mechanical type deaeration

Mechanical Type Deaeration in Boiler Systems

Deaeration is a critical process in steam generation and boiler feedwater treatment. It ensures the removal of dissolved gases such as oxygen (O₂) and carbon dioxide (CO₂), which are highly corrosive to boiler and steam plant materials. Without proper deaeration, these gases accelerate corrosion, reduce equipment life, and compromise safe operation.  

There are two main types of deaeration: mechanical deaeration and chemical deaeration. This article focuses on the mechanical type, its working principle, and its importance in boiler systems.  

🔍 What is Mechanical Deaeration?

- Mechanical deaeration works on the principle of Henry’s Law of Physics, which states that the solubility of a gas in a liquid decreases as the temperature increases.  

- By heating water and creating conditions for gas release, mechanical deaerators strip dissolved gases from boiler feedwater.  

- Unlike chemical methods, mechanical deaeration removes gases physically rather than transforming them into neutral compounds.  

⚙️ Why is Deaeration Important?

- Oxygen Corrosion: Dissolved oxygen reacts with steel surfaces, forming oxides (rust).  

- Carbon Dioxide Corrosion: CO₂ combines with water to form carbonic acid, which attacks piping and equipment.  

- Accelerated Damage: Corrosion rates increase at higher temperatures, making untreated feedwater dangerous for boilers.  

- Economic Value: By reducing oxygen and CO₂ to safe levels, mechanical deaeration allows the use of carbon steel instead of expensive alloys in boiler construction.  

🌍 Working Principle of a Mechanical Deaerator

1. Heating the Water  

   - Feedwater is heated close to saturation temperature.  

   - As temperature rises, dissolved gases lose solubility and are released.  

2. Gas Removal  

   - Oxygen and carbon dioxide are vented out of the system.  

   - Non-condensable gases are also expelled.  

3. Storage and Distribution  

   - The deaerated water is stored in a tank and supplied to the boiler.  

   - Continuous venting ensures residual gases are kept at minimal levels.  

📊 Performance of Mechanical Deaeration

- Oxygen Removal: Mechanical deaerators can reduce dissolved oxygen to below 7 ppb (parts per billion), which meets common boiler standards.  

- Carbon Dioxide Removal:  

  - Free CO₂ is removed to non-detectable levels.  

  - Chemically bound CO₂ may remain depending on pH, but levels are typically below 5 ppm, which is acceptable for boiler operation.  

🔥 Methods of Deaeration

1. Mechanical Deaeration  

   - Removes gases physically by heating and venting.  

   - Commonly used in power plants and industrial boilers.  

2. Chemical Deaeration  

   - Uses oxygen scavengers (e.g., sodium sulphite, hydrazine) to react with dissolved oxygen.  

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

📌 Conclusion

Mechanical deaeration is a proven and highly effective method for protecting boilers and steam systems from corrosion. By reducing dissolved oxygen to <7 ppb and eliminating free CO₂, it ensures:  

- Longer equipment life  

- Safer operation  

- Reduced maintenance costs  

- Improved efficiency of steam generation  

For industries relying on steam, mechanical deaeration is not just a treatment step—it is a critical safeguard for reliability and sustainability.