Water tube boilers

A water tube steam boiler consists of a large number of closely spaced water tubes connected to one or more drums, which act as water pockets and steam separators, giving rapid water circulation and quick steaming.
On their way to the funnel the flue gases from the boiler pass a superheater and an economizer. In many marine boilers an air preheater is installed after the economizer, to preheat the combustion air before it is blown into the boilers' furnaces.
Other types of water tube boilers are Babcock & Wilcox, Eckrohr and Yarrow boilers.

1. Smoke uptake
   
2. Economizer
   A heat exchanger that transfers heat from Boiler Flue Gases to Boiler Feedwater.
3. Steam Outlet
   Saturated steam from the Steam Drum to the Superheater
4. Cyclone
   A device inside the drum that is used to prevent water and solids from passing over with the steamoutlet.
5. Stay tube
   for superheater
6. Stays
   for superheater tubes
7. Superheated steam outlet
   
8. Superheater
   A bank of tubes, in the exhaust gas duct after the boiler, used to heat the steam above the saturation temperature.
9. Superheater Headers
   Distribution and collecting boxes for the superheater tubes.
10. Water Drum
    
11. Burner
    
12. Waterwall Header
    Distribution box for Waterwall and downcomers.
13. Foting
    
14. Waterwall
    Tubes welded together to form a wall.
15. Waterwall Header
    Distribution box for Waterwall and downcomers.
16. Back side Waterwall
    
17. Boiler hood
    
18. Waterwall Header
    Collecting box for Waterwall and risers.
19. Riser
    The water-steam emulsion rises in these tubes toward the steamdrum.
20. Downcomer
    A tube through which water flows downward. These tubes are normally not heated, and the boiler water flows through them to supply the generating tubes.
21. Steam Drum
    Separates the steam from the water.
22. Economizer Header
    Distribution box for the economizer tubes.