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

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

Watertube boiler construction

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

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

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

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

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

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

Watertube boiler construction Economiser header distribution box for the economizer tubes

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

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

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

Natural water circulation

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

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

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

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.

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

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

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.

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

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

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

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

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

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

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