Marine Installation Manual
2021-08
4-78
4 Ancillary Systems
4.6 Fuel oil system
X72DF
4.6.4
Fuel oil treatment
The latest version of the
Concept Guidance
for fuel oil treatment (DG 9723) is
provided on the WinGD webpage under the following link:
Settling tanks
Gravitational settling of water and sediment from modern heavy fuel oils is an
extremely slow process due to the small difference in densities. The time required
for the settling to occur depends on the depth of the tank, as well as on the vis
-
cosity, temperature and density difference. Tanks that are shallower with a wider
diameter enable better separation than thinner, taller tanks.
Further design features consider a level monitoring device and remote closing
discharge valves to the separator(s) and engine systems, a connection to an over
-
flow tank, and a self-closing cock just above the bottom of the tank for removal of
the sludge and water.
Service tanks
Most of the service tank design features are similar to the settling tanks, however,
there is no direct connection to the overflow tank. Instead a recirculating line,
with an inlet just above the bottom of the service tank, leads back to the settling
tanks.
Diesel oil service tanks are similar to heavy oil service tanks, with the possible
exception of tank heating, although this may be incorporated for vessels con
-
stantly trading in cold climates.
Water in fuel
Due to condensation or heating coil leakage, water may be present in the fuel
after the separators. This can be manually removed by a self-closing cock. In ad
-
dition, the recirculation connection close to the bottom of the tank ensures that
contaminated fuel is recirculated to the settling tank.
Cleaning of fuel
The fuel is cleaned from the settling tank to the service tank. Ideally, when the
main engine is operating at CMCR, the fuel oil separator(s) should be able to
maintain a continual overflow from the service tank to the settling tank. The
cock, used to remove sludge and water, is to be operated at regular intervals to
observe the presence of water, a significant indication for the condition of the
separator(s) and heating coils.
Centrifugal fuel oil separators
There are two types of oil separators:
•
Type 1
—
Separators with gravity discs
•
Type 2
—
Separators without gravity discs
NOTE
Separators with gravity discs represent outdated technology and are
therefore not supported by WinGD.
