boiler emergancy

8/2/2019 Boiler Emergancy

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HANDLING OFBOILERDURINGEMERGENCIES


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BOILER EMERGENCIES

1)ONE ID FAN TRIPPED

2)ONE FD FAN TRIPPED

3)BOTH ID FANS TRIPPED

4) BOTH FD FANS TRIPPED

5) ONE PA FAN TRIPPED 6) BOTH PA FANS TRIPPED


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7) COAL MILL TRIPPED

8)DRUM LEVEL VERY LOW

9)DRUM LEVEL VERY HIGH

10) ONE BFP TRIPPED

11)BOTH BFP TRIPPED 12) FURNACE DRAFT VERY LOW

13) FURNACE DRAFT VERY HIGH


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HANDLING OF BOILER DURING EMERGENCY

EMERGENCY OPERATIONS

Major emergency situations in Boiler and

Auxiliary areas and suggested actions:

1. High Furnace Pressure

Probable Reasons:

One I.D. fan tripped or maloperation of control

vanes of I.D,F.D,P.A. fans or closing of damper.

Unstable furnace flame condition, Sudden

starting of coal mill, Low windbox pressure

nder normal F.D. fans loading conditions),

proper air distribution at elevations.

Un-equal burner tilts at corners or Burner tilt in

extreme up or Down.

Fouling in Air heater, Air heater tripped.

Furnace water seal broken, ES.P. or flue gas path

manhole opened.

Water wall tube rupture/leakage.


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Action to be taken:See that two mills are tripped or

otherwise trip them.Take running I.D. fans control onmanual & increase for loading. Checkthe cause of I.D. fan tripping and try torestart it, if everything is normal. Checkgas dampers indication & draft readingalong flue gas path. If some damper isclosed try to open that damper.

Take F.D. / P.A. fan control onmanual. Check control damperoperation. Adjust air flow.


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Action to be taken:Check air for correct flow. Check com bustionregime, openings of Auxiliary air and fuel airdam pers. wind box p ressure. See cold air andhot air dampers. Watch Furnace flame. TripBoiler if flam e is very much unstable. Purge outexplosive m ixture by maintaining h igh air flow .

Check Burner tilt at all corners is equal.Adjust Burner tilt between + 10 to -10 andcheck control air pressure.

See air-preheaters are rotating. Restarttripped air preheater and do A .H. soot blowing.

Check Furnace seal, water flow through sealtrough overflow. Re-establish seal.

Stop the boiler in case of tube leakage assoon as possible.


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2. Furnace Pressure LowProbable Reasons:

I.D. fan auto control

failure. I.D. fan vane controlmechanism failure causingvanes to open wide

Sudden decrease in airinput or tripping of one F.D.fan.

Sudden tripping of one ormore mills or choking of

mills/raw coal feeder pipe .

Partial flame failure


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Action to be taken

Take I.D. fans control on manual &reduce load on I.D. fans

Check I.D. fan control mechanism forproper functioning.

Check air flow, correct if necessary. Afterchecking restart F.D. fan if it had tripped.

Control the furnace pressure by adjustingI.D. fan vanes. Simultaneously try standbymill. Remove the choking of affected mill /Raw coal feed pipe.

Take the oil gun i.nto service to establishflame that locations / corner.

See the proper functioning of secondary airpath damper.

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3. Drum Level Low

Probable Reasons:

Mal-operation of Feed Auto Control or

Feed Regulator or Scoop auto.

Tripping of one of working feed pump

(standby pump does not start).

Sudden reduction of load.

Sudden increase in firing e.g. starting of

mills having sufficient coal left before

previous stopping.

Tube rupture/puncture.

Inadvertent opening of low point drain

valves or Emergency drum drain valve.

A i b k


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Action to be taken:

Take feed control valve on

manual and increase feeding

rate. Take scoop tube controlon hand increase scoop tube

position.

Check that water flow through

each pump does not exceed

capacity. Check feed watercontrol valve and tube control

linkages.

Starts reserve feed pump on

tripping of running feed pump,if auto starting fails.

Try to increase the load if not

possible, reduce firing rate

accordingly to control drumpressure.

A ti t b t k


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Action to be taken:

Reduce firing rate by suitablyadjusting the feed rate ofrunning mills. Check water flow andcompare with previous feedingrate and steam flow. High feedflow indicates tube failure.Inspect waterwall and

economizer or any tubeleakage,If tube leakage observed stopthe boiler as soon as possible,. Check drum drains and, low

point drains for closing.

Note: If drum level goes belowgauge glass and low drum leveltrip protection fails, trip boiler

at on low level.


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4. High Drum Level

Probable Reasons:

Mal-operation of feed watercontrol

Sudden increase in load

resulting in drum pressuredrop.

Sudden decrease in firing

rate e.g. tripping of the

running mills . B.F.P. scoop

tube position suddenly

increased

A ti t b t k


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Action to be taken:

Take feed control valve on

manual and reduce feedingrate.

Try to decrease the load as

far as possible.

Increase feeding range of

running mills.

Check differential pressureacross feed control valve and

maintain 5 Kg / cm2 by

adjusting scoop tube position.

5 Flame Failure At anElevvation


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5. Flame Failure At anElevvation

Probable Reasons:

Closing of trip valves on H.O./ W.U. Oil

/ Igniter (Causing loss of ignitionsupport energy) Where F.O. is beingused as support fuel or when only oil isbeing used.

Sudden decrease of mill feeder speedsto minimum.

Too low or too high windbox pressurecausing unstable combustion.

Water wall tube failure.

Malfunction of flame scanners due to

supply failure or scanner air failure, slagor soot onscanner lenses etc.

Burner tilt mechanism negativeextreme due to air failure to powercylinders.

Rapid load changes without adjusting

airflow leading to improper combustion.

Action to be taken


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Action to be taken:

Do not attempt to introduce igniters oroil guns at elevation where No flamecondition persist.

Trip out the coal mills of feedingelevation where No flame conditions ispersisting. Allow sometime for purgingthen introduce oil support adjacent toworking mills until furnaceflame is stabilized.

Check that secondary air wind boxdampers are modulating to maintainabout 80m.m.wcwind box to furnace differentialpressure.

Check furnace for tube failure.

If two elevations scanners show Noflame trip the boiler manually

Check burner tilt keep it between /+10 .

Check furnaces flame condition.


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6.0ne Fan Trips (Other in Service)

Probable Reasons:

It Is presumed that ID, FD, PA

fan de-interlocking switches areon Interlock position.

Fan Bearing temperature, highand/or

Fan motor Bearing temperaturehigh and/or

Lube oil pressure for motorbearings low and/or

Corresponding Air heatertripped (provided de-inter lockingswitch is on Interlock position)and/or.

Motor protection operated.

Action to be taken


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Action to be taken:

Takes draft control or manual, and / orincrease the loading on running fan and

maintain furnace draft.

Check corresponding fan is trippedthrough interlock.

Take secondary airflow controls onmanual and maintain correct airflow.

Cut in oil burner adjacent to workingmills. .

Check drum level is controlled on autoif necessary, take drum level control On

manual and maintain level.

Check pulverizers in excess of 3 aretripped starting from bottom.

Check that the load on the generatorhas reduced to 100 - 120 MW (partial

load relay energized).


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Check that interconnecting

dampers on air and flue gas side

open and tripped fans are

correctly isolated through

interlocks.

Check windbox pressure left and

right is maintained normal (about

75 mmwc).

Maintain steam temperature.

Check furnace flames condition.

Check that tripped pulverizers

are correct isolated (hot air gatesclose, cold air dampers come to

minimum).

Investigate the cause of trip.

Correct it & restart the tripped fan.


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7. One Feeder Trips

Probable Reasons:

Support energy is removedwithin 3 minutes of feederand/or.

No. coal flow alarm comes& low current relay picks upsimultaneously. (Feeder

shear pin given way) and/or.

Mill trips and/or.

Feeder motor supply fails.


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Action to be taken:

Check that hot air gate closes & cold air

damper opens full if pulverizer is running.

Clear the mill of the coal before stopped.

Stop the pulverizer if feeder cannot be

restarted immediately.

Check that running mills share the loading,

thermal load is on auto.

Reduce the load on generator and, maintainsteam parameters.

If 3 mills at less than 50% feeder speed or

2 mills are left in service, cut in oil gun

adjacent to working mills.

Check furnace draft, airflow and drum level

is normal.

Check flame is stable and scanners sense

Flame on.

Check that associated elevation fuel air

damper close and windbox pressure is

maintained 70 mmwc.


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8. One Mill Trills

Probable Reasons:

Mill discharge valves areclosed and/or

Loss of elevation D.c.supply for more than 2 secs

and lor

Support ignition energy isremoved with 3 minutes offeeder starting and / or .

Motor protection operatesand / or

One P.A. Fan trips (mill inexcess of 3 will trip starting

from bottom).


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Action to be taken:

Check the running mills sharethe load if thermal load control ofmills is on auto.

Reduce the generator load ifpressure starts dropping.

Start reserve mill and take load.

Check furnace draft is maintainenormal.

Check the correct airflow ismaintained.

Check that drum level ismaintained normal.

Check that tripped mill isisolated (hot air gate closed, coldair damper minimum open,feeder tripped).


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9. Hang-up in Mill

Probable Reasons:

Choking of coal atinlet to mill. H-ighmoisture in coal and /

or

Too much fineness incoal with moisture and/ or

Foreign material atRC feeder inlet

Action to be taken


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Action to be taken:

Check feeder trip on No Coal

flow & low current protection.

Check mill outlet temperature

is less than 85C.

Check mill hot air gate closes

on mill outlet temperature high

protection. Close hot air gate

and check mill.

Cold air damper opens full.

Check the flame condition at

the sick mill elevation.

Trip the sick mill after

clearing it coals.


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Increase the load on

running mills if the thermalload control is on manual.

Start reserve mill.

Maintain steam pressure

and temperature by reducing

load.

Check that furnace draft

and airflow are normal.

If 3 mills (or less) are inservice with speed below

50% take oil support atelevation adjacent to running

mills in service.


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10. Water Wall Tube Leakage

Probable Reasons:

Starved water walls due to very

low drum level and/or

Sustained flame impingementon water wall tubes and / or

Blocked tube, scaling of tube,

resulting in overheating of tube

Metal, pitting, corrosion of tubesand/or

Soot blower steam impingement

(wet steam impingement or directimpingement of steam)and/or

Circulation affected due toopening of low point drains.

Action to be taken:


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Action to be taken:

Compare feed water flow andsteam flow, assess the

magnitude of tube leakage.

Maintain drum level byincreasing feed water flow.

Inspect the furnace for tubeleakage.

If the tube leakage is minutethen take the unit out as a

planned shutdown to cold.

If tube leakage is heavy & itis likely to damage other tubesor likely to disturb the flame

stability trip out the unit.


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Keep close watch in

furnace flame.

As the load is beingreduced try to locate

burst tubes.

Check economizer

hoppers for water

leakage steam noise

etc. every shift.

Check that furnace

draft is maintained

normal.

11 Reheater /SuDerheater /


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11. Reheater/SuDerheater /

Economizer Tube Failure

Probable Reasons:

Sustained high metaltemperature due to waterwall

Slagging or forcing boiler at the

time of hot restart and / or

Erosion on tubes due to highexcess air, high ash content in

coal, dislocated tubes, soot

blowing and/or

Blocked tubes causingoverheating and/or

S lt d iti d t hi h


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Salt deposition due to high

water level in drum. poor

quality of water and/or

Inadequpte flow due to open

Superheater, Reheater drain

and / or

Fire side corrosion of tubesand / or

Economizer tube can fail due

to over heating if concentrationof Fe, Cu is more in feed water,

Steaming in economizer occurs

causing salt deposition and

harming the tubes.


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Action to be taken:

As soon as leakage isdetected start load

reduction and trip out

the boiler at theearliest possible time.

Try to locate leakthrough manholesbefore boiler isdepressurized.


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