Feed Water Tanks
The importance of the boiler feedtank, where boiler feedwater and make-up water are stored and into which condensate is returned, is often underestimated. Most items of plant in the boiler house are duplicated, but it is rare to have two feedtanks and this crucial item is often the last to be considered in the design process.
The feedtank is the major meeting place for cold make-up water and condensate return. It is best if both of these, together with flash steam from the blowdown system, flow through sparge pipes installed well below the water surface in the feedwater tank. The sparge pipes must be made from stainless steel and be adequately supported.
Feed Water Storage
After feed water has been treated it must be stored ready for use by the boiler. A simply, but well-insulated tank is normally sufficient. The deaerator can sometimes be conveniently combined with the feed water tank to save space. Some chemicals may be added to storage tank to complete the boiler feed water treatment program.
The feed water tank should be:
- Well-insulated to prevent heat loss from deaerated water and returned condensate.
- Sufficiently big to supply the boiler for about 1 hour if the raw water supply fails.
- As small as possible to reduce heat loss and capital costs.
Covered to limit the surface area in contact with the air, and so reduce the possibility of redissolving gases.