VARIOUS EMERGENCY SITUATIONS DURING OPERATION:-
1. Drum level low and low-low
2. Drum level high and high high
3. Furnace Draft high and high high
4. Bed Temperature High
5. Bed Temperature Low
6. Water wall / screen tube / evaporator tube failure
7. Super heater tube failure
8. High super heater temperature
9. Low Super heater temperature
10. Flame Failure
11. Furnace Explosion
12. Boiler pressure high
13. Coal feeder failure
14. PAH / SAH tube failure
15. Boiler feed pump failure
16. Fan Failure
1. 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.
(B) EFFECT :-
1. Overheating of water wall tubes due to starvation
(C) ACTION :-
1. 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.
1a. Attempt to control with feed valve.
1b. If feed valve is stuck up open parallel line valve or bypass valve.
1c. Take care while increasing feed flow that running
B.F.P. do not trip on feed flow high.
1d. If low level is due to tripping of feed pump start stand by pump, if it is on manual.
2. If water level is below safe level, allow to trip the boiler on drum level lo-lo to protect the boiler drum and tubes.
2. DRUM LEVEL HIGH AND HIGH HIGH :-
(A) CAUSE
1. Failure of drum level controller
2. Extra ordinary increase in load
3. Sudden increase in firing rate
(B) EFFECT:-
1. Carry over with sharp fall in super heater temperature
2. Water may enter turbine and serious damages to turbine may occur.
3. Super Heater deposit and fouling
4. Turbine Deposit and increase in sp. Steam consumption
(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 E.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.
3. FURNACE DRAFT HIGH AND HIGH HIGH
(A) CAUSE :-
1. Due to faulty operation of fan control.
2. Disturbed combustion
3. Un-controlled fuel entry
(B) EFFECT:-
1. Boiler may damage due to high furnace pressure.
2. Weak parts of furnace (ductings and enclosures) may explode due to high furnace pressure.
(C) ACTION :-
1. 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 negative.
2. If furnace pressure has increased beyond limit allow
boiler to trip on furnace draught high high.
4. BED TEMP. HIGH :-
(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
6. Faulty Bed Ash Draining
(B) EFFECT :-
1. Chances of clinker formation
2. Chances of refractory failure
3. Chances of screen tube failure
(C) ACTION :-
1. Control bed temp by recirculation ash through recirculation feeder.
2. Start sand feeder if bed height permits.
3. Increase P.A. flow up and increase S.A. flow.
4. Reduce the load by cutting coal feeder.
5. Coal feeders trip, if temp rises above limit and allow boiler to trip, if temp exceeds beyond safe limit to save bed from clinkerisation.
6. Check the bed temp thermocouple.
5. BED TEMP LOW :-
(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 bed material into furnace.
4. Recirculation ash feeder speed may increase.
5. Faulty bed temp. thermocouple.
6. Water tube / screen tube / evaporator tube failure.
(B) EFFECT :-
1. Boiler steam flow will reduce.
2. Super heater temp drops.
3. Furnace draft will fluctuate.
(C) ACTION :-
1. Reduce P.A. Fan flow, if excessive / reduce S.A. flow, if excessive.
2. Reduce speed of recirculation ash feeder.
3. Stop bed material supply, if running.
4. Check bed temp thermocouple.
5. Check any leakage sound from furnace.
6. Check coal feeder and coal supply.
6. WATER WALL / SCREEN TUBE / EVAPORATOR TUBE FAILURE
(A) CAUSE :-
1. Starved water wall due to low drum level
2. Block tube, eroded tube, pitted tube, salt deposits
3. Circulation affected due to open low point drains
(B) EFFECT :-
1. Hissing steam leakage noise from boiler.
2. Drop on Boiler Water Conductivity
3. Unstable flame fluctuating draught.
4. Bed temperature drops sharply.
5. High feed water flow for given steam generation / increase in make up water.
(C) ACTION :-
1. Every shift check low point drain valve are fully closed.
2. Every shift check the furnace to detect steam noise.
3. At first diagnostics of tube failure, start load reduction; trip out unit before damage become serious. Quicker shutdown reduces extensive damage.
4. Try to locate tube at low level.
5. Don’t allow the drum level to go beyond a danger level.
6. Start another BFP, if drum level is not maintained by running BFP.
7. SUPER HEATER TUBE FAILURE :-
(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.
(B) EFFECT :-
• Hissing noise
• 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 SH tubes1.4
(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.
8. HIGH SUPER HEATER TEMP
(A) CAUSE :-
1. Delayed combustion
2. Burner tilt positive
3. Low feed water temp HP Heater not in service at constant firing / load.
4. Sudden increase in firing rate to increase steam pressure.
5. In adequate spray.
6. Lodging of soot on the water walls considerably.
7. Delayed Combustion
(B) EFFECT :-
Rise in (+ve) positive turbine expansion.
1. Creep rate increase in tube metal, turbine parts, steam piping
2. Increase of heat load on condenser
(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
5. Use tilting or cut down upper level burner
9. LOW SUPER HEATER TEMP. :
(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
7. Faulty Separators
(B) EFFECT :-
1. Turbine expansion may be negative.
2. May induce thermal stresses in S.H.
3. Chance of turbine LP blade damage due to water hammer
(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
6. Check health of separators at the next possible opportunity
10. FLAME FAILURE :-
(A) CAUSE :-
1. Dirty Oil / Gas Burner
2. improper atomization
3. Faulty Flame Scanner
4. Failure of Blower
5. Furnace Pressure High
6. Low Combustion Air
(B) EFFECT :-
1. Boiler will trip on flame failure
2. Chances of furnace explosion, if un-burnt oil / gas / coal mixture entered in furnace.
3. Steam pressure fall.
4. Super Heater Steam Temp. drop sharply.
5. Variation observed in drum level.
(C) ACTION :-
1. Purge the boiler before putting burner back and purge burner as per cycle time given by supplier.
2. Check the flame scanner and clean the photocell, if found dirty.
3. Check the sparking circuit and high voltage transformer supply.
4. Check spark plug, if found dirty, clean it and set the gap.
5. Clean the burner tip, if nozzles (holes) are found chocked.
6. Check the air blower and maintain air fuel ratio.
7. Check the explosion doors, close it if opened.
11. FURNACE EXPLOSION
(A) CAUSE :-
1. Accumulation of un-burnt fuel during lit up / start up of boiler.
2. Improper burning.
3. Inadequate air.
4. Secondary combustion.
5. Over riding Purge permissive during restart after flame failure
(B) EFFECT :-
1. 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. 22
12. BOILER PRESSURE HIGH
(A) CAUSE :-
1. Sudden drop in load / steam flow.
2. Un-controlled fuel entry.
3. Turbine / prime mover trips.
(B) EFFECT :-
1. Disturbance in drum water level.
2. Safety valves may life if pressure rise is up to that extent.
3. Boiler may trip on high pressure.
(C) ACTION :-
1. Open start up vent valve.
2. Control fuel input and drum level.
3. Check coal feeder feeding rate.
4. Adjust the load on unit, if it has dropped.
5. If TG / prime mover has tripped first, allow boiler to trip but safety valve may lift.
13. COAL FEEDER FAILURE :-
(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
(B) EFFECT :-
1. Boiler pressure may fall down
2. SH steam temp fall sharply.
3. Bed temp. will decrease.
4. Variation in furnace pressure (LOW)
5. Variation in drum level (Low)
(C) ACTION :-
1. Control boiler pressure by reducing load on turbine / prime mover or process.
2. Control super heater steam temp by closing spray valve.
3. Reduce PA / SA flow to control bed temp.
4. Control furnace draft and drum level.
5. Check electrical fault or emergency stop push button & restart coal feeder.
6. Check VFD fault, if any.
7. Restart coal feeder after checking cause of failure.
14. PAH / SAH TUBE FAILURE
(A) CAUSE :-
1. Erosion of tube.
2. Corrosion of tube.
(B) EFFECT :-
1. Flue gas temp after APH will fall down.
2. Increases in O2 percentage at ESP inlet.
3. PA / SA Fan overloaded.
4. Bed temp may be increased.
(C) ACTION :-
1. Control flue gas temp by passes PAH.
2. Reduce coal feeding to maintain O2 percentage.
3. Control bed temp.
4. If leakage of tubes are more stop the boiler and plug / replaced.
15. BOILER FEED PUMP FAILURE :-
(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
(B) EFFECT :-
1. If standby pump is available, it will start on auto or start it manually.
2. If standby pump does not start on auto & manual, drum level may go very low, which may trip the boiler.
(C) ACTION :-
1. 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.
2. See the proper operation of recirculation valve and C.W. Valve.
3. Analyze and rectify the fault in the main feed pump. Put it on auto.
4. Restore the bus supply, if it has lost and make the pump available.
5. Check the deaerator level and if it falls below safe limit, stop the feed pump, immediately.
6. Check the BFP suction strainer and clean it, if found chocked.
16. LOSS OF ID FANS
(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
(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.
(2) P.A. FAN FAILURE :-
(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.
(B) EFFECT :-
1. 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.
(3) S.A. FAN FAILURE:-
(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.
(B) EFFECT :-
1. Boiler will trip on low furnace draft.
(C) ACTIONS :-
1. Rectify electrical fault, if any.
2. Check cause for boiler, trip & normalize it.
3. Check fan / motor-bearing temp.
4. Restart the S.A. Fan after checking the cause of tripping and taking corrective actions.
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