on the reverse osmosis membrane can be reduced and the formation of scaling precipitation of insoluble inorganic salts in seawater on the surface of the reverse osmosis membrane can be effectively prevented. The above method improves the accuracy of the control of the multi-stage closed-circuit desalination system based on reverse osmosis.

[0062] Specifically, when the data analysis unit determines that the seawater entering the raw water tank is unqualified, the control unit determines to control the first control valve to control the unqualified seawater to re-enter the pretreatment module for secondary pretreatment.

[0063] Specifically, under the condition that the data analysis unit determines that the seawater entering the raw water tank is qualified, the control unit determines to control the first valve to control the qualified seawater to enter the raw water tank for seawater desalination.

[0064] Specifically, the present invention improves the accuracy of controlling a multi-stage closed-circuit desalination system based on reverse osmosis by performing secondary pretreatment on unqualified seawater to obtain qualified seawater for subsequent desalination treatment. At the same time, it avoids the occurrence of pipeline blockage and osmotic membrane damage caused by large particles of impurities in seawater.

[0065] Specifically, the control unit determines that the first valve is controlled to control qualified seawater to enter the raw water tank for seawater desalination, and the adjustment unit determines to adjust the pretreatment process according to a comparison result of the number of consecutive times N that the replacement cycle of the reverse osmosis membrane in the reverse osmosis tank is less than the preset replacement cycle T and the preset number of times N0;

[0066] If N<N0, the adjustment unit determines not to adjust the preprocessing process;

[0067] If N≥N0, the adjustment unit determines to adjust the preprocessing process;

[0068] Among them, the value of the preset number N0 is the historical average value of the number of times the replacement cycle of the reverse osmosis membrane that has passed the pretreatment is less than the preset replacement cycle, but the above value is not limited to this, and those skilled in the art can also adjust the value according to actual needs.

[0069] The preset replacement period in the embodiment of the present invention is the average value of the historical replacement periods of the reverse osmosis membrane, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0070] Specifically, the present invention determines whether to adjust the pretreatment process by comparing the consecutive number of times the replacement cycle of the reverse osmosis membrane is less than the preset replacement cycle with the preset number of times. If the consecutive number of times is greater than the preset number, it means that the damage frequency of the reverse osmosis membrane is high and thus the pretreatment process of the seawater is unqualified, and the pretreatment process needs to be adjusted. The present invention avoids the contingency of reverse osmosis membrane damage by analyzing the consecutive number of times the replacement cycle of the reverse osmosis membrane is less than the preset replacement cycle and thus accurately judges the eligibility of the pretreatment process. The above method improves the accuracy of control of the multi-stage closed-loop desalination system based on reverse osmosis.

[0071] Specifically, under the condition of determining to adjust the pre-process, the adjusting unit determines to adjust the preset evaluation value with a first adjustment coefficient K1.

[0072] Specifically, the first adjustment coefficient K1 is calculated and set by the following formula:

[0073]

[0074] The adjusted preset evaluation value is set to P0′=K1×P0.

[0075] Specifically, under the condition that the adjustment unit determines that the pretreatment process is not adjusted, the adjustment unit determines the adjustment of the seawater desalination process according to the comparison result of the seawater desalination efficiency G and the preset desalination efficiency Gi;

[0076] If G<G1, the adjustment unit determines to adjust the seawater desalination process;

[0077] If G1≤G<G2, the adjustment unit determines not to adjust the seawater desalination process;

[0078] If G≥G2, the adjustment unit determines to perform a secondary determination;

[0079] Among them, i=1, 2; the value of the first preset desalination efficiency G1 is seven-tenths of the historical maximum value of the seawater desalination efficiency of the same specification, and the value of the second preset desalination efficiency G2 is nine-tenths of the historical maximum value of the seawater desalination efficiency of the same specification, but the above values ​​are not limited to this, and those skilled in the art can also adjust the values ​​according to actual needs.

[0080] The seawater of the same specifications in the embodiment of the present invention includes but is not limited to “the same seawater element content, the same seawater volume and the same seawater turbidity”.

[0081] Specifically, the present invention determines the adjustment of the seawater desalination process according to the comparison result of the seawater desalination efficiency with the preset desalination efficiency through the adjustment unit. If the desalination efficiency is less than the first preset desalination efficiency, it means that the permeate of the reverse osmosis membrane of the desalination system is low and the permeate of the reverse osmosis membrane needs to be adjusted. If the desalination efficiency is greater than or equal to the first preset desalination efficiency and less than the second preset desalination efficiency, it means that the desalination efficiency of the desalination system is qualified. If the desalination efficiency is greater than or equal to the second preset desalination efficiency, it means that the desalination efficiency of the desalination system is excellent. At this time, the purity of the product water is determined. The above method improves the control accuracy of the multi-stage closed-circuit desalination system based on reverse osmosis, thereby producing high-quality product water.

[0082] Specifically, under the condition that the adjustment unit determines to perform a secondary determination, the adjustment unit determines to adjust the seawater desalination process according to the comparison result of the purity D of the product water with the preset purity range D0;

[0083] If D is within D0, the adjustment unit determines not to adjust the seawater desalination process;

[0084] If D is not within D0, the adjustment unit determines to adjust the seawater desalination process;

[0085] The preset purity range D0 is the purity range of product water of the seawater desalination standard, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0086] The purity of the product water described in the embodiment of the present invention includes but is not limited to "pH value, calcium hardness and total alkalinity"; the preset purity range includes but is not limited to "the pH value range of product water is 6.5-8.5, the calcium hardness range of product water is 60-120 mg / L, and the total alkalinity range of product water is greater than 50 mg / L".

[0087] Specifically, the present invention determines adjustments to the seawater desalination process by comparing the purity of product water with qualified desalination efficiency with a preset purity range, thereby improving the accuracy of controlling the multi-stage closed-circuit desalination system based on reverse osmosis, thereby efficiently obtaining high-quality product water.

[0088] Specifically, under the condition of determining the adjustment of the seawater desalination process, the adjustment unit determines the adjustment method according to the comparison result of the difference ΔG between the seawater desalination efficiency G and the second preset desalination efficiency G2 and the preset difference ΔG2;

[0089] If ΔG>ΔG2, the adjustment unit determines to adjust the seawater desalination process in a first adjustment manner;

[0090] If ΔG≤ΔG2, the adjustment unit determines to adjust the seawater desalination process in a second adjustment manner;

[0091] The value of the preset difference ΔG2 is set to one tenth of the second preset desalination efficiency, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0092] Specifically, under the condition that the seawater desalination process is adjusted in the first adjustment mode, the adjustment unit determines the control mode of the third valve and the fourth valve by the adjustment control unit;

[0093] Under the condition that the second adjustment unit determines to adjust the seawater desalination process in a second adjustment manner, the second adjustment unit determines to adjust the preset replacement period of the reverse osmosis membrane by a second adjustment coefficient K2.

[0094] Specifically, the second adjustment coefficient K2 is calculated and set by the following formula:

[0095]

[0096] The adjusted preset replacement period is set to T'=K2×T.

[0097] In an embodiment of the present invention, the adjustment unit determines to adjust the control mode of the control unit over the third valve and the fourth valve, including adjusting the initial state in which the control unit controls the third valve and the fourth valve to control the flow of concentrated water to the raw water tank to the control unit controlling the third valve and the fourth valve to control the flow of concentrated water to the second high-pressure pump and the third high-pressure pump in sequence under the condition that the desalination efficiency is qualified.

[0098] Specifically, the present invention determines the adjustment method according to the comparison result of the difference between the seawater desalination efficiency and the second preset desalination efficiency and the preset difference through the adjustment unit. If the difference is greater than the preset difference, it means that the purity of the desalinated product water is unqualified. The third valve and the fourth valve are used to control the concentrated water to flow to the second high-pressure pump and the third high-pressure pump respectively to improve the utilization rate of raw water and thus improve the purity of the product water. The above method improves the accuracy of the control of the multi-stage closed-loop desalination system based on reverse osmosis, thereby efficiently obtaining high-quality product water. In addition, the present invention adopts a multi-stage closed-loop desalination system to increase the system complexity and reduce the system flexibility, thereby overcoming the problem that the first reverse osmosis membrane is prone to pollution and the last reverse osmosis membrane is prone to scaling. The present invention improves the utilization rate of raw water and saves energy consumption through cyclic pressurization. The present invention uses the second adjustment coefficient to reduce the preset replacement cycle of the reverse osmosis membrane, increase the number of adjustments to the pretreatment process, and thus reduce the erosion of the reverse osmosis membrane.

[0099] Thus far, the technical solutions of the present invention have been described in conjunction with 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 may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

[0100] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A multi-stage closed-circuit desalination system based on reverse osmosis, characterized in that: include: a pre-treatment module comprising a filter for filtering seawater and a treatment tank for chemically treating the seawater; The reverse osmosis module is connected to the pretreatment module and includes a raw water storage tank for storing pretreated seawater, a primary reverse osmosis tank, a secondary reverse osmosis tank, and a tertiary reverse osmosis tank for desalinating seawater, and a product water storage tank for storing desalinated product water; A high-pressure pump module connected to the reverse osmosis module includes a first high-pressure pump, a second high-pressure pump, and a third high-pressure pump for applying pressure to concentrated water; a valve module connected to the reverse osmosis module, comprising a first valve for controlling the flow direction of pretreated seawater, a second valve for controlling the flow direction of concentrate in the primary reverse osmosis tank, a third valve for controlling the flow direction of concentrate in the secondary reverse osmosis tank, and a fourth valve for controlling the flow direction of concentrate in the tertiary reverse osmosis tank; The control module is connected to the pretreatment module, the reverse osmosis module, the high-pressure pump module and the valve module respectively, and the control module includes: A data analysis unit, which is used to determine the eligibility of seawater entering the raw water tank based on the pre-processed seawater state evaluation value P; a control unit connected to the data analysis unit, for controlling the opening and closing of the valve according to the analysis result of the data analysis unit; an adjustment unit connected to the control unit and configured to determine adjustments to the seawater desalination process according to the performance of the desalination system; The adjustment unit preliminarily determines the adjustment of the seawater desalination process according to the desalination efficiency of the desalination system, and further analyzes the purity of the desalinated product water to determine the adjustment of the seawater desalination process under the condition that the seawater desalination efficiency G is qualified; The data analysis unit determines that the seawater entering the raw water tank is unqualified based on a comparison result that the seawater state evaluation value P determined by the pH value of the seawater and the free chlorine content in the seawater after pretreatment is less than a preset evaluation value P0, and the data analysis unit determines that the seawater entering the raw water tank is qualified based on a comparison result that the seawater state evaluation value P determined by the pretreatment is greater than or equal to the preset evaluation value P0; When the data analysis unit determines that the seawater entering the raw water tank is unqualified, the control unit determines to control the first control valve to control the unqualified seawater to re-enter the pretreatment module for secondary pretreatment; The data analysis unit determines that the seawater entering the raw water tank is qualified, and the adjustment unit determines that the preset evaluation value P0 is adjusted by the first adjustment coefficient K1 according to the comparison result that the replacement cycle of the reverse osmosis membrane in the reverse osmosis tank is less than the preset replacement cycle for a consecutive number N greater than or equal to the preset number N0; The seawater state evaluation value P is calculated by the following formula, set: Wherein, P represents the seawater state evaluation value, X represents the pH value of the pretreated seawater, Y0 represents the preset free chlorine content of the pretreated seawater, and Y represents the free chlorine content of the pretreated seawater; The first adjustment coefficient K1 is calculated and set by the following formula: The adjusted preset evaluation value is set to P0′=K1×P0.

2. The multi-stage closed-circuit desalination system based on reverse osmosis according to claim 1, characterized in that: The adjustment unit determines the adjustment of the seawater desalination process according to the comparison result that the seawater desalination efficiency G is less than the first preset desalination efficiency G1.

3. The multi-stage closed-circuit desalination system based on reverse osmosis according to claim 2, characterized in that: The adjustment unit determines to perform a secondary determination on the adjustment of the seawater desalination process according to the comparison result that the seawater desalination efficiency G is greater than or equal to the second preset desalination efficiency G2.

4. The multi-stage closed-circuit desalination system based on reverse osmosis according to claim 3, characterized in that: The adjustment unit determines to adjust the seawater desalination process according to the comparison result that the purity of the product water is not within a preset purity range under the condition of determining to perform a secondary judgment.

5. The multi-stage closed-circuit desalination system based on reverse osmosis according to claim 4, characterized in that: If D is not within D0, the adjustment unit determines to adjust the seawater desalination process. Under the condition of determining to adjust the seawater desalination process, the adjustment unit determines to adjust the control mode of the control unit for the third valve and the fourth valve according to a comparison result that the difference ΔG between the seawater desalination efficiency G and the second preset desalination efficiency G2 is greater than the preset difference ΔG2; Wherein, D0 represents a preset purity range, and D represents the purity of the product water.

6. The multi-stage closed-circuit desalination system based on reverse osmosis according to claim 5, characterized in that: If D is not within D0, the adjustment unit determines to adjust the seawater desalination process. Under the condition that the adjustment unit determines to adjust the seawater desalination process, The adjustment unit determines to adjust the preset replacement period T of the reverse osmosis membrane by the second adjustment coefficient K2 according to the comparison result that the difference ΔG between the seawater desalination efficiency G and the second preset desalination efficiency G2 is less than or equal to the preset difference ΔG2; The second adjustment coefficient K2 is calculated and set by the following formula: The adjusted preset replacement period is set to T'=K2×T.

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