Preferred FlexFit 110 - Fuel-Air > FGR

Parameters 4-69
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
PP
AA
RR
AA
MM
EE
TT
EE
RR
SS
P2.4.2 MInuteS Per rePeat, o2 trIM
Menu > Tuning > O2 Trim Parameters Password Level: Technician Restricted? No
This determines the PID Integral ramp rate, expressed in Minutes-per-Repeat. A smaller value makes the integral ramp in less time,
faster.
Options: 0.20 to 2.50 [Default 0.50]
Note If the Minutes-per-Repeat is too small, then O
2
Trim will oscillate; if it is too large, then O
2
Trim will be slow getting to
setpoint.
P2.4.3 SP lag tIMe o2 trIM
Menu > Tuning > O2 Trim Parameters Password Level: Technician Restricted? No
This determines O
2
Trim lag time (seconds). This time delay accounts for the transit time from the burner to the stack at lower ring rates.
Options: 2.0 to 16.0 [Default 8.0]
Note It is important to set "SP Lag Time O2 Trim" properly for correct trim operation at lower ring rates.
P2.4.4 +/- Max FIre trIM, o2
Menu > Tuning > O2 Trim Parameters Password Level: Technician Restricted? No
This limits the O
2
Trim range to + or - this value. (E.g. A value of 10.00 limits O
2
Trim to a range of -10.00 to +10.00). This is the trim
amount before ring rate scaling is applied.
Options: 0.10 to 15.00 [Default 10.00]
P2.4.5 MIn FIre trIM Scaler, o2/aIr trIM
Menu > Tuning > O2 Trim Parameters Password Level: Technician Restricted? No
This determines the O
2
Trim scaling multiplier at minimum re. The "Firing Rate Trim Scaling Multiplier" decreases in proportion to
the fuel servo position and the "Min Fire Trim Scaler, O2/Air Trim" (E.g. The PID is calling for an unscaled trim of +10.00% and "Min
Fire Trim Scaler, O2/Air Trim" = 0.25. Then at maximum ring rate, scaled trim = +10.00; at minimum ring rate, scaled trim = +2.50;
and at mid-fuel servo position, scaled trim = +6.25).
Initially, rough set "Min Fire Trim Scaler, O2/Air Trim" to the burner turndown percentage. (I.e. 12:1 = 0.08, 10:1 = 0.10, 8:1 = 0.13, 5:1
= 0.20, 4:1 = 0.25). See Trim Tuning in the oxygen analyzer manual for more information.
Options: 0.01 to 0.60 [Default 0.20]
P2.4.6 % FIrIng rate dISable, o2 trIM
Menu > Tuning > O2 Trim Parameters Password Level: Technician Restricted? No
This determines at what ring rate O
2
Trim will be disabled. O
2
Trim is nulled (i.e. set to 0) when the ring rate is less than this value.
Options: 1.0 to 40.0 [Default 5.0]
P2.4.7 burner warM uP delay Sec, o2 trIM
Menu > Tuning > O2 Trim Parameters Password Level: Technician Restricted? No
This determines the O2 Trim warm up delay time (seconds). After light-off, the O2 Trim remains nulled for this amount of time.
Options: 30 to 300 [Default 120]
Fuel-Air > FGR
A common method used to reduce burner ue gas NO
X
is to mix ue gas with fresh air at the FD fan inlet. This is called Flue
Gas Recirculation (FGR). Typically, the suction at the FD fan inlet is used to move ue gas into the burner; this is called induced
FGR. The FGR reduces the oxygen level from the normal ~20.6% in fresh air down to approximately 15–18% and correspondingly
increases the percentage of the non-combustible gases entering the burner. The extra non-combustible gases reduce the ame
temperature and thus the formation of thermal NO
X
.
For most installations, the FGR damper position is simply positioned based on a fuel valve vs. FGR damper curve that is estab-
lished during burner commissioning. After that, the FGR ow rate is not monitored or adjusted.
Parameter "P2.5.6 FGR Servo Check Mode" controls the action of the FGR servo during the servo check procedure. The options
are "Closed then Open" or "Open then Closed". The action is usually determined by how the burner manufacturer wants the position
of the FGR damper during the burner purge. To minimize the time it takes for purge to start, this should be set so the servo check
nishes as close as possible to the FGR servo purge position. E.g. if the FGR servo is closed during purge, then the "FGR Servo
Check Mode" should be set to "Open then Closed".
P2.5.1 Fgr teMP low FIre hold oPtIon
Menu > Optional Features > FGR Low Fire Hold Password Level: Technician Restricted? No
Determines if the Flue Gas Return (FGR) temperature low re hold option is used
Options: Disabled: The FGR temperature low re hold option is not used.
Enabled: After light-off, the FlexFit holds the burner at low re until the ue temperature is greater than "P2.5.2
Release Temp, FGR LFH". While holding at low re, the FGR is cutback in proportion to the ue gas temperature.
The maximum amount of FGR cutback is determined by "P2.5.4 Fuel 1 Cutback % at FGR Min Temp" or "P2.5.5