Calculation Method A — Slope Method U.K.
The operator shall use the following equations for determining PFC emissions:
CF4 emissions [t] = AEM × (SEFCF4/1 000) × PrAl
C2F6 emissions [t] = CF4 emissions * FC2F6
Where:
=
Anode effect minutes/cell-day;
=
Slope emission factor [(kg CF4/t Al produced)/(anode effect minutes/cell-day)]. Where different cell-types are used, different SEF may be applied as appropriate;
=
Annual production of primary Aluminium [t];
=
Weight fraction of C2F6 (t C2F6/t CF4).
The anode effect minutes per cell-day shall express the frequency of anode effects (number anode effects/cell-day) multiplied by the average duration of anode effects (anode effect minutes/occurrence):
AEM = frequency × average duration
:
The emission factor for CF4 (slope emission factor, SEFCF4) expresses the amount [kg] of CF4 emitted per tonne of aluminium produced per anode effect minute/cell-day. The emission factor (weight fraction FC2F6) of C2F6 expresses the amount [t] of C2F6 emitted proportionate to the amount [t] of CF4 emitted.
:
The operator shall use technology-specific emission factors from Table 1 of this section of Annex IV.
:
The operator shall use installation-specific emission factors for CF4 and C2F6 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(1). The operator shall determine each emission factor with a maximum uncertainty of ± 15 %.
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 1:
Technology-specific emission factors related to activity data for the slope method
| Technology | Emission factor for CF4 (SEFCF4)[(kg CF4/t Al)/(AE-Mins/cell-day)] | Emission factor for C2F6 (FC2F6)[t C2F6/t CF4] |
|---|---|---|
| Centre Worked Prebake (CWPB) | 0,143 | 0,121 |
| Vertical Stud Søderberg (VSS) | 0,092 | 0,053 |
International Aluminium Institute; The Aluminium Sector Greenhouse Gas Protocol; October 2006; US Environmental Protection Agency and International Aluminium Institute; Protocol for Measurement of Tetrafluoromethane (CF4) and Hexafluoroethane (C2F6) Emissions from Primary Aluminum Production; April 2008.