Exhaust Gas Silencer; Spark Arrester - Man B&W S50MC-C8-TII Project Manual

MAN B&W

Exhaust gas silencer

The typical octave band sound pressure levels
from the diesel engine's exhaust gas system – at a
distance of one meter from the top of the exhaust
gas uptake – are shown in Fig.15.04.0.
The need for an exhaust gas silencer can be de-
cided based on the requirement of a maximum
permissible noise level at a specific position.
The exhaust gas noise data is valid for an exhaust
gas system without boiler and silencer, etc.
The noise level is at nominal MCR at a distance of
one metre from the exhaust gas pipe outlet edge
at an angle of 30° to the gas flow direction.
For each doubling of the distance, the noise level
will be reduced by about 6 dB (farfield law).
When the noise level at the exhaust gas outlet to
the atmosphere needs to be silenced, a silencer
can be placed in the exhaust gas piping system
after the exhaust gas boiler.
The exhaust gas silencer is usually of the absorp-
tion type and is dimensioned for a gas velocity of
approximately 35 m/s through the central tube of
the silencer.
An exhaust gas silencer can be designed based
on the required damping of noise from the ex-
haust gas given on the graph.
In the event that an exhaust gas silencer is re-
quired – this depends on the actual noise level
requirement on the bridge wing, which is normally
maximum 6070 dB(A) – a simple flow silencer of
the absorption type is recommended. Depending
on the manufacturer, this type of silencer nor-
mally has a pressure loss of around 0 mm WC at
specified MCR.
MAN B&W S50MC6, S50MC-C/ME-C7/8, S50ME-B8/9
Fig. 15.04.02: ISO's NR curves and typical sound pres-
sure levels from the engine's exhaust gas system. The
noise levels at nominal MCR and a distance of 1 metre
from the edge of the exhaust gas pipe opening at an angle
of 30 degrees to the gas flow and valid for an exhaust
gas system – without boiler and silencer, etc. Data for a
specific engine and cylinder no. is available on request.

Spark arrester

To prevent sparks from the exhaust gas being
spread over deck houses, a spark arrester can be
fitted as the last component in the exhaust gas
system.
It should be noted that a spark arrester contrib-
utes with a considerable pressure drop, which is
often a disadvantage.
It is recommended that the combined pressure
loss across the silencer and/or spark arrester
should not be allowed to exceed 100 mm WC at
specified MCR. This depends, of course, on the
pressure loss in the remaining part of the system,
thus if no exhaust gas boiler is installed, 00 mm
WC might be allowed.
MAN Diesel
15.04
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