Chemical Cleaning of a Brass-Tubed Turbine Condenser after Five Years of Operation with Ferrous Sulphate Dosing

摘要

The purpose of chemically cleaning the brass-tubed turbine condenser was to remove the ferrous oxide layer and corrosion products which are mainly copper oxide Cu sub 2 O. Laboratory tests were conducted where 1 m long pieces of tube were installed in a small acid circuit which was designed to simulate the condenser circuit. The solubility of the oxide coating was tested in hydrochloric, sulfuric, formic and citric acids at different concentrations. The oxide coating was soluble in all cases, but the tube pieces treated with citric acid looked best. Citric acid was chosen because of its low corrosive effect on brass, its low cost and because it was also the only one permitting on-site handling which was more or less safe. In addition, citric acid also proved to be particularly suitable for dissolving a ferrous oxide layer from the chemical point of view, since it forms stable metal chelates with iron (III) ions. The pH value remains nearly constant even with complete conversion of the citric acid into iron citrate. Starting from the pure citric acid, the dissolution of the iron oxide begins at pH 2.3 and, with quantitative conversion of the citric acid into the complex, ends at pH 3.0. The optimum concentration of citric acid was determined to be a maximum of 1% and lab tests showed three cleaning cycles would be required. The technical implementation of the chemical cleaning process is also described. (ERA citation 10:044167)