Quick-Pick by System
| System Type | Oxygen Scavenger | Dose Range | Max Pressure | Food-Grade |
|---|---|---|---|---|
| Low-pressure steam boiler (<15 bar) | Sodium sulfite (catalyzed) | 10–15 mg/L excess SO₃ | <15 bar | No |
| Medium-pressure boiler (15–40 bar) | Sodium sulfite or carbohydrazide | 5–10 mg/L excess SO₃ or 3–5 ppm CHZ | 40 bar | No / Yes (CHZ) |
| High-pressure boiler (40–120 bar) | Carbohydrazide or DEHA | 0.5–2 ppm active | 120 bar | DEHA (FDA) |
| Supercritical / HRSG (>120 bar) | Hydrazine or DEHA | 0.01–0.1 ppm excess N₂H₄ | Unlimited | No / Yes (DEHA) |
| Food-grade steam (direct injection) | Erythorbic acid / DEHA | 1–5 ppm | Any | Yes |
| District heating (closed loop) | Sodium sulfite or DEHA | 20–50 mg/L excess SO₃ | <25 bar | No |
| Condensate return system | DEHA or filming amine blend | 0.1–0.5 ppm DEHA | Any | Yes (DEHA) |
| Deaerator polishing (feedwater) | Catalyzed sodium sulfite | 5–10 ppm excess | Any | No |
All Grades (by chemistry class)
Sodium Sulfite — Low-Pressure Standard(1)
Sodium sulfite (Na₂SO₃) and sodium bisulfite (NaHSO₃) are the lowest-cost oxygen scavengers for boilers below 40 bar. The reaction (2Na₂SO₃ + O₂ → 2Na₂SO₄) is exothermic, fast at temperature (reaction rate doubles per 10°C increase), and complete in seconds at boiler operating temperatures. Cobalt or manganese catalysts accelerate the reaction at low temperatures (<60°C) in feedwater heater applications. The limitation: sodium sulfite adds dissolved solids (each mg/L O₂ consumed requires ~8 mg/L Na₂SO₃, producing ~12 mg/L Na₂SO₄), which restricts use above 40 bar where TDS limits are tight.
Hydrazine — High-Pressure & Supercritical(1)
Hydrazine (N₂H₄, 35–80% aqueous solution) is the traditional high-pressure boiler oxygen scavenger: N₂H₄ + O₂ → N₂ + 2H₂O. The products are only nitrogen and water — no dissolved solids added, making it ideal for supercritical and once-through boilers. Hydrazine also passivates metal surfaces by forming magnetite (Fe₃O₄) protective film. Increasingly restricted due to carcinogenicity (IARC Group 2A). New installations prefer carbohydrazide or DEHA; existing high-pressure fleet may still use hydrazine where regulatory exemptions exist.
Carbohydrazide — Hydrazine Replacement(1)
Carbohydrazide (CHZ, carbonyl dihydrazide) thermally decomposes to hydrazine above 100°C in the boiler, then reacts with oxygen: CHZ yields 2 mol N₂H₄ equivalent per molecule. Effective range: 40–200 bar. Non-carcinogenic at use concentrations, not classified as IARC Group 2A, and acceptable in most jurisdictions where hydrazine is restricted. Dose: 3–8 ppm active carbohydrazide in boiler feedwater; requires >120°C water for full thermal decomposition to activate.
DEHA — Volatile Organic, Food-Grade Compatible(1)
Diethylhydroxylamine (DEHA) is a volatile, film-forming oxygen scavenger that distributes throughout the steam-condensate system, providing both oxygen scavenging and metal surface passivation in condensate return lines where sulfite and hydrazine do not penetrate. FDA 21 CFR 173.310 approves DEHA for food-grade steam at ≤15 ppm in steam. DEHA also acts as a mild reducing agent that maintains low redox potential (ORP) in the boiler water, suppressing iron and copper corrosion.
Erythorbic Acid / Sodium Erythorbate — Natural Food-Grade(1)
Erythorbic acid (D-isoascorbic acid) and its sodium salt are FDA GRAS oxygen scavengers used in low-to-medium pressure food-grade steam systems, brewery CIP steam, and district heating where natural-origin chemistry is preferred. Reaction: C₆H₇O₆Na + ½O₂ → dehydroerythorbate + H₂O. Fully bio-degradable breakdown products. Dose 5–20 ppm in feedwater. Less cost-effective than DEHA per unit oxygen consumed but preferred where food contact requires GRAS certification.
Imported Brand → China Equivalent
Equivalents are indicative; verify against TDS for project-critical applications.
| International Brand Grade | China Equivalent | Major Chinese Producers |
|---|---|---|
| NALCO 8314 (catalyzed Na₂SO₃) | Catalyzed sodium sulfite boiler grade | 天津同德化工、济南康隆、无锡美通 |
| Kurita K-700 series (Na₂SO₃) | Sodium sulfite boiler 97%+ purity | 天津同德化工、河南博源 |
| BWT Reasil OX (carbohydrazide) | Carbohydrazide 99% active | 上海科萃、北京恒普 |
| Drew Marine Deox-O-Gon II (carbohydrazide) | Carbohydrazide technical grade | 上海科萃、天津康达 |
| Ashland Drewox 7000 (DEHA) | DEHA diethylhydroxylamine 85% | 上海科萃、北京嘉美福 |
| NALCO 77285 (DEHA boiler) | DEHA 85% technical grade | 上海科萃、天津同德 |
| Veolia Hydrex 1840 (erythorbic acid) | Sodium erythorbate food grade | 郑州瑞普、上海飞燕 |
| Ashland Drewamine (hydrazine 35%) | Hydrazine hydrate 35% boiler grade | 湖北民瑞（已受限）、天津永晟（工业级） |
Frequently Asked Questions
▶Why can't I just rely on the deaerator and skip chemical oxygen scavenging?
Mechanical deaerators achieve 7–20 ppb residual dissolved oxygen under ideal conditions — this is still above the ASME guideline of <7 ppb. During startup, load swings, or poor deaerator venting, residual O₂ spikes to 50–200 ppb. Chemical oxygen scavengers provide the polishing buffer that keeps O₂ <7 ppb regardless of deaerator performance.
Why can't I just rely on the deaerator and skip chemical oxygen scavenging?
Mechanical deaerators achieve 7–20 ppb residual dissolved oxygen under ideal conditions — this is still above the ASME guideline of <7 ppb. During startup, load swings, or poor deaerator venting, residual O₂ spikes to 50–200 ppb. Chemical oxygen scavengers provide the polishing buffer that keeps O₂ <7 ppb regardless of deaerator performance.
▶Sodium sulfite vs carbohydrazide — how do I decide?
Use sodium sulfite below 40 bar where TDS is acceptable — it's 5–8× cheaper per unit oxygen consumed. Use carbohydrazide above 40 bar where TDS limits are strict, or where steam purity requirements prohibit dissolved solids. Carbohydrazide also works at lower temperatures and produces no dissolved solids.
Sodium sulfite vs carbohydrazide — how do I decide?
Use sodium sulfite below 40 bar where TDS is acceptable — it's 5–8× cheaper per unit oxygen consumed. Use carbohydrazide above 40 bar where TDS limits are strict, or where steam purity requirements prohibit dissolved solids. Carbohydrazide also works at lower temperatures and produces no dissolved solids.
▶Is DEHA safe for food-grade steam systems?
Yes — FDA 21 CFR 173.310 approves DEHA (diethylhydroxylamine) for boiler water treatment where the steam may contact food, at ≤15 ppm in the final steam. DEHA is also approved by the EU (Regulation EC 1831/2003) and UK Food Standards. Supply with FDA compliance documentation.
Is DEHA safe for food-grade steam systems?
Yes — FDA 21 CFR 173.310 approves DEHA (diethylhydroxylamine) for boiler water treatment where the steam may contact food, at ≤15 ppm in the final steam. DEHA is also approved by the EU (Regulation EC 1831/2003) and UK Food Standards. Supply with FDA compliance documentation.
▶How do I measure residual oxygen scavenger in boiler water?
Sodium sulfite residual: titration with iodine solution (standard APHA 4500-SO₃ method) or colorimetric test kit (target 10–20 mg/L excess SO₃). DEHA and carbohydrazide: colorimetric field test kits (HACH or CHEMetrics). Hydrazine: specific colorimetric method (APHA 4500-N₂H₄).
How do I measure residual oxygen scavenger in boiler water?
Sodium sulfite residual: titration with iodine solution (standard APHA 4500-SO₃ method) or colorimetric test kit (target 10–20 mg/L excess SO₃). DEHA and carbohydrazide: colorimetric field test kits (HACH or CHEMetrics). Hydrazine: specific colorimetric method (APHA 4500-N₂H₄).
▶What is the minimum order quantity and available packaging?
Sodium sulfite: 25 kg bags, MOQ 1 ton. Hydrazine 35%: 30 kg HDPE drums (hazmat), MOQ 500 kg. Carbohydrazide: 25 kg drums, MOQ 100 kg. DEHA 85%: 25 kg or 200 kg HDPE drums, MOQ 100 kg. Erythorbic acid: 25 kg bags, MOQ 100 kg. All ship with proper hazmat classification where required.
What is the minimum order quantity and available packaging?
Sodium sulfite: 25 kg bags, MOQ 1 ton. Hydrazine 35%: 30 kg HDPE drums (hazmat), MOQ 500 kg. Carbohydrazide: 25 kg drums, MOQ 100 kg. DEHA 85%: 25 kg or 200 kg HDPE drums, MOQ 100 kg. Erythorbic acid: 25 kg bags, MOQ 100 kg. All ship with proper hazmat classification where required.