Furnaces International Issue 2

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

www.aluminiumtoday.com/furnaces/ Issue 2

FURNACE TECHNOLOGY

CELEBRATED BY OUR CUSTOMERS AROUND THE WORLD

Our customer’s celebration dinner held inside a newly constructed TECO furnace

www.teco.com

®

ONE GROUP - SIX COMPANIES TOLEDO ENGINEERING / TECOGLAS / ZEDTEC / KTG ENGINEERING / KTG SYSTEMS / EAE TECH

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

Do you receive our FREE weekly newsletter?

Keep up-to-date with the latest industry news and receive the free weekly newsletter straight to your inbox

Register online at www.glass-international.com/e-newsletter Glass_Half_Page.indd 1

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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)

www.aluminiumtoday.com/furnaces/

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.

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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.

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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;

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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

www.aluminiumtoday.com/furnaces/

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.

Turbo 2 Treater ® Efficiency in Power HARDENING

BRAZING

TEMPERING

ANNEALING

BENEFITS: Short standard delivery time Rapid startup at customer site Capacity: 800 kg High heating rate by convective heating High quenching speed and directed gas flow High pressure gas quenching (12 bar) and automatic redirection of cooling gas flow High process reliability with Ipsen program control Vacu Prof 4.2

Ipsen International GmbH Flutstraße 78 | 47533 Kleve | Germany eMail: sales@ipsen.de | www.ipsen.de