India's largest coal handling agency - Mjunction

Expert Speak
Refractory lining work for lower oven doors in progress in COP
body was replaced with insulating castable Insulite-15. Top
surface was finished with 70 mm LC-45 dense castable. About
78 upper oven doors have been replaced with the new lining
since September 31, 2009. None of these freshly lined doors
have failed so far.
There is a proposal to use ceramic fibre modules for upper
door lining. Orders have already been placed for imported
and indigenous modules, particularly for the upper door
lining, the results of which can be seen only after installation.
Lower Oven Doors
The first instance of damage of lower oven door commenced
almost within two to three months of the first start-up of coke
oven battery nos. 7 and 8. Similar to the upper door lining,
changes were made in the lower door lining also, mainly
the peripherals, which receive maximum external abrasions.
These were lined with dense LC-45 castable on top of Hysil
boards. A pictorial representation of the extent of repairs done
almost over a year after September 31, 2009 is given herewith.
None of these freshly lined doors have failed till date.
Bridge Pipes
It was observed that the ceramic fibre lining of the bridge
pipes was failing repeatedly and fallen refractory material
was blocking the suction ports. It was also observed initially
that the temperature inside the bridge pipes was shooting up
as high as 1450°C leading to fusion and melting down of not
only the refractory material, but also the mild steel body of the
bridge pipes, thereby creating gaping holes.
It was also observed that certain amounts of combustibles
were being carried over to the bridge pipe region. The
operating procedure being followed at that point of time
(before September 31, 2009) had a flaw, although it was as
per the instructions given by the Chinese suppliers. The two
primary air windows provided in the upper oven doors were
completely closed for the initial three hours after charging of
ovens. Since the plant was being operated almost at full load,
one oven was being pushed and charged every 45 minutes. As
a result, unburnt volatiles escaped continuously to the bridge
pipe and branch headers. Another mistake which further
aggravated the problem was that a tertiary hole was made by
some agency at the bottom of the uptake just after the fourlinked
arch, which provided additional combustion air to the
unburnt volatiles.
A third observation was that when bridge pipes were
being changed, flue hole cleaning was overlooked at times and
bridge pipes were also being changed only on one side, that is,
either the coke side or the pusher side, ignoring the condition
of the other side. This resulted in more flow of gas through
one of the bridge pipes leading to higher temperature and
meltdown. The following steps were undertaken to overcome
the problem of bridge pipe failure:
a) Immediate plugging of tertiary holes with strict instructions
to never open them in future.
b) Keeping the primary air windows open right from the
time after charging, closing it fully only when the oven
is ready and regulating it in between as per combustion
requirement.
c) Keeping the levels of the combustibles in flue gas, particularly
carbon monoxide and hydrogen at trace levels.
d) To take up bridge pipe replacement either simultaneously
on both the coke side and the pusher side or at a small gap
of maximum one week.
e) Use of dense castable LC-45 in the top layer in contact with
the hot gas.
f) To do compulsory suction port cleaning with every bridge
pipe replacement.
The above mentioned steps have brought in drastic
improvements in the condition and life of the bridge pipes
and their lining. Over the last one year, more than 100 out of
a total of 192 bridge pipes have been replaced, none of which
have failed as yet. With full load operation at 36 pushing per
day, some damages temporarily resurfaced but were quickly
controlled. The key to the solution to the problem was basically
lowering the temperature of the flue gas to about 1100°C to
1150°C which is as per the design and the liner material can
withstand the same.
The author is working as Vice President in the coke manufacturing
unit of Bhushan Power and Steel Limited, Jharsuguda, Orissa.
Right from its inception in 2007, the plant has been facing problems
of massive failure of refractory lining of bridge pipes, upper oven
doors, lower oven doors and branch headers. Many trial and error
processes were carried out with different material and massive
maintenance work was taken up to combat the failures, but fruitful
results were not coming up. Finally after doing an in-depth study
of various operational and maintenance aspects, a viable solution to
this endemic problem could be found with the combined efforts of all
related disciplines.
The author is grateful to M/s K. Vijayan, S. Mukherjee, Sanjeev
Srivastav, Sanjit Kumar and the entire coke oven team for their
relentless efforts in bringing about the improvements in the operation
and maintenance of the coke oven plant.
COAL INSIGHTS 57 October 2010