Thermal Processes in the Metallurgical Industry

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Thermal processes in the metallurgical industrySuggested Revisions by Environment Canada including comments arising from

discussions in Geneva at EGB II 1 in 2005 and comments submitted by February

2006 to the Stockholm Secretariat.

28.April.2006

Guidelines on BAT and Guidance on BEP Environment Canada Revision, April 28, 2006


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Table of contents

TABLE OF CONTENTS.................................................................................................................................3

V.D Thermal processes in the metallurgical industry:............................................................................5

SUMMARIESBYSOURCECATEGORIES PART III OF ANNEX C ....................................................................6

VI.B. Thermal processes in the metallurgical industry not mentioned in Annex C, Part II: ..................6

SECTION V 8

GUIDANCE/GUIDELINES BY SOURCE CATEGORY:

SOURCE CATEGORIES IN PART II OF ANNEX C..................................................................................8

V.D. THERMALPROCESSESINTHEMETALLURGICALINDUSTRY...................................................................8

(i) Secondary copper production...............................................................................................................8

(ii) Sinter plants in the iron and steel industry........................................................................................21

(iii) Secondary aluminium production.....................................................................................................34

(iv) Secondary zinc production................................................................................................................47

SECTION VI.

GUIDANCE/GUIDELINES BY SOURCE CATEGORY

SOURCE CATEGORIES IN PART III OF ANNEX C......................................................................... .....57

VI.B THERMALPROCESSESINTHEMETALLURGICALINDUSTRYNOTMENTIONEDIN ANNEX C, PART II. .58

(i) Secondary lead production.................................................................................................................58

(ii) Primary aluminium production.........................................................................................................67

(iii) Magnesium production.....................................................................................................................77

(iv) Secondary steel production...............................................................................................................89

(v) Primary base metals smelting..........................................................................................................106



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Section IV. Compilation of summaries of Sections V and VI

V.D Thermal processes in the metallurgical

industry:(i) Secondary copper production

Secondary copper smelting involves copper production from copper scrap, sludge, computer andelectronic scrap, and drosses from refineries. Processes involved in copper production are feed

pretreatment, smelting, alloying and casting. Organic materials in feed such as oils, plastics andcoatings, and temperatures between 250C and 500C, may give rise to chemicals listed in AnnexC of the Stockholm Convention.

Best available techniques include presorting, cleaning feed materials, maintaining temperaturesabove 850C, utilizing afterburners with rapid quenching, activated carbon adsorption and fabricfilter dedusting.

Achievable performance levels for secondary copper smelters: < 0.51 ng I-TEQ/Nm3.1

(ii) Sinter plants in the iron and steel industry

Sinter plants in the iron and steel industry are a pretreatment step in the production of iron wherebyfine particles of iron ores and, in some plants, secondary iron oxide wastes (collected dusts, millscale) are agglomerated by combustion. Sintering involves the heating of fine iron ore with fluxand coke fines or coal to produce a semi-molten mass that solidifies into porous pieces of sinterwith the size and strength characteristics necessary for feeding into the blast furnace.

PCDD and PCDF appear to be formed in the iron sintering process via de novo synthesis. PCDFgenerally dominate in the waste gas from sinter plants. The PCDD/PCDF formation mechanismappears to start in the upper regions of the sinter bed shortly after ignition, and then the dioxins,

furans and other compounds condense on cooler burden beneath as the sinter layer advances alongthe sinter strand towards the burn-through point.

Primary measures identified to prevent or minimize the formation of PCDD/PCDF during ironsintering include the stable and consistent operation of the sinter plant, continuous parametermonitoring, recirculation of waste gases, minimization of feed materials contaminated with

persistent organic pollutants or contaminants leading to formation of such pollutants, and feedmaterial preparation.

Secondary measures identified to control or reduce releases of PCDD/PCDF from iron sinteringinclude adsorption/absorption (for example, activated carbon injection) and high-efficiencydedusting, as well as fine wet scrubbing of waste gases combined with effective treatment of thescrubber waste waters and disposal of waste-water sludge in a secure landfill.

The achievable performance level for an iron sintering plant operating according to best availabletechniques: < 0.2 ng TEQ/Nm3.

(iii) Secondary aluminium production

Secondary aluminium smelting involves the production of aluminium from used aluminiumproducts processed to recover metals by pretreatment, smelting and refining.

Fuels, fluxes and alloys are used, while magnesium removal is practised by the addition ofchlorine, aluminium chloride or chlorinated organics. Chemicals listed in Annex C of the

1 1 ng (nanogram) = 1 10-12 kilogram (1 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured

at 0 C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the presentguidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgicalsources.



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Stockholm Convention probably result from organics in the feed, chlorine compounds andtemperatures between 250C and 500C.

Best available techniques include high-temperature advanced furnaces, oil- and chlorine-free feeds(if alternatives are available), afterburners with rapid quench, activated carbon adsorption anddedusting fabric filters.

The achievable performance level for secondary aluminium smelters: < 0. 51 ng I-TEQ/Nm3.

(iv) Secondary zinc production

Secondary zinc smelting involves the production of zinc from materials such as dusts from copperalloy production and electric arc steel making, and residues from steel scrap shredding andgalvanizing processes. Production processes include feed sorting, pretreatment cleaning, crushing,sweating furnaces to 364C, melting furnaces, refining, distillation and alloying. Oils and plasticsin feed, and temperatures between 250C and 500C, may give rise to chemicals listed in AnnexC of the Stockholm Convention.

Best available techniques include feed cleaning, maintaining temperatures above 850C, fume andgas collection, afterburners with quenching, activated carbon adsorption and fabric filter dedusting.

The achievable performance level for secondary zinc smelters: < 0.51 ng I-TEQ/Nm3.

Summaries by source categories Part III of Annex C

VI.B.Thermal processes in the metallurgicalindustry not mentioned in Annex C, Part II:

(i) Secondary lead production

Secondary lead smelting involves the production of lead and lead alloys, primarily from scrapautomobile batteries, and also from other used lead sources (pipe, solder, drosses, lead sheathing).Production processes include scrap pretreatment, smelting and refining. Oils and plastics in feed,and temperatures between 250 and 500 C, may give rise to chemicals listed in Annex C of theStockholm Convention.

Best available techniques include the use of plastic-free and oil-free feed material, high furnacetemperatures above 850 C, effective gas collection, afterburners and rapid quench, activatedcarbon adsorption, and dedusting fabric filters.

The achievable performance levels for secondary lead smelters: < 0.1 ng I-TEQ/Nm3.

(ii) Primary aluminium production

Primary aluminium is produced directly from the mined ore, bauxite. The bauxite is refined intoalumina through the Bayer process. The alumina is reduced into metallic aluminium by electrolysisthrough the Hall-Hroult process (either using self-baking anodes Sderberg anodes or using

prebaked anodes).

Primary aluminium production is generally thought not to be a significant source of chemicalslisted in Annex C of the Stockholm Convention. However, contamination with PCDD and PCDF is

possible through the graphite-based electrodes used in the electrolytic smelting process.

Possible techniques to reduce the production and release of chemicals listed in Annex C from theprimary aluminium sector include improved anode production and control, and using advancedsmelting processes. The achievable performance level in this sector should be < 0.1 ng TEQ/Nm3.

(iii) Magnesium production



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SECTION V. Guidelines/guidance by source category: Part II of Annex C 7

Magnesium is produced either from raw magnesium chloride with molten salt electrolysis, ormagnesium oxide reduction with ferrosilicon or aluminium at high temperatures, as well as throughsecondary magnesium recovery (for example, from asbestos tailings).

The addition of chlorine or chlorides, the presence of carbon anodes and high process temperaturesin magnesium production can lead to the formation of chemicals listed in Annex C of the

Stockholm Convention and their emission in air and water.

Alternative techniques may include the elimination of the carbon source by using non-graphiteanodes, and the application of activated carbon. However, achievable performance depends on thetype of process and controls utilized.

(iv) Secondary steel production

Secondary steel is produced through direct smelting of ferrous scrap using electric arc furnaces.The furnace melts and refines a metallic charge of scrap steel to produce carbon, alloy and stainlesssteels at non-integrated steel mills. Ferrous feed materials may include scrap, such as shreddedvehicles and metal turnings, or direct reduced iron.

Chemicals listed in Annex C of the Stockholm Convention, such as PCDD and PCDF, appear to bemost probably formed in the electric arc furnace steel-making process via de novo synthesis by thecombustion of non-chlorinated organic matter such as polystyrene, coal and particulate carbon inthe presence of chlorine donors. Many of these substances are contained in trace concentrations inthe steel scrap or are process raw materials such as injected carbon.

Primary measures include adequate off-gas handling and appropriate off-gas conditioning toprevent conditions leading to de novo synthesis formation of PCDD/PCDF. This may include post-combustion afterburners, followed by rapid quench of off-gases. Secondary measures includeadsorbent injection (for example, activated carbon) and high-level dedusting with fabric filters.

The achievable performance level using best available techniques for secondary steel production is< 0.1 ngI-TEQ/Nm3.

(v) Primary base metals smelting

Primary base metals smelting involves the extraction and refining of nickel, lead, copper, zinc andcobalt. Generally, primary base metals smelting facilities process ore concentrates. Most primarysmelters have the technical capability to supplement primary concentrate feed with secondarymaterials (for example, recyclables).

Production techniques may include pyrometallurgical or hydrometallurgical processes. Chemicalslisted in Annex C of the Stockholm Convention are thought to originate through high-temperaturethermal metallurgical processes; hydrometallurgical processes are therefore not considered in thissection on best available techniques for primary base metals smelting.

Available information on emissions of PCDD and PCDF from a variety of source sectors (for

example, incinerators, steel electric arc furnaces, iron sintering plants) suggests that processtechnologies and techniques, and associated off-gas conditioning, can influence the formation andsubsequent release of PCDD/PCDF. Consideration should be given to hydrometallurgical

processes, where technically feasible, as alternatives to pyrometallurgical processes whenconsidering proposals for the construction and commissioning of new base metals smeltingfacilities or processes.

Primary measures include the use of hydrometallurgical processes, quality control of feed materialsand scrap to minimize contaminants leading to PCDD/PCDF formation, effective process control toavoid conditions leading to PCDD/PCDF formation, and use of flash smelting technology.Identified secondary measures include high-efficiency gas cleaning and conversion of sulphurdioxide to sulphuric acid, effective fume and gas collection and high-efficiency dust removal.

The achievable performance level using best available techniques for base metals smelters is < 0.1ng I-TEQ/Nm3.



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8 SECTION V. Guidelines/guidance by source category: Part II of Annex C

Section V

Guidance/guidelines by source category:Source categories in Part II of Annex C

V.D. Thermal processes in the metallurgical industry

(i) Secondary copper production

1. Process descriptionSecondary copper smelting involves pyrometallurgical processes dependent on the copper contentof the feed material, size distribution and other constituents. Feed sources are copper scrap, sludge,computer scrap, drosses from refineries and semi-finished products. These materials may containorganic materials like coatings or oil, and installations take this into account by using de-oiling anddecoating methods or by correct design of the furnace and abatement system (EuropeanCommission 2001, p. 201202). Copper can be infinitely recycled without loss of its intrinsic

properties.

The quoted material that follows is from Secondary Copper Smelting, Refining and Alloying, areport of the Environmental Protection Agency of the United States of America (EPA 1995).

Secondary copper recovery is divided into 4 separate operations: scrap pre-treatment,smelting, alloying, and casting. Pre-treatment includes the cleaning and consolidation ofscrap in preparation for smelting. Smelting consists of heating and treating the scrap forseparation and purification of specific metals. Alloying involves the addition of 1 or moreother metals to copper to obtain desirable qualities characteristic of the combination ofmetals.

Scrap pre-treatment may be achieved through manual, mechanical, pyrometallurgical, orhydrometallurgical methods. Manual and mechanical methods include sorting, stripping,shredding, and magnetic separation. Pyrometallurgical pre-treatment may include sweating(the separation of different metals by slowly staging furnace air temperatures to liquefyeach metal separately), burning insulation from copper wire, and drying in rotary kilns to

volatilize oil and other organic compounds. Hydrometallurgical pre-treatment methodsinclude flotation and leaching to recover copper from slag. Leaching with sulphuric acid isused to recover copper from slime, a byproduct of electrolytic refining.


Summary

Secondary copper smelting involves copper production from copper scrap, sludge, computerand electronic scrap, and drosses from refineries. Processes involved in copper production arefeed pretreatment, smelting, alloying and casting. Organic materials in feed such as oils,

plastics and coatings, and temperatures between 250 and 500C, may give rise to chemicalslisted in Annex C of the Stockholm Convention.

Best available techniques include: presorting, cleaning feed materials, maintaining temperaturesabove 850 C, utilizing afterburners with rapid quenching, activated carbon adsorption andfabric filter dedusting.

Achievable performance levels for secondary copper smelters: < 0.51 ng I-TEQ/Nm3.


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Smelting of low-grade copper scrap begins with melting in either a blast or a rotaryfurnace, resulting in slag and impure copper. If a blast furnace is used, this copper ischarged to a converter, where the purity is increased to about 80 to 90 percent, and then toa reverberatory furnace, where copper of about 99 percent purity is achieved. In these fire-refining furnaces, flux is added to the copper and air is blown upward through the mixtureto oxidize impurities.

These impurities are then removed as slag. Then, by reducing the furnace atmosphere,cuprous oxide (CuO) is converted to copper. Fire-refined copper is cast into anodes, whichare used during electrolysis. The anodes are submerged in a sulphuric acid solutioncontaining copper sulphate. As copper is dissolved from the anodes, it deposits on thecathode. Then the cathode copper, which is as much as 99.99 percent pure, is extracted andrecast. The blast furnace and converter may be omitted from the process if average coppercontent of the scrap being used is greater than about 90 percent.

In alloying, copper-containing scrap is charged to a melting furnace along with 1 or moreother metals such as tin, zinc, silver, lead, aluminium, or nickel. Fluxes are added toremove impurities and to protect the melt against oxidation by air. Air or pure oxygen may

be blown through the melt to adjust the composition by oxidizing excess zinc. The alloyingprocess is, to some extent, mutually exclusive of the smelting and refining processesdescribed above that lead to relatively pure copper.

The final recovery process step is the casting of alloyed or refined metal products. Themolten metal is poured into moulds from ladles or small pots serving as surge hoppers andflow regulators. The resulting products include shot, wire bar, anodes, cathodes, ingots, orother cast shapes.

Figure 1 expressespresents the process in diagrammatic form.



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Figure 1. Secondary copper smelting



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Smeltingreduction

Converter

Anode furnace

Electrolyticrefining

Flux, scrap,air, oxygen

Clean scrap,reductant, air

Input Potential output

Lower grade

residues, fluxes,

coke, oxygen

Blackcopper

Convertercopper

Anodes

Ni, etc.

Slime

Particulate matter

Air emissions CODust, metal oxide fume recycledDioxins, volatile organic compoundsLand emissions

Furnace linings

Land releasesemissions,filter dust (recycled), furnacelinings

Air emissions:, SO2,

metals, dust

Slag

Slag

CathodesFinal slag

Construction

Anode scrap

Smeltingreduction

Converter

Anode furnace

Electrolyticrefining

Flux, scrap,air, oxygen

Clean scrap,reductant, air

Input Potential output

Lower grade

residues, fluxes,

coke, oxygen

Blackcopper

Convertercopper

Anodes

Ni, etc.

Slime

Particulate matter

Air emissions CODust, metal oxide fume recycledDioxins, volatile organic compoundsLand emissionsFurnace linings

Land releasesemissions,filter dust (recycled), furnacelinings

Air emissions:, SO2,

metals, dust

Slag

Slag

CathodesFinal slag

Construction

Anode scrap


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Source: European Commission 2001, p. 217

Artisinal and small enterprise metal recovery activities maybe significant, particularly indeveloping countries and countries with economies in transition. These activities may contributesignificantly to pollution and have negative health impacts. For example, artisinal zinc smelting is

an important atmospheric mercury emission source. The technique used to smelt both zinc andmercury is simple; the ores are heated in a furnace for a few hours, and zinc metal and liquidmercury are produced. In many cases there are no pollution control devices employed at all duringthe melting process. Other metals that are known to be produced by artisinal and small enterprisemetal recovery activities include antimony, iron, lead, manganese, tin, tungsten, gold, silver,copper, and aluminum.

These are not considered best available techniques or best environmental practices.However, as a minimum, appropriate ventilation and material handling should be carriedout.



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2. Sources of chemicals listed in Annex C of the Stockholm

Convention

The formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans(PCDF) is probably due to the presence of chlorine from plastics and trace oils in the feed material.As copper is the most efficient metal to catalyse PCDD/PCDF formation, copper smelting is aconcern.

2.1. General information on emissions from secondary copper smelters

Airborne emissions consist of nitrogen oxides (NOx), carbon monoxide (CO), dust and metalcompounds, organic carbon compounds and PCDD/PCDF. Off-gases usually contain little or nosulphur dioxide (SO2), provided sulphidic material is avoided. Scrap treatment and smeltinggenerate the largest quantity of atmospheric emissions. Dust and metal compounds are emittedfrom most stages of the process and are more prone to fugitive emissions during charging andtapping cycles. Particulate matter is removed from collected and cooled combustion gases byelectrostatic precipitators or fabric filters. Fume collection hoods are used during the conversion

and refining stages due to the batch process, which prevents a sealed atmosphere. NOx isminimized in low-NOx burners, while CO is burnt in hydrocarbon afterburners. Burner controlsystems are monitored to minimize CO generation during smelting (European Commission 2001,

p. 218229).

2.2. Emissions of PCDD/PCDF to air

PCDD/PCDF are formed during base metal smelting through incomplete combustion or by de novosynthesis when organic and chlorine compounds such as oils and plastics are present in the feedmaterial. Secondary feed often consists of contaminated scrap.

The process is described in European Commission 2001, p. 133:

PCDD/PCDF or their precursors may be present in some raw materials and there is a

possibility of de-novo synthesis in furnaces or abatement systems. PCDD/PCDF are easilyadsorbed onto solid matter and may be collected by all environmental media as dust,scrubber solids and filter dust.

The presence of oils and other organic materials on scrap or other sources of carbon(partially burnt fuels and reductants, such as coke), can produce fine carbon particles whichreact with inorganic chlorides or organically bound chlorine in the temperature range of250 to 500 C to produce PCDD/PCDF. This process is known as de-novo synthesis and iscatalysed by the presence of metals such as copper or iron.

Although PCDD/PCDF are destroyed at high temperature (above 850 C) in the presenceof oxygen, the process of de-novo synthesis is still possible as the gases are cooled throughthe reformation window. This window can be present in abatement systems and in cooler

parts of the furnace e.g. the feed area. Care taken in the design of cooling systems tominimise the residence time in the window is practised to prevent de-novo synthesis.

2.3. Releases to other media

Process, surface and cooling water can be contaminated by suspended solids, metal compounds andoils. Most process and cooling water is recycled. Waste-water treatment methods are used beforedischarge. By-products and residues are recycled in the process as these contain recoverablequantities of copper and other non-ferrous metals. Waste material generally consists of acid slimeswhich are disposed of on site. Care must be taken to ensure the proper disposal of slimes in orderto minimize copper and dioxins exposure to the environment.

3. Recommended processes



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Process design and configuration is influenced by the variation in feed material and quality control.Processes considered as best available techniques for smelting and reduction include the blastfurnace, the mini-smelter (totally enclosed), the sealed submerged electric arc furnace, and ISAsmelt. The top-blown rotary furnace (totally enclosed) and Pierce-Smith converter are bestavailable techniques for converting. The submerged electric arc furnace is sealed and is cleanerthan other designs if the gas extraction system is adequately designed and sized.

The use of blast furnaces for scrap melting is becoming less common due to difficulties ineconomically preventing pollution. Shaft furnaces without a coal/coke feed are being used instead(Personal Communication, February 2006).

Clean copper scrap devoid of organic contamination can be processed using the reverberatoryhearth furnace, the hearth shaft furnace or Contimelt process. These are considered to be bestavailable techniques in configurations with suitable gas collection and abatement systems.

No information is available on alternative processes to smelting for secondary copper processing.

4. Primary and secondary measures

Primary and secondary measures of PCDD/PCDF reduction and elimination are discussed below.

4.1. Primary measures

Primary measures are regarded as pollution prevention techniques to reduce or eliminate thegeneration and release of persistent organic pollutants. Possible measures include:

4.1.1.Presorting of feed material

The presence of oils, plastics and chlorine compounds in the feed material should be avoided toreduce the generation of PCDD/PCDF during incomplete combustion or by de novo synthesis.Feed material should be classified according to composition and possible contaminants. Storage,handling and pretreatment techniques will be determined by feed size distribution andcontamination.

Methods to be considered are (European Commission 2001, p. 232):

Oil removal from feed (for example, thermal decoating and de-oiling processes

followed by afterburning to destroy any organic material in the off-gas);

Use of milling and grinding techniques with good dust extraction and abatement.

The resulting particles can be treated to recover valuable metals using density or pneumaticseparation;

Elimination of plastic by stripping cable insulation (for example, possible

cryogenic techniques to make plastics friable and easily separable);

Sufficient blending of material to provide a homogeneous feed in order to promote

steady-state conditions.Additional techniques for oil removal are solvent use and caustic scrubbing. Cryogenicstripping can be used to remove cable coatings.

4.1.2.Effective process control

Process control systems should be utilized to maintain process stability and operate at parameterlevels that will contribute to the minimization of PCDD/PCDF generation, such as maintainingfurnace temperature above 850 C to destroy PCDD/PCDF. Ideally, PCDD/PCDF emissions would

be monitored continuously to ensure reduced releases. Continuous emissions sampling ofPCDD/PCDF has been demonstrated for some sectors (for example, waste incineration), but

research is still developingongoingin this fieldfor applications to other sources. In the absence ofcontinuous PCDD/PCDF monitoring, other variables such as temperature, residence time, gas



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Catalytic oxidation is an emerging technology used in waste incinerators to eliminate PCDD/PCDFemissions. This process should be considered by secondary base metals smelters as it has proveneffective for PCDD/PCDF destruction in waste incinerators. However, catalytic oxidation can, besubject to poisoning from trace metals and other exhaust gas contaminants.;, vValidation workwould be necessary before use of this process.

Catalytic oxidation processes organic compounds into water, carbon dioxide (CO2) andhydrochloric acid using a precious metal catalyst to increase the rate of reaction at 370 to 450C.In comparison, incineration occurs typically at 980 C. Catalytic oxidation has been shown todestroy PCDD/PCDF with shorter residence times, lower energy consumption and >99%efficiency, and should be considered. Off- Particulate matter should be removed from exhaustgases should be dedusted prior to catalytic oxidation for optimum efficiency. This method iseffective for the vapour phase of contaminants. The resulting hydrochloric acid is treated in ascrubber while the water and CO2 are released to the air after cooling (Parvesse 2001).

Fabric filters used for dust removal can also be treated with a catalytic coating to promoteoxidation of organic compounds at elevated temperature.

6. Summary of measures

Table 1. Measures for recommended processes for new secondary copper smelters

Measure Description Considerations Other comments

Recommendedprocesses

Variousrecommendedsmelting processesshould beconsidered for newfacilities

Processes tobe considered include:

Blast furnace, mini-smelter, top-

blown rotary furnace, sealedsubmerged electric arc furnace,ISA smelt, and the Pierce-Smithconverter

Reverberatory hearth furnace,

the hearth shaft furnace andContimelt process to treat cleancopper scrap devoid of organiccontamination

These are considered to be bestavailable techniques inconfiguration with suitable gascollection and abatement.

The submerged electric arcfurnace is sealed and can be

cleaner than other designs if thegas extraction system isadequately designed and sized

Table 2. Summary of primary and secondary measures for secondary copper smelters


Primary measures

Presorting offeed material

The presence of oils,plastics and chlorinecompounds in the feedmaterial should be avoidedto reduce the generation ofPCDD/PCDF duringincomplete combustion or

by de novo synthesis

Processes to be consideredinclude:

Oil removal from feed

material

Use of milling and grinding

techniques with good dustextraction and abatement

Elimination of plastic by

stripping cable insulation

Thermal decoating and de-oiling processes for oilremoval should befollowed by afterburningto destroy any organicmaterial in the off-gas

Effective process

control

Process control systems

should be utilized tomaintain process stability

PCDD/PCDF emissions may be

minimized by controlling othervariables such as temperature,

Continuous emissions

sampling of PCDD/PCDFhas been demonstrated for



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and operate at parameterlevels that will contributeto the minimization ofPCDD/PCDF generation

residence time, gascompositionnents and fumecollection damper controls afterhaving established optimum

operating conditions for thereduction of PCDD/PCDF

some sectors (for example,waste incineration), butresearch is stilldevelopongoing for

applications to othersourcesin this field

Secondary measures

Fume and gascollection

Effective fume and off-gascollection should beimplemented in all stagesof the smelting process tocapture PCDD/PCDFemissions

Processes tobe consideredinclude:

Sealed furnaces to contain

fugitive emissions whilepermitting heat recovery andcollecting off-gases. Furnaceor reactor enclosures may benecessary

Proper design of hooding and

ductwork to trap fumes

Roofline collection offume is to be avoided dueto high energyrequirements

High-efficiencydust removal

Dusts and metalcompounds should beremoved as this material

possesses high surfacearea on whichPCDD/PCDF easilyadsorb. Removal of thesedusts would contribute tothe reduction of

PCDD/PCDF emissions


Fabric filters (most effective

method)

Wet/dry scrubbers and

ceramic filters

Dust removal is to befollowed by afterburnersand quenching.

Collected dust must betreated in high-temperaturefurnaces to destroyPCDD/PCDF and recovermetals

Afterburners andquenching

Afterburners should beused at temperatures > 950C to ensure fullcombustion of organiccompounds, followed byrapid quenching of hotgases to temperatures

below 250C

Considerations include:

PCDD/PCDF formation at

250500C, and destruction> 850 C with O2

Requirement for sufficient O2in the upper region of thefurnace for completecombustion

Need for proper design of

cooling systems to minimize

reformation time

De novo synthesis is stillpossible as the gases arecooled through thereformation window

Adsorption onactivated carbon

Activated carbon treatmentshould be considered asthis material possesseslarge surface area onwhich PCDD/PCDF can

be adsorbed from smelteroff-gases


Treatment with activated

carbon using fixed or movingbed reactors

Injection ofpowdered carbon

particulate into the gas streamfollowed by removal as a filterdust

Lime/carbon mixtures canalso be used

Emerging research

Catalytic Catalytic oxidation is an Considerations include: Catalytic oxidation has



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oxidation emerging technology forsources in this sector(demonstrated technologyfor incinerator

applications) whichshould be considered dueto its high efficiency andlower energyconsumption. Catalyticoxidation transformsorganic compounds intowater, CO2 andhydrochloric acid using a

precious metal catalyst

Process efficiency for the

vapour phase of contaminants

Hydrochloric acid treatment

using scrubbers while waterand CO2 are released to the airafter cooling

been shown to destroyPCDD/PCDF with shorterresidence times, lowerenergy consumption and

>99% efficiency.Particulate matter should

be removed from Off-exhaust gases should bededusted prior to catalyticoxidation for optimumefficiency

7. Achievable performance levels

The achievable performance level2 for emissions of PCDD/PCDF from secondary copper smeltersis < 0.51 ng I-TEQ/Nm3.

References

A.J. Gunson, Yue Jian, Artisanal Mining in The People's Republic of China, Mining,Minerals and Sustainable Development (MMSD), International Institute for Environmentand Development (IIED), September 2001

EPA (United States Environmental Protection Agency). 1995. Secondary Copper Smelting,Refining and Alloying. Background Report AP-42, Section 12.9.www.epa.gov/ttn/chief/ap42/ch12/final/c12s09.pdf.

European Commission. 2001.Reference Document on Best Available Techniques in the Non-Ferrous Metals Industries. BAT Reference Document (BREF). European IPPC Bureau, Seville,Spain. eippcb.jrc.es.

Feng Xinbin, Qui Guangle, Li Guanghui, Li Ping, Wang Shaofeng, Mercury Emissionsfrom Artisanal Zinc and Mercury Smelting in Guizhou, PR China, GoldschmidtConference Abstracts 2005, The Geochemistry of Mercury, page A705

Hbner C., Boos R., Bohlmann J., Burtscher K. and Wiesenberger H. 2000. State-of-the-ArtMeasures for Dioxin Reduction in Austria. Vienna.www.ubavie.gv.at/publikationen/Mono/M116s.htm.

Parvesse T. 2001. Controlling Emissions from Halogenated Solvents. Chemical Processing.Chemical Processing [Chem. Process.]. Vol. 64, no. 4, pp. 48-51. Apr 2001/.

Personal communication from Expert Group Best Available Techniques Best EnvironmentalPractices, Finland Member, February 2006

2 1 ng (nanogram) = 1 10 -12 kilogram (1 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0

C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgical sources.

http://www.epa.gov/ttn/chief/ap42/ch12/final/c12s09.pdfhttp://eippcb.jrc.es/http://eippcb.jrc.es/http://www.ubavie.gv.at/publikationen/Mono/M116s.htmhttp://www.epa.gov/ttn/chief/ap42/ch12/final/c12s09.pdfhttp://eippcb.jrc.es/http://www.ubavie.gv.at/publikationen/Mono/M116s.htm


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Personal communication, Member, Japan, Expert Group Meeting, 1 December, 2006

UNEP, Compilation of comments received from Parties and others on the draft Guidelines on BestAvailable Techniques and provisional Guidance on Best Environmental Practices, October 14,

2005http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5.pdf

UNEP Environment Program News Centre,http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=en, as read on January 20, 2006

UNEP Environment Program News Centre,http://www.unep.org/Documents.Multilingual/Default.asp?

DocumentID=284&ArticleID=3204&l=en, as read on January 20, 2006

Xinbin Feng, Xianwu Bi, Guangle Qiu, Guanghui Li, Shunlin Tang, Mercury Pollution inGuizhou, China - A status Report,http://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htm , as read onDecember 29th, 2005

http://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5.pdfhttp://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5.pdfhttp://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5.pdfhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htmhttp://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5.pdfhttp://www.pops.int/documents/meetings/bat_bep/EGBATBEP1/meetingdocs/EGBATBEP_1_inf5.pdfhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=284&ArticleID=3204&l=enhttp://pbc.eastwestcenter.org/abstracts2005/abstract2005fengxinbin.htm


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(ii) Sinter plants in the iron and steel industry

1. Process description

Iron sintering plants are associated with the manufacture of iron and steel, often in integrated steelmills. The sintering process is a pretreatment step in the production of iron whereby fine particlesof iron ores and, in some plants, secondary iron oxide wastes (collected dusts, mill scale) areagglomerated by combustion. Agglomeration of the fines is necessary to enable the passage of hotgases during the subsequent blast furnace operation (UNEP 2003, p. 60).

Sintering involves the heating of fine iron ore with flux and coke fines or coal to produce a semi-

molten mass that solidifies into porous pieces of sinter with the size and strength characteristicsnecessary for feeding into the blast furnace. Moistened feed is delivered as a layer onto acontinuously moving grate or strand. The surface is ignited with gas burners at the start of thestrand and air is drawn through the moving bed, causing the fuel to burn. Strand velocity and gasflow are controlled to ensure that burn-through (i.e., the point at which the burning fuel layerreaches the base of the strand) occurs just prior to the sinter being discharged. The solidified sinteris then broken into pieces in a crusher and is air cooled. Product outside the required size range isscreened out, oversize material is recrushed, and undersize material is recycled back to the process.Sinter plants that are located in a steel plant recycle iron ore fines from the raw material storage andhandling operations and from waste iron oxides from steel plant operations and environmentalcontrol systems. Iron ore may also be processed in on-site sinter plants (Environment Canada 2001,

p. 18).


Summary

Sinter plants in the iron and steel industry are a pretreatment step in the production of ironwhereby fine particles of iron ores and, in some plants, secondary iron oxide wastes (collecteddusts, mill scale) are agglomerated by combustion. Sintering involves the heating of fine ironore with flux and coke fines or coal to produce a semi-molten mass that solidifies into porous

pieces of sinter with the size and strength characteristics necessary for feeding into the blastfurnace.

PCDD and PCDF appear to be formed in the iron sintering process via de novo synthesis.PCDF generally dominate in the waste gas from sinter plants. The PCDD/PCDF formationmechanism appears to start in the upper regions of the sinter bed shortly after ignition, and thenthe dioxins, furans and other compounds condense on cooler burden beneath as the sinter layeradvances along the sinter strand towards the burn-through point.

Primary measures identified to prevent or minimize the formation of PCDD/PCDF during ironsintering include the stable and consistent operation of the sinter plant, continuous parametermonitoring, recirculation of waste gases, minimization of feed materials contaminated with

persistent organic pollutants or contaminants leading to formation of such pollutants, and feedmaterial preparation.

Secondary measures identified to control or reduce releases of PCDD/PCDF from iron sinteringinclude adsorption/absorption (for example, activated carbon injection) and high-efficiencydedusting, as well as fine wet scrubbing of waste gases combined with effective treatment ofthe scrubber waste waters and disposal of waste-water sludge in a secure landfill.

The achievable performance level for an iron sintering plant operating according to bestavailable techniques: < 0.2 ng TEQ/Nm3.


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A blast furnace is a vertical furnace using tuyeres to blast heated or cold air into thefurnace burden to smelt the contents. Sinter is charged into the top of the blast furnace inalternating layers with coke.

The flexibility of the sintering process permits conversion of a variety of materials, including iron

ore fines, captured dusts, ore concentrates, and other iron-bearing materials of small particle size(for example, mill scale) into a clinker-like agglomerate (Lankford et al. 1985, p. 305306).

Waste gases are usually treated for dust removal in a cyclone, electrostatic precipitator, wetscrubber or fabric filter.

Figure 1 provides a schematic of an iron sintering plant using a wet scrubbing systemer.

It has been suggested that this diagram does not represent the entire steel industry regardingsecondary sinter off-gas cleaning; that wet scrubbing systems will be shut down and replaced byfabric filters with injection of hydrated lime / activated carbon / zeolite etc.; and that due to

problems and the costs of the waste water treatment this process can only be used effectively wherethe waste water (after filtering and dilution to the salt concentration of the sea water) may bereleased to the ocean (Personal Communication, February 2006).

Figure 1. Process diagram of a sinter plant using a web scrubbing system

W a t e r

M a s h i n g S t a g e

F i n e S c r u b b e r s

E S P

T h i c k e n e r

S l u d g e

W a t e r T r e a t m e n t I m m o b i l i s a t i o n

D e p o t

S l a g

R e c y c l i n g

F e - C o m p o n e n t s

S i n t e r M a c h i n e

P r o c e s s A i r

C l e a n e d W a t e r

D i s c h a r g eW a t e r

S l u d g e T a n k

F l o a t i n g S l u d g et o B F

W a t e r

N a t .G a sR e h e a t i n g

E m i s s i o nM o n i t o r i n g

F a n

M a i n F a n

Q u e n c h

M a s h i n gW a t e r

S l u d g eW a t e r

Source: Hofstadler et al. 2003.

2. Sources of chemicals listed in Annex C of the Stockholm

Convention

As regards emissions of chemicals listed in Annex C of the Stockholm Convention, iron sinteringhas been identified as a source of PCDD and PCDF. The formation and release ofhexachlorobenzene (HCB) and polychlorinated biphenyls (PCB) are less understood from this

potential source.

2.1. Releases to air

2.1.1.General information on emissions from iron sinteringplants



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The following information is drawn from Environment Canada 2001, p. 2325.

Emissions from the sintering process arise primarily from materials-handling operations,which result in airborne dust, and from the combustion reaction on the strand. Combustiongases from the latter source contain dust entrained directly from the strand along with

products of combustion such as CO, CO2, SOx, NOx, and particulate matter. The

concentrations of these substances vary with the quality of the fuel and raw materials usedand combustion conditions. Atmospheric emissions also include volatile organiccompounds (VOCs) formed from volatile material in the coke breeze, oily mill scale, etc.,and dioxins and furans, formed from organic material under certain operating conditions.Metals are volatilized from the raw materials used, and acid vapours are formed from thehalides present in the raw materials.

Combustion gases are most often cleaned in electrostatic precipitators (ESPs), whichsignificantly reduce dust emissions but have minimal effect on the gaseous emissions.Water scrubbers, which are sometimes used for sinter plants, may have lower particulatecollection efficiency than ESPs but higher collection efficiency for gaseous emissions.Significant amounts of oil in the raw material feed may create explosive conditions in the

ESP. Sinter crushing and screening emissions are usually controlled by ESPs or fabricfilters. Wastewater discharges, including runoff from the materials storage areas, aretreated in a wastewater treatment plant that may also be used to treat blast furnacewastewater.

Solid wastes include refractories and sludge generated by the treatment of emission controlsystem water in cases where a wet emission control system is used. Undersize sinter isrecycled to the sinter strand.

2.1.2.Emissions of PCDD and PCDF

(William Lemmon and Associates Ltd. 2004, p. 2021)

The processes by which PCDD/PCDF are formed are complex. PCDD/PCDF appear to be formed

in the iron sintering process via de novo synthesis. PCDF generally dominate in the waste gas fromsinter plants.

The PCDD/PCDF formation mechanism appears to start in the upper regions of the sinter bedshortly after ignition, and then the dioxin/furan and other compounds condense on cooler burden

beneath as the sinter layer advances along the sinter strand towards the burn-through point. Theprocess of volatilization and condensation continues until the temperature of the cooler burdenbeneath rises sufficiently to prevent condensation and the PCDD/PCDF exit with the flue gas. Thisappears to increase rapidly and peak just before burn-through and then decrease rapidly to aminimum. This is supported by the dioxin/furan profile compared to the temperature profile alongthe sinter strand in several studies.

The quantity of PCDD and PCDF formed has been shown to increase with increasing carbon and

chlorine content. Carbon and chloride are present in some of the sinter feed materials typicallyprocessed through a sinter plant.

2.1.3.Research findings of interest

(William Lemmon and Associates Ltd. 2004)It appears that the composition of the feed mixture has an impact on the formation of PCDD/PCDF,i.e., increased chlorine content results in increased PCDD/PCDF formation while the replacementof coke as a fuel with anthracite coal appears to reduce PCDD/PCDF concentration.

The form of the solid fuel may also impact furan emissions. Coal, graphite, and activated coke in aJapanese laboratory research programme reduced pentachlorinated dibenzofuran emissions byapproximately 90%.

The operating parameters of the sintering process appear to have an impact on theformation of PCDD/PCDF. (William Lemmon and Associates Ltd. 2004)



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2.2. Releases to other media

No information was identified on releases of chemicals listed in Annex C from iron sinteringoperations to other media such as through waste water or collected dusts.

3. Alternatives

In accordance with the Stockholm Convention, when consideration is being given to proposals forconstruction of a new iron sintering plant, priority consideration should be given to alternative

processes, techniques or practices that have similar usefulness but avoid the formation and releaseof chemicals listed in Annex C. Adoption of alternative processes, techniques or practices canhave implications on other parts of the mill, careful assessment is needed on a case by case basis.

Alternative processes to iron sintering include:

The FASTMET process: This process converts iron oxide pellet feed, oxide fines, and/or

steel mill wastes into metallic iron, and produces a direct reduced iron product suitable foruse in a blast furnace. Emission concentration of PCDD and PCDF from the FASTMET

process is reported to be < 0.1 ng TEQ/m3.3

Direct reduction processes: This technique, also known as Direct Reduction Iron (DRI) or

Hot Briquetted Iron (HBI), processes iron ore to produce a direct reduced iron product thatcan be used as a feed material to steel-manufacturing electric arc furnaces, iron-making

blast furnaces, or steel-making basic oxygen furnaces. Natural gas is reformed to makehydrogen and carbon dioxide, where hydrogen is the reductant used to produce the directreduced iron. The availability and cost of natural gas will impact the feasibility of usingthis technique. Two new direct reduction processes for iron ore fines, Circored andCircofer are available. Both processes use a proven two-stage configuration, combining aCirculating Fluidized Bed (CFB) with a bubbling Fluidized Bed (FB). The Circored

process uses hydrogen as reductant. The first-of-its-kind Circored plant was built in

Trinidad for the production of 500,000 t/a of HBI and commissioned in 1999. In theCircofer process, coal is used as reductant. (Personal Communication, February 2006). Insome direct reduction process systems (eg. FASTMET), various carbon sources can beused as the reductant. Examples of carbon sources that may be used include: coal, coke

breeze and carbon bearing steeel mill wastes (blast furnace dust, sludge, BOF dust, millscale, EAF dust, sinter dust). This process converts iron oxide pellet feed, oxide fines,and/or steel mill wastes into metallic iron, and produces a direct reduced iron productsuitable for use in a blast furnace. Emission concentration of PCDD and PCDF from this

process is reported to be < 0.1 ng TEQ/m3.4

Direct smelting processes: Direct smelting replaces the traditional combination of sinter

plant, coke oven and blast furnace to produce molten iron. A number of direct smeltingprocesses are evolving and are at various stages of development and commercialization.

4. Primary and secondary measures

Primary and secondary measures for reducing emissions of PCDD and PCDF from iron sinteringprocesses are outlined below. Much of this material has been drawn from William Lemmon andAssociates Ltd. 2004.

3 1 ng (nanogram) = 1 10 -12 kilogram (1 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0

C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines.4 1 ng (nanogram) = 1 10 -12 kilogram (1 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured at 0

C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the present guidelines.



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The extent of emission reduction possible with implementation of primary measures only is notreadily known. It is therefore recommended that consideration be given to implementation of both

primary and secondary measures at existing plants.

4.1. Primary measures

Primary measures are understood to be pollution prevention measures that will prevent or minimizethe formation and release of chemicals listed in Annex C. These are sometimes referred to as

process optimization or integration measures. Pollution prevention is defined as: The use ofprocesses, practices, materials, products or energy that avoid or minimize the creation of

pollutants and waste, and reduce overall risk to human health or the environment (see sectionIII.B of the present guidelines).

Primary measures have been identified that may assist in preventing and minimizing the formationand release of chemicals listed in Annex C. Emission reductions associated with implementation ofthe following primary measures only is not known. It is recommended that the following measures

be implemented together with appropriate secondary measures to ensure the greatest minimizationand reduction of emissions possible. Identified primary measures include the following:

4.1.1.Stable and consistent operation of the sinter strandResearch has shown that PCDD/PCDF are formed in the sinter bed itself, probably just ahead ofthe flame front as the hot gases are drawn through the bed. Disruptions to flame front (i.e., non-steady-state conditions) have been shown to result in higher PCDD/PCDF emissions.

Sinter strands should be operated to maintain consistent and stable process conditions (i.e., steady-state operations, minimization of process upsets) in order to minimize the formation and release ofPCDD, PCDF and other pollutants. Operating conditions requiring consistent management includestrand speed, bed composition (consistent blending of revert materials, minimization of chlorideinput), bed height, use of additives (for example, addition of burnt lime may help reducePCDD/PCDF formation), minimization of oil content in mill scale, minimization of air in-leakagethrough the strand, ductwork and off-gas conditioning systems, and minimization of strand

stoppages. This approach will also result in beneficial operating performance improvements (forexample, productivity, sinter quality, energy efficiency) (European Commission 2000, p. 47; IPPC2001, p. 39).

4.1.2.Continuous parameter monitoring

A continuous parameter monitoring system should be employed to ensure optimum operation ofthe sinter strand and off-gas conditioning systems. Various parameters are measured duringemission testing to determine the correlation between the parameter value and the stack emissions.The identified parameters are then continuously monitored and compared to the optimum

parameter values. Variances in parameter values can be alarmed and corrective action taken tomaintain optimum operation of the sinter strand and emission control system.

Operating parameters to monitor may include damper settings, pressure drop, scrubber water flowrate, average opacity and strand speed.

Operators of iron sintering plants should prepare a site-specific monitoring plan for the continuousparameter monitoring system that addresses installation, performance, operation and maintenance,quality assurance and record keeping, and reporting procedures. Operators should keep recordsdocumenting conformance with the identified monitoring requirements and the operation andmaintenance plan (EPA 2003).

4.1.3.Recirculation of off-gases

Recycling of sinter off-gas (waste gas) has been shown to minimize pollutant emissions, andreduce the amount of off-gas requiring end-of-pipe treatment. Recirculation of part of the off-gasfrom the entire sinter strand, or sectional recirculation of off-gas, can minimize formation and

release of pollutants. For further information on this technique see ECSC 2003 and EuropeanCommission 2000, p. 5662.



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Recycling of iron sintering off-gases can reduce emissions of PCDD/PCDF, NOx and SO2.

4.1.4.Feed material selection

Unwanted substances should be minimized in the feed to the sinter strand. Unwanted substancesinclude persistent organic pollutants and other substances associated with the formation ofPCDD/PCDF, HCB and PCB (for example, chlorine/chlorides, carbon, precursors and oils).

A review of feed inputs should be conducted to determine their composition, structure, andconcentration of substances associated with persistent organic pollutants and their formation.Options to eliminate or reduce the unwanted substances in the feed material should be identified.For example:

Removal of the contaminant from the material (for example, de-oiling of mill

scales);

Substitution of the material (for example, replacement of coke breeze with

anthracite);

Avoidance of the use of the contaminated material (for example, avoid processing

electrostatic precipitator sinter dusts, which have been shown to increase PCDD/PCDFformation and release) (Kasai et al. 2001);

Specification of limits on permissible concentrations of unwanted substances (for

example, oil content in feed should be limited to less than 0.02%) (EPA 2003).

Documented procedures should be developed and implemented to carry out the appropriatechanges.

4.1.5.Feed material preparation

Fine feed materials (for example, collected dusts) should be adequatelyagglomerated before they are placed on the sinter strand and feed materials should

be intimately mixed or blended. These measures will minimize formation and

entrainment of pollutants in the waste gas, and will also minimize fugitiveemissions.

4.1.6.Urea injection

Tests using urea injection to suppress formation of dioxins and furans have been conducted at aniron sintering plant in the United Kingdom. Controlled quantities of urea prills were added to thesinter strand, and this technique is thought to prevent or reduce both PCDD/PCDF and sulphurdioxide emissions. The trials indicate that PCDD/PCDF formation was reduced by approximately50%. It is estimated that a 50% reduction in PCDD/PCDF would achieve a 0.5 ng TEQ/m 3emission concentration. Capital costs are estimated at UK0.5 to 1.0 million per plant(approximately US$0.9 million to $1.8 million) (Entec UK Ltd. 2003, p. D10D20).

At Canadas only sinter plant, operated by Stelco Inc. in Hamilton, Ontario, trials have beencompleted using a new similar process in order to reduce dioxins emissions. Stelco found thatsealing the furnace to reduce the amount of oxygen and adding a small amount of urea interferedwith the chemical reaction that produces dioxins, resulting in reduced emissions. This new processconfiguration, combined with air-scrubbing systems released 177 pg/m 3 of dioxins in a test. Thisresult surpasses the 2005 Canada-wide Standard limit of 500 pg/Rm 3 and is below the 200 pg/Rm3limit for 2010. It also represents a 93% reduction from the 1998 measured levels of 2700 pg/Rm3.The improvement clearly does not depend on scrubbing dioxins out of the stack gases, but isthought to result from "true pollution prevention", as chlorine is needed to produce dioxins and theurea releases ammonia, which captures chlorides in the dust, reducing its availability for dioxinformation. (The Hamilton Spectator, March 1, 2006)

4.2. Secondary measures



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Secondary measures are understood to be pollution control technologies or techniques, sometimesdescribed as end-of-pipe treatments.

Primary measures identified earlier should be implemented together with appropriate secondarymeasures to ensure the greatest minimization and reduction of emissions possible. Measures thathave been shown to effectively minimize and reduce PCDD and PCDF emissions include:

4.2.1.Removal techniques

4.2.1.1. Adsorption/absorption and high-efficiency dedusting

This technique involves sorption of PCDD/PCDF to a material such as activated carbon, togetherwith effective particulate matter (dedusting) control.

For regenerative activated carbon technology (William Lemmon and Associates Ltd. 2004) anelectrostatic precipitator is used to reduce dust concentration in the off-gases prior to entry to theactivated carbon unit. The waste gas passes through a slowly moving bed of char granules whichacts as a filter/adsorption medium. The used char is discharged and transferred to a regenerator,where it is heated to elevated temperatures. PCDD/PCDF adsorbed to the char are decomposed anddestroyed within the inert atmosphere of the regenerator. This technique has been shown to reduce

emissions to 0.1 to < 0.3 ng TEQ/m3.

Another sorption technique is the use of lignite or activated carbon injection, together with a fabricfilter. PCDD/PCDF are sorbed onto the injected material, and the material is collected in the fabricfilter. Along with good operation of the sinter strand, this technique is associated withPCDD/PCDF emission concentrations ranging from 0.1 to 0.5 ng TEQ/m3 (IPPC 2001, p. 135).

4.2.1.2. Fine wet scrubbing system

The Airfine scrubbing system, developed by Voest Alpine Industries (Austria), has been shown toeffectively reduce emission concentrations to 0.2 to 0.4 ng TEQ/m3. The scrubbing system uses acountercurrent flow of water against the rising waste gas to scrub out coarse particles and gaseouscomponents (for example, sulphur dioxide (SO2)), and to quench the waste gas. (An electrostatic

precipitator may also be used upstream for preliminary dedusting.) Caustic soda may be added toimprove SO2 absorption. A fine scrubber, the main feature of the system, follows, employing high-

pressure mist jet co-current with the gas flow to remove impurities. Dual flow nozzles eject waterand compressed air (creating microscopic droplets) to remove fine dust particles, PCDD and PCDF(William Lemmon and Associates Ltd. 2004, p. 2930; European Commission 2000, p. 7274).

This technique should be combined with effective treatment of the scrubber waste waters andwaste-water sludge should be disposed of in a secure landfill (European Commission 2000).

4.2.2.General measures

The following measures can assist in minimizing pollutant emissions, but should be combined withother measures (for example, adsorption/absorption, recirculation of off-gases) for effective controlof PCDD/PCDF formation and release.

4.2.2.1. DedustingRemovalofparticulate matter from the sinter off-gases

It has been suggested that effective removal of dust can help reduce emissions of PCDD andPCDF. Fine particles in the sinter off-gas have an extremely large surface area for adsorption andcondensation of gaseous pollutants, including PCDD and PCDF (Hofstadler et al. 2003). The bestavailable technique fordedustingremoval of particulate matteris the use of fabric filters to remove

particulate matter. Use of fFabric filters used atfor sinter plants areis associated with particulatematter emission concentrations of < 10 to < 30 mg/m3 (UNECE 1998; IPPC 2001, p. 131).

Other dedustingparticulate control options that are commonly used for sinter plant off-gasesinclude electrostatic precipitators and wet scrubbers, however their p. Particulate removalefficienciesyareis not as high as for fabric filters. Good performance of electrostatic precipitatorsand high-efficiency wet gas scrubbers is associated with particulate matter concentrations of < 30to 50 mg/m3 (IPPC 2001; William Lemmon and Associates Ltd. 2004, p. 26; UNECE 1998).



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Adequately sized capture and particulate emissiondedusting controls for both the feed anddischarge ends should be required and put in place.

4.2.2.2. Hooding of the sinter strand

Hooding of the sinter strand reduces fugitive emissions from the process, and enables use of other

techniques, such as waste gas recirculation.

5. Emerging research

5.1. Catalytic oxidation

Selective catalytic reduction has been used for controlling NO x emissions from a number ofindustrial processes, including iron sintering. Modified selective catalytic reduction technology(i.e., increased reactive area) and select catalytic processes have been shown to decompose PCDDand PCDF contained in off-gases, probably through catalytic oxidation reactions. This may beconsidered an emerging technique with potential for reducing emissions of persistent organic

pollutants from iron sintering plants and other applications.

A study investigating stack emissions from four sinter plants noted lower concentrations of

PCDD/PCDF (0.9952.06 ng TEQ/Nm3) in the stack gases of sinter plants with selective catalyticreduction than a sinter plant without (3.10 ng TEQ/Nm 3), and that the PCDD/PCDF degree ofchlorination was lower for plants with selective catalytic reduction. It was concluded that selectivecatalytic reduction did indeed decompose PCDD/PCDF, but would not necessarily be sufficient asa stand alone PCDD/PCDF destruction technology to meet stringent emission limits. Add-ontechniques (for example, activated carbon injection) may be required (Wang et al. 2003, p. 11231129).

Catalytic oxidation can, subject to catalyst selection, be subject to poisoning from trace metals andother exhaust gas contaminants. Validation work would be necessary before use of this process.Further study of the use of selective catalytic reduction and other catalytic oxidation techniques atiron sintering applications is needed to determine its value and effectiveness in destroying and

reducing PCDD/PCDF released from this source.

Urea injection

Tests using urea injection to suppress formation of dioxins and furans have been conducted at aniron sintering plant in the United Kingdom. Controlled quantities of urea prills were added to thesinter strand, and this technique is thought to prevent or reduce both PCDD/PCDF and sulphurdioxide emissions. The trials indicate that PCDD/PCDF formation was reduced by approximately50%. It is estimated that a 50% reduction in PCDD/PCDF would achieve a 0.5 ng TEQ/m 3

emission concentration. Capital costs are estimated at UK0.5 to 1.0 million per plant(approximately US$0.9 million to $1.8 million) (Entec UK Ltd. 2003, p. D10D20).

6. Summary of measures

Tables 1 and 2 present a summary of the measures discussed in previous sections.

Table 1. Alternatives and requirements for new iron sintering plants


Alternativeprocesses

Priority consideration shouldbe given to alternativeprocesses with potentially lessenvironmental impacts thantraditional iron sintering

Examples include:

Pelletisation

PlantsFASTMET

Direct reduction of iron

(FASTMETC,Circored and

Circofer) Direct smelting



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Performancerequirements

New iron sintering plantsshould be permitted toachieve stringent performanceand reporting requirements

associated with best availabletechniques

Consideration should begiven to the primary andsecondary measures listedin Table 2 below

Performance requirementsfor achievement shouldinclude:

< 0.2 ng TEQ/Rm3 for

PCDD/PCDF

< 20 mg/Rm3 for particulatematter

Table 2. Summary of primary and secondary measures for iron sintering plants


Primary measures

Stable andconsistent

operation of thesinter plant

The sinter strand should beoperated to maintain stable

consistent operatingconditions (e.g., steady-stateconditions, minimization of

process upsets) to minimizeformation of PCDD, PCDFand other pollutants

Conditions to optimizeoperation of the strand

include: Minimization of

stoppages

Consistent strand speed

Bed composition

Bed height

Additives (e.g., burnt

lime)

Minimization of oil

content

Minimization of air in-leakage

This approach will haveco-benefits such as

increased productivity,increased sinter qualityand improved energyefficiency

Continuousparametermonitoring

A continuous parametermonitoring system should beemployed to ensure optimumoperation of the sinter strandand off-gas conditioningsystems.

Operators should prepare asite-specific monitoring planfor the continuous parametermonitoring system and keep

records that documentconformance with the plan

Correlations betweenparameter values and stackemissions (stable operation)should be established.Parameters are thencontinuously monitored incomparison to optimumvalues. System can bealarmed and correctiveaction taken when

significant deviations occur

Recirculation ofwaste gases

Waste gases should berecycled back to the sinterstrand to minimize pollutantemissions and reduce theamount of off-gas requiringend-of-pipe treatment

Recirculation of the wastegases can entail recycling of

part of the off-gas from theentire sinter strand, orsectional recirculation of off-gas

This technique will resultin only a modestreduction ofPCDD/PCDF

Feed materialselection:Minimization of

feed materialscontaminated

A review of feed materials andidentification of alternativeinputs and/or procedures to

minimize unwanted inputsshould be conducted.

Examples include:

Removal of the

contaminant from the

material (e.g., de-oilingof mill scales)



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with persistentorganic

pollutants orleading to their

formation

Documented proceduresshould be developed andimplemented to carry out theappropriate changes

Substitution of the

material (e.g.,replacement of coke

breeze with anthracite)

Avoid use of the material

(e.g., collected sinterelectrostatic precipitatordust)

Specification of limits on

permissibleconcentrations ofunwanted substances(e.g., oil content in feedshould be limited to lessthan 0.02%)

Feed materialpreparation

Fine material (e.g., collecteddusts) should be agglomerated

before being placed on thesinter strand. Feed materialsshould be intimately mixed

before placement on the sinterstrand

These measures will helpreduce entrainment of

pollutants in the wastegas, and minimizefugitive emissions

Secondary measures

The following secondary measures can effectively reduce emissions of PCDD/PCDF and should beconsidered as examples of best available techniques

Adsorption/absorption andhigh-efficiencydedusting

Use of this technique shouldinclude an adsorption stagetogether with high-efficiency

particulate control as keycomponents of the off-gasconditioning system

Two adsorption techniqueshave been demonstrated:

Regenerative activated

carbon technologywhereby off-gases arefirst cleaned byelectrostatic precipitator,and passed throughmoving adsorption bed(char) to both adsorbPCDD/PCDF and tofilter particulates.Adsorptive material is

then regenerated Injection of activated

carbon, lignite or othersimilar adsorptivematerial into the gasstream followed byfabric filter dedusting

These techniques areassociated with thefollowing emissionconcentration levels:

< 0.3 ng TEQ/m3

0.1 to 0.5 ng TEQ/ m3

Fine wetscrubbing ofwaste gases

Use of this technique shouldinclude a preliminarycountercurrent wet scrubber to

quench gases and removelarger particles, followed by a

The fine wet scrubbingsystem under the tradename Airfine, as

developed by VoestAlpine Industries, has



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fine scrubber using highpressure mist jet co-currentwith off-gases to remove fine

particles and impurities

been shown to reduceemission concentrationsto 0.2 to 0.4 ng TEQ/m3

The following secondary measures should not be considered best available techniques on their own. Foreffective minimization and reduction of PCDD, PCDF and other persistent organic pollutants, the followingshould be employed in concert with other identified measures

DedustingRemoval of

particulatematter fromofwaste gases

Waste gases should betreateddedusted using high-efficiency techniques, as thiscan help minimizePCDD/PCDF emissions. Arecommended best availabletechnique forparticulatecontroldedusting is the use of

fabric filters.Feed and discharge ends of thesinter strand should beadequately hooded andcontrolled to capture andmitigatededust fugitiveemissions

Fabric filters have beenshown to reduce sinter off-gas particulate emissions to< 10 to < 30 mg/m3

Otherparticulate controldedusting techniquesused include electrostatic

precipitators and high-efficiency scrubbers.Good performance ofthese technologies isassociated with

particulate concentrationsof < 30 to 50 mg/m3

Hooding of thesinter strand

The sinter strand should behooded to minimize fugitive

process emissions

Hooding of the strandwill enable use of othermeasures, such as wastegas recirculation

7. Achievable performance levels

Achievable levels were identified for emissions of PCDD/PCDF only. No levels were identified forother chemicals listed in Annex C or for releases to other media.

The achievable performance levels for emissions of PCDD/PCDF from iron sintering plants areidentified in Table 3.

Table 3. Achievable performance for emissions of PCDD/PCDF

Source type Emission limit value5

New plants < 0.2 ng TEQ/Nm3

Adsorption/absorption and high-efficiency dedusting 0.1 to< 0.5 ng TEQ/Nm3

Fine wet scrubbing system 0.2 to < 0.4 ngTEQ/Nm3

References

5 1 ng (nanogram) = 1 10-12 kilogram (1 10-9 gram); Nm3 = normal cubic metre, dry gas volume measured

at 0 C and 101.3 kPa. For information on toxicity measurement see section I.C, paragraph 3 of the presentguidelines. The operating oxygen concentration conditions of exhaust gases are used for metallurgicalsources.



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EPA (United States Environmental Protection Agency). 2003.National Emission Standards forHazardous Air Pollutants: Integrated Iron and Steel Manufacturing: Final Rule. 40 CFR Part 63,Federal Register 68:97. EPA, Washington, D.C. www.epa.gov.

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(iii) Secondary aluminium production

1. Process description

Processes used in secondary aluminium smelting are dependent on feed material. Pre -treatment,furnace type and fluxes used will vary with each installation. Production processes involve scrap

pretreatment and smelting/refining. Pre-treatment methods include mechanical, pyrometallurgicaland hydrometallurgical cleaning. Smelting is conducted using reverberatory or rotary furnaces.Induction furnaces may also be used to smelt the cleaner aluminium feed materials.

Reverberatory furnaces consist of two sections: a smelting chamber heated by a heavy oil burnerand an open well where aluminium scraps of various sizes are supplied. Rotary furnaces consist ofa horizontal cylindrical shell mounted on rollers and lined with refractory material. The furnace isfired from one end usually using gas or oil as the fuel.

Feed consists of process scrap, used beverage cans, foils, extrusions, commercial scraps, turningsand old rolled or cast metal. Skimmings and salt slags from the secondary smelting process are alsorecycled as feed. Pre-sorting of scrap into desired alloy groups can reduce processing time. Scrap isoften contaminated with oil or coatings which must be removed to reduce emissions and improve

melting rate (European Commission 2001, p. 279).The following summary of the process is drawn from EPA 1994:

Most secondary aluminium recovery facilities use batch processing in smelting andrefining operations. The melting furnace is used to melt the scrap, and remove impuritiesand entrained gases. The molte