ALUMINIUM
GLASS
STEEL
GLASS
Finding the right furnace
A NOx removal process from exhaust gas in a glass furnace
Increasing energy efficiency in electric arc furnaces
Advancements in regenerative gas burner technology
www.aluminiumtoday.com/furnaces/ Issue 1
‘Ipsen’s UK & Ireland agents’
Comment Editor: Sally Love Tel: +44 (0) 1737 855132 Email: sallylove@quartzltd.com
Comment
Designer: Nikki Weller Sales/ Advertisement production: Esme Horn Tel: +44 (0) 1737 855136 Email: esmehorn@quartzltd.com Sales director: Ken Clark
ALUMINIUM
GLASS
STEEL
GLASS
Finding the right furnace
A NOx removal process from exhaust gas in a glass furnace
Increasing energy efficiency in electric arc furnaces
Advancements in regenerative gas burner technology
Welcome to the first issue of the revitalised Furnaces International, a digital reincarnation of the popular industry magazine. I’ve been told there’s a gap in
Email:
the market for a publication focused on industrial
kenclark@quartzltd.com www.aluminiumtoday.com/furnaces/ Issue 1
furnaces, and so I hope that the industry gets involved and finds the articles informative and the community
Managing Editor:
helpful.
Steve Diprose
From my initial foray into the furnaces industry, Chief Executive Officer:
it seems that it is often affected by elements
Paul Michael
that are out of its control. For example, in Europe manufacturing industries face government emissions
Subscription:
targets and energy taxes that are not imposed in
Elizabeth Barford
other countries around the world. These are issues
Email:
that can negatively impact the productivity of
subscriptions@quartzltd.com 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 Annual subscription: £90
manufacturing industries, and thus filter down to
‘Ipsen’s UK & Ireland agents’
Front cover: Ipsen www.ipsen.de
become a priority for furnace makers. This is where furnace manufacturers can (attempt to) come to the rescue, when governments can’t or won’t: more and more often, producers of metals, glass, and ceramics, etc. are looking directly to the furnace to solve their energy problems. The industrial furnace is, after all, essential to industrial manufacturing, and to that end this magazine will provide a variety of articles on developments and initiatives from across the industry that demonstrate improvements in the field of heat treatment and furnace technology. If you have any comments, news items that you think should be broadcast, case studies, or technical features that you would like to share with the industry, then just get in touch. Sally Love Editor, Furnaces International sallylove@quartzltd.com
© Quartz Business Media Ltd, 2016
2 r Furnaces International Issue 1
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Contents
4
News
Aluminium Finding the right furnace Long-life rollers
6 9
24
Heat Treatment 11 Efficient heat treatment
BIFCA 23 Introducing BIFCA
Glass 14 Prolonging the campaign life of a glass furnace 17 A NOx removal process from exhaust gas in a glass furnace 20 Energy saving concepts for glass containers and tableware furnaces
6
www.aluminiumtoday.com/furnaces/
24 28
11
Glass Advancements in regenerative gas burner technology Steel Increasing energy efficiency in electric arc furnaces
9
Issue 1 Furnaces International r 3
News
Fort William aluminium smelter future uncertain
Workers at the aluminium
Rio Tinto said the review
smelter at Fort William,
would include its assets in
Scotland have been told that
Lochaber.
the owners are reviewing its operations. The announcement from
the 160 full-time jobs.
announcement.
The Scottish government
The smelter is Rio Tinto's
said Highlands and Islands
only operational site in the
Enterprise was "engaging with
UK and is unique in that it
largest employers in the area.
the company" to understand
generates its own power from
It is thought to support more
the potential impacts of the
two hydro electric schemes.
The plant is one of the
Record year for electric melting specialist
Iranian steelmaker SKS plans major expansion
UK-based electric melting
Korea; electric boosting projects
The Kish South Kaveh Steel
specialist Electroglass has
in Indonesia and elsewhere; and
Company (SKS) in Iran says it
400 tonnes of steel using
reported a ten-year record in its
continuing development and
is investing heavily in steel
equipment including an electric
2015 results.
sales of our Precision Control
production projects that will
arc furnace (EAF/EBT/170/7500
Bubbling Systems.
create around 1,000 direct and
model).
“Despite uncertainty and slow-down in a number of
“Also holding up well are
indirect jobs in the country.
To date, SKS has produced
The equipment in question is
world markets, we have had an
sales of hardware, notably
CEO Ali Dehaqin, says
excellent year”, said Managing
the Molycool and Vertical
that SKS intends to play an
foundry machine with a tundish
Director Richard Stormont.
Splashguard ranges of electrode
important role in the ongoing
capacity of 30 tonnes and it
holders and our dry-type
development of the Iranian steel
is predicted to be capable of
forehearth electrodes,” he added.
industry.
producing billets at nominal
“All-electric furnace and forehearths projects for fluoride opal tableware glass, in south
“The rest of 2016 sees the
“Annual [Iranian steel]
a CCM/6 strand/120-150-200
capacity.
Asia in particular, have been
commissioning of several
production of 55Mt has been
significant contributors to
recently supplied systems and
envisaged until 2025,” he said,
production project is currently
this, along with borosilicate
work is expected to start on
adding that phase one of SKS’s
under way and is expected to
electric forehearths work in the
a number of significant new
steel production project was
come on stream in March 2017,
USA; gas-to-electric soda-lime
projects for the company.”
launched with a capacity of
according to project manager
1.2Mt/yr.
Shahram Salmasi.
forehearth conversions in South
Phase two of SKS’s steel
EU considers China steel import duties Amid the on-going crisis facing
steel industry has problems.
Chinese steel, as has the British
the UK's steel industry, the
We are now investigating
government, which blocked
President of the European
steel production in China to
a previous attempt by the EU
forward as a potential buyer for
Commission, Jean-Claude
determine whether it is dumped
to introduce higher tariffs on
the Port Talbot plant in Wales.
Juncker, has said the EC is
in the market and we will take
Chinese steel imports.
investigating whether the
other measures if necessary.”
Chinese steel industry is
The EU has previously been
This move may well have backfired, with Tata Steel
dumping subsidised steel into
criticised by steelmakers for
announcing the sale of its UK
the European markets.
its lack of action with regards
steel operations in a move that
to imposing tariffs onto
puts up to 40,000 British jobs at
Mr Juncker said: “The 4 r Furnaces International Issue 1
risk if no buyer can be found. So far, only Liberty has come
Jean-Claude Juncker
News
Glaston closes deal for three FC500 furnaces in the USA Glaston Corporation has closed a significant deal with U.S based
Glassrobots’ machines. Trulite Glass & Aluminum
and hear the obvious excitement
“Glaston continues to raise
they have for the future growth
the bar, with industry leading
Trulite Glass & Aluminium
Solutions is one of North
of their operations, and how
solutions that produce superior
Solutions for three FC500
America’s largest architectural
Glaston plays a significant role
optical surface quality in high
tempering furnaces.
glass and aluminum fabricators.
in this”, said Arto Metsänen,
performance glass products.
This includes the iControL
The company manufactures
Glaston Corporation’s President
“Along with these investments,
Quantum Automation and
and distributes architectural
Reporting system, and Glaston
aluminum, insulated units,
Care service agreements.
mirrors, tempered, laminated,
President, Trulite Glass and
projects and we look forward
The machines are to be
& CEO. Paul Mahedy, Executive Vice
Trulite is also well underway with four other Glaston furnace
and decorative glass from their
Aluminum Solutions, said:
to a mutually beneficial
delivered during the first and
28 locations throughout the U.S.
“Trulite Glass & Aluminum
partnership.”
second quarters in 2016.
and Canada.
Solutions is very excited to build
In addition to the FC500
‘It was a true pleasure to meet
Launched in 2011, the Glaston
on our partnership with a true
FC500 tempering line has
furnace deal, the parties agreed
with Trulite’s management at
leader in convection furnace
gained a solid position on the
on major upgrades for two
Glass Build America in Atlanta,
technology.
market.
Furnace life website for manufacturers PaneraTech has released
The content also illustrates
a dedicated website for
exactly how its patented
SmartMelter, a technical
sensors work to map erosion
solution for furnace life
of furnace walls and measure
optimisation.
residual wall thickness.
SmartMelter provides
The site includes detailed
comprehensive asset
papers about Research &
management for glass melting
Development, and a blind
furnaces.
validation trial of the RTS
The website allows glass manufacturers to learn more
The new factory will go into
it was honoured to have
operation at the beginning of
been selected as the furnace
2017 and produce 300 tons per
supplier by Bastürk Glass for its
day of glass containers.
greenfield project in Turkey. Bastürk is a new player to the
Sorg said it 'wanted to thank Y & H Foreign Trade Limited for
glass industry and is building
its assistance in securing the
a site in Malatya in the Eastern
prestigious order and Bastürk
Province of Turkey.
Glass for placing its trust in us'.
PaneraTech plans to release additional validation trial in
outlines service and licensing
the near future.
The website is designed
German company Sorg said
Sensor.
about the technology and options.
Bastürk Glass selects Sorg
PaneraTech invites manufacturers to visit
to answer the most frequent
smartmelter.com and contact
questions that glass
their office to discuss service
manufacturers ask about the
options.
solution.
U.S. Steel delays $230m furnace U.S. Steel has delayed construction of a US$230
efficient. The delay comes after
has also idled mills in Texas and Illinois to cater to reduced
pipe. Steelmakers also continue
million electric arc furnace
the company closed its
in Alabama, due to the
blast furnace operations in
challenging market conditions
Birmingham, also in Alabama, in
to delay the new electric arc
faced by both the gas, steel and
the summer of 2015.
furnace was caused by oil prices
feel the effect of these energy
hitting an eight-year low.
market conditions, along with
The resulting drop in
low steel prices and continued
oil industries. The project was considered pivotal in the company’s target of becoming more energy
At that time, 1,100 of the plant’s 1,500 workers were made redundant. In the past year, U.S. Steel
www.aluminiumtoday.com/furnaces/
demand. The company said its decision
to be affected by imports from China. “The company continues to
exploration activity by drillers
high levels of imports,” U.S.
has reduced demand for steel
Steel said. Issue 1 Furnaces International r 5
Aluminium
Finding the right B
y no means exhaustive, this article aims to give a feel to the many styles and varieties of furnace used and related to the aluminium
industry. The ‘pot’ is probably the first furnace in a long line of furnace operations aluminium will see. More conventional furnaces appear throughout our industry, and this article looks at a varied list of types and
furna The aluminium industry is dependent upon many types of industrial furnaces across all sectors of aluminium operations. Technically, even the very first stage in production of aluminium is carried out inside a furnace, as Keith Watkins* explains.
applications. depending upon the properties required. Temperatures Classically, we all appreciate the reverbs – or melters
may be 155°C to 175°C for precipitation, and 525°C to
and holders to most of us, as these are the backbone
545°C for solution treatment. Cooling may be carried
of alloy production. Used for casting and alloying, with
out in air or hot water.
capacities of up to >150 tonnes, they can be found in
Slab
primary and secondary aluminium plants.
Slabs will almost always be ‘rolled’ either hot or So, let’s look along the production line and find out
cold, depending upon final usage, sheet thickness or
what other furnaces can be found. Once we have cast
alloy; initially the slabs will undergo heat treatment
a product, should it be ingot, slab, billet, coil or de-ox,
(re-heating). Typically, soaking pits or continuous
there will be another furnace waiting next in the queue.
re-heat furnaces are used. Soaking pits will normally be electrically heated. Slabs are loaded into the pit
Ingot
with the help of an overhead crane. After heating and
Inevitably, ingots get re-melted again and cast into
soaking, aluminium slabs are discharged from the pit
a range of items. Those items will generally be heat
one-by-one for the rolling operation. Alternatively,
treated to finalise the required metallurgical properties.
continuous pre-heating furnaces are used. These
Precipitation and solution heat treatments are normal,
allow the slabs to be continuously charged and then Figure 1: Ageing oven
discharged onto the rolling mill one at a time. Precipitation, annealing and homogenising processes are carried out on slabs as required by the applications, up to temperatures as follows: r Precipitation - up to 210°C operating temperatures r Annealing - up to 425°C operating temperatures r Homogenising - up to 500°C operating temperatures
Billet Billet is normally produced for subsequent extrusion
6 r Furnaces International Issue 1
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Aluminium Artificial ageing Magnesium and silicon are the major alloying elements in 6000 series alloys. These elements combine to
ace
form magnesium silicide. The artificial ageing process produces fine grain magnesium silicide precipitates that will increase the strength of the 6000 alloys. Due to the effects on the magnesium silicide precipitates, this process may also be called precipitation heat treatment. The ageing process also occurs naturally (uncontrolled) over time. However, by controlling the times and temperatures in the artificial ageing ovens (Fig.1), maximum strength and benefits may be achieved.
processing. In general the furnaces found relating to
Coil
billet are billet homogenisers, pre-heaters, ageing, and
Out of the mill comes rolled coil or foils. Mostly, coils
solution heat treatments. Pre-heaters are used adjacent
and foils have to be annealed, which takes us on to
to the ‘press’. As the extrusion billet must be pre-heated
coil and foil annealing furnaces. These furnaces for
to enter the canister of the press, it is important to
coils are usually high flow furnaces that use high
get the billet temperature correct. Either a gas fired or
velocity gas impingement at the coil sides to maximise
induction heated pre-heater may be employed. Due to
heat transfer and reduce heat up rates. Design is very
the nature of friction within the die of the press, ‘taper’
important for temperature uniformity. Either electrically
heating can be used to differentially heat the length
heated or gas heated are suitable. When it comes to foil
of the billet to compensate for friction heating while
annealing, care has to be taken that gas flows are not
pressing. This ensures a constant billet temperature
high enough to tear the foils during processing.
throughout the pressing operation. Subsequent
Induction melters
extrusions then need to be heat treated further.
Commonly, induction melters are used for a variety
Solution heat treatment
of aluminium melting processes. Mostly involved in
This process is performed by maintaining the proper
re-melt and production of castings, you will find many
exit temperature as the extrusion emerges from the
in the automotive industry. They are also used in the
press during the extrusion process, and then quenching
production of aluminium-lithium alloys.
it at the proper rate. Temperatures and rates vary by
Scrap
alloy. Holding the extrusions at the proper temperature allows the aluminium, along with any alloying elements, to enter into a solid solution.
Figure 2: Gas nitriding furnace
At times it is important to pre-heat scrap prior to re-melting. Due to the nature of scrap storage and its origin, scrap may contain high levels of moisture. This can cause excessive evolution of steam in a very short time, creating explosive conditions in the re-melt environment. Pre-heating furnaces are used to pre-dry scrap or sows to eliminate hazardous moisture. Once pre-heated, the material is then safe for re-melting. Some reverbs are equipped with a hearth above the melt line to enable pre-heating without the need for a separate furnace. Here, we must mention rotary furnaces. These are used almost exclusively for scrap and dross re-melting. Originally, rotaries were horizontal and fixed axis, but required a lot of salt in operation, typically 1.5:1 of the non metallic content of the batch to be melted. With the advent of tilting rotary furnaces, it is normal to use ox-fuel burners and less salt: 0.35-0.5:1 salt ratio
www.aluminiumtoday.com/furnaces/
Issue 1 Furnaces International r 7
Aluminium Rolling mill rolls, extrusion dies, gravity and highpressure dies are mostly made from (H13) hot work steel. During manufacture these require heat treatment by a variety of heat treatment furnaces: r Sealed quench furnaces are gas tight furnaces with two chambers and are radiant tube heated. Normally, an endothermic gas is circulated inside the furnace. This gas can be modified to achieve varying carbon potential. Depending upon the metallurgical requirements, this carbon potential may be varied for decarburising to neutral or carburising by automatic controls. Most are fitted with internal oil quench tanks for fast cooling. r Tempering furnaces are utilised to modify the full hardness of the hardened material, to achieve a is fairly typical today. Energy requirements and yields
Figure 3: Vacuum furnace
have also improved.
core hardness and structure appropriate to the application. This is usually a further and separate stage to the hardening process.
Others It is important to recognise that not all of the furnaces
r Vacuum furnaces are more likely to be used for
important to the aluminium industry directly treat the
the H13 steel, as it is a fully hardening steel,
aluminium itself! So where are we going with this?
where carburising is not required. Vacuum furnace hardening will allow the rolls or dies to be kept
Many furnaces heat treat the steels, so are essential to
clean throughout the heat treatment process, by
the processing of aluminium.
eliminating oxygen. No oxygen means no oxidising of the steel, and hence the dies will come out bright
Inside every aluminium extrusion shop you will find ‘die
and shiny. Many of the modern vacuum furnaces
ovens’. Die ovens heat the extrusion dies prior to them
combine tempering in one prolonged cycle within
being inserted into the press. We have multi cell die
the vacuum furnace. Instead of oil quenching,
ovens, and today single cell die ovens are proving more
high-pressure gas is used to quench the steel inside
popular. It is important that the die is preheated to the
the furnace at pressures up to 10 bars. High purity
correct temperature before applying it in the press. The
nitrogen is typically the gas used.
die must not be overheated or heated for too long as ‘back tempering’ will ensue and soften the die interior,
Beds and baths
causing premature die failure.
Finally, you may find furnaces such as salt baths and fluid bed furnaces used for the above treatments. Salt
Of course, in the die shop of the extrusion department
baths heat the products in a molten salt environment
you will usually find the means to harden the surface
and fluid bed furnaces utilise zircon sand fluidised
of dies. A gas nitriding furnace (Fig.2) is used to form
by gases as the heating media. In both cases, neutral
a very hard surface onto the die, and brand new dies
conditions or nitriding conditions can be applied. In
between each use as they get older. This is normally
the case of the salt baths, this is achieved by the use of
carried out a 535°C in an ammonia rich atmosphere.
special salts, which imparts a nitride layer to extrusion
Occasionally, plasma furnaces equipped with vacuum
dies. For fluid bed furnaces, ammonia gas is bubbled
systems may also be found nitriding in the die shop, but these are rare. It is essential that the metallurgical properties of other ‘steels’ in the aluminium industry receive the correct heat treatments. So we also have sealed quench furnaces, tempering furnaces, vacuum furnaces (Fig.3), salt bath furnaces and fluidised bed furnaces.
8 r Furnaces International Issue 1
Contact Keith Watkins GW Consumables www.furnace consult.co.uk
through the sand media to fluidise and impart the nitriding. It is evident that there are many types of furnaces used in the aluminium sphere, and that the variety is very varied and complex. There are dozens of companies manufacturing furnaces globally, and all have their particular specialism and expertise.
www.aluminiumtoday.com/furnaces/
Aluminium
Long-life rollers Figure 1: The new rollers in the furnace.
Even a good design can be improved upon, and Granco Clark, a global supplier of equipment to the aluminium extrusion industry, has made some major changes to its furnace design lately. These changes are focused on a few key areas, including efficiency, durability, and ease of maintenance. First, the burners were spread around the perimeter
The furnace tunnel has also been redesigned to allow
of the log. Past designs had the burners in a row
the exhaust gases to flow the length of the furnace in
down the side of the logs on the smaller sizes, or
a chamber well away from the burners. In this fashion,
staggered 22° over/under centre on the larger sizes.
the velocity of the exhaust gases does not affect the
The new design has the burners 40° over/under
direction or shape of the flame, again allowing the
centre on all sizes. This promotes uniform heating,
best possible heat transfer from the burner.
as the flame is distributed in near perfect symmetry about the log centreline. Also, there is a ‘sweet spot’
Durability
in the flame where maximum heat transfer occurs.
The focus on durability is all about the roller bed
The new design accommodates a smaller range of
system (Fig.1). The new roller design is four times
diameters to ensure that any log diameter in the
larger in diameter than the old roller, and therefore
furnace falls into the best heat transfer range of the
rotates only once for every time the old roller rotated
burners. Older models would accommodate 6”-9”,
four times. An added benefit to the larger diameter
8”-12”, 11”-16”, etc. New models have ranges such as
is that the wear surfaces are far removed from the
10”-12” or 9”-11” or 8”-10”.
flames and operate at much cooler temperatures.
www.aluminiumtoday.com/furnaces/
Issue 1 Furnaces International r 9
Aluminium
Granco Clark expects a lifespan of at least five years, at which time the roller trunnions can be sleeved and re-machined to extend their service another five years.
Ease of maintenance The company’s final focus was on ease of maintenance (Fig.3). The crown blocks still hinge open like before, but the side panels of the burner section can also be removed with just a few bolts. That means the roller bed can be serviced while standing on the floor with everything waist high – instead of working from only the top, as before. The removable side panels come out with the gas train Figure 2: The new roller design has an anticipated lifespan of five years.
and burner blocks intact, meaning that they can be rebuilt remotely rather than in place. One could conceivably maintain a second replacement set of
The faces of the roller that contact the log are
panels for a quick rebuild when downtime must be
machined and are at a much steeper angle than
minimised.
before, resulting in better tracking of the log through the furnace (Fig.2). Again, the narrowed
The new furnace design is not for everyone – for
range of diameters allows for this steeper angle. The
example, the larger diameter roller limits the length
trunnions of the roller are also machined and ride in
of precut billets to a minimum of 16”. If you require
machined bores in replaceable bushing blocks. All
a wide range of log diameters, or very short precut
of the machining results in rollers that run truer and
billets, then the old design would still be the best
turn easier than before - you can actually push a 12”
choice.
diameter by 20” log into the furnace by hand.
Contact www.grancoclark.com
Figure 3: Granco Clark’s improved furnace design aims to increase energy efficiency.
10 r Furnaces International Issue 1
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Heat Treatment
Efficient heat treatment Ipsen, a specialist in industrial furnaces, has updated its Turbo²Treater vacuum furnace with several new technical details and functions. Martina Satzinger* explains how the new additions work to make heat treatment processes more efficient and varied.
Whether hardening, tempering, brazing or annealing, the Turbo2Treater furnace’s new technical details are
circulation, alternating flow direction of the cooling gas is also available as an option.
engineered to save electricity, cooling gas and time (in the form of a higher throughput rate).
Flexibility
At the same time, critical power components in this universal single-chamber vacuum furnace were
Due to its wide range of standard and optional functions and its process variety, the Turbo2Treater
optimised for maximum performance.
offers maximum flexibility and can meet the requirements of a large number of industries
To improve quenching performance, the cooling gas pressure was increased to 12 bars, which is ideal for hardening low-alloyed materials. The quenching rate at the start of the cooling phase is also significantly increased with Ipsen’s patented LCP (Low Current Power) Start. This is possible as the fan motor starts during the vacuum phase, thus ensuring that gas flows in when the cooling fan is running at maximum speed. To ensure that all workpieces in the work zone are uniformly cooled, Ipsen has also optimised the cooling gas circulation by running gas flow simulations. Targeted cooling gas circulation in the Turbo2Treater allows the cooling gas to cover the entire width and length of the batch at high flow rates. Besides the standard vertical cooling gas www.aluminiumtoday.com/furnaces/
Issue 1 Furnaces International r 11
Heat Treatment
and companies. The Turbo2Treater is used in the
Worthy of special mention are the Turbo2Treater
aerospace and automotive industries, in commercial
furnace’s new functions for extended automatic
heat treatment plants, in the medical sector and in
control of the quenching parameters for the cooling
the toolmaking industry, to name a few.
gas pressure and the cooling motor operation.
Besides the standard processes (e.g. hardening,
S, M or XL
annealing, tempering and soldering), processes such
Due to its compact design, this vacuum furnace fits
as low-pressure carburising (AvaC), low-pressure carbonitriding (AvaC-N), high-temperature solution nitriding (SolNit) and deep cooling are also available as options with this new heat treatment furnace. The Turbo2Treater can be adapted to suit a plethora
Contact Ipsen, Germany www.ipsen.de/EN/
into a standard truck or container, allowing it to be delivered and installed quickly. The Turbo2Treater is available in three standard sizes with a maximum batch width of 910mm, batch length of 1,220mm, batch height of 910mm and batch weight of 2,000kg.
of materials, geometries and loads and can be used
The Ipsen Vacu-Prof 4.2 control software guarantees
for the heat treatment of a wide range of parts –
process reliability and simple, intuitive operation of the Turbo2Treater vacuum furnace.
long and thin workpieces, multilayer batches, tools, stamped parts, gears, drills, saw blades, etc.
12 r Furnaces International Issue 1
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We set Standards in Heat Treatment.
Turbo 2 Treater ® Efficiency in Power HARDENING
BRAZING
TEMPERING
ANNEALING
BENEFITS: Short standard delivery time Rapid startup at customer site Capacity: 800 kg High heating rate by convective heating High quenching speed and directed gas flow High pressure gas quenching (12 bar) and automatic redirection of cooling gas flow High process reliability with Ipsen program control Vacu Prof 4.2
Ipsen International GmbH Flutstraße 78 | 47533 Kleve | Germany eMail: sales@ipsen.de | www.ipsen.de
Glass
Prolonging the campaig Fernando Salvino* reviews the techniques used to extend the campaign life of glass furnaces, and identifies operational practices, remedial actions and aspects of plant design that help achieve this
In recent years, there has been an increased need to extend the campaign life of a furnace. In order to reduce hot glass costs by reducing manpower requirements and capital costs, glass companies have increased the size and reduced the number of their glass furnaces. In many cases there is no longer a standby furnace to be brought into operation during
From the beginning, one of the common problems
furnace rebuilds. Consequently, long campaigns with
for users of the continuous furnace in the glass
minimum repair periods are essential. As well as this,
industry was its short lifespan. A series of research
the cost of rebuilding or the cold repair of a furnace
and development was carried out in order to extend
can be very high, and may represent a large proportion
the furnace campaign life. Current glass melting
of the total capital expenditure of a company.
technology, based on continuous furnaces initially designed and developed around 1860 by the Siemens
The techniques for prolonging the life of of glass
Brothers in Germany, has evolved in response to
furnaces can be summarised into three categories:
manufacturing requirements. The development of melting techniques is, however, hampered by the
r Operational practices: The control of the glass
industry’s peculiar characteristic of being segmented
furnace process has an important effect on the life
into the sectors of container, flat, fibre and speciality
of the furnace. The furnace must be operated in a
glasses, with those segments further divided within
manner that maximizes furnace life, compatible
themselves.
with production requirements. To do this, it will often be necessary to modify operating practices
Over the last 50 years, major improvements in furnace
as the campaign progresses and in response to
campaign life have been achieved, and numerous
problem areas.
glass furnaces in Europe and around the world have now surpassed a lifespan of 13 years. The basis of
r Remedial actions and hot repairs: Once wear or
a long campaign life is good design, equipment,
damage that may affect the life of the furnace
and refractory developments – primarily, replacing
becomes evident, engineering repair techniques
original fireclay alumina by AZS; comprehensive
must be utilised or developed to maximize
instrumentation; comprehensive monitoring;
campaign life (Fig.1).
continuous, smooth operation; and remedial actions. Furnaces that have recently been rebuilt have
r Improved designs of the future: As improved
benefitted from the development of technology
materials and equipment are developed, they
that extends campaign life, with many furnaces now
should be incorporated into future rebuilds to
aiming for a campaign life of 13 to 18 years or more
extend the life of critical areas of the furnace,
(Table 1).
where it is cost effective to do so. Table 1: Campaign furnace life and total campaign production, in the period 1920–2015
To prolong the life of existing furnaces and those that
Years
Life
t/m2
1920
0.5
300
1940
2
1150
1960
4
2000
1980
6
5000
recent years. In this context, one important factor is
2000
10
10000
the development of remedial actions such as new
2015
13
12000
14 r Furnaces International Issue 1
have been rebuilt without the facilities for a long life, or for those that operate at high productivity, repair techniques play an important role. Engineering techniques, planning, and the speed of execution of repairs and rebuilds have improved markedly in
techniques for hot repair: mainly ceramic welding, hot bottom repair, anchoring and overcoat.
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Glass
gn life of a glass furnace or loss of efficiency can occur. This type of external ceramic welding is performed with powder mixtures specifically designed for the application. Cleaning of regenerators: The sulfate deposited on regenerator checkers causes an increase in pressure and the consumption of the furnace, and can be damaging to the furnace life. With regular cleaning using special lances, the sulfates, which
Hot repair techniques Internal ceramic welding: Using a special lance, a homogeneous mixture of very fine refractory powder and metal is sprayed in a stream of oxygen onto the area to be repaired. The oxidation of the metal
Figure 1: Burner ports repair by ceramic welding. 2A (left) is before ceramic welding, and 2B (right) shows after ceramic welding.
clog the cruciform, can be removed in a targeted manner and restore the efficiency of the furnace. In a recent case, following five days of thermal checker cleaning in a boucle furnace powered by fuel oil, the pressure decreased from 240Pa to 160Pa resulting in a recovery of 80Pa (33.3%). If the number of days
particles begins at a temperature of 2500°C. The high
is increased it is possible to reach a pressure of
temperatures reached on the existing refractory part
120/110Pa (50%).
cause it to melt on the surface, ensuring excellent anchoring of these parts with the weld material.
Anchoring blocks: Preserving the integrity of the
This molten liquefied mass is able to fill every hole,
original blocks is better than any replacement or
join or crack and solidifies when the furnace reaches
ceramic welding, which is why in the case of cracked
working temperature, forming a single compact
or unstable blocks we act promptly, drilling holes
mass with the structure. The welded refractory part
with thermal lances and anchoring them with Inconel
is virtually identical to the original refractory; this
bars to the carpentry. In the case of crumbling walls,
eliminates stress and reactions, obtaining a longer
it is possible to prevent their collapse by inserting
lasting repair (Fig. 2).
cooled hooks. The large holes that arise on the crown can be repaired with the positioning of pendulums
Sealing by external ceramic welding: Using lances it is possible to externally seal every joint, spacing or part of the superstructure in which heat dissipation
Figure 2: Remedial actions for each zone of glass furnaces
– bricks tied to the carpentry using chains, and subsequently fixed with internal welding or externally with a layer of special concrete for high temperatures. Grenaillage bottom repair: If the floor has consumed zones, the grenaillage technique can be used. Grinded refractory material is inserted on to the target area, in order to restore the original level and reduce the consumption process, using the same quality refractory material as the original bottom. This method can be performed while the melt tank is full or empty, so with or without draining. With an empty tank we can easily look at the condition of the damaged areas during this hot repair.
Furnace inspections Inspections and audits are important tools to analyse the conditions of the furnace, refractories and steelworks during the campaign life. A variety of inspection services is available, using state of the
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Issue 1 Furnaces International r 15
Glass
early detection of problem areas so that remedial actions can be scheduled, such as ceramic welding, to extend furnace life. Maximum use should be made of computers to process and analyse primary data, giving the operations staff both rapid information and advice on potential problem areas. art instruments such as infrared cameras and watercooled video cameras. Thermography: A technique that is particularly effective in locating local hot spots.
Figure 3: Regenerator crowns repair by ceramic welding. Left is before ceramic welding and right is after ceramic welding.
Proactive works, remedial actions such as hot repairs, and furnaces inspections are key elements in maximizing campaign life, especially on existing furnaces which may not incorporate the most modern design features. These repairs include ceramic welding (with a variety of mixtures of powders
The outside temperature of a refractory-lined
available to prolong refractory retention).
construction is determined with an infrared camera. The remaining thickness of the refractory lining is
With more advanced repair techniques available,
calculated using the temperature measured and the
and the large capital and production costs involved
design temperature. On the basis of the inspection
in a full furnace rebuild, more glass companies are
results, an estimate can be made of the remaining
adopting the philosophy of hot repairs, particularly to
life time or, if required, a repair procedure can be
extend the pay-back and save money and also when
determined.
there is no stock capacity to cover furnaces under cold repair.
Clavé endoscope: Clavé is a linear endoscope with water-cooling which, by connecting high-
For further improvements in glass furnace campaign
performance SLR cameras, allows internal inspections
life, the continual development of materials and
to be performed in every part of the furnace
techniques is essential, particularly in critical
(superstructure, walls, breast walls, chambers,
areas. The effect of hot repairs is important when
regenerators, feeders, etc.). (Fig. 1 photo by clavé
prolonging the campaign life, and an extension of
endoscope).
this is improvements in anchoring, new materials, and new techniques.
Video endocope: The video endoscope (or the endoscope for welding) has the same structure of
The reduction in cooling member failure and
the lances used for welding, to ensure a constant
subsequent glass leakage is also an important factor
cooling of the camera. Its use arises from the
in extending furnace life, as are scheduled audits
need to see in real time the points where it is not
including for visual, thermography and endoscopy, as
possible to weld at sight, in order to improve the
a means of identifying key maintenance work.
performance of these interventions. It is often performed with ad hoc shapes dependent on the
As the age of the furnace increases, all of these
accessibility within the furnace and the position of
aspects need to be run in conjunction to prolong the
the area to be repaired. The technology allows us to
furnace campaign life to the maximum.
record videos during the work, which is the reason it is also used to inspect the regenerator cruciform from the basement (Fig. 3).
Conclusions For a long campaign life, a glass furnace should be operated at a productivity that enables stable and smooth operation. Comprehensive instrumentation and routine techniques, such as furnace inspections, are essential for stable operation and to enable the
16 r Furnaces International Issue 1
Contact Fernando Salvino Engineering Manager IRF Europa Casier Italy fernando.salvino@irf-europa.com www.irf-europa.com
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Glass
A NOx removal process
from exhaust gas in a glass furnace
N
ihon Yamamura Glass (NYG) has four major business fields, namely glass bottle, plastics, new glass, and engineering with extensive
domestic and overseas networks throughout these fields. In its glass bottle business, NYG has the largest market share in Japan with three glass bottle plants,
Ryota Tsuji* outlines how an investigation by Nihon Yamamura Glass has increased the reaction efficiency of the plasma process and in de-NOxing thanks to the use of a plasma and chemical hybrid process.
nine furnaces and 28 production lines, totaling a production capacity of approximately 450,000 tons/
Background
year.
The NOx emission regulation (450 ppm at O2 =15% conversion) defined in the Air Pollution Control
In NYG, the Environment Affairs Department is one of
Law of Japan is lax compared to other countries.
the main departments in the company headquarters,
As global environmental problems increase, NOx
and has environmental ‘defense’ and ‘offence’ as
emission regulation is also expected to become
its core mission. ‘Defense’ refers to environmental
more stringent for exhaust gas from glass melting
management, such as ISO-14001, waste management,
furnaces. In fact, local regulation levels are more
and upholding government regulations, etc. ‘Offense’
stringent than the law.
refers to the development of environmental business, such as exhaust heat utilisation and the improvement
As for de-NOx, the Selective Catalytic Reduction
of rare metal handlings, etc. This paper is about de-
method (SCR), generally used for exhaust gas
NOx technology, which is a part of ‘offense’.
treatment in coal-fired power plants, and the Low Air Ratio Combustion method, are famous.
Production process In glass manufacturing plants, materials are dissolved
In the SCR method, NOx is reduced by NH3 through
at approximately 1500C by liquefied natural gas
a catalyst. The main reaction to remove NOx can be
combustion or heavy oil in the melting furnace.
sustained if the temperature is held between 250C
The exhaust gas of the melting process contains
and 450C.
environmental pollutants such as NOx, SOx, and dust. In general, SOx is removed by semi-dry or wet de-SOx equipment to be used as a desulfurising agent such as caustic soda. Dust is removed by an electrostatic precipitator and/or bag filter. A semi-dry type exhaust gas treatment system consists of a semi-dry de-SOx reactor, an electrostatic precipitator and a bag filter. In a de-SOx reactor, SOx is reacted with ‘wet’ NaOH spray to form ‘dry’ Na2SO4, therefore this system is called a ‘semi-dry’ system. A wet type exhaust gas treatment system consists of an exhaust gas heat boiler, a wet de-SOx scrubber, a mist eliminator, and an electrostatic precipitator. SOx is transformed into a Na2SO4 water solution by a wet NaOH shower, and therefore this system is called a ‘wet’ system. Both systems do not include de-NOx equipment.
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Figure 1: Production equipment at the glass bottle plant.
Issue 1 Furnaces International r 17
Glass However, when SOx is included in exhaust gas, (NH4)2SO4 or NH4HSO4 is generated by a different side reaction. This side reaction, including dust, develops catalyst poison and clogging problems. Therefore, SCR is difficult to use in glass melting furnaces because the exhaust gas includes the adhesive dust derived from raw materials and highconcentration SOx. For the Low Air Ratio Combustion method, the generation mechanism of thermal NOx is explained by the reaction: N2 + O ↔ _NO + N, O2 + N ↔ _NO + O, and N + OH ↔ _NO + H
Figure 3: showing the placement of the demonstration equipment at the wet type system.
The NOx generated by combustion is mainly NO. While N2 and O2 in the air and retention time
PCHP technology is the preferred system in gas
increase, the NOx generation also increases.
boilers and ship exhausts. NYG has been involved in
Therefore, NOx can be decreased by lowering the
a collaborative investigation with Osaka Prefecture
air ratio of the combustion. However, low air ratio
University since 2011 for practical use of PCHP in
combustion causes an incomplete combustion,
glass melting furnaces.
consequently losing heat energy.
Outline of PCHP For these reasons, NYG investigated de-NOx
PCHP is a technology that combines the plasma
systems available for use in glass furnaces.
process, de-SOx process and chemical process. PCHP
However, suitable systems could not be found,
can achieve simultaneous de-SOx and de-NOx.
so NYG developed a new technology called the
When PCHP is applied to the exhaust gas treatment
Plasma and Chemical Hybrid Process (PCHP) for
system of a glass melting furnace, the NOx removal
simultaneously removing NOx and SOx from the
process is explained below.
exhaust gas of glass furnaces. First, NO in the exhaust gas is oxidised to waterPCHP is de-NOx technology without the use of
soluble NO2 by a plasma process, using ozone
catalysts that cause clogging problems when SOx
(O3) generated from non-equilibrium plasma
and dust are included in the exhaust. Therefore,
at atmospheric pressure (Reaction O2+O➝O3,
NO+O3➝NO2+O2). Sodium Sulfite (Na2SO3) is then produced as a by-product of a de-SOx process (Reaction SO2+2NaOH➝Na2SO3+H2O), after
which NO2 is reduced to N2 gas by a chemical process involving Sodium Sulfite (Reaction
2NO2+4Na2SO3➝N2+4Na2SO4). NOx is thus
removed. The Na2SO4 generated by the reduction of NO2 can be reused as a raw material for glass manufacturing.
Unlike SCR, a high concentration of SOx and the existence of adhesive dust does not affect the PCHP. This process requires low maintenance and can also be applied easily into existing exhaust gas treatment equipment for de-SOx, consequently reducing the initial and running costs compared to Figure 2: Semi-dry type and wet type exhaust gas treatment systems.
18 r Furnaces International Issue 1
installing an SCR.
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Glass The issue with installing PCHP in a glass
entrance of the system. The O3 is broken down
to O2 in temperatures of more than 150C, losing
effectiveness in NO oxidation. The temperature of exhaust gas should be cooled to less than 100C for effective NO oxidation by O3.
Therefore, the focus of this development is to form a localised low-temperature area by spraying water before introducing the O3. This low-temperature area is necessary for the Plasma and Chemical
reaction process, both of which are required to
NOx concentration [O2=15%] (ppm)
gas which is between 300C and 450C at the
Inlet of reactor
500
Outret of reactor
450
Removal efficiency
400
50 45
Exhaust gas volume: 8,030 m3NH/h Injected ozone volume: 1,443 g/h
40
NOx removal efficiency 34% From 322 ppm to 211 ppm
350
35
300
30
250
25
200
20
150
15
100
10
50
50 0
0
0
20
40 60 80 100 120 140 Elapsed time (minutes)
Removal efficiency (%)
furnace is the high temperature of the exhaust
Reaction efficiency 86% from 120 ppm to more than SOx > 99%
NO2 30 ppm
The conc. and removal efficiency of NOx by PCHP
NO2 31 ppm NO NOx 291 ppm 322 ppm Before processing
NO NOx 180 ppm 211 ppm After processing
Figure 3: showing the placement of the demonstration equipment at the wet type system.
remove NOx from the exhaust gas.
Demonstration
be 200C to protect the duct, bag filter and so on.
For a pilot scale test of the PCHP, NYG had a demonstration in 2013 for the wet type system in
To succeed demonstration of the semi-dry type
Harima plant. O3 is produced by seven ozonisers
system, NYG has to achieve two items concurrently:
connected with four machines supplying oxygen
One is the formation of a localised low-temperature
(3.6kW) and three machines with PSA (3.1kW) to
area for oxidation by O3 and NO2 reduction by
supply O2. The resulting O3 is then injected into a cooling zone with the water spray at the entrance
Na2SO3; another is to maintain the temperature of the outlet exhaust gas at 200C.
of the de-SOx scrubber.
Conclusion In this demonstration, exhaust gas volume was 8,030Nm3/h, and injected O3 volume was 1,443g/h. During the demonstration’s elapsed time, O3 was
NYG began a collaborative investigation with Osaka
injected from the 20 minute to the 120 minute
of the wet type system succeeded in 2013, with the
mark, consequently reducing NOx emission from
first trial of the semi-dry type system in 2014. The
322ppm to 211ppm during that time frame. Due
second trial was done in August 2015.
Prefecture University in 2011, and a laboratory experiment was performed in 2012. Demonstration
to the small pilot scale of this demonstration, NYG had a limited supply of ozone, but nevertheless a
Comparing both results, it showed that there was
high reaction efficiency was achieved. The reaction
progress in increasing the reaction efficiency of
efficiency of injected O3 was 86%, which indicated
the Plasma process and total de-NOx, yet NYG was
that more ozone injected into the system results in
able to identify more room for improvement, thus
the removal of more NOx. The de-SOx process was
a third trial is being planned for the end of the
not affected because SOx emissions decreased more
year. After a successful demonstration, NYG will
than 99% at the exit. With the wet type exhaust gas
push forward with the commercialisation of the
treatment system demonstration, it was concluded
de-NOx equipment for a semi-dry type exhaust gas
that application of the PCHP to an actual exhaust
treatment system.
gas of a glass furnace is effective for a wet type exhaust gas treatment system.
Current development status Due to lower cost and simpler operation, the semidry type system is more popular than the wet-type variation. Therefore, NYG is currently developing a
Contact Ryota Tsuji Assistant Manager
semi-dry type of de-NOx system. For effective NO
Environmental Affairs Office
oxidation by O3, an area with a temperature lower
Nihon Yamamura Glass, Hyogo, Japan
than 100C is necessary. However, the temperature of
www.yamamura.co.jp
the exhaust gas at the outlet of the system should
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Issue 1 Furnaces International r 19
Glass
Energy saving concepts for glass container and tableware furnaces AGC Ceramics Co (AGCC) has been a refractory specialist since 1916 and an engineering services company since 1976. Here, Masami Kitano* outlines some energy saving concepts that have recently been certified by the Japanese government for their environmental credentials.
T
o meet the cost reduction needs of the glass
Second, refractory corrosion and glass defects
industry today, performance improvement of
are also discussed. For example, to improve glass
the melting furnace has inevitably been put
quality, high temperature melting is an effective
on the agenda. It is not easy to find the right answer
method but an excessively high temperature
due to the many factors involved with a high
damages the refractory. A large amount of corrosion
temperature operation.
affects intractable quality issues, the so-called ‘cat scratch’. AGCC has analysed the defects and
Two topics are discussed in this paper. First,
has proposed a counter measure to minimise cat
an energy saving concept is introduced. AGCC’s
scratch.
concept, which consists of a hyper-regenerator and a thermotect-wall, has attained 10% to 15%
Energy saving concept
energy savings compared to a conventional design.
The main concept of the hyper-regenerator is the
A milestone in 2015 was AGCC’s technology
double-pass chamber for the checker package as
being certified by the Japanese Environment
shown in Fig. 1. A longer passage is logically better
Ministry, while one Japanese customer received a
for the heat exchange, however, maintaining the
government subsidy for its forthcoming project.
flow route, adjusting gas velocity and optimum utilisation of the checker package are tougher
Double pass regenerator 2nd chamber
introduced in Europe but it is not widely used today due to checker troubles and insufficient energy
1st chamber
Port
Fire clay checker
subjects. In the past, the double pass concept was
Single pass regenerator
performance. Port
Port Basic checker
Basic checker
One of the important issues of the double pass is to prevent the gas/air flow separation and make it a synchronised route (Fig. 1). The other issue is checker clogging. This is
Fire clay checker
improved by setting up the temperature area of Na2SO4 condensation near the rider arch to easily drop it off to below the rider arch. Improvements such as this over the 40 years of AGCC’s engineering
Figure 1: Schematic diagram of AGCC’s concept furnace.
20 r Furnaces International Issue 1
services lifetime have produced highly efficient
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Glass between 10% to 15% energy savings compared with Unit requirement (litre/TG)
a conventional design as shown in Fig. 2.
Refractory corrosion and cat-scratch The pull rate for the melting area, indicated by ton/ day/m2, is one of the most important factors for furnace performance. The excessive pursuit of it (the so called ‘Glass Load Olympic’) often causes over-
10-15% lower
heating because it requires higher temperature melting in a small furnace. It may damage the 0
50
100
150
200
250
300
refractory and shorten the furnace life. A well-
Pull rate [tonne/day]
known case is the sagging of the silica crown due to a high melting temperature over 1600C.
Figure 2: The flow of secondary air and waste gas in a double pass and single pass regenerator.
Fig. 3 shows the corrosion speed of a fused cast refractory at the laboratory. If the temperature
Corrosion depth [mm]
8 Soda lime glass 48 hrs TEST 6 MB-G Aβ-Alumina
4
increases by 50C, the corrosion speed roughly
ZB-1681 33%-AZS
becomes more than double.
ZB-1691 35%-AZS
Fig. 4 shows the change in thickness of the sidewall
ZB-1711 41%-AZS
refractory at the furnace with both a simulation result and an actual measured result. The corrosion progress is rapid at the initial stage and the
2 0 1250
progress becomes slower due to the cooling effect from outside, if the residual thickness becomes 1300
1350
1400
1450
1500
1550
thinner. For instance, if operation temperature
1600
is 1600C, more than 200mm of fused cast AZS is
Temperature [˚C]
corroded within 12 months. It means that many Figure 3: Fuel consumption at the furnaces supplied by AGCC. The red dots are furnaces that are furnished with the 4G hyper regenerator and thermotect-wall.
sources of the refractory defects, such as cat scratch, flow into the molten glass at the initial stage.
products with a lifetime of more than 10 years. AGCC now confidently presents its 4th generation of 0.5
15
0.4 ZrO2 (wt%)
Thermotect-wall The thermotect-wall consists of an insulation material by the trade name of Thermotect (TMT). TMT is a high thermal insulating monolithic
10
0.3 0.2
5
0.1
material, which has the same performance as
Others (wt%)
hyper-regenerator.
ZrO2 Al2O3 Na2O CaO
0 0 8.25 8.3 8.35 8.4 8.45 8.5 8.55
ceramic fibre. Therefore, this monolithic is usable at a temperature up to 1600C with excellent volume
Distance (cm)
stability. The advantages of TMT compared to ceramic fibre are durability for long-term operation and joint-free configuration. It is also safer for operators, as it does not contain RCF (Refractory Ceramic Fiber), which is identified by the World Health Organisation (WHO) as a possible human carcinogen. AGCC developed TMT using internal raw material technologies.
gas burner to the concept furnace, and has attained
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Figure 4: The relation between temperature and corrosion speed of fused-cast refractory.
250
ion (mm)
AGCC also integrated other improvements such as oil/
200
1300˚C
1350˚C Issue 1 Furnaces International r 21 1400˚C 1450˚C
Glass The Glass Load Olympic obviously requires melting at a higher temperature in a small furnace. This is
stagnant glass by design and refractory selection. As
Contact
a supportive care, a stirrer is recommend to mix the
feasible in the short term period, but a damaged
Masami Kitano
refractory negatively impacts the rate of energy
AGC Ceramics Co., Ltd.
consumption, glass quality and furnace life in the
Glass Engineering
long term. As a result, it may not be a good cost
Division
performance overall. Multiple factors should be considered when aiming
condensation.
Conclusion A fundamental knowledge of glass furnaces is essential for good performance. A solid concept,
Osaka, Japan
for structure, material selection and innovative
www.agcc.jp
application, contributes to increased energy savings and glass quality.
for a well-balanced furnace, as well as selection and application of refractory.
AGCC has produced refractory materials for 100
Cat-scratch
years and engineering service for 40 years, and
Many cat-scratches have been analysed, and they
the hyper-regenerators and thermotect-walls are a
are now classified into three types.
good example of the culmination of the company’s activities.
The first is ZrO2. This generates predominantly from the AZS refractory type in the melter. Ordinarily, the
250
mark is not very strong, has multiple knots, and the Refractory corrosion (mm)
diffusion speed is slow. The second is Al2O3. It normally generates from
the alumina refractory in the working-end and the forehearth. Generally, the mark is strong with a single knot, and the diffusion speed is fast. The third is the mixed type, as shown in Fig. 5.
200 150 100 50 0
Al2O3 is hidden behind ZrO2 .
0
3
6
9 12 15 18 21 24 27 30 33 36
1300˚C 1350˚C 1400˚C 1450˚C 1500˚C 1550˚C 1580˚C 1600˚C Higher curve (measured) Lower curve (meansured)
Time (month)
Unfortunately, cat scratch is an unavoidable symptom, however it can be reduced by solutions such as optimum operation, and a reduction of
Figure 5: The corrosion speed of sidewall, calculated by one dimensional refractory corrosion model.
250 Refractory corrosion (mm)
1300˚C 1350˚C 1400˚C 1450˚C 150 1500˚C 1550˚C 100 takes place in Abu Dhabi’s ADNEC centre this 10th The Glassman Middle East exhibition and conference and 1580˚C 1600˚C 11th May. The conference and exhibition are free to attend, and will feature a variety of heat treatment, meltHigher curve ing technology, and furnace manufacturers including50Stara Glass, Horn Glass, LWN Lufttechnik, Sorg, Electro(measured) glass, and Henry F. Teichmann, amongst others. Lower curve The conference also has a focus on furnaces and furnace technology, with presentations from the Technical 0 (meansured) 0 3 6technology; 9 12 15 18 24 27 30Leader 33 36from Eurotherm Director of Stara Glass, who will discuss its Centauro furnace the21Technical 200
at Schneider Electric, who will discuss recent improvements in electrical furnace boosting systems; and Time glass (month) Fernando Salvino, Engineering Manager at IRF Europa, who will present his paper on prolonging glass furnace life which can be found in this magazine. To find out more and pre-register for the event visit: www.glassmanevents.com/mid-east/
22 r Furnaces International Issue 1
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BIFCA
British Industrial Furnace Constructors Association Introducing BIFCA
T
he British Industrial Furnace Constructors Association (BIFCA) has seen considerable changes since it first began its life in 1947, as
the Society for Industrial Furnace Engineers (SIFE). It is now the UK Trade Association representing the
BIFCA will be supplying a regular column for Furnaces International, and took the opportunity to use this first issue to introduce themselves and what they do.
interests of designers, manufacturers, and the leading component suppliers of thermprocessing equipment and services to the furnace industry. BIFCA courses are aimed primarily at Through its involvement with government and
end users, but are equally beneficial to
industry bodies, meetings, seminars, conferences and
manufacturers and suppliers with attendees
exhibitions, BIFCA seeks to promote and represent
having originated from international
the views of its members and the industry in general,
companies on numerous occasions in recent years.
helping to influence EU and UK policy, legislation, and industry standards relevant to the manufacture
BIFCA also actively participates in the work
and use of industrial furnaces and laboratory ovens. BIFCA will present a column in each issue of Furnaces
of CECOF, the European Federation of Furnace
International and will discuss a range of these topics.
Associations, where BIFCA is represented on the Executive Committee and where its members are able to benefit from the activities of CECOF.
Membership of BIFCA is open to companies with registered offices in the UK who are involved in the design and manufacture of industrial furnaces
In partnership with CECOF, BIFCA endorses certain
and ovens, or who supply component and ancillary
European and worldwide furnace exhibitions that are
equipment to the industry.
visited in their thousands by delegates from many high profile companies throughout the global furnace industry.
The association provides a series of technical courses that focus on furnace operation and efficiency, with courses on burner technology, furnace controls,
BIFCA is involved with a number of activities and
modelling and induction technology. These courses
initiatives that are aimed at promoting the UK
have been designed to meet the requirements of the furnace industry for specialist information, knowledge and training. The courses are reviewed, assessed and updated regularly to take advantage of any advancement in technology or amendments to legislation.
Contact BIFCA National Metalforming Centre 47 Birmingham Road
furnace industry and best practice within it. One of the initiatives implemented by BIFCA is the promotion of an energy efficiency mark. This is open to manufacturers and suppliers who can demonstrate, through product design or installation, a saving in energy costs via increased productivity, lower energy usage or higher throughput.
West Bromwich, UK BIFCA is continually monitoring the industry for topics
B70 6PY
End users can also qualify for this mark in
that can be added to its technical programme, with
enquiry @bifca.org.uk
partnership with their supplier by demonstrating an
courses on vacuum technology, refractories and gas safety awareness all currently being considered.
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www.bifca.org.uk
energy saving gained through investment in product, process or installation.
Issue 1 Furnaces International r 23
Glass
Advancements in regenera
Figure 1: The Eclipse BrightFire 200 Burner with gimbal bracket and refractory block.
Dave Fontes* describes how an upgraded natural gas regenerative burner has been installed in several container, float, and tableware furnaces in Europe, Asia and the Americas.
Eclipse, Inc has introduced its upgraded natural gas
The glass industry continues to push for
regenerative burner, BrightFire 200. The company has
advancements in regenerative gas burner technology,
a successful history with regenerative natural gas
including:
burners, with the 03R then the 03V developed in the late 1970s and 1980s.
1) improved heat transfer for lower energy use;
These were the first ‘sealed-in’ burners that improved
2) reduced NOx emissions;
flame control and reduced energy. According to the company, they were also the first easily adjustable
3) easy to use, setup, and adjust; and
burners in the industry, allowing flame length to be adjusted ‘on the fly’, without removing the burners
4) enhanced flexibility in flame adjustment and
from the port and changing tips.
performance.
In the mid-1990s, the company improved the burner
To address these needs, Eclipse developed the
further with the development of its dual gas injection
BrightFire 200 burner, shown in Fig. 1. The burner
technology in the original BrightFire burner. This
includes the following features:
allowed two separate streams of gas to be injected through a single burner, inhibiting the formation of
r Completely separate inner and outer gas jets
NOx and improving flame control. The BrightFire burner was widely accepted in the industry, with
r Simple controls for each gas jet located on the
thousands of burners installed throughout the world
burner
in every type of glass furnace. 24 r Furnaces International Issue 1
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Glass
ative gas burner technology r Single gas inlet
Both mechanisms employ an easy to read scale to allow a precise and repeatable setting of the
r Continued use of the Eclipse sealed-in burner
adjustments.
design
Up to 25% less NOx r A nozzle design updates using the most successful
The combination of these two adjustments has
design-base in the industry
shown an improvement in flame control. In one case with an underport firing arrangement on a large float
Referencing the burner in Fig. 2, the area adjustment
furnace, the flame length could be adjusted from
and flow adjustment are identified. The area
30% to more than 80% of the furnace width without
adjustment allows the area between the inner and
altering the gas flow.
outer nozzles to be increased or decreased, which alters the overall length of the flame and the flame
Additionally, NOx was demonstrated to be 15% to
velocity.
25% less compared to other burners on end port and side port furnaces. NOx was reduced substantially on
The second adjustment is the flow adjustment. This
an end port furnace in Europe where a typical burner
changes the distribution of gas between the inner
supplied by a furnace designer was replaced.
and outer nozzles. Flow adjustments are typically to or further from the burner/port. Additionally, the
A NOx reduction greater than 20% was realised, achieving the goal of less than 550 mg/Nm3. Fig. 3
flow adjustment provides the operator with a tool to
shows a BrightFire 200 burner installed in an under
lower NOx for a given flame length setting.
port arrangement.
The area and flow variables can be altered
The ability to alter the heat release position within
independently. This provides various settings to
the flame and thus within the melter has shown
tailor the flame shape and performance to the exact
promising gains in energy efficiency. In one case
situation at hand, including furnace design, glass
involving a container furnace, the under glass
chemistry and production rate.
electric boost was reduced by more than 10% with
made to move the heat transfer from the flame closer
Figure 2: BrightFire 200 adjustments.
Area adjustment
Flow adjustment
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Issue 1 Furnaces International r 25
Glass inlets for each gas jet, complicating the gas piping to the burner and increasing the associated costs. Other burners today have the inner and outer gas jet controls on the burner, but they have no means of adjusting the inner nozzle relative to the outer nozzle. Only the BrightFire 200 combines all these features into one burner, using updated burner tip technology based on 40 years of experience with the most successful regenerative burner systems in the glass industry. The BrightFire 200 is currently installed in several container, float, and tableware furnaces in Europe, Asia and the Americas. All firing arrangements are in use: side of port and under port firing on both side and end port furnaces. In many locations, customers are adding the BrightFire 200 to multiple furnaces
Figure 3: Eclipse BrightFire 200 installation.
based on the improvements realised on an initial furnace installation.
a small reduction in natural gas use and no effects on production. In this case, the burner includes an optional gas swirler for the outer gas jet, which increases the flame surface area and further improves the heat release to the glass melt.
Contact Dave Fontes, Glass Industry Manager Elster Thermal
Along with the adjustment features and design elements described above, the burner can be provided with an oil lance for easy change to oil firing. The nozzles can also be designed for firing both oil and natural gas simultaneously.
Fig. 4 shows the BrightFire 200 operating in a small
Solutions,
cross-fired furnace. Thermal imagery was used to
www.elster-thermal-
Finally, with Elster Thermal Solutions’ global service
better assess the flame characteristics and to more
solutions.com
and sales network, the company is able to support the
thoroughly understand other interactions occurring
glass producer anywhere in the world.
inside the melter.
Improved heat transfer Improved batch line control was observed due to the improved heat transfer of the BrightFire 200.
Figure 4: Thermal image from inside a furnace with BrightFire 200 burners.
This resulted in the batch line pulling back and subsequently a reduced seed count was reported by the customer. An additional benefit of the BrightFire 200 was improved flame stability, which kept the flame off of the batch piles and reduced carryover into the regenerators. Better heat transfer from the flame also put more heat into the glass melt, reducing crown temperatures and increasing bottom temperatures. These improvements can help increase the life of the furnace while simultaneously reducing the overall energy costs associated with production. Another key feature of the BrightFire 200 is the single gas inlet. This allows the burner controls for the inner and outer gas jets to be located on the burner. In many other dual injection burners, there are separate
26 r Furnaces International Issue 1
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BIFCA Ad.0:Layout 1
24/5/11
11:25
Page 1
BRITISH INDUSTRIAL FURNACE CONSTRUCTORS ASSOCIATION BIFCA is the British Trade Association for the Furnace Industry providing its members access to information, events and networking opportunities throughout Europe and the rest of the world. Training Course s Furnac Training Courses e Mod urses How to Co elling improve ng . furnace Traini design logy ormance of fuel fired furnaces and ope no ch ration perf Burner Technology by simp le mod optimum Duratio rnace Te elling n techniqu rial Fulved in the efficient design and 1 day es. An overview of best practice in burner technology and selection. Indust tices invo s and prac Principle
n Duratio 2 days
Venue The cou rse Alternat will normally be held ively, it can at contact BIFCA for be held at you the BIFCA offic es. r premises details. Venue - please The course will normally be held at the BIFCA offices. Course Overview Alternatively, it can be heldse?at your premises please Redu this cour ent envir cing costs, contact BIFCA fromdetails. increasing fit for onme the effici
Duration 1 day
A offices. se at the BIFC be held r premises - plea Venue normally you rse will held at The cou can be ively, it details. Alternat BIFCA for contact
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Who will manageme how do goals of the meeting other emis ation, it Course ces. ved in the Simp benefit Overview Who should attend thischoo course? furnace n and you legisl nnel invol industrial furna eting of le desktop by from this user se betw computerand identify es of carbo of • Perso to ent • Furna changing and mark of sales combustion technology applied furnaces An introduction course? een diffe and whereto gaseous lopm the principlesical ce desig models• Process and plant managers / supervisors. major sourc costs and efficiency of satisfy the deve rent ners and provide in techn liquid fuels, coveringved a wide range of applications but prod with the main heat focusis towards Overview furnaces are of rising fuel • Energ going, asuctio a route thermal operators. user mustproduction Course t such wher Energy invol y and envir technologyn can be incre ment. & environmental managers. to evalu erature a resul to enhance the designer and high temperature • Staff processes. ant areas ased. They•e energ n equip onmental ating y asing • savin relev (heat Perso ustio High tempprocesses. As ce incre in the gs can recovery, ns respo comb ing also help Equipment best optio managers. importanttion. The furna ating costs, and suppliers. made and nsible contr • Original evaluate beManufacturers combustio ns. They industrial increasingly staff work transfer. Cour rchlook ident thestaff The course also at developments in minimising combustion se Sylla emissions whilst ols,• furna and operaof reducing oper Resea n equip for the efficient returworking • will Salesceand project withify combustion ices n and heat whether insula becoming their design n on inves bus • ment The nts Plant ustio pract operation tion, ty. . coursan interactive ‘question maintaining comb plant efficiency, including practical examples and reme managers etc).furnaces, kilns, tmenovens related aspects of and of iples and uct quali with t in new improving icting requi • Desc e will: and opera • Techn answer’ session. the princ ired furnaces,and ving prod ribe ical mark dryers. tors. often conflt, and impro ding of fuel-f plant and informatiohow simple, eting and tion of understan of their throughpu n to impro easy-to-us• Research staff working in relevant areas. sales perso greater optimum opera al efficiency ion • How, e, comp Course Syllabus association. ve the nnel. provide and with the uter Certificat e is offered in operation the therm Certificat e will organ design aid of a This course will cours cover the following topics: improve • Provi and desig models can provi of Glam This cours with efficient from desktop This ipants to Attendees ion n of furna demoissues. de the University computer, • Combustion Principles: Fuel types & properties / heat de transfer feedback the nstrations gh essential associatedon enabling partic ces. non-speci ssion and successful are presented of their red throu fit, with Certification of discu alist staff •bene Burner Types: Basic principles, burner types / fuel air components and systems use in a completion emphasis The & be delive e. with a a result will cour cours as can with range of Attendees are presented a certificate on se and EN746-2 the issues use these of the cours a certificate years of nted withsystems Content maximum / oxy fuel technology / oilprese atomisation products. •/ safety practical cover: Combusti will several obtain ipants. on e. successful completion of thecatio course. models. completion appli dees are ed over e partic on and , but to Atten ns. • Emission & Control on Strategies: / control options / flameless successfulTypes of NOx•burners heat trans has evolv earlier cours course notes Refre e The ns. shme mass balan icate fer in furna The cours advisors and nts / combustioncertif rehensive Course ssion sessio ce. • The ces. by comp ipate in discu notes and Notes of t energ industrial a ybuffe basics lunch are modeand all supported Efficiency & Low NOx Burners: Cold air,ding recuperative partic Refreshments / Notes s • inclu l. regenerative fuels - • Energy provided. refreshments Cond lectures are invited to ts Designdevelopments / applying uction nts / Note hmen mics.burner including low NOx to energy efficiency. Course notes and all refreshments including a buffet and liquid and conv delegates • Types Refreshme and all refres a buffe gaseous burner aero-dyna ection. t lunch are provided. notes costs versus potential of math rties of • Economic Issues: savings / non-combustion cost and CourseEnergy ustion ion: Prope Combustion provided. Syllabus - the single ematical mode savings in and benefits. cts. Delega Course and Combust ls. and comb lunch are well-stirre and produ oil burners. te Com s flames heat transfer - the long an open dsession zone. where • Fuel , Criteria: Basic selection guidelines • Selection ments erties of n reactants ers and furnace ce walls ments / includes tion propflames. Convectivegh furna combustio tion of gas burn model. delegates will have an opportunity transapplications. te Comto discuss -their : Radia oil ient cond s throu and opera Furnaces Delega gas and uctio heat losse “The cou n. sfer in atn model. tion from in furnaces, Tran mptio radia look rse has consu There will • Heat uction Thermal ol of fic fuel how we made us in-depth be demo a lot - nstra products. n systems. Cond . ency, speci ation and contr re. operate think abo iled andown furna rmity tions al effici eratu ceaces ment furn data. deta Who will benefit this course? And of g our temp combustio erature unifo Therm Delegate Comments ut Instru the : fired “A y Godson furn above fuel• ure and provokin Furnaces efficiency. models. e burners. load temp , Boal UK aces”. ght iency in Use of thermal of furnace press regenerativ Attendees ation of Delegatess,will benefit effic from gaining an appreciation and understanding of the following high thou math tion on ol “Good introduction material” e and ient Oper ctorie ematical can and ul and bringawareness important aspects of Burner Technology: • Effic of furnace opera control, contr , recuperativ al mass refra models “Great along their J. Ho of usef to predi ngers ratio as an ove therm Effects processes. ct NOx BOC tion” A brief air/fuel from excha losses, low iques appreci ustion • Effective emissions. rview and - techn Burner Selection. informa h covered,introduction to more furnaces, of waste heat atio ion in comb structural SOx, NOx n. although general Steve Tho n” • Reducing Emissions. Nigel Trot Recovery of wall and of oxygen addit ustio , smoke, comb Ltd the cours complex comp t n ” “Overall content was very helpful” formation uter based e will focus mas perheat Reduction coatings. Effec ce desig “Flameless Pollutant • Increasing Performance. CELSA and physi on simpl R. Glassonbury Stork Coo sions: aid to furna models furnaces. Manufac e, easycal mode emissivity zoneEnergy. ace Emis ls as an erature To atte to-us ls will Saving turing UK and Spirax Sarco Ltd e tools 2123 ical mode mics (CFD•) and rol of Furn in high temp nd this for quick also be A/Acou techniques • Cont Ltd BIFC : Mathematnal fluid dyna : lling solutions. reduction • Understanding Combustion Principles. aces Ref rse NOx mode for please form gn of Furn computatio experimental complet mal Desi Application of scale booking • Ther e the acco . Small tion. British anying Industria and opera design case study mpany accomp National l ce ing boo - furna ns. MetalformFurnace Cons plete the West Brom king form tructors ing Cent se com applicatio Asso wich plea re, 47 , West To attend this course please complete the(0)accompanying booking ciationRef: BIFCA/A2123 Tel: +44 Ref: BIFC Birmingha form course ciation Midla m Road A/A212 ors Asso Email: enqu 121 601 6350 nds, United nd this , Kingdom, , 3 Construct ngham Road 6PY To atte • Fax: iry@bifca.o +44 B70 6PY B70 l Furnace 47 Birmi British Industrial Furnace Constructors Association rg.uk • Web (0) 121 601 Industria ing Centre, United Kingdom, 6387 : www.bifca 6387 British 601 nds, National Metalforming Centre, 47 Birmingham Road, Metalform (0) 121 .org.uk .org.uk National wich, West Midla• Fax: +44 .bifca West Bromwich, West Midlands, United Kingdom, B70 6PY West Brom 121 601 6350 • Web: www Tel: +44 (0) 121 601 6350 • Fax: +44 (0) 121 601 6387 (0) rg.uk Tel: +44 iry@bifca.o Email: enquiry@bifca.org.uk • Web: www.bifca.org.uk Email: enqu
BIFCA Furnace Industry Training Courses Developed and delivered by qualified respected industry professionals, BIFCA offers specialised training courses in: Furnace and Burner Controls, Industrial Furnace Technology (in conjunction with the University of Glamorgan), Furnace Modelling, Induction Melting and Energy Efficiency.
BIFCA Annual Safety & Standards Seminar and Events Keeping the industry informed on all current and future European and world standards and legislation and the implications for the furnace industry.
BIFCA Energy Efficiency Mark BIFCA operates an Energy Efficiency Mark which is open to members and non members who can demonstrate energy saving initiatives they have made for their customers.
CECOF BIFCA is a founder member of CECOF, the Federation of European Furnace Associations, regulating European harmonised standards and safety issues. For more information please contact: BIFCA, The National Metalforming Centre, 47 Birmingham Road, West Bromwich B70 6PY, United Kingdom Telephone: +44(0) 121 601 6350 Facsimile: +44(0) 121 601 6387
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Steel
Increasing energy efficiency in electric arc furnaces Marcus Kirschen*, Reinhard Ehrengruber**, and Karl-Michael Zettl* present their findings on increasing the energy efficiency of electric arc furnaces in steel plants, by excellence in bottom gas purging.
M
odern electric arc furnace (EAF) processes
Why implement gas purging?
are subject to the cost-optimised production
The EAF process is characterised by the large
of raw steel melt, in combination with very
flexibility regarding production volume and raw
flexible productivity. Excellent mixing of the steel
materials. With recent ferrous raw material price
melt helps to improve mass and heat transfer, in
increases, the requirement to produce high quality
order to accelerate the melting of scrap and direct
steels from lower quality scrap, direct reduced iron
reduced iron (DRI), decarburisation, homogeneous
(DRI), hot briquetted iron (HBI), hot metal (HM) and
superheating, alloy distribution, and to avoid skull
varying quality ferrous scrap blends has increased.
formation. Direct bottom gas purging not only
Maximising the yield from ferrous raw materials,
promotes efficient mixing of the steel melt in the
oxygen, carbon, and alloys as well as minimising
entire steel bath, but also provides constant gas
energy costs are of the highest priority.
bubble columns to avoid CO boiling retardation. For a few years EAF gas purging systems have been experiencing a comeback. Recent case studies and new developments on refractory and gas control units are presented here, and show that gas purging systems represent a safe and modern EAF technology to increase energy efficiency with minimum pay-back period. Control on the entire gas purging technology from refractory to valve control and purging strategy is crucial for high reliability and availability of the purging system. With years of purging experience, RHI/STOPINC presents a newly developed gas control system for application at the EAF, BOF, ladles etc. in secondary metallurgy.
28 r Furnaces International Issue 1
Figure 1: Efficient steel melt mixing in the lower and upper bath using three gas purging plugs in the EAF hearth (figure based on CFD modelling of steel flow pattern).
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Steel At modern high productivity levels, even small process improvements provide considerable cost
100
savings. Such improvements can be realised, for example, by efficiently increasing mass and energy transfer in the EAF. Therefore, optimising flow
80
patterns in the steel bath is important for efficient scrap and DRI melting and high melt homogeneity.
60
EAF bottom gas purging technology Typical EAF technology provides few sources of momentum to move and mix the steel melt and slag. For example, AC electric arcs and oxygen injectors
40 2000
2003
2006
2009
2012
2015
affect the surface of the steel volume with restricted efficiency as a viscous slag layer covers the steel melt. In addition, although a DC electric field is applied to
Figure 2: Increasing number of customers using direct EAF bottom gas purging systems based on RHI deliveries (axis: deliveries vs year).
the central steel bath above the bottom electrodes, by far the most efficient movement of the entire steel melt is generated by gas purging, where columns of
standards as the hearth ramming mix is installed,
bubbles rise from the bottom to the top of the steel
de-aired, compacted, and sintered without interfering
bath (Fig. 1). Since the early 1980s, various oxygen
with the purging system. The remaining gap around
and inert gas injection systems have been introduced
the purging plug is filled with two special filling
to improve melting efficiency in the EAF. Refractory
mixes, optimised for the special sintering behaviour
materials, installation procedure, and gas control
required near the purging plug (Fig. 3). By using
units have been significantly improved in the last
this standardised lining strategy, the highest safety
years. Design of purging plugs was optimised and gas
requirements are fulfilled and breakout incidents
consumption was minimised.
have become a thing of the past.
Bottom purging systems based on gas injection
Gas is supplied to the steel bath through numerous
through a single tube or multi-hole plugs have been developed that are either buried in the EAF hearth ramming mix (i.e., indirect purging) or in contact with the steel melt (i.e., direct purging). However, current direct purging systems with a multi-hole design represent the majority of bottom purging systems in EAFs in the steel industry worldwide; for example the RHI direct purging plug (DPP) series. Nitrogen and/ or Argon gas is applied depending on availability and metallurgical constraints. Overall, approximately 9% of EAFs are equipped with bottom gas purging systems today, and with a common trend towards more cost-efficient EAF operations in the steel industry the tendency towards bottom gas purging is increasing (Fig. 2). Globally, RHI delivers DPP plugs to more than 80 customers for
steel tubes (Fig. 4). By providing multiple small holes, infiltration of the brick by melt or slag at low gas flow rates is restricted to the upper few millimetres of the plug. The reopening of blocked tubes, by melt movement caused by gas ingress through neighbouring tubes, occurs and is reported as common during RADEX DPP gas purging operations. In contrast, single-hole purging plugs typically remain blocked after deep infiltration of the one tube. A wear indicator in the purging plug is based on a pressurised gas line. A pressure drop through the opened wear line indicates a remaining minimum brick length and the purging plug can be closed safely. In small EAFs used at foundries for example, very low
EAFs with tap weights between 6–250 tonnes.
gas flow rates are applied to avoid an open eye in
Safety of the EAF gas purging system
Sometimes only one purging plug is installed and
Gas purging plugs are installed into the EAF hearth
high reliability of gas purging is needed. Very low
through a channel comprising of surrounding blocks
gas flow rates require precise gas control to avoid
(Fig. 3), thus (1) facilitating exchange of the purging
infiltration and blocking. RADEX DPP purging plugs,
plug in the EAF hearth and (2) increasing safety
with an optimised number of gas tubes and special
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the steel melt, due to the decreased slag thickness.
Issue 1 Furnaces International r 29
Steel hybrid plugs, have performed very well in small EAFs
flow rate not only provides maximum gas efficiency
when operated at very low gas flow rates.
but also avoids the formation of an open eye at the steel surface. This so-called ‘soft bubbling’ is the
Gas injection
common mode of operation in most DPP applications.
Typical DPP gas flow rates range from 10–100 l/
However, some customers apply higher gas flow rates
min or higher if required (Table 1). Nitrogen and/or
to reach their targets under special EAF operating
Argon gas is applied depending on availability and
conditions.
metallurgical constraints. A few centimetres above large number of well-distributed gas bubbles that
Gas control for EAF bottom purging systems
rise to the steel’s surface. Consequently, the impact
RHI provides the entire gas purging system
of gas flow on melt movement depends primarily on
comprising the refractory bricks and mixes,
the gas volume applied, and to a lesser degree on the
installation procedure, process support and the gas
tube number, tube diameter, or tube arrangement.
control unit. The gas control unit was developed by
the hot face of the plug, the gas is divided among a
Interstop/RHI, based on decades of experience with A large number of small tubes decrease the risk of blocking and provide a high number of gas bubbles even at very low gas flow rates. In addition, a low gas
Table 1: Characteristics of EAF Bottom Gas Purging Systems
gas purging. A typical gas control station to supply one to six
Type of EAF bottom Direct gas purging plugs Indirect gas purging purging Multi-hole design Single-hole design* DPP (n.a. by RHI) VVS or TLS
Purging plug position Gas supply refractory Tube configuration Open tube diameter
Hot face in contact with steel melt
In hearth ramming mix
MgO-C brick
MgO-C brick
Special ramming mix
Multiple tubes
Single tube
-
1 mm
2.5–5 mm
-
Typical gas flow rates per plug
10–100 l/min
100–250 l/min
30–70 l/min
Mode of gas injection
Soft bubbling
Jetting
Soft bubbling
Stirring efficiency per m3 gas
High
Medium
Low
Plug infiltration characteristics
Low
High
n.a.
Unlikely
n.a.
Reopening during campaign Increase of hearth service time
Likely to reopen
-
Influence on hearth lining Wear rate of purging plug
No or slight increase in wear rate
Main objective
Decreased wear
0.2–1.0 mm/hour purging
Lifetime
300-1300 heats
(equivalent to hearth lining)
n.a.
As permanent lining
*not supported by RHI for EAF gas purging applications.
30 r Furnaces International Issue 1
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Steel RADEX DPP purging plugs in the EAF is shown in Fig. 5. Each plug is controlled separately, and either
Hearth ramming mix
Surrounding blocks
DPP purging plug
nitrogen and/or argon is used. The gas flow rates
Special ramming mixes for gap filling
can be regulated independently of the EAF control, by using particular EAF operating parameters or by incorporating it into the EAF control system. Technical advantages of the gas purging systems from Interstop/RHI are as follows: r Modular, maintenance-friendly design (Fig. 6) r 100% leak-free system due to o-ring sealed standard blocks instead of pipes r Opportunities to control the stirring efficiency r Visual realisation of all input and output signals based on customer demand Wear indicator
r Error report with failure detection r Process data availability through embedding i
Stirring gas
Figure 3: Schematic of an installed RADEX DPP in the EAF hearth lining, showing the surrounding brick channel, central purging plug, and special gap-filling ramming mixes.
into existing IT infrastructure for data transfer and processing r Simple and cost-effective serviceability due to r Programme language is Siemens Step 7/WinCC
modular design
flexible or TIA Portal r Highly precise mass flow control – latest r Accurate and individual flow control for multi-plug
generation of MFCs
purging systems r Quick response of flow rate to set value r Typical parameters include 100 % leak-free system; accuracy of +/-3%; setting time <500 ms
r Integrated solution from gas supply and control, purging plug, and metallurgical know-how r User-friendly, intuitive control panel
The general characteristics of the Interstop/RHI gas purging systems for EAF and secondary metallurgy
r Compact design implies very low space
are:
requirement
r Holistic EAF gas purging solution - control on the
r Customer-specific software solution
entire gas purging technology from refractory to valve control and purging strategy
r Exact adjustability of purging gas type and -flow rate over whole heat
r One-stop project management for systems and refractories
r Programmable gas flow rates for distinct steel grades or production programmes
r Technical support by experts with process knowledge
Steel plants and refractory suppliers mainly focus on refractory purging products such as plugs and
r Full integration in customersâ&#x20AC;&#x2122; process control
their characteristics in terms of bubble generation,
system at Level 0 to Level 2
flow, pressure, and lifetime. Whilst the importance of
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Issue 1 Furnaces International r 31
Steel the more it becomes apparent that the function of all single system items - including the piping and coupling - must be ensured. It is recommended that there is clear ownership of the gas purging process across all units in a steel plant to avoid a single unit receiving more focus compared to others. During the design of Interstop system parts (Figs. 7A & B), a uniform spare part concept was introduced. Hence, the same basic components can be used for EAF, BOF, and ladle purging stations. This supports easy and rapid maintenance because one specialist in the steel plant can maintain all purging stations. Fig.
Figure 4: RADEX DPP purging plug for EAF gas stirring.
8 shows an example of the modular design.
these factors is undisputed, the same attention must
Benefits of gas purging to the EAF process
also be paid to the gas regulation, piping, and system
The EAF process benefits realised using direct gas
maintenance.
purging systems are related to an overall increased steel bath movement as well as increased mixing
Mass flow controller
between the lower and upper steel melt volumes.
A centrepiece of modern purging systems is the mass
The specific reported benefits of RADEX DPP bottom
flow controller (MFC). In older installations these are
gas purging systems for stainless steel production
manually controlled mass flow metres, whereas the
include:
latest MFC (Fig. 6) has the following features: r Increased thermal and temperature homogeneity r Based on a caloric measuring system.
in the steel melt:
r Enables precision of +/- 1.5%
r Decreased melting time of scrap and DRI
r Flow regulation using a proportional directional
r Increased heat transfer during the superheating
valve.
period
r Depending on the application, regulation ranges are for example:
1. Furnace control system 2. Operation and control box
r 0.5 Nl/min up to 20 Nl/min; 2 Nl/min up to 100
3. Gas control box
Nl/min
4. Direct purging plugs RADEX DPP 5. Argon and/or nitrogen gas supply
r 6 Nl/min up to 300 Nl/min; 12 Nl/min up to 600 Nl/min
4 2
r 24 Nl/min up to 1â&#x20AC;&#x2122;200 Nl/min; 30 Nl/min up to 1â&#x20AC;&#x2122;500 Nl/min
3
r Setting time < 500 ms Fig. 6 shows the compact arrangement of a gas control box based on a standard block and the complete gas control unit.
System availability and maintenance The more a holistic system approach is adopted,
32 r Furnaces International Issue 1
Figure 5: Setup of a gas control station and supply of the gas purging plugs in the EAF.
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Steel
r Increased efficiency of power transfer
r Decreased specific electrical energy demand
r Decreased deviation between the measured
steel temperature in the EAF and the ladle furnace
r Avoidance of skull formation or debris in
the EAF hearth after tapping, decreased or avoided build-up of EAF hearth in stainless steelmaking (‘clean furnace’) r Increased chemical homogeneity in the steel melt:
r Increased metal yield
r Increased use of secondary ferrous raw materials
Temperature sensors
Heating element
(e.g. DRI, HBI, HM) Figure 6: Mass flow controller.
r Decreased variation in steel analysis - better
process control shortest payback time compared to other measures
r Increased yield from alloy addition
that increase EAF energy efficiency.
r Increased rate of carbon oxidation, in particular
Case studies
for hot metal charges
Recent DPP system installations provided the following specific improvements to the unalloyed EAF
r[C] x [O] levels closer to equilibrium conditions,
steelmaking process:
resulting in less alloy addition, better alloy prediction, and more stable ladle furnace
r A 250t EAF used for the production of construction
operations
steels, based on 100% steel scrap melting, was equipped with five DPPs operated at a gas flow
r Improved dephosphorisation
rate of 40–70 l/min. The productivity increased by 0.9 heats a day, the tapping weight increased by
r Improved efficiency of oxygen injection
1.6t, and the yield increased by 1.6%.
r Generation of gas bubble columns in the steel
r A 130t EAF was equipped with four DPPs. The
melt:
electrical energy consumption decreased by 7.3kWh/tonne with a slightly increased oxygen
r Avoidance of instantaneous or retarded CO
input of 0.9m3/t. The temperature control during
boiling in the steel melt
EAF tapping was improved.
The typical benefits observed from a series of case
r Three DPPs were installed in a 45t EAF. The
studies at customers with very specific targets for
electrical energy consumption decreased by
the DPP system included a higher than 5kWh/t
8.7kWh/t at an increasing mean transformer rate
electrical energy saving, a 0.5 minute decrease in the
(e.g., + 0.23MW). Coal addition was decreased
power-on-time, and a 0.5% increase in the yield. The corresponding overall cost savings were customer-
by 0.4kg/t and the total oxygen consumption reduced by 0.25m3/t. Concurrently, the rate
specific, with a minimum value in the order of 1.5 €/t,
of decarburisation increased by 0.05 %/hour.
and higher savings often achieved.
The yield was improved by 0.6%, the power- on time decreased by 1.5 minutes, and the
Bottom gas purging systems are claimed to have the
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productivity increased by 1.9t/hour.
Issue 1 Furnaces International r 33
Steel
Magnetic valves
Valve block
Pressure transmitter Mass flow controller
Figure 7A & B: Compact arrangement of RHI/Interstop gas control unit (left) and gas control box (right).
Application of DRI or HBI
oxygen in the molten metal significantly helps avoid
Application of DRI or HBI usually increases the
concentration gradients and improves yields.
specific electrical energy demand of the EAF process (Fig. 8), due to the addition of 2-6% oxide gangue
In foundries, metallurgical fine-tuning of the molten
material to the EAF that requires increasing the lime
metal is often performed in the EAF. The yield of
(and dololime), and due to the endothermic reduction
ferroalloys is dependent on the activity of the metal
of additional FeO + C = Fe + CO.
alloy in the steel melt and the activity of its oxides in the slag. Compositional gradients in the molten metal
1-2 % C remains in the DRI/HBI and requires
lead to higher alloy oxidation than necessary. Stirring
additional oxygen injection, compared to the
the melt using DPPs increases homogeneity of the
equivalent of steel scrap.
melt and the yield.
Increased mixing of the molten metal by gas purging,
DPP gas purging systems have been installed in EAFs
however, improves both the melting of DRI due to
used for stainless and special steel production as
increased bath movement, and the metallurgical
well as in foundry EAFs. For these applications, the
reactions due to decreasing chemical gradients
EAF bottom gas purging systems rapidly proved to be
and improving chemical homogeneity. Sudden CO
sustainable EAF technology for the customers:
discharge and boiling by abrupt mixing of C-rich steel volumes with O-rich steel volumes are avoided with
r The recent installation of a bottom purging system
active gas purging.
with three DPPs in a 100t EAF used for stainless steel production resulted in a yield increase of
Case studies of gas purging in stainless steel production
0.5 %, as well as an oxygen consumption decrease
Additional constraints apply to the production of
energy demand. Depending on the EAF process
alloyed or high-alloyed chromium or Cr-Ni molten
step, gas flow rates between 50 and 110 l/min
metal in the EAF. As carbon and chromium oxidation
were applied.
of 0.5m3/t and a 5kWh/t reduction in the electrical
in the molten metal occurs at very similar oxygen activities, special care is taken to minimise chromium
r Three DPP bricks were installed in a 140t EAF
loss during oxygen injection in the EAF.
used for stainless steel production and operated at a constant gas flow rate of 100 l/min. By
A high oxidation of chromium in the EAF is, in
increasing the bath agitation and thermal
most cases, caused by carbon deficiency in the
exchange, the electrical energy transfer efficiency
molten metal area affected by the oxygen injector. A
was increased and the oxygen
homogeneous distribution of carbon, chromium, and
was significantly decreased by 10m3/t. The most
34 r Furnaces International Issue 1
consumption
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Steel important result of the decreased oxygen input
gas purging systems in worldwide steel production.
was the 4.5% yield increase and a reduction in the tap-to-tap time of 9 minutes. With a decrease
r (2) Inert gas systems have become crucial
in Cr deslagging, the lime requirement was
tools as the quality and cost requirements for steel
reduced by 2kg/t.
production have increased. These systems not only offer simple gas flow control, but are also capable
r The application of a single DPP bottom gas
of complex operations and provide a high-level
purging system in a 6t foundry EAF used
operator interface when improved controllers, PLCs,
for specialty steel and high-alloyed steel products
and HMIs are added. In addition, a consolidated
resulted in a significant yield increase from the
system approach is key to achieving the desired
alloy addition. A 10 l/min gas flow rate was
metallurgical results with advantageous cost savings
applied.
due to the highest degree of process control.
r The installation of a DPP system in a 10t EAF
r (3) It is also very important not to separate the
increased the ferroalloy yield and decreased both
gas regulation system and the functional refractory
the tap-to-tap time and electrical energy demand.
purging products, but to consider the gas purging
One DPP was installed at a gas flow rate of 7â&#x20AC;&#x201C;10
system, refractory purging elements, and maintenance
l/min.
concept holistically. The approach offered by RHI and Interstop for EAF, BOF, AOD and ladle, results in an
r The installation of four DPP purging bricks in a
improved overall process control and cost savings
150t EAF for stainless steel production resulted
due to the multiple advantages described.
in a lower tap-to-tap time and a clear production increase. Gas purging has become EAF standard operation. r One DPP purging brick was installed at a
Ball valve (outlet line)
30t EAF for high alloyed and stainless steel production. Metallic yield increased by 3%, yield of alloys by 8%. Power-on time was reduced
Back pressure transmitter Bypass valve Shut off valve
by 7 min. r The corresponding overall cost savings were customer-specific, but in favour to the gas purging system for all customers. Bottom gas purging systems are claimed to have the shortest payback
MFC
time compared to other measures that increase EAF energy efficiency.
Figure 8: Modular design provides rapid maintenance, and fewer parts are required in stock.
Conclusions r (1) For the EAF process in unalloyed and high alloyed steel making, bottom gas purging provides cost benefits by increasing bath homogeneity, oxygen efficiency, decarburisation, and consequently the
Contact
yield from alloying elements, as well as decreasing electrical energy demand.
RHI AG, Austria marcus.kirschen@rhi-ag.com
The additional advantage of this technology includes
www.rhi-ag.com/internet_en
a more homogeneous melt, enabling improved process monitoring and control. Control on FeO in the
STOPINC AG, Switzerland
slag is increased. Process safety is increased by the
reinhard.ehrengruber@rhi-ag.com
decrease of sudden discharge and boiling of CO gas,
www.stopinc.ch
due to retarded mixing and oxidation reaction. RHI has numerous references of EAFs with RADEX DPP
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Issue 1 Furnaces International r 35