Wartsila 31 Product Manual page 53

Wärtsilä 31 Product Guide
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.
6.3.2.2 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.
6.3.2.3 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.
The leak fuel piping should be fully closed to prevent dirt from entering the system.
6.3.2.4 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.
6.3.3 Fuel treatment
6.3.3.1 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.
Classification rules require the separator arrangement to be redundant so that required capacity
is maintained with any one unit out of operation.
All recommendations from the separator manufacturer must be closely followed.
Centrifugal disc stack separators are recommended also for installations operating on MDF
only, to remove water and possible contaminants. The capacity of MDF separators should be
sufficient to ensure the fuel supply at maximum fuel consumption. Would a centrifugal separator
be considered too expensive for a MDF installation, then it can be accepted to use coalescing
Wärtsilä 31 Product Guide - a1 - 18 October 2016
6. Fuel Oil System
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