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FURNACE SAFEGUARD SUPERVISORY SYSTEM

F.S.S.S. facilitates remote manual/automatic control of fuel firing equipments through mechanized system and suitable interlocks/logics.

It is designed to ensure the execution of a safe, orderly operating sequence in start up and shutdown of fuel firing equipments and to prevent errors of omission in following such a safe operating procedure.

The system provides protection against malfunction of fuel firing equipment and associated air system.

The safety feature of system are designed for protection in most common emergency situations.

F .S.S.S. Equipment can be grouped under three heads

1. The Operating and Indicating Console

This consists of all switches for initiating controls and also indications of status of all fuel firing equipment & their auxiliaries.

2.Relay and Logic Cabinets:

The cabinets consists of relays, timers, programmers, circuit breakers for AC and DC control suppliers flame scanner unit, number of coal flow units etc. They control the process logic

Field Equipments Field equipments are those which help in actual remote operation

of fuel firing equipments and those which provide the status to the

operating console and relay logic cabinet.

Ignitor/H.O Trip Valves, H.O atomizing steam, Scavenging atomizing nozzle valve (Hydramotor type), Gun advance/retract mechanisms, Oil gun assembly, Ignitors and its cabinets, Flame scanner and ignitor air fans, Pressure switches, temperature switches, flow switches and limit

switches, Mill Discharge valves, hot air gates, sealing air valves, cold air,

tramp iron gate etc.

Functions of FSSSTo start complete furnace purge when all technological

conditions are fulfilled.

To start and monitor ignitors

H.O. guns, (oil guns) starting, stopping and supervision.

Pulveriser and feeder starting, stopping and supervision

Flame scanner intelligence and checking.

Furnace flame monitoring and overall furnace flame failure protection.

Functions of FSSS

To start-stop igniter and scanner air fans.

To effect secondary air damper control with indication of auxiliary and fuel air damper modulation/close.

To trip out all boiler fires when boiler safety is threatened

To provide boiler trip signal to other equipments such as P .A. Fan, Turbine, Generator etc.

• BURNER MANAGEMENT SYSTEM

• BOILER PROTECTIONS

• MILLING SYSTEM

• FUEL OIL SYSTEM

• UNIT PURGE

• SEC. AIR DAMPER CONTROL

• SOOT BLOWER CONTROL

• AUX. PRDS CONTROL

• HP-BYPASS CONTROL

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LOCAL CONTROL BOX AIR

DAMPER

BMS

FUELV/V

FLAMEDETECTOR

IGNITER

DAS

MILLCONTROL

BOILER PLANT

IGNITION CONTROL PANEL

FURNACE PURGE

Purpose: :Complete Removal of unburnt fuel from entire

furnaceProcedure:Ensure that all fuel to furnace is cut off and all flame is

outProvide adequate air flow through furnace (30 to 40%) Initiate a MANDATORY purge time cycle (9 min)

Consequence:Master Fuel Trip Relays are resetFiring of fuel into the furnace is allowed

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Boiler Purge Logic

All HFO nozzle valves are closedAll Pulverizers are offNo MFT condition presentAll feeders are offAll scanners sensing no flame.All auxiliary air dampers modulatingBoth PA fans offAll HAGs closedAir flow more than 30% and less than 50%HFO trip valve is closedWind box to furnace DP is adequate.

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PURGE PERMISSIVES

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TO FSSS

All HFO nozzle valves closed

All pulverisers OFF

All feeders OFF

No MFT condition present

All scanners senses no flame

All Auxiliary Air dampers modulating

Both PA fans OFF

All Mill HAGs closed

Air flow more than 30% and less than 50%

HFO trip valve is closed

Wind box to furnace DP is adequate

Purge Logic

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AIR DAMPER-AIR DAMPER ARE DIVIDED AS FOLLOWS-

1-FIVE ELEVATION OF FOUR SECONDARY AIR.

2- 4 ELEVATION OF 4 AIR TO OIL/S.A.D

3-8 ELEVATION OF 4 AIR TO P.F. BURNER.

4-TWO ELEVATION OF FOUR OVERFIRE AIR.BURNER NOZZLE NOZZLE MILL GROUPGROUP ELEVATION TYPE GROUPNUMBER NUMBER 4 13---------------------------SECONDARY AIR 12---------------------------COAL--------------------------- -F 11---------------------------OIL AND S/A3 10 --------------------------COAL-----------------------------E 9 --------------------------SECONDARY AIR 8---------------------------COAL------------------------------D2 7-------------------------- OIL AND S/A 6---------------------------COAL------------------------------C 5---------------------------SECONDARY AIR 4---------------------------COAL------------------------------B1 3---------------------------OIL AND S/A 2---------------------------COAL------------------------------A 1-------------------------- SECONDARY AIR

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Oil Trip Valve operation logic

This logic ensures that oil trip valve can be opened after the purge cycle is completed and no MFT condition is present, if the following conditions are also satisfied.

All nozzle valves are closed.

HFO supply pressure is satisfactory.

HFO header temperature is satisfactory.

Similarly, this logic ensures the closure of oil trip valve in case of MFT.

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OIL ELEVATION LOGIC

There are four heavy oil elevations AB, CD, EF & GH. For all these elevations, logics are same.

Oil elevation can be placed in service auto/manual.

For a particular elevation, only one command is given for all the four corners together. (e.g. One common start command for elevation AB-1, 2, 3 and 4 guns).

Start command goes to corners 1 to 4 sequentially. First command goes to corner 1; after 15 seconds start commend goes to corner 3; again after a lapse of 15 seconds start commend goes to corner 2; and again after a gap of 15 seconds start command goes to corner 4.

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Oil elevation logicStart of oil elevations AB,CD,EF and GHSequential operation with start commandCorner1,corner3,corner2 and corner4Gun advance,igniter advanceSpark,atomizing valve open,oil valve openSensing of discriminatory flameRetract of igniter

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Oil elevation logicStop of oil elevationClosure of oil valve,opening of scavenge valveIgniter advance and sparkingClosure of atomizing valve and scavenge

valveRetract of igniter and gun

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A particular corner takes the start command only if the following conditions are satisfied:-

The particular corner oil gun engaged feedback is available.

The steam scavenge valve is closed for the particular corner.

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The sequence of operation taking place for a particular oil gun once the command is given is as follows:-

First the oil gun is advanced. Once gun advanced feedback is available the HEA igniter is

advanced. Then atomizing steam valve is opened for the particular corner. Then HFO nozzle valve gets open command. ‘Spark’ command is given to igniter transformer, thus

producing a spark at the spark tip. Then for this particular corner ‘HFO flow satisfactory’ feedback

comes from the flow switch in the oil line. The corner oil gun proves when the DISCR FLAME SCANNER

senses FLAME. When 25 seconds elapses after oil valve open, igniter spark

signal is removed and spark rod is retracted. If the corner oil gun did not prove FLAME by this time, ‘Oil

nozzle valve’ and atomizing steam valve closes. Gun and igniter are retracted.

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Scanner air fans logic It monitors the scanner air duct to

furnace DP and ensures starting of scanner air fan - A or in case it fails to start, scanner air fan - B. This logic gives an open command to scanner fan outlet damper after starting the fan.

Also, in case of both FD fans not running, it ensures the scanner air emergency damper is open.

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Seal air fans logic

Monitors seal air header to cold air duct DP and ensures the starting of seal air fan - A or B ( in case A does not start), provided at least one PA fan is running.

Gives an open command to seal air fan discharge damper once fan starts.

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Coal elevation logicFeeder start logicPulverizer onOutlet temperature adequateSpeed demand minimumNo MFTFeeder stop logicHad/cad logic

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Coal elevation logicPulverizer start logicAvailability of PA permitAvailability of ignition permitSeal air /bowl differential pressure No MFTLube oil pressure adequatePulverizer stop logic

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COAL ELEVATION LOGIC

PULVERISER LOGICThis logic takes the count of total no. of

pulverisers in service at any point of time, the no. of FD Fans and PA fans in service.

With PA Fan ‘ON’ and PA Header Pressure adequate (>560 mmwcl), it gives “PA permit” to start the Pulverizer.

In case of PA Header Pressure going low-low or PA/ FD fans trips, it ensures the shut down of Pulverizers from top elevation to bottom elevation in a timed sequence.April 18, 2023 32

Each mill can be taken in to service manually

or automatically. Auto manual selection push

button is available on FSSS console for each

mill. Initially, “Pulverizer Ignition Permit”

signal must be established for the mill to start.

Other condition required to be established for

starting the mill are as follows:-

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Mill lub oil pressure adequate.Start permit from FSSS.Mill Discharge valve open.Mill outlet temp. > 93OC.(200OF)Cold Air Gate (CAG) open.Tramp iron vale (Top Reject Gate) open.Feeder inlet gate open.Seal air DP adequate (200 mmwcl).Feeder local switch in remote.

Once the mill is ON, associated HAG can be opened and feeder can be placed in service.

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INTERMEDIATE OIL BURNERELEVATION FIRING

OR

30% BOILER LOAD

ADJACENT MILL FIRING

PA FAN IN SERVICE

AND

AND

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OIL BURNER FIRING ON MILL BEING BROUGHT INTO SERVICE-

FOR ANY MILLS(A,B,C,D,E,F,G,H)1-AT LEAST THREE OIL BURNER S FIRING IN SELECTED ELEVATION.2- (A) BOILER LOAD > 30% BCMR

AND (B) UPPER OR LOWER ADJACENT COAL BURNER IN OPERATION

EXAMPLE: FOR MILL A START PERMISSIVE: 1- ELEVATION AB 3/4 OIL BURNER FIRING.

OR 2- MILL B FIRING

AND BOILER LOAD >30% BCMR.

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FOR B,D,F MILL(A) AT LEAST 3 OIL BURNERS FIRING IN THE BURNER GROUP ABOVE

AND (B) ADJACENT COAL BURNER ABOVE IN OPERATION

AND(C) THIS ELEVATION IS HIGHEST IN THE BURNER GROUP.

EXAMPLE- FOR MILL B START PERMISSIVE-(1) ELEVATION AB 3 / 4 OIL BURNER ARE I/ S .

OR (2) MILL A FIRING OR MILL C FIRING

AND BOILER LOAD > 30% OF BCMR.

OR (3) MILL C FIRING

AND ELEVATION CD 3 / 4 OIL BURNER ARE I/S.* NOTE THAT B ELEVATION IS HIGHEST IN THE BURNER GROUP AB.

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FOR MILL C,E,G(A) AT LEAST 3 OIL BURNER FIRING IN THE BURNER GROUP BELOW.

AND(B) ADJACENT COAL BURNER BELOW IN OPERATION.

AND(C) THIS ELEVATION IS LOWEST IN THE BURNER GROUP.

EXAMPLE- FOR MILL C START PERMISSIVE –(1) ELEVATION CD 3 / 4 OIL BURNER I/S.

OR (2) MILL B FIRING OR MILL D FIRING

AND LOAD > 30% OF BCMR.

OR (3) MILL B FIRING

AND ELEVATION AB 3 / 4 OIL BURNER ARE I/S.* NOTE THAT C ELEVATION IS LOWEST IN THE BURNER GROUP CD

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Flame Scanners

MASTER FUEL TRIP (MFT)

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• MFT or Boiler Trip means: Complete isolation of all fuel to furnace under certain

conditions

• Automatic Procedure:

All oil valves are given closing command All mills and feeders are given trip command

All Primary Air (PA) Fans are given trip command

All Hot Air Gates (to mills) are given closing command• Further Consequences:

Turbine protection is initiated (to trip turbine) All SH and RH spray valves are given closing command All elevation SADC are given full open command Furnace pressure & Air flow controls are set to manual

Unit LogicMFT consequences

Trips all millsTrips all feedersTrips PA fansCloses HFO trip valveCloses all elevation nozzle valvesClose all HAGs

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Both FD fans OFFBoth ID fans OFF

MFT RELAY

Air flow less than 30% and boiler load not greater than 30%

Loss of 220 V DC Supply for more than 2 seconds Manual Emergency PB trip

Both Secondary APHs OFF

Loss of Unit Critical Power for more than 2 seconds

Unit flame failure

All feeders OFF and loss of AC Supply to the elevation in service

Loss of all fuel

Furnace pressure very low (2/3 logic)

Furnace pressure very high (2/3 logic)

Drum level very low for more than 10 seconds (2/3 logic)

Drum level very high for more than 10 seconds (2/3 logic)All BFPs tripped

Loss of Reheat Protection for greater than 10 seconds

Inadequate water wall circulation for more than 5 seconds

Reheater Protection

Reheater Protection Arming

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THANK YOU …QUESTIONS ?