Flue Gas Recirculation (Fgr) Function (Lmv50/Lmv51.3/Lmv52); Function Principle Of Flue Gas Recirculation (Fgr) - Siemens LMV50 Series Manual

Β
Β
Building Technologies
20 Flue gas recirculation (FGR) function
(LMV50/LMV51.3/LMV52)
20.1 Function principle of flue gas recirculation
(FGR)
The flue gas recirculation (FGR) function is used to reduce the NOx content of flue
gases. This is accomplished by feeding a certain proportion of the flue gas back to the
combustion chamber, causing the flame's temperature to drop. The amount of
recirculated flue gas is set via auxiliary actuator 3.
Caution!
When carrying out the settings, it is important to remember that, if the flue gas
recirculation quantity is too high, the flame may lift off the burner (stability limit
of the flame).
Caution!
Extra care must be taken when using flue gas recirculation in combination with
O2 control.
It is essential for the following physical effects to be taken into consideration:
1. Pressures have reciprocal effects
2. The reduction of O2 can lead to a significant increase of NOx levels
As a result of these reciprocal effects, the setting of the fuel-air ratio control, O2 trim
control, and the flue gas recirculation (FGR) function is difficult or impossible.
Even if it is possible to make adjustments, it may be the case during operation that the
flame is unstable or the required NOx values cannot be achieved.
This does not affect the use of the O2 monitoring function.
Note!
Problems in connection with condensation near the intake
In the intake duct, the hot and humid flue gas mixes with cold supply air.
This means that the recirculated flue gas can lead to condensation in the vicinity of the
burner intake, depending on flue gas and supply air temperature.
Result:
Water enters the burner; in the case of oil-firing possibly with parts of sulfurous acid.
Note!
Reduction of maximum burner output
Use of the flue gas recirculation (FGR) function or the flue gas mass introduced to the
supply air duct might lower the burner's maximum output.
This means that the maximum amount of combustion air that can be introduced will be
reduced.
Hence, the amount of fuel for high-fire operation must be reduced to ensure correct
combustion values.
Basic Documentation LMV5...

20 Flue gas recirculation (FGR) function (LMV50/LMV51.3/LMV52)

289/327
CC1P7550en
22.05.2018