I. Background and significance
As a water scarcity country, fresh water resource per capita in China only accounts for 1/4 of the world average; water scarcity in coastal cities and on islands is much more serious. Besides the traditional means for solving water scarcity, such as water transfer and reservoir engineering, waste water saving and recycling, seawater desalinization technology is attached more and more importance to.
Reverse osmosis is a kind of pressure-driven isolation technique. Since there is no phase transition during desalinization, it is featured by remarkable energy saving. Application of energy recovery device lowers the power consumption for seawater desalinization by reverse osmosis down to 4KWh/m3, especially applicable for desalinization process aiming at potable water on islands, in coastal cities and areas.
II. Main technological details
Corresponding pretreatment will be performed according to different seawater quality after it is taken out from the water head, aiming at making the seawater reach the guideposts such as SDI<3 prior to entering into the reverse osmosis membrane to ensure the service life of the membrane. Qualified seawater after pretreatment will be sent to the reverse osmosis membrane stack by high pressure pump. Water that passes through the reverse osmosis membrane will be collected and sent to the pipeline network system after proper pretreatment for users make use of. High pressure thick salt water that does not pass through the reverse osmosis membrane will enter into the energy recovery device to reclaim its energy and then sent back to ocean.
Reverse osmosis membrane has developed into a very mature product abroad. So, the essence of the seawater desalinization system by reverse osmosis is to design reasonably the pretreatment system, select proper high pressure pump and energy recovery device, design perfect control system for monitoring and control and adopt scientific materials and corrosion prevention measures to avoid corrosion of pipelines and system. Meanwhile, for the water fetched by open method, besides the contamination index of the system, scientific sterilization and alga removal measures must be taken to prevent invasion of microorganisms to the system.
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Technical features of seawater desalinization by reverse osmosis membrane：
1. low investment: investment cost is only 1/2 of that for other techniques
2. little land occupation: about 1/2 of that for other techniques
3. low energy consumption: 20% lower than that for other techniques
4. strong adaptability to seawater and strong equipment flexibility |
Economic indexes of seawater desalinization technique by reverse osmosis：
1. ratio of desalinization 99.5 ％
2. coefficient of water recovery 35 ％－ 40 ％
3. power consumption per ton water: 3KWH
4. operating cost per ton water: RMB 3 |
