High output automatic flush 3000L reverse osmosis seawater desalination / Well Water Desalination membrane filter

Process flow

Pretreatment

Whether it is desalination or desalinization of brackish water, feedwater pretreatment is the key to ensuring long-term stable operation of the reverse osmosis system. Adequate consideration should be given to the development of seawater pretreatment programmes: the presence of large amounts of microorganisms, bacteria and algae in seawater. The growth of bacteria, algae and microbial growth in seawater not only causes many troubles for water intake facilities, but also directly affects the normal operation of desalination equipment and process pipelines. Periodically rising tides, low tides, and a large amount of sediment in the seawater, the turbidity changes greatly, and the seawater pretreatment system is unstable. The seawater is highly corrosive. The materials of the equipment, valves and pipelines used in the system must be screened and the corrosion resistance should be good.

Bactericidal algae

In foreign seawater desalination projects, chemical reagents such as liquid chlorine, NaClO and CuSO4 are added to sterilize algae. Considering the various factors such as transportation, it is difficult to add chemical reagents to kill algae. In the process of developing the equipment, seawater sodium hypochlorite generator is specially used. After the seawater pump is taken, a small amount of pressurized seawater is separated and enters the sodium hypochlorite generator to generate NaClO under the action of a DC electric field. The difference is directly injected into the beach sinkhole to kill bacteria, algae and microorganisms in the seawater.
Due to the high hardness of seawater, the direct electrolysis of seawater to produce N aC lO must overcome the problem of electrode fouling. In the development process, the electrodialysis frequent reverse polarity (EDR) technology was used, that is, the polarity of the electrode was reversed every 5~10m in, which effectively solved the problem of scale precipitation of sodium hypochlorite generator.

Coagulation filtration

Coagulation filtration is designed to remove colloids from seawater, suspend impurities, and reduce turbidity. In the reverse osmosis membrane separation process, the pollution index (FI) is usually used to measure the FI value of the feed water entering the reverse osmosis equipment <4. Due to the large specific gravity of seawater, high pH value and large seasonal variation of water temperature, FeCl3 is used as a coagulant in the system. It has the advantages of being unaffected by temperature, large and firm, and fast sedimentation speed.

Chemical regulation

In order to prevent the insoluble inorganic salts, such as CaCO3 and CaSO4, from being concentrated due to the concentration of seawater during seawater desalination, the scale is precipitated on the surface of the reverse osmosis membrane and the piping parts of the system, and the seawater is added with a scale inhibitor before entering the reverse osmosis desalination system.
Adding H2SO4 to adjust the pH value of seawater to decompose HCO-3 in seawater to prevent CaCO3 precipitation is the most common and economical method for seawater desalination. Addition of (NaPO3)6 (SHMP) is an effective method to prevent the precipitation of CaSO4, but the by-product phosphate produced by (NaPO3)6 at the same time as scale inhibition promotes the growth of microorganisms, bacteria and algae, and has certain limitations. The high price of special high molecular polymer scale inhibitor imported from western countries will directly affect the operating cost of seawater desalination project. The project finally uses H2SO4 as a scale inhibitor to control the pH of the feedwater of the reverse osmosis system between 6.8 and 7.0, and at the same time control the water recovery rate of the desalination system to prevent the precipitation of CaSO4.
Considering that the composite membrane element with aromatic polyamide as the membrane material in the reverse osmosis desalination system has poor oxidation resistance, the residual chlorine content in the influent is less than 0.1 mg/L, so the seawater is injected before entering the membrane system. Add NaHSO3 to control the oxidation-reduction potential (ORP) of seawater before entering the reverse osmosis unit, so that the seawater oxidation-reduction potential (ORP) before the reverse osmosis unit is 280-320 mV. The dosage of NaHSO3 is three times that of the residual chlorine in seawater. .

Except odor

The seawater around the island is greatly affected by the surrounding environment. The chemical oxygen demand (COD) of seawater is 1.7-2.5 m g/L, especially in summer and autumn, sometimes the seawater has a large smell and odor. Therefore, in addition to the addition of NaClO for oxidation, an activated carbon filter is added, and the fruit-type granular activated carbon with high mechanical strength can effectively adsorb organic matter and odor and odor, improve the quality of reverse osmosis water production, and at the same time reduce the pollution of reverse osmosis membrane surface. , extend the membrane life.
Security filtering
The security filter uses 316L filter, 5&micro;m filter, filters the seawater before the high pressure pump, blocks the seawater with a diameter larger than 5&micro;m particles, ensures high pressure pump, energy recovery device and reverse osmosis membrane components for safe and long-term operation.
High pressure pump and energy recovery device
The high-pressure pump and energy recovery device are important equipments for energy conversion and energy saving for reverse osmosis seawater desalination. According to the flow and pressure selection required for reverse osmosis desalination, we use a single-stage centrifugal pump with a flow rate of 60m3/h. 640Psi; energy recovery device is HTC-300 type, with hydraulic turbine structure, can use reverse osmosis to discharge concentrated seawater pressure to increase reverse osmosis water pressure by 30%, effectively reducing energy consumption.

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