Optimal Design and Upkeep of Ultra-Pure Water Polishing Mixed Bed System

After the reverse osmosis and EDI water purification system, the polishing mixed bed is used to generate theoretically pure water with a conductivity of 0.055 uS/cm (resistivity of 18.2 Mcm) for electronic, pharmaceutical, and other sectors. The mixed bed resin used for polishing is a combination of anion and cation resins with similar specific gravity. The polishing resin loses its effectiveness and must be removed after usage because it is not possible to separate the anion and cation resins and regenerate them individually using acid and alkali.

Figure 1 Water Polishing Mixed Bed System

Typically, a flow rate of 40-60 m/h is used when designing a polishing mixed bed. Pipes in a pristine water distribution system are often fabricated from PVDF. To get the cleanest and safest water possible, the polishing mixing bed should be set up as close to the tap as possible. Whether put at the site or the factory end, the polishing mixed bed requires little in the way of upkeep and has no effect on management.

Points to Note

  1. The polishing mixed bed system has high standards and requirements for the quality of incoming water. When the EDI product water tank is not sealed, the purity of the water will be significantly reduced when it comes into contact with air. If this water enters the polishing mixed bed system, it will cause damage to the resin’s lifespan. Without an inert gas-sealed condition, the resin’s lifespan is only around 4 months, but with an ammonia-sealed condition, the resin’s lifespan can be extended to 8-12 months.
  2. The polishing resin is a mixture of hydrogen-type strong acid cation exchange resin and hydroxide-type strong base anion exchange resin.
  3. If water needs to be added for ease of filling during operation, pure water must be used, and the amount of water should not be excessive. At the same time, the water must be immediately pumped out or drained after the resin is loaded into the resin tank to avoid resin stratification. If filling the resin by hand, wash your hands thoroughly and do not bring any grease into the resin tank.Figure 2 Cation Anion
  4.  If resin replacement is necessary, the tank and collector must be thoroughly cleaned, and no residue of old resin should be left at the bottom of the tank, as it may contaminate the water quality.
  5. The distributing device used must be regularly inspected and replaced. At the same time, relevant components must be checked for damage during each replacement, and if any damage is found, it must be replaced immediately. The collector should be checked for blockage and cleared if necessary.
  6. When using an FRP tank as the resin bed, the collector pipe should be placed in the tank before filling the resin. During the resin sealing process, the collector pipe should be shaken irregularly so that the position of the collector pipe can be adjusted and the cover can be installed at the end.
  7. If the water filter resin is filled first, it may be difficult to insert the collector pipe. If it is necessary to fill the resin first before inserting the collector pipe, the filled FRP tank can be laid flat on the ground and rolled slowly to loosen the resin, and then the collector pipe can be slowly inserted into the resin.Figure 3 Resin Filling
  8. After the resin filling is completed and the pipeline is connected, the air vent hole at the top of the tank should be opened first, and water should be slowly introduced until the air vent hole overflows with water and no bubbles are generated, then the air vent hole should be tightly closed, and water collection can begin.
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