[ Hongjie Water ] The process of seawater desalination by reverse osmosis

Desalination refers to the technology and process of obtaining fresh water from seawater. There are many types of desalination technologies, including distillation, membrane (reverse osmosis, electrodialysis membrane evaporation, etc.), ion exchange, etc., but only distillation and reverse osmosis are suitable for large-scale desalination.

The following is a detailed introduction to the process of seawater desalination using reverse osmosis.

1. Sterilization and algae removal in seawater

Since 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 water intake facilities, but also directly affect the normal operation of seawater desalination equipment and process pipelines. Therefore, seawater desalination projects often use chemical agents such as liquid chlorine, sodium hypochlorite and copper sulfate to sterilize and kill algae.

2. Coagulation and filtration

In order to further improve the water quality of reverse osmosis inlet water and reduce the turbidity of the inlet water, a multi-media filter is usually added after coagulation and filtration to further remove tiny suspended matter and particulate matter in the water, ensuring further improvement of water quality.

3. Antiscalants and reducing agents

The composition of seawater is very complex, with very high hardness and alkalinity. In order to make the reverse osmosis system run better and keep the system running without scaling, it is necessary to add corresponding scale inhibitors according to the specific water quality. In addition, because oxidants are added for sterilization in the reverse osmosis pretreatment, reductants need to be added to reduce the reverse osmosis water inlet, so that the residual chlorine in the reverse osmosis system is less than 0.1ppm (or ORP<200mV), meeting the reverse osmosis system's requirements for the content of oxidizing substances in the inlet water.

4. Security Filter

Because the salt content of seawater is very high, the security filter is required to be made of 316L material, and the filter element pore size is usually 5μm. It filters the seawater before entering the high-pressure pump and blocks particle impurities with a diameter greater than 5μm in the seawater, ensuring the safe, long-term and stable operation of the high-pressure pump, energy recovery device and reverse osmosis membrane element.

5. High-pressure pump and energy recovery device

High-pressure pumps and energy recovery devices are important equipment for providing energy conversion and energy saving for reverse osmosis desalination equipment. They are selected according to the flow and pressure required by the reverse osmosis desalination equipment. The energy recovery device has a hydraulic turbine structure, which can use the pressure of concentrated seawater discharged from reverse osmosis to increase the reverse osmosis water inlet pressure by 30%, so that the energy of concentrated water is effectively utilized, while reducing energy consumption, thereby effectively reducing operating costs.

6. Reverse osmosis elements and devices

Reverse osmosis membrane elements are the core components of reverse osmosis desalination equipment. Desalination membranes corresponding to the desalination equipment system should be selected. Different membrane elements can be selected according to different system designs. Reverse osmosis membrane elements have high desalination rate, good pressure resistance, oxidation resistance and pollution resistance. The material of the seawater desalination reverse osmosis equipment system should be 316L or higher stainless steel in the high-pressure part to prevent the high-salt content of seawater from corroding the high-pressure pipeline.

7. System control

The control system of the reverse osmosis desalination equipment usually adopts a programmable controller PLC to form a control system with decentralized sampling control and centralized monitoring operation. According to the process parameters, high and low pressure protection switches and automatic switching devices are set. When the conductivity, flow and pressure are abnormal, automatic switching, automatic interlocking alarm and shutdown can be realized to protect the high-pressure pump and reverse osmosis membrane elements. The start and shutdown of the high-pressure pump are controlled by frequency conversion to realize the soft operation of the high-pressure pump, save energy consumption, and prevent the damage of the high-pressure pump and membrane elements due to water hammer or back pressure. The program design can realize low-pressure automatic flushing before and after the start and shutdown of the reverse osmosis device. Especially when it is shut down, the metastable state of concentrated seawater will be transformed into precipitation and pollute the membrane surface. The automatic flushing of low-pressure desalinated water can replace the concentrated seawater, protect the membrane surface from pollution, and extend the service life of the membrane. The system temperature, flow, water quality, water production and other related parameters can be displayed, stored, counted, tabulated and printed. The dynamic process flow screen in the monitoring operation is clear and intuitive, and the system control simplifies manual operation to ensure that the system can operate automatically, safely and reliably.

The above is the common sense introduction about water treatment equipment. I hope it can be helpful to you. If you want to know more about water treatment, please pay attention to our website wwww.siboyougou.com to learn more about water treatment knowledge. Thank you for your reading and I wish you a happy life!