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8/10/2019 PREM BOILER EMERGENCIES.ppt
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Boiler Emergencies of 500 MW
R Prem Anand
Manager
NTPC LTD
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Coal Mills Fire / PA Fan duct Fire
Observations:
Fire reported by Local Engineer
Coal Mill outlet temperature going hi
Coal Mill outlet temperature hi" annunciation on UCP / Alarm CRT
Actions
Inform Fire department
Close Hot Air Gate of the coal mill having fire
Unload and stop the coal mill having fire and close Cold Air Gate
Ensure whether inert steam is applied
Monitor coal mill outlet temperature
In case of burner oil / gas pressure raising, take additional available guns orelevation in service
Reduce the coal / fuel oil ratio pot for reducing the loading of other coal mills in
case if they are on auto
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FD Fan Stalling
Observations
Annunciation on UCB / Alarm CRT Combustion going bad
Rise in MS & RH Steam temperature
Difference in suction flow and current of both FD fans
Actions
Take blade pitch control of both the fans on manual and reduce slightly the loading of
healthy fan seeing the current and suction flow - Boiler master on manual, Turbine follow
mode
In case the load is > 250 MW, adjust fuel firing equal to 250 MW Load
Monitor boiler metal temperatures
Operate blade pitch control of affected fan to minimum position and load the fan slowlyby watching current and suction flow
When both FD fans are normal, put blade pitch control on Auto. Put Boiler master on
Auto and select Boiler follow mode
Increase generation as per requirement
In case the affected fan blade pitch control link has given away, then follow procedure for
one fan operation
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Coal Mill Seal Air Differential Pressure Hi
Observations
Alarm on UCP / Alarm CRT
Actions
Inform OE / AOE (Boiler) to check Delta P from local indicator / transmitter
If Delta P is on higher side, take standby filter in service
Isolate choked filter
Confirm with additional officer that no coal powder is coming out from journal bearing
and if there is no improvement in Delta P, unload and take out corresponding coal mills
In case of burner oil / gas pressure raising, take additional available guns or elevation in
service
Reduce the coal / fuel oil ratio pot for reducing the loading of other coal mills in case if
they are on auto
Stop seal air fans on that side and isolate
Inform MMD
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All LDO Oil Pumps Tripping
Observations
Alarm on UCP / Alarm CRT
LDO Oil Pumps trip indication on UCP / CRT
Fuel oil burner / header pressure zero
Fuel oil elevations wipe out
LDO oil CPRV goes close
LDO oil trip valve goes close
Runback active, load will drop to the capability coal mill (U5) in service
Coal mill will get overloaded
Boiler Trip in case of full oil firing leading to Main Turbine Trip
Actions
Inform AOE (Fuel) to rack out corresponding unit tripped LDO oil pumps breaker
In case coal feeder are on auto, take coal feeders on manual and maintain coal flow within
operating limits and stabilise load as per fuel firing
In case of boiler trip - follow procedure for MFT and Main Turbine Trip
Confirm the cause of LC oil pumps tripping
Inform LD / EMD / MMD / IMD
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RAPH Fire
Observations
For the RAPH on fire following annunciations will appear on Alarm CRT
Flue Gas outlet temperature Hi-Hi
RAPH Differential Pressure Hi-Hi Secondary Air Outlet Temperature Hi
Furnace Draft Hi
Combustion going bad
Stack emission going bad
Actions
Monitor all the parameters
Sound fire siren
Inform Fire Department / LD / M(O)
Prepare for One Fan Operation to isolate the RAPH on fire
Drop Load to 250 MW by creating run-back by removing Coal Mills
Close flue gas inlet & outlet damper of the referred RAPH
Close air inlet & outlet damper of the referred RAPH
Stop the RAPH on fire and its lube oil pumps
Stop ID fans and the associated FD Fan
Start RAPH wash pumps and extinguish RAPH fire
Monitor parameters and stabilise the conditions at 250 MW
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Loss of all Coal Mills with One LDO Oil elevation In Service
Observations
Annunciation on UCP / Alarm CRT
Coal mills which are in service will trip on PA header pressure Lo
Running PA Fans has gone in stalling mode
Difference in PA Fan currents and Primary Air flow
Runback active, Load will drop to the capability of fuel oil elevations in service
Boiler master on manual, Turbine follow mode Boiler master goes negative
Actions
Take Fuel oil control on manual
Take Fuel oil elevations in service Adjust Fuel oil CPRV bypass to bypass to have margin on CPRV
Maintain Drum level, Dearator level and hotwell level
Unload and load slowly PA Fan which has gone to stalling mode
Normalise the conditions, Take controls on Auto
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Excessive Drum Pressure Rising with HP / LP Bypass Available / Not
Available
Observations
Alarm on UCP / LCN / Alarm CRT
Drum pressure rising leading to boiler master deviation going positive
Increase in throttle steam pressure
Drop in Drum level, increase in BFP speed
Main Turbine HP control valves throttling
Reduction in fuel on auto
Causes
Main turbine HP control valves (throttling side)
Superheater spray flow control valves (opening)
Burner tilt (coming down) FD fans control vane (opening)
Fuel control valves (opening)
Coal feeder speed (increasing)
Load throw off
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Actions
With HP / LP Bypass Available
Increase load if margin is available. Inform LD
If main turbine HP control valves are hunting, arrest the hunting by investigating the
cause, else go for valve wide open operation
Take main steam spray control valves on manual and reduce the superheater spray flow
Take burner tilt on manual and raise it
If FD fan/s control vane malfunctions, take control on manual and adjust secondary air
flow according to load
If fuel control valves malfunction, take control on manual and adjust fuel flow according
to load
Monitor fuel oil burner pressure, take fuel oil guns out of service if necessary
Take coal feeders (which are in service) on manual and reduce coal flow accordingly
Arrest the boiler master increasing
At boiler master deviation of +10 bar, HP / LP bypass may come into service, start standbyCEP
Note : During the disturbance
Monitor condenser vacuum, drum level, deaerator level and hotwell level
Monitor FD / ID / PA fan parameters
Normalise the conditions when boiler master is normal
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With HP / LP Bypass Not Available
Increase load if margin is available. Inform LD
If main turbine HP control valves are hunting, arrest the hunting by investigating the
cause, else go for valve wide open operation Take main steam spray control valves on manual and reduce the superheater spray flow
Take burner tilt on manual and raise it
If FD fan/s control vane malfunctions, take control on manual and adjust secondary air
flow according to load
If fuel control valves malfunction, take control on manual and adjust fuel flow according
to load
Monitor fuel oil burner pressure, take fuel oil guns out of service if necessary
Take coal feeders (which are in service) on manual and reduce coal flow accordingly
Arrest the boiler master increasing
If boiler master is still increasing, ERV (if available) will open on auto, else main steam /
reheat steam lines safety valves may lift
Note : During the disturbance
Monitor condenser vacuum, drum level, deaerator level and hotwell level
Monitor FD / ID / PA fan parameters
Normalise the conditions when boiler master is normal
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RAPH LUB Oil Pumps Tripping
Observations
Alarms on UCP / Alarm CRT
Case1 - Only 1 Guide Bearing OR Support Bearing Lube Oil Pump TripsActions
Inform Boiler OE / AOE and start standby Lube Oil Pump
Check Lube Oil Tank level and Lube Oil Pump discharge pressure
Monitor RAPH Bearing Temperature
Case 2 - Both Guide Bearing Lube Oil Pumps not coming in service
Actions
Monitor Guide Bearing Temperature closely.
Investigate the cause of Lube Oil Pumps not coming in service.
In case Guide Bearing Temperature goes above 90 C,
Inform LD and reduce Load to 250 MW for one Fan operation
Follow procedure for one fan operation
Case 3 - Both Support Bearing Lube Oil Pumps not coming in service
Actions
Monitor Support Bearing Temperature closely
Check Tank level is OK
Investigate the cause of Lube Oil Pumps not coming in service
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One PA Fan Tripping
Both PA Fans In Service
Observations
Annunciation on UCP / Alarm CRT
Coal mills which are in service will trip on PA header pressure Lo
Other PA Fan which is in service will get loaded to 100% and current > 210 amps
Fuel oil flow will increase
Runback active, Load will drop to the capability of fuel oil elevations in service Boiler master on manual, Turbine follow mode
Boiler master goes negative
Actions
If Fuel oil is in service take control on manual other wise take fuel oil Adjust Fuel oil CPRV bypass to bypass to have margin on CPRV
Maintain Drum level, Dearator level and hotwell level
Unload the running PA Fan and maintain PA Fan current under limit
Confirm that tripped PA Fan discharge damper has gone closed or get it closed manually
Normalise the conditions, Take controls on Auto
Note down the relay targets for the tripped PA Fan
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Only One Fan In Service
Observations
Annunciation on UCP / Alarm CRT
Coal mills which are in service will trip on PA header pressure Lo
Actions
If Fuel oi; is in service, take fuel oil control on manual
Adjust Fuel oil CPRV bypass to bypass to have margin on CPRV
Normalise the conditions, Take controls on Auto
Note down the relay targets for the tripped PA Fan
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Two PA Fan Tripping
Observations
Annunciation on UCP / Alarm CRT Coal mills which are in service will trip on PA header pressure Lo
Unit tripping
Boiler master goes negative
Actions
If Fuel oil is in service, take fuel oil control on manual
Adjust Fuel oil CPRV bypass to bypass to have margin on CPRV
Maintain Drum level, Dearator level and hotwell level
Normalise the conditions, Take controls on Auto
Confirm the relay targets for the tripped PA Fans
If Boiler trips follow MFT procedure.
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One FD Fan Tripping
Observations
FD Fan trip annunciation / indication on UCP / LCN / Alarm CRT
Load runback to 300 MW (if load was more than 300 MW)
Corresponding ID Fans will trip
Actions
In case of runback, follow procedure for runback active
Ensure that sufficient airflow is maintained for proper combustion (if required take running
FD fan blade pitch control may be taken on manual)
Coal mills may trip due to PA header pressure Lo, on loss of PA Fan, take fuel oil / gas
elevation(s) in service as per requirement. (Fuel oil / gas elevations adjacent to the tripped
coal mills can not be taken in service for 180 seconds after tripping of coal mills)Maintain drum level, deaerator level and hotwell level
Stabilise the conditions
Ensure that outlet damper of FD fan that has tripped goes close
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FURNACE PRESSURE HIGH
One I.D. Fan tripped or Mal-operation
of control vanes of I.D./F.D./P.A. Fans or closing of
damper
Unstable furnace flame conditions.
Furnace water seal broken, E.P. or flue gas path
manhole opened.
Water wall tube rupture/leakage.
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FURNACE PRESSURE LOW
I.D. Fan auto control Failure.
I.D. Fan vane control mechanism Failure causing
vanes to open wide.
Sudden decrease in air input or tripping of one
F. D. fan.
Sudden tripping of one or more mills or choking
of mill/raw coal Feeder pipe.
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ID FAN TRIP
Electrical protection trip.
Emergency Push Button pressed.
Stop command from UCB.
Post trip purge furnace pressure high/low.
Fan/Motor bearing temperature high-high. (>1000
C)
Lube oil pressure low-low. (850
C)
Hydraulic coupling oil temperature high-high.
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FD FAN TRIPPED
Running FD fan trips in case of the following:
Electrical protection trip.
Emergency PB pressed.
Stop command from UCB.
No ID fan running or one ID fan and one FD fan already in
service.
Post trip purge furnace pressure high/low.
Fan/Motor bearing temperature high-high.(>1000 C)
Dampers fail to open in 180 sec after fan starting.
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PA FANS Logics :1. Hot PA header pr. Low -560 mm WCL
2. Hot PA header pr. Lowlow
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PA FAN TRIPPED
If a running PA fan trips, then : If 5 or more than 5 mills are in service ,the tripping will
be as follows :
H mill trips immediately
G mill trips 2 sec. delay
F mill trips 4 sec. delay
E mill trips 6 sec. delay
When 4 mills are ON then, PA Fan trip signal causing
mills trip will not be effective.
(When one PA or one FD fan trips ,the sequence is same
as above)
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PA fan tripping
Effects :
- Top two mill will trip on FSSS interlock
- Unit load may come down to approx. 300MW
- PA header pressure will come down
- Other running PA fan may get overloaded
Action:
-Other PA fan loading to be reduced to avoid its
overloading (if it is in auto)- Reduction of sec. air flow
(excess sec. air will disturb the flame)
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FD or PA fan stalling
Effect :
Stalled fans current will come down
Stalled fans discharge will reduce
Vibration of fan will increase
Abnormal sound in local Other fan may get overloaded.
sec air flow or pa flow will reduce.
Action :
Reduce other fans loading ( if it is in auto take inmanual).
Match both fans loading.
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AIR PRE-HEATER
Air pre heater bearing temperature very high.
Air pre-heater electric motor tripped.
APH electric drive tripped and air motor fails
to start.
Air pre-heater on fire.
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DRUM LEVEL LOWMal-operation of Feed Auto Control or Feed Regulator or
scoop auto.Tripping of one of working feed pump (standby pump
does not start)
Sudden increase of load.
Sudden increase in firing rate
Starting of mills having sufficient coal left before previous
stopping.
Tube rupture/puncture of low point drain valves orEmergency drum drain Valve
Inadvertant opening of low point drain valves or
Emergency Blowdown (EBD) valve/CBD valve.
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HIGH DRUM LEVEL
Mal-operation of feed water control.
Sudden decrease in firing rate e.g. tripping of
the running mills.
B.F.P. Scoop tube position suddenly increased.
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FLAME FAILURE AT AN ELEVATION
Closing of trip valves on H.F.O. Oil/ Ignitor (Causing loss of
ignition support energy) Where HFO is being used as
support fuel or when only oil is being used
Sudden decrease of mill feeder speeds to minimum.
Too low or too high wind box pressure causing unstable
combustion. Water wall tube failure
Malfunction of flame scanners due to supply failure or
scanner air failure,
Slag or soot on scanner lenses etc.
Burner tilt mechanism negative extreme due to air failure
to power cylinders.
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ONE FEEDER TRIPS
Effect :
No coal flow alarm comes.
Mill trips
Support energy is removed within 3 minutes
of feeder starting.
Load gets affected
ONE MILL TRIPS
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ONE MILL TRIPS
Auto stop command is present.
Stop PB operated from FSSS console in manual mode. Primary air trip command is present.
Boiler trip.
Pulveriser discharge valve not open.
Ignition permit required and ignition permit lost.
Lub oil pressure low trip.
EPB pressed.
Seal air header / pulveriser under bowl DP is < 5 WCL.
Elevation power not available for more than 2 sec.
Pulveriser can be started after 2 sec of trip.
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WATER WALL TUBE LEAKAGE
Starved water walls due to very low drumlevel.
Sustained flame impingement on water walltubes.
Blocked tube, scaling of tube, resulting inoverheating of tube metal, pitting, corrosion oftubes.
Soot blower steam impingement (wet steamimpingement or direct impingement of steam).
Circulation affected due to opening of lowpoint drains.
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SGWC or CC PUMP trip
Running SGWC pump trips in case of the followingconditions :
Discharge valve - 1 not fully open
Discharge valve - 2 not fully open
Motor cavity temperature high - 60oCEffect :
Pump DP will come down
Drum level may go high
Action :
Reduce BLI below 60% (MCR 1720 t/hr)
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ECONOMISER /SUPFRHEATER/ REHEATER
TUBE FAILURE
Sustained high metal temperatures due to water wallSlagging or forcing boiler at the time of hot restart.
Erosion on tubes due to high excess air, high ashcontent in coal dislocated tubes, soot blowing.
Blocked tubes causing overheating.Salt deposition due to high water level in drum, poor
quality of water.
Inadequate flow due to open superheater, reheater
drain.