2 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.
3 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.
4 F .S.S.S. Equipment can be grouped under three heads The Operating and Indicating ConsoleThis 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
5 Field EquipmentsField 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.
6 Functions of FSSSTo start complete furnace purge when all technological conditions are fulfilled.To start and monitor ignitorsH.O. guns, (oil guns) starting, stopping and supervision.Pulveriser and feeder starting, stopping and supervisionFlame scanner intelligence and checking.Furnace flame monitoring and overall furnace flame failure protection.
7 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 threatenedTo provide boiler trip signal to other equipments such as P .A. Fan, Turbine, Generator etc.
8 SEC. AIR DAMPER CONTROL SOOT BLOWER CONTROL AUX. PRDS CONTROL BURNER MANAGEMENT SYSTEMBOILER PROTECTIONSMILLING SYSTEMFUEL OIL SYSTEMUNIT PURGESEC. AIR DAMPER CONTROLSOOT BLOWER CONTROLAUX. PRDS CONTROLHP-BYPASS CONTROL
9 SIMPLIFIED BLOCK DIAGRAM OF BURNER MANAGEMENT SYSTEM. LOCALCONTROLBOXFUELV/VDASAIRDAMPERMILLCONTROLFLAMEDETECTORIGNITIONCONTROLPANELIGNITERBOILERPLANT15 April 2017
10 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 allowed15 April 2017
11 Boiler Purge Logic All HFO nozzle valves are closed All 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.15 April 2017
12 A N D PURGE PERMISSIVES All HFO nozzle valves closed All pulverisers OFFAll feeders OFFNo MFT condition presentAll scanners senses no flameTOFSSSA N DAll Auxiliary Air dampers modulatingBoth PA fans OFFAll Mill HAGs closedAir flow more than 30% and less than 50%HFO trip valve is closedWind box to furnace DP is adequate15 April 2017
14 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.D3-8 ELEVATION OF 4 AIR TO P.F. BURNER.4-TWO ELEVATION OF FOUR OVERFIRE AIR.BURNER NOZZLE NOZZLE MILL GROUPGROUP ELEVATION TYPE GROUPNUMBER NUMBERSECONDARY AIRCOAL FOIL AND S/ACOAL ESECONDARY AIRCOAL DOIL AND S/ACOAL CSECONDARY AIRCOAL BOIL AND S/ACOAL ASECONDARY AIR15 April 2017
18 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.15 April 2017
19 Oil elevation can be placed in service auto/manual. OIL ELEVATION LOGICThere 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 4.15 April 2017
21 Oil elevation logic Start of oil elevations AB,CD,EF and GH Sequential operation with start commandCorner1,corner3,corner2 and corner4Gun advance,igniter advanceSpark,atomizing valve open,oil valve openSensing of discriminatory flameRetract of igniter15 April 2017
22 Oil elevation logic Stop of oil elevation Closure of oil valve,opening of scavenge valveIgniter advance and sparkingClosure of atomizing valve and scavenge valveRetract of igniter and gun15 April 2017
23 The particular corner oil gun engaged feedback is available. 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.15 April 2017
24 First the oil gun is advanced. 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.15 April 2017
26 Scanner air fans logicIt 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.15 April 2017
27 Seal air fans logicMonitors 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.15 April 2017
30 Coal elevation logic Feeder start logic Pulverizer on Outlet temperature adequateSpeed demand minimumNo MFTFeeder stop logicHad/cad logic15 April 2017
31 Coal elevation logic Pulverizer start logic Availability of PA permit Availability of ignition permitSeal air /bowl differential pressureNo MFTLube oil pressure adequatePulverizer stop logic15 April 2017
32 COAL ELEVATION LOGICPULVERISER 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.15 April 2017
33 Each mill can be taken in to service manually or automatically 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:-15 April 2017
34 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.15 April 2017
35 MILL PERMISSIVE: 30% BOILER LOAD AND OR ADJACENT MILL FIRING PA FAN IN SERVICEANDORINTERMEDIATE OIL BURNERELEVATION FIRING15 April 2017
36 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.15 April 2017PMI Revision 00
37 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.15 April 2017
38 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 CD15 April 2017
39 VOTING OF ELEVATION – VOTING IN AB ELEVATION WILL BE AVAILABLE (1) MILL A FEEDER OR MILL B FEEDER I/S AND ELEVATION AB 2 / 4 FLAMES IN INTRLOCKED WITH ( ALL BURNER IN AB ELEVATION SATISFACTORY S/D OR 3 / 4 OIL BURNER IN THAT ELEVATION ARE I/S.) (2) VOTING IN BC ELEVATION WILL BE AVAILABLE MILL B FEEDER OR MILL C FEEDER I/S AND ELEVATION B 2 / 4 FLAMES IN. VOTING WIL NOT BE AVAILABLE – (1) BOTH FEEDERS ON BURNER ELEVATION ARE NOT I/S OR (2) 2/4 FLAME ARE NOT SENSED INTERLOCKED WITH 3 / 4 OIL BURNER ARE NOT FIRING OR (3) OIL GUN IN THAT ELEVATION NOT SATISFACTORLY SHUTDOWN INTROLOCKED WITH 3 / 4 OIL BURNER IN THAT ELEVATION NOT FIRING.Flame Scanners15 April 2017
41 MASTER FUEL TRIP (MFT) MFT or Boiler Trip means: Complete isolation of all fuel to furnace under certain conditionsAutomatic Procedure:All oil valves are given closing commandAll mills and feeders are given trip commandAll Primary Air (PA) Fans are given trip commandAll Hot Air Gates (to mills) are given closing commandFurther Consequences:Turbine protection is initiated (to trip turbine)All SH and RH spray valves are given closing commandAll elevation SADC are given full open commandFurnace pressure & Air flow controls are set to manual15 April 2017
42 Unit Logic MFT consequences Trips all millsTrips all feedersTrips PA fansCloses HFO trip valveCloses all elevation nozzle valvesClose all HAGs15 April 2017
44 O R Both FD fans OFF Both ID fans OFF Inadequate water wall circulation for more than 5 secondsLoss of Reheat Protection for greater than 10 secondsAll BFPs trippedDrum level very high for more than 10 seconds (2/3 logic)Drum level very low for more than 10 seconds (2/3 logic)Furnace pressure very high (2/3 logic)Furnace pressure very low (2/3 logic)MFTRELAYO RLoss of all fuelAll feeders OFF and loss of AC Supply to the elevation in serviceUnit flame failureLoss of Unit Critical Power for more than 2 secondsBoth Secondary APHs OFFLoss of 220 V DC Supply for more than 2 secondsManual Emergency PB tripAir flow less than 30% and boiler load not greater than 30%15 April 2017