Firetube boilers typically have a lower initial cost, are more fuel efficient and are easier to operate, but they are limited generally to capacities of 25 tonnes per hour and pressures of 17.5 kg per cm2.
Features of Firetube boilers:
- Firetube boilers consist of a series of straight tubes that are housed inside a water-filled outer shell.
- The tubes are arranged so that hot combustion gases flow through the tubes.
- As the hot gases flow through the tubes, they heat the water surrounding the tubes.
- The water is confined by the outer shell of boiler. To avoid the need for a thick outer shell firetube boilers are used for lower pressure applications.
- Generally, the heat input capacities for firetube boilers are limited to 50 mbtu per hour or less, but in recent years the size of firetube boilers has increased.
Figure : Firetube Boiler
Types of Firetube boilers:
Firetube boilers are subdivided into three groups.
- Horizontal return tubular (HRT) boilers typically have horizontal, self-contained firetubes with a separate combustion chamber.
- Scotch, Scotch marine, or shell boilers have the firetubes and combustion chamber housed within the same shell.
- Firebox boilers have a water-jacketed firebox and employ at most three passes of combustion gases.
- Most modern firetube boilers have cylindrical outer shells with a small round combustion chamber located inside the bottom of the shell.
- Depending on the construction details, these boilers have tubes configured in either one, two, three, or four pass arrangements.
- Because the design of firetube boilers is simple, they are easy to construct in a shop and can be shipped fully assembled as a package unit.
- These boilers contain long steel tubes through which the hot gases from the furnace pass and around which the hot gases from the furnace pass and around which the water circulates.