In a steam
distribution system, steam leaves the boiler and enters the main steam header.
Branch lines feed steam through a riser to the steam heated equipment. At the
heating equipment heat is transferred to the building space or process. As the
steam releases heat to the building space or process, it is cooled, returning
back to water (condensate). The condensate is separated from the steam by a steam
The steam trap
allows condensate to pass but not steam. The condensate passes through the condensate
return line, is collected and directed back to the boiler to repeat the steam-
equipment - softeners and de-mineralizers - are used to remove as much of the
dissolved solids as possible before they enter the boiler. To remove any solids
that enter the boiler system, chemicals are added to react with the solids creating
sludge. Periodically, opening valves from the bottom of the boiler and relieving
it to the drain removes this sludge. This operation is called blow down.
can shorten boiler life from corrosion brought on by the oxygen content in feedwater.
Pretreatment for the removal of oxygen is performed in a deaerator, but the removal
is not complete. Chemical additions are made to aid in improving the oxygen removal
The water supplied to the boiler that is converted into steam is called feedwater.
The two sources of feedwater are: (1) condensate, or condensed steam returned
from the processes and (2) makeup water (usually city water), which must come
from outside the boiler room and plant processes. For higher boiler efficiencies,
feedwater can be preheated. This preheating is usually accomplished by using economizers.
The feedwater system provides water to the boiler and regulates it automatically
to meet the demand for steam.