International Aluminium Institute | www.world-aluminium.org
International Aluminium Institute
Results of the 2012 Anode Effect Survey Report on the Aluminium Industry’s Global Perfluorocarbon Gases Emissions Reduction Programme
International Aluminium Institute | www.world-aluminium.org
Contents Summary & Conclusions .......................................................................................................... 1
Industry Trends ........................................................................................................................ 2
2012 Anode Effect Survey ........................................................................................................ 3
Global Emissions Estimations .................................................................................................. 9
Uncertainties .......................................................................................................................... 12
Benchmark Data ..................................................................................................................... 13
Appendix A – Facility Emissions Calculation Methodologies ................................................. 19
Tables Table 1 – Aluminium smelting technology categories .............................................................. 3
Table 2 - 2012 Anode Effect Survey participation by technology, with respect to global
aluminium production ............................................................................................................... 4
Table 3 – Perfluorocarbon emission results from facility data reporting to the 2012 Anode
Effect Survey ............................................................................................................................ 7
Table 4 – Production weighted mean PFC emissions per unit production of reporting entities,
2006-2012 ................................................................................................................................ 8
Table 5 – Total global 2012 PFC emissions ........................................................................... 10
Table 6 - Slope and overvoltage coefficients by technology, including uncertainty (Source:
IPCC, 2006) ............................................................................................................................ 19
International Aluminium Institute | www.world-aluminium.org
Figures Figure 1 –Location of primary aluminium production, 1990 & 2006-2012 (SOURCE: IAI &
CRU) ........................................................................................................................................ 2
Figure 2 – Primary aluminium smelting technology mix, 1990-2011 (SOURCE: IAI & CRU) .. 2
Figure 3 – 2012 Anode Effect Survey reporter aluminium production coverage by technology
................................................................................................................................................. 4
Figure 4 – 2012 Anode Effect Survey reporter PFC emissions (as CO2e) coverage by
technology ................................................................................................................................ 4
Figure 5 – Reporting production & rate 1990-2012 .................................................................. 5
Figure 6 – Median PFC emission rates (as CO2e) per tonne of production of reporting
entities, per technology, 2006-2012 ......................................................................................... 8
Figure 7 – Reporting rates (aluminium production) per technology, 2006-2012 ...................... 8
Figure 8 – PFC emissions (as CO2e) per tonne of aluminium production, 2006-2012 .......... 10
Figure 9 – Absolute PFC emissions (as CO2e) and primary aluminium production, 1990-
2012 ....................................................................................................................................... 11
Figure 10 – PFC emissions (as CO2e per tonne Al) performance of reporters, benchmarked
as cumulative fraction within technologies, 2012 ................................................................... 14
Figure 11 –PFC emissions performance of reporters (t CO2e/t Al), benchmarked as
cumulative production within technologies, 2012 ................................................................... 14
Figure 12 - PFC emissions performance of reporters (t CO2e/t Al), benchmarked as
cumulative production within technologies, 1990 & 2012 ....................................................... 15
Figure 13 - Average anode effect frequency of reporters benchmarked by technology type,
2012 ....................................................................................................................................... 16
Figure 14 - Average anode effect duration of reporters benchmarked by technology type,
2012 ....................................................................................................................................... 16
Figure 15 - Average anode effect minutes per cell day of reporters benchmarked by
technology type, 2012 ............................................................................................................ 17
Figure 16 - Average anode effect overvoltage of reporters benchmarked by technology type,
2012 ....................................................................................................................................... 18
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International Aluminium Institute | www.world-aluminium.org
Summary & Conclusions Global aluminium industry 2012 PFC emissions (as CO2e) per tonne of production
(calculated to be 0.56 t CO2e/t Al) were 30% lower than those in 2006. With PFC emissions
per tonne cut by almost 90% since 1990 and strong growth in aluminium production over the
same period, total annual emissions of PFCs to the atmosphere by the aluminium industry
have been reduced by 71% while primary aluminium production has increased by 135%.
Survey data is published on the International Aluminium Industry (IAI)’s website. The IAI
online statistical system does not report separate company data, but rather aggregates PFC
emissions by different technologies.
http://www.world-aluminium.org/statistics/perflurocarbon-pfc-emissions/#data
The IAI PFC Emissions Reduction Voluntary Objective (2006-2020)
The primary aluminium industry seeks to achieve the long term elimination of
perfluorocarbon (PFC) emissions.
Following an 86% reduction in PFC emissions per tonne of primary aluminium produced
between 1990 and 2006, the global aluminium industry will further reduce emissions of
PFCs per tonne of aluminium by at least 50% by 2020 as compared to 2006.
The IAI is striving to increase the global aluminium production coverage of its annual
Surveys to over 80%.
Based on IAI annual survey results, by 2020 IAI member companies commit to operate
with PFC emissions per tonne of production no higher than the 2006 global median level
for their technology type.
Progress will be monitored and reported annually and reviewed periodically by a
recognised and independent third party. There will be interim reviews to ensure
progress towards achievement of the 2020 objective.
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International Aluminium Institute | www.world-aluminium.org
Industry Trends Growth in primary aluminium production continues to be driven by China and the Arabian
Gulf. Global primary aluminium production in 2012 was a record 46 million tonnes.
Figure 1 –Location of primary aluminium production, 1990 & 2006-2012 (SOURCE: IAI & CRU)
Figure 2 – Primary aluminium smelting technology mix, 1990-2012 (SOURCE: IAI & CRU)
0
5
10
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25
30
35
40
45
50
1990 2006 2007 2008 2009 2010 2011
Pri
mar
y A
lum
iniu
m P
rod
uct
ion
(mill
ion
to
nn
es)
China
Arabian Gulf
Other Asia
Africa
Oceania
South America
CIS
Europe
North America
0
5
10
15
20
25
30
35
40
45
50
1990
1995
1998
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2002
2003
2004
2005
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2007
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2012
An
nu
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rim
ary
Alu
min
ium
Pro
du
ctio
n
(mill
ion
to
nn
es)
HSS
VSS
SWPB
PFPB
CWPB
NB:technology category details in Table 1
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International Aluminium Institute | www.world-aluminium.org
2012 Anode Effect Survey
Survey Process The International Aluminium Institute has collected anode effect data directly from primary
aluminium producers for the purposes of calculating sectoral PFC emission inventories for
over a decade, with annual surveys carried out since 2000.
The IAI Anode Effect Survey requests data from all aluminium smelting facilities around the
world, via IAI member companies (http://www.world-aluminium.org/about/members/), direct
correspondence with non-member producers and regional industry associations. Facilities
are requested, where possible, to report by potline, and to separate data from different
technologies within a single plant. As well as anode effect process data, reporters are also
asked for information that allows for quality control (by comparison against other facilities
and within reporters’ data over time) and for the IAI to take a snapshot and monitor over time
the adoption of anode effect mitigation technologies such as prediction and automatic
termination software. The reporting form and guidelines (PFC001) can be found from the IAI
website (http://www.world-aluminium.org/media/filer_public/2013/01/15/pfc001.pdf).
BROAD TECHNOLOGY
CATEGORY
TECHNOLOGY
CATEGORY
ALUMINA FEED
CONFIGURATION
ACRONYM
Prebake
(anodes pre-baked)
Centre Worked
Bar broken centre feed CWPB
Point centre feed PFPB
Side Worked Manual side feed SWPB
Søderberg
(anodes baked in-situ)
Vertical Stud
Manual side feed
Point feed
VSS
Horizontal Stud Manual side feed HSS
Table 1 – Aluminium smelting technology categories
Participation Rate It is significant that the 2012 survey results include data from 100% of SWPB, 100% of VSS
and 99% of HSS technology production. On average, these technologies produce more
emissions per tonne of aluminium produced than the CWPB and PFPB categories (see
Table 3).
As the aluminium production in China represents an increasing proportion of the industry,
non-reported data are predominantly from China, the overall reporting rate shown in Figure 5
keeps decreasing. Outside of China, 20 smelters, representing around 4.6 million tonnes of
production (equivalent to 10% of worldwide production), did not report 2012 anode effect
data to IAI, compared to 91 smelters that did.
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International Aluminium Institute | www.world-aluminium.org
TECHNOLOGY
2012 primary
aluminium
production
(1,000 tonnes)
2012 production
represented in
survey
(1,000 tonnes)
2012 participation rate
by production
CWPB 1,220 610 50%
PFPB (Rest of
World) 19,680 15,666 80 %
39%
PFPB (China) 20,267 0 0 %
SWPB 606 606 100 %
VSS 3,586 3,586 100 %
HSS 543 540 99 %
All Technologies
(excluding China) 25,562 21,006 82 %
All Technologies
(Including China) 45,902 21,006 46 %
Table 2 - 2012 Anode Effect Survey participation by technology, with respect to global aluminium
production
Note: any inconsistencies due to rounding
The high coverage of the survey data outside China (with respect to both metal production
and emissions) and of the higher emitting technologies, combined with the fact that actual
measurements and secondary information are available to make an informed estimate of
Chinese industry performance, means that the IAI is able to develop estimates of PFC
emissions from the global aluminium industry, with some degree of accuracy.
Figure 3 – 2012 Anode Effect Survey reporter
aluminium production coverage by technology
Figure 4 – 2012 Anode Effect Survey reporter
PFC emissions (as CO2e) coverage by
technology
Reporting PFPB & CWPB
Reporting SWPB
Reporting Søderberg
Non Reporting PFPB (China)
Non Reporting PFPB & CWPB (ROW)
Non Reporting Søderberg
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International Aluminium Institute | www.world-aluminium.org
Figure 5 – Reporting production & rate 1990-2012
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0
5
10
15
20
25
30
35
40
45
50
Reporting rate
Annual Primary Aluminium Production
(Million tonnes)
Reporting Production Non Reporting Rest of World
Non Reporting China Reporting Rate (RHS)
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International Aluminium Institute | www.world-aluminium.org
Data Requested Annual (1 January – 31 December 2012) data required include:
Annual primary aluminium metal production (MP), the mass of molten metal (in
metric tonnes) tapped from pots in reporting period;
Anode effect frequency (AEF), the average number of anode effects occurring per
cell day over the reporting period;
Anode effect duration (AED), the average time (in minutes) of each anode effect
over the reporting period;
Anode Effect Overvoltage (AEO), the average cell voltage (in millivolts) above the
target operating voltage, when on anode effect, over the reporting period.
Overvoltage is specifically requested from operators employing Rio Tinto Alcan AP-18 or
AP-3x PFPB technologies and SWPB facilities using control technology that records
overvoltage rather than anode effect duration. These anode effect performance data allow
for the calculation, by the Intergovernmental Panel on Climate Change (IPCC) Tier 2 or Tier
3 methodologyF
1F, of facilities’ total annual tetrafluoromethane (CF4) and hexafluoroethane
(C2F6) emissions, and hence tonnes of CO2 equivalent (CO2e) emitted per tonne of
aluminium produced.
It should be noted that the IPCC Tier 1 methodology of multiplying metal production by a
technology-specific coefficient to estimate PFC emissions is not good practice, as the results
are not derived from process data and consequently have a very high uncertainty attached
to them. IAI does not use the Tier 1 methodology in any of its PFC emissions calculations.
2012 Survey Results Anode effect data was collected from 230 reporting entities (smelters & potlines)
representing 21 million tonnes of primary aluminium production Results are summarised in
Table 3 below.
Facilities that have made PFC measurements by which Tier 3 calculation of PFC emissions
is possible account for 58% of the total reported CF4 emissions from survey participants. It
should be noted that Tier 3 calculations typically carry an uncertainty of +/- 15%, with well
controlled systems down to +/- 12%, while uncertainty in Tier 2 calculations can be as high
as +/- 50%."
1 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Primary Aluminium Production, Chapter 3,Section 4.4, http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_4_Ch4_Metal_Industry.pdf.
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International Aluminium Institute | www.world-aluminium.org
Technology IPCC Tier
Number of
reporting
entities
Reported
production
(kt Al)
Total CF4
emissions
(Gg CF4)
Total C2F6
emissions
(Gg C2F6)
Median CF4
emission
factor
(kg CF4/t Al)
Median C2F6
emission
factor
(kg C2F6/t
Al)
Mean C2F6:
CF4 weight
ratio
Total PFC
emissions2
(kt CO2e)
Median
PFC
emission
factor
(t CO2e/t
Mean PFC
emission
factor
(t CO2e/t Al)
CWPB 2 1 325 0.005 0.001
0.025 0.004 0.15 116 0.20 0.19 3 1 285 0.010 0.002
PFPB
2 Slope 68 5,550 0.222 0.027
0.026 0.003 0.11 3,954 0.19 0.25 3 Slope 32 5,790 0.150 0.015
2 OV 18 2,565 0.095 0.011
3 OV 8 1,761 0.062 0.004
SWPB 2 5 154 0.089 0.022
0.352 0.111 0.24 2,301 3.29 3.80 3 3 451 0.176 0.041
VSS 2 22 915 0.161 0.009
0.116 0.007 0.06 3,582 0.81 1.00 3 54 2,671 0.347 0.023
HSS 2 14 290 0.033 0.003
0.136 0.012 0.10 972 0.99 1.82 3 4 250 0.096 0.011
ALL - 230 21,006 1.446 0.166 - - 0.12 10,926 - 0.52
Table 3 – Perfluorocarbon emission results from facility data reporting to the 2012 Anode Effect Survey
Note: any inconsistencies due to rounding
2 Carbon dioxide equivalent (CO2e) emissions for survey participants are calculated by multiplying the total tonnes of each PFC component gas by the Global Warming Potential (GWP) values reported in the IPCC Second Assessment Report (i.e. 6,500 for CF4 and 9,200 for C2F6). IPCC Second Assessment Report GWP values are employed to maintain consistency with Kyoto Protocol conventions and Clean Development Mechanism (CDM) and Joint Implementation (JI) accounting.
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International Aluminium Institute | www.world-aluminium.org
The range of anode effect and PFC emissions performance within technologies is explored
further in the “Benchmark Data” section below. Changes in median emission performance
(in t CO2e/t Al) within technologies between 2006 and 2012 are shown in the following chart.
As can be seen, the higher emitting technologies have the highest reporting rates.
Figure 6 – Median PFC emission rates (as
CO2e) per tonne of production of reporting
entities, per technology, 2006-2012
Figure 7 – Reporting rates (aluminium
production) per technology, 2006-2012
Reported average (production weighted mean) PFC emissions (as CO2e) per tonne of
production have been reduced by 36% between 2006 and 2012 (CF4 by 41%, C2F6 by 43%):
Reporting
production (kt
Al)
Reporting rate
by production
CF4
emission
factor
(kg CF4/t Al)
C2F6
emission
factor
(kg C2F6/t Al)
Total PFC
emission
factor
(t CO2e/t Al)
2012 21,006 46% 0.069 0.008 0.52
2011 22,413 51 % 0.079 0.009 0.60
2010 21,774 53 % 0.071 0.009 0.54
2009 22,184 60 % 0.069 0.008 0.52
2008 24,741 63 % 0.089 0.010 0.67
2007 23,903 63 % 0.106 0.013 0.81
2006 23,177 68 % 0.116 0.014 0.87
Table 4 – Production weighted mean PFC emissions per unit production of reporting entities, 2006-2012
0 1 2 3 4 5 6 7 8 9
2006
2007
2008
2009
2010
2011
2012
t CO2e/t Al
SWPB VSS HSSCWPB PFPB
2006
2007
2008
2009
2010
2011
2012
Reporting Rate
SWPB VSS HSSCWPB PFPB
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International Aluminium Institute | www.world-aluminium.org
Global Emissions Estimations
Methodology A more realistic picture of the global aluminium industry’s PFC emissions inventory should
include some estimate of the non-reporting industry year on year. In fact, the IAI voluntary
objective is an objective for the industry as a whole, not just IAI membership or reporting
companies and so is based on such a global estimate.
The IAI uses median PFC emissions performance per technology (as shown in Table 3
above) applied to non-reporting production by technology in order to calculate the global
PFC emissions inventory from aluminium production.
Non-reporting aluminium production tonnage data is taken from three sources. The majority
(China 2012 primary aluminium production of 20,267,471 metric tonnes) is reported by the
China Nonferrous Metals Industry Association (CNIA). Around 4 million tonnes of production
(n=13) is from other IAI surveys – primarily IAI Form 100 “Primary Aluminium Production”
(http://www.world-aluminium.org/media/filer_public/2013/01/15/iai_form_100.pdf). Finally,
just under 770,000 metric tonnes of production is data kindly provided by the CRU Group
(www.crugroup.com), for facilities where there is no direct IAI data collection (n=7).
Accounting for China Recent (2008-2010) PFC emissions measurements at 13 PFPB facilities in China,
undertaken as part of the Asia Pacific Partnership for Clean Development & Climate
(www.asiapacificpartnership.org) and by the Aluminum Corporation of China (Chinalco),
have yielded a median emission factor of 0.69 tonnes CO2e per tonne of aluminium
produced (CF4 median 0.100 kg/t Al; C2F6:CF4 weight fraction 0.043); , compared with a
PFPB survey reporter median performance of 0.19 tonnes CO2e per tonne of aluminium
(0.026 kg CF4/t Al; C2F6:CF4 weight ratio = 0.11).
This China-specific value (0.69 t CO2e/t Al) is applied to the 2012 Chinese non-reporting
PFPB cohort, in place of the IAI PFPB survey median, and has also been applied to Chinese
non-reporting production from 2006 to 2011, to derive a time series that more accurately
reflects Chinese smelter performance and global emissions than one based on rest-of-world
averages, albeit one that remains static over time.
2012 Global Aluminium Industry PFC Emissions Summing the emissions and production data from reporting and non-reporting facilities and
then dividing total global PFC emissions (t CO2e) by total global production (t Al), gives a
production weighted average 2012 PFC emissions performance for the global aluminium
industry of 0.56 tonnes of CO2e per tonne of primary aluminium produced, as outlined in
Table 5 – Total global 2012 PFC emissions
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International Aluminium Institute | www.world-aluminium.org
Total PFC
emissions
(1,000 t CO2e)
Total aluminium
production
(1,000 tonnes)
PFC
emission
factor
(t CO2e/t Al)
Reported 10,926 21,006 0.52
Calculated from non-reporters 14,864 24,895 0.60
TOTAL GLOBAL 25,790 45,902 0.56
Table 5 – Total global 2012 PFC emissions
Note: any inconsistencies due to rounding
Global Aluminium Industry PFC Emissions Reduction Performance (1990-2012) Global PFC emissions (as CO2e) per tonne of production have been reduced by 31% since
2006, on course to meet the IAI voluntary objective of a 50% reduction by 2020 on a 2006
baseline. The 31% improvement since 2006 takes the overall improvement since 1990 to
87%.
Figure 8 – PFC emissions (as CO2e) per tonne of aluminium production, 2006-2012
With PFC emissions per tonne cut by almost 90% since 1990 and primary aluminium
production having grown by 135% over the same period, absolute emissions of PFCs by the
aluminium industry have been reduced from approximate 90 million tonnes of CO2e in 1990
to 26 million tonnes in 2012, a fall of over 70%.
0
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PF
C E
mis
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O2e
/t A
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International Aluminium Institute | www.world-aluminium.org
Figure 9 – Absolute PFC emissions (as CO2e) and primary aluminium production, 1990-2012
0
10
20
30
40
50
60
70
80
90
100
Annual Primary Aluminium Production (Mt Al)
Total Annual PFC Emissions (Mt CO2e)
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International Aluminium Institute | www.world-aluminium.org
Uncertainties Understanding sources and magnitude of uncertainty in the calculation of global industry
PFC emissions is important, not only in terms of the current emissions inventory and its
relationship to top-down measurements of PFCs in the atmosphere, but also with respect to
quantifying the industry’s performance over time.
Given that the 2012 data presented above indicates a significant reduction in total PFC
emissions (as CO2e) since 1990, it is necessary to consider the uncertainties inherent in the
1990 baseline number and the 2012 performance number and to quantify the probability that
the reduction has been made.
Potential significant sources of uncertainty include:
the application of average industry IPCC Tier 2 calculation factors,
use of Tier 2 factors for calculating PFC emissions for survey participants where
suitable facility specific measurements are not available, and,
estimates of PFC emissions for producers that do not participate in the anode effect
survey.
Uncertainty arises from the use of IPCC Tier 2 average industry factors due to the
uncertainty in the mean slope and overvoltage coefficients. Additional PFC measurements
will reduce the uncertainty of the mean coefficient values. However, for all technology
groups there is considerable variance in the individual values of slope and overvoltage
coefficients, from which the means are calculated. For this reason, calculations of PFC
emissions with Tier 2 coefficients will be more uncertain than calculations made with Tier 3
coefficients, calculated from PFC measurements made using good measurement practices.
Calculations of PFC emissions for non-reporters is even more uncertain where, due to lack
of availability of anode effect performance, the median emission factors of reporters per
technology is applied to non-reporters.
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International Aluminium Institute | www.world-aluminium.org
Benchmark Data The IAI Anode Effect Survey provides respondents with valuable benchmark information,
allowing producers to judge their performance relative to others operating with similar
technology. The benchmark data are presented in this section in the form of cumulative
probability graphs and calculated PFC emissions benchmark data as both cumulative
probability and cumulative production graphs.
The cumulative probability graphs show, on the horizontal axis, the benchmark parameter:
PFC emissions per tonne of aluminium;
Anode effect frequency (AEF);
Anode effect duration (AED);
Anode effect minutes per cell day (AEM) and
Anode effect overvoltage (AEO).
The vertical axes show the cumulative fraction of reporting facilities that perform at or below
the level chosen on the vertical axis. For facilities reporting data from multiple potlines, a
data point is shown for each potline.
To illustrate how the graph in Figure 10 is interpreted consider, for example, the 0.5 point on
the vertical axis, at which the HSS data point is 0.98 t CO2e/t Al. The interpretation is that
50% of all potlines/facilities reporting HSS anode effect data operate at or below 0.98 t
CO2e/t Al. At 1.0 on the vertical axis the HSS point is 4.23 t CO2e/t Al. The interpretation is
that all HSS facilities reported anode effect data that reflected PFC emissions performance
at or below 4.23 t CO2e/t Al or, in other words, the maximum value calculated for HSS
operators in 2012 was 4.23 t CO2e/t Al.
PFC Emissions per Tonne of Aluminium
The lowest PFC emissions per tonne of aluminium produced are produced by PFPB
facilities, although with a wide range of performance. The VSS and HSS facilities show a
similar distribution, but with higher average emissions factor. The highest PFC emissions per
tonne of aluminium produced and the widest range in performance result from SWPB cells.
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International Aluminium Institute | www.world-aluminium.org
Figure 10 – PFC emissions (as CO2e per tonne Al) performance of reporters, benchmarked as cumulative
fraction within technologies, 2012
Figure 11 –PFC emissions performance of reporters (t CO2e/t Al), benchmarked as cumulative production within technologies, 2012
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0
Cu
mu
lati
ve F
ract
ion
of
Rep
ort
ing
En
titi
es
PFC Emission Factor (t CO2e/t Al) CWPB & PFPB SWPB HSS VSS
Note: SWPB 86th and 100th percentile
outliers are at 10.8 tCO2e/t Aland 16.7 t CO2e/t Al respectively.
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 5 10 15 20
PFC
Emissions (t CO2‐eq/tonne Al)
Cumulative Aluminium Production of Reporting Facilities (Million tonnes)
PFPB&CWPB
SWPB
HSS
VSS
Note: SWPB outlier at 22.0 Mt Al is 16.7 t CO2e/t Al
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International Aluminium Institute | www.world-aluminium.org
Taking the 1990 reporting cohort and plotting it against 2012 data shows improvement both from existing facilities over this time but also,
importantly, the positive contribution of new (predominantly PFPB) capacity added since 1990.
Figure 12 - PFC emissions performance of reporters (t CO2e/t Al), benchmarked as cumulative production within technologies, 1990 & 2012
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
0 5 10 15 20
PFC
Emissions (t CO2‐eq/tonne Al)
Cumulative Aluminium Production of Reporting Facilities (Million tonnes)
PFPB&CWPB
SWPB
HSS
VSS
2012
1990
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International Aluminium Institute | www.world-aluminium.org
Anode Effect Frequency & Duration
The following graphs shows the distribution of anode effect frequency and duration data for
reporting facilities in 2012. As can be expected from the greater degree of control capability
of PFPB cells, this technology has the lowest AEF distribution of the five groups.
Figure 13 - Average anode effect frequency of reporters benchmarked by technology type, 2012
Figure 14 - Average anode effect duration of reporters benchmarked by technology type, 2012
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Cu
mu
lati
ve F
ract
ion
of
Rep
ort
ing
En
titi
es
Anode Effect Frequency (number of AE per cell day)
CWPB & PFPB SWPB VSS HSS
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Cu
mu
lati
ve F
ract
ion
of
Rep
ort
ing
En
titi
es
Anode Effect Duration (minutes)
CWPB & PFPB SWPB VSS HSS
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International Aluminium Institute | www.world-aluminium.org
Anode Effect Minutes per Cell Day
Anode Effect Minutes per Cell Day (AEM) are the product of anode effect frequency and
duration and, for facilities employing the Slope Method. AEM relate directly to PFC emissions
per tonne of aluminium produced through a slope factor that is either technology specific
(IPCC Tier 2 methodology) or facility specific (Tier 3 methodology).
Both PFPB and CWPB technologies have the same Tier 2 value for slope: 0.143 kg CF4/t Al
per AEM. However, the IPCC Tier 2 slope parameter for SWPB, VSS and HSS technologies
are considerably different. The slope value is highest for the SWPB technology group, 0.272
kg CF4/t Al per AEM. The comparable slope values for VSS and HSS are 0.092 and 0.099,
respectively.
Figure 15 - Average anode effect minutes per cell day of reporters benchmarked by technology type, 2012
Anode Effect Overvoltage
Figure 16 shows the benchmarking graph for anode effect overvoltage for PFPB cells
operating with Rio Tinto Alcan AP technologies and which calculate PFC emissions from
overvoltage process data. For these operators, the AEO parameter relates directly to anode
effect related PFC emissions per tonne of aluminium produced.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0
Cu
mu
lati
ve F
ract
ion
of
Rep
ort
ing
En
titi
es
Anode Effect Minutes per Cell Day (minutes)
CWPB & PFPB SWPB HSS VSS
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Figure 16 - Average anode effect overvoltage of reporters benchmarked by technology type, 2012
Positive overvoltage reporting now predominates over algebraic overvoltage reporting. The
positive overvoltage should give a better correlation with PFC emissions per tonne of
aluminium than algebraic overvoltage since algebraic overvoltage recording can result in
subtractions of voltage during the anode effect treatment period that do not relate to PFC
emissions.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 5 10 15 20
Cu
mu
lati
ve F
ract
ion
of
Rep
ort
ing
En
titi
es
Anode Effect Overvoltage (mV)
Positive
Algebraic
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International Aluminium Institute | www.world-aluminium.org
Appendix A – Facility Emissions Calculation Methodologies
Slope Method The basic equations for calculation of PFC emission rates from facilities reporting anode effect frequency and duration are:
and
/
where
kilograms of emitted
kilograms of emitted
slope coefficient for
/ weight fraction of to
While AEF and AED are reported data, the slope coefficient for CF4 can be either “facility specific” (IPCC Tier 3 methodology), or “technology specific” (IPCC Tier 2 methodology). The first of these options, Tier 3, is the more certain method for calculating emissions and involves use of a slope coefficient (and weight fraction) derived from direct measurement of PFC emissions at the facility. The Tier 2 method involves the use of slope coefficients that are an average of measurement data available in 2005 taken from facilities around the world within technology classes.
Table 6 - Slope and overvoltage coefficients by technology, including uncertainty (Source: IPCC, 2006)
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Participants in the Anode Effect Survey are asked to report if a facility-specific direct measurement of PFC emissions had been made and if a Tier 3 slope coefficient and weight fraction are available for calculating PFC emissions from the smelter. The remainder of the PFC emissions data are calculated using IPCC Tier 2 methodology with industry average coefficients.
Overvoltage Method For smelters that report overvoltage data, the following equations are employed:
100
and
/
where
kilograms of
kilograms of
overvoltage coefficient for
current efficiency, expressed as %
/ weight fraction of to
Again, a Tier 3 methodology applies a facility specific overvoltage coefficient and weight fraction, derived from on site PFC measurements and anode effect data and reported as part of the Survey return. Tier 2 calculations apply technology specific, average coefficients, which are outlined in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories.
Global Warming Potentials Carbon dioxide equivalent (CO2e) emissions for survey participants are calculated by multiplying the total tonnes of each PFC component gas by the Global Warming Potential (GWP) values reported in the IPCC Second Assessment ReportF
3F (i.e. 6,500 for CF4 and
9,200 for C2F6):
6500 9200
For benchmarking purposes (that is to say, comparing emissions performance between facilities of the same technology but with different levels of production), total (or “absolute”) CO2e emissions are divided by relevant aluminium production, to give an emission factor in tonnes of CO2e per tonne of aluminium produced:
3 The IPCC Second Assessment Report GWP values are employed to maintain consistency with Kyoto Protocol conventions and Clean Development Mechanism (CDM) and Joint Implementation (JI) accounting. The latest data published by IPCC in the Fourth Assessment Report reports the CF4 GWP as 7,390 and the C2F6 GWP as 12,200.
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