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Mariano de Cordova, Jorge Madias
metallon, San Nicolas, Argentina
Coke Oven Life Prolongation
A Multidisciplinary Approach
Introduction
Coke Battery Life
Blend Design
Battery Heating
Operating Control
Refractory Maintenance
Diagnostics of the Battery State
Conclusions
Content
Consulting & Training for the Steel Industry
Technical assistance
Open, in company and self-learning courses
Library services
Lab services
Technical texts for trade journals
Introduction
metallon
Content based on
Experience of Mariano de Cordova & battery team
while working at Ternium Siderar coke plant
Material prepared in 2014 for a short course in San
Nicolas, Argentina, with attendance from coke
plants of Brazil, Chile and Argentina (to be repeated
August 6-7, 2015)
Introduction
Background
Introduction
Factors for longer battery life
Useful life
After each charge, oven
walls suffer a strong
temperature drop
This, with other factors,
can decrease resistance to
thermal shock, from 15
years life onwards
Coke Battery Life
Factors in battery life
Kasay 2008
Mechanisms for oven damage
Coke Battery Life
Factors in battery life
Blend design, besides coke quality, has to take
into account
Pressure on walls: cracks, open joints, deformation
Maximum value: 2 psi
Industrial values: 0.5 -1.0 psi
Assessment: Movable wall pilot oven
Increased by: Higher share of low volatile coal, faster coking
rate, larger charge density
Charge shrinkage: cracks, open joints, deformation
Acceptable values: -7 to -15%
Assessment: Sole-heating Oven Test ASTM D 2014
Blend design
Influence on battery life
Ash chemistry: Spalling in some cases
Assessment: Test of ash penetration on silica brick sample
Fe2O3 + CaO + MgO must be low
Stamped charging: Risk of destroying walls
Extreme case of very high charge density >1000 kg/m3
Not a problem in non-recovery ovens
ZKS in Germany, start up in 1984, replacement in 2010 and later
by other stamped charging batteries
Tata Steel Jamshedpur: battery 7 started-up in 1989, failures since 2005; all ovens recovered by 2010
Blend design
Influence on battery life
Average battery temperature
Must be maintained within a range to avoid early
damage
Recommended range: around 1300 ºC to 1100ºC
Covers the field of stability of tridymite 1470ºC to 870ºC
Crosswall temperature Temperature of flues of a wall, when coking process
ends
Its control is an assessment of thermal homogeneity along the walls
One series of walls should be measured daily
Battery Heating
Influence on battery life
Results show actual
temperature curve and
deviation in comparison
with the standard
If larger deviations are
detected, inspections and
corrective actions must
be prioritized
A thermal map can be
built, displaying normal,
cool and hot zones in the
battery
Battery Heating
Influence on battery life
Before correction
After correctión
Deviation 109ºC
Standard 50ºC
Deviation 47ºC
Standard 50ºC
Evolution of average deviation in batteries 3 & 4,
Ternium Siderar
Battery Heating
Influence on battery life
Year
Goal ± 25º C
Leakage of raw gas
Leakage through cracks and open joints in the walls, needs to be controlled periodically
Leakage damages the wall, decreasing wall temperature and increasing black emissions by the chimney
Control: visual inspection of the flues that are not burning, from the battery roof, during the first five minutes after charging
Ten points for a large leakage, four for medium and one for small
Gas leakage index = Total points/(Total of flues x 2)
Gas leakage index <40 % is acceptable
Battery Heating
Influence on battery life
Visual inspection
Automatic
monitoring system,
measuring the
opacity of the waste
gas exiting the stack
Battery Heating
Influence on battery life
Vertical temperature Difference between upper and lower zones of the charge
Lower temperature too high: excessive coking, heavy pushing, reduced coking in the upper part, more fines
Opposite situation: high temperature in the free space, high deposition of graphite in wall and roof, heavy pushing
Reference values: 60ºC for COG, 35ºC for MG
Adjustment: corrections of O2 in the off-gas
Some flue designs have several levels of air burning and in some cases recirculation of waste gas to improve vertical distribution, mostly in tall batteries
Battery Heating
Influence on battery life
Free space temperature
Temperature between the coal line and the oven roof
Increases with battery and vertical temperature, and
lower oven charge
Usually in the order of 800ºC. If higher, excessive
graphite is formed in the walls, thus generating heavy
pushing with risk of wall damage
To have this temperature in range, the right charging
height is relevant, in agreement with the design of the
battery and the control of O2 in off-gas
Battery Heating
Influence on battery life
Responsible for thermal and operating uniformity, and for the control of the operating variables that influence the health of the battery Coking machines
High Reliability and availability
Emergency equipment and installations
Effective preventive maintenance
Delays
Cycling time (between two pushings) must be constant
An objective of admissible delays is recommended, as well as the recording of these delays and their causes, to be able to reduce them along time
Operating Control
Influence on battery life
Pushing regularity (delays)
SSAB Ruukki Coking Plant,
Finland.
Goal:+6 / - 10min
Ternium Siderar Coking Plant,
Argentina
Goal: 0 / - 10 min / oven
Operating Control
Influence on battery life
Year 1 Year 2 Year 3
Year
Operating uniformity
Assessed taking into account the average daily gross
coking time
The delays and advances in pushing, exceeding the
aimed standard range, are detected and corrected
When the production level is to be modified, it is
recommendable to change 15 min/day or 5 % or working
index each 5 to 7 days
Operating Control
Influence on battery life
Evolution of range of gross coking time, Ternium
Siderar
Operating Control
Influence on battery life
Year
Goal : ± 0,5 hs
Thermal uniformity Assessed by the range of average daily net coking time,
detecting and correcting the ovens with larger deviation
Causes for deviation Changes in blend moisture
Changes in charge weight
Wall temperature variations
Operating delays or advances
Gas combustion variations
Manual or automatic corrections to the heating system using data of thermocouples in the stand pipe
Semiautomatic adjustment including calorific power of gas; Wobbe index or complex control loops, including thermal balance of the battery
Operating Control
Influence on battery life
Operating Control
Influence on battery life
Deviation of net
coking time
(thermal uniformity),
ArcelorMittal
Tubarao, Brazil
Control of process variables Charge height: Low charge height means excessive graphite
deposition and high temperature in the free space. The control is through adjustment of charging and leveling operations and periodical measurements.
Vertical contraction: Too large contraction implies excessive graphite and high free space temperature. Oil injection to the blend and decrease in volatile matter are measures of control
Pushing force: must be monitored in all ovens, this allows identify heavy pushing and to detect blending, heating or refractory problems.
Oven internal pressure: It is recommended to eliminate air ingress that will damage refractories, by means of operating adjustment or with individual control system of ovens
Operating Control
Influence on battery life
Ceramic welding For hot repairing of oven walls in the long range: cracks, joints, spalling,
holes, patching, Contributes to minimize emission of black smokes.
Gunning Complementary to ceramic welding, to keep sealed the oven walls and
reduce emission of black smoke by the stack by repairing the open joints.
Dry sealing Sealing of very small cracks in the free space of the oven
Only effective if applied after eliminating major leakages
Sole maintenance Applied to level sole (floor floating), recover worn profile (dry sintering) and
partial reconstruction with new bricks.
Refractory Maintenance
Influence on battery life
Luting To seal cracks in the silica ducts transporting coke oven gas to the flues
Hot repairing of headers To make battery life longer for 10 or 20 years more
Too damaged walls are selected. The first 4 or 6 end flues are rebuilt, including roof and sole, forming repair group of one to four walls
Tasks in regenerators, improvements in the roof and bracing system are included
As a result, there are heating improvements, less raw gas leakages, less
heavy pushing and less emission of black smokes to the stack
Maintenance of heating system Cleaning and changes of the components of the heating system
Maintenance of doors To assess raw gas leakage using EPA or BCRA standards, Results are
useful to avoid air ingress to the ovens
Refractory Maintenance
Influence on battery life
Standpipes and raw gas cooling system Cleaning of standpipes, to avoid accumulation of
graphite, making difficult the gas exit and the operation
Control of flushing liquor nozzles, to avoid ingress to the oven
Bracing system Control, adjust or change springs
Inspect buckstays and change them, if necessary
Thermal imaging is useful for tie rod control, as shown by DTE Energy
Refractory Maintenance
Influence on battery life
The method developed by NSC allows to assess the state of
conservation of the battery periodically, taking into account five
index
Temperature deviation
Leakage of raw gas through the oven walls
Crack propagation in walls
General damage in walls
Dilatation of refractory structure
A yearly measurement is recommended
Diagnostics of the Battery State
Results: Ternium Siderar coke oven batteries, Argentina
Diagnostics of the Battery State
Deviation of temperature: good results
Gas leakage index: good results
Diagnostics of the Battery State
Brick damage index, good results
Dilatation index, bad results
Overall result: Well, continue operating after 42 years
Right blend, heating practice, good operation and
preventive refractory maintenance all along the life
time of the battery, are keys to a prolonged battery
life
Hot repairs of headers and diagnostics of damage
are important to achieve this aim
Conclusion
Thank You
Mariano de Cordova, Jorge Madias
metallon, San Nicolas, Argentina
www.metallon.com.ar