Water intake system, pretreatment filtration system, seawater desalination and desalination system, energy recovery system, chemical cleaning system, chemical dosing system, power supply and distribution and automatic control system of the unit.
The basic process flow of seawater desalination is as follows: Seawater enters quartz sand (multi-media filter) and activated carbon filtration system for filtration by water supply pump. The filtered water enters the precision and security filtr Under the treatment of the membrane stack, part of the high-pressure seawater passes through the membrane to form fresh water. After the water quality is adjusted, it enters the fresh water tank for storage. The remaining high-pressure concentrated shrinkage enters the pressure exchange energy recovery device to recover energy and then discharge.ation system after water quality reduction, pH adjustment and scale inhibitor addition. The filtered low-pressure seawater enters the high-pressure pump for pressurization and the pressure exchange energy recovery device. The pressurized seawater is pressurized by the booster pump and mixed with the effluent of the high-pressure pump into the reverse osmosis membrane reactor system.
Whether it is seawater desalination or brackish water desalination, feedwater pretreatment is the key to ensure the long-term stable operation of reverse osmosis system. When formulating Seawater Pretreatment scheme, it should be fully considered that there are a large number of microorganisms, bacteria and algae in seawater. The reproduction of bacteria and algae and the growth of microorganisms in seawater will not only bring a lot of trouble to the water intake facilities, but also directly affect the normal operation of seawater desalination equipment and process pipelines. Periodic rising and falling tide, a large amount of sediment is entrained in seawater, and the turbidity changes greatly, which is easy to cause unstable operation of Seawater Pretreatment System. Seawater is highly corrosive. The materials of equipment, valves and pipes used in the system shall be selected to have good corrosion resistance.
Sterilization and algae killing
Foreign seawater desalination projects mostly use chemical reagents such as input to kill bacteria and algae. Considering traffic and other factors, it is difficult to add chemical reagent to kill bacteria and algae. Seawater sodium hypochlorite generator is specially used in the equipment development process of the project. After the seawater intake pump, a small stream of pressurized seawater is separated into the sodium hypochlorite generator, which is generated under the action of DC electric field and directly injected into the beach open caisson by potential difference to kill bacteria, algae and microorganisms in the seawater.
Due to the high hardness of seawater, the problem of electrode scaling must be overcome. In the development process, the electrodialysis frequent pole reversal (EDR) technology is used for reference, that is, the electrode polarity is changed every 5 ~ 10min, which effectively solves the problem of scaling and sedimentation of sodium hypochlorite generator.
Coagulation filtration aims to remove colloid and suspended impurities in seawater and reduce turbidity. In the reverse osmosis membrane separation project, the pollution index (FI) is commonly used to measure, and the fi value of feed water entering the reverse osmosis equipment is required to be less than 4. Due to the large specific gravity of seawater, high pH value and large seasonal variation of water temperature, the system selects it as the coagulant, which has the advantages of not affected by temperature, large and solid alum, fast sedimentation speed and so on.
Reverse osmosis desalination
Seawater has high salt content, high hardness, great corrosion to equipment, and large seasonal variation of water temperature, which makes the reverse osmosis seawater desalination system much more complex than the conventional brackish water desalination system, and the project investment and energy consumption are 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.
Removal of organic matter
The seawater around the island is greatly affected by the surrounding environment. The chemical oxygen demand (COD) of seawater is 1.7 ~ 2.5m g / L. especially in summer and autumn, sometimes the seawater has great odor. Therefore, in addition to adding for oxidation, the addition of activated carbon filter and the selection of fruit granular activated carbon with high mechanical strength can effectively adsorb organic matter and odor, improve the quality of reverse osmosis produced water, reduce the pollution to the reverse osmosis membrane surface and prolong the service life of the membrane.
The security filter adopts 316L filter and 5-micron filter element to filter the seawater in front of the high-pressure pump, block the particle impurities with diameter greater than 5-micron in the seawater, and ensure the safe and long-term operation of the high-pressure pump, energy recovery device and reverse osmosis membrane element.
High pressure pump and energy recovery
High pressure pump and energy recovery device are important equipment to provide energy conversion and energy saving for reverse osmosis seawater desalination. They are selected according to the flow and pressure required for reverse osmosis seawater desalination.
Reverse osmosis membrane elements and devices
Reverse osmosis membrane element is the core component of reverse osmosis seawater desalination. The reverse osmosis device adopts a one-stage and one-stage combined structure with 6 membrane elements in series and 6 pressure main pipes in parallel, and is equipped with low-pressure automatic flushing and drainage and low-pressure automatic flushing and replacement of desalinated water, and automatic switching and drainage device for unqualified produced water. The system is also equipped with high and low pressure protection, high-pressure pump and interlocking of cleaning pump.