FSSS Logic

1. Master Fuel Trip Logic
Circulating Fluidized Bed (CFB) Boiler

2. Contents
• Process Followed
• Segregation of Control Systems in DCS
• Major Boiler Hazards, Causes & Protections
• Master Fuel Trip (MFT)
• How is MFT generated?
• What are the post MFT actions?
• Logics are referenced from EPTL logic
• In presentation, logics are presented in simplified manner

3. Process Followed
Includes
• Hub Power Station
Boiler Protection Logic
Scope
Development
Bench Marking Internal Review
Includes
• E&I Team Internal Review
• Cross Functional Review
Includes
• Design Review
• NFPA-85 ( Boiler and
Combustion Hazards Code)
• EPTL Logic diagram
Literature Review

4. Segregation of Control Systems in DCS
• Used for indication of values to the operator
• Example: Individual fluidizing air blowers outlet pressure
DAS
(Data Acquisition System)
• Used for the controlling of process.
• Example: Fluidizing air blowers pressure control.
MCS
(Modulating Control System)
• Used for sequential control & interlocks (on/off operation)
• Example: Fluidizing air blower cut-in logic.
SCS
(Sequential Control System)
• Used for sequential control & interlocks of burners and coal feeders. It can be
considered as a special purpose SCS.
• Example: Tripping of individual burner on its loss of flame.
BMS
(Burner Management System)
• Used for boiler protection.
• Example: Master Fuel Trip (MFT) on furnace pressure very high.
FSSS
(Furnace Safety &Supervision
System)

5. Boiler Hazards – Boiler Explosion
Un-burnt Fuel
• Improper combustion
will lead to unburnt
fuel
• Accumulated fuel will
create vapor / gas
mixture
• On Light-up this
mixture can cause
explosion
Trips:
• Air flow < 25%
• Loss of both PA fans (Only on coal fuel)
• Furnace temp LL (Only on coal fuel)
• Loss of all flame (Only on oil fuel)
Purge Requirement before start-up:
• If Furnace Temp < Adequate

6. Boiler Hazards – Boiler Explosion
Furnace Over
Pressure
• Balanced draft boiler
(SA and ID fans)
• Draft Imbalance will
cause disturbance
furnace pressure
• Over pressurized
furnace can explode
Trips:
• Loss of both ID Fans
• Furnace pressure HH (152 mmH2O)
• Less than 02 Fluidizing Air blowers running
• After MFT, if furnace press HHH (254mmH2O), then cut-
out both PA and SA Fans
Load Rejection:
• If single ID Fan trips, then cut-out corresponding SA
fan.

7. Boiler Hazards – Boiler Implosion
Furnace Under
Pressurization
• Balanced draft boiler
(SA and ID fans)
• Draft Imbalance will
cause disturbance
furnace pressure
• Excessive Negative
Pressure in furnace can
cause implosion
Trips:
• Trip on loss of both SA Fans
• Trip on furnace pressure LL (220mmH2O)
• After MFT if furnace pressure LLL (229mmH2O), then trip both
ID fans
Load Rejection:
• If single SA Fan trips, corresponding ID fan trips as well

8. Boiler Hazards – Boiler Tube Failure
Over Temperature
• Different causes like
steam / water starvation
in water wall tubes can
excessive temperature
• It can cause boiler tubes
to fail
Trips:
• Drum Water LL (-254mm)

9. Boiler Trip Conditions
S.No Boiler Trip
1 Both SA Fans Stopped
2 Both ID Fans Stopped
3 Turbine Trip
4 MFT Push Button
5 Total Air Flow < 25% (5 sec)
6 Furnace Pressure HH (152mm H2O)
7 Furnace Pressure LL (-220 mm H2O)
8 Drum Level HH (+254 mm) (5 seconds)
9 Drum Level LL (-254 mm) (5 seconds)
10 Less than 02 Fluidized Air Blower Running
11 Loss of Fuel Trip
12 Furnace Temp <620 C AND Both PAF Stopped
13 Both PAF Stopped (On Coal Fuel Only)
14 Primary Air Flow (On Coal Fuel Only)
15 Furnace Temp < Adequate (On Coal Fuel Only)

10. Signals for Boiler Load Rejection
S.No Boiler Load Rejection
1 Fuel Flow < Demand
2 Air Flow < Demand
3 Feed Water Flow < Demand
4 Primary Air Pressure < Demand
5 Fluidizing Air Pressure < Demand
6 Furnace Temperature < Demand
7 Drum Pressure < Demand
8 First Stage Pressure < Demand
9 Turbine Inlet Pressure < Demand
10 Either ID Fan Trip
11 Either SA Fan Trip
12 Either PA Fan Trip
13 Either Turbine Driven FWP Trip

11. MFT ( Main Fuel Trip)
BOTH SAFs STOPPED
BOTH IDFs STOPPED
TURBINE TRIP
MFT PUSH BUTTON
TOTAL AIR FLOW < 25% (5 sec)
FURNACE PRESSURE HH
(152 mm H2O)
FURNACE PRESSURE LL
(-220 mmH2O)
DRUM LEVEL LL (5 sec)
DRUM LEVEL HH (5 sec)
LOSS OF FUEL TRIP (LOFT)
<2 FLUID AIR BLOWERS ON
CONDITION # 1
CONDITION # 2
CONDITION # 3
OR
RESET
PURGE COMPLETED
MFT
PULSE:
( 5 sec )

12. Condition #1
FURNACE TEMPERATURE <
ADEQUATE (620°C)
BOTH PAF STOPPED
ANY COAL FEEDER ON
ANY COAL CONVEYOR (A/K)
ON
NO START-UP BURNER OIL
VALVE OPEN
AND
AND
OR CONDITION # 1

13. Condition #2
AND
ANY COAL FEEDER ON
ANY COAL CONVEYOR (A/K) ON
NO START-UP BURNER OIL
VALVE OPEN
PRIMARY AIR FLOW LOW
CONDITION # 2

14. Condition #3
AND
ANY COAL FEEDER ON
ANY COAL CONVEYOR (A or K)
ON
NO START-UP BURNER OIL
VALVE OPEN
FURNACE TEMPERATURE <
ADEQ FOR SOLID FUEL
CONDITION # 3

15. Furnace Purge
FSSS DPU POWER NO ALARM
AND
ALL SU BURNERS NO FLAME
ALL SU BNRS OIL TRIP VLVS CLSD
ALL COAL FEEDERS OFF
ALL COAL FEEDER TRIP VLV CLSD
EITHER PA FAN ON
ALL LS ROTARY VALVE OFF
PA FLOW >30%
NO MFT CONDITION STANDING
ALL COAL CONVEYOR (A&K) OFF
ALL SU BNRS AIR DMPERS OPEN
AND
NOT RESET
DELAY TIMER :
0 min 5 min
FURN.
TEMP.>ADEQ FOR
SOLID FUEL
NOT
PURGE
COMPLETE
PURGE
INPROGRESS
PURGE
BREAK
PURGE START COMMAND
AND

16. Post MFT Actions
All coal feeder will STOP
All individual burner oil valve will CLOSE
Oil supply main oil valve will CLOSE
Boiler air flow control to MANUAL
Boiler soot blower will STOP
Limestone feeders will STOP
Turbine BFPs inlet steam valves to CLOSE, and motor-BFP to START
Turbine Trip will INITIATE

17. Special Situations for Boiler Fans (1/2)
FURNACE PRESSURE LLL
(-229 mmH2O)
MFT DELAY TIMER
( 20 sec )
AND
FURNACE PRESSURE HHH
(254 mmH2O)
MFT
ID Fans Trip
AND
BOTH SA FANs TRIP
SA Fans Trip
PA Fans Trip
FABs Trip
SA Fans Trip
PA Fans Trip
FABs Trip
ID Fans Trip
ID Fans Trip
PA Fans Trip
FABs Trip

18. Special Situations for Boiler Fans (2/2)
BOTH ID FANs TRIP
LESS THAN 02 FABs RUNNING
DRUM LEVEL LL (-254 mm)
PA Fans Trip
PA Fans Trip
SA Fans Trip
PA Fans Trip
FABs Trip

19. Way Forward
Following protections need further review:
1. MFT on Furnace Temperature LL (820 °C on coal fuel)
• NFPA 85, sets this limit to 649 °C
2. MFT on Fluidizing Air Blower < 02 running
• To be reviewed for low load scenario.
3. MFT on Turbine Trip
• Considering the HP/LP bypass provision, MFT on turbine trip needs to be reviewed
4. MFT on Drum Level HH
• Utility of boiler trip on Drum Level HH to be reviewed
5. MFT on Furnace Temp HH
• Introduction of Furnace Temp HH trip to be evaluated.

20. THANK YOU

21. BACK UP SLIDES

22. LOFT (Loss of Fuel Trip)
ANY COAL FEEDER ON
ANY COAL CONVEYOR (A or K)
ON
ANY START-UP BURNER OIL
VALVE OPEN
ALL COAL FEEDER OFF
FUEL OIL HEADER SHUTOFF
VALVE OPEN
MFT > 5 sec
ANY INDUCT BURNER OIL
VALVE OPEN
ALL COAL CONVEYOR (A, K)
OFF
OR
OR
NOT
OR
NOT
S
AND
LOFT
R

23. Special Conditions Matrix
Selected Inputs Outputs
MFT(20 sec) and Furnace Press LLL
ID Fan Trip
SA Fan Trip (corresponding)
Drum Level LL
PA Fan Trips
MFT and Furnace Press HHH
More than 02 FABs stopped
Both ID Fan Trips
ID Fan trip (corresponding)
SA Fan Trips
MFT and Furnace Press HHH
Both ID Fans Trip
Both ID Fans Trip FAB Trips

24. Furnace Temperature (1/2)
FURNACE UPPER FRONT TEMP 8
FURNACE LOWER FRONT TEMP 8
FURNACE UPPER FRONT TEMP 7
AVERAGE
FURNACE UPPER FRONT TEMP 6
FURNACE LOWER FRONT TEMP 6
FURNACE LOWER FRONT TEMP 5
AVERAGE
FURNACE LOWER REAR TEMP 1
FURNACE UPPER REAR TEMP 1
FURNACE LOWER REAR TEMP 2
AVERAGE
FURNACE UPPER REAR TEMP 2
FURNACE LOWER REAR TEMP3
FURNACE UPPER REAR TEMP 3
AVERAGE
FURNACE LOWER REAR TEMP 4
FURNACE UPPER REAR TEMP 4
AVERAGE
H/L
(510°C)
H
L
H
AVERAGE
H/L
(650°C)
H
L
H
L
H/L
(***°C)
H
L
SOLID FUEL
PERMIT
SU BURNER CAN
BE TURNED
DOWN
FURNACE
TEMP>ADEQ FOR
SOLID FUEL

25. Furnace Temperature (2/2)
FURNACE UPPER FRONT TEMP 8
FURNACE LOWER FRONT TEMP 8
FURNACE UPPER FRONT TEMP 7
AVERAGE
FURNACE UPPER FRONT TEMP 6
FURNACE LOWER FRONT TEMP 6
FURNACE LOWER FRONT TEMP 5
AVERAGE
H/L
(620°C)
H
L
H
H
L
H/L
(620°C)
H
L
AND
FURNACE
TEMP>ADEQ

26. OFT (Oil Fuel Trip)
MANUAL OFT PUSH BUTTON
MFT
ALL OIL BURNERS VALVE
CLOSED
FUEL OIL HEADER SHUTOFF
VALVE CLOSED
ANY BURNER VALVE CLOSE
FAILURE
NO MFT
ALL OIL BURNERS VALVE
CLOSED
AND
OR
RESET
OFT

27. Air Flow Measurement
Total Air Flow
Primary Air Flow
Hot PA – Right (Average)
x03
Hot PA – Left (Average)
x03
Cold PA
(Sum of Coal Feeder PA)
x10
Fluidizing Air Blower Flow
Cyclone A
(Sum of FAB entering into
seal pot)
x02
Cyclone B
(Sum of FAB entering into
seal pot)
x02
Cyclone C
(Sum of FAB entering into
seal pot)
x02
Secondary Air Flow
SA Left
(Sum of SA entering into
furnace Left side)
x10
SA Right
(Sum of SA entering into
furnace Left side)
x10
Burner SA
(Sum of B,C,D,E)
x04