Abstract
Flue gas corrosion produces a severe attack in metal surfaces of stainless steel tubes in coke calciner heat recuperators. This corrosion is produced due to the presence of sulphur and vanadium in the calcining process which forms low melting and volatile corrosion products together with the reaction between the metal and the atmospheric oxygen at elevated temperatures. In an attempt to avoid this type of corrosion, advanced silica based coatings have been developed and applied over stainless steel samples and have been characterized and tested under laboratory conditions (microstructure, adherence and abrasion resistance, thermal resistance). Besides, a specific corrosion test has been designed in order to check chemical resistance to sodium vanadate salts at high temperature.
Due to the excellent behavior of the coating, showing a complete protection of the samples, several coated prototypes were prepared and installed in the hottest part of one coke calciner heat recuperator to certificate the protective performance of the coating under real conditions (T Fumes = 700 °C; T Steel = 580 °C). After 4 years of validation tests, 800 tubes of 310S stainless steel (63,50 mm OD x 2,41mm WT and 5000mm lenght) were coated to build a whole coke calciner heat recuperator unit, with an average coating thickness of 150 μm. In 2018, after 12 months in operation, visual inspection reports that ceramic coating remains in place and none of the tubes has been corroded.
