CATION CONDUCTIVITY MEASUREMENT IN A THERMAL POWER PLANT
What is a Cation Conductivity?
This term is generally applicable in boiler water treatment. The concept is the same as how a Strong Acid Cation (SAC) column works in a DM Plant. To measure the cation conductivity, a water sample is passed through a cation column filled with cation resin in the hydrogen [H+] form. It is also known as acid conductivity.
Why it is important to measure Cation Conductivity?
Cation resin removes positively charged ions (cations) and replaces them with [H+] ions. In a high purity water cation present in ppb levels very small amount. For instance, if NaCl is present in this case, when we pass the sample through the cation column, the [Na⁺] ion is removed & the [Cl⁻] ion reacts with the [H⁺] ion to produce HCl (hydrochloric acid) that has a higher conductivity.
Please keep in mind that a particular cation or anion is separately not present in water. Always they are present in combination with each other. e.g., NaCl, MgCl₂, etc.
As the name suggests, it is a measurement of the conductivity after removing cations from a water sample.
It is an indirect measurement of anions present in water, mainly chloride & sulphate present in steam samples.
In other words, cation conductivity magnifies the anion present in water and indicates steam purity. Most steam turbine manufacturers recommend a cation conductivity limit of less than 0.3 µs/cm.
High conductivity is observed in the water sample due to the below points:
- 1) Exhausted cation column
- 2) Overfeed of amine & oxygen scavenger chemicals
- 3) Total organic carbon or organic decomposition products (acetate, formate) present in high level
- 4) A high level of anion contamination is present in water.
In practice, well controlled and maintained feedwater chemistry can consistently maintain cation conductivity below 0.5 µs/cm when using organic amine and organic oxygen scavengers.