Marine Installation Manual
2021-08
4-56
4 Ancillary Systems
4.4 Fuel gas system
X72DF
Gas filter
The filter is a full-flow unit, preventing impurities from entering the engine’s fuel
gas system. The pressure drop over the filter is monitored and an alarm is acti
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vated when the pressure drop is higher than the permitted value, which is caused
by a dirty filter.
Control system
Readings from the sensors on the GVU as well as the opening and closing of
valves are electronically or electro-pneumatically controlled by the GVU control
system. The Local Display Unit (LDU), which is mounted on the control cab
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inet, indicates all valve statuses and readings from sensors.
4.4.8
Fuel gas venting
During normal operation of the X-DF engine, there are certain situations defined
where the fuel gas piping must be safely depressurised. For example, during a
stop sequence in gas operation mode, the gas venting valves on the iGPR or
GVU, as well as on the engine itself will automatically open to quickly reduce the
gas pressure to atmospheric pressure. Also, in case of an emergency stop, an ad
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ditional pressure relief valve in the FGSS will release pressure from the fuel gas
piping, upstream of the iGPR or GVU.
Venting of fuel gas
This small amount of fuel gas can be released outward to a place carrying no risk
of ignition. Instead of venting to the atmosphere, other means of disposal such as
a suitable furnace or gas-recovery system can be considered. However, this kind
of arrangement must be accepted by the classification society on a case-by-case
basis.
Interconnection
of vent lines
To prevent gas venting to another engine during maintenance, vent lines from
the fuel gas supply (or from the iGPR or GVU) of different engines must not be
interconnected. However, vent lines from the same engine can be interconnected
to a common header.
Ventilation of double-wall fuel gas piping
All fuel gas piping on the engine is of the double-wall type. The annular space in
the double-wall piping is ventilated by suction pressure, as created by a ventila
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tion fan, which is to be installed in a safe area outside of the engine room. The
ventilation fan’s suction side is connected to the ventilation outlet pipe just be
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fore the engine inlet in the case of an iGPR installation. Alternatively, the con
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nection is on the top of the GVU.
Location of
ventilation air inlets
One ventilation air inlet to the annular space is located on the engine. The venti
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lation air is to be taken from a safe area through dedicated piping. The second
ventilation air inlet is located at the other end of the fuel gas supply double-wall
piping, and in a safe area outside of the engine room.
NOTE
• All venting pipes that may contain fuel gas must be designed to pre
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vent the accumulation of fuel gas inside the piping.
• The pressure drop in the venting lines must be kept to a minimum.
