Inhibition of Gypsum Scale Formation on Heat Exchanger Surfaces by Polymeric Additives

Abstract

1. ABSTRACT The formation and adherance of calcium sulfate dihydrate, hemihydrate, and anhy-drite scales is a problem in many heat exchanger applications where the equipment is fed with waters containing high levels of calcium and sulfate. Industrial processes are affected by the deposition of sulfate scales including cooling, boiler, desalination (i.e., flash distillation), and oil recovery. Historically, polymeric and non-polymeric additives have been used in these processes to prevent the formation and deposition of scaling salts. In the present study, the influence of polymeric additives on gypsum (CaSO4 • 2H2O) scale on heat exchanger surfaces has been investigated. It has been observed that polymer composition, molecular weight, ionic charge and charge density, and polymer dosage have a significant impact on the performance of the polymeric additive. 2. INTRODUCTION The crystallization and adherence of scale-forming minerals (i.e., calcium sulfate, calcium carbonate, calcium phosphate, calcium phosphonate, etc.) on heat exchanger surface continues to present performance limitations for industrial water systems (i.e., cooling tower, boiler, flash distillation, etc.). In cooling water systems, gypsum (calcium sulfate dihydrate) is the most commonly encountered calcium sulfate scale whereas calcium sulfate hemihydrate and calcium sulfate anhydrite are the most frequently formed salts in high temperature processes (i.e., high temperature boilers, multistage flash distillation). The deposits that form can markedly reduce heat transfer causing energy losses or material damage, especially when coupled with corrosion. Various factors such as bubble