Fire Tube/Smoke Tube Boiler:
Hot gases (products of combustion) pass through tubes, running through a sealed container of water i,e (hot gases- inside the tubes and water- outside the tubes).Also called as smoke tube boiler.
> Operating pressure - limited to 16 bar.
> Steam generation rate is lower.
> Generally, internally fired.
> Operating cost is low.
> Bursting risk is less. Efficiency is upto 75%.
> Best Examples are: Cochran boiler, Lancashire boiler, Scotch boiler etc.
Water Tube Boiler:
Water tube boilers are 2nd generation boilers with modification in the construction and working principle of the smoke tube boiler. Water circulates in tubes and is heated externally by hot gases. Fuel is burned inside the furnace. i.e (hot gases- outside the tubes and water- inside the tubes).
> Operating pressure is upto 100 bar.
> Efficiency is upto 90%
> Steam generation rate is high.
> Operating cost is high.
> Bursting risk is high.
> Water treatment is necessary.
> Best example from our daily life is Pressure cooker. Famous water tube boilers are : Babcock & Wilcox boiler, Foster wheeler D-type boiler, Foster wheeler ESD type boiler etc.
Difference Between Fire Tube & Water Tube Boilers
Smoke Tube Boiler
> Suitable for low pressure range- 16 bar
> High thermal stresses
> Low quality and quantity of steam
> Less efficient
> Large diameter tube
> Heavy in weight
> Risk of explosion is less
Water Tube Boiler
> Suitable for high pressure range – 100 bars
> Low thermal stresses
> High quality and quantity of steam
> Highly efficient
> Small diameter tube
> Light in weight for same capacity
> Risk of explosion is high