Seawater desalination pretreatment: Seawater pretreatment: Whether it is seawater desalination or brackish water desalination, water pretreatment is the key to ensure the long-term stable operation of the reverse osmosis system. When formulating a seawater pretreatment plan, full consideration should be given to the presence of a large number of microorganisms, bacteria and algae in seawater.
1. The reproduction of bacteria, algae and the growth of microorganisms in seawater will not only cause a lot of trouble to the water intake facilities, but will also directly affect the normal operation of seawater desalination equipment and process pipelines. Periodic high tides and low tides, a large amount of silt is entrained in the seawater, and the turbidity changes greatly, which can easily cause the seawater pretreatment system to operate unstably. Seawater is highly corrosive, and the materials of the equipment, valves, and pipe fittings used in the system must be screened to a certain extent, and the corrosion resistance must be good.
2. Coagulation and filtration: Coagulation and filtration aims to remove colloids and suspended impurities in seawater and reduce turbidity. In reverse osmosis membrane separation projects, the pollution index (F1) is usually used for measurement. The F1 value of the feed water entering the reverse osmosis equipment is required to be (4. Due to the large specific gravity of seawater, high pH value, and large seasonal changes in water temperature, the system uses FeC3 as a coagulant, which has the advantages of being unaffected by temperature, large and solid alum flowers, and fast sedimentation speed.
3. Seawater desalination: Seawater has high salt content and hardness, which is highly corrosive to equipment. In addition, the large seasonal changes in water temperature make the reverse osmosis seawater desalination system much more complicated than the conventional brackish water desalination system, and the project investment and energy consumption are also much higher. Therefore, it is particularly important to reduce project investment and energy consumption through careful process design and reasonable equipment configuration, thereby reducing unit water production costs and ensuring stable operation of the system.
4. Seawater sterilization and algae removal: Foreign seawater desalination projects mostly use chemical reagents such as liquid ammonia, NaCIO and CusO4 to sterilize and kill algae. Considering factors such as transportation, it is difficult to add chemical reagents for sterilization and algae removal. In the process of equipment development in this project, The door uses a seawater sodium hypochlorite generator. A small stream of pressurized seawater is separated from the seawater pump and enters the sodium hypochlorite generator. Under the action of the DC electric field, NaClO is produced and directly injected into the beach caisson by potential difference to kill bacteria, algae and microorganisms in the seawater. Due to the high hardness of seawater, direct electrolysis of seawater to produce NaCO must overcome the problem of electrode scaling. During the development process, the frequent reversal of electrodialysis (EDR) technology was used for reference, that is, the electrode polarity is reversed every 5-10 minutes, which effectively solved the scaling and precipitation problem of the sodium hypochlorite generator.
