Bergen B35:40, Руководство по проекту

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, Gas Fuel gas supply system
Page 1 : 4
2.05
0717 BC
F
UEL GAS SUPPLY SYSTEM
Introduction
The major component in the fuel gas supply system
is the gas regulating unit (GRU) is always included in
Rolls-Royce Marine AS scope of supply.
It is mounted separately from the engine, but the
pipe length and pipe diameter must be within limits
given by RRMEB. Typically max. 10 m. Each engine
has separate gas regulating unit with gas pressure
regulator.
The gas regulating unit shall ensure supply of fuel
gas with correct pressure and purity to the engine,
and shall also cater for the required safety shut-off
functions.
Gas pressure regulator
The gas pressure is controlled by an electronic
governor mounted inside the engine control cabinet.
A 4-20 mA signal is fed from the governor and
converted by an I/P converter to a pneumatic signal
(pilot control air). The pilot control air governs the
pressure control valve (61FG) by an actuator in order
to obtain the desired gas pressure. The pressure
control valve is sensing the gas pressure through
separate measuring and return (feedback) lines.
Control air is fed through a 25 micron filter before it is
distributed to control air consumers. The filter is
equipped with automatic water drain.
Filtration
The gas pressure regulator (tag no. in P&ID; 61FG)
and the engine are protected by a fine filter (53 FG)
upstream the pressure regulator.
See chapter 1.05 for required filtration grade.
Fuel gas quality
See part 1.05, fuel gas specification
Flowmeter
The flowmeter is used for measuring the mass flow
rate of fuel gas. At the same time, the system also
measures fluid density and fluid temperature.
Fire safety
All types of fuel gases are flammable, and have a
range in concentration in which an explosion can
occur, and should therefore be treated with care.
Gas piping system
The gas piping system is double walled and
therefore of the "inherently gas safe concept".
Stainless steel pipes must be used in the fuel gas
supply system between the gas ramp unit and the
engine.
For the purpose of preventing excessive pressure
losses in the piping system, the gas velocity should
not exceed:
.............10 m/s before and after pressure regulator.
Block and Bleed system
On the GRU a "Block and Bleed" (BnB) system is
included. The BnB systems task is to empty the gas
supply pipe and gas manifold of fuel gases, and also
stop more fuel gas entering the supply pipe from the
GRU, during and after an engine shut down. Mean
while the BnB system shuts off the fuel gas supply
from the GRU, the last engine cycle are used to pump
out any remaining fuel gas that is trapped between
the engine gas flow control valves and inlet ports.
A normal engine shut down procedure, as described
above, is sufficient enough to prevent any fuel gases
from entering the engines intake receiver, and
thereby also preventing any fuel gas seeping out
past the compressor wheel and entering the ships
engine room.
Shut-off valves
A “double-block-and-bleed” arrangement is used,
with 2 off pneumatically operated gas shut-off valves
(63FG) in series, and with 2 off venting valves (75FG,
76FG) for bleeding.
The shut-off valve air actuators have built-on 24V DC
solenoid valves for remote control.
The venting valves are also remotely controlled 24V
DC solenoid valves.
Normal working pressure of 7 bar is supplied to the
air actuators of shut-off valves.
Note: The max inlet pressure is 6 bar g. If the inlet pressure is
above 6 bar g, a SSV (Safety Shut-off valve) must be fitted.
Electrical connections
The gas regulating unit has terminal boxes in nonEX
versions for all electric connections.