What boiler layup treatments are recommended and why is it important?
The wet storage method is recommended when a
boiler needs to be on temporary or emergency standby. In this method, the
boiler should be filled to the normal water level with deaerated feedwater.
Then, one of two solutions is added:
- Caustic soda and sodium sulfite
to maintain SO3
- Diethyhydroxylamine (DEHA)
and morpholine to control oxygen and pH levels
The drain between the
non-return and the main steam stop valve should be left wide open. All other
drains and vents are to be left closed tight. The boiler water is tested on a
regular basis, with additional treatment being added whenever necessary to
maintain the minimum treatment levels.
When a boiler needs to be
kept idle with hot, treated water, an alternative wet method is used, called
the Cascade method. This involves connecting the continuous blowdown line from
an operating boiler, to a convenient bottom drain line or blowdown line of the
boiler that is to be laid-up. Enough hot surface blowdown from the operating
boiler must be available on a continuous basis to keep the standby boiler, its
exterior tubes, and other boiler components warm enough to prevent condensation.
Chemical levels also need to be properly maintained in the operating boiler
during this time.