Cation Conductivity Measurement and Cation Conductivity Panels
Cation conductivity measurement in boiler water and steam at power plants: resin columns, degassed cation conductivity panels and SWAS integration.
Measurement methods: Conductometric Conductivity
What is cation conductivity and why is it measured?
Cation conductivity is the conductivity measured after the sample has passed through a strong acid cation resin. The resin exchanges the positive ions of bases such as ammonia and amines for hydrogen, leaving the acidic forms of anions such as chloride, sulfate and acetate. Anionic impurities that cause corrosion in feedwater can thus be monitored separately, without being masked by the high direct conductivity from chemical dosing. Because carbon dioxide also raises this measurement, CO₂ is removed from the sample in degassed cation conductivity.
In power plants, cation conductivity is monitored continuously in boiler water, steam and condensate as an early indicator of condenser leakage and anionic contamination.
Where is cation conductivity measured?
- Thermal and combined-cycle power plants: In feedwater, boiler water, main steam and condensate.
- Plants using steam boilers: In chemistry control of the water-steam cycle.
How is cation conductivity measured?
The system consists of three sections. First, the sample passes through a cation resin column; when the resin is exhausted, the column is regenerated or the resin replaced. Then, for degassed measurement, the sample is heated or boiled to remove dissolved CO₂. Finally, a conductometric sensor measures conductivity and applies temperature compensation. Panel solutions offer these three steps on a single backplate together with temperature and flow monitoring.
Choosing a cation conductivity panel
- Resin capacity and regeneration interval
- Sample flow and temperature; sample cooler requirement
- Whether the panel will be used standalone or within a SWAS
- Supply voltage and output signals
Cation conductivity measurement with Tetra
Tetra supplies the SENTRY DCCP degassed cation conductivity panel and RC series resin columns. It provides sample preparation, cooling and integration into multi-parameter SWAS systems, commissioning, calibration and spare parts support.
Frequently asked questions
What is the difference between direct conductivity, cation conductivity and degassed cation conductivity?
Direct (specific) conductivity shows all the ions in the sample together with the dosed alkalizing chemicals. Cation conductivity is measured on a sample passed through cation resin and highlights anionic impurities. In degassed cation conductivity, CO₂ is also removed, so that CO₂ from air ingress can be distinguished from corrosive anions.
What unit is cation conductivity monitored in, and how are target values determined?
Cation conductivity is monitored in µS/cm, compensated to 25 °C. Target and alarm values are determined according to boiler pressure, the water chemistry program and the turbine manufacturer's requirements. Technical guidance from organizations such as IAPWS is widely used as a reference for setting these values.
When should a cation resin column be replaced?
The resin is exhausted when saturated with ammonia or amines in the sample, and cation conductivity then begins to be measured incorrectly. In columns with color-changing indicator resin, the exhausted zone can be seen by eye. The replacement interval is determined by the alkalizing agent concentration in the sample, sample flow and column volume.
Why does cation conductivity read high after new resin is fitted?
In the first hours, soluble components and residues from new resin can pass into the sample, causing temporarily high readings. After a resin change, allow a rinse period until the reading stabilizes. Air bubbles that enter when the line is opened can also cause temporary deviations.
Products measuring this parameter
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