External Exhaust Gas System - WÄRTSILÄ 46DF Product Manual

Wärtsilä 46DF Product Guide
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.
Fig 11-5
11.3.1 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. 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.
DBAD209883
External exhaust gas sys-
tem
1 Duel Fuel engine
2 Exhaust gas ventilation unit
3 Rupture discs
4 Exhaust gas boiler
5 Silencer
11. Exhaust Gas System
11-5