8.1 United States
In the United States the US EPA promulgates National Emission Standards for Hazardous Air Pollutants (NESHAP) for Source Categories through the Federal Register, which define the Maximum Achievable Control Technology (MACT) standard.
US National Emission Standards for Hazardous Air Pollutants for Secondary Aluminium Production, Final Rule (US EPA, 23 March 2000) MACT standard for PCDD and PCDF, for affected plants, is to upgrade or install a fabric filter or a lime-injected fabric filter (i.e. a fabric filter to which lime or other alkaline reagent is continuously injected). Alternatively, plants may be required to add a thermal incinerator or afterburner, a thermal incinerator and a lime-injected fabric filter, and/or apply pollution prevention techniques to limit the type of scrap charged and the type and amount of fluxing agents used. Many of these measures are designed to control pollutants other than PCDD and PCDF; for example, lime will help control acid gases such as HCl and SO2. Table 19 summarises the PCDD and PCDF emission limits specified in the standard.
Table 19: Secondary aluminium NESHAPs (US EPA, 23 March 2000)
Thermal chip drier (that is a major or area source)
2.5 µg TEQ per tonne feed
Scrap drier/de-lacquering kiln (that is a major or area source)
0.25 µg TEQ per tonne feed
Scrap drier/de-lacquering kiln (that is a major or area source) equipped with an afterburner with a 1-second residence time at 750°C
5.0 µg TEQ per tonne feed
Sweat furnace (used to reclaim aluminium from scrap containing iron)
Group 1 furnace (that is a major or area source)a
15 µg TEQ per tonne feed
a A Group 1 furnace means a furnace that melts, holds or processes aluminium that contains paint, lubricants or coating, or processes clean charge with reactive fluxing (gas, liquid or solid flux that results in a HAP emission).
US National Emission Standards for Hazardous Air Pollutants from Iron and Steel Foundries were proposed in December 2002 (US EPA, 23 December 2002), which include emission limits for metal and organic hazardous air pollutants (HAPs) and operating limits for capture systems and control devices. Carbon monoxide (CO) limits are set as a surrogate for organic HAPs from cupolas. NESHAPs are set for three furnace types: cupolas, electric induction and electric arc. The primary method for reducing organic HAP emissions from cupolas is identified as afterburning at about 700°C or higher. Emission test data suggested that well-controlled cupolas are well below the detection limit for current EPA methods. For existing and new sources, the MACT standard for organic HAP emissions is a CO emission limit of 200 parts per million by volume (ppmv). Organic HAP emissions from electric induction furnaces are not considered significant, and no MACT has been set, although scrap quality and pre-heaters are considered to be integral to induction furnace operation, and volatile organic compounds (VOC) have been used as a surrogate for organic HAP from scrap pre-heating. Afterburners are the MACT floor for existing and new scrap pre-heating and must achieve a 98% or greater reduction in VOC or 20 ppmv. The EPA believes this level of control to be achievable by afterburners and most scrap pre-heaters employing direct flame pre-heating. The MACT floor for organic HAPs from EAFs is the implementation of a scrap selection and inspection programme to minimise the organic impurities. This is because the organic HAP concentrations are already so low that no technically feasible control technologies could be identified.
MACT requirements for ferro-alloys were promulgated on 20 May 1999. [www.epa.state.oh.us/dapc/mact/frame1.html.]
Regulatory limits for new facilities in Japan (Nakamura, 2000) have been set for EAFs for steel scrap recycling and the manufacture of aluminium alloys. The limits are 0.5 ng-TEQ/Nm3 and 1.0 ng-TEQ/Nm3 respectively.
8.3 European Union
The European Commission (EC) promulgates guidance on best available techniques (BAT) for individual industry sectors through the Integrated Pollution and Prevention Control (IPPC) sector reference documents. The guidance is adopted into regulations and guidance documents through local jurisdictions within the European Union.
Key BAT considerations for secondary metals are: purchasing and inspecting scrap to avoid contaminated material; furnace design; suitable raw material pre-treatment and process controls, including blending raw materials; optimising temperature and optimising pressure and gas flow to control combustion. Operator training and the use of the correct feed material for the particular furnace or process are also considered to be important.
Techniques considered to be BAT for preventing and destroying PCDD and PCDF in the non-ferrous metals sector are (European Commission 2001a):
- correctly designed and operated afterburners and rapid quenching of the hot gases to less than 250°C to minimise de novo synthesis
- optimising combustion conditions using oxygen injection in the upper part of a furnace to ensure complete combustion of furnace gases
- activated carbon absorption in a fixed bed or moving bed reactor, or by injection into the gas stream and fabric filtration
- very high-efficiency dust removal, such as using ceramic filters, high-efficiency fabric filters,
- a catalytic oxidation stage, or fabric filters that incorporate a catalytic coating
- treatment of collected dusts in high-temperature furnaces to destroy dioxins and to recover metals.
Fume generation in all furnaces is required to be minimised by effective furnace control, although this alone is likely to give sufficient abatement to be considered to meet BAT for only copper or cupro-nickel alloys.
The emission concentrations associated with the above techniques range from <0.1 to 0.5 ng/Nm3 I-TEQ depending on the feed, the smelting or melting process, and the techniques or combination of techniques that are used for PCDD and PCDF removal.
An EC BAT document for smitheries and foundries is under development (European Commission, 2003). The proposed BAT in relation to PCDD and PCDF formation focuses on the primary and secondary controls. Primary measures to prevent PCDD and PCDF formation include:
- providing a secondary chamber, interlocked with the primary chamber such that the primary chamber cannot be used until the afterburner is up to temperature, and ensuring a residence time of 2 seconds with an oxygen level of >6%
- continuous temperature monitoring and control in the secondary chamber (T >850°C)
- maintaining the particulate matter concentration at a level <20 mg/m3
- providing quick quenching of the off-gases through the de novo synthesis range of 250-650°C
- preventing or minimising the build-up of dust along the cooling trajectory of the flue gas, especially in the heat exchanger (e.g. using vertical heat exchanger tubes, efficient internal cleaning, high-temperature de-dusting).
Abatement measures that may be considered are activated carbon injection with high-efficiency fabric filtration, and catalytic oxidation.
The EC BAT reference document for ferrous metal processing (European Commission, 2001a) addresses re-heating and heat treatment furnaces. It focuses on thermal efficiency and good combustion. It does not specifically address PCDD and PCDF emissions.
8.4 United Kingdom best practice
The UK Environment Agency also promulgates technical guidance documents for Integrated Pollution Control (IPC) and Local Authority Air Pollution Control, which are being revised to reflect the requirements of the IPPC directive.
Under the UK regulatory regime smaller, potentially less polluting processes are designated as Part B processes and control over air emissions is the responsibility of the local authorities. The relevant Local Authority Process Guidance Control (LAPC) Process Guidance Notes available from, which are used to assist in the development of legally binding plant-specific authorisations for the metallurgical industry, are currently being reviewed. These guidelines relate to Part B processes. Part A processes (i.e. larger operations) are dealt with on a case-by-case basis through the licensing process.
The following guidance notes relevant to this study are available from the Environment Agency's website (www.environment-agency.gov.uk). All are Draft Process Guidance Notes for Technical Working Group Consultation issued in December 2002, but are comprehensive in relation to PCDD and PCDF from small secondary-metal-processing operations.
- PG 2/1 Furnaces for the Extraction of Non-Ferrous Metal from Scrap (UK Environment Agency, 2002c) - covers the extraction of non-ferrous metals from scrap (i.e. refining operations to cleanse, reduce or remove unwanted materials); primarily covers recycling facilities physically treating mixed scrap.
- PG 2/3 Electrical, Crucible and Reverberatory Furnaces (UK Environment Agency, 2002b)- covers furnaces in which iron and steel or ferrous alloys are melted and refined, held or poured.
- PG 2/5 Hot and Cold Blast Cupolas and Rotary Furnaces (UK Environment Agency, 2002d)- covers furnaces in which iron and steel or ferrous alloys are melted and refined, held or poured.
- PG 2/6a Processes for Melting and Producing Aluminium and Aluminium Alloys (UK Environment Agency, 2002e)- covers aluminium foundries melting and producing aluminium and alloys from aluminium ingots or clean returned scrap with limited refining.
- PG 2/8 Copper and Copper Alloy Processes (UK Environment Agency, 2002a)- for melting and producing copper and its alloys with limited refining; covers the main alloys of copper including brass, bronze and gunmetal.
The BAT for secondary metal recovery from guidance note PG 2/1 are summarised in Table 20.
Table 20: BAT for non-ferrous metal recovery (PG 2/1)
Source of PCDD and PCDF
Substance contributing to formation
Charging the furnace
Products of incomplete combustion
Afterburner temperature should be maintained at > 850°C
Stack emissions from the furnace
Products of incomplete combustion and metal oxides
Use of afterburner and dry filtration plant to minimise emissions
Chloride and fluoride
Minimise flux use to the extent practicable; dry filtration plant where necessary to abate particulate matter
Under PG 2/1 (UK Environment Agency, 2002c), scrap metal facilities will be required to have an afterburner. The afterburner is to burn any products of incomplete combustion that may arise from the primary melter as a result of incorrect fuel-to-air ratios, overloading, or incorrect operating temperatures.
The general techniques to minimise PCDD and PCDF emissions identified in the guidance notes are feedstock control, good combustion and abatement of particulate matter. The specific requirements relating to PCDD and PCDF minimisation are as follows:
If feedstock, fluxes or fuel contains chloride or fluoride (e.g. engine oil, plastic, grease, synthetic materials, potassium aluminium fluoride)
1. Is secondary chamber (after burner) interlocked with primary chamber such that the primary chamber cannot be used until the after burner is up to temperature?
2. Is the temperature in the secondary chamber continuously monitored?
3. Is the temperature in the secondary chamber maintained at >850°C?
4. Is the secondary chamber designed to achieve a residence time of at least two seconds?
5. Is the secondary chamber designed to achieve an oxygen level within the combustion chamber of >6%?
6. Is there a continuous indicative monitor for particulate matter?
7. Is the particulate matter concentration maintained at less than 20 mg per cubic metre?
If the answer is NO to any of the above questions (1-7) then there is an annual monitoring requirement for dioxins and a limit of 1.0 ng/m3. [The reference conditions are specified as 273K, 101.3 kPa; the oxygen and water references should be those corresponding to the normal operating conditions of the process concerned.]
Furthermore, where gases from the secondary chamber are filtered or scrubbed prior to emission in order to achieve the emission limit for particulate matter of 20 mg/m3, then the gases should be cooled quickly (quick quench, within about two seconds) through the de novo synthesis zone of 650 to 250°C.
The Canadian Council of Ministers for the Environment (CCME, 2003) has promulgated a Canada-Wide Standard (CWS) for PCDD and PCDF for steel manufacturing in electric arc furnaces, which includes the recovery of steel resources (i.e. secondary metals processing as defined in this study).
The CWS applicable for new and existing furnaces is as follows: [Rm3 is the volume at 25°C, 101.3 kPa, dry gas basis and operating O2levels.]
New and modified furnaces
Dioxin and furans emissions shall be less than 100 pg ITEQ/Rm3 from any new or modified steel manufacturing EAF.
Phase 1 Dioxin and furans emissions shall be less than 150 pg ITEQ/Rm3 at all existing steel manufacturing EAFs by 2006.
Phase 2 Dioxin and furans emissions shall be less than 100 pg ITEQ/Rm3 at all existing steel manufacturing EAFs by 2010.