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 type filters instead. A coalescing filter is usually
installed on the suction side of the circulation pump in the fuel feed system. The filter must have a low
pressure drop to avoid pump cavitation.
Separator mode of operation
The best separation efficiency is achieved when also the stand-by separator is in operation all the time,
and the throughput is reduced according to actual consumption.
Separators with monitoring of cleaned fuel (without gravity disc) operating on a continuous basis can handle
fuels with densities exceeding 991 kg/m
3
at 15°C. In this case the main and stand-by separators should
be run in parallel.
When separators with gravity disc are used, then each stand-by separator should be operated in series
with another separator, so that the first separator acts as a purifier and the second as clarifier. This arrange-
ment can be used for fuels with a density of max. 991 kg/m
3
at 15°C. The separators must be of the same
size.
Separation efficiency
The term Certified Flow Rate (CFR) has been introduced to express the performance of separators according
to a common standard. CFR is defined as the flow rate in l/h, 30 minutes after sludge discharge, at which
the separation efficiency of the separator is 85%, when using defined test oils and test particles. CFR is
defined for equivalent fuel oil viscosities of 380 cSt and 700 cSt at 50°C. More information can be found in
the CEN (European Committee for Standardisation) document CWA 15375:2005 (E).
The separation efficiency is measure of the separator's capability to remove specified test particles. The
separation efficiency is defined as follows:
where:
separation efficiency [%]
n =
number of test particles in cleaned test oil
C
out
=
number of test particles in test oil before separator
C
in
=
Separator unit (1N02/1N05)
Separators are usually supplied as pre-assembled units designed by the separator manufacturer.
Typically separator modules are equipped with:
•
Suction strainer (1F02)
•
Feed pump (1P02)
•
Pre-heater (1E01)
•
Sludge tank (1T05)
•
Separator (1S01/1S02)
•
Sludge pump
•
Control cabinets including motor starters and monitoring
54
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
6. Fuel System
