Wartsila ?31DF Series Product Manual page 160

11. Exhaust Gas System
After the first fixing point resilient mounts are recommended. The mounting supports should
be positioned at stiffened locations within the ship's structure, e.g. deck levels, frame webs
or specially constructed supports.
The supporting must allow thermal expansion and ship's structural deflections.
11.2.6 Back pressure
The maximum permissible exhaust gas back pressure is stated in chapter Technical Data. The
back pressure in the system must be calculated by the shipyard based on the actual piping
design and the resistance of the components in the exhaust system. The exhaust gas mass
flow and temperature given in chapter Technical Data may be used for the calculation.
Each exhaust pipe should be provided with a connection for measurement of the back pressure.
The back pressure must be measured by the shipyard during the sea trial.
11.2.7 Exhaust gas bellows (5H01, 5H03)
Bellows must be used in the exhaust gas piping where thermal expansion or ship's structural
deflections have to be segregated. The flexible bellows mounted directly on the turbocharger
outlet serves to minimise the external forces on the turbocharger and thus prevent excessive
vibrations and possible damage. All exhaust gas bellows must be of an approved type.
11.2.8 SCR-unit (11N14)
The SCR-unit requires special arrangement on the engine in order to keep the exhaust gas
temperature and backpressure into SCR-unit working range. The exhaust gas piping must be
straight at least 3...5 meters in front of the SCR unit. If both an exhaust gas boiler and a SCR
unit will be installed, then the exhaust gas boiler shall be installed after the SCR. Arrangements
must be made to ensure that water cannot spill down into the SCR, when the exhaust boiler
is cleaned with water.
In dual fuel engines the SCR system is not required, as IMO Tier 3 is met in gas mode.
More information about the SCR-unit can be found in the Wärtsilä Environmental Product
Guide.
11.2.9 Exhaust gas boiler
If exhaust gas boilers are installed, each engine should have a separate exhaust gas boiler.
Alternatively, a common boiler with separate gas sections for each engine is acceptable.
For dimensioning the boiler, the exhaust gas quantities and temperatures given in chapter
Technical data may be used.
11-6
Wärtsilä 31DF Product Guide
DBAE248994