Use of Seawater to Regenerate Shallow-Shell Cation Resin
By Donald D. Downey
Efficiently using seawater to regenerate strongly acidic cation (SAC) resins used in softening applications has been a long sought after alternative versus using excessive and costly amounts of sodium chloride (NaCl) brine. The limitations for using seawater have been isolated to the inefficiencies of the ion-exchange (IX) bead matrix. Early studies show that upwards of 150 gallons per cubic feet (g/ft3) (20 bed volumes [BV]) of seawater used to regenerate SAC resin could provide 22 kilograins per cubic foot (Kgr/ft3) of operating capacity (OC) to 2 milligrams per liter (mg/L) (parts per million [ppm]) leakage end point (1). Normal softening requires 50 g/ft3 (6.5 BV) for the same OC and leakage. In present day operations the need for higher regeneration efficiency not only drives the economics of the IX process, but also increasingly, has become a limitation on new IX considerations because of restrictions on regenerant waste disposal. Recent developments in resin bead functionalization techniques have led to a new family of resins with improved regenerant utilization and reduced waste volume discharge (2). This article presents a combined lab report and a field study carried out using seawater to regenerated shallow-shell SAC resin.
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