11.3 External exhaust gas system
Each engine should have its own exhaust pipe into open air. Backpressure, thermal expansion and supporting
are some of the decisive design factors.
Flexible bellows must be installed directly on the turbocharger outlet, to compensate for thermal expansion
and prevent damages to the turbocharger due to vibrations.
Duel Fuel engine
1
Exhaust gas ventilation unit
2
Rupture discs
3
Exhaust gas boiler
4
Silencer
5
Figure 11.6
External exhaust gas system
11.3.1
System design - safety aspects
Natural gas may enter the exhaust system, if a malfunction occurs during gas operation. The gas may ac-
cumulate in the exhaust piping and it could be ignited in case a source of ignition (such as a spark) appears
in the system. The external exhaust system must therefore be designed so that the pressure build-up in
case of an explosion does not exceed the maximum permissible pressure for any of the components in the
system. The engine can tolerate a pressure of at least 200 kPa. Other components in the system might
have a lower maximum pressure limit. The consequences of a possible gas explosion can be minimized
with proper design of the exhaust system; the engine will not be damaged and the explosion gases will be
safely directed through predefined routes. The following guidelines should be observed, when designing
the external exhaust system:
•
The piping and all other components in the exhaust system should have a constant upward slope to
prevent gas from accumulating in the system. If horizontal pipe sections cannot be completely avoided,
their length should be kept to a minimum. The length of a single horizontal pipe section should not
exceed five times the diameter of the pipe. Silencers and exhaust boilers etc. must be designed so
that gas cannot accumulate inside.
•
The exhaust system must be equipped with explosion relief devices, such as rupture discs, in order
to ensure safe discharge of explosion pressure. The outlets from explosion relief devices must be in
locations where the pressure can be safely released.
In addition the control and automation systems include the following safety functions:
•
Before start the engine is automatically ventilated, i.e. rotated without injecting any fuel.
•
During the start sequence, before activating the gas admission to the engine, an automatic combustion
check is performed to ensure that the pilot fuel injection system is working correctly.
•
The combustion in all cylinders is continuously monitored and should it be detected that all cylinders
are not firing reliably, then the engine will automatically trip to diesel mode.
Product Guide Wärtsilä 34DF - 3/2012
105
Product Guide
11. Exhaust Gas System
