Furnaces International Issue 5

COMPANY PROFILE

CASE STUDY

REFRACTORIES

ENERGY EFFICIENCY

Glassmaker Verallia Ukraine invests in modernised furnace

Arcelor Mittal: Environmentally friendly walking beam furnace

Morgan; PaneraTech; Lubisol

Innoval: Aluminium ingot pre-heating

www.aluminiumtoday.com/furnaces/ Issue 5

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Contents

Regulars Comment News

4 5

Company profile: Verallia Glassmaker Verallia Ukraine invests in modernised furnace

8

Heat treatment Keith Watkins: Drop quench furnaces

14

Case study: Steel Arcelor Mittal: Environmentally friendly walking beam furnace

16

BIFCA Column

21

Refractories Morgan Advanced Materials: How to ensure effectlive furnace lining efficiency

Furnce guide cover_FINAL.indd 1

24

Front cover: www.grancoclark.com

9/20/16 7:52 AM

PaneraTech: A solution for measuring refractory thickness in glass furnaces 26 Lubisol: A method to improve regenerator crown insulation

29

Blast furnaces SAIL: Impact of cooling on campaign life and operation of a blast furnace

31

Energy efficiency Innoval Technology: Aluminium ingot pre-heating

34

22

www.aluminiumtoday.com/furnaces/

Issue 5 Furnaces International r 3

Comment

Editor: Sally Love Tel: +44 (0) 1737 855154 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

Comment This will be my last issue of Furnaces International, as I am leaving Quartz for pastures new.

Taking over from me will be Nadine Firth, who many of you will recognise as the Editor of Aluminium International Today.

I’ve enjoyed working on Furnaces, and learning more about the industry. The thing that strikes me most is that across so many different sectors it really is the burning heart of the industrial process - if you’ll excuse the pun.

Without the furnace, the metals and glass industries simply couldn’t exist. It provides the crucial starting point for the end product, and sets the pace for the entire operation.

As the most energy intensive part of the manufacturing process, it is also where a lot of the innovative, new technology is coming from. The drive to reduce emissions has led to a fascinating amount of developments within the furnace industry, with a focus on energy efficiency, productivity, and cost reduction.

For such an historic piece of equipment, it really is interesting to see how many modern advances are being made. Despite having been around for millenia, it is still possible to improve on the design and performance of a furnace and its technology - I personally can’t think of another piece of equipment that can boast this accolade.

This is information that you will already know, but it has been interesting for me to learn about it in more depth and I will look forward to learning more in the future issues of the magazine when Nadine takes over.

Sally Love

© Quartz Business Media Ltd, 2016

4 r Furnaces International Issue 5

Editor, Furnaces International sallylove@quartzltd.com

www.aluminiumtoday.com/furnaces

News

100s of news jobs to be created at UK’s Lochaber smelter

The new owners of the UK’s last

The auto-components

housing and other services for

in the Highlands was because

aluminium smelter plan to make

manufacturing plant forms

workers.

people welcomed us here.

vehicle components on the site

the centrepiece of a planned

Aluminium currently made at

“That’s been reinforced by the

in a move that could create

£120m first phase of longer

the smelter, which lies in the

positive response of the many

hundreds of jobs.

term investment in the smelter

foothills of Ben Nevis, is taken

agencies in the new Lochaber

Liberty British Steel and Simec

that could eventually run to an

elsewhere to be made into

Delivery Group who showed

Lochaber Power took over the

estimated £450m.

various products.

today that they are eager to

running of the Lochaber Smelter

Phase one could create a mix

Sanjeev Gupta, executive

play their part in delivering the

near Fort William last year.

of up to 600 new direct and

chairman of the GFG Alliance,

goal of a clean, competitive

The new project would involve

indirect jobs.

which owns Liberty and Simec,

and sustainable manufacturing

the creation of a steel rolling

Longer term, production at the

said: “I am delighted to report

sector in the Highlands.”

mill and facilities for making

site could support 1,000 direct

excellent progress in our work

GFG Alliance took over the

components such as alloy

and 1,000 indirect jobs and add

programme with partners in

smelter from Rio Tinto in a

wheels.

£1bn to the Scottish economy.

Scottish government and local

£330m deal last year.

It could add 600 jobs to the 170

The overall investment would

agencies.

already involved with the yard.

include the construction of

“One of the reasons we invested

CHTA heat treatment conference returns to UK in October The Surface Engineering & Heat Treatment Industry Conference/ Exhibition returns to the UK on the 13th October.

2015’s highly successful and convivial event in

Engineering Association and

responsible for organising

quality, efficiency and

Wolfson Heat Treatment Centre,

the heat treatment sessions,

environmental aspects”.

the second event will be held

said: “The first event attracted

at the historic Kenilworth’s

numerous high-profile speakers,

Surface Engineering & Heat

Chesford Grange hotel.

from the international heat

Treatment Industry Conference/

Advances in industrial heat

Initial details of the second

treatment community, who

Exhibition, including

Stratford-upon-Avon was

treatment processing remains

updated with a wealth of new

opportunities for sponsorship

the first international event

the theme of the heat treatment

information.

and table-top exhibiting, appear

encompassing heat treatment

sessions, to be staged alongside

in England for over 12 years.

presentations for metal

will again be on practical

finishers and an exhibition

developments aimed at

covering both disciplines.

reducing costs and increasing

Co-sponsored by the UK’s Contract Heat Treatment Association (CHTA), the Surface

CHTA’s Alan J Hick,

www.aluminiumtoday.com/furnaces/

“This time the emphasis

at www.sea.org.uk/industryconference/.

productivity whilst enhancing Issue 5 Furnaces International r 5

News

Aerospace supplier orders titanium rotary hearth forging furnace from Can-Eng Can-Eng Furnaces International

aircraft Titanium and Nickel

to press manipulation within in

and sealing system.

has begun the commissioning

based alloy closed-die structure

their existing plant layout.

The system is scheduled to be

of a turnkey 36 foot diameter

forgings.

The system is capable of

commissioned to the United

‘Pancake’ style rotary hearth

The furnace system features an

processing up to 250,000

States in the third quarter of

furnace for a leading North

advanced low NOx combustion

pound load capacity in a 24/7

2017.

American Based aerospace

system designed to meet the

production environment.

CAN-ENG Furnaces

supplier.

most stringent environmental

The furnace system complies

International is a global

The open hearth configuration

and temperature uniformity

with thermal performance

provider and leader of thermal

allows for flexible loading and

requirements.

requirements laid out in

processing systems.

uniform heating.

Special dual-door design

AMS2750E, integrates a low

The furnace will be used in the

provides the customer with

shrinkage ceramic fiber lining,

production of large fixed wing

significant flexibility for forging

unique rotating hearth drive

HWI selects Ohio site for monolithics refractory plant US refractory supplier HarbisonWalker International (HWI) has selected The Point Industrial Park in South Point, Lawrence

monolithics from the southern-most point in Ohio to any location

County, Ohio as the location for construction of its new monolithic

around the globe.

refractories manufacturing facility.

Set on the section of the Ohio River that is the largest weight/ volume inland port in the United States, The Point invested $4.5

HWI said the $30 million facility will be one of the most technologically advanced refractories plants built in the US and will be operational by early 2018.

Initial capacity at the plant will be 80,000 tonnes per year and groundbreaking for the facility is expected to start this summer.

The Point is one of Ohio’s fastest-growing industrial parks and encompasses 50 acres in the south of the state. The site

million to build a port that offers a direct link to destinations around the world at the lowest possible price.

Douglas Hall, senior vice president, Integrated Supply Chain, HarbisonWalker International, said: “Unlike any other location, The Point offers transportation, logistics and business amenities that combine to create an ideal and cost-effective match for the requirements of our new facility.”

is positioned to provide HWI with the capability to move its

6 r Furnaces International Issue 5

www.aluminiumtoday.com/furnaces/

News

New recycling furnace for Constellium Constellium N.V. has announced that it has installed a new recycling furnace at its Muscle Shoals, Ala. facility in an effort to expand recycling capabilities in North America.

The now fully operational furnace is expected to increase the total recycling output by 170 million pounds, or about 5.2 billion additional used beverage cans per year. The Muscle Shoals facility will then be expected to recycle the equivalent of nearly 20 billion cans per year – almost one-fifth of the cans sold in the United States.

“This new furnace is a major step for our Muscle Shoals facility, great news for our customers and an exciting step forward in our commitment to promote recycling and sustainability,” said Mike Tanchuk, president and CEO of the plant. “This increased recycling capacity will enable us to better leverage aluminium’s infinite recyclable properties.”

Joe Pampinto, Muscle Shoals’ plant manager, added: “I am proud of the team who delivered this state-of-the-art equipment. The furnace

plant is one of the largest recyclers of used beverage containers

is now fully operating and this added recycling capacity will increase

in the world. This capacity, which enables the plant to recycle

the molten metal supply required for customer deliveries.”

products at their end-of-life (EOL) as well as scrap from customers,

Using advanced technologies, the new furnace, which meets

contributes to Constellium’s overall engagement to ‘close the loop’

the Best Available Control Technology (BACT) environmental

in beverage can recycling. Constellium is part of the Sustainable

requirements, is expected to improve the safety, energy efficiency

Committee of the American Aluminum Association and works

and environmental footprint of the plant.

closely with the Can Manufacturers Institute to raise environmental

Known as Element 13, the recycling facility at the Muscle Shoals

awareness and promote recycling within communities.

Seco/Warwick successfully commissions walking beam solution SECO/WARWICKhas recently commissioned a 3.96 ton per hour capacity Walking Beam Furnace at NHK Springs India Ltd., Andhra Pradesh, India.

NHK Spring India Ltd., is a manufacturer of Automotive Suspension Components for passenger cars, commercial

vehicles and utility vehicles

fired burners, automatic ignition

continuous production in case

that will use this solution

system, flame monitoring

of short supply/unavailability

for mass production. Walking

system, furnace pressure

of any one fuel with minimum

Beam Systems made by SECO/

monitoring system, highly

switchover time. The furnace

WARWICK for spring application

equipped gas train system with

operation is controlled by

are best suited to automotive

mass flow meter, oil pumping

PLC except loading of leaf on

and railway industries.

system and hydraulic systems.

charging end.

SECO/WARICK’s Walking Beam System is equipped with dual –

The dual fuel system will enable NHK to stay in

International line-up for Furnace Solutions 12 This year’s conference Furnace Solutions conference is truly international.

Dr. Yakup Bayram, of PaneraTech and Fosbel’s Joe

the first time and presenting a

Dismatec covering extending

paper relating to the important

the life of electric furnaces,

interesting and enjoyable to

role of electricity in glass

maintaining regenerators,

float, container and fibre glass

forming and conditioning.

repairing fibre furnaces and the

engineers with strong relevant

inspection of furnaces.

papers and time to network

Training Day 5 will also

The two days will be of

McKintosh, both from the USA,

be of interest to furnace

are first time visitors as is Tunc

engineers. Peter West from

extending furnace life and

Goruney from Sisecam, Turkey.

Ardagh Glass will discuss the

service is the correct inspection

Training Day takes place at

repairing of Silica Crowns, with

and selection of refractories,

Lucideon in Stoke -on-Trent, UK

UK’s Electroglass will also be

additional papers from Fives

which will be covered by Sam

on June 7 and 8.

attending the conference for

Stein, Lizmontagens, Teco and

Franklin

Richard Stormont from the

www.aluminiumtoday.com/furnaces/

An important element to

with fellow professionals.

Furnace Solutions and

www.furnacesolutions.co.uk Issue 5 Furnaces International r 7

Company profile: Verallia

Glassmaker Verallia Ukraine invests in modernised furnace

Verallia Ukraine’s new furnace number 2 at its Zorya plant means the company can offer more complex-shaped bottles as well as more flexibility to its customers. Managing Director Daniel Saksik discusses the recent investment.

What benefits will the new furnace bring to Verallia and its customers?

The modernisation of furnace #2 has given us more opportunities to produce complex-shaped bottles. Verallia can now offer another service – short-run production for market players in the segment of lowvolume premium editions.

This installation is also a strategic move that will have a significant impact on Western European countries, with Verallia plants becoming more flexible to serve customer orders and support one another.

Why did you decide to modernise?

Having observed an increased demand in recent years for limited editions made of high quality flint glass, Verallia in Ukraine decided in 2013 to respond to this market’s requirements by launching the production of extra flint glass.

8 r Furnaces International Issue 5

Daniel Saksik, MD of Verallia Ukraine.

To achieve this, we use special high quality raw materials. This was one of the first steps in presenting Verallia in Ukraine as a high-end market producer of premium bottles.

Between 2013 and 2016 demand for short runs grew significantly, and Verallia in Ukraine implemented in its Zorya plant the single gob process and, for the first time in Ukraine, the Flex Line, supplied by Glass Production Service.

Considering demand in both domestic and export markets for premium products, Verallia in Ukraine consequently modernised its furnace in 2016. Its furnace #2 now feeds three production lines equipped with Flex Line technology, enabling several articles to be produced simultaneously: small runs that offer customers greater flexibility.

Is it a larger furnace than before? www.aluminiumtoday.com/furnaces/

Company profile: Verallia

The team at the Verallia Ukraine Zorya plant.

As Verallia decided to fully modernise the furnace, yes, capacities were also slightly increased. But even more than capacity, our main target was flexibility. And in this respect we are successful.

Will the furnace allow Verallia to extend its offering to customers?

The new furnace is taking our premiumisation strategy one step further.

Thanks to this new installation and the equipment already installed, we are able to increase our production flexibility, providing Verallia in Ukraine with a range of technical capabilities to produce a variety of products with complex shapes, thicker bases, and different types of body and finish.

Historically, Ukrainian customers prefer strong drinks. The market has become more marketing-driven and glass needs to adapt to create different designs, shapes and colours with perfect quality. All these factors are important to appeal to customers Can you tell me more about the 200 models the plant makes?

The number is rather impressive, considering we mostly manufacture different types of bottles.

But thanks to the flexible line on which we were able to produce 1-3 different items, we had 200 models per year. The latest modernisation improvements and additional Flex Lines will help us meet tomorrow’s challenges. www.aluminiumtoday.com/furnaces/

What other complementary modernisation actions occurred?

Furnace #2 was fully modernised in 2016.

The hot and cold ends were completely revamped and new inspection machines were installed. In addition to significant changes on the technical side, Verallia also improved working conditions for its 566 Ukranian employees.

We have also taken advantage of Verallia’s operational excellence programme, which lets us apply best practices, train our teams to the highest standards in the glass industry and offer top products to our customers.

How long did the refurbishment take?

A three-year programme in terms of preparation, this quite complex project was completed in 65 days from glass to glass on the Zorya plant. But what is even more important – all rebuilding and restarting deadlines were met. The first glass products were produced just as planned. This was quite an achievement.

The new equipment installed in 2016 is only one step in the global investment programme to fully refurbish the Zorya plant, which began in 2014.

This will be a step-change in Verallia’s expansion through an increase in our flint and extra flint production capacity, further product quality improvements for the benefit or our Ukrainian and non-Ukrainian customers as well as an optimisation of our energy efficiency.

Did you have any specific environmental specifications when you chose the furnace supplier?

During the rebuilding of the furnaces, which takes place every 10 to 14 years, Verallia always uses the most energy efficient technologies for glass melting. For instance, our proficiency in melting has enabled us to lower the energy consumption of furnace #2 in Zorya by more than 20%.

Our Zorya plant has put a huge effort to decrease the non-melting energy consumption, thanks to three main actions : � Optimisation of energy consumption on lehrs and feeders: Optimising burning and additional isolation on feeders.

Issue 5 Furnaces International r 9

Company profile: Verallia

� Energy saving on compressors : Optimisation of compressor station usage, elimination of air leaks. � Installation on furnace #2 energy saving lighting. Diode lamps installed are more efficient and consume less energy in less time.

Regarding waste, the priority is to set up solutions to reduce the quantities generated and for recycling and recovery.

The improvement in the integration of cullet,

both in quality and in quantity, is one of Verallia’s main objectives. Verallia uses internal and external cullet at its Zorya plant.

Who are the plant’s main customers?

Our customers are the biggest Ukrainian spirits and food producers, such as Bayadera Group, Nemiroff, and Eastern Beverage Trading in spirits, and Mondelez, Chumak, and Fozzi Group in food. Verallia in Ukraine has a high proportion of export sales.

Zorya’s furnace #2 is dedicated to high quality extra-flint and flint glass production has been completely rebuilt, together with its three production lines. Verallia has accordingly given itself the means to boost its position on the small and medium-run high-end markets. These new installations will also enable Verallia in Ukraine to extend its partnerships with many customers who have, over the years, expressed a real preference for extra-flint glass.

Where does the plant export to?

We export glass products to 16 countries. Many Western and Eastern European customers have already partnered with us to launch products in different market segments.

Our main export markets are Poland, Germany, Romania, Hungary and the Baltic countries. �

Contact *Managing Director, Verallia Ukraine, Zorya plant. www.ua.verallia.com

10 r Furnaces International Issue 5

www.aluminiumtoday.com/furnaces/

■ Bubbler Systems ■

There is more than one way to solve a problem i

■ Bubbler Systems ■ Electric Furnaces

■ Drains ■ Electro Boost ■ Electrode Holders ■ Engineering Services ■ High Q Holders ■ HVP Forehearth ■ Isothermal Unit ■ Mathematical Modelling

, Tomorrow s Technology Today

Investment

Verallia invests €30 million in its largest glass furnace Continuing its spending spree, Verallia has just invested €30 million on modernising its Azuqueca plant in Spain, to improve its standards of innovation and sustainable development.

A new furnace and facilities were installed at the plant, with the furnace being one of the world’s largest glass furnaces.

The new equipment was inaugurated in the presence of Verallia’s main customers, suppliers and local authorities at a ceremony led by Jean-Pierre Floris, President and CEO of Verallia (pictured).

This latest-generation furnace is the upgraded plant’s flagship innovation.

It is the largest the company has ever installed anywhere in the world.

It is also more sustainable, as it emits less C02 per metric tonne of glass produced.

With this new furnace, Verallia Azuqueca can produce two million containers a day (more than 500 jars a minute).

During the event, Jean-Pierre Floris pointed out that “Verallia is continuing to invest with the longer-term future in mind while aiming to continuously improve quality, flexibility and productivity.”

The Azuqueca renovation is proof of Verallia’s commitment to sustainable development, to reducing its consumption of virgin raw materials and to optimising its 12 r Furnaces International Issue 1

capacity for including recycled glass in its production processes.

It has also introduced a whole range of food safety improvements and workplace safety conditions for its employees with new ergonomic workstations that incorporate noise and heat protection and improved lighting.

Azuqueca is Verallia’s oldest plant in Spain and it specialises in the manufacture of food jars, with differentiating features according to clients’ demands so that their products stand out on the shelf.

www.aluminiumtoday.com/furnaces/

, Tomorrow s Technology Today

ms ■ Electric Furnaces ■ Drains ■ Electro Boost ■ Electrode Holders ■ Engineering Services ■ High Q Holders ■ HVP Forehearth ■ Isothermal Unit

e-glass ■ container glass ■ float glass ■ display glass ■ electric furnaces ■

www.fic-uk.com +44 (0) 1736 366 962

■ Mathematical Modelling ■ Bubbler Systems ■ Electric Furnaces ■ Drains ■ Electro Boost ■ Electrode Holders ■ Engineering Services ■ High Q Holders

...but the world’s leading glass companies come to FIC to solve theirs

, The World s Number One in Furnace Technology

FIC (UK) Limited, Long Rock Industrial Estate, Penzance, Cornwall TR20 8HX, United Kingdom GLASS SERVICE

A Division of Glass Service

Heat treatment

Drop quench furnaces Keith Watkins explains drop quench furnaces, for solution heat treating of aluminium components.

Drop bottom quench solution treatment furnaces are primarily used for solution treatment of aluminium parts prior to forming.

The requirement is a quick quenching of aluminium parts usually within five to 10 seconds so that the material arrives at ideal precipitation hardened condition. When heated evenly to a temperature of up to 550째C, a solid solution of copper is formed in the aluminium structure which flows throughout the microstructure. The furnaces are of inverted type with charge lifting and lowering facility to accommodate the high speed quenching including de-clamping, door opening and quenching. The furnaces can be of standalone type with charge carrier loader and quenching tank moving on the floor or floor mounted with charge carrier loader and quench tank/s sliding into a pit.

As the requirement is very fast quenching they are fully automated by the use of PLC and SCADA. These furnaces can also be used for continuous ageing cycle ranging from 16 - 24 hours time. Various quench media such as water, glycol or other polymer oils as per process requirement are used. Areas of application are generally used in aerospace industries for solution treatment and ageing of structural parts, also in forging industries for aluminium alloy forgings.

14 r Furnaces International Issue 5

Aerospace aluminium components sometimes require solution heat treatment combined with rapid water quenching. Drop Quench furnaces are specifically designed for just such applications.

Conformance to NADCAP (AMS2750E) is essential for aerospace applications and any furnace must meet temperature control, uniformity and data recording requirements.

Furthermore, the water quenching time must meet seven to 10 seconds to full immersion of the components.

The typical drop quench furnace is designed with the heating chamber elevated above rails, which carry a water quenching bath. The bath can be moved from underneath the furnaceheating chamber to accommodate loading and unloading the component-charging basket.

For certain applications a glycol based water solution is used for quenching. When glycol is utilised, it is common to have a separate rinse tank to clean the components of the glycol solution. Usually, the rinse tank is fitted with a spray system for the purpose of rinsing.

Spraying is effective, as it prevents glycol returning to the product surface one rinsed.

Drop quench furnace have a typical maximum operating temperature of 650째C and as processed for solution heat treatment at 475-530째C, annealing at 360-450째C and www.aluminiumtoday.com/furnaces/

Heat treatment precipitation hardening at 120-175°C. In some applications the precipitation process will be carried out in a separate furnace, mounted alongside the drop quench.

Heating is provided by nickel chrome sheathed rod elements positioned behind the side duct sheets and isolated from the working area to prevent heat radiating directly on to any part of the furnace charge, in the case of electrically heated equipment, otherwise gas burners are employed.

Process times may range from 20 minutes for annealing processes and up to 14 hours for hardening. Charge sizes may range from around a 1m cube up to a 3m cube. In some instances, special furnaces may be designed and built that are capable of treating very large components, such as aluminium plate sections and long extruded products in special alloy.

Within the furnace, high velocity air is circulated to assist in faster heat up rates and achieving the required temperature uniformity. Often this requires two or more specialist fans to be installed appropriately in adjacent positions to the main charge.

Usually, T4 and T6 heat treatment solution standards are required. A variety of options are available with the furnaces, which may include: � Temperature uniformity +/-5C � Temperature uniformity +/-3C � Quench speeds 5, 7, 10 or 15 seconds � Quench tank cooling systems � Glycol management system � Gas burner recuperation � Additional quench tanks Normal features include: � Fastest ramp-up and lowest consumption � Dual speed electro-mechanical

or pneumatic winch system, simple

and reliable � Electric or gas heating � Ceramic fibre block module insulation � Stainless steel air baffle � Sliding or swinging door � High volume recirculating stainless

steel fans www.aluminiumtoday.com/furnaces/

�

Pneumatically operated doors Tank mounted on mobile cart with rails � Heating elements and belt driven

circulating fan mounted

in protected chambers beside and

above working area �

Contact

Keith Watkins, GW Consumables

Recently, Thermserve Ltd of Telford, UK has built a medium sized drop quench furnace. Thermserve’s drop quench furnaces are designed for an intensive and continuous use up to 650°C. The loading and quenching systems are fully automated

by PLC. The dual speed pneumatic winch system permits a controlled acceleration/ deceleration of the load descent and has proven to be very reliable and sturdy when compared with more commonly used systems. The insulation of drop bottom ovens consists of 150mm of ceramic fibre modules. This high efficiency material assures minimum heat loss and heat storage for rapid heat cycling and energy economy. Contrary to layered blanket arrangement, ceramic blocks have a great resistance to high air velocity abrasion. This configuration is extra durable and requires very little if no maintenance.

A complementary Precipitation Hardening is the heat treatment process generally undertaken between 100 and 200°C and causes dissolved alloying elements to finely precipitate within the aluminium. This results in the alloy becoming harder and stronger. This process is time dependant, hence, the term “age hardening” is often used.

Types of products heat treated for the general engineering sector include fastenings, manifolds for diesel engines in the marine sector, medical parts such as wheel chair frames, various tubular fabrications etc. In the automotive sector from major integral parts such as turbo housings, cylinder heads, cylinder blocks through to bumper brackets and aerospace high integrity components for military and civil applications.

With the advancing growth in aluminium use, the demand for more drop quench furnaces is increasing. �

Issue 5 Furnaces International r 15

Case study: Steel

Environmentally friendly walking beam furnace ArcelorMittal Hamburg’s decision to choose an environmentally friendly, high performance/low emissions walking beam furnace for 16.5 m special steel billets could offer up the benchmark for quality and operational costs in long products heating systems.

By A Biliotti* and D Garassino**

Fig.1: General overview of a walking beam furnace.

A Danieli Centro Combustion (DCC) furnace equipped with a control system supplied

by Danieli Automation has been chosen by ArcelorMittal Hamburg.

The furnace has been designed for safe and reliable operation and offers a thermal profile that achieves optimum heating efficiency thanks to improved convective heat exchange in the furnace’s unfired zone. Proprietary flameless burners, supplied by DCC, reduce the environmental impact of the equipment.

The ‘state-of-the-art’ equipment, coupled with Danieli Automation’s fully automatic control logic, will allow the most flexible reheating practices to match production mix requirements at the plant for low and medium carbon, bearing, spring and cold heading steel.

During the next shutdown period, the existing mill will be connected to the new furnace and this will allow the steelmaker to increase the weight of coil to 2 tonnes and improve productivity and efficiency at the special steel wire rod mill on-site.

A walking beam furnace for billets 16 r Furnaces International Issue 5

Fig. 2: Discharging of a billet.

The walking beam furnace supplied by DCC guarantees a production rate of 175 tonnes/hr at a discharging temperature of 1,250°C (Fig. 1). The furnace can achieve a 235 tonnes/hr production capacity meaning that ArcelorMittal Hamburg can increase production going forward by acting on the installed thermal power.

The furnace can process a wide range of products including 140x140 mm billets with lengths ranging from 9m to 16.5m (Fig. 2).

Products are charged into the furnace in a single row, with processed steel grades ranging from low carbon to more valuable metals such as 100Cr6, 34CrMo4, 42CrMoS4, 30NiCrMo3.

The furnace has six combustion control zones which include two types of burners (frontal for the walls and radiant for the roof designed using Ultra Low NOx technology) with different heating capacities according to zone requirements. This configuration ensures the best heating quality and the fastest response time when a change in production is required. Frontal MAB burners (Multi Air Burners) are designed to operate with PHL (Proportional High Low) control logic to create optimal conditions at all operating levels. This is achieved by cyclically turning the burners on

Case study: Steel and off to reduce thermal flow according to requirements. This results in higher process heating quality and easier furnace management.

MAB and radiant burners rely upon flameless technology to reduce Nox emissions, while offering a more uniform heating in all burner areas.

DCC will supply ArcelorMittal Hamburg with all the necessary handling equipment upstream and downstream of the furnace from billet charging on the stock yard to the first stand of the rolling mill, including pawl tables, transfer devices, weighing and measuring systems, reject devices, diverter and pinch roll.

To xidizin material and energy loss, DCC’s and DA’s combined technology ensures that no billet is rejected in the case of mill cobles: along the 90-metre long rollerway between furnace and pinch roll, machines and logics have been designed to have constant control of billet temperature, and in case of mill stoppage, up to two billets can be charged back in the furnace.

Flameless burners New burner design has been greatly influenced by national and international norms and regulations concerning environmental protection: a modern burner guarantees optimal efficiency while complying with ever-decreasing limits on pollutant concentrations in waste gas exhausts.

Furnace efficiency is generally increased by pre-heating combustion, a technique that recovers part of the heat from the exhaust fumes, while increasing flame temperature.

Unfortunately, combustion temperature amplifies Nox emissions. For this reason, over the past few years innovative combustion technologies have been developed, with the aim of maintaining high burner efficiency and reducing polluting emissions into the environment.

Two of these technologies are ‘staged combustion’ and ‘flameless combustion’.

DCC’s R&D department has been particularly active in this field, with theoretical simulations and experimental campaigns (research furnace exclusively dedicated to burner testing), which have enabled a complete range of highwww.aluminiumtoday.com/furnaces/

performance burners to be developed.

The main advantages of flameless combustion are: • Significant reduction of polluting emissions • Uniformity of flame temperature, therefore higher product quality • Increased furnace efficiency • Reduction of combustion noise.

Fig. 3: Staged combustion; semi-visible flame.

Fig 4: Flameless combustion; invisible flame.

DCC has developed a new generation burner that guarantees extremely low Nox emissions and uniformity over the entire operational range and for any temperature of the furnace chamber. This is achieved by using two different combustion techniques: staged combustion (below self-ignition temperature) and flameless combustion (above self-ignition temperature).

The fundamental concept, which is common to both techniques, is to xidizin temperature peaks and oxygen presence in the combustion reaction by diluting the reacting gases with those that have already been combusted.

Staged combustion is performed by injecting combustion air in different steps, thereby obtaining a primary combustion zone which is rich in fuel (reducing zone), and a secondary combustion zone rich in air ( xidizing zone), which is highly diluted by fume recirculation. This allows a gradual and complete combustion, avoiding the coincidence of high oxygen content and high reaction temperature.

The system is based on the specific geometry of the air diffuser inside the burner, which leads the primary and secondary air flows to the different combustion zones, with the appropriate speed and angle. This type of staged combustion permits a substantial reduction in Nox emissions and the high recirculation factor reduces the temperature gradient along the flame length (Fig. 3).

Once the furnace temperature is above the self-ignition temperature, the flameless combustion mode can be activated, by switching gas entry to a separate gas lance while keeping the same air feeding. The special fluid-dynamic design and the high gas and air speeds further increase flue gas recirculation and cause an expansion Issue 5 Furnaces International r 17

Case study: Steel burner is increased uniformity of furnace temperature. This implies an improved temperature uniformity in the furnace charge, and higher quality final products.

The burner has proven to be extremely flexible and can be used either with high calorific value fuels (such as natural gas) or with low calorific value fuels; combustion air can be pre-heated to temperatures in excess of 500°C, in order to increase combustion efficiency and overall furnace performance.

Fig. 5: NOx emissions (ppm), measured with natural gas firing.

Optimisation model Danieli Automation (DA) Furnace Level 2 is a software package consisting of several modules that work in real time in order to optimise the reheating process. They can be grouped into the following tasks: • Material tracking and communication with other systems • Process Models • Process Control • User interface

Fig. 6: An example of furnace consumptions in the long run.

of the reaction process to a larger volume; the low oxygen content in the reaction ensures a diluted combustion that makes the flame invisible (Fig. 4).

Burner performances Fig. 5 shows experimental measurements of NOx emissions as a function of furnace temperature and air excess (evaluated in terms of O2 content in the fumes); the three curves in the upper left refer to the staged combustion mode, while the three curves in the lower right refer to the flameless mode.

The best NOx performance is obtained by operating the burner in the green areas: staged combustion is used for heating up the furnace, and in pre-heating zones working at a low temperature; at higher temperatures the burner is switched to flameless combustion, which cuts emissions by 50%.

Another advantage of the DCC flameless 18 r Furnaces International Issue 5

The use of instruments to measure billet temperature in a furnace has always been debated. As the noisy environment makes a direct measurement very difficult, a mathematical model of the heating process is used as a virtual sensor and, at the same time, it is applied in the set-up of the control strategy as explained below. It is based on a finite difference model in order to evaluate material bulk temperature and uniformity. All the relevant thermo-physical characteristics of steels and interactions within the furnace chamber and among billets are considered for the calculation of temperatures when the mathematical model is used as a virtual sensor.

The furnace model is used for the control strategy based on a Model Predictive Control (MPC) technique. It uses a feed-forward algorithm to estimate furnace behaviour from its actual condition and evaluates the proper actions needed to get the desired product output, while fulfilling constraints and optimising furnace performances. In fact the heating process is slow and requires the right amount of energy and time to be given to the products. In addition the state of the furnace is not observable until the end of the process, when it is too late to get any correcting action. www.aluminiumtoday.com/furnaces/

Case study: Steel The first aim of MPC is to automatically calculate furnace set points in order to minimise the difference between the mean product temperature and their heating practice.

Heating practices describe the heating rules for each product and are open to process engineers, who can manage them in order to achieve the desired results, like fuel consumption saving or following special heating strategies (low decarburisation, alloyed steels, …).

A dedicated system for combustion monitoring installed in the chimney provides online fumes. Typical monitored emissions are nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2) and sulfure oxides (SOx). These values can be stored by a trending and can be used for certification according to the regulation in force.

Industry 4.0 Fully in line with the Industry 4.0 paradigm, the data-driven philosophy exploits the hidden value of the usual parameters for process control. In fact, even if obtaining a quantitative estimation of consumption savings is immediate, additional constraints can be addressed by applying online and real time multi-objective techniques. In this context, DA’s online control system maximises furnace efficiency and directly acts on environmental impact and other aspects. Proper combustion ensures that emission limits are met and production yield is increased as a consequence of reduced weight loss due to scale formation (Fig. 6).

Quality assurance is made possible by a reporting system that provides all the necessary data for periodical evaluation of the furnace, such as fuel-specific consumption, temperatures, ratios, and analysis.

The combination of adaptive mathematical models and the feed-forward strategy allows the MPC to maintain consistent behaviour during stationary conditions and a quick reaction to transitory productions.

In the first instance it allows the steel maker to balance furnace loads according to installed heating power. In the latter case, it anticipates furnace behaviour according to the incoming production, optimising www.aluminiumtoday.com/furnaces/

transitions of productivity (full to slow production and back), product geometry, charging temperature and steel quality.

Getting value from data From the 1960s automation systems and equipment have gained in popularity in the steel industry. Today, all steel plants are equipped with a series of complex systems that monitor relevant data and control processes automatically.

Danieli Automation Q3 Intelligence, a business intelligence platform dedicated to the metallurgical production process, can improve things further by merging, storing, processing and evaluating data from, say, Danieli Automation Furnace Level 2, and transforming it into knowledge.

In a scenario where smart systems are applied more and more to industry, Q3 Intelligence Analytics allows exploration and investigation of past process performances to gain insight and drive process design and planning, via advanced statistical methods and predictive modeling. Q3 Intelligence Analytics can help answer questions such as “why is this happening?”; “what if these trends continue?”; “what will happen in the future?” (predictions); “what is the best that can happen?” (optimisation).

Contact

* Danieli Centro Combustion, process engineer ** Danieli Automation, design engineer – process Control Systems www.danieli.com

Conclusions DCC has proposed a new generation of furnaces that integrate the sharp edge of combustion technology with the integrated design of both the process and environmental aspects. In this context, the staged/flameless burner is yet another example of DCC’s focus on innovation. The company’s chief objective is to provide leading-edge technology, allowing high product quality, lower operating costs, trouble-free operation and ever-increasing environmental friendliness.

Danieli Automation Level 2 is a robust control system which allows users of the DCC furnace to achieve uniform operation, process cost savings and product quality. A careful analysis of its performance indicators can also lead to product flow optimisation and improved performance of the entire plant.

Issue 5 Furnaces International r 19

FUTURE STEEL FORUM

REGISTER NOW TAKE ADVANTAGE OF OUR GROUP RATE Book 5 or more passes to receive a 20% discount

2017 14-15 JUNE • SHERATON WARSAW HOTEL • WARSAW

Applying Industry 4.0 to the steel industry What is Industry 4.0 and how can it assist the global steel industry in its quest for greater efficiencies? Two questions, among many others, that will be answered by the experts at the Future Steel Forum in Warsaw in June 2017.

The Future Steel Forum is a live discussion of the issues surrounding Industry 4.0 or ‘smart manufacturing’ and will endeavour to cover all bases, including the all-important subject of cyber security, the role of human beings in the factory of the future, how to survive a cyber attack and the all-important process safety and control.

Speakers from academia, the steel industry and the world of steel production technology will explain the key concepts behind the digitalisation of steel manufacturing. Myths will be exploded, ideas challenged and terminology explained.

SPEAKERS INCLUDE:

Pinakin Chaubal, ArcelorMittal Global R&D

Jane Zavalishina, Yandex Data Factory

Dr. Michael Eder, Voestalpine

Michael Bremicker, KPMG AG

www.FutureSteelForum.com 20 r Furnaces International Issue 5

www.aluminiumtoday.com/furnaces/

BIFCA column

British Industrial Furnace Constructors Association

Top 10 tips to improve efficiency in heat treatment processes Heat treatment processes involve high energy usage 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 noncompliant waste product and costly fines. Here, Amber Watkins of Eurotherm, Scheider Electric, discusses No. 5, 6 and 7 of how to get better efficiency in heat treatment processes while meeting industry standards, with furnace applications in mind.

No 5: Safety & over temperature alarms During the heat treatment of valuable materials, it is sensible to use an over temperature alarm unit also known as a load policeman in order to trip heaters in the event of a serious control fault. If the heater gets stuck “on� for any reason, the workpiece will overheat, possibly resulting in the waste of a high cost product. For failsafe operation, a separate controller or indicator is used and the alarm will typically be set a few degrees above the high limit to trip the alarm in the case of a failure. Different batches of product may have different critical temperature limits and a common problem is that the operator needs to change the setpoint of the load policeman manually for each type of material. This leaves a lot of room for error as the operator can forget to set the limit or incorrectly enter the data.

A simple way to solve this problem is to use a main controller that can retransmit its SP via 4- 20mA I/O or digital communications, to a policeman controller with a Remote Setpoint Input feature. The remote SP signal fed into the policeman can then be configured to trigger an alarm at a specified number of degrees above the SP, for example +10°C. Using this method www.aluminiumtoday.com/furnaces/

prevents operator errors and is a reliable way to prevent any type of material from exceeding its critical temperature limit.

The same theory can be applied to heat treatment furnaces where personal safety can be compromised in the event of an excessive temperature and to meet safety standards such as NFPA 86. If the upper tolerance of the personal safety temperature limit is breached, not only can you alarm using the overtemperature policeman instrument, but you can also use the device to automatically remove the power input to the furnace, protecting personnel from harm and the plant from a hazardous fire situation. AMS2750 allows the over-temperature instrument to also serve as the high temperature reading and pick up the hot part of the Workzone based on the most recent furnace survey, as long as this temperature is recorded for certain instrument types. A digital recorder can be used to record the temperature measurement from the policeman controller.

The benefit of using modern control and digital recording equipment is that alarms can be sent directly to the engineer by email or SMS, and the data from the event is digitally recorded for review afterwards.

Issue 5 Furnaces International r 21

BIFCA column

No 6: Moving from paper to digital recorders For heat treaters who are still using paper recorders, there are ongoing problems involving cost and maintenance of replacing charts and pens, plus secure storage of the data in paper chart form. There is also the possibility of pens or paper running out during a batch. Missing data can result in wasted time for quality engineers while assessing the non-conforming process and can result in the possible scrapping of the product.

There are several benefits of moving to secure digital recorders. Firstly, there is a cost saving as you no longer need to buy, store and conscientiously dispose of paper and pen consumables. Secondly, you will save on maintenance time as there is no need to replace paper and pens on a regular basis and the product is more reliable due to less mechanical parts. Last but not least, the data is stored in digital format which is much more convenient to view on a PC, Tablet or Smartphone. Full featured secure digital recorders store data in a secure tamper resistant file format within the product which can be securely transferred to removable media (USB etc.) or servers over a network. The data can then easily be retrieved for quality checking, reporting and auditing, unlike paper charts which can easily be mis-filed, lost, or run out during the process.

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

No 7: What do we mean by Secure Data?

By 2015, AMS2750 standards stated that any electronic records created during calibration or the heat treatment process must be unalterable without detection; presentable in a both a human readable and electronic form for inspection; show evidence that the record was reviewed; and provide methods to limit system access to those authorising. The data must also be securely stored in an archive system, but readily available for retrieval throughout the required retention period.

Many data recording systems such as those within SCADA, PLCs and basic data loggers save data in .csv file format. This format, while very useful for easy import into spreadsheets, is in no way safe from tampering, or able to indicate that it has been tampered with, and therefore cannot be used for processes that require high level data integrity like 3rd party audits and government standards. Another problem can arise from the way data is collected. Some SCADA software packages record data not from within the recording product but over communication lines. If communication is lost, so is the data, making this kind of system unsuitable for regulated heat treatment applications.

When choosing a method of recording, the first feature to look for is a secure file format that is not editable. Data recorders and some precision PLCs are available that save data in binary check summed files which are resistant to tampering and only viewable using specific software. This is a much better solution than using .csv files which are easily editable and therefore not secure. An added benefit is that 22 r Furnaces International Issue 5

the files can be compressed so more data can be stored on the product itself before transferring to other media. Another important feature to look for is that the data is recorded at the point of measurement, i.e. in the recording or control product, which solves the problem if communications are temporarily lost during transfer of data. Look for products with self-healing store-and-forward strategies that automatically backfill any missing data caused by breaks in communication as this will save time compared to transferring missing data manually.

Full featured recording products have security management options that provide a tamper resistant audit trail for recording User Names, Passwords and Access Permissions. All operator activity is logged and recorded in a secure database. For example, an operator could be given permission to change configuration by digital signature or they may need to get a second You can read the final level of authorization from installment from a quality engineer. The important point is that the Eurotherm’s top ten tips on changes will be logged improving effeciency in for quality personnel and auditors to review should heat treatment in the next they need to. issue of Furnaces Features like these International, out in June that bring traceability of ‘who did what’ in a process aid compliance to standards like NADCAP and AMS2750. www.aluminiumtoday.com/furnaces/

Photo credit: Quais de Saône - Lyon - Marie Perrin

WHERE THE HOLLOW GLASS INDUSTRY MEETS TO DO BUSINESS

After the success of 2015, Glassman Europe is returning to Lyon, 6-7 September at the CCC Lyon. Over 600 senior-level executives attended and with a packed conference theatre, Glassman Europe is expected to be popular once again this year.

Glassman Lyon will be the ideal opportunity to network with industry professionals from all around the world whilst learning about the latest products and services on the market. The exhibition and conference are free-to-attend so make sure you don’t miss out.

PUT THE DATES IN YOUR DIARY NOW Stay in touch:

Official media partner:

Join the Glassman Events Group Organised by:

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Refractories

How to ensure effective furnace lining efficiency In this article, Steve Chernack from Morgan’s Thermal Ceramics business outlines his top five tips for achieving maximum furnace lining efficiency.

Refractory engineers remain under constant pressure to increase the performance of furnaces, incinerators and reactors to maximise energy efficiency. Although there are many materials that can enhance the efficiency of furnaces, many still lose heat when in operation through flue gas, excess moisture in fuel, or continued opening of the furnace door. This is preventing many engineers from realising maximum energy efficiencies, causing businesses to focus their attention on reliable insulation and lining of furnaces from the floor to the stack, to contain as much heat as possible during operation. Companies such as Morgan Advanced Materials are responding to this challenge with a variety of lightweight, energy saving solutions with unique refractory designs that significantly minimise heat loss in these units.

The central processing unit in many refineries and petrochemical plant furnaces consumes more energy than any other piece of equipment, making it essential that all the correct measures are put in place to realise as much energy efficiency as possible. An efficient furnace is key to reducing overall maintenance costs and ensuring that these facilities run smoothly without undue revenue loss caused by downtime.

The right refractory materials deliver a protective and insulating layer of heat resistance attached to the inside of the shell, hearth, and tap holes of a furnace. Not only does this protect furnace parts from extreme heat caused by smelting, but it also prevents excessive heat loss and can lead to greater overall energy efficiency. However, identifying the need for new furnace lining 24 r Furnaces International Issue 5

and installing the right material is not an easy task. In order to get this right, we have outlined five top tips for maximum furnace lining efficiency:

“Products such as Morgan’s Superwool Plus insulating fibre offer up to 20% lower thermal conductivity when compared with other products, making it 17% more energy efficient than traditional Refractory Ceramic Fibres (RCF), and Alkaline Earth Silicate (AES) insulations.”

Use infrared (IR) thermography inspection to evaluate existing lining Ensuring lining quality is critical to protecting the steel from heat and minimising instances of heat loss. Furnaces which have developed cracks over time are prone to leakage. Some may also have design issues that are not visible from the outside, which can cause heat loss issues over time. This is not uncommon with furnaces that have a painted surface.

In order to identify hot spots where the unit is leaking or reducing performance, infrared thermography scans are essential.

This typically involves pointing an infrared camera at several points on the furnace casing to analyse the external temperature and identify any areas where heat loss is occurring. Although these can be conducted from within the furnace, such scans are more effective when performed from the outside because this enables engineers to keep the furnace in operation. It is advised that specially trained application engineers carry out any infrared imaging, analyse the scans, and provide recommendations on the most appropriate repair options.

Make repairs on-line whenever possible In the instance that an infrared thermography inspection reveals a need for repair, Morgan always advises that this be done on-line wherever possible. This is the most effective method of maintenance and is reliable, fast and economical, since www.aluminiumtoday.com/furnaces/

Refractories the unit is still in operation. After all, boilers and process units are constantly generating revenue so any downtime experienced will likely impact a business quite significantly.

Of course, this option does depend on the temperature of the furnace, the difficulty of accessing a particular area, and how large the hotspot is.

Morgan’s Superwool and Kaowool insulating pumpable solutions can be installed by pumping from the outside of a furnace or boiler, filling cracks and voids caused by deteriorated insulation. Effective and simple to apply, these products are ideal for providing thermal insulation efficiencies behind boiler tubes in sidewalls, seals and floors. They can also be used to repair ovens, furnaces, and other process equipment.

For traditional repairs, the furnace must be shut down and cooled until it is safe for maintenance personnel to enter and repair the lining with fibre blankets, pumping solutions, or monolithics.

Consider engineering design carefully In order to realise maximum operating efficiency for the materials specified for furnace relining, it is important to ensure that the engineering design is suitable. Not only must the materials have enough studs to hold them in place, they also require sufficient joints for expansion or shrinkage.

If you install a brick lining without adequate expansion joints, the brick can grow so large that it pushes up the entire lining off the furnace wall. This will lead to further inefficiency, requiring the entire process to be repeated.

Select the right material for furnace rebuilds Some repairs identified by infrared thermology scanning can be too large to address on-line and instead the unit must be shut down for a furnace reline, or process heater reline. In this scenario, it is important to select the right refractory materials to facilitate a successful furnace rebuild. This will lead to greater efficiency, reliability and lower maintenance costs.

The best place to start when selecting this material is by using a heat flow analysis www.aluminiumtoday.com/furnaces/

Superwool pumpable

Superwool blanket

software programme, in which temperature and use factors are inputted to obtain information on the best materials to be used. Properties including hardness, density, mechanical resistance and insulating factor will vary depending upon the furnace application.

If your furnace is an older model, it will likely have a different type of insulation to that which is commonly specified today, presenting an ideal opportunity to upgrade when relining the furnace. Products such as Morgan’s Superwool Plus insulating fibre offer up to 20% lower thermal conductivity when compared with other products, making it 17% more energy efficient than traditional Refractory Ceramic Fibres (RCF), and Alkaline Earth Silicate (AES) insulations.

This is made possible due to maximised fibre material contained within the solution.

Its low bio-persistence also makes it a reliable and effective replacement for RCF insulation.

Ensure a successful installation The final point to consider when lining a furnace is to ensure that the installation is completed correctly by somebody who has the required level of skills for the task. The number of products available for furnace lining is vast, and all come with their own unique installation requirements. Getting this wrong will cause inefficient lining, as well as wasting large sums of money.

An example of these specific installation requirements can be seen with concrete.

If concrete is not mixed with the right volume of water at the correct temperature, the material will not develop properly, it will be difficult to place, and is unlikely to reach expected properties. An ineffective, or inaccurate installation is as bad as not having a good design and not making the right material choice. Get all these points done correctly and you can benefit from an effective and efficient furnace lining for many years to come.

Contact Morgan Advanced Materials http://www.morganthermalceramics.com/furnace-lining Issue 5 Furnaces International r 25

Refractories

A solution for measuring refractory thickness in glass furnaces PaneraTech has developed its SmartMelter technology in partnership with glass industry leaders such as O-I and Libbey Glass, which has led to a breakthrough solution in the ongoing problem of refractory thickness measurement. Yakup Bayram* discusses below:

Furnace life optimisation has always been an imperfect goal for glass manufacturers.

The lack of deterministic methods for measuring refractory thickness has made it risky to push a furnace campaign too far without performing maintenance. Because of the high cost of repair, the industry has tried for many years to find a way to maximize furnace campaign without high risk.

Unfortunately, the best methods these efforts have produced only ‘improved speculation’. After decades of research, the industry appears to have conceded to the fact that this will always be a flawed process. The balance between leak prevention and asset optimisation has become an accepted struggle - accepted as an unsolvable problem.

However, PaneraTech, a company that specialises in developing radar-based sensor solutions for asset life and process optimisation, was approached by O-I and Libbey Glass to work on a solution for refractory thickness measurement. Because of its experience in developing advanced radar technologies, PaneraTech’s engineers had the right background to find a method for ‘seeing through’ furnace walls.

The research was funded by Libbey Glass, O-I, and the National Science Foundation (NSF) Industrial Partnership Division.

Libbey supplied the development furnaces, 26 r Furnaces International Issue 5

PaneraTech supplied experienced engineers, and the teams worked closely together to develop a method for measuring refractory thickness. The result is a comprehensive furnace inspection and maintenance solution called SmartMelter.

Building on existing applications Advanced radar technology is used in many applications to detect anomalies, and PaneraTech’s engineers have experience working with this technology for defense applications and more. For example, radar can detect the early presence of tumors in the brain by identifying cracks and voids.

This same technology is used to find pipes underground. The collaborative research team believed that the science behind these techniques could lead to a similar application for furnace walls.

The PaneraTech engineers applied their experience with radar imaging and computer tomography to develop sensors that detect areas of erosion inside furnace walls. These sensors launch radar waves into refractory walls to collect erosion data and refractory thickness measurements.

Trained personnel can take measurements easily from the outside walls with the touch of a button. This process is safe and unintrusive, using the same radio waves that your phone uses, but with significantly less power - about one million times less.

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Refractories

The comprehensive solution, which has been validated in several trials with major industry leaders, includes transmission of the collected data to a software system for evaluation and record keeping.

Measuring the walls The SmartMelter solution requires a onetime mapping of the furnace walls for accurate measurement analysis. Sidewall blocks are mapped as numbers, and insulation sections are mapped as letters.

Once this has been completed, furnace inspection is a two-step process: take measurements and analyse the data.

Two different sensors are used to detect glass infiltration and measure wall thickness; the collected data is transmitted to SmartMelter XSight software for a ‘view’ of actual wall conditions. This enables condition-based maintenance for the first time in the history of glass manufacturing.

The Refractory Thickness Sensor (RTS) records the interface between the glass and the wall to measure residual refractory www.aluminiumtoday.com/furnaces/

thickness, such as fused cast AZS. The RTS is placed in direct contact with the AZS wall. The Furnace Tomography Sensor (FTS) interacts with the insulation layers to map early-stage glass penetration and measure residual insulation thickness; it is placed directly on the insulation wall.

Each measurement takes about one second to record. Depending on accessibility to walls and size of the furnace, total furnace inspection can take from half a day to two days to complete. SmartMelter is shown to work on the following refractories and insulations: Fused Cast AZS, High Zirconia Fused Cast AZS (96%), Bonded AZS, Super Duty Fire Brick, IFB, Fire Board, Clay Flux, Sillimanite - just about any insulation material used in the furnaces.

The entire system is self-diagnostic and maintenance-free. The SmartMelter sensors do not interfere with other instruments, and can be used in hot environments. The sensors have touched surfaces as high as 1650°F (900°C) without incurring any damage, and they are designed to shut Issue 5 Furnaces International r 27

Refractories down at dangerous levels.

has also been validated by a successful demonstration on a float line furnace.

A global float glass manufacturer was preparing to lower the glass line for hot repair and invited PaneraTech to perform a blind trial on one of its furnaces in Europe.

Without knowledge of the actual thickness of the fused-cast AZS block, PaneraTech measured a total of eight blocks from both sides of the float line furnace.

One week after the measurements were taken and submitted to the manufacturer, the glass was lowered to a safe level.

The blocks were recovered and the manufacturer compared the SmartMelter RTS Sensor data with the actual AZS thickness. The SmartMelter measurements were within 5mm (0.2 inches) of the actual thickness of the blocks.

Analysing the data Once the measurements have been collected, the data is transmitted to software and displayed for analysis and visualisation. Each mapped refractory block and furnace section is labeled in the software for a complete visualisation of refractory thicknesses and glass penetration areas. The software system also keeps records of all furnace inspections, including thermal images, endoscopy, and visual reports.

With this clear view into refractory walls, no speculation is necessary to make decisions about furnace maintenance.

Costly measures such as applying an overcoat or shutting down for repairs can be postponed without risk until the actual condition of the furnace requires it. The glass industry no longer has to accept the struggle between safety and furnace life optimisation.

Case study: container glass furnace The SmartMelter RTS Sensor has been validated on a container glass furnace at Vidrala. PaneraTech was approached under the International Partners in Glass Research (IPGR) to perform a blind trial of the RTS Sensor before the furnace was drained for cold repairs. PaneraTech mapped the furnace walls and collected measurements five days before the drain, with no prior knowledge of actual wall thickness. Eleven spots were measured on the furnace from both sidewalls, a doghouse, and the area between the throats. Before the furnace was drained, the collected data was submitted to Vidrala.

Vidrala recovered the original blocks and measured the actual residual thickness after the furnace drain. They compared these measurements with the measurements recorded by the SmartMelter RTS Sensor. The overall thickness of the wall at the glass line was within 4mm (0.15 inch) of the measurements taken by the SmartMelter.

SmartMelter demonstration programme PaneraTech is currently enrolling customers for its SmartMelter demonstration programme. Through this programme, glass manufacturers can experience SmartMelter first hand. The participating company identifies a furnace that is at critical stage.

Before operations cease for maintenance or rebuilding, PaneraTech maps the furnace and trains personnel to collect data with the sensors and evaluate the data in XSight software. PaneraTech inspects the furnace along with the company personnel to ensure that they are trained to measure walls correctly. The company receives complete data on the condition of furnace walls and retains access to XSight software for 6 months. More information on how to join the programme is available on PaneraTech’s website.

Contact *CEO, PaneraTech, USA www.smartmelter.com

Case study: floatline furnace The Refractory Thickness Sensor (RTS) 28 r Furnaces International Issue 5

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Refractories

A method to improve regenerator crown insulation Prof. Stan Lyutskanov* highlights how the thermal insulation of furnace crowns can have an impact on energy efficiency and cost savings for manufacturers.

Bulgarian company Lubisol can offer energy and fuel savings thanks to the efficient thermal insulation of glass furnace crowns.

Lubisol’s crown insulation design is based on the principle that efficiency can be improved by applying a combination of light insulating bricks with its 2-SL insulating material.

Lubisol 2-SL contains foamed aluminium phosphate (AlPO4) in the form of granules, with a specific density of 0.33kg/dm³ and low thermal conductivity. The material is suitable for high temperature applications.

Its insulation package has been applied on a large number of glass furnace crowns, including regenerator crowns, with excellent results.

The efficiency of the regenerator crown insulation is often underestimated. The area of the regenerators is only 50% smaller than the melter crown area and the design with improved efficiency should be considered as an important source of energy and fuel savings.

Lubisol has gathered plenty of positive experience, taking into account the specific conditions connected with the regenerator’s crown design. The maximum temperature in the regenerator crown is usually about 1250°C, which is much lower than the 1560 – 1600°C temperature that prevails in melter crowns.

The lower maximum temperature allows the application of more efficient insulation and larger energy and fuel savings.

� Fig. 1: Heat losses of a typical glass regenerator crown with a silica crown

� Fig. 2: Heat losses and temperatures after the upgrading of the same crown after apply-

thickness of 300mm and two layers of light silica bricks.

ing a layer of 114mm Lubisol 2-SL.

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Issue 5 Furnaces International r 29

Refractories � The latest Lubisol crown insulation package has been applied to 80 glass furnaces worldwide in the past 10 years.

Sodium silicate furnaces The heat losses and temperature distribution of magnesite regenerator crowns of a furnace melting sodium silicate were studied. The heat losses were high: 4708W/m². The same crown showed an improved design with a Lubisol insulation package. Heat losses were reduced to 1064W/m². The reduction of the heat losses was 3544W/m² and fuel savings was 4961m³/m²/year. For an area of 100.6m² the amount of saved fuel will be 499,136m³/year at a cost of €124,784/ year. This case history shows that the heat losses can be high when the importance of the efficiency of the regenerator crown is underestimated.

Upgrading to improve efficiency is applicable on all kinds of regenerator crowns, made out of silica, magnesite, mulite, sillimanite or fused-cast refractories.

The Lubisol insulation package is suitable for application on all types of glass melting furnaces, including float, container, tableware, technical glass, sodium silicate and others.

The latest Lubisol crown insulation package has been applied to 80 glass furnaces worldwide in the past 10 years.

About 70 of them also have insulation on the regenerator crowns. Lubisol insulation has also been applied on two float glass furnaces – one in Turkey and one in Bulgaria. The results have been excellent with a large amount of fuel saved.

Insulation has also been applied on 12 container plants in Turkey and eight in India. The best reference for Lubisol is the fact that one single large glass manufacturer has applied its insulation on 18 glass furnaces.

Lubisol has a computer programme for heat loss calculations, which shows the temperature distribution among the different layers of the glass furnace crowns.

The calculations have made it possible to optimise the total insulation effect by choosing the suitable thickness for the layer of Lubisol 2-SL. Several cases below highlight the improved efficiency of regenerator crown insulations carried out by Lubisol.

Container glass furnace regenerator crowns Fig. 1 displays the heat losses of a typical glass regenerator crown with a silica crown of 300mm thickness and two layers of light silica bricks. The heat losses are 2034W/m².

Fig. 2 shows heat losses and temperatures after the upgrading of the same crown after applying a 114mm layer of Lubisol 2-SL. The heat losses are reduced to 923W/m². The difference of 1111W/m² brings fuel savings of 1540m³/m²/year natural gas. For an insulated area of 90m² the amount of saved fuel is 130,500m³/year at a cost of €32,625/year.

Float glass furnaces The heat loss calculations and the temperature distributions shown in Figs. 1 and 2 are also valid for regenerator crowns in a typical float glass furnace. The heat losses are reduced from 2034W/m² to 923W/m² after upgrading the crown with Lubisol insulation.

The amount of saved energy is 1111 W/m² and the amount of saved fuel is 1540m³/m²/year natural gas. For an area of 210m² the total amount of the saved fuel is 323400m³/year at a cost of €80,850/year.

30 r Furnaces International Issue 5

Contact *Manager, Lubisol, Sofia, Bulgaria Email: office@lubisol.com www. Lubisol.com www.aluminiumtoday.com/furnaces/

Blast furnaces

Impact of cooling on campaign life and operation of a blast furnace The life of the refractory lining and the type of cooling system employed in a blast furnace has a major influence on campaign life. By improving the method of cooling the lining life can be prolonged which leads to increases in campaign life and so a reduction of down-time for furnace repair, so improving productivity and therefore decreasing the unit cost of the hot metal.

Lining life, cooling system and operating practice all have a major influence on the campaign life of a blast furnace. By improving the method of cooling, lining life can be prolonged which will lead to an increase in the campaign life of the furnace. This facilitates a reduction of down-time of the furnace which leads to a decrease in hot metal cost.

The improved process efficiency in blast furnace operations combined with ever larger furnaces has increased the heat flux with consequent requirement for greater levels of cooling to ensure a long life of the shell. The heat flux has a major influence on blast furnace operation, optimum heat flux being required for smooth furnace operation. Heat flux is thus used as a tool to set the burden distribution to optimise the use of the furnace gas.

The traditional function of the cooling elements and water cooling circuits is the protection of the shell. To achieve this goal the cooling system must remove sufficient heat from the refractory lining.

The cooling water circuit must also keep the wall temperature of the cooling elements, plates or staves, within prescribed limits to optimise campaign life.

By recording the thermal status when the furnace is running in an optimum condition, heat loss may be minimised by optimising the quality of water, its thermal conductivity and that of its cooling materials. A small rise in water temperature is preferred which may be achieved by adjusting water flow and selecting materials of www.aluminiumtoday.com/furnaces/

desired thermal conductivity. Any reduction of the heat load/loss will influence production costs.

Evolution of cooling Blast furnace cooling systems have been developing since 1884. Until the late 1920s, cooling was applied to the hearth and bosh areas only. Cooling for the stack region was developed between 1930-1940. External cooling methods such as shower and jacket cooling of the furnace shell were tried. This method relied on extracting the heat through the furnace shell to the cooling medium, which generated high thermal stresses and hence reduced the life and integrity of the shell. This problem was later eliminated by the use of plate coolers and stave coolers in which heat is extracted from the furnace before it reaches the furnace shell. The developments of various generations of cast iron stave coolers continued until the late 1980s. Further developments of stave coolers in the 80s & 90s gave birth to copper stave coolers. To support the advancements in cooling elements, the cooling water system has likewise seen an evolution from raw water ‘once through’ to sophisticated soft/ demineralised water closed loop circuits.

Types of cooling Cooling systems are often compared based on their maximum heat flux capability. Selection of cooler type must be made on the basis of equilibrium heat flux (load) in the specific region of the furnace. External spray cooling was the earliest development and is still extensively used Issue 5 Furnaces International r 31

Blast furnaces

Fig. 1: Installed cooling plate.

to protect the hearth shell and in some cases bosh. Spray or shower cooling is simply the addition of a water spray or curtain down the outer shell of the furnace. The advantages include low cost, easy repair, minimal refractory consumption and no chance of water leakage inside the furnace. High wear areas such as the slag zone can be cooled using spray or shower cooling at very low investment. The main disadvantages are high thermal stresses on the furnace shell along with lower rates of heat removal. An additional drawback is that the heat transfer decreases with time due to scaling and deposition of dust and microbiological impurities on the surface of the furnace shell. External spray cooling also has problems counteracting hot spot formation over large areas, since boiling of the film of water may occur away from the zones of impingement.

Plate cooling Plate coolers are located inside the furnace shell in the refractory (Fig 1) and are normally made of copper or cast iron thus providing intensive cooling while withstanding high heat fluxes inside the furnace. Furnace cooling intensity can be increased in regions of high heat load, such as the bosh, belly and lower stack by varying the spacing between the coolers. It is also observed that relatively few plate coolers use copper resulting in lower costs when compared to other coolers, such as copper staves. The limitations are that the plates take a greater width on the refractory, which reduces the working volume of the furnace and the installation requires large openings in the furnace shell. Also, cooling can be non-uniform (Fig 2) which leads to uneven 32 r Furnaces International Issue 5

Fig. 2: Uneven wear of plates.

refractory wear and disruption of the flow of the process gases in the furnace. Moreover, it is also often difficult to mount or replace coolers in the tuyere zone of the furnace.

Stave cooling Stave coolers are generally used in the bosh and stack region of the furnace. These are large water cooled blocks of metals, usually with refractory inserts between them and the hot face. Initially they were constructed of cast iron with steel pipes cast inside for water to circulate through. Copper is now generally used to improve the cooling performance and to allow the formation of a freeze layer to provide extra protection.

The advantages of stave cooler are uniform cooling; the possibility of directly inspecting the furnace shell for hot spots; long life; and the copper from end-of-life stave coolers can be recovered. The limitations are: difficult to replace during furnace operation; and expensive, as a large amount of copper is required in the designs. Hence, some stave coolers are still made of grey cast iron or SG cast iron. Four generations of staves have now evolved (Fig 3): Generation I – Staves are deficient in corner cooling; Generation II – Staves have improved corner cooling; Generation III – Staves are better developed to provide refractory support by providing a nose above the straight stave face. Serpentine pipes for nose and additional zig-zag pipe arrangement provide better cooling; Generation IV – These have edge cooling at top and bottom, ledge cooling and serpentine pipe behind the primary vertical part. The www.aluminiumtoday.com/furnaces/

Blast furnaces circuit water and secondary cooling. d. Closed loop cooling water (Fig 4): In this system there is no chance of atmospheric contamination of the cooling water. This will prevent scaling/corrosion of coolers these, in the long run, leading to lower thermal conductivity or water leaking into the furnace – a major reason for damage to the refractory.

front face of the stave is provided with slots for fixing refractory blocks.

Cooling medium & circuit There are four main types of water circuits for furnace cooling systems in use around the globe: a. Once through cooling water: Requires very large volume of water, usually pumped from a natural source. The disadvantages include difficulty in controlling chemical composition of discharge water which is environmentally hazardous and a large volume of water is also discharged. b. Open re-circulating with cooling tower: Here water is heated as it cools the shell of the furnace and then passes to a hot sump. Pumps are installed to transfer the hot water to the cooling tower and cooled water is then held in a cold sump from where it is recirculated. c. Open re-circulating with indirect cooling: In the case of an open recirculating system with indirect cooling, the heat is removed from the water by means of heat exchangers, either to air or to water.

There is no direct contact between the

Fig. 3: Generations of staves with enhanced cooling.

Contact

By S Sudhir, RR Kumar, RK Singh, VK Jha, BK Das & A Arora of RDCIS, SAIL, Ranchi-834002, India.

Heat loss in blast furnace In general, the heat losses in a blast furnace are 3-6% through the cooling circuit and 2-5% through the top gas.

Therefore, the total heat loss is 5-10%.

Within this total, around 50-60% of the heat loss takes place in the stave/plate coolers, around 25-30% from the tuyeres, about 10-12% in the hot blast valve and about 5-7 % from the hearth area.

Results An effective cooling system keeps the hot face temperature of the refractory linings at a sufficiently low temperature to form a skull on the inside lining. The lower the hot face temperature, the greater tendency to form a stable skull. The temperature of the hot face depends on the rate of heat extraction from the lining refractory.

This skull formation acts as a thermal barrier and protects the refractory lining from some of the attack mechanism such as alkali and chemical attack, oxidation by CO2, H2O & O2 and abrasion / erosion.

The cooling system counters some of the attack mechanisms on the refractory face, for example, heat load and temperature fluctuations.

A rough estimate indicates that reducing cooling loss through the tuyere by 5% would result in saving of 0.7-1kg coke/tHM. In conclusion, an efficient cooling system contributes significantly to a longer campaign life, higher productivity and safe operation of a blast furnace.

Quantification of the thermal load is necessary to design the cooling system and requires calculation of water flow rates for different zones to optimise water flow in each cooler thereby ensuring increased life and minimising the use of excessive water.

Fig. 4: Close loop cooling water circuit. www.aluminiumtoday.com/furnaces/

Issue 5 Furnaces International r 33

Energy efficiency

Aluminium ingot pre-heating

Andy Darby of Innoval Technology talks us through how using modeling can save energy and money when heating aluminium ingot in a furnace.

Air Exhaust gas losses

leakage Burner

from lid

Stack Burner

Burner

Recuperator Ingot load

Fan

Fan

Cold air leakage into furnace

Cold air leakage into furnace

Fig. 1: Schematic of a typical gas-heated, direct-fired pit furnace with recuperator.

Preparing a direct-chill (DC) cast aluminium ingot for hot rolling is both time and energy consuming. It can require about 1.2 MJ of energy per kilogram of final product to perform the homogenisation and preheating operations. This compares with about 0.2 MJ/kg for the hot rolling process itself. Pit-type furnaces for pre-heating are still in widespread use by rollers of aluminium flat products. Although they may not be the most efficient method of pre-heating, they do provide a flexible store of ingots to maximise availability of metal to the ‘hot line’ (rolling mills). There 34 r Furnaces International Issue 5

are different configurations of pit furnace – some with the heating air flowing top-tobottom (or vice-versa), others with the air flowing horizontally. There are also ‘pushertype’ preheating furnaces, where generally the airflow is from bottom-to-top – albeit over the shorter length of the width of the rolling face of each ingot.

A key role of the pre-heat facility is to ensure that the ‘hot’ mills, where the greatest capital is tied up, are kept occupied with production. Fig. 1 shows a schematic of a gas-fired pre-heat pit furnace also showing the major sources of energy loss from the furnace.

The pre-heat furnace usually performs the dual functions of homogenising the metal and of holding it at a temperature suitable for rolling. In order to achieve satisfactory final properties, the temperature distribution in the ingot following the preheat must be uniform.

For this reason, pre-heat cycles are sometimes excessive in length to ensure that uniformity has been achieved – bearing in mind that the only information a process operator has to go on is one or more surface temperatures. It would be an advantage to know the temperature distribution in the ingot throughout the pre-heat so that the duration of heating cycles can be optimised. www.aluminiumtoday.com/furnaces/

Energy efficiency

Ingot width Thickness

HTC (top)

Air flow

Height

HTC (sides)

HTC (edges)

HTC (bottom)

Fig. 2: Division of an ingot into elements for modeling.

Shortening cycle time is one of the best ways of saving energy per kilogram rolled, as heat is lost from the furnace even when the ingot is simply being held at temperature. Improving the temperature uniformity within the ingot prior to rolling is one of the best ways of reducing losses (scrapped material) at all subsequent stages further down the process line – thereby reducing energy consumption and incurred 500 celcius costs through wasted effort everywhere.

flows for each surface.

Consequently it is possible to model the effects on energy consumption of a range of different ingot sizes in a given load and different furnace geometries. The best heat transfer coefficients are achieved where local air velocities are highest.

However, significant heat transfer can also be achieved by using very hot air. For some aluminium alloys however, melting may occur at temperatures well below the frequently and usually remembered 660°C. Fig. 3 shows the temperature distribution inside the ingot in the vertical plane at the mid-width position for a typical pre-heat process after five hours in the furnace.

There could be about 100°C difference at this stage between the top and bottom of the ingot. As the air passes down over the ingot it loses energy (temperature) into the ingot. The rate of heat transfer is not often uniform everywhere on the ingot surface.

Shortening heat-up times One of the important methods of judging how to improve the cycle is by minimising the gap between the hottest (leading) and coldest (lagging) temperatures anywhere TOP in the ingot through the cycle. Fig. 4 shows the leading and lagging temperatures Furnace modelling through the heat-up time for a typical pit It is possible to model the temperature at furnace. In order to achieve the required all locations within the ingot during the material properties for rolling, the pre-heat cycle. Fig. 2 shows how the ingot temperature difference between ‘lead’ and may be discretised for modeling purposes. ‘lag’ must be minimised (ideally, zero) and A model may perform [3D] transient this can easily be assessed with a calibrated calculations of temperature at the centre model. It may be noted from Fig. 4 that in of all the elements in the ingot, shown in this illustration the ingot temperature does Fig. 2, throughout the heating cycle. The not become uniform until quite close to the boundary conditions for the model are end of the heat-up period. the air temperature and the heat transfer The generalised heat transfer equation coefficients (HTC) on the ingot surfaces. may be expressed as: 403 celcius BOTTOM Q=h*A*ΔT These can be determined from first principles and then the model calibrated Apart from making design changes to Position through thickness against experimental data from furnace the furnace and fan equipment (effectively trials. controlling the overall heat transfer Fig. 3: Modeled temIn general, these types of furnaces rely coefficient ‘h’), the other part of the perature distribution on the flow of heated air, usually using governing equation worthy of attention inside an ingot after five hours of heating. one or more fan units. Except in unusual is the temperature difference ‘ΔT’ – in this The temperatures are circumstances, the airflow will not be instance the difference between ingot shown in the plane uniform around and over each surface of surface and hot air temperatures. through the thickness the load of ingots, and hence the model It is often possible to accelerate the early at the mid-width position. will benefit from a means of estimating the part of the cycle by using higher set-point www.aluminiumtoday.com/furnaces/

Issue 5 Furnaces International r 35

Energy efficiency Air temperature set-point

Leading ingot temperature

ENERGY

TEMPERATURE

Effect of air ingress

Effect of recuperator Lagging ingot temperature TIME

Fig. 4: Leading and lagging temperatures in an ingot during the heat-up part of a pre-heat cycle.

TIME

Fig. 5: Effect of using a recuperator and of air leakage on the energies supplied.

air temperatures. Fig. 4 shows significantly higher than target air temperatures used at the beginning of the heat-up. The model indicates that for the time the high air temperatures are used, there is no danger of over-heating any part of the ingot. Because a model effectively can give warning of excess temperature anywhere on the ingot it allows a more aggressive heating regime, which can enable a reduction in overall heating time without danger of damaging the ingot.

This technique pre-supposes that there is sufficient power in the burners (or heating elements if electrically heated) to maintain the air temperature at or near its set value. It is important to include the power limits in the modelling and thus calculate the actual air temperature, not just the set-point value. The problem of power limitation is most acute at the start of the cycle when the ingots can absorb heat at a high rate because they are relatively cold.

evenly spaced (by the ‘shoes’ they sit on to be transported through the furnace). In a pit furnace, difficulties in loading ingots into confined spaces can easily lead to narrow gaps between adjacent ingots or ingots resting against furnace walls for example.

Together with the natural gaps created by loads of dissimilar ingot sizes it is easy to see how air flows may not be uniform and hence not treating all the ingots equally.

In extreme cases, air may not flow over parts of the ingot surface at all – so-called ‘dead spots’ can arise. This is not to say that the parts of the ingot in such regions will not heat up at all, they will – but the local heat transfer coefficient will be different (and most probably lower) and lead to even greater temperature variations than those illustrated in Fig. 3.

The modelling approach is able to identify the effects of such non-uniform ingot loading and enable suitable remedial approaches to be taken.

Uniformity of heat transfer In the main, ingots are heated up by being exposed to heated air flowing over their exposed surfaces. The higher the velocity, the better the heat transfer coefficient is likely to be, and therefore the resulting rise in ingot temperature. Air, being a typical fluid, will, however, always find the path of least resistance in its path around the furnace and load. Generally speaking, it will predominantly tend to flow through the largest openings.

One of the advantages of the pusher-type furnace is that the ingots are automatically

Reducing energy consumption As seen from Fig. 1, energy is lost by conduction through the furnace walls, up the exhaust stack (when gas-fired) and by leakage of air into and out of the furnace.

It is typical for about twice as much energy to be supplied to the furnace as is required to raise the temperature of the ingot. A small but not insignificant proportion of this is the electrical energy expended to circulate air around the furnace. Efficient and appropriate fans (and motors) are essential to minimising the costs of operation of these furnaces.

36 r Furnaces International Issue 5

www.aluminiumtoday.com/furnaces/

Energy efficiency Electrical energy is more expensive than gas energy and has a bigger carbon footprint so it is worth minimising its use.

Usually there are parts of the furnace that operate below the ambient static air pressure. This is often close to the intakes of the re-circulating fans.

If the furnace is not well-sealed in this region, cold air can be pulled into the furnace from outside. This has a more serious effect than air leaking out, as the in-coming cold air must be heated right up to the operating temperature of the furnace.

Fig. 5 also shows the effect of a possible leakage of air into a pit furnace.

The energy loss over the 25-hour period can amount to an increase in energy of 10%. Leakages of air into the furnace are not as obvious to the operators as there are no visible effects, in contrast to what occurs with air leaking out.

Damage to furnace structures, refractories and skins is all too easy – and cumulative.

Even with skilled and careful operators, ‘placing’ ingots weighing upwards of 20 tonnes, often suspended beneath a gantry crane, over a very hot furnace pit is likely to result in a bump or two. Punctures to the furnace skin or welded seam damage may not be easily visible, but air ingress can result nevertheless.

Recuperation In a direct-fired gas furnace, a mass of air corresponding to the combustion gas and air must be extracted from the furnace and exhausted up the stack. This represents a significant energy loss. However, it can be considerably reduced by the use of a recuperator, which recovers heat from the exhaust stream and transfers it to the incoming combustion air.

A recuperator is a heat exchanger consisting of a tube stack enclosed in a shell or box. The hot exhausting air passes through the recuperator tubes and the incoming combustion air is drawn over the external surfaces of the tube stack. The air is thus heated on its route to the burners.

Fig. 5 shows the benefit that may be obtained by using a recuperator. As energy becomes more expensive and as the drive to reduce carbon emissions increases, recuperators will become more and more attractive. Sometimes the recuperators are fitted to the burners themselves. These are known as recuperative burners. They are generally smaller and cheaper but less efficient than stand-alone recuperators.

Air leakage Another contribution to the energy lost from furnaces is due to air leakage out of or into a furnace. If no recuperator is fitted, it is possible to tolerate quite large leakages of air out of the furnace without affecting the energy efficiency. This is because the combustion air must be extracted up the stack and air leaking out of the furnace simply reduces the flow up the stack by the same amount.

However, if the air leakage exceeds the combustion air requirement then there will then be significant energy loss. This can more easily occur towards the end of the cycle when the gas firing level is low.

Furthermore, if a recuperator is fitted, even modest levels of air leakage out of the furnace are important as the recuperator can only recover heat from air, which passes through it. www.aluminiumtoday.com/furnaces/

Summary This modelling approach can yield practical pointers to shortening ingot preheat times by enabling more aggressive heat-up schemes, without danger of overheating the ingot. It also indicates ways of reducing the energy losses of the process.

Models are being used more and more as part of the process control and it is possible to envisage that in the near future these furnace models will be running online, calculating the best future settings for the furnace and providing warnings of furnace malfunction much earlier than would otherwise be recognised.

Contact Andy Darby, Senior Consultant Engineer, Innoval Technology, part of the Danieli Group www.innovaltec.com

Issue 5 Furnaces International r 37