PFC emission sources

5.3.1 Primary aluminium production

Primary aluminium production has been identified as a major emission source of the two PFCs tetrafluoromethane (CF4) with GWP100 6,500 and hexafluoroethane (C2F6) with GWP100

9,200 times that of CO2. During normal operating conditions, an electrolytic cell used to produce aluminium does not generate measurable amounts of PFC. PFC is only produced during brief upset conditions known as "anode effects". These conditions occur when the level of aluminium oxide drops too low and the electrolytic bath itself begins to undergo electrolysis. Since the aluminium oxide level in the electrolytic bath cannot be directly measured, surrogates such as cell electrical resistance or voltage are most often used in modern facilities to ensure that the aluminium in the electrolytic bath is maintained at the correct level.

For EU-28, the GAINS model uses the production volumes of primary aluminium as the activity driver for calculating emissions from this source. Primary aluminium production data for historical years (2005 and 2010) and projections are taken from the PRIMES (2016) reference projection for the EU. Four different types of activities are distinguished based on the technology used; point-feeder prebake (PFPB), side-worked prebake (SWPB), vertical stud söderberg (VSS), and center-worked prebake (CWPB) technology. As per the information provided by the MS, there was a significant reduction of primary aluminium production in Slovenia due to economic crisis in 2010 as the new electrolysis unit operated less than half of its capacity. According to most recent data submitted in Slovenia’s National Inventory Report 2015, primary aluminium production amounted to 84 kt in 2013, which is close to maximal capacity of 85 kt per year of the existing plant. Therefore, we have used primary aluminium production of 85 kt per year in Slovenia for 2015. Shares of different primary aluminium production technologies were adopted from the aluminium industry website and from national communications to the UNFCCC (2015). The latter source is also used for final verification of emissions. Emission factors depend on the production technology and on a number of site-specific conditions and are taken from Harnisch and Hendricks (2000).

Conversion of SWPB, VSS or CWPB technology to PFPB technology removes over 90 percent of PFC emissions, while retrofitting of the three technologies would remove about a quarter of emissions (Harnisch and Hendricks 2000). Data on mitigation costs is taken from the same source. As emissions from the primary aluminium production is regulated under the EU-ETS system, control options with marginal costs falling below the expected ETS carbon price in the reference scenario (projected with PRIMES) are adopted in the reference scenario.

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This means that with the natural turn-over of capital, all EU member states will have phased-in PFPB technology by 2020.

The development of inert anodes is sometimes promoted as a promising mitigation option, which could eliminate emissions of PFCs from the electrolysis process (Bernstein et al., 2007). In the Energy Technology Perspective (ETP) 2010 by the International Energy Agency (IEA/OECD, 2010), deployment of inert anode technologies is expected to start in 2015-2020 with full commercialization by 2030. If realized, inert anode technology would have significant energy, cost, productivity, and environmental benefits for the aluminium industry worldwide (Inert Anode Roadmap, 1998; RUSAL, 2010). The technology is expected to eliminate PFC emissions from primary aluminium production altogether. However, the commercial aspects of inert anodes have not yet been proven (Kvande and Drabløs, 2014).

Despite promising initial results, the technology still needs further development before it can be introduced as a viable alternative to PFPB technology. In GAINS, inert anode technology is assumed available as a mitigation option from 2035 onwards, however, no adoption in the reference scenario is assumed.

Figure 14 shows PFC emissions from primary aluminium production in EU-28 as estimated by the GAINS model and in comparison with emissions reported to UNFCCC for years 2005 and 2010.

Figure 14: PFC emissions (in kt CO2eq) from primary aluminium production in the GAINS model and as reported to UNFCCC for years 2005 and 2010.

5.3.2 Semiconductor industry

The semiconductor industry uses HFC-23, CF4, C2F6, octafluoropropane (C3F8), carbon tetrafluoride (c-C4F8), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3) in two production processes: plasma etching thin films (etch) and plasma cleaning chemical vapour deposition (CVD) tool chambers (IPCC, 2000a). Both the PFCs (GWP100=6500) and NF3 are

potent greenhouse gases (GWP100=17200). PFCs have been regulated under the Kyoto Protocol, while NF3 is added to the ‘basket’ of six greenhouse gases (covered by the KP in the first commitment period) with effect from 2013 and the commencement of the second commitment period of the protocol. The semiconductor industry has been switching from PFCs to NF3 as part of a voluntary agreement to reduce PFCs. The commitment has been to reduce PFC emissions to ten percent below the 1995 baseline level by 2010 (ESIA 2006;

WSC 2008). In 2008 the industry was close to reaching this target (WSC 2008). Under well managed conditions and certainly in the EU and the US, a switch from PFC to NF3 reduces the net global warming effect because about 98 percent of NF3 is destroyed by industry in the process (UNFCCC 2012b). With a release of about 60 percent of the PFCs used in the industry, the switch to NF3 contributes to a net reduction in greenhouse gas emissions by about 85 percent. As the proposal to include NF3 among the Kyoto gases has not yet been ratified, the global warming effect of NF3 emissions is currently not accounted for in the estimation of non-CO2 emissions from EU countries.

As PFC is only used by a few companies in a country and because the amount of PFC use allows deriving production volumes, data on the use is often confidential. The activity variable used in GAINS for this sector is the volume of PFC emissions as reported by member states to UNFCCC (2015). We use the reported emissions for the years 2005 and 2010 while future projections follow growth in value added for manufacturing industry.

The European semiconductor manufacturers have been part of the voluntary commitment to reduce PFC emissions from this source (ESIA, 2006). We assume that the reduction attained by the industry in 2005 will continue into the future. This corresponds to an application of control to 86 percent of the production from 2010 onwards. Costs for switching to NF3 use were taken from Harnisch et al. (2000), Harnisch and Hendriks (2000) and Tohka (2005).

Figure 15 shows the GAINS model estimates of current future emissions of PFC from semiconductor industry in EU member states.

Figure 15: PFC emissions (in kt CO2eq) from semiconductor industry in the GAINS model and as reported to UNFCCC for years 2005 and 2010.

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