4.12.2.2 HP SCR system - bypass
In this operation mode, the HP SCR system is bypassed. The engine operates in Tier II mode.
Urea solution is not injected.
If you change from Tier III mode to bypass mode, the HP SCR control system changes the valve
conditions and starts the preservation sequence. If a condition for correct operation for Tier III
mode is not given, the HP SCR control system automatically changes to bypass mode.
•
First the valves have the conditions that follow (refer to Figure 4-11):
○
V1 - Slowly changes from open to closed
○
V2 - Slowly changes from open to closed
○
V3 - Open
○
V4 - Controlled by the ECS, can be more opened to decrease the scavenge air flow
and thus to increase the exhaust gas temperature
○
V7 - Closed, can be opened to decrease the pressure in the reactor
•
Then the preservation sequence starts as follows to prevent corrosion of the reactor and of
the pipes (refer to Figure 4-12):
○
The purging sequence uses compressed air to remove the remaining urea solution
from the injection equipment, from the pipes and from the reactor.
○
The venting/sealing unit starts and the valve V7 opens for some minutes. Thus the
compressed air removes the exhaust gas to the exhaust gas system of the plant.
•
If the venting/sealing unit is unserviceable, decrease the pressure in the reactor and drain
the condensation.
Fig 4-11 HP SCR system - change from Tier III to bypass
V1 V2
V3
V7
V4
003
001
007
006
005
004
002
00525
X72-B
AA00-9270-00AAA-043A-A
Operation Manual HP Selective catalytic reduction system
Winterthur Gas & Diesel Ltd.
- 100 - Issue 003 2021-12
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