FURNACE SAFEGUARD SUPERVISORY SYSTEM (FSSS)

JAYPEE BINA THERMAL POWER PLANT 2X250 MW

FURNACE SAFEGUARD SUPERVISORY SYSTEM( FSSS )

Prepared By Rahul Chauhan Control & Instrumentation

OBJECTIVE OF CONTROL & INSTRUMENTATION

SAFE OPERATION OF PLANT.

LONGEST EQUIPMENT LIFE.

MINIMUM ENVIROMENTAL EFFECT.

MAXIMUM EFFICIENCY

INTRODUCTION

FSSS means furnace safeguard & supervisory system , the system which is used in almost all types of boiler. The system has been designed to offer maximum protection and to ensure the execution of a safe, orderly operating sequence in the start up and shutdown of fuel firing equipment in a boiler and to prevent errors which may be committed by an operator due to ignorance.

FSSS is designed to perform the following functions:

Prevent any fuel firing unless a furnace purge sequence has been completed.

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

Make continued operation of fuel firing equipment subject to certain safety interlocks remaining satisfied.

Provide component status feedback to the operator and in some cases, to the unit control system.

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

Initiate a fuel trip when certain abnormal operating condition exists

Light Oil (LO) as the start-up fuel. Heavy Oil (HO) fired boiler with coal as the primary fuel

/ warm up and stabilisation. Three elevations of high energy arc (HEA) igniters. Previously Three elevations of oil guns with provision

for firing LDO oil in AB elevation only, HFO in elevation AB, CD & EF elevation.

Now modification has been done that provision of firing LDO oil in all 3 elevation i.e. AB , CD , EF elevation. With these modification desk engineer will able to minimize the Boiler light – up to synchronization time.

FSSS provided for this project is designed for a natural circulation:

DESCRIPTION OF BURNER BLOCK ASSEMBLY

Burner block assembly is divided into 14 elevation. There are 6 elevations of coal nozzles for firing the main

fuel. These are defined as A to F. There are 3 elevations of oil burner assembly for firing

start up/ stabilizing fuel (EL. AB , CD & EF ). 3 elevations acts as auxiliary air dampers ( BC, DE & FF ). 2 nos. of over fire air compartment at the top of the wind

box. They are designated as OFA-L (Over fire air - Lower) & OFA-U ( Over fire air - Upper) respectively.

Flame scanners are mounted at 5 different elevation i.e. AB,BC,CD,DE & EF.

If Secondary air is admitted to a fuel compartment in service, is referred as Fuel air Damper.

Secondary air is admitted to the furnace through air compartments and fuel compartments not in service, is termed as Auxiliary air damper.

FURNACE PURGE Furnace purging is done to remove all unburnt particles

which may have been inside the furnace during earlier unit operation.

Before Boiler is lighted up Furnace purge is done for which following interlocks should be satisfied:

Establish 110 V AC from UPS & 220 V DC from 4.5 mtr switchgear power to FSSS and the related equipment.

Establish normal drum level ( 0 mmwc NWL). Run at least one ID and one FD fan in service. Establish airflow between 30% and 40% MCR i.e.

300 to 400 TPH through the furnace. Press the purge start push button HMI ( purge time

5 min)

If the "Purge ready” light signal does not come on after the above conditions have been completed, check other these condition :

The light oil trip valve is fully closed. All the light oil nozzle valves are proven closed. The heavy oil trip valve is proven closed. All the heavy oil nozzle valves are fully closed. All PA Fans are off. All feeders are off. All hot air gates are fully closed. All the flame scanners sense "No Flame". No boiler trip command is present. All auxiliary dampers are modulating ( open condition ). At the end of the five minutes, the boiler trip circuit is

reset .

PLACE OIL GUN IN SERVICE Oil elevation AB is provided with Light Oil / Heavy Oil firing. Light

oil or Heavy oil firing can be selected from the console insert by pressing the appropriate push button provided in graphic.

LIGHT OIL TRIP VALVE ( LOTV ) CONTROL

Once the Boiler trip circuit is reset and all the light oil nozzle valves are proven closed, pressing the light oil trip valve "open" command , will open light oil trip valve provided the light oil header pressure is adequate.

LIGHT OIL TRIP VALVE (LOTV) Open permissive: All LONVs are closed. Furnace Purge Completed & MFT reset. Light oil header pressure Adequate >15.6kg/cm2. Unit 24 V DC power available from DCDB system

Protection close: Light oil header press V. Low < 4.2kg/cm2. Atomising air pressure V. Low < 3.5kg/cm2. MFT acted The LOTV will be commanded to close on loss of +24V

DC.

HIGH ENERGY ELECTRIC IGNITOR The HEA igniter assembly is designed to ignite a

variety of fuel ranging from high speed diesel to heavy fuel oil. The equipment gives high intensity electrical spark which ignite the oil particles surrounding the spark . The major component of BHELSPARK igniter are:

Spark generator Box. Flexible cable assembly. Spark rod assembly. Spark tip. Retractor assembly

SPARK GENERATOR BOX

The spark generator box contains the high voltage step – up transformer , produce high energy electric discharge spark .

Input voltage = 110 VAC, 50 Hz Output voltage = 3000 V DC

FLEXIBLE CABLE ASSEMBLEY Flexible cable assembly is used to connect

the spark tip and the spark rod assembly to the spark generator box. The flexibility of the cable is required for advancing and retracting the igniter tip using pneumatic actuator.

Length = 4000 mm Operating voltage = 3000 V DC

SPARK ROD ASSEMBLY The spark rod assembly used to connect

the spark tip to the flexible cable so the electrical discharges are transmitted to the spark tip to generate the sparks for ignition.

Construction : SS Wire& SS Tube Operating Voltage : 3000VDC

SPARK TIP

The spark-tip is a critical component in the igniters which converters the electrical discharge into high energy sparks. Care should be taken to clean the tip periodically and before any boiler light-up for reliable ignition. The tip life will reduce and some times the tip will get damaged if it is kept for longer duration at flame zone exposing to higher temperature.

Length of the spark tip = 180 mm Diameter = 15.9 mmSpark rate = 5 Sparks/second

RETRACTOR ASSEMBLY

The retractor assembly is a pneumatically operated system to advance the spark tip into the burner zone and retract the spark tip after successful ignition. The retract assembly is equipped with solenoid valve for controlling the pneumatic cylinder and also end point limit switches to signal the advanced or retracted position of the spark-tip.

Air cylinder stroke = 200 mm Air pressure = 4 – 5 kg/cm2Solenoid operating voltage = 110 V ACLimit switches = 2 nos.

OIL ELEVATION START PERMIT TO PLACE OIL GUN IN SERVICE “OIL ELEVATION START

PERMIT” MUST SATISFIED Select light oil or Heavy oil firing. LOTV or HOTV valve proven fully open. Purge Completed & MFT reset. Burner Tilt Horizontal & Air flow < 40% MCR. ( cold

condition ) OR. Any oil elevation in service ( warm up condition ) OR Any feeder on ( Running condition ). Local maintenance switch in remote position. Oil gun engaged. Scavenge valve closed. Manual isolation valve open.

LDO START SEQUENCE

To place the light oil guns in service following sequence is defined in four steps:

HEA Rod advance command. Open air atom valve. Open LONV valve and HEA Spark command. Step complete.

There are two type of firing in oil elevation (a) Pair mode (b) Elevation mode

A pair firing mode is selected when no feeder is in service . Elevation firing mode is selected when at least one feeder is selected.

TO TAKE LDO OIL GUN IN – PAIR MODE

To place the light oil guns in service “Oil elevation start permit” should be available.

LDO oil can be fired at EL. AB & in pair basis. Corners 1 and 3 make one pair, while corners 2 and 4 make the other pair.

The corners making up a pair are diagonally opposite. By pressing the associated pair start command ( i.e. 1-3 or 2-

4), will initiate a 70 seconds start time to place the associated pair of LDO oil guns in service.

When corner 1 & 3 is selected a start command is sent to oil corner 1 , fifteen seconds later a start command is sent to oil corner 3.

When HEA rod is advanced and the atomising Air valve is proven open and LONV valve gets open command & HEA igniter gets command for sparking. 15 seconds later, HEA igniter advance and spark command is removed.

If the flame is established within the above 15 seconds then the oil gun is said to have been successfully placed in service and will continue to operate.

If the flame is not established by the end of 15 seconds, corner trip will be initiated which will close the oil nozzle valve & atomising valve of the particular corner.

FLAME ON CONDITION FOR OIL = INTENSITY > 30 % & FREQ > 20 HZ

FLAME ON CONDITION FOR COAL = INTENSITY > 30 % & FREQ > 4 HZ

ELEVATION MODE OPERATION

Elevation mode is automatically active when the following condition exits :

Either adjacent feeder associated with the oil elevation is proven on .

for example Elevation AB is automatically active in elevation mode when the adjacent feeder A OR B is proven.

When the elevation mode is selected, the oil AB elevation is in service as follows (assuming the “OIL ELEVATION START PERMIT” remains established).

An elevation start command is established for corners 1 and 3 on the associated elevation.

After the “elevation start” command is established, a forty second counting period is started to establish an “elevation start” command for corners 2 and 4.

Corners 1 and 3 are now placed in service in the same manner as described in the “PAIR MODE OPERATION section.

After the forty second counting period expires, corners 2 and 4 are placed in operation in the same manner as described in the “PAIR MODE OPERATION”section.

At the end of 70 secs. , a minimum of 3 LO Gun are in service at that elevation if not, an unsuccessful elevation start alarm is initiated. This will trip corners 1-3 and 40 seconds later corner 2-4 as described in shut down procedure.

Elevation mode is not in service at our station for reliable operation .

OIL SHUTDOWN SEQUENCE Heavy oil shutdown sequence in pair mode is defined

in five steps:

Close cmd to HONV valve. Open atomizing steam valve. Open Scavenge valve & HEA Rod advance & Spark Cmd

for 15 secs. A 5 min.Scavenge period is started. Close Scavenge valve & atom. steam valve. Step complete

BOILER PROTECTIONS

PROTECTION OF BOILER:

To detect the abnormal condition by constantly measuring the various parameter under normal and faulty condition . If any abnormality happened trip the boiler to prevent from major damage.

NEEDS OF PROTECTION

To avoid operational faults. Equipment safety. To avoid accidents . To avoid systems disturbances

BOTH ID FAN TRIP

TRIP CAUSES:

MFTAND

Logic Gate

PURPOSE : Protection to prevent furnace pressurization

IDF VFD CHANNEL FAULT. IDF POST PURGE TRIP. IDF BRG TEMP V.HI. IDF WINDING TEMP V.HI. IDF VIBRATION V.HI. ELECTRICAL PROTECTION OPERATED. EPB OPERATED.

IDF – B Off (Off Feedback)

IDF – A Off (Off Feedback)

BOTH FD FAN TRIP

TRIP CAUSES:

MFTAND

Logic Gate

FDF – B Off (Off Feedback)

FDF – A Off (Off Feedback)

PURPOSE : Protection to prevent reducing firing condition.

FDF POST PURGE TRIP. FDF BRG TEMP V.HI. FDF WINDING TEMP V.HI. FDF VIBERATION V.HI. ELECTRICAL PROTECTION OPERATED. EPB OPERATED.

DRUM LEVEL VERY LOW

Tripping value = < - 225 mmwc

Alarm = < -125 mmwcTime delay = 5 sec. PURPOSE : To

prevent water wall tubes starvation.

DRUM LEVEL VERY HIGH

Tripping value = > + 225 mmwc

Alarm = > + 125 mmwc

Time delay = 10 sec. PURPOSE : To

prevent water carry over to super heater header

and to turbine.

T1

T2

T3

2/3 Logic MFT

Transmitters Range = - 425 to 762 mmwc

FURNACE PRESSURE VERY HIGH

Tripping value = > + 150 mmwc

Alarm 1 = > + 30 mmwcAlarm 2 = > + 75 mmwc

PURPOSE : To stop fuel firing under explosive tendency of

furnace , prevent furnace structural distortion

FURNACE PRESSURE

VERY LOWTripping value = < - 175

mmwcAlarm 1 = < - 30 mmwcAlarm 2 = < - 100 mmwc

PURPOSE : To stop fuel firing under implosive tendency of

furnace , prevent furnace structural distortion

2/3 Logic

2/3 Logic MFT

MFT

V.High 1

V.High 2

V.High 3

V.Low 1

V.Low 2

V.Low 3

2/3 Logic

2/3 Logic MFT

MFT

V.High 1

V.High 2

V.High 3

V.Low 1

V.Low 2

V.Low 3

Switches

Switches

LOSS OF FUEL TRIP The loss of fuel trip circuit becomes armed when any

one nozzle valves open from closed position in any elevation.

AND LOGIC GATE

LOSS OF FULE TRIP ARMING

ALL FEEDER TRIPPED

HOTV TRIPPEDOR

ALL HONV CLOSED

LOTV TRIPPEDORALL LONV CLOSED

Once the trip circuit is armed, loss of fuel trip will occur if,

All feeders are off. AND

HO trip valve tripped OR All HO nozzle valves closed.

AND

LO trip valve tripped OR Elev. AB All LO nozzle valves closed.

UNIT FLAME FAILURE TRIP

2 S

ANY FEEDER PROVEN FLAME FAILURE TRIP ARMING

EL . F VOTED NO FLAME

EL . E VOTED NO FLAME

EL . D VOTED NO FLAME EL . C VOTED NO FLAME

EL . B VOTED NO FLAME

EL . A VOTED NO FLAME

AND LOGIC GATE

The Flame failure trip circuit is armed when any one feeder is proven .

once the trip circuit is armed, flame failure trip protection will occur if ,

Any feeder proven ( flame arming ) AND All elevation shows voted no flame

EXAMPLE ELEVATION – A VOTED NO FLAME

Elevation AB 2 / 4 nozzle valves not open AND Elev. AB scanner shows NO FLAME .

OR

Feeder A is not proven ( Off Feedback)

ELEVATION – B VOTED NO FLAME

Elev. AB 2 / 4 nozzle valves not open AND Elev. AB & BC scanner shows NO FLAME.

OR

Feeder B OFF

REHEATER PROTECTION REHEATER PROTECTION ENABLE (a) Boiler drum pressure > 8.2 kg/cm2 (b) Any feeder on (c) Boiler firing

PROTECTION : 1 WHEN BOILER IS 'WORKING / REHEATER PROTECTION ENABLE

(a) GENERATOR CIRCUIT BEAKERS OPEN &. BOTH SATISAFIED (b) HPBP OR LPBP VALVES REMAIN CLOSED

2 WHEN BOILER IS 'WORKING / REHEATER PROTECTION ENABLE (a) TURBINE TRIPPED & (b) HPBP OR LPBP VALVES REMAIN CLOSED

BOILER SHALL BE TRIPPED AFTER 10 Sec.

contact

Contact

Contact

2/3 Logic

MFT

LESS THAN FIRE BALL & 110V AC POWER FAIL

If all feeders are off AND Elevation AB started and loss of 110v AC OR Elevation CD started and loss of 110v AC OR Elevation EF started and loss of 110v AC

110 V AC USED: 110v AC supply used in all OIL nozzles valve , HEA

Igniter , Feeder outlet gate , All hot air gates , mill discharged valve.

LOSS OF 220 V DC If 220v DC supply fails for 2 sec.

220v DC supply used main oil valve HOTV , HORV , LOTV & scanner emergency damper.

LOSS OF 24V DC

24V DC is used for functioning of DCS cards , TG governing and field instruments ( Transmitters , switches , I/P converter ).

PURPOSE : If 24V fails , the DCS system cannot execute any logic

TOTAL AIR FLOW < 30% If (secondary air + primary air) flow < 300 TPH.

BOILER TRIP THROUGH EMERGENCY PUSH BUTTON

UCP panel. From boiler HMI push button

MFT NETWORK FAILURE

If any 2 DPU cards out of 3 of MFT panels go into failed status it will initiate MFT Protection.

PURPOSE : This ensure that At least 2 DPU cards are in healthy condition at any point of time when boiler is in service. Failure the DPU cards leads to unsafe condition.

2/3 Logic

DPU2

DPU3

DPU1

MFT

(DPU = DIGITAL PROCESSING UNIT)

THANK YOU