Wastewater

Effect of Polymers for Gypsum Scale Control in Industrial Water Systems

By Zahid Amjad, Ph.D.

CHEMICAL TREATMENT SCALING TESTING

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Abstract

Scaling of heat exchangers, reverse osmosis (RO) membrane, and equipment surfaces by carbonates, phosphates, silicates, and sulfates of alkaline earth metals are an unwanted occurrence in industrial water systems. The scale deposits can cause a number of operational problems such as reduced heat transfer, deterioration of metallic parts, increased pumping costs, lost production due to unscheduled downtime, and premature equipment replacement. In cooling water and RO-based desalination systems, gypsum (calcium sulfate dihydrate, CaSO4.2H2O) is the most commonly encountered calcium sulfate scale whereas calcium sulfate hemi-hydrate (CaSO4.ᄑH2O) and calcium sulfate anhydrite (CaSO4) are the most frequently formed salts at high temperature processes (i.e., boiler, and multi-stage distillation). The scale formation mainly depends upon super-saturation of calcium sulfates, pH, temperature, and the flow velocity. The scale deposition problems can be mitigated by the application of properly designed treatment programs.

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