FSSS WRITEUP

7/31/2019 FSSS WRITEUP

1/41

FSSS WRITE-UP, VINDHYACHAL, 2 X 500 MW

NATIONAL THERMAL POWER CORPORATION LIMITED

VINDHYACHAL THERMAL POWER STATIONUNITS 9 & 10, 2 X 500 MW

CUSTOMER NUMBER 0624 & 0625

WRITE UP ON F S S S

PREPARED CHECKED APPROVED REV.

NO.

DATE

M.K.THANUJA K. ANANTHAKRISHNAN K. ANANTHAKRISHNAN 00 27/03/2004

1 of 33

NTPCDRG

NO.2240-108-01TR-PVI-

V.K.Jain2004.08.09 08:37:12 ZCAT-II

Signature Not Verified


2/41


IMPORTANT NOTE

This write up is meant for general guidelines and better understanding of the

system. However it may be noted that All the logic conditions spelt in English

Language may not be exact equivalent of pictorial representation of logics. It is

mandatory that the operating personal should refer to the respective contract logics.

It must be recognised that no amount of written instruction can replace

intelligent thinking and reasoning on the part of boiler operators, especially when

coping with unforeseen operating conditions. It is operators responsibility to

become thoroughly familiar, not only with immediate steam generating equipment

but also with all pertinent control equipment. Satisfactory performance and safety

depend to a great extent on proper functioning of controls and auxiliary

equipment.

2 of 33


3/41


KEY

The logic sequences are represented in English as statements, which are to be executed

in certain order of precedence as described below.

The logical gates are represented in Upper case Letters, preceded and followed by dots.

eg. .AND. , .OR.

The logical function combining two statements in the same line is executed first.

eg. xxxxxxxxxxxxxxx .AND. xxxxxxxxxxxxxxx

The logical function in the right most position is executed next and so on.

eg. xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

.AND.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

The logical function at the left most position is executed last.

eg. xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

.OR.

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Both logical operators .AND. , .OR. have equal precedence between them. For better

understanding the following example with mixed logical expressions is marked with the

order of execution.

eg. xxxxxxxxxxxxx

.OR.5

xxxxxxxxxxxxx

.AND.4

xxxxxxxxxxxxxxxxxxxxxxxxxx .OR.1 xxxxxxxxxxxxxxxxxxxx

.AND.2

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

.OR.3

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

NB: xxxxxxxxxxxx represent logical statements.

3 of 33


4/41


CONTENTS

1.0 Figures ( Fig 1 to 8 )

2.0 Introduction.

3.0 Heavy Oil Recirculation Valve Control

4.0 Furnace Purge

5.0 Selection of Light Oil / Heavy Oil Firing.

6.0 Light Oil Trip Valve Control

7.0 Heavy Oil Trip Valve Control

8.0 Light Oil Elevation Start (Elevation AB - Pair Mode)

9.0 Heavy Oil Elevation Start up (Elevation-AB, CD, EF, GH, JK Pair Mode)

10.0 Heavy Oil Elevation Start up (Elevation-AB, CD, EF, GH, JK Elevation

mode)

11.0 Pulveriser Ignition Permit

12.0 Pulveriser Ready

13.0 Pulveriser Start

14.0 Pulveriser in service

15.0 Pulversier Trip

16.0 Pulveriser Shut-down

17.0 Oil Elevation Shutdown (Elevation-AB, CD, EF, GH & JK - Pair mode)

18.0 Oil Elevation Shutdown (Elevation AB, CD, EF, GH & JK - Elevation Mode)

19.0 Boiler Trip conditions

20.0 Scanner Air Fan Control

21.0 Seal Air Fan Control

22.0 Secondary Air Damper Control

4 of 33


5/41


6/41


7/41


8/41


9/41


10/41


11/41


12/41


13/41


2.0 INTRODUCTION

The Furnace Safeguard Supervisory System (FSSS) is designed to ensure theexecution of a safe, orderly operating sequence in the start up and shutdown of fuel firingequipment and to prevent errors of omission and commission in following such a safe

operating procedure.

The system provides protection, should there be a malfunction of fuel firing equipmentand associated air systems. The safety features of the system are designed for protection inmost common emergency situations. However the system cannot supplement theintelligence and the reasonable judgement of the operator in all the situations.

In some phases of operation the Furnace Safeguard Supervisory System providespermissive interlocks only to ensure safe start up sequence of equipment. Once the equipmentis in service, the operator must use normally acceptable safe operating practices.

It is important that the operator is familiar with the overall operation of the unit andthe operation of individual equipment as outlined in the various equipment sections of operatingand instruction manual.

It is essential that all parts of the Furnace Safeguard Supervisory System are inservice at all times, if the system is to provide protection for which it is designed. Propermaintenance and periodic inspection of the system and associated hardware is essential

for continued reliable operations.This instruction section of the system gives a complete description of the Furnace

Safeguard Supervisory System furnished for this unit as it is related to the various operatingphases and operation of the fuel firing equipment and associated air systems.

Basically the system is designed to perform the following functions:

Prevent any fuel firing unless a satisfactory furnace purge sequence has first beencompleted

Prevent start-up of individual fuel firing equipment unless certain permissiveinterlocks have first been satisfied

Monitor and control the proper sequence (Manual or Automatic) during start-up andshut-down of fuel firing equipment

Make continued operation of fuel firing equipment subject to certain safety interlocksremaining satisfied

Provide status feedback to the operator and in some cases, to the unit controlsystem

Provide flame supervision when fuel firing equipment is in service and effect afuel trip upon certain adverse operating conditions

Initiate a fuel trip when certain abnormal operating conditions exists

Furnace Safeguard Supervisory System (FSSS) provided for this project is anatural circulation, Heavy Oil (HO) fired boiler with coal as the primary fuel and Light Oil (LO) asthe start-up fuel and Heavy Oil as the fuel for warm up and stablisation. This system providesfor the remote/manual operation of five elevations of high energy arc (HEA) ignitors, fiveelevations of oil guns with provision for firing light oil in elevation AB only, heavy oil in

5 of 33


14/41


elevation AB, CD, EF, GH & JK and ten pulverisers, serving ten elevations of 40 coal nozzlesfrom a remote, console mounted control panel (Refer Figure-1).

From the console insert Heavy oil trip valve, Light oil trip valve & HO RecirculationValve can be opened/closed, Purge cycle can be started, Scanner Fans & Seal Air Fans canbe started/stopped, Pulv. Discharge Gate & Hot Air Gate can be opened / closed, Pulv. &Feeder can be started / stopped. Indicating lights on the console insert shows the operatingstatus of various field equipments connected to FSSS.

The following operational functions are included in FSSS.

Furnace purge supervision

Secondary air damper modulation, on/off control and supervision

Light oil on-off control and supervision

Heavy oil on-off control and supervision

Pulveriser and feeder on-off control and supervision

Flame scanner intelligence and checking

Overall boiler flame failure protection

Boiler trip protection

The Furnace Safeguard Supervisory System has been designed forEnergise to openand Energise to Close philosophy. However the final control drives are designed for De-Energised to trip as per the contract requirements from customer. This means any on/offdevice or equipment has to get a continuous command to change its present state and regainto the original state upon loss of this command.

3.0 HEAVY OIL RECIRCULATION VALVE CONTROL (HORV - Refer Figure-3)

3.1 LONG RECIRCULATON :

The Heavy oil must be heated to the proper temperature to attain the correct viscositybefore it can be fired. This is accomplished by recirculating the oil through the system when the

heavy oil recirculation valve and other manual valves are open.The Heavy oil recirculation valve must be opened before the Heavy oil trip valve can be

opened.

Depressing the HO Recirculation Valve OPEN Push Button will open the HOrecirculation valve, provided all heavy oil nozzle valves are closed and No MFT beingpresent. When the recirculation valve is open the HO RECIRCULATION VALVE OPENlight comes on. The HO trip valve can now be opened. During coal firing (i.e. any feeder isproven) and when last oil gun is removed from service (All elevations all H.O. nozzle valvesclosed), the H.O recirculation valve will automatically open.

Depressing the HO Recirculation Valve CLOSE Push Button will close the HORecirculation valve.

The HO Recirculation valve will close automatically after any corner heavy oil nozzlevalve leaves the closed position or on occurrence of MFT ( 2 second pulse ). Under

occurrence of MFT, H.O Recirculation can be re-established as an operator function.

3.2 SHORT RECIRCULATION:

H.O. Short recirculation valve can be opened by depressing the OPEN P.B. of

6 of 33


15/41


H.O. Short recirculation valve when H.O. Trip valve is closed.

H.O. Short Recirculation valve can be closed by depressing the CLOSE P.B. of H.O.Short recirculation valve or automatically closes when H.O. Trip valve is not closed.

4.0 FURNACE PURGE

Before any fuel firing can take place (initially or following a boiler trip ), a satisfactory

purge cycle must be completed. To start a furnace purge cycle proceed as follows.

Energise all the system power Supplies (AC & DC)

Place at least one ID (induced draft ) fan in service

Place at least one FD (forced draft ) fan in service

Establish a minimum of 30% of full load air flow through the unit and furnace draft at theappropriate value

Establish a proper water level in the drum

After the PURGE READY and the PUSH TO PURGE lights comes on, a furnacepurge cycle can be started.

When both these lights come on it indicates that all the purge requirements aresatisfied (see note1 below ).

NOTE1 :

If both the PURGE READY and the PUSH TO PURGE lights do not come onafter conditions 1 through 5 above are satisfied, check to see that:

Elevation AB all Light oil nozzle valves are proven closed

All the Heavy oil nozzle valves are proven closed

The Light oil Trip valve is proven closed

The Heavy oil Trip valve is proven closed

All Feeders off

All P.A. Fans off

All Scanners show no flame

A No Boiler Trip command is established

All Hot air gates are closed

Air flow between >30% and


16/41


(PURGE READY) and another furnace purge cycle started by depressing the PUSH TOPURGE Push Button.

At the end of the nine minutes furnace purge cycle, provided the purge permissivesremain satisfied, the boiler trip is reset.

This is indicated by the MFR TRIP light going off, the PURGING and PUSH TOPURGE lights going off. A No MFR Trip condition is now established and the CAUSE OF

TRIP memories are reset.The operator may open the various trip valves as described in the following sections.

5.0 SELECTION OF LIGHT OIL / HEAVY OIL FIRING

Either Light Oil or Heavy Oil can be fired at elevation AB, when selected by the operator.

Depressing the Select LIGHT OIL Push Button will select light oil, provided all theHO nozzle valves and LO nozzle valves are fully closed .AND. both pairs have been stopped.When the above conditons are satisfied, the El. AB LIGHT OIL SELECTED light comes on.

Depressing the Select HEAVY OIL Push Button will select Heavy oil, provided allthe HO nozzle valves and LO nozzle valves are fully closed .AND. both pairs have been

stopped. When the above conditions are satisfied, the El. AB HEAVY OIL SELECTED lightcomes on.

6.0 LIGHT OIL TRIP VALVE CONTROL (LOTV - Refer Figure-2)

Depressing the Open Light oil trip valve Push Button after the furnace purge cycleis completed, (boiler trip reset) will open the light oil trip valve, provided the following conditionsare satisfied.

Light oil supply pressure is adequate

Elevation AB all the light oil nozzle valves remain closed

When the Light oil trip valve open condition is indicated by a light coming on, the LOelevation trip command is removed and LO elevation start permit (No LO elevation Trip) isnow established provided the LFO isolation valve before FCV (LO-23A) is open .AND. LO FCV(LO-23A) not < 2% open .OR. the LFO isolation valve before FCV (LO-23B) open .AND. LOFCV (LO-23B) not < 2% open .OR. LFO bypass line inching valve not closed.

NOTE3 :

For this isolation valve / Bypass valve , open close Push Buttons and open / close statuslamps are provided in CRT/MMI.

Depressing the LOTV CLOSE Push Button will close the valve provided the valve isnot closed already. The LOTV also closes automatically under following conditions provided thevalve is not closed already.

Master fuel trip. OR.

Any light oil nozzle valve not closed. AND.

Light oil header pressure very low for more than 5 seconds (From 2/3 logic).OR.

8 of 33


17/41


Atomising air pressure very low for more than 5 seconds (From 2/3 logic).AND.

No light oil elevations in start or stop. AND.

Any Light oil nozzle valve not closed.

The LOTV is commanded to close on Loss of unit +24V DC power.

7.0 HEAVY OIL TRIP VALVE CONTROL (HOTV - Refer Figure-3)

Depressing the HO Trip valve OPEN Push Button will open the Heavy Oil Trip Valve ifeither of the following conditions are present:

HO recirculation valve is fully open. AND. trip valve close command is not present

All heavy oil nozzle valves are closed. AND.The heavy oil supply pressure is adequate. AND.The heavy oil temperature is adequate

. AND.No MFT condition is present.

When the Heavy oil trip valve is opened the HO Trip valve OPEN light comes on. TheHO elevation trip command is removed. HO Elevation start permit is now establishedprovided the HFO isolation valve before FCV (HO-33A) open. AND. HO FCV (HO-33A) not 30% .AND. feeder E .OR. G is in service at greater than 50%

loading.

PULVERISER G

A minimum of 3 of the 4 elevation GH oil nozzle valves proven open.

.OR.

Boiler loading is greater than 30% .AND. feeder F .OR. H is in service at greater

than 50% loading.

14 of 33


23/41


.OR.

A min. of 3 of the 4 elevation EF oil nozzle valves proven open. AND.

Feeder F is in service at greater than 50% loading.

PULVERISER H

A minimum of 3 of the 4 elevation GH oil nozzle valves proven open..OR.

Boiler loading is greater than 30% .AND. feeder J .OR. G is in service at greater than

50% loading.

PULVERISER J

A minimum of 3 of the 4 elevation JK oil nozzle valves proven open.

.OR.

Boiler loading is greater than 30% .AND. feeder K .OR. H is in service at greater

than 50% loading.

.OR.A min. of 3 of the 4 elevation GH oil nozzle valves proven open. AND.

Feeder H is in service at greater than 50% loading.

PULVERISER K

A minimum of 3 of the 4 elevation JK oil nozzle valves proven open.

.OR.

Boiler loading is greater than 30% .AND. feeder J is in service at greater than 50% loading.

12.0 PULVERISER READY

Prior to starting a pulveriser, a pulveriser start permit condition for the respectivepulveriser must be established by confirming the following conditions being satisfied:

Each condition is indicated by a yellow light on FSSS console (Refer Note-5)

Pulveriser discharge valve open

Pulveriser outlet temperature not high

Cold air gate open (Refer Note-5)

Pulveriser/Oil Elevation start permit

Tramp iron hopper valve open

Bunker outlet gate open (Refer Note-5)

Feeder inlet gate open

15 of 33


24/41


Primary air permit

Pulveriser No unsuccessful auto start

Lube oil system healthy

All Burner isolation gate open (Refer Note-5)

No Pulveriser trip

When all the above conditions are satisfied for the respective pulveriser, its associatedpulveriser ready condition is satisfied.

NOTE5 :Pulveriser Discharge valves, Cold air gate, Bunker outlet gates and Burner Isolation

gates are provided with On/Off type pneumatic power cylinders open-close solenoidassisted. These are getting commands from FSSS. For status feedback, open and closelimit switches are available. These could be opened or closed from MMI screen and

status feedback are also available in MMI. These gates could be opened before startingthe pulveriser, manually from MMI screen or Automatically from Auto Plant Start upsystem (APS) command - Pulveriser Auxiliary Start/On. These gates could be closedonly when the respective Pulveriser is Off, from the MMI screen.

Cold air gate will be commanded to open when the pulveriser is on and the

pulveriser outlet temperature is adequate (greater than 80 C) and will be closedautomatically when any one of the above is not present.

13.0 PULVERISER STARTPulveriser & the associated equipment can be started either automatically or manually.

Auto/Manual mode of pulveriser start can be selected by means of selector pushbuttonsprovided on coal Elevation console insert.

13.1 PULVERISER START ( MANUAL MODE )

By establishing Ignition energy available and pulveriser ready conditions for therespective pulveriser, it may be placed in service as follows:

Ensure pulveriser ready condition and ignition energy available condition are present.

Start pulveriser by pressing its associated "Pulveriser START push button. First,seal air valve opens, after seal air to bowl DP adequate is established, pulveriserwill start

When the pulveriser is proven on as indicated by the (Red) pulveriser "ON" light,open the hot air gate by pressing its "OPEN" button and allow the pulveriser to comeup to the temperature

16 of 33


25/41


When the pulveriser comes upto temperature, (more than 120 F) start the feeder bypressing its associated "Feeder START" push button. Coal flow must be proveneither by the coal on belt signal or satisfactory pulveriser current within 5 seconds,after the feeder is started (Refer Note-6)

50 seconds after the feeder is started, the feeder output is released to the includefeeder in the totalizing circuit

When the feeder is ON for 50 seconds the feeder speed is released to autocontrol and the fuel air dampers are opened to modulate as a function of feederspeed

When a minimum of two feeders are established at greater than 50% loading, theassociated oil elevations may be shut down provided the feeder has been ON for aminimum of 3 minutes

A single feeder in service for fifty seconds at its minimum speed setting willestablish a `fireball' in the furnace (a single fireball is established when a coal elevation is placedin service. When additional coal elevations are placed in service, this single fireball is merely

enlarged). If the support ignition energy is removed, the fireball will be monitored by theassociated elevation flame scanners. However, good operator procedure dictates that anadjacent feeder be placed in service and both feeder speeds be increased to 50% beforeremoving the support of the fireball. When removing feeders from service the inverseprocedure should be followed and support ignition energy should be reinstated when only twofeeders remain in service at 50% feeder speed.

NOTE5 :In the seal air line to feeders, pneumatically operated seal air valve is provided.

This gets open command once the pulveriser is ON or by a command from CRT/MMIscreen. This seal air valve could be closed from MMI screen once the feeder is OFF.Status feedbacks are also available in CRT screen.

Whenever the Feeder is started, manually or in auto mode of operation, first theFeeder outlet gate is opened automatically. Same may be opened manually from CRTscreen once the pulveriser is ON, provided no close command for the Feeder outlet gatebeing present. Feeder outlet gate is closed automatically once the feeder is OFF orPulveriser trip present or for a close command from CRT screen and the Feeder isOFF. Status feedbacks are available in CRT screen.

13.2 PULVERISER START (AUTO MODE )

The selected pulveriser can be placed in operation automatically if all the followingconditions are satisfied:

The associated " Pulveriser Ready " condition remains satisfied.

The " AUTO " mode is selected for the associated pulveriser.

The pulveriser is started by momentarily depressing the pulveriser "START" push button.The following events will occur;

17 of 33


26/41


A 180 second counting period is started to prove the associated pulveriser /feeder in service.

If the pulveriser ignition energy permissive is not satisfied an "AUTO STARTSUPPORT IGNITION '' command is established and the associated HFOelevation is automatically placed in operation. (Refer to " Elevation Mode Operation"section for details).

When the associated support ignition elevation start time has expired (both seventysecond " pair start " counting periods have expired) and the pulveriser ignitionpermissive is satisfied, the " auto start pulveriser " and "open hot air gate"commands are established simultaneously.

A pulveriser " start " command is established and the pulveriser is started in thesame manner as previously described in pulveriser manual mode.

When the pulveriser is proven ON the following events occur:

i) The hot air gate is opened, provided the pulveriser outlet temperature is

less than 94 Degree C.

ii) A 60 seconds counting period is started to establish an "Start feeder auto"command.

When the 60 seconds counting period expires, an "auto start feeder" command isestablished for 5 seconds. A "start feeder " command is now established, providedthe hot air gate is open. The feeder is put into service in the same manner aspreviously described. After the 180 second "elevation start" counting period expiresand the pulveriser is on and the feeder is off, the unsuccessful elevation start isestablished. When the feeder is off for more than 180 seconds, the pulveriserrevceives an "Stop pulveriser Auto" command and is shutdown.

14.0 PULVERISER IN SERVICE

With the pulveriser / feeder in service , several operational parameters are continuouslymonitored. However it is left to the operator's discretion to investigate and take furthercorrective action.

An operating pulveriser and feeder are subject to the following operational checks:

The feeder speed will be run back to minimum if the pulveriser bowl differentialpressure is high or Pulveriser motor current is high.

If the pulveriser outlet temperature is high ( greater than 94 Degree C), then thefollowing events occur:

i) Pulveriser air and temperature control is released from auto mode. The hot airdampers close and the cold air dampers open to 100% pulveriser air flow position.

18 of 33


27/41


ii) The hot air gate is closed after a 30 seconds time delay to allow the associateddampers to react.

Any of the following conditions will give signal to run the feeder speed to minimumuntil the initiating condition is corrected.

Pulveriser bowl differential pressure high

Pulveriser motor current high

Loss of coal flow and low pulveriser current will trip the feeder and close hot air damper.The operator should take appropriate corrective action, then reopen the hot air damper andrestart the feeder.

High pulveriser outlet temperature (above 94 deg. C) will open cold air damper and close the hotair damper. It will close Hot Air Gate after 30 sec delay.

15.0 PULVERSIER TRIP

The following conditions will initiate a pulveriser trip command

Pulveriser discharge valve not open

Loss of unit +24V DC power

Pulveriser ignition permit is not available .AND. support ignition required

MFT (See boiler trip section for details)

Loss of primary air

Seal air header to pulveriser differential pressure low (125 mm WC) .AND.Pulvurizer on for more than 60 seconds

Any coal burner Isolation Valve of that elevation is not open

Loss of PA fan/FD fan (Trip Pulveriser - applicable for Pulveriser-F to Konly)

Mill bearing temperature very high

Mill motor bearing temperature very high

Mill motor winding temperature very high

Mill motor bearing vibration very high

Mill motor electrical trip

19 of 33


28/41


When the primary air duct pressure falls below the low set point (for more than 5seconds) all pulverisers in service receive stop command.

When both PA fans stop or the primary air duct pressure goes very low, all thepulverisers are tripped instantaneously.

When one PA fan or one FD fan trips and 5 or more pulverisers are in service,each pulveriser with a 2 sec time delay a trip command will be given starting from thepulveriser serving top most coal elevation, until the number of pulverisers remaining in serviceis reduced to 5.

16.0 PULVERISER SHUT-DOWN

16.1 PULVERISER SHUT-DOWN ( Manual mode )

When manual pulveriser control mode is selected, manual shut down of a pulveriser isaccomplished as follows:

Start the associated oil elevation if it is not in service.

Reduce the feeder speed to minimum.

Close the hot air gate by depressing its "CLOSE" push button.

When the pulveriser outlet temperature is reduced to below 49.5 deg C then shutdown the feeder by pressing its "OFF" push button.

Allow the pulveriser to run for about 2 minutes to ensure that it is completely emptyof coal, then shut down the pulveriser by pressing its "OFF" push button.

16.2 PULVERISER SHUT-DOWN (Auto mode)

When in the auto mode of operation, the pulveriser is shutdown as described below.

The operator initiates a pulveriser auto shutdown sequence by momentarilydepressing the associated "stop" pushbutton. The following events will occur.

i) The "auto stop memory" signal is established and the "auto start memory" isreset.

ii) Start oil elevation auto command is generated to establish and ensure,availability of support ignition energy during auto stop pulveriser programme.

iii) A 600 seconds "elevation stop" counting period is started.

20 of 33


29/41


When the support ignition time has expired (both 70 seconds HO pair startingperiods have been expired) and the pulveriser ignition permissive is satisfied,thenthe following commands are established simultaneously.

i) Run the feeder speed demand to minimum.The feeder speed will be reducedthrough auto control.

ii) Auto close hot air gate.The associated hot air gate is closed in the mannerpreviously described (see PULVERISER MANUAL SHUT DOWN section).

When the hot air gate is closed and the pulveriser outlet temperature has been

reduced below 120 F the associated feeder will receive an "stop feeder auto"command. The feeder will now be shut down.

When the feeder is off for 3 minutes, the associated pulveriser will receive an"auto pulveriser stop" command. The pulveriser will now be shut down.

If the pulveriser is to remain on "stand by" then the discharge valve should remainopen to allow air to flow through the pulveriser. If required , the discharge valve is

closed by depressing the associated close push button (provided the pulveriser isoff).

The associated HO elevation can be shut down when the furnace and boilerconditions have been stabilised.

When the 600 seconds "elevation stop" count period expires, an "unsuccessfulelevation shut down" signal will be sent to the alarm if any of the following conditions exist atthe associated coal elevation:

The pulveriser is on.

The feeder is on.

The hot air gate is not closed.

17.0 OIL ELEVATION SHUTDOWN (Elevation AB - LO/HO Pair mode)

(Typical for HO firing at Elevation CD, EF, GH & JK. LO firing is not applicable for

elevation CD, EF, GH & JK)

When adjacent coal elevations are not in service and elevation back up trip exists .OR.when all feeders are off, the associated warm-up (LO / HO) elevations are automaticallyselected to the Pair operation Mode and the warm-up (LO / HO) elevation can be shut down,pair-wise.

Under pair operation mode the oil elevation is removed from service in the followingmanner.

Either pair (1-3) or (2-4) can be initially shutdown. Each pair of oil guns are shutdown inthe following manners.

Depressing PAIR (1-3 or 2-4) STOP PB momentarily will establish a stop signal forthat pair. This will cause the following events to occur:

21 of 33


30/41


A 375 second elevation pair stop counting period is started.

The associated Elevation PAIR (1-3 or 2-4) STOP light comes on.

A stop command for corner 1 (or corner 2) is established, and a fifteen sec.counting period is started to establish a stop command for corner 3 (or corner 4).

The corner oil (LO/HO) nozzle valve will receive a CLOSE command.

(When the corner oil nozzle valve is moved to the fully closed position, the oil valvesCLOSED light comes ON and the associated DISC. SCANNERS NO FLAME light comeson.)

After the warm-up (LO / HO) nozzle valve is closed, the scavenge nozzle valve receivesopen command. Also the spark rod of HEA is advanced and gives spark for a period of 15seconds. After the scavenge valve is fully open, a 300 seconds counting period is started.

After the 300 seconds scavenge trial time expires, the scavenge valve receives close

command. When the scavenge valve is moved from the fully open position, the five minutecounting period is reset.

When the scavenge valve is closed, the associated atomising (air/steam) nozzle valvereceives a close command.

When the 20 seconds counting period expires, a stop command is established forcorner 3 (or corner 4) which is removed from service in the same manner as previouslydescribed for corner 1 (or corner 2).

After the pair stop time expires, the scavenge valve memory is reset. The other pair(1-3 or 2-4) is stopped similarly by depressing the PAIR STOP Push Button (see Note10

below).

NOTE7 :Simultaneously, a 360 second counting period is started to establish a warm-up

elevation back up trip after the first pair (1-3 or 2-4) of oil guns have been shut down and thestop command for the first oil gun of the second pair (1-3 or 2-4) is established.The associated pair of oil guns are shut down in the same manner as previously described forthe other pair of oil guns (1-3 or 2-4).

When the 360 second counting period expires, a warm-up elevation back up tripcondition is established. This pair back up trip establishes a redundant stop command toensure that the oil guns are shut down.

The signal to position the warm-up oil elevation dampers for oil firing is removed. Afterthe warm-up oil elevation back up trip is established, an Unsuccessful warm-up oilelevation shut down condition is established when both 375 second counting period expireand any warm-up (LO / HO) nozzle valve is not closed or any HEA IGNITOR is not retracted inthe associated elevation. This initiates oil elevation unsuccessful shut down alarm.

22 of 33


31/41


A warm-up oil (LO/HO) gun may also be shut down and scavenged individually byplacing its local oil gun maintenance switch in the SCAVENGE position. The warm-up oilgun will be shut down and scavenged as described above.

To return the warm-up oil gun to service, return the local maintenance control switch toREMOTE position and depress the associated warm-up oil elevation PAIR START PushButton.

Any one of the conditions listed below will trip an individual warm-up oil corner byissuing a corner trip signal.

Associated local maintenance control switch turned to OFF position.Warm-up oil gun not engaged.

Atomising (air/steam) Manual isolating valve not open.Corner not in scavenge.AND.Corner start time expired.AND.Warm-up oil nozzle valve not open

.OR.Atomising steam nozzle valve not open.OR.

Discriminating scanner no flameElevation back up trip.LO (HO) selected when HO ( LO) is fired.

18.0 OIL ELEVATION SHUT DOWN (Elevation AB - HO Elevation mode)

(Typical for HO firing at Elevation CD, EF, GH & JK)

When either of the coal elevation associated with the warm-up oil elevation, is in service,the warm up oil elevation can be shut down under this elevation mode. The subject elevationcan be shut down as described in the following section.

Under Elevation mode, the oil elevation is removed from service in the following manner.

Depressing the PAIR STOP Push Button (1-3 .OR. 2-4) will establish a cornerSTOP command (see Note8 below).

NOTE8 :The PAIR STOP command will establish a corner STOP command provided both

coal elevations associated with the warm-up elevation have been ON for at least three minutesor both associated coal elevations are not in service.

The corner STOP command will cause the following events to occur:

A 375 second elevation pair counting period is started for corner 1 and 3.

A 40 second counting period is started to establish a STOP command for corner 2and 4.

23 of 33


32/41


The Elevation PAIR 1-3 STOP light comes on. A STOP command for corner 1 isestablished and a 20 second counting period is started to establish a STOP command forcorner 3.

After the STOP command is established, the oil gun at corner 1 is removed fromservice in the same manner as previously described.

When the 20 second counting period expires, the STOP command for corner 3 isestablished and is removed from service in the same manner as corner 1. When the 40 secondcounting period expires, the STOP command is established causing the following eventsto occur. A 375 second elevation pair counting period is started for corners 2 and 4. TheElevation PAIR 2-4 STOP light comes on.

Corner 2 stop command is established and a 20 second counting period is started toestablish a stop command for corner 4.

The oil gun at corner 2 is removed from service in the same manner as previouslydescribed.

When 20 second counting period expires the STOP command for corner 4 isestablished and is removed from service in the same manner as corner 2. All other interlocksi.e., Backup trip, elevation unsuccessful shutdown etc. are same as described earlier.

19.0 BOILER TRIP CONDITIONS

19.1 MASTER FUEL TRIP (MFT)

Master Fuel Trip is initiated by any one of the following conditions:

Less than fire ball and loss of A.C. at any elevation elevation in service.

Drum level very low for more than 5 seconds.

Drum level very high for more than 10 seconds.

Both FD Fans off.

Both ID Fans off.

Air flow is less than 30%

Furnace pressure very low.

Furnace pressure very high.

Loss of all fuel trip (See the NOTE 11)

Unit flame failure trip (See the NOTE 12)

Both emergency trip Push Buttons pressed (Operator initiated boiler trip)

Spare trip. Loss of reheater protection.

Loss of 220V DC for more than 2 seconds

All Secondary Air Heaters off.

Water wall circulation not correct for more than 5 seconds

Boiler feed pumps tripped for more than 10 seconds

24 of 33


33/41


NOTE9 :

A spare channel for boiler tripping is provided for use at a later date if required.Otherwise it should be left unconnected.

MFT command will initiate the following actions.

All fuel inputs are stopped by tripping all the mills, all the feeders, closing all hot

air gates, closing all the nozzle valves (LO/HO) and trip valves (LO/HO).

In addition to the above,

The HO elevations revert to pair operation mode.

The upper (elevations K,J,H,G&F) and lower (elevations E,D,C,B&A) fuel airdampers are opened and transfer to manual.

Transfer the auxiliary air control to manual and open all auxiliary air dampers.

After 5 secconds and the loss of fuel trip arming memory is reset and the loss of

fuel trip arming signal is removed The furnace pressure recorder speed is changed for 30 seconds when the

furnace pressure is not high and not low after 30 seconds the recorder reverts to itsoriginal speed.

After a Master fuel trip occurs, a feed forward to furnace draft controlsignal is established for 30 seconds. After 30 seconds this signal is removed.

NOTE10 :

Less than fire ball and loss of AC in any elevation in service conditionoccurs,when all the feeders are not in service and there is a loss of power supply (110V AC) atany of the elevation in service. Under this condition as ignition energy will not be proper (nofire ball), the HO elevation (Oil) cannot be allowed to run without control (as there is no power

supply). Hence the boiler has to be tripped to shut down the elevation.

NOTE11 :

Loss of All Fuel Trip circuit is armed as soon as oil firing is introduced into thefurnace, through any one of the following conditions. i.e. if any oil burner comes into service.This condition also indicates that the Boiler is on.

Elevation AB any LO nozzle valve .NOT. closed

Elevation AB any HO nozzle valve .NOT. closed

Elevation CD any HO nozzle valve .NOT. closedElevation EF any HO nozzle valve .NOT. closed

Elevation GH any HO nozzle valve .NOT. closed

Elevation JK any HO nozzle valve .NOT. closed

19.2 Loss of All Fuel Trip :

25 of 33


34/41


Loss of All Fuel Trip condition is generated if all the following conditions exist alongwith Loss of all fuel trip arming condition.

All feeders are off.AND.

Elevation AB Backup trip .OR. All LO valves are closed.OR.

LO trip valve is not open.AND.Elevation AB back up trip .OR. All HO valves are closed

.AND.Elevation CD back up trip .OR. All HO valves are closed

.AND.Elevation EF back up trip .OR. All HO valves are closed

.AND.Elevation GH back up trip .OR. All HO valves are closed

.AND.Elevation JK back up trip .OR. All HO valves are closed

.OR.HO trip valve not open.Loss of all fuel trip arming memory is reset 5 seconds after MFR trip occurs.

19.3 Unit Flame Failure Trip :

Unit Flame Failure Trip occurs if all the 10 elevations vote for No flame along withthe arming signal.

Conditions for the generation of No Flame voting Elevation wise is given below :

Elevation 'A' :

Elevation 'A' feeder not proven > 2 secondsOR.Elevation 'AB' started & loss of 110 V AC power > 2 seconds

.OR.Elevation 'AB' 2/4 nozzle valves not proven .AND. Elevation 'AB' 3/4 FB scannershow no flame

.AND.Elevation AA 3/4 FB scanners show no flame.

Elevation 'B' :

Elevation 'B' feeder not proven > 2 seconds.OR.Elevation 'AB' started & loss of 110 V AC power > 2 seconds

.OR.

26 of 33


35/41


Elevation 'AB' 2/4 nozzle valves not proven .AND. Elevation 'AB' 3/4 FB scannershow no flame

.AND.Elevation BC 3/4 FB scanners show no flame.

Elevation 'C' :

Elevation 'C' feeder not proven > 2 seconds.OR.Elevation 'CD' started & loss of 110 V AC power > 2 seconds

.OR.Elevation 'CD' 2/4 nozzle valves not proven .AND. Elevation 'CD' 3/4 FB scannershow no flame

.AND.Elevation BC 3/4 FB scanners show no flame.

Elevation 'D' :

Elevation D feeder not proven > 2 seconds.OR.Elevation 'CD' started & loss 110 V AC power > 2 seconds

.OR.Elevation 'CD' 2/4 nozzle valves not proven .AND. Elevation 'CD' 3/4 FB scannershow no flame

.AND.Elevation DE 3/4 FB scanners show no flame.

Elevation 'E' :

Elevation E feeder not proven > 2 seconds.OR.Elevation 'EF' started & loss of 110 V AC power > 2 seconds

.OR.Elevation 'EF' 2/4 nozzle valves not proven .AND. Elevation 'EF' 3/4 FB scannershow no flame

.AND.Elevation DE 3/4 FB scanners show no flame.

Elevation 'F' :

Elevation F feeder not proven > 2 seconds

.OR.Elevation 'EF' started & loss of 110 V AC power > 2 seconds.OR.

Elevation 'EF' 2/4 nozzle valves not proven .AND. Elevation 'EF' 3/4 FB scannershow no flame

.AND.Elevation FG 3/4 FB scanners show no flame.

Elevation 'G' :

27 of 33


36/41


Elevation G feeder not proven > 2 seconds.OR.Elevation 'GH' started & loss of 110 V AC power > 2 seconds

.OR.Elevation 'GH' 2/4 nozzle valves not proven .AND. Elevation 'GH' 3/4 FB scannershow no flame.

.AND.Elevation FG 3/4 FB scanner show no flame.

Elevation 'H' :

Elevation H feeder not proven > 2 seconds.OR.Elevation 'GH' started & loss of 110 V AC power > 2 seconds

.OR.

Elevation 'GH 2/4 nozzle valves not proven .AND. Elevation 'GH' 3/4 FB scannershow no flame

.AND.Elevation HJ 3/4 scanners show no flame.

Elevation 'J' :

Elevation J feeder not proven > 2 seconds.OR.Elevation 'JK' started & loss of 110 V AC power > 2 seconds

.OR.Elevation 'JK' 2/4 nozzle valves not proven .AND. Elevation 'JK' 3/4 scanner show noflame

.AND.

Elevation HJ 3/4 scanners show no flame.

Elevation 'K' :

Elevation K feeder not proven > 2 seconds.OR.Elevation 'JK' started & loss of 110 V AC power > 2 seconds

.OR.Elevation 'JK' 2/4 nozzle valves not proven .AND. Elevation 'JK' 3/4 scanner show noflame

.AND.Elevation KK 3/4 scanners show no flame.

NOTE12 :

Unit Flame failure Trip circuit is armed 2 sec. after any coal elevation is put into service.(i.e. any feeder proven position).

28 of 33


37/41


19.4 FIRST OUT TRIP SYSTEM

A First Out Trip System provided allows the operator to determine the cause of aboiler trip by observing the indication lamps located on the Unit Console insert under FirstCause of Trip.

When an event that causes occurance of boiler trip, the associated Cause Of Tripmemory is set, and the indicating lamp for trip command, responsible for the boiler trip isilluminated and the while successive trip commands to the other indications are blocked.

When the event that caused the boiler trip is corrected & boiler purging is completed theCause Of Trip memory is reset.

This indicates that a No Boiler Trip Command is established. The memories arereset automatically after a successful 9 minute furnace purge cycle has been completed.The FIRST CAUSE OF TRIP light that caused the boiler trip will go off.

19.5 POST PURGE EXCURSION PROTECTION

A post purge excursion protection circuit has been designed in the Furnace SafeguardSupervisory System. It operates as described below:

When all the following conditions are satisfied, a 5 minute counting period is started.

Light oil trip valve closed.

Elevation AB all LO nozzle valves closed.

Heavy oil trip valve closed.

All elevation all HO nozzle valves closed.

All Feeders off.

Air flow > 30 % MCR.

All scanners show no flame.

All Hot air gates closed.

All aux. air dampers modulating

All PA fans off.

After 5 minute counting period expires, the Post Purge Fan Trip memory is set, if veryhigh or very low furnace pressure exists, the post purge fan trip command is issued (for trippingFD&ID fans). When any HO / LO valve is open, this is reset.

19.6 FEED FORWARD COMMAND TO FURNACE DRAFT CONTROL

29 of 33


38/41


A 30 seconds Feed Forward command to Furnace draft control is given if either of theconditions listed below exists.


Occurrence of Master Fuel Trip, when the boiler is on (i.e., Loss of all fuel triparming is present).

19.7 FURNACE PRESSURE RECORDER SPEED CHANGE

This contact has been provided to switch the Furnace Pressure Recorder to thealternate speed (if Dual speed recorder is provided) under the conditions mentioned below, toobserve Furnace Draft fluctuations.

MFT


Furnace Pressure High or Low

For condition 1 mentioned above, the Recorder speed is reverted back to original valueafter 30 seconds. For condition 3, the Recorder is set to original value 30 seconds after

condition 3 is removed.

20.0 SCANNER AIR FAN CONTROL (Refer Figure-6)

Two scanner air fans (1 AC main + 1 DC stand-by) are provided for the unit. Eitherscanner air fan can be placed in service in the following manner.

Start command to any of the scanner fan can be given from the CRT / Unit Consoleinsert.

After a Purge complete and No MFT, a start command is also establishedautomatically for scanner air fan A (AC operated), if the scanner duct to furnace

differential pressure is low for more than 5 seconds If this low condition exists formore than 10 sec., the same is annunciated as Scanner Duct To Furnace DPLow greater than 10 seconds.

A start command is also established for the stand-by scanner air fan (ie. DC) if thefirst fan fails to start within 5 seconds after receiving the start command or if it trips.

Loss of unit 24 V DC establishes start command for both scanner air fans.

The scanner air fan can be stopped by momentarily depressing the STOP PushButton, provided the scanner duct of furnace differential pressure is not low. When both thescanner fans fail to start within 10 seconds from getting auto start command, an alarmis generated as Both Scanner fans failed to start and this will reset start memory ofboth scanner fans, to avoid toggling between Fan-A and B.

The status of Scanner air Fans is displayed on the CRT / Console insert.

The scanner emergency damper is opened when all FD fans are off .OR. Unit +24V DCpower is lost. If both these conditions are not present, the scanner emergency damper will beclosed.

NOTE13:

30 of 33


39/41


Each Scanner fan is provided with an outlet damper, power cylinder operated-Solenoid assisted. When fan is on .OR. On Loss of unit +24V DC power, its outlet damper isopened and when the fan is off its outlet damper is closed. Status lamps are provided on theCRT.

21.0 SEAL AIR FAN CONTROL (Refer Figure-7)

There are two seal air fans that serve this unit,one working and one standby.

Any seal air fan can be started manually by depressing its START Push Button. Thisaction gives start command to the motor.

The seal air fans which is not in service is started on Auto command if,Any PA fan is on and seal air header to cold PA header DP is low for > 10 seconds

The seal air fan A will start automatically 5 seconds after the seal air fan B trips orfails to start on receiving start command (SA fan B starts automatically if SA fan A fails tostart).

Any seal air fan can be stopped by depressing its STOP Push Button providedthe following conditions are satisfied.

Seal Air Header /Cold PA DP Not low.AND.Both Seal Air fans on

Both Seal Air Fans are tripped once all PA Fans are off > 15 Seconds.

22.0 SECONDARY AIR DAMPER CONTROL (SADC)

For a complete description of the Secondary Air Damper Control refer the write upon SADC system. Operation of the secondary air damper control as effected by the FSSS isdescribed here.

22.1 AUXILIARY AIR DAMPER CONTROL

All elevations of the aux. air dampers will be automatically switched to Manual controland then commanded to open 100%, if any one of the following conditions exist.

All FD fans are off

All ID fans are off

Master fuel trip exists for more than 2 seconds

Loss of Unit +24 V DC power

When the auxiliary air control is placed in the Auto mode of operation , the auxilaryair dampers modulate to control windbox to furnace differential pressure at a predetermined setpoint.

31 of 33


40/41


During the furnace purge cycle, all auxilary air dampers modulate to maintainwindbox to furnace differential pressure at a predetermined set point.

When the unit load exceeds 30% of MCR, the following events occurs :

The windbox to furnace differential set point is gradually increased as the unit loadis increased. Conversely, the differential pressure set point is gradually decreased as unit load

is decreased. The rate of increase (or decrease) is controlled by the auxilary dampercontroller.

When the Unit Load is increased above 30% MCR, the Auxilary air dampers on ElevationAB, BC, CD, DE, EF, FG, GH, HJ & JJ are closed in a timed sequence (10 secondsinterval) provided the associated coal elevations are not in service and the associated oilelevations are not in service.The auxiliary air dampers are closed, starting from the topelevation, progressing towards the lowest elevation.

When the unit load is reduced below 30% of MCR, the following events occur:

The wind-box to furnace differential pressure set point reverts to its original

value. The auxiliary air dampers associated with the coal and LO/HO elevations not in

service are opened in a timed sequence (10 sec. interval) starting at the lowestelevation, progressing towards the top.

When a LO/HO Elevation is started (i.e. when the associated elevation back-up tripis removed) the associated auxiliary air dampers in that elevation are set to preset position forLO/HO firing.

When the Post Trip Purge Time Expired command is established and all FD / IDfans are not off and a Master fuel trip command doesnt exist, then a 35 seconds countingperiod is started. After it expires, the Open All Auxiliary Air Dampers command is removed

from memory.

22.2 FUEL (coal) AIR DAMPERS CONTROL

All elevations of fuel air dampers are commanded to open 100% when any one of thefollowing conditions exist.

All FD fans are off

All ID fans are off

Master fuel trip exists for more than 2 seconds

Loss of Unit +24V DC power

When a coal elevation is in service, the associated fuel air dampers modulate as afunction of feeder speed as indicated by the associated coal elevation MODULATING lightcoming on.

When the coal elevation is shut down, the associated fuel air dampers are closed, asindicated by a CLOSED light .

32 of 33


41/41


When the Post Trip Purge Time Expired command is established and all FDand ID fans are not off and a Master fuel trip command doesnot exist, the open upperfuel air dampers (elevation K, J, H, G & F) command is removed from memory. Thirtyseconds later, the open lower fuel air dampers (elevation E,D,C,B & A ) command isremoved from memory.

oooOOOooo

Documents

FSSS WRITEUP