Power plant boiler steam drum

What is boiler steam drum?

 

Boiler steam drum is a cylindrical pressure vessel of natural circulation water-tube boiler. A boiler may have different numbers of drum: single, double (bi drum boiler) or three. Steam drum provides a storage for water/steam at the upper end of water wall. Moreover, it plays as phase separator for mixed water/steam. Steam quality is improved to the highest level by process like chemical dosing, continuous blowdown, demisting, etc.

 

 

Functions of steam drum

 

1. It is the connection center for heating, evaporation, superheating of water. It connects with riser and downcomer of water cooled membrane wall to form the natural circulation. Boiler drum receives water from economizer and riser, and gives saturated steam to superheater.
2. Boiler drum has a reservoir of water and steam. It has considerable heat & mass storage function. When working condition changes, it provides a buffer for pressure fluctuation.
3. Saturataed steam dryness. Inside boiler drum, cyclone steam seaprator and chevron vanes are equipped to prevent carryover of mist in steam.
4. Chemical dosing to prevent scaling and corrosion.
5. Continuous surface blowdown to avoid concentration of impurities during continuing evaporation of steam.
6. Emergency discharge. Drain pipe could lower water level to ensure safety.
7. Pressure gauge, level meter, safety valve, emergency relief is equipped to ensure safe operation.

 

Steam drum internals

 

A steam drum has quite complex structures inside. See as below pictures.

 

 

 

Steam drum necessary parts

 

It should have the following components like:

 

• Feedwater inlet pipe from economizer.
• Saturated steam outlet pipe.
• Downcomer/riser pipe.
• Continuous blowdown pipe.
• Chemical dosing pipe.
• Orifice plate for uniform distribution of steam.
• Cyclone separator.
• Cheveron separator.
• Level gauge/transmitter.
• Pressure transmitter.
• Emergency discharge valve.
• Safety valve.