Goal
To ensure the safe use of cargo as fuel.
16.1 General
Except as provided for in 16.9, methane (LNG) is the only cargo whose
vapour or boil-off gas may be utilized in machinery spaces of category A, and, in
these spaces, it may be utilized only in systems such as boilers, inert gas
generators, internal combustion engines, gas combustion unit and gas turbines.
16.2 Use of cargo vapour as fuel
This section addresses the use of cargo vapour as fuel in systems such
as boilers, inert gas generators, internal combustion engines, gas combustion units
and gas turbines.
16.2.1 For vaporized LNG, the fuel supply system shall
comply with the requirements of 16.4.1, 16.4.2 and 16.4.3.
16.2.2 For vaporized LNG, gas consumers shall exhibit
no visible flame and shall maintain the uptake exhaust temperature below 535°C.
16.3 Arrangement of spaces containing gas
consumers
16.3.1 Spaces in which gas consumers are located shall
be fitted with a mechanical ventilation system that is arranged to avoid areas where
gas may accumulate, taking into account the density of the vapour and potential
ignition sources. The ventilation system shall be separated from those serving other
spaces.
16.3.2 Gas detectors shall be fitted in these spaces,
particularly where air circulation is reduced. The gas detection system shall comply
with the requirements of chapter 13.
16.3.3 Electrical equipment located in the double wall
pipe or duct specified in 16.4.3 shall comply with the requirements of chapter
10.
16.3.4 All vents and bleed lines that may contain or be
contaminated by gas fuel shall be routed to a safe location external to the
machinery space and be fitted with a flame screen.
16.4
Gas fuel supply
16.4.1
General
16.4.1.1 The requirements of this section shall apply
to gas fuel supply piping outside of the cargo area. Fuel piping shall not pass
through accommodation spaces, service spaces, electrical equipment rooms or control
stations. The routeing of the pipeline shall take into account potential hazards,
due to mechanical damage, in areas such as stores or machinery handling areas.
16.4.1.2 Provision shall be made for inerting and
gas-freeing that portion of the gas fuel piping systems located in the machinery
space.
16.4.2
Leak detection
Continuous monitoring and alarms shall be provided to indicate a leak in
the piping system in enclosed spaces and shut down the relevant gas fuel supply.
16.4.3
Routeing of fuel supply pipes
Fuel piping may pass through or extend into enclosed spaces other than
those mentioned in 16.4.1, provided it fulfils one of the following conditions:
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.1 it is of a double-wall design with the space
between the concentric pipes pressurized with inert gas at a pressure
greater than the gas fuel pressure. The master gas fuel valve, as required
by 16.4.6, closes automatically upon loss of inert gas pressure; or
-
.2 it is installed in a pipe or duct equipped
with mechanical exhaust ventilation having a capacity of at least 30 air
changes per hour and is arranged to maintain a pressure less than the
atmospheric pressure. The mechanical ventilation is in accordance with
chapter 12, as applicable. The ventilation is always in operation when there
is fuel in the piping and the master gas fuel valve, as required by 16.4.6,
closes automatically if the required air flow is not established and
maintained by the exhaust ventilation system. The inlet or the duct may be
from a non-hazardous machinery space, and the ventilation outlet is in a
safe location.
16.4.4
Requirements for gas fuel with pressure greater than 1 MPa
16.4.4.1 Fuel delivery lines between the high-pressure
fuel pumps/compressors and consumers shall be protected with a double-walled piping
system capable of containing a high pressure line failure, taking into account the
effects of both pressure and low temperature. A single-walled pipe in the cargo area
up to the isolating valve(s) required by 16.4.6 is acceptable.
16.4.4.2 The arrangement in 16.4.3.2 may also be
acceptable providing the pipe or trunk is capable of containing a high pressure line
failure, according to the requirements of 16.4.7 and taking into account the effects
of both pressure and possible low temperature and providing both inlet and exhaust
of the outer pipe or trunk are in the cargo area.
16.4.5
Gas consumer isolation
The supply piping of each gas consumer unit shall be provided with gas
fuel isolation by automatic double block and bleed, vented to a safe location, under
both normal and emergency operation. The automatic valves shall be arranged to fail
to the closed position on loss of actuating power. In a space containing multiple
consumers, the shutdown of one shall not affect the gas supply to the others.
16.4.6
Spaces containing gas consumers
16.4.6.1 It shall be possible to isolate the gas fuel
supply to each individual space containing a gas consumer(s) or through which fuel
gas supply piping is run, with an individual master valve, which is located within
the cargo area. The isolation of gas fuel supply to a space shall not affect the gas
supply to other spaces containing gas consumers if they are located in two or more
spaces, and it shall not cause loss of propulsion or electrical power.
16.4.6.2 If the double barrier around the gas supply
system is not continuous due to air inlets or other openings, or if there is any
point where single failure will cause leakage into the space, the individual master
valve for the space shall operate under the following circumstances:
16.4.6.3 If the double barrier around the gas supply
system is continuous, an individual master valve located in the cargo area may be
provided for each gas consumer inside the space. The individual master valve shall
operate under the following circumstances:
16.4.7
Piping and ducting construction
Gas fuel piping in machinery spaces shall comply with 5.1 to 5.9, as
applicable. The piping shall, as far as practicable, have welded joints. Those parts
of the gas fuel piping that are not enclosed in a ventilated pipe or duct according
to 16.4.3, and are on the weather decks outside the cargo area, shall have full
penetration butt-welded joints and shall be fully radiographed.
16.4.8
Gas detection
Gas detection systems provided in accordance with the requirements of
this chapter shall activate the alarm at 30% LFL and shut down the master gas fuel
valve required by 16.4.6 at not more than 60% LFL (see 13.6.17).
16.5
Gas fuel plant and related storage tanks
16.5.1
Provision of gas fuel
All equipment (heaters, compressors, vaporizers, filters, etc.) for
conditioning the cargo and/or cargo boil off vapour for its use as fuel, and any
related storage tanks, shall be located in the cargo area. If the equipment is in an
enclosed space, the space shall be ventilated according to 12.1 and be equipped with
a fixed fire-extinguishing system, according to 11.5, and with a gas detection
system according to 13.6, as applicable.
16.5.2
Remote stops
16.5.2.1 All rotating equipment utilized for
conditioning the cargo for its use as fuel shall be arranged for manual remote stop
from the engine-room. Additional remote stops shall be located in areas that are
always easily accessible, typically cargo control room, navigation bridge and fire
control station.
16.5.2.2 The fuel supply equipment shall be
automatically stopped in the case of low suction pressure or fire detection. Unless
expressly provided otherwise, the requirements of 18.10 need not apply to gas fuel
compressors or pumps when used to supply gas consumers.
16.5.3
Heating and cooling mediums
If the heating or cooling medium for the gas fuel conditioning system is
returned to spaces outside the cargo area, provisions shall be made to detect and
alarm the presence of cargo/cargo vapour in the medium. Any vent outlet shall be in
a safe position and fitted with an effective flame screen of an approved type.
16.5.4
Piping and pressure vessels
Piping or pressure vessels fitted in the gas fuel supply system shall
comply with chapter 5.
16.6
Special requirements for main boilers
16.6.1
Arrangements
16.6.1.1 Each boiler shall have a separate exhaust
uptake.
16.6.1.2 Each boiler shall have a dedicated forced
draught system. A crossover between boiler force draught systems may be fitted for
emergency use providing that any relevant safety functions are maintained.
16.6.1.3 Combustion chambers and uptakes of boilers
shall be designed to prevent any accumulation of gaseous fuel.
16.6.2
Combustion equipment
16.6.2.1 The burner systems shall be of dual type,
suitable to burn either: oil fuel or gas fuel alone, or oil and gas fuel
simultaneously.
16.6.2.2 Burners shall be designed to maintain stable
combustion under all firing conditions.
16.6.2.3 An automatic system shall be fitted to change
over from gas fuel operation to oil fuel operation without interruption of the
boiler firing, in the event of loss of gas fuel supply.
16.6.2.4 Gas nozzles and the burner control system
shall be configured such that gas fuel can only be ignited by an established oil
fuel flame, unless the boiler and combustion equipment is designed and approved by
recognized organization to light on gas fuel.
16.6.3
Safety
16.6.3.1 There shall be arrangements to ensure that gas
fuel flow to the burner is automatically cut-off, unless satisfactory ignition has
been established and maintained.
16.6.3.2 On the pipe of each gas-burner, a manually
operated shut-off valve shall be fitted.
16.6.3.3 Provisions shall be made for automatically
purging the gas supply piping to the burners, by means of an inert gas, after the
extinguishing of these burners.
16.6.3.4 The automatic fuel changeover system required
by 16.6.2.3 shall be monitored with alarms to ensure continuous availability.
16.6.3.5 Arrangements shall be made that, in case of
flame failure of all operating burners, the combustion chambers of the boilers are
automatically purged before relighting.
16.6.3.6 Arrangements shall be made to enable the
boilers to be manually purged.
16.7
Special requirements for gas-fired internal combustion engines
Dual fuel engines are those that employ gas fuel (with pilot oil) and
oil fuel. Oil fuels may include distillate and residual fuels. Gas only engines are
those that employ gas fuel only.
16.7.1
Arrangements
16.7.1.1 When gas is supplied in a mixture with air
through a common manifold, flame arrestors shall be installed before each cylinder
head.
16.7.1.2 Each engine shall have its own separate
exhaust.
16.7.1.3 The exhausts shall be configured to prevent
any accumulation of unburnt gaseous fuel.
16.7.1.4 Unless designed with the strength to withstand
the worst case overpressure due to ignited gas leaks, air inlet manifolds, scavenge
spaces, exhaust system and crank cases shall be fitted with suitable pressure relief
systems. Pressure relief systems shall lead to a safe location, away from
personnel.
16.7.1.5 Each engine shall be fitted with vent systems
independent of other engines for crankcases, sumps and cooling systems.
16.7.2
Combustion equipment
16.7.2.1 Prior to admission of gas fuel, correct
operation of the pilot oil injection system on each unit shall be verified.
16.7.2.2 For a spark ignition engine, if ignition has
not been detected by the engine monitoring system within an engine specific time
after opening of the gas supply valve, this shall be automatically shut off and the
starting sequence terminated. It shall be ensured that any unburnt gas mixture is
purged from the exhaust system.
16.7.2.3 For dual-fuel engines fitted with a pilot oil
injection system, an automatic system shall be fitted to change over from gas fuel
operation to oil fuel operation with minimum fluctuation of the engine power.
16.7.2.4 In the case of unstable operation on engines
with the arrangement in 16.7.2.3 when gas firing, the engine shall automatically
change to oil fuel mode.
16.7.3
Safety
16.7.3.1 During stopping of the engine, the gas fuel
shall be automatically shut off before the ignition source.
16.7.3.2 Arrangements shall be provided to ensure that
there is no unburnt gas fuel in the exhaust gas system prior to ignition.
16.7.3.3 Crankcases, sumps, scavenge spaces and cooling
system vents shall be provided with gas detection (see 13.6.17).
16.7.3.4 Provision shall be made within the design of
the engine to permit continuous monitoring of possible sources of ignition within
the crank case. Instrumentation fitted inside the crankcase shall be in accordance
with the requirements of chapter 10.
16.7.3.5 A means shall be provided to monitor and
detect poor combustion or misfiring that may lead to unburnt gas fuel in the exhaust
system during operation. In the event that it is detected, the gas fuel supply shall
be shut down. Instrumentation fitted inside the exhaust system shall be in
accordance with the requirements of chapter 10.
16.8 Special requirements for gas turbine
16.8.1
Arrangements
16.8.1.1 Each turbine shall have its own separate
exhaust.
16.8.1.2 The exhausts shall be appropriately configured
to prevent any accumulation of unburnt gas fuel.
16.8.1.3 Unless designed with the strength to withstand
the worst case overpressure due to ignited gas leaks, pressure relief systems shall
be suitably designed and fitted to the exhaust system, taking into consideration
explosions due to gas leaks. Pressure relief systems within the exhaust uptakes
shall be lead to a non-hazardous location, away from personnel.
16.8.2
Combustion equipment
An automatic system shall be fitted to change over easily and quickly
from gas fuel operation to oil fuel operation with minimum fluctuation of the engine
power.
16.8.3
Safety
16.8.3.1 Means shall be provided to monitor and detect
poor combustion that may lead to unburnt gas fuel in the exhaust system during
operation. In the event that it is detected, the gas fuel supply shall be shut
down.
16.8.3.2 Each turbine shall be fitted with an automatic
shutdown device for high exhaust temperatures.
16.9 Alternative fuels and technologies
16.9.1 If acceptable to the Administration, other cargo
gases may be used as fuel, providing that the same level of safety as natural gas in
this Code is ensured.
16.9.2 The use of cargoes identified as toxic products
shall not be permitted.
16.9.3 For cargoes other than LNG, the fuel supply
system shall comply with the requirements of 16.4.1, 16.4.2, 16.4.3 and 16.5, as
applicable, and shall include means for preventing condensation of vapour in the
system.
16.9.4 Liquefied gas fuel supply systems shall comply
with 16.4.5.
16.9.5 In addition to the requirements of 16.4.3.2,
both ventilation inlet and outlet shall be located outside the machinery space. The
inlet shall be in a non-hazardous area and the outlet shall be in a safe
location.