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Division Calculation Method B — Overvoltage Method

United Kingdom

Original text. Later amendments are not shown.

Where the anode effect overvoltage is measured, the operator shall use the following equations for the determination of PFC emissions:

CF4 emissions [t] = OVC × (AEO/CE) × PrAl × 0,001

C2F6 emissions [t] = CF4 emissions × FC2F6

Where:

OVC

  • Overvoltage coefficient (‘emission factor’) expressed as kg CF4 per tonne of aluminium produced per mV overvoltage;

    • AEO

  • Anode effect overvoltage per cell [mV] determined as the integral of (time × voltage above the target voltage) divided by the time (duration) of data collection;

    • CE

  • Average current efficiency of aluminium production [%];

    • PrAl

  • Annual production of primary Aluminium [t];

    • FC2F6

  • Weight fraction of C2F6 (t C2F6/t CF4);

    • The term AEO/CE (Anode effect overvoltage/current efficiency) expresses the time-integrated average anode effect overvoltage [mV overvoltage] per average current efficiency [%].

    Emission factor

  • The emission factor for CF4 (‘overvoltage coefficient’ OVC) shall express the amount [kg] of CF4 emitted per tonne of aluminium produced per millivolt overvoltage [mV]. The emission factor of C2F6 (weight fraction FC2F6) shall express the amount [t] of C2F6 emitted proportionate to the amount [t] of CF4 emitted.

    • Tier 1

  • The operator shall apply technology-specific emission factors from Table 2 of this section of Annex IV.

    • Tier 2

  • The operator shall use installation-specific emission factors for CF4 [(kg CF4/t Al)/(mV)] and C2F6 [t C2F6/t CF4] established through continuous or intermittent field measurements. For the determination of those emission factors, the operator shall use the most recent version of the guidance mentioned under tier 3 of section 4.4.2.4 of the 2006 IPCC Guidelines. The operator shall determine the emission factors with a maximum uncertainty of ± 15 % each.

    • The operator shall determine the emission factors at least every three years or earlier where necessary due to relevant changes at the installation. Relevant changes shall include a change in the distribution of anode effect duration or a change in the control algorithm affecting the mix of the types of anode effects or the nature of the anode effect termination routine.

    Table 2:

    Technology-specific emission factors related to overvoltage activity data

    TechnologyEmission factor for CF4[(kg CF4/t Al)/mV]Emission factor for C2F6[t C2F6/t CF4]
    Centre Worked Prebake (CWPB)1,160,121
    Vertical Stud Søderberg (VSS)N.A.0,053