1, seawater kills seedlings and algae; Chemical reagents such as CL, NaCI0 and CuS04 are often used to kill bacteria and algae in seawater desalination projects abroad. Considering the traffic and other factors, it is difficult to kill bacteria and algae by adding chemical reagents. In the process of equipment development in this project, the sodium hypogase generator is specially used. After the seawater is pumped, a small stream of seawater under pressure is separated, which enters the sodium hypochlorite generator, generates NaC10 under the action of direct current electric field, and is directly injected into the beach open caisson by the potential difference to kill bacteria, bacteria and microorganisms in seawater.

2. Coagulation and filtration; Coagulation filtration aims to remove colloid and suspended impurities in seawater and reduce turbidity. Pollution index (F1) is usually used to measure in membrane separation engineering of anti-seawater permeability, and the FI value of feed water entering anti-seawater permeability equipment is required to be less than 4. Due to the large specific gravity of seawater, high pH value and seasonal variation of water temperature, FeC13 is selected as coagulant in the system, which has the advantages of being unaffected by temperature, large alum flower and fast settling speed.

The surface contact coagulation filtration technology is adopted, which consists of double-layer pumping and activated carbon pumping. Two double-layer mechanical filters and two activated carbon filters are set up respectively, and the pumping speed is between 7 and 8 m/s. The filter is lined with steel, coated with marine paint, and equipped with ABS water cap for water distribution and 316L stainless steel pipe for gas distribution. In order to reduce the seawater pretreatment system and instantaneous load and improve the water recovery rate, a gas-liquid backwashing system with reverse osmosis concentrated water as backwashing water for the overflow device is set up.

3. Reverse osmosis seawater desalination; Seawater has high salt content, high hardness, great corrosiveness to equipment, and large seasonal variation of water temperature, which makes the reverse paint seawater desalination system much more complicated than the conventional brackish water desalination system, and the engineering investment and energy consumption are also much higher. Therefore, it is particularly important to reduce the project investment and energy consumption through careful process design and reasonable equipment configuration, so as to reduce the unit water production cost and ensure the stable operation of the system. 4, chemical conditioning treatment; In order to prevent insoluble inorganic salts, such as CaC03 and CaS04, from scaling and depositing on the surface of reverse osmosis membrane and system piping during seawater desalination, an anti-scaling agent should be added before seawater enters the anti-seawater desalination system.

Adding H2S04 to adjust the pH value of seawater and decompose HC0-3 in seawater to prevent CaC03 precipitation is a common and economical method in seawater desalination. Adding (NaPO3)6(SHMP) is an effective method to prevent the precipitation of CaS04. However, the by-product phosphate produced by (NaPO3)6 can promote the growth of microorganisms, bacteria and algae, and its use has certain limitations. However, the price of special polymer scale remover imported from western countries is high, which will directly affect the operation cost of seawater desalination project. In this project, H2S04 is selected as the cationic scale agent, and the pH value of the feed water of the anti-seawater penetration system is controlled between 6.8 and 7.0, while the water recovery rate of the seawater desalination system is controlled to prevent the precipitation of CaS04.

Considering that the composite membrane element with aromatic polyamide as membrane material is used in the reverse osmosis seawater desalination system, its oxidation resistance is poor, and it is required that the residual gas content in the influent is less than 0.1m q, so NaHS03 is added to the seawater before entering the membrane system, and the oxidation-reduction potential (ORP) of seawater before entering the reverse osmosis device is controlled, so that the oxidation-reduction potential (ORP) of seawater before entering the reverse osmosis device is 280 ~ 320 mV. Nahs.

5. Remove organic matter and peculiar smell in seawater; The seawater around the island is greatly influenced by the surrounding environment. The chemical oxygen consumption (COD) of seawater is 1.7~2.5m g, especially in summer and autumn. Therefore, in addition to adding NaCIO for oxidation, adding activated carbon filter and selecting fruit granular activated carbon with high mechanical strength can effectively adsorb organic matter and odor, improve the quality of water produced by anti-seawater permeation, and at the same time reduce the pollution on the surface of anti-seawater permeation membrane and prolong the service life of membrane.

6. Security filtering; Security filter adopts 316L filter and 5um filter element to filter the seawater before the high-pressure pump, so as to block the particulate impurities with the diameter greater than 5um in seawater, and ensure the safe and long-term operation of the high-pressure pump, energy recovery device and anti-seawater permeable membrane element.

7. High-pressure pump and energy recovery device; High-pressure pump and energy recovery device are important equipment to provide energy conversion and energy saving for reverse osmosis seawater desalination. According to the flow rate and pressure required for reverse osmosis seawater desalination, we choose a single-stage centrifugal pump specially developed for seawater desalination project, with a flow rate of 60m3/ and a lift of 640Psir. The energy recovery device is HTC-300 with a hydraulic turbine structure, which can increase the inlet pressure of reverse osmosis seawater by 30% by using the pressure of concentrated seawater discharged from the reverse osmosis seawater, effectively reducing energy consumption.

8. Anti-sea permeable seawater desalination membrane elements and devices; Anti-seawater permeable membrane elements used in seawater desalination equipment are the core components of anti-seawater permeable seawater desalination. The anti-seawater permeable device adopts a one-stage and one-stage combined structure with six membrane elements connected in series and six pressure main pipes connected in parallel, and is equipped with low-pressure automatic flushing and discharge and low-pressure automatic flushing and replacement of desalinated water, and automatic switching and discharge devices for unqualified water production. In this system, high and low voltage protection and high pressure pump are also set to clean the interlock of the pump.