6.3.2 External fuel gas system
Figure 6.3
Example of fuel gas system (DAAF022750B)
Pipe connections
System components
Gas inlet
108
Gas valve unit
10N05
Gas system ventilation
708
Air inlet to double wall gas system
726
The fuel gas can typically be contained as CNG, LNG at atmospheric pressure, or pressurized LNG. The
design of the external fuel gas feed system may vary, but every system should provide natural gas with the
correct temperature and pressure to each engine.
Double wall gas piping and the ventilation of the piping
The annular space in double wall piping is ventilated artificially by underpressure created by ventilation
fans. The first ventilation air inlet to the annular space is located at the engine. The ventilation air is to be
taken from a location outside the engine room, through dedicated piping. The second ventilation air inlet
is located at the tank room end of the double wall piping. The ventilation air is taken from both inlets and
lead through annular space of double wall pipe to the enclosure of the gas valve unit. From the enclosure
of the gas valve unit a dedicated ventilation pipe is connected to the ventilation fans and from fans the pipe
continues to safe area. The 1,5 meter hazardous area will be formed at the ventilation air inlet and outlet
and is to be taken in consideration when the ventilation piping is designed.
Gas valve unit (10N05)
Before the gas is supplied to the engine it passes through a Gas Valve Unit (GVU). The GVU include a gas
pressure control valve and a series of block and bleed valves to ensure reliable and safe operation on gas.
The unit includes a manual shut-off valve, inerting connection, filter, fuel gas pressure control valve, shut-
off valves, ventilating valves, pressure transmitters/gauges, a gas temperature transmitter and control
cabinets.
The filter is a full flow unit preventing impurities from entering the engine fuel gas system. The fineness of
the filter is 5
μ
m absolute mesh size. The pressure drop over the filter is monitored and an alarm is activated
when pressure drop is above permitted value due to dirty filter.
Product Guide Wärtsilä 34DF - 3/2012
45
Product Guide
6. Fuel System
