Novel Identification Method for Seawater Contamination into Water-Steam Cycles

ABSTRACT

In the water-steam cycle of power plants, cation conductivity is measured to promptly detect contamination by impurities such as seawater and prevent corrosion damage to equipment and piping. Cation conductivity is obtained by measuring the electrical conductivity of the sample after the cation exchange pretreatment, making the highly sensitive detection of anion impurities possible. However, due to a policy of increased introduction of renewable energy, frequent start and stop operation of combined cycle power plants is increasing. As a result, interference with cation conductivity measurements by carbon dioxide which enters from the air during plant outages will increase, making the delayed detection of contamination by impurities a matter of concern. Therefore, a novel identification method for impurities based on the pH, specific conductivity, and cation conductivity, which are monitored conventionally in the water-steam cycle, has been investigated.

As a result of the calculation of impurity concentrations using the novel model of the simulated water quality of a water-steam cycle prepared by chemical equilibrium calculation software, it has been confirmed that the calculation error for carbon dioxide concentrations not from seawater is 0.0 % to 18 % more than 0.1 mg ⋅ L^–1, and that for seawater contamination is 0.0 % to 20 % more than 1 · 10^–6 m³ ⋅ m^–3, which is regarded as good agreement. Additionally, the calculated results with measured data from two power plants are consistent with the assumed behavior based on the plant status. In conclusion, it is indicated that the amount of seawater can be precisely estimated even in the case of the presence of both carbon dioxide and seawater by using this novel method.

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