4.14 LP Selective catalytic reduction system
The Low Pressure Selective Catalytic Reduction (LP SCR) system is an optional system to
decrease the level of nitrogen oxides in the exhaust gas. This makes sure that the emissions of
nitrogen oxides obey the Tier III regulations of the International Maritime Organization (IMO).
Nitrogen oxides are dangerous and are made in secondary reactions in the engine during fuel
combustion.
The LP SCR system is installed after the turbocharger. The system design and the supply of
components is divided between the LP SCR system supplier, the shipyard and WinGD/engine
builder.
The LP SCR system adds a urea water solution to the exhaust gas flow. Chemical reactions
change nitrogen oxides to molecular nitrogen and water, which are not dangerous.
Because of the low exhaust gas temperature after the turbocharger ammonia bisulfates are
formed in the LP SCR reactor. You must regularly change to bypass operation and do a
regeneration procedure to remove these deposits, refer to the related documentation of the
manufacturer. During this procedure the LP SCR system cannot operate.
NOTE: For a DF engine: The LP SCR system can only be used in diesel mode.
NOTE: For further details about the operation, maintenance and troubleshooting aspects of
the LP SCR system, please refer to the manuals of the manufacturer.
4.14.1 Description of the LP SCR system
4.14.1.1 LP SCR system parts
The LP SCR system has the parts shown in the paragraphs that follow (see Figure 4-14 and
Figure 4-15):
•
Urea pump unit
This unit supplies the urea solution from the tank to the urea solution dosing unit. This
keeps the applicable pressure in the related pipes.
•
Urea dosing unit
The urea dosing unit controls the supply of urea solution to the decomposition unit.
•
Burner
The burner heats up the exhaust gas flow that is used to inject the urea.
•
Decomposition unit
In the decomposition unit the exhaust gas and the urea is mixed to form ammonia.
•
LP SCR reactor
The LP SCR reactor has a steel wall and has an inlet and an outlet cone. A steel
structure holds the catalyst layers. At the catalytic surface of the catalyst layers the
nitrogen oxides (NO and NO
2
) react with the ammonia into molecular nitrogen (N
2
) and
water (H
2
O). These gases are part of the ambient air and are not dangerous.
Manholes in the reactor walls are used to examine and, if necessary, to clean or replace
the catalyst elements.
X92DF
AA00-9270-00AAA-043B-A
Operation Manual LP Selective catalytic reduction system
Winterthur Gas & Diesel Ltd.
- 106 - Issue 002 2020-08
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