Wartsila ?31DF Series Product Manual page 118

6. Fuel Oil System
HFO pipes shall be properly insulated. If the viscosity of the fuel is 180 cSt/50°C or higher,
the pipes must be equipped with trace heating. It shall be possible to shut off the heating of
the pipes when operating on MDF (trace heating to be grouped logically).
6.4.6.1 Starting and stopping
In diesel mode operation, the engine can be started and stopped on HFO provided that the
engine and the fuel system are pre-heated to operating temperature. The fuel must be
continuously circulated also through a stopped engine in order to maintain the operating
temperature. Changeover to MDF for start and stop is not required.
Prior to overhaul or shutdown of the external system the engine fuel system shall be flushed
and filled with MDF.
6.4.6.2 Changeover from HFO to MDF
The control sequence and the equipment for changing fuel during operation must ensure a
smooth change in fuel temperature and viscosity. When MDF is fed through the HFO
feeder/booster unit, the volume in the system is sufficient to ensure a reasonably smooth
transfer.
When there are separate circulating pumps for MDF, then the fuel change should be performed
with the HFO feeder/booster unit before switching over to the MDF circulating pumps. As
mentioned earlier, sustained operation on MDF usually requires a fuel oil cooler. The viscosity
at the engine shall not drop below the minimum limit stated in chapter Technical data.
6.4.6.3 Feeder/booster unit (1N01)
A completely assembled feeder/booster unit can be supplied. This unit comprises the following
equipment:
● Two suction strainers
● Two fuel feed pumps of screw type, equipped with built-on safety valves and electric motors
● One pressure control/overflow valve
● One pressurized de-aeration tank, equipped with a level switch operated vent valve
● Two circulating pumps, same type as the fuel feed pumps
● Two heaters, steam, electric or thermal oil (one heater in operation, the other as spare)
● One automatic back-flushing filter with by-pass filter
● One viscosimeter for control of the heaters
● One control valve for steam or thermal oil heaters, a control cabinet for electric heaters
● One temperature sensor for emergency control of the heaters
● One control cabinet including starters for pumps
● One alarm panel
The above equipment is built on a steel frame, which can be welded or bolted to its foundation
in the ship. The unit has all internal wiring and piping fully assembled. All HFO pipes are
insulated and provided with trace heating.
Fuel feed pump, booster unit (1P04)
The feed pump maintains the pressure in the fuel feed system. It is recommended to use a
screw pump as feed pump. The capacity of the feed pump must be sufficient to prevent
pressure drop during flushing of the automatic filter.
A suction strainer with a fineness of 0.5 mm should be installed before each pump. There
must be a positive static pressure of about 30 kPa on the suction side of the pump.
6-34
Wärtsilä 31DF Product Guide
DBAE248994