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Expert Speak
Heat recovery chinese coke ovens:
Problems & solutions
Abhijit Sen
Heat Recovery Chinese Coke Ovens made headway in
Indian Steel plants with M/s Jaiswal Neco going for
the first two Chinese bee-hive batteries with stamp
charging facilities. The contract was with Beijing Sino-Steel
Industry and Trade Group Corporation (SSIT), China and the
technology provider was SPCDI (Shanxi Provincial Chemical
Design Institute). Subsequently, VISA Steel, JSPL, BPSL, and
Hooghly Met coke have all opted for the Heat Recovery Ovens
of Chinese design of SPCDI-SSIT combination in various
capacities.
The BPSL Jharsuguda coke oven plant is one of the best
operating plants among all these Chinese plants with almost
100 percent production load consistently, since inception.
However, certain problems did occur notwithstanding its
excellent performance. Moreover, it was observed that some
of the problems were common to almost all the Chinese plants
supplied by SSIT. One such problem was of the damage of
bridge pipes which connect the battery to the branch headers
carrying gas to the chimney.
Basically all these ovens are large bee-hive ovens which
carbonise coking coal in partial presence of air near the top
layer of the coal cake. Since the charging system belongs to
the stamping category, a large coal cake weighing about 47.00
MT is introduced through the ram side door opening. The VM
released from the coal first burns in the space above the coal
cake and the concave roof of the oven arch acts as a concave
mirror reflecting the radiations from the fire ball in the oven
top space. Since the oven operates under chimney suction, the
flue gas after combustion is drawn through the four linked
arches below the sole, the vertical uptakes, the bridge pipes,
the branch headers and the main headers leading to the
chimney. Theoretically speaking, the temperature of the oven
top arch region should be 1200°C to 1250°C and that at the sole
flue should be about 1300°C to 1350°C.
The fire in the oven is to be controlled in such a way that the
entire combustion of the evolved volatile matter burns out in
the oven and the sole flue. No un-burnt coke oven gas should
escape the sole flue. In the uptake region, the temperature of
the flue gas should be below 1100°C and in the bridge pipe
also the temperature should be below 1100°C.
The Refractory
The typical refractory constitution of the oven arch, the oven
sole, the sole flue and the oven walls are all made of silica
bricks which are well suited to bear temperatures up to
1450°C. The bridge pipes are metal fabrications lined with
ceramic fibre board and ceramic fibre castable, which can
stand temperatures up to 1250°C. These bridge pipes connect
the battery to the branch headers, which are lined with folded
modules of ceramic fibre blanket.
The specified temperature in the branch header is about
1000°C and the refractory installed is also suitable to withstand
this temperature. In the Chinese design, the door linings were
also made of ceramic fibre board and ceramic fibre castable.
The use of ceramic fibre in designing the door, bridge pipe and
headers was mainly recommended to reduce the weight of the
refractory lining in these areas.
A brief history of damages
Replacement of a branch header segment is in progress in COP
1) Upper Oven Doors
The damages to the upper oven door started with a small
defect in the implementation work of the lining during the
project stage itself. It comprised the wrong erection of one row
of L-shaped bricks at the bottom of the upper door. Although
the entire linings of upper and lower doors were executed
under close supervision of Chinese experts, this small item
was overlooked. The problem was detected when all doors
were erected, the plant commissioned and was subsequently
taken on range for full load operation.
Although the first upper door replacement was done in
August 2008, the damage actually had started much earlier,
along with the lower oven doors. Due to faulty erection, the
COAL INSIGHTS 55 October 2010