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International Aluminium Institute

Results of the 2013

Anode Effect

Survey Report on the Aluminium Industry’s Global

Perfluorocarbon Gases Emissions Reduction

Programme


Contents

Global Aluminium Industry PFC Emissions Reduction Performance 2013 ............................. 4

Industry Trends ..................................................................................................................... 5

2013 Anode Effect Survey ..................................................................................................... 6

Adoption of revised GWPs and its consequence ................................................................... 9

Global Emissions Estimations ..............................................................................................13

Uncertainties ........................................................................................................................16

Benchmark Data...................................................................................................................17

Appendix A – Facility Emissions Calculation Methodologies.................................................23

Tables

Table 1 – Aluminium smelting technology categories ............................................................ 6

Table 2 - 2013 Anode Effect Survey participation by technology ........................................... 7

Table 3 - IPCC GWP Values ................................................................................................. 9

Table 4 – Perfluorocarbon emission results from facility data reporting to the 2013 Anode Effect

Survey ..................................................................................................................................11

Table 5 – Production weighted mean PFC emissions per unit production of reporting entities,

2006-2013 ............................................................................................................................12

Table 6 – Total global 2013 PFC emissions .........................................................................14

Table 7 - Slope and overvoltage coefficients by technology, including uncertainty (Source:

IPCC, 2006) .........................................................................................................................24


Figures

Figure 1 –Location of primary aluminium production, 1990 & 2006-2013 (SOURCE: IAI & CRU)

.............................................................................................................................................. 5

Figure 2 – Primary aluminium smelting technology mix, 1990-2013 (SOURCE: IAI & CRU) .. 5

Figure 3 – Reporting production & rate 1990-2013 ................................................................ 8

Figure 4 – Reporting rates (aluminium production) per technology, 2006-2013 ..................... 8

Figure 5 – Median PFC emission rates (as CO2e) of reporting entities, per technology, 2006-

2013 .....................................................................................................................................10

Figure 6 – PFC emissions (as CO2e) per tonne of aluminium production, 2006-2013 ..........15

Figure 7 – Absolute PFC emissions (as CO2e) and primary aluminium production, 1990-2013

.............................................................................................................................................15

Figure 8 – PFC emissions (as CO2e per tonne Al) performance of reporters, benchmarked as

cumulative fraction within technologies, 2013 .......................................................................18

Figure 9 –PFC emissions performance of reporters (t CO2e/t Al), benchmarked as cumulative

production within technologies, 2013 ....................................................................................18

Figure 10 - PFC emissions performance of reporters (t CO2e/t Al), benchmarked as cumulative

production within technologies, 1990 & 2013 ........................................................................19

Figure 11 - Average anode effect frequency of reporters benchmarked by technology type,

2013 .....................................................................................................................................20

Figure 12 - Average anode effect duration of reporters benchmarked by technology type, 2013

.............................................................................................................................................20

Figure 13 - Average anode effect minutes per cell day of reporters benchmarked by technology

type, 2013 ............................................................................................................................21

Figure 14 - Average anode effect overvoltage of reporters benchmarked by technology type,

2013 .....................................................................................................................................22

4


Global Aluminium Industry PFC Emissions Reduction Performance

2013

Global aluminium industry perfluorocarbon (PFC) emissions intensity (as CO2e per tonne of

production) has been reduced by more than 35% since 2006, almost 90% since 1990.

With primary aluminium production having grown by over 150% over the same period,

absolute emissions of PFCs by the aluminium industry have been reduced from approximate

100 million tonnes of CO2e in 1990 to 32 million tonnes in 2013.

The International Aluminium Institute (IAI) 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 2013 Anode Effect Survey generated data from 218 reporting entities (smelters & potlines)

representing 20 million tonnes of primary aluminium production, with emissions from the

remaining 30 million tonnes of global primary aluminium production (the majority in China),

modelled using historic, sampled or technology average data.

This survey report outlines year 2013 data collection and analysis methodologies and global

results. Historically IAI has used global warming potential (GWP) values for perfluorocarbon

gases as published in the IPCC Second Assessment Report (1996), to align with a 1998

decision of the Conference of the Parties to the Kyoto Protocol (Decision 2/CP.3). The 2011

decision by the Conference of the Parties serving as the meeting of the Parties to the Kyoto

Protocol (Decision 4/CMP.7) to utilise revised GWPs from the IPCC Fourth Assessment

Report (2007), for the second commitment period (from 2013) has necessitated recalculation

of aluminium industry PFC emissions (as CO2e). This report outlines this process and, where

appropriate, delivers data using both sets of GWP. However, for all future reports (and for

online historic datasets and baselines), only 2006 GWPs will be employed.

Current and historic PFC emissions data (utilising revised GWPs) can also be found on the

International Aluminium Institute’s website http://www.world-

aluminium.org/statistics/perflurocarbon-pfc-emissions/#data. As in this report, separate

company or country PFC emissions data is not published, but rather is aggregated by

production technology

http://www.world-aluminium.org/statistics/perflurocarbon-pfc-emissions/#data


5


Industry Trends

Growth in primary aluminium production continues to be driven by China and the GCC

countries and, since the late 1990s, based on latest point fed prebake technology. Global

primary aluminium production in 2013 was a record 51 million tonnes.

Figure 1 –Location of primary aluminium production, 1990 & 2006-2013 (SOURCE: IAI & CRU)

Figure 2 – Primary aluminium smelting technology mix, 1990-2013 (SOURCE: IAI & CRU)

0

5

10

15

20

25

30

35

40

45

50

55

1990 2006 2007 2008 2009 2010 2011 2012 2013

Pri

mary

Alu

min

ium

Pro

du

cti

on

(millio

n t

on

nes)

China

GCC

Other Asia

Africa

Oceania

South America

CIS

Europe

North America

0

10

20

30

40

50

60

19

90

19

95

19

98

19

99

20

00

20

01

20

02

20

03

20

04

20

05

20

06

20

07

20

08

20

09

20

10

20

11

20

12

20

13

An

nu

al

Pri

mary

Alu

min

ium

Pro

du

cti

on

(m

illi

on

to

nn

es)

HSS

VSS

SWPB

PFPB

CWPB

NB:technology category details in Table 1

6


2013 Anode Effect Survey

Perfluorocarbons, or PFCs, are a group of potent greenhouse gases with long atmospheric

lifetimes (in the tens of thousands of years), of which the greatest volume is emitted from

industrial processes. PFCs can be produced in the primary aluminium electrochemical

smelting process, during events referred to as anode effects.

An anode effect is a process upset condition, where an insufficient amount of alumina (Al2O3),

the raw material for primary aluminium production, is dissolved in the electrolyte bath,

contained in the electrolytic cells (or pots) within a smelter reduction line (potline). This causes

the voltage in the pot to be elevated above the normal operating range, resulting in the

emission of gases containing the PFCs tetrafluoromethane (CF4) and hexafluoroethane

(C2F6).

Data on anode effects generated by process monitoring systems allows one to calculate such

emissions. 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

http://www.world-aluminium.org/About+IAI/Links

http://www.world-aluminium.org/media/filer_public/2013/01/15/pfc001.pdf

7


Participation Rate

It is significant that the 2013 survey results include data from 100% of SWPB, VSS and HSS

technology production. On average, these technologies produce more emissions per tonne

of aluminium produced than the CWPB and PFPB categories (see Error! Reference source

not found.).

As the aluminium production in China represents an increasing proportion of the industry and

non-reported data are predominantly from China, the overall reporting rate shown in Figure 5

continues to decrease (40% in 2013). Outside China, 24 smelters, representing over 5 million

tonnes of production (equivalent to around 10% of worldwide production), do not report data

to the IAI.

TECHNOLOGY

2013 primary

aluminium production

(1,000 tonnes)

2013 production

represented in survey

(1,000 tonnes)

2013

participation rate

by production

CWPB 1,412 613 43%

PFPB

(Rest of World) 19,988 15,257 76 %

34% PFPB

(China) 24,936 0 0 %

SWPB 514 514 100 %

VSS 3,378 3,378 100 %

HSS 373 373 100 %

All Technologies

(excluding China) 25,666 20,135 78 %

All Technologies

(Including China) 50,602 20,135 40 %

Table 2 - 2013 Anode Effect Survey participation by technology

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, means that the IAI is able to develop estimates of

PFC emissions from the global aluminium industry, with some degree of accuracy.

8


Figure 3 – Reporting production & rate 1990-2013

Figure 4 – Reporting rates (aluminium production) per technology, 2006-2013

Data Requested

Annual (1 January – 31 December 2013) 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.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0

5

10

15

20

25

30

35

40

45

50

Report

ing r

ate

Annual P

rim

ary

Alu

min

ium

Pro

duction

(Mill

ion t

onnes)

Reporting Production Non Reporting Rest of World

Non Reporting China Reporting Rate (RHS)

0%

20%

40%

60%

80%

100%

2006 2007 2008 2009 2010 2011 2012 2013

PFPB

CWPB

HSS

VSS

SWPB

9


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.

Adoption of revised GWPs and its consequence

The 2011 adoption, by the Conference of the Parties to the Kyoto Protocol, of revised global

warming potentials (GWPs) for greenhouse gas emissions calculations in the protocol’s

second commitment period (2013-2020) has necessitated recalculation of the industry’s PFC

data (current and historic).

Historically, IAI reports have used IPCC 2nd Assessment Report (1996) GWPs to calculate

carbon dioxide equivalency for CF4 and C2F6 emissions, in alignment with the first commitment

period recommended values. Recommended GWPs for the second commitment period are

now drawn from the IPCC 4th Assessment Report 2007).

GWPs IPCC 2nd

Assessment Report

IPCC 4th

Assessment Report

CF4 6,500 7,390

C2F6 9,200 12,200

Table 3 - IPCC GWP Values

As a result, IAI has recalculated and republished its historic PFC emissions data, based on

the revised 2007 GWPs (http://www.world-aluminium.org/statistics/perflurocarbon-pfc-

emissions/#data) and from 2013 onwards will report only using these values.

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.



http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_4_Ch4_Metal_Industry.pdf

http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_4_Ch4_Metal_Industry.pdf

10


2013 Survey Results

Anode effect data was collected from 218 reporting entities (smelters & potlines) representing

20 million tonnes of primary aluminium production Results are summarised in Error!

Reference source not found. below.

Facilities that have made PFC measurements by which Tier 3 calculation of PFC emissions is

possible account for 46% 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%."

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 2013 are shown in Figure 5.

Figure 5 – Median PFC emission rates (as CO2e) of reporting entities, per technology, 2006-2013

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%).

0 1 2 3 4 5 6 7 8 9 10

2006

2007

2008

2009

2010

2011

2012

2013

t CO2e/t Al

IPCC 4th GWP

SWPB VSS HSS

CWPB PFPB

0 1 2 3 4 5 6 7 8 9 10

2006

2007

2008

2009

2010

2011

2012

2013

t CO2e/t Al

IPCC 2nd GWP

SWPB VSS HSS

CWPB PFPB

11


Technology IPCC

Tier

No. of

reporting

entities

Reported

production

(kt Al)

Total CF4

emissions

(Gg CF4)

Total C2F6

emissions

(Gg C2F6)

Median

CF4

intensity

(kg CF4/

t Al)

Median

C2F6

intensity

(kg C2F6/

t Al)

Mean

C2F6: CF4

weight

ratio

IPCC 4th GWP IPCC 2nd GWP

Total PFC

emissions2

(kt CO2e)

Median

PFC

intensity

(t CO2e/

t Al)

Mean

PFC

intensity

(t CO2e/

t Al)

Total PFC

emissions

(kt CO2e)

Median

PFC

intensity

(t CO2e/

t Al)

Mean

PFC

intensityr

(t CO2e/

t Al)

CWPB 2 1 324 0.005 0.001

0.022 0.003 0.15 123 0.20 0.20 105 0.17 0.17 3 1 288 0.008 0.001

PFPB

2

Slope

64 5,753 0.151 0.018

0.023 0.003 0.12 4,040 0.20 0.27 3471 0.17 0.23 3

Slope

27 5,413 0.134 0.017

2 OV 18 1,462 0.091 0.011

3 OV 6 1,761 0.082 0.007

SWPB 2 6 111 0.007 0.002

0.264 0.089 0.25 1,875 2.97 3.65 1,581 2.48 3.08 3 2 403 0.107 0.032

VSS 2 67 2,620 0.390 0.021

0.146 0.008 0.06 4,116 1.17 1.22 3,577 1.02 1.06 3 9 759 0.121 0.007

HSS 2 13 162 0.022 0.002

0.150 0.013 0.10 918 1.26 2.46 791 1.09 2.12 3 4 211 0.084 0.009

ALL - 218 20,135 1.269 0.140 - - 0.11 11,072 - 0.55 9,525 0.47

Table 4 – Perfluorocarbon emission results from facility data reporting to the 2013 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 4th Assessment Report (i.e. 7,390 for CF4 and 12,200 for C2F6). Calculations using GWP contained in the IPCC 2nd

Assessment Report (i.e. 6,500 for CF4 and 9,200 for C2F6) are also listed here for reference.

12


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)

Total PFC

emission

factor

(t CO2e/t

Al)


2013 20,135 40% 0.063 0.007 0.55 0.47

2012 21,006 44% 0.069 0.008 0.61 0.52

2011 22,413 51 % 0.079 0.009 0.68 0.60

2010 21,774 53 % 0.071 0.009 0.63 0.54

2009 22,184 60 % 0.069 0.008 0.61 0.52

2008 24,741 63 % 0.089 0.010 0.78 0.67

2007 23,903 63 % 0.106 0.013 0.95 0.81

2006 23,177 68 % 0.116 0.014 1.03 0.87

Table 5 – Production weighted mean PFC emissions per unit production of reporting entities, 2006-2013

13


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 Error!

Reference source not found. 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 2013 primary aluminium production of 24,936,070 metric tonnes) is reported by the

China Nonferrous Metals Industry Association (CNIA). Around 3.5 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 1.2 million 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 (2008-2013) PFC emissions measurements at 27 PFPB facilities in China have yielded

a median emission factor of 0.80 tonnes CO2e per tonne of aluminium produced (CF4 median

0.100 kg/t Al; C2F6:CF4 weight fraction 0.046), compared with a PFPB survey reporter median

performance of 0.20 tonnes CO2e per tonne of aluminium (0.023 kg CF4/t Al; C2F6:CF4

weight ratio = 0.12).

This China-specific value (0.80 t CO2e/t Al) is applied to the 2013 Chinese non-reporting

PFPB cohort, in place of the IAI PFPB survey median, and has also been applied to historical

Chinese non-reporting production, 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.

http://www.world-aluminium.org/media/filer_public/2013/01/15/iai_form_100.pdf

http://www.crugroup.com/

14


2013 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 2013 PFC emissions performance for the global aluminium

industry of 0.63 tonnes of CO2e per tonne of primary aluminium produced, as outlined in Table

6 – Total global 2013 PFC emissions

Total PFC

emissions

(1,000 t

CO2e)

Total

aluminium

production

(1,000

tonnes)

PFC

emission

factor

(t CO2e/t

Al)

PFC

emission

factor

(t CO2e/t

Al)


Reported 11,072 20,135 0.55 0.47

Calculated from non-

reporters 20,928 30,467 0.69 0.61

TOTAL GLOBAL 32,000 50,602 0.63 0.56

Table 6 – Total global 2013 PFC emissions

Note: any inconsistencies due to rounding

Global PFC emissions (as CO2e) per tonne of production have been reduced by 33% since

2006, on course to meet the IAI voluntary objective of a 50% reduction by 2020 on a 2006

baseline. The 33% improvement since 2006 takes the overall improvement since 1990 to

88%.

With PFC emissions per tonne cut by almost 90% since 1990 and primary aluminium

production having grown by 159% over the same period, absolute emissions of PFCs by the

aluminium industry have been reduced from approximate 100 million tonnes of CO2e in 1990

to 32 million tonnes in 2013, a fall of over 68%.

15


Figure 6 – PFC emissions (as CO2e) per tonne of aluminium production, 2006-2013

Figure 7 – Absolute PFC emissions (as CO2e) and primary aluminium production, 1990-2013

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

PF

C E

mis

sio

ns (

t C

O2

e/t A

l)


0

20

40

60

80

100

120Annual Primary Aluminium Production (Mt Al)

Total Annual PFC Emissions (Mt CO2e)

16


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 2013 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 2013 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.

17


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 8 is interpreted consider, for example, the 0.5 point on

the vertical axis, at which the HSS data point is 1.26 t CO2e/t Al. The interpretation is that

50% of all potlines/facilities reporting HSS anode effect data operate at or below 1.26 t CO2e/t

Al. At 1.0 on the vertical axis the HSS point is 4.64 t CO2e/t Al. The interpretation is that all

HSS facilities reported anode effect data that reflected PFC emissions performance at or

below 4.64 t CO2e/t Al or, in other words, the maximum value calculated for HSS operators in

2013 was 4.64 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.

18


Figure 8 – PFC emissions (as CO2e per tonne Al) performance of reporters, benchmarked as cumulative

fraction within technologies, 2013

Figure 9 –PFC emissions performance of reporters (t CO2e/t Al), benchmarked as cumulative production

within technologies, 2013

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

racti

on

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 8.1 tCO2e/t Aland 12.6 t CO2e/t Al respectively.

0

2

4

6

8

10

12

14

0 5 10 15 20

PFC

Em

issi

on

s (t

CO

2-e

q/t

on

ne

Al)

Cumulative Aluminium Production of Reporting Facilities (Million tonnes)

PFPB&CWPB

SWPB

HSS

VSS

19


Taking the 1990 reporting cohort and plotting it against 2013 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 10 - PFC emissions performance of reporters (t CO2e/t Al), benchmarked as cumulative production within technologies, 1990 & 2013

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20

PFC

Em

issi

on

s (t

CO

2-e

q/t

on

ne

Al)

Cumulative Aluminium Production of Reporting Facilities (Million tonnes)

PFPB&CWPB

SWPB

HSS

VSS

20131990

20


Anode Effect Frequency & Duration

The following graphs shows the distribution of anode effect frequency and duration data for

reporting facilities in 2013. 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 11 - Average anode effect frequency of reporters benchmarked by technology type, 2013

Figure 12 - Average anode effect duration of reporters benchmarked by technology type, 2013

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 5.0Cu

mu

lati

ve F

racti

on

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

racti

on

of

Rep

ort

ing

E

nti

ties

Anode Effect Duration (minutes)

CWPB & PFPB SWPB VSS HSS

21


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).

𝐸𝐹𝐶𝐹4= 𝑆𝐶𝐹4

× 𝐴𝐸𝑀

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 13 - Average anode effect minutes per cell day of reporters benchmarked by technology type, 2013

Anode Effect Overvoltage

Figure 14 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

Fra

cti

on

of

Re

po

rtin

g E

nti

tie

s

Anode Effect Minutes per Cell Day (minutes)

CWPB & PFPB SWPB HSS VSS

22


Figure 14 - Average anode effect overvoltage of reporters benchmarked by technology type, 2013

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 2 4 6 8 10 12 14

Cu

mu

lati

ve

Fra

cti

on

of

Re

po

rtin

g E

nti

tie

s

Anode Effect Overvoltage (mV)

Positive

Algebraic

23


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:

𝐸𝐶𝐹4= 𝑆𝐶𝐹4

× (𝐴𝐸𝐹 × 𝐴𝐸𝐷) × 𝑀𝑃

and

𝐸𝐶2𝐹6= 𝐸𝐶𝐹4

× 𝐹𝐶2𝐹6/𝐶𝐹4

where

𝐸𝐶𝐹4= kilograms of 𝐶𝐹4emitted

𝐸𝐶2𝐹6= kilograms of 𝐶2𝐹6emitted

𝑆𝐶𝐹4= slope coefficient for 𝐶𝐹4

𝐹𝐶2𝐹6/𝐶𝐹4= weight fraction of 𝐶2𝐹6 to 𝐶𝐹4

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.

24


Table 7 - Slope and overvoltage coefficients by technology, including uncertainty (Source: IPCC, 2006)

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:

𝐸𝐶𝐹4= 𝑂𝑉𝐶 ×

𝐴𝐸𝑂

𝐶𝐸100⁄

× 𝑀𝑃

and

𝐸𝐶2𝐹6= 𝐸𝐶𝐹4

× 𝐹𝐶2𝐹6/𝐶𝐹4

where

𝐸𝐶𝐹4= kilograms of 𝐶𝐹4𝑒𝑚𝑖𝑡𝑡𝑒𝑑

𝐸𝐶2𝐹6= kilograms of 𝐶2𝐹6𝑒𝑚𝑖𝑡𝑡𝑒𝑑

𝑂𝑉𝐶 = overvoltage coefficient for 𝐶𝐹4

𝐶𝐸 = current efficiency, expressed as %

𝐹𝐶2𝐹6/𝐶𝐹4= weight fraction of 𝐶2𝐹6 to 𝐶𝐹4

25


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 Fourth Assessment ReportF

3:

𝐸𝐶𝑂2𝑒 = (𝐸𝐶𝐹4× 7390) + (𝐸𝐶2𝐹6

× 12200)

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:

𝐸𝐹𝐶𝑂2𝑒 =𝐸𝐶𝑂2𝑒

𝑀𝑃

3 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.

Published by:

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10 Charles II Street

London

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United Kingdom

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Email: [email protected]

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mailto:[email protected]

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