Section 4 Gas consumers

4.1 Special requirements for main boilers

4.1.1 Arrangements

Each boiler shall have a separate exhaust uptake.
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.
Combustion chambers and uptakes of boilers shall be designed to prevent any accumulation of gaseous fuel.

4.1.2 Combustion equipment

The burner systems should be of dual type suitable to burn either:
- fuel oil.
- gas fuel.
- oil and gas fuel simultaneously.
Burners shall be designed to maintain stable combustion under all firing conditions.
In the event of loss of fuel gas supply an automatic system shall be fitted to change over from fuel gas operation to fuel oil operation without interruption of the boiler firing.
Gas nozzles and the burner control system shall be configured such that fuel gas can only be ignited by an established fuel oil flame, unless the boiler and combustion equipment is designed and approved by LR to light on fuel gas.
Fuel oil alone is to be used for starting up. It should be possible to change over easily and quickly from gas to fuel oil operation. These requirements should apply unless otherwise agreed by the Administration. Each boiler is to have a separate uptake to the top of the funnel or a separate funnel.
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 interlocking device is to be provided to prevent the gas fuel supply being opened until the oil and air controls are in the firing position.

4.1.3 Safety

There shall be arrangements to ensure that fuel gas flow to the burner is automatically cut off unless satisfactory ignition has been established and maintained.
On the pipe of each gas burner a manually operated shut-off valve shall be fitted.
Provisions shall be made for automatically purging the fuel gas supply piping to the burners, by means of an inert gas, after the extinguishing of these burners.
The automatic fuel changeover system required by Pt 11, Ch 16, 4.1 Special requirements for main boilers 4.1.2.(c) shall be monitored with alarms to ensure continuous availability.
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.
Arrangements shall be made to enable the boilers to be manually purged.
An inert gas or steam purging connection is 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 methane gas is used for firing purposes.
Each burner supply pipe is to be fitted with a gas shut-off cock and a flame arrester unless this is incorporated in the burner. An audible alarm is to be provided giving warning of loss of minimum effective pressure in the fuel oil discharge line or failure of the fuel pump.
In addition to the low water level fuel shutoff and alarm required by Pt 5, Ch 10, 15.7 Low water level fuel shut-off and alarm or Pt 5, Ch 10, 16.7 Low water level fuel shut-off and alarm of the Rules and Regulations for the Classification of Ships (hereinafter referred to as 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.
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 relighting the oil burners’.

4.2 Special requirements for gas-fired internal combustion engines

4.2.1 General

In addition to the requirements for gas-fired internal combustion engines outlined in this Chapter, the requirements of Pt 5, Ch 2 Engines are to be complied with.
Dual fuel engines are those that employ fuel gas (with pilot oil) and fuel oil. Fuel oils may include distillate and residual fuels. Gas only engines are those that employ fuel gas only.

4.2.2 Arrangements

When fuel gas is supplied in a mixture with air through a common manifold, flame arrestors shall be installed before each cylinder head.
Each engine shall have its own separate exhaust.
The exhausts shall be configured to prevent any accumulation of unburnt gaseous fuel.
Unless designed with the strength to withstand the worst case over pressure due to ignited gas leaks, then 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.
Each engine shall be fitted with vent systems independent of other engines for crankcases, sumps and cooling systems.

4.2.3 Combustion equipment

Prior to admission of fuel gas, correct operation of the pilot oil injection system on each unit shall be verified.
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 unburned gas mixture is purged from the exhaust system.
For dual fuel engines fitted with a pilot oil injection system an automatic system shall be fitted to change over from fuel gas operation to fuel oil operation with minimum fluctuation of the engine power.
In the case of unstable operation on engines with the arrangement in (c) when gas firing, the engine shall automatically change to fuel oil mode.

4.2.4 Safety

During stopping of the engine the gas fuel shall be automatically shut off before the ignition source.
Arrangements shall be provided to ensure that there is no unburnt fuel gas in the exhaust gas system prior to ignition.
Crankcases, sumps, scavenge spaces and cooling system vents shall be provided with gas detection. See Pt 11, Ch 13, 1.6 Gas detection 1.6.17.
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 Pt 11, Ch 10 Electrical Installations.
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 Pt 11, Ch 10 Electrical Installations.

4.2.5 Additional requirements for gas-fired internal combustion engines and gas turbines

Main engines are to be of the dual-fuel type capable of immediate changeover to fuel oil only. All starting is to be carried out on fuel oil alone.
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.
In the event of a fault in the timing mechanism or a cylinder misfire, the exhaust, scavenge and air inlet manifolds are to be protected against the effect of an explosion. Where explosion relief valves are fitted they are to relieve to a safe location.
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.
The crankcase is to be fitted with gas detecting, or equivalent, equipment, and a means for the injection of inert gas. The inert gas injection is to be capable of remote operation from a safe location.
Crankcase relief valves are also to be fitted as required by Pt 5, Ch 2,6 of the Rules for Ships.

4.3 Special requirements for gas turbines

4.3.1 General

In addition to the requirements for gas turbines outlined in this Chapter, the requirements of Pt 5, Ch 3 Steam Turbines are to be complied with.

4.3.2 Arrangements

Gas turbines are also to comply with Pt 11, Ch 16, 4.2 Special requirements for gas-fired internal combustion engines 4.2.5.
Each turbine shall have its own separate exhaust.
The exhausts shall be appropriately configured to prevent any accumulation of unburnt gas fuel.
Unless designed with the strength to withstand the worst case over pressure due to ignited gas leaks, pressure relief systems shall be suitably designed and fitted to the exhaust system, taking into consideration of explosions due to gas leaks. Pressure relief systems within the exhaust uptakes shall be lead to a non-hazardous location, away from personnel.

4.3.3 Combustion equipment

An automatic system shall be fitted to change over easily and quickly from fuel gas operation to fuel oil operation with minimum fluctuation of the engine power.

4.3.4 Safety

Means shall be provided to monitor and detect poor combustion that may lead to unburnt fuel gas in the exhaust system during operation. In the event that it is detected, the fuel gas supply shall be shut down.
Each turbine shall be fitted with an automatic shutdown device for high exhaust temperatures.