ANNEX IV U.K. Activity-specific monitoring methodologies related to installations (Article 20(2))

8. PFC emissions from production or processing of primary aluminium as listed in Annex I to Directive 2003/87/EC U.K.

B. Determination of PFC emissions U.K.

Calculation Method B — Overvoltage Method U.K.

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) × Pr_Al × 0,001

C₂F₆ emissions [t] = CF₄ emissions × F_C2F6

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 [%];

Pr_Al

=

Annual production of primary Aluminium [t];

F_C2F6

=

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 F_C2F6) 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

Technology	Emission factor for CF4[(kg CF4/t Al)/mV]	Emission factor for C2F6[t C2F6/t CF4]
Centre Worked Prebake (CWPB)	1,16	0,121
Vertical Stud Søderberg (VSS)	N.A.	0,053