INTRODUCTION
- TO DAYS POWER DEMAND IN THE COUNTRY PUTS A LOT OF STRESS ON THE AVAILABILITY OF STEAM GENERATORS.
- EVEN THOUGH THIS IS AN IMPORTANT CONSIDERATION, THE STRESS ON THE SAFETY OF THE PERSONNEL AND EQUIPMENTS CAN NOT BE IGNORED.
- TODAYS TREND IS TO GO FOR HIGHER CAPACITY BOILERS.
- AS THE CAPACITY OF THE BOILER INCREASES THE COMPLEXITY OF FUEL FIRING SYSTEM INCREASES AND SO ALSO COMPLEXITY OF OPERATIONS.
- EXPLOSIONS RESULT IN EXTENSIVE DAMAGE TO THE EQUIPMENTS AND/OR PERSONNEL AND IN SOME INSTANCES FATALITIES HAVE OCCURRED IN THE HISTORY OF BOILER OPERATIONS.
- MAJORITY OF EXPOLSIONS ARE FOUND TO OCCUR DURING LIGHT UP OR AFTER SHUTDOWN OF BOILER.
- IT IS ALSO FOUND AS STATISTICS THAT A MAJORITY OF CAUSES FOR FURNACE EXPLOSIONS ARE HUMAN ERRORS
- A NUMBER OF EXPLOSIONS HAVE ALSO OCCURRED DUE TO THE INADEQUATE CONTROLS PROVIDED TO THE BOILER WITHOUT WHICH THE OPERATOR IS UNABLE TO TAKE SEVERAL DECISIONS ALL AT A TIME OR QUICK DECISION UNDER CERTAIN PRECAUTIOUS SITUATIONS
- THE BASIC REASON FOR AN EXPLOSION IS AN ACCUMULATION OF COMBUSTIBLES IN THE PRESENCE OF IGNITION SOURCE.
- NOMALLY THE BURNERS SUPPLY THE AIR AND FUEL MIXTURE AND BURNS QUICKLY WHEN IGNITION ENERGY IS AVAILABLE.
- AS LONG AS THERE IS CONTINUOUS IGNITION ENERGY AVAILABLE TO THIS CONTROLLED MIXTURE EITHER FROM ITS OWN FLAME OR THROUGH IGNITION SOURCES AVAILABLE IN ITS PROXIMITY,THE CHANCES OF ACCUMULATION OF FUEL IS RARE.
Reasons for accumulation of unburnt material in Boiler
- Improper sequencing of initial and subsequent ignition.
- Interruption and recurrence of combustion reactant mixture.
- Fuel delivered to the combustion chamber improperly prepared to ignite and burn with the given furnace design.
- Fuel and air delivered to the furnace in non-combustible ratios or improperly combined to promote the desired ignition and firing pattern.
Some of the logging done on boiler explosions are non-stopping of fuel to the furnace under a flame failure protection
- Loss of flame on decreasing load
- Reducing load, coal flame out but reignition by the ignitors
- Loss of flame, reignition by hot slag
- Unsteady load, lost fire but mill not tripped
- Loss of flame on load reduction
- Unstable fire due to wet coal and flame out
- Unstable coal flame after support fuel is removed and flame out
- Wet coal, lost a feeder, coal firing went unstable resulting in flame out and reignition
Causes of Explosion
- The roll of Burner Management system is to prevent furnace explosion mainly from accumulation of fuel under flame out condition.
- Unreliable flame scanners
- Improper sequencing of fuel firing system
- Improper preparation of fuel oil – fuel oil pressure, atomising medium pressure, fuel oil temperature
- In case of coal firing – low primary air pressure, low temperature of primary air
- Incorrect fuel – air ratio
- Repeated Unsuccessful attempts to light off without appropriate purging.
Remedies
- Cleaned and healthy scanners
- Proper sequencing of fuel firing equipment
- Proper fuel oil pressure, temperature, atomising medium pressure
- Proper control of primary air pressure and temperature
- Proper operation of fuel air and auxiliary air dampers – dampers on auto control
- Furnace draft control to avoid explosion/implosion
- Purging of boiler after every tripping