1. Watertube Boiler

2. Content Introduction Watertube boiler construction
Steam generation process
Watertube boiler classification
Raising steam

3. Introduction
Boiler = a closed pressure vessel in which feed water is heated in order to produce steam
Watertube boiler
Firetube boiler

4. Introduction
Watertube boiler is a type of boiler in which water circulates in tubes heated externally by the fire.

5. Watertube boiler construction

6. Watertube boiler construction
Smoke uptake
Economiser a heat exchanger that transfers heat from boiler flue gases to boiler feedwater
Steam outlet saturated steam from the steam drum to the superheater

7. Watertube boiler construction
Cyclone a device inside the drum that is used to prevent water and solids from passing over with the steam outlet
Stay tube for superheater
Stays for superheater tubes
Superheated steam outlet

8. Watertube boiler construction
Superheater a bank of tubes, in the exhaust gas duct after the boiler, used to heat the steam above the saturation temperature
Superheater headers distribution and collecting boxes for the superheater tubes
Water Drum
Burner

9. Watertube boiler construction
Waterwall header distribution box for waterwall and downcomers
Footing
Waterwall tubes welded together to form a wall

10. Watertube boiler construction
Back side waterwall
Boiler hood
Waterwall header collecting box for waterwall and risers
Riser the water-steam emulsion rises in these tubes toward the steam drum

11. Watertube boiler construction
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
Steam Drum separates the steam from the water

12. Watertube boiler construction
Economiser header distribution box for the economizer tubes

13. Steam generation process
furnace or combustion chamber
air is supplied to the boiler furnace - to enable combustion of fuel to take place

14. Steam generation process
burning of fuel (LNG, liquid fuels, etc.) to release its energy - heat is developed
the energy released by the burning fuel in the boiler furnace is stored (as temp. and pressure) in the steam produced

15. Steam generation process
feed water circulates from the water drum to the steam drum and is heated in the process

16. Natural water circulation

17. Steam generation process
some of the feed water passes through tubes surrounding the furnace, i.e. waterwall and floor tubes, where it is heated and returned to the steam drum

18. Steam generation process
steam is further heated and 'dried‘ (i.e. all traces of water are converted into steam) in the superheater
temperature of superheated steam will be above that of steam in the drum

19. Steam generation process
an 'attemperator', i.e. a steam cooler, may be fitted in the system to control the superheated steam temperature
superheated steam then leaves the boiler for use in system

20. Application
Where main propulsion is steam powered, one or more large watertube boilers will be fitted to produce steam at very high temperatures and pressures.
On a vessel with diesel propulsion, a smaller (usually firetube type) boiler may be fitted to provide steam for additional ship services.

21. Watertube boiler
uses small diameter tubes, has a small steam drum, enables the generation or production of steam at high temperatures and pressures
weight of the boiler is much less than an equivalent firetube boiler
steam raising and steam generation process is much quicker

22. Watertube boiler design arrangements are flexible, efficiency is high
the design facilitates good natural circulation of feed water
these are some of the many reasons why the watertube boiler has replaced the firetube boiler as the major steam producer

23. Watertube boiler classification
Classification according to:
types
Application
Pressure
Number of drums
main boiler – auxiliary boiler (donkey boiler)
low-pressure b. , intermediate-pressure b. , high-pressure b.
single-drum b., two- drum b., three-drum b.

24. Watertube boiler classification
Classification according to:
types
Tube inclination
Arrangement of gas flow
horizontal - vertical
single-flow b., double-flow b.

25. Raising steam
the forced draught fan should be started and air passed through the furnace for several minutes to 'purge' it of any exhaust gas or oil vapours
the air slides (checks) at every register, except the 'lighting up' burner, should then be closed

26. Raising steam
the operating burner can now be lit and adjusted to provide a low firing rate with good combustion
the fuel oil pressure and forced draught pressure should be matched to ensure good combustion with a full steady flame

27. Raising steam
the superheater header drains may be closed once steam issues from them
the boiler must be brought slowly up to working pressure in order to ensure gradual expansion and to avoid overheating the superheater elements and damaging any material

28. Raising steam
the main and auxiliary steam lines should now be warmed through then the drains closed
the water level gauges should be blown through and checked for correct reading

29. Raising steam
when the steam pressure is about 300kN/m2 (3 bar) below the normal operating value the safety valves should be lifted and released using the easing gear
once at operating pressure, the boiler may be put on load and the superheater circulating valves closed

30. Raising steam
all other vents, drains and bypasses should then be closed
the water level in the boiler should be carefully checked and the automatic water regulating arrangements observed for correct operation