Page 108 - Introduction to Marine Engineering

Boilers 95

Air sleeve Electric igniter
operating
cylinder
Oil and steam
hand controls
Flame monitor

Steam inlet
Oil inlet

Outer casing

Burner tip

Figure 4.l7(b) Air register for roof-fired boiler

The presence of dissolved oxygen and carbon dioxide in boiler
feedwater can cause considerable corrosion of the boiler and feed
systems. When boiler water is contaminated by suspended matter, an
excess of salts or oil then 'foaming' may occur. This is a foam or froth
which collects on the water surface in the boiler drum. Foaming leads to
'priming' which is the carry-over of water with the steam leaving the
boiler drum. Any water present in the steam entering a turbine will do
considerable damage.