Furnaces International Issue 3 by Quartz

HEAT TREATMENT

HEAT RECOVERY

STIRRING TECHNOLOGY

FLEXIBLE STEELMAKING

Fives Stein: Bespoke melting & conditioning technologies

Stara Glass: Advanced heat recovery for glass furnaces

Altek: Aluminium furnace stirring technologies

Tenova: Electric-free steelmaking

www.aluminiumtoday.com/furnaces/ Issue 3

VAS are the UK’s number 1 provider of products & services for the heat treatment industry. Boasting the most comprehensive engineers, VAS are the single biggest provider of services for both Vacuum Furnaces, & Atmosphere Furnaces. Now agents for the world’s largest furnace manufacturer, Ipsen, VAS are also able to provide the most technological advanced, & highest quality heat treatment furnaces. VAS not only boasts the most experienced furnace engineers within the industry, but are global experts in the following – 

Vacuum Furnace Repairs, Relines & Overhauls



Atmosphere Furnace Repairs Relines & Overhauls



Heat Treatment Relocations



New & Used Vacuum & Atmosphere Furnaces



Spare Parts for all Heat Treatment Equipment



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VAS have had the privilege of undertaking work on all manufactures of Heat Treatment Furnaces, such as Ipsen, Schmetz, Seco/Warwick, TAV, BMI, Wellman Etc... Using this to our advantage VAS has built a vast knowledge, & gained priceless experience which is why we are the number one heat treatment service company within the industry. For all enquiries please contact us on +44 121 544 4385, or Email - enquiries@vacat.co.uk

Contents

Regulars Comment News Heat recovery Advanced heat recovery for glass furnaces

4 5

ELECTRIC STEELMAKING

ORES AND MINERALS

How to achieve a sustainable casthouse

Process improvement with electromagnetic stirring

Advances in titania-magnetite ore processing on a blast furnace

Stirring technology Aluminium furnace stirring technologies

Heat treatment Bespoke melting and conditioning technologies

Investment Stolzle Flaconnage in ÂŁ17 million furnace upgrade

Heat treatment Aluminium nitriding solutions

Flexible steelmaking Tenova: Electric free steelmaking

Furnace design The self driving glass melting process

Thermal processing Hot wall pulsed plasma nitriding systems

Oxygen steelmaking JSW Steel: Converter vessel replacement

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ENERGY EFFICIENCY

ArcelorMittal

www.aluminiumtoday.com/furnaces/ Issue 2

Heat treatment Steelmaking: Heat treatment for bars

BIFCA column Top ten tips for improving efficiency in heat treatment

CASE STUDY

Front cover: TECO www.teco.com

22 39 Issue 3 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 Email: kenclark@quartzltd. com Subscriptions: Elizabeth Barford Email: subscriptions@quartzltd.com Managing Director: Steve Diprose Chief Executive Officer: Paul Michael Published by Quartz Business Media Ltd, Quartz House, 20 Clarendon Road, Redhill, Surrey RH1 1QX, UK. Tel: +44 (0)1737 855000. Fax: +44 (0)1737 855034. Email: furnaces@quartzltd.com Website: www.aluminiumtoday.com/furnaces/ Furnaces International is published quarterly and distributed worldwide digitally

4 r Furnaces International Issue 3

Comment I must admit, I was struggling to write my leader this time round – I couldn’t think of a ‘theme’. The obvious topic for any furnaces magazine is energy efficiency: after all, it’s the bread and butter of the industry at the moment; it is the thing that each and every manufacturer will be looking to you for, and it is arguably the single most important topic in the industry right now – perhaps cost of fuel aside, but you can go on and link that back to energy efficiency, so…. “But I wrote about that a mere two issues ago!” I cried. Well, after racking my brains, and determined not to repeat myself, and also after some discussion with my editorial colleagues, it suddenly occurred to me in a light-bulb moment – is there anything else going on?! I also work on Glass International, and here at Quartz Business Media we publish Steel Times International, and in both of these industries there are discussions raging around Industry 4.0, which, having originated from the ever-industrious Germany, is taking a variety of industries by storm. With it being events season I have attended a few conferences and exhibitions recently, and when I asked furnace manufacturers about this fourth industrial revolution, I

must say the response wasn’t overly enthusiastic. Is this something that furnace manufacturers should be focusing on more, or is it not entirely applicable? Surely, linking the data from the furnace to the overall data from the plant in an ‘internet of things’ is one of the next crucial steps for the furnace industry? The furnace is the beating heart of so many industries, and so logic follows that the data from it must be necessary to completing an overall picture of the ‘smart factory’ of the future – Perhaps not. At a recent trade exhibition I didn’t get any sense or urgency from those I approached on the subject. So the big question is: how do you feel about digital manufacturing, the so-called ‘internet of things’ and other aspects of smart manufacturing? Feel free to say what you think, and if your company is making any headway in this area – or you have a good reason as to why you feel it doesn’t need to – then do let me know: sallylove@quartzltd.com. I look forward to receiving your comments. Sally Love Editor, Furnaces International sallylove@quartzltd.com

www.aluminiumtoday.com/furnaces

News

Tenova Pyromet on track for 2017 PGM furnace handover High capacity furnace and

structures are also complete,

operate the furnace either as

and off gas handling plant, as

smelting plant specialist,

while the placing of the 12m

a submerged arc operation or

well as the furnace building

Tenova Pyromet has completed

diameter furnace shell marks

brush arc operation, and will

and all associated civil works,

50% of Northam Platinum’s new

another significant milestone,

therefore have a sufficiently

infrastructure and services.

platinum group metals (PGM)

with the site establishment

broad operating range to

furnace at its Zondereinde

of the mechanical installation

accommodate feedstock with a

that forms part of the technical

smelter operation in

contractor.

widely varying mineralogy.

solution includes Tenova

Thabazimbi, South Africa, The project has met all major project milestones to date. As a result, handover of a

The contract, which was

Tenova Pyromet’s scope on

State-of-the-art technology

Pyromet electrodes, copper

awarded to Tenova Pyromet

the project covers the PGM

cooling elements, and off gas

by Northam Platinum in

smelting furnace, feed system

handling and furnace controller.

2015, will support Northam

Ferrobamba and Tenova sign cooperation agreement

fully operational 20 MW furnace

Platinum’s planned growth in

will be on track in August 2017.

PGM production, which requires

Project milestones achieved

the flexibility to process high

include the first steel being

chromite, low base metal

raised on site in mid July 2015

and high sulphur contained

Ferrobamba has signed a

investment” stated Alfonso

concentrates.

cooperation agreement with

Navarro, CEO of Ferrobamba.

as per the scheduled date. This is the first of over 1,000

With Northam’s

Tenova to develop its iron ore

“Our company will be in a position to produce a premium quality DRI that is

tonnes of structural steelwork

pyrometallurgical approach

mine in the Aymaraes region

that will be used on the project.

and Tenova Pyromet’s technical

of Peru.

More than 20% of the civil

ability, Northam will be able to

New agent for Electroglass Electroglass has appointed Interglass, based in Guadalajara, Mexico, as its agent for Mexico, Central and South America. With its established position and reputation as suppliers to the

The company has chosen Tenova HYL Micro Module technology in order to oversee

not currently available in the region”. In fact, Ferrobamba’s

the technological design

Aymares Project is potentially

and provide the equipment

one of the highest quality,

to develop and build a

lowest cost iron ore projects

500,000t/y pelletisation plant

in the Americas with a

area’s glass industry, Interglass is sure to bring a valuable extra level

and a 250,000t/y DRI high

significant resource upside

of local support to Electroglass’s existing and new customers in the

carbon DRI plant.

potential of 3’400Mt of iron

region. Electroglass is an independent UK based company that specialises

‘‘The Tenova HYL Micro Module will allow our

ore. Iron ores will be first

in the development, design and manufacture of electric glass

company to add significant

crushed and pelletised and

melting systems and equipment.

value to our iron ore deposit

then processed to direct

in Aymaraes, producing high

reduction (DR) grade pellets.

Verallia in €22 million investment

carbon DRI with the proven

These pellets are fed into a

ZR (zero reformer) technology

Tenova HYL ZR Micro Module

used since 2010 in the

DRI plant where they are

Emirate steel.

reduced to metallic iron.

“The Micro Module uses

The DRI produced is the

Verallia, a container glass manufacturer that predominantly focuses

the same ZR technology

highest quality available with

on wine bottles, has invested €22 million in a new furnace at its

applied in Nucor’s Louisiana

high carbon content (around

Oiry site in France.

plant, but is one 10th of

4%) and can easily substitute

the size and allows junior

pig iron or high quality scrap

mining companies like ours

for use in the electric steel

to enter the DRI production

making operation, to produce

market with a limited capital

high grade steel.

Work is currently being undertaken to dismantle the current 515 tonnes per day furnace which will be replaced later this month. More than 350 workers will work on site with production of the first bottle from the kiln expected to begin in early October. The current 100m2 furnace has been in place for 12 years operating at 1200 degrees celsius for 24 hours a day. www.aluminiumtoday.com/furnaces/

Issue 3 Furnaces International r 5

News

CAN-ENG installs and commissions system for Metex Heat Treating

enhanced energy reduction design features achieved through the benefits of recuperative burner technology providing improved system efficiencies and reduced emissions. Founded in 1983, by Surjit Bawa P.Eng, Metex Heat Treating serves high volume, Tier 1 automotive manufacturers of stampings, fasteners and final assemblies in the Ontario, Quebec, Ohio and Michigan markets. From its three plants in Ontario, Canada, Metex processes over 60 million pounds of heat-treated product each year.

CAN-ENG Furnaces

commissioned for the hardening

wash systems and a supervisory

International has installed

and tempering of high volume

control and data acquisition

ENG Furnaces International

and commissioned a 6000lb/

fasteners and includes

(SCADA) system, integrating

has grown to become a leading

hour continuous mesh belt

a computerised loading

enhanced features to support

designer and manufacturer of

atmosphere furnace system

system, mesh belt controlled

compliance with CQI-9

thermal processing equipment

for Metex Heat Treating, of

atmosphere hardening furnace,

guidelines.

for ferrous and non-ferrous

Brampton, Ontario, Canada.

oil quench system, mesh belt

This new system was

tempering furnace, pre and post

The continuous quench and

Established in 1964, CAN-

metals.

tempering system incorporates

Horn Glass acquires ggENOx Horn Glass Industries has

Horn Glass, a German

manufacture and supply of

effective on the 1st January

successfully completed their

specialist in the design and

different furnace types for the

2016, and the two parties have

takeover discussions for

supply of complete glass

production of lighting ware,

agreed unanimously that sole

ggENOx technology.

melting technology is a

tableware, containers, cast

ownership of the system and

solution partner for the

glass, float glass, solar glass

its technology will be taken

worldwide glass industry.

and technical glassware.

over by Horn Glass.

ggENOx system is applicable on existing and newly built regenerative end-port furnaces

With its subsidiary

The range of products

This contract includes

and serves to considerably

companies in Czech Republic,

and services includes utility

complete transfer of

reduce NOx and save energy.

India, Malaysia and China,

equipment such as combustion

technological and commercial

Horn Glass matches the glass

systems and electric control

details as well as responsibility

international customers report

industryâ&#x20AC;&#x2122;s requirements for

equipment, modern process

for customer after-sale service.

highly satisfactory results of,

local and fast activities.

controlling with SCADA

Several European and

Future developments and

for example, NOx reduction of

With more than 125 years

systems of the highest

upgrades of ggENOx system

over 20% and at the same time

of experience in glass melting,

standard, as well as the design

will also be executed by Horn

significant energy savings of

Horn has a wide range of

engineering and site services.

Glass.

more than 2.5%.

expertise in the design,

6 r Furnaces International Issue 3

The contract became

www.aluminiumtoday.com/furnaces/

News

No new furnace, but profits jump expected for Hyundai Steel Co. A report in the Korea Herald

The paper is now reporting

The Dangjin Steel Mill

• Hyundai Steel Co is

suggests that Hyundai Steel is

that the original report was

operates three furnaces

expected to post a ‘significant

not planning to build another

groundless, based on comments

with a combined capacity of

jump in operating profits’ for Q2

furnace at its Dangjin steel mill,

from Hyundai’s public relations

1.2Mt. One of the furnaces

2016 with an operating profit

having previously reported that

department. The story now

has experienced temperature

of 406 won, up 51%, according

the steelmaker was considering

is that a problematic furnace

maintenance problems since

to HMC Investment Securities

another furnace to be put into

at the plant will be fully

last month. The furnace in

projected on 16 June.

action within two to three

operational again by the end of

question became operational in

years.

the month.

January 2010.

Source: The Korea Herald.

Vetrotex repairs at Litomysl Heye completes quad gob job in Mexico Vetrotex, part of the SaintGobain family and producer of glass fibre, has extended the capacity in one of its three furnaces in the Czech Republic. The furnace was repaired

capacity during this repair by 10,000 t/year. The new furnace has been equiped with the latest Vetrotex fiberglass yarn technology. A total of 37M€ has been

after having reached the end

invested in furnace repairs

of its lifetime.

and capacity extensions in

In order to keep up with increased customer demand,

the Czech plant over the past two years.

Vetrotex extended the

The Heye glass plant team in Monterey, Mexico has completed work on a quad gob production job. Quad gob productions are always challenging and require a highly experienced production team. Heye contributed the machine belt, including the new highspeed servo-pusher type 2158 with three servo axis. The optimised motion profile results in a parallel pusher movement to the conveyor belt. Most of the movable parts are located below the machine conveyor level inside the pusher housing, protecting them from environmental influences such as heat and dirt.

Grieve releases 1400°F box furnace The furnace, No. 863, is an

The unit has 7” thick

electrically heated 1400°F

insulated walls with stainless

(~760°C) box furnace from

steel covers and the oven

Grieve, currently used for

was specially built with inert

preheating moulds.

atmosphere construction.

52KW are installed in nickel

This consists of a

chrome wire coils supported by

continuously welded outer

a stainless steel frame.

shell, high temperature door

A heat resisting alloy

gasket, sealed heater terminal

recirculating blower is powered

boxes, inert atmosphere inlet

by a 7½ HP motor with a V-belt

and inert atmosphere outlet.

drive. The blower provides upward airflow to the oven. Workspace dimensions are

Controls onboard No. 863 include a motor-operated vertical lift door and a 4-point strip chart recorder.

30” wide x 48” deep x 30” high. www.aluminiumtoday.com/furnaces/

Issue 3 Furnaces International r 7

Heat recovery

Advanced heat recovery for glass furnaces Alessandro Mola, Giorgio Minestrini, Ernesto Cattaneo, Francesco Prosperi and Giampaolo Bruno*, Stara Glass

Centauro, Stara Glass’s latest furnace technology, has been installed in four container plants in Europe and has been applauded by manufacturers for the energy savings it offers. Here, the benefits of this heat recovery system for glass furnaces are discussed. Centauro is a hybrid heat recovery system for glass furnaces patented by Stara Glass that allows manufacturers to obtain the thermal performance of a regenerative furnace even in plants that do not allow the setup of properly dimensioned regeneration chambers. Centauro consists in a double stage heat recovery system, regenerative for the higher temperature part and recuperative for the lower temperature part, with a continuous metallic recovery system downstream to a ceramic one. Furthermore, with Centauro it is possible to recover all the useful heat stored in waste gas with the production of hot clean air, expelling waste gas at the most convenient temperature. The furnace may also be sized so as to allow the installation of an SNCR system. From an energy point of view, a glass furnace is a device that absorbs energy through fuel combustion and/or electric power to melt glass. For this reason, the way to push the furnace efficiency to its highest level is to take advantage of all the heat provided, with the benefits of reduced plant managing costs, emissions and pollution. In order to achieve this goal, it is necessary to analyse where and how the incoming heat goes. As a first analysis, the main output results of a glass furnace heat 8 r Furnaces International Issue 3

balance (80-95% of total output heat) are: • Heat provided to the glass for endothermic reactions, water evaporation and glass temperature increase; • Heat loss through the structures; • Heat lost with the waste gas flow. The first point depends mainly on the type and quality of the glass, the cullet percentage used in the batch, crown and bottom temperatures and batch humidity, all of which cannot be easily reduced. As for the second point, the heat losses have to be limited with a proper structural insulation, but the insulation costs and the expected furnace life have to be considered as well. What certainly can be done to improve the furnace performance relates to the final point, which is to take advantage of the highest quota of heat stored in waste gas, first of all, to preheat combustion air. It is not possible to take advantage of all the heat contained in waste gas to preheat combustion air, as there is more heat than combustion air can store. In fact, introducing the concepts of heat and temperature efficiencies as: ηh = Heat pre-heated air / Heat waste gas = Ta ∙ Ca ∙ Ma / Twg ∙ Cwg ∙ Mwg ηt = ηtemperature = T combustion air / T waste gas www.aluminiumtoday.com/furnaces/

Heat recovery

Temperature (C)

consideration: analysing the trend of the air and waste gas temperature in a regenerator, it is evident that the chambers work for a large part of the height (about 60%) at a preheated air temperature lower than 800°C, which is compatible with a metallic exchanger (Fig. 1). It is subsequently possible to assume that an important part of the refractory heat exchange system could be substituted with a simple, cheaper, and more flexible metallic exchanger.

Chamber height (%)

while ηt may ideally tend to 1, so Ta = Twg, ηh cannot, because it results in Ca < Cwg and Ma < Mwg. The common limit values of ηh are 0.70 ÷ 0.72. This means that 28–30% of waste gas heat cannot physically be transferred to combustion air and it is therefore important to find another way to take advantage of it. If the energetic performance of regenerative and recuperative solutions respectively are compared, by considering, for the sake of convenience, a furnace heated by fossil energy solely (neglecting the ordinary structural differences), it shows that in the same product, i.e. pullrate and quality, the consumption of a Unit Melter is higher than those of regenerative by more than 30%. The most obvious aspect is the preheated air temperature that for an end port reaches between 1100 and 1300°C, and for a unit melter is about 500°C lower. As a result, in a recuperative furnace the performance is strongly penalised by the high temperature of the waste gas at the recuperator outlet, on average 400°C higher than that in a regenerative. Therefore, with the intent to push heat recovery technology as far as possible, we have to start from a regenerative solution and improve it. Centauro is a hybrid regenerativerecuperative heat recovery system that allows the performance of a regenerative system without the need for huge civil works, and also the highest possible quota of heat stored in waste gas. The idea originates from the following www.aluminiumtoday.com/furnaces/

Fig. 1: Typical temperature trends in a glass furnace regenerator.

The five advantages of Centauro are: • Lower overall vertical dimensions of regenerators; • Additional clean hot air stream available (additional free thermal power); • Extreme flexibility in layout design, both on the height of where to ‘cut’ the chambers and where to place the recuperator; • The hybrid solution allows the ceramic part to work in the same conditions as the upper part of usual regenerators, avoiding plugging problems and guaranteeing the best heat exchange performances. This moves the sulphate compounds condensation to the metallic part, where it is more simple to intervene; • Correct window temperature, in a proper zone, that allows for the installation of an SNCR system. Some aspects that qualify Centauro are: • A recuperative furnace can be upgraded to regenerative performance with reduced impact; • A regenerative furnace with undersized chambers can have its performance optimised with the setup of a bottom metallic recuperator; • Double-pass regenerative furnaces can work without the secondary chambers by substituting them with a metallic recuperator, avoiding all the related problems of low efficiency and plugging. Centauro also offers an opportunity to improve the efficiency of the glass Issue 3 Furnaces International r 9

Heat recovery

production plant. By oversizing the air flow through the metallic heat recovery system and taking out the excess air prior to the refractory section of the system, it is possible to extract an important additional part of the thermal energy stored in waste gas. This reduces its temperature to the lowest required level (usually about 200°C, to avoid acid condensation, instead of the 450-600°C typical of a regenerative furnace, or temperatures of 900°C and more for recuperative furnaces). This means the additional energy will be available as a hot, clean air flow, easily extractable at the end of each stage of the metallic part of the recovery system, which can be useful both in process and in services (Fig. 2). It is convenient to add a convective heat exchanger (Fig. 3) to optimise the thermal exchange in the lowest temperature area. This type of component guarantees a high efficiency at low thermal levels and noticeable design flexibility. The required maintenance operations (performed for a few days each year with the unit by-passed) do not affect the plant’s energy efficiency. Another important feature of the Centauro system is the possibility of installing a non-catalytic system for NOx abatement. 10 r Furnaces International Issue 3

Fig. 2: Example of Centauro thermal, energy and mass profile.

Contact *Stara Glass, Genoa, Italy www.staraglass. com

The problem of nitrogen oxide production in high temperature combustions, such as happens in regenerative furnaces, is important and the laws surrounding NOx emissions are more restrictive. The catalytic abatement of NOx by SCR technologies is always a possiblity, but it implies high managing and investment costs for the plant, related to the installation of a catalyst reactor. Non-catalytic abatement (SNCR), on the other hand, is not applicable to regenerative furnaces, because the reaction has acceptable efficiency only in a certain temperature range of waste gases (Fig. 4), available only inside the checkers, where it is not possible to inject the reactant. Centauro’s thermal profile can be designed to have a temperature between 750-900°C in the waste gas duct that connects regenerators and recuperators. That allows the non-catalytic abatement (SNCR) of nitrogen oxide by a simple injection of aqueous solution of ammonia or, more conveniently, urea, without big plant investments and operating costs. The NOx emission level can be reduced to a low level (below 300mg/Nmc) by managing a proper quantity of reactant.

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Heat recovery

Five Centauro furnaces were installed between 2008 and 2016:

Fig. 3: Constructive elements of Centauro.

Case study 1: double pass end port conversion The Bormioli Luigi furnace in Abbiategrasso, Milan, Italy in 2008 represents the first example of Centauro. The furnace, which produces extra-white perfumery ware, comes from the rebuilding of a doublechambered end port, in which the second chamber was substituted by the typical metallic part. Case study 2 and 3: unit melter conversion

Fig. 4: SNCR for Centauro furnace.

O-Iâ&#x20AC;&#x2122;s furnace No.4 in San Polo, Italy, 2011. The former unit melter furnace, which produced coloured glass for containers, had to be completely rebuilt. Due to the land situation, a deep excavation for a transformation to a standard end port furnace was not applicable. Thanks to the advantages offered by Centauro, the bottom floor of the regenerators is only 1.5m below the machine floor. During 2014, a second unit melter furnace in the same plant was converted to a Centauro, achieving the same results.

Case study 4: unit melter conversion The Seves Vitrablok furnacein the Czech Republic in 2014 produces flint glass for glass brick production and was transformed from an existing recuperative furnace. Case study 5: greenfield Centauro The Vetreria Etrusca furnace in Savona, Italy earlier this year is the fifth example of the advantages that the Centauro furnace offers and is the first Centauro built on greenfield land. The furnace, startedâ&#x20AC;&#x201C;up in January 2016, produces flint glass for special and high quality bottles. The company chose this solution for its energy and environmental advantages (the SNCR system in particular), despite not having any layout constraints in terms of land space. r

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Issue 3 Furnaces International r 11

Heat treatment

Steelmaking:

Heat treatment for bars Danieli Olivotto FerrĂ¨ has supplied a heat treatment furnace for bars to be supplied to top quality steel producer ABS. In February 2015 Acciaierie Bertoli Safau (ABS) contracted Italian steel technology specialist Danieli Olivotto FerrĂ¨ to provide engineering, manufacturing and installation of a new bar heat treatment at the steelmakerâ&#x20AC;&#x2122;s Cargnacco plant. The Cargnacco facility anneals, tempers, normalises and stress relieves 6,000 tonnes/month of a wide range of bar profiles, from smaller bar bundles (25 mm) up to single 600 mm diameter bars. Lengths are variable, ranging from 3m to 14m while all steel grades are covered, from low carbon to high alloy. The line consists of six bases and two direct firing lift-off type furnaces that function by means of

12 r Furnaces International Issue 3

burners fed with natural gas; two lift-off cooling hoods incorporating a cooling system; a crane for liftoff handling; a waste gas exhaust system including six damper valves and ducts to one common natural draught chimney; an electrical power distribution system and a Level 1 control system supplied by Danieli Automation. According to Danieli, important technological improvements were made including low fuel consumption and reduced emissions. Improved chamber temperature uniformity in order to achieve Furnace Certification AMS 2750 was also implemented into the plant design. The modular batch design of the plant leaves room for future

expansion and includes high efficiency and state-of-the-art combustion technology. Userfriendly loading procedures and bar positioning, easy access for inspection and maintenance also give rise to a safer plant. Danieli reports that annealing and normalising cycles demonstrated a 20-30 % decrease in gas consumption compared with previous generation furnaces (at the very start of the commissioning phase). r

Contact http://www.danieli.com/en/ worlwide/business-units/danieliolivotto-ferre.htm

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Stirring technology

Aluminium furnace stirring technologies Rob Morello*, Altek

Fifteen years ago the issue was ‘do you need to stir a furnace?’ rather than ‘what to stir it with’. Advances in stirrer technology, however, has led to a different way of thinking in the present day. This article will examine why melting furnaces need to be continually stirred, and then look at why one electromagnetic stirrer is not necessarily the same as the next. air cooled linear induction and also permanent magnet stirring and pumping technology). In 2004, Altek undertook a detailed study of permanent magnet stirring and pumping technology in association with the Institute of Physics in Latvia.

Fig. 1: Furnace heat transfer diagram.

Over the past fifteen years the industry has witnessed a proliferation within the field of stirring technology for melting and holding furnaces. This increase in available technology has culminated in a situation where it is sometimes difficult to see ‘the wood for the trees’ when selecting the appropriate technology for your furnace. Altek has been ever present during the evolution of furnace stirrer technology and as a result has been involved with all types of pumping or stirring technology (metallic graphite pumps, EMP, mains frequency linear induction technology, low frequency 14 r Furnaces International Issue 3

Why continually stir a furnace? A furnace should be stirred to assist the melting of scrap within an aluminium melting furnace. When considering what the electromagnetic stirrer is doing in terms of assisting the melting of scrap within an aluminium melting furnace, it is sometimes easier to relate it to the ‘Iceberg’ with the submerged scrap. If the scrap never became submerged within the aluminium bath then there would be no need to stir the metal, as radiated heat to the exposed scrap is the most efficient mode of heat transfer. The exposed scrap pile at the beginning of a melting cycle is ‘melted’ by means of the well-known radiated heat transfer (Q) effect from the burner and the hot refractory (T⁴ effect). Qtot = Qrad_gas + Qrad_wall (Fig. 1). If we take the typical dry hearth melting furnace represented in Fig. 2, you can see the effect of the scrap pile from its initial charge, reducing as the liquid heel develops www.aluminiumtoday.com/furnaces/

Stirring technology and part of the scrap is submerged. In some furnace operations this is done through successive charges (laying scrap on the sill to pre-heat and then push into the bath as it develops, typical of many extrusion melting furnaces for example). This submerged part of the scrap pile has a colder outer boundary layer that insulates the scrap from the warmer bath (heel). The aluminium bath has its hottest aluminium at its surface (due to the heating effect of the combustion space above it) and becomes colder the lower you go in the bath. Without stirring, the submerged scrap would take a very long time to melt down as it relies on conduction and convection heat transfer.

Why choose an electromagnetic stirrer? Stirring the bath breaks this limitation and the heat transfer is greatly increased by convection effects. This is valid if the stirrer technology in place generates a horizontal flow pattern. The electromagnetic (EM) stirrer uniquely utilises the relatively high density and low viscosity of aluminium to generate lots of eddy currents in the melt. This creates a turbulent flow mixing the melt also in the vertical direction. This strong ‘mixing’ has several positive benefits: 1. The heat penetration depth into the aluminium bath is increased and consequently the melting performance will be improved. 2. The bath surface is ‘cooled’ down, increasing the temperature difference between melt and roof and the heat-pick up (Stefan Bolzman equation) leading to a better utilization of the energy from the burners. 3. In addition, this colder bath surface is

less prone to oxidation, thus reducing dross generation. To achieve these benefits, the following conditions must be met: 1. There must be liquid, which can be stirred. 2. The liquid must be super-heated, otherwise it cannot melt other metal. 3. The stirrer must not be blocked by solid metal. With the stirrer, the thermal stratification differences inside the aluminium bath are usually very quickly equalized as Fig. 3 correctly shows (some graphs published show an equal trend of the lower and upper temperatures, which is not correct).

Can you have any stirrer on any furnace? Clearly the furnace type is an important factor in determining which stirrers are

Fig. 2: Generation of a liquid heel on a dry hearth melting furnace

Fig. 3: Graph showing the rate of temperature homogeneity between the top and bottom of the bath in a 65T melting furnace.

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Issue 3 Furnaces International r 15

Stirring technology incorrect assumption as the flow patterns have significant variations. A water cooled stirrer has quite a different flow pattern in the bath compared to air cooled stirring technology, due to the design of the coil and the method of driving the current to the coil. Permanent magnet stirrers also have quite different flow patterns, as these are revolving drums that have a continual and fixed magnetic flux intensity.

Fig. 4: Altek bottom mounted electro magnetic stirrer.

appropriate for an application. A round top charge furnace with a basement would utilise any of the bottom mounted stirrers whether tilting or static, if tilting furnace certain systems would not be appropriate from an installation or practical operational point of view (Fig. 4). Stationary furnaces with no basement would require side stirring, and there are a variety of different products available for that application (Fig. 5). It is important to look at the stirring pattern, the starting heel requirement, the ability to control in the cycle at different intensities, space availability around the outside walls of the furnace, clearance and access requirements for maintenance and installation and impact zone of the magnetic field. Side well furnaces can benefit from conventional pumps and also allow for side stirring technology to be applied quite successfully. Again, the location of the stirrer to ensure the correct flow pattern (to maximise the impact of melting the scrap), and mixing the bath for homogeneity, are both important factors to consider, along with many identified in the previous paragraph. Twin and three chamber furnaces tend to utilise pumps for flow between the two chambers, but stirrers have also been used to aid further homogeneity through the whole bath depth to ensure effective heat flux in the metal being transferred by the pumps. It is a common misconception within the industry that all stirrers have the same stirring pattern in the furnace. This is an 16 r Furnaces International Issue 3

Why is the flow pattern within the furnace important? The flow pattern is important when aiming to achieve certain objectives within the furnace, whether this be for melting scrap, alloy additions or simply mixing the metal to gain homogeneity. Each device can deliver quite a different result. Linear flow, as depicted in Figs. 6 and 7, is far more effective at melting scrap, and by carrying the frequency of the applied 2 or 3 phase current to the inductor it allows for both the speed of flow and the intensity of flow to be varied during the cycle. Types of Stirrers • Water cooled induction stirrer (low frequency 0.2 to 2Hz) • Air cooled induction stirrer (low frequency 0.2 – 2Hz) • Water cooled induction stirrer (mains frequency – 50/60Hz) • Electromagnetic pump (mains frequency – 50/60Hz) • Permanent magnet stirrer

Fig. 5: Altek side mounted electromagnetic stirrer.

The big difference in the induction stirring units is their operational frequency. For the inductor’s magnetic flux field to

Stirring technology

electromagnetic stirring is issues surrounding safety and maintenance. Removing the water cooling requirement of conventional stirrers from the basement area under or next to a furnace has provided operators with peace of mind if there was ever a furnace break or leak. Fig. 6: Typical linear Water cooling systems are also prone flow pattern on an Altek bottom mounted to leaks and build-up of deposits in the linear electromagnetic pipes which, should failure occur, would inductor. cause major repair work and downtime. Operations that have traditionally used water cooled stirrer have now moved over to air cooled stirrer technology for these reasons alone, or in addition to its ultra-low energy usage. Fig. 7: Typical linear flow pattern on an Altek side mounted electromagnetic inductor..

penetrate the full refractory thickness of a standard furnace and the physical stainless steel plate, this needs to be a low frequency type device (air or water cooled). These devices can penetrate refractory/steel combined thicknesses in excess of 700mm and still deliver a powerful magnetic field in the aluminium bath, of which there are many examples of this around the world. The higher frequency devices will have to work through much thinner refractory thickness (in some cases only a ceramic plate of 50mm thickness), to enable full penetration of the magnetic flux field into the bath. This clearly gives furnace safety and potential overall integrity issues. The permanent magnetic field strength is defined by the type of permanent magnets that are installed onto the rotating drum. There are a wide variety of permanent magnets commercially available in the market and the choice of correct magnets is an important consideration, as this will determine both the strength of the magnetic flux field but also the operating temperatures that the device can withstand without irreversible magnetic field decay.

Safety considerations One of the main reasons the industry is beginning to turn towards air cooled www.aluminiumtoday.com/furnaces/

Installation considerations When considering installation, it is important to establish the location relative to what you are trying to achieve and what space is available. Common aspects to then consider on the different technologies are: • Can I vary the flux intensity during the cycle to suit the particular part of the cycle time, to gain maximum efficiency from my investment on my particular application? For example, the permanent magnet technology is based on a fixed array of magnets located on a drum, so has a permanent field that cannot be varied or tuned. • Can I increase the frequency of the field and thereby the speed of flow in the furnace? • Will the magnetic flux field decay or change over time or with temperature? • Will temperature have an effect on the stirrer? • Safety considerations around the stirrer Issue 3 Furnaces International r 17

Stirring technology

(particularly side stirrer installations) due to the magnetic field. There is a natural decay of the EM field around linear inductors as they are closed type inductors unlike the ‘open’ permanent field in a PM device which will interact with all objects surrounding it. • Cooling systems – how to organise and manage the impact on the stirrer of any unforeseen high temperature events over the furnace life or construction (copper, insulation, magents/magnetism etc,) • Do you need the stirrer to work on multiple furnaces? Altek has designed its electromagnetic stirrers in such a way that makes them extremely versatile, enabling them to potentially be installed on any type of furnace regardless of size or thickness of refractory. This is possible due to the unique design of the air-cooled, low frequency (0.2 – 1.5 Hz) inductor and the way the magnetic field is developed as mentioned earlier for it to be effective as both a side mounted unit or a bottom mounted unit. When choosing a correct location for the stirrer it is important to look at the stirring pattern required within the furnace, the type of furnace operation (dry hearth or heeled), ultimate bath depth, type of scrap to be charged and where it is charged, the ability to control in the cycle at different stirring intensities, space availability around the outside walls of the furnace (for side mount type), or available space in the basement, clearance and access requirements for maintenance etc. (Figs. 8 & 9).

Fig. 8: Altek’s bottom mounted TYPE 700 furnace to work through 750mm refractory floor.

Contact

*Rob Morello, Technical Sales Engineer & Marketing Manager, Altek www.altek-al.com

Fig. 9: Altek’s Type 500 stirrer in tunnel beneath multiple furnace operation.

misapprehension about energy usage in linear electromagnetic stirrers being very high, and having very high electrical operating costs as a consequence. This is true of the water cooled stirrers which do use considerably more electrical energy than the modern air cooled stirrers. As a typical rule of thumb, the electrical energy cost for the Altek stirrer is about €10 to €15 per furnace melt cycle, so this is irrelevant in the scheme of the savings that can be obtained per furnace cycle with such technology. Recent data from some of the Altek installations has shown energy savings (gas) of between 10 to 15% per cycle, providing a return on investment for those implementing Altek electromagnetic stirrers.

Concluding thoughts Modern low energy air cooled linear induction stirrer technology provides a very versatile device for stirring almost all types of aluminium melting or holding furnace. With operating energy costs almost negligible in the context of the energy savings attainable, and the flexible ‘in cycle’ controllability of stirring speed, magnetic flux and power, these stirrers provide a very efficient tool for the aluminium cast house to increase productivity and efficiency. With the low energy costs, associated safety benefits of not having water under the basement of a furnace (those people that have had leaks or bleed outs under the furnace due to hearth failures will know this well), and powerful circulation, understandably the take up in this technology is very strong. r

Operating cost considerations There can also sometimes be a 18 r Furnaces International Issue 3

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Heat treatment

Bespoke melting and conditioning technologies Andrew Reynolds*, Fives Stein Ltd

Andrew Reynolds* discusses how tailored solutions can provide the best option for manufacturers looking to increase performance and reduce total cost of ownership.

Fig. 1: Working-end for container glass (BHF 400/4000 Technology) available with Prium PlanerTec system for increased thermal homogeneity and improved fuel efficiency.

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Heat treatment

Fig. 2: CFD Modelling of PlanarTek Burner System.

Fig. 3: CFD modelling is used now in most projects to tailor and verify design details.

In the field of glass manufacturing, every producer has his own idea of what is special or unique, what makes their product different from the competition, and what particular issues they face in manufacturing and selling their product. In the context of this article, we refer to special and non-special glasses. By ‘special’ we generally refer to glass types manufactured in lower-volume, often resulting in a higher-value/kg product. That is not to say that considerations and technologies applied to special glasses are not also relevant for ‘non-special’ glasses, i.e. container, architectural float, etc., especially in a world of increasing focus on energy efficiency, life and quality.

High-volume production (container) Fives is well recognised for its ability to supply complete float production lines through its main glass engineering subsidiary, Fives Stein SA, in France. Fives Stein Limited in the UK leads the non-flat glass sectors, principally container, fibre, insulation products, tableware, cosmetics, and pharmaceutical. Within the container industry, Fives Stein UK’s main business activity involves supply of conditioning technology (working ends and forehearths) through the company’s BH-F ancestry. Conditioning in this sense www.aluminiumtoday.com/furnaces/

means removing heat from the melt whilst establishing and retaining thermal homogeneity. This business is still central to Fives and recent developments have been targeted at updating proven BHF 400/4000 Series technology. The introduction of new nozzlemix and slotted flame burners (Prium PlanarTek burner system, Fig. 1) and the ability to offer heat recovery on forehearth combustion (Fig.2) has given a significant boost to achievable performances. The first of these updated systems have now been in operation long enough to prove the benefits in terms of glass homogeneity and fuel consumption. A key factor in these successes is that systems are not ‘out-of-the-box’, but rather tailored to a client’s particular needs. We prefer to engage with end-users about Total Cost of Ownership (TCO); improving performance may have an initial cost, but this is frequently paid back in multiples by improved performance. A strong clientsupplier relationship is required to promote understanding and ensure the best final result is achieved.

Melting technology Although willing and able to offer melting (furnace) technology for container glasses, this is not the focal business of Fives Stein UK; instead we chose to specialise in technologies for ‘special glass’ sectors, often providing a greater opportunity to apply our core melting expertise. Just as the conditioning technology in Fives comes from our BHF legacy, melting technology is derived from the company’s other historical connection, Penelectro, a leading supplier of electric melting and boosting technology, which merged with Issue 3 Furnaces International r 21

Heat treatment

Fig. 5: Secondary refiner used for delivery to float tin bath (cover glass).

Fig. 4: Section though furnace for melting basalt for fibre production; design specialised combustion system with heat recovery and supplemental electric heating immersed electrodes.

BH-F Engineering to create Fives Stein Limited in 2008. Since then, and with a close coupling of resources within Fives Stein SA and other parts of the Fives Group, the company has developed its melting expertise to include air-gas, oxy-gas and oxy-oil technologies. Fives has invested significantly in research and development aided by strategic alliances with customers and with other engineering and technology providers. Working with partners such as Celsian Glass & Solar has grown our understanding of melting processes though laboratory melting trials and CFD modelling programmes (Fig. 3). Partnerships with end-users has allowed us to hone technical plant in-situ to best suit a clientâ&#x20AC;&#x2122;s needs. These work programmes have resulted in the development and launch of new designs of furnace and ancillary systems (including complete hot-end solutions encompassing both melting and conditioning technologies).

Case study 1: Low transmission glasses The production of foam glass (for insulation or related construction fields) involves a two stage process: (1) production of cullet with high-sulphate and iron content; 22 r Furnaces International Issue 3

(2) mixing of the cullet with carbon and reheating to initiate a foaming reaction. Production of the cullet in the first stage requires a particular approach. The molten glass has extremely poor heat transmission characteristics, making the use of indirect gas-heated systems impossible. The use of electric heating through electrodes is also problematic, as the highly oxidized glass is corrosive to molybdenum (the most practical electrode material) and highgassing levels makes a stable batch layer difficult to establish. In 2015, Fives Stein UK was contacted by Pittsburgh Corning Europe to design and build a new foam glass melting facility in the Czech Republic. Supply scope included batch plant and melting furnace. PCE also wished to apply a new process for producing the cullet at the first stage. The solution proposed by Fives Stein was an innovative combination of electric-boosting, air-gas combustion and specialised waste gas treatment. A new type of forehearth arrangement also had to be designed to suit the cullet forming machinery and particular thermal characteristics of the glass melt at low temperatures, and again combined heating technologies were adopted. After one year of successful operation, the technical solution has been proven to the clientâ&#x20AC;&#x2122;s complete satisfaction. The production of reinforcement fibre from basalt (rock) presented an even greater challenge, as the melt heat transfer www.aluminiumtoday.com/furnaces/

Heat treatment characteristics are worse than foam glass. Here again, a combination of electric and gas-fired technologies resulted in success. Standard combustion and electro-boosting methods were not applicable and so Fives Stein designed a completely new type of nozzle mix high intensity combustion system (Fig. 4).

Case study 2: Use of multiple chambers Most modern furnace designs utilise a single chamber to achieve melting, fining (de-gassing of melt) and re-fining (reabsorption of small bubbles). In these furnaces however, mixing (recirculation) between processes occurs, the extent of which is dependent on the design (for example the effectiveness of the ‘thermal barrier’). This factor ultimately limits achievable glass quality and is the reason why furnaces have relatively large Geometry Residence Times (GRT) compared to the shorter theoretical times required to complete fining and refining. Idealised conditions where glass can be refined in much shorter times can only be achieved by physical separation of melt/ fining and refining processes. Faced with multiple requests to design systems to offer high-alumina or borosilicate cover glass, Fives Stein has developed secondary refiner technology (Fig. 5), where refining processes are performed outside the main melting chamber. These systems are designed to accommodate quite precise inlet and outlet conditions and must be properly matched to the downstream processes. Again, these projects have been implemented in close collaboration with end-users, even as far as managing joint CFD modelling programmes to determine optimum design and operational parameters. Case study 3: Heat recovery on oxy-fuel Combining electric boosting at a relatively high level into a furnace using oxy-gas is no longer a new approach. The use of boost dramatically increases the overall energy efficiency of the system, reduces emissions and improves product quality and output flexibility. Improving the ability to control where electric heat is applied can allow www.aluminiumtoday.com/furnaces/

optimisation of the furnace conditions (and combustion efficiency), but there comes a point where further gains can only be realised by applying some form of heat recovery to the combustion system. Driven by specific clients’ needs, expressed in the drive to reduce fuel and oxygen usage, Fives has developed and applied the patented Heat Recovery Area (HRA, Fig. 6) which, after extensive model analysis, is now operating on the first installation melting high quality neutral borosilicate.

Contact

*Andrew Reynolds, Managing Director, Fives Stein Limited, UK. www.fivesgroup. com

Conclusion The key message of this article is that, whereas standard (off-the-shelf) solutions often provide the lowest project capital cost, a more precisely tailored solution to meet a project’s ambitions can often reduce the TCO. Projects involving ‘special’ glass types often have particular criteria that lend themselves to the application of solutions utilising electric, gas and oxyoxygen technologies. If applied sensibly, with proper contingencies to manage technical risk, the integration of new, innovative technologies offers interesting and credible commercial as well as technical solutions. With this approach, Fives aspires to build project specifications and designs that more closely align with clients’ ambitions. Of course, the ultimate objective of every project is to find the right compromise that reduces TCO whilst maximising performance and product quality. Bespoke solutions, arrived at by the proper collaboration between supplier and end-user, has to be the best way forward. r

Fig. 6: The HRA can achieve 10% saving in fuel consumptions without any significant detriment to cost.

Issue 3 Furnaces International r 23

Investment

Stölzle Flaconnage

in £17 million furnace upgrade

Stölzle Flaconnage in Knottingley, UK is currently undergoing a furnace revamp as part of a £17 million investment.

The shutdown of the furnace at Stolzle began on July 4th and the furnace will be back in operation on September 1st. The new 175 tonnes per day furnace will pull glass on 65 metres2 and, as before, two out of the five flint production lines will be capable of feeder colouring. The rebuild is part of the company’s strategy to develop the Knottingley site into a dedicated prestige and luxury spirits factory. As well as the furnace rebuild there will also be modifications on its hot and cold end facilities. Two new modern IS machines will contribute to the quality level and increase the company’s portfolio. The upgrade of one cold end line with new inspection technology, article handling and fully automated palletising follows the company strategy to be the number one partner for the prestige spirits industry. 24 r Furnaces International Issue 3

Substantial improvements to the plant’s water, energy and compressed air supply will also be realised to ensure high energy efficiency and an environmentally friendly operation. There will also be further developments to the company’s decoration capabilities such as new printing devices, capable of more colours as well as alternative technologies. Further automation projects will be realised as part of the company’s improvement process in order to be more flexible and competitive. r

Contact www.stoelzle.com

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Heat treatment

Aluminium nitriding solutions Keith Watkins, GW Consumables

RGB has shipped a large gas nitriding furnace to Texas, USA. The gas nitrider is used for nitriding extrusion dies for extruders across the United States. Keith Watkins* explains.

gas nitriding furnace is used to form a very hard surface onto extrusion dies. Both brand new dies and used dies are nitride between each use, as they get older. This is normally carried out in a 535oC ammonia rich atmosphere. Nitriding is initiated when gaseous ammonia is cracked or “dissociated” using a steel surface as the catalyst at about 480oC. Active nitrogen produced during this reaction moves into the surface of the steel and combines with Chromium and other alloy constituents to form their respective “nitrides”. RGB has built and supplied the furnace in association with Thermserve Ltd, of Telford, UK. Furnace characteristics include PLC/ HMI control for fully automatic operation. Mass flow control is incorporated for accurate nitriding potential function; along with an accurate ammonia gas analyser. Multi-programme recipes are included and the furnace is equipped with fast cooling, hydraulic lid and complete dissociation control. In the business of aluminium extrusion, the extrusion die is arguably the key production tool. If the die does not perform to its optimum, then the efficiency and profitability of the extrusion plant is reduced. RGB Ltd has been able to make enhancements to the control philosophy and software to provide end users with fully www.aluminiumtoday.com/furnaces/

Fig. 1: Extrusion dies loaded into gas nitrider.

automatically regulated systems. Efficiency and profitability are established by continuous extrusion of sections, which are to size specification, with acceptable surface finish and fulfil order commitments in the minimum time. If the die shows premature wear or surface damage then this flow is interrupted, resulting in lower plant efficiency. Die reliability is essential. There are a number of factors affecting die performance; some concerned with the quality of the die itself and some concerned with die management and extrusion practices. Issue 3 Furnaces International r 25

Heat treatment Die quality - major factors • Die design • Steel selection – analysis (H13, H11 etc) • Steel cleanliness • Die bulk heat treatment • Die surface hardening. Extrusion practices - major factors • Extrusion temperature • Extrusion speed Die management – including cleaning, correction and die pre heating Die pre heating is an extremely important factor regarding conservation of the quality of the nitride case. Ideally, it should be in a specially controlled atmosphere die oven for a maximum of eight hours. There are many published papers and points of view on all these important factors, and as a supplier to this industry, it is important to have a reasonable understanding of the issues involved in the extruding of aluminium, especially where they impact on the performance of the product supplied. All of the production factors listed above can have dramatic effects upon die performance and many can reduce the effectiveness of any surface hardening treatment. There are a number of die surface hardening techniques and while many have been tried and discarded some are still being used. These include Hard Chromium plating, Ion implantation, TiN and other exotic ceramic combination coatings. However, possibly due to its apparent simplicity, cost effectiveness and robust nature, the gas Nitriding process has established itself as one of the most cost effective solutions to increasing die life and performance. It is used extensively as an “in–house” process and there are now a number of suppliers of such equipment. The understanding of the physics and thermodynamics of the Nitriding process has increased tremendously since its original “discovery,” probably when steel blades were quenched in urine; the blade

26 r Furnaces International March 2016

Fig. 2: Gas nitrider under manufacture in Telford, UK.

edge was found to have that something special compared to normal water quenching (possibly the aroma!) due to effect of dissolved Ammonia.

Nitriding Nitriding is initiated when gaseous Ammonia is cracked or “dissociated” using a steel surface as the catalyst at about 480°C. Active Nitrogen produced during this reaction moves into the surface of the steel and combines with Chromium and other alloy constituents to form their respective “Nitrides”. These Nitrides are extremely hard (1200Hv to 1500Hv) and increase the

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Heat treatment average hardness of the surface layers of the steel. As a general rule, the processes will double the hardness of the original steel. It is important to understand the basic process before selecting a furnace, which will be a production tool and hopefully a friend for up to 20 years. Plasma Nitriding should also be mentioned. It has been around since the beginning of the twentieth century but only lately (last 30 years) with improvements in electronics has become a feasible commercial process. The process uses only small amounts of Nitrogen and Hydrogen gas in an approximate ratio of 1:3 and is environmentally friendly. It has had limited success in the aluminium extrusion business as it is a very geometrically sensitive process and can be difficult to control when used on complex shaped extrusion dies. It is also best suited to a very clean working environment. However, some companies are producing very good results. As shown above, the actual chemistry is quite simple and early furnaces were no more than basic stainless steel sealed tubs in which the work was placed and then heated in a suitable brick lined furnace. Ammonia flow was not greatly controlled and temperature approximated at about 500°C. The process was not popular due to the long process times, the quality and reliability of the hard case produced and the smell (Ammonia this time not urine). However, the low or zero distortion characteristics of the process made it ideal for certain applications. Automatic Gas Analysis and Control, by RGB may be using Infrared ammonia analysis or H2 analysis, via a special probe mounted inside the furnace. In gas nitriding, the donor is a nitrogen rich gas, usually ammonia (NH3), which is why it is sometimes known as ammonia or gas nitriding. When ammonia comes into contact with the heated work piece it dissociates into nitrogen and hydrogen. The nitrogen then diffuses from the surface into the surface of the material

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and produces hard Nitrides with alloy constituents such as Chromium and aluminium. This process has existed for nearly a century, though only in the last few decades has there been a concentrated effort to investigate the thermodynamics and kinetics involved. Recent developments have led to a process that can be accurately tailored and controlled. The thickness and phase constitution of the resulting nitriding layers can be selected and the process optimised for the particular properties required.

The advantages of gas nitriding over the other surface treatments are: • Uniform Nitriding on all surfaces • (except those protected by special paints • if required) • Large batch sizes possible - the • limiting factor only being furnace size. • With modern computer control of • the Nitriding atmosphere the nitriding • results can be closely controlled to give • desired case properties. • Relatively low equipment cost - especially compared with other • alternatives such as plasma or automated r • salt/fluid bed.

Contact Keith Watkins, GW Consumables

Issue 3 Furnaces International r 27

Flexible steelmaking

Electric-free

steelmaking 1) Cesare GIAVANI1, Beppe VIRGILI, 2) Cristian CATTALINI; Tommaso Maria SARPIETRO (1. Tenova SpA; 2. Tenova Industrial Technologies Beijing))

Cesare Giavani discusses the use of hot metal in an EAF in an attempt to combat high energy prices and a shortage of scrap, predominantly in Asian countries such as India. Tenova has developed a furnace concept specifically aimed at steelmakers using this option, which will allow them to return to scrap based steelmaking in the future.

Steelmaking is highly influenced by the availability of raw materials and energy. Asian steelmaking, in particular, is facing a significant scrap shortage and high electric energy prices. In this scenario, several steelmakers have found the use of hot metal in their electric arc furnace (EAF) a convenient alternative, and as a method it is gaining popularity. However, it is known that in the future scrap will gradually revert to being the primary raw material for steel mills, since scrap based steelmaking has a lower overall costs and environmental footprint. Therefore, Tenova has developed a new furnace concept, specifically targeted at steelmakers that currently use a significant amount of hot metal in their charge mix, yet are prepared to move or return to scrap based steelmaking: the Flexible Modular Furnace (FMF). This solution is also suitable for those steelmakers that are looking for a transition from BOF to EAF based steelmaking, and for those EAF steel shops that want to increase the hot metal percentage in their charge mix. In its simplest form, the so-called â&#x20AC;&#x2DC;Base Moduleâ&#x20AC;&#x2122;, the FMF can be configured for hot metal based steelmaking and, according to the characteristics of the charge, it can efficiently operate without electric power (similar to a BOF). The electric power module (transformer, electrodes etc.) can be installed later on, as the most convenient charge mix changes, introducing larger amounts of scrap and DRI, according to the market. In its final configuration, the FMF can be transformed into a fully featured Consteel EAF with continuous scrap feeding and pre-heating. In recent years the steel business has experienced a shift in profitability towards the owner of raw materials, in such a way that steelmakers have been forced to adapt to having a tight market price and an unstable cost basis (ref. [1]). In China, the high availability of virgin iron and the immaturity of the scrap market led the steel industry to reduce EAF based production, and increase the amount of hot metal in the EAF still in operation. While the global raw material and energy instability will remain a major condition, the general trend of steelmaking is moving Fig.1: An explosion view of the FMF base module concept design.

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Flexible steelmaking toward more environmentally friendly and less energy intensive processes, and so to increasing the scrap percentage in the charge mixes. From 2020, Chinese scrap availability will substantially increase along with the share of EAF production (ref. [1] [2]). In this context, Tenova developed the FMF solution, summarising scrap-based EAF and the working practices adopted in China in those EAF that use a high hot metal percentage in the charge mix. This study presents FMF main equipment, a process simulation example, and the related economic considerations.

Mechanical equipment Tenova FMF is a modular concept for a smelting furnace that can be developed from core ‘Base Module’ equipment by means of specific add-ons, following an ‘investment on demand’ approach (Fig. 1). Each module is designed with specific features in order to fit the requirements of the charge mix (ref.[3]). The Base Module is designed for high hot metal percentage in the charging mix and includes all the features needed to manage high reactivity processes in what we call converter mode, and to allow subsequent system reconfiguration and upgrades, such as transformer and electrode packages. No electrical power is needed in the FMF Base Module configuration, and consequently several investments typical of a standard EAF can be avoided (i.e. electrode arms, secondary system, transformer, hydraulic unit portion for electrode regulation and related auxiliaries).

the bath temperature and therefore promote dephosphorisation (~1550°C); and Consteel minimises the number of roof openings, positively affecting both energy savings and productivity. • Energy recovery: iRecovery is the energy recovery technology developed by Tenova for steelmaking furnaces. In relation to FMF, the iRecovery system is composed of a high temperature and a low temperature section that recovers thermal energy from the furnace off -gases. The energy recovery system is likely to be installed together with the FMF base module because of the energy intensive process of the converter mode operation. • Substantial increase of the scrap in the charge mix: In order to deal with a scrap percentage greater than 25 - 30%, electrical equipment needs to be implemented. The transformer, secondary system, electrode arms and electrode regulation system, hydraulic system and auxiliaries have to be upgraded. Consteel works as a scrap conveyor and preheating system, and the more scrap percentage increases in the charging mix the more Consteel comes back to its original function and well known advantages in terms of efficiency and productivity. • Module robots: Robots are already helping or replacing operators in dangerous operations, in order to improve the efficiency and safety of the furnace environment. FMF can be integrated with the following robot add-ons: Tenova’s Auto Tapping System (TAT), a temperature and sampling device robot, a slag door automatic cleaning robot, and an electrode automatic charging robot.

Add-on options The FMF Base Module has add-on options such as: • Consteel: According to recent users, a small Consteel that works as a temperature regulator is a unique technology in order to use the FMF in converter mode. There are two main advantages: Consteel allows the manufacturer to add scrap, ferroalloy, lime, or dololime at any point during the process without affecting productivity, to regulate

Economical comparison Converter mode is the most challenging configuration for FMF, and the following analysis shows an example of production data comparison between BOF and FMF Base Module (Ref [5]). The production data refers to the FMF process example presented above and to a similar BOF process. The result shows that the FMF process is efficient in terms of productivity with a high hot metal percentage in the charge mix.

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Issue 3 Furnaces International r 29

Flexible steelmaking

In terms of conversion costs, that is to say oxygen, electrical energy, refractory consumption, natural gas, nitrogen, argon, and fluxes, the FMF achieves a figure of around US$18/tls, which is comparable to BOF operations.

Contact

References: [1] Scarcity and Saturation – Steel and the challenges of volatile raw

www.tenova.com

materials, flat margins, and overcapacities – Metals & Mining Practice Spring 2013 – Mckinsey & Company, Inc. [2] Speech on the 7th China International Metal Recycling and Application Conference – Zhu Jimin – 2014.

Conclusions The data collected in this study, together with the reference plants in operation and the ongoing projects, draw a clear picture of opportunities and application for the FMF. A full range of metallic charges can be smelted with capital costs reduced to the minimum level. Flexibility is clearly the greatest advantage of this solution for markets that are developing towards lower carbon footprint steelmaking operations. Data also shows how FMF fits certain specific charge mixes, becoming even more convenient than classical solutions. Tenova believes that in China the FMF can be the first step for the modernisation

[3] Scrap vs. Hot Metal. iBOF and Flexible Modular Furnace: Tenova Answers to Flexible Technologies Demand - Davide Masoero，Doug Zuliani，Vittorio Scipolo，Cristian Cattalini, Beppe Virgili. [4] Static Model for Converter Steelmaking by Using Limestone - Biao Tang, Wei Zhang, Xiaoming Wang, Guangqi Sun, Yibo He, Zongshu Zou, Aibing Yu. [5] The making shaping and treating of steel,11° edition Steelmaking and refining volume, 1998.

of oxygen steel plants, offering a smoother transition to the scrap era. r

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19/04/2016 13:25

Furnace design

The self driving glass melting process Muijsenberg, H.P.H., Glass Service, a.s./ Eisenga M., Glass Service, B.V.

Erik Muijsenberg recently presented a paper at the Society of Glass Technologyâ&#x20AC;&#x2122;s centenary conference, outlining how intelligent furnace design systems can improve the efficiency of a glass furnace, focusing on how electricity use can best be monitored and managed. Fig. 1: End fired furnace with melter and barrier electric boosting.

The car industry is one example of an industry that is quickly changing, and using more sensors such as radar, sonar and visual cameraâ&#x20AC;&#x2122;s â&#x20AC;&#x201C; for example, in self driving cars. Furthermore, most cars today use partial or already fully electric engines to put the car into motion. This revolution is also possible for a glass-melting furnace. This advancement is possible thanks to cheaper sensors and a change in electricity costs thanks to resources such as renewable energy. Even in the Middle East, where oil is cheap, the sun is powering oil pump jacks. Today renewable resources in the EU on average generate around 30% of the required electricity, and on some windy and sunny days this can rise to around 80%, making electricity price negative at some points www.aluminiumtoday.com/furnaces/

during the day. The glass industry and glass furnaces can also make use of this advantage, but to do this they need an intelligent, fully automatic control system that can use the dynamic change in the availability and pricing of electricity, and even plan ahead to anticipate these changes. The electricity market itself can provide future predictions that can be fed into a smart control such as Expert System III. Intelligent furnace design and operating practices can increase overall glass furnace efficiency, by utilising advanced furnace modeling to help select the most-optimal furnace design for a certain type of glass and pull. This can be achieved by installing (more) electric heating in unique ways. The

Issue 3 Furnaces International r 31

Furnace design average residence time of a common glass furnace can be, for example, 30 hours, while the minimum residence time is sometimes only three hours, so the whole available space volume is poorly used. Furthermore, flexible top-firing energy input is optimised in conjunction with the electric boost, in the most optimal combination (Fig. 1). Altogether this can significantly save energy, increase furnace pull-rate, and reduce emissions. A flexible furnace using natural gas and electric heating can be operated at higher pulls per square metre and cubic metre when necessary, and at the same time reduce energy costs at a given pull rate. A furnace designed in this way can also be economically optimised, using advanced Model Based Predictive Control (MBPC). MBPC can decide better than a human operator when to use which energy input in the most optimal way, keeping the balance between temperature stability, glass quality, furnace lifetime and actual, to-the-minute costs of the used energy source (especially electricity).

Operating the optimal furnace design (with gas firing and electric heating/ boosting) with fully automatic Model Based Predictive Control allows the glass producer to operate the furnace in the most costeffective way with the minimum use of operators. Besides the energy costs savings, the system also delivers temperature stability to the melting process resulting in higher glass quality and production rates. The technology can offer also often a pull increase and emission reduction, while energy cost reduction can be 2-6%. This leads to payback times of only 3-6 months. r

Contact *Erik Muijsenberg, Glass Service (Czech Republic) *M Eisenga, Glass Service B.V. www.gsl.cz/en/glass-service.html

Economical preheating furnace Barry Woodrow* describes VHE’s preheating furnace, which is economical in use and is priced to offer an excellent ROI. It is currently in use at Rio Tinto’s smelter in Straumsvík, Iceland. VHE has installed a preheating furnace for the Rio Tinto Alcan smelter at Straumsvík in Iceland.

Most smelters add cold aluminium metal to the charge of molten aluminium in the casthouse furnaces. This metal may be in the form of sows, pure offcuts, or other scrap arisings. Such metal is frequently stored outdoors and can be wet. Charging of damp aluminium to hot furnaces results in the generation of large volumes of steam, and can cause steam explosions, in the worst cases 32 r Furnaces International Issue 3

blasting molten aluminium around the casthouse. Traditionally, scrap metal has been heated with a gas flame to remove moisture, but such localised heating can never fully remove water, and steam explosion can still occur. VHE‘s furnace, which is semiautomatic, is able to heat 15 tonnes of scrap to 200°C within two hours. At this temperature all water and many low-boiling point organics

are fully removed. The oven is electrically heated and uses the recirculating air principle for best efficiency. r

Contact Barry Woodrow, Commercial Manager, VHE, barry@vhe.is www.vhe.is www.aluminiumtoday.com/furnaces/

Thermal processing

Hot wall pulsed plasma nitriding systems Andrés Bernal*, Electron Thermal Processing Equipment Plasma nitriding is a case hardening process, widely used to improve surface properties of metal parts such as cutting and forging tools, injection moulds, bearings, gears, engine component, etc. here, Andrés Bernal* discusses Electron’s hot wall pulsed plasma nitriding equipment. Mainly used for steel, the plasma nitriding process is environmentally friendly and uses clean gases (nitrogen, hydrogen, and argon). An applied electrical field ionizes the gases, and bombards target parts to create a nitride-containing, hard compound layer at the surface of the parts, and a so-called ‘diffusion zone’ after that with excellent mechanical bearing properties. Electron Thermal Processing Equipment BV, based in The Netherlands, has over 25 years’ experience in the engineering and production of thermal processing equipment. Part of their scope of supply is the plasma nitriding equipment, IonHeat. Since 2012, IonHeat (Fig. 1) has developed equipment for the plasma nitriding process, known as Glow-Tech systems, employing the latest technologies that exist within this field. Ion Heat’s plasma nitriding systems incorporate hot wall chambers with separate heating and cooling zones, so as to provide optimal temperature control and distribution throughout the process. These systems furthermore operate with pulsed DC current with an extremely fast arc detecting system, enabling high control of the plasma. The combination of these two attributes considerably reduces the difficulty of arcing, resulting in a higher surface integrity of the treated www.aluminiumtoday.com/furnaces/

Fig. 1: The IonHeat machine, from Electron.

Contact *Andrés Bernal, Electron Thermal Processing Equipment BV, The Netherlands www.electron-tpe. com

parts. The increased control of the process additionally allows the equipment to treat parts with different geometry in one same batch Ion Heat’s tandem systems, comprising two treatment chambers, share resources for vacuum, plasma generation, and gas supply through an optimised patentpending technology, which allows the system to run plasma treatment continuously between the two chambers. That is, while chamber 1 is under plasma treatment, chamber 2 can be loaded and pre-heated to process temperature so that as soon as chamber 1 goes into cooling, the plasma can be generated in chamber 2 for nitriding to begin. This technology allows savings of up to seven hours per day in processing time. In addition, the systems are designed for ease of maintenance, the heating elements can be easily changed (unlike other hot wall systems), and the pump and control cabinets are easily accessible. r Issue 3 Furnaces International r 33

Oxygen steelmaking

Converter vessel replacement C. Dinesh Kumar*, V.S.N Muthy*, K.D Trivedi*, V.R.Sekhar*, G.S Rathore*, JSW Steel

To increase steelmaking capacity from 3.45Mt/yr to 3.8Mt/yr, JSW Steel planned to replace three converters in 2012. This article discusses the strategy adopted for the complete replacement of the converter and trunnion assembly as a single unit, from initial planning through engineering, fabrication, installation, start-up and continuous operation.

Fig. 1: Sectional view of the JSW converter.

JSW Steel, Vijayanagar works, Steel Melt Shop 1 (SMS-1), has been in operation since 1998 and has gone through several improvements over the years to become one of the most productive shops in the country. The converters of SMS-1 at JSWâ&#x20AC;&#x2122;s Vijayanagars works were built in late 1990s 34 r Furnaces International Issue 3

and were designed for a heat size of 120 tonnes. Over the years the convertersâ&#x20AC;&#x2122; capacity was increased to 130 tonnes by re-designing the refractory lining. Commissioned in 1998, the old converter-1 in SMS-1 had a tendon suspension system for vessel support. At this time, there was a problem with high Si and Mn hot metals as a direct result www.aluminiumtoday.com/furnaces/

Oxygen steelmaking

Dimension

Old converter (mm)

New converter (mm)

4700

2733

3910

3942

1832

1932

835

773

6890

6920

9380

600

170

155

10800

2100

Table 1: Comparison of converter dimensions.

of the non-availability of quality iron ore. As a result, blowing operations during this period had a severe thermal impact on the converter shell and suspension systems. Over the years, due to continuous 3X3 operation, the suspension systems and vessel geometry reached a critical point. Due to high thermal stresses, the converter vessel was progressively deformed and started touching the trunnion ring during tapping and at the charging pad. The resulting reduction in clearance between converter vessel and trunnion ring decreased the cooling effect. Detailed investigations suggested a need for improving the shell material so that it can withstand the prevailing operating conditions. In addition to heat impact, the need to produce critical automotive grades forced operators to improve the quality of tapped steel in terms of temperature, bath oxygen and phosphorus. Online studies established that intensifying bottom agitation by increasing the number of plugs improved the reaction kinetics. Taking these factors into consideration, it was decided to replace the converter during a scheduled www.aluminiumtoday.com/furnaces/

shutdown of blast furnace 1. This was the first converter vessel change for JSW steel. The changes planned and expected benefits [1] that would result included: 1. Standardisation of the refractory lining for reducing the inventory carrying cost in all three converters. (Converters 1 and 2 were from SMS Siemag and converter 3 an old model from Lawnworks, UK). 2. The converter vessel showed signs of stress deformation due to high thermal loads, and for this reason some design modifications were required. 3. Vessel suspension has been upgraded to a lamella system from the existing tendon system, enabling vessel size enhancement. 4. Changes to the vessel’s bottom stirring system – from four plugs to eight plugs –improved yield and dephosphorisation. 5. To withstand higher temperatures, vessel construction material was upgraded from P-275NH to P-355NH. Several brainstorming sessions were started with potential equipment suppliers and the ideas combined with operator experience to help finalise the project’s scope and develop a practical vessel design that satisfied most of the requirements. Some of the design changes – such as larger tap weight and faster vessel movement – were expected to increase productivity. The new vessel design had to take into account the physical constraints presented by existing shop facilities and be quick to install. Fig. 1 shows a sectional view of the JSW Converter. Table 1 offers a comparison of the old and new converter dimensions. The diameter of the vessel was not increased, but the barrel and lower cone height was increased to accommodate higher hot metal. The volume of the new converter increased by 12m3. Other key changes are shown in Table 2. Shell material was changed to P-355 as this grade is perfect for such high temperature exposure and still has acceptable weldability[2].

Timeline and project planning Two out of the three converters were Issue 3 Furnaces International r 35

Oxygen steelmaking planned to be replaced one after the other. The entire replacement work for each converter was to be carried out with the other two in operation. A tight time period of less than four weeks per converter was allowed and linked with the scheduled pre-shutdown of blast furnace 1 in the steel Material construction

Old converter

New converter

Top cone

P-275NH

P-355NH

Barrel

P-275NH

P-355NH

Bottom cone

P-355NH

Bottom dish

P-275NH

P-355NH

Suspension system

Tendon

Lamella

Bottom stirring system

4 plugs

8 plugs

Volume inside lining 119 m3

works. Such synchronisation was essential to avoid production loss at the steel making shop. Ambitious solutions were needed as the ambient conditions of the existing equipment and installations presented several challenging problems. Extensive drawings and field verification were needed to identify any potential interference with existing structures, equipment and melt shop facilities. SMS Siemag was appointed to handle engineering and for the supply of the trunnion ring vessel and suspension. Innovative techniques in technology, design, project management and construction were employed to complete the project on time and make it a success. Project events were planned to hourly accuracy.

Key initiatives implemented in planning The 25-day project duration from the last heat of the old vessel to first heat of the new one demanded perfect preparation and meticulously detailed scheduling of all works and performances (Table 3) [3]. Details of the various innovative steps and activities carried out during the whole process are listed below (Figs 2 & 3):

131

Table 2: Comprison of key features.

Pre-assembly of the trunnion work started

September 13th, 2015

Delivery of converter to site

September 15th, 2015

Shutdown of old converter No 1

February 6th, 2015

First heat charged:

March 4th, 2015

Table 3: Timeline of the 1st converter replacement.

Fig. 2: Pre-assembling of the new converter. 36 r Furnaces International Issue 3

1. Dismantling of the floor in front of converter for the transportation of the assembled converter shell with trunnion and suspension system. 2. Minimal removal of the doghouse for the safe replacement of the old converter with the new one. This is essential, so as to revive the doghouse at the earliest opportunity after the new converter is back in position. 3. In-house designed and manufactured vessel transfer car for to and fro movement of the vessel from its

Fig. 3: Dismantling of the old converter. www.aluminiumtoday.com/furnaces/

Oxygen steelmaking installed position to the charging bay. 4. Constraint of crane capacity led to in situ welding of the top cone. 5. A pre-assembled converter vessel is fabricated and both DE and NDE bearing blocks are installed on trunnion shafts to reduce installation time. 6. Pre-fabricated bottom stirring system piping is installed on the vessel to reduce on-site fabrication and installation time. 7. Pre-fabricated vessel top cone cooling piping is installed on the vessel to reduce on-site fabrication and installation time. 8. Top cone cooling and Argon rotary assembly are pre-installed on the converter before onsite vessel positioning.

Project implementation Micro planning and precise logistics, in co-ordination with the operations team and tight project management, were key features for the success of this project. The equipment and systems to be installed included converter shells, trunnion rings and bearings, converter suspension systems, pedestals, tilting drives, rotary joints, slag skirt, doghouse, off-gas hoods and operating platform. Manufactured converters were shipped to the harbour facilities nearer to JSW Vijayanagar by sea. Each trunnion ring was delivered in four parts and the converter vessels in three sections. To keep converter downtime to a minimum, on-site pre-assembly work was maximised. The weight of the pre-assembled converter units was kept under 220 tonnes due to the limitations of the charging crane. The operating platform of the existing converterâ&#x20AC;&#x2122;s charging side, along with civil concrete, had to be removed so that the charging crane could move the converter safely. Because of extremely restricted space, a new, highly compact and maintenance-free converter suspension system was employed to allow use of converters with the largest possible reaction volume. This innovative solution features two horizontal links and eight vertical lamellae that accommodate thermal deformations of converter and www.aluminiumtoday.com/furnaces/

Fig. 4: Transferring the old converter to the repair bay using the charging crane.

References 1.

Cotchen,

and

Mueller, E. and Fraser, N., Recent Arc Furnace Revamps for Improved Performance, AISTech 2006. 2.

Di Napoli D., De Ol-

iveira J.G., Staudinger G., MĂźller J., Design Aspects of the Ideal LD Steelmaking Converter, AISE Annual Convention 2003, Pittsburgh, Pansilvania, USA. 3.

G. Staudinger, P. Il-

lecker, I. Staniewski, R. Konieczny, S. Cichonski, Implementation of 350-T BOF Converter at ArcelorMittal Poland, AISTech 2014 Proceedings.

trunnion ring. To minimise total project time, the trunnion ring parts were transported prior to the vessel parts, the advantage being that site welding can start earlier. The majority of the vessel, vessel suspension and trunnion ring assemblies were performed before the old furnace was shut down. Because the converter had to be changed in the running shop where liquid steel is produced, all activities have to be carefully planned and take into consideration the steelmaking operation â&#x20AC;&#x201C; in particular the use of overhead cranes. The charging crane was used for all major and most minor lifts. For removal and installation, it was necessary to dismount part of the converter platform located at elevation 9.1 metres to enable the old converter vessel to be removed on a special shifting/lifting device (Fig. 4). Given the space available, the primary drives were dismounted beforehand to allow the main gear unit to be pulled off the trunnion pin. The installation of the vessel was closely co-ordinated between the technology supplier, the construction engineer and the installation contractor so that production outage was minimised. This involved daily co-ordination meetings during installation to minimise interference among the workers. A novel dismantling and installation concept was introduced, using a lifting rig for handling the trunnion ring, vessel, and vessel suspension together. A special car was designed with suitable hydraulic lifting and shifting equipment for the removal and smooth reinstallation of the converter vessel (Fig. 5). This cut the Issue 3 Furnaces International r 37

Oxygen steelmaking

Fig. 5: Transferring the pre-assembled converter to the installation site.

typical revamp time for converters of this size. Accurate balancing of converter and trunnion ring torques enabled the existing converter drive assembly to be re-used. The shifting/lifting device was used to insert the converter accurately to the millimeter into the enclosure. Once the converter was aligned exactly and deposited in its final position, the converter gear unit was fitted. While the job site was a very busy and crowded place, not a single incident occurred during installation. Erection and commissioning engineers stationed on the site were instrumental in maintaining a safe workplace. In addition to increasing the converter size, another key factor for productivity enhancement was extending the lining life of the converter from 4,200 to 5,000 heats per campaign. This was achieved by increasing the converterâ&#x20AC;&#x2122;s bottom stirring system lines from four plugs to eight plugs resulting in a flow rate reduction per plug.

Fig. 6: The new converter in operation.

Contact C. Dinesh Kumar*, V.S.N Muthy*, K.D Trivedi*, V.R.Sekhar*, G.S Rathore*, r

JSW Steel, Vijayanagar Works, India. Email: dinesh. kumar@jsw.in www.jsw.in

Start-up and operational results After successful installation, Converter no. 1 was started on 4 March 2015. A total of Converter parameters

Old converter

New converter

Comparison time

June 2014

June 2015

Steel output, t/day

2916.76

3618.00

Average heat size, t

132.58

134.00

Heats per day

Table 4: Comparison of the operational performance of the old and new converters. 38 r Furnaces International Issue 3

20 heats were tapped from the converter on day one, providing immediate plant availability. After start-up, production was rapidly ramped up and production targets for the start-up were being exceeded during the first week of operation. The converter shell, bottom plugs, suspension system and the auxiliary units worked satisfactorily without any post commissioning shutdowns. Table 4 shows a comparison of the operational performance of the old and new converters after complete stabilisation. Key achievements were an increase in the average heat size by 4 tonnes/heat and reduction in bath oxygen by 150ppm due to increased bottom plugs. Fig. 6 shows the doghouse and revamped converter in operation. After Converter 1, the shell replacement of Converter 3 was taken up and completed in 20 days, surpassing the previous record of 25 days.

Conclusions JSW steel completed the replacement of a 134-tonne converter in a working shop within a period of 25 days. It took 20 days for Converter 3, thanks to the application of innovative and exceptional solutions in design, transportation, dismantling and re-erection of converters. The meticulous pre-planning led to smooth equipment installation within the anticipated schedule and without injuries or major setbacks. The new converter with the lamella suspension system has adapted to the process-related thermal load. Since the installation, both the vessels have operated well with improved productivity and quality. r www.aluminiumtoday.com/furnaces/

BIFCA

British Industrial Furnace Constructors Association

Top 10 tips: improving efficiency in heat treatment As part of our series of columns from the British Industrial Furnace Constructors Association (BIFCA), member Amber Watkin of Eurotherm gives an overview of the top 10 ways in which to improve efficiency in heat treatment processes while meeting industry standards, using modern technology designed with furnace applications in mind. In part 1 of this series, we look at the first three recommendations.

s part of our series of columns from the British Industrial Furnace Constructors Association (BIFCA), member Amber Watkin of Eurotherm gives an overview of the top 10 ways in which to improve efficiency in heat treatment processes while meeting industry standards, using modern technology designed with furnace applications in mind. In part 1 of this series, we look at the first three recommendations. Heat treatment processes involve high energy use and compliance to strict industrial regulations. Poor control of the process can lead to large amounts of wasted energy and quality issues that result in non- compliant waste product and costly fines. Precise temperature control is critical for the heat treatment of automotive and www.aluminiumtoday.com/furnaces/

aerospace parts that need to comply to standards such as Nadcap/AMS2750 and CQI-9. Poor control leads to components that have been overheated, under-heated or not soaked at the correct temperature for the specified length of time. Many difficulties can arise during heating, cooling, ramps and dwells including control of overshoot, rate of temperature change and stability. Add to this the necessity to prove the process was carried out to specification by securely recording and archiving the data, and you will find you really need to select the right equipment for the job. These problems are easily solved using modern precision PID control and secure tamper resistant data recording techniques with smart reporting tools. Our following tips show the benefits of precision control and secure data recording not only to help comply to standards Issue 3 Furnaces International r 39

BIFCA

1. Achieving the fastest ramp time without affecting quality The faster a process can run the more profitable it can ultimately be, but to maintain efficiency the speed must not affect the quality of the end product. Some materials and intricate workpieces have specifications that limit the rate at which they can be heated or cooled so as not to damage the material microstructure or distort the shape of the product. Ramping the temperature too fast can detrimentally affect the process, resulting in quality variations and possible scrap material. The difficulty of achieving a uniform temperature across large furnace areas and workpieces during the ramp is due to thermal lag (also known as thermal gradient and Delta T), and in the case of material for aerospace and automotive applications it is often a requirement to prove that the rate of temperature change in the workpiece did not exceed specified limits during the ramp in order to meet regulatory standards. Multiple temperature measurements must be made across the workpieces and the results fed into the temperature controller to help control a uniform temperature across each workpiece. The data must be recorded for reporting and audits. The secret to achieving ramps to the set-point temperature as fast as possible without exceeding the limits of the material is to use a high accuracy precision controller with a Ramp Rate feature built into the functionality of the programmer. This kind of controller has high accuracy inputs and outputs that will maintain tighter control of the process variable (PV), keeping it closer to the set-point (SP) than basic controller models. Often, this type of controller will also contain special algorithms that help prevent overshoot at the end of the ramp. For simple configuration of the ramp rate feature, look for set point programmers with data entry 40 r Furnaces International Issue 3

Fig. 1: Ramp Rate. A Ramp Rate feature controls the rate of change to set-point, keeping the material within its specified temperature limits and preventing damage and distortion in the workpiece.

in a spreadsheet style format where the individual ramps can be set by Rate (the rate at which to ascend or descend to the set-point per second, minute or hour) or Time (the time in which to achieve the setpoint). Modern controllers with LCD, OLED or TFT display screens can show the plotted ramp-rate SP against actual PV, so you can visualise how your furnace or oven is adhering to set requirements, and if the temperature uniformity data is also being recorded to prove compliance to standards, the information can give an accurate overview of the temperature consistency in the ramp phase. Precision controllers and PLCs are now available with ramp rate features within the set-point programmer, along with secure recording features that not only help with compliance to standards but also provide enhanced process data for internal analysis and reporting on the overall efficiency of the furnace.

www.aluminiumtoday.com/furnaces/

BIFCA

2. Compliance to critical temperature limits Processes in aerospace and automotive industries need to comply to strict standards such as NADCAP, AMS2750, CQI-9 and TS16949. Specifications covering topics such as monitoring and recording instrumentation, calibration and electronic records, sensors and control must be adhered to, and failure to comply can lead to hefty fines, lost business and loss of respect for the company involved. Field Test Instruments and Controlling, Monitoring or Recording instruments must meet the calibration accuracy demanded, typically with a readability of 1째F or 1째C, and the material being treated must not be heated outside of its specified limits. By investing in precision PID control with accurate Inputs and Outputs, and better rejection to noise, you can be sure that the temperature you set is the temperature you get, and that you are meeting your limits while getting ROI by reducing your energy bills over the lifetime of the controller. Thermocouple sensors used in high temperature environments degrade over time and heat treatment standards dictate the upper temperature limits and number of times a particular thermocouple sensor type should be used before replacement. Control and Automation products are available that can calculate the time, temperature and number of instances a thermocouple has risen above a certain threshold temperature, triggering alarms to indicate expired sensor periods. www.aluminiumtoday.com/furnaces/

Fig. 3: Precision Control. Precision PID control contains special algorithms that help to keep the PV as close to SP as possible, even during ramps and other unexpected temperature variations.

Process data needs to be securely recorded and stored for a length of time. While this is much simpler nowadays using a digital data recorder, recent innovations in precision PID controllers and PLC products include built in secure recording and colour TFT displays with wash down fronts for use in dirty industrial environments. Full featured digital recorder products have batch functionality that enables the operator to record individual batches with a start and stop button on the screen, or by external input via a bar code scanner, for example. The data from the batch is then easily retrievable for assessment purposes via a PC. Software for reviewing the secure files can be used to zoom into areas where problems occurred and the historical data also shows all messages whether triggered by an alarm or entered manually. The reviewing software also allows digital signatures to be added to the batch for sign off. The main advantage of digital batch recording

and signing is it saves time and gives all the data they need for easy reporting and compliance to standards. To help maintain accuracy, proficient companies also provide services such as Calibration, Temperature Uniformity Surveys (TUS) and System Accuracy Tests (SATs) at regular intervals, to ensure that temperature measurement products and systems are not drifting over time. The most efficient calibration services are those that are managed digitally. Modern companies offer online calibration services that give you a complete overview of the whole plant calibration status via a web browser and automatically inform you when calibration is due. For companies that wish to carry out TUS themselves, some equipment manufactures supply field test instruments specifically designed for the calibration of furnaces. They include independently adjustable thermocouple input channels compliant to within +/-1째F or 0.6째C. Issue 3 Furnaces International r 41

BIFCA

3. Reducing temperature overshoot for better efficiency During the heating and cooling cycle of heat treatment processes, whenever the temperature overshoots or undershoots energy is being wasted. When heating, once the furnace has reached its set-point the heaters will switch off, but due to residual heat in the walls and heaters themselves the temperature of the furnace continues to rise, causing it to overshoot. Energy is wasted and the work piece could be damaged by overheating, needing intervention for quality assessment. Time is also wasted while the PV returns to SP, meaning overshoot results in a longer process time, wasted energy and wasted time for the quality engineer. For processes where time and energy is being wasted in this way, the solution is to replace the temperature control with a Precision PID Temperature Controller or Precision PLC. Intelligent models have specific algorithms embedded in the control strategy that take care of common heating and cooling problems, keeping the PV as close to the set-point as possible to prevent the unnecessary waste of energy while carrying out the process in the fastest conceivable time. In heat treatment applications where it is important to comply to the relevant standards, useful control features to look for are algorithms that inhibit temperature overshoot during the start-up heating phase, reduce overshoot during ramps, and stabilise the PV during dwells. The easiest models to configure incorporate pre-made function blocks for features such as PID (control) Cutback (overshoot inhibition) and Cascade (fast response to SP change to reduce temperature lag in the load) with typical default values set for easy configuration. Basic controllers do not have the features to achieve the level of precision control that can save energy costs, 42 r Furnaces International Issue 3

reduce processing time and prevent the overheating of valuable materials. In most furnaces, the cost of moving to precision control is minimal compared to the savings made over the lifetime of the furnace. r

Fig. 2: Overshoot. When operating temperatures are outside the desired set-point, the result is wasted time and energy; under or over heated material; possible non-conformance to critical temperature limits, leading to scrap product.

You can read the next installment from Eurothermâ&#x20AC;&#x2122;s top ten tips on improving effeciency in heat treatment in the next issue of Furnaces International, out in December.

Contact BIFCA National Metalforming Centre 47 Birmingham Road West Bromwich, UK B70 6PY enquiry @bifca.org.uk www.bifca.org.uk

www.aluminiumtoday.com/furnaces/

Thermal imaging

Thermal imaging borescope for glass-melt tanks Ametek Land, a non-contact temperature measurement specialist, has launched a thermal imaging Near Infrared Borescope, designed specifically for use in glass-melt tanks.

Contact www.landinst.com/products/nir-borescope-glass

Ametek’s new thermal imaging NIR-B Glass provides continuous real-time temperature data combined with a crystal clear thermal video image, allowing a single solution to replace the traditional approaches of visual cameras and periodic hand-held pyrometry. With over 324,000 available temperature measurement points in the field of view, the NIR-B Glass solution can also be used to monitor the drift in crown roof thermocouples.

Optimising performance Designed specifically for the glassmelt furnace working environment, the NIR-B Glass is designed to withstand the high ambient temperatures through an integral cooling system, with a specially designed air purge to keep the 90 degree lens clear of contaminants so the instrument provides 24/7 data to the plant. An optional auto-retract unit is available as additional instrumentation protection in the event of either air purge fail, water cooling fail, power fail, or an overtemperature condition at the probe tip. The NIR-B Glass solution has been www.aluminiumtoday.com/furnaces/

proven to provide an operating plant with the ability to clearly ‘see’ cold spots from air leaks coming through structural refractory, meaning that cracks or collapses are easily detected. This, combined with the ability to visualise flames, allows the plant to optimise the flame pattern and burn efficiency. The ability to overlay thermal profiles across the crown and along the melt allows for accurate batch line control, production throughput optimisation and batch transit time recording. Advanced software features allow multiple visual or output alarm controls to be set as specified by the plant. This can be critical in extending the lifespan of the melt tank refractory and in providing greater asset protection through more accurate, remote infrared temperature measurement and live thermal imaging. The NIR-B Glass provides an operator access to real-time, continuous data through enhanced thermal video images, combined with highly accurate temperature measurements anywhere within the scene. The end results are increased

production efficiency and longer refractory campaign life.

Visual checks Critical areas, such as port arches, can be continuously monitored for overheating with automated alarms set for over-temperature conditions. Long-term data trending then allows maintenance planning to be data driven rather than responsive. The NIR-B image, which can be monitored from the comfort of the control room, features an accurate, high-resolution radiometric thermal imaging camera, which provides high-quality thermal video. This enables precise product control and monitoring. Thermal imaging inside refractorylined glass-melt tanks normally requires the plant operator to cut large openings in the refractory to view critical areas. With the NIR-B Glass solution, it is possible to use the proven technology of the NIR-B thermal imager to accurately profile the temperature of the entire furnace with only a small wall opening. The wide 90º horizontal Field of View allows operators to see and measure large scenes using just one device. r Issue 3 Furnaces International r 43