Page 67 - Tcexpression2021 - Sept to Dec 2020

However, few accidents are still occurring even today, Corrosion can arise either from waterside (caustic
mainly due to operational errors or poor maintenance. attack, oxygen pitting, stress corrosion, etc.) or fireside
(high-temperature oxidation, coal ash corrosion).
Major boiler accidents normally can be expected
due to sudden rise in furnace pressure beyond its Accumulation of slag in tube surface due to ineffective
design pressure which disturbs the furnace integrity wall blowing operation or firing off-design coal and
and releases very high-temperature flue gases to the falling large chunk of molten ash on water-filled bottom
surrounding area. Formation of fuel-rich pockets in ash hopper also led to accidents in the past. Awareness
the furnace due to improper combustion followed by and following of standard operating procedures can
sudden combustion of the accumulated fuel pressurises rule out such possibility. Spreading/accumulating
the furnace to unacceptable levels. pulverised coal near the boiler area, due to leaks from
coal mills / fuel pipes coupled with poor housekeeping,
However, these issues are addressed in the revised could become a source of uncontrolled fire/explosion.
boiler safety standards by introducing boiler purge with
robust automation controls, thus minimising possible Boiler start-up from the cold condition is a critical task
accidents. and more prone to accidents. Chances of incomplete
combustion, accumulation of unburnt fuel in pockets
Rupture of tubes carrying high-pressure water, with the and steep rise in SH metal temperatures are high.
addition of flashed steam, sometimes increases flue gas
volume beyond the induced draft (ID) fan’s capacity and However, it can be dealt with safely by following
increases the furnace pressure. standard operating procedures.

Even though boiler tubes are well designed and Commissioning of a new boiler till completion of its
fabricated, failures do occur, particularly when reliable operation is a critical period and a challenge
subjected to off-design fuel firing, poor operation for operating personnel mainly due to non-availability
& maintenance , improper feed water quality, and of benchmark parameters, lack of knowledge of boiler
ageing, leading to reduced tube thickness, hot spots, behaviour and on-going tuning of control loops.
or reduced material strength. Overheating tubes would Switching to coal firing during this period should
reduce its material strength, and prolonged corrosion therefore need extra care.
/ erosion would reduce tube thickness and make the
tubes susceptible to failure.

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