Short-process variable-working-condition seawater desalination system

Abstract

The invention discloses a short-flow variable-working-condition seawater desalination system which comprises a membrane tank, a membrane tank water producing pump, a first-stage high-pressure pump, a second-stage high-pressure pump, an energy recovery device, a reverse osmosis membrane stack and other units, and a water outlet pipe of the membrane tank is sequentially connected with the membrane tank water producing pump, the first-stage high-pressure pump, the second-stage high-pressure pump and the reverse osmosis membrane stack; a concentrated water port of the reverse osmosis membrane stack is connected with a high-pressure water inlet of the energy recovery device through a pipeline; a high-pressure water outlet pipe of the energy recovery device is sequentially connected with a booster pump and a secondary high-pressure pump water outlet pipe; and a stirrer, an immersed membrane and an aeration pipe are arranged in the membrane tank. The system has the advantages of being short in technological process, small in occupied area and high in impact load resistance, the double high-pressure pumps are connected in series, pressure can be efficiently adjusted, and the working conditions of large seawater salinity and temperature changes are met.

Description

Technical Field

[0001] The invention belongs to the technical field of seawater desalination, and in particular relates to a short-process variable-operating-condition seawater desalination system. Background Art

[0002] For desalination projects in estuaries, due to the geographical conditions of shallow water and gentle slopes and the restrictions on the use of sea areas, most water intake projects use river water. Since river water bodies are affected by multiple factors such as land-based pollutants, runoff, tidal latitude, etc., the organic matter, suspended matter, salinity, temperature and other factors in the water body undergo drastic changes. The desalination projects that take water from estuaries have natural characteristics such as high suspended matter, high organic matter, and large temperature and salinity fluctuations. Reverse osmosis desalination projects need to face complex and changeable water quality conditions, and seawater quality has a greater impact on the reverse osmosis system.

[0003] In terms of pretreatment, the removal of organic matter, suspended matter, colloids, microorganisms and certain harmful substances in seawater by pretreatment can slow down membrane pollution, extend the life of reverse osmosis membranes, and ensure the long-term stable operation of reverse osmosis systems. At present, most studies focus on mainstream processes such as coagulation and sedimentation, flotation, filter tank filtration, and membrane filtration. The combination of traditional processes and new membrane filtration processes is used to improve water quality, such as coagulation-sedimentation-sand filtration-external ultrafiltration, flotation-sand filtration-external ultrafiltration, etc. However, there are problems such as long process flow, large floor space, and unstable process operation. In terms of high-pressure water supply regulation, the reverse osmosis system needs to meet the pressure changes caused by temperature and salinity fluctuations. At present, it is mainly achieved through motor frequency conversion regulation. This method is widely used in engineering, but it is limited by the efficiency, flow, heat dissipation and other requirements of the centrifugal pump body. The range of efficient adjustment is small, and long-term low-frequency operation will shorten the life of the water pump. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a short-process variable-operating-condition seawater desalination system.

[0005] The technical solution of the present invention is summarized as follows:

[0006] A short-process variable-operating-condition seawater desalination system comprises a membrane pool 1 and a backwash pool 6, wherein the outlet pipe of the membrane pool 1 is connected in sequence to a membrane pool water production valve 14, a membrane pool water production pump 4, a primary high-pressure pump water inlet valve 15, a primary high-pressure pump 7, a secondary high-pressure pump water inlet valve 18, a secondary high-pressure pump 8 and a reverse osmosis membrane stack 10 water inlet pipe; the outlet pipe of the membrane pool water production pump 4 is connected in sequence to a backwash pool water replenishment valve 16 and the backwash pool 6; the outlet pipe of the backwash pool 6 is connected in sequence to a backwash pump 5, a membrane pool backwash valve 13 and a membrane pool outlet pipe; the outlet pipe of the primary high-pressure pump 7 is connected in sequence to a secondary high-pressure pump bypass valve 17 and an outlet pipe of the secondary high-pressure pump 8; the reverse osmosis membrane stack The concentrated water pipe 10 is connected to the high-pressure water inlet pipe of the energy recovery device 11; the outlet pipe of the first-level high-pressure pump inlet valve 15 is connected to the low-pressure water inlet pipe of the energy recovery device 11; the high-pressure water outlet pipe of the energy recovery device 11 is connected to the outlet pipes of the booster pump 9 and the second-level high-pressure pump 8 in sequence; the low-pressure water outlet pipe of the energy recovery device 11 is connected to the concentrated brine discharge pipe; the reverse osmosis membrane stack water production pipe is connected to the product water pipe; an agitator 19, an immersed membrane 2 and an aeration pipe 20 are arranged inside the membrane pool, and the aeration pipe is connected to the aeration fan 3 through a pipeline; a sludge discharge pipe is arranged at the bottom of the membrane pool 1, and the sludge discharge pipe is connected to the sludge discharge valve 12 and then connected to the sludge discharge pipe.

[0007] Preferably, the lift of the first-stage high-pressure pump 7 is 400m-500m, and the lift of the second-stage high-pressure pump 8 is 100m-200m.

[0008] Advantages of the present invention:

[0009] (1) The system of the present invention integrates coagulation, sedimentation, aeration and membrane filtration in pretreatment, has the advantages of short process flow, small footprint and strong resistance to shock load, and can ensure the water quality requirements of reverse osmosis inlet water.

[0010] (2) The high-pressure water supply regulation adopts a combination of dual high-pressure pumps (primary high-pressure pump 7 and secondary high-pressure pump 8), which has the advantages of high operating efficiency and a large regulation range, and can meet the working conditions with large changes in seawater salinity and temperature;

[0011] (3) The system of the present invention can directly connect the pre-treated water to the high-pressure pump, eliminating the need for a conventional intermediate water tank and a reverse osmosis water supply pump, thereby shortening the overall process route and reducing equipment investment and floor space. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of a short-process variable-operating-condition seawater desalination system of the present invention.

[0013] 1-membrane pool, 2-submerged membrane, 3-aeration fan, 4-membrane pool water production pump, 5-backwash pump, 6-backwash pool, 7-first-stage high-pressure pump, 8-second-stage high-pressure pump, 9-boosting pump, 10-reverse osmosis membrane stack, 11-energy recovery device, 12-sludge discharge valve, 13-membrane pool backwash valve, 14-membrane pool water production valve, 15-first-stage high-pressure pump inlet valve, 16-backwash pool water supply valve, 17-second-stage high-pressure pump bypass valve, 18-second-stage high-pressure pump inlet valve, 19-agitator, 20-aeration pipe. DETAILED DESCRIPTION

[0014] The present invention will be further described below with reference to the accompanying drawings.

[0015] A short process variable working condition seawater desalination system, see Figure 1 , including a membrane pool 1 and a backwash pool 6, the outlet pipe of the membrane pool 1 is connected to the membrane pool water production valve 14, the membrane pool water production pump 4, the first-level high-pressure pump water inlet valve 15, the first-level high-pressure pump 7, the second-level high-pressure pump water inlet valve 18, the second-level high-pressure pump 8 and the reverse osmosis membrane stack 10 water inlet pipe in sequence; the outlet pipe of the membrane pool water production pump 4 is connected to the backwash pool water replenishment valve 16 and the backwash pool 6 in sequence; the outlet pipe of the backwash pool 6 is connected to the backwash pump 5, the membrane pool backwash valve 13 and the membrane pool outlet pipe in sequence; the outlet pipe of the first-level high-pressure pump 7 is connected to the second-level high-pressure pump bypass valve 17 and the outlet pipe of the second-level high-pressure pump 8 in sequence; the concentrated water pipe of the reverse osmosis membrane stack 10 is connected to The high-pressure water inlet pipe of the energy recovery device 11 is connected; the outlet pipe of the first-level high-pressure pump inlet valve 15 is connected to the low-pressure water inlet pipe of the energy recovery device 11; the high-pressure water outlet pipe of the energy recovery device 11 is connected to the outlet pipes of the booster pump 9 and the second-level high-pressure pump 8 in sequence; the low-pressure water outlet pipe of the energy recovery device 11 is connected to the concentrated brine discharge pipe; the reverse osmosis membrane stack water production pipe is connected to the product water pipe; an agitator 19, an immersed membrane 2 and an aeration pipe 20 are arranged inside the membrane pool, and the aeration pipe is connected to the aeration fan 3 through a pipeline; a sludge discharge pipe is arranged at the bottom of the membrane pool 1, and the sludge discharge pipe is connected to the sludge discharge valve 12 and then connected to the sludge discharge pipe.

[0016] The lift of the first-stage high-pressure pump 7 is 500m (it can also be any value between 400m-500m, such as 400m or 450m), and the lift of the second-stage high-pressure pump 8 is 150m (it can also be any value between 100m-200m, such as 100m or 200m).

[0017] Example 1

[0018] The short-process variable-operating-condition seawater desalination system of the present invention is used to desalinate seawater.

[0019] Working condition 1:

[0020] (1) The raw seawater first enters the membrane pool 1, the agitator 19 is turned on, and flocculants and coagulants are added to carry out coagulation reaction;

[0021] The original seawater has a salt content of 31504 mg / L, suspended solids of 55 mg / L, and a temperature of 10-12°C;

[0022] The water flux of submerged membrane 2 is 12.5LMH, the submerged membrane material is PVDF, and the average pore size is 50nm;

[0023] The flocculant was added with 10 mg / L of polyaluminium chloride and the coagulant aid was added with 1 mg / L of polyacrylamide;

[0024] Membrane pool water SDI 15 is 2.5;

[0025] (2) Open the membrane pool water production valve 14, the backwash pool water supply valve 16, and start the membrane pool water production pump 4;

[0026] (3) After the backwash tank is filled with water, open the first-level high-pressure pump inlet valve 15 and the second-level high-pressure pump inlet valve 18, close the second-level high-pressure pump bypass valve 17, close the backwash tank water supply valve 16, start the booster pump 9, start the first-level high-pressure pump 7 and the second-level high-pressure pump 8, and the system enters the normal water production state;

[0027] Reverse osmosis membrane flux 13.0LMH, reverse osmosis membrane stack 10 recovery rate 45%, reverse osmosis membrane model SW30HRLE-440;

[0028] The lift of the first-stage high-pressure pump is 500m, the lift of the second-stage high-pressure pump is 150m, the first-stage high-pressure pump operates at industrial frequency, the second-stage high-pressure pump operates at variable frequency, the operating pressure is 63bar, the salt content of the produced water is 84mg / L, and the water production time is set to 60min (any value from 30-120min can also be selected);

[0029] Reverse osmosis membrane stack inlet flow rate 926m 3 / h, reverse osmosis membrane stack product water flow rate 417m 3 / h, reverse osmosis membrane stack brine flow rate 509m 3 / h;

[0030] (4) When the water production operation reaches the set time, turn off the secondary high-pressure pump 8, the primary high-pressure pump 7, turn off the booster pump 9, turn off the membrane pool water production pump 4, close the membrane pool water production valve 14, the primary high-pressure pump inlet valve 15, and the secondary high-pressure pump inlet valve 18, open the membrane pool backwash valve 13, turn on the membrane pool backwash pump 5 and the aeration fan 3, and the system enters the backwash state;

[0031] The backwash flux of the submerged membrane is 30LMH, and the backwash time is set to 2min (any value between 2-3min can also be selected);

[0032] (5) After the backwash operation reaches the set time, turn off the membrane pool backwash pump 5 and the aeration fan 3, close the membrane pool backwash valve 13, and operate again from step (2) in this cycle;

[0033] (6) After water is produced for 10 hours (or any value between 10 and 20 hours), the mud discharge valve 12 is opened and the system enters the mud discharge state; the mud discharge lasts for 3 minutes.

[0034] Working condition 2:

[0035] (1) The raw seawater first enters the membrane pool 1, the agitator 19 is turned on, and flocculants and coagulants are added to carry out coagulation reaction;

[0036] The original seawater has a salt content of 15640 mg / L, suspended solids of 42 mg / L, and a temperature of 10-12°C;

[0037] The water flux of submerged membrane 2 is 12.5LMH, the submerged membrane material is PVDF, and the average pore size is 50nm;

[0038] The flocculant was 8 mg / L of polyaluminium chloride and the coagulant aid was 1 mg / L of polyacrylamide;

[0039] Membrane pool water SDI 15 is 2.3;

[0040] (2) Open the membrane pool water production valve 14, the backwash pool water supply valve 16, and start the membrane pool water production pump 4;

[0041] (3) After the backwash tank 6 is filled with water, open the first-level high-pressure pump water inlet valve 15 and the second-level high-pressure pump bypass valve 17, close the second-level high-pressure pump water inlet valve 18, close the backwash tank water supply valve 16, start the booster pump 9, start the first-level high-pressure pump 7, and the system enters the normal water production state;

[0042] Reverse osmosis membrane flux 13.0LMH, reverse osmosis membrane stack 10 recovery rate 45%, reverse osmosis membrane model SW30HRLE-440,

[0043] The lift of the first-stage high-pressure pump is 500m, the lift of the second-stage high-pressure pump is 150m, the first-stage high-pressure pump operates with variable frequency, the second-stage high-pressure pump 8 does not operate, the operating pressure is 37bar, the salt content of the produced water is 41mg / L, and the water production time is set to 75min (any value between 30-120min can also be selected);

[0044] Reverse osmosis membrane stack inlet flow rate 926m 3 / h, reverse osmosis membrane stack product water flow rate 417m 3 / h, reverse osmosis membrane stack brine flow rate 509m 3 / h;

[0045] (4) When the water production operation reaches the set time, turn off the first-level high-pressure pump 7, turn off the booster pump 9, turn off the membrane pool water production pump 4, close the membrane pool water production valve 14, the first-level high-pressure pump inlet valve 15, and the second-level high-pressure pump bypass valve 17, open the membrane pool backwash valve 13, turn on the membrane pool backwash pump 5 and the aeration fan 3, and the system enters the backwash state;

[0046] The backwash flux of the submerged membrane is 30LMH, and the backwash time is set to 2min (any value between 2-3min can also be selected);

[0047] (5) After the backwash operation reaches the set time, turn off the membrane pool backwash pump 5 and the aeration fan 3, close the membrane pool backwash valve 13, and operate again from step (2) in this cycle;

[0048] (6) After the water is produced for 12 hours (or any value between 10 and 20 hours), the mud discharge valve 12 is opened and the system enters the mud discharge state; the mud discharge lasts for 3 minutes.

[0049] For a specific embodiment, the lift of the primary high-pressure pump and the secondary high-pressure pump needs to be determined according to the operating pressure range of the reverse osmosis membrane stack (obtained by the salinity and temperature of the original seawater through the calculation software of reverse osmosis membrane manufacturers such as Dow, Hyden, and Toray). For example, when the operating pressure range is 25bar-50bar, the lift of the primary high-pressure pump is selected to be 400m, which is adjusted within 250m-400m by frequency conversion, and the lift of the secondary high-pressure pump is selected to be 100m, which is adjusted within 50m-100m by frequency conversion; ... When the pressure range is 25bar-65bar, the lift of the first-stage high-pressure pump is selected to be 450m, which can be adjusted within 250m-450m through frequency conversion, and the lift of the second-stage high-pressure pump is selected to be 200m, which can be adjusted within 150m-200m through frequency conversion; when the operating pressure range is 35bar-65bar, the lift of the first-stage high-pressure pump is selected to be 500m, which can be adjusted within 350m-500m through frequency conversion, and the lift of the second-stage high-pressure pump is selected to be 150m, which can be adjusted within 100m-150m through frequency conversion.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the field within the technical scope disclosed in the present invention should be covered within the protection scope of this aspect.

Claims

1. A short-process variable-operation-condition seawater desalination system, comprising a membrane tank (1) and a backwash tank (6), characterized in that The outlet pipe of the membrane pool is connected to the membrane pool water production valve (14), the membrane pool water production pump (4), the first-level high-pressure pump water inlet valve (15), the first-level high-pressure pump 7, the second-level high-pressure pump water inlet valve (18), the second-level high-pressure pump (8) and the reverse osmosis membrane stack (10) water inlet pipe in sequence; the outlet pipe of the membrane pool water production pump is connected to the backwash tank water replenishment valve (16) and the backwash tank in sequence; the outlet pipe of the backwash tank is connected to the backwash pump (5), the membrane pool backwash valve (13) and the membrane pool outlet pipe in sequence; the outlet pipe of the first-level high-pressure pump (7) is connected to the second-level high-pressure pump bypass valve (17) and the outlet pipe of the second-level high-pressure pump in sequence; the concentrated water pipe of the reverse osmosis membrane stack is connected to The high-pressure water inlet pipe of the energy recovery device (11) is connected; the outlet pipe of the first-stage high-pressure pump inlet valve is connected to the low-pressure water inlet pipe of the energy recovery device; the high-pressure water outlet pipe of the energy recovery device is connected to the outlet pipes of the booster pump (9) and the second-stage high-pressure pump in sequence; the low-pressure water outlet pipe of the energy recovery device is connected to the concentrated brine discharge pipe; the reverse osmosis membrane stack water production pipe is connected to the product water pipe; the membrane pool is provided with an agitator (19), an immersed membrane (2) and an aeration pipe (20), and the aeration pipe is connected to the aeration fan (3) through a pipeline; a sludge discharge pipe is provided at the bottom of the membrane pool, and the sludge discharge pipe is connected to the sludge discharge valve (12) and then connected to the sludge discharge pipe.

2. A short-flow variable-operating-condition seawater desalination system according to claim 1, characterized in that The lift of the first-stage high-pressure pump 7 is 400m-500m, and the lift of the second-stage high-pressure pump 8 is 100m-200m.

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