coke oven life prolongation a multidisciplinary approach
TRANSCRIPT
COKE OVEN LIFE PROLONGATION:
A MULTIDISCIPLINARY APPROACH
Mariano de Córdova, Jorge Madias
ABM Week, Riocentro, Rio de Janeiro, Brazil, August 17th 2015
Content
Introduction
Coke Battery Life
Blend Design
Operating Control
Refractory Maintenance
Diagnosis of the Battery State
Conclusions
2
Introduction
Consulting & training for the steel industry
Technical assistance
Open, in-company and self-learning courses
Library services
Met lab services
Technical texts for trade journals
3
Introduction
Content based on
Experience of Mariano de Cordova & battery team
while working at Ternium Siderar coke plant
Material prepared for a short course in San Nicolas,
Argentina, in August 2014 and 2015 (with attendance
of specialists from coke plants in Argentina, Brazil and
Chile)
4
Introduction
Factors for longer battery life
5
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
6
Kasay 2008
Introduction
Factors for longer battery life
Mechanisms for oven damage
7
Blend design
Influence on battery life
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
8
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
9
Battery Heating
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
10
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
11
Battery Heating
Automatic measurement
Auto-Therm system: optical fibre in pusher ram – Hyundai
Steel
12
Battery Heating
Influence on battery life
Evolution of average deviation, batteries 3/4, Ternium
Siderar
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Battery Heating
Influence on battery life
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
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Battery Heating
Visual inspection
Automatic monitoring
system, measuring the
opacity of the off-gas
exiting the stack
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Battery Heating
On line control
Opacity of every oven charged
Permitted opacity:
16
≤ 40 %
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 off-gas to improve vertical distribution, mostly in tall batteries
17
Battery Heating
Combyflame system: 3 stage of air and off- gas recirculation
More uniform vertical temperature
18
Battery Heating
Vertical temperatura
Measurement
19
Portable pyrometer from
battery top
Pyrometers on guide car
(three levels)
Optical fibre sensor in
pusher ram (three levels)
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
20
Operating Control
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
21
Operating Control
Pushing regularity (delays)
SSAB Ruukki Coking Plant,
Finland
Goal:+6 / - 10min
Ternium Siderar Coking Plant,
Argentina
Goal: 0 / - 10 min / oven
22
Operating Control
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 % of working
index each 5 to 7 days
23
Operating Control
Operating uniformity
Automatric control: schedule, delays, gross coking time
24
Operating Control
Evolution of range of gross coking time, Ternium
Siderar
25
Operating Control
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 standpipe
Semiautomatic adjustment including calorific power of gas; Wobbe index or complex control loops, including thermal balance of the battery
26
Operating Control
Automatic control system
Determines the energy for heating the batterie
27
Δ Coking time
Energy imput
Δ Pause time
Δ Energy demand
Operation Control
Deviation of net
coking time
(thermal
uniformity),
ArcelorMittal
Tubarão, Brazil
28
Operating Control
Control of process variables Charge height: Low charge height may imply excessive graphite
deposition and high temperature in the free space Controlled by 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 to 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
29
Refractories
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.
30
Refractories
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
31
Refractory
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
32
Refractories
Inspection of battery roof and tie rod in EES Coke batery
33
Diagnosis
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
34
Diagnosis
Results: Ternium Siderar
35
Diagnosis 36
Conclusion
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
37
Thank you! 38
Mariano de Cordova, Jorge Madias
metallon, San Nicolas, Argentina