Water tube boiler is a form of boiler in which water
rotates and circulates in tubes heated externally by the fire. Used as
high pressure boilers, fuel is burned inside the furnace producing hot
gas which heats up the water in steam generating tubes. Sometimes, water
tube boilers are also regarded as steam generating units.
Operation
The heated water is sent into the steam drum where saturated steam is
drawn off at the top of drum. Though water droplets can cause damage to
the turbine blades, thus steam is superheated to about 730°F
(390°C) or higher than that. From the bottom of steam drum,
cool water is returned to the feed water drum through large bore down
comer tubes. The exhaust gases are used to pre heat the air blown into
the furnace and warm the feed water supply.
Water tube boiler vs fire tube boiler
Fire tube boiler has a much weaker structure, usually used for
pressures above than 350 psi (2.4 MPa). Whereas water tube boiler has
advantages over them. There are less chances of catastrophic failure in
water tube boilers as compared with fire tube boilers.
Types of water tube boilers
- D-type Boiler:Applicable in both stationary and marine
applications, this is the most common form of small-medium sized
boiler. The boiler has large steam drum vertically attached to a
smaller water drum via multiple steam-generating tubes.
- Low Water Content: Termed as "furnace-less"
boiler, this has a lower and upper header linked by water tubes that
are directly impinged upon from the burner. This boiler can generate
steam and react to load changes quickly.
- Babcock & Wilcox Boiler:This boiler has a single
drum, with feed water drawn from the source of the drum into a
header that supplies inclined water-tubes. The water tubes produce
steam back into the top of the drum.
- Stirling Boiler:Mainly used as stationery boiler, this
boiler has three upper drums connected to two lower drums by water
tubes.
- Thornycroft Boiler:This is a single steam boiler,
comprised with two sets of water tubes at either side of the
furnace.
- Yarrow Boiler: This boiler has three drums in a delta
formation linked by water tubes, allowing for easy tube-cleaning.
- White-Forster: Similar to yarrow boiler, this boiler has
tubes which are curved in shape.
Applications
Widely used in versatile applications like as follows:
- Land-based: Water tube boilers are vastly used for power
generation and have the ability to work under high pressure and
temperature conditions.
- Marine: High pressure water tube boilers are highly
workable in marine boilers.
- Railway locomotives: They are exclusively used in varied
railway locomotives.
