Prevention of calcium sulfate formation in seawater desalination by ion exchange

Abstract

In mechanical vapor compression (MVC) desalination, high operating temperatures (>120°C) allow for high heat transfer coefficients and reduced compressor size, both of which lower total capital costs. To prevent formation of calcium sulfate scale on high-temperature desalination heat exchangers, the inverse solubility of calcium sulfate requires high sulfate removal. To selectively remove sulfate from seawater, a weak-base anion-exchange resin (Relite MG 1/P) was used. In synthetic seawater, the resin shows high sulfate selectivity. Conveniently, the exhausted resin can be regenerated with concentrated acidified (pH 4) blowdown brine from the desalination heat exchanger. Using the same exhaustion and regeneration times, high desalination concentration factors increase chloride concentrations in the blowdown brine, which allows for slower regenerant flow rates thereby increasing regeneration efficiency and sulfate removal. Using a high concentration factor helps regeneration; however, this must be balanced...