Wartsila ?31DF Series Product Manual page 101

Wärtsilä 31DF Product Guide
Pipe
size
P6
P7
P8
6.3.1.5 Master fuel gas valve
For LNG carriers, IMO IGC code requires a master gas fuel valve to be installed in the fuel gas
feed system. At least one master gas fuel valve is required, but it is recommended to apply
one valve for each engine compartment using fuel gas to enable independent operation.
It is always recommended to have one main shut-off valve directly outside the engine room
and valve room in any kind of installation.
6.3.1.6 Fuel gas venting
In certain situations during normal operation of a DF-engine, as well as due to possible faults,
there is a need to safely ventilate the fuel gas piping. During a stop sequence of a DF-engine
gas operation the GVU and DF-engine gas venting valves performs a ventilation sequence to
relieve pressure from gas piping. Additionally in emergency stop V02 will relief pressure from
gas piping upstream from the GVU.
This small amount of gas can be ventilated outside into the atmosphere, to a place where
there are no sources of ignition.
Alternatively to ventilating outside into the atmosphere, other means of disposal (e.g. a suitable
furnace) can also be considered. However, this kind of arrangement has to be accepted by
classification society on a case by case basis.
In case the DF-engine is stopped in gas operating mode, the ventilation valves will open
automatically and quickly reduce the gas pipe pressure to atmospheric pressure.
The pressure drop in the venting lines are to be kept at a minimum.
To prevent gas ventilation to another engine during maintenance vent lines from gas supply
or GVU of different engines cannot be interconnected. However, vent lines from the same
engine can be interconnected to a common header, which shall be lead to the atmosphere.
Connecting the engine or GVU venting lines to the LNGPac venting mast is not allowed, due
to risk for backflow of gas into the engine room when LNGPac gas is vented!
6.3.1.7 Purging by inert gas
Nitrogen requirements
Wärtsilä recommends nitrogen with the following properties as a medium for purging.
Table 6-5
Property
Content of mix-
ture out of N2
Oxygen content
Dew point (atmo-
spheric pressure)
DBAE248994
DN50 DN80 DN100
GVU GVU GVU
OD18 OD28 OD42
OD22 OD28 OD28
10mm 10mm 10mm
All breathing and ventilation pipes that may contain fuel gas must always be built
sloping upwards, so that there is no possibility of fuel gas accumulating inside the
piping.
Nitrogen properties as a medium for purging
Unit Value
≥ 95.0 %
≤ 1.0 %
≤ 40 °C
NOTE
6. Fuel Oil System
6-17