Page 121 - Introduction to Marine Engineering

108 Feed systems

De-aerator
The de-aerator completes the air and vapour removal process begun in
the condenser. It also functions as a feed heater, but in this case operates
by direct contact. The feedwater is heated almost to the point of boiling,
which releases all the dissolved gases which can then be vented off.
One type of de-aerator is shown in Figure 5.9. The incoming
feedwater passes through a number of spray valves or nozzles: the water

Water inlet conn.
Atmospheric vent conn.
Water inlet manifold
Spray vatv«
air cooler baffle
Lower air cooler
baffle
Pfiroary hcaW
directing baffle

Overflow
conn.

Inspection
cover
•Supports

Figure 5.9 De-aerator

spray thus provides a large surface area for contact with the heating
system. Most of the feedwater will then fall onto the upper surface of the
de-aerating cone where it is further heated by the incoming steam. The
feedwater then enters the central passage and leaves through a narrow
opening which acts as an eductor or ejector to draw steam through with
the feed. The feedwater and condensed steam collect in the storage tank
which forms the base of the de-aerator. The heating steam enters the
de-aerator and circulates throughout, heating the feedwater and being
condensed in its turn to combine with the feedwater. The released
gases leave through a vent connection and pass to a vent condenser or
devaporiser. Any water vapour will be condensed and returned. The