Bergen B35:40, Руководство по проекту

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, Gas Ventilation system
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2.04
0611 BC
V
ENTILATION SYSTEM
Introduction
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.
Exhaust ventilation system
The complete exhaust gas piping system must be
flush with air prior to start of engine, to avoid the risk
of a gas explosion.
Each engine is connected to a separate exhaust duct
leading to open air.
The exhaust system should be provided with air
ventilation system connected to the exhaust pipe
within 2m from the turbocharger outlet.
The ventilation system can draw air from the engine
room.
The ventilation system should be able to flush
exhaust pipe with volume of air at least equal to 3
times the volume of the exhaust gas system after the
turbocharger in 2 minutes.
Min. air velocity in typical pipe section is 1.5m/s.
Cold air, cold exhaust pipe and the lowest engine
room pressure with respect to outside should be
assumed in the calculation.
Any additional or supplementary requirements from
classification society may also need to be considere
As shown on figure a pipe with angle no less than
30ºC should be inserted into the exhaust pipe to
direct the ventilation air in correct direction.
1. Air ventilation fan
2. Flow switch
3. Temperature sensor
4. Shut off valve
5. Siphon for water drain
6. Flexible steel bellow
The system will consist of a centrifugal fan, an
actuator - operated valve, tempertature and
pressure transmitters, and a control panel.
To protect the fan, an electrically operated shut off
valve must be installed between the fan and the hot
exhaust pipe. The valve and steel bellow must be
dimensioned for a temperature of no less than
450ºC.
To ensure that the valve is closed, a temperature sen-
sor must be mounted between the valve and the
ventilation fan. A flow switch should be mounted
just after the fan to ensure that there is an air flow in
the system.
Start and stop of the ventilation fan can be control-
led by engine control system.
Fuel ventilation
To avoid fuel gas being released to the engine room
due to leakage in pipes and valves, all pipes and
valves are double walled. This also includes flanges.
The double walled pipes consist of a fuel gas pipe
and an outer duct pipe. The air between the double
wall pipes (annular gap) is sucked to a gas detection
unit in a separate compartment.
At the end of the main gas pipe and the pre chamber
gas pipe there is placed a hole to let in air to the
annular gap. This is to secure a positive flow to the
gas detection unit. The air is taken from a designated
safe area, preferably dry air to avoid condensation
build ups in the annular gap. The air in the annular
gap is exchanged minimum 30 times each hour.
From the detection unit the air is ventilated to a safe
area outside the ship. If fuel gas is detected, a signal
will be sent to the engines control system, and nec-
essary actions must be taken (close gas supply etc.)
Because of the gas-free engine room, the engines
combustion air can be taken directly from the engine
room.