Transcript BEST AVAILABLE TECHNIQUES ON THE PRODUCTION OF …

BEST AVAILABLE TECHNIQUES
ON THE PRODUCTION OF IRON
AND STEEL
Group 9
IRON AND STEEL INDUSTRY
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This BREF covers the processes involved in the
production of iron and steel in integrated
steelworks.
Iron and steel are important products that are
widely used.
The production of crude steel in the European
Union stood about 20% of world production.
STEEL PRODUCTION IN THE EU
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The figure shows
Germany to have
the largest steel
industry in Europe.
ENVIRONMENTAL RELEVANCE OF
THE IRON AND STEEL INDUSTRY
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The iron and steel industry is highly intensive both in
materials and energy.
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Only about half of the input results in crude steel and
the other half are solids residues and off gases. *
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Air pollution remains to be the most important issue of
this sector.
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Copper and nickel emissions to air from electric arc
fournaces are also of significant relevance.
BEST AVAILABLE TECHNIQUES
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Best available techniques are defined as:
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Techniques
Include both the technology used and the design, built,
maintenance and operation installation.
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Available
Techniques developed in the relevant industrial sector,
under economically and technically viable conditions.
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Best
Most effective.
BASIC OXYGEN STEELMAKING AND
CASTING
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Two thirds of crude steel are produced via the basic
oxygen furnace (BOF).
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The primary raw materials are liquid hot metal from blast
furnace and steel scrap.
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Raw materials are charged into the Basic oxygen furnace
vessel.
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Oxygen (99,5% pure) is blown into the BOF at
supersonic velocities in order to oxidizes the carbon and
silicon contained in the hot metal liberating great
quantities of heat which melts the scrap.
BOF-BAT
Process-integrated measures
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PI.1 Energy recovery from the BOF gas.
PI.2 Lowering the zinc-content of scrap.
PI.3 On-line sampling and analysis of steel.
End-of-pipe techniques
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EP.1
EP.2
EP.3
EP.4
EP.5
EP.6
Primary de-dusting.
Particulate matter abatement from pig iron pre-treatment.
Secondary de-dusting.
Dust hot-briquetting and recycling.
Treatment of wastewater from wet de-dusting.
Treatment of wastewater from continuous casting.
BOF-BAT
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PI.1 Energy recovery from the BOF gas.
Generally, two systems can be used to recover energy
from the BOF gas:
Combustion of BOF gas in the converter gas duct and
subsequent recovery of the sensible heat in a waste heat
boiler.
Suppression of BOF gas combustion and storage of the
BOF gas in a gasholder for subsequent use.
BOF-BAT
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PI.2 Lowering the zinc content of scrap
A high zinc content in the blast furnace has an
adverse affect on correct operation. This zinc
mainly originates from the scrap charged into
the basic oxygen furnace. The release of Zn can
fluctuate strongly from one cast to another. The
same problem, but to a lesser extent, applies to
lead (Pb) or cadmium (Cd).
BOF-BAT
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PI.3 On-line sampling and steel analysis
Oxygen steelmaking is a batch process. In order
to monitor progress samples are taken from the
steel bath for analysis. It used to be necessary
to interrupt oxygen blowing and tilt the BOF in
order to take the sample. This was a time
consuming process and it increased emissions
from the BOF. In a modern plant samples are
taken on-line during oxygen blowing by means
of a sub-lance.
BOF-BAT
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EP.1 Primary de-dusting
During
oxygen
blowing,
BOF
gas
is
generated.This gas is loaded with a large
amount of particulate matter. The BOF gas is
recovered for use as a fuel. Primary de-dusting
is usually performed by venturi-type scrubbers
(approximately 90% of the plants) or dry
electrostatic precipitators. Prior to the venturi or
the ESP, coarse particulates are usually removed
by means of a deflector
BOF-BAT
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EP.2 Particulate matter abatement
from pig iron pre-treatment
BOF-BAT
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EP.3 De-dusting of secondary off-gases
Secondary
operations:
off-gases
result
from
following
Reladling and deslagging of hot metal.
BOF charging.
Tapping of liquid steel and slag from BOF (converters).
Secondary metallurgy and tapping operations.
Handling of additives.
Continuous casting.
BOF-BAT
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EP.4 Dust hot-briquetting and recycling
with recovery of high Zn concentrated
pellets for
external
reuse.
BOF-BAT
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EP.5 Treatment of wastewater from wet
de-dusting
In most oxygen steelmaking plants, scrubbers
are used to reduce emissions to air from the
primary gas flow. This potentially transfers
pollution from air to water so the wastewater
generated is usually recycled and treated before
discharge. The water from the scrubbers mainly
contains suspended solids; Zinc and lead being
the main heavy metals present.
BOF-BAT
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EP.6 Treatment of wastewater from
continuous casting.
ELECTRIC STEELMAKING AND
CASTING
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Electric arc furnaces (EAF) play an important
and increasing role in modern steel works
concepts.
Today the percentage of electric arc furnace
steel of the overall steel production in the EU are
35,3%.
In Italy and Spain the production of EAF steel is
higher than steel production via BOF.
EAF-BAT
Process-integrated measures:
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PI.1 EAF process optimisation.
PI.2 Scrap preheating.
PI.3 Closed loop water cooling system.
End-of-pipe techniques:
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EP.1 Advanced emission collection systems.
EP.2 Efficient post-combustion in combination with
advanced off gas treatment.
EP.3 Injection of lignite coke powder for off gas
treatment.
EP.4 Recycling of EAF slags.
EP.5 Recycling of EAF dusts.
EAF-BAT
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PI.1 EAF process optimisation
EAF-BAT
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PI.2 Scrap preheating
EAF-BAT
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PI. 3 Closed loop water cooling
system
The most relevant use of water considered here
is the water used for the cooling of the elements
of the furnace. Additionally, some water may be
used for the cooling of waste gas or in the
secondary metallurgy section.
EAF-BAT
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EP.1 Advanced emission collection systems
The primary and secondary emissions to air are of high
relevance. The available abatement techniques should
be fed with the raw emissions as complete as possible.
Thus the collection of the emissions is important. The
combination of 4th hole (in case of three electrodes)
respectively of 2nd hole (in case of one electrode) direct
extraction with hood systems (or furnace enclosure) or
total building evacuation are the most favorite systems.
EAF-BAT
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EP.2 Efficient post-combustion in
combination with advanced off gas
treatment
Post combustion in the furnace is developed to
use a maximum of chemical energy of the CO in
the furnace and to improve the energy balance,
but CO and H2 are never completely oxidised in
the furnace; for this reason, it needs post
combustion.
EAF-BAT
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EP.3 Injection of lignite coke powder
for off gas treatment
In order to reduce organic micropollutants in the
total off gas (primary and secondary emissions),
especially PCDD/F lignite coke powder can be
dosed to the duct before the bag filters.
EAF-BAT
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EP.4 EAF slag recycling
EAF slag can be regarded as an artificial rock,
similar to natural rock, consisting of iron-oxides
(FeO), lime (CaO), silicium-oxide (SiO2), and
other oxides (MgO, Al2O3, MnO) EAF slags are
characterised by high strength, good weathering
resistance, and also high resistance against
polishing. They also have properties, that make
them suitable for use in hydraulic engineering.
EAF-BAT
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EP.5 EAF dust recyling
There are two method of dust recycling:
•
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Recycling of precipitated dusts
Zinc recovery and removal of heavy metals
EMERGING TECHNIQUES AND
FUTURE DEVELOPMENTS
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Scrap sorting.
The emissions of organochlorine compounds
can be reduced by minimising the input with
the scrap.
This compounds are contained in several
technical devices like washing machines, hair
driers, cooker hoods, fluorescent lamps…
EMERGING TECHNIQUES AND
FUTURE DEVELOPMENTS
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New furnace concepts.
In recent years new furnace types have
been introduced that might be realised at
industrial scale.
COMELT EAF
COMELT EAF
ADVANTAGES
 Integrated shaft scrap preheating.
 Complete off gas collection.
 A lowered sound level.
 High productivity.
 Reduction of total energy consuption.
 Reduction of electrode consuption.
 Reduction in maintenance costs.