Scale and Corrosion Prevention in Cooling Water Systems Part II: Calcium Sulphate

ABSTRACT

This paper describes an experimental study on calcium sulphate scaling and prevention by newly treated polyacrylamide in a laboratory model. In order to study the inhibiting capacity of the chemical used, experiments were performed in solutions involving treatment of synthetic sea water with different concentrations of the polymer. Polyacrylamide gave significantly lower precipitation rate compared to the treatment in absence of inhibitor. The inhibitor probably is adsorbed on the active growth sites of the initially formed crystals. The performances of scale inhibitor with different concentrations were analyzed in terms of the amount of soluble calcium ions in solution. The results showed that the amount of scale was reduced to 0.00%, with, 10-15 ppm polymer additions, after 1 day incubation at 90°C. Antiscale agents specific to calcium sulphate deposits have recently been developed and tested on a laboratory scale. The work was also extended to study the corrosion inhibition of polyacrylamide to both C-steel and copper specimens in contact with synthetic cooling water environment. Electrochemical polarization techniques reveal that the inhibitor acts as anodic type with respect to C-steel and mixed type for copper. Corrosion current j_corr and corrosion rate CR were reduced and inhibition efficiency IE% increases with polymer additions. The inhibition effects are due to the formation of protective film. Morphological investigation for CaSO₄. 2H₂O gypsum crystals formed in synthetic sea water indicate reduction of calcium sulphate crystals in the presence of the polymer as indicated by scanning electron microscopic (SEM) studies.

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