Cation Conductivity: Who, What, Where, When, Why, How

Who
Cation Conductivity also known as Acid Conductivity and Conductivity After Cation Exchange (CACE) is the measure of electrolytic conductivity of a liquid sample after that liquid sample has passed through an ion exchange resin column containing cation resin in the hydrogen form.

In the power industry the values are typically reported as uS/cm (microsiemens per centimeter).

What
Cation Conductivity in the power plant is used for identifying low level contamination by potentially corrosive anion contaminants such as chlorides, sulfates, and organic acids

Where
Typically measured on Main Steam or Reheat Steam samples, Condensate samples, Feedwater samples, and Boiler or Heat Recovery Steam Generator evaporator drum samples

When
Measured continuously on flowing samples during all phases of operation

Why
The measurement was adopted for monitoring the power plant steam / water cycle as it can detect low levels of anion contaminants such as chlorides, sulfates, and organic acids (parts per billion) on a continuous basis, while at the same time the measurement is very simple and easy to maintain.

How
In the power plant cycle the circulating steam and water is maintained at a high purity level to minimize the potential for corrosion and deposition.  This steam and water will typically be conditioned with an alkaline chemical such as ammonia to further reduce the potential for corrosion.

When cation conductivity is measured on a power plant cycle sample, the cation exchange resin removes the alkaline chemical and converts any anion contaminants present into their acidic form (e.g. if sodium chloride is passed through the column the sodium ion is exchanged for a hydrogen ion, converting the sodium chloride to hydrochloric acid).  This eliminates the conductivity from the added alkaline chemical while at the same time increases the conductivity of many anionic contaminants present (by converting them to their acidic form).

The result is a sensitive measurement of anionic contaminants.

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