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Kinetic and Morphological Investigation of Calcium Sulfate Dihydrate (gypsum) Scale Formation on Heat Exchanger Surfaces in the Presence of Inhibitors

Gypsum scale formation takes place directly on the surface of heat exchanger without  bulk or spontaneous precipitation in the reaction cell. Polymeric and non-polymeric inhibitors have been examined for their effects on the rate of scale formation.

Product Number: 51317--9020-SG
ISBN: 9020 2017 CP
Author: Zahid Amjad
Publication Date: 2017
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The formation and adherence of calcium sulfate dihydrate (CaSO4.2H2O gypsum) hemihydrate (CaSO4.1/2 H2O plaster of Paris) and anhydrite (CaSO4) scales on heat exchanger and equipment surfaces poses serious challenge in the efficient operation of many industrial processes utilizing feed and/or recirculating waters containing high levels of calcium and sulfate ions. Industrial processes affected by the deposition of sulfate scales include boiler cooling desalination by evaporation and reverse osmosis methods gas scrubbers and oil recovery utilizing water flooding technique.In the present work the kinetics of gypsum scale formation on heat exchanger surfaces from aqueous solutions has been investigated by a highly reproducible technique. It has been found that gypsum scale formation takes place directly on the surface of heat exchanger without any bulk or spontaneous precipitation in the reaction cell. The kinetic data also suggest that the rate of scale formation is a function of solution supersaturation heat exchanger surface area and the metallurgy of the heat exchanger. A variety of polymeric (synthetic and natural) and non-polymeric inhibitors have been examined for their effects on the rate of scale formation. The results indicate that the amount of gypsum scale formed on heat exchanger surface is strongly affected by changing of functional group (type and ionic charge) molecular weight and the concentration of the inhibitor. Scanning electron microscopic investigations of the gypsum crystals grown in the presence of inhibitors show that structures of these crystals are highly modified. A mechanism based on the surface adsorption of inhibitors on the growing crystals will be presented.

Key words: calcium sulfate dihydrate, gypsum, scale, maleic acid polymers, brass heat exchanger, crystal morphology

The formation and adherence of calcium sulfate dihydrate (CaSO4.2H2O gypsum) hemihydrate (CaSO4.1/2 H2O plaster of Paris) and anhydrite (CaSO4) scales on heat exchanger and equipment surfaces poses serious challenge in the efficient operation of many industrial processes utilizing feed and/or recirculating waters containing high levels of calcium and sulfate ions. Industrial processes affected by the deposition of sulfate scales include boiler cooling desalination by evaporation and reverse osmosis methods gas scrubbers and oil recovery utilizing water flooding technique.In the present work the kinetics of gypsum scale formation on heat exchanger surfaces from aqueous solutions has been investigated by a highly reproducible technique. It has been found that gypsum scale formation takes place directly on the surface of heat exchanger without any bulk or spontaneous precipitation in the reaction cell. The kinetic data also suggest that the rate of scale formation is a function of solution supersaturation heat exchanger surface area and the metallurgy of the heat exchanger. A variety of polymeric (synthetic and natural) and non-polymeric inhibitors have been examined for their effects on the rate of scale formation. The results indicate that the amount of gypsum scale formed on heat exchanger surface is strongly affected by changing of functional group (type and ionic charge) molecular weight and the concentration of the inhibitor. Scanning electron microscopic investigations of the gypsum crystals grown in the presence of inhibitors show that structures of these crystals are highly modified. A mechanism based on the surface adsorption of inhibitors on the growing crystals will be presented.

Key words: calcium sulfate dihydrate, gypsum, scale, maleic acid polymers, brass heat exchanger, crystal morphology

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