•
The exhaust gas system is ventilated by a fan after the engine has stopped, if the engine was operating
in gas mode prior to the stop. The control of this function must be included in the external automation
system.
11.3.2
Exhaust gas ventilation unit (5N01)
An exhaust gas ventilation system is required to purge the exhaust piping after the engine has been stopped
in gas mode. The exhaust gas ventilation system is a class requirement. The ventilation unit is to consist
of a centrifugal fan, a flow switch and a butterfly valve with position feedback. The butterfly valve has to
be of gas-tight design and able to withstand the maximum temperature of the exhaust system at the location
of installation.
The fan can be located inside or outside the engine room as close to the turbocharger as possible. The
exhaust gas ventilation sequence is automatically controlled.
Figure 11.7
Exhaust gas ventilation arrangement (3V76A2955)
Unit components
Ball valve
5
Switch
1
Bellow
6
Fan
2
Blind flange
7
Bellow
3
Flange
8
Butterfly valve
4
11.3.3
Relief devices - rupture discs
Explosion relief devices such as rupture discs are to be installed in the exhaust system. Outlets are to dis-
charge to a safe place remote from any source of ignition. The number and location of explosion relief
devices shall be such that the pressure rise caused by a possible explosion cannot cause any damage to
the structure of the exhaust system.
This has to be verified with calculation or simulation. Explosion relief devices that are located indoors must
have ducted outlets from the machinery space to a location where the pressure can be safely released.
The ducts shall be at least the same size as the rupture disc. The ducts shall be as straight as possible to
minimize the back-pressure in case of an explosion.
For under-deck installation the rupture disc outlets may discharge into the exhaust casing, provided that
the location of the outlets and the volume of the casing are suitable for handling the explosion pressure
pulse safely. The outlets shall be positioned so that personnel are not present during normal operation, and
the proximity of the outlet should be clearly marked as a hazardous area.
11.3.4
Piping
The piping should be as short and straight as possible. Pipe bends and expansions should be smooth to
minimise the backpressure. The diameter of the exhaust pipe should be increased directly after the bellows
on the turbocharger. Pipe bends should be made with the largest possible bending radius; the bending
radius should not be smaller than 1.5 x D.
106
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
11. Exhaust Gas System
