An oxygen scavenger is a chemical used to bind residual dissolved oxygen after mechanical deaeration in a boiler system. It does not replace a deaerator, correction of air ingress, or representative sampling. Active chemistry, dosage, injection point, and residual target depend on pressure, temperature, reaction time, steam use, metallurgy, and the plant programme.
PT Beta Pramesti Asia supplies boiler oxygen scavengers within its BETAGARD programme. Their role is chemical polishing of residual oxygen before feedwater reaches vulnerable piping, economisers, and boiler surfaces.
How Oxygen Scavenger Works
An oxygen scavenger reacts with dissolved oxygen and forms oxidation products determined by its active chemistry. Reaction and decomposition products may affect total dissolved solids, steam purity, condensate, or a process using the steam, so “oxygen scavenger” is not a complete product specification.
For sodium sulfite, the simplified reaction is:
2 Na₂SO₃ + O₂ → 2 Na₂SO₄
The Veolia Water Handbook gives a stoichiometric requirement of 7.88 mg pure sodium sulfite per 1 mg dissolved oxygen. Actual demand is higher because of product strength, reserve residual, contact time, temperature, pH, side reactions, blowdown, and handling loss. Use 7.88 as a mass-balance check, not a pump setpoint.
Illustrative example: feedwater flow is 100 m³/h and dissolved oxygen (DO) after the deaerator is 0.010 mg/L. Oxygen load is 100,000 L/h × 0.010 mg/L = 1,000 mg/h, or 1.0 g/h. Theoretical pure sodium sulfite is 1.0 × 7.88 = 7.88 g/h. If a solution were confirmed at 20% active, the theoretical equivalent would be 7.88 ÷ 0.20 = 39.4 g/h before reserve and other demand. The 0.010 mg/L and 20% figures are examples, not BETAGARD specifications or recommendations.
| Selection boundary | Question to answer | Programme implication |
|---|---|---|
| Mechanical deaeration | Are deaerator temperature, pressure, steam distribution, venting, and level at design condition? | Correct the deaerator first; chemical overfeed cannot repair poor gas stripping |
| Scavenger chemistry | Are pressure, steam end use, attemperation, metallurgy, TDS, and decomposition products compatible? | Sulfite, organic/volatile products, and other programmes are not interchangeable on price alone |
| Injection point | Is there contact time before the economiser, with no path that prohibits solids or treatment chemicals? | Verify the P&ID, residence time, pump pressure, and current product technical data sheet and SDS |
| Measurement | Are DO and residual taken at a consistent point, method, flow, temperature, and verified instrument? | Hold dose changes when sample quality has not passed review |
| Corrosion evidence | Do pitting, iron/copper, pH, deposits, and shutdown condition support oxygen attack? | Do not explain all corrosion from one DO or residual result |
The DOE Energy Efficiency Handbook treats the deaerator as the primary oxygen-removal device and the scavenger as control for trace oxygen. It also cautions that alternate scavenger selection for higher-pressure service should be made by qualified personnel and evaluated under operating procedures.
Sample Quality Controls the Decision
Low-level DO is easily biased by air entering tubing, fittings, or the sample cell. Use a closed, continuously flowing sample path as required by the instrument and OEM, remove bubbles, stabilise flow and temperature, verify calibration, and record boiler load. Do not pour a sample into an open beaker for trace-DO measurement.
Scavenger residual is also not stand-alone proof. Interpret it with post-deaerator DO, tank use, pump output, pH, iron/copper, and pitting inspection. Mark changes in instrument, reagent, sample point, or timing on the trend.
Importance of Oxygen Scavenger in Industry
Oxygen control matters because pitting can concentrate in feedwater lines, economisers, and boilers. Programme acceptance must nevertheless separate mechanical performance, chemical delivery, sample quality, and corrosion evidence.
| Data pattern | First hypothesis | Action before changing dose |
|---|---|---|
| DO after the deaerator is high or unstable | Venting/steam distribution, temperature, pressure, load swing, or air ingress | Verify deaerator operation and the sample system; correct the oxygen source |
| DO is stable, residual is low, product use rises | Solution strength, pump output, injection quill/check valve, contaminant demand, or test method | Run a calibration drawdown and repeat the test with verified reagent/method |
| DO is low and residual is well above the control envelope | Overfeed or an unrepresentative residual sample | Do not increase dose; confirm the result and assess a controlled reduction |
| DO/residual appear normal while iron or pitting worsens | Air ingress elsewhere, pH/condensate issue, deposit, shutdown, or another corrosion mechanism | Broaden the inspection; do not declare scavenger failure without damage location and pattern |
| Pump setting agrees but tank drawdown does not | Siphoning, leakage, backpressure, pulsation, density/strength, or fill records | Reconcile mass or volume over the same period and repair the feed system |
Commissioning and acceptance checklist:
- document the P&ID, pressure, flow, temperature, makeup, condensate return, steam use, and attemperation;
- establish injection and sample points that provide relevant reaction time;
- verify pump output by drawdown or weighing at operating backpressure;
- baseline DO, residual, pH, conductivity/TDS, iron/copper, and inspection findings;
- define control and action limits, hold/stop conditions, and change authority;
- reconcile product use with flow and inventory movement; and
- review trends at comparable load, including startup, shutdown, and lay-up.
Selection, storage, PPE, spill response, and disposal must follow the current product SDS and plant procedure. For materials classified as hazardous in Indonesia, consult Government Regulation No. 74 of 2001 on hazardous and toxic materials; it does not set an oxygen-scavenger dose.
Conclusion
An oxygen scavenger is a polishing step after deaeration, not a universal answer to boiler corrosion. Select chemistry from pressure, feedwater temperature, steam use, metallurgy, total dissolved solids, residence time, and the current product technical data sheet and SDS; accept the programme through DO, residual, consumption, iron/copper, and inspection trends.
For the whole cycle, review the industrial boiler chemical programme. If delivery rather than chemistry is failing, Watermart dosing pumps are the relevant equipment handoff; capacity at backpressure, wetted materials, turndown, pulsation, and interlocks must suit the product and injection point.
Contact Us
Send boiler pressure and capacity, feedwater flow, deaerator outlet temperature, DO, makeup and condensate return, pH, conductivity/TDS, iron/copper, steam use, injection point, pump output, residual, pitting history, and shutdown condition through the Beta Pramesti Asia contact page. Beta can review the mechanical-versus-chemical boundary before selecting BETAGARD and a trial plan.
Technical sources: DOE Energy Efficiency Handbook—oxygen removal and scavengers; DOE Steam Tip Sheet No. 18—Deaerators; Veolia Water Handbook—Preboiler and Boiler Corrosion Control; and Indonesia Government Regulation No. 74 of 2001.