2012 Anode Effect Survey Report - World Aluminium · Anode Effect Overvoltage (AEO), the average...

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


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


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

1


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.

2


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

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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

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50

1990

1995

1998

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2012

An

nu

al P

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

3


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.

4


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

5


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)

6


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.

7


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


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.

8


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

9


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

10


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


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%.

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/t A

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Figure 9 – Absolute PFC emissions (as CO2e) and primary aluminium production, 1990-2012

0

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60

70

80

90

100

Annual Primary Aluminium Production (Mt Al)

Total Annual PFC Emissions (Mt CO2e)

12


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.

13


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.

14


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

15


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

16


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

17


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

18


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

19


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)

20


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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2012 Anode Effect Survey Report - World Aluminium · Anode Effect Overvoltage (AEO), the average...

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