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Watertube Boiler. Content. Introduction Watertube boiler construction Steam generation process Watertube boiler classification Raising steam. Introduction. Boiler = a closed pressure vessel in which feed water is heated in order to produce steam Watertube boiler Firetube boiler.
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Content Introduction Watertube boiler construction Steam generation process Watertube boiler classification Raising steam
Introduction Boiler = a closed pressure vessel in which feed water is heated in order to produce steam Watertube boiler Firetube boiler
Introduction Watertube boiler is a type of boiler in which water circulates in tubes heated externally by the fire.
Watertubeboilerconstruction • Smoke uptake • Economisera heat exchanger that transfers heat from boiler flue gases to boiler feedwater • Steam outletsaturated steam from the steam drum to the superheater
Watertubeboilerconstruction • Cyclonea device inside the drum that is used to prevent water and solids from passing over with the steam outlet • Stay tubefor superheater • Staysfor superheater tubes • Superheated steam outlet
Watertubeboilerconstruction • Superheatera bank of tubes, in the exhaust gas duct after the boiler, used to heat the steam above the saturation temperature • Superheater headersdistribution and collecting boxes for the superheater tubes • Water Drum • Burner
Watertubeboilerconstruction • Waterwall headerdistribution box for waterwall and downcomers • Footing • Waterwalltubes welded together to form a wall • Waterwall headerdistribution box for waterwall and downcomers
Watertubeboilerconstruction • Back side waterwall • Boiler hood • Waterwall headercollecting box for waterwall and risers • Riserthe water-steam emulsion rises in these tubes toward the steam drum
Watertubeboilerconstruction • Downcomera 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 Drumseparates the steam from the water
Watertubeboilerconstruction • Economiser headerdistribution box for the economizer tubes
Steamgenerationprocess • furnace or combustion chamber • air is supplied to the boiler furnace - to enable combustion of fuel to take place
Steamgenerationprocess • 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
Steamgenerationprocess • feed water circulates from the water drum to the steam drum and is heated in the process
Steamgenerationprocess • 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
Steamgenerationprocess • 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
Steamgenerationprocess • 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
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.
Watertubeboiler 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
Watertubeboiler 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
Watertubeboilerclassification 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.
Watertubeboilerclassification Classification according to: types • Tube inclination • Arrangement of gas flow • horizontal - vertical • single-flow b., double-flow b.
Raisingsteam 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
Raisingsteam 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
Raisingsteam 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
Raisingsteam 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
Raisingsteam 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
Raisingsteam 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
