AFTER CATION CONDUCTIVITY(ACC)

BY / DILIP KUMARNTPC LIMITED, INDIA

POWER PLANT CHEMISTRY

What is After Cation Conductivity(ACC)

• 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. 

WHY ACC IS MEASURED

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

Where ACC Measured?Typically measured on Main Steam or Reheat Steam samples, Condensate samples, Feed-water samples, and Boiler or Heat Recovery Steam Generator evaporator drum samples

TYPICAL DIAGRAM OF A POWER PLANT

SIGNIFICANCE OF ACC• In the power plant Steam-water cycle 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.

• In practice, a cooled sample of condensate or high purity water flows through a cation exchanger in the hydrogen form. The cation resin replaces contaminating cations such as Ca++, Mg++, Na+, NH4+, and amines in the sample with hydrogen ions.

HOW ACC MEASURED

NaCl, KCl , CaSO4,MgCl , NH4OH etc Contaminated Sample with minerals

HCl, H2SO4, H2O etc

+ Na+Cl- Na+ + HCl

ION-EXCHANGE REACTIONS

(CATION EXCHANGE RESIN)(MINERAL) (ACID)

CATION COLUMN

HOW ACC MEASURED…• The hydrogen ions exchanged for the other cations

in the sample increase the conductivity contributed by the contaminant salts of mineral acid anions listed above by 3 or 4 times. Thus the cation exchange column can be thought of as a "conductivity amplifier" for mineral and organic acid contaminants; increasing the sensitivity of the conductivity analyzer to low levels of contamination. "

IN CASE OF CONTAMINATION

IN CASE OF NORNAL SAMPLE CONDITIONING

CATION COLUMN ARRENGEMENT IN SWAS PANEL

CATION COLUMN ARRENGEMENT IN SWAS PANEL

THREE-WAY VALVE

CONDUCTIVITY CELL

CATION COLUMN

THANKS