Use of Cargo as Fuel

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.

LR 16.1–01 The fuel supply to essential consumers shall be arranged with redundancy and segregation, so that failure does not lead to an unacceptable loss of essential services.

LR 16.1–02 The following information and plans are to be submitted for consideration:

• General arrangement of plan.
• Gas piping systems, together with details of interlocking and safety devices.
• Heating or cooling arrangements for gas fuel temperature control including heat exchangers.
• Gas compressors and their prime movers.
• Gas storage pressure vessels.
• Gas and oil fuel burning arrangements.
• Pressure/flow regulation and depressurisation system.
• Stress analysis of the high pressure piping system taking into account pulsation and vibration loads, if any.
• For high pressure gas double wall piping, an outer pipe integrity analysis to confirm the integrity of the outer pipe in the event of a high pressure leakage from the inner pipe.
• Details of liquefied gas pumps, including low and high pressure, intended to be used as part of the system using cargo as a fuel.

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.

LR 16.3-01 There shall be separate vent lines from areas such as gas fuel tanks and gas consumers (engines etc.) that are independent of each other. Bleed lines shall also be independent of the vent lines. Vent and bleed lines shall all be led to a safe location in the cargo area. Such vent and bleed lines shall not be connected to a common header unless they are from a same area.

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:

• .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.

LR 16.4–01 Local manually operated shut-off arrangements are also to be fitted in the gas supply upstream of the automatic double block and bleed valve to each consumer.

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:

• .1 automatically by:

  • .1 gas detection within the space;

  • .2 leak detection in the annular space of a double-walled pipe;

  • .3 leak detection in other compartments inside the space, containing single-walled gas piping;

  • .4 loss of ventilation in the annular space of a double-walled pipe; and

  • .5 loss of ventilation in other compartments inside the space, containing single-walled gas piping; and

• .2 manually from within the space, and at least one remote location.

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:

• .1 automatically by:

  • .1 leak detection in the annular space of a double-walled pipe served by that individual master valve;

  • .2 leak detection in other compartments containing single-walled gas piping that is part of the supply system served by the individual master valve; and

  • .3 loss of ventilation or loss of pressure in the annular space of a double-walled pipe; and

• .2 manually from within the space, and at least one remote location.

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.

LR 16.4-02 Gas fuel piping systems are to have sufficient structural strength to accommodate stresses due to the weight of the piping system, acceleration loads (if significant), and internal pressure and loads induced by hog and sag of the ship, see Pt 3, Ch 4 of the Rules for Ships. For gas fuel piping systems with design temperatures lower than –110°C, consideration shall be given to the effects of thermal stresses.

LR 16.4-03 For gas fuel systems with pressure no greater than 1 MPa, the gas fuel piping in the machinery space is to be tested in place by hydraulic pressure to 0,7 MPa or twice the working pressure, whichever is the greater. Subsequently, the lines are to be tested by air at the working pressure using soapy water, or equivalent, to verify that all joints are absolutely tight.

LR 16.4-04 For gas fuel systems with pressure greater than 1 MPa, all gas fuel piping shall be subjected to a strength test with a suitable fluid. The test pressure shall be at least 1,5 times the design pressure for liquid lines and 1,5 times the maximum system working pressure for vapour lines. When piping systems or parts of systems are completely manufactured and equipped with all fittings, the test may be conducted prior to installation on board the ship. Joints welded on board shall be tested to at least 1,5 times the design pressure.

LR 16.4-05 For double wall fuel piping systems with pressure greater than 1 MPa, the outer pipe or duct shall also be pressure tested to show that it can withstand the expected maximum pressure at pipe rupture. The design pressure of the outer duct shall be taken as the higher of the following:

1. the maximum built up pressure: static pressure in way of the rupture resulting from the gas flowing in the annular space;
2. local instantaneous peak pressure in way of the rupture: this pressure shall be taken as the critical pressure given by the following expression:

LR 16.4-06 After assembly on board, the fuel piping system shall be subjected to a leak test using air, or other suitable medium to a pressure depending on the leak detection method applied.

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.

LR 16.5–01 Provision is to be made to enable the machinery and associated pipework used for preparing and supplying the gas boil-off to be purged of flammable gas prior to being opened up for maintenance or survey.

LR 16.5–02 Gas fuel heat exchangers and compressors, of watertight construction, may be installed on the open deck provided they are suitably located and protected from mechanical damage. Where the heat exchangers and compressors are installed in a compartment outside the machinery space, the compartment is to be treated as a hazardous area to which the requirements of Chapter 10 for electrical equipment are 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.

LR 16.5–03 The prime movers for the gas compressors are to be regulated to maintain a positive suction pressure and arranged to stop automatically if the pressure on the suction side of the compressors is lower than 0,0035 MPa gauge or other approved positive pressure appropriate to the cargo tank system or dedicated fuel tank.

LR 16.5–04 The suction and discharge connections to the compressors are to be fitted with isolating valves.

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.

LR 16.5–05 Pressure vessels for storing gas are to be of approved design and fitted with pressure relief valves discharging to atmosphere in a safe position in accordance with 8.2.12.

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.

LR 16.6–01 The firing equipment is to be of combined gas and oil type and be capable of burning both fuels simultaneously. The gas nozzles are to be so disposed as to obtain ignition from the oil flame. An inter-locking device is to be provided to prevent the gas fuel supply being opened until the oil and air controls are in the firing position.

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.

LR 16.6-02 For auxiliary boilers, 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 specifically designed for lighting directly on gas fuel, in which case details of the associated safeguards including processes and procedures are to be submitted.

LR 16.6–03 Oil fuel alone is to be used for starting up and, unless automatic transfer to oil fuel is provided, also for manoeuvring and port operations. It should be possible to change over easily and quickly from gas to oil fuel operation. These requirements should apply unless otherwise agreed by the Administration.

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.

LR 16.6–04 Each burner supply pipe is to be fitted with a gas shut-off valve and a flame arrester unless this is incorporated in the burner.

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.

LR 16.6–05 An inert gas or steam purging connection is also to be provided on the burner side of the shut-off arrangements so that the pipes to the gas nozzles can be purged immediately before and after gas is used for firing purposes.

16.6.3.4 The automatic fuel changeover system required by 16.6.2.3 shall be monitored with alarms to ensure continuous availability.

LR 16.6-06 An audible alarm is to be provided giving warning of loss of minimum effective pressure in the oil fuel discharge line or failure of the fuel pump.

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.

LR 16.6–07 In addition to the low water level fuel shut-off and alarm required by Pt 5, Ch 10,15.7 or 16.7 of the Rules for Ships for oil-fired boilers, similar arrangements are to be made for gas shut-off and alarms when the boilers are being gas-fired.

LR 16.6-08 A notice board is to be provided at the firing platform stating:

‘If ignition is lost from both oil and gas burners, the combustion spaces are to be thoroughly purged of all combustible gases before re-lighting the oil burners’.

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.

LR 16.7–01 An isolating valve and flame arrester is to be provided at the inlet to the gas supply manifold for each engine. The isolating valve is to be arranged to close automatically in the event of low gas pressure, or failure of any cylinder to fire. Arrangements are to be made so that the gas supply to each engine can be shut off manually from the control position.

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.

LR 16.7–02 Each cylinder is to be provided with its own individual gas inlet valve admitting gas either to the cylinder or to air inlet port. The timing of this valve is to be such that no gas can pass to the exhaust during the scavenge period nor to the inlet port after closure of the air inlet valve.

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.

LR 16.7–03 Dual-fuel type engines shall be capable of immediate change-over to oil fuel only. All starting is to be carried out on oil fuel alone.

LR 16.7-04 For gas fuel only installations, the fuel supply system shall be arranged with full redundancy and segregation all the way from the fuel tanks to the consumer, so that a failure in one system does not lead to an unacceptable loss of power. The gas fuel supply shall be available from more than one tank. However, in ships fitted with one Type C tank only, the supply from this tank may be accepted if two completely separate fuel supply connections are installed on the tank.

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).

LR 16.7–05 Where trunk piston type engines are used, a means of injecting inert gas into the crankcase is to be provided.

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.

LR 16.9-01 A risk-based study of the fuel supply system and associated ancillaries is to be undertaken to a recognised Standard in accordance with LR’s ShipRight procedure for Risk Based Certification (RBC). The studies are to be documented so that the risks and how they are eliminated or mitigated are clearly identified and an appropriate level of dependability of essential systems and overall safety is demonstrated. The scope of the risk-based study is to include aspects of the cargo handling system that are also part of fuel supply, the fuel supply and the consumers.

LR 16.9-02 The purpose of the risk-based study referred to in LR 16.9-01 is to:

1. demonstrate that an equivalent level of safety and dependability can be achieved as when using natural gas as a fuel in accordance with these Rules;
2. identify the need for alternative or additional safety measures due to the differences in chemical and physical characteristics of the cargo to be used as fuel compared to natural gas. The physical and chemical properties to be considered should include but not be limited to the following:
   1. boiling temperature at 1 bar [°C]
   2. density at 15°C [kg/m³]
   3. lower heating value [MJ/kg]
   4. vapour density
   5. flash point (TCC) [°C]
   6. auto ignition temperature [°C]
   7. flammability limits
   8. minimum ignition energy at 25°C [mJ]; and
3. specially consider areas of the design where it has been necessary to deviate from the requirements of this Chapter. Special attention should be paid to fire protection requirements, fuel containment, ventilation and leakage detection in spaces containing gas consumers, processing equipment and piping.

LR 16.10 Survey

LR 16.10–01 The gas compressors, heat exchangers, pressure vessels and pumps intended to be used in the fuel system and piping are to be constructed under Special Survey, and the installation of the whole plant on board the ship is to be carried out under the supervision of LR’s Surveyors. On completion, the installation is to be tested to prove its capability.