Scale and Corrosion Prevention in Cooling Water Systems Part II: Calcium Sulphate
This paper describes an experimental study on calcium sulphate scaling and prevention by newly treated poly- acrylamide in a laboratory model. In order to study the inhibiting capacity of the chemical used, experiments were per- formed in solutions involving treatment of synthetic sea water with different concentrations of the polymer. Polyacryla- mide 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 jcorr and corrosion rate CR were reduced and inhibi- tion 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 cal- cium sulphate crystals in the presence of the polymer as indicated by scanning electron microscopic (SEM) studies.
Evaluation of maleic acid based polymers as scale inhibitors and dispersants for industrial water applications
Abstract The formation of inorganic scale deposits of the alkaline earth metals is a persistent problem. Dispersion of solid particles separating out from the fluids is also very important for fouling due to deposition. Scale formation and stabilization of suspensions are often overcome through the use of water soluble polymers. In the present work, a series of polymeric compounds were tested as inhibitors of calcium carbonate and calcium sulfate dihydrate (gypsum) precipitation and as dispersion agents of hematite (Fe2O3) suspensions in electrolyte solutions. Acrylic acid (AA) and maleic acid (MA) polymers were found to inhibit the precipitation of calcium carbonate and gypsum from supersaturated solutions to extents exceeding 90% at concentrations as low as 2 ppm. The molecular weight (MW) was an important parameter in determining the activity of the tested inhibitors. Lower MW polymers (ca. 2000) proved to be more efficient than higher MW polymers. A similar trend was exhibited for the dispersion ability of the hematite particles. AA and MA copolymers in which functional groups were introduced (pyrrole, sulfono and amide groups) were efficient precipitation inhibitors and dispersion agents, but the efficiency depended strongly on the co-polymer architecture. Copolymers containing sulfono groups improved inhibitory activity and dispersion ability and showed higher calcium ion tolerance.
Investigation on fouling behaviors of low-energy surface and fouling fractal characteristics
Although many measures have been taken to mitigate the formation of deposits on the heat transfer surface, fouling is still a serious problem in industrial processes. This article describes the fouling behavior of two types of copper-modified surfaces with low surface energy. CaCO3 crystallization fouling experiments were carried out on the modified heat transfer surfaces in a simulated cooling hard water system. The results suggest that the fouling process is enhanced in the presence of desorbed air bubbles on the modified surfaces. The fractal theory is used to analyze the fouling geometric texture. The results demonstrate that the fractal dimension values D of CaCO3 fouling on the modified surfaces are higher than that on the copper surface.