Page 162 - Introduction to Marine Engineering

148 Auxiliaries

SOIL
VENT IMLfT
o
HUM AN BOD V
WASTE FROM
WeVAHO
URIMAL3

CONTROL PANE U

MAWCi ni»»f CHLORINE AERATION SETTLING AERATION
CONTACT
Figure 7.10 Biological sewage treatment plant

replacement as they are used up. The activated sludge in the settling
tank is continuously recycled and builds up, so that every two to three
months it must be partially removed. This sludge must be discharged
only in a decontrolled area.

Incinerator

Stricter legislation with regard to pollution of the sea, limits and, in some
instances, completely bans the discharge of untreated waste water,
sewage, waste oil and sludge. The ultimate situation of no discharge can
be achieved by the use of a suitable incinerator. When used in
conjunction with a sewage plant and with facilities for burning oil
sludges, the incinerator forms a complete waste disposal package.
One type of incinerator for shipboard use is shown in Figure 7.11.
The combustion chamber is a vertical cylinder lined with refractory
material. An auxiliary oil-fired burner is used to ignite the refuse and oil
sludge and is thermostatically controlled to minimise fuel consumption.
A sludge burner is used to dispose of oil sludge, water and sewage sludge
and works in conjunction with the auxiliary burner. Combustion air is
provided by a forced draught fan and swirls upwards from tangential
ports in the base. A rotating-arm device accelerates combustion and also
clears ash and non-combustible matter into an ash hopper. The loading
door is interlocked to stop the fan and burner when opened.