FUNCTIONS OF FSSS

FUNCTIONS OF FSSS

• Prevent any fuel firing unless a satisfactory furnace purge sequence has first been completed.
• Prevent start-up of individual fuel firing equipment unless certain permissive, interlocks have been satisfied.
• Monitor and control proper component sequencing during start-up and shut-down of fuel firing equipment.
• Subject continued operation of fuel firing equipment to certain safety interlocks remaining satisfied.
• Provide component status feedback to the operator and, in some cases, to the unit control system  and / or to the data logger.
• Provide flame supervision when fuel firing equipment is in service and effect an Elevation Fuel Trip or Master Fuel Trip upon certain condition of unacceptable firing / load combination.
• Effect a Master Fuel Trip upon certain adverse Unit operating condition

INTERLOCKS COVERED UNDER FSSS

• PURGE PERMISSIVES   
• 1. POST TRIP PURGE CYCLE
• 2. FURNACE PURGE CYCLE
• HOTV OPEN/CLOSE INTERLOCKS
• HORV OPEN/CLOSE INTERLOCKS
• OIL GUNS START/STOP CYCLE
• BOILER PROTECTION LOGICS
• PA FAN INTERLOCKS COVERED UNDER FSSS
• COAL MILL START/STOP INTERLOCKS
• COAL FEEDER START/STOP INTERLOCKS
• SCANNER AIR FANS
• SEAL AIR FANS
• DAMPER INTERLOCKS

POST-FIRING PURGE PURGE PERMISSIVE

•  All HFO Nozzle Valves Closed
•  HFO Trip Valve closed
•  All Pulverizers Off.
•  All Feeders Off
•  All Flame Scanners Sense No Flame
•  Air Flow > 30 %
•  Mode Permit Proven (Air Flow < 40 % And Nozzle Tilt Horizontal)

PRE-FIRING PURGE PURGE PERMISSIVE

•  All HFO Nozzle Valves Closed
•  HFO Trip Valve closed
•  No Boiler Trip From MFR A & B
•  All Pulverizers Off.
•  All Feeders Off
•  All Flame Scanners Sense No Flame
•  All Auxiliary Air Dampers Modulating and furnace to wind box P OK
•  Both PA fans Off
•  All HAGS Closed
•  Air Flow > 30 %
• Mode Permit Proven (Air Flow < 40% And Nozzle tilt Horizontal)
• Drum Level Satisfactory
• FSSS AC / DC Power Available.

HOTV INTERLOCKS

TO OPEN HOTV :
Permissives : 
SET I 

• No. Boiler Trip persisting
• HFO Header temperature  satisfactory >950 C
• HFO supply press sat. > 15 Kg / cm2
• All HONV’s closed
• No close / Trip command
• Open PB depressed 

OR
SET II 

• All HONV’s closed
• MFT acted
• HORV open
• Open PB depressed

HOTV INTERLOCKS

1. HOTV CLOSES AUTOMATICALLY UNDER FOLLOWING CONDITIONS : 
Any HONV not closed  AND
a) HFO pressure low < 3 Kg/cm2 
OR
b) Atom. steam Pr. low < 3.5 Kg/cm2 
OR 
c) HFO Header Temperature Lo-Lo for > 2  secs.  < 95 0 C
2. Any HONV not closed and MFT acted
3. Loss of critical power > 2 Secs
4. HOTV can be closed manually by pressing the close push button.

HORV INTERLOCKS

•  HORV can be opened by pressing the OPEN Push button (PB)  from Console if All the HONV s are  closed.
•  HORV closes automatically when any HONV is not closed OR  by  pressing close PB.

PAIR FIRING MODE (START UP)

• Pair firing mode is selected when no feeder is in service. Pairs are made for the opposite corners. (Pair 1-3 and Pair 2-4)
• When pair 1-3 start push button is pressed the following events take place
• A  30 second counting period is started
• A  70 second counting period is started
• Oil Gun No-1 advances from retracted position if
• It is engaged, corresponding scavenge valve is closed, atomising steam and HFO isolation valves are open.
• HEA ignitor advances.
• Atomising steam valve opens.
• Ignitor starts sparking.
• HFO Nozzle valve for corner 1 opens
• HFO catches fire and flame indication comes.
• After 25 seconds ignitor retracts.
• When the 30 second counting period expires command will 
• go to corner 3 and same events will take place.
• Corner 2-4 can also be placed exactly in the same manner.

ELEVATION FIRING MODE (START UP)

• Elevation firing mode is selected when any feeder is proven.
• Oil elevation is placed in service when Pair 1-3 or Pair   2-4 start Push Button is pressed. In elevation firing mode also the oil guns are proven on pair basis.
• First command goes for placing Pair 1-3 into service and Pair 1-3 is placed into service exactly in the same way as in the pair mode.
• First start command goes to corner-1 then after 30 second start command goes to corner-3.
• After the start command has gone to corner 3, a 30 second counting period is started. When 30 seconds counting period expires then start command goes for corner 2-4 and corner   2-4 are placed into service exactly in the same manner as in the pair mode.

PAIR FIRING MODE (SHUT DOWN)

• Pair firing mode is selected when no feeder is in service. Pairs are made for the opposite corners. (Pair 1-3 and Pair 2-4)
• When pair 1-3 stop push button is pressed the following events take place
• A  30 second counting period is started
• A  340 second counting period is started
• Oil Gun No-1 HFO nozzle valve closes.
• Scavenge and atomising steam valve opens.
• HEA ignitor advances and spark remains for 15 seconds.
• When atomising steam valve is proven fully open, a 5 minutes counting period starts.
• When 5 minutes counting period expires scavenge valve and atomising steam valve closes and further closing command goes HFO nozzle valves to reinsure that they are fully closed.
• Oil Gun corner no-1 retracts to its home position.
• When the 30 second counting period expires stop command will go to corner 3 and same events will take place.
• Corner 2-4 can  be shut-down exactly in the same manner.

ELEVATION FIRING MODE (SHUTDOWN)

• Elevation firing mode is selected when any feeder is proven.
• By pressing stop push-button of  Pair 1-3 or Pair 2-4 the following events will take place.
• Corner 1-3 will be shut-down in the similar way as in the pair mode.
• When stop command has gone to corner 3, a 30 second counting period is started.
• When 30 seconds counting period expires then stop command goes for corner 2-4 and corner 2-4 are shut-down exactly in the same manner as in the pair mod

BOILER TRIP CONDITIONS

• Both FD Fans Off
• All ID Fans Off
• Inadequate Waterwall Circulation
• Loss  Of Reheat Protection
• Deaerator level Lo-Lo  ( -2134 mm 2 / 3 logic)
• All Boiler Feed Pumps Off
• Drum Level High-High (> + 250 mm, delay of 10 seconds)
• Drum Level Lo-Lo (< - 375 mm, delay 10 seconds)
• Elevation Power Failure For > 2 seconds.
• Furnace Pressure High-High  (> + 325 mmWC, 2 / 3 logic)
• Furnace Pressure Lo-Lo  ( < -250 mmWC, 2 / 3 logic )
• Loss Of  All Fuel
• Unit Flame Failure
• Loss Of Critical Power For > 2 seconds
•  Loss Of  220 V DC For >  2 seconds
• Loss Of ACS Power >  2 seconds
• Simulator Trip
• Air Flow < 30 %
• Both Emergency Push Buttons Pressed. 

BOILER TRIP

• When the boiler trips the following events takes place
• Boiler trip red lamp comes on.
• MFT A & B trip lamp comes on and reset lamp goes off.
• Cause of trip memory can not be reset till the furnace purge is completed.
• F D Fans Control is transferred to manual. 
• I D fans vane position is transferred to manual.
• Pulverizers are tripped.
• Coal feeders are tripped.
• P A  Fans are tripped.
• Cold air dampers opens 100 %.
• HFO trip valve closes.
• All HFO Nozzle valves closes.
• Upper and Lower Fuel air damper opens.
• Auxiliary air damper opens and control is transferred to manual.
• Loss of all fuel trip protection disarms.
• S/H and R/H spray block valves S-82 & R-31 closes and can not be opened unless furnace purge is completed.
• Turbine Trips

INADEQUATE WATER WALL CIRCULATION

• BOILER LOAD < 60 % AND NO BCW PUMP ON OR PUMP ON AND DIFFERENTIAL PRESSURE < 10 PSI.
• BOILER LOAD > 60 % AND LESS THAN TWO PUMPS  OR  PUMP ON AND DIFFERENTIAL PRESSURE < 10 PSI.

REHEAT PROTECTION

• TURBINE TRIP OR GENERATOR CIRCUIT BREAKER OPEN AND HP/LP BYPASS OPENING < 2 %.
• TURBINE WORKING (HP & IP CVS OPENING > 2 % AND LOAD SHEDDING RELAY OPERATED AND HP/LP BYPASS OPENING < 2 %.
• TURBINE NOT WORKING AND BOILER WORKING AND  HP/LP BYPASS OPENING < 2 %

MILL INTERLOCKS   

START PERMISSIVES :

• Mill starts after the ‘ON’ push button is pressed if following
• conditions are fulfilled.
• Pulveriser Ready available signal will be available if following conditions are fulfilled
• M.D.V. is open (all four)
• Mill outlet temp < 93 0 C
• Feeder local switch in Remote
• Pulv. start permit (if Nozzle tilt Horizontal  & air flow < 40 % )

OR 

( Any feeder  proven and NO MFT )

• Cold air gate open
• Tramp iron valve open
• Feeder inlet gate open
• Lub oil level & temp. adequate
• Lub oil pressure not low for more than 300 sec
• No Mill trip existing
• P.A. permit available. 

1. Hot P.A. duct Pressure. not low ( < 625 mm wc)
2. P.A. duct pr. not lo-lo ( > 500 mmWc AND  
3. Both FD s ON and both PA fans ‘ON’ or (Any PA fan ON and any FD Fan  ‘ON’ and > 4 mills not ON)   

•  No Auto pulv unsuccessful start
•  Seal air Header to mill under bowl DP satisfactory > 8" wc
•  Mill not ‘ON’
•  Pulv Ignition permit available.

 FOR Mill A

•  AB elevation 3/4 HONV’s open

OR  

•  Boiler load > 30 % and Feeder - B speed > 50 % ( > 30 T/hr.)

For Mill B

•  AB elevation proven 3/4 HONV’s open

OR

•  Boiler load > 30 % and Feeder A or Feeder C proven.

For Mill C

•  CD elevation proven  

         OR

•  AB oil elevation and feeder B proven  

        OR

•  Boiler load > 30 % & either feeder B or Feeder D proven

For Mill D

•  CD elevation proven

OR

• Boiler load > 30 % and either feeder C or feeder E proven.
• For Mill E,F,G & H identical logic.

PULVERISER TRIP CONDITIONS

• Auto / manual mode selected to manual & stop PB depressed.   
• Pulv. start command given  & not ‘ON’ for > 2 Secs.
• Loss of Elevevation OR Unit Power for > 2 Secs
• Pulv ‘ON’ & seal air / under DP Low  > 1 min < 5”wc
• Pulv  ‘ON’ and lub oil pump OFF > 10 sec.
• Pulv ‘ON’ and lub oil pr. low > 10 secs. < 1.76 Kg/cm2
• Ignition permit required (> 180 secs) & ignition permit lost (i.e. within 180 sec of feeder start)
• Any of the MDV is  not fully open
• Hot PA duct. pr. Lo < 625 mm of WCL (delay 5 sec)
• Hot PA duct. pr. Lo - Lo  =  < 525mm WC (instantaneous)
• MFT    
• PA / FD Fan trip

1. If both PA Fans & both FD fans running  & any PA or any FD Fan trips then mills start tripping from top elevations with 2 secs time delay till 4 mills are available.
2. If both PA / FD fans trip then all mills will trip.

PULV. SEAL AIR VALVES INTERLOCKS

•  Valve opens when Pulv. start command is given OR Mill is ON
•  Valve closes when Pulv. is OFF

HOT AIR GATE INTERLOCKS

•  Hot  air gate (HAG) opens when Pulv is ‘ON’ AND Hot air gate open P.B depressed  or auto HAG open command is  there  AND  NO HAG  close command.
•  Hot air gate closes when

1. Loss of power > 2 secs

2. Pulv. off

3. Pulv. outlet temp > 93 0 C

4. Close P.B. depressed

5. Feeder Trips.(Delay 40 sec) 

6. Auto pulv. unsuccessful start 

7. Auto pulv. run feeder speed to minimum 

FEEDER START  PERMISSIVES

•  Pulveriser Ready is available
•  Feeder speed demand at minimum
•  Pulveriser manual mode
•  Pulveriser ignition permit available
•  No feeder stop command
•  No  MFT
•  Pulveriser ‘ON’

FEEDER TRIP CONDITION

•  Ignition energy removed within 180 secs of feeder start
•  Feeder in manual mode & stop PB depressed 
•  Auto Pulv. Feeder stop command
•  Pulv. OFF 
•  MFT
•  No coal on belt Discharge plugged