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.
The temperature in HFO settling tanks should be maintained between 50°C and 70°C, which requires
heating coils and insulation of the tank. Usuallly MDF settling tanks do not need heating or insulation, but
the tank temperature should be in the range 20...40°C.
Day tank, HFO (1T03) and MDF (1T06)
Two day tanks for HFO are to be provided, each with a capacity sufficient for at least 8 hours operation at
maximum fuel consumption.
A separate tank is to be provided for MDF. The capacity of the MDF tank should ensure fuel supply for 8
hours.
Settling tanks may not be used instead of day tanks.
The day tank must be designed so that accumulation of sludge near the suction pipe is prevented and the
bottom of the tank should be sloped to ensure efficient draining.
HFO day tanks shall be provided with heating coils and insulation. It is recommended that the viscosity is
kept below 140 cSt in the day tanks. Due to risk of wax formation, fuels with a viscosity lower than 50 cSt
at 50°C must be kept at a temperature higher than the viscosity would require. Continuous separation is
nowadays common practice, which means that the HFO day tank temperature normally remains above
90°C.
The temperature in the MDF day tank should be in the range 20...40°C.
The level of the tank must ensure a positive static pressure on the suction side of the fuel feed pumps. If
black-out starting with MDF from a gravity tank is foreseen, then the tank must be located at least 15 m
above the engine crankshaft.
Leak fuel tank, clean fuel (1T04)
Clean leak fuel is drained by gravity from the engine. The fuel should be collected in a separate clean leak
fuel tank, from where it can be pumped to the day tank and reused without separation. The pipes from the
engine to the clean leak fuel tank should be arranged continuosly sloping. The tank and the pipes must be
heated and insulated, unless the installation is designed for operation on MDF only.
In HFO installations the change over valve for leak fuel (1V13) is needed to avoid mixing of the MDF and
HFO clean leak fuel. When operating the engines in gas mode and MDF is circulating in the system, the
clean MDF leak fuel shall be directed to the MDF clean leak fuel tank. Thereby the MDF can be pumped
back to the MDF day tank (1T06).
When switching over from HFO to MDF the valve 1V13 shall direct the fuel to the HFO leak fuel tank long
time enough to ensure that no HFO is entering the MDF clean leak fuel tank.
Refer to section "Fuel feed system - HFO installations" for an example of the external HFO fuel oil system.
The leak fuel piping should be fully closed to prevent dirt from entering the system.
Leak fuel tank, dirty fuel (1T07)
In normal operation no fuel should leak out from the components of the fuel system. In connection with
maintenance, or due to unforeseen leaks, fuel or water may spill in the hot box of the engine. The spilled
liquids are collected and drained by gravity from the engine through the dirty fuel connection.
Dirty leak fuel shall be led to a sludge tank. The tank and the pipes must be heated and insulated, unless
the installation is designed for operation exclusively on MDF.
Fuel treatment
Separation
Heavy fuel (residual, and mixtures of residuals and distillates) must be cleaned in an efficient centrifugal
separator before it is transferred to the day tank.
Product Guide Wärtsilä 34DF - 3/2012
53
Product Guide
6. Fuel System
