PREM BOILER EMERGENCIES.ppt

8/10/2019 PREM BOILER EMERGENCIES.ppt

1/33

Boiler Emergencies of 500 MW

R Prem Anand

Manager

NTPC LTD


2/33

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


3/33

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


4/33

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


5/33

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


6/33

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


7/33

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


8/33

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


9/33

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


10/33

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


11/33

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


12/33

One PA Fan Tripping

Both PA Fans In Service

Observations



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


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


Note down the relay targets for the tripped PA Fan


13/33

Only One Fan In Service

Observations



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


Note down the relay targets for the tripped PA Fan


14/33

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



Confirm the relay targets for the tripped PA Fans

If Boiler trips follow MFT procedure.


15/33

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


16/33

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.


17/33

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.


18/33

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.


19/33

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.


20/33

PA FANS Logics :1. Hot PA header pr. Low -560 mm WCL

2. Hot PA header pr. Lowlow


21/33


22/33

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)


23/33

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)


24/33

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.


25/33

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.


26/33

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.


27/33

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.


28/33

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.


29/33

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


30/33

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.


31/33

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.


32/33

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)


33/33

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.

PREM BOILER EMERGENCIES.ppt

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