Page 95 - Introduction to Marine Engineering

82 Boilers

to the combustion chamber access door and the primary and secondary
quart.
Fully automatic controls are provided and located in a control panel at
the side of the boiler.

Cochran boilers
The modern vertical Cochran boiler has a fully spherical furnace and is
known as the 'spheroid' (Figure 4.8). The furnace is surrounded by
water and therefore requires no refractory lining. The hot gases make a
single pass through the horizontal tube bank before passing away to
exhaust. The use of small-bore tubes fitted with retarders ensures better
heat transfer and cleaner tubes as a result of the turbulent gas flow.

Composite boilers
A composite boiler arrangement permits steam generation either by oil
firing when necessary or by using the engine exhaust gases when the
ship is at sea. Composite boilers are based on firetube boiler designs.
The Cochran boiler, for example, would have a section of the tube bank
separately arranged for the engine exhaust gases to pass through and
exit via their own exhaust duct.

Refractory

Burner

Figure 4.8 Cochran spheroid boiler