WinGD X72DF, Installation Manual

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Marine Installation Manual 2021-08 4-43
4 Ancillary Systems
4.4 Fuel gas system
X72DF
Pressurised FGSS If an LNG tank is designed to withstand pressure (along with the FGSS), then
generally the system will be less complex than a system with a non-pressurised
tank (along with the FGSS). The system will be less complex since the NBOG
management will not be as demanding as for the other non-pressurised systems.
Two examples of solutions for a non-LNGC FGSS are provided.
Type C tank – Solution 1
Figure 4 - 24 shows a pressurised Type C tank where fuel gas is provided to the
main engine only as FBOG and where only the gensets utilise the NBOG. If re -
quired, the gensets have the possibility to supplement with forced boil-off from
LNG. In many cases, the amount of NBOG being generated can be consumed by
a single gas-fuelled genset. This makes solution 1 a simple and cost efficient solu
-
tion, as only a low-pressure NBOG compressor may be required, depending on
the design tank pressure and the gas feed pressure demand of the gensets.
Figure 4 - 24 Pressurised Type C tank solution with NBOG handling by the gensets
Type C tank – Solution 2
Figure 4 - 25,  4-44 shows a pressurised Type C tank where fuel gas is provided
to the main engine as a combination of FBOG and NBOG. The gensets are fed
by a reduction valve from the main engine supply. This system design ensures
that the NBOG is also utilised, even when the generated NBOG is greater than
the genset consumption. However, this additional flexibility comes at a greater
cost as the NBOG compressor is designed for a higher delivery pressure.
SM-0681
BOG
LNG
Gas-fuelled genset
GVU
GVU
GVU
X-DF
main
engine
iGPR/GVU
Gas supply to
gas-fired boiler
Emergency pressure release
From the bunkering station
Cryogenic
submerged pump
Pre-heater
Low-pressure
NBOG compressor
Type C tank
Mostly for LNG-fuelled
vessels and small LNGCs
Low-pressure vaporiser
up to 16 bar(g)
Gas-fuelled genset
Gas-fuelled genset
e.g. up to 6 bar(g)
up to 16 bar(g)
e.g. up to 0.3 bar(g)
Pressurised Type C tank solution
with NBOG handling by the gensets