Abstract
An important key to a successful use of carbon steel-based heat exchanger tubes in geothermal binary-cycle power plants is to understand how to efficiently prevent the deposition on them of silica scales. These deposits are caused by the high sensitivity to silica of ferric oxide layer occupying the outermost surface sites of carbon steel. We evaluated the usefulness of two high-temperature performance coatings, polyphenylenesulfide (PPS) and polytetrafluoroethylene (PTFE)-blended PPS, in inhibiting silica scaling. To obtain this information, the coated steel panels were immersed for up to 7 days in 200 °C silica-rich brine. As a result, the surfaces of the unblended PPS coating underwent some degree of brine-induced oxidation. Although the amount of silica deposited was negligible, it was found that the sulfur–oxygen derivatives formed on the surfaces by oxidation make them susceptible to silica scaling. In contrast, the PTFE-blended PPS coating had a high potential as the anti-silica fouling barrier. The major reason for this was due to the segregation of anti-oxidant, hydrophobic PTFE top surface layer above a PPS layer in the coating.
Published Version
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