De-Mineralization / De-Ionization Plants
De Mineralization Plants/De Ionization: The name explains is a term normally used for reduction of charged ions to very low levels. Alternatively called as Demineralization. The deionization is normally a two stage process. In first stage the cations & in second stage anions are removed respectively. Sometimes a polisher unit called mixed bed is also employed when the water quality requirement is stringent.There are variations in column design. In vessel configuration, the two basic types are down flow & Up flow design. In Downflow vessels regeneration is carried out in two methods
- Co-Flow Unit – The regenerant flows in same direction as that of water.
- Counter-Flow Unit – In this design the regenerant flows in opposite direction as that of water. This method is usually envisaged where very low leakage levels are expected.The very large polishers have external regeneration systems also.
The required scheme is normally decided based on feed water quality, outlet quality required and flow rate between two regenerations. Following schemes are normally employed.
- Strong Acid Cation – Strong Base Anion
- Strong Acid Cation – Degasser – Strong Base Anion
- Strong Acid Cation – Degasser – Weak Base Anion – Strong Base Anion
- Weak Acid Cation – Strong Acid Cation – Degasser – Weak Base Anion – Strong Base Anion
A Mixed Bed is added if the quality requirements are stringent.
MIXED BED UNITS:- After passing water through cation then anion exchanger it is passed through mixed bed unit. In mixed bed cation and anion resins are mixed and while water passes through it as it passes through thousands of cation/anions exchanger ‘resulting final effluent of very good quality water.