Studies on the Deposit Structure in the Cooling Systems of Steam Turbines at TPPs

Resumo

When untreated natural water is used in the reverse cooling systems with tower-shaped evaporative cooling stacks of thermal power plants, negative processes occur, namely sparingly soluble substance deposition onto heat-exchange surfaces, corrosion, sludging of flow paths, bio-fouling, etc., which significantly worsens the thermal efficiency of TPPs as a whole, leads to equipment deterioration, and worsening hydrodynamic performance. This paper is devoted to the study of the physicochemical structure of deposits formed in reverse cooling systems of thermal power plants using IR spectroscopy and elemental analysis. At the Kazan TPP-3 with a conjugated reverse cooling system, samples of deposits have been taken from the rotary chamber and the condenser tubes of a turbine as well as from the sprayers of a tower-shaped evaporative cooling stack. The analysis of IR spectra of the samples showed that the base of deposits in the tower-shaped evaporative cooling stack consists of calcium carbonate that includes iron compounds (mainly hematite Fe₂O₃), inorganic sulfates, silicates, magnesium carbonate. Dense parts of the deposits in the condenser of turbines consist of iron silicate with the impurities of other substances. The deposits in the reverse cooling system are most intensely formed in the areas with the highest heating temperature, such as turbine condensers and spraying nozzles in the tower-shaped evaporative cooling stack. At the Naberezhnye Chelny TPP, the deposits have been taken from a forechamber gate of the reverse cooling system. In total, four different samples of deposits that differ in appearance from each other have been chosen. As shown by infrared spectroscopy, the main part of deposits is formed by the corrosion products of metal structures coated with the layers of sparingly soluble compounds, including calcium and magnesium carbonates, iron oxides, silicates, and organic compounds, such as humic substances.