6Watertube boiler construction Smoke uptakeEconomiser a heat exchanger that transfers heat from boiler flue gases to boiler feedwaterSteam outlet saturated steam from the steam drum to the superheater
7Watertube boiler construction Cyclone a device inside the drum that is used to prevent water and solids from passing over with the steam outletStay tube for superheaterStays for superheater tubesSuperheated steam outlet
8Watertube boiler construction Superheater a bank of tubes, in the exhaust gas duct after the boiler, used to heat the steam above the saturation temperatureSuperheater headers distribution and collecting boxes for the superheater tubesWater DrumBurner
9Watertube boiler construction Waterwall header distribution box for waterwall and downcomersFootingWaterwall tubes welded together to form a wall
10Watertube boiler construction Back side waterwallBoiler hoodWaterwall header collecting box for waterwall and risersRiser the water-steam emulsion rises in these tubes toward the steam drum
11Watertube 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 tubesSteam Drum separates the steam from the water
12Watertube boiler construction Economiser header distribution box for the economizer tubes
13Steam generation process furnace or combustion chamberair is supplied to the boiler furnace - to enable combustion of fuel to take place
14Steam generation process burning of fuel (LNG, liquid fuels, etc.) to release its energy - heat is developedthe energy released by the burning fuel in the boiler furnace is stored (as temp. and pressure) in the steam produced
15Steam generation process feed water circulates from the water drum to the steam drum and is heated in the process
17Steam 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
18Steam generation process steam is further heated and 'dried‘ (i.e. all traces of water are converted into steam) in the superheatertemperature of superheated steam will be above that of steam in the drum
19Steam generation process an 'attemperator', i.e. a steam cooler, may be fitted in the system to control the superheated steam temperaturesuperheated steam then leaves the boiler for use in system
20ApplicationWhere 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.
21Watertube boileruses small diameter tubes, has a small steam drum, enables the generation or production of steam at high temperatures and pressuresweight of the boiler is much less than an equivalent firetube boilersteam raising and steam generation process is much quicker
22Watertube boiler design arrangements are flexible, efficiency is high the design facilitates good natural circulation of feed waterthese are some of the many reasons why the watertube boiler has replaced the firetube boiler as the major steam producer
23Watertube boiler classification Classification according to:typesApplicationPressureNumber of drumsmain boiler – auxiliary boiler (donkey boiler)low-pressure b. , intermediate-pressure b. , high-pressure b.single-drum b., two- drum b., three-drum b.
24Watertube boiler classification Classification according to:typesTube inclinationArrangement of gas flowhorizontal - verticalsingle-flow b., double-flow b.
25Raising steamthe forced draught fan should be started and air passed through the furnace for several minutes to 'purge' it of any exhaust gas or oil vapoursthe air slides (checks) at every register, except the 'lighting up' burner, should then be closed
26Raising steamthe operating burner can now be lit and adjusted to provide a low firing rate with good combustionthe fuel oil pressure and forced draught pressure should be matched to ensure good combustion with a full steady flame
27Raising steamthe superheater header drains may be closed once steam issues from themthe 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
28Raising steamthe main and auxiliary steam lines should now be warmed through then the drains closedthe water level gauges should be blown through and checked for correct reading
29Raising steamwhen 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 gearonce at operating pressure, the boiler may be put on load and the superheater circulating valves closed
30Raising steamall other vents, drains and bypasses should then be closedthe water level in the boiler should be carefully checked and the automatic water regulating arrangements observed for correct operation