Boiler Deaerator

Deaeration Process in Boilers:

Importance, Types, and Working Principle

Boiler feedwater quality is one of the most critical factors influencing the efficiency, safety, and longevity of steam-generating equipment. Among the various treatment processes, deaeration plays a vital role in protecting boilers from corrosion and ensuring reliable operation.  

🔍 What is Deaeration?

Deaeration is the process of removing oxygen (O₂), carbon dioxide (CO₂), and other non-condensable gases from boiler feedwater. These gases, if left untreated, cause severe corrosion in boiler pressure parts, piping, and steam plant equipment.  

- Oxygen reacts with steel surfaces, forming oxides (rust).  

- Carbon dioxide combines with water to form carbonic acid, which accelerates corrosion.  

- The rate of corrosion increases with higher temperatures, making untreated feedwater highly damaging.  

By removing these gases, deaeration ensures:  

- Longer equipment life  

- Reduced maintenance costs  

- Safer and more efficient boiler operation  

⚙️ Types of Deaeration

There are two main types of deaeration:  

1. Mechanical Deaeration

- Works on the principle of Henry’s Law of Physics, which states that the solubility of gases in a liquid decreases as temperature increases.  

- Feedwater is heated close to saturation temperature, causing dissolved gases to lose solubility and be vented out.  

- Mechanical deaerators are designed to:  

  - Remove oxygen to 0.005 cc/l (7 ppb) or less.  

  - Remove carbon dioxide to a non-detectable level.  

  - Operate effectively across all load conditions (0–100% of rated capacity).  

- Capacity Requirement: The deaerator capacity must exceed the steam system demand and provide at least 10 minutes of storage capacity to the overflow.  

2. Chemical Deaeration

- Uses oxygen scavengers (e.g., sodium sulfite, hydrazine, or modern alternatives) to chemically react with dissolved oxygen.  

- Chemicals can also neutralize carbon dioxide.  

- Often used as a backup or in systems where mechanical deaeration is not feasible.  

- Provides additional protection when mechanical deaeration alone cannot achieve desired oxygen levels.  

🌍 Working Principle of a Deaerator

The primary purpose of a deaerator is to reduce dissolved oxygen and carbon dioxide to levels that eliminate their corrosive potential under boiler operating conditions.  

Process Steps:  

1. Heating: Feedwater is heated close to saturation temperature using steam.  

2. Gas Release: As temperature rises, dissolved gases lose solubility and are released.  

3. Ventilation: Non-condensable gases are vented out of the system.  

4. Storage: Deaerated water is stored in a tank and supplied to the boiler.  

By maintaining low oxygen levels, industries can use carbon steel instead of expensive alloys for boiler construction, offering significant economic value.  

📊 Benefits of Deaeration

- Corrosion Prevention: Protects boiler tubes, drums, and piping.  

- Efficiency Improvement: Ensures better heat transfer and reduces maintenance downtime.  

- Safety: Prevents equipment failures caused by corrosion-related leaks or ruptures.  

- Cost Savings: Reduces chemical treatment needs and prolongs equipment life.  

📌 Conclusion

The deaeration process is indispensable in boiler feedwater treatment. By removing oxygen and carbon dioxide, it safeguards equipment, improves efficiency, and reduces operating costs.  

- Mechanical deaeration ensures precise removal of gases using Henry’s Law.  

- Chemical deaeration provides additional protection when mechanical methods are insufficient.  

- Together, these processes ensure reliable, safe, and economical boiler operation.  

For industries relying on steam, investing in a properly designed deaerator is not just a technical requirement—it is a strategic choice for sustainability and long-term performance.