Fire Tube Boiler: Construction, Working, Types

 

Fire Tube boiler is the simplest form of the internal furnace, vertical fire tube boiler. Fire tube boilers are a portable boiler and it requires a small floor space.

The steam rating in fire tube boilers doesn’t exceed 2500 kg per hour and pressure is limited to 10 bars.

Construction:

• Fire tube boiler consists of a vertical, cylindrical shell, equipped with a fire box in the bottom, water space in the middle portion and steam space in the upper portion. The fire grate is placed at the bottom of the fire box and coal is fired at the fire box. An ash pit is located at the bottom of the grate to collect the ash of burnt coal, which is periodically removed.
• One or more cross tubes are either flanged or riveted to the water space are located in the fire box to increase the heating surface area to improve the water circulation. A short chimney is connected at the top of the fire box to discharge the waste flue exhaust gases at some greater height. Manhole and hand holes are provided for cleaning the interior of the boiler shell and cross tubes.
• The boiler consists of a pressure gauge, water level indicator, safety valve, steam stop valve and a manhole as mountings to provide safety and ease of working.

Working:

Fuel burns on the grate in the fire box. The resulting hot flue gases are allowed to pass around the cross tubes. The water surrounding the cylindrical fire box also receives heat by convection and radiation. Thus steam is produced. The water circulation in the boiler depends on the density difference in water, created by the temperature difference in water.

Types of Fire Tube Boilers:

1. Cornish boiler
2. Lancashire boiler
3. Locomotive boiler
4. Scotch marine boiler
5. Admiralty-type direct tube boiler
6. Horizontal return tubular boiler
7. Immersion fired boiler
8. Vertical fire-tube boiler