Man B&W L35MC6-TII, Project Manual

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MAN B&W 7.06
Page 1 of 2
MAN Diesel
MAN B&W MC/MC-C, ME/ME-C/ME-GI/ME-B engines 198 38 828.3
The emulsification of water into the fuel oil reduc-
es the NO
x
emission with about 1% per 1% water
added to the fuel up to about 20% without modifi-
cation of the engine fuel injection equipment.
A Water In Fuel emulsion (WIF) mixed for this pur-
pose and based on Heavy Fuel Oil (HFO) is stable
for a long time, whereas a WIF based on Marine
Diesel Oil is only stable for a short period of time
unless an emulsifying agent is applied.
As both the MAN B&W twostroke main engine
and the MAN Diesel GenSets are designed to run
on emulsified HFO, it can be used for a common
system.
It is supposed below, that both the main engine
and GenSets are running on the same fuel, either
HFO or a homogenised HFO-based WIF.
Special arrangements are available on request for
a more sophisticated system in which the GenSets
can run with or without a homogenised HFO-
based WIF, if the main engine is running on that.
Please note that the fuel pump injection capacity
shall be confirmed for the main engine as well as
the GenSets for the selected percentage of water
in the WIF.
Temperature and pressure
When water is added by emulsification, the fuel
viscosity increases. In order to keep the injection
viscosity at 10-15 cSt and still be able to operate
on up to 700 cSt fuel oil, the heating temperature
has to be increased to about 170 °C depending on
the water content.
The higher temperature calls for a higher pressure
to prevent cavitation and steam formation in the
system. The inlet pressure is thus set to 13 bar.
In order to avoid temperature chock when mixing
water into the fuel in the homogeniser, the water
inlet temperature is to be set to 7090 °C.
Safety system
In case the pressure in the fuel oil line drops, the
water homogenised into the Water In Fuel emul-
sion will evaporate, damaging the emulsion and
creating supply problems. This situation is avoid-
ed by installing a third, air driven supply pump,
which keeps the pressure as long as air is left in
the tank ‘S’, see Fig. 7.06.01.
Before the tank ‘S’ is empty, an alarm is given and
the drain valve is opened, which will drain off the
WIF and replace it with HFO or diesel oil from the
service tank.
The drain system is kept at atmospheric pressure,
so the water will evaporate when the hot emulsion
enters the safety tank. The safety tank shall be
designed accordingly.
Impact on the auxiliary systems
Please note that if the engine operates on Water
In Fuel emulsion (WIF), in order to reduce the NO
x
emission, the exhaust gas temperature will de-
crease due to the reduced air / exhaust gas ratio
and the increased specific heat of the exhaust gas.
Depending on the water content, this will have an
impact on the calculation and design of the fol-
lowing items:
• Freshwater generators
• Energy for production of freshwater
• Jacket water system
• Waste heat recovery system
• Exhaust gas boiler
• Storage tank for freshwater
For further information about emulsification of wa-
ter into the fuel and use of Water In Fuel emulsion
(WIF), please refer to our publication titled:
Exhaust Gas Emission Control Today and
Tomorrow
The publication is available at: www.mandiesel.com
under ‘Quicklinks’
→
‘Technical Papers
Water In Fuel Emulsification