A. Conductivity – Conductivity is the measurement of a liquid’s ability to transfer electrical current. In power plants, conductivity instruments are used to measure contaminants (consisting primarily of mineral salts) in high-purity water. Air intrusion into surface condensers, and the injection of other treatment chemicals such as ammonia, amines, etc., however, can affect conductivity. These instruments cannot differentiate between minerals and gases.
There are two types of conductivity measurements: specific and cation. Specific conductivity can detect only large amounts of contaminants. Condenser tube leaks normally start out very small, and may increase over time. For example, condensate flow may be 5,000 gpm, and the “leak” 0.1 gpm. On a volumetric basis, this is 20 ppm. Specific conductance instruments may not be able to detect this small leak unless the cooling water conductivity is very high to start.
Cation conductivity instruments pass the condensate sample through a cation (ion exchange) resin to convert cations (sodium, calcium, etc.) to the hydrogen form, producing an acidic effluent. Since acids are much more conductive than mineral salt solutions, the effective sensitivity is increased dramatically. The generally accepted lowest detection limit (LDL) is 0.05 microsiemens per centimeter (μS/cm). With such sensitivity, cation conductivity can be a very useful measurement to detect condenser tube leaks.
From: Boiler Feedwater & HRSG: A New Method for Exposing Condenser Leaks – On-Line Particle Detection - by Robert L. Bryant
Industrial WaterWorld November, 2007
Retrieve on 29-SEP-2008 from http://ww.pennnet.com/display_article/313937/64/ARTCL/none/none/1/Boiler-Feedwater-&-HRSG:-A-New-Method-for-Exposing-Condenser-Leaks-%E2%80%93-On-Line-Particle-Detection-/
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