CASE STUDY
ENERGY EFFICIENCY
ELECTRIC STEELMAKING
ORES AND MINERALS
ArcelorMittal
How to achieve a sustainable casthouse
Process improvement with electromagnetic stirring
Advances in titania-magnetite ore processing on a blast furnace
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Contents
Regulars Comment News
CASE STUDY
ENERGY EFFICIENCY
ELECTRIC STEELMAKING
ORES AND MINERALS
ArcelorMittal
How to achieve a sustainable casthouse
Process improvement with electromagnetic stirring
Advances in titania-magnetite ore processing on a blast furnace
4 5 www.aluminiumtoday.com/furnaces/ Issue 2
Case Study: ArcelorMittal Steelmaking: Fixing blast furnace #2
8
Lubrication Choosing the right grease for high temperature operations
11
BIFCA Phil McCarthy reports on the recent BIFCA seminar
15
Energy Efficiency Saint-Gobain tests HyGear’s Hy.REC system How to achieve a sustainable casthouse Heat oxy-combustion to contribute to COP21 ambitions
Front cover: TECO www.teco.com
16 18 21
Heat Technology Blast furnace cooling stave design
24
10
Electric Steelmaking Process improvement with electromagnetic stirring Coreless induction in micro mills
28 32
Ores and Minerals Advances in titania-magnetite ore processing on a blast furnace
www.aluminiumtoday.com/furnaces/
38
22
Issue 2 Furnaces International r 3
Comment
Editor: Sally Love Tel: +44 (0) 1737 855132 Email: sallylove@quartzltd.com Designer: Nikki Weller Sales/Advertisement production: Esme Horn Tel: +44 (0) 1737 855136 Email: esmehorn@quartzltd.com Sales Director: Ken Clark
Comment
Email: kenclark@quartzltd.com
Things are a bit ‘up in the air’ in the UK at Managing Director: Steve Diprose Chief Executive Officer: Paul Michael Subscriptions: Elizabeth Barford Email: subscriptions@quartzltd.com
the moment. Listening to arguments for and against the UK remaining part of the European Union, it’s fair to say that business and the economy was perhaps the major reason being touted by both sides as the best argument for their cause. Some manufacturers publicly declared their wish to remain, while others accused
Published by Quartz Business Media Ltd,
the EU of having a stranglehold on British
Quartz House,
businesses.
20 Clarendon Road,
There are countless ways in which the
Redhill, Surrey RH1 1QX, UK.
EU affects manufacturing industries that
Tel: +44 (0)1737 855000.
rely on furnaces, such as the new REACH
Fax: +44 (0)1737 855034.
guidelines, the Circular Economy efforts,
Email: furnaces@quartzltd.com Website: www.aluminiumtoday.com/furnaces/ Furnaces International is published quarterly and
emissions targets, and trade agreements to name but a few. In some manufacturing industries, being part of the EU was seen in a positive light. The UK hollow glass industry, for example, benefitted from EU efforts to enforce strict
distributed worldwide digitally
recycling measures, and similarly, from the
Annual subscription: £90
both measures promote glass against its
emissions targets set (and achieved), as competitors as a sustainable product. This emphasis on emissions targets had huge benefits for the furnace industry. It’s safe to say it caused the biggest
in a less favourable light. The UK steel industry, for example, has of late been sorely affected by the EU’s refusal to apply sufficient anti-dumping measures against Chinese imports. However, it’s worth noting here that the UK government is one of the 14 nations that was blocking EU plans to impose tougher sanctions on China. So, while the US has raised its anti-dumping tariffs against Chinese coldrolled steel to 522%, what is there to say that leaving the EU will actually make a difference to the steel industry in Britain? With the UK voting to leave the EU by a small majority, it will remain to be seen over the coming years what effect this will have on British manufacturing in particular, and what knock-on effects, if any, it will have on Europe as a whole. Will these results impact on manufacturing in Europe or will it be ‘business as usual’? Will the UK’s manufacturing industry be stronger or weaker than it was? For the furnace industry specifically, will leaving the EU push the UK to reinvest in its own manufacturing facilities, or will it hinder progress? We can only wait and see.
push for innovation in recent years, and the challenge of helping manufacturers achieve their emissions targets also led to © Quartz Business Media Ltd, 2016
4 r Furnaces International Issue 2
big business. In other industries, the EU was seen
Sally Love Editor, Furnaces International sallylove@quartzltd.com
www.aluminiumtoday.com/furnaces
News
Can-Eng installs furnace for electric automotive manufacturer Can-Eng Furnaces International
parameters were developed for
has successfully installed
each component, as part of the
and commissioned a T7
component family and once
automated furnace line for
validated were integrated as
the production of thin walled
part of the product recipe.
high pressure die cast (hpdc)
Can-Eng was chosen for
aluminum automotive structural
this new light-weighting
components.
project because its
Can-Eng Furnaces
flexible, cost effective heat
International has completed the
treatment technology allows
installation and commissioning
manufacturers to integrate
ahead of schedule for an
new processing systems into
all-electric automotive
existing manufacturing cells,
manufacturer located in
avoiding prohibitive large-scale
California. The T7 system for
continuous processing systems
the heat treatment of HPDC
capital costs. Can-Eng focuses
aluminum automotive structural
on the development of high
components was designed
volume continuous industrial
for the thermal processing of
furnaces for challenging
components related to family of
fixtures, Can-Eng’s Precision
chambers, distribution nozzles,
applications and is the industry
parts for a the launch of a new
Air Quench (PAQ) system, an
dampers and directional
leader in the development
model.
artificial aging system and
ductwork that uniformly
of automated heat treating
The high volume T7 roller
controls integrated into a Level
delivers conditioned quench
systems for the processing
hearth heat treating system
II SCADA system. Can-Eng’s
media leading to repeatable
of thin-walled, light-weight
includes a solution furnace with
PAQ system integrates a unique
and uniform property and
aluminum automotive structural
customised structural product
combination of recirculating air
dimensional results. Quench
components.
British Steel up and running British Steel is up and running
‘a strong partnership’ between
British Steel’s first day of trading
following the successful
the company’s employees,
as ‘a momentous occasion’.
completion of the sale of Tata
their union representatives,
Steel UK’s Long Products Europe
customers and suppliers.
business to Greybull Capital. Peter Hogg, British Steel’s
“Our industry has faced challenging times over the last
“I am delighted we are
future investments. Greybull’s Marc Meyohas was equally delighted. “We have
relaunching our fantastic
confidence in the transformation
business as British Steel,” said
plan and the ability of
McBean.
management and the workforce
commercial director commented,
few years, but we are confident
“Today marks the first day of
that our new venture, built on
arranged a £400m investment
business for our new company
our core values of pride, passion
and financing package to
and we are delighted to be
and performance, will not only
support the turnaround plan
professionalism’ shown by the
launching under the iconic
reinvigorate this business, but
being implemented by the
workforce and the trade unions.
British Steel brand.”
position it as a world leader,” he
management and employees.
said.
The financing has been provided
4,800 people (4,400 in the UK
entirely by a combination of
and 400 in France) and will
Mr Hogg thanked local and national government and local
Hogg’s sentiments were
Greybull Capital has
to implement the required changes,” he said. Meyohas praised the ‘great
The new British Steel employs
MPs for their support and
echoed by Paul McBean,
shareholders and their banks
produce 2.8Mt of steel every
stressed that the formation of
chairman of the Scunthorpe
and is available to British Steel
year.
British Steel was all thanks to
site’s Multi Union, who described
to fund working capital and
www.aluminiumtoday.com/furnaces/
Issue 2 Furnaces International r 5
News
HarbisonWalker International plots growth US refractory producer
Steve Delo, chairman
The company has also
commercial operations to make
HarbisonWalker International
and CEO, HarbisonWalker
invested in business processes
it easier to provide solutions for
(HWI) has described how it
International, said: “While
and building cross-functional
customers across all industries
is transforming itself and
transformation of this company
teams to drive innovation and
and geographic locations.
repositioning its brand for
is ongoing, the launch of our
continuous improvement.
aggressive growth.
new external branding is a
The company also unveiled a
In early 2015, the company
“We needed to ensure that
rebranded to become
milestone that marks the right
we are putting the right people
HarbisonWalker International
branding campaign to mark the
time to tell the story of our
in the right seats, as we are
after market research among
next era of its evolution.
progress and plans.”
looking ahead to broaden our
employees and customers
refractory related offerings,”
pointed to high awareness and
noted Delo.
equity in the HarbisonWalker
HWI serves virtually every
He said HWI is rebuilding,
major industry that requires
realigning and rebranding
refractory solutions.
itself to grow within its
In 2013, the privately held
“Among almost 2,000 people
name. Formerly known as
core industries, while
across our global network of
ANH Refractories Company, its
company owned by two
pursuing additional business
19 manufacturing plants, 30
family of companies included
asbestos trusts emerged from
opportunities adjacent with its
global sourcing centres and
longtime industry companies,
bankruptcy and its board
core customer base.
two technology facilities, we
A.P. Green Refractories
found incredible levels of
Company, North American
appointed Stephen Delo as CEO.
Rebuilding internally at
It recently announced that
HWI during the past two
dedication, expertise, creativity
Refractories Company, and
Martha Collins, PhD joined the
years has also included a
and commitment.”
Harbison-Walker Refractories
company in May 2016 as chief
focus on creating a culture of
technology officer.
accountability.
During the past two years, the
Company.
company has transformed its
Hotwork International launches in Mexico thanks to Glassman success
Iran smelter MoU According to reports, National
Having been introduced to
Aluminium Company (Nalco)
the Latin American market
and Iranian Mines & Mining
during the Glassman Latin
Industries Development
American Show 2015, Hotwork
Renovation Organisation
International is officially in
(IMIDRO) have signed a
Mexico as ‘Heat Up Latin
memorandum of understanding
America’.
(MoU) to jointly explore the
Strategically situated in
possibility of setting up an
Cuernavaca, 80km outside
aluminium smelter in Iran.
Mexico City, the newly
The signing of the MoU
inaugurated office and
coincides with the visit of prime
warehouse has in-stored heat
minister Narendra Modi to Iran.
up equipment with the latest
The smelter-come-gas based
added safety control features
power plant, is slated to be part
for burners with Programmable
of a joint venture aluminium
Logic Controller (PLC) and
company to be set up by Nalco
safety components for gas and
the team in Mexico have
oil with the latest version of
been thoroughly trained in
Hotwork’s high velocity heat
maintenance, operation and
International is more than
refinery in India. The MoU also
up burner.
safety standards and with the
ready to serve the clients in
envisages tolling arrangement
full back-up of 120 service
Mexico and throughout Latin
with existing smelters in Iran
engineers and more than 250
America.
for producing aluminium from
As a subsidiary of Hotwork International in Europe,
heat up equipment sets. With that, Hotwork
in that country. It will utilise supply of alumina from Nalco’s
alumina supplied by Nalco and
6 r Furnaces International Issue 2
www.aluminiumtoday.com/furnaces/
News
Alba appoints Bechtel as EPCM Contractor for Line 6 Expansion Project Aluminium Bahrain (Alba)
site aluminium smelter.
delivering the Line 6 Expansion
and quality, high expectations
Its production will be
Project, which is a significant
and pride in achievement have
Bechtel (Bechtel) as the
boosted by 540,000 metric
milestone for the Kingdom of
underpinned project success
engineering, procurement, and
tonnes per annum (mtpa)
Bahrain.
since our first engagement with
construction management
bringing Alba’s total production
(EPCM) contractor for its
capacity to 1,500,000 mtpa.
has announced International
landmark Line 6 Expansion Project. Under the terms of the
Line 6 will have 424 pots
years, and we are confident that
Line 5 in 2005.
Bechtel will deliver excellence
EGA DX+ Ultra technology
at all times.”
thus significantly increasing
responsible for designing and
operating efficiencies. Commenting on this occasion,
Alba over 25 years ago, to our most recent, the completion of
that will use the proprietary
contract, Bechtel will be constructing the sixth potline
“Alba and Bechtel have a history that spans over 25
Commenting on this occasion,
“When Alba added Line 5, it was at that time the world’s longest potline. We are proud
Bechtel’s President for Mining
to be working with Alba again
and Metals, Shaun Kenny said:
to add Line 6, to make Alba the
as well as industrial support
Alba’s Chairman of Board of
services.
Directors, Shaikh Daij Bin
privileged to have been
the world and mark another
Salman Bin Daij Al Khalifa said:
selected to work with Alba to
world class achievement for
develop the sixth potline.
Bahrain, Alba and Bechtel.”
Upon completion of the Line 6 Expansion Project, Alba will be the world’s largest single-
“The appointment of Bechtel is a step forward towards
“Bechtel is grateful and
largest single site smelter in
“Our shared values of safety
Lucideon offers refractories training for industry
Tata Steel buyout delayed by EU referendum
Lucideon, the international
understanding of refractories
Tata Steel in India, the parent
materials expert, is offering
from manufacturing to end use,
refractories training courses
and everything in between.”
for industry. The courses
As a UKAS ISO 17025:2005
are designed for refractories
accredited testing laboratory
manufacturers, installers,
(No. 0013), Lucideon provides
of the UK business, has announced that it will keep its Port Talbot steelworks and explore a joint venture with the German industrial group Thyssenkrupp,
Other companies in the running included Indian steelmaker JSW and a Chinese steel producer; ironic in the sense that cheap Chinese imported steel dumped on
suppliers, distributors, contactors
a comprehensive refractories
and users in high temperature
testing service to both national
processes, and will be delivered
(BS, ASTM), international
at alternative and more
decision to pull the plug on its
at Lucideon’s Stoke-on-Trent HQ.
standards (ISO) and in-house,
sustainable portfolio solutions
UK operations.
UKAS-accredited standards.
for the European business”.
The joint venture talks
The testing services at
The company looked at
with Thyssenkrupp are at an
Lucideon’s experts can provide on-site courses to meet specific
It has decided to “look
the UK market was a key factor behind Tata Steel India’s
Lucideon are wide ranging
seven possible bids and
early stage and any deal to
and include physical,
weighed up the impact of the
co-operate would need to be
Technology Partner Manager
chemical, mineralogical and
Brexit vote and the British
made in tandem with a long-
at Lucideon, said: “We have
thermomechancial. Lucideon
Steel pension fund, before
term plan for the British Steel
designed these modules to
also inspect and sample
ending the sale process of its
pension scheme, which has
offer something for everyone
refractory materials on-site
Port Talbot plant.
130,000 members and a deficit
within a refractories-related role,
or before shipment to ensure
whether that is technical and
materials are suitable for use
included offers from Sanjeev
Tata’s other businesses in
manufacturing or marketing.
and to avoid costly delays.
Gupta’s Liberty House and the
Stocksbridge and Rotherham
management buy-out team
as well as two of its three
business requirements. Caroline Mullington,
“Our experts will draw upon
To find out more about
The seven prospective bids
of around £700m.
case studies from their many
Lucideon’s refractory training
from Port Talbot going by the
tube mills in Hartlepool will
years of experience, as well as
modules, visit www.lucideon.
name Excalibur.
now be sold separately.
providing hands on, technical
com/refractories-training.
training to give a well-rounded www.aluminiumtoday.com/furnaces/
Issue 2 Furnaces International r 7
Case study: ArcelorMittal
Steelmaking: Fixing blast furnace #2 In September 2012 a break-out took place at tap hole #3 on blast furnace #2 at ArcelorMittal’s Poland site. As a consequence – and in addition to an unprepared technological stoppage and a very difficult restart – the reliability of the two remaining tap holes was limited. Once the break-out was stabilised towards the end of 2012, the decision was taken to prepare spot repairs to tap holes #1 and 3 and return the blast furnace to a reliable condition. By Gabriel Gilis*
B
last Furnace no. 2 within ArcelorMittal’s Poland operations is a 12-metre hearth
Fig. 2: Missing central tap hole block
furnace equipped with four tap holes. On 23
September 2012 a break-out of tap hole #3 took place, forcing the blast furnace team to develop, in co-operation with experts from the steel company, a viable method of tap hole repair.
Cause of application As a result of the tap hole break-out shown in Fig.1, one of the tap hole staves was completely damaged and the central tap hole block was disintegrated creating an opening directly to the hearth. As a result of this incident, the blast furnace team decided to remove the damaged part of the shell with the old stave, install new cooling elements and This tap hole was temporarily secured and
shell and finally inject carbon mass inside the tap hole to fill the space created by the missing central block as presented in Fig 2.
Fig. 1: Damage of tap hole
idled. The entire operation took six days and as the blast furnace was not prepared for such long stoppage, restart was rather difficult particularly with a partially chilled hearth. Starting up a blast furnace with a limited number of tuyeres above the remaining tap holes in order to get a connection for liquid evacuation demanded the use of a high number of oxy-pipes. This caused a predicted but extensive degradation of tap holes 1 and 3, which had already been idled. As a consequence, the nominal capacity of the furnace with a limited number of tuyeres was reduced from an initial 7.2kt/day to 5kt/day to sustain reliability of damaged elements. Following the successful recovery of furnace operations, the next decision was to perform spot repairs to tap holes 1 and 3 and continue the campaign of the furnace, which had started in 2006.
8 r Furnaces International Issue 2
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Case study: ArcelorMittal r Immobilisation of large blocks in stable mechanical condition r Keeping good gas tightness between dry joints r Possibility of lining spot repairs Based on visual inspection of carbon blocks from September 2012, a decision was taken to manufacture three rows by three blocks each including tap hole as indicated in Fig. 3 and Fig.4. The main issue linked to having no clear picture regarding profile and shape of side walls in the surroundings of the tap hole was to determine wall thickness with high accuracy in order to prepare Fig. 3: Horizontal section of replaced blocks
the correct engineering. As we can observe in Fig. 5, the existing thickness of the old wall linings would determine the maximal length of tap hole
Conceptual preparation of relining
blocks connected with UCAR bricks and good
In December 2012 the project team received the
force propagation. Based on this assumption, a set
following boundary condition of tap hole relining:
of core drilling surveys was undertaken. What is
r Time of relining less than 40 days
significant in the achieved results is that in parallel
r Preparation of relining less than five months. To
to healthy cores (as presented in Fig. 6), some
be ready in mid-May 2013 for blow-down
empty spaces and discontinuity were found. At this
r Avoid wet quenching of hearth due to high alkaline penetration of micro-porous carbon blocks r Restore two damaged tap holes to full reliability
stage in the research the project team linked the Fig. 5: Small bricks connection with old lining
In co-operation with the technical office of ArcelorMittal, the project team approved a method of mixed carbon block installation. This consisted of the installation of dry-joined large blocks, tap hole and adjacent ones according to the original design and connection with the old lining side walls using Graftech UCAR mortar bricks. This application had been successfully used in several ArcelorMittal steelmaking locations. The main advantages of this method are: r Good propagation of forces from new lining to old side walls
Fig. 4: Vertical section of replaced blocks
existence of a brittle layer in the surroundings of the tap holes. Based on the survey together with Pirson, engineering the repair of the tap holes, as presented in Fig. 7, was developed.
Preparation to relining As a result of the aforementioned boundary condition and taking into consideration the high level of health and safety requirements, the following order of works and events was planned: r Blow-down of the furnace r Salamander tapping r Flattening of dead-man on the level of tuyeres with removal of coke excess through jumbo cooler r Covering of dead-man with concrete layer to isolate hot coke in hearth r Safety blast in stack
www.aluminiumtoday.com/furnaces/
Issue 2 Furnaces International r 9
Case study: ArcelorMittal released 360 tons of hot metal and slag. In the next step all tuyeres sets were opened and with the use of Pirson’s bobcat vehicles the surface of the deadman was flattened. After this operation the tuyeres section area was covered with a layer of concrete. Following isolation of the hearth where hot coke had been banked, a movable platform was installed through the main top opening. Over the next 48 hours the r Installation of movable platform through top opening
Fig. 6: Sample of core drilling
r Cleaning of the shaft from slag accumulation
whole stack was cleaned and any massive particles that might have fallen down were removed. In the next step, with the use of heavy equipment, tap
(H&S requirement)
hole #3 was demolished and hot burden removal
r Opening of technological entrance at hearth shell
started, releasing 700m3 of coke along with some
(tap hole #3)
quantities of slag. Dumping the burning coke had
r Demolition of tap hole #3 lining r Hot burden removal r Demolition of tap hole #1 lining from inside of furnace r Closing of shell at tap hole #3 r Installation of lining on both tap holes r Reconstruction of tuyeres belt with castable high alumina material. r Shotcreting of stack, bosh, belly and hearth r Gas tightness test of furnace r Drying of furnace r Restart of furnace Bearing in mind the above, 38 days were allotted for planning, while the preparation phase was scheduled for five and a half months, starting from January 2013.
Course of relining Relining started with blow-down of the furnace on 11 May, without any disturbance. The whole process went smoothly and on 12 May salamander tapping
Fig. 8: Hearth Survey prepared by SGL Fig. 7: Tap hole engineering done by Pirson
been arranged with the use of a special ramp to reduce the cycles of vehicles moving between two points. During hot burden removal no intensive oxidation on the carbon surface was observed. However, during the first days the temperature was around 200 ÂşC. The first inspection of the hearth as a whole and a detailed inspection of the side walls led to the following findings: r Below the lowest expected course of carbon block prepared for dismantling (level VII) layer VI also had significant damage from the hot phase and a reduction in thickness. (See Fig.8). r There were empty spaces and gaps in the carbon blocks close to tap hole. r Steam penetration of the level V top surface of carbon blocks. Visible roughness on carbon surface. r Vertical cracks in carbon blocks. As a result of a visual survey of both repaired tap holes the scope of relining was extended to an additional three blocks in level VI on both spots.
10 r Furnaces International Issue 2
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Case study: ArcelorMittal Currently, blast furnace no. 2 is operating under stable conditions without problems at the tap holes.
Conclusion The relining took 37 days and 18 hours, meeting the target and becoming a great planning and organisational success for the entire project team. Not a single lost time injury occurred, which is significant taking into account 300,000 working hours. Since the outlined method of tap hole relining took place, Blast Furnace #2 has proved to be reliable in operation. There have been no hot spots, and no tap hole has shown any symptoms of failure or reduced reliability. Furthermore, hot burden removal, which was performed for the first Extra sidewalls were dismantled to remove blocks
Fig. 9: Leveling of layer VI
time in ArcelorMittal Poland, has proved that with a
with discontinuities in structure. A decision was
proper level of risk assessment it can be done in a
taken to shorten virgin blocks to avoid intensive
safe way securing the remaining carbon lining and
projection in relation to the existing hearth profile
avoiding water quenching.
and resultant mechanical stresses. Installation started with the cleaning of the top surface of the
Acknowledgments
carbon block (layer V) and partial machining to
The author wishes to express his gratitude to all
improve the flatness of existing carbon blocks. This
those who supported what was a difficult relining
operation is visible in Fig 9.
project. He extends special thanks – for guidance and criticism – to Andrzej Chyzy, Yves de Langhe,
Following installation of first three blocks in relation to layer VI, parallel works involving the
Patrick Negro and the entire blast furnace and
installation of mortar bricks were started. UCAR
engineering department at ArcelorMittal and wishes
bricks were glued with graphite mortar directly
to express his gratitude to the companies involved
to the staves to get good heat transfer to cooling
in the relining, including Pirson Group, SGL Group,
system. Cold phase layers have been built using
Graftech and HPR Centrex.
NMD type bricks (~70W/m°K) and hot phase with
Contact
NMA bricks (~18W/m°K), which have a higher wear resistance. In terms of quality parameters, it was
Blast furnace relining manager, ArcelorMittal
important to secure proper thickness of mortar joints, but not greater than 2mm. Second, tight insertion of each brick with
Fig. 10: Casted protection of tuyeres belt
Poland. http://corporate.arcelormittal.com
connection to the old lining was performed using hydraulic pumps. This installation method was continued until the last level of large carbon blocks (level 9). Starting from the newly created flat surface the entire lining up to the tuyeres level was built with only UCAR material. On reaching the tuyeres level, however, the project team decided to cast parts of the protective ceramics with a high alumina material as presented in Fig.10 above both tap holes. This solution satisfied the requirements of shorttime application and created good, solid protection by the time fresh slag made skull. Finally, all new tap hole blocks were equipped with thermocouples to establish continuous monitoring of the thermal state. Directly after relining, some spot grouting was necessary to stabilise blast furnace gas leakages.
www.aluminiumtoday.com/furnaces/
Issue 2 Furnaces International r 11
Lubrication
Choosing the right grease for high temperature operations Jarmo Vihersalo* discusses how to ensure the lubrication selected for use in a furnace protects the equipment in the long term.
T
he steel industry is well known for
in position, or re-lubrication is infrequent,
its high-temperature operating
difficult, or simply not economical. A few
Boosting productivity with synthetics
environment. As a result, operators
examples include drive shaft couplings,
One company to benefit from the use of
universal joints and fan shaft bearings.
advanced greases in a high temperature
require lubricants including greases that are
environment is an aluminium plant in
specifically designed to ensure consistent performance and longevity in such conditions. Choosing the right grease can play an
High temperature operations In extreme temperature applications, there
Germany. To protect wheel bearings, the plant had
essential role in helping to protect equipment
is a risk that a grease will perform poorly
been using a grease with a base oil viscosity
and ensure a trouble-free operation. However,
due to degradation resulting from thickener
of 100cSt and had been experiencing
in selecting a grease which will help to
and base oil oxidation, or due to the loss of
routine bearing failures and significant
maximise equipment protection and increase
base oil from grease bleed and evaporation.
mechanical wear and tear due to lubricant
productivity, it is vital to not only consider
One of the driving factors that can limit the
degradation as a result of excessive heat. In
the quality and performance of a product, but
ability of a grease to provide lubrication at
addition, the plant was also incurring high
also the requirements and challenges of the
higher temperatures is proper viscosity and
lubricant costs.
specific application.
oxidative resistance. Oxidation is a chemical
A team of ExxonMobil technical experts
Operations that function at extreme
reaction that occurs between oxygen and the
were asked by the plant’s maintenance team
temperatures and under intense pressure
in-service lubricant, and is accelerated in high
to help provide a comprehensive analysis
pose a number of lubrication challenges
temperatures.
of the plant’s operations and equipment
which can only be met by technology
A grease’s oxidation rate generally doubles
maintenance practices to help address the
that is specifically designed to meet such
with every 15°C rise in temperature above
issues. Following the audit, the ExxonMobil
requirements. Factors such as base oil type,
60°C. This rule-of-thumb varies, based on
team made specific recommendations to
viscosity, thickener type, stability of the
the type of thickener used in the grease, and
convert the lubricant protecting the wheel
composition and operating temperature must
for soap thickeners, the amount of metal
bearings to Mobil SHC Polyrex 462, in
all be considered in order to ensure that the
contained in the structure (lithium, calcium,
addition to implementing a best practice
most appropriate grease is selected.
aluminum, etc).
programme to help increase re-greasing
Typically, greases with synthetic base oils
intervals.
Grease formulation
can provide a wider operating temperature
It is important for maintenance professionals
range than conventional, mineral-based
by Mobil SHC Polyrex 462 provided
to understand how greases are formulated
greases. For example, the Mobil SHC Polyrex
the machinery with improved levels
in order to ensure that they select a grease
Series is a range of high performance,
of protection, resulting in a noticeable
which will deliver the performance required
synthetic bearing greases that uses advanced
reduction in component damage. The
to protect their equipment in the long term.
polyuera thickener technology in order
introduction of Mobil SHC Polyrex led to an
to achieve excellent high temperature
overall improvement in performance and
performance up to 170°C.
resulted in an annual saving of €39,000 for
A simple way to think of grease is to consider it like a sponge soaked with lubricating oil. Upon application of external stresses,
Even at these extreme temperatures, the polyurea thickener technology resists
The higher base oil viscosity offered
this customer. With ongoing developments in machinery
such as heavy loads or high temperatures,
oxidation and loss of structural stability
to increase output, and the high ambient
the thickener (sponge) releases the oil to
allowing re-lubrication intervals to be
temperatures of many industrial sectors,
lubricate the mechanical parts. When the
extended while maintaining equipment
lubricants that can operate effectively in
stress is removed, the thickener re-absorbs a
protection. This carefully balanced
extreme conditions will enable companies
portion of the released oil for later use.
combination of thickener, base oils, and
to build a competitive advantage into their
additives yields a grease with excellent load
operations by reducing downtime and
carrying capabilities and rust protection.
increasing productivity.
Typically, greases are applied to mechanisms in which a lubricant cannot stay
12 r Furnaces International Issue 2
www.aluminiumtoday.com/furnaces/
Contact *Industrial Marketing Advisor, EAME, ExxonMobil www.mobilindustrial.com
BIFCA
British Industrial Furnace Constructors Association Phil McCarthy reports on the recent BIFCA seminar
B
IFCA held its annual Safety and Standards Seminar on the 21st April at the National Metalforming Centre, West Bromwich.
The event was opened by Arthur Watson who
welcomed delegates in what was to be a highly informative day, explaining and unravelling the application of a variety of standards and legislations applicable to the furnace industry. The first presentation, given by Morgan Advanced Materials, was entitled ‘What’s New in RCF Technology’, and outlined what has happened with refractory ceramic fibres over the last three years. Later on, an update from CECOF on EU activities
Dr Franz Beneke of CECOF talking at the BIFCA Safety & Standards Seminar.
related to furnaces, kilns, and ovens offered an update on the strategy that will “transfer” the ISO-
Combustion Plant - Directive) and the EN 16726
Standards into the European CEN/TC186, which
(Gas infrastructure - Quality of gas - Group H).
incorporates EN 746. The last presentation before lunch was ‘CE
Finally, the controversial plans to fluctuate the quality of gas throughout Europe and the impact
Marking’, which discussed when it is required,
this could have on the UK and what this could mean
when must it not be undertaken (e.g. product
for the UK Gas supply was discussed.
out of scope, or ‘partly completed machinery’),
The date for next year’s BIFCA Seminar has been
and what does it involve? What is a
scheduled for Thursday 23rd March 2017, and the
‘Declaration of Incorporation’ and
association welcomes both members and non-
what responsibilities arise as a
members to the event.
result of incorporating ‘partly completed machinery’. After lunch, a
If you have any suggestions for topics of interest you would like to see covered please email them to enquiry@bifca.org.uk
presentation was given on the significance of CE
We look forward to seeing you again next year.
marking on components incorporated into machinery assemblies, when the machinery assemblies are first placed on
Contact
the market or when incorporated into machine
BIFCA
assemblies already in use.
National Metalforming Centre
The above presentation was followed by ‘Updates on Therm Process Equipment’, which focused on ErP (Energy using Products - Directive), IED (Industrial Emission Directive), MCP (Medium
www.aluminiumtoday.com/furnaces/
47 Birmingham Road West Bromwich, UK B70 6PY enquiry @bifca.org.uk www.bifca.org.uk
Issue 2 Furnaces International r 15
Venue: Tankersley Manor, Church Lane, Tankersley, Barnsley, South Yorkshire S75 3DQ. Tel: 01226 744 700
ArcelorMittal Dofasco - Tom Vert, Vice President Manufacturing - What do steelmakers really want... How refractory suppliers can add value TATA Scunthorpe/LISI - Dave Colllins/Stuart Woodliffe - Queen Anne Blast Furnace Reline UK Steel - EEF/ISSB - Richard White - UK steel industry and its future Pahage - Ashley Webster, Director - topic TBC Almatis - Sebastian Klaus, Application & Market Development Engineer - Fused and sintered aggregates Elkelm - Dr. Hong Peng, Reasearch Scientist - Cement free castables Dupre Minerals - Speaker TBC - Perlite & vermiculite, sources, quality and insulation applications Kerneos - Fabien Simonin
Energy efficiency
Saint-Gobain Glass is currently testing HyGear’s Hy.REC system in its float glass facility in Herzogenrath, near Aachen, Germany.
Saint-Gobain tests HyGear’s Hy.REC system
T
he Hy.REC system is designed to recover the
Fig. 1 : Saint-Gobain flat glass production facility (above)
used hydrogen-nitrogen gas mixture so it can be reused in the glass production process.
Saint-Gobain is continuously seeking for
technologies to optimise the glass production
HyGear. Saint-Gobain is testing the system on performance and reliability (Fig.1). “It is great to work with such a leading company
process and improve glass quality. One of these
as Saint-Gobain”, stated Mr Niels Lanser, sales
technologies is the Hy.REC system, developed by
director at HyGear. “Saint-Gobain has provided us with valuable input during the design phase of the Hy.REC. Its feedback on the system performance is also of great relevance for the further improvement of the system.”
Advantages of gas recycling The Hy.REC system was developed to recover the gas mixtures from the tin bath in float glass production and the metal industry (Fig.2). Currently, substantial amounts of the hydrogen-nitrogen gas mixture, in combination with pollutants, are left at the exit of industrial processes and are unutilised. The Hy.REC system can recover this used and polluted mixed gas atmosphere from the process in a cost-effective way. By feeding the polluted Fig. 2 : Molten float glass
18 r Furnaces International Issue 2
gas mixture into HyGear’s Gas Recovery System, a large fraction of the hydrogen and nitrogen
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Energy efficiency can be recovered and reused as a new reductive gas mixture. This reduces costs and improves the product quality due to the increased atmosphere refreshment rate.
Other gas recovery systems
Contact Hygear, Arnhem, The Netherlands www.hygear.nl
oxygen are removed from the main stream. The third gas recovery stage is the post-treatment module. A key part of the post-treatment is the TSA to dry the hydrogen-nitrogen stream. The customer’s waste heat can optionally be used for the regeneration phase to increase the energy efficiency even further.
HyGear is not the first company to offer a gas recovery system. The reason for the limited market penetration of previously launched systems is the low internal rate of return, caused by the high capital investment and high-energy consumption. Since the economical viability of industrial gas recycling systems depends on the value of the recovered gas in relation to the energy consumption of the system, the Hy.REC mix is designed to consume the lowest possible electricity, which results in a higher economical rate of return. A key part of the integrated post-treatment module is the advanced Temperature Swing Adsorption (TSA) with an ultralow pressure drop to further reduce operational expenses.
Working principle In the first section of the Hy.REC, dust and contaminants are removed from the gaseous mixture (Fig.3). In the second stage, sulphur and
Fig. 3 : Process and working principle of the advanced Hy.REC technology
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19/04/2016 13:25
Issue 2 Furnaces International r 19
Energy efficiency
How to achieve a sustainable casthouse This article looks at automated solutions for casthouse technology in recyclers and producers of semi-finished light-metal products. By Maarten Meijer*
A
s a supplier of material handling solutions for primary production, casthouses and semi-finished
producers, Hencon is regularly invited to have a closer look at improving furnace tending operations such as skimming, cleaning and charging. Such invitations do not only provide the opportunity to start detailed discussions with customers, but they often lead to better and more sustainable solutions than anticipated beforehand. Two of the most recent of those discussions has led to new product lines with a sustainable footprint. But first let us define sustainability. Sustainable business, or green business, has
Figure 2: Manual skimming on smaller furnaces (unknown location)
minimal negative impact on the global or local environment, community, society or
adapts these guidelines with a focus on
facilities, which strive towards reusable
economy - a business that strives to meet
opportunities for customers as well as its
energy and smart use of waste. For instance,
the triple bottom line.
own business ethics. The direct effect of
the factory in the Netherlands is using
this policy can be seen in the company’s
geothermal energy to heat the building
When it comes to Hencon, the company
in winter and cool it down in summer. In Russia, it uses its own waste to heat up the building and subsidiaries all over the world socially support their local community. However, the main goal remains to bring a sustainable product line towards our light metal customers.
Sustainable skimmers Most of the time, machines are operated by Case A) Homogeneous oxide skin grows on the surface of the metal bath. Case B) Due to a change in crystal structure and the different heat expansion of liquid metal and oxide the oxide skin breaks up. Oxide particles charged within the scrap floats to the surface. Case C) The breaking of the oxide skin is additionally supported by bath movement. Case D) During skimming, metal is trapped in the oxides being removed. Fig. 1: Oxide skin formation on a liquid metal bath (“Handbook of Aluminium Recycling�, Christopher Smitz (2006 Springer Verlag) 20 r Furnaces International Issue 2
humans and we are all aware of the ever increasing HSE standards. So it was only natural to start the development of a more sustainable product by following the HSE standards. At some point this was not good enough anymore and we took the lead
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Energy efficiency with a new approach: Do things once and do them right! Or as described in the lean method, avoid waste. In order to understand this better let’s focus on the nature of a molten aluminium bath as described in the ‘Handbook of Aluminium Recycling’, Christopher Smitz (2006 Springer Verlag). On page 79 a comprehensive picture describes the stages of the oxide layer during the melting and alloying process. Just before the melt is ready, this layer needs to be skimmed off, which results in a mixture of oxides and aluminium to be taken out of the furnace (Fig. 1). Despite the progress being made on larger furnaces and the use of forklifts and specially designed equipment to improve
Figure 4: Hencon Furnace Charger (2002)
skimming conditions, the majority of furnaces in use are too small to actually be
for automation or potential improvements
is now doing his job in a comfortable and
able to mechanise the skimming. As a result
of the situation. For a long time it was
safe cabin. On top of that modern feedback
even today it is not unusual on the smaller
considered ‘mission impossible’ to improve
systems allow for much faster and direct
furnaces to see an operator doing the job as
the working conditions, to reduce the
skimming of a bath, thus resulting in a more
shown in Fig. 2.
time the door needed to be opened and
constant quality (Fig. 3)
This kind of operation requires physical
to improve the skimming process by
endurance and is dangerous (30% of skin
controlling the depth of the skimming
Sustainable scrap loading
burns come from this kind of skimming).
blade.
More or less in that same period the
It also results in more aluminium to be
Hencon took on the challenge to develop
company received a request to have a closer
collected in the waste, loss of heat (due to
not only a safer and more sophisticated
look at charging high volumes of scrap
the long time it requires the operator to
manipulator but also a drive line with
into a newly designed furnace capable of
finish his job) and in the end a relatively
zero emission. This resulted in the first
recycling post-consumer scrap into pure
high range on the quality of the alloy.
mechanised skimmer capable to mechanise
aluminium.
However, until now the design of the door
manual labour at compact melting and
and the shallow well made it difficult to
alloying furnaces. Main improvement of
use a rail bound scrap loader per furnace
reach the melt and did not give much room
course is the safety of the operator who
and have dump trucks driving to the scrap
The original idea of this recycler was to
loader in order to charge the charging bucket as fast as possible up to the desired charging capacity and then charge the furnace with the scrap into the chamber. This request could have easily resulted in a charging machine such as the one that we designed and delivered in 2002 (Fig. 4), which would not have been not the best sustainable solution we could deliver. The advantage of this old design was the fact that it seals off the furnace while the furnace door is open for charging. This results in less heat loss and a better climate inside the casthouse. However, the requirement for frequent travel at high speed and the relatively short time the Figure 3: Hencon compact skimmer with zero emission drive line replacing manual skimming jobs (2014)
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dump trucks have to recharge again form a considerable disadvantage. Furthermore,
Issue 2 Furnaces International r 21
Energy efficiency Once loaded the box will travel 250 metres to the selected furnace. On approaching the furnace the shelter is locked on the furnace and the furnace door is opened. After confirmation of that procedure the scrap loading box will be charged inside the furnace and retracted again. In the meantime the driver of the dump truck can prepare the next box while the scrap loader is executing its task. Once returned to the loading station, the whole cycle starts again. From a sustainable point of view, it meant less fume during charging and a reduction in the use of materials and diesel by a reduction of rolling equipment with 77%. The whole system was developed in less than a year and has in the meantime already delivered 6,000 production hours. In the near future Hencon will continue
Figure 5: Loading station (2015)
to use automated solutions in order this equipment gets relatively expensive
system consists of a loading station (Fig.
to improve process stability and the
(and ridged in the layout of the casthouse)
5) and an automatic guided scrap loader
environmental footprint of our customers.
if it has to work for multiple furnaces. Not to
(Fig. 6).
In the long-term this will lead to more
mention the additional housekeeping and
The loading station is designed to be a
zero-emission-solutions to enter the market
loss of scrap due to the transport of scrap
natural barrier between the dump truck
in order to serve clients in the light metal
from the scrap yard to the hot site of the
and the automated area, meaning that
industry with sustainable solutions that
furnace.
as long as the dump truck is loading the
improve process conditions.
It was for this reason that we took an
scrap box, the box is down on the ground
approach towards a new solution by using
allowing for fast and precise loading. Once
full automation from scrap yard to furnace.
the box is full, the loading station will bring
To give you an idea, the original solution by
it to the desired height for the automated
Maarten Meijer
using a charger as shown in Fig. 4 would
scrap loader. The scrap loader then weighs
Business Development, Hencon BV
require a total of six machines to carry
the box and confirms its final destination
www.hencon.nl
out the task. A scrap box needed to be
while loading the box inside its shelter.
Contact
transported for approximately 250 metres to one of the three scrap loaders waiting in front of the furnaces. You can imagine the transport challenges and difficulties faced in the tight space. A compact transport design was required. In close cooperation with the customer, Hencon decided to develop one compact and fully automated transporter that was able to: 1. Pick up a scrap box 2. Transport the scrap box 3. Dock it to the furnace and 4. Execute the desired furnace loading function. Instead of six machines just two machines would be adequate enough to reach the desired capacity to put in just under 20 minutes per pay load. The total
22 r Furnaces International Issue 2
Figure 6: Automatic scrap loader (2015)
www.aluminiumtoday.com/furnaces/
Energy efficiency
Heat oxy-combustion
to contribute to COP21 ambitions
L
ast December, the United Nations Conference of the Parties, better known as COP21, reached an agreement [1] to
combat climate change. Together, the EU along with 185 nations pledged to limit the global average temperature to a rise ‘well below’ 2°C (3.6°F) compared to pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C.
Air Liquide’s energy-efficient technology was awarded at the last COP21 conference on climate change in Paris. Luc Jarry* and Taekyu Kang report how heat oxy-combustion technology can be used to meet the growing environmental needs of the glass industry
Such an ambitious goal will require not only
Oxy-combustion is widely used within glass and
the immediate halt
metallurgical industries to improve the combustion
of greenhouse-
process, reduce air-pollutant emissions and save
gas emission
fuel. The main principle of heat oxy-combustion is
increases,
that heat extracted from the combustion fumes is
but also a
used to heat oxygen and fuel, thereby improving
serious effort
oxy-combustion performance by 10%. Compared
to decrease
to air combustion, this technology provides up to
emissions
50% energy savings and up to 50% CO2 emission
throughout
reduction (Excluding emissions generated for
the rest of the
oxygen production).
century. This
Powerful features
global agreement will put immediate pressure on industrial processes, which account for one-third of global energy use and 40% of CO2 emissions worldwide.
Fig. 1: By simply heating pure oxygen and fuel with fumes, combustion performance is increased by as much as 50%.
Unlike current oxy-fuel technologies, which don’t take advantage of wasted energy recovery from combustion fumes, heat oxy-combustion recovers a substantial portion of the heat lost through flue gases by indirectly preheating fuel and oxygen (Fig. 1).
Meaningful change Decarbonisation for fossil fuel-based industries has proven to be difficult. Although industrial intensity (energy consumption per unit of value added) has fallen in developed countries since the 1990s, there still aren’t enough alternative energy sources or innovation-based solutions available. Therefore, the development of new technologies is crucial. On the occasion of the COP21, the FranceChina Committee awarded Heat Oxy-Combustion technology its 2015 Innovation Award focused on ‘Climate Solutions’. Heat Oxy-Combustion, based on oxycombustion, is a technology that aims to reduce the environmental impact of the glass-melting process. It is recognised as one of the best available technologies for reducing CO2 through fuel savings, while also reducing NOx and dust emissions.
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Issue 2 Furnaces International r 23
Energy efficiency
To develop this patented technology, safe and reliable equipment is designed and fully integrated with glass-melting furnaces. This equipment is made of specific materials suited for hot reactants. For more than 10 years, various materials had
(Above-right) As a new technology, heat oxycombustion is improving in both efficiency gains and competitive equipment cost
Compatible with many types of fuel, all types of glass and a variety of furnaces, the technology can also operate with air, cold oxygen or cold fuel in backup mode. Such flexibility helps to reduce energy-sourcing dependency and associated risks.
to be tested for cyclic oxidation, ignition and flame propagation with hot oxygen, as there was
Proven
no industrial standard for hot oxygen-compatible
As a new technology, heat oxy-combustion is
materials (>200°C) [2].
improving in both efficiency gains and competitive
Safety studies and analyses of oxygen hazards
equipment cost. In the near future, manufacturers
have been extensively performed with top-notch
can expect higher preheating temperatures,
institutes and experts from Germany and the
enhanced design and materials, and greater cost-
United States to build know-how in hot-oxygen
efficiency.
handling. Three glass manufacturers – Paşabahçe
Heat oxy-combustion technology can also be
Bulgaria EAD, AGC France and AGC Czech Republic
implemented with additional energy-recovery
– have validated the concept of preheating oxygen
systems, such as a compact organic Rankine cycle,
to 550°C and natural gas to 450°C for oxy-fuel
which will be implemented on the discharged
combustion [3].
hot-air line after the oxygen/natural gas heaters to
Heat oxy-combustion consists of the following
produce electricity. The remaining hot air can also
technological components:
be used for other purposes such as drying fibres
r Oxygen supply: Liquid Oxygen storage (LOx),
or heating buildings of the plant and warehouse.
or low pressure gaseous state through Floxal
Heat oxy-combustion equipment is then sized to
Oxygen, an on-site oxygen-production solution
maximise heat extraction from the fumes to supply
that provides the required quantity of oxygen
hot air accordingly.
supply. r Glass melting technologies: A unique and
Heat recovery
patented combination of heat exchangers: one
Many new greenhouse gas-reduction technologies
recovers heat from hot fumes to air; others
were developed to recover the energy contained
transfer heat from air to fuel and oxygen.
in the flue gas of industrial furnaces, such as
r Burners: non-water-cooled oxy-fuel burners
steam boilers, electric generators, steam/ Organic
made of specific materials to accommodate high-
Rankine Cycle and synthesis gas CO-H2 production
temperature fuel and oxygen.
by thermal or catalytic decomposition or load
r Valve trains: are automated control systems
preheating. For glass furnaces, most heat-recovery
to monitor oxy-fuel burners and their fuel and
solutions have the major drawback of a lengthy
oxygen supply systems.
pay-back time, sometimes equaling the full life
24 r Furnaces International Issue 2
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Energy efficiency
example, a power-generation unit with an ORC
Helping the industry be efficiently compliant
cycle, installed to a glass furnace, reaches a
In conclusion, as an effective and proven
maximum efficiency (20%) at a full-furnace pull
technology, heat oxy-combustion will enable the
rate, but decreases rapidly (15%) as soon as the
glass industry to comply with current environmental
furnace reduces capacity.
regulations. Its energy improvements – including
of the installation. They also lack flexibility. For
Others, such as syngas or load preheating, leads
up to 10% reduction in fuel and oxygen and 10% in
to substantial changes in furnace operation. For
CO2 compared to traditional oxy-combustion – have
broader deployment, heat-recovery technologies
been validated by three industry references. A large
will need to manage capital-investment costs to
reduction in NOx and particulate emissions was
achieve ROI in less than three years. Among these
also reported.
technologies, heat oxy-combustion helps to reduce
This new technology is universal in that it can
CAPEX thanks to its simple and direct way of
be applied to any type of glass or glass furnace. In
transforming wasted energy into value.
addition, thanks to the simple concept of preheating
The equipment needed to preheat lower volumes
oxygen and fuel with wasted energy from flue gas,
of combustion oxygen and fuel is less expensive
the ease of operation makes the solution more
than what is needed to preheat larger volumes of
attractive from a practical point of view.
combustion air. Unlike other combustion-related
Combining this concept with patented process
technologies, heat oxy-combustion requires no
and component technologies from 10 years of R&D,
DeNOx system to treat combustion fumes in the
heat oxy-combustion is safe, robust, flexible and
vast majority of cases, so manufacturers avoid all
affordable, and is expected to be rapidly deployed.
the extra investment, operating costs and waste
It will continue to be revolutionised to meet the
associated with such a system.
growing needs and challenges of the glass industry, today and tomorrow.
Making strides Taking into account the main cross-media effect of
Acknowledgement
oxy-fuel combustion, represented by the upstream
The authors thank the European Commission, which
emissions of a power plant using electrical energy
has partly financed this work through the Life+
to produce oxygen, on average the reduced CO2
programme.
emissions with oxy-combustion outweigh the
http://www.ecoheatox.com/
emissions associated with the oxygen production
http://www.oxyfuel-heatrecovery.com/
itself. CO2 from oxygen production is extremely
References
difficult to quantify and varies greatly depending
[1] “Adoption of the Paris agreement—Proposal by the
on the case. The environmental impact of oxygen
President—Draft decision -/CP.21”
production is mostly due to the emissions
[2] AlglassTM Heat recovery :an advanced Oxy-combustion
associated with electricity generation. Estimating
technology with heat recovery makes sustainable
it requires taking into account the oxygen
performances for glass furnaces. Y. Joumani, r. Tsiava, Air
consumption, the method of oxygen production and
Liquide Research and Development, B. Leroux, Air Liquide
the average emissions from electricity production
Altec O. Douxchamps, A. Contino AGC Glass Europe CRD.
as reported by national statistics.
VOL.16 N°5 • DECEMBRE 2010 Verre.
In addition to CO2 reduction in proportion to energy savings, by preheating the natural gas
[3] Oxygen and natural gas preheating for oxy-float glass. Glass international magazine July/August 2010.
and oxygen, CO2 emissions from combustion are reduced by an additional 10%, and CO2 for oxygen production (compared to traditional oxycombustion) adds another 10% reduction on top of that. Global carbon footprint must be evaluated on a
Contact r
Luc Jarry, Glass Market Manager,
Air Liquide, Paris, France. Taeky R&D Project Manager,
case-by-case basis. However, for every Heat Oxy-
r
Combustion reference, it has been demonstrated
Air Liquide, Paris, France.
that the technology has greatly reduced CO2
www.airliquide.com
emissions.
www.aluminiumtoday.com/furnaces/
Issue 2 Furnaces International r 25
Heat technology
Blast furnace cooling stave design C
ooling the steel shell of the blast furnace with water became an increasing design issue from the
late 19th century and a variety of cooling boxes and external shell cooling and double skin cooling were developed to achieve this. By the mid-20th century cast iron stave cooling panels were in use in blast furnaces,
Martin P Smith*, Jeremy Fletcher*, Richard W Harvey*, and Robert Horwood* highlight the benefits of choosing the correct furnace lines and cooling systems, as well as the detail design of cooling panels, to provide long life, low maintenance, and a high yield from the furnace.
firstly developed in the Soviet Union and then in Japan. By the 1970s cast iron stave
Blast furnace cooling system
which is achieved via a set of empirically
cooling panels were the accepted and
The use of copper staves in the high heat
established rules that have been developed
modern method for cooling a pressurised
load areas of the blast furnace increased
and expanded through many years of
blast furnace shell. As furnaces were driven
rapidly from the turn of the century as
experience with differing cooling concepts
larger and pushed for maximum throughput
confidence in their durability grew. As more
and operating philosophies. Continuing and
it was evident that the cast iron staves were
installations came into service, however,
successful long-term operations at copper
wearing in the hotter parts of the blast
initial problems were reported at some
stave installations has shown the developed
furnace.
plants with stave cooling circuit failures due
rules are proven to provide an optimum
to the effects of thermal expansion. More
furnace profile concept.
Copper stave cooling panels were developed in the late 1980s and early
recently, failures have been reported due to
1990s for use in these hot areas of the blast
premature wear of the staves themselves.
advantages in rebuild situations where the
furnace – the bosh, belly and lower stack. By
This has raised questions over the long-
thinner wall sections allow for a significant
the turn of the last century copper staves
term design concept, although many plants
increase in the working volumes of the
mixed with cast iron staves became the
do still continue to operate without such
blast furnace, especially if replacing plate
standard modern design of blast furnace
concerns.
coolers. This advantage, however, must
cooling. Primetals was involved in the early
The incorporation of copper staves into
The copper stave solution provides
be considered in combination with any
use of both cast iron staves in the mid-
a blast furnace cooling system cannot be
negative effects that may be transferred to
1970s at British Steel’s Redcar plant, and
analysed simply as fitting individual items
the furnace profile. Only once the furnace
also with copper staves from the 1990s to
of unit equipment. The design starts with
profile has been established as suitable for
the present day.
ensuring a suitable blast furnace profile,
the desired production environment can the
Fig. 1: Cooling circuit – closed type
Fig. 2: Cooling circuit – optimised water flow
Fig. 3: Cooling circuit – closed type
26 r Furnaces International Issue 2
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Heat technology stave design be detailed. Once the profile is
of the return water to a tundish. This relied
established then decisions on the cooling
on the skill of an operator.
concept can be enhanced, allowing for the
Modern furnace systems from Primetals
size and number of staves to be fixed. Again,
naturally put more onus on the control
rebuild situations can have a significant
system while relying on the experience
bearing on these decisions, such as tailoring
of the operator in the background. Leak
staves to enable maximum re-use of
detection solutions can vary from simple
existing shell penetrations.
manual intervention to progressively
The use of copper staves also requires a reliable cooling system with sufficient monitoring to allow understanding of
isolating parts of the circuit and checking Fig. 4: Blast furnace cooling circuit design
the day-to-day operational conditions,
for pressure integrity through auxiliary circuit options, which can be used via manual or automatic valves to switch
ensuring the stability of the furnace shell
requirement of the copper stave design.
groups of elements or individual elements
temperatures.
The option also has the added advantage of
on and off the master water circuit (Fig. 3
A typical solution in Fig.1 involves
reducing pipework around the tuyere area,
and Fig. 4). Further levels of review can be
closed circuit cooling utilising soft water
which can be useful in rebuild scenarios
applied with automatic pressure checks
and thus ensuring that the quality of the
when multiple work fronts can become a
carried out on the circuit, all initiated from
water within the staves can be easily
bottleneck to progress.
the main control room.
monitored and controlled. Demineralised
In all designs, heat flux monitoring and
water is also an option, but is considered
leak detection are of paramount importance.
volume required to cool the stave element
more expensive and of no real advantage
Heat flux monitoring in its most simple
based on a water velocity of 1.8 m/s in a
in terms of performance in practical terms.
sense relates to flow and temperature
channel of a certain size, the actual cooling
An expansion tank allows for control of the
measurement on a zonal basis. Again, the
system developed can be designed to suit a
internal circuit pressures to avoid boiling
balance between cost and provision of an
plant’s requirements in terms of operational
and gas leakage and is the key element in
operating system needs to be considered.
benefits and capital cost.
the approach to leak detection. Primetals
The needs of the zonal approach in terms
Standard design parameters along with
favours an approach to the circuit design
of instruments must, of course, be matched
the use of 3D CAD software make it possible
using a small vertical pressure vessel for
with that of the piping arrangement.
to produce the ideal design even in short
the leak detection role where the vessel
Vertical and horizontal (circumferential)
and demanding deadlines.
can be considered to sit on the circuit in
zones are the norm for Primetals, albeit
order to be the pressure control point. A
with no hard or fast rule to be applied to
in the stack area of the blast furnace. In
gas separation role is not considered part
any particular project, rather a clear desire
recent times 3D models are produced for
of the Primetals circuit design. The physical
to agree with the customer what is required.
both design analysis and integration into a
position of the pressure vessel is dependent
From the simple starting point of a water
Fig. 5 shows a typical copper stave design
While heat flux monitoring can
full blast furnace site model where erection
on available nitrogen pressure while the
be summarised as a combination of
methodologies can be made clearer by the
clear preference is to locate at ground level
temperature and flow measurements, leak
local to the circulating pumps.
detection represents a far broader and
There are, however, many variations on
interesting topic for discussion. The pressure
these concepts, which can be adjusted to
vessel previously noted is the core to
suit specific site conditions. Overall cooling
Primetals’ leak detection analysis. Any leak
system complexity can be increased by
in the water circuit will result in a loss of
splitting the water circuit into areas, such
water volume and therefore a loss of level
as hearth, copper staves, cast iron staves.
in the vessel. The choice of a vertical vessel
This breakdown offers advantages for
derives from a desire to maximise sensitivity
monitoring and leak detection but increases
to change in volume. Within the control
capital cost.
system, alarms can be configured to notify
Fig. 2 shows one such example
the operator of a change in level beyond
successfully implemented to suit available
the norm most likely signifying a leakage.
water quantities where a double pass
This, of course, is the start of the process of
circuit in the copper stave zone of the
finding the guilty party in terms of leakage.
water system was created. The idea reduces
From the old and established arrangement
water consumption in this area to a half
of open circuit cooling, a leak could be
of that required with the basic design
identified by a change in the characteristic
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Fig. 5: Standard Primetals Copper Stave
Issue 2 Furnaces International r 27
Heat technology Primetals’ blast furnace design centre of competency and the impact to the area was seen first hand. It was, therefore, of great joy when SSI purchased the blast furnace and announced that they were to restart it. [The subsequent closure of the plant and shutdown of the furnace in 2015 was described as “industrial vandalism” at the time and is still being felt in the area now]. In 2010, when it was restarted, replacement copper staves were required for four rows within the furnace. Being a large furnace there was an existing Fig. 6: Existing openings in the Redcar blast furnace shell
arrangement of 48 staves per row, however, these staves had encountered problems
creation of 3D movies which demonstrate
lines. Being a new blast furnace designed by
with bending in the previous campaign and
how the staves are to be installed.
Primetals, focus was not lost on the criticality
were very large in their width. Primetals
JSW blast furnace #3 and #4
of this, as has been seen on other blast
proposed replacing each row of 48 staves
Two examples of copper staves that have
furnace designs across the world, which can
with a row of 72 staves, therefore reducing
been designed for a new blast furnace shell
have detrimental effect to the performance
the individual width, which would reduce
by Primemetals are at JSW, India. These were
and life span of the copper stave.
any movements during operation. The holes
two large blast furnaces that commenced
in the shell were designed for old cast iron
Case studies: Re-line solutions
staves which made it a great challenge to
Designing copper staves to be integrated
design the copper staves not only to fit the
combination of cast iron and copper staves
into an existing shell can be a challenge.
shell and its openings, but also to re-use
throughout the full blast furnace from the
A blast furnace shell that was previously
the existing holes as much as possible to
hearth up to the throat. Five rows of copper
a plate-cooled furnace or an older cast
minimise rework on the shell. The existing
staves are installed in the high heat flux
iron stave-cooled furnace presents many
holes in the shell can be clearly seen in
zones of the Bosh, Belly and Lower Stack.
problems and design constraints that need
Fig 6.
Four inlet pipe connections at the base of
to be overcome. Generally, projects that
the stave feed into four vertical cooling
involve such scope have shut downs where
accommodated and further to this the
channels up to the top of the stave where
time constraints are very much paramount.
addition of copper stave wear rods on each
four outlet pipe connections are located.
Therefore, minimising any re-work to the
row was arranged. Utilising the fixed pin
Compensators are installed around the
blast furnace shell is vital.
of the stave to accommodate additional
operation in 2009 and 2011 respectively. Their cooling systems comprise a
copper pipes to allow for movement of the
Existing instrumentation locations were
instrumentation along with the copper wear
stave during operation. Fixing bolts, which
SSI Redcar blast furnace re-line
are initially used for the installation of the
In 2010 the blast furnace at Redcar in the
holes in the furnace shell and hence saved
staves, are also positioned towards the
UK was mothballed. This site is local to
further time.
rods eliminated the requirement for more
corners of the stave to help alleviate the ‘banana’ effect that has been seen where the corners of the stave fold in to the furnace. Both a guide and fixed pin are installed to help control the movements of the stave when it sees higher temperatures and expands. The fixed pin is the only fixed point of the stave whereas the guide pin controls the movement of the stave at the lower end to stop it from bowing in axially towards the centre of the blast furnace. Working with a new blast furnace shell gave the designer a lot of freedom in utilising a typical and standard stave design. As always, attention was given to the blast furnace
28 r Furnaces International Issue 2
Fig. 7: First row of copper stave installation almost complete
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Heat technology Since the previous campaign’s blast furnace shell was designed for the use of copper staves, Primetals’ standard stave was seen as the ideal solution to the blast furnace. The main difference from the Primetals design to the previous stave design is that of the fixing bolts which were located much lower than Primetals advise, and hence did not prevent the stave from bending in at the corners. This presented a problem to the installation of the Primetals Fig. 8: Refractory inserts into the hot face of the copper stave
Fig. 9: Primetals pipe fixing design
standard as the existing bolt holes needed to be re-used while stopping the corners bending in once more. The design
Proposing to simply plug all the existing
carbide inserts and graphite would be used
experience at Primetals led to the use of a
holes in the shell and drill new ones to
in a complementary manner so that the
patented fixing detail at Lulea, which was
suit the standard design was not seen as
best possible protection would be achieved.
previously designed and implemented on a
a practical solution by Primetals as the
Silicon Carbide’s high-strength, low-thermal
blast furnace at VA Stahl.
importance of getting the blast furnace
expansion and excellent abrasive properties
back online as quickly as possible was
make it an ideal material for the rigours
9 prevents the stave from bending in at
of greater significance. These needs are
of the blast furnace environment. Using
the corners while still allowing the stave
realised with the final installation of the
graphite alongside silicon carbide conducts
to thermally expand and move during its
staves as seen in Fig 7.
the cooling of the stave to that of the
operation. It is accepted by Primetals that
silicon carbide, maintaining the excellent
during operation the copper stave will
abrasive properties of the silicon carbide
expand and move, this cannot be prevented,
and supplying the stave with its protection.
but it can be controlled so that failures do
The arrangement can be seen in Fig 8.
not occur.
Ternium’s blast furnace number two Ternium Siderar had a shutdown in 2012 to reline its blast furnace. The shutdown was
In addition to the refractory lining it was
The pipe fixing design as shown in Fig.
The design implemented during the
required much earlier in the campaign than
also decided to install a system of wear
reline at Lulea further demonstrates the
anticipated due to the performance of their
monitoring devices that could give an
understanding and versatility of Primetals
staves, which had been installed just a few
indication to the operators on the condition
in reline and rebuilds. While understanding
years earlier. Extreme wear had occurred on
of the lining in front of the copper staves.
and supporting the requirement of a tight
a number of their copper staves over a short
This consists of copper wear rods that are
shut down period the design of the stave is
period of operation. In some instances the
inserted at strategic positions on the stave
never compromised.
wear exposed the cooling channels causing
rows that can be accessed during furnace
some innovative thinking by the operations
operation and measurements taken of the
Results and conclusion
team to keep the blast furnace running.
length of the rod. If there is any abrasive
Primetals promotes its standard copper
wear present on the front face then this can
stave design as the optimum solution for
copper staves in the last campaign, it made
be immediately picked up and fed back for
blast furnace cooling. While this is the
it a relatively simple option to introduce
suitable action.
basis for all designs, the requirements and
Since the blast furnace had incorporated
restrictions of the blast furnace itself, or the
the Primetals standard design of stave into the blast furnace. Utilising existing bolt
SSAB Lulea blast furnace #3
shutdown period, are always considered as
holes, pipe holes and fixed pin holes kept
Primetals was awarded the contract to reline
a major part of the design. Primetals can
furnace shell modifications to a minimum.
blast furnace number 3 at Lulea in Sweden
adapt the standard design and its features
The addition of a guide pin on each stave
in August 2014. The shut down in June 2015
to provide the optimum solution for
meant that just one extra hole per stave
involved a full replacement of both cast iron
individual blast furnaces.
was required in the furnace shell.
and copper staves. Three rows of copper
Due to the severe nature of wear that
staves in the bosh belly and lower stack were
occurred in the previous campaign it was
replaced with full utilisation of the existing
decided that extra protection of the hot
openings in the furnace shell. In its previous
face would be required. This resulted in
campaign the ‘banana’ effect became
the addition of refractory inserts into the
apparent, causing a particular problem on
castellations of the staves. Both silicon
row three of the copper staves.
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Contact * Primetals Technologies, Stockton-onTees, UK www.primetals.com
Issue 2 Furnaces International r 29
Electric steelmaking
Process improvement with electromagnetic stirring In the electric arc furnace (EAF) process, there are a number of factors that can impact negatively on productivity and cost-efficiency, many of which can be reduced or completely eliminated with the application of electromagnetic stirring (EMS) to deliver improved productivity, reduced costs and a safer, more reliable and energy-efficient operation. By Lidong Teng*, Helmut Hackl*, Pär Ljungqvist**, and Joakim Andersson**
F
inding ways to maximise process
proportionate to the current of the stirrer.
output and minimise costs is
Since the stirrer is extended over the entire
more important than ever in this
diameter of the furnace, effective stirring
competitive and financially challenging
forces are obtained over the whole bath and
landscape. New technologies that
the entire melt is stirred.
provide process improvements can
The melt flow pattern at the steel/slag
help steel producers make the most of
interface and bottom in a 100-tonne spout
what they already have and contribute
tapping stainless steel furnace is presented
to improved profitability. However, with
in Fig. 2[2]. The designed average volume
limited investment budgets come higher expectations as well as technology that solves problems and delivers tangible process improvements. The latest EMS technology for EAF, known as ArcSave, has been applied on a 90-tonne
Fig. 1: Flow pattern in the melt in a spout tapping furnace fitted with an ArcSave stirrer
melt velocity induced by the ArcSave is around 0.2~0.5 m/s. It can be seen from Fig. 2 that ArcSave creates a global circulation
EAF process for both plain carbon and high
in the melt and thereby provides efficient
alloyed steel production.
mixing of the complete bath. This is one of
Fig. 1 illustrates the flow pattern
the major advantages of ArcSave compared
spout tapping furnace for stainless steel
occurring in a spout tapping arc furnace
to the bottom gas stirring by porous
production at Outokumpu Stainless Steel
mounted with an ArcSave stirrer underneath
plugs. Mixing the entire melt accelerates
AB (OSAB) in Avesta, Sweden, with the aim
the furnace bottom shell. The stirrer is
homogenisation of the temperature and
of delivering improved productivity, lower
placed under a non-magnetic (austenitic
chemical composition of the steel, as well
costs and elimination of furnace bottom
stainless steel) steel plate bottom or
as the chemical reactions between steel
skulls, all of which have been successfully
window. ArcSave has no physical contact
and slag.
achieved.
with the steel melt; therefore the system
ArcSave stirring is automatically
requires very little maintenance. The low
ArcSave electromagnetic stirring
controlled by a designed stirring profile
frequency electric current passes through
which is customised to match the needs of
ABB has delivered electromagnetic stirring
the stirrer windings to form a traveling
different EAF process steps, such as scrap
for EAF operation since 1947, enhancing
magnetic field which penetrates the
heating, homogenisation, melting of alloys,
process performance at 150 customer sites
furnace bottom, thereby generating forces
decarburisation, de-slagging and tapping.
worldwide. ArcSave, was developed in
in the molten steel [1]. When the traveling
Operation is characterised by low stirring
response to demand for stronger stirring
field is reversed, the melt will flow in the
cost, reliable and safe operation and creates
power that goes further to optimize the
opposite direction. The melt flow rate is
optimum conditions for reproducible
30 r Furnaces International Issue 2
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Electric steelmaking
Figure 2. Melt flow velocity vectors simulated in a 100 ton spout tap EAF [2]
production of high quality steel and precise
productivity. The process benefits due to
due to faster melting of big scrap bundles
logistics.
improved kinetic conditions for heat and
and reduced scrap cave-ins. Fig. 3 shows
mass transfer obtained with ArcSave are
that current swings were reduced with
ArcSave project objective at OSAB
discussed in this article. The hot test results
ArcSave. The standard deviation of current
The OSAB melt shop consists of an EAF,
at OSAB are based on three months without
swings is 9.3 without stirring and 3.7 with
AOD, ladle furnace, continuous casting
and three months with ArcSave.
ArcSave, resulting in a higher power input
and grinding. The EAF has a 110 MVA transformer with a 90-tonne capacity. The
and, therefore, reduced power-on time. The
Test results
reduction of electrode current swings with
EAF is equipped with a lance-manipulator
ArcSave has also been observed in the EBT
consisting of four lances to inject O2, N2,
Improved scrap melting and arc stability
FeSi and Carbon. In combination with
The main difference between the EAF
electric power, three oxy-fuel burners are
with and without ArcSave is the intensity
Arc heating efficiency and energy savings
used. Special steel grades, containing a
of convection in the melt bath. Forced
Temperature gradients in the flat bath
high amount of chromium, are produced at
convection induced by electromagnetic
during scrap melting in conventional AC
OSAB. For these steel grades a high amount
stirring enhances the melting of larger
arc furnaces without stirring have been
of FeCr alloys are added in the furnace.
scrap pieces and bundles, and makes scrap
reported to be in the range of 50-70oC [4]
Due to the FeCr alloys’ high melting point,
stratification less significant. CFD simulation
and the temperature gradient with EMS
problems with skulls in the bottom of the
results show that melt velocity is increased
is about 25% of that without EMS during
furnace appear. This leads to variations
by a factor of 10 by ArcSave compared with
the power-on period[1]. This means that
in tapping weight, high electric power
only natural convection in the melt bath
stirring reduces the melt surface superheat
consumption and problems when charging
[2]. The stronger convection inside the melt
and the heat from the arc zone is quickly
the scrap baskets. The objective of the
contributes to a homogenous temperature
transmitted to the bulk melt [5]. The
ArcSave installation is to solve the FeCr
distribution and a higher scrap melting
decreased surface superheat temperature
melting problem, reduce costs and increase
rate. ArcSave has also stabilised the arc
reduces heat losses to the furnace wall and
Fig. 3: Current swings were reduced with ArcSave
www.aluminiumtoday.com/furnaces/
type furnace for carbon steel production [3].
Fig. 4 Effect of ArcSave on energy loss to furnace water cooling panels
Issue 2 Furnaces International r 31
Electric steelmaking roof during the power-on period, thereby reducing electricity consumption. Fig. 4 shows that at OSAB furnace energy loss to
Table 1 Process improvements after ArcSave® at OSAB[5]
mixing in the melt, was reduced by around 70%. In fact, there is no need to use N2 at
the water-cooling panels is reduced by 26
Items
kWh/tonne with ArcSave, corresponding
Total energy consumption
-3~4 %
to more than 5% energy saving.
Electrode consumption
-8~10 %
Reduced consumption of FeSi and slag
Simultaneously, stirring increases the scrap
Power on time
-4~5 %
builders
and/or ferrochromium melting rate and/or
Tap temperature hit ratio
100 %
During the reference test FeSi consumption
decarburisation rate and, therefore, saving time and further contributing to lowering energy losses in the furnace process. The more stable arcing, reduction in superheat, oxidised slag and electrical power
Improvements
from the slag door manipulator to improve
Tapping temperature reduction Tap weight hit ratio N2
-20~30˚C +24% (reached 93%) -70%
consumption results in 9% lower electrode consumption.
all with ArcSave.
in the OSAB EAF was higher than normal for stainless steel arc furnace operation, since O2 was used to create extra energy to help melt FeCr skulls. After ArcSave the addition of FeSi has been tentatively reduced. Of course, reduction of FeSi will increase
Improved slag-metal reaction and reduced
electrical energy consumption accordingly.
Cr2O3 content in slag
With ArcSave overall energy consumption
Bath homogenisation and tapping
ArcSave delivers a stirring effect on the
is, however, reduced by 3-4%. Si reduction
temperature reduction
slag due to the steel/slag interface friction
reduces SiO2 content in the slag, thereby
The bulk turbulent flow induced by
bringing different parts of the slag and
cutting lime consumption since slag basicity
ArcSave stirring brings a thorough
melt to the reaction zone all the time.
is kept constant. ArcSave’s positive influence
mixing of the whole melt, resulting in
In the absence of stirring, transportation
on arc stability makes it possible to reduce
superior temperature and composition
of all parts of the melt to and from
slag thickness.
homogenisation. Fig. 5 shows ArcSave
the reaction zone has to take place by
temperature distribution when measured
diffusion only. With induction stirring,
Enhanced ferrochromium melting and tapping
in two positions with a 1-2 minute time
the bath and slag movements take care
weight control
interval for the same heat after power-off.
of most of this transportation. Diffusion
High FeCr addition and short tap-to-
The corresponding temperature difference
distances are thus reduced considerably
tap time (less than 60 minutes) has its
at two positions is less than 2˚C on average.
and this is an important factor for
drawbacks, including the formation of
Good homogeneity is important for a
desulphurisation and Cr2O3 reduction. It
un-melted FeCr skulls on the furnace
number of reasons. It implies a reliable
is very important when chromium, which
bottom. The resulting furnace bottom
measurement and prediction of bath
has been oxidized during the oxidizing
build-up reduces the effective volume of
composition and temperature. Bath
period and has entered the slag, is reduced
the bath, making bucket charging difficult.
homogenisation with ArcSave makes
back into the steel. By optimising the
FeCr, with its higher melting temperature
it possible to obtain an exact tapping
stirring profile the slag/metal reaction
and density, tends to rest on the bottom
temperature for different steel grades,
can be enhanced and efficient slag
of the furnace, where the melt is cooler. In
which is very important for a smooth
reduction obtained. It is found that the
the absence of stirring, dissolving can be
downstream AOD operation. Tapping
Cr2O3 content in the slag is reduced by
problematic. Following ArcSave installation
temperature is reduced by an average of 20-
an average of 3.1% with ArcSave together
the temperature is equalised throughout
30˚C without any change to the AOD arrival
with O2 injection practice optimisation.
the entire bath and the melting of FeCr
temperature.
Consumption of N2, traditionally injected
and even heavy scrap pieces is enhanced.
Fig. 5: Comparison of two temperature measurements in different positions in the bath after power off
32 r Furnaces International Issue 2
Fig. 6: Tap weight hit ratio without stirring and with ArcSave
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Electric steelmaking in tapping weight. Slag reduction is also enhanced by stirring, resulting in lower FeSi consumption and higher Cr yield. The reduction in surface superheat temperature and efficient heat transfer under stirring reduces heat losses to the furnace wall and roof and result in lower electricity and electrode consumption. Shorter tap-totap time and consistent furnace operation also greatly increase productivity. At OSAB ArcSave successfully achieved the customer’s objectives including elimination of furnace bottom sculls, improved productivity and lower operating costs. ABB’s ArcSave technology is proven to improve EAF process performance. Helping steel producers to overcome many of the challenges facing them today, it delivers benefits that simultaneously reduce costs, increase productivity and allow for a safer, more reliable and energy-efficient operation. Both temperature homogenisation and
lining, but clearly reduced refractory
forced convection of melt help with FeCr
wearing in hot spot and slag-line areas.[4]
dissolution. The furnace bottom is also
References 1. Fornander S. and Nilsson F.: Inductive stirring in
shown to be cleaner with ArcSave than
AOD operation benefits
arc furnace. Journal of Metals, 188 (1950):1, pp33
without stirring and the problem with
Improved accuracy in tapping weight and
and pp.256
furnace bottom skulls has been eliminated.
tapping temperature from EAF makes it
2. Widlund, O., Sand, U., Hjortstam, O. and Zhang, X.:
Fig. 6 shows that the tap weight hit ratio
possible to obtain consistent AOD. The
Proc. of 4th Int. Conf. on Modelling and Simulation
is increased by roughly 24% thanks to
correct tapping weight will eliminate extra
of Metallurgical Processes in Steelmaking (SteelSim),
improved FeCr melting.
alloying additions in the AOD converter,
Stahlinstitut VDEh, Düsseldorf, Germany, (2011).
which would otherwise lead to increased
3. Lidong Teng, Aaron Jones, Helmut Hackl, Mike
Greater process reliability and safety
FeSi, lime and O2 consumption in AOD. An
Meador: ArcSave® -Innovative solution for higher
initial AOD tapping temperature, which is
productivity and lower cost in the EAF, AISTech
The positive effect of ArcSave on the
lower than necessary, also increases FeSi
2015 Proceedings. © 2015 by AIST, Cleveland, OH,
EAF process discussed in the sections
consumption in order to create the chemical
USA, 4–7 May 2015.
above will have a significant impact on
energy to increase the bath temperature.
4. McIntyre, E.H. and Landry, E.R.: EAF Steelmaking
improving process reliability. The fast
A consistent AOD operation can also
–Process and Practice Update, Iron & Steelmaker,
melt-down of big scrap and ferrochromium
mean increased productivity and reduced
17:5 (1993), 61-66.
provides efficient homogenisation
operating costs.
5. Samuelsson P. Energy saving using induction
of the melt bath on both chemical
stirrer in an arc furnace, ASEA Journal, 1985, (5-
composition and temperature, which
Conclusion
delivers the targeted steel tapping weight
Electromagnetic stirring enhances the
and temperature. Stirring in the melt
kinetics of heat and mass transfer in the
bath reduces scrap cave-ins, stabilises
arc furnace process and gives a more
electrodes, and reduces electrode
homogenous melt bath. The test results at
breakage risk. Homogeneous temperature
OSAB show that ArcSave enhances scrap and
*ABB Metallurgy, Process Automation,
in the whole bath provides smooth
ferrochromium melting and reduces energy
ABB AB, Västerås, SE-721 59, Sweden.
tapping and reduces tapping delays.
consumption. The bath temperature is more
www.abb.com
Elimination of thermal stratification in the
homogeneous and tapping temperature
melt bath reduces tapping temperature.
is controlled more correctly, providing for
**Outokumpu Stainless AB, A
ArcSave eliminates hot and cold spots in
smoother AOD operations. With stirring,
vesta, SE-774 41, Sweden.
the bath and didn’t create any negative
the ferroalloy is melted efficiently, thus
www.outokumpu.com
effects on the bottom hearth refractory
giving better steel yield and more accuracy
www.aluminiumtoday.com/furnaces/
6):18-23.
Contact
Issue 2 Furnaces International r 33
Electric steelmaking
Coreless induction in micro mills
E
lectric steelmaking using primarily scrap and some sponge iron now accounts for almost 50% of the world’s steel production, not
including China. In some countries, such as India or the Middle East, such mills provided as much as 60 and 80%, respectively, of output in 2011 [1]. As a primary melting source, the electric arc
furnace (EAF) has proven its merits in this context for many years; however, the induction furnace
Growing demand for micromills with an annual capacity of between 50kt and 400kt has prompted a growth in use of coreless induction furnaces in countries where there is a high scrap availability, such as India, Iran, South Africa and the Middle East. R Bode*, W Schmitz and D Trauzeddel* discuss the advantages and disadvantages of induction furnaces compared to electric arc furnaces.
poses a serious alternative today if one takes into account specific application conditions. In line with the trend in local scrap markets, the demand
scrap or sponge iron – and on the grade of steel to
for electric micro mills with an annual capacity of
be produced. Basically, such metallurgical steps may comprise:
50kt to 400kt is growing. It is here that coreless
r The removal of carbon, phosphorus, sulphur and
induction furnaces have become increasingly
oxygen;
widespread in recent years, especially in countries with high scrap availability such as, India, Iran,
r Alloying;
South Africa and the Middle East. A combination
r The removal of gases and non-metallic impurities. It should be noted that melt decarburisation and
of an electric arc furnace with a coreless induction
the reduction of sulphur and phosphorus levels
furnace also presents an interesting solution, for instance, when it comes to efficiently upgrading the capacity of an existing EAF steelmaking plant [2]. The required metallurgical treatment in an EAF steel mill depends on the quality of the feedstock –
Fig. 1: Typical arrangement of a medium-frequency coreless induction furnace plant
can be efficiently performed in an EAF furnace; the same applies to de-slagging operations. A coreless induction furnace can sustain these operations to a limited extent only, but it offers benefits when it comes to alloying because of the bath movement and low melting loss it can provide. In all, the EAF – which, in process engineering terms, must be classified as a hearth furnace – is indisputably to be preferred for metallurgical tasks. However, for economic reasons, it has become standard practice to carry out such tasks with the aid of separate equipment such as ladle furnaces and converters while using the EAF as a melting furnace only. For structural steels and associated scrap grades, such treatments will be unnecessary, so the need for a secondary metallurgical furnace is often eliminated altogether.
Design and operation Induction melting has become an increasingly widespread process in the foundry and semifinished products industries given its technical and economic performance potential. Its basic
34 r Furnaces International Issue 2
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Electric steelmaking advantages derive from the direct input of heat into the metal with almost no temperature overshoot and from the fact that the bath movement can be selectively controlled. These properties provide an accurate temperature and process control capability, low melting loss, reduced environmental and workplace pollution, and highly stable and precise analyses, all with high energy efficiency. The step to digitally controlled medium-frequency furnaces based on advanced frequency converter systems has brought a significant increase in power density and process engineering capabilities. An advanced high-power induction melting system as shown in Fig. 1 is essentially made up of: r The melting unit with furnace body and cradle; r The electric power supply system with transformer, frequency converter and capacitor rack; r The process control system with weigher, operator cabinet and melt processor;
Fig. 3: Multi-frequency technology
One key feature of the coreless induction furnace, distinguishing it fundamentally from all other melting sources, is the movement of the metal
r The peripheral equipment including water recooler, charger and dust collection system.
bath created by electromagnetic forces (Fig. 2). The
State-of-the-art furnaces with advanced
electromagnetic forces generate a flow pattern
frequency converter systems can be operated with a
resembling two rotational toroids in the melt. In
selectable frequency usually in the range between
a high-power furnace, the local flow velocity may
60 and 1,000 Hz. In new coreless furnace projects,
amount to as much as 1-2m/s. Moreover, a so-called
they have completely supplanted mains frequency
bath meniscus will form at the surface of the melt.
installations due to their numerous advantages.
The intensity of this bath movement firstly depends on the furnace power; the higher the power input,
A major benefit, thanks to the higher frequency,
the more vigorous the bath movement will be.
is that the furnace can be started on solid charge
However, the flow intensity also depends on the
material without any losses and it can be reliably operated with a power density, which is a multiple of that of mains-frequency furnaces.
Fig. 2: Bath movement and meniscus
frequency of the alternating current fed to the coil: the lower the frequency, the stronger the bath movement. This implies first of all that for a given fixed frequency, the heat input into the melt and the intensity of the bath movement are always correlated. Moreover, for a given specified furnace power, the intensity of the bath movement can be selectively controlled by choosing a suitable operating frequency. This bath movement is very important from a technological viewpoint since it facilitates optimum melt homogenisation and stir-down of constituents and thus ensures a uniform melt composition and high temperature accuracy at the same time.
Special circuitry From a metallurgical point of view, the ideal induction melting process is one in which both the input of thermal power and the melt flow can be controlled to match given technological needs. In addition, the power input and bath
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Issue 2 Furnaces International r 35
Electric steelmaking IGBT converters has come to play an increasingly important role in electrothermal processes. These systems involve the use of Insulated Gate Bipolar Transistors (IGBTs) instead of thyristors in the inverter. Technical progress has yielded process-oriented IGBT converter systems for manifold applications. Provision of an IGBT converter with two separate inverters and a system ensuring a phase-shifted operation of the furnace coil sections forms the technical basis for controlling the bath movement within wide limits. In the charge melt-down phase, the furnace can thus be run at an appropriate nominal frequency of, say, 250 Hz and to increase Fig. 4: Layer formation in the crucible wall
the bath agitation at low power the frequency can be controlled steplessly below 100 Hz. The amount of phase offset between the two coil
movement should be mutually decoupled, i.e., the
sections is likewise adjustable to provide a selective
desired melt movement in the furnace should be
control of the flow pattern (i.e., direction of rotation
adjustable independently of the respective power
and velocity) in the central coil area of the furnace.
input. While it is no problem technologically to
This way, the region of maximum flow velocity can
control the electric power and hence, the input of
be moved to the centre of the molten metal bath
thermal energy into the melt, it takes very special
to obtain more effective intermixing of the entire
circuit engineering to achieve control of the bath
melt. The technical options available for influencing
movement independently of this energy input.
bath movement in a coreless induction furnace can
Moreover, when discussing intense bath
be implemented and combined in manifold ways to
movement, it is necessary to distinguish between
address specific metallurgical tasks.
deep intermixing of the entire melt and mere Based on R&D advances achieved over the
Steel metallurgy in a coreless induction furnace
last few years, Otto Junker has established its
Factors in favour of the coreless induction furnace
Power-Focus and Multi-Frequency technologies
as a metallurgical treatment resource include its
– two special circuit systems meeting the above
exceptional ability to provide selective control
surface flows, as shall be explained later.
of the bath movement, as mentioned earlier, and
requirements which have by now proven their merits in numerous installed furnace systems. Power-Focus technology permits an automatic or
Fig. 5: The sintered layer is removed
its substantial flow velocities achieved. On the downside, its unfavourable surface-area-to-volume
freely selectable concentration of power in that coil section (top or bottom) in which it is needed most. Multi-Frequency technology enables switching between different operating frequencies during the melting process. For melting cast iron, for example, the system will choose the right frequency of 250 Hz in this case. For the input of carburising agents and alloying additives, the system automatically switches to a lower frequency, such as 125 Hz. Practice has shown that this changeover to a reduced frequency can greatly accelerate the carbon pick-up in cast iron analysis adjustment (Fig. 3). These options are substantially expanded further by developments utilising the technical advantages of IGBT converter technology. Apart from proven thyristor-based frequency converters, the successful development of special
36 r Furnaces International Issue 2
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Electric steelmaking r Production of high-purity metals including pouring under vacuum; r Production of super-alloys. Of the special circuit features embodied on coreless induction furnaces, as mentioned above, the Multi-Frequency technology is one that has found its way into steel melting applications. The options opened up by the process-oriented frequency converter technology have proven effective in melting fine-grained ferro alloys.
Comparison between EAF and coreless induction furnace From the figures available in the literature,[4, 2] which all relate to specific application cases and hence do not represent average values, it emerges that the coreless induction furnace has a 3% to 4% cost efficiency advantage in terms of operating cost per tonne of steel. ratio and the rather thin and sensitive refractory lining need to be mentioned.
Fig. 6: DUOMELT technology
In particular, the coreless induction furnace avoids the cost of electrodes, and the slightly
In today’s steelmaking practice it is not at all
higher cost of its refractory lining does not wipe
unusual for certain metallurgical operations to be
out this benefit. Another major advantage is the
performed in a coreless induction furnace. Thus,
low melting loss of only 1% to 2% versus 3% to 7%
refining is carried out via the addition of iron oxide
for the EAF, which translates into clear savings of
(ore or scale), which provides a certain degree of
costly alloying elements.
decarburisation and intense bath mixing. Inert gas
The slightly higher energy demand of the coreless
purging, typically with argon, via bubbling plugs
induction furnace amounts to approximately 5% to
in the furnace bottom is known to reduce the
8%, depending on the literature source consulted.
hydrogen, nitrogen and oxygen content of the melt. On the other hand, such operations can provide
In the overall economic performance assessment, advantages such as lower capital investment,
only minor corrections of the melt composition and
smaller equipment footprint, lower demands on the
are not always cost-efficient.
power supply system, and lower environmental and
For adding alloying elements, the coreless induction furnace with its good melt stirring capability is well-suited to deliver high yields and
labour safety requirements speak in favour of the coreless induction furnace. The process technology drawbacks of the coreless
an accurate and homogeneous control of the target
induction furnace as a metallurgical treatment
melt analysis.
device are of no consequence if the furnace is
In melting down very rusty scrap and sponge iron,
used as a melting source only and is backed by
it should be noted that a particular approach is
appropriate secondary metallurgical processes and
needed because of the intense slag formation. From
equipment.
the experience gathered in electric steelmaking practice, up to 85% iron sponge is assumed to be feasible in a coreless induction melting furnace if a liquid heel regime and repeated de-slagging (approximately three times) are used. It should also be mentioned that vacuum-
The disadvantages of the EAF can be stated thus: r Higher loads on the electrical power supply mains; r Increased cost of dust collection and noise protection; r Higher melting loss (approximately 3% to 7%);
type coreless induction furnaces are successfully
r Cost of graphite electrodes;
employed in producing high-purity steel alloys.
r Higher equipment cost compared to a coreless
Typical applications include the following: r De-oxidation of high-grade steel melts;
induction furnace system of comparable output. On the other hand, it provides these advantages:
r Carbon reduction of molten steel;
r Ability to load very bulky scrap;
r Melt adjustment to minimum gas content;
r Support of metallurgical slag work;
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Issue 2 Furnaces International r 37
Electric steelmaking are necessary for a continuous operating regime. In some countries, acidic masses are still used for cost and availability reasons. The spinel-forming compounds predominantly employed in coreless induction furnaces today are alumina-magnesia mixes which, when heat is applied, will form the so-called genuine spinel (MgOxAl2O3=MA) via a solid diffusion process. MA spinel has the following characteristic properties: r Good thermal shock resistance; r Good chemical resistance; r High refractory performance; r Good strength at high temperatures. The lining of a coreless induction furnace is made with the aid of a lost former using vibratory compacting. The lining material is then heated either by induction or by pre-heating the furnace interior with a gas burner and subsequent introduction of a 1600–1700°C hot melt. The foregoing is followed by rapid induction r Thick-walled refractory lining; r Comparatively long lining life. The coreless induction furnace has the following drawbacks: r Very restricted usefulness for metallurgical slag work;
Fig. 7: Layout of a coreless induction furnace plant comprising two 25-tonne furnaces
heating to the required sintering temperature (at least 1700°C, or 50°C above the operating temperature). Experience has shown that the sintering temperature should be held for at least 1 to 2 hours. This will produce enough MA spinel to impart
r Thin refractory lining, calling for frequent relining
sufficient strength and density to the hot-face lining
and involving a higher risk of mechanical damage;
to make it resistant against attack of the liquid melt.
r Limitation of maximum scrap dimensions by the
In the course of furnace operation, three zones
much smaller melting vessel (compared to an
will form in the lining made of dry ramming mix: the
EAF).
sintered layer, the fritted layer, and the loose layer
Its advantages include the following:
(Fig. 4).
r Lower capital investment;
This layer structure makes it possible to conduct
r Smaller footprint;
up to 10 or more intermediate repairs on the lining.
r Easier to operate;
Here, a distinction is made between two methods
r Minimum metal loss;
commonly referred to as ‘black relining’ or ‘white
r High alloying efficiency:
relining’.
r Low dust collection requirements, no noise problem;
The term relining’ or ‘patching’ refers to a renovation of the original hot-face lining. A common
r Multiple units provide more redundancy;
rule states that for such relining to be performed,
r Low load on power supply system.
the wall thickness must be down to a residual 60%
Practical experience
at least and the gap size should be 70mm minimum. In the white relining process, the sintered layer (20 to 25mm) is mechanically removed by means of a
Refractory lining Coreless induction furnaces in micro mills are
pneumatically operated chisel (Fig.5). Next, the top layer is removed all the way to the
generally lined with so-called dry ramming mixes
topmost cooling coil. After that a 10mm to 20mm
based on SiO2 (acidic compounds) and Al2O3-MgO
thick layer is applied to the bottom of the coreless
(spinel-forming compounds). The SiO2-based lining
induction furnace.
provides only a very short service life (8 to 15 heats),
Then the lost former is inserted, aligned and fixed
meaning that the furnace must be relined every day.
in place, and finally the normal lining procedure is
Accordingly, at least two coreless induction furnaces
carried out.
38 r Furnaces International Issue 2
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Electric steelmaking A ‘black relining’ is understood to be one in which the hot-face lining is not removed, except for the topmost layer. It is performed at a residual wall thickness of approximately 50%. The last charge is superheated by roughly 50% so that any accretions
with the nominal power rating, most systems are run on 250 Hz but 500 Hz are also used. A powerful coreless induction furnace plant might be characterised by the following characteristic data: Four coreless induction furnaces with a capacity of
will come off more easily and the hot-face lining
25 tonnes each, running on two switchgear systems
itself will become virtually slag-free. The interior of
with an output of 15 MW each and an energy
the furnace must be iron-free in this process.
consumption of 540 kWh/t, can deliver approximately
Next, a 10mm to 20mm thick bottom packing bed is placed in the coreless induction furnace. The rest of the process is the same as in white relining.
1000 tonnes per day so that an annual output of over 300kt of steel becomes achievable. As regards the floorspace required for such a
A comparison of the various methods in terms of
system, a surface area of two times 22 x 24 m would
the consumption of refractories is presented below:
be sufficient as shown in the layout drawing in Fig. 7. Apart frm the four furnaces and two switchgear
Without relining = ~ 5.0 kg/t
systems, and including the transformers in the
With 5 relinings = ~ 4.0 kg/t
basement, this surface area includes the charging
With 10 relinings = ~ 3.0 kg/t
chutes on the furnace platform. Needless to say, the requisite cooling equipment – i.e., air/water or water/
Accordingly, an average consumption of 2 kg/t – 4 kg/t can be expected with this relining and repair
water heat exchangers – is installed outside the building.
technology; best values range around 1.75 kg/t [5].
Summary Furnace systems used
With the coreless induction furnace now firmly
It is evident from the available data that, contrary
established as a melting source in the foundry and
to what might be expected, coreless induction
non-ferrous semi-finished products industries, new
technology does not target very large furnaces
application fields are continuously opening up
holding 50 tonnes of liquid steel and more. Instead,
thanks to technological advances.
units in the 25 to 30t capacity range dominate this application. This is also the size range of coreless induction furnaces supplied by Otto Junker for electric steel mills. In order to achieve the required melt output
These include the equipment’s use as an alternative primary melting furnace in micromills. Already, many successful international applications can be referred to and are known to address specific process engineering and economic criteria. And
with high availability rates, it is frequent practice
the specific metallurgical capabilities of induction
to run two, three or four furnaces on one or two
furnace technology are still far from exhausted.
switchgear systems. The converter output can thus be put to use continuously by feeding two
References
furnaces, or else it is possible to feed three or four
[1] World Steel Association: Steel Statistical Yearbook 2011/2012
furnaces alternately from two converter systems.
[2] Anthony B. Phillips: BSE Symposium, April 2009
Fig. 6 illustrates the principle of such a solution
[4] Dötsch, E.: Induktives Schmelzen und Warmhalten [Induction
(DUOMELT technology).
melting and holding], Vulkan-Verlag, 2nd ed.
Two furnaces are necessary for continuous melting, if only because the service life of the
[5] Bode, R.: Presentation 2015, Dörentrup Feuerfestprodukte GmbH & Co. KG
crucible can be very short indeed, especially with an acidic-type furnace lining. Also in terms of their power density in kW/t (i.e., connected load per
Contact Dr. Ing. Wilfried Smith, Head of R&D at Otto
tonne of furnace capacity) these furnaces are in
r
the moderate range of less than 700 kW/t. While
Junker, Simmerath, Germany.
peak power densities of 1000 kW/t are achievable
r
on smaller furnace systems, they are not (yet)
Feuerfestprodukte, Doerentrup, Germany
feasible in this size class for process or equipment
r
engineering reasons. As regards the selected operating frequency, which has a key influence on bath movement along
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Ralf Bode, Sales & Service. Dorentrup Dr. Ing. Dietmar Trauzeddel, Freelancer, Otto
Junker. www.otto-junker.de/en/
Issue 2 Furnaces International r 39
Ores and minerals
Advances in titania-magnetite
ore processing on a blast furnace
S
pecific to a blast furnace operation producing vanadium and containing hot metal is the presence of
titania. Vanadium occurs naturally in about 65 different minerals and in fossil fuel deposits. It is produced in China and Russia from steel smelter slag, and is mainly used to produce speciality steel alloys such as
Evraz NTMK, one of the largest Russian steel production plants with a complete processing cycle, has developed the major principles of effective blast furnace operation with a high titania load. By S. Filatov*, S. Zagainov**, L. Gileva** Y. Gordon***, V. Filippov****.
high-speed tool steels. Titanium solubility in hot metal is limited, and various titanium refractory compounds and titanium oxides are formed in the furnace hearth.
Table 1: Equilibrium constant and equilibrium concentration of titanium reduction at 1753 K temperature and 0.41 MPa pressure
reduction in a blast furnace. Possible reactions of titania reduction are presented in Table 1. According to Table 1, reactions (1), (4), (5)
Under conventional blast furnace operation, titanium nitrides and titanium
and (6) are the most probable for titania
carbides increase the melt viscosity
reduction. The equilibrium constant and equilibrium
and melt residence time in a reducing atmosphere, and as a result increase the
concentration of TiC and Ti are functions
loss of metal to slag, deterioration of the
of melt temperature and pressure at
hearth operation, problems with metal and
slag basicity B2=CaO/SiO2 =1.2. They are
slag tapping, and loss of tuyeres.
presented in Fig. 1 and Fig. 2. It is evident that increasing the blast
With more than 50 years experience in processing titania-magnetite ore from
furnace pressure to suppress the formation
Kachkanar, the only source of vanadium-
of titanium carbides is more effective than
bearing iron ore in Russia, Evraz NTMK has
through temperature control. That is why a blast furnace operating with a titania-
developed the major principles of effective blast furnace operation with a high titania load (40-50 kg TiO2/thm): r Rigid rules on the hearth’s thermal condition;
burden preparation;
magnetite burden should be equipped with
r Optimal hearth design.
bell-less top charging device, allowing for a considerable increase in furnace pressure.
Thermodynamic analysis
Fig. 3 compares calculated titanium
r Rigid tapping schedule;
The literature data [1-3] was used
content in hot metal with actual operating
r Rigid requirements for burden quality and
for thermodynamic analysis of titania
data for NTMK’s BF #6. Lower actual
Fig. 1: Temperature influence on titanium reduction
40 r Furnaces International Issue 2
Fig. 2: Pressure influence on titanium reduction
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Ores and minerals
Fig. 4: Deviation of Ti and TiO2 concentrations from equilibrium as a function of hearth design
Fig. 3: Relationship between actual and calculated content of Si and Ti in hot metal
titanium concentration leads to the conclusion that the titania reduction process in the blast furnace hearth has
An increase in coke particle size increases
=
not reached equilibrium, hence it greatly
4
N≠ (d m.ch / 2) [ 8 (d m / 2)
b g (d m
/ 2) + Pw ]
in residence time is greater than for a viscous slag.
specifically on melt residence time in the high temperature zone. An analysis of the thermodynamics of
its residence time in the furnace hearth (equation (2)). For a fluid slag, the reduction
(2)
depends on reduction kinetics and
the filtration velocity of slag and reduces
Here N – the number of channels for slag filtration in
1m2
of furnace cross-section;
It was also found that the hot metal/ slag titanium distribution coefficient very
dm.ch – channel median diameter; dm –
much depends on the CSR value. Significant
showed that the main principles to reduce
particle median diameter and Pw – tuyere
destruction of coke at lower CSR increases
formation of titanium carbides and titanium
blast pressure.
the area of contact between coke carbon
titanium oxides reduction in a blast furnace
nitrides are as follows:
For the regular blast furnace of 2000-
and melt, and as a result reduces the
r Increase in blast furnace pressure;
2300m3, a useful volume for the ratio
melt’s filtration velocity and increases the
r Operation of blast furnace with low RAFT;
between height and diameter of the hearth
residence time of slag in the blast furnace
r Reduction in residence time of melt at
is Hh/Dh = 0.34. An increase in Hh/Dh while
hearth. Increasing the CSR above 55-60%
high temperatures, reducing conditions in
retaining the same hearth volume makes
significantly reduces the fine coke fraction
the bottom segment of the blast furnace;
the movement of melt faster, which reduces
and extent of titanium reduction, thus
its residence time in a furnace hearth. This
improving blast furnace performance.
is especially important for the melts with
Uncontrolled disturbances of blast
r High burden permeability. Major factors influencing production of
elevated viscosities. The estimated results
furnace operation represent significant risks,
of deviation in Ti and TiO2 concentration,
especially in the case of low silicon hot
during its movement from the hearth’s top
at an increase to 0.47 Hh/Dh ratio, are
metal production. A cyclical advancement
point located opposite the tap hole to the
presented in Fig. 4.
in pellet descent compared to sinter
low Si and Ti hot metal The residence time of melt in a hearth
centre of the tap hole (distance ‘L’) depends
Fig. 4 results show that with an increase
on the hearth diameter, its height and melt
in Hh/Dh, the residence time of melt in the
of limestone on the furnace top strongly
velocity, and could be estimated by the
furnace hearth decreases and the deviation
affects thermal conditions in the hearth.
following formula:
of actual Ti concentration from equilibrium
It was found that the mixing of metallic
one is greater, while content of Ti in hot
burden components before charging into
metal is lower. Based on these results the
the furnace is very important to mitigate
=
L
=
≠ 1 2
(
2
d h2 + hh2 + d h )
Hh/Dh ratio at NTMK’s
2200m3
volume blast
furnaces was increased to 0.47. According to equation (2), the filtration
(1)
movement and a non-uniform loading
such uncontrolled cyclical disturbances. Experimental investigations and mathematical modeling revealed that
velocity of melt in a hearth rises with an
limestone distribution across the burden
increase in furnace pressure, while the
depends on the location of the flux within
residence time of melt reduces, which leads
the bell-less top weigh hopper. Limestone
furnace hearth; dh – hearth diameter, hh –
to the reduction of Ti content in hot metal
should be charged to the middle or upper
hearth height, - velocity of melt filtration
and an increase of TiO2 concentration in
part of the weigh hopper, otherwise it
through the coke packing:
slag.
will be distributed generally around
where - residence time of melt in a
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Issue 2 Furnaces International r 41
Ores and minerals enrichment is accompanied by 8˚C in
Table 2: Equilibrium constants and equilibrium concentration of TiO formation at 1753 K Chemical reaction
1
2
Equilib. constant
TiC+2MnO =TiO+2Mn+CO
(TiO) =
3.4·10-3
TiC+2FeO = TiO+2Fe+ CO
TiO fraction in slag
(TiO) =
4.3·103
2 K E aMnO 2 aMn CO
aTiC Ptotal
2 K E a FeO aTiC 2 a Fe
CO Ptotal
100
RAFT increase; r 1% of oxygen enrichment increases RAFT by 17-20˚C; r At these conditions, the amount of titania reduced at the bottom segment of the blast furnace remains constant.
100
The negative effect of oxygen enrichment and (as a consequence) increase in RAFT on the formation of titania carbides could be
the periphery of the furnace leading to
distribution of gas, slag, coke and hot metal
annulled by the reduction in melt residence
instability in hot metal composition.
temperatures along the height of blast
time at high temperature zone and
furnace.
promotion of non-equilibrium conditions by
It was found that at silicon content in hot metal 0.05-0.08% the slag binary basicity
Oxygen enrichment is a common way to
all the means described above.
B2 should be in the range of B2=CaO/SiO2 =
increase blast furnace productivity. With
1.23-1.25 to maintain sulphur in hot metal
respect to titania-magnetite blast furnace
blast furnace operation with increased
at an acceptable level.
this was studied and discussed in literature
oxygen enrichment are presented in Table 3.
[2, 6]. It was concluded that stable operation
The results of operation in 2006 were
It is well known that titanium carbides
The average annual results of titania
could be destructed by manganese and iron
of the blast furnace could be maintained
used as a basis for relative changes
oxides [4]. The equilibrium constants for TiC
only in the case of constant or reduced
in furnace parameters. Table 3 results
reactions with MnO and FeO are presented
RAFT and oxygen content in blast limited
confirmed the possibility of increasing
in Table 2.
by 25%.
oxygen enrichment up to 29-30%. At the
The influence of MnO and FeO on TiO content in slag is presented in Fig. 5.
At the same time, the simplified heat balance equation
in oxygen content leads to 44˚C RAFT increase for each percent of O2 enrichment
Analysis of reactions between TiO and MnO and FeO allows the conclusion that MnO plays a significantly stronger role than FeO in FeC destruction in a blast furnace
same time, it was shown that if an increase
Wg*Cg*(Tginitial-Tgfinal)= Wmat*Cmat*(Tmatinitial – Tmatfinal)
(2009 results), the increase in productivity is accompanied by an increase in coke rate. Limiting RAFT increase by 25˚C for each % in O2 increase allows improvement in
hearth.
Increasing blast furnace productivity
(4)
furnace productivity with a simultaneous reduction in coke rate.
shows that materials in a blast
The kinetics of the titania/titanium
furnace could be preheated to the same
behaviour in a blast furnace depends on the
temperature either by a small volume of
Results of blast furnace modernisation
size and quality of coke, viscosity of slag and
the gas with high temperature or by higher
A comparison of operating and design
intensity of melting, which is a function of
volume of the gas with lower temperature.
parameters of blast furnace #6 before and
blast oxygen content. In general, the rate of
Here ‘g’ relates to gas flow and ‘mat’ – to
after reconstruction is presented in Table 4.
titania reduction can be expressed by the
material flow; W – material or gas flow; T –
At that time, blast furnaces operated with
following formula:
temperature; C – specific heat.
natural gas injection as supplemental fuel.
v=
dx = K (x d
A joint resolution
xE )
(3)
of the heat transfer model alongside the thermodynamics and kinetics of titania oxide
Here, K is the rate of reaction constant.
reduction, with oxygen
Both the rate constant and equilibrium
content in a blast
constants are functions of temperature.
furnace in the range of
A mathematical model of heat transfer in
24.8 - 30.8% for NTMK’s
the bottom segment of a blast furnace [5]
blast furnaces led to the
incorporates four heat transfer equations
following conclusions:
for slag, hot metal, gas and coke. This
r Increase in blast
model allows one to analyse the effect
furnace productivity by
of coke sizing and slag composition on
1% because oxygen
42 r Furnaces International Issue 2
Fig. 5: Influence of MnO and FeO on TiO content in slag
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Ores and minerals Table 3: Influence of oxygen enrichment on furnace performance BF 6 performance
2006
2007
2009
2011
Productivity, thm/day
4716
4831
5738
6577
Coke rate, kg/thm
413
418,2
415.6
404.2
Natural gas rate, Nm /thm
122.2
115
115.5
131.3
O2 blast content, %
24.75
23.99
26.29
29
RAFT, ˚C
1828
1846
1896
1867
-0.76
1.54
4.25
Change in RAFT, ˚C
18
68
39
Relative change in RAFT, ˚C/% O2
-23
44
9
Relative productivity change, %/% O2
2.44
21.67
39.46
Relative coke rate change, kg/thm/%O2
-6.84
1.69
-2.07
3
Change in oxygen content, %
Table 5: Blast furnace performance with natural gas and combined injection
Table 4: Operating and design parameters of blast furnace #6, before and after modernisation Parameter
Before Modernization
After Modernization
Titania load, kg/thm
40-50
40-50
BF inner volume, m3
2700
2200
Productivity, thm/m3/day (WV)
2.5
3.6
Coke rate, kg/thm
430
395
Natural gas rate, Nm3/thm
102
121
Blast O2 content, %
25.1
28
Wind rate, Nm3/thm
1285
925
Blast pressure, MPag
0.232
0.37
Blast temperature, ˚C
1096
1213
RAFT, ˚C
2030
1959
HM tap temperature, ˚C
1450
1433
Hot metal Si, %
0.18-0.25
0.09
Parameter
2012
2013
2014
Annual production, thm/year
13904
14124
13904
Specific productivity, thm/m3/day
3.16
3.2
3.16
Hot metal Ti, %
0.21-0.28
0.128
Coke rate, kg/thm
398
342
367.1
Hot metal V. %
0.44-0.46
0.459
0
101
57.4
Hot metal S, %
0.033
0.024
NG rate, Nm3/thm
132
83
101
Hot metal Mn, %
0.3-0.33
0.341
Equivalent carbon rate, kg/thm
424
435.9
429.6
358
360
Blast’ O2 content, %
30
30.7
31
1.07 - 1.012
1.24-1.25
2020
2019
2019
47.1
51.12
PCI rate, kg/thm
RAFT, ˚C
Pulverized coal injection (PCI) was implemented at NTMK at the end of 2012. It allowed operation with 100% of PCI, 100% of NG or co-injection of these two supplemental fuels. A comparison of operating parameters on
Slag volume, kg/thm B2= CaO/SiO2 η CO
r Maximum possible increase in furnace pressure; r Implementing preliminary mixing of metallic burden and fluxes; r Optimisation of slag basicity to minimise sulfur in hot metal;
OAO NTMK, Stal,(2010), No. 5, pp. 30–32. Steel in Translation, (2010), Vol. 40, No. 5, pp. 443–445. © Allerton Press, Inc., 2010 4. N?s?v, S.?. a.o., Manganese is an important element in processing of titania-magnetite ore in metallurgy, Stal, (2003, ?3), p.p. 14-18
two identically designed blast furnaces with
r Usage of larger size and higher CSR coke;
5. Sobianina, O.N. a.o., Study of titania reduction in
natural gas injection (2012) and co-injection
r Operation of blast furnace with reduced
blast furnace, Steel, ?3, p.p.9-11, 2012
of natural gas and PCI (2013 and 2014) is presented in Table 5. It is clear that a similar efficiency of the blast furnace operation, could be maintained at any supplemental fuel injection.
RAFT and hot metal temperature; r Addition of manganese ore to destruct titanium carbides; r Operation at high rates of oxygen
6. Volkov, V.V. a.o., Implementation of titaniamagnetite melting practice in blast furnace with oxygen enrichment, Metallurgical treatment of complex ores, Sverdlovsk, p.p.7-13, 1986
enrichment within the limits of RAFT increase.
Conclusions
As a result of all these improvements, the
Theoretical and experimental analysis of
coke rate is reduced while iron yield and
melt reduction behaviour and movement
furnace productivity are increased.
in NTMK’s titania blast furnace hearth
Contact *Novo-Lipetsk Iron & Steel Works,
concluded that a successful production of
References
low silicon and titanium hot metal, alongside
1. Smirnov, L.A. a.o., BOF Processing of Vanadium Hot
**Ural Federal University, Ekaterinburg,
a high efficiency of blast furnace operation
Metal, Ural Institute of Ferrous Metals, Ekaterinburg,
Russia
could be achieved with implementation
Mid-Urals Publishing House, p. 528, 2000
***Hatch Ltd., ON, Canada
of the following design and operating
2. Smirnov, L.A. a.o., Metallurgical Treatment of
****NTMK – EVRAZ, Sverdlovsk region,
parameters:
Vanadium Containing Titanium-Magnetite, M.,
Russia
r Increase in the ratio between height and
Metallurgy, p. 256, 1990
www.hatch.com
diameter of the furnace hearth;
www.aluminiumtoday.com/furnaces/
Lipetsk, Russia
3. Filatov, S.V. a.o., Smelting Low Silica Hot Metal at
Issue 2 Furnaces International r 43
We set Standards in Heat Treatment.
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