Fire-tube boilers are those device in which hot gases,
which originates from the fire passes through one or more tubes within
the boiler. After three main historical forms of boilers ( low-pressure
tank or haystack boilers, tube boilers, high-pressure water-tube boilers
), fire tube boilers are manufactured. In these boilers, hot gases pass
through one or more tubes running through a sealed container of water.
According to thermal conduction, the heat energy of the gases pass away
from the sides of the tubes, resulting into the heating of water and
finally steam.They are important boilers that are available in both
horizontal and vertical configurations. They are also some times
referred as smoke-tube boiler.
Construction and usage
Usually, the tank of the boiler is cylindrical in shape. It can also be
either vertical or horizontal. Also regarded as shell boiler, smoke tube
boiler and fire pipe, fire tube boilers are highly used on all steam
locomotives in the horizontal locomotive form. Other than used as
locomotives, they are extensively used in stationary engineering fields
and producing low pressure steam like for heating of a building.
Operation
The fuel is burnt in a firebox to generate hot combustion gases. Steam
is produced by heating water along a series of fire tubes perforating
the boiler. The generated steam raises the steam dome, which also
controls the exit of steam. In regards to superheat and dry generated
steam, saturated steam is always forced into the super heater through
the larger flues at the back in the locomotive fire tube boiler. With
the help of steam directed to the turbine or cylinders, mechanical power
is induced and the exhaust gases are used to heat the feed water for
increasing boiler's efficiency.
Advantages
Fire tube boilers are perfectly used for space heating and various
industrial process applications. They are compact in size, easy to clean
and maintain. The tubes are easily replaceable and cost maintenance is
very low. They are available in wide range of sizes.
Disadvantages
- They are limited for generating high capacity steam.
- Fire tube boilers are not appropriate for very high pressure
applications.
Types of Fire tube boilers
- Cornish Boiler: This boiler has a long horizontal
cylinder with a single large flue consisting the fire.
- Lancashire boiler: Same as Cornish boiler, this has two
large flues comprising the fires.
- Scotch marine boiler: This form of boiler uses large
number of small diameter tubes. It provides greater heating surface
arena for both weight and volume.
- Locomotive boiler: It has three major constituents,
double walled firebox, horizontal and cylindrical boiler barrel
consists with small flue tubes and smoke box provided with chimney
for exhaust gases. They are vastly used in traction engines, steam
rollers, portable engines and some other steam road vehicles.
