Commission Implementing Decision (EU) 2022/2110 of 11 October 2022 establishing the best available techniques (BAT) conclusions, under Directive 2010/75/EU of the European Parliament and of the Council on industrial emissions, for the ferrous metals processing industry (notified under document C(2022) 7054) (Text with EEA relevance)

a.

Energy efficiency plan and energy audits

An energy efficiency plan is part of the EMS (see BAT 1) and entails defining and monitoring the specific energy consumption of the activity/processes (see BAT 6), setting key performance indicators on an annual basis (e.g. MJ/t of product) and planning the periodic improvement targets and related actions.

Energy audits are carried out at least once a year to ensure that the objectives of the energy management plan are met.

The energy efficiency plan and the energy audits may be integrated in the overall energy efficiency plan of a larger installation (e.g. for iron and steel production).

The level of detail of the energy efficiency plan, of the energy audits and of the energy balance record will generally be related to the nature, scale and complexity of the plant and the types of energy sources used.

b.

Energy balance record

Drawing up on an annual basis of an energy balance record which provides a breakdown of the energy consumption and generation (including energy export) by the type of energy source (e.g. electricity, natural gas, iron and steel process gases, renewable energy, imported heat and/or cooling). This includes:

• defining the energy boundary of the processes;

• information on energy consumption in terms of delivered energy;

• information on energy exported from the plant;

• energy flow information (e.g. Sankey diagrams or energy balances) showing how the energy is used throughout the processes.

Design and operation

a.

Optimum furnace design for feedstock heating

This includes techniques such as:

• optimisation of key furnace characteristics (e.g. number and type of burners, air tightness and furnace insulation using suitable refractory materials);

• minimisation of heat losses from furnace door openings, e.g. by using several liftable segments instead of one in continuous reheating furnaces;

• minimisation of the number of feedstock-supporting structures inside the furnace (e.g. beams, skids) and use of suitable insulation to reduce the heat losses from water cooling of the supporting structures in continuous reheating furnaces.

Only applicable to new plants and major plant upgrades.

b.

Optimum galvanising kettle design

This includes techniques such as:

• uniform heating of the galvanising kettle walls (e.g. by using high-velocity burners or radiant design);

• minimisation of heat losses from the furnace using insulated outer/inner walls (e.g. ceramic lining).

Only applicable to new plants and major plant upgrades.

c.

Optimum galvanising kettle operation

This includes techniques such as:

minimisation of heat losses from the galvanising kettle in hot dip coating of wires or in batch galvanising, e.g. by using insulated covers during idle periods.

Generally applicable.

d.

Combustion optimisation

See Section 1.7.1.

Generally applicable.

e.

Furnace automation and control

See Section 1.7.1.

Generally applicable.

f.

Process gas management system

See Section 1.7.1.

The calorific value of iron and steel process gases and/or CO-rich gas from ferrochromium production is used.

Only applicable when iron and steel process gases and/or CO-rich gas from ferrochromium production are available.

g.

Batch annealing with 100 % hydrogen

Batch annealing is carried out in furnaces using 100 % hydrogen as a protective gas with increased thermal conductivity.

Only applicable to new plants and major plant upgrades.

h.

Oxy-fuel combustion

See Section 1.7.1.

Applicability may be restricted for furnaces processing high-alloy steel.

Applicability to existing plants may be restricted by furnace design and the need for a minimum waste gas flow.

Not applicable to furnaces equipped with radiant tube burners.

i.

Flameless combustion

See Section 1.7.1.

Applicability to existing plants may be limited by furnace design (i.e. furnace volume, space for burners, distance between burners) and the need for a change of the refractory lining.

Applicability may be limited for processes where close control of temperature or temperature profile is required (e.g. recrystallisation).

Not applicable to furnaces operating at a temperature lower than the auto-ignition temperature required for flameless combustion or to furnaces equipped with radiant tube burners.

j.

Pulse-fired burner

The heat input to the furnace is controlled by the firing duration of the burners or by the sequential start of the individual burners instead of adjusting combustion air and fuel flows.

Only applicable to new plants and major plant upgrades.

Heat recovery from flue-gases

k.

Feedstock preheating

Feedstock is preheated by blowing hot flue-gases directly onto it.

Only applicable to continuous reheating furnaces. Not applicable to furnaces equipped with radiant tube burners.

l.

Drying of workpieces

In batch galvanising, the heat from flue-gases is used to dry the workpieces.

Generally applicable.

m.

Preheating of combustion air

See Section 1.7.1.

This may be achieved for example by using regenerative or recuperative burners. A balance has to be achieved between maximising heat recovery from the flue-gas and minimising NOX emissions.

Applicability to existing plants may be restricted by a lack of space for the installation of regenerative burners.

n.

Waste heat recovery boiler

The heat from hot flue-gases is used to generate steam or hot water that is used in other processes (e.g. for heating pickling and fluxing baths), for district heating or for generating electricity.

Applicability to existing plants may be restricted by a lack of space and/or a suitable steam or hot water demand.

Feedstock reheating

Hot rolled coils (strips)

MJ/t

1 200–1 500 ⁽¹⁾

Heavy plates

MJ/t

1 400–2 000 ⁽²⁾

Bars, rods

MJ/t

600–1 900 ⁽²⁾

Beams, billets, rails, tubes

MJ/t

1 400–2 200

Feedstock intermediate heating

Bars, rods, tubes

MJ/t

100–900

Feedstock post-heating

Heavy plates

MJ/t

1 000–2 000

Bars, rods

MJ/t

1 400–3 000 ⁽³⁾

Annealing after cold rolling (batch and continuous)

MJ/t

600–1 200 ^{(1) (2)}

Feedstock heating before hot dip coating

MJ/t

700–1 100 ⁽¹⁾

Batch galvanising

kWh/t

300–800 ^{(1) (2) (3)}

Avoiding or reducing the need for degreasing

a.

Use of feedstock with low oil and grease contamination

The use of feedstock with low oil and grease contamination prolongs the lifetime of the degreasing solution.

Applicability may be limited if the feedstock quality cannot be influenced.

b.

Use of a direct-flame furnace in the case of hot dip coating of sheets

The oil on the surface of the sheet is burnt in a direct-flame furnace. Degreasing before the furnace may be needed for some high-quality products or in the case of sheets with high residual oil levels.

Applicability may be limited if a very high level of surface cleanliness and zinc adhesion is required.

Degreasing optimisation

c.

General techniques for increased degreasing efficiency

These include techniques such as:

• monitoring and optimising the temperature and the concentration of degreasing agents in the degreasing solution;

• enhancing the effect of the degreasing solution on the feedstock (e.g. by moving the feedstock, agitating the degreasing solution or by using ultrasound to create cavitation of the solution on the surface to be degreased).

Generally applicable.

d.

Minimisation of drag-out of degreasing solution

This includes techniques such as:

• using squeeze rolls, e.g. in the case of continuous degreasing of strip;

• allowing for a sufficient dripping time, e.g. by slow lifting of workpieces.

Generally applicable.

e.

Reverse cascade degreasing

Degreasing is carried out in two or more baths in series where the feedstock is moved from the most contaminated degreasing bath to the cleanest.

Generally applicable.

Extending the lifetime of the degreasing baths

f.

Cleaning and reuse of the degreasing solution

Magnetic separation, oil separation (e.g. skimmers, discharge launders, weirs), micro- or ultrafiltration or biological treatment is used to clean the degreasing solution for reuse.

Generally applicable.

a.

Acid heating with heat exchangers

Corrosion-resistant heat exchangers are immersed in the pickling acid for indirect heating, e.g. with steam.

b.

Acid heating by submerged combustion

Combustion gases pass through the pickling acid, releasing the energy via direct heat transfer.

Avoiding or reducing the need for pickling

a.

Minimisation of steel corrosion

This includes techniques such as:

• cooling the hot rolled steel as fast as possible depending on product specifications;

• storing the feedstock in roofed areas;

• limiting the storage duration of the feedstock.

Generally applicable.

b.

Mechanical (pre)descaling

This includes techniques such as:

• shot blasting;

• bending;

• sanding;

• brushing;

• stretching and levelling.

Applicability to existing plants may be restricted by a lack of space.

Applicability may be restricted due to product specifications.

c.

Electrolytic prepickling of high-alloy steel

Use of an aqueous solution of sodium sulphate (Na2SO4) to pretreat high-alloy steel before pickling with mixed acid, in order to speed up and improve the removal of the surface oxide scale. The waste water containing hexavalent chromium is treated using technique BAT 31 (f).

Only applicable to cold rolling.

Applicability to existing plants may be restricted by a lack of space.

Pickling optimisation

d.

Rinsing after alkaline degreasing

Carry-over of alkaline degreasing solution to the pickling bath is reduced by rinsing feedstock after degreasing.

Applicability to existing plants may be restricted by a lack of space.

e.

General techniques for increased pickling efficiency

These include techniques such as:

• optimisation of the pickling temperature for maximising pickling rates while minimising emissions of acids;

• optimisation of the pickling bath composition (e.g. acid and iron concentrations);

• optimisation of the pickling time to avoid over-pickling;

• avoiding drastic changes in the pickling bath composition by frequently replenishing it with fresh acid.

Generally applicable.

f.

Cleaning of the pickling bath and reuse of free acid

A cleaning circuit, e.g. with filtration, is used to remove particles from the pickling acid followed by reclamation of the free acid via ion exchange, e.g. using resins.

Not applicable if cascade pickling (or similar) is used, as this results in very low levels of free acid.

g.

Reverse cascade pickling

Pickling is carried out in two or more baths in series where the feedstock is moved from the bath with the lowest acid concentration to the one with the highest.

Applicability to existing plants may be restricted by a lack of space.

h.

Minimisation of drag-out of pickling acid

This includes techniques such as:

• using squeeze rolls, e.g. in the case of continuous pickling of strip;

• allowing for a sufficient dripping time, e.g. by slow lifting of workpieces;

• using vibrating wire rod coils.

Generally applicable.

i.

Turbulence pickling

This includes techniques such as:

• injection of the pickling acid at high pressure via nozzles;

• agitation of the pickling acid using an immersed turbine.

Applicability to existing plants may be restricted by a lack of space.

j.

Use of pickling inhibitors

Pickling inhibitors are added to the pickling acid to protect metallically clean parts of the feedstock from over-pickling.

Not applicable to high- alloy steel.

Applicability may be restricted due to product specifications.

k.

Activated pickling in hydrochloric acid pickling

Pickling is carried out with a low hydrochloric acid concentration (i.e. around 4–6 wt-%) and a high iron concentration (i.e. around 120–180 g/l) at temperatures of 20–25 °C.

Generally applicable.

Hydrochloric acid, 28 wt-%

kg/t

13–30 ⁽¹⁾

a.

Rinsing of workpieces after pickling

In batch galvanising, carry-over of iron to the fluxing solution is reduced by rinsing workpieces after pickling.

Applicability to existing plants may be restricted by a lack of space.

b.

Optimised fluxing operation

The chemical composition of the fluxing solution is monitored and adjusted frequently.

The amount of fluxing agent used is reduced to the minimum level required to achieve the product specifications.

Generally applicable.

c.

Minimisation of drag-out of fluxing solution

The drag-out of the fluxing solution is minimised by allowing enough time for it to drip off.

Generally applicable.

d.

Iron removal and reuse of the fluxing solution

Iron is removed from the fluxing solution by one of the following techniques:

• electrolytic oxidation;

• oxidation using air or H2O2;

• ion exchange.

After iron removal, the fluxing solution is reused.

Applicability to existing batch galvanising plants may be restricted by a lack of space.

e.

Recovery of salts from the spent fluxing solution for production of fluxing agents

Spent fluxing solution is used to recover the salts contained therein to produce fluxing agents. This may take place on site or off site.

Applicability may be restricted depending on the availability of a market.

a.

Reduction of the generation of bottom dross

The generation of bottom dross is reduced, e.g. by sufficient rinsing after pickling, removing the iron from the fluxing solution (see BAT 15 (d)), using fluxing agents with a mild pickling effect and avoiding local overheating in the galvanising kettle.

b.

Prevention, collection and reuse of zinc splashes in batch galvanising

The generation of zinc splashes from the galvanising kettle is reduced by minimising carry-over of the fluxing solution (see BAT 26 (b)). Zinc splashes out of the kettle are collected and reused. The area surrounding the kettle is kept clean to reduce contamination of the splashes.

c.

Reduction of the generation of zinc ash

The formation of zinc ash, i.e. zinc oxidation on the bath surface, is reduced for example by:

• sufficient drying of the workpieces/wires before dipping;

• avoiding unnecessary disturbances of the bath during production, including during skimming;

• in continuous hot dipping of wires, reducing the bath surface that is in contact with air using a floating refractory cover.

Extending the lifetime of the treatment baths

a.

Cleaning and reuse of the phosphating or passivation solution

A cleaning circuit, for example with filtration, is used to clean the phosphating or passivation solution for reuse.

Treatment optimisation

b.

Use of roll coaters for strips

Roll coaters are used to apply a passivation or a phosphate-containing layer on the surface of strips. This allows better control of the layer thickness and thus the reduction of the consumption of chemicals.

c.

Minimisation of drag-out of chemical solution

The drag-out of chemical solution is minimised, e.g. by passing the strips through squeeze rolls or by allowing for sufficient dripping time for workpieces.

a.

Water management plan and water audits

A water management plan and water audits are part of the EMS (see BAT 1) and include:

• flow diagrams and a water mass balance of the plant;

• establishment of water efficiency objectives;

• implementation of water optimisation techniques (e.g. control of water usage, water recycling, detection and repair of leaks).

Water audits are carried out at least once every year to ensure that the objectives of the water management plan are met.

The water management plan and the water audits may be integrated in the overall water management plan of a larger installation (e.g. for iron and steel production).

The level of detail of the water management plan and water audits will generally be related to the nature, scale and complexity of the plant.

b.

Segregation of water streams

Each water stream (e.g. surface run-off water, process water, alkaline or acidic waste water, spent degreasing solution) is collected separately, based on the pollutant content and on the required treatment techniques. Waste water streams that can be recycled without treatment are segregated from waste water streams that require treatment.

Applicability to existing plants may be limited by the layout of the water collection system.

c.

Minimisation of hydrocarbon contamination of process water

The contamination of process water by oil and lubricant losses is minimised by using techniques such as:

• oil-tight bearings and bearing seals for working rolls;

• leakage indicators;

• regular inspections and preventive maintenance of pump seals, piping and working rolls.

Generally applicable.

d.

Reuse and/or recycling of water

Water streams (e.g. process water, effluents from wet scrubbing or quench baths) are reused and/or recycled in closed or semi-closed circuits, if necessary after treatment (see BAT 30 and BAT 31).

The degree of water reuse and/or recycling is limited by the water balance of the plant, the content of impurities and/or the characteristics of the water streams.

e.

Reverse cascade rinsing

Rinsing is carried out in two or more baths in series where the feedstock is moved from the most contaminated rinsing bath to the cleanest.

Applicability to existing plants may be restricted by a lack of space.

f.

Recycling or reuse of rinsing water

Water from rinsing after pickling or degreasing is recycled/reused, if necessary after treatment, to the preceding process baths as make-up water, rinsing water or, if the acid concentration is sufficiently high, for acid recovery.

Generally applicable.

g.

Treatment and reuse of oil- and scale-bearing process water in hot rolling

Oil- and scale-bearing waste water from hot rolling mills is treated separately using different cleaning steps including scale pits, settling tanks, cyclones and filtration to separate oil and scale. A large proportion of the treated water is reused in the process.

Generally applicable.

h.

Water spray descaling triggered by sensors in hot rolling

Sensors and automation are used to track the position of the feedstock and adjust the volume of the descaling water passing through the water sprays.

Generally applicable.

Hot rolling

m³/t

0,5–5

Cold rolling

m³/t

0,5–10

Wire drawing

m³/t

0,5–5

Hot dip coating

m³/t

0,5–5

a.

Residues management plan

A residues management plan is part of the EMS (see BAT 1) and is a set of measures aiming to (1) minimise the generation of residues; (2) optimise the reuse, recycling and/or recovery of residues; and (3) ensure the proper disposal of waste.

The residues management plan may be integrated in the overall residues management plan of a larger installation (e.g. for iron and steel production).

The level of detail and the degree of formalisation of the residues management plan will generally be related to the nature, scale and complexity of the installation.

b.

Pretreatment of oily mill scale for further use

This includes techniques such as:

• briquetting or pelletising,

• reducing the oil content of oily mill scale, e.g. by thermal treatment, washing, flotation.

Generally applicable.

c.

Use of mill scale

Mill scale is collected and used on site or off site, e.g. in iron and steel production or in cement production.

Generally applicable.

d.

Use of metallic scrap

Metallic scrap from mechanical processes (e.g. from trimming and finishing) is used in iron and steel production. This may take place on site or off site.

Generally applicable.

e.

Recycling of metal and metal oxides from dry waste gas cleaning

The coarse fraction of metal and metal oxides originating from dry cleaning (e.g. fabric filters) of waste gases from mechanical processes (e.g. scarfing or grinding) is selectively isolated using mechanical techniques (e.g. sieves) or magnetic techniques and recycled, e.g. to iron and steel production. This may take place on site or off site.

Generally applicable.

f.

Use of oily sludge

Residual oily sludge, e.g. from degreasing, is dewatered to recover the oil contained therein for material or energy recovery. If the water content is low, the sludge can be directly used. This may take place on site or off site.

Generally applicable.

g.

Thermal treatment of hydroxide sludge from the recovery of mixed acid

Sludge generated from the recovery of mixed acid is thermally treated in order to produce a material rich in calcium fluoride that can be used in argon oxygen decarburisation converters.

Applicability may be restricted by a lack of space.

h.

Recovery and reuse of shot blast media

Where mechanical descaling is carried out by shot blasting, the shot blast media are separated from the scale and reused.

Generally applicable.

a.

Recycling of fabric filter dust

Dust from fabric filters containing ammonium chloride and zinc chloride is collected and reused, e.g. to produce fluxing agents. This may take place on site or off site.

Only applicable in hot dipping after fluxing.

Applicability may be restricted depending on the availability of a market.

b.

Recycling of zinc ash and top dross

Metallic zinc is recovered from zinc ash and top dross by melting in recovery furnaces. The remaining zinc-containing residue is used, e.g. for zinc oxide production. This may take place on site or off site.

Generally applicable.

c.

Recycling of bottom dross

Bottom dross is used, e.g. in the non-ferrous metals industries to produce zinc. This may take place on site or off site.

Generally applicable.

a.

Cleaning and reuse of grinding emulsion

Grinding emulsions are treated using lamellar or magnetic separators or using a sedimentation/clarification process in order to remove the grinding sludge and reuse the grinding emulsion.

b.

Treatment of grinding sludge

Treatment of grinding sludge by magnetic separation for recovery of metal particles and recycling of metals, e.g. to iron and steel production.

c.

Recycling of worn working rolls

Worn working rolls which are unsuitable for texturing are recycled to iron and steel production or returned to the manufacturer for refabrication.

a.

Near-net-shape casting for thin slabs and beam blanks followed by rolling

See Section 1.7.1.

Only applicable to plants adjacent to continuous casting and within the limitations of the plant layout and product specifications.

b.

Hot/direct charging

Continuous-cast steel products are directly charged hot into the reheating furnaces.

Only applicable to plants adjacent to continuous casting and within the limitations of the plant layout and product specifications.

c.

Heat recovery from skids cooling

Steam produced when cooling the skids supporting the feedstock in the reheating furnaces is extracted and used in other processes of the plant.

Applicability to existing plants may be restricted by a lack of space and/or of a suitable steam demand.

d.

Heat conservation during transfer of feedstock

Insulated covers are used between the continuous caster and the reheating furnace, and between the roughing mill and the finishing mill.

Generally applicable within the limitations of the plant layout.

e.

Coil boxes

See Section 1.7.1.

Generally applicable.

f.

Coil recovery furnaces

Coil recovery furnaces are used as an addition to coil boxes to restore the rolling temperature of coils and return them to a normal rolling sequence in the event of rolling mill interruptions.

Generally applicable.

g.

Sizing press

See BAT 39 (a).

A sizing press is used to increase the energy efficiency in feedstock heating because it enables the hot charging rate to be increased.

Only applicable to new plants and major plant upgrades for hot strip mills.

a.

Sizing press

The use of a sizing press before the roughing mill enables the hot charging rate to be significantly increased and results in a more uniform width reduction both at the edges and centre of the product. The shape of the final slab is nearly rectangular, reducing significantly the number of rolling passes necessary to reach product specifications.

Only applicable to hot strip mills.

Only applicable to new plants and major plant upgrades.

b.

Computer-aided rolling optimisation

The thickness reduction is controlled using a computer to minimise the number of rolling passes.

Generally applicable.

c.

Reduction of the rolling friction

See Section 1.7.1.

Only applicable to hot strip mills.

d.

Coil boxes

See Section 1.7.1.

Generally applicable.

e.

Three-roll stand

A three-roll stand increases the section reduction per pass, resulting in an overall reduction of the number of rolling passes required for producing wire rods and bars.

Generally applicable.

f.

Near-net-shape casting for thin slabs and beam blanks followed by rolling

See Section 1.7.1.

Only applicable to plants adjacent to continuous casting and within the limitations of the plant layout and product specifications.

Hot rolled coils (strips), heavy plates

MJ/t

100–400

Bars, rods

MJ/t

100–500⁽¹⁾

Beams, billets, rails, tubes

MJ/t

100–300

a.

Computer-aided quality control

The quality of slabs is controlled by a computer which allows the adjustment of the casting conditions to minimise surface defects and enables manual scarfing of the damaged area(s) only rather than scarfing of the entire slab.

Only applicable to plants with continuous casting.

b.

Slab slitting

The slabs (often cast in multiple widths) are slit before hot rolling by means of slitting devices, slit rolling or torches either manually operated or mounted on a machine.

May not be applicable for slabs produced from ingots.

c.

Edging or trimming of wedge-type slabs

Wedge-type slabs are rolled under special settings where the wedge is eliminated by edging (e.g. using automatic width control or a sizing press) or by trimming.

May not be applicable for slabs produced from ingots. Only applicable to new plants and major plant upgrades.

a.

Crop optimisation

The cropping of the feedstock after roughing is controlled by a shape measurement system (e.g. camera) in order to minimise the amount of metal cut off.

b.

Control of the feedstock shape during rolling

Any deformations of the feedstock during rolling are monitored and controlled in order to ensure that the rolled steel has as rectangular a shape as possible and to minimise the need for trimming.

Collection of emissions

a.

Enclosed scarfing and grinding combined with air extraction

Scarfing (other than manual scarfing) and grinding operations are carried out completely enclosed (e.g. under closed hoods) and air is extracted.

Generally applicable.

b.

Air extraction as close as possible to the emission source

Emissions from slitting, descaling, roughing, rolling, finishing, levelling and welding are collected, for example using hood or lip extraction. For roughing and rolling, in the case of low levels of dust generation, e.g. below 100 g/h, water sprays can be used instead (see BAT 43).

May not be applicable for welding in the case of low levels of dust generation, e.g. below 50 g/h.

Waste gas treatment

c.

Electrostatic precipitator

See Section 1.7.2.

Generally applicable.

d.

Fabric filter

See Section 1.7.2.

May not be applicable in the case of waste gases with a high moisture content.

e.

Wet scrubbing

See Section 1.7.2.

Generally applicable.

Dust

mg/Nm³

< 2–5 ⁽¹⁾

Ni

0,01–0,1 ⁽²⁾

Pb

0,01–0,035 ⁽²⁾

a.

Continuous rolling for low-alloy and alloy steel

Continuous rolling (e.g. using tandem mills) is employed instead of conventional discontinuous rolling (e.g. using reversing mills), allowing for stable feed and less frequent start-ups and shutdowns.

Only applicable to new plants and major plant upgrades.

Applicability may be restricted due to product specifications.

b.

Reduction of the rolling friction

See Section 1.7.1.

Generally applicable.

c.

Computer-aided rolling optimisation

The thickness reduction is controlled using a computer to minimise the number of rolling passes.

Generally applicable.

Cold rolled coils

MJ/t

100–300 ⁽¹⁾

Packaging steel

MJ/t

250–400

a.

Monitoring and adjustment of the rolling emulsion quality

Important characteristics of the rolling emulsion (e.g. oil concentration, pH, emulsion droplet size, saponification index, acid concentration, concentration of iron fines, concentration of bacteria) are monitored regularly or continuously to detect anomalies in the emulsion quality and take corrective action, if needed.

Generally applicable.

b.

Prevention of contamination of the rolling emulsion

Contamination of the rolling emulsion is prevented by techniques such as:

• regular control and preventive maintenance of the hydraulic system and the emulsion circulation system;

• reducing bacterial growths in the rolling emulsion system by regular cleaning or operating at low temperatures.

Generally applicable.

c.

Cleaning and reuse of the rolling emulsion

Particulate matter (e.g. dust, steel slivers and scale) contaminating the rolling emulsion is removed in a cleaning circuit (usually based on sedimentation combined with filtration and/or magnetic separation) in order to maintain the emulsion quality and the treated rolling emulsion is reused. The degree of reuse is limited by the content of impurities in the emulsion.

Applicability may be restricted due to product specifications.

d.

Optimal choice of rolling oil and emulsion system

Rolling oil and emulsion systems are carefully selected to provide the optimum performance for the given process and product. Relevant characteristics to be considered are, for example:

• good lubrication;

• potential for easy separation of contaminants;

• stability of the emulsion and dispersion of the oil in the emulsion;

• non-degradation of the oil over a long idling time.

Generally applicable.

e.

Minimisation of oil/rolling emulsion consumption

The consumption of oil/rolling emulsion is minimised by using techniques such as:

• limiting the oil concentration to the minimum required for lubrication;

• limiting carry-over of emulsion from the previous stands (e.g. by separating the emulsion cellars, shielding of the mill stands);

• using air knives combined with edge suction to reduce the residual emulsion and oil on the strip.

Generally applicable.

Collection of emissions

a.

Air extraction as close as possible to the emission source

Emissions from decoiling, mechanical predescaling, levelling and welding are collected, for example using hood or lip extraction.

May not be applicable for welding in the case of low levels of dust generation, e.g. below 50 g/h.

Waste gas treatment

b.

Fabric filter

See Section 1.7.2.

Generally applicable.

Dust

mg/Nm³

< 2–5

Ni

0,01–0,1 ⁽¹⁾

Pb

≤ 0,003 ⁽¹⁾

a.

Dry tempering

No water or lubricants are used for tempering.

Not applicable to tinplate packaging products and other products with high elongation requirements.

b.

Low-volume lubrication in wet tempering

Low-volume lubrication systems are employed to supply precisely the amount of lubricants needed for reducing the friction between the working rolls and the feedstock.

Applicability may be restricted due to product specifications in the case of stainless steel.

Collection of emissions

a.

Air extraction as close as possible to the emission source

Emissions from rolling, wet tempering and finishing are collected, for example using hood or lip extraction.

Waste gas treatment

b.

Demister

See Section 1.7.2.

c.

Oil mist separator

Separators containing baffle packing, impingement plates or mesh pads are used to separate the oil from the extracted air.

TVOC

mg/Nm³

< 3–8

Reduction of generation of emissions

a.

Minimisation of carry-over of lead

Techniques include the use of anthracite gravel to scrape off lead and the coupling of the lead bath with in-line pickling.

b.

Floating protective layer or tank cover

See BAT 49.

Floating protective layers and tank covers also reduce emissions to air.

Collection of emissions

c.

Air extraction as close as possible to the emission source

Emissions from the lead bath are collected, for example using hood or lip extraction.

Waste gas treatment

d.

Fabric filter

See Section 1.7.2.

Dust

mg/Nm³

< 2–5

Pb

mg/Nm³

≤ 0,5

Collection of emissions

a.

Enclosed drawing machine combined with air extraction

The entire drawing machine is enclosed in order to avoid dispersion of dust and air is extracted.

Applicability to existing plants may be restricted by the plant layout.

b.

Air extraction as close as possible to the emission source

Emissions from the drawing machine are collected, for example using hood or lip extraction.

Generally applicable.

Waste gas treatment

c.

Fabric filter

See Section 1.7.2.

Generally applicable.

Dust

mg/Nm³

< 2–5

Collection of emissions

a.

Air extraction as close as possible to the emission source

Emissions from oil quench baths are collected, for example using lateral hood or lip extraction.

Waste gas treatment

b.

Demister

See Section 1.7.2.

a.

Air knives for coating thickness control

After leaving the molten zinc bath, air jets stretching over the width of the strip blow the surplus coating metal off the strip surface back into the galvanising kettle.

b.

Stabilisation of the strip

The efficiency of the excess coating removal by air knives is improved by limiting the oscillations of the strip, e.g. by increasing strip tension, using low-vibration pot bearings, using electromagnetic stabilisers.

a.

Air or nitrogen wiping

After leaving the molten zinc bath, circular air or gas jets around the wire blow the surplus coating metal off the wire surface back into the galvanising kettle.

b.

Mechanical wiping

After leaving the molten zinc bath, the wire is passed through wiping equipment/material (e.g. pads, nozzles, rings, charcoal granulate) which takes the surplus coating metal off the wire surface back into the galvanising kettle.

a.

Optimised dipping time

The dipping time is limited to the duration required to achieve the coating thickness specifications.

b.

Slow withdrawal of workpieces from the bath

By withdrawing the galvanised workpieces slowly from the galvanising kettle, the drain-off is improved and zinc splashes are reduced.

Collection of emissions

a.

Enclosed pretreatment section with extraction

The entire pretreatment section (e.g. degreasing, pickling, fluxing) is encapsulated and the fumes are extracted from the enclosure.

Only applicable to new plants and major plant upgrades

b.

Extraction by lateral hood or lip extraction

Acid fumes from the pickling tanks are extracted using lateral hoods or lip extraction at the edge of the pickling tanks. This may also include emissions from degreasing tanks.

Applicability in existing plants may be restricted by a lack of space.

Waste gas treatment

c.

Wet scrubbing followed by a demister

See Section 1.7.2.

Generally applicable

Reduction of generation of emissions

d.

Restricted operating range for hydrochloric acid open pickling baths

Hydrochloric acid baths are strictly operated within the temperature and HCl concentration range determined by the following conditions:

1. 4 °C < T < (80 – 4 w) °C;

2. 2 wt-% < w < (20 – T/4) wt-%,

where T is the pickling acid temperature expressed in °C and w the HCl concentration expressed in wt-%.

The bath temperature is measured at least once every day. The HCl concentration in the bath is measured every time fresh acid is replenished and in any case at least once every week. To limit evaporation, movement of air across the bath surfaces (e.g. due to ventilation) is minimised.

Generally applicable

HCl

mg/Nm³

< 2–6

Coil boxes

Insulated boxes are installed between the roughing mill and the finishing mill to minimise temperature losses from feedstock during coiling/uncoiling processes and allow for lower rolling forces in hot strip mills.

Combustion optimisation

Measures taken to maximise the efficiency of energy conversion in the furnace while minimising emissions (in particular of CO). This is achieved by a combination of techniques including good design of the furnace, optimisation of the temperature (e.g. efficient mixing of the fuel and combustion air) and residence time in the combustion zone, and use of furnace automation and control.

Flameless combustion

Flameless combustion is achieved by injecting fuel and combustion air separately into the combustion chamber of the furnace at high velocity to suppress flame formation and reduce the formation of thermal NOX while creating a more uniform heat distribution throughout the chamber. Flameless combustion can be used in combination with oxy-fuel combustion.

Furnace automation and control

The heating process is optimised by using a computer system controlling in real time key parameters such as furnace and feedstock temperature, the air to fuel ratio and the furnace pressure.

Near-net-shape casting for thin slabs and beam blanks followed by rolling

Thin slabs and beam blanks are produced by combining casting and rolling in one process step. The need to reheat the feedstock before rolling and the number of rolling passes are reduced.

Optimisation of the SNCR/SCR design and operation

Optimisation of the reagent to NOX ratio over the cross-section of the furnace or duct, of the size of the reagent drops and of the temperature window in which the reagent is injected.

Oxy-fuel combustion

Combustion air is replaced fully or partially with pure oxygen. Oxy-fuel combustion can be used in combination with flameless combustion.

Preheating of combustion air

Reuse of part of the heat recovered from the combustion flue-gas to preheat the air used in combustion.

Process gas management system

A system that enables iron and steel process gases to be directed to the feedstock heating furnaces, depending on their availability.

Recuperative burner

Recuperative burners employ different types of recuperators (e.g. heat exchangers with radiation, convection, compact or radiant tube designs) to directly recover heat from the flue-gases, which are then used to preheat the combustion air.

Reduction of the rolling friction

Rolling oils are carefully selected. Pure oil and/or emulsion systems are used to reduce the friction between the working rolls and the feedstock and to ensure minimal oil consumption. In HR, this is usually carried out in the first stands of the finishing mill.

Regenerative burner

Regenerative burners consist of two burners which are operated alternately and which contain beds of refractory or ceramic materials. While one burner is in operation, the heat of the flue-gas is absorbed by the refractory or ceramic materials of the other burner and then used to preheat the combustion air.

Waste heat recovery boiler

Heat from hot flue-gases is used to generate steam using a waste heat recovery boiler. The generated steam is used in other processes of the plant, for supplying a steam network or for generating electricity in a power plant.

Combustion optimisation

See Section 1.7.1.

Demister

Demisters are filter devices that remove entrained liquid droplets from a gas stream. They consist of a woven structure of metal or plastic wires, with a high specific surface area. Through their momentum, small droplets present in the gas stream impinge against the wires and coalesce into bigger drops.

Electrostatic precipitator

Electrostatic precipitators (ESPs) operate such that particles are charged and separated under the influence of an electrical field. Electrostatic precipitators are capable of operating under a wide range of conditions. Abatement efficiency may depend on the number of fields, residence time (size), and upstream particle removal devices. They generally include between two and five fields. Electrostatic precipitators can be of the dry or of the wet type depending on the technique used to collect the dust from the electrodes. Wet ESPs are typically used at the polishing stage to remove residual dust and droplets after wet scrubbing.

Fabric filter

Fabric filters, often referred to as bag filters, are constructed from porous woven or felted fabric through which gases are passed to remove particles. The use of a fabric filter requires the selection of a fabric suitable for the characteristics of the waste gas and the maximum operating temperature.

Flameless combustion

See Section 1.7.1.

Furnace automation and control

See Section 1.7.1.

Low-NOX burner

The technique (including ultra-low-NOX burners) is based on the principles of reducing peak flame temperatures. The air/fuel mixing reduces the availability of oxygen and reduces the peak flame temperature, thus retarding the conversion of fuel-bound nitrogen to NOX and the formation of thermal NOX, while maintaining high combustion efficiency.

Optimisation of the SNCR/SCR design and operation

See Section 1.7.1.

Oxy-fuel combustion

See Section 1.7.1.

Selective catalytic reduction (SCR)

The SCR technique is based on the reduction of NOX to nitrogen in a catalytic bed by reaction with urea or ammonia at an optimum operating temperature of around 300–450 °C. Several layers of catalyst may be applied. A higher NOX reduction is achieved with the use of several catalyst layers.

Selective non-catalytic reduction (SNCR)

SNCR is based on the reduction of NOX to nitrogen by reaction with ammonia or urea at a high temperature. The operating temperature window is maintained between 800 °C and 1 000 °C for optimal reaction.

Wet scrubbing

The removal of gaseous or particulate pollutants from a gas stream via mass transfer to a liquid solvent, often water or an aqueous solution. It may involve a chemical reaction (e.g. in an acid or alkaline scrubber). In some cases, the compounds may be recovered from the solvent.

Adsorption

The removal of soluble substances (solutes) from the waste water by transferring them to the surface of solid, highly porous particles (typically activated carbon).

Aerobic treatment

The biological oxidation of dissolved organic pollutants with oxygen using the metabolism of microorganisms. In the presence of dissolved oxygen, injected as air or pure oxygen, the organic components are mineralised into carbon dioxide and water or are transformed into other metabolites and biomass.

Chemical precipitation

The conversion of dissolved pollutants into an insoluble compound by adding chemical precipitants. The solid precipitates formed are subsequently separated by sedimentation, air flotation or filtration. If necessary, this may be followed by microfiltration or ultrafiltration. Multivalent metal ions (e.g. calcium, aluminium, iron) are used for phosphorus precipitation.

Chemical reduction

The conversion of pollutants by chemical reducing agents into similar but less harmful or hazardous compounds.

Coagulation and flocculation

Coagulation and flocculation are used to separate suspended solids from waste water and are often carried out in successive steps. Coagulation is carried out by adding coagulants with charges opposite to those of the suspended solids. Flocculation is carried out by adding polymers, so that collisions of microfloc particles cause them to bond to produce larger flocs.

Equalisation

Balancing of flows and pollutant loads at the inlet of the final waste water treatment by using central tanks. Equalisation may be decentralised or carried out using other management techniques.

Filtration

The separation of solids from waste water by passing them through a porous medium, e.g. sand filtration, microfiltration and ultrafiltration.

Flotation

The separation of solid or liquid particles from waste water by attaching them to fine gas bubbles, usually air. The buoyant particles accumulate at the water surface and are collected with skimmers.

Nanofiltration

A filtration process in which membranes with pore sizes of approximately 1 nm are used.

Neutralisation

The adjustment of the pH of waste water to a neutral level (approximately 7) by the addition of chemicals. Sodium hydroxide (NaOH) or calcium hydroxide (Ca(OH)2) is generally used to increase the pH, whereas sulphuric acid (H2SO4), hydrochloric acid (HCl) or carbon dioxide (CO2) is generally used to decrease the pH. The precipitation of some substances may occur during neutralisation.

Physical separation

The separation of gross solids, suspended solids and/or metal particles from the waste water using for example screens, sieves, grit separators, grease separators, hydrocyclones, oil-water separation or primary settlement tanks.

Reverse osmosis

A membrane process in which a pressure difference applied between the compartments separated by the membrane causes water to flow from the more concentrated solution to the less concentrated one.

Sedimentation

The separation of suspended particles and suspended material by gravitational settling.