A Comprehensive Look at Conductivity Measurement in Steam and Power Generation Waters

Abstract

Conductivity has been the simplest, oldest, most common, most reliable and lowest cost measurement used for determining water purity. Nevertheless, this lowly measurement has provided the means for protecting and assuring efficient operation of billions of dollars worth of power and steam generation equipment throughout the world for over three-quarters of a century. Recent innovations in measurement accuracy, temperature compensation, and sample conditioning have enabled this basic detection method to provide more information and to expand its use even further. From the simplest TDS meter to the most sophisticated ion chromatograph, conductivity measurement is the core technology. The widespread use of this measurement often outpaces the understanding of it. Provided here are the fundamentals and application of conductivity measurement as used in power and steam generation, including ionic conductance, cell constant, measuring techniques and temperature effects. In addition, various means of sample conditioning are discussed, covering the measurements of cation conductivity, degassed cation conductivity, pH and CO 2 calculations and even TOC (total organic carbon) measurements. It is hoped this discussion will assist those applying conductivity measurement in any of its incarnations to have a greater understanding and to obtain better results. CONDUCTIVITY THEORY Conductivity is an intrinsic property of a solution—the ion-facilitated electron flow through it. Electrons will not flow through water by themselves but their charge can be carried by ions. Conductivity is nearly proportional to ionic concentration and is therefore a good indication of water purity. The more ions, the more conductive is the solution. Conductivity will not detect non-ionic materials such as oils or many other organics. When a voltage is applied to two electrodes immersed in a solution, ions between them will be attracted by their opposite charge and will move toward them to produce a current. To prevent ion migration and electrochemical reactions in the sample, AC voltage is always used for conductivity measurements. The polarity changes frequently enough that ions don't move or react significantly.