11.2 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.
Engine1
Exhaust gas bellows2
Transitions piece3
Exhaust gas ventilation unit *4
Connection for measurement of back pressure5
Drain with water trap, continuosuly open6
Bilge7
Rupture disc *8
Selective Catalytic Reactor (SCR)9
Urea injection unit (SCR)10
Silencer with spark arrestor11a
CSS silencer element11b
Fig 11-5 External exhaust gas sys-
tem (DAAF391527)
NOTE
* Only applicable for DF installations
11.2.1 System design - safety aspects
Natural gas may enter the exhaust system if a malfunction occurs during gas operation. The
gas may accumulate 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. 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.
DBAE248994 11-3
11. Exhaust Gas SystemWärtsilä 31DF Product Guide
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