Statistical Model for Scaling and Corrosion Potentials of Cooling-System Source Waters

Abstract

Abstract

Determination of make-up cooling water scaling and corrosion potentials for power plants is essential to prevent cooling system fouling challenges linked to source water quality. In this study, a statistical model is proposed to evaluate the probability that scaling or corrosion could occur. These probabilities were determined from derived distributions for the Langelier saturation index (LSI) and the aggressive index (AI), computed from a fitted joint normal distribution for pH, log[Ca²⁺], log([Ca²⁺]+[Mg²⁺]), and log[Alk]. In most cases only one outcome (scaling or corrosion) exhibited a probability of concern, though highly variable source waters could exhibit significant probability for both. To illustrate application of the method, freshwater and treated municipal wastewater samples collected from the western Pennsylvanian region were analyzed for alkalinity, pH, [Mg²⁺] and [Ca²⁺] concentrations. The LSI and AI were calculated using the measured characteristics of the water samples, and their observed distributions were compared to the derived normal distributions for each. This study used the uncertainty associated with water quality inputs to evaluate the uncertainty of scaling and corrosion potentials, and provides a practical approach for power plant operators to evaluate the uncertainty associated with scaling and corrosion indices of cooling waters without use of expensive software or complicated coding.