MAN B&W 3.03
Page 1 of 2
MAN Diesel
198 58 94-7.1MAN B&W MC/MC-C, ME/ME-C/ME-GI/ME-B Engines
The NOx in the exhaust gas can be reduced with
primary or secondary reduction methods. Primary
methods affect the engine combustion process
directly, whereas secondary methods reduce the
emission level without changing the engine per-
formance using equipment that does not form
part of the engine itself.
For further information about emission control we
refer to our publication:
Exhaust Gas Emission Control Today and Tomorrow
The publication is available at www.mandiesel.com
under ‘Quicklinks’ → ‘Technical Papers’
Engine with Selective Catalytic Reduction System
Option: 4 60 135
If a reduction between 50 and 98% of NO
x
is re-
quired, the Selective Catalytic Reduction (SCR)
system has to be applied by adding ammonia or
urea to the exhaust gas before it enters a catalytic
converter.
The exhaust gas must be mixed with ammonia be-
fore passing through the catalyst, and in order to
encourage the chemical reaction the temperature
level has to be between 300 and 400 °C. During
this process the NO
x
is reduced to N
2
and water.
This means that the SCR unit has to be located
before the turbocharger on twostroke engines
because of their high thermal efficiency and there-
by a relatively low exhaust gas temperature.
The amount of ammonia injected into the ex-
haust gas is controlled by a process computer
and is based on the NO
x
production at different
loads measured during the testbed running. Fig.
3.03.01.
As the ammonia is a combustible gas, it is sup-
plied through a doublewalled pipe system, with
appropriate venting and fitted with an ammonia
leak detector (Fig. 3.03.01) which shows a simpli-
fied system layout of the SCR installation.
NOx Reduction by SCR
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