Oxygen Scavenger Measurement: Boiler Water Analyzer
Online measurement of oxygen scavenger residual in boiler feedwater and condensate: a process analyzer for corrosion control.
What is an oxygen scavenger and why is it measured?
Oxygen scavengers are chemicals that react with dissolved oxygen in boiler feedwater and consume it. Trace oxygen remaining after mechanical deaeration is removed by these chemicals, preventing corrosion in the water-steam cycle. If dosing is insufficient, oxygen causes corrosion; excess creates chemical waste and unwanted side effects. Continuously monitoring the amount of oxygen scavenger remaining in the water, the residual, is therefore the key feedback for dose control.
Where is oxygen scavenger measured?
- Boiler feedwater: At the deaerator outlet and on the feed pump line.
- Condensate line: In returning condensate.
- Plants using steam boilers: Thermal power plants, refineries and industrial steam systems.
How is oxygen scavenger measured?
An online oxygen scavenger analyzer is a process instrument that continuously measures the residual in the sample. While a dissolved oxygen sensor shows the presence of oxygen, this analyzer tracks the chemical scavenger itself; assessing the two together makes dose adjustment safer. The instrument connects to the sample line and, as required, transfers data to the chemical dosing pump or control system through a current output and alarm. Versions with a protective enclosure are offered as an option for field installation.
Choosing an oxygen scavenger analyzer
- Type of oxygen scavenger chemical used
- Sample pressure, temperature and cooling requirement
- Plan for assessment together with dissolved oxygen and pH measurements
- Reagent and maintenance requirements
Oxygen scavenger measurement with Tetra
Tetra supplies Thermo Orion process analyzers in Türkiye and provides installation, supply of reagents and consumables, commissioning, calibration and service.
Frequently asked questions
Which chemicals are used as oxygen scavengers?
Boiler water applications use chemicals such as hydrazine, carbohydrazide, DEHA (diethylhydroxylamine), sodium sulfite and erythorbate. Because sulfite leaves solids, it is preferred mostly in low-pressure boilers. The chemical is chosen according to boiler pressure, system metallurgy and the plant's water chemistry program.
What unit is oxygen scavenger residual measured in?
The residual is generally expressed in µg/L (ppb) or mg/L (ppm), in terms of the chemical used. The target range is determined by the type of chemical and the water chemistry program. Results for different chemicals cannot be converted directly into one another, so it is necessary to know which chemical the analyzer is set for.
How is an oxygen scavenger analyzer calibrated?
Calibration is performed with standard solutions of known concentration of the chemical used. Because oxygen scavenger solutions react with oxygen in the air, standards must be freshly prepared and contact with air minimized. Periodically comparing results with laboratory analysis increases the reliability of the measurement.
Is an oxygen scavenger used in every boiler water program?
No. Some power plants, particularly those with systems containing no copper alloys, apply oxidizing water chemistry programs that use no oxygen scavenger. In these programs, dissolved oxygen and cation conductivity become even more critical monitoring parameters. The program to be applied is determined by the requirements of the boiler and turbine manufacturers and the plant's metallurgy.
Products measuring this parameter
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