Water Treatment and Purification
There are a lot of pollutants in water that needs to be dealt with. All sources of water can be treated for suspended solids, colloidal particles, odour, etc through steps designed for specific purposes.
Softeners
Application
These ion-exchangers are used to produce soft water by removing all hardness.
Operation
These ion-exchangers contain strong action cation resin in Sodium form. When the water to be treated flows past the cation resin, the resin gives up the sodium ions for the positively charged ions (cations) such as that of calcium and magnesium resulting in soft water coming out of the exchanger. As the sodium ions are replaced with other cations on resin exchange sites, the number of possible exchange sites reduces and the resin gets exhausted. The Softener is taken out of service and "REGENERATION" is carried out with Sodium Chloride (Common Salt).
Weak Acid Cation Exchanger (WAC)
Application
These ion-exchangers are used to produce de-cationized water by removing cations associated with alkalinity.
Operation
These ion-exchangers contain weak acid cation resin. As the water to be treated flows past the weak acid cation resin, the resin gives up the hydrogen ions for positively charged ions (cations) associated with alkalinity. As the hydrogen ions are replaced with other cations on resin exchange sites, there are less and possible exchange sites for exchange and the resin is exhausted. The Weak Acid Cation Exchanger is then taken out of service and ’REGENERATION’ is then carried with Hydrochloric or Sulphuric acid.
Strong Acid Cation Exchanger (SAC)
Application
These ion-exchangers are used to produce de-cationized water by removing all cations.
Operation
These ion-exchangers contain strong acid cation resin. When the water to be treated flows past the cation resin, the resin gives up the hydrogen ions for positively charged ions (cations) of calcium, magnesium, sodium etc resulting in decationized water coming out of the exchanger. As the hydrogen ions are replaced with other cations on resin exchange sites, there are less and possible exchange sites for exchange and the resin gets exhausted. The Strong Acid Cation Exchanger is then taken out of service and ’REGENERATION’ is then carried with Hydrochloric or Sulphuric acid.
Degasser Tower
Application
These units are used to produce Degasified water, that is, water from which Dissolved Carbon Dioxide has been removed.
Operation
These units contain special media - called Raschig rings. Media loading depth specific to each size if Degasser Tower is to be referred so as to ensure that the Tower contain the correct depth and type of media on loading. This equipment is normally used for stripping dissolved gases in water. It has a counter current flow of water with air. In DM plants it is most commonly used after the Strong Acid Cation Exchanger to strip Carbon Dioxide (Carbonic Acid) which results in the removal of the bicarbonates and the carbonates in water.
Weak Base Anion Exchanger (WBA)
Application
These ion-exchangers are used to produce demineralised water by removing strong acid anions.
Operation
These ion-exchangers contain weak base anion resin. As the water to be treated flows past the anion resin, the resin gives up the hydroxide ions for negatively charged ions (anions) of chlorides, sulphates, nitrates. As the hydroxide ions are replaced with other anions on resin exchange sites, there are less and possible exchange sites for exchange and the resin gets exhausted. The Weak Base Anion Exchanger is then removed from service and ’REGENERATION’ is then carried with Sodium Hydroxide.
Strong Base Anion Exchanger (SBA)
Application
These ion-exchangers are used to produce demineralised water by removing all anions including dissolved silica & carbon dioxide.
Operation
These ion-exchangers contain strong base anion resin. As the water to be treated flows past the anion resin, the resin gives up the hydroxide ions for negatively charged ions (anions) of carbonates, chlorides, sulphates, nitrates, silica etc resulting in demineralised water coming out of the exchanger. As the hydroxide ions are replaced with other anions on resin exchange sites, there are less and possible exchange sites for exchange and the resin gets exhausted. The Strong Base Anion Exchanger is then taken out from service and ’REGENERATION’ is then carried with Sodium Hydroxide.
Mixed Bed Exchanger (MB)
Application
These ion-exchangers are used to produce demineralised water by removing traces of ions slipping out of preceding units.
Operation
These ion-exchangers contain cation resin & anion resin and used for polishing the output from an Anion Exchanger or when inlet ionic loads are very low. Influent water enters the ion-exchanger at top via service inlet valve. As the water to be treated flows past the cation resin, the resin gives up the hydrogen ions for positively charged ions (cations) of calcium, magnesium, sodium etc and as the water flows past the anion resin, the resin gives up the hydroxide ions for negatively charged ions (anions) of carbonates, chlorides, nitrates, silica etc resulting in demineralised (polished) water coming out of the exchanger. As the hydroxide ions are replaced with other anions & hydrogen ions are replaced with other cations on resin attachment sites, there are less and possible exchange sites for other anions & cations. This means that the resin will be exhausted. High conductivity or high silica leakage indicates this. When these anions & cations are able to pass through the resin without exchanging with hydroxide & hydrogen ions such that maximum leakage of these anions & cations is exceeded the mixed bed will be removed from service. ’REGENERATION’ is then carried with caustic soda for the anion resin & hydrochloric or sulphuric acid for the cation resin.
