Economiser Fire on Bulk Carrier
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Transcript Economiser Fire on Bulk Carrier
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CASE STUDY-I
ECONOMIZER FIRE
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Incident
On 24th June, during morning 4 to 8 watch on a UMS
vessel 5/E was sole engineer on duty
Watch selector was kept on E/R
2nd Engineer was off watch
At 0600 hrs Low steam pressure alarm sounded in
E/Room
5/Er assumed it is due to excessive consumption of
steam & throttled steam to FO DBs
Economizer exhaust gas high temperature alarm sounded
after about 30 minutes
2nd Engineer was informed
It was noted by 2nd Engineer that boiler water
circulating pump was found not working & stand-by
pump was also not working
2/E noticed economizer casing red hot
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Subsequent Action
Bridge was informed
C/E was informed
Engine rpm was reduced to maneuvering speed.
Engine was stopped after C/E arrived.
Aux blowers were cut off
Office was informed
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Actions after discussion with
office
T/C casing was covered
Engine casing & all air inlets were sealed
Fire fighting means were rigged near economizer and
also for boundary cooling
Circulating water inlet & outlet to economizer were
closed
Economizer was allowed to cool down on its own
Funnel boundary cooling was started
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Reason of Fire
Boiler water circulating pump in use stopped due to
bearing seizure
Other pump though kept in stand-by mode did not cut in
No alarm sounded for abnormal stop of running pump
Economizer ran dry for long period
Excessive heat of exhaust gases caused tubes to heat,
resulting in ignition
Economizer fire started
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Damage
Economizer which is 3
pass water tube type
suffered sever damage of
lower most pass. 50% of
the tubes were severely
damaged
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Damage
7 tubes of middle pass were found damaged
Middle pass found sagged by 20 ~ 25 cm
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Damage
Stoppage of approximately 26 hours leading to off hire &
delays
Repair cost
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What went wrong ?
Engine room was manned without senior engineer’s
present. Responsibility of E/R was left on 5/E
Watch keeper did not monitor the stopped pump
Steam low pressure alarm was taken casually by 5/E
He did not inform the senior watch keeper & did not
even check if alarm was reset
Watch keeper did not investigate the cause of low steam
pressure alarm
Second engineer was called on subsequent second steam
low pressure alarm, who noticed that circulating pump
was failed
Stand-by operation of pump failed
Abnormal stop alarm failed
The Economizer high temperature alarm setting was
6000 C which is way above and leads to delay in
detection of fire
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Root Cause
Boiler water circulating pump bearing seized, even
though pump was overhauled 1 month before this
incident
Later investigation revealed that steam leaking from
gland found it’s way into adjacent bearing. Water flinger
on the shaft was not put back after the overhaul. This led
to loss of lubrication and complete seizure of bearing.
Poor monitoring of machinery
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Scope of Repairs
Complete lower pass was cut & removed
7 tubes on second pass were fitted with bypass
Lower header was joined to middle pass using new
boiler tubes employing TIG welding
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Causes
Excessive soot deposit
Poor combustion leading to deposit of particulates &
un-burnt hydrocarbons
Excessive burning of lubricating oil causing
particulates to become sticky
Prolonged low speed running of engine
Soot cleaning routines, soot blowing not followed
Insufficient cooling of economizer tubes, leading to
overheating
Scaling on water side
Corrosion and rust
Soot on fire side
Absence of water in economizer
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What Causes Ignition…
Three factors which are all needed for a soot fire: soot
deposits, oxygen and ignition
The exhaust gas smoke from a diesel engine, due to its
high air excess ratio, contains about 14% oxygen
Ignition of soot may arise in the presence of sufficient
oxygen when the deposits of combustible materials have
a sufficiently high temperature (higher than the flash
point) at which they will liberate sufficient vapour, which
may be ignited by a spark or a flame
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Main Constituent
The main constituent of the soot deposit is particulates
but, in addition, some un-burnt residues of fuel and
lubricating oils may be deposited in the boiler because of
faulty combustion equipment and, in particular, in
connection with starting and low speed running of the
engine
The potential ignition temperature of the soot layer is
normally in the region of 300-400 Deg C, but the
presence of un-burnt oil may lower the ignition
temperature to approx. 150 Deg C, and under extreme
conditions even down to 120 Deg C
This means that ignition may also take place after stop of
the main engine as a result of glowing particles (sparks)
remaining on the boiler tubes
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Other Factors
Exhaust gas velocity inside economizer
In a Class NK survey of over 53 vessels it was found
that all exhaust gas boilers based on a design gas
velocity lower than 10 m/s had soot fire trouble,
whereas relatively few boilers based on a design gas
velocity higher than 20 m/s had such trouble
Inlet Piping to Boiler
Another factor that can reduce the actual gas
velocity in a specific part of the boiler is the design
of the inlet piping to the boiler
Higher Gas Velocities generally help self cleaning of soot
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What Should We Do?
Proper maintenance of injection and combustion
equipments
Regular cleaning of Economizer tubes and daily soot
blowing practice
Need to inculcate traditional watch keeping procedures
where equipments are felt by hand for temp & vibrations,
sound characteristics are noticed, proper rounds are
taken
Regular rounds of machinery space and realistic logging
of parameters
Regular testing of alarms and trips and standby
machinery operation is essential, especially on UMS
vessels
Need for calibration of measuring equipments.
Training and experience of personnel before assigning
higher responsibilities
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Take care of your Boilers well!
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