Demineralization of water is the removal of essentially all inorganic salts by ion exchange. In this process, strong acid cation resin in the hydrogen form converts dissolved salts into their corresponding acids, and strong base anion resin in the hydroxide form removes these acids. Demineralization produces water similar in quality to distillation at a lower cost for most fresh waters .
Principles of Demineralization
A demineralizer system consists of one or more ion exchange resin columns, which include a strong acid cation unit and a strong base anion unit. The cation resin exchanges hydrogen for the raw water cations as shown by the following reactions :
A measure of the total concentration of the strong acids in the cation effluent is the free mineral acidity (FMA).
As a cation exchange unit nears exhaustion, FMA in the effluent drops sharply, indicating that the exchanger should be Regenerated. Resin is regenerated with an acid solution, which returns the exchange sites to the hydrogen form.
To complete the demineralization process, water from the cation unit is passed through a strong base anion exchange resin in the hydroxide form. The resin exchanges hydrogen ions for both highly ionized mineral ions and the more weakly ionized carbonic and silicic acids, as shown below :
The above reactions indicate that demineralization completely removes the cations and anions from the water. In reality, because ion exchange reactions are equilibrium reactions, some leakage occurs. Most leakage from cation units is sodium. This sodium leakage is converted to sodium hydroxide in the anion units. There-fore, the effluent pH of a two bed cation-anion demineralizer system is slightly alkaline. The caustic produced in the anions causes a small amount of silica leakage.
To produce High Purity Water OR as the application calls for, outlet from Anion Exchange column is passed through Mixed Bed Demineraliser
A mixed bed exchanger has both cation and anion resin mixed together in a single vessel. As water flows through the resin bed, the ion exchange process is repeated many times, “polishing” the water to a very high purity. During regeneration, the resin is separated into distinct cation and anion fractions as shown in Figure 8-12. The resin is separated by backwashing, with the lighter anion resin settling on top of the cation resin. Regenerant acid is introduced through the bottom distributor, and caustic is introduced through distributors above the resin bed. The regenerant streams meet at the boundary between the cation and anion resin and discharge through a collector located at the resin interface. Following regenerant introduction and displacement rinse, air and water are used to mix the resins. Then the resins are rinsed, and the unit is ready for service
DEION Offers Various capacities of Demineralisers starting from 0.1 m3/Hr. capacity up to 100 m3/Hr. Capacity and with Pressure Vessel Material of construction in FRP / MSRL.