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Steam Distribution Systems

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 trap.

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- to-water process.

Water pretreatment 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.

Waterside problems 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 process.

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.