Rotating film deaerator

Function

 

To ensure thermal power plant safety, reliability and economical efficiency, boiler feedwater deaeration is an important process in water treatment. Dissolved oxygen is the major material that causes corrosion for boiler. And corrosion product FeO would deposit on boiler tubes and form scales, which inhibit heat transfer. Rotating film deaerator is thermal deaeration product for oxygen removal along with other gases. It is featured with high oxygen removal, wide adaptability, good stability, high thermal efficiency, etc.

 

Deaerator working principle:

 

Thermal deaerator design is based on Henry’s Law and Dalton’s Law. According to these laws, following requirement must be met with to achieve satisfying oxygen removal.

 

1. Heat transfer coefficient, steam/water contact area, temperature difference as big as enough.
2. Mass transfer area & unbalanced differential pressure as big as enough.
3. In time removal of non-condensable gases.

 

Rotating film deaerator consists of a head, where most of the deaeration happens, and a tank, which has storage and buffer function. Condensate water and makeup water enters film tube through small holes on it under differential pressure caused by water level, and forms jet flow. As film tube inside is filled with rising steam, rotating water film will entrain steam around it. This would result in a strong mixing & heating in a short travel in a very short time. Heated water film keeps moving downward along with film tube in helical path, and forms swirling film skirt. Water in turbulence is optimal for heat & mass transfer. Water is heated to saturation temperature. Oxygen is released and gets discharged together with rising steam through vent. Spray type deaerator or tray type deaerator could release oxygen, but part of the oxygen is brought back to water tank due to downward spraying water. This is the reason why deaeration performance is not good enough. 90% of oxygen is released during this stage.

 

Then water is distributed onto packings. Water flows along packing surface in a thin film counter-current to steam flow. During this stage, water has enough retention time to exchange heat with superheated steam. Residual oxygen is furtherly released. Finally, oxygen content in feed water for low pressure boiler could reach <15μg/l. and for high pressure boiler, it could reach <7μg/l.

 

Advantages of rotating film deaerator:

 

1. Wide adaptability. Overload operation within short period is available. Stable operation when water temperature is low.
2. Small exhaust steam.
3. High oxygen removal efficiency, stable oxygen removal performance.
4. Reliable operation, convenient maintenance.
5. Atmospheric deaerator or pressurized deaerator for choice.
6. Suitable for constant & sliding pressure oepartion