This document discusses various operational aspects and emergencies that can occur in an atmospheric fluidized bed combustion (AFBC) boiler. It outlines important parameters to monitor such as bed height, air pressures, temperatures, and fuel sizes. It then describes several emergency conditions that can happen including low or high drum levels, high furnace pressure, high or low bed/furnace temperatures, tube failures, and flame failures. For each condition, it discusses potential causes, effects on the boiler, and recommended actions to address the problem.

1. 1
OPERATION ASPECTS
&
BOILER EMERGENCIES

2. 2
IMPORTANT PARAMETERS IN AFBC BOILER
1. Bed Height / F.D. Air Pressure
2. Primary Air Pressure
3. Bed Temperature / Furnace Temperature
4. Fuel Size
5. Bed Material Size & Specifications
6. Air & Fuel Ratio

3. 3
1. BED HEIGHT / FD AIR PRESSURE
• Static height for AFBC boiler is to be maintained
250 to 300mm during initial light up of boiler.
• Expand bed height for AFBC boiler is to be
maintained 500 to 600 mmwc.
• FD air discharge pressure is to be maintained 600 to
650mmwc
• Wind box or air box pressure is to be maintained 500
to 600mmwc
High W.B. pressure increases the erosion of bed coils
& low WBP affect fluidization.

4. 4
2. PRIMARY AIR PRESSURE
 P.A. fan air header pressure for AFBC boiler
is to be maintained 1000 to 1150 mmwc.
 Diff. of Primary Air Pressure & F.D. Wind Box
pressure is to be maintained approximately 500
mmwc.
High P.A. Pressure increases the high bed coil
erosion and carryover.
Low P.A. pressure cause the blockage of P.A.
lines and puffing in boiler and also increases
chances of clinkerization.

5. 5
3. BED TEMP. / FURNACE TEMPERATURE
• Depends upon the type of fuel & firing method.
• For (Indian Coal) bed temp. in FBC/AFBC/CFBC is to
be maintained 850o
C to 900o
C.
• For Imported Coal bed temp. in FBC/AFBC/CFBC is
to be maintained bed 875o
C to 925o
C.
• For lignite bed temp. in FBC/AFBC/CFBC is to be
maintained 800o
C to 850o
C.
• For Petcock bed temp. in FBC/AFBC/CFBC is to be
maintained 875o
C to 950o
C.

6. 6
• For Rice husk and other Bio-mass fuel bed
temperature in FBC/AFBC/CFBC is to be
maintained 850o
C to 900o
C.
• For Stoker firing furnace temperature is
maintained around 1100o
C to 1200o
C.
• For Pulverized Fuel firing furnace temperature is
maintained 1100o
C to 1300o
C.
• For oil & gas fuel firing furnace temperature is
1100o
C to 1500o
C.
3. BED TEMP. / FURNACE TEMPERATURE

7. 7
4.FUEL SIZE
For FBC / AFBC / CFBC Boiler
Size : 0 to 8 mm,
less then 1mm not allowed more then 20%
Distribution : 1 to 5mm – 70%
5 to 8mm – 20%
0 to 1mm – 10%
Lower the size of coal higher the un-burnt in fly ash.
Higher the size of coal higher the erosion of bed coils
and blockage of fuel air pipe & clinkerization in Boiler.

8. 8
For Stoker fired Boiler
Size : 5 to 25mm,
less then 5mm not allowed more then 5%
Distribution : 5mm to 15mm – 25 %
15mm to 25mm – 75%
0 to 5mm – 05%
Lower the size of coal higher unburnt in fly
ash & carryover through Boiler.

9. 9
For Pulverized Fired Boiler
Raw Coal Feeder Inlet – 0 to 25mm( higher size will
be effected by pulverizer (Pulverizer Inlet)
performance and more rejection )
Pulverized Coal Size – 70% through 200 mesh
Size Distribution : 150 – 200 - 60%
100 – 150 - 30%
75 - 100 - 10%
Higher the size of pulverized coal below 100 mesh
results unburnt in bottom ash.

10. 10
5. BED MATERIAL SIZE & SPECIFICATIONS
Bed Material Size :-
Size:0.85mm o 2.36mm (not below 0.85mm)
Distribution : 0.85 mm to 1.0mm –10%
1.0 mm to 1.5mm – 50%
1.5 to 2.36 mm – 40%

11. 11
Bed Material Specifications :
Crushed Fire Bricks Castable IS8 grade Bricks or
River Silica Sand
Fusion Temperature : 1300 Deg. C.
Shape : Spherical Angular
Bulk Density : 1050 Kg/m3
Silica (SiO2) : 68 %
Al203 : 28 %
Fe203 : 1.05%
PiO2 : 1.67%
MnO : Trace
CaO : 0.54%
MgO : 0.23%
P2O5 : 0.08%
A2O : 0.22%
K2O : 0.45%

12. 12
6. AIR & FUEL RATIO
Typical excess air to achieve highest efficiency for
different fuels are:
• Power plant boilers normally run about 10 to 20 %
• Fuel Oil Fired boilers may run as low as 5 to 15%.
• Natural gasfired boilers may run as low as 5 to 10%
• Pulverized coalfired boilers may run with 15 to 20%
• Gas turbines run very lean with up to 300%

13. 13
COMPARISON OF FLUIDISED BED BOILER
WITH SPREADER STOKER & PF
CHARACTERISTICS FLUIDESED BED SPREADER
STOKER
PF
Fuel quality (Ash, Calorific value.
Volatile matter, Size
distribution)
Has no effect on
operation
Output affected
by coal quality
Output
affected by
coal quality
Maintenance
No moving
parts; less
maintenance
Moving grate in
high temp. zone;
required frequent
maintenance
Frequent
maintenance
due to
pulverizer
Efficiency (for typical Indian Coal
with 45% ash) About 86% Around 76% 86 – 87 %
Efficiency at low load
Better Poor Less
Soot Blowers Not required Necessary Necessary
NOx Formation Low High High

14. 14
EMERGENCY CONDITIONS

15. 15
Various Emergency Conditions:
Drum level low and low-low
Drum level high and high high
Furnace Draft high and high high
Bed Temperature High
Bed Temperature Low
Water wall / screen tube / evaporator tube
failure
Super heater tube failure
High super heater temperature
Low Super heater temperature
Flame Failure
Furnace Explosion
Boiler pressure high
Coal feeder failure
PAH / SAH tube failure
Boiler feed pump failure
Fan Failure

16. 16
DRUM LEVEL LOW AND LOW-LOW:
(A) CAUSE :
1. Failure of boiler feed pump.
2. Failure of drum level controller.
3. Inadvertent opening of C.B.D.
4. Extraordinary change in load. (Sudden reduction in
load)
5. Water tube failure.

17. 17
DRUM LEVEL LOW AND LOW-LOW:
(B) EFFECT : Boiler may damage badly.
(C) ACTION :
• Run the boiler if drum level is within safe limit (Lo
alarm and lo-lo alarm came). If it goes beyond safe
limit allow boiler to trip.
• Attempt to control with feed valve.
• If feed valve is stuck up open parallel line valve or
bypass valve.
• Take care while increasing feed flow that running
B.F.P. do not trip on feed flow high.
• If low level is due to tripping of feed pump start
stand by pump, if it is on manual.
• If water level is below safe level, allow to trip the
boiler on drum level lo-lo to protect the boiler drum
and tubes.

18. 18
(A) CAUSE:
1. Failure of drum level controller.
2. Extra ordinary increase in load
3. Sudden increase in firing rate.
DRUM LEVEL HIGH AND HIGH HIGH:

19. 19
(B) EFFECT:
 Water may enter turbine and serious damages to turbine may occur.
 Joint valve on main steam pipe work leaks.
 Carry over with sharp fall in super heater temperature
(C) ACTION :
1. Run the boiler if drum level is within safe limit (drum level high and
high high alarm came). If goes beyond limit allow boiler to trip.
• Attempt to control with feed valve.
• If feed valve is stuck up close isolating valve.
• Attempt to control drum level by opening C.B.D.
• Close Economizer inlet valve and allow feed pump to run in
recirculation.
• If above measures fail trip the feed pump.
2. If level is due to sudden rise in load. If high level rises above normal
level allow boiler to trip on drum level high high.
• If main steam temperature drop takes place open steam pipe drains.
• Trip the turbine / prime mover when steam
temperature falls.
DRUM LEVEL HIGH AND HIGH HIGH:

20. 20
(A) CAUSE :
1. Due to faulty operation of fan control.
2. Disturbed combustion
3. Un-controlled fuel entry
FURNACE PRESSURE HIGH & HIGH HIGH:

21. 21
(B) EFFECT:
– Boiler may damage due to high furnace pressure.
– Weak parts of furnace (ductings and enclosures)
may explode due to high furnace pressure.
(C) ACTION :
– If it is due to faulty operation of I.D./P.A./S.A. fan
control, take it on manual and maintain the
furnace in suction.
– If furnace pressure has increased beyond limit
allow boiler to trip on furnace draught high high.
FURNACE PRESSURE HIGH & HIGH HIGH:-

22. 22
(A) CAUSE :
1. High CV and low ash coal used.
2. Low P.A. flow / S.A. flow
3. Sudden change in load
4. Faulty bed temp thermocouple
5. Ash recirculating system trouble
BED TEMPERATURE HIGH IN FBC BOILER

23. 23
(B) EFFECT :
 Chances of clinker formation
 Chances of refractory failure
 Chances of screen tube failure
(C) ACTION :
 Control bed temp by recirculation ash through
recirculation feeder.
 Start sand feeder if bed height permits.
 Increase P.A. flow up and increase S.A. flow.
 Reduce the load by cutting coal feeder.
 Coal feeders trip, if temp rises above limit and allow
boiler to trip, if temp exceeds beyond safe limit to save
bed from clinkerisation.
 Check the bed temp thermocouple.
BED TEMPERATURE HIGH IN FBC BOILER

24. 24
(A) CAUSE :
1. High PA with respect to load / high SA flow
w.r.t. load.
2. Low CV high ash coal used.
3. Coal interruption or coal feeder trips or
overfeeding of coal into furnace.
4. Recirculation ash feeder speed may increase.
5. Faulty bed temp. thermocouple.
6. Water tube / screen tube / evaporator tube
failure.
BED TEMPERATURE LOW IN FBC BOILER

25. 25
(B) EFFECT :
 Boiler steam flow will reduce.
 Super heater temp drops.
 Furnace draft will fluctuate.
(C) ACTION :
 Reduce P.A. Fan flow, if excessive / reduce S.A.
flow, if excessive.
 Reduce speed of recirculation ash feeder.
 Stop bed material supply, if running.
 Check bed temp thermocouple.
 Check any leakage sound from furnace.
 Check coal feeder and coal supply.
BED TEMPERATURE LOW IN FBC BOILER

26. 26
(A) CAUSE :
1. Starved water wall.
2. Block tube, eroded tube, pitted tube, salt
deposits.
3. Circulation affected due to open low point
drains.
WATER WALL/ SCREEN/ EVAPORATOR TUBE
FAILURE:

27. 27
(B) EFFECT :
 Hissing steam leakage noise from boiler.
 Unstable flame fluctuating draught.
 Bed temperature drops sharply.
 High feed water flow for given steam generation /
increase in make up water.
 Increase in I.D. Fan loading.
 Below screen temperature drops sharply.
 Flue gas outlet temperature decreased.
WATER WALL/ SCREEN/ EVAPORATOR TUBE
FAILURE:

28. 28
(C) ACTION :
 Every shift check low point drain valve are fully
closed.
 Every shift check the furnace listen furnace to detect
steam noise.
 At first diagnostics of tube failure, start load
reduction; trip out unit before damage become
serious. Quicker shutdown reduces extensive
damage.
 Try to locate tube at low level.
 Don’t allow the drum level to go beyond a danger
level.
 Start another BFP, if drum level is not maintained by
running BFP.
WATER WALL/ SCREEN/ EVAPORATOR TUBE
FAILURE:

29. 29
(A) CAUSE :
1. Sustaining high metal temp due to water wall
slagging or inadequate steam flow and high gas
temp during hot start.
2. Erosion on tubes due to high excess air.
3. Blocked tubes.
4. Starvation of tubes.
5. Salt deposition due to high water level in drum.
Poor quality of spray water.
SUPER HEATER TUBE FAILURE:

30. 30
(B) EFFECT :
• Hissing noise notices.
• Flue gas temp drops.
• High feed water consumption compared to steam
flow.
• Over loading on I.D. Fan.
• Erosion of other tubes and damages to other SAH
tubes.
(C) ACTION :
1. As soon as leakages noticed start reducing the load
and trip the boiler.
2. Listen the SH region for steam leakage.
3. Try to locate leakage through manholes before the
boiler is depressurized.
SUPER HEATER TUBE FAILURE:

31. 31
(A) CAUSE :
1. High excess air.
2. Low feed water temp HP Heater not in service at
constant firing / load.
3. Sudden increase in firing rate to increase steam
pressure.
4. In adequate spray.
5. Lodging of soot on the water walls considerably.
HIGH SUPER HEATER TEMPERATURE:

32. 32
(B) EFFECT :
Rise in (+ve) positive turbine expansion.
– Creep rate increase in tube metal, turbine parts,
steam piping.
(C) ACTION :
1. Check feed water temp. If HP heaters are available,
put in service and if not reduce the load.
2. Slow down firing rate.
3. Reduce excess air, if more.
4. Check Spray control
HIGH SUPER HEATER TEMPERATURE:

33. 33
(A) CAUSE :
1. Dirty super heater
2. Inadequate air flow.
3. High Spray
4. Too high feed water temp.
5. Sharp increase in load and pressure drop.
6. High Drum level.
LOW SUPER HEATER TEMPERATURE:

34. 34
(B) EFFECT :-
1. Turbine expansion may be negative.
2. May induce thermal stresses in S.H.
(C) ACTION :-
1. Check air flow – increase, if necessary.
2. Reduce spray, if more.
3. Check feed water temp.
4. Avoid sharp rise in load to boiler pressure drop.
5. If, it is due to high drum level – allow unit to trip and
open main steam drains.
LOW SUPER HEATER TEMPERATURE:

35. 35
(A) CAUSE :
1. Dirty Oil / Gas Burner
2. Faulty Flame Scanner
3. Failure of Blower
4. Furnace Pressure High
5. Low Combustion Air
FLAME FAILURE:

36. 36
(B) EFFECT :
 Boiler will trip on flame failure
 Chances of furnace explosion, if unburnt oil / gas /
coal mixture entered in furnace.
 Boiler steam pressure may fall down.
 Super Heater Steam Temp. drop sharply.
 Variation observed in drum level (drum level low).
FLAME FAILURE:

37. 37
(C) ACTION :
 Purge the boiler before putting burner back and
purge burner as per cycle time given by supplier.
 Check the flame scanner and clean the photocell, if
found dirty.
 Check the sparking circuit and high voltage
transformer supply.
 Check spark plug, if found dirty, clean it and set the
gap.
 Clean the burner tip, if nozzles (holes) are found
chocked.
 Check the air blower and maintain air fuel ratio.
 Check the explosion doors, close it if opened.
FLAME FAILURE:

38. 38
(A) CAUSE :
1. Accumulation of unburnt fuel during lit up / start
up of boiler.
2. Improper burning.
3. Inadequate air.
4. Secondary combustion.
(B) EFFECT : Furnace explosion can cause extensive
damage.
(C) ACTION :
1. Always purge the boiler with 40% full load air for
about five minutes. No cut short in purging
allowed.
2. Adjust fuel air ratio.
FURNACE EXPLOSION:

39. 39
(A) CAUSE :
1. Sudden drop in load / steam flow.
2. Un-controlled fuel entry.
3. Turbine / prime mover trips.
BOILER PRESSURE HIGH:

40. 40
(B) EFFECT :-
 Disturbance in drum water level.
 Safety valves may life if pressure rise is up to that
extent.
 Boiler may trip on high pressure.
(C) ACTION :-
 Open start up vent valve.
 Control fuel input and drum level.
 Check coal feeder feeding rate.
 Adjust the load on unit, if it has dropped.
 If TG / prime mover has tripped first, allow boiler
to trip but safety valve may lift.
BOILER PRESSURE HIGH:

41. 41
(A) CAUSE :
1. Electrical supply failed
2. V.F.D. fault
3. Bed temperature high
4. Furnace draft high
5. Furnace draft low
6. Drum level high
7. Drum level low
COAL FEEDER FAILURE:

42. 42
(B) EFFECT :
 Boiler pressure may fall down
 SH steam temp fall sharply
 Bed temp. will decrease
 Variation in furnace pressure (LOW)
 Variation in drum level (Low)
COAL FEEDER FAILURE:

43. 43
(C) ACTION :
 Control boiler pressure by reducing load on
turbine / prime mover or process.
 Control super heater steam temp by closing spray
valve.
 Reduce PA / SA flow to control bed temp.
 Control furnace draft and drum level.
 Check electrical fault or emergency stop push button
& restart coal feeder.
 Check VFD fault, if any.
 Restart coal feeder after checking cause of failure.
COAL FEEDER FAILURE:

44. 44
(A) CAUSE : Erosion & Corrosion of tube.
(B) EFFECT :
 Flue gas temp after APH will fall down.
 Increases in O2 percentage at ESP inlet.
 PA / SA Fan overloaded.
 Bed temp may be increased.
(C) ACTION :
 Control flue gas temp by passes PAH.
 Reduce coal feeding to maintain O2 percentage.
 Control bed temp.
 If leakage of tubes are more stop the boiler
and plug / replaced.
PAH/ SAH TUBE FAILURE:

45. 45
(A) CAUSE :
1. Motor protection relay operates
2. Lube oil temperature high
3. Discharge flow high
4. Motor bearing temperature high
5. Deaerator level low
6. BFP suction pressure low
BOILER FEED PUMP FAILURE:

46. 46
(B) EFFECT :
 If standby pump is available, it will start on auto or
start it manually.
 If standby pump does not start on auto & manual,
drum level may go very low, which may trip the
boiler.
BOILER FEED PUMP FAILURE:

47. 47
(C) ACTION :
 Start the stand by pump, if it does not start on auto.
Adjust the load to maintain the drum level as well as
to prevent the tripping of this pump on high feed
water flow.
 See the proper operation of recirculation valve and
C.W. Valve.
 Analyze and rectify the fault in the main feed pump.
Put it on auto.
 Restore the bus supply, if it has lost and make the
pump available.
 Check the deaerator level and if it falls below safe
limit, stop the feed pump, immediately.
 Check the BFP suction strainer and clean it, if found
chocked.
BOILER FEED PUMP FAILURE:

48. 48
(A) CAUSE :-
1. Electrical motor protection
2. Fan bearing temp becomes high high
3. Motor bearing temp becomes very high
4. Drive fault (MCC fault)
5. Boiler trip
LOSS OF FANS:
(1) ID FAN FAILURE

49. 49
(B) EFFECT :
1. Furnace may get pressurized
2. Boiler will trip on boiler furnace pressure high.
(C) ACTION :
1. Check emergency or field stop.
2. Rectify electrical fault, if any.
3. Check cause for boiler trip & normalize it.
4. Check fan / motor-bearing temp.
5. Restart I.D. Fan after checking cause of tripping
and taking corrective actions.
LOSS OF FANS:
(1) ID FAN FAILURE

50. 50
(A) CAUSE :
1. Electrical motor protection.
2. Fan bearing temp. becomes high high.
3. Motor bearing temp. becomes very high.
4. MCC fault.
5. Boiler trip.
6. Run feed back off.
7. ID Fan trip.
8. SA trip.
(1) PA FAN FAILURE
LOSS OF FANS:

51. 51
(B) EFFECT :
 Boiler will trip on
a. Furnace draft low
b. P.A. flow low.
(C) ACTION :
1. Rectify electrical fault, if any.
2. Check cause for boiler trip and normalize it.
3. Check fan / motor-bearing temp.
4. Restart the P.A. Fan after checking the cause of
tripping and taking corrective actions.
(1) PA FAN FAILURE
LOSS OF FANS:

52. 52
(A) CAUSE :
1. Electrical motor protection.
2. Fan bearing temp becomes high high.
3. Motor bearing temp becomes very high.
4. MCC fault.
5. Boiler trip.
6. Run feed back off.
7. I.D. Fan trip.
(1) SA FAN FAILURE
LOSS OF FANS:

53. 53
(B) EFFECT : Boiler will trip on low furnace draft.
(C) ACTIONS :
 Rectify electrical fault, if any.
 Check cause for boiler, trip & normalize it.
 Check fan / motor-bearing temp.
 Restart the S.A. Fan after checking the cause of
tripping and taking corrective actions.
(1) SA FAN FAILURE
LOSS OF FANS:

54. 54
T H A N K
Y O U