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.



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


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

http://www.metallon.com.ar/

coke oven life prolongation a multidisciplinary approach

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