Mercury may be emitted from various locations in an integrated iron and steel facility, including the sinter plant, the blast furnace that produce iron, the basic oxygen process (BOP) furnaces that produce steel, among others. The major pathway for mercury releases is via air, and to a lesser extent in wastes/residues. The most relevant environmental issues with regard to the sinter plant are the off-gas emissions from the sinter strand, which contains a wide range of pollutants such as dust, heavy metals, SO2, HCl, HF, PAHs and organochlorine compounds.
According to Berndt (2003), the mercury that is emitted to the air from the sintering process is predominantly in elemental form. A study conducted at one of the plants in Minnesota indicated that an average of 93.3% of mercury emissions were in Hg(0) form, with almost all of the remainder emitted as oxidized mercury Hg(II) (HTC, 2000).
Filters with electrostatic precipitators (ESP) reduce particulate matter concentrations with an efficiency of >95%. In some cases efficiency of 99% is achievable. Operational data for sinter plants are in the range of 20 to 160 mg/Nm3. Emission values for moving Electrode type Electrostatic Precipitator (MEEP) and electrostatic space charge system (ESCS) may achieve < 40 mg/Nm3.
ESP with energy pulse superimposition may achieve 20 to 30 mg/Nm3 according to BREF Iron & Steel (2001). Moreover, electrostatic precipitators can be installed at both new and existing plants.
Relevant legislation and NGO policy work
The Minamata Convention on Mercury, Article 8 concerns controlling and where feasible, reducing emissions of mercury and mercury compounds, to the atmosphere though measures to control emissions from certain point sources (Annex D) – but it does not include steel production, at least for now.
For the US see relevant pieces of laws and regulations at https://www.epa.gov/mercury#regs
On April 22, 2004, EPA issued a regulation to control emissions from iron and steel foundries. The rule included emission limits for manufacturing processes and pollution prevention-based requirements to reduce air toxics from furnace charge materials and coating/binder formulations. The rule also included a work practice requirement to ensure removal of auto mercury switches from scrap.
In the EU
The industrial activity of Iron and Steel Industries is covered under the Integrated Pollution Prevention and Control (IPPC) Directive (96/61/EC).
In 2010- the Integrated Pollution Prevention and Control (IPPC) Directive (96/61/EC) was replaced by the Industrial Emissions Directive (IED),which has entered into force on 6 January 2011 and wastransposed into national legislation by Member States by 7 January 2013.
Although the principle is the same as for IPPC, the role of the Best Available Technique (BAT) Reference Documents (BREFs) has been strengthened, providing more opportunities to the legislator to question why mercury process may still be permitted in the sector.
IED sets out the main principles for the permitting and control of installations based on an integrated approach and the application of best available techniques (BAT) which are the most effective techniques to achieve a high level of environmental protection, taking into account the costs and benefits. For more information on the directive please visit the EC website.
Through the implementation of the IED, the role of the BREFs has been strengthened. After a BREF is completed, it should be subject to BAT conclusions that are adopted through a comitology decision (implementing act). The right of initiative however rests with the Commission. BAT conclusions contain parts of the BREF, their description, information on applicability, including BAT Associated Emission Levels (BATAELs) for different pollutants (meaning emission levels that can be achieved for a pollutant if the industry is implementing BAT) as well as associated consumption levels and monitoring.
It may also include site remediation measures “where appropriate”. Within 4 years after publication of the comitology decision on the relevant BAT conclusions, local authorities should review and update all the permits to the respective industries in order to make sure the industrial activity operates according to the requirements set out in the BAT conclusions.
The provision in the IED requires that Emission Limit Values (ELVs) for pollutants set out in the permit should not exceed the relevant BATAEL. However the permit writer may derogate in specific cases and set higher ELVs under certain conditions.
An assessment needs to demonstrate that the application of the BATAEL would lead to disproportionate higher costs compared to the benefits due to the local conditions (technical characteristics of the plants, or geographical location or local environmental conditions).
In any case no significant pollution may be caused and a high level of protection of the environment as a whole is achieved. Environmental Quality Standards also need to be respected. These derogations are subject to public participation and scrutiny by the public concerned, which includes NGOs.
The benchmarks or criteria on which BAT relies are described in the BAT Reference Documents (BREFs). The first Iron and Steel BREF was adopted in 2001. The BREF was revised in 2012, and BAT conclusions were adopted in March 2012.
According to the BAT conclusions:
- BAT for primary emissions from sinter strands is to prevent or reduce mercury emissions by selecting raw materials with a low mercury content (see BAT 7) or to treat waste gases in combination with activated carbon or activated lignite coke injection. The BAT-associated emissions level for mercury is < 0,03 – 0,05 mg/Nm3, as the average over the sampling period (discontinuous measurement, spot samples for at least half an hour).
- BAT for the electric arc furnace (EAF) process is to prevent mercury emissions by avoiding, as much as possible, raw materials and auxiliaries which contain mercury (see BAT 6 and 7).
- BAT for the electric arc furnace (EAF) primary and secondary dedusting (including scrap preheating, charging, melting, tapping, ladle furnace and secondary metallurgy) is to achieve an efficient extraction of all emission sources by using one of the techniques listed below and to use subsequent dedusting by means of a bag filter:
- a combination of direct off-gas extraction (4th or 2nd hole) and hood systems
- direct gas extraction and doghouse systems
- direct gas extraction and total building evacuation (low-capacity electric arc furnaces (EAF) may not require direct gas extraction to achieve the same extraction efficiency).
The overall average collection efficiency associated with BAT is > 98 %.
The BAT-associated emission level for dust is < 5 mg/Nm3, determined as a daily mean value.
The BAT-associated emission level for mercury is < 0,05 mg/Nm3, determined as the average over the sampling period (discontinuous measurement, spot samples for at least four hours).