Coke oven life prolongation a multidisciplinary approach

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

 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

 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
Before correction
After correctión
Deviation 109ºC
Standard 50ºC
Deviation 47ºC
Standard 50ºC

Evolution of average deviation in batteries 3 & 4,
Ternium Siderar
Battery Heating
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

Visual inspection
Automatic
monitoring system,
measuring the
opacity of the waste
gas exiting the stack
Battery Heating

 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

 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

 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

 Pushing regularity (delays)
 SSAB Ruukki Coking Plant,
Finland.
 Goal:+6 / - 10min
 Ternium Siderar Coking Plant,
Argentina
 Goal: 0 / - 10 min / oven
Operating Control
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

 Evolution of range of gross coking time, Ternium
Siderar
Operating Control
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

Operating Control
 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

 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

 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

 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

 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
Deviation of temperature: good results
Gas leakage index: good results

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

Coke oven life prolongation a multidisciplinary approach

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