L 228/160
EN
Official Journal of the European Union
15.9.2023
The anode effect minutes per cell-day expresses 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
(Equation 23)
Emission factor: 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 per cell-day.
The emission factor (weight fraction FC2F6) of C2F6 expresses the amount [kg] of C2F6 emitted proportionate to the amount [kg] of CF4 emitted.
Minimum requirement: Technology-specific emission factors from Table 2 of this Annex are used.
Recommended improvement: Installation-specific emission factors for CF4 and C2F6 are established through continuous or intermittent field measurements.
For the determination of those emission factors industry best practice shall be applied, in particular the most recent guidelines provided by the International Aluminium Institute.
The emission factor shall also take into account emissions related to non-anode effects.
Each emission factor shall be determined with a maximum uncertainty of ± 15 %.
The emission factors shall be determined 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 activity data for the slope method Emission factor for CF4 (SEFCF4) [(kg CF4/t Al)/(AE-Mins/ cell-day)]
Emission factor for C2F6 (FC2F6) [t C2F6/ t CF4]
Legacy Point Feed Pre Bake (PFPB L)
0,122
0,097
Modern Point Feed Pre Bake (PFPB M)
0,104
0,057
– (*)
– (*)
Centre Worked Prebake (CWPB)
0,143
0,121
Side Worked Prebake (SWPB)
0,233
0,280
Vertical Stud Søderberg (VSS)
0,058
0,086
Horizontal Stud Søderberg (HSS)
0,165
0,077
Technology
Modern Point-Fed Prebake without fully automated anode effect intervention strategies for PFC emissions (PFPB MW)
(*) The installation has to determine the factor by own measurements.
If this is technically not feasible or involves unreasonable costs, the values for CWPB methodology shall be used.
B.7.2.
Calculation Method B – Overvoltage Method
For the overvoltage method, the following equations shall be used: CF4 emissions [t] = OVC × (AEO/CE) × PrAl × 0,001 C2F6 emissions [t] = CF4 emissions × FC2F6
(Equation 24) (Equation 25)
Where: OVC
is the overvoltage coefficient (‘emission factor’) expressed in kg CF4 per tonne of aluminium produced per mV overvoltage;
AEO
is the 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;