Steam Purity Monitoring of Low Sodium by Ion Selective Electrode Method

Abstract

The steam supplied to steam turbines at geothermal plants contains impurities, such as silica and chloride ions, as well as gases, which cause scales to stick to the turbine or that reduce the vacuum in a condenser. To accurately control the plant water (steam) quality, online measurements of both the steam water quality and gas volume have to be taken. In EDC, the chloride in steam is determined by analyzing the sodium component and multiplied with a factor to convert it to chloride. The current system of on-line sodium monitoring is the Flame photometric method. It is, however, quite difficult to put an on-line system in the power plant area wherein the unit utilizes an LPG as fuel. The method is also not suitable for continuous, unattended monitoring. The Ion-Selective Electrode method is a simple analytical technique for directly analyzing small concentrations of cation species like sodium (Na+) in a solution. The ROSS Sodium electrode is used as the indicator electrode in conjunction with an 808 Titrando meter. Low level concentration standards from 0.02 ppm to 5.0 ppm sodium is used for the direct calibration of the instrument. An ionic strength adjustor (ISA) is added in the form of NH4Cl/NH4OH solution. Here we present our efforts in ISE analysis of low sodium from steam condensate samplesin comparison to Atomic Absorption (AA) spectrophotometric results.