Fgr Duct System - Riello DB 3 SE FGR Installation, Use And Maintenance Instructions

4.10

FGR duct system

– Normally the duct would connect to the stack as shown in
Fig. 18, with a 45° cut facing the flue gas flow and with the
centre of the cut centred in the stack.
The duct could be made to the smoke box, but must still be
located with the same 45° cut facing the flue gas flow stream
and with the centre of the cut in the centre of the stream.
– The duct should be routed in a manner that has the minimum
number of elbows and provides for the normal expansion and
contraction of the piping.
Long duct runs can change length by over 1" and can put an
extreme load on the connecting points that could cause com-
ponent failures.
The design must include offsets that will allow for the required
movement of the piping without undue force on the burner or
stack.
– Duct expansion and contraction can be managed by using
two relatively long duct runs that are 90° opposed to each
other.
A small movement in the angle between these two legs will
provide the space needed to absorb the expansion and con-
traction. The ends of the FGR duct must be securely attached
to allow this to work properly, and prevent high loads from be-
ing applied to the burner or stack.
– A condensation drip leg must be provided upstream of the
FGR control valve and the FGR shut-off valve (if used). There
must be sufficient condensate drip legs and catch space (vol-
ume of drip legs) to prevent the condensation from flowing
through the control valves and into the fan.
In cases of heavy condensation, a condensate drip leg may
be required on the bottom of the housing, to remove conden-
sate.
EXEMPLIFYING SCHEME
3 7
6
1
Key (Fig. 18)
1 Primary gas supply inlet
2 Inducted FGR modulating damper
3 Flue gas recirculation pipe
4 Boiler stack
5 Alternate Construction Using "T"
Installation
– Determine if pipe reducers are needed for the connection to
the FGR control valve and the FGR shutoff valve.
– The duct must be properly supported, handling both the
weight of the duct and to control the thermal expansion and
contraction. The supports may need to be anchored to pro-
vide this stability in the FGR duct.
Uncontrolled condensation can cause premature
failure of the control valves, fan and motor.
Adequate means must be provided to remove
CAUTION
condensation from the system.
Cold startup will generate significant amounts of
condensation.
– The FGR duct is normally made from 6" or DN 150 pipe be-
cause it is easily obtainable and inexpensive.
5" or DN 125 pipe can also be used for this application.
– The duct components must be seal welded, flanged or
screwed together to provide an air tight duct.
Air leakage into the duct will prevent the system from working
properly. It is sufficient to only inspect the welds for a proper
seal, they do not need to be leak tested.
The flue gas recirculation ducts must be made of
stainless steel to prevent corrosion due to con-
densation.
WARNING
4
8
9
S9655
6 Burner
7 Boiler
8 Drain Valve (Manual Ball Valve, Stainless Steel)
9 Drain line
10 Condensate Trap
18 GB
3
5
2
8
10
Fig. 18
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