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Friday, June 27, 2008

CAUSES AND PROCEDURE TO AVOID BOILER FURNACE EXPLOSION





CAUSES OF FURNACE EXPLOSION ARE ACCUMULATION OF UNBURNT FUEL IN THE FURNACE DUE TO INCOMPLETE COMBUSTION,LOSS OF IGNATION , FUEL VALVE LEAKAGE, MIXTURE OF UNBURNT FUEL WITH AIR IN EXPLOSIVE PROPORTIONS,ENTRANCE OF FUEL IN UNBURNT STATE INTO FURNACE DUE TO LEAKING FUEL VALVES OF IDLE BURNER OR IGNITOR ROWS.FIRE EXTINGUSHED BUT FUEL IS NOT CUT OFF PROPERLY, INCOMPLETE COMBUSTION.


TO AVOID FURNACE EXPLOSIONS BE SURE THAT THERE IS NOT LEAKAGE OF OIL INTO FURNACE,IF FLAME DISAPPEARS,TRIP THE BOILER, PURGE THE FURNACE AFTER TRIP OUT, IF AT THE START OF IGNITORS OR OIL ROWS THE FLAME IS NOT ESTABLISHED IMMEDIATELY THEN PURGE THE FURNACE AND RELIGHT AGAIN.

MINOR AND MAJOR BOILER TUBE LEAKAGE





IF THE BOILER TUBE LEAKAGE IS MINOR AND IF IT IS POSSIBLE TO HOLD DRUM LEVEL AND DEARATOR LEVEL THE BOILER CAN BE TAKEN OUT OF SERVICE IN THE NORMAL MANNER.SYMPTONS OF BOILER TUBE LEAKAGE ARE ABNORMAL NOISE, HISSING, INCREASE IN FEED FLOW, VISIBLE LEAKAGE OUTSIDE THE UNIT, STACK EMMISSION, UNSTABLE FLAME, DROP IN THE FLUE GAS TEMPERATURE AND DROP IN DRUM LEVEL.IN ABOVE CASES REDUCE THE LOAD ON THE SET AND PREPARE TO WITHDRAW THE UNIT AS QUICKLY AS POSSIBLE.


IN CASE OF MAJOUR TUBE BURST,IT CAN CAUSE FURTHER DAMAGE TO OTHER PRESSURE PARTS IN THE VICINITY.IT CAN CAUSE FLAME FAILURE IF THE TUBE LEAKAGE HAPPENS TO BE THE FURNACE ZONE.IN THIS CONDITION IT WILL BE DIFFICULT TO MAINTAIN LEVEL IN THE DRUM.THIS TYPE OF TUBE BURST WILL BE APPARENT BY THE LOUD NOICE OF THE STEAM.IN SUCH CASES TRIP THE BOILER IMMEDIATELY,SHUT OFF FEED WATER TO THE BOILER,SHUT OFF F D FANS.LET THE I D FANS RUN AT THE MINIMUM LOAD TO EVACUATE ESCAPING STEAM TO STACK.TWO OR THREE HOURS AFTER THE PRESSURE IS OFF ,OPEN THE MANIFOLDS AND LET THE BOILER COOL DOWN WITH MINIMUM AIR FLOW.

REHEATER PROTECTION UPON LOSS OF LOAD




STOPAGGE OF STEAM FLOW THROUGH THE REHEATER WHEN THE ENTERING GAS TEMPERATURE IS HIGH CAN RESULT IN OVERHEATING AND DAMAGE TO THE REHEATER TUBING.TO PREVENT THIS CONDITION,MEASURES TO BE TAKEN.TURBINE VALVE CLOSURE-IF LOSS OF LOAD SHOULD CAUSE THE TURBINE VALVES TO CLOSE.ALL FUEL SHOULD BE TRIPPED AUTOMATICALLY.UNDER A MFT RESULTING FROM TURBINE CONTROL VALVE CLOSURE AN IMMEDIATE RESTART IS FEASIBLE IN SOME INSTANCES,AS THE TURBINE IS STILL ROLLING AND WILL BE AVAILABLE TO TAKE STEAM AS SSON AS THE GOVERNER HAS THE TURBINE SPEED UNDER CONTROL.

TURBINE TRIP-IF LOSS OF LOAD OCCURS IN WHICH THE TURBINE IS TRIPPED THE REHEATER SHOULD BE AUTOMATICALLY AND INSTANTANEOUSLY TRIPPED.
REHEATER SAFETY VAVLES WILL PROTECT AGAINST OVERPRESSURE IN THE REHEATER.THE REHEATER CONDENSER DRAINS SHOULD BE OPENED TO VACUATE THE STEAM IN THE REHEATER.

DISTURBANCE IN BOILER DRUM LEVEL



DISTURBANCE IN BOILER DRUM WATER LEVEL-IF THERE IS SUDDEN LOAD THROW OFF THE WATER LEVEL WILL GO DOWN AND PRESSURE WILL RISE.HENCE WHENEVER THERE IS POSSIBILITY OF LOAD DROP,OPERATOR SHOULD BE CAREFUL TO CONTROL WATER LEVEL.DUE TO SUDDEN LOAD PICK UP WATER LEVEL WOULD RISE,IF TOOMUCH COLD WATER IS FED TO THE BOILER WATER WULD RISE.IF THERE IS ANY DOUBT ABOUT WATERLEVEL THEN CHECK THE WATER LEVEL AT DRUM GAUGE GLASS.IF NONE OF YHE GAUGE GLASSES ARE IN SERVICE IT IS PREFERABLE TO WITHDRAW BOILER FROM SERVICE.IF WATER LEVEL VASHES OUT OF SIGHT AND FEED FLOW IS NOT AVAILABLE FOR CONSIDERABLE TIME IT IS PREFERABLE NOT TO FILL IN WATER UNTIL THE BOILER HAS COOLED DOWN NATURALLY.THIS IS TO AVOID QUENCHING OF HOT METAL PARTS.

POSSIBLE CAUSES OF WATER LEVEL DROPPING IS FEED PUMP FAILURE, FEED WATER PRESSURE REGULATING VALVE MALFUNCTION, ECONOMISER LEAKAGE, BOILER OR WATER WALL TUBE FAILURE, EXTRAORDINARY CHANGE IN LOAD.

ABNORMALLY HIGH WATER LEVEL SHOULD BE AVOIDED AS IT MAY LEAD TO CARRY OVER AND EVEN PRIMING.USE EMERGENCY BLOWDOWN VALVE TO REDUCE LEVEL.

CARRY OVER-IF CARRY OVER OCCURS,AS INDICATED BY LOWER THAN NORMAL STEAM TEMPERATURE OR SUDDEN DROP IN STEAM TEMPERATURE THEN LOWER DRUM LEVEL,CHECK BOILER CONCENTRATION,IF IT IS HIGH REDUCE THE SAME BY BLOWING DOWN THROUGH CBD,INVESTIGATE DRUM INTERNALS ON THE EARLIEST OPPORTUNITY.

Electrostatic Precipitators for Pollution control

Electrostatic Precipitators for Pollution control
ESP