External Fuel Oil System - Wartsila 31 Product Manual

6. Fuel Oil System
6.3

External fuel oil system

The design of the external fuel system may vary from ship to ship, but every system should
provide well cleaned fuel of correct viscosity and pressure to each engine. Temperature control
is required to maintain stable and correct viscosity of the fuel before the injection pumps (see
Technical data). Sufficient circulation through every engine connected to the same circuit must
be ensured in all operating conditions.
The fuel treatment system should comprise at least one settling tank and two separators.
Correct dimensioning of HFO separators is of greatest importance, and therefore the
recommendations of the separator manufacturer must be closely followed. Poorly centrifuged
fuel is harmful to the engine and a high content of water may also damage the fuel feed system.
Injection pumps generate pressure pulses into the fuel feed and return piping. The fuel pipes
between the feed unit and the engine must be properly clamped to rigid structures. The
distance between the fixing points should be at close distance next to the engine. See chapter
Piping design, treatment and installation.
A connection for compressed air should be provided before the engine, together with a drain
from the fuel return line to the clean leakage fuel or overflow tank. With this arrangement it is
possible to blow out fuel from the engine prior to maintenance work, to avoid spilling.
6.3.1 Fuel heating requirements HFO
Heating is required for:
● Bunker tanks, settling tanks, day tanks
● Pipes (trace heating)
● Separators
● Fuel feeder/booster units
To enable pumping the temperature of bunker tanks must always be maintained 5...10°C
above the pour point, typically at 40...50°C. The heating coils can be designed for a temperature
of 60°C.
The tank heating capacity is determined by the heat loss from the bunker tank and the desired
temperature increase rate.
6.3.2 Fuel tanks
The fuel oil is first transferred from the bunker tanks to settling tanks for initial separation of
sludge and water. After centrifuging the fuel oil is transferred to day tanks, from which fuel is
supplied to the engines.
6.3.2.1 Settling tank, HFO (1T02) and MDF (1T10)
Separate settling tanks for HFO and MDF are recommended.
To ensure sufficient time for settling (water and sediment separation), the capacity of each
tank should be sufficient for min. 24 hours operation at maximum fuel consumption.
The tanks should be provided with internal baffles to achieve efficient settling and have a
sloped bottom for proper draining.
6-8
In multiple engine installations, where several engines are connected to the same
fuel feed circuit, it must be possible to close the fuel supply and return lines
connected to the engine individually. This is a SOLAS requirement. It is further
stipulated that the means of isolation shall not affect the operation of the other
engines, and it shall be possible to close the fuel lines from a position that is not
rendered inaccessible due to fire on any of the engines.
NOTE
Wärtsilä 31 Product Guide - a1 - 18 October 2016
Wärtsilä 31 Product Guide