Smoke tube Boilers
Tank (scotch) Boiler
These were the most common form of boiler design before the introduction of water tube designs. See Comparisons of water tube and Smoke tube boilers.This style of boiler still see active service were low quantities of low quality steam are required, such as for cargo and fuel tank heating when in port.
This style of boiler is relatively cheap, supplied as a packaged unit and requires less stringent feed water conditioning and level control.
DesignConsists of a shell wrapper plate to which is welded ( or for later designs riveted, end plates.. Pressure is naturally container in the shell plate due to is cylindrical design. The flat end plates, however, must be 'stayed' to prevent buckling and distortion. The combustion chamber is of similar section and is also 'stayed'.
The boiler shown above is a single furnace, two pass design. Larger boilers may have multiple furnaces and have multiple passes by replacing the exhaust stack with a return chamber and fitting another bank of tubes.
The smoke tubes may be plain or threaded to act as stays. There are one stay tube for every three plain tubes approx.
To aid circulation the tubes are arranged in vertical rows to offer minimum resistance.
Fuel is combusted in the corrugated watercooled furnace. The corrugations increase the surface area and allow a degree of flexibility to allow for expansion and contraction.The hot gas passes to the water cooled combustion space though to the smoketubes. The upper portion of the combustion chamber lies close to the water level and is therefore liable to distortion due to in correct water level maintenance.
Access to the boiler is via a manhole door on the upper shell plate. In addition a smaller door may be fitted below the furnace to allow inspection and scale/sludge removal.