Exhaust Gas System For Main Engine; Exhaust Gas Piping System For Main Engine - Man B&W S50MC-C8-TII Project Manual

MAN B&W

Exhaust Gas System for Main Engine

At the specified MCR of the engine, the total
backpressure in the exhaust gas system after the
turbocharger (as indicated by the static pressure
measured in the piping after the turbocharger)
must not exceed 350 mm WC (0.035 bar).
In order to have a backpressure margin for the
final system, it is recommended at the design
stage to initially use a value of about 300 mm WC
(0.030 bar).
The actual backpressure in the exhaust gas
system at specified MCR depends on the gas
velocity, i.e. it is proportional to the square of the
exhaust gas velocity, and hence inversely propor-
tional to the pipe diameter to the 4th power. It has
by now become normal practice in order to avoid
too much pressure loss in the pipings to have an
exhaust gas velocity at specified MCR of about
35 m/sec, but not higher than 50 m/sec.
For dimensioning of the external exhaust pipe
connections, see the exhaust pipe diameters for
35 m/sec, 40 m/sec, 45 m/sec and 50 m/sec re-
spectively, shown in Table 5.07.02.
As long as the total backpressure of the exhaust
gas system (incorporating all resistance losses
from pipes and components) complies with the
abovementioned requirements, the pressure
losses across each component may be chosen in-
dependently, see proposed measuring points (M)
in Fig. 5.05.0. The general design guidelines for
each component, described below, can be used
for guidance purposes at the initial project stage.

Exhaust gas piping system for main engine

The exhaust gas piping system conveys the gas
from the outlet of the turbocharger(s) to the at-
mosphere.
The exhaust piping is shown schematically in
Fig. 5.04.0.
MAN B&W MC/MCC, ME/MEC/MEGI/ME-B engines
The exhaust system for the main engine com-
prises:
• Exhaust gas pipes
• Exhaust gas boiler
• Silencer
• Spark arrester (if needed)
• Expansion joints (compensators)
• Pipe bracings.
In connection with dimensioning the exhaust gas
piping system, the following parameters must be
observed:
• Exhaust gas flow rate
• Exhaust gas temperature at turbocharger outlet
• Maximum pressure drop through exhaust gas
system
• Maximum noise level at gas outlet to atmos-
phere
• Maximum force from exhaust piping on
turbocharger(s)
• Sufficient axial and lateral elongation ability of
expansion joints
• Utilisation of the heat energy of the exhaust gas.
Items that are to be calculated or read from tables
are:
• Exhaust gas mass flow rate, temperature and max-
imum back pressure at turbocharger gas outlet
• Diameter of exhaust gas pipes
• Utilisation of the exhaust gas energy
• Attenuation of noise from the exhaust pipe outlet
• Pressure drop across the exhaust gas system
• Expansion joints.
MAN Diesel
15.03
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