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 (i.e. stop,
emergency stop or shutdown in gas operating mode, or transfer to diesel operating mode) 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.
NOTE!
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.
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.
Venting lines from one engines gas supply system is to be kept separate from other venting lines. Venting
pipes are to be designed for maximum security.
Purging by inert gas
Before beginning maintenance work, the fuel gas piping system has to be de-pressurized and inerted with
an inert gas. If maintenance work is done after GVU and the enclosure of the GVU doesn’t need to be
opened it is enough to inert gas pipe between GVU and engine. If the maintenance work is done on GVU
and the enclosure of the GVU need to open the fuel gas piping upstream from GVU double-block-and-
bleed-valves need to be inerted from gas storage system. The piping of the Wärtsilä 34DF engine and the
gas valve unit is equipped with inerting connections for inert gas (Nitrogen).
There might be a need for inerting the fuel gas piping as a normal procedure during engine operation. This
arrangement has to be considered on a case by case basis. A connection for inerting purposes has been
installed on the GVU to be able to inert piping between the GVU and the engine.
Gas feed pressure
The required fuel gas feed pressure depends on the expected minimum lower heating value (LHV) of the
fuel gas, as well as the pressure losses in the feed system to the engine. The LHV of the fuel gas has to be
above 28 MJ/m
3
at 0°C and 101.3 kPa.
•
A fuel gas with a lower heating value of 28 MJ/m
3
at 0°C and 101.3 kPa correspond to a required fuel
gas pressure of 515 kPa (gauge pressure) at the GVU inlet at 100% engine load.
•
Fuel gas LHV of 36 MJ/m
3
at 0°C and 101.3 kPa correspond to 472 kPa (gauge pressure) at the GVU
inlet. The required fuel gas pressure do not change at higher LHVs at 100% engine load.
•
For fuel gas with LHV between 28 and 36 MJ/m
3
at 0°C and 101.3 kPa, the required gas pressure
can be interpolated.
•
The pressure losses in the gas feed system to engine has to be added to get the required gas pressure.
•
A pressure drop of 120 kPa over the GVU is a typical value that can be used as guidance.
•
The required gas pressure to the engine depends on the engine load. This is regulated by the GVU.
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Product Guide Wärtsilä 34DF - 3/2012
Product Guide
6. Fuel System
