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Boiler Types & Construction
Firetube vs watertube boilers, construction methods, and common configurations.
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Firetube Boilers
In a firetube boiler, hot combustion gases pass through tubes surrounded by water. The water is on the outside of the tubes.
- Hot gases inside tubes, water outside
- Simple design, easy to clean and maintain
- Lower initial cost than watertube
- Slower response to load changes
- Higher water volume = greater stored energy = larger explosion potential
- Common types: Scotch marine (most common), HRT (Horizontal Return Tube), locomotive
Firetube boilers have more water volume per BHP, making them more dangerous in an explosion.
Watertube Boilers
In a watertube boiler, water flows inside the tubes and hot gases pass around the outside. Used for higher pressures and capacities.
- Water inside tubes, hot gases outside
- Higher pressure capability
- Faster response to load changes
- Lower water volume = less explosion energy
- More complex design, harder to clean internally
- Used for high-pressure steam and power generation
Other Boiler Types
Several specialized boiler types serve specific applications.
- Cast iron sectional: low-pressure heating boilers, assembled from individual sections
- Electric boiler: uses resistance elements or electrodes, no combustion
- Package boiler: factory-assembled, skid-mounted, ready to install
- Coil-type (steam generator): water flows through a continuous coil heated by burner