Corrosion control in thermoelectric power plant cooling systems using impaired waters as alternative sources.

摘要

The growing demand for fresh water and water shortages in many parts of the U.S. have led the power industry, one of the largest water consumers, to look for alternative water sources to meet their cooling needs. However, one of the main challenges when impaired waters are used in recirculating cooling water systems is the management of corrosion due to the degraded quality of the waters.;A method based on the electrochemical polarization resistance method was developed to measure instantaneous corrosion rate. The method was calibrated using cumulative weight loss measurements versus time made with the gravimetric weight loss method. A semi-empirical constant was derived and used to convert polarization resistance to instantaneous corrosion rate for measurements with particular metal alloys in particular corrosive environments. The instantaneous corrosion rate measured by polarization resistance thus can be used as an index of whether a particular water has an acceptable or unacceptable corrosivity with respect to the metal alloy of interest.;The feasibility of using secondary treated municipal wastewater or passively treated abandoned mine drainage in power plant cooling water systems was investigated by conducting laboratory experiments with a bench-scale recirculating water system and then field experiments with several pilot-scale cooling towers. Different corrosion control strategies by involving different types, combinations, and doses of corrosion inhibitors were evaluated. It was found that, with respect to corrosion control, secondary treated municipal wastewater can be used directly without any addition of corrosion inhibitor and passively treated abandoned mine drainage can be used with the addition of the inhibitor mixture of TTA, polymaleic acid, and ortho-phosphate to control corrosion to acceptable levels. Secondary treated municipal wastewater has lower corrosivity than passively treated abandoned mine drainage since the former has higher scaling potential, which protects metal alloys in cooling systems.;The effectiveness of the TTA protection of copper in the presence of free chlorine and monochloramine, common biocides used in cooling water systems, was investigated through potentiodynamic polarization measurements, polarization resistance measurements, and density analysis of Cu-TTA surface adsorption films. It was found that the copper surface can act as a catalyst for free chlorine to degrade TTA, while monochloramine increased the average adsorption density of Cu-TTA film, due to the complexation of TTA with Cu attacked by monochloramine. The catalytic effect was not significant for monochloramine. Free chlorine attacked the copper surface more extensively and aggressively than monochloramine. Thus, with respect to corrosion control, monochloramine represents a better option as a cooling system biocide.;This study was focused on evaluation of corrosion and corrosion control strategies when using secondary treated municipal wastewater and passively treated abandoned mine drainage in power plant cooling systems. The specific objectives of the study were to develop a rapid electrochemical method to evaluate the corrosion of metal alloys in a bench-scale recirculating water system, to investigate the feasibility of using secondary treated municipal wastewater and passively treated abandoned mine drainage in power plant cooling water systems with respect to corrosion control, and to evaluate the effectiveness of tolyltriazole (TTA) corrosion protection of copper against oxidizing agents such as free chlorine and monochloramine.