Fire Tube Boiler

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.
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• Lancashire boiler: Same as Cornish boiler, this has two large flues comprising the fires.
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• 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.
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• 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.