What is a Boiler Storage Vessel?

A boiler storage vessel is an industrial-grade storage container used to hold boiler water and steam during and after the heating process. The vessel is attached to the deaerator, which is used to remove dissolved gases, primarily oxygen and carbon dioxide, from feedwater before it enters the boiler.

The normal sizing of a vessel is for it to provide 10 minutes of storage to the overflow point. A vessel which provides 10 minutes of storage has a volume equivalent to the boiler evaporation rate (gallons/minute) multiplied by the number of minutes started. A 50,000 pph boiler has a full evaporation rate of gpm. If the vessel is sized for 10 minutes of storage, it will have a capacity of 1,000 gallons to overflow.

Do I Need an Expanded Vessel?

The standard vessel sizing criteria may not provide enough storage capacity to allow the vessel to capture all the returns. The standard storage capacity will generally be sufficient for systems which have less than 50% pumped returns. If the pumped returns exceed 50% of the system capacity, expanding the vessel size to
accommodate surges is recommended.

If the returns exceed 50%, an expanded storage vessel is definitely in order, especially if the returns are being pumped from several locations and controlled by simple on-off switches.

Several pumps starting at one time can cause a surge making the extra storage capacity necessary. System startups also cause a surge. An exception to this is when
all the condensate comes from a separate single-surge receiver with the make-up water added at this point. Under these conditions, the in-flow to the deaerator is modulated to match the outflow to the boiler.

Expanded storage capacity is also required if a solid fuel fired boiler is used. An expanded storage section should always be used for this application since a boiler of
this type continues to make steam for quite some time after the boiler is shut down.

In most systems, increasing the storage capacity to provide 15-20 minutes of storage will be sufficient to collect all the returns. However, in some systems with extensive piping, such as refineries, storage capacities equivalent to 20 or 30 minutes of storage may be necessary.