Influence of solution hydrodynamics on the deposition of CaSO₄ scale on aluminum

The dissolution of hard and adherent scaling species depositing from process fluid streams is a serious problem experienced by the world's processing and petrochemical industries. Scaling/fouling causes a significant economic loss. Scaling is a complex process; therefore, this laboratory study employed a rotating cylinder electrode apparatus to develop a basic understanding of the scaling phenomenon. The effect of solution hydrodynamics was investigated at various rotational speeds on the deposition of calcium sulfate (CaSO ₄) scale on aluminum substrate having surface roughness profiles produced with 120 and 600 grit silicon carbide emery papers and at temperatures of 60 and 70°C. The results indicate a strong impact of solution hydrodynamics on the deposition rate of calcium sulfate on aluminum specimens. Morphological examinations of the deposited scale crystals under scanning electron microscope and energy dispersive X-ray spectrometry revealed prismatic needles and rodlike crystals growth at nucleation sites branching out randomly over the substrate. Secondary growth on the already existing primary crystals of CaSO₄was also discerned.