PAH Substance Report - draft1 - CIRCABC - Welcome · Web viewFor further detail the reader is...
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PAH Substance Report - draft1
Project contract no. 037038
SOCOPSE
Source Control of Priority Substances in Europe
Specific Targeted Research Project
Work Package 3 D.3.1
An Inventory and Assessment of Options for Reducing Emissions:
PAH
Second Draft
Due date of delivery: June 2008
Actual submission date: October 2008
Start date of project: 1st November 2006
Duration: 36 months
Lead partner for this deliverable: SOTON
Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006)
Dissemination Level
PU
Public
X
PP
Restricted to other programme participants (including the Commission Services)
RE
Restricted to a group specified by the consortium (including the Commission Services)
CO
Confidential, only for members of the consortium (including the Commission Services)
An Inventory and Assessment of Options for Reducing Emissions:
PAH
_____________
Draft 2
This report was prepared within Work Package 3 of project SOCOPSE.
Author:
Susanne Ullrich (5)
Contributors:
Jean-Marc Brignon (1), Lourens Feenstra (2), Willy van Tongeren (2), Ralph Lindeboom (3), Frank I.H.M. Oesterholt (3), Arnt Vlaardingerboek (3), Janusz Krupanek (4), Ursula Zielonka (4), Susanne Ullrich (5)
(1) Institut National de lEnvironment Industriel et des Risques (INERIS)
(2) Nederlands Organisatie Voor Toegepast Natuurwetenschappelijk Onderzoek (TNO)
(3) KIWA WATER RESEARCH B.V. (Kiwa WR)
(4) Institut Ekologii Terenw Uprzemysowionych (IETU/Envitech)
(5) University of Southampton, School of Civil Engineering & the Environment (SOTON)
Contents
3Contents
1.Executive summary1
2.Introduction1
3.General information2
3.1Presentation of the substance group2
3.2Classification and labelling3
3.3Regulations and controls for the substance group4
4.Production, uses and emissions8
4.1Production and uses8
a)Production8
b)Uses9
4.2Emissions10
a)Environmental fate10
b)Emission sources12
5.Options for reducing emissions: detailed information14
5.1Source control options14
a)Process-oriented options14
b)Emerging Technologies Source control27
5.2End-of-pipe options for the substance29
6.Options for reducing emissions: synthesis35
7.Conclusion40
8.Acknowledgements41
9.References42
1. Executive summary
[still to be completed]
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants formed mainly by the incomplete combustion of carbon-containing fuels such as wood, coal, diesel, and oil. Only anthracene and naphthalene are intentionally produced. PAHs are substances of high concern due to their toxicity and persistence in the environment.
Pollution by PAH is caused by . point sources. Emissions to water arise mainly from xxx, and to a lesser extent from xxxxx. Options for reducing emissions include source control and end-of-pipe options for water treatment. These abatement measures are presented below.
Table 1 shows possible emission abatement measures related to emission sources.
Table 1: Emission sources and possible emission abatement measures
Sources
Primary aluminium production
Production of carbon and graphite
Coke oven plants
Bitumen production / refineries
Waste incinerators
Power stations
Residential combustion appliances
Wood treatment plants
Waste water
Urban runoff
Sewage sludge
Measures
Source control
Use of pre-bake anodes
O
Use of inert anodes
O
Low PAH coal tar pitch blend
O
Improved transport and storage at wood impregnation plants
X
Process modification at wood impregnation plants
X
Use of wood preservation products with a lower PAH content
X
Alternative wood preserving techniques
O
Use of alternative construction materials
X
Combustion optimisation
X
X
Fuel replacement
X
End-of-pipe
Wastewater pre-treatment: Tar removal
X
Biological wastewater treatment
X
X
Gas-tight operation of the gas treatment plant
X
Wastewater pre-treatment: Sour water stripping (SWS)
X
Flue gas incineration
X
O
X
Wet flue gas scrubbing
X
X
X O
X
Dry flue gas scrubbing
X
X
X
X
Use of condensation and electrostatic precipitators
X
X
Biofilters
O
Ozonation and anaerobic digestion
O
Community level measures
X
Enhancing user awareness
Regulatory measures
Application of product standards
X
Ozone oxidation?
Activated carbon?
Nanofiltration?
Reverse osmosis?
Note: X = available measure; O = emerging measure;
Table 2 presents the evaluation of source abatement measures.
Table 2: Assessment of source abatement measures
Assessment
Remarks
Measure / source
Technical feasibility
Performance
Costs
State of the art
Source control
Use of pre-bake anodes
Total score: +
Total score: ++
Total score:
Total score: +
Applicable to new plants only.
Pol.: point source
Rge: wide
Eff.: high
IC: high
OC: ?
St.: BAT for primary aluminium plants
App.: numerous
Use of inert anodes
Total score: 0
Total score: ++
Total score: 0
Total score:
- Requires improvements in anode production processes and retrofit methods.
- Commercialisa-tion expected by 2010-2015.
Pol.: point source
Cmp.: medium / high
Eff.: up to 100%
Oth.: yes
En.: reduction
CE: reduction
W: no
IC: ?
OC: ?
St.: emerging technology
App.: ?
Low PAH coal tar pitch blend
Total score: +
Total score: +
Total score: +
Total score:
- Particularly suitable for use in Sderberg-type anodes for aluminium smelting.
- U.S. patent.
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: ?
Eff.: 40%
En.: no
CE: ?
W: no
IC: medium?
OC: low
St.: emerging technology
App.: ?
Improved transport and storage at wood impregnation sites
Total score: ++
Total score: +
Total score: ?
Total score: ++
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: none
Eff.: ?
En.: no
CE: ?
W: no
IC: ?
OC: ?
St.: BAT for wood treatment
Process modification at wood impregnation plants
Total score: +
Total score: +
Total score: ?
Total score: ++
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: ?
Eff.: high?
En.: yes
CE: ?
W: yes
IC: ?
OC: ?
St.: BAT for wood treatment
Use of wood preservation products with a lower PAH content
Total score: +
Total score: +
Total score: ++
Total score: +
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: ?
Eff.: ?
En.: no
CE: ?
W: no
IC: none
OC: low
St.: existing technology
App.: ?
Alternative wood preserving techniques
Total score: ?
Total score: ?
Total score: ?
Total score: ?
Techniques still under development?
Use of alternative construction materials
Total score: +
Total score: +
Total score: ?
Total score: ++
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: ?
Eff.: 100%
En.: ?
CE: yes
W: no
IC: ?
OC: ?
St.: existing technology
App.: ?
Combustion optimisation
Total score: ++
Total score: ++
Total score: ++
Total score: ++
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: none/low
Eff.: >50% to >90%
Oth.: yes
En.: no
W: no
IC: none/low
OC: none/low
St.: BAT
App.: yes
Fuel replacement
Total score: +
Total score: +
Total score: ++
Total score: +
Pol.: point source
Rge: wide
Cmp.: low
Imp.: low
Lim.: low
Eff.: ?
W: no
IC: none/low
OC: none/low
St.: existing technology
End-of-pipe
Wastewater pre-treatment: Tar removal
Total score: ++
Total score: ++
Total score: ?
Total score: ++
- Recommended for pre-treatment of coal water prior to biological wastewater treatment.
Pol.: point source
Cmp.: ?
Rge: wide
Lim.: low
Eff.: 99%
Oth.: ?
W: yes
IC: low?
OC: low?
St.: BAT for coke oven plants
App.: yes
Biological wastewater treatment
Total score: ++
Total score: ++
Total score: +
Total score: ++
Pol.: point source
Cmp.: ?
Rge: wide
Lim.: low
Eff.: high (>90%)
Oth.: yes
En.: yes
CE: no
W: yes
IC: medium
OC: medium
St.: BAT for coke oven plants
App.: yes
Gas-tight operation of the gas treatment plant
Total score: ++
Total score: ++
Total score: ?
Total score: ++
Pol.: point source
Cmp.: low
Rge: wide
Lim.: low
Eff.: high
Oth.: yes
En.: no
CE: no
W: no
IC: low?
OC: low?
St.: BAT for coke oven plants
App.: yes
Wastewater pre-treatment: Sour water stripping (SWS)
Total score: ++
Total score: +
Total score: ?
Total score: ++
- Recommended for pre-treatment of waste water from bitumen blowing.
Pol.: point source
Cmp.: low
Rge: wide
Lim.: low
Eff.: medium / high?
Oth.:
En.:
CE:
W:
IC: high?
OC: medium?
St.: BAT in bitumen blowing
App.: yes
Flue gas incineration
Total score: ++
Total score: ++
Total score: ?
Total score: ++
- A novel regenerative afterburner has been used in a number of applications.
Pol.: point source
Cmp.:
Rge: wide
Lim.:
Eff.: high (100%)
Oth.: yes
En.: yes
CE:
W: no
IC: ?
OC: ?
St.: BAT in bitumen blowing
App.: yes
Wet flue gas scrubbing
Total score: ++
Total score: +
Total score: ?
Total score: ++
- A novel oil scrubber could be employed at waste incinerators.
Pol.: point source
Cmp.:
Rge: wide
Lim.:
Eff.: medium/high
Oth.: yes
En.: yes
CE: yes
W: yes
IC: high?
OC: high?
St.: BAT in bitumen blowing
App.: yes
Dry flue gas scrubbing
Total score: ++
Total score: ++
Total score: +
Total score: ++
Pol.: point source
Cmp.:
Rge: wide
Lim.:
Eff.: high
Oth.: yes
En.: yes
CE:
W: yes
IC: low/medium
OC: low
St.: BAT for primary Al-smelters, power plants and incinerators
App.: yes
Use of condensation and electrostatic precipitators
Total score: +
Total score: ?
Total score: ?
Total score: +
Pol.: point source
Cmp.:
Rge:
Lim.:
Eff.: ?
Oth.: yes
En.: yes
CE: yes
W:
IC: ?
OC: ?
St.: existing technology
App.: yes
Biofilters
Total score: ?
Total score: +
Total score: ++
Total score:
- Potentially applicable to urban runoff.
Pol.: diffuse
Cmp.:
Rge:
Lim.:
Eff.: medium/ high
Oth.:
En.:
CE:
W:
IC: low
OC: low
St.: emerging technology
App.: no
Ozonation and anaerobic digestion
Total score: ?
Total score: +
Total score: ?
Total score:
- Potentially applicable as a pre-treatment for sewage sludge prior to its use on agricultural land.
Pol.: point source
Cmp.:
Rge:
Lim.:
Eff.: medium
Oth.: yes
En.:
CE:
W:
IC: ?
OC: ?
St.: emerging technology
App.: no
Community level measures
Enhancing user awareness
Total score: ++
Total score: +
Total score: +
Total score: 0
Pol.: point source
Cmp.: low
Rge: wide
Lim.: none
Eff.: 30-40%
IC: none/low
OC: low/medium
St.: n/a
App.: ?
Regulatory measures
Application of product standards
Total score: ++
Total score: ?
Total score: ?
Total score: ++
Pol.: point source
Cmp.: medium
Rge: wide
Eff.: ?
IC: ?
OC: ?
St.: yes
App.: ?
Scores (five levels): for very bad; for bad; 0 for average; + for good; ++ for very good;
Global assessment: green = all scores positive (good or very good); yellow = at least one moderate score (average) but no negative score (bad or very bad); red = at least one negative score (bad or very bad);
Sub-criteria (with possible values): Pol. = Type of pollution (point source, diffuse); Rge = Range of concentration (small, medium, wide); Lim. = Limits and restrictions (low, medium, high); Cmp. = Complexity of implementation (low, medium, high); Imp. = Impact on the process, on the factory (low, medium, high); Eff. = Efficiency of emission reduction (in %); Oth. = Removal of other pollutants (list of other pollutants removed); En. = Consumption of energy (no, low, medium, high); CE = Cross-effects (list of cross-effects); W = Production of waste (list of waste); IC = Investment costs (no, low, medium, high); OC = Operational costs (no, low, medium, high); St. = Status of the technique (BAT, existing, emerging); App. = Number of applications (none, some, numerous).
2. Introduction
The overall objective of this document is the inventory and assessment of technical options for reducing the water emissions of Polyaromatic Hydrocarbons (PAH) in Europe. Options include end-of-pipe techniques (e.g. waste water treatment) and process-integrated technical options (e.g. substitution or closed-circuit operation). The document aims to identify main uses and emission sources for PAH and to assess in terms of costs, effectiveness, and feasibility the technical means to abate emissions in water. It has been developed to give stakeholders a background material and an overview of possible reduction options at the European scale in the perspective of future emission reduction strategies to be developed.
The document is a result of the SOCOPSE project (Source Control of Priority Substances in Europe), a European research project funded by the EU 6th Framework Program for Research. The goal of this project is to support the implementation process of the EU Water Framework Directive (WFD) by providing guidelines and decision support system for the management of priority substances.
The scope of the document is the pollution in continental waters. It covers the most important sectors responsible for direct and indirect emissions, discharges and losses to the aquatic environment in Europe. Therefore, the control of pollution to air and land is out of the scope, and polluted air and land will be considered only as potential sources of pollution to water.
The document was prepared as follows. The identification of main uses and emission sources for PAH was achieved in a separate project task based on literature review and expert judgement. Here are reported the main conclusions.
As concerns the assessment of technical options, a literature review was conducted on both existing and emerging options to abate emissions to water. At the same time a survey was carried out with the main contributors to emissions to evaluate the options applied or considered in practice. Both information sources were compared and compiled in a first draft document which then was sent to stakeholders and debated during a one-day technical workshop. A second draft document included the workshop remarks. The final document takes into account the results of case studies conducted at the latter stages of the SOCOPSE project.
Survey questionnaire, list of contacted organisations and list of participants to workshop are attached in appendices.
The document plan is as follows. Section 3 gives general information on PAH. Section 4 presents results on main uses and emissions of the substance. Section 5 reviews the technical options to reduce emissions, with a synthesis in Section 6. Section 7 concludes the document, with acknowledgements in Section 8 and references in Section 9.
3. General information
3.1 Presentation of the substance group
Polyaromatic hydrocarbons (PAHs), also called Polycyclic Aromatic Hydrocarbons or Polynuclear Aromatic Hydrocarbons, are a group of organic chemicals comprising two or more fused benzene rings. They are ubiquitous environmental contaminants formed mainly by the incomplete combustion of carbon-containing fuels such as wood, coal, diesel, and oil. Only anthracene and naphthalene are intentionally produced. PAHs are substances of high concern due to their toxicity and persistence in the environment. Many PAHs and/or their metabolites are known or suspected carcinogens.
The physical and chemical properties of PAHs are largely determined by their size and the ring linkage pattern. Most are solid at room temperature and have relatively high melting and boiling points. They are relatively insoluble in water, but have good lipid solubility. The aqueous solubility and vapour pressure decreases with increasing molecular size. Table 3 gives the chemical identity of some environmentally significant PAHs that have been included on the EU priority list (see section 3.3). More detailed information on physical and chemical properties and toxicity data is given elsewhere [ref. 1, 2, 3 and others].
Table 3: Chemical identity of selected polyaromatic hydrocarbons
CAS1#
EINECS2#
Substance name
Short name
Formula
Structure
91-20-3
202-049-5
Naphthalene
C10H8
120-12-7
204-371-1
Anthracene
C14H10
206-44-0
205-912-4
Fluoranthene
C16H10
50-32-8
200-028-5
Benzo(a)pyrene
B(a)P
C20H12
205-99-2
205-911-9
Benzo(b)fluoranthene
B(b)F
C20H12
207-08-9
205-916-6
Benzo(k)fluoranthene
B(k)F
C20H12
191-24-2
205-883-8
Benzo(g,h,i)perylene
B(g,h,i)P
C22H12
193-39-5
205-893-2
Indeno(1,2,3-cd)pyrene
I(1,2,3-cd)P
C22H12
1CAS: Chemical Abstract Services. 2EINECS: European Inventory of Existing Commercial chemical Substances.
3.2 Classification and labelling
The European chemical Substances Information System ESIS [4] gives the classification for a number of substances belonging to the group of polyaromatic hydrocarbons, according to the criteria set up in the amended Annex VI of Directive 67/548/EEC on the classification, packaging and labelling of dangerous substances (last amendment: Directive 2001/59/EC) [5]. Table 4 shows the classification for the abovementioned PAHs, where available.
Table 4: Classification for selected polyaromatic hydrocarbons
PAH
Classification and Labelling
Naphthalene
Carc. Cat. 3; R40 Xn; R22 N; R50-53
Anthracene
This chemical substance is not classified in the Annex I of Directive 67/548/EEC.
Fluoranthene
This chemical substance is not classified in the Annex I of Directive 67/548/EEC.
Benzo(a)pyrene*
Carc. Cat. 2; R45 Muta Cat. 2; R46 Repr. Cat. 2; R60-61 R43 N; R50-53
Benzo(b)fluoranthene
Carc. Cat. 2; R45 N; R50-53
Benzo(k)fluoranthene
Carc. Cat. 2; R45 N; R50-53
Benzo(g,h,i)perylene
This chemical substance is not classified in the Annex I of Directive 67/548/EEC.
Indeno(1,2,3-cd)pyrene
This chemical substance is not classified in the Annex I of Directive 67/548/EEC.
*Classification codes dependent on specific concentration limits. Source: ESIS Status: August 2007
Table 5 gives the meaning of the indications of danger, the CMR (carcinogenic, mutagenic, and reproductive toxicity) classification, the risk phrases (R-phrases), and the safety phrases (S-phrases) applicable to the classified PAHs. IUCLID Chemical Data Sheets are available for naphthalene and anthracene, and for coal tar pitch which contains a mixture of PAHs [6].
Table 5: Toxicity, risk phrases and safety phrases applicable to the above PAHs
Classification/Labelling
Meaning
Xn;
Harmful
T;
Toxic
N;
Dangerous for the environment
Carcinogenic category 2
Substances which should be regarded as if they are carcinogenic to man.
There is sufficient evidence to provide a strong presumption that human exposure to a substance may result in the development of cancer, generally on the basis of:
- appropriate long-term animal studies,
- other relevant information.
Carcinogenic category 3
Substances which cause concern for man owing to possible carcinogenic effects but in respect of which the available information is not adequate for making a satisfactory assessment.
There is some evidence from appropriate animal studies, but this is insufficient to place the substance in category 2.
Mutagenic category 2
Substances which should be regarded as if they are mutagenic to man.
There is sufficient evidence to provide a strong presumption that human exposure to the substance may result in the development of heritable genetic damage, generally on the basis of appropriate animal studies or other relevant information.
Reprod. tox. category 2
Substances which should be regarded as if they impair fertility in humans.
There is sufficient evidence to provide a strong presumption that human exposure to the substance may result in impaired fertility on the basis of:
- clear evidence in animal studies of impaired fertility in the absence of toxic effects, or, evidence of impaired fertility occurring at around the same dose levels as other toxic effects but which is not a secondary non-specific consequence of the other toxic effects,
- other relevant information.
Substances which should be regarded as if they cause developmental toxicity to humans.
There is sufficient evidence to provide a strong presumption that human exposure to the substance may result in developmental toxicity, generally on the basis of:
- clear results in appropriate animal studies where effects have been observed in the absence of signs of marked maternal toxicity, or at around the same dose levels as other toxic effects but which are not a secondary non-specific consequence of the other toxic effects,
- other relevant information.
R22
Harmful if swallowed.
R40
Limited evidence of a carcinogenic effect.
R43
May cause sensitization by skin contact.
R45
May cause cancer.
R46
May cause heritable genetic damage.
R60
May impair fertility.
R61
May cause harm to the unborn child.
R50/53
Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment.
S2
Keep out of the reach of children.
S36/37
Wear suitable protective clothing and gloves.
S45
In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible).
S46
If swallowed, seek medical advice immediately and show this container or label.
S53
Avoid exposure obtain special instructions before use.
S60
This material and its container must be disposed of as hazardous waste.
S61
Avoid release to the environment. Refer to special instructions/Safety data sheets.
Note that several different reporting conventions are used for PAHs; information on these is given in the Annex. Benzo(a)pyrene is often used as a guideline substance to monitor emissions.
3.3 Regulations and controls for the substance group
Water Framework Directive
The Water Framework Directive (2000/60/EC), also called WFD, stipulates the adoption of specific measures against pollution of water by individual pollutants or groups of pollutants presenting a significant risk to or via the aquatic environment [7]. In accordance with Article 16 of the WFD, Decision No 2455/2001/EC established the first list of priority substances in the field of water policy [8]. The 2001 Decision identifies polyaromatic hydrocarbons (PAH) as priority hazardous substances (PHS) and lists five typical representatives as indicative parameters for this substance group (benzo-a-pyrene, benzo-b-fluoranthene, benzo-k-fluoranthene, benzo-g,h,i-perylene, and indeno(1,2,3-cd)pyrene). In addition, three other PAHs were identified as priority substances in their own right: naphthalene and anthracene were provisionally identified as priority substances (PS) subject to a review for their identification as possible priority hazardous substances (PHS), and fluoranthene was included on the list of priority substances as an indicator of other, more dangerous PAHs. Priority substances (PS) are subject to controls for the progressive reduction of discharges, emissions and losses, whilst priority hazardous substances (PHS) will be subject to cessation or phasing out of discharges, emissions and losses within 20 years.
Environmental Quality Standards
In July 2006, the European Commission adopted a proposal for a new Directive (COM(2006)397 final) setting environmental quality standards (EQS) for the priority substances which Member States must achieve by 2015 to ensure "good chemical surface water status" [9]. In addition to complying with the proposed surface water EQS, Member States shall also ensure that concentrations of priority pollutants do not increase in sediments and biota. The proposed surface water EQS for PAHs are given in Table 6.
In its communication COM(2006) 397 final, the Commission also reviewed the status of the provisionally classified priority substances and identified anthracene as a priority hazardous substance (PHS). The proposal as amended by Parliament at its First Reading in May 2007 subsequently also identified naphthalene as a PHS [10]. The European Parliament and Council have recently adopted the proposal for Directive.
Table 6: Environmental quality standards (EQS) for PAH included in the EU priority list
Substance
AA-EQS
MAC-EQS
Inland surface waters
Other surface waters
Inland surface waters
Other surface waters
Naphthalene
2.4
1.2
not applicable
not applicable
Anthracene
0.1
0.1
0.4
0.4
Fluoranthene
0.1
0.1
1
1
Benzo(a)pyrene
0.05
0.05
0.1
0.1
Benzo(b)fluoranthene
=0.03
=0.03
not applicable
not applicable
Benzo(k)fluoranthene
Benzo(g,h,i)perylene
=0.002
=0.002
not applicable
not applicable
Indeno(1,2,3-cd)pyrene
Notes:AA = annual average; MAC = maximum allowable concentration; Unit = g/L
Where the MAC-EQS are marked as non-applicable, the AA-EQS values are also protective against short-term pollution peaks
since they are significantly lower than the values derived on the basis of acute toxicity.
For the PAH considered as a group of priority substances (i.e. the first five in the above list), each individual EQS shall be complied with, i.e., the EQS for Benzo(a)pyrene and the EQS for the sum of Benzo(b)fluoranthene and Benzo(k)fluoranthene and the EQS for the sum of Benzo(g,h,i)perylene and Indeno(1,2,3-cd)pyrene must be met.
Drinking water quality
The EU Drinking Water Directive (98/83/EC) sets the following limit values for PAHs: 0.010 g/L for B(a)P, and 0.10 g/L for the sum of concentrations of B(b)F, B(k)F, B(g,h,i)P, and I(1,2,3-cd)P [11]. Note that the limit value of 0.010 g/L for B(a)P is considerably stricter than the WHO guideline value of 0.7 g/L B(a)P for drinking water [12].
International Agreements
Several international agreements identify PAHs as substances of concern. The 1998 Aarhus Protocol on Persistent Organic Pollutants (POPs) under the UNECE Convention on Long-Range Transboundary Air Pollution calls for emission reductions of PAH (as indicated by the four species B(a)P, B(b)F, B(k)F, and I(1,2,3-cd)P) to below 1990 levels, or to levels of an alternative year between 1985 and 1995 [13]. PAH are also on the HELCOM Priority List [14], and (with the exception of naphthalene) on the OSPAR List of Chemicals for Priority Action, set out in Annex 2 of the Strategy with regard to Hazardous Substances [15]. Regulation (EC) No 850/2004 on POPs translates the Aarhus Protocol under the UNECE Convention into Community law [16].
In contrast to the EU, the USEPA regulates a group of 16 PAHs. Apart from the eight PAHs on the WFD list, the USEPA list also contains the following eight compounds: Benzo(a)anthracene, Dibenzo(a,h)anthracene, Chrysene, Phenanthrene, Fluorene, Pyrene, Acenaphthene, and Acenaphthylene. The pending EU Risk Assessment Report (EU-RAR) on high-temperature coal tar pitch (CAS# 65996-93-2) will consider toxicity data for all 16 homocyclic EPA PAHs, and possibly also some heterocyclic PAHs [1].
Marketing restrictions
Directive 2001/90/EC places restrictions on the marketing and use of substances and preparations containing creosote, creosote oil, coal tar distillates, anthracene oil, tar acids, and low temperature tar oil [17]. These substances may not be used in the treatment of wood, and wood so treated may not be placed on the market. However, exceptions apply to industrial installations and professional in situ re-treatment (provided that the B(a)P content is less than 0.005% by mass), and to old previously treated wood that is placed on the market for re-use.
Directive 2005/69/EC places restrictions on the marketing and use of PAH-rich extender oils and blends used for the production of tyres [18]. According to the Directive, extender oils may not be placed on the market and used for the production of tyres if they contain more than 1 mg/kg B(a)P, or more than 10 mg/kg of the sum of all listed PAHs. Furthermore, tyres and treads for retreading manufactured after 1 January 2010 may not be placed on the market if they contain extender oils exceeding these limits.
Anthracene oil was withdrawn from use as a pesticide with effect from 25 July 2003 by Commission Regulation (EC) No 2076/2002 under Directive 91/414/EEC [19]. The use of anthracene oil and coal tar in cosmetic products was prohibited by Directive 76/768/EC and 97/45/EC, respectively [20].
Cleaner fuels
Under the EU Auto-Oil programme (Auto-Oil I and II), tighter specifications were agreed for automotive fuels to reduce greenhouse gases and other pollutants. From 2000, the maximum content of polyaromatic hydrocarbons in diesel was limited to 11% by weight. A recent proposal for a revised Directive on fuel specifications [21] stipulates, amongst other things, that from 1 January 2009 the limit for polycyclic aromatic hydrocarbons in diesel be further reduced from 11% to 8%.
Air Quality
The fourth Air Quality Daughter Directive (2004/107/EC) uses Benzo(a)pyrene as a marker for the carcinogenic risk of PAHs and establishes a target value of 1.0 ng/m3 for B(a)P in ambient air [22]. The target value should not be exceeded in Member States after 31 December 2012. Other PAHs, including as a minimum Benzo(a)anthracene, Benzo(b)fluoranthene, Benzo(j)fluoranthene, Benzo(k)fluoranthene, Indeno(1,2,3-cd)pyrene, and Dibenz(a,h)anthracene, should also be monitored at a limited number of sites.
The European Committee for Standardization (CEN) issued voluntary emission standards for solid fuel residential combustion appliances (stoves, cookers, boilers, open fire places, and insert appliances EN 12809, 12815, 13229, 13240) in 2001 which may also contribute to reducing PAH emissions to air [23].
Integrated Pollution Prevention and Control
The Directive on Integrated Pollution Prevention and Control (IPPC Directive 96/61/EC) controls emissions and discharges of priority substances to the aquatic environment, including emissions to air of pollutants that may reach the aquatic environment through deposition [24]. The deadline for the full implementation of the Directive was 30 October 2007, from which date both new and existing installations must comply with "best available techniques" (BAT). Until now, best available techniques specifically for PAHs are rarely described. There are however many techniques that reduce PAH emissions concurrently with other pollutants.
4. Production, uses and emissions
4.1 Production and uses
a) Production
Naphthalene
Naphthalene is obtained by crystallisation from naphthalene oils. There are two sources for the manufacture of naphthalene in the EU. These are coal tar (which accounts for the majority of production) and petroleum. The total annual production of naphthalene in the EU has been estimated to be in the order of 200,000 tonnes/a, including 20,000 tonnes/a of naphthalene oil being at least 90% pure, and excluding lower grade naphthalene which has a separate CAS number [25]. Companies producing naphthalene are located on 17 sites in the UK, Belgium, France, Italy, Netherlands, Denmark, Germany, Austria and Spain [6]. Production figures from individual producers range from 4,000 to 70,000 tonnes/a [25].
Anthracene
Anthracene is produced from light anthracene oil by crystallisation and distillation. Anthracene oil is a semisolid, greenish brown crystalline material and is obtained in two fractions from the primary distillation of coal tars. The lower-boiling fraction (light anthracene oil) has a high content of phenanthrene, anthracene and carbazole. The higher-boiling fraction (heavy anthracene oil) has a high content of fluoranthene and pyrene. Light anthracene oil, the starting material for the production of pure anthracene, makes up about 20% of coal tar and usually has an anthracene content of 6-7% [20].
There is only one European manufacturer of anthracene, operating in Germany. In recent years the production of pure anthracene is thought to have dropped to around 1,000 tonnes/a. Approximately 99% of the 1999 production was exported to outside the EU. No importation of anthracene into the EU appears to take place [20].
Products containing anthracene and other PAHs as part of complex mixtures are coal tar and coal-tar containing products (paints, waterproof membranes, etc), and creosote. Coal tars and creosote contain mainly volatile, but also heavier PAHs.
- Coal tars are by-products of the destructive distillation of coal, also called carbonisation or coking. They are complex mixtures of hydrocarbons, phenols and heterocyclic compounds. Two main classes of coal tars are distinguished, depending on the temperature of carbonisation. The anthracene content of high-temperature coal tars is about 1.5%, whereas low-temperature coal tars contain only negligible amounts. Coal tar distillation is conducted at 10 distillation plants in Europe (on each in Germany, Belgium, France, the Netherlands, Italy, Denmark, and two each in the UK and Spain). The amounts of coal tar produced and distilled in the EU during 1997-1999 were about 1 million and 1.8 million tonnes [20].
- Creosote is made up of a blend of several coal-tar distillation fractions. It is a dark oily liquid of variable composition, containing about 160-200 compounds of which only about 30 have so far been identified. PAHs (including anthracene, naphthalene and phenanthrene derivatives) generally account for 75-85% of creosote. In the EU, creosote is manufactured according to grades specified by the West European Institute for Wood Preservation (WEI). The maximum B(a)P content of WEI Grade A creosote is 500 ppm and that of WEI Grades B and C 50 ppm. Anthracene concentrations in creosote lie at a maximum of 1.5% [20].
Other PAHs
There is no known commercial production of benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(g,h,i)perylene, indeno(1,2,3-cd)pyrene, or fluoranthene.
b) Uses
Naphthalene
Naphthalene is largely manufactured for use as a chemical intermediate (eg. phthalic anhydride), which accounts for approx. 70% of its use [26]. It is used in the manufacture of a wide range of products, including dyestuffs, alpha and beta-naphthols, tetralin, decalin, chlorinated naphthalenes, naphthalene sulphonates, phenol, propylene oxide, superplasticisers for concrete additives, non-agricultural pesticides, celluloids, solvents, lubricants, cutting fluids, synthetic tanning products, wood preservatives (eg. creosote), emulsion breakers, asphalt, detergents, resins, antiseptics, air fresheners and lacquers [27]. The use of naphthalene as a moth repellent and insecticide has decreased since the introduction of chlorinated compounds such as p-dichlorobenzene [26]. Figures for the amount of naphthalene used within the EU vary, but have been estimated at approximately 140,000 tonnes/a, with the remaining tonnage being exported [25]. Table 7 shows some typical use categories for naphthalene and approximate annual tonnages.
Table 7: Principal uses of naphthalene in Europe
Process
Approximate annual tonnage
Phthalic anhydride production
40,000
Manufacture of dyestuffs
46,000
Naphthalene sulphonic acid manufacture
24,000
Alkylated naphthalene solvent production
15,000
2-naphthol production
12,000
Pyrotechnics manufacture
15
Mothballs manufacture
1,000
Grinding wheels manufacture
350
Source: [25]
Anthracene
Until recently, the main uses of anthracene which could give rise to releases were two specific types of chemical synthesis (production of anthraquinone and anthracene-9-aldehyde). These processes have now ceased and the only known remaining uses of anthracene in the EU relate to the production of carbon black and to the use of small amounts of anthracene in the manufacture of pyrotechnics (approx. 0.2 tonnes/a) and in scientific research laboratories [20]. Therefore, practically all consumption of anthracene in the EU, which until recently was carried out by two main industrial users, has now stopped and almost all anthracene produced in Europe is exported [20].
Uses of products containing anthracene and/or other PAHs
- Creosote is used almost exclusively in wood impregnation. Recent estimates put the amount of creosote used in the EU at approximately 107,000 tonnes/a [20]. There are 9 bulk wood impregnation plants in the EU. The marketing and use of creosote in the EU are strictly regulated by Directive 2001/90/EC (see section 3.3).
- Coal-tar containing products: Coal tar and its distillates are used in some specialist paints, damp-proofing materials, waterproof membranes, coal tar epoxy paints and coal tar polyurethane sealers [20]. Tar paints are no longer used in Germany, and Scandinavian countries are moving away from them. Coal tar paints usually contain 0.5% anthracene, while the anthracene content of other products seems to be below 0.5%. No information on the number of plants or the production volumes of these products in Europe is available [20]. Historic uses of anthracene oil and coal tar in cosmetics are now prohibited [20].
Petroleum pitch and coal-tar pitch are used as a binder material in the production of carbon and graphite. Coke or carbon is usually bound with pitch (14-18% by weight) to produce a green paste which then undergoes a number of shaping, baking, impregnation and graphitising stages to produce the final product [28]. Green paste is also used directly for Sderberg electrodes or paste. Table 8 gives annual production figures for various carbon and graphite products in Europe. The aluminium industry is the largest user of pre-bake anodes, Sderberg paste and cathode blocks [28].
Table 8: Annual production of carbon and graphite in the EU and Norway
Product type
Production (t/a)
Green mix for Sderberg electrodes or paste
410 000
Anodes for primary Al
1380 000
Electrodes
420 000
Specialty carbon and graphite
25 000
Source: [28]
There is no known commercial use of benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(g,h,i)perylene, indeno(1,2,3-cd)pyrene, and fluoranthene.
4.2 Emissions
a) Environmental fate
PAHs are regarded as semi-volatile organic substances. They tend to have low vapour pressures and are usually adsorbed onto particulate matter in the atmosphere. Lower molecular weight PAHs (1,400 - 4,500
high
high
B(b)F
very low
low
significant
no data
high
high
B(k)F
very low
insignificant
strong
no data
high
high
B(g,h,i)P
very low
insignificant
strong
no data
high
high
I(1,2,3-cd)P
very low
insignificant
strong
no data
no data
high
*Adapted from data presented in [26].
With the exception of naphthalene which is of moderately high toxicity, PAHs appear to be highly toxic to aquatic organisms. Many PAH compounds are more toxic in the presence of UV light (photo-induced toxicity) [26].
Aquatic organisms may accumulate PAHs from water, sediments and food. The potential for bioaccumulation appears to increase with increasing number of rings in the PAH molecule. High octanol-water partition coefficients suggest a high bioaccumulation potential. However, most PAHs are also readily adsorbed to solids and dissolved humic matter, which may reduce bioavailability and hence bioaccumulation. The ultimate sink for PAHs in aquatic systems will generally be sediments, but sediment incorporation does not appear to be an important fate process for naphthalene [26].
b) Emission sources
Releases of PAHs to the environment occur from a multitude of point and diffuse sources. Major sources of PAH emissions include fossil fuel combustion in residential and industrial units, road transport (mainly petrol but also diesel engines), wood burning, and a variety of industrial processes (e.g. coke ovens, coal tar distillation, aluminium production, iron and steel production, anode baking, wood impregnation). Other sources include accidental discharges during the use, transport and disposal of petroleum products, waste incineration and disposal, run-off from roads, and natural sources such as forest fires and geothermal activity. For those PAHs which are manufactured intentionally, there may also be inputs associated with their production, storage and use [26]. Table 10 presents the main emission sources of PAHs to air, land, and water, including for water the direct and indirect routes.
As the vast majority of PAH emissions occur initially to air, atmospheric deposition is a significant pathway of soil and surface water contamination. Direct contamination of the aquatic environment is most frequently associated with discharges from the chemical and petroleum industries and accidental spillages or leakages of petroleum products to land or water [27]. Small amounts of PAHs may be released to soils and surface water from wood products treated with creosote.
Run-off from industrially contaminated sites can be a source of secondary surface water pollution by PAH. Industrially contaminated sites may include e.g. coal gasification and coking plants, gasworks, waste dumps, coal tar refineries, pine tar factories, and wood treatment plants [27]. Groundwater contamination may also occur, for example as a result of seepage from underground petrol storage facilities, from uncontrolled landfill leachates, and from disused industrial sites such as coal gasification plants [27].
Since atmospheric deposition is a significant pathway of surface water contamination by PAH, the management options discussed in the following section will also include some information on how atmospheric emissions of PAH from selected industrial sectors could be curbed, as well as information on wastewater treatment techniques.
Table 10: PAH emissions to air, land and water *
Medium
Sources
Importance1
Air2
Combustion of fuels (39.9%):
- Residential plants (28.01%)
- coal combustion in residential units
- Energy Industries (1.18%)
- coal combustion in utility boilers (power plants)
- coal combustion central heating plants
- residual oil combustion
- Industry (6%)
- Primary (smelters) non-ferrous metal production (2.9%)
- Other (plaster and other furnaces, cement, lime, glass, mineral wool, bricks and tiles) (1.19 %)
- coal combustion in industrial boilers and technological processes,
Agriculture/Forestry/Fishing (2.27%)
39.9
Road transport and other mobile sources and machinery
15.9
Metal production (13.83%) and coke production (2.1%):
- cast iron and steel processes
- aluminium production
- electric steel production
- graphite electrode production
15.93
Major uses of PAH:
- various applications
11.72
Various industries:
- cement production
- petrochemical and related industries
- bitumen and asphalt industries
- rubber tyre manufacturing
- creosote and wood preservatives
10.9
Waste disposal incineration:
- incineration of municipal / hazardous / hospital wastes
2.9
Agriculture
- field burning of agricultural wastes
1.54
Land3
Disposal of wastes from various manufacturing processes except food
30
Agricultural wastes
20
Mining and quarrying wastes
10
Disposal of fly ash & bottom ash from power plants and waste incineration
10
Land-filling of urban refuse and municipal sewage sludge
10
Municipal sewage sludge agricultural application
5
Atmospheric deposition to terrestrial ecosystems (IETU estimate 3000 t/a)
significant
Water4
Combustion of fossil fuels - Power plants and industrial
35
Metal industry
35
Mineral oil and gas refineries
12
Plants for pre-treatment of fibres or textiles
13
Basic organic chemicals
2
Municipal Wastewater treatment plants
low
Major uses of PAHs - creosote
low
Sediment re-suspension
significant
Erosion
significant
Atmospheric deposition to European seas and surface waters
(IETU estimate 400 t PAH in Europe in 20035)
significant
1 Percent of total Hg emissions to medium (air/land/water) in Europe.
2 Atmospheric emissions 2500 Mg in Europe in 2003 (based on EMEP data).
For B(a)P, B(b)F, B(k)F and I(1,2,3-cd)P the sector split (15 countries in Europe in 2003) is as follows: Residential 58%, metal production 17% Public electricity and heat production 3%, Manufacturing industries and construction 5%, Road transportation 5% and other 11%.
3 Engineering guess IETU team 3000 Mg/annum.
4 Around 40 t/a for IPPC installations (based on EPER data, excluding atmospheric deposition).
5 Calculated only for surface water areas and potentially impacted sea areas (BaP: 30 t; sum of BaP, B(k)F, B(b)F, and I(1,2,3-cd)P: 80 t).
______________________________________
* Data from SOCOPSE WP2
Figure 1. MFA diagram for 5 PAHs (Benzo(a)pyrene, Benzo(k)fluoranthene, Benzo(b)fluoranthene, Indeno(1,2,3-cd)pyrene, and Benzo(a)pyrene) in Europe at the beginning of the 2000s (numbers in tonnes/year)
5. Options for reducing emissions: detailed information
5.1 Source control options
a) Process-oriented options
Techniques for air pollution control are too numerous to be listed. Only the main ones are mentioned. For further detail the reader is referred to the relevant BAT Reference Documents (BREFs).
(i) Controlling emissions from primary aluminium production and the production of carbon and graphite
Description of the phenomenon
Primary aluminium production
At primary aluminium plants of the Sderberg type, tar and PAHs are emitted during the electrolysis due to the self-baking anode. Emissions occur by evaporation from the carbonisation of the paste. Stud pulling is the operation giving rise to the most significant emissions. The magnitude of emissions depends on the anode design, the quality of the paste, and operating practises [28]. Estimated B(a)P emissions to air from primary aluminium smelters are 5 20 g/t Al for plants operating by the Sderberg process. Emissions of PAH (Boneff 6) to water from primary aluminium electrolysis plants are estimated at 0 0.01 g/t Al for Pre-baked and 8 15 g/t Al for Sderberg plants [28].
Production of carbon and graphite
Paste for anodes, other electrodes and most special carbon products are produced from petroleum coke and coal tar pitch [28]. Coal tar pitch contains PAHs, which will be released during carbonisation in the baking furnaces. Emissions to air also occur during the storage of pitch, during mixing and shaping, and during impregnation. Total uncontrolled emissions of PAHs by anode baking can be as much as 0.432 kg per tonne anode [28].
Water pollution is generally a minor issue in the carbon industry as the production processes are dry and contained cooling water systems are generally used. Surface water is used for cooling only in exceptional circumstances. Where wet electrostatic precipitators (wet EPs) are used to remove hydrocarbons (and PAHs) from furnace exhaust gases, this is a potential source of contaminated wastewater [28].
The production of anodes is an integral part of the production process at some primary aluminium plants [28]. The raw gas content of PAH from anode production in a plant associated with a primary aluminium smelter is estimated at 0.15 0.5 kg/tonne aluminium [28].
Mitigation measures
The BAT reference document for the non-ferrous metals industries [28] makes a number of recommendations how emissions from primary aluminium production can be mitigated. For Sderberg cells, complete hood coverage of the anode top, which is connected to a separate gas exhaust and dry alumina scrubber, is recommended. Alternatively, a dry anode top in combination with stud hole paste and an increase in the anode height may be used, depending on the effectiveness that is demonstrated. Burners for incineration of CO and low molecular weight PAHs and other hydrocarbons in pot exhaust gases should be well-designed and maintained. If a wet scrubber is used for sulphur removal, this should be used together with a system to remove fluoride, HF and tars. For combined anode plants, the use of an alumina scrubber and fabric filter system or carbon coated filters to remove tar fumes from the milling, blending and baking stages is recommended.
Consideration should also be given to automatic multiple point feeding of the alumina, the collection and treatment of ventilation gases, minimisation of the time for changing anodes and other actions that need cell covers to be removed, butt cooling in an enclosure, and the use of a computer-controlled system for cell operations and maintenance [28].
Table 11: Abatement options for PAH from primary aluminium plants
Measure
Description
Alumina scrubber
Emissions from the electrolysis and process gases from the anode plant should be treated by an alumina scrubber and fabric filter system. Ventilation gases can also be treated.
Wet scrubber
Primarily used for SOx removal. Also removes fluorides, tars, PAHs, and other pollutants.
Low NOx burners/ Oxy-fuel firing
The firing of the furnace should be optimised to reduce PAH and NOx emissions.
Afterburner
Used to destroy cyanides, tars and PAHs if these are not removed by other abatement.
For new smelters, using the pre-bake technology rather than the traditional Sderberg technology would lead to a significant reduction in emissions. PAH emissions from the electrolysis in pre-bake plants are negligible, since the anodes are baked in a separate operation. (Note, however, that installations including an anode production plant will have a source of tars and PAHs from this part of the process). Very small amounts of tar and PAHs may be emitted from a limited number of pre-bake plants using carbon paste for anode pin connection and protection collars [28].
Priority should also be given to the development of alternative processes having less environmental impacts than traditional primary aluminium production plants, such as for example the use of inert anodes (section x).
In the production of carbon and graphite, the most significant emissions arise from anode baking. A number of measures can be taken to reduce emissions. Treatment methods for gaseous components containing tars and PAHs include gas collection, condensation and electrostatic precipitator (EP), afterburner, alumina scrubber and fabric or carbon filters (Table 12). Wet scrubbers may be employed for SO2 removal. In modern plants, emissions from mixing and baking are cleaned e.g. in condensing systems followed by dry scrubbing systems using alumina in a plant associated with a primary aluminium smelter, or coke/lime where the hydrocarbons and PAH are returned to the production process. Alternatively, afterburners and wet EPs can be used depending on the site and scale of production. A variety of novel afterburning systems have been developed to destroy tars and PAHs [28].
Table 12: Abatement options for PAH from the production of carbon and graphite
Process stage
Component in off-gas
Treatment method
Materials handling and storage
Dust, hydrocarbons and PAH (potentially significant)
Prevention, Cooler, Afterburner
Mixing and forming
Dust, hydrocarbons and PAH
(handling dried material)
Afterburner, Coke filter
Anode baking
Dust, SO2, hydrocarbons and PAH.
(EP can be used to remove condensable materials)
Afterburner.
Cooler, lime/carbon adsorption and fabric filter.
Alumina scrubber and fabric filter if integrated with primary aluminium smelter.
Baking or re-baking of other electrodes
Dust, SO2, hydrocarbons and PAH.
(EP can be used to remove condensable materials)
Cooler and coated filter.
Afterburner (and fabric filter).
Impregnation
Hydrocarbons and PAH, odours, organic solvents, metal fume.
Afterburner.
Gas collection and filter.
Source: [28]
Fume collection systems should exploit furnace or reactor sealing systems and operate under reduced pressure to avoid leaks and fugitive emissions [28].
Technical feasibility
Both the dry alumina scrubber and wet scrubbers are well-established techniques that are used at many primary aluminium plants to abate the emissions caused by the electrolysis. Emissions from the production of green anodes and anode baking can be reduced by dry adsorption combined with dust removal. Some novel regenerative afterburners are still under development [28].
Dry adsorption combined with dust removal
The technique is used to absorb acid gases and adsorb metallic or organic components on the surface of a dry particulate medium. PAHs (as well as fluorides and hydrocarbons) tend to adhere to the sorbent particles which can then be removed from the flue gas by regular dust abatement equipment (e.g. fabric filters). Alumina, coke dust and lime can be used as adsorption media. Prior to adsorption, flue gases may require pre-treatment by a conditioning tower or electrostatic precipitator. The adsorption medium has to be periodically removed from the system and is often re-used within the production processes. For example, spent alumina can be re-used for the electrolysis and coke dust for anode production. The PAHs and condensable hydrocarbons are burned at the high temperatures of these processes [28].
Most aluminium plants already apply dry adsorption with alumina combined with dust removal to reduce the emissions from the electrolysis. Alumina scrubbers are also often applied to treat the flue gases from anode production. Other plants apply systems based on coke dust as adsorption medium that is re-used within the production process (e.g. stand-alone anode production) [28].
Dry adsorption combined with dust removal is often applied together with other techniques (e.g. condensation, and sometimes wet scrubbing) and is associated with additional energy consumption.
Wet scrubbing
Wet scrubbing is mainly applied for sulphur dioxide (SO2) removal but will also reduce emissions of fluoride and dust. In the aluminium industry wet scrubbing is generally employed in addition to dry scrubbing. It can be applied to gases from the electrolysis cells as well as to the pot room ventilation air [28].
Various cleaning agents can be used as the scrubbing medium. Within the aluminium industry, seawater is most commonly applied, but sodium hydroxide (NaOH) or sodium carbonate (Na2CO3) can also be used. All of these media convert the SO2 into aqueous sulphates. Another possibility is to convert the SO2 to gypsum, using lime containing scrubbing agents such as lime hydrate, limestone or mixtures of calcium- and magnesium hydroxides [28].
Depending on the type of scrubber (e.g. sea water or NaOH), waste water, liquid waste (NaOH / Na2SO3) or gypsum is produced. Plants using seawater scrubbing will normally have wastewater treatment facilities including a flocculation and sedimentation stage. The resultant sludge has to be disposed. Seawater scrubbing requires an additional energy consumption of about 150 kWh per tonne aluminium.
Scrubbers operated with NaOH produce a concentrated effluent (about 1 m3 per tonne aluminium) that has to be discharged [28].
Condensation and EP
Volatile hydrocarbons emitted during anode baking can be condensed and the condensed particulates can be removed from the flue gas by regular dust abatement methods (i.e. fabric filters or electrostatic precipitators). Since PAHs tend to adhere to the condensed hydrocarbon particulates, PAH emissions are also reduced. The method is applicable as a pre-treatment stage for several process abatement stages. The condensed hydrocarbons can be recovered for use in the process. Some additional energy costs are incurred for cooling [28].
Regenerative afterburner
Afterburners destroy organic compounds by thermal oxidation, producing dust, carbon dioxide, water, SOx, NOx, and other combustion residues (further abatement is necessary to remove these). A novel regenerative afterburner has been used in a number of applications. It requires less energy input compared to conventional afterburners and can have a lower gas volume. The energy content of the contaminants (hydrocarbons and PAHs) is used to heat the support materials, thereby permitting auto-thermal operation [28].
Performance
The dry alumina scrubber is efficient at removing PAHs and tars from an anode plant or from Sderberg cells. Wet scrubbers for the ventilation gases will also remove some PAHs, especially the particulate fraction [28]. Techniques such as afterburners or carbon/lime injection and catalytic reactors/filters which are generally employed for the removal of dioxin and hydrocarbons also reduce PAH emissions. Table 13 gives an overview of reported PAH emissions according to the type of abatement system.
Table 13: General reported range of PAH emissions by type of abatement system
Abatement Technique
Reported emissions of PAH (EPA)
minimum
maximum
Afterburner
< 1 g/Nm3
2500 g/Nm3
Alumina scrubber
< 20 g/Nm3
2000 g/Nm3
Cooler, electrostatic precipitator, lime/carbon adsorption and fabric filter
0.1 mg/Nm3
6 mg/Nm3
Source: [28]
Generally PAH (OSPAR-11) emissions to air associated with the use of BAT at primary aluminium plants are
