DISSOLVED OXYGEN INSTRUMENTS MONITORING OXYGEN POWER

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Abstract

Dissolved oxygen (DO) is recognized as being a key parameter to be monitored in the power plant cycle chemistry by most of the guidelines, including Electrical Power Research Institute (EPRI), VGB, and more recently by the European guideline EN12952-12:2003. Common chemistry types requiring tight oxygen control include reducing all-volatile treatment (AVT(R)), oxidizing all-volatile treatment (AVT(O)), and oxygenated treatment (OT) (1-3). OT chemistry is gaining in popularity as it contributes to the prevention of corrosion and flow accelerated corrosion (FAC) by reducing the quantity of iron to as low as 0.5 micrograms per kilograms-1 (ﾵg kg-1). This popularity can also be explained by the result of EPRI benchmarking. This study shows that the most reliable and best performing units in the world operate on OT or AVT(O) (1). While the reliability of OT chemistry is achieved through the formation of a very low solubility protective layer of ferric oxide hydrate (FeOOH) on, and within the pores of the magnetite layer, the formation of this protective layer is not 100% using AVT(O) chemistry. Typical oxygen levels in the feedwater are < 10-ﾵg kg-1 for AVT chemistries, and 30 to 150-ﾵg kg-1 for OT chemistry.

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