Prediction of silica carry-over and solubility in steam of boilers using simple correlation

Silica content of the boiler water is critical for steam turbines and scaling of boiler heat transfer surfaces. Silica (SiO2) can volatilize with the steam in sufficient concentrations to deposit in steam turbines leading to scale formation on boiler surfaces. In this work, a simple correlation is presented to predict silica (SiO2) solubility in steam of boilers as a function of pressure and water silica content. The solubility of silica in steam directly depends on both the density and temperature of steam. With decreasing temperature and density, solubility of silica reduces. As the pressure affects steam density which has a strong bearing on steam temperature, it has an important effect on the solubility of silica in steam. The proposed correlation predicts the solubility of silica (SiO2) in steam for pressure up to 22,000 kPa and boiler water silica contents up to 500 mg/kg. The predictions from the proposed correlation have been compared with reported data and found good agreement with average absolute deviation being around 4%. This simple-to-use correlation can be of immense practical value for the engineers to have a quick check on silica (SiO2) solubility in steam of boilers as a function of pressure and water silica content at various conditions without performing any experimental measurements. In particular, personnel dealing with the utility boilers would find the proposed approach to be user friendly involving no complex expressions with transparent calculations. (C) 2009 Elsevier Ltd. All rights reserved.