How to Use DEHA (Diethylhydroxylamine) as a Boiler Oxygen Scavenger

Overview

Diethylhydroxylamine (DEHA, CAS 3710-84-7) is a volatile organic oxygen scavenger widely used in medium-pressure boiler feedwater systems (40–100 bar) and steam condensate return lines. Unlike sodium sulfite, DEHA adds zero dissolved solids (TDS) to boiler water because its reaction products are volatile: DEHA + O₂ → diethylnitrone + water. This makes DEHA ideal for higher-pressure boilers where tight TDS limits apply.

Beyond simple oxygen scavenging, DEHA functions as a filming amine and metal passivator. It adsorbs onto iron and copper surfaces throughout the steam-condensate circuit, forming a monomolecular protective film that suppresses flow-accelerated corrosion (FAC) and reduces condensate iron pickup. This dual action distinguishes DEHA from inorganic scavengers and makes it particularly effective in systems with extensive copper alloy heat exchangers.

DEHA is also approved for use in food-contact steam (indirect food processing) under NSF/ANSI 60 and FDA 21 CFR 173.310 guidelines, provided residual levels are within limits.

Reaction summary: 4(C₂H₅)₂NOH + 9O₂ → 8CO₂ + 10H₂O + 2N₂ (complete oxidation pathway). At boiler temperatures, DEHA is fully volatile and carries no residual solids to the steam drum.

Preparation & Dissolution

DEHA is supplied as an 85% active liquid — it does not require dissolution. However, neat DEHA should always be diluted before injection for accurate dosing pump control.

Recommended working solution: 5–10% DEHA in deaerated or demineralized water.

1. Add the required volume of neat DEHA (85%) to a clean HDPE or stainless steel dosing tank
2. Dilute with demineralized water to the target concentration (5–10%)
3. Mix briefly — DEHA is fully miscible with water
4. Do not use carbon steel tanks (DEHA will pick up iron contamination)
5. Prepare fresh solution every 2–4 weeks; store tank sealed to minimize atmospheric oxygen absorption
6. Label the tank clearly with concentration, date, and product name

Safety during preparation: DEHA is mildly alkaline (pH 10.5–11.5 at 1%) and has a faint amine odor. Work in a ventilated area. Wear chemical-resistant gloves and safety glasses. Avoid skin contact.

Dosing Guide

Application	DEHA Dose	Residual Target	Notes
Low-pressure boilers (< 40 bar)	0.2–0.5 mg/L feedwater	0.05–0.1 mg/L boiler water	Consider sodium sulfite as more economical
Medium-pressure boilers (40–100 bar)	0.5–1.5 mg/L feedwater	0.05–0.2 mg/L boiler water	DEHA preferred — no TDS addition
High-pressure boilers (> 100 bar)	Not typically recommended	—	Use carbohydrazide or hydrazine above 100 bar
Condensate return protection	0.05–0.2 mg/L	0.02–0.1 mg/L condensate	Film-forming action protects return lines
Layup (wet)	5–10 mg/L	2–5 mg/L in layup water	Inhibits oxygen pitting during shutdown
Food-contact steam (21 CFR 173.310)	≤ 2 mg/kg steam condensate	Regulatory limit	Do not exceed FDA-permitted level

Stoichiometry: 0.55 mg DEHA theoretically scavenges 1 mg O₂ dissolved oxygen, but in practice dose at 3–5x stoichiometric to achieve the necessary residual and filming effect.

Application Procedure

1. Verify deaerator performance first — measure feedwater dissolved oxygen at deaerator outlet. Target < 7 ppb before DEHA injection. Chemical scavenging is the secondary defense.
2. Set injection point immediately downstream of the deaerator and upstream of the feed pump — this maximizes contact time in the feedwater system.
3. Commission a stainless steel or HDPE metering pump rated for precise low-flow delivery (peristaltic pumps work well).
4. Start DEHA injection at the lower end of the dose range and test residual in boiler water after 24 hours of steady operation.
5. Adjust pump stroke to achieve the target boiler water residual (0.05–0.2 mg/L for medium pressure).
6. For condensate system protection, consider a second smaller injection point at the condensate return header if the steam system is large.
7. Monitor condensate iron levels weekly — declining iron indicates the protective film is establishing.
8. During boiler layup, increase DEHA dose to 5–10 mg/L to protect surfaces during shutdown.

Monitoring & Control

Parameter	Frequency	Target	Method
Dissolved O₂ (deaerator outlet)	Daily	< 7 ppb	Inline DO sensor or Orbisphere
DEHA residual (boiler water)	2x weekly	0.05–0.2 mg/L	Colorimetric test kit (ferricyanide method)
DEHA residual (condensate)	Weekly	0.02–0.1 mg/L	Colorimetric test kit
Iron in feedwater	Weekly	< 50 ppb	ICP-OES or colorimetric
Copper in condensate (if Cu alloys present)	Weekly	< 10 ppb	ICP-OES
Boiler water conductivity	Daily	Per OEM limits	Inline conductivity meter
Condensate pH	Weekly	8.5–9.5	pH meter

Common Mistakes

• Injecting neat DEHA without dilution: Concentrated DEHA at 85% can cause dosing pump cavitation and inaccurate flow control. Always dilute to a working solution of 5–10% before injection.
• Treating DEHA as a direct drop-in for sodium sulfite at equal mass dose: DEHA and sodium sulfite have very different stoichiometries and residual test methods. Recalculate dose from scratch when switching products; do not rely on the old sodium sulfite pump settings.
• Neglecting the deaerator: DEHA is not designed to handle more than ~20–30 ppb dissolved oxygen. If the deaerator is underperforming and passing 50–100 ppb O₂, no dose of DEHA will protect the system adequately. Troubleshoot the deaerator first.
• Using DEHA in very high-pressure boilers (> 100 bar): At pressures above 100 bar, carbohydrazide or hydrazine provide more reliable and well-documented performance. DEHA's reaction kinetics at extreme conditions are less well characterized. Consult OEM guidelines.
• Monitoring boiler water only and ignoring condensate: DEHA's primary advantage is condensate protection via filming. If you are not measuring DEHA residual and iron levels in the condensate, you are missing the most important performance indicator.

Storage & Handling

• Shelf life: 12 months from manufacture date in sealed drums
• Temperature: Store at 5–35°C. Freezing at < 0°C may occur with dilute solutions. Do not allow product to freeze.
• Container: Original 200 kg HDPE drums. Do not transfer to carbon steel containers.
• Safety: DEHA is combustible (flash point ~75°C). Mild irritant to eyes and skin. Wear nitrile gloves, safety glasses, and ensure area ventilation. No specific hazardous decomposition products under normal storage. SDS must be available at point of use.
• Spill response: Dilute with water and collect. DEHA is biodegradable — dilute spills to municipal drain. Do not allow concentrated spills to enter waterways.