Sodium Measurement: Boiler Water and Steam Sodium Analyzers
Low-level sodium measurement in feedwater, steam and condensate: ion-selective electrode sodium analyzers and SWAS systems, used for turbine protection.
Measurement methods: Ion-Selective Electrode
What is sodium and why is it measured?
Sodium is one of the most sensitive indicators of purity in steam boilers and turbines. Sodium salts carried into steam can deposit on turbine blades, causing loss of efficiency and stress corrosion cracking. Sodium is also an early warning of condenser leakage, ion exchanger exhaustion or inadequate demineralization. In power plants, sodium in steam and feedwater is therefore monitored continuously at trace level.
Where is sodium measured?
- Main steam and superheated steam samples: For the quality of steam going to the turbine.
- Feedwater and condensate: For detecting condenser leakage.
- Demineralized water and ion exchanger outlets: For early warning of resin exhaustion.
How is sodium measured?
Online sodium analyzers work by the ion-selective electrode (ISE) method. A sodium-sensitive glass electrode and a reference electrode produce a voltage dependent on the sodium activity in the sample; this value is converted to concentration with temperature compensation. For accurate measurement at very low sodium levels, the sample's pH is raised with a base reagent (for example DIPA), which reduces hydrogen ion interference and stabilizes the measurement. The analyzer can be calibrated automatically or semi-automatically with standard solutions at set intervals.
Choosing a sodium analyzer
- Expected sodium level and measurement range
- Reagent (alkalizer) consumption and maintenance kit
- Sample cooling and pressure reduction; integration within a SWAS
- Installation in a protective enclosure or inside a panel
Sodium measurement with Tetra
Tetra supplies Thermo Orion process analyzers in Türkiye and provides installation, supply of reagents and consumables, commissioning, calibration and service. For power and treatment plants, complete SWAS or panel systems with sample cooling and conditioning are built at its facility in İzmir.
Frequently asked questions
What unit and levels is sodium measured at?
In boiler water and steam applications, sodium is generally measured in µg/L (ppb), at trace level. Target and alarm values are determined according to boiler pressure, the water chemistry program and the turbine manufacturer's requirements. The lower limit of the analyzer's measurement range should therefore be comfortably below the plant's target value.
How is a sodium analyzer calibrated?
Sodium analyzers are calibrated with sodium standard solutions of known concentration or by the known addition method. Because measurement is at trace level, it is critical that the containers and water used in calibration carry no sodium contamination. Many analyzers can carry out calibration automatically or semi-automatically at set intervals.
What problems are common in low-level sodium measurement?
Running out of alkalizing reagent or dosing too little lowers the pH and causes high readings through hydrogen ion interference. The electrode surface loses sensitivity over time, which slows the response, so the electrode is periodically reconditioned according to the manufacturer's instructions. Contamination in the sample line and temperature fluctuations also affect measurement stability.
How is online sodium measurement verified by laboratory analysis?
A grab sample taken from the sample point the analyzer measures can be analyzed by a sensitive laboratory method such as ion chromatography, and the results compared. At trace level, particular care should be taken that the sample container and transport process introduce no contamination. Systematic differences should be investigated in terms of calibration or reagent dosing.
Products measuring this parameter
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