Two-stage reverse osmosis + EDI ultrapure water preparation process flow diagram Two-stage reverse osmosis--technology introduction
Reverse osmosis technology is the most advanced and energy-efficient membrane separation technology today. The principle is that under the effect of the osmotic pressure of the solution, other substances can leave these substances and moisture according to the impermeability of the semi-permeable membrane. Because the membrane pore size of the reverse osmosis membrane is very small (only about 10A), it can effectively remove dissolved salts, colloids, microorganisms, organic matter, etc. in the water (removal rate up to 97% -98%). Reverse osmosis is currently the most widely used type of desalination technology in high-purity water equipment. Its separation objects are organic substances with a range of ions in the solution and a molecular weight of several hundred; reverse osmosis (RO), ultrafiltration (UF), microporous membrane filtration ( MF) and electrodialysis (EDI) technologies are membrane separation technologies.
In the past 30 years, reverse osmosis, electrodialysis, ultrafiltration and membrane filtration have entered industrial applications, mainly used in electronics, chemical, food, pharmaceutical and drinking pure water fields.
How reverse osmosis works
Osmotic and osmotic pressure
Penetration is common in nature. For example, when a cucumber is placed in salt water, the cucumber will become smaller due to dehydration. The process of the water molecules in cucumber entering the saline solution is the infiltration process. If a pool is divided into two parts by a membrane that only water molecules can penetrate, pure water and saline are injected on the two sides of the diaphragm to the same height. After a while, you can see that the level of pure water has decreased, while the level of saline has increased. We call the phenomenon that water molecules migrate through this membrane into salt water. The elevation of the salt water level is not endless, and a certain point will reach an equilibrium point. At this time, the pressure represented by the liquid level difference between the two ends of the diaphragm is called osmotic pressure. The osmotic pressure is directly related to the concentration of saline.
2. Reverse osmosis phenomenon and reverse osmosis water purification technology
After the above device reaches equilibrium, if a certain pressure is applied to the liquid surface of the brine end, at this time, the water molecules will migrate from the brine end to the pure water end. The phenomenon that liquid molecules migrate from a dilute solution to a concentrated solution under pressure is called the reverse osmosis phenomenon. If brine is added to one end of the above facility and a pressure exceeding the osmotic pressure of the brine is applied at that end, we can obtain pure water at the other end. This is the principle of reverse osmosis water purification.
There are two keys to producing pure water in reverse osmosis facilities. One is a selective membrane, which we call a semi-permeable membrane, and the other is a certain pressure. Simply put, there are numerous pores on the reverse osmosis semi-permeable membrane. The size of these pores is comparable to that of water molecules. Because bacteria, viruses, most organic pollutants and hydrated ions are much larger than water molecules, they are impermeable It is separated from the water phase passing through the reverse osmosis semi-permeable membrane. Among the many impurities in water, soluble salts are the most difficult to remove. Therefore, the water purification effect of reverse osmosis is often determined according to the level of salt removal. The reverse osmosis salt removal rate is mainly determined by the selectivity of the reverse osmosis semi-permeable membrane. At present, the salt rejection rate of higher selectivity reverse osmosis membrane elements can be as high as 99.7%.
EDI ultrapure water introduction
EDI is a pure water manufacturing equipment that combines ion exchange technology, ion exchange membrane technology and ion electrotransfer technology. During the EDI desalination process, ions are dissociated into hydrogen ions and hydroxide ions under the action of an electric field. These ions continuously regenerate the ion exchange resin to keep the ion exchange resin in an optimal state.
EDI is effective in removing weak electrolytes such as carbon dioxide and colloidal silicon.
◆ Continuous operation, product water quality is stable
◆ No need to regenerate with acid and alkali
◆ Saved recoil and cleaning water
◆ Produce ultrapure water with high yield (yield can be as high as 95%)
◆ No reclaimed sewage, no need for sewage treatment facilities
◆ No need for acid-base storage and acid-base dilution transportation facilities
◆ Small size and small footprint
◆ It is safe and reliable to avoid artificial contact with acid and alkali
◆ Reduce maintenance cost of running machine
◆ Simple installation and low installation cost