Desalination

Desalination refers to the process of producing fresh water by removing salt from seawater. The reverse osmosis method is often also called ultrafiltration, as it employs a semi-permeable membrane that allows only the solvent to pass through while blocking solutes, thereby separating seawater from fresh water. Under normal conditions, fresh water diffuses through the semi-permeable membrane into the seawater side, causing the liquid level on the seawater side to rise gradually until it reaches a certain height and then stabilizes; this process is known as osmosis.

If an external pressure greater than the osmotic pressure of seawater is applied to the seawater side, pure water from the seawater will undergo reverse osmosis into the freshwater side in the equipment system.

　　 Seawater desalination is essential because seawater’s extremely high salinity renders it unsuitable for direct use. Two primary methods are employed: distillation and reverse osmosis. Distillation is mainly used for very large-scale desalination projects in regions with abundant thermal energy, while reverse osmosis is widely applied due to its broad applicability and exceptionally high desalination efficiency. In the reverse-osmosis process, seawater is first extracted and subjected to preliminary treatment to reduce turbidity and inhibit the growth of microorganisms such as bacteria and algae. It is then pressurized by a specialized high-pressure pump to force it through a reverse-osmosis membrane. Given the high salinity of seawater, the reverse-osmosis membrane must exhibit high desalination performance, corrosion resistance, high-pressure tolerance, and fouling resistance. After passing through the membrane, the salinity of the seawater is significantly reduced, with total dissolved solids (TDS) dropping from approximately 36,000 mg/L to around 200 mg/L. The quality of the desalinated water can even surpass that of municipal tap water, making it suitable for industrial, commercial, residential, and maritime applications, including ships and naval vessels.

　　The entire reverse osmosis seawater desalination control system is designed with advanced computer-based process control technologies, both domestic and international. It comprises an industrial PC operator station and a programmable logic controller (PLC), forming a distributed data acquisition and control system with centralized monitoring and operation. High- and low-pressure protection switches are configured according to process parameters, along with automatic transfer devices; when abnormal readings are detected for conductivity, flow rate, or pressure, the system automatically switches modes, activates interlock alarms, and shuts down to protect the high-pressure pump and the reverse-osmosis membrane elements. Variable-frequency drives are used to control the start-up and shutdown of the high-pressure pump, enabling soft-start and soft-stop operations that reduce energy consumption and prevent damage to the pump and membrane elements caused by water hammer or backpressure. The control program is programmed to perform automatic low-pressure flushing before and after startup and shutdown of the reverse-osmosis unit; particularly during shutdown, the metastable state of concentrated brine can lead to precipitation and fouling on the membrane surface. Low-pressure fresh-water flushing effectively displaces the concentrated brine, protecting the membrane from contamination and extending its service life. The system also provides display, storage, statistical analysis, tabulation, and printing functions for key parameters such as temperature, flow rate, water quality, and production output. The dynamic process-flow display during monitoring is clear and intuitive, simplifying manual intervention in system control and ensuring automated, safe, and reliable operation.

Industrial Park Wastewater Treatment

Water Quality Improvement

Industrial Park Wastewater Treatment

Water Quality Improvement

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